OPTICAL PROPERTIES OF III-N NANOSTRUCTURES

Andrés CantareroUniversity of ValenciaSpain

Valence bandComposing one of the most important facets of Valencia's music scene, both past and present, are its internationally renowned "bandes." Found in every city and village of the Valencian community, these "bandes" are performing brass bands that play an integral part in festivals; in fact, they even have a music festival of their own: the Certamen Internacional de Bandas de Música (International Band Competition). Taking place annually since 1886, thousands of musicians descend upon the city as parts of regional, national, international, civilian and military brass bands.

Banda de Chiva

Valencia and its University Valencia, 138 bce

810,000 p;1,500,000 mr

The University was founded in 1499

We have 45,000 students

Outline

Interest in nitride semiconductors: applications

Generalities on III-N semiconductors GaN/AlN self-assembled quantum dots

Growth of GaN/AlN/SiC self-assembled QDs Optical properties of polar and non polar QDs

Q1D semiconductor nanostructures InN nanowires

Growth of InN nanowires Optical properties of InN nanowires

Conclusions

Optical storage devices

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CD DVD HD/BD VD NG-VD

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World database on installed optical memories

Sony launches its Blue-ray recorder (Sept 20th, 2006)

54 Gb capacity

400 nm laser (Nichia Corp)

Prof. Nakamura (UCSB) fabricated a 443.9 nm laser based on NP InGaN/GaN

White LEDs

Kittilä (Finland) , 2.2.2009

1st prize street (ecological) illumination Fallas 2009

Nitride semiconductors

wurtzite

zincblende

Lattice constant (wurtzite c , zincblende a ) 0 0 (10 m)-10

Ba

nd g

ap

ene

rgy

E g(

eV)

Ph

oton w

avelen

gth

hc/ E g (nm

)

Wurtzite lattice constant (10 m)-10

Crystal structure

GaN crystallizes in the wurtzite structure under normal conditions

Difference of packing between wurtzite and ZB

Origin of PSP in Ga-face GaN

Structural parameters and PSP

F. Bernardini, V. Fiorentini, D. Vanderbilt, PRB 56, R10024 (1997).

But, it is grown on Al2O3, SiC or Si(111)

There is, additionally, PPZ

1010 disl/cm2

Growth of GaN/AlN QDs

AlN

6H-SiC

Ga + NGa

Modified Stranski-Krastanow mode

Elastic relaxation

GaNdot

AlN

AlN [0001]

[2-1-10]

2nm

GaNdot

AlN

AlN [0001]

[2-1-10]

2nm

C. Adelmann et al APL 81, 3064 (2002); N. Gogneau et al JAP 94, 2254 (2003)

PL and electric field

1 10 100

200

400

600

800

1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

0.0

0.2

0.4

0.6

0.8

1.0

FW

HM

(m

eV)

GaN Periods

3 periods 10 periods 50 periods 200 periods

Norm

alize

d P

L

Energy (eV)

Photoluminescence of different samples growth with different number of periods

0.5 1.0 1.5 2.0 2.5 3.0

2.0

2.5

3.0

3.5

4.0

4.5

5.0

2 4 6 8 10 12

Ref a Ref b Ref c Ref d Ref e

PL

Em

issi

on

En

erg

y (

eV

)d

QW (nm)

Absorption Emission

Stokesshift

GaN Bulk

dQW

(ML)

(0001) GaN/AlN QWs

F=10 MV/cm

(a): J. M. Llorens, PhD (2006), Univ. Valencia; (b) Salviati et al., J. Phys. Cond. Matt. 16, S115 (2004); (c) Miyamura et al., APL 80 3937 (2002); (d) Kako et al., APL 83, 984 (2003); (e) Widmann et al., APL 83, 7619 (1998).

The built in electric field manifests in the optical properties of GaN/AlN heterostructures through the Stark effectIs there a way to reduce dislocations and Stark effect?

Non polar QDs5 nm

[1-100]

[0001]

HRTEM

AFM

S. Founta et al, APL 86, 171901 (2005)

a- and m-plane contain the same amount of Ga and N per layer

2,0 2,2 2,4 2,6 2,8 3,0 3,4 3,6 3,8 4,0

a-plane QDsc-plane QDsRT

Inte

nsity

(arb

. uni

ts)

Energy (eV)

100 Wcm-2

10 Wcm-2

1 Wcm-2

N. Garro et al., APL 87, 011101 (2005)

[0001]Plano a

[1120]

2.0 2.2 2.4 2.6 2.8 3.0 3.4 3.6 3.8 4.0 4.2

a-plane QDsc-plane QDs

RT

1 Wcm-2

Inte

nsit

y (a

rb. u

nits

)

Energy (eV)

GaN Laser

V and electric field

A-plane QD

Z

X

X

Z

C-plane QD

-20 -15 -10 -5 0 5 10 15 20

-0,4

-0,2

0,0

0,2

0,4

-6 -4 -2 0 2 4 6 8

-1,0

-0,5

0,0

0,5

1,0

-8

-6

-4

-2

0

2

4

-0,5

0,0

0,5

1,0

Pot

entia

l (V

)

Z (nm)

Ele

ctric

Fie

ld (

MV

/cm

)

Pot

entia

l (V

)

Z (nm)

piezo

spont

tot

Ele

ctric

Fie

ld (

MV

/cm

)

Etot

Growing interest in SNWs

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Published papers on semiconductor NWs (Web of Sciences)

Comparison of the number of citations on QDs and NWs

•Quasi-one dimensional symmetry•Large surface/volume ratio•New possible heterostructures•High quality materials (strain free)•High quality heterointerfaces (larger LM)

From QWs to NWs

Thanks to Bruno Daudin, CEA Grenoble

Ingredients:-lattice mismatch -(2.5 % Da/a GaN on AlN)- surface energy (Ga bilayer)

AlNGaN

N-rich conditions

Ga bilayer conditions

GaN grown on AlN

Fixed N flux

Self-organized growth of InN NWs

Growth details

SampleTs (ºC)

In-BEP (10-8 mbar)

N2 Flux (sccm)

G053 400 3.0 2.0

G071 475 3.0 2.0

G047 500 3.0 2.0

G044 500 3.0 1.5

G041 500 1.5 1.5

Two sets of samples:

Set A: Different substrate temperature.

Set B: Different In-BEP and N2 flux conditions.

InN nanocolumns growth: • Grown by plasma-assisted MBE. • p-Si (111) substrate.• Growth time of 300 minutes.• N2 rich conditions.

Ts: Substrate temperature.In-BEP: Base equivalent pressure of In.

J. Segura et al, ICNS7 (Las Vegas), 2007.

Raman modes of the wurtzite structure

546 (TO)732 (LO)

555 (TO) 741 (LO)

137 592 cm-1

447 (TO)585.4 (LO)

476 (TO) 593 (LO) 87 490.1 cm-1InN

GaNWurtzite : hexagonal structure with 4 atoms in the unit cell.

A 1 E 1 B 1l B 1h E 2l E 2h

G=2A1+2B1+2E1+2E

Raman scattering results

420 440 460 480 500 580 600

0.0

0.4

0.8

1.2

(x2)

Eh

2 G041 G053

Inte

nsi

ty (

arb

. u

nits

)

Raman shift (cm-1)

E1(LO)

A1(LO)

E1(TO)

PLP-

A1(TO)

Very narrow E2h non polar mode

peak, an indication of the high crystalline quality

Forbidden modes

Lower plasmon-LO coupled (PLP-) mode is observed

Sample E2h* FWHM (E2h)

E1(LO) FWHM (E1(LO))

G041 489,46 3,62 592,83 7,29

G071 489,24 3,45 592,53 7,79

G047 489,24 3,51 592,73 9,14

G044 488,92 4,45 591,42 7,55

G053 489,36 4,20 592,00 9,22

*X. Wang et al. Appl. Phys. Lett. 89, 171907 (2006).

Raman results

NCs homogeneous (G041) or with tapering effect (G071).

570 580 590 600 610

0,0

0,4

0,8

G041 G053

Inte

nsi

ty (

arb

. u

nits

)

Raman shift (cm-1)

E1(LO)

A1(LO)

NCs with Baseball bate shape (G047) and coalescence (G053).

Forbidden modes can be observed in the Raman spectra because the laser light enters and scatters mainly from the lateral surface of the NCs.

Higher intensity of E1(LO) peak is observed in samples with morphologies which allow an easier access to the NCs lateral surface.

J. Segura et al, ICNS7 (Las Vegas), 2007; J. Segura et al, Phys. Rev. B 79, 115305 (2009).

Conclusions

GaN QDs GaN QDs grown along the c axis emit in the green

region of the spectrum due to the Stark effect GaN QDs grown on non polar directions show

quantum confinement and emit in the UV InN NWs

NCs have a high crystalline quality and are strain-free

The appearance of forbidden modes has been correlated to the sample morphology

Raman scattering shows the existence of two emitting regions, a surface region giving rise to PLP modes and an inner region