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Review ArticleEmission Mechanisms of Si Nanocrystals andDefects in SiO2 Materials

Joseacute Antonio Rodriacuteguez1 Marco Antonio Vaacutesquez-Agustiacuten2

Alfredo Morales-Saacutenchez3 and Mariano Aceves-Mijares2

1 Instituto Superior Politecnico de Tecnologia e Ciencias (ISPTEC) Avenida Luanda Sul Rua Lateral Via S10Talatona Belas Luanda Angola

2Department of Electronics INAOE 72840 Puebla PUE Mexico3 Centro de Investigacion en Materiales Avanzados SC Unidad Monterrey-PIIT 66600 Apodaca NL Mexico

Correspondence should be addressed to Mariano Aceves-Mijares macevesieeeorg

Received 24 March 2014 Accepted 22 June 2014 Published 26 August 2014

Academic Editor Anukorn Phuruangrat

Copyright copy 2014 Jose Antonio Rodrıguez et alThis is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in anymedium provided the originalwork is properly cited

Motivated by the necessity to have all silicon optoelectronic circuits researchers around the world are working with light emittingsilicon materials Such materials are silicon dielectric compounds with silicon content altered such as silicon oxide or nitrideenriched in different ways with Silicon Silicon Rich Oxide or silicon dioxide enriched with silicon and silicon rich nitride arewithout a doubt the most promising materials to reach this goal Even though they are subjected to countless studies the lightemission phenomenon has not been completely clarified So a review of different proposals presented to understand the lightemission phenomenon including emissions related to nanocrystals and to point defects in SiO

2is presented

1 Introduction

The luminescence of different silicon-basedmaterials such ashydrogenated amorphous silicon (a-SiH) and silicon oxide(SiO2) has been known for a long time However it was only

after the finding of Canham [1] on strong visible room tem-perature photoluminescence (PL) from porous silicon (p-Si)that the development of efficient light sources based on siliconand related compounds was considered a real possibility Asa consequence the establishment of a common silicon-basedtechnological platform for opto- andmicroelectronic devicesand the production of all-silicon optoelectronic circuits wereenvisioned Beginning with the pioneer works related tothis phenomenon the origin of the emission was attributedto quantum confinement effects taking place in the siliconnanoparticles (Sinc) produced by electrochemical etching(nanocrystals or nanoclusters depending on the aggregationstate crystalline or amorphous) The necessity to passivatethe nanocrystal surface to eliminate nonradiative centers wasalso established The passivation can be produced duringthe electrochemical process by a posttreatment under H

2

or by forming gas atmosphere via SindashH bonds (hydrides)it can also be achieved through a native oxidation processunder atmospheric conditions even for a short time orby annealing it in an oxidizing atmosphere at an elevatedtemperature via different oxygen passivation configurationsAs evidenced theoretically and experimentally the emissionmechanism and the properties of the emitted radiationsignificantly depend not only on the Sinc dimension butalso on the chemistry of the nanocrystal surface beingin general different for hydrogen and oxygen passivationFor applications generally the oxygen process is utilizedTherefore the importance of a system formed by siliconagglomerates surrounded by amorphous SiO

2(SincSiO

2) as

a basic material for light-emitting devices has been firmlyestablished Such a system simply known as Silicon RichOxide (SRO) has been a matter of extensive research dueto the transformation of agglomerates in nanocrystals andthe emission taking place in the nanocrystals or aroundthem

An alternative mechanism of emission in SRO filmsespecially with low silicon excess is related to point defects

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2014 Article ID 409482 17 pageshttpdxdoiorg1011552014409482

2 Journal of Nanomaterials

in the SiO2matrix The different chemical vapor deposi-

tion (CVD) techniques are naturally inclined to producedefects in the matrix of deposited materials High tempera-ture techniques as low pressure chemical vapor deposition(LPCVD) are even more predisposed to such molecularchanges However in spite of the defect formation whenthe mentioned techniques are used it is uncommon tofind studies that relate the emission with point defects inSRO

The poor chemical and mechanical properties of p-Si stimulated the research work with other silicon-basedluminescentmaterials duringmore than twodecadesAmongthem are materials based on Sinc embedded in an SiO

2

matrix which can be obtained by different techniques suchas Si+ implantation into thermal SiO

2 plasma enhanced

chemical vapor deposition (PECVD) LPCVD and Sol-gelThe Si nanostructures are then autoassembled from individ-ual atoms under a high temperature annealing in an inertatmosphere This process produces the Si diffusion nucle-ation and crystallization Other SincSiO

2-based materials

are obtained by co-Sputtering pulsed laser deposition (PLD)and oxidation of layers of Si nanoparticles synthesized fromthe gas phase In the next section some of the main synthesistechniques will be described

So far it has not been possible to find a physicalmodel explaining the emission processes underlying all theseSincSiO

2-basedmaterials A good and unifying effort in our

opinion is that of Koch and Petrova-Koch [2] Instead a rushof models (sometimes contradictory to one another) havebeen proposed to fundament this phenomenon for specificmaterials obtained by specific techniques under concretetechnological parameters As a rule a good agreement isreported between the results of the specific model andthe experimental results for a particular material It seemsthat these facts reflect a reality of nature that is intenseluminescent radiation in a wide spectral range (from infraredto ultraviolet) can be produced in these materials followingdifferent physical mechanisms which will be reviewed inSection 3

The intention of this paper is to review the mechanismof emission due to Sinc and the defects embedded in adielectric matrix (SiO

2) In Section 2 we present some tech-

niques commonly used to obtain SRO and related materialsIn Section 3 a review of the different possible emissiontheories and defects is presented We finish this sectionshowing specifically the emission of off-stoichiometric oxidedue to different excitation which can be related to pointdefects

2 Synthesis of Materials

The most extensive way to obtain silicon nanoparticlesembedded in dielectric layers either silicon oxide or nitrideis through the segregation of the excess silicon atoms insilicon enriched layers with a thermal annealing at a hightemperature [3 4] Here the technological parameters suchas the duration of the thermal treatment the annealingtemperature and the Si excess content all determine the final

size of the particle the size dispersion and its nature eitheramorphous or crystalline However different techniques arealso used to produce SincSiO

2-based materials

21 Porous Silicon (p-Si) Porous silicon was discovered byUhlir at the Bell laboratories (US) in 1956 [5] Despite thisearly discovery the scientific community was not interestedin p-Si until the late 80s when Canham proposed that p-Si could display quantum confinement effects [1] In hispublished experimental results strong light emission fromsilicon was obtained after subjecting the Si-wafers to anelectrochemical and chemical dissolution Different PL peakswere observed depending on the porosity of the layer Thesenovel results stimulated the interest of the scientific commu-nity in the study of the nonlinear optical and electroopticalproperties of silicon especially due to their potential appli-cations Despite the strong room temperature luminescenceobserved in p-Si it was found that it suffers from poormechanical and chemical stability producing degradation inthe PL properties [6 7] Multiple studies have been done toovercome this limitation such as modifications introduced inthe etching procedure [8 9] Some authors have reported thata postetching treatment in H

2O2leads to a decrease of the

nanoparticle core size and also to some extent changes thesurface oxide for the modulation of the photoluminescencecolor [8]

22 Ion Implantation In the ion implantation technique athermal silicon oxide grown on a silicon wafer is implantedwith silicon ions at a specific dose and energy With thistechnique both chemical and structural changes are intro-duced by the implanted ions To activate the implanted ionsand to repair the damage produced a thermal annealingis necessary In the case of Si ions implanted into silicondioxide matrix a silicon agglomeration in the form of siliconnanoparticles is obtained after the thermal annealing processThe dose and energy of implantation determine the siliconexcess and the depth profile respectively [10ndash13] In somecases multiple silicon ion implantations are used to obtaina uniform depth profile of silicon excess and a uniform Sincdensity [10]

23 Chemical Vapor Deposition (CVD) There are a greatnumber of forms of CVDThese processes differ by themeansin which chemical reactions are initiated (eg activationprocess) and process conditions In a typical CVD processthe wafer or substrate is exposed to one or more volatileprecursors which react andor decompose on or near thesubstrate surface to produce the desired deposit The mainCVD techniques used for Sinc fabrication are LPCVD andPECVD SRO films are easily deposited by PECVD andLPCVD techniques using oxidant species like nitrous oxide(N2O) and silicon compounds (ie silane SiH

4) as reactant

gasses [14ndash17] For these techniques Si excess in the deposited

Journal of Nanomaterials 3

films is controlled by a parameter 119877119900defined by (1) which

relates to the flux of the reactant gases N2O and SiH

4

119877119900=119865 (N2O)

119865 (SiH4) (1)

After SROfilms are thermally annealed at a high temperaturea phase separation occurs between Si and SiO

2creating Si

agglomerates that can be nanocrystalline or not Again theSinc formation and size depend on the silicon excess insidethe deposited films as well as the time and the temperatureof thermal annealing

For LPCVD SRO is deposited at subatmospheric pres-sures and at a temperature of around 700∘C [14 15] Reducedpressures tend to reduce unwanted gas-phase reactions andimprove film uniformity across the wafer Meanwhile SRO-PECVD utilizes a radio frequency (RF) discharge to enhancethe chemical reaction rates of the precursors [16 17] PECVDprocessing allows deposition at lower temperatures typically300∘C which is often critical in the manufacturing of semi-conductors

24 Sol-Gel SincSiO2-based materials are also obtained

through the synthesis of SRO films by the Sol-gel methodusing triethoxysilane (TREOS) or the innocuous hex-aethoxydisilane (hexaet) and hexamethoxydisilane (hex-amet)monomers followed by a subsequent thermal treatment[18ndash20] In the last case the mentioned precursors (hexaet orhexamet) are mixed with ethanol and subsequently dilutedwith acidic water The resulting solution is stirred in a sealeddisposable beaker The polymer is condensed and then driedin an annealing furnace at a low temperature These SROfilms are thermally annealed at a high temperature to obtainthe silicon nanoparticles [20]Through this method it is alsopossible to control the PL spectra by varying the parametersof the technological process [18ndash20]

25 Sputtering In this technique plasma is created and theions from this plasma are accelerated into a source targetmaterial etching it If the sample surface is placed next to thetarget or in the path of the sputtered atoms they will collideand eventually be adsorbed onto the sample forming a thinfilm

To deposit SRO films SiO2and Si targets are used The

amount of silicon excess can be controlled by adjusting theratio at which each target is sputtered [21]The low depositionrate hasmade this technique proper for obtaining superlatticestructures and for the engineering of band gaps for silicon-based materials [21ndash23]

3 Emission Mechanisms

In this study the materials based on the system SincSiO2

that is silicon nanocrystals either embedded in a SiO2matrix

or capped by SiO2shells will be discussed A rush of models

has been proposed to explain the experimental results ofthe interaction of light (absorption and luminescence) withthese materials In the next sections an insight into these

models will be explored based on published works We willfocus separately on the mechanisms related to Sinc core toSincSiO

2interface and to SiO

2matrix Then a review of

known SindashO emissive defects in silica is presented Finally theemission related to such defects is linked specifically to SROobtained by LPCVD

31 Sinc Core Related Emission Quantum Confinement EffectThe strong visible luminescence first observed by Canham[1] in porous silicon and subsequently obtained by otherresearches in different SincSiO

2-based materials has been

explained by a model based upon the quantum confinementor quantum size effect [1 24 25] Theoretical evidence wasestablished by Delerue et al [26] under the frame of thelinear combination of the atomic orbitals (LCAO) techniqueGiven that silicon is an indirect-gap semiconductor thephonon-assisted radiative recombination is very inefficientMoreover as its gap at room temperature is around 11 eVvisible emission is precluded A different scenario is encoun-tered by reducing the particle dimensions under a fewnanometersWhen the nanostructure diameter (crystallite orcluster supposed spherical) is less than the size of the freeexciton Bohr radius 43 nm in bulk c-Si [27] the quantumsize effect takes place the electronic levels which exhibita quasi-continuous spectrum for bulk materials becomediscrete and the effective band gap enlarges as the diameter(119889) is reduced (Figure 1) In this case such 0-dimensionalnanostructures are called ldquoquantum dotsrdquo and their physicalfeatures are described by the classical text book ldquoparticlein a boxrdquo scheme In this diameter range the band gapincreases according to an approximate 119889minus2 law the oscillationstrength increases and the radiative lifetime varies from amillisecond to a nanosecond as calculated in the frame ofan effective-mass approximation [28] However the moreprecise considerations ofDelerue et al [26] allowed obtaininga 119889minus139 behavior for small enough particles with the energygap of silicon nanoparticles (119864

119892) being calculated through the

following semiempirical expression

119864119892(eV) (119889) = 119864

1198920(eV) + 373119889(nm)139

(2)

where 1198641198920

is the energy gap of bulk silicon According to thismodel the emission spectrum can be tuned from infraredto blue by reducing the structure diameter if the particlesurface is passivated with SindashH bonds a fact experimentallyobserved by Gupta et al [29] Figure 2 depicts a comparisonof theoretical and experimental results as reported byGarridoet al [30] on ion beam synthesized Sinc in SiO

2 In this

figure the experimental results obtained by these authors forband gap as obtained from photoluminescence excitationmeasurement and photoluminescence peak position arecontrasted and agree well with the behaviors theoreticallycalculated by Delerue et al [26] Wang and Zunger [31] andTakagahara and Takeda [28]

Another example of Sinc core-related emission isobserved in Figure 3 The photoluminescence spectraobtained for Sol-gel SRO annealed one hour in N

2

atmosphere at different temperatures are depicted The


Eg0 Eg

Bulksemiconductor

Quantumdot

CB

VB

Figure 1 Diagram illustrating the effect of quantum confinement inthe energy band structure

40

35

30

25

20

15

10

Gap

ener

gy (e

V)

0 2 4 6 8 10

Mean nanocrystal diameter (nm)

026 eV

PLE measurementsPL measurementsTakagahara et al [42]

Delerue et al [40]Wang et al [44]

Figure 2 (Figure 14 from [30]) Theoretical (solid dotted anddashed lines) and experimental (circles) data for the band gap energyas well as experimental PL peak energies (squares) as a function ofnanocrystal diameter The double arrow indicates the value of theStokes shift

as-synthesized samples are obtained as described in epigraph2 by using a hexaethoxydisilanemonomer as a precursorThedramatic increase of PL intensity for annealing temperaturesin the range of 1050ndash1100∘C corresponding to crystallizationof the Sinc as well as the redshift of maximum PL forincreasing annealing temperature and time is observed Thisfact corresponds to an increase of Sinc diameter accordingto the quantum confinement effect The crystalline natureof the Sinc was verified by Raman shift measurements asindicated in Figure 4

Unfortunately the simple behavior just described is notalways observed in SincSiO

2materials Important discrep-

ancies with this simple picture have been encountered inpractice and will be raised later

4

3

2

1

0

PL in

tens

ity (times

104

coun

ts)

PL in

tens

ity (times

102

coun

ts)

0 300 600 900

Wavelength (nm)

0 300 600 900

Wavelength (nm)

(d) 1150∘C 3h

(a)

(a)

(b)

(b)

(c)

(c)

(d)

30

25

20

15

10

5

0

(a) As-synt(b) 950∘C(c) 1000∘C

(c) 1150∘C(a) 1050∘C(b) 1100∘C

Figure 3 (Figure 1 from [20]) PL spectra for Sol-gel SRO (hexaet-based) annealed for one hour (if not specified) at increasingtemperatures Low intensity curves are separately shown in the insetfor clarity

3000

80

60

40

20

Ram

an in

tens

ity (c

ount

s)

400 450 500 550 600

Raman shift (cmminus1)

Hexamet 1100∘C

(a)(b)

(c)

(d)

(e)

Figure 4 (Figure 4 from [20]) Raman shift spectra for some of thesamples as in Figure 3 Curves (a)ndash(d) correspond to the samplestreated at 1050 1100 1150 and 1150∘C (3 h) respectively Curve (e)is from a SRO obtained from a mixture of hexamet and hexaet Acurve for a pure hexamet-based sample is also shown

Another consequence of the quantum confinement is thedramatic increase of the radiative recombination efficiencyIn quantum confined systems the extremely reduced dimen-sions lead to a major spread of the wave vector value in thereciprocal space according to the uncertainty principle thus


producing a relaxation of the moment selection rule and thepossibility of zero-phonon direct radiative optical transitions

Qualitatively the confinement due to reduced particlesize produces an increase of the overlap between electron andhole wave functions in 119896-space which leads to an increaseof the radiative recombination probability Moreover assize is reduced the probability of finding a nonradiativerecombination center in the particle decreases provided thatthe particle surface is appropriately passivated This is basedon Sinc embedded in silicon oxide or other dielectrics such asa silicon nitride matrix with a higher band gap thus produc-ing a quantum well Consequently carrier diffusion from theparticle towards external nonradiative recombination centersis avoided The mentioned facts lead to the photolumines-cence increase from Sinc few orders of magnitude larger thanfor bulk silicon as experimentally observed

Attributing the emission phenomenon in SincSiO2sys-

tems to direct optical transitions has been somewhat con-troversial Indeed lines of evidence on zero-phonon as wellas on TO phonon-assisted transitions were encountered bySychugov et al in their studies of oxidized Si quantumdots emission by single-dot luminescence spectroscopy [32]Furthermore Garrido et al [30] argued that the dominantmechanism of emission for their ion beam synthesized Sincembedded in SiO

2is a fundamental (indirect) transition

located at the interface SiSiO2with the assistance of a local

SindashO vibrationThe first observations on direct transitions inSinc-based materials were those fromWilcoxon et al [33] intheir research on the optical and electronic properties of Sinanoclusters synthesized in inverse micelles

Moreover there is proverbial uncertainty reported in theliterature relating to the determination of the size and thesize distribution of nanocrystals from electron microscopydue to a low contrast between Si and SiO

2 This has been a

main drawback in establishing a stable correlation betweenstructural and optoelectronic properties of Sinc embeddedin SiO

2 which has led to ambiguities in determining the

emission mechanisms However in the paper of Garrido etal [30] a successful method was explored for imaging Sinc inSiO2matrices by using high-resolution electron microscopy

in conjunction with conventional electron microscopy indark field conditions

On the other hand the quantum confinement effect is notalways observed in practice for SincSiO

2-based materials

According to this model a blueshift of the PL energypeak should take place as the diameter of the nanoparticlesdecreases in the range of few nanometers However not onlya blueshift but also a redshift should occur [34] and nodependence on this parameter has been observed [35ndash37]In addition a redshift of PL spectrum as large as 1 eV hasbeen observed after exposure to oxygen in porous siliconquantum dots [38] and a discontinuity at about 590 nmof PL spectral behavior with reducing size has also beenreported [8 38] These discrepancies may be understood byconsidering that the PL spectra in SincSiO

2-based materials

are really the result of besides the quantum confinementeffect the simultaneous action of various other emissionmechanisms [34] Most of these are based on models whichattribute a key role in the luminescence phenomenon through

the interface between the Sinc and the dielectric matrixSuch are the cases of emission due to exciton confined inthe SincSiO

2interface [35 39] and the emission through

carrier energy levels introduced in the quantum dot bandgap by surface Si=O bonds (nonbridged oxygen passivation)[8 38 40] by defects in the silicon suboxide (SiOx) orsilicon oxide shell surrounding the nanocrystal [41] orby surface states generated in the perturbed Si-bonded toO and H [2] Other luminescence mechanisms have beenassociated with structural defects of the silicon oxide matrix[36] or with different silicon-based chemical species likesiloxane (Si

3O3H6) [42] and polysilane (SiH

2)119899[43] In

the next epigraphs the luminescence mechanisms relatedto SincSiO

2-matrix interface (surface confined excitons

surface carrier energy levels introduced by passivant bondsor by perturbed crystalline Si structure) and oxide matrixdefects will be considered

32 Emission Mechanisms Related to SincSiO2Interface

Among the rush of works and models published after Can-hamrsquos we distinguish a line of continuity and developmentbeginning with the pioneers papers through Kanemitsu etal [35 39] and Kanemitsu [44] and those from Koch andPetrova-Koch [2] Wolkin et al [38] Wilcoxon et al [33]Nishida [45] and Dohnalova et al [8] In [35] the authorsreport the results of their research work on free-standingp-Si thin films formed by nm-sized Si crystalline spheresdispersed in an amorphous phase In [39] the authors studynm-sized spherical Sinc obtained by synthesis from vaporphase and subsequently oxidized The experimental resultsof both papers suggest that the photogeneration of carriersoccurs in the Sinc core where the band gap is modified bythe quantum confinement effect while the strong PL (size-independent sim165 eV) (see Figure 5) comes from the near-surface region of small crystallites They proposed a three-regionmodel (Figure 6) in which the Sinc core is surroundedby a shell of amorphous silicon oxide (a-SiO

2) and a transition

interfacial layer The composition of this intermediate layercorresponds to a nonstoichiometric silicon oxide (SiOx 119909 lt2) and its band gap energy is lower than that of the Sinccore for core diameters le 5ndash7 nm According to the modelthe carriers photogenerated in the core diffuse througha thermally activated mechanism towards this interfacialregion where the intense PL radiation is produced via two-dimensional confined excitons The observed temperaturedependence on the PL intensity unambiguously confirms thisproposition These arguments also explain the increase of PLintensity as the crystallite diameter is reduced In this casethe efficiency of carrier diffusion from core to near-surfacelayer as well as the excitonsrsquo confinement also increases In thepaper [39] the authors explicitly refute the possibility that theemission takes place via localized states as the states usuallyact as nonradiative centers

The next report fromKanemitsu in 1994 [44] was devotedto the same material system seen in [39] (oxidized sphericalSinc obtained by synthesis from vapor phase) with a meancrystallite diameter of 37 nm A time-resolved PL study wasaccomplished Also PL spectra under weak continuous wave


103

102

10

5

0

Nor

mal

ized

in

tens

ity (a

u)

Abso

rptio

nco

effici

ent120572

(cm

minus1)

400 600 800 1000 1200

Wavelength (nm)

PLAbs

(a)

10

5

0

Nor

mal

ized

in

tens

ity (a

u)

103

102Ab

sorp

tion

coeffi

cien

t120572(c

mminus1)

400 600 800 1000 1200

Wavelength (nm)

PLAbs

(b)

400400 600 800 1000 1200

10

5

0

Nor

mal

ized

in

tens

ity (a

u)

103

Abso

rptio

nco

effici

ent120572

(cm

minus1)

Wavelength (nm)

PL

Abs

(c)

Figure 5 (Figure 4 from [35]) Absorption and PL spectra of p-Sifilms (a) 119889 sim2 nm (b) 119889 sim35 nm and (c) 119889 sim9 nm

(cw) excitation as well as time averaged PL spectra underintense and weak pulsed-laser excitation were obtainedReference was made neither to the interfacial region nor tothe emission mechanism through two-dimensional confinedexcitons rather the emissions were associated with surfacelocalized states

Figure 7 summarizes the results of optical absorption andPL spectra under cw and pulsed-laser excitation A weakabsorption tail in the visible region and a strong absorptionabove 3 eV are observed Furthermore in continuous excita-tion a strong stable broad (sim03 eV full width at half max-imum FWHM Gaussian-like shape) slow (microsecondorder) and nonexponential decay (stretched exponentiallyinstead) red band (sim760 nm) is obtained According to itsproperties this band is associatedwith the hopping of carriersamong the localized surface states (the energy levels of whichform a band tail) from the high energy levels to the lowenergy ones followed by radiative recombination throughthe band gap of these surface regions This proposition issupported by the ab initio calculations of Takeda and Shiraishi[46] who obtained a value of 17 eV for the band gap of acompletely oxidized Si sheet very similar to the Sinc surfacein the SincSiO

2system This value roughly coincides with

the spectral position of the red PL band Under short pulsedexcitation a new fast nonexponential decay blue-green bandemerges in addition to the red oneThe intensity of this band

0

Egapcore

EgapI

minus16nm

(a)c-Si core

(b)a-SiO2

(c)Interfacial

layer

Band

gap

ener

gy

Dcore2 Dtotal2

Radius

Figure 6 (Figure 4 from [39]) Energy gap diagram of the three-region model proposed by Kanemitsu et al

02

01

0

1

0

200 400 600 800

Abso

rban

ce

Wavelength (nm)PL

inte

nsity

(au

)

Pulse

(a)

(b)

cw

Figure 7 (Figure 1 from [44]) Optical absorption spectrum PLspectrum under cw 325 nm laser excitation and the first 200 nsaveraged PL spectra under 5 ns 335 nm pulsed laser excitation of (a)sim100 120583Jcm2 (solid line) and (b) sim06 120583Jcm2 (broken line) at roomtemperature

increases with the excitation intensity and eventually the redband disappears Its spectral position roughly agrees with theband gap energy (24 eV) of a 37 nm Sinc [28] Therefore itsorigin is attributed to carrier radiative recombination in theSinc core Its appearance has been considered a result of thesaturation of the localized surface statesrsquo populationwhen thematerial is excited by short and energetic laser pulses It isdue to the low density of states and the large recombinationlifetime (microsecond order) of localized states Under theseexcitation conditions part of the photogenerated carriers


4

3

2

1

0

PL in

tens

ity (a

u)

10 15 20 25 30

Photon energy (eV)

H25

H900

H1000

(times3)

H600

(times150)H1100

(times5)

300K

Figure 8 (Figure 2 from [2]) Room temperature PL spectrum ofa set of thermally oxidized p-Si samples (rapid thermal oxidation30 s) H25 is the as-prepared sampleThe others have been treated atthe temperature indicated The diameter of the Sinc decreases whenthe oxidation temperature is increased

stays in the core and recombines there thus producing theso mentioned blue-green band

In 1996 based on experimental results Koch andPetrova-Koch [2] tried to establish a model accounting for the prop-erties of the most studied Sinc-based luminescent materialsreported to date that is hydrided and oxidized p-Si oxidizedSinc synthesized from a gas phase and ion beam synthesizedSinc in SiO

2 In this and in other related papers [47ndash49]

they followed a surface state model somewhat similar tothat of Kanemitsu in [44] In this model the absorption(carrier generation) took place in the Sinc core following thequantum size effect but the recombination occurred via local-ized defect states in the passivated surface layerThe size effectwas observed in the PL spectra for hydrided p-Si For theoxidized one the pinning of the PL energy peak in the rangeof 15 eVndash17 eV as well as the discrete emergence of a fast blueband was observed as the diameter of the Sinc decreased dueto increased oxidation temperature(see Figure 8)

Figure 9 shows the behavior of Si+ implanted SiO2and

annealed in forming gas Observe the continuous redshiftof the PL peak energy as the annealing time increases incorrespondence with the growth of the Sinc This behavioris not explained here according to the conventional quantumconfinement effect for recombination that takes place in theSi core Rather thementioned surface state model is adoptedSincs larger than about 15 nm are considered as a centralcrystalline core formed by perfect Si-tetrahedra and a surfacelayer with thickness of the dimension of a Si unit cell formedby Si-tetrahedra which are perturbed due to bonds withother matrix atoms As a result a spectrum of disorder-induced states is formed in this region with energies lowerthan the states in the unperturbed core Therefore excitedelectrons and holes localized recombine in this layer As the

Photon energy (eV)

900 800 700 600 500 400

Nor

mal

ized

PL

inte

nsity

15 20 25 30

Eex = 41 eV T = 300K implantation dose 5 times 1016

and annealing in form gas at 900∘C if not spec otherwise

30min

30min

1050∘C

3h

9min3min

30 s10 s

0 s1 times 10

16cm2

Wavelength (nm)

cm2

(a)

Nor

mal

ized

PL

inte

nsity

Photon energy (eV)15 20 25 30

Dry oxidation after 1050∘C annealing for 15min each

900∘C

950∘C

1000∘CBefore

(b)

Figure 9 (Figure 3 from [2]) PL spectra for Si+ implantedSiO2 annealed at high temperature in forming gas for increasing

annealing time (a) and isochronal (15min) dry oxidation of thesamples annealed at 1050∘C in forming gas for increasing oxidationtemperature (b)

nanocrystals grow the increased separation of the electron-hole pair implies a lower PL energy and a longer lifetime inagreement with the experiment

The PL spectra obtained after subsequent isochronaldry oxidation at different temperatures from the samplespreviously annealed at 1050∘C for 30min are also depicted inFigure 9 (lower half) As the oxidation temperature increasesthat is as the diameter of the Sinc is reduced the PL peakenergy pins around 16-17 eV (slow decay red band) untilit finally vanishes with the simultaneous emergence of thefast decay blue band in complete analogy with the behaviorof oxidized p-Si (Figure 8) The origin of this fixed energyred band is easily explained within the frame of the samesurface state model In this case the emission occurs inan interfacial SiOx (119909 lt 2) layer formed at the oxidationfront where the authors assume localized defect-type of statesto explain the fixed energy at around 17 eV Therefore theauthors compared their model with the three-region model


3

2

1

0

minus1

minus20 1 2 3 4 5

Ener

gy (e

V)

Diameter (nm)

Zone III Zone II Zone I

CB energyVB energy

Trapped electronTrapped hole

Figure 10 (Figure 3 from [38]) Calculated energy band structure inSi nanocrystals as a function of cluster size and surface passivationTrapped electron and hole states according to diameter values areobserved

of Kanemitsu et al [35 39] but argued about the difficulty toimagine an interfacial SiOx (119909 lt 2) layer with a band gaplower than that of the Si-crystallite No mention is made ofKanemitsursquos report [44] where the origin of the red fixedband is associated with surface localized states The origin ofthe blue band is not discussed in the paper and rather thereader is remitted to [50]

An important clarification of the SincSiO2surface-

related emissionmechanismwas presented in 1999 byWolkinet al [38] regarding their results on silicon quantum dots inp-Si These authors analyzed experimentally the PL emissionfrom the p-Si in a range of dot diameters below 5 nm for twogroups of samples one of them remained at all times in an Ar(oxygen-free hydrogen passivated) atmosphere and the otherone was exposed to air (oxygen passivated) after the etchingprocedure They also developed a theoretical model whichshows the presence of new carrier states in the band gap ofthe smallest quantum dots when the Si=O bonds are formedAs seen in the framework of their model Figure 10 depictsthe calculated energy band structure in Si nanocrystals asa function of cluster size and surface passivation On theother hand Figure 11 shows the theoretical results for freeexciton band gap energy (upper line) and for the lowesttransition energy in the presence of a Si=O bond (lowest line)as a function of crystallite diameter The experimental roomtemperature PL peak energies for both the aforementionedgroups of samples oxidized and not oxidized (hydrogenpassivated) are also depicted in this figure A good agreementbetween experiment and theory is observed In additionthe effect of oxidation depends on the crystallite size threedifferent zones with different emission mechanisms may bedistinguished For crystallites with diameters larger thanabout 3 nm (zone I) even when the samples are oxidized or

Ener

gy (e

V)

Diameter (nm)


1 15 2 25 3 35 4

4

35

3

25

2

15

Figure 11 (Figure 4 from [38]) Theoretical results for the freeexciton band gap energy (upper line) and for the lowest transitionenergy in the presence of a Si=O bond (lowest line) as a functionof crystallite diameterThe experimental room temperature peak PLenergies for both the oxidized (I) and the nonoxidized or hydrogenpassivated (e) samples are also depicted

not the PL peak energy increases with decreasing nanocrys-tal sizes the emission involves free excitons and the scenariocorresponds to the quantum confinement effect This is thearea generally covered by most of the published works whichcorresponds to the PL spectrum in the orange-red zone Fordiameters lower than about 3 nm the emission correspondsto transition from a trapped electron state to a valence band(zone II) or from a trapped electron state to a trapped holestate (trapped exciton) (zone III) These results explain thesignificant Stokes shift for the smallest nanocrystallites [38]the pining of the PL spectra at about 21 eV (590 nm) withdecreasing crystallite diameters [8 38] and a PL spectrumred shift as high as 1 eV for p-Si samples after exposure to air[38]

An apparent contradiction between this model and thosefrom Kanemitsu et al and Koch et al deserves attentionIn these last models it was firmly established that whena Sinc-based luminescent material is oxidized at a hightemperature so as to reduce the Sinc size below a few nmno matter what is its method of synthesis the PL peakpins at about 16-17 eV However according to Wolkinrsquosresults for p-Si with decreasing Sinc size the PL spectrapin at about 21 eV after oxidation at room temperature inair or pure oxygen atmospheres These different behaviorsmight be associated in our opinion with differences in theoxygen passivation configurations [51] produced by differentoxidation conditions (room or high temperature oxidation)leading to different oxidation-related energy band structuresIn Figure 12 we reproduce Figure 5 from the paper byNishida [45] In his paper the author theoretically examinedthe effect of the configuration of oxygen on the electronicstructure of a Sinc in order to clarify the mechanism of theoxidation-induced redshifts in the PL spectra for H-coveredp-Si Nishida consistently calculated the electronic state of


45

40

35

30

25

20

15

10

Ener

gy g

ap (e

V)

1 12 14 16 18 2

D (nm)

No oxygenDouble-bonded

BackbondedInserted

Figure 12 (Figure 5 from [45]) Calculated HOMO-LUMO energygaps as a function of the Sinc diameter (119863) for double-bondedbackbonded and inserted oxygen configurations in comparisonwith the unoxidized case and with the oxidation-induced peakenergy at sim21 eV in the PL spectra observed in p-Si

Sinc with diameters 1-2 nm by using the extended Huckel-type nonorthogonal tight-binding (EHNTB) method forthree possible oxygen configurations (i) double-bonded (ii)backbonded and (iii) inserted Figure 12 shows the calculatedHOMO-LUMO energy gap as a function of the Si dotdiameter (119863) in comparison with the case for the unoxidizedSi dots andwith the oxidation-induced peak energy atsim21 eVin the PL spectra observed in p-Si As observed the energygaps calculated for the backbonded oxygen configurationin all Si dots studied coincide well with the observed PL-peak energy whereas those calculated for the double-bondedoxygen configuration gradually decrease from 22 eV up toabout 17 eV with the increase in dot size in the range of 1-2 nm This last value resembles those from Kanemitsursquos andKochrsquos results for Sinc diameters higher than 3 nm In viewof the precedent arguments one is tempted to explain thementioned contradiction as follows for oxidation at hightemperature which reduces the Sinc diameter as in the worksof Kanemitsu et al and Koch et al the backbonded oxygenconfiguration is observed For room temperature oxidationhowever a double-bonded oxygen configuration is obtained

The experimental results for PL peak energy as a functionof nanocrystal diameter for the Sinc-basedmaterials are sum-marized byWilcoxon et al in their paper of 1999 [33] on opti-cal and electronic properties of Si nanoclusters synthesizedin inverse micelles Figure 13 reproduces Figure 10 of thatpaper where the results of their own work as well as the datafrom the literature are depicted The first observation madeby the authors is the different dependences on size reportedby the different papers This fact is partially attributed to

0 1 2 3 4 5 6 7 8 9

Diameter (nm)

4

3

2

1

Peak

PL

ener

gy (e

V)

Si nanoclusters

Present workPresent workPresent workOsaka et al4

Risbud et al7

Takagi et al3

Saunders et al5

Littau et al2

Schuppler et al34

Iwasaki et al6

Klm35aKanemitsu8

Figure 13 (Figure 10 from [33]) Summary of experimental data(from reference [33] and from papers previously published andreferenced in [33]) on peak PL energy versus Si nanocluster size

uncertainties in size The exciton binding energy (as high assim350meV as reported by [33]) might also have importancein the different values reported Furthermore all PL peaksof SiO

2-capped Sinc or Sinc embedded in glass matrices fall

into the shaded region of the diagramwhile the experimentaldata for the oxygen-free samples (at the same value as thediameter) fall above this shaded region So it can be clearlyconcluded that the interface situation plays a significant rolein the luminescence response for these materials

Let us finally pay attention to the discrete fast (F) blueband appearing in the PL spectra of Sinc-based materialsjointly with the slow (S) red one when reducing Sinc sizeas seen in the paper from Dohnalova et al [8] As wasmentioned before both bands were observed in the workfrom Kanemitsu [44] for oxidized spherical Sinc obtained bysynthesis from the vapor phase excited under short intensepulsed laser radiation and in that from Koch and Petrova-Koch [2] for thermally oxidized p-Si as well as for oxidizedSinc (thermally segregated from Si+-implanted SiO

2) In

the first paper the origin of the F-band was attributed tofundamental carrier recombination in the crystalline core oftheir 37 nm oxidized Sinc In the second one the reader isremitted to [50] for an explanation of the origin of the blueband However the explanation in the last reference is notclearThis last paper is just devoted to the study of the fast andslow visible luminescence bands of oxidized p-Si however atthe end the authors confessed that the work does not resolvethe questions as to how the red and blue PL originate

A detailed analysis of the point is realized in [8] for p-Si with a high porosity obtained through a modification ofSi-wafer electrochemical etching In particular the use of an


400 500 600 700 800

H2O2

poste

tchi

ng

Wavelength (nm)

PL in

tens

ity (a

u)

Figure 14 (Figure 1(b) from [8]) General behavior of the contin-uous wave excited PL spectra as the Sinc size decreases for highporosity aged (oxidized) p-Si obtained through the use of a H

2O2

postetching to reduce the Sinc diameter

H2O2postetching (to reduce the Sinc diameter) is studied

via the time-resolved PL spectroscopyThe authors developeda series of experiments starting with the electrochemicaletching and applying an increasing H

2O2postetching with

the corresponding reduction in the Sinc size the so-calledstandard (no postetching) yellow white and blue samplesNomeasurements of the real sizes are reportedThe emissionstudy is performed after the samples are aged (oxidized)the color of the standard sample for instance is changedfrom green to orange-red in this process In their paper[8] the authors survey the treatment of both bands in theliterature thus verifying that most published papers dealseparately with either the F- or the S-bands which precludeany analysis about the possible relationship between bothemission mechanisms Figure 14 reproduces Figure 1(b) frompaper [8] which shows the general behavior of the continuouswave excited PL spectra as the Sinc size decreasesThe resultscan be summarized as follows a red slow (S) band appearson the microsecond timescale This band blueshifts but stopsat about 590 nm Simultaneously a blue fast (F) band emergesin the nanosecond timescale whose relative intensity (relativeto the S-band which finally fades away) increases Thereforea discontinuity in the spectral blueshift occurs as Sinc size isreduced which is attributed to switching between S- and F-band emissions

The authors declare as consensus that the origin of theS-band is the result of recombination through quantizedstates in relatively large Sinc in cooperation with the surfacepassivation species Figure 14 represents the ideas of the basicmodels described above In our opinion this band is alsorelated with relatively small Sinc The PL spectra whichredshift and pin at about 590 nm are due to oxidation

SiSi

OO

O O

O

O O

120572 = 120∘ndash180∘

d = 154ndash169 A

Figure 15 Ideal representation of silicon dioxide the oxygen joiningtwo silicon atoms is a bridging atom

according to the model of Wolkin et al [38] Moreover theauthors declare a priori that there is no obvious reason whythe blueshift of the S-band should stop at the ldquomagicrdquo 590 nmboundary rather than continue up to blue and argue thatthe only plausible reason would be that the Sinc reachedits smallest possible size This argument ignores the samephenomenon of the pinning of the PL spectra just at this spec-tral position (590 nm or 21 eV) for aged p-Si [38] They alsoanalyzed the abrupt switching from one emissionmechanism(S-band) to another (F-band) and proposed a model basedon spatial restructuralization that is the Sinc changes froma crystalline to an amorphous state for very small sizes withthe corresponding changes in optical properties

Finally the authors analyzed the controversial origin ofthe F-band with their experimental results Different possibleradiative channels have been discussed in relation to previ-ously published works a prevailing view is that luminescentdefect states are localized in the interface SincSiOx-SiO2(please consult directly the paper for details) However theysupport that the F-band is due to a quasi-direct radiativerecombination inside the Si nanoparticlesrsquo (nanocrystalsor nanoclusters) core in correspondence with Kanemitsursquosproposition [44]

33 SiO2Defect-Related Emission Point Defects It is well

known that the color of gemstones is determined by the lightabsorption reflection or emission of intrinsic or extrinsicdefects in natural oxides Nowadays the point defects orcolor centers are relevant in understanding the emissiveproperties of materials that have a variety of applications inour high technology lifestyle Silicon dioxide in its differentforms including quartz and off stoichiometric oxide has beenstudied because it can be used to produce light Ideally SiO

2

is a continuum arrangement of silicon surrounded by fouroxygen atoms forming tetrahedrons as shown in Figure 15However real silicon dioxide and especiallymaterials like off-stoichiometric oxide would have a high density of defects Inreality materials defects are produced because oxygen atomscan be bonded together or they are gone in the tetrahedralstructure The same can be said for the silicon atoms [52 53]Generically they are known as point defects


S1S2

T1

S0 ground state

Figure 16 Energy interactions allowed in a point defect Absorptionof a photon (solid arrow) from the ground state to a single S

1

produces an electron that rapidly relaxes by internal conversion toa lower vibrational energy (horizontal arrow) Next it can decay tothe S0singlet emitting a photon (dotted arrow) or it can relax to the

triplet T1 It is also possible that the decay to the ground state does

not produce an emission

With quartz being the crystalline and purest formof SiO2

it has been used to study the different point defects relatedto the absorption and emission of light in silicon oxide andelectronic structure So a parabolic distribution of electronicstates related to the molecular vibration has been established[60 61] and some photon-electron interactions have beenproposed [53 61] Figure 16 shows some transition allowedin point defects

Point defects are studied mainly by resonance spec-troscopy specifically paramagnetic centers can be deter-mined by this technique Others for example diamagneticcenters have to be studied using other techniques Opticalabsorption and emission are another important way todetermine point defects In [62] techniques as impedancespectroscopy (IS)four-point dc conductivity thermogravi-metric analysiscoulometric titration dilatometry high-temperatureKelvin probe andKelvin probe forcemicroscopyscanning tunneling microscopy (STM)spectroscopy X-rayphotoelectron spectroscopy (XPS) X-ray absorption spec-troscopy secondary ionmass spectroscopy (SIMS) andX-rayand neutron diffraction (XRD) are mentioned to determinedifferent characteristics of point defects

Paramagnetic point defects in SiO2have been acutely

studied in relation to light emission in quartz The E1015840 centertwofold coordinated Si the neutral oxygen vacancy and thenonbridging oxygen hole center (NBOHC) are well-knowncenters related to the emission of light in quartz [54 55 57]The E1015840 center is formed by an unpaired electron in a danglingorbital sp3 of a three-coordinated Si atom Represented asOequivSi∙ the equiv denotes the coordinated three oxygen bondsand the ∙ denotes the unpaired electron The neutral oxygenvacancy is formed when one oxygen atom is missing andtwo silicon atoms are directly bonded Then it is described

as OequivSiminusSiequivO The two coordinated Si are represented by

Ondash∙∙

SindashO where (∙∙) represents two paired electrons in thesame orbital

Figure 17 presents different point defects that have beendetermined by electron spin resonance (ESR) A detailedanalysis of the E1015840 center in its different variation is found in[56] ESR as its name states is the magnetic field frequencyat which resonance occurs and the resonance is determinedexclusively for each paramagnetic center [52] The oxygendeficient center in general can be positively or negativelycharged allowing specific optical absorption and electronictransitions

Also diamagnetic defects such as neutral oxygen vacan-cies (equivSindashSiequiv) two-coordinated silicon atoms (OndashSindashOndash)and peroxy linkages (equivSindashOndashOndashSiequiv) could be found inquartz The diamagnetic defects also have absorption opticalbands associated with electron transitions [55]

A recent study on generation of color centers dealswith the kinetics and growth of defects in silica In [63]the generation due to heavy ion impact is presented Theyuse bromide ions accelerated with 5MV The evolution ofNBOHC E1015840 and the oxygen deficient center was studiedusing the optical absorption characteristic in the visible andUV range The authors show that the kinetic of the colorcenters follows the Poisson law

New advances in the detection system have improvedthe characterization of defects Reference [64] presents thediffusion and clustering of the E1015840 centers in quartz theauthor shows 2D images of SPR (surface plasmon resonance)portraying the variation in the cluster after different heattreatments The defects do not follow simple diffusion lawsand they try to stay in the high density areas

In Silicon RichOxide most of the work has been centeredon thermal silicon dioxide implanted with different mate-rials mainly silicon see for example [58 65] The secondreference is a very interesting paper and includes besidesthe Si implantation studies on SRO obtained by reactivesputtering of SiO and O The authors accepted that somecathode luminescence emission bands are related to defectsNBOHC with 650 nm (19 eV) red-luminescence the blueand UV bands 460 and 290 nm (27 and 43 eV) with the Sirelated oxygen deficient center (Si-ODC)They also proposedthat in absence ofH stressed orweak bonds (sdot sdot sdot ) could be theprecursors of defects and proposed the following equation

equivSindashOsdot sdot sdotSiequiv997888rarrequivSindashO∙ + ∙Siequiv (3)

This study included different implantation doses to produceSiOx with 119909 varying between 0 and 2 Besides annealingat different temperatures and how these two parametersinfluence the emission were also presented In this studyFourier Transform Infrared (FTIR) was used to calibrate thestoichiometry of the layer with a threshold value of 119909 wherethe emission can be clearly observedThey also proposed thatthe thermal annealing promotes the rearrangement of thesilicon atoms in small clusters as chains or rings within theSiO119909network The arrangements can be separated into cores

of siliconndashsilicon bonds and the surface where both silicon


Si

O

O

O

(a)

Si

O

O

(b)

Si

O

O

O O

(c)

Si

OO

O

Si

O OO

(d)

Si

O

OO

O

O

(e)

Figure 17 Paramagnetic point defects in SiO2 (a) The E1015840 center [54ndash56] (b) twofold coordinated silicon [53] (c) nonbridging oxygen hole

center (NBOHC) [55] (d) the neutral oxygen vacancy and (e) peroxy radical [53 56] All of these are well-known centers related to theemission of light in quartz [57]

350 400 450 500 550 600 650 700 750 800 850 900 950

0

20

40

60

80

100

120

140

Phot

olum

ines

cenc

e (au

)

Emission wavelength (nm)

SRO30 0minSRO30 180minSRO20 0min


Figure 18 PL intensity from samples of SRO deposited by LPCVDas deposited and after annealing at 1100∘C Deposited films have aweak emission however after annealing at 1100∘C the PL increasesespecially for the off-stoichiometric layer with silicon excess lowerthan 8 (Ro = 20 and 30)

and oxygen have dangling bonds They observed that largeextended cluster reduces the luminescence

The most common technique to obtain SRO is the CVDin its different forms perhaps it is the most studied togetherwith silicon implantation in thermal oxide In particularLPCVD is characterized by deposition at high temperaturesin order to dissociate the reactive gases For example silane(SiH4) andnitrous oxide (N

2O) and temperatures of at least of

700∘C are used regularly Under such conditions and duringthe deposition many reactions take place and a variety ofSindashObonds are expected [66] As deposited the films scarcelyhave emission but after high temperature treatments intenseemission is developed as shown in Figure 18 This indicatesthat films obtained by LPCVD are full of defects and thatafter annealing they become precursors of efficient emissivecenters

As previously mentioned Si implanted SiO2

filmsannealed at a high temperature have emission However onlythose with high implantation dose at around 1017 atomscm2have emission Berman et al experimented combining thehigh silicon excess obtained in a simple way using LPCVDand that obtained by ion implantation [67] In this study theSRO films of different silicon concentrations were enrichedthrough silicon implantation Unexpectedly the results showthat the highest emission was obtained in films with low


0

20

40

60

80

100

120

140

160

180

200

220

240

260

14 16 18 20 22 24 26 28 30

020406080100120140160180200220240

PL in

tens

ity (a

u)

Energy (eV)

14 16 18 20 22 24 26 28 30

Energy (eV)PL in

tens

ity (a

u)

5 times 1015

5 times 1015

2 times 1016

2 times 1016

t = 0mint = 90min

t = 180min

Ro = 30 dose = 5 times 1015

TT = 1100∘C

Figure 19 PL intensity from SRO films super enriched with siliconimplantation [58] Ro = 20 and 30 correspond to a silicon excess ofaround 5 to 7 denoted by squares and circles respectively The PLintensity increased after thermal annealing at 1100∘Cduring 180minas shown in the inset

50 100 150 200 250 300 350

TL in

tens

ity (a

u)

Temperature (∘C)

350nm

290nm

260nm

230nm

Figure 20 Thermo-luminescent emission induced by UV irradia-tion of samples SRO20 obtained by LPCVD after 1100∘C annealing[59]Thewavelength used to charge the traps is shown in each curveas the photon energy increases the thermoluminescent emissionreduces

silicon excess As shown in Figure 19 Si implantation witha dose as low as 1 times 1015 atsdotcmminus2 and silicon excess as lowas 5 deposited by LPCVD generates after annealing highphotoluminescence

DiMaria et al observed electroluminescence in filmsobtained by LPCVD However they divided the films intoSRO and off-stoichiometric silicon oxides (OSO) accordingto the silicon excess Low silicon excess say less than7 represented by Ro ge 20 is OSO and high silicon

excess say more than 10 and represented by Ro le 10is SRO [68 69] The deposited SRO has many siliconnanocrystals and the density increases rapidly when thefilms are subjected to high temperature annealing How-ever neither DiMaria nor our group found Sinc in OSO[68 70]

In [67] FTIR studies of SRO and OSO demonstratethat the stretching frequency increases after annealing forall silicon excess This result suggests a phase separationduring the thermal annealing and then an increase ofoxidized compounds Moreover they include XPS studiesshowing that after annealing at 1100∘C a phase separationof elemental silicon non stochiometric silicon oxide andSiO2 is produced for low silicon excess the SiOx phase

dominates They conclude that two competitive morpho-logical mechanisms take place during annealing one isthe formation of silicon agglomerates and the other is theformation of silicon and oxygen compounds If silicon excessis high enough the silicon agglomerates will form intonanocrystals As Si content is decreased however siliconoxidation states will dominate due to the larger separationbetween elemental silicons As silicon excess increases theSRO will tend towards a polysilicon layer conversely assilicon is reduced the SRO film will move towards a stoi-chiometric SiO

2 In between these extremes agglomeration

of silicon shifts towards the agglomeration of Si-oxygen com-pounds as the silicon excess moves from high to low siliconexcess

Thermoluminescence TL is a technique similar to PL inthis case temperature is used instead of light TL is mostlyused in anthropology in the dating of antique objects Theprinciple involved in this technique is that some materialsafter exposure to radiation (eg sun light) store chargesdue to defects Then when they are heated the electronsare released and they recombine emitting light [71 72]While this technique can be used to study emission inmaterials damaged by radiation such as quartz few reportscan be found in the literature on this subject [73] andeven less for SRO or for OSO Piters et al present astudy of thermoluminescence found in SRO [59] the spec-trum of emission is shown in Figure 20 where the emittedwavelength is not determined However the intensity ofthe emission depends on the radiation used to charge thesample However a model is proposed that deals with chargetrapped in acceptor traps and their emitting decay afterheating

Cathodo- and electroluminescence CL and EL are usedto determine the emissive centers that cannot be excitedin PL and also all the emissive electronic states can bereached [74] In both techniques electrons are injected intothe conduction band of the material so that more energetictraps can be reached CL and EL have been used to studythe emission of SRO where electrons are injected into thefilm by a high acceleration field or by biasing the samplewith a voltage [70 75 76] Figure 21 shows the whole rangeof emissions of OSO that goes from 400 to 850 nm PL onlyemits in a short part of the spectrum The most energetictechnique is CL which produces a spectrum within themore energetic side of the spectrum EL emission increases


400 500 600 700 800 900

00

02

04

06

08

10

CL P

L an

d EL

lum

ines

cenc

e (au

)

Wavelength (nm)

CL-SRO30

CL-SRO20

PL-SRO30

V = 50

Figure 21 Photo- cathodo- and electroluminescence behavior ofOSO films deposited by LPCVD EL was biased by 50 volts It isclear that CL and EL include the PL and the full emission range isfrom 400 to 450 nm As the bias voltage increases the EL blue peakincreases more than the red one and the EL spectrum tends towardsthat of the CL

as more voltage is applied that is as the energy increasesthe emission shifts to that of the CL In the referencesmentioned because of the lack of nanocrystals the authorsconclude that the whole range of emission is due to SindashOcompounds All of these emissions are characteristics of SindashO defects [77 78] So we can say that OSO is a materialthat emits basically by point defect centers either individuallyor forming chains or rings However in spite of that OSOcan be considered as a reference material where the emissionis due to defect center To our knowledge there is no studyrelating the emission with paramagnetic or diamagneticcenters

4 Conclusions

In summary different models have been published to explainthe physical mechanisms underlying the luminescent emis-sion of Sinc-based materials and specifically those related toSinc core to SincSiO

2interface and to the SiO

2matrix As

common characteristics to most of them we distinguish thefollowing (i) there is a key role to the interface between thesilicon (core) and the silicon oxide (ii) the light absorptiontakes place in the nanometer-sized core following a quantumconfinement effect whereas the (radiative) recombinationoccurs at the interface and (iii) the quantum size phe-nomenon is the basic emission mechanism in a definiterange of the luminescence spectral distribution when thematerials are obtained posttreated and measured underdefinite conditions

For these materials and concerning Sinc core and Sincsurface twomain PL bands should be considered slow decayband (microsecond time scale) and a discrete fast blue band

(nanosecond time scale) The spectral behavior of the firstband depends on the electronic states on Sincsurface For H-passivated Sinc this band continuously varies from infraredto ultraviolet as Sinc size decreases according to the quantumconfinement effect On the contrary for oxidized Sinc-basedmaterials the band pins at about 17 eV if the oxidation hastaken place at an elevated temperature and at about 21 eV ifit has been achieved at room temperature in free atmospheredue to differences in the oxygen passivation configurations

Concerning the SiO2matrix emission is basically related

to different point defects both paramagnetic and diamag-netic Paramagnetic defects have been well established inquartz using resonance techniques However diamagneticdefects are more difficult to determine and other tech-niques have been proposed to study them The E1015840 centertwofold coordinated Si the neutral oxygen vacancy and thenonbridging oxygen hole center (NBOHC) are well knowncenters related to the emission of light in quartz Alsodiamagnetic defects for example neutral oxygen vacancies(equivSindashSiequiv) two-coordinated silicone atoms (OndashSindashOndash) andperoxy linkages (equivSindashOndashOndashSiequiv) could be found in quartzand determined optically The emission range observed inthe point defects goes from UV to the near infrared Alsothe CVD deposition technique especially LPCVD is used toobtain the SRO and OSO that tends to produce many defectsit is likely that the light emission in the range from 400 to850 nm is due mostly to point defects

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors appreciate the English revision done by RebekahHosse Clark Also the authors appreciate the support ofCONACyT

References

[1] L T Canham ldquoSilicon quantum wire array fabrication byelectrochemical and chemical dissolution of wafersrdquo AppliedPhysics Letters vol 57 no 10 p 1046 1990

[2] F Koch and V Petrova-Koch ldquoLight from Si-nanoparticlesystemsndasha comprehensive viewrdquo Journal of Non-CrystallineSolids vol 198-200 no 2 pp 840ndash846 1996

[3] F Iacona G Franzo and C Spinella ldquoCorrelation betweenluminescence and structural properties of Si nanocrystalsrdquoJournal of Applied Physics vol 87 no 3 pp 1295ndash1303 2000

[4] F Iacona C Spinella S Boninelli and F Priolo ldquoFormation andevolution of luminescent Si nanoclusters produced by thermalannealing of filmsrdquo Journal of Applied Physics vol 95 p 37232004

[5] A Uhlir ldquoElectrolytic shaping of germanium and siliconrdquo TheBell System Technical Journal vol 35 no 2 pp 333ndash347 1956

[6] M A Tischler R T Collins J H Stathis and J C TsangldquoLuminescence degradation in porous siliconrdquo Applied PhysicsLetters vol 60 no 5 pp 639ndash641 1992


[7] I M Chang S C Pan and Y F Chen ldquoLight-induceddegradation on porous siliconrdquo Physical Review B vol 48 no12 pp 8747ndash8750 1993

[8] K Dohnalova L Ondic K Kusova I Pelant J L Rehspringerand R-R Mafouana ldquoWhite-emitting oxidized siliconnanocrystals discontinuity in spectral development withreducing sizerdquo Journal of Applied Physics vol 107 no 5 ArticleID 053102 22 pages 2010

[9] C-C Tu Q Zhang L Y Lin and G Cao ldquoBrightly photolu-minescent phosphor materials based on silicon quantum dotswith oxide shell passivationrdquo Optics Express vol 20 no 1 ppA69ndashA74 2012

[10] C Lin and G Lin ldquoDefect-enhanced visible electrolumines-cence of multi-energy silicon-implanted silicon dioxide filmrdquoIEEE Journal of Quantum Electronics vol 41 no 3 pp 441ndash4472005

[11] R J Walters J Kalkman A Polman H A Atwater and M JA de Dood ldquoPhotoluminescence quantum efficiency of densesilicon nanocrystal ensembles in SiO

2rdquo Physical Review B vol

73 Article ID 132302 2006[12] T S Iwayama T Hama D E Hole and I W Boyd ldquoEnhanced

luminescence from encapsulated silicon nanocrystals in SiO2

with rapid thermal annealrdquo Vacuum vol 81 no 2 pp 179ndash1852006

[13] H Z Song X M Bao N S Li and J Y Zhang ldquoRelationbetween electroluminescence and photoluminescence of Si+-implanted SiO

2rdquo Journal of Applied Physics vol 82 no 8

Article ID 4028 5 pages 1997[14] A Morales J Barreto C Domınguez M Riera M Aceves and

J Carrillo ldquoComparative study between silicon-rich oxide filmsobtained by LPCVD and PECVDrdquo Physica E vol 38 p 54 2007

[15] M Aceves-Mijares A A Gonzalez-Fernandez R Lopez-Estopier et al ldquoOn the origin of light emission in silicon richoxide obtained by low-pressure chemical vapor depositionrdquoJournal of Nanomaterials vol 2012 Article ID 890701 11 pages2012

[16] X Y Chen Y Lu L Tang et al ldquoThermal-wave nondestructiveevaluation of cylindrical composite structures using frequency-domain photothermal radiometryrdquo Journal of Applied Physicsvol 97 pp 014911ndash014913 2005

[17] J Barreto M Peralvarez J A Rodriguez et al ldquoPulsed electro-luminescence in silicon nanocrystals-based devices fabricatedby PECVDrdquo Physica E vol 38 pp 193ndash196 2007

[18] G D Soraru S Modena P Bettotti G Das G Mariotto and LPavesi ldquoSi nanocrystals obtained through polymer pyrolysisrdquoApplied Physics Letters vol 83 no 4 pp 749ndash751 2003

[19] G Das L Ferraioli P Bettotti et al ldquoSi-nanocrystalsSiO2thin

films obtained by pyrolysis of sol-gel precursorsrdquo Thin SolidFilms vol 516 no 20 pp 6804ndash6807 2008

[20] J A Rodrıguez C Fernandez Sanchez C Domınguez SHernandez and Y Berencen ldquoBulk silica-based luminescentmaterials by sol-gel processing of non-conventional precur-sorsrdquo Applied Physics Letters vol 101 no 17 Article ID 1719082012

[21] S TH Silalahi H Y Yang K Pita andYMingbin ldquoRapid ther-mal annealing of sputtered silicon-rich oxideSiO

2superlattice

structurerdquo Electrochemical and Solid-State Letters vol 12 no 4pp K29ndashK32 2009

[22] S J Huang and G Conibeer ldquoSputter-grown Si quantum dotnanostructures for tandem solar cellsrdquo Journal of Physics DApplied Physics vol 46 no 2 Article ID 024003 2013

[23] D Y Shin J H Park S Kim S Choi and K J Kim ldquoGraded-size Si-nanocrystal-multilayer solar cellsrdquo Journal of AppliedPhysics vol 112 no 10 Article ID 104304 2012

[24] V Lehmann and U Gosele ldquoPorous silicon formation aquantum wire effectrdquo Applied Physics Letters vol 58 no 8 p856 1991

[25] W Wu X F Huang L J Chen et al ldquoRoom temperaturevisible electroluminescence in silicon nanostructuresrdquo Journalof Vacuum Science amp Technology A vol 17 no 1 pp 159ndash1631999

[26] C Delerue G Allan and M Lannoo ldquoTheoretical aspects ofthe luminescence of porous siliconrdquo Physical Review B vol 48no 15 pp 11024ndash11036 1993

[27] A D Yoffe ldquoLow-dimensional systems quantum size effectsand electronic properties of semiconductor microcrystallites(zero-dimensional systems) and some quasi-two-dimensionalsystemsrdquo Advances in Physics vol 42 pp 173ndash262 1993

[28] T Takagahara and K Takeda ldquoTheory of the quantum con-finement effect on excitons in quantum dots of indirect-gapmaterialsrdquo Physical Review B vol 46 no 23 pp 15578ndash155811992

[29] A Gupta M T Swihart and H Wiggers ldquoLuminescentcolloidal dispersion of silicon quantum dots from microwaveplasma synthesis exploring the photoluminescence behavioracross the visible spectrumrdquo Advanced Functional Materialsvol 19 no 5 pp 696ndash703 2009

[30] B Garrido Fernandez M Lopez C Garcıa et al ldquoInfluence ofaverage size and interface passivation on the spectral emissionof Si nanocrystals embedded in SiO

2rdquo Journal of Applied Physics

vol 91 no 2 pp 798ndash807 2002[31] L W Wang and A Zunger ldquoElectronic structure pseudopoten-

tial calculations of large (approximately 1000 atoms) Si quantumdotsrdquo Journal of Physical Chemistry vol 98 no 8 pp 2158ndash21651994

[32] I Sychugov R Juhasz J Valenta and J Linnros ldquoNarrowluminescence linewidth of a silicon quantum dotrdquo PhysicalReview Letters vol 94 no 8 Article ID 087405 2005

[33] J P Wilcoxon G A Samara and P N Provencio ldquoOptical andelectronic properties of Si nanoclusters synthesized in inversemicellesrdquo Physical Review B Condensed Matter and MaterialsPhysics vol 60 no 4 pp 2704ndash2714 1999

[34] T Torchynska F G Becerril Espinoza Y Goldstein et alldquoNature of visible luminescence of co-sputtered Si-SiOx sys-temsrdquo Physica B vol 340ndash342 pp 1119ndash1123 2003

[35] Y Kanemitsu H Uto Y Masumoto T Matsumoto T Futagiand H Mimura ldquoMicrostructure and optical properties of free-standing porous silicon films size dependence of absorptionspectra in Si nanometer-sized crystallitesrdquo Physical Review Bvol 48 no 4 pp 2827ndash2830 1993

[36] S M Prokes ldquoLight emission in thermally oxidized porous sili-con evidence for oxideminusrelated luminescencerdquo Applied PhysicsLetters vol 62 p 3244 1993

[37] V Petrova-Koch T Muschik A Kux B K Meyer F Koch andV Lehmann ldquoRapid-thermal-oxidized porous Si-the superiorphotoluminescent Sirdquo Applied Physics Letters vol 61 no 8 pp943ndash945 1992

[38] M V Wolkin J Jorne P M Fauchet G Allan and C DelerueldquoElectronic states and luminescence in porous silicon quantumdots The role of oxygenrdquo Physical Review Letters vol 82 no 1pp 197ndash200 1999


[39] Y Kanemitsu T Ogawa K Shiraishi and K Takeda ldquoVisiblephotoluminescence from oxidized Si nanometer-sized spheresexciton confinement on a spherical shellrdquoPhysical ReviewB vol48 no 7 pp 4883ndash4886 1993

[40] P T Huy and P H Duong ldquoIntense photoluminescence andphotoluminescence enhancement of silicon nanocrystals byultraviolet irradiationrdquoAdvancedMaterials Research vol 31 pp74ndash76 2007

[41] L Khomenkova N Korsunska V Yukhimchuk et al ldquoNatureof visible luminescence and its excitation in Si-SiOx systemsrdquoJournal of Luminescence vol 102-103 pp 705ndash711 2003

[42] M S Brandt H D Fuchs M Stutzmann J Weber and MCardona ldquoThe origin of visible luminescencefrom ldquoporoussiliconrdquo a new interpretationrdquo Solid State Communications vol81 no 4 pp 307ndash312 1992

[43] S M Prokes O J Glembocki V M Bermudez R Kaplan L EFriedersdorf and P C Searson ldquoSiHx excitation an alternatemechanism for porous Si photoluminescencerdquo Physical ReviewB vol 45 no 23 pp 13788ndash13791 1992

[44] Y Kanemitsu ldquoLuminescence properties of nanometer-sized Sicrystallites core and surface statesrdquo Physical Review B vol 49no 23 pp 16845ndash16848 1994

[45] M Nishida ldquoCalculations of the electronic structure of siliconquantum dots oxidation-induced redshifts in the energy gaprdquoSemiconductor Science and Technology vol 21 pp 443ndash4492006

[46] K Takeda and K Shiraishi ldquoElectronic structure of silicon-oxygen high polymersrdquo Solid State Communications vol 85 no4 pp 301ndash305 1993

[47] F Koch and V Petrova-Koch ldquoThe surface state mechanism forlight emission from porous siliconrdquo Porous Silicon pp 133ndash1471994

[48] F Koch ldquoModels and mechanisms for the luminescence ofPorous SirdquoMRS Proceedings vol 298 p 319 1993

[49] F Koch V Petrova-Koch and T Muschik ldquoThe luminescenceof porous Si the case for the surface state mechanismrdquo Journalof Luminescence vol 57 no 1ndash6 pp 271ndash281 1993

[50] D I Kovalev I D Yaroshetzkii T Muschik V Petrova-Kochand F Koch ldquoFast and slow visible luminescence bands ofoxidized porous Sirdquo Applied Physics Letters vol 64 no 2 pp214ndash216 1994

[51] H Yu J-Q Zeng and Z-R Qiu ldquoSilicon nanocrystalsrdquo inCrystalline Silicon-Properties and Uses S Basu Ed InTechHampshire UK 2011

[52] D L Griscom ldquoOptical properties and structure of defects insilica glassrdquo Journal of the Ceramic Society of Japan vol 99 no1154 pp 923ndash942 1991

[53] L Skuja ldquoOptically active oxygen-deficiency-related centers inamorphous silicon dioxiderdquo Journal of Non-Crystalline Solidsvol 239 no 1ndash3 pp 16ndash48 1998

[54] R AWeeks ldquoParamagnetic spectra of E21015840 centers in crystalline

quartzrdquo Physical Review vol 130 no 2 pp 570ndash576 1963[55] R Salh ldquoDefect related luminescence in silicon dioxide net-

work a reviewrdquo in Crystalline SiliconmdashProperties and Uses SBasu Ed chapter 8 pp 135ndash172 InTech 2011

[56] E H Poindexter andW LWarren ldquoParamagnetic point defectsin amorphous thin films of SiO

2and Si3N4 updates and

additionsrdquo Journal of the Electrochemical Society vol 142 no7 pp 2508ndash2516 1995

[57] E P OrsquoReilly and J Robertson ldquoTheory of defects in vitreoussilicon dioxiderdquo Physical Review B vol 27 no 6 pp 3780ndash37951983

[58] H Fitting T Barfels A N Trukhin B Schmidt A Gulans andA von Czarnowski ldquoCathodoluminescence of Ge+ Si+ and O+implanted SiO

2layers and the role of mobile oxygen in defect

transformationsrdquo Journal of Non-Crystalline Solids vol 303 no2 pp 218ndash231 2002

[59] T M Piters M Aceves D Berman-Mendoza L R Berriel-Valdos and J A Luna-Lopez ldquoDose dependent shift of the TLglow peak in a silicon rich oxide (SRO) filmrdquo Revista Mexicanade Fısica S vol 57 no 2 pp 26ndash29 2011

[60] J S Shie ldquoThe absorption band shape of color centers withmany-mode interactionrdquo Chinese Journal of Physics vol 15 no1 pp 23ndash28 1977

[61] M Cannas Point defects in amorphous SiO2 optical activity in

the visible UV and vacuum-UV spectral regions [PhD thesis]Universita Degli Studi Di Palermo 1998

[62] H L Tuller and S R Bishop ldquoPoint defects in oxides tailoringmaterials through defect engineeringrdquo Annual Review of Mate-rials Research vol 41 pp 369ndash398 2011

[63] J Manzano-Santamarıa J Olivares A Rivera O Pena-Rodrıguez and F Agullo-Lopez ldquoKinetics of color center for-mation in silica irradiated with swift heavy ions thresholdingand formation efficiencyrdquo Applied Physics Letters vol 101 no15 Article ID 154103 4 pages 2012

[64] E Suhovoy V Mishra M Shklyar L Shtirberg and A BlankldquoDirect micro-imaging of point defects in bulk SiO

2 applied to

vacancy diffusion and clusteringrdquo Europhysics Letters vol 90no 2 Article ID 26009 2010

[65] R Salh ldquoNanocluster in silicon dioxide cathodoluminescenceenergy dispersive X-ray analysis and infrared spectroscopystudiesrdquo inCrystalline SiliconmdashProperties andUses S Basu EdInTech 2011

[66] A Sherman Chemical Vapor Deposition for MicroelectronicsPrinciples Technology and Applications Noyes PublicationsPark Ridge NJ USA 1987

[67] D Berman M Aceves A Gallegos et al ldquoSilicon excess andthermal annealing effects on the photoluminescence of SiO

2

and silicon rich oxide super enriched with siliscon implanta-tionrdquo Physica Status Solidi C vol 1 pp S83ndashS87 2004

[68] D J DiMaria J R Kirtley E J Pakulis et al ldquoElectrolumi-nescence studies in silicon dioxide films containing tiny siliconislandsrdquo Journal of Applied Physics vol 56 no 2 pp 401ndash4161984

[69] D Dong E A Irene and D R Young ldquoPreparation and someproperties of chemically vaporminusdeposited Siminusrich SiO

2and

Si3N4filmsrdquo Journal ofThe Electrochemical Society vol 125 pp

819ndash823 1978[70] M Aceves-Mijares A A Gonzalez-Fernandez R Lopez-

Estopier et al ldquoOn the origin of light emission in silicon richoxide obtained by low-pressure chemical vapor depositionrdquoJournal of Nanomaterials vol 2012 Article ID 890701 11 pages2012

[71] D Richter ldquoAdvantages and limitations of thermoluminescencedating of heated flint from paleolithic sitesrdquo Geoarchaeologyvol 22 no 6 pp 671ndash683 2007

[72] Z Jacobs and R G Roberts ldquoAdvances in optically stimulatedluminescence dating of individual grains of quartz from arche-ological depositsrdquo Evolutionary Anthropology vol 16 no 6 pp210ndash223 2007

[73] T W Hickmott ldquoThermoluminescence and color centers in rf-sputtered SiO

2filmsrdquo Journal of Applied Physics vol 43 no 5

p 2339 1972


[74] B G Yacobi and D B Holt Cathodoluminescence Microscopy ofInorganic Solids Springer New York NY USA 1990

[75] R Lopez-Estopier M Aceves Z Yu and C Falcony ldquoDetermi-nation of the energy states of the donor acceptor decay emissionin silicon rich oxide prepared by low-pressure chemical vapordepositionrdquo Journal of Vacuum Science and Technology B vol29 no 2 Article ID 021017 2011

[76] R Lopez-Estopier M Aceves and C Falcony ldquoCathodo- andphoto-luminescence of silicon rich oxide films obtainedrdquo inCathodoluminescence N Yamamoto Ed pp 978ndash953 InTech2012

[77] L Skuja K Kajihara M Hirano and H Hosono ldquoVisible tovacuum-UV range optical absorption of oxygen dangling bondsin amorphous SiO

2rdquo Physical Review B Condensed Matter and

Materials Physics vol 84 no 20 Article ID 205206 2011[78] M Cannas ldquoLuminescence properties of point defects in silicardquo

in GNSR 2001 State of Art and Future Development in RamanSpectroscopy and Related Techniques G Messina and and SSantangelo Eds IOS Press 2002

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


in the SiO2matrix The different chemical vapor deposi-

tion (CVD) techniques are naturally inclined to producedefects in the matrix of deposited materials High tempera-ture techniques as low pressure chemical vapor deposition(LPCVD) are even more predisposed to such molecularchanges However in spite of the defect formation whenthe mentioned techniques are used it is uncommon tofind studies that relate the emission with point defects inSRO

The poor chemical and mechanical properties of p-Si stimulated the research work with other silicon-basedluminescentmaterials duringmore than twodecadesAmongthem are materials based on Sinc embedded in an SiO

2

matrix which can be obtained by different techniques suchas Si+ implantation into thermal SiO

2 plasma enhanced

chemical vapor deposition (PECVD) LPCVD and Sol-gelThe Si nanostructures are then autoassembled from individ-ual atoms under a high temperature annealing in an inertatmosphere This process produces the Si diffusion nucle-ation and crystallization Other SincSiO

2-based materials

are obtained by co-Sputtering pulsed laser deposition (PLD)and oxidation of layers of Si nanoparticles synthesized fromthe gas phase In the next section some of the main synthesistechniques will be described

So far it has not been possible to find a physicalmodel explaining the emission processes underlying all theseSincSiO

2-basedmaterials A good and unifying effort in our

opinion is that of Koch and Petrova-Koch [2] Instead a rushof models (sometimes contradictory to one another) havebeen proposed to fundament this phenomenon for specificmaterials obtained by specific techniques under concretetechnological parameters As a rule a good agreement isreported between the results of the specific model andthe experimental results for a particular material It seemsthat these facts reflect a reality of nature that is intenseluminescent radiation in a wide spectral range (from infraredto ultraviolet) can be produced in these materials followingdifferent physical mechanisms which will be reviewed inSection 3

The intention of this paper is to review the mechanismof emission due to Sinc and the defects embedded in adielectric matrix (SiO

2) In Section 2 we present some tech-

niques commonly used to obtain SRO and related materialsIn Section 3 a review of the different possible emissiontheories and defects is presented We finish this sectionshowing specifically the emission of off-stoichiometric oxidedue to different excitation which can be related to pointdefects

2 Synthesis of Materials

The most extensive way to obtain silicon nanoparticlesembedded in dielectric layers either silicon oxide or nitrideis through the segregation of the excess silicon atoms insilicon enriched layers with a thermal annealing at a hightemperature [3 4] Here the technological parameters suchas the duration of the thermal treatment the annealingtemperature and the Si excess content all determine the final

size of the particle the size dispersion and its nature eitheramorphous or crystalline However different techniques arealso used to produce SincSiO

2-based materials

21 Porous Silicon (p-Si) Porous silicon was discovered byUhlir at the Bell laboratories (US) in 1956 [5] Despite thisearly discovery the scientific community was not interestedin p-Si until the late 80s when Canham proposed that p-Si could display quantum confinement effects [1] In hispublished experimental results strong light emission fromsilicon was obtained after subjecting the Si-wafers to anelectrochemical and chemical dissolution Different PL peakswere observed depending on the porosity of the layer Thesenovel results stimulated the interest of the scientific commu-nity in the study of the nonlinear optical and electroopticalproperties of silicon especially due to their potential appli-cations Despite the strong room temperature luminescenceobserved in p-Si it was found that it suffers from poormechanical and chemical stability producing degradation inthe PL properties [6 7] Multiple studies have been done toovercome this limitation such as modifications introduced inthe etching procedure [8 9] Some authors have reported thata postetching treatment in H

2O2leads to a decrease of the

nanoparticle core size and also to some extent changes thesurface oxide for the modulation of the photoluminescencecolor [8]

22 Ion Implantation In the ion implantation technique athermal silicon oxide grown on a silicon wafer is implantedwith silicon ions at a specific dose and energy With thistechnique both chemical and structural changes are intro-duced by the implanted ions To activate the implanted ionsand to repair the damage produced a thermal annealingis necessary In the case of Si ions implanted into silicondioxide matrix a silicon agglomeration in the form of siliconnanoparticles is obtained after the thermal annealing processThe dose and energy of implantation determine the siliconexcess and the depth profile respectively [10ndash13] In somecases multiple silicon ion implantations are used to obtaina uniform depth profile of silicon excess and a uniform Sincdensity [10]

23 Chemical Vapor Deposition (CVD) There are a greatnumber of forms of CVDThese processes differ by themeansin which chemical reactions are initiated (eg activationprocess) and process conditions In a typical CVD processthe wafer or substrate is exposed to one or more volatileprecursors which react andor decompose on or near thesubstrate surface to produce the desired deposit The mainCVD techniques used for Sinc fabrication are LPCVD andPECVD SRO films are easily deposited by PECVD andLPCVD techniques using oxidant species like nitrous oxide(N2O) and silicon compounds (ie silane SiH

4) as reactant

gasses [14ndash17] For these techniques Si excess in the deposited




4

119877119900=119865 (N2O)

119865 (SiH4) (1)


2creating Si






















119864119892(eV) (119889) = 119864

1198920(eV) + 373119889(nm)139

(2)

where 1198641198920


2 In this



2



Eg0 Eg

Bulksemiconductor

Quantumdot

CB

VB


40

35

30

25

20

15

10

Gap

ener

gy (e

V)

0 2 4 6 8 10


026 eV








4

3

2

1

0

PL in

tens

ity (times

104

coun

ts)

PL in

tens

ity (times

102

coun

ts)

0 300 600 900

Wavelength (nm)

0 300 600 900

Wavelength (nm)

(d) 1150∘C 3h

(a)

(a)

(b)

(b)

(c)

(c)

(d)

30

25

20

15

10

5

0

(a) As-synt(b) 950∘C(c) 1000∘C

(c) 1150∘C(a) 1050∘C(b) 1100∘C


3000

80

60

40

20

Ram

an in

tens

ity (c

ount

s)

400 450 500 550 600


Hexamet 1100∘C

(a)(b)

(c)

(d)

(e)












2 This has been a






2-based materials


2-based materials






2)119899[43] In






2) and a transition




103

102

10

5

0

Nor

mal

ized

in

tens

ity (a

u)

Abso

rptio

nco

effici

ent120572

(cm

minus1)

400 600 800 1000 1200

Wavelength (nm)

PLAbs

(a)

10

5

0

Nor

mal

ized

in

tens

ity (a

u)

103

102Ab

sorp

tion

coeffi

cien

t120572(c

mminus1)

400 600 800 1000 1200

Wavelength (nm)

PLAbs

(b)

400400 600 800 1000 1200

10

5

0

Nor

mal

ized

in

tens

ity (a

u)

103

Abso

rptio

nco

effici

ent120572

(cm

minus1)

Wavelength (nm)

PL

Abs

(c)






0

Egapcore

EgapI

minus16nm

(a)c-Si core

(b)a-SiO2

(c)Interfacial

layer

Band

gap

ener

gy

Dcore2 Dtotal2

Radius


02

01

0

1

0

200 400 600 800

Abso

rban

ce

Wavelength (nm)PL

inte

nsity

(au

)

Pulse

(a)

(b)

cw




4

3

2

1

0

PL in

tens

ity (a

u)

10 15 20 25 30

Photon energy (eV)

H25

H900

H1000

(times3)

H600

(times150)H1100

(times5)

300K








Photon energy (eV)

900 800 700 600 500 400

Nor

mal

ized

PL

inte

nsity

15 20 25 30



30min

30min

1050∘C

3h

9min3min

30 s10 s

0 s1 times 10

16cm2

Wavelength (nm)

cm2

(a)

Nor

mal

ized

PL

inte

nsity



900∘C

950∘C

1000∘CBefore

(b)






3

2

1

0

minus1

minus20 1 2 3 4 5

Ener

gy (e

V)

Diameter (nm)


CB energyVB energy






Ener

gy (e

V)

Diameter (nm)


1 15 2 25 3 35 4

4

35

3

25

2

15





45

40

35

30

25

20

15

10

Ener

gy g

ap (e

V)

1 12 14 16 18 2

D (nm)


BackbondedInserted




0 1 2 3 4 5 6 7 8 9

Diameter (nm)

4

3

2

1

Peak

PL

ener

gy (e

V)

Si nanoclusters


Risbud et al7

Takagi et al3

Saunders et al5

Littau et al2

Schuppler et al34

Iwasaki et al6

Klm35aKanemitsu8






2) In




400 500 600 700 800

H2O2

poste

tchi

ng

Wavelength (nm)

PL in

tens

ity (a

u)


2O2




2O2postetching with



SiSi

OO

O O

O

O O

120572 = 120∘ndash180∘

d = 154ndash169 A






2



S1S2

T1

S0 ground state


1










Ondash∙∙











Si

O

O

O

(a)

Si

O

O

(b)

Si

O

O

O O

(c)

Si

OO

O

Si

O OO

(d)

Si

O

OO

O

O

(e)



350 400 450 500 550 600 650 700 750 800 850 900 950

0

20

40

60

80

100

120

140

Phot

olum

ines

cenc

e (au

)












0

20

40

60

80

100

120

140

160

180

200

220

240

260

14 16 18 20 22 24 26 28 30

020406080100120140160180200220240

PL in

tens

ity (a

u)

Energy (eV)

14 16 18 20 22 24 26 28 30

Energy (eV)PL in

tens

ity (a

u)

5 times 1015

5 times 1015

2 times 1016

2 times 1016

t = 0mint = 90min

t = 180min


TT = 1100∘C


50 100 150 200 250 300 350

TL in

tens

ity (a

u)

Temperature (∘C)

350nm

290nm

260nm

230nm












400 500 600 700 800 900

00

02

04

06

08

10

CL P

L an

d EL

lum

ines

cenc

e (au

)

Wavelength (nm)

CL-SRO30

CL-SRO20

PL-SRO30

V = 50



4 Conclusions



2matrix As








Acknowledgments


References





























2superlattice






















































2 applied to





2




2and








p 2339 1972
















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






4

119877119900=119865 (N2O)

119865 (SiH4) (1)


2creating Si






















119864119892(eV) (119889) = 119864

1198920(eV) + 373119889(nm)139

(2)

where 1198641198920


2 In this



2



Eg0 Eg

Bulksemiconductor

Quantumdot

CB

VB


40

35

30

25

20

15

10

Gap

ener

gy (e

V)

0 2 4 6 8 10


026 eV








4

3

2

1

0

PL in

tens

ity (times

104

coun

ts)

PL in

tens

ity (times

102

coun

ts)

0 300 600 900

Wavelength (nm)

0 300 600 900

Wavelength (nm)

(d) 1150∘C 3h

(a)

(a)

(b)

(b)

(c)

(c)

(d)

30

25

20

15

10

5

0

(a) As-synt(b) 950∘C(c) 1000∘C

(c) 1150∘C(a) 1050∘C(b) 1100∘C


3000

80

60

40

20

Ram

an in

tens

ity (c

ount

s)

400 450 500 550 600


Hexamet 1100∘C

(a)(b)

(c)

(d)

(e)












2 This has been a






2-based materials


2-based materials






2)119899[43] In






2) and a transition




103

102

10

5

0

Nor

mal

ized

in

tens

ity (a

u)

Abso

rptio

nco

effici

ent120572

(cm

minus1)

400 600 800 1000 1200

Wavelength (nm)

PLAbs

(a)

10

5

0

Nor

mal

ized

in

tens

ity (a

u)

103

102Ab

sorp

tion

coeffi

cien

t120572(c

mminus1)

400 600 800 1000 1200

Wavelength (nm)

PLAbs

(b)

400400 600 800 1000 1200

10

5

0

Nor

mal

ized

in

tens

ity (a

u)

103

Abso

rptio

nco

effici

ent120572

(cm

minus1)

Wavelength (nm)

PL

Abs

(c)






0

Egapcore

EgapI

minus16nm

(a)c-Si core

(b)a-SiO2

(c)Interfacial

layer

Band

gap

ener

gy

Dcore2 Dtotal2

Radius


02

01

0

1

0

200 400 600 800

Abso

rban

ce

Wavelength (nm)PL

inte

nsity

(au

)

Pulse

(a)

(b)

cw




4

3

2

1

0

PL in

tens

ity (a

u)

10 15 20 25 30

Photon energy (eV)

H25

H900

H1000

(times3)

H600

(times150)H1100

(times5)

300K








Photon energy (eV)

900 800 700 600 500 400

Nor

mal

ized

PL

inte

nsity

15 20 25 30



30min

30min

1050∘C

3h

9min3min

30 s10 s

0 s1 times 10

16cm2

Wavelength (nm)

cm2

(a)

Nor

mal

ized

PL

inte

nsity



900∘C

950∘C

1000∘CBefore

(b)






3

2

1

0

minus1

minus20 1 2 3 4 5

Ener

gy (e

V)

Diameter (nm)


CB energyVB energy






Ener

gy (e

V)

Diameter (nm)


1 15 2 25 3 35 4

4

35

3

25

2

15





45

40

35

30

25

20

15

10

Ener

gy g

ap (e

V)

1 12 14 16 18 2

D (nm)


BackbondedInserted




0 1 2 3 4 5 6 7 8 9

Diameter (nm)

4

3

2

1

Peak

PL

ener

gy (e

V)

Si nanoclusters


Risbud et al7

Takagi et al3

Saunders et al5

Littau et al2

Schuppler et al34

Iwasaki et al6

Klm35aKanemitsu8






2) In




400 500 600 700 800

H2O2

poste

tchi

ng

Wavelength (nm)

PL in

tens

ity (a

u)


2O2




2O2postetching with



SiSi

OO

O O

O

O O

120572 = 120∘ndash180∘

d = 154ndash169 A






2



S1S2

T1

S0 ground state


1










Ondash∙∙











Si

O

O

O

(a)

Si

O

O

(b)

Si

O

O

O O

(c)

Si

OO

O

Si

O OO

(d)

Si

O

OO

O

O

(e)



350 400 450 500 550 600 650 700 750 800 850 900 950

0

20

40

60

80

100

120

140

Phot

olum

ines

cenc

e (au

)












0

20

40

60

80

100

120

140

160

180

200

220

240

260

14 16 18 20 22 24 26 28 30

020406080100120140160180200220240

PL in

tens

ity (a

u)

Energy (eV)

14 16 18 20 22 24 26 28 30

Energy (eV)PL in

tens

ity (a

u)

5 times 1015

5 times 1015

2 times 1016

2 times 1016

t = 0mint = 90min

t = 180min


TT = 1100∘C


50 100 150 200 250 300 350

TL in

tens

ity (a

u)

Temperature (∘C)

350nm

290nm

260nm

230nm












400 500 600 700 800 900

00

02

04

06

08

10

CL P

L an

d EL

lum

ines

cenc

e (au

)

Wavelength (nm)

CL-SRO30

CL-SRO20

PL-SRO30

V = 50



4 Conclusions



2matrix As








Acknowledgments


References





























2superlattice






















































2 applied to





2




2and








p 2339 1972
















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Eg0 Eg

Bulksemiconductor

Quantumdot

CB

VB


40

35

30

25

20

15

10

Gap

ener

gy (e

V)

0 2 4 6 8 10


026 eV








4

3

2

1

0

PL in

tens

ity (times

104

coun

ts)

PL in

tens

ity (times

102

coun

ts)

0 300 600 900

Wavelength (nm)

0 300 600 900

Wavelength (nm)

(d) 1150∘C 3h

(a)

(a)

(b)

(b)

(c)

(c)

(d)

30

25

20

15

10

5

0

(a) As-synt(b) 950∘C(c) 1000∘C

(c) 1150∘C(a) 1050∘C(b) 1100∘C


3000

80

60

40

20

Ram

an in

tens

ity (c

ount

s)

400 450 500 550 600


Hexamet 1100∘C

(a)(b)

(c)

(d)

(e)












2 This has been a






2-based materials


2-based materials






2)119899[43] In






2) and a transition




103

102

10

5

0

Nor

mal

ized

in

tens

ity (a

u)

Abso

rptio

nco

effici

ent120572

(cm

minus1)

400 600 800 1000 1200

Wavelength (nm)

PLAbs

(a)

10

5

0

Nor

mal

ized

in

tens

ity (a

u)

103

102Ab

sorp

tion

coeffi

cien

t120572(c

mminus1)

400 600 800 1000 1200

Wavelength (nm)

PLAbs

(b)

400400 600 800 1000 1200

10

5

0

Nor

mal

ized

in

tens

ity (a

u)

103

Abso

rptio

nco

effici

ent120572

(cm

minus1)

Wavelength (nm)

PL

Abs

(c)






0

Egapcore

EgapI

minus16nm

(a)c-Si core

(b)a-SiO2

(c)Interfacial

layer

Band

gap

ener

gy

Dcore2 Dtotal2

Radius


02

01

0

1

0

200 400 600 800

Abso

rban

ce

Wavelength (nm)PL

inte

nsity

(au

)

Pulse

(a)

(b)

cw




4

3

2

1

0

PL in

tens

ity (a

u)

10 15 20 25 30

Photon energy (eV)

H25

H900

H1000

(times3)

H600

(times150)H1100

(times5)

300K








Photon energy (eV)

900 800 700 600 500 400

Nor

mal

ized

PL

inte

nsity

15 20 25 30



30min

30min

1050∘C

3h

9min3min

30 s10 s

0 s1 times 10

16cm2

Wavelength (nm)

cm2

(a)

Nor

mal

ized

PL

inte

nsity



900∘C

950∘C

1000∘CBefore

(b)






3

2

1

0

minus1

minus20 1 2 3 4 5

Ener

gy (e

V)

Diameter (nm)


CB energyVB energy






Ener

gy (e

V)

Diameter (nm)


1 15 2 25 3 35 4

4

35

3

25

2

15





45

40

35

30

25

20

15

10

Ener

gy g

ap (e

V)

1 12 14 16 18 2

D (nm)


BackbondedInserted




0 1 2 3 4 5 6 7 8 9

Diameter (nm)

4

3

2

1

Peak

PL

ener

gy (e

V)

Si nanoclusters


Risbud et al7

Takagi et al3

Saunders et al5

Littau et al2

Schuppler et al34

Iwasaki et al6

Klm35aKanemitsu8






2) In




400 500 600 700 800

H2O2

poste

tchi

ng

Wavelength (nm)

PL in

tens

ity (a

u)


2O2




2O2postetching with



SiSi

OO

O O

O

O O

120572 = 120∘ndash180∘

d = 154ndash169 A






2



S1S2

T1

S0 ground state


1










Ondash∙∙











Si

O

O

O

(a)

Si

O

O

(b)

Si

O

O

O O

(c)

Si

OO

O

Si

O OO

(d)

Si

O

OO

O

O

(e)



350 400 450 500 550 600 650 700 750 800 850 900 950

0

20

40

60

80

100

120

140

Phot

olum

ines

cenc

e (au

)












0

20

40

60

80

100

120

140

160

180

200

220

240

260

14 16 18 20 22 24 26 28 30

020406080100120140160180200220240

PL in

tens

ity (a

u)

Energy (eV)

14 16 18 20 22 24 26 28 30

Energy (eV)PL in

tens

ity (a

u)

5 times 1015

5 times 1015

2 times 1016

2 times 1016

t = 0mint = 90min

t = 180min


TT = 1100∘C


50 100 150 200 250 300 350

TL in

tens

ity (a

u)

Temperature (∘C)

350nm

290nm

260nm

230nm












400 500 600 700 800 900

00

02

04

06

08

10

CL P

L an

d EL

lum

ines

cenc

e (au

)

Wavelength (nm)

CL-SRO30

CL-SRO20

PL-SRO30

V = 50



4 Conclusions



2matrix As








Acknowledgments


References





























2superlattice






















































2 applied to





2




2and








p 2339 1972
















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials












2 This has been a






2-based materials


2-based materials






2)119899[43] In






2) and a transition




103

102

10

5

0

Nor

mal

ized

in

tens

ity (a

u)

Abso

rptio

nco

effici

ent120572

(cm

minus1)

400 600 800 1000 1200

Wavelength (nm)

PLAbs

(a)

10

5

0

Nor

mal

ized

in

tens

ity (a

u)

103

102Ab

sorp

tion

coeffi

cien

t120572(c

mminus1)

400 600 800 1000 1200

Wavelength (nm)

PLAbs

(b)

400400 600 800 1000 1200

10

5

0

Nor

mal

ized

in

tens

ity (a

u)

103

Abso

rptio

nco

effici

ent120572

(cm

minus1)

Wavelength (nm)

PL

Abs

(c)






0

Egapcore

EgapI

minus16nm

(a)c-Si core

(b)a-SiO2

(c)Interfacial

layer

Band

gap

ener

gy

Dcore2 Dtotal2

Radius


02

01

0

1

0

200 400 600 800

Abso

rban

ce

Wavelength (nm)PL

inte

nsity

(au

)

Pulse

(a)

(b)

cw




4

3

2

1

0

PL in

tens

ity (a

u)

10 15 20 25 30

Photon energy (eV)

H25

H900

H1000

(times3)

H600

(times150)H1100

(times5)

300K








Photon energy (eV)

900 800 700 600 500 400

Nor

mal

ized

PL

inte

nsity

15 20 25 30



30min

30min

1050∘C

3h

9min3min

30 s10 s

0 s1 times 10

16cm2

Wavelength (nm)

cm2

(a)

Nor

mal

ized

PL

inte

nsity



900∘C

950∘C

1000∘CBefore

(b)






3

2

1

0

minus1

minus20 1 2 3 4 5

Ener

gy (e

V)

Diameter (nm)


CB energyVB energy






Ener

gy (e

V)

Diameter (nm)


1 15 2 25 3 35 4

4

35

3

25

2

15





45

40

35

30

25

20

15

10

Ener

gy g

ap (e

V)

1 12 14 16 18 2

D (nm)


BackbondedInserted




0 1 2 3 4 5 6 7 8 9

Diameter (nm)

4

3

2

1

Peak

PL

ener

gy (e

V)

Si nanoclusters


Risbud et al7

Takagi et al3

Saunders et al5

Littau et al2

Schuppler et al34

Iwasaki et al6

Klm35aKanemitsu8






2) In




400 500 600 700 800

H2O2

poste

tchi

ng

Wavelength (nm)

PL in

tens

ity (a

u)


2O2




2O2postetching with



SiSi

OO

O O

O

O O

120572 = 120∘ndash180∘

d = 154ndash169 A






2



S1S2

T1

S0 ground state


1










Ondash∙∙











Si

O

O

O

(a)

Si

O

O

(b)

Si

O

O

O O

(c)

Si

OO

O

Si

O OO

(d)

Si

O

OO

O

O

(e)



350 400 450 500 550 600 650 700 750 800 850 900 950

0

20

40

60

80

100

120

140

Phot

olum

ines

cenc

e (au

)












0

20

40

60

80

100

120

140

160

180

200

220

240

260

14 16 18 20 22 24 26 28 30

020406080100120140160180200220240

PL in

tens

ity (a

u)

Energy (eV)

14 16 18 20 22 24 26 28 30

Energy (eV)PL in

tens

ity (a

u)

5 times 1015

5 times 1015

2 times 1016

2 times 1016

t = 0mint = 90min

t = 180min


TT = 1100∘C


50 100 150 200 250 300 350

TL in

tens

ity (a

u)

Temperature (∘C)

350nm

290nm

260nm

230nm












400 500 600 700 800 900

00

02

04

06

08

10

CL P

L an

d EL

lum

ines

cenc

e (au

)

Wavelength (nm)

CL-SRO30

CL-SRO20

PL-SRO30

V = 50



4 Conclusions



2matrix As








Acknowledgments


References





























2superlattice






















































2 applied to





2




2and








p 2339 1972
















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




103

102

10

5

0

Nor

mal

ized

in

tens

ity (a

u)

Abso

rptio

nco

effici

ent120572

(cm

minus1)

400 600 800 1000 1200

Wavelength (nm)

PLAbs

(a)

10

5

0

Nor

mal

ized

in

tens

ity (a

u)

103

102Ab

sorp

tion

coeffi

cien

t120572(c

mminus1)

400 600 800 1000 1200

Wavelength (nm)

PLAbs

(b)

400400 600 800 1000 1200

10

5

0

Nor

mal

ized

in

tens

ity (a

u)

103

Abso

rptio

nco

effici

ent120572

(cm

minus1)

Wavelength (nm)

PL

Abs

(c)






0

Egapcore

EgapI

minus16nm

(a)c-Si core

(b)a-SiO2

(c)Interfacial

layer

Band

gap

ener

gy

Dcore2 Dtotal2

Radius


02

01

0

1

0

200 400 600 800

Abso

rban

ce

Wavelength (nm)PL

inte

nsity

(au

)

Pulse

(a)

(b)

cw




4

3

2

1

0

PL in

tens

ity (a

u)

10 15 20 25 30

Photon energy (eV)

H25

H900

H1000

(times3)

H600

(times150)H1100

(times5)

300K








Photon energy (eV)

900 800 700 600 500 400

Nor

mal

ized

PL

inte

nsity

15 20 25 30



30min

30min

1050∘C

3h

9min3min

30 s10 s

0 s1 times 10

16cm2

Wavelength (nm)

cm2

(a)

Nor

mal

ized

PL

inte

nsity



900∘C

950∘C

1000∘CBefore

(b)






3

2

1

0

minus1

minus20 1 2 3 4 5

Ener

gy (e

V)

Diameter (nm)


CB energyVB energy






Ener

gy (e

V)

Diameter (nm)


1 15 2 25 3 35 4

4

35

3

25

2

15





45

40

35

30

25

20

15

10

Ener

gy g

ap (e

V)

1 12 14 16 18 2

D (nm)


BackbondedInserted




0 1 2 3 4 5 6 7 8 9

Diameter (nm)

4

3

2

1

Peak

PL

ener

gy (e

V)

Si nanoclusters


Risbud et al7

Takagi et al3

Saunders et al5

Littau et al2

Schuppler et al34

Iwasaki et al6

Klm35aKanemitsu8






2) In




400 500 600 700 800

H2O2

poste

tchi

ng

Wavelength (nm)

PL in

tens

ity (a

u)


2O2




2O2postetching with



SiSi

OO

O O

O

O O

120572 = 120∘ndash180∘

d = 154ndash169 A






2



S1S2

T1

S0 ground state


1










Ondash∙∙











Si

O

O

O

(a)

Si

O

O

(b)

Si

O

O

O O

(c)

Si

OO

O

Si

O OO

(d)

Si

O

OO

O

O

(e)



350 400 450 500 550 600 650 700 750 800 850 900 950

0

20

40

60

80

100

120

140

Phot

olum

ines

cenc

e (au

)












0

20

40

60

80

100

120

140

160

180

200

220

240

260

14 16 18 20 22 24 26 28 30

020406080100120140160180200220240

PL in

tens

ity (a

u)

Energy (eV)

14 16 18 20 22 24 26 28 30

Energy (eV)PL in

tens

ity (a

u)

5 times 1015

5 times 1015

2 times 1016

2 times 1016

t = 0mint = 90min

t = 180min


TT = 1100∘C


50 100 150 200 250 300 350

TL in

tens

ity (a

u)

Temperature (∘C)

350nm

290nm

260nm

230nm












400 500 600 700 800 900

00

02

04

06

08

10

CL P

L an

d EL

lum

ines

cenc

e (au

)

Wavelength (nm)

CL-SRO30

CL-SRO20

PL-SRO30

V = 50



4 Conclusions



2matrix As








Acknowledgments


References





























2superlattice






















































2 applied to





2




2and








p 2339 1972
















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




4

3

2

1

0

PL in

tens

ity (a

u)

10 15 20 25 30

Photon energy (eV)

H25

H900

H1000

(times3)

H600

(times150)H1100

(times5)

300K








Photon energy (eV)

900 800 700 600 500 400

Nor

mal

ized

PL

inte

nsity

15 20 25 30



30min

30min

1050∘C

3h

9min3min

30 s10 s

0 s1 times 10

16cm2

Wavelength (nm)

cm2

(a)

Nor

mal

ized

PL

inte

nsity



900∘C

950∘C

1000∘CBefore

(b)






3

2

1

0

minus1

minus20 1 2 3 4 5

Ener

gy (e

V)

Diameter (nm)


CB energyVB energy






Ener

gy (e

V)

Diameter (nm)


1 15 2 25 3 35 4

4

35

3

25

2

15





45

40

35

30

25

20

15

10

Ener

gy g

ap (e

V)

1 12 14 16 18 2

D (nm)


BackbondedInserted




0 1 2 3 4 5 6 7 8 9

Diameter (nm)

4

3

2

1

Peak

PL

ener

gy (e

V)

Si nanoclusters


Risbud et al7

Takagi et al3

Saunders et al5

Littau et al2

Schuppler et al34

Iwasaki et al6

Klm35aKanemitsu8






2) In




400 500 600 700 800

H2O2

poste

tchi

ng

Wavelength (nm)

PL in

tens

ity (a

u)


2O2




2O2postetching with



SiSi

OO

O O

O

O O

120572 = 120∘ndash180∘

d = 154ndash169 A






2



S1S2

T1

S0 ground state


1










Ondash∙∙











Si

O

O

O

(a)

Si

O

O

(b)

Si

O

O

O O

(c)

Si

OO

O

Si

O OO

(d)

Si

O

OO

O

O

(e)



350 400 450 500 550 600 650 700 750 800 850 900 950

0

20

40

60

80

100

120

140

Phot

olum

ines

cenc

e (au

)












0

20

40

60

80

100

120

140

160

180

200

220

240

260

14 16 18 20 22 24 26 28 30

020406080100120140160180200220240

PL in

tens

ity (a

u)

Energy (eV)

14 16 18 20 22 24 26 28 30

Energy (eV)PL in

tens

ity (a

u)

5 times 1015

5 times 1015

2 times 1016

2 times 1016

t = 0mint = 90min

t = 180min


TT = 1100∘C


50 100 150 200 250 300 350

TL in

tens

ity (a

u)

Temperature (∘C)

350nm

290nm

260nm

230nm












400 500 600 700 800 900

00

02

04

06

08

10

CL P

L an

d EL

lum

ines

cenc

e (au

)

Wavelength (nm)

CL-SRO30

CL-SRO20

PL-SRO30

V = 50



4 Conclusions



2matrix As








Acknowledgments


References





























2superlattice






















































2 applied to





2




2and








p 2339 1972
















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




3

2

1

0

minus1

minus20 1 2 3 4 5

Ener

gy (e

V)

Diameter (nm)


CB energyVB energy






Ener

gy (e

V)

Diameter (nm)


1 15 2 25 3 35 4

4

35

3

25

2

15





45

40

35

30

25

20

15

10

Ener

gy g

ap (e

V)

1 12 14 16 18 2

D (nm)


BackbondedInserted




0 1 2 3 4 5 6 7 8 9

Diameter (nm)

4

3

2

1

Peak

PL

ener

gy (e

V)

Si nanoclusters


Risbud et al7

Takagi et al3

Saunders et al5

Littau et al2

Schuppler et al34

Iwasaki et al6

Klm35aKanemitsu8






2) In




400 500 600 700 800

H2O2

poste

tchi

ng

Wavelength (nm)

PL in

tens

ity (a

u)


2O2




2O2postetching with



SiSi

OO

O O

O

O O

120572 = 120∘ndash180∘

d = 154ndash169 A






2



S1S2

T1

S0 ground state


1










Ondash∙∙











Si

O

O

O

(a)

Si

O

O

(b)

Si

O

O

O O

(c)

Si

OO

O

Si

O OO

(d)

Si

O

OO

O

O

(e)



350 400 450 500 550 600 650 700 750 800 850 900 950

0

20

40

60

80

100

120

140

Phot

olum

ines

cenc

e (au

)












0

20

40

60

80

100

120

140

160

180

200

220

240

260

14 16 18 20 22 24 26 28 30

020406080100120140160180200220240

PL in

tens

ity (a

u)

Energy (eV)

14 16 18 20 22 24 26 28 30

Energy (eV)PL in

tens

ity (a

u)

5 times 1015

5 times 1015

2 times 1016

2 times 1016

t = 0mint = 90min

t = 180min


TT = 1100∘C


50 100 150 200 250 300 350

TL in

tens

ity (a

u)

Temperature (∘C)

350nm

290nm

260nm

230nm












400 500 600 700 800 900

00

02

04

06

08

10

CL P

L an

d EL

lum

ines

cenc

e (au

)

Wavelength (nm)

CL-SRO30

CL-SRO20

PL-SRO30

V = 50



4 Conclusions



2matrix As








Acknowledgments


References





























2superlattice






















































2 applied to





2




2and








p 2339 1972
















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




45

40

35

30

25

20

15

10

Ener

gy g

ap (e

V)

1 12 14 16 18 2

D (nm)


BackbondedInserted




0 1 2 3 4 5 6 7 8 9

Diameter (nm)

4

3

2

1

Peak

PL

ener

gy (e

V)

Si nanoclusters


Risbud et al7

Takagi et al3

Saunders et al5

Littau et al2

Schuppler et al34

Iwasaki et al6

Klm35aKanemitsu8






2) In




400 500 600 700 800

H2O2

poste

tchi

ng

Wavelength (nm)

PL in

tens

ity (a

u)


2O2




2O2postetching with



SiSi

OO

O O

O

O O

120572 = 120∘ndash180∘

d = 154ndash169 A






2



S1S2

T1

S0 ground state


1










Ondash∙∙











Si

O

O

O

(a)

Si

O

O

(b)

Si

O

O

O O

(c)

Si

OO

O

Si

O OO

(d)

Si

O

OO

O

O

(e)



350 400 450 500 550 600 650 700 750 800 850 900 950

0

20

40

60

80

100

120

140

Phot

olum

ines

cenc

e (au

)












0

20

40

60

80

100

120

140

160

180

200

220

240

260

14 16 18 20 22 24 26 28 30

020406080100120140160180200220240

PL in

tens

ity (a

u)

Energy (eV)

14 16 18 20 22 24 26 28 30

Energy (eV)PL in

tens

ity (a

u)

5 times 1015

5 times 1015

2 times 1016

2 times 1016

t = 0mint = 90min

t = 180min


TT = 1100∘C


50 100 150 200 250 300 350

TL in

tens

ity (a

u)

Temperature (∘C)

350nm

290nm

260nm

230nm












400 500 600 700 800 900

00

02

04

06

08

10

CL P

L an

d EL

lum

ines

cenc

e (au

)

Wavelength (nm)

CL-SRO30

CL-SRO20

PL-SRO30

V = 50



4 Conclusions



2matrix As








Acknowledgments


References





























2superlattice






















































2 applied to





2




2and








p 2339 1972
















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




400 500 600 700 800

H2O2

poste

tchi

ng

Wavelength (nm)

PL in

tens

ity (a

u)


2O2




2O2postetching with



SiSi

OO

O O

O

O O

120572 = 120∘ndash180∘

d = 154ndash169 A






2



S1S2

T1

S0 ground state


1










Ondash∙∙











Si

O

O

O

(a)

Si

O

O

(b)

Si

O

O

O O

(c)

Si

OO

O

Si

O OO

(d)

Si

O

OO

O

O

(e)



350 400 450 500 550 600 650 700 750 800 850 900 950

0

20

40

60

80

100

120

140

Phot

olum

ines

cenc

e (au

)












0

20

40

60

80

100

120

140

160

180

200

220

240

260

14 16 18 20 22 24 26 28 30

020406080100120140160180200220240

PL in

tens

ity (a

u)

Energy (eV)

14 16 18 20 22 24 26 28 30

Energy (eV)PL in

tens

ity (a

u)

5 times 1015

5 times 1015

2 times 1016

2 times 1016

t = 0mint = 90min

t = 180min


TT = 1100∘C


50 100 150 200 250 300 350

TL in

tens

ity (a

u)

Temperature (∘C)

350nm

290nm

260nm

230nm












400 500 600 700 800 900

00

02

04

06

08

10

CL P

L an

d EL

lum

ines

cenc

e (au

)

Wavelength (nm)

CL-SRO30

CL-SRO20

PL-SRO30

V = 50



4 Conclusions



2matrix As








Acknowledgments


References





























2superlattice






















































2 applied to





2




2and








p 2339 1972
















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




S1S2

T1

S0 ground state


1










Ondash∙∙











Si

O

O

O

(a)

Si

O

O

(b)

Si

O

O

O O

(c)

Si

OO

O

Si

O OO

(d)

Si

O

OO

O

O

(e)



350 400 450 500 550 600 650 700 750 800 850 900 950

0

20

40

60

80

100

120

140

Phot

olum

ines

cenc

e (au

)












0

20

40

60

80

100

120

140

160

180

200

220

240

260

14 16 18 20 22 24 26 28 30

020406080100120140160180200220240

PL in

tens

ity (a

u)

Energy (eV)

14 16 18 20 22 24 26 28 30

Energy (eV)PL in

tens

ity (a

u)

5 times 1015

5 times 1015

2 times 1016

2 times 1016

t = 0mint = 90min

t = 180min


TT = 1100∘C


50 100 150 200 250 300 350

TL in

tens

ity (a

u)

Temperature (∘C)

350nm

290nm

260nm

230nm












400 500 600 700 800 900

00

02

04

06

08

10

CL P

L an

d EL

lum

ines

cenc

e (au

)

Wavelength (nm)

CL-SRO30

CL-SRO20

PL-SRO30

V = 50



4 Conclusions



2matrix As








Acknowledgments


References





























2superlattice






















































2 applied to





2




2and








p 2339 1972
















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Si

O

O

O

(a)

Si

O

O

(b)

Si

O

O

O O

(c)

Si

OO

O

Si

O OO

(d)

Si

O

OO

O

O

(e)



350 400 450 500 550 600 650 700 750 800 850 900 950

0

20

40

60

80

100

120

140

Phot

olum

ines

cenc

e (au

)












0

20

40

60

80

100

120

140

160

180

200

220

240

260

14 16 18 20 22 24 26 28 30

020406080100120140160180200220240

PL in

tens

ity (a

u)

Energy (eV)

14 16 18 20 22 24 26 28 30

Energy (eV)PL in

tens

ity (a

u)

5 times 1015

5 times 1015

2 times 1016

2 times 1016

t = 0mint = 90min

t = 180min


TT = 1100∘C


50 100 150 200 250 300 350

TL in

tens

ity (a

u)

Temperature (∘C)

350nm

290nm

260nm

230nm












400 500 600 700 800 900

00

02

04

06

08

10

CL P

L an

d EL

lum

ines

cenc

e (au

)

Wavelength (nm)

CL-SRO30

CL-SRO20

PL-SRO30

V = 50



4 Conclusions



2matrix As








Acknowledgments


References





























2superlattice






















































2 applied to





2




2and








p 2339 1972
















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0

20

40

60

80

100

120

140

160

180

200

220

240

260

14 16 18 20 22 24 26 28 30

020406080100120140160180200220240

PL in

tens

ity (a

u)

Energy (eV)

14 16 18 20 22 24 26 28 30

Energy (eV)PL in

tens

ity (a

u)

5 times 1015

5 times 1015

2 times 1016

2 times 1016

t = 0mint = 90min

t = 180min


TT = 1100∘C


50 100 150 200 250 300 350

TL in

tens

ity (a

u)

Temperature (∘C)

350nm

290nm

260nm

230nm












400 500 600 700 800 900

00

02

04

06

08

10

CL P

L an

d EL

lum

ines

cenc

e (au

)

Wavelength (nm)

CL-SRO30

CL-SRO20

PL-SRO30

V = 50



4 Conclusions



2matrix As








Acknowledgments


References





























2superlattice






















































2 applied to





2




2and








p 2339 1972
















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




400 500 600 700 800 900

00

02

04

06

08

10

CL P

L an

d EL

lum

ines

cenc

e (au

)

Wavelength (nm)

CL-SRO30

CL-SRO20

PL-SRO30

V = 50



4 Conclusions



2matrix As








Acknowledgments


References





























2superlattice






















































2 applied to





2




2and








p 2339 1972
















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials

























2superlattice






















































2 applied to





2




2and








p 2339 1972
















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




































2 applied to





2




2and








p 2339 1972
















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials


















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



reviewarticle - isptec · reviewarticle emission mechanisms of si nanocrystals and defects in sio 2...

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