Literature Review:

Mishra, Srivastava, Prakash, Yadav, and Panday (2011),

In this paper, cadmium sulfide (CdS) quantum dots (QDs) are synthesized

by a simple co-precipitation method. X-ray diffraction (XRD) confirmed

the formation of a cubical zinc blend structure of CdS nanoparticles.

Transmission Electron Microscopy (TEM) images revealed that the CdS

QDs are of 2-5 nm in size. To study the photoconductivity, the field

dependence of the photocurrent and the dark-current was assessed, as was

the time-resolved rise and decay photocurrent spectrum and wavelength

dependence photocurrent spectrum assessment of the CdS QDs. The

wavelength-dependence of the photocurrent was found to be close to the

absorption and PL spectrum. These CdS QDs can find potential

application in optoelectronic devices and photodetectors.

Chen, Wang, Chien, Chang, Chuang (2011),

In this paper, proposes a new method for reducing power consumption

and enhancing the luminous efficiency of powder inorganic

electroluminescence devices by introducing a composite dielectric layer

into their structure. The composite dielectric layer contains a composite

BaTiO3-carbon nanotube (CNT) film, which is formed by adding single-

wall CNTs into a BaTiO3 layer. With an appropriate CNT mixing ratio,

the power consumption decreased by more than 30%, and the luminous

efficiency increased by approximately 50% at a brightness of 400 nits and

an operation frequency of 1 kHz.

Mishra, Srivastava, Srivastava, Panday, Prakash (2011),

In this paper, simple, low-cost, and direct route is used for the UV-

photodetection and photoluminescent zinc-oxide nanoparticles (NPs) by

decomposing zinc acetate in air at 400 0C for 12 hrs. The X-ray

diffraction (XRD) result indicates that the synthesized ZnO NPs is pure

1

and single crystalline structure with wurtzite type. The synthesized ZnO

NPs exhibits several photoluminescence peaks centered at 396 nm, 418

nm, 441 nm, 481 nm and 522 nm. The variation of photo and dark-current

with applied field is found to follow power law i.e I α V. At low voltage

the behavior is sub-linear which becomes super-linear at high voltages.

Mishra, Srivastava, Prakash, Yadav, Panday (2011),

In this paper, Mn-doped CdS nanoparticles (NPs) have been synthesized

by co-precipitation method and effect of Mn concentration on the

structural, photoluminescence and photoconductivity properties have

been studied. The X-ray diffraction (XRD) patterns show that the

synthesized NPs have a cubical (zinc blende) phase. In photoconductivity

study, variation of photocurrent with voltage on ln-ln scale is found to

follow power law superlinearly due to injection of additional charge

carriers from one of the electrodes. The growth and decay in photocurrent

spectra exhibit anomalous behaviors which may be attributed to photo-

induced chemisorptions of oxygen molecules on surface of NPs.

Maurya, Chauhan, Mishra, Srivastava (2011),

In this paper, the influence of two different calcination temperatures 80 ◦C

and 450 ◦C on the structural, optical and charge transport properties of

rutile TiO2 nanocrystals has been investigated. TiO2 nanocrystals have

been prepared at low temperature by a simple hydrolysis method using

titanium tetrachloride as starting precursor. The results of X-ray

diffraction (XRD) showed that the prepared nanocrystals have a rutile

tetragonal crystalline structure. The red-shift in photoluminescence (PL)

is attributed to the change in strain from compressive to tensile.

Photoconductivity (PC) measurements showed that capture cross-section

of 80 ◦C (R1) and 450 ◦C (R2) calcinated rutile nanocrystals are

55.10×10−10

and 39.50×10−10

cm2 respectively.

2

Kripal, Gupta, Srivastava, Mishra (2011),

In this paper, photoconductivity and photoluminescence studies of ZnO

nanoparticles (NPs) synthesized by coprecipitation method capped with

thioglycerol are carried out. The effect of annealing at 300 0C is also

studied. The transmission electron micrograph (TEM) and X-ray

diffraction (XRD) pattern confirm the hexagonal wurtzite structure of

ZnO nanoparticles. The photoluminescence (PL) spectra of assynthesized

ZnO NPs show band edge emission as well as blue–green emission. After

annealing band edge emission is quenched. Photocurrent is found to vary

super linearly at high voltage for both as-synthesized as well as annealed

ZnO NPs. Time resolved rise and decay photocurrent spectra are found to

exhibit anomalous photoconductivity for as-synthesized as well as

annealed ZnO NPs wherein the photocurrent decreases even during

steady illumination.

Nalla, Polavarapu, Manga, Goh, Loh, Xu and Ji (2010),

In this paper, a water soluble conjugated thiophene polymer, sodium salt

of poly[2-(3-thienyl)ethoxy-4-butylsulfonate] (TPP), and graphene oxide

(GO) composite film (GO–TPP) device was prepared. Transient

photoconductivity measurements were carried out on the GO–TPP

composite film using 150 ns laser pulses of 527 nm wavelength. The

relationships of the film photoconductivity, photocurrent decay time and

electron decay times with the incident light intensity were investigated.

The photoconductive gain of the film was determined to be greater than

40% and to be independent of the light intensity.

Chen, Chen, Lien, Ding, and He (2010),

In this paper, the Au nanoparticle (NP) decoration as an effective way to

enhance both photocurrent and photoconductive gain of single ZnO

3

nanowire (NW) photodetectors (PDs) through localized Schottky effects.

The enhancement is caused by the enhanced space charge effect due to

the existence of the localized Schottky junctions under open circuit

conditions at the NW surfaces, leading to a more pronounced electron-

hole separation effect. Since the band-bending under illumination varies

relatively small for an Au NP-decorated ZnO NW, the decay of gain is

less prominent with increased excitation power, demonstrating the

feasibility for a PD to maintain a high gain under high-power

illumination.

Singh, Mishra, Srivastava and Gopal (2010),

In this paper, semiconductor quantum dots (QDs) and their assemblies

have shown potential research interest due to their size dependent optical

and electronic properties. Most of the available reports in this field are

related to the laser induced modification of shape, size, and morphology

of noble metal nanoparticles, while only few exist for semiconductors.

UV-visible absorption, XRD, TEM, and PL spectroscopic methods are

utilized for the characterization of as synthesized QDs and raw NPs. Size

and hence optical properties of produced selenium QDs are found to be

highly dependent on the time of irradiation. The size of the produced

selenium QDs follows a second order exponential decay function of

irradiation time, while the rate of size reduction, da/dt, is directly

dependent on the diameter, a, of the instantaneous QDs, very similar to

the radioactive decay model.

Antic, Krsmanovic, Marinovic-Cincovic and Dramicanin (2010),

In this paper, there is an increasing interest in obtaining and investigating

composite materials that comprise nanoparticles as fillers and polymers

as matrix. Such composites may display combined features of both

4

components, and sometimes even novel properties resulting from their

mutual interactions. It is important that both unique size-dependent

properties of nanoparticles and favorable properties of polymer material

remain preserved in the composite. Influence of Gd2O3:Eu3+

filler on the

modification of glass transition and thermo-degradable properties of the

polymer matrix is also investigated. Thermal analyses give evidence of

unchanged thermal stability of polymer phase in the composites.

Zou and Gao (2010),

In this paper, we have reported our most recent work on processing and

microstructure of nano-structured oxides and their photoluminescence

and photo-catalysis properties. Zinc oxide and related transition metal

oxides such as vanadium pentoxide and titanium dioxide were produced

by a combination of magnetron sputtering, hydrothermal growth and

atmosphere controlled heat treatment. These structures showed special

properties such as much enhanced photoluminescence and chemical

reactivity. The photo-catalytic properties have also been promoted

significantly. The transition metal oxides with different band gaps have

much enhanced photoluminescence under laser stimulation. The mixed

oxide complex may provide a promising way to high-efficiency photo

emitting materials and photo-catalysts.

MISHRA, SRIVASTAVA, PRAKASH, YADAV, and PANDAY

(2010),

In this paper, ZnO nanoparticles (NPs) with particle size of 20–50 nm

have been synthesized by hydrothermal method. Photoluminescence (PL)

and photoconductive device characteristics, including field response, light

intensity response, rise and decay time response, and spectral response

have been studied systematically. In spectral response curve of ZnO NPs,

the wavelength dependence of the photocurrent is very close to the

5

absorption and photoluminescence spectra. The photo generated current,

Ipc = (Itotal – Idark) and dark current Idc varies according to the power law

with the applied field Ipc α Vr and with the intensity of illumination Ipc α

ILr, due to the defect related mechanism including both recombination

centers and traps. The photo and dark conductivities of ZnO NPs have

been measured using thick film of powder without any binder.

SRIVASTAVA, MISHRA, YADAV, SRIVASTAVA, PANDAY,

PRAKASH (2010),

In this paper, an attempt has been made to study the photoconductivity

and dark-conductivity characteristics of doped ZnS nanoparticles.

Photoconductivity and dark-conductivity are measured at room

temperature under visible illumination. The Mn-doped ZnS nanoparticles

synthesized by co-precipitation technique are found to exhibit anomalous

behavior of photocurrent which decreases with increased intensity of

illumination. At 5000 lux of illumination photocurrent is found to be even

lower than the dark-current. The variation of photocurrent with applied

voltage is super-linear. Structural studies using XRD and TEM have been

performed.

Kripal, Gupta, Mishra, Srivastava, Pandey, Prakash (2010),

In this paper, Mn2+

doped ZnS nanoparticles are characterized using UV–

vis, photoluminescence and photoconductivity studies. The size of Mn2+

doped ZnS NPs is estimated to be 2–4nm by X-ray diffraction. UV–vis

spectra show a blue shift in absorption edge as compared to bulk

counterpart. Photoluminescence spectra indicate that orange

luminescence varies with Mn2+

concentration. The Mn2+

doped ZnS

nanoparticles are found to be photosensitive. The doping of Mn2+

ions

6

improves the photosensitivity of the ZnS nanoparticles system. The time-

resolved rise and decay of photocurrent indicate anomalous behavior

during steady state illumination.

MISHRA, MISHRA, PRAKASH (2009),

In this paper, transparent conducting tin oxide (SnO2) thin film has been

deposited on glass substrate by spray pyrolysis technique, taking starting

material tin chloride solution (SnCl2.2H2O) and using ultrasonic nebulizer

at substrate temperature 300±10 oC. The XRD result shows a regular,

smooth morphology. The deposited film was found to be polycrystalline..

The optical absorption, transmittance, reflectance and optical

conductivity have been measured. It was found that the average

transmittance of the film is around 78 % at wavelength 550 nm. Finally

the ethanol gas sensing properties of the film was also performed.

Wang, Ye, Zhang, Li, G. H. (2009),

In this paper, ZnTiO3 thin films were prepared by radio frequency

cosputtering of ZnO and TiO2. It was found the as-prepared film is

amorphous and the cubic phase ZnTiO3 films form after annealing at

temperature above 500°C. The absorption spectra indicate that the optical

band gap of the crystalline ZnTiO3 film is about 3.70 eV. A strong

photoluminescence band centered at 355 nm consisting of two emission

peaks was observed in 800°C annealed ZnTiO3 thin film, and the peak

positions of these two emission move to short wavelength with increasing

annealing temperature.

Mishra, Srivastava, Prakash (2009),

In this paper, we report on the photoconductivity (PC), dark-conductivity

and photoluminescence (PL) measurements of hydrothermally

synthesized Zinc oxide (ZnO) nanoparticles (NPs) with particle size 20-

7

50 nm. The photoconductivity is observed in ZnO nanoparticles due to

photoexcitation in the visible range (400 nm- 691 nm). The photo and

dark current behavior as a function of various parameters such as field

response, rise and decay time response was studied. The photocurrent

(Ipc) and dark-current (Idc) follows power law with applied field, Ipc α V r

due to the defect related mechanism including both recombination centers

and traps.

Aizawa, Ohtani (2009),

In this paper, we fabricated and characterized electroluminescence (EL)

devices using ferroelectric polyvinylidene fluoride/trifluoroethylene

(PVDF/TrFE) copolymer composites mixed with Mn- and Cu-activated

ZnS phosphor particles. Increases of the luminescence were observed in

the fabricated EL devices using PVDF/TrFE copolymer in comparison

with using PVDF polymer as dielectrics. EL emission intensities were

also enhanced by applying the bipolar pulses. These results suggest an

effect of polarization reversal in the composite films.

Cheng, Lu, Shambat, Yu, Saraswat, Vuckovic, and Nishi (2009),

In this paper, we report the room temperature electroluminescence (EL)

at 1.6 μm of a Ge n+/p light emitting diode on a Si substrate. Unlike

normal electrically pumped devices, this device shows a superlinear

luminescence enhancement at high current. By comparing different n type

doping concentrations, we observe that a higher concentration is required

to achieve better efficiency of the device. Thermal enhancement effects

observed in temperature dependent EL spectra show the capability of this

device to operate at room temperature or above. These detailed studies

show that Ge can be a good candidate for a Si compatible light emitting

device.

8

Chassaing, Demangeot, Paillard, Zwick, Combe, Pagès, Kahn,

Maisonnat and Chaudret (2007),

In this paper, surface optical phonons in freestanding cylindrical ZnO

nanoparticles surrounded by organic molecules have been theoretically

investigated using a dielectric continuum model and experimentally with

Raman spectrometry. We also investigate the dispersion of these modes

regarding the dielectric constant of the outer medium. By modelling the

organic shell of nanoparticles with a dielectric constant and based on

experimental results of Raman spectrometry, we show that we observed a

top surface mode of nanoparticles.

O’Brien, Kherani, Zukotynski, Ozin, Vekris, Tetreault, Chutinan,

John, Mihi, and Míguez (2007),

In this paper, photonic crystals (PCs) are a remarkable class of materials

wherein the periodicity of the index of refraction can be engineered to

obtain unprecedented optical properties that have no parallels in other

materials. Some interesting optical phenomena inherent to PCs include

second harmonic generation, the super-prism effect, photonic bandgaps

(PBGs) and “slow photons”. The ability of defect modes in PCs to

confine photons is expected to provide the infrastructure for optical

circuits. Moreover, lossless light propagation along PBG waveguides

with coupling to quantum dots or optical cavities could provide new

avenues for quantum information processing.

VOMVAS1, POMONI, TRAPALIS, TODOROVA (2007),

In this paper, thin TiO2 sol-gel films, with and without ammonia

treatment, were prepared using the dip-coating technique and then heat

treated at 500 ºC. The time dependences of the photoconductivity at

various light intensities were studied in vacuum and in air at 27 ºC. The

9

transient photoconductivity is very sensitive to the environment and

dramatically higher than the dark one for samples both in vacuum and in

air. The results are discussed in terms of the competition of the

photogeneration, recombination, thermal release, and the influence of

NH3 treatment.

LI, CHEN, SHEN, JIANG, ZHANG (2007),

In this paper, α-Si3N4 was prepared using MgO and Al2O3 as the sintering

additives and spark plasma sintering (SPS) technique. The SPS sintering

behavior and mechanism have been discussed. The relationship between

the content of sintering additives, sintering temperature, and relative

densities of the samples has been analyzed. The phase composition was

determined by XRD, the microstructures of the fracture surfaces were

observed by SEM and the dielectric properties have been tested. The

dielectric loss, influenced by the liquid phase, is less than 1×10–2

.

WODECKA-DUŚ, LISIŃSKA-CZEKAJ, ORKISZ, ADAMCZYK,

OSIŃSKA, KOZIELSKI, CZEKAJ (2007),

In this paper, the sol-gel derived powders of the chemical composition

(Ba0.6Sr0.4)TiO3 (BST) were used in the preparation of ceramic samples.

Barium acetate, strontium acetate and tetra-butyl titanate were used as

starting materials. The free sintering method was used for the final

densification of ceramics. The ceramic samples were characterized in

terms of their crystalline structure (X-ray diffraction), microstructure

(scanning electron microscopy), chemical composition (energy dispersive

spectroscopy), and dielectric properties.

Tang, Teng, hao, Liang, Wang (2007),

In this paper, photoconductivity is considered to be an important tool for

providing information regarding the nature of the photo-excitations. Since

10

last decade the photoconductive properties of the inorganic nanoparticles

have become subject of intensive study.

He, Lin, McConney, Tsukruk, and Wang (2007),

In this paper, UV photodetector fabricated using a single ZnO nanobelt

NB has shown a photo response enhancement up to 750 times higher than

that of a bare ZnO NB after coating with -20 nm plasma polymerized

acrylonitrile PP-AN nanoscale film. The mechanism for this colossal

photoconductivity is suggested as a consequence of the efficient exciton

dissociation under UV illumination due to enhanced electron transfer

from valence band of ZnO NB to the PP-AN and then back to the

conduction band of ZnO. This process has demonstrated an easy and

effective method for improving the performance of the nanowire/NB-

based devices, possibly leading to supersensitive UV detector for

applications in imaging, photosensing, and intrachip optical

interconnects.

Hu, Zhang, and Gao (2006),

In this paper, solid-state electroluminescent devices based on organic

polymers have been extensively studied in recent years for potential

display and lighting applications. Electroluminescence (EL) is the

generation of light by electrical excitation. For a material to exhibit EL, a

general criterion is that it must also possess photoluminescence (PL),

which is an intrinsically more efficient process, as electrons and holes are

always created in pairs and in close proximity, making radiative

recombination a favorable process. A material that is not

photoluminescent or whose PL is heavily quenched is therefore very

unlikely to be a good candidate for EL. Although most “conventional”

polymer light-emitting diodes (PLEDs) are metal–insulator–metal (MIM)

structures based on pristine luminescent polymers, EL from polymers can

11

be achieved alternatively by the formation of a light-emitting p–n

junction via in situ electrochemical doping.

ANDRI, ANIN, JOKANOVI, ANIN, MITRI, VIANA (2006),

In this paper, the luminescent properties of a composite made from

isotactic polypropylene and silicate nano powder doped with trivalent

europium ion were investigated. The method for obtaining the

investigated composite is presented. Thermo-chemical properties of the

composite were determined by DSC and TG measurements, while the

structure was checked by X-ray diffraction measurements. Luminescent

properties for two differently crystallized nano-composites were

determined by measuring room temperature excitation and emission

spectra, as well as the emission lifetime of the 5D0-7F2 transition. In

addition, much stronger luminescence intensity was noticed for the case

of polypropylene of higher crystallinity.

Murphy, Moazzami and Phillips (2006),

In this paper, a strong photoconductive response is observed for ZnO

epilayers in the presence of both above bandgap and below bandgap

photoexcitation. Photoexcitation for energies larger than the band gap,

results in a photoconductive response with fast and slow time constants

on the order of nanoseconds and larger than milliseconds respectively. A

model for the photoconductive response based on rate equations is

presented providing an accurate fit to measured photoconductivity data.

The passivation of the ZnO surface with SiO2 shows significantly reduced

photoconductive transient decay time constants, suggesting a significant

reduction of deep surface defects on the ZnO material.

Hui and Onga, Lee and Dai (2005),

12

In this paper, the effects of AlOx-cap layer on the optical and

photoelectrical properties of ZnO films have been studied by

cathodoluminescence (CL), photoluminescence (PL), and

photoconductivity (PC). Both the PL and CL show that the cap layer

improves the emission characteristics of ZnO by enhancing the band-edge

emission while at the same time reducing the deep-level emissions. To

study the origin of improvement, depth-resolved CL has been carried out

to map out the emissions at different depths. The PC measurement on the

capped ZnO at room temperature shows a distinctive excitonic feature at

3.29 eV and an overall increment of photo-response above the band gap.

SINGH, GANDOTRA, SINGH and CHAKRAVARTY (2005),

In this paper, minority carrier lifeline, t, is one of the most important

parameters which has a decisive effect on the performance of silicon

devices based on excess carriers. The value of t is greatly affected by the

presence of impurities and defects in silicon and its value provides a fair

indication of quality of the material. Photoconductivity decay (PCD) and

photocurrent generation (PCG) methods are simple and low cost methods

of measurement of minority carrier lifetime in silicon wafers. However,

their application requires care. For PCG method the t measurement under

vacuum conditions provides correct and consistent results.

BENOUIS, JUAREZ, AIDA, HAMZAOUI, BENHALILIBA (2005),

In this paper, the photoconductivity of ZnO thin films prepared by spray

pyrolysis of the zinc dehydrated was studied. The electrical, optical

behaviors and structural spectra show an important effect of substrate

temperature Ts and deposition time td. Under illumination, the

conductivity of as grown sample increased due to desorption of oxygen.

A small photoconductivity is representative of the electrical behavior of a

quasi intrinsic material. By following cessation of illumination, we

13

remarked a saturation of decay photoconductivity; this can be attributed

to a trap which captures carriers.

Scheblykin, Lepnev, Vitukhnovsky, Auweraer (2001),

In this paper, a composite material of poly(phenylenevinylene) (PPV)

doped by dye aggregates was prepared. A very efficient and temperature

activated energy transfer (ET) from the PPV to the dye aggregates was

attributed to F. orster ET accompanied by exciton diffusion. A clear

complementary relation between the photoluminescence (PL) and

electroluminescence (EL) images was observed for thin (15 nm) PPV-

based OLEDs. So-called „„black spots‟‟ in EL become bright ones when

the photoluminescence of the same area was excited. This effect was

attributed to the presence of an insulating layer between the polymer and

aluminum.

Cordero, Carson, Estabrook, Strouse, and Buratto (2000),

In this paper, we show that the luminescence from CdSe quantum dot

monolayers can be strongly influenced by the interaction of water

molecules adsorbed on the surface. Light induced alterations in the

surface states following adsorption of water, results in quasi-reversible

luminescence changes in the quantum dot. The exciton emission exhibits

an exponential blue shift of nearly 16 nm (60 meV) over 1 h of

illumination. Our model suggests that water molecules adsorbed on the

surface of the quantum dot act to passivate surface traps, which results in

increased luminescence, similar to an effect well-known for bulk CdSe

surfaces.

Tajkhorshid, Suhai (1999),

In this paper, we performed DFT calculations, using the DMOL

implementation of the COSMO solvent model, to investigate the effect of

14

different dielectric responses of the environment on the structure and

electronic configuration of two un-substituted Schiff base models of

retinal, including three and four conjugated double bonds, as well as a

monomethylated model. The results show that the application of different

dielectric constants in the calculations significantly influences the proton

affinity of the molecule.

Studenikin, Golego, and Cocivera (1998),

In this paper, photoluminescent, undoped ZnO films have been fabricated

using spray pyrolysis of zinc nitrate solution. The luminescent films had a

polycrystalline hexagonal wurtzite type structure with no preferred

orientation. Photoluminescence intensity was critically dependent on

substrate temperature during spray pyrolysis and on post-annealing

temperature. Green, photoluminescent films possessed a porous structure

while orange films possessed a close packed granular morphology. Green

luminescence appears to be due to oxygen vacancies in a layer just below

the crystallite surface.

Studenikin, Golego, and Cocivera (1998),

In this paper, slow relaxation of the photoconductivity over a period of

days was studied in polycrystalline ZnO and TiO2 films prepared by

spray pyrolysis. The phenomenon is described by a model involving deep

sensitizing hole traps in the forbidden gap. The trap state distribution

based on this model was calculated using an improved Laplace transform

method. For ZnO and TiO2 films, the density of states was shown to have

a peak-like distribution with a maximum near the lower third of the

energy gap.

Shen and Perera (1998),

15

In this paper, the photoconductivity generation mechanism and

photoconductive gain in internal photoemission infrared detectors have

been studied. A simple model is proposed and it shows that the

photoconductive gain of internal photoemission detectors is less than but

close to unity and independent of the number of the emitter layers, while

the current responsivity is proportional to the number of emitter layers.

The results, in good agreement with the experiments, are contrary to

those of quantum-well photodetectors due to the different photocarrier

generation mechanisms between the quantum-well photodetectors and

internal photoemission detectors.

Bernatskii (1994),

In this paper, the photoluminescence (PL) spectrum of thin films of

cadmium fluoride (CdF2), activated by manganese chloride (MnC12),

consists of a band with )~ max = 520 nm, characteristic of the Mn 2 +

ion in this compound, and bands with maxima 685 and 780 nm, which

depend on the energy of the exciting radiation . In the x-ray and cathode

luminescence spectra, bands with maxima 375, 530 and 530 nm,

respectively, are observed, and in the electroluminescence spectrum a

band with hma x = 530 nm.

Devi and Prakash (1994),

In this paper, we deals with the photoconductivity studies of (PbCrO4-

HgO-ZnO) composites comprising of base materials of three different

energy gaps. The response of (10%PbCrO4-80%HgO-10%ZnO) and

(20%PbCrO4-60%HgO-20%ZnO) composites is faster than that of other

compositions and of base materials. The dark current for (20%PbCrO4-

60%HgO-20%ZnO) is trap limited-space charge limited at higher

voltages while it shows non-ohmic behavior at lower voltages. The

photocurrent for (20%PbCrO4-60%HgO-20%ZnO) composition shows

16

non-ohmic behavior at lower voltages and tends to saturation at higher

voltages. The photocurrent for the above composition varies sublinearly

with the intensity of illumination.

Lee, Yu, Moses, and Heeger (1994),

In this paper, we report the results of transient-photoconductivity

measurements on films of poly (phenylenevinylene) (PPV) in the sub-

nanosecond-time regime. The initial fast transient photocurrent decays

exponentially with a decay time of about 100 ps, followed by a slower

component with a decay time of about 600 ps. The magnitude of the fast

component is proportional to the light intensity and independent of

temperature, while the magnitude of the slower component is

proportional to the square root of the light intensity and decreases as

temperature decreases with thermal-activation energy of about 100 meV.

We attribute the initial response to photo-generated electrons and holes

{polarons) and the following slower decay to bipolarons in the non-

degenerate ground-state conducting polymer.

Watanabe, Haga, Tosomiya (1992),

In this paper, it has been shown that the photoconductive characteristics

of a dispersion composite of a photoconductive inorganic metal oxide,

such as TiO2, with a polymer are significantly enhanced by annealing.

For the poly (methyl methacrylate) (PMMA) dispersion composite TiO2-

PMMA, the relative sensitivity is 101 ∼ 10

2 times higher than that of the

unannealed sample. The space-charge limited current is observed in the

dark current-voltage characteristics of the annealed TiO2-PMMA. From

the light intensity index of the annealed TiO2-PMMA, it is found that the

annealed sample has a large sensitizing effect.

Objective of the present work:

17

1. Study the dielectric material and its applications

2. Study of material with X-ray Diffraction (XRD)

3. Techniques or methods used for the fabrication of cell

4. Study the properties of photoconductivity in different ratio of the

material

5. Study the Photoelectret property of the material

6. Study the property of electroluminescence in different ratio of the

composite