Página 1 dos resultados de 315 itens digitais encontrados em 0.001 segundos

Efeito da fotocondução em diodos com camada ativa de derivados de poli(p-fenileno vinileno) (PPV); Photoconduction effect in single layer diodes based on PPV derivatives.

Cazati, Thiago
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 18/01/2008 PT
Relevância na Pesquisa
27.57%
Esta tese de doutorado é resultado do estudo da fotocondutividade em materiais poliméricos, com particular enfoque em diodos poliméricos com camada ativa de derivados do poli (p-fenileno vinileno) (PPV): OC10-PPV, SY e MEH-PPV, em estrutura tipo sanduíche (ITO/polimérico/Metal) de camada única, utilizando eletrodos metálicos com diferentes funções trabalho depositados sobre o mesmo filme. Para isso, foi necessária a realização de todas as etapas de fabricação de dispositivos orgânicos, como descritas neste trabalho, para obter resultados com o máximo de reprodutibilidade, bem como o domínio das técnicas de caracterização. As propriedades ópticas dos filmes poliméricos foram analisadas através dos espetros de absorção e de fluorescência estacionária na região do visível. O comportamento fotocondutivo dos dispositivos foi realizado através de medidas de corrente-tensão (I-V) e da espectroscopia de fotocorrente no estado estacionário em regime dc sob incidência de luz com diferentes comprimentos de onda, ora através do ITO, ora através dos eletrodos metálicos semitransparente, para o dispositivo sob diferentes valores de tensões aplicadas. A variação desses parâmetros permitiu verificar como estes influenciam na fotogeração e no transporte de portadores de cargas e assim adaptar e aplicar um modelo teórico que levasse em consideração o campo elétrico aplicado para ajustar a fotocorrente obtida experimentalmente...

Efeito fotovoltaico e fotocondutividade em dispositivos poliméricos; Photovoltaic effect and photoconductivity in polymer devices

Olivati, Clarissa de Almeida
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 16/03/2000 PT
Relevância na Pesquisa
37.28%
Os polímeros conjugados têm sido objeto de estudo nos últimos vinte anos devido à grande variação observada em sua condutividade quando sob dopagem química. A maioria dos polímeros dessa família passa de isolante, quando não dopados ou fracamente dopados, a bons condutores de eletricidade quando fortemente dopados. Em dopagens intermediárias apresentam um comportamento semicondutor, inclusive efeitos de fotocondução, fotovoltagem e luminescência. Nesse trabalho exploramos algumas dessas propriedades, mais comuns aos semicondutores inorgânicos, e mostramos que é possível obter dispositivos eletrônicos e/ou optoeletrônicos com os polímeros orgânicos. Em estruturas de diodos, tipo Schottky e pin, fabricamos e caracterizamos dispositivos fotovoltaicos com polianilina e poli(o-metoxianilina). Nesses materiais, sob fraca dopagem foi observado um efeito de fotocondução negativa. Já com o poli(2-metoxi, 5-hexiloxi-1,4fenileno vinileno) fabricamos e caracterizamos células fotovoltaicas e mostramos que esse tipo de estrutura permite a fabricação de um dispositivo reversível: fotovoltaico e eletroluminescente.; Conjugated polymers have been extensively studied in the last twenty years due to their high conductivity variation under doping. They are insulating materials when non-doped or weakly doped and good conductors when strongly doped. In intermediate doping concentration they behave as semiconductors...

O efeito da fotocondutividade e a estrutura eletrônica de poços quânticos de GaAs/InGaAs/GaAs com dopagem planar do tipo "n" na barreira.; The effect of photoconductivity and electronic structure of quantum wells of GaAs / InGaAs / GaAs doped planar type "n" in the barrier.

Cavalheiro, Ademir
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 23/11/2001 PT
Relevância na Pesquisa
37.28%
Neste trabalho, a estrutura eletrônica de poços quânticos de GaAs/In IND.0.15 Ga IND.0.85As/GaAs com dopagem planar de silício na barreira superior foi investigada utilizando-se medidas de Shubnikov-de Haas em função do tempo de iluminação, observou-se que uma quantidade significativa de elétrons estava faltando na região ativa (formada pela camada de InGaAs e pela região delta-dopada) de todas as estruturas analisadas. Um efeito fotocondutivo persistente (que persiste pelo menos 27 horas depois que a excitação óptica é desligada) foi observado em todas as amostras. Durante o processo de iluminação, portadores são liberados pela iluminação e fortes modificações nas mobilidades quânticas das sub-bandas foram observadas. Uma analise fenomenológica dos dados é apresentada, baseada em cálculos autoconsistentes da estrutura eletrônica dos sistemas analisados.; In this work, the sub-band electronic structure of de GaAs/In IND.0.15 Ga IND.0.85As/GaAs quantum wells with a Si delta-doped layer in the top barrier was investigated by Shubnikov-de Haas measurements as a function of the illumination time of the samples. Before the exposure of the heterostructure to any illumination time, we observed that a significant quantity of electrons was missing in the active region (consisting of the quantum well formed by the InGaAs layer and the Si delta-doped region) of all the analyzed structures. A persistent photoconductivity effect (which persisted at least for 27 hours after the optical excitation was turned off) was observed in all samples. During the illumination process...

Photoconductivity excitation spectrum for stretch-oriented PPV

Miranda, P. B.; Santos, L. F.; Reis, F. T.; Scalvi, LVA
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 77-80
ENG
Relevância na Pesquisa
37.45%
We have obtained the photoconductivity (PC) excitation spectrum for a stretch-oriented poly(paraphenylene vinylene) film over a wide spectral range (up to 5 eV). The measurements were performed in the surface cell configuration with the electric field parallel or perpendicular to the stretch direction. Although the sample had a stretch ratio of similar to 4, the dark conductivity and the steady-state photoconductivity were both about 40 and 20 times higher with the electric field parallel to the average chain direction, respectively. However, the shape of the PC excitation spectrum was independent of field direction and did not show a significant rise in the ultraviolet, as is usually observed for measurements in the photodiode configuration. The implications of these results to the charge photogeneration mechanism in conjugated polymers are discussed.

Investigation of temperature influence on photo-induced conductivity in n-type AlxGa1-xAs

Taquecita, Marco H.; Scalvi, Luis V A; Oliveira, L.; Li, M. Siu; Parreira, S. B.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 175-186
ENG
Relevância na Pesquisa
27.45%
We present conductance as function of temperature (G×T) under influence of monochromatic light in the range 0.5-1.5 μm for direct as well as indirect bandgap n-type AlxGa1-xAs. Results obtained below 60 K in indirect bandgap sample show the presence of another level of trapping, besides the DX centre, probably a X-valley effective mass state. In direct bandgap samples, these G×T curves show that above bandgap light increases conductivity to higher values than at room temperature and below bandgap light is not enough to avoid trapping. Photoconductivity spectra in indirect bandgap AlxGa1-xAs show that above ≅120 K, the absence of persistent photoconductivity contributes for a very clean spectrum. The mobility of AlxGa1-xAs is modelled considering dipole scattering. Data of transient decay of persistent photoconductivity is simulated using this approach.

Oxygen related defects excitation and photoconductivity dependence of SnO2 sol-gel films with several light sources

Messias, Fabio R.; Scalvi, Luis V.A.; Siu Li, M.; Santilli, C. V.; Pulcinelli, S. H.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 391-395
ENG
Relevância na Pesquisa
37.57%
Since oxygen vacancies act as donors in SnO2, the electrical properties are related to deviation from stoichiometric composition. Depending on stoichiometry SnO2 can be highly insulating or may exhibit fairly high n-type conductivity. Since bandgap transitions are in the ultraviolet range, its photoconductivity is strongly dependent on the excitation source. We have measured variation of photoconductivity excitation with wavelength for tin dioxide grown by dip-coating sol-gel technique using several light sources: tungsten lamp, xenon, mercury and deuterium, and present selected results. The main band is obtained in the range 3-4eV according to light source spectrum in the ultraviolet range. The presence of oxygen in the cryostat also affects the spectrum since electron-hole pairs react with adsorbed oxygen specimens. © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Gordon and Breach Science Publishers imprint.

Novos materiais fotorrefrativos : propriedades ópticas e elétricas; New photorefractive materials : optical and electrical properties

Tatiane Oliveira dos Santos
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 12/08/2009 PT
Relevância na Pesquisa
27.45%
Foi realizado o estudo de novos materiais fotorrefrativos através das técnicas Fotocon-dutividade Resolvida por Comprimento de Onda e Speckle-foto-fem. Dentre esses materiais encontram-se titanosillenitas com diferentes dopantes e os materiais fotorrefrativos do grupo II-VI como o telureto de c´admio (CdTe) e telureto de zinco (ZnTe), também dopados, e cujo interesse está no fato de terem uma banda proibida menor que as sillenitas, e serem bem mais rápidos que as sillenitas. O modelo matemático que descreve o efeito foto-fem com um padrão de "speckle" oscilante e de grande amplitude foi desenvolvido, tornando-se o modelo mais completo até hoje existente. O novo modelo prêve o aparecimento de um máximo no sinal de speckle-foto-fem para um determinado valor da amplitude normalizada sobre o tamanho do speckle d , em conformidade com os resultados experimentais. Verificou-se também, que a posição deste máximo depende fortemente da relação entre a condutividade no escuro e fo-tocondutividade (Rd). Através da técnica Fotocondutividade Resolvida por Comprimento de Onda foi estudado as amostras de BTO puro e dopado, CdTe e ZnTe dopados, onde foi possível identificar alguns estados localizados dentro da banda proibida destes materiais. A partir disto...

Electrical and photoelectronic properties of hexagonal GaN

Seitz, R.; Gaspar, C.; Monteiro, T.; Pereira, L.; Pereira, E.; Schön, Q.; Heuken, M.
Fonte: Wiley-VCH Verlag Berlin GmbH Publicador: Wiley-VCH Verlag Berlin GmbH
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
27.45%
Photoconductivity of a non-intentionally doped GaN layer is observed for above band gap excitation. No below band gap excitation causes photoconductivity, but photoconductivity is optical quenched at energies of 1.28, 1.41, 1.53 and ≈2eV. The dark current and the yellow photoluminescence band show the same activation energy (42 meV) supporting therefore the model that relates the yellow band to a shallow donor to a deep acceptor transition. The photocurrent is thermally quenched with an activation energy of 77 meV.; Praxis XXI/BD/16284/98; Brite-Euram Project Rainbow (contract në BRPR-CT96-0340).

The Photoconductivity of Chloroplasts and the Far Red Light Effect

Ichimura, Shoji
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1960 EN
Relevância na Pesquisa
27.45%
The photoconductivity of chloroplast films in the dry and the wet state has been investigated. These films were found to behave like typical semiconductors, in agreement with the results of Arnold and co-workers, who have used only dry films. It was found that a steady photocurrent produced in a chloroplast film by blue or red light, can be either stimulated or quenched—depending on the intensity of the illumination—by simultaneous application of far red or near infrared light. This reminds one of the quenching of the photoconductivity of phosphors by infrared light. The interaction of long wave light with light of shorter wavelength in the production of photoconductivity is of interest in relation to the “second Emerson effect,” which suggests a similar interaction in photosynthesis.

Giant Persistent Photoconductivity of the WO3 Nanowires in Vacuum Condition

Huang, Kai; Zhang, Qing
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em 30/09/2010 EN
Relevância na Pesquisa
27.45%
A giant persistent photoconductivity (PPC) phenomenon has been observed in vacuum condition based on a single WO3 nanowire and presents some interesting results in the experiments. With the decay time lasting for 1 × 104 s, no obvious current change can be found in vacuum, and a decreasing current can be only observed in air condition. When the WO3 nanowires were coated with 200 nm SiO2 layer, the photoresponse almost disappeared. And the high bias and high electric field effect could not reduce the current in vacuum condition. These results show that the photoconductivity of WO3 nanowires is mainly related to the oxygen adsorption and desorption, and the semiconductor photoconductivity properties are very weak. The giant PPC effect in vacuum condition was caused by the absence of oxygen molecular. And the thermal effect combining with oxygen re-adsorption can reduce the intensity of PPC.

Steady-state photoconductivity and multi-particle interactions in high-mobility organic semiconductors

Irkhin, P.; Najafov, H.; Podzorov, V.
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 19/10/2015 EN
Relevância na Pesquisa
27.66%
Fundamental understanding of photocarrier generation, transport and recombination under a steady-state photoexcitation has been an important goal of organic electronics and photonics, since these processes govern such electronic properties of organic semiconductors as, for instance, photoconductivity. Here, we discovered that photoconductivity of a highly ordered organic semiconductor rubrene exhibits several distinct regimes, in which photocurrent as a function of cw (continuous wave) excitation intensity is described by a power law with exponents sequentially taking values 1, 1/3 and ¼. We show that in pristine crystals this photocurrent is generated at the very surface of the crystals, while the bulk photocurrent is drastically smaller and follows a different sequence of exponents, 1 and ½. We describe a simple experimental procedure, based on an application of “gauge effect” in high vacuum, that allows to disentangle the surface and bulk contributions to photoconductivity. A model based on singlet exciton fission, triplet fusion and triplet-charge quenching that can describe these non-trivial effects in photoconductivity of highly ordered organic semiconductors is proposed. Observation of these effects in photoconductivity and modeling of the underlying microscopic mechanisms described in this work represent a significant step forward in our understanding of electronic properties of organic semiconductors.

Strain-induced photoconductivity in thin films of Co doped amorphous carbon

Jiang, Y. C.; Gao, J.
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 23/10/2014 EN
Relevância na Pesquisa
27.66%
Traditionally, strain effect was mainly considered in the materials with periodic lattice structure, and was thought to be very weak in amorphous semiconductors. Here, we investigate the effects of strain in films of cobalt-doped amorphous carbon (Co-C) grown on 0.7PbMg1/3Nb2/3O3-0.3PbTiO3 (PMN-PT) substrates. The electric transport properties of the Co-C films were effectively modulated by the piezoelectric substrates. Moreover, we observed, for the first time, strain-induced photoconductivity in such an amorphous semiconductor. Without strain, no photoconductivity was observed. When subjected to strain, the Co-C films exhibited significant photoconductivity under illumination by a 532-nm monochromatic light. A strain-modified photoconductivity theory was developed to elucidate the possible mechanism of this remarkable phenomenon. The good agreement between the theoretical and experimental results indicates that strain-induced photoconductivity may derive from modulation of the band structure via the strain effect.

Real-time measurement of laser induced photoconductivity in sol-gel derived Al doped ZnO thin films

Eskandari, F.; Ranjbar, M.; Kameli, P.; Salamati, H.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 28/12/2014
Relevância na Pesquisa
27.45%
In this paper Al doped ZnO (AZO) thin films with 0, 3, 6 and 12 at. % Al concentration were prepared by sol-gel method on glass substrates. The deposited films were annealed at different temperatures of 300, 350, 400, 450 and 500 {\deg}C for 1 h in air. X-ray diffraction (XRD) showed wurtzite crystalline structure for the films annealed above 400 {\deg}C. The films were subsequently irradiated by beams of excimer (KrF, {\lambda}=248 nm) laser. The evolution of crystal structure, surface morphology and optical properties were studied using XRD, filed emission scanning electron microscope (FE-SEM) and UV-Vis spectrophotometer, respectively. Real-time measurement of electrical conductivity during laser irradiation showed a transient or persistent photoconductivity effect. The effect of laser energy on this photoconductivity was also investigated. Based on the observed photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS), the observed photoconductivity effect was described.

Oscillatory ac- and photoconductivity of a 2D electron gas: Quasiclassical transport beyond the Boltzmann equation

Dmitriev, I. A.; Mirlin, A. D.; Polyakov, D. G.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.45%
We have analyzed the quasiclassical mechanism of magnetooscillations in the ac- and photoconductivity, related to non-Markovian dynamics of disorder-induced electron scattering. While the magnetooscillations in the photoconductivity are found to be weak, the effect manifests itself much more strongly in the ac conductivity, where it may easily dominate over the oscillations due to the Landau quantization. We argue that the damping of the oscillatory photoconductivity provides a reliable method of measuring the homogeneous broadening of Landau levels (single-particle scattering rate) in high-mobility structures.; Comment: Small changes, published version, 10 pages, 3 figures

Microwave photoconductivity of two-dimensional electron systems with unidirectional periodic modulation

Dietel, J.; Glazman, L.; Hekking, F.; von Oppen, F.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/07/2004
Relevância na Pesquisa
27.66%
Motivated by the recently discovered microwave-induced ``zero-resistance'' states in two-dimensional electron systems, we study the microwave photoconductivity of a two-dimensional electron gas (2DEG) subject to a unidirectional static periodic potential. The combination of this potential, the classically strong magnetic field, and the microwave radiation may result in an anisotropic negative conductivity of the 2DEG. Similar to the case of a smooth random potential, two mechanisms contribute to the negative photoconductivity. The displacement mechanism arises from electron transitions due to disorder-assisted microwave absorption and emission. The distribution-function mechanism arises from microwave-induced changes in the electron distribution. However, the replacement of a smooth random potential by the unidirectional one, leads to different relative strengths of the two contributions to the photoconductivity. The distribution function mechanism dominates the photoconductivity in the direction of the static potential modulation, while both mechanisms contribute equally strongly to the photoconductivity in the perpendicular direction. The unidirectionality of the static potential simplifies greatly the evaluation of the photoconductivities...

Photoconductivity of CdS-CdSe granular films: influence of microstructure

Meshkov, A. S.; Ostretsov, E. F.; Pogosov, W. V.; Ryzhikov, I. A.; Trofimov, Yu. V.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.57%
We study experimentally the photoconductivity of CdS-CdSe sintered granular films obtained by the screen printing method. We mostly focus on the dependences of photoconductivity on film's microstructure, which varies with changing heat-treatment conditions. The maximum photoconductivity is found for samples with compact packing of individual grains, which nevertheless are separated by gaps. Such a microstructure is typical for films heat-treated during an intermediate (optimal) time. In order to understand whether the dominant mechanism of charge transfer is identical with the one in monocrystals, we perform temperature measurements of photoresistance. Corresponding curves have the same peculiar nonmonotonic shape as in CdSe monocrystals, from which we conclude that the basic mechanism is also the same. It is suggested that the optimal heat-treatment time appears as a result of a competition between two mechanisms: improvement of film's connectivity and its oxidation. Photoresistance is also measured in vacuum and in helium atmosphere, which suppress oxygen and water absorption/chemisorption at intergrain boundaries. We demonstrate that this suppression increases photoconductivity, especially at high temperatures.; Comment: 12 pages...

Carrier Heating and Negative Photoconductivity in Graphene

Heyman, J. N.; Stein, J. D.; Kaminski, Z. S.; Banman, A. R.; Massari, A. M.; Robinson, J. T.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 27/10/2014
Relevância na Pesquisa
27.57%
We investigated negative photoconductivity in graphene using ultrafast terahertz techniques. Infrared transmission was used to determine the Fermi energy, carrier density and mobility of p-type CVD graphene samples. Time-resolved terahertz photoconductivity measurements using a tunable mid-infrared pump probed these samples at photon energies between 0.35eV to 1.55eV, approximately one half to three times the Fermi energy of the samples. Although interband optical transitions in graphene are blocked for pump photon energies less than twice the Fermi energy, we observe negative photoconductivity at all pump photon energies investigated, indicating that interband excitation is not required to observe this effect. Our results are consistent with a thermalized free carrier population that cools by electron-phonon scattering, but inconsistent with models of negative photoconductivity based on population inversion.; Comment: 15 pages, 4 figures

Nonlinear effects in microwave photoconductivity of two-dimensional electron systems

Ryzhii, V.; Suris, R.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.57%
We present a model for microwave photoconductivity of two-dimensional electron systems in a magnetic field which describes the effects of strong microwave and steady-state electric fields. Using this model, we derive an analytical formula for the photoconductivity associated with photon- and multi-photon-assisted impurity scattering as a function of the frequency and power of microwave radiation. According to the developed model, the microwave conductivity is an oscillatory function of the frequency of microwave radiation and the cyclotron frequency which turns zero at the cyclotron resonance and its harmonics. It exhibits maxima and minima (with absolute negative conductivity) at the microwave frequencies somewhat different from the resonant frequencies. The calculated power dependence of the amplitude of the microwave photoconductivity oscillations exhibits pronounced sublinear behavior similar to a logarithmic function. The height of the microwave photoconductivity maxima and the depth of its minima are nonmonotonic functions of the electric field. It is pointed to the possibility of a strong widening of the maxima and minima due to a strong sensitivity of their parameters on the electric field and the presence of strong long-range electric-field fluctuations. The obtained dependences are consistent with the results of the experimental observations.; Comment: 9 pages...

Semiconducting-to-metallic photoconductivity crossover and temperature-dependent Drude weight in graphene

Frenzel, A. J.; Lui, C. H.; Shin, Y. C.; Kong, J.; Gedik, N.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 14/03/2014
Relevância na Pesquisa
27.57%
We investigated the transient photoconductivity of graphene at various gate-tuned carrier densities by optical-pump terahertz-probe spectroscopy. We demonstrated that graphene exhibits semiconducting positive photoconductivity near zero carrier density, which crosses over to metallic negative photoconductivity at high carrier density. Our observations are accounted for by considering the interplay between photo-induced changes of both the Drude weight and the carrier scattering rate. Notably, we observed multiple sign changes in the temporal photoconductivity dynamics at low carrier density. This behavior reflects the non-monotonic temperature dependence of the Drude weight, a unique property of massless Dirac fermions.

Computer simulation of photoconductivity decay in AgBr microcrystals: Relaxation model

Hailstone, Richard; Erdtmann, David
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Artigo de Revista Científica Formato: 68438 bytes; application/pdf
EN_US
Relevância na Pesquisa
37.45%
Previous workers have explained photoconductivity decay in AgBr microcrystals by proposing a model involving lattice relaxation following shallow surface trapping of electrons. This model is investigated using Monte Carlo simulations in which the electron and hole undergo a random walk in the volume of the microcrystals and are shallowly trapped at the surface. The decay rate is controlled by the thermal barrier that must be overcome to achieve a lower-energy lattice configuration, as well as by the density and cross section of the shallow surface traps. The simulation results lend support to the lattice relaxation model, but also suggest a significant role of free-electron/trapped-hole recombination in the photoconductivity decay. The experimentally observed increase in decay time with increasing microcrystal size is also seen in the simulations. This size dependence is due to the effect of the surface-to-volume ratio on the distribution between free and shallowly trapped states for the electron.