Query: Theory of photoconductivity in semiconductor films.

Candidate papers:

abstract: Photoconductive films of the lead salt family are composed of a system of crystallites separated by intercrystalline barriers. The crystallites are lead salts while the intercrystalline barriers are an oxide of lead or of the lead salt. Space charge regions are present at the surface of the crystallites. The lifetime of hole electron pairs is determined in part by surface states while the resistivity is strongly affected by intercrystalline barriers.
author_names: Richard L Petritz
title: Theory of Photoconductivity in Semiconductor Films
year: 1956

abstract: 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.
author_names: Y C Jiang

J Gao
title: Strain induced photoconductivity in thin films of Co doped amorphous carbon
venue: Scientific reports
year: 2014

abstract: Zn In Se thin films were fabricated on the ultrasonically cleaned glass substrates masked with clover shaped geometry by thermal evaporation of its elemental sources. Temperature dependent conductivity characteristics of the films were investigated under dark and illuminated conditions. The semiconductor type of the films was found as n type by thermal probe test. According to the van der Pauw technique, the dark electrical conductivity analyses showed that the variations of conductivity of unannealed and annealed at [Formula: see text]C samples are in exponential dependence of temperature. These conductivity profiles were found to be dominated by the thermionic emission at high temperature region whereas their behaviors at low temperatures were modeled by hopping theory. On the contrary, as a result of the further annealing temperatures, the surface of the samples showed semi metallic characteristics with deviating from expected Arrhenius behavior. In addition, the temperature dependent photoconductivity of the films was analyzed under different illumination intensities and the results were explained by the supra linear characteristic based on the two center recombination model.
author_names: Hasan Huseyin Gullu

Mehmet Parlak
title: INVESTIGATION OF CONDUCTIVITY CHARACTERISTICS OF Zn In Se THIN FILMS
venue: Surface Review and Letters
year: 2019

abstract: A method for improving the discrimination of semiconductor thin film gas sensors, which utilises the amplitude and phase of the photocurrent response to a modulated light source, is proposed. The photoconductivity of microcrystalline silicon films is examined before and after exposure to the vapour of an iodine solution in ethanol. Preliminary results are presented which suggest that the density and/or capture properties of localised states may be reversibly modified. For cadmium selenide however, a small but systematic temperature dependent phase lead is observed in this material at low frequencies, even under vacuum annealed conditions. This is in contrast to present theory, which predicts that for an arbitrary localised state distribution the photocurrent response must lag the applied excitation.
author_names: Steve Reynolds

Zdravka I Aneva

Z Levi

Diana Nesheva

Charlie Main

Vladimir A Smirnov
title: Potential gas sensor applications of semiconductor thin films based on changes in photoresponse
year: 2007

abstract: Abstract This article addresses band edge electronic structure of transition metal/rare earth (TM/RE) non crystalline and nano crystalline elemental and complex oxide high k dielectrics for advanced semiconductor devices. Experimental approaches include X ray absorption spectroscopy (XAS) from TM, RE and oxygen core states, photoconductivity (PC) and visible/vacuum ultra violet (UV) spectroscopic ellipsometry (SE) combined with ab initio theory is applied to small clusters. These measurements are complemented by Fourier transform infra red absorption (FTIR) X ray photoelectron spectroscopy (XPS) high resolution transmission electron microscopy (HRTEM) and X ray diffraction (XRD) Two issues are highlighted: Jahn Teller term splittings that remove d state degeneracies of states at the bottom of the conduction band, and chemical phase separation and crystallinity in Zr and Hf silicates and ternary (Zr(Hf)O2)x(Si3N4)y(SiO2)1 x y alloys. Engineering solutions for optimization of both classes of high k dielectric films, including limits imposed on the continued and ultimate scaling of the equivalent oxide thickness (EOT) are addressed.
author_names: Gerald Lucovsky
title: Band edge electronic structure of transition metal/rare earth oxide dielectrics
year: 2006

abstract: In a recent paper the photoconductivity of lead sulphide films was discussed in terms of a barrier mechanism Large single crystals of lead telluride have now been grown and, with these, single barrier photocells can be prepared The simplest barrier is formed at a metal semiconductor contact. Such barriers, as exhibited in rectifiers, have been mainly studied It is found that the photosensitivity and time constant of such cells is determined by the total current at the contact point, as expected from barrier theory. The variation in barrier height with temperature and time has also been determined
author_names: Alan Frank Gibson
title: Single Contact Lead Telluride Photocells
year: 1952

abstract: The optical properties of natural and synthetic melanin have been characterized for a number of laser wavelengths in the visible region. Natural melanin was prepared from hydrolyzed melanosomes isolated from normal, bovine retinal pigment epithelium. The inverse adding doubling method based on the diffusion approximation and radiative transport theory was employed to determine the absorption, scattering, and scattering anisotropy coefficients of melanin from the measurements of diffuse transmission, diffuse reflection and collimated transmission using double integrating spheres. The results obtained by the use of the inverse adding doubling method were compared to the Monte Carlo simulation technique. Characterization of melanin is now being extended to include electrical photoconductivity of melanin thin films on a semiconductor substrate.
author_names: Randolph D Glickman

Dhiraj K Sardar

Felipe S Salinas

M C Hobbs
title: Optical and electrical characterization of natural and synthetic melanin
venue: Proceedings of the Second Joint 24th Annual Conference and the Annual Fall Meeting of the Biomedical Engineering Society] [Engineering in Medicine and Biology
year: 2002

abstract: The optical properties of natural and synthetic melanin have been characterized for anumber of laser wavelengths in the visible region. Natural melanin was prepared from hydrolyzed melanosomes isolated from normal, bovine retinal pigment epithelium. The inverse adding doubling method based on the diffusion approximation and radiative transport theory was employed to determine the absorption, scattering, and scattering anisotropy coefficients of melanin from the measurements of diffuse transmission, diffuse reflection and collimated transmission using double integrating spheres. The results obtained by the use of the inverse adding doubling method were compared to the Monte Carlo simulation technique. Characterization of melanin is now being extended to include electrical photoconductivity of melanin thin films on a semiconductor substrate. Keywords Lasers, Melanin, Optical Properties, Radiative Transport, Electrical, Photoconductivity
author_names: Universityof Texas
title: OPTICAL AND ELECTRICAL CHARACTERIZATION OF NATURAL AND SYNTHETIC MELANIN
year: 2002

abstract: Amorphous carbon films with an intermediate content of sp3 atoms are finding applications as resistive switches in devices for bio sensing and for neuromorphic pattern recognition. To understand resistive switching and photoconductivity in amorphous semiconductors dominated by hopping conduction, we present a theory that unifies the optical and electronic properties. The theory considers all of the states to be localized to various extents instead of being extended electronic states. The electronic density of states (eDOS) is modeled with Gaussian functions, symmetric in energy around the Fermi energy. A "hopping mobility" between localized states that is explicitly both energy and temperature dependent is introduced. We describe an example application to amorphous carbon films prepared by using high power impulse magnetron sputtering that have a range of sp3 hybridization fractions of the carbon atoms. The electronic bandgaps of the films are observed to correlate with their optical bandgaps. The eDOS is benchmarked against optical property measurements made by ellipsometry. The theory explains the temperature dependence of the resistivity and predicts that the films should show a temperature dependent hopping photoconductivity. Measurements confirm the presence of the photoconductivity and reveal its spectral dependence. A link is made between persistent hopping photoconductivity and resistive switching.
author_names: Zijun C Zhao

Thomas J Raeber

Billy James Murdoch

Jim G Partridge

Dougal G McCulloch

David R Mckenzie
title: Unifying the optical and electrical properties of amorphous carbon: application to hopping photoconductivity and memristance
year: 2020

abstract: The composition of amorphous oxide semiconductors, which are well known for their optical transparency, can be tailored to enhance their absorption and induce photoconductivity for irradiation with green, and shorter wavelength light. In principle, amorphous oxide semiconductor based thin film photoconductors could hence be applied as photosensors. However, their photoconductivity persists for hours after illumination has been removed, which severely degrades the response time and the frame rate of oxide based sensor arrays. We have solved the problem of persistent photoconductivity (PPC) by developing a gated amorphous oxide semiconductor photo thin film transistor (photo TFT) that can provide direct control over the position of the Fermi level in the active layer. Applying a short duration (10 ns) voltage pulse to these devices induces electron accumulation and accelerates their recombination with ionized oxygen vacancy sites, which are thought to cause PPC. We have integrated these photo TFTs in a transparent active matrix photosensor array that can be operated at high frame rates and that has potential applications in contact free interactive displays.
author_names: Sanghun Jeon

Seung-Eon Ahn

I-hun Song

Chang Jung Kim

U-In Chung

Eunha Lee

In-kyeong Yoo

Arokia Nathan

Sungsik Lee

John Robertson

Kinam Kim
title: Gated three terminal device architecture to eliminate persistent photoconductivity in oxide semiconductor photosensor arrays.
venue: Nature materials
year: 2012