Showing papers on "Photoconductivity published in 1988"
TL;DR: In this article, the first high-detectivity (D* = 1.0×1010 cm 1/2/W) and high-responsivity (Rv = 30 000 V/W ) GaAs/AlxGa1−xAs multiquantum well detector, sensitive in the long-wavelength infrared band at λ=8.3 μm (operating at a temperature of T= 77 K).
Abstract: We report the first high‐detectivity (D*=1.0×1010 cm (Hz)1/2/W), high‐responsivity (Rv =30 000 V/W) GaAs/AlxGa1−xAs multiquantum well detector, sensitive in the long‐wavelength infrared band at λ=8.3 μm (operating at a temperature of T= 77 K). Because of the mature GaAs growth and processing technologies as well as the potential for monolithic integration with high‐speed GaAs field‐effect transistors, large focal plane arrays of these detectors should be possible.
177 citations
TL;DR: In this article, the authors classified infrared detectors into three categories: 1.1. General classification of infrared detectors 2.2. Photoconductive detectors, 2.3.3, and 2.4.
163 citations
TL;DR: In this paper, the carrier generation in benzimidazole perylene/tetraphenyldiamine thin film structures was studied using xerographic, pulsed photoconductivity and fluorescence measurements, and the results showed that carrier generation is dominated by an extrinsic mechanism involving exciton dissociation into free carriers at the pigment/transport layer interface.
75 citations
TL;DR: In this paper, the authors measured the continuous infrared (λ∼10 μm) photoconductivity spectrum for an inter-band absorption photoexcited tunneling quantum well detector and showed that the line shape is broadened and asymmetrical with respect to the zero-bias Lorentzian absorption spectrum.
Abstract: We have measured, for the first time, the continuous infrared (λ∼10 μm) photoconductivity spectrum, for an intersubband absorption photoexcited tunneling quantum well detector. The line shape is broadened and asymmetrical with respect to the zero‐bias Lorentzian absorption spectrum. We show that this is a result of the uncertainty principle lifetime broadening due to the rapid tunneling escape of the photoexcited electrons.
72 citations
TL;DR: In this paper, the temperature of the chemical bath used in the electroless deposition of cadmium sulphide thin films has been found to affect the deposition rate, optical transmission T (%), film morphology, photoconductivity σph, photoconductor to dark conductivity ratio (CdS/σd) and photocurrent decay time τ 0.0, 20−103 s.
53 citations
TL;DR: In this article, the authors applied transient photocapacitance and transient junction photocurrent measurements to the study of undoped hydrogenated amorphous silicon (a•Si:H) films, and found that the electronic optical transition from the dominant deep defect is very similar in energy to the D−→D0+e optical transition identified in n • type doped a:Si-H films.
Abstract: We have applied transient photocapacitance and transient junction photocurrent measurements to the study of undoped hydrogenated amorphous silicon (a‐Si:H) films, and find that the electronic optical transition from the dominant deep defect is very similar in energy to the D−→D0+e optical transition identified in n‐type doped a:Si:H films. In addition, we have observed a competing hole thermal transition, and we have obtained estimates of its thermal emission rate and of the thermal gap. We have used the difference between photocapacitance and photocurrent in the valence‐band tail region to determine the quantity (μτ)hNT at different temperatures. Finally, we have observed that light‐induced metastable defects have a hole capture cross section significantly larger than that of the intrinsic defects.
50 citations
TL;DR: In this paper, the Staebler-Wronski effect was shown to be related to the density of recombination centers in high quality undoped hydrogenated amorphous silicon.
Abstract: The number of deep defects (as measured by sub‐band‐gap optical absorption) and the number of recombination centers (as measured by steady‐state photoconductivity) in high quality undoped hydrogenated amorphous silicon are monitored as the film undergoes light‐induced defect generation and thermal annealing (the Staebler–Wronski effect). The kinetics of the growth in the density of deep defects agree well with the kinetics of spin centers reported by Stutzmann, Jackson, and Tsai. [Appl. Phys. Lett. 45, 1075 (1984)]. The density of recombination centers is directly related, though not simply proportional to, the density of deep defects; as samples are annealed, the recombination center density drops much more quickly than the total defect density. This behavior is shown to arise if the distribution of defect energy levels corresponds to a distribution of defect annealing energies.
45 citations
DOI•
01 Jun 1988TL;DR: In this article, an analysis of the carrier diffusion and surface recombination processes in gap-structure MIC devices at quasi-CW laser excitation is presented, where simple analytical expressions are obtained for the effective laser-induced photoconductivity and the plasma penetration depth.
Abstract: The paper presents an analysis of the carrier diffusion and surface recombination processes in gap-structure MIC devices at quasi-CW laser excitation. Quite simple analytical expressions are obtained for the effective laser-induced photoconductivity and the plasma penetration depth. The formulas have been confirmed by experiment, and allow application of the well-known lumped element analysis of the gap region (often used in the field of optoelectronic microwave switching) even under quasi-CW or pure-CW excitation condition.
42 citations
TL;DR: Turn-on and turn-off of bulk semiconductor switches, based on excitation and quenching of photoconductivity, respectively, have been demonstrated with copper-doped II-VI semiconductor crystals as discussed by the authors.
Abstract: Turn‐on and turn‐off of bulk semiconductor switches, based on excitation and quenching of photoconductivity, respectively, have been demonstrated with copper‐doped II‐VI semiconductor crystals. The increase of the conductivity (turn‐on) was realized with a xenon flash‐lamp pulse of 15‐μs duration. A reduction of the conductivity (turn‐off) was obtained by irradiating the samples with IR light using an 8‐ns Nd:YAG laser pulse (YAG denotes yttrium aluminum garnet). For turn‐on in CdS:Cu the conductivity follows the xenon flash excitation. The turn‐off time constant was 250 ns. ZnS and ZnSe crystals showed a slower response. A memory effect for the IR light was observed.
41 citations
TL;DR: In this paper, the intrinsic and doped amorphous silicon carbide hydrogen alloy prepared by radio-frequency glowdischarge decomposition of a silane-methane mixture was studied in detail.
Abstract: Various properties, including the chemical composition, optical gap, infrared and photoluminescence spectra, dark and photoconductivity, and activation energy of the intrinsic and doped amorphous silicon carbide hydrogen alloy prepared by radio‐frequency glow‐discharge decomposition of a silane‐methane mixture have been studied in detail. The gas‐phase composition of CH4, i.e., Xg=CH4/(CH4+SiH4), was varied from 0 to 0.8 and the B2H6 and PH3 mole fraction in the gas phase was varied from 0.09% to 2%. It is found that the carbon mole fraction in the film is smaller than 0.12 for Xg≤0.8 and the incorporation of carbon for Xg≤0.4 makes the film inhomogeneous, i.e., forming Si‐ and SiC‐rich regions. The observed variation of optical and electrical properties as a function of doping and carbon mole fraction are explained in a consistent way.
39 citations
TL;DR: In this article, the influence of the deposition conditions in the ECR plasma CVD method on the properties of a-Si:H films was studied and the properties were correlated with plasma optical emission spectra of similar deposition conditions.
Abstract: Hydrogenated amorphous silicon (a-Si:H) films were prepared by the microwave electron-cyclotron-resonance (ECR) plasma CVD method using SiH4 gas without intentional substrate heating. The influence of the deposition conditions in the ECR plasma CVD method on the properties of a-Si:H films was studied and the properties were correlated with plasma optical emission spectra of similar deposition conditions. Photoconductivity of ~10-6 (Ω cm)-1 under simulated AM1 (100 mW/cm2) illumination was obtained for the as-grown film with an optical gap of ~2.1 eV at the SiH4 gaspressure of 2×10-4 Torr. The photoconductivities, the optical gaps and the B values estimated from optical absorption measurements were widely changed when SiH4 gas pressure condition was changed. Infrared absorption spectra also showed that the Si-H2 stetching mode at ~2100 cm-1 and (Si-H2)n wagging mode at ~845 cm-1 increased as SiH4 gas pressure increased. Measurements of optical emission spectra in the SiH4 ECR plasma showed that the emission intensity ratio of Si (288 nm) to SiH (414 nm) was larger than that in conventional RF plasma CVD, and that the photoconductivities and optical gaps increased as this ratio increased.
TL;DR: In this paper, a horn antenna was used to allow cooling of samples to 77 K outside the waveguide and testings of large-size samples, and a good agreement was established between lifetime results from the contactless microwave reflection technique and the standard photoconductivity decay method using two ohmic contacts.
Abstract: Photoconductivity lifetime measurements on narrow band‐gap HgCdTe thin films and bulk slices using a contactless microwave reflection technique have been demonstrated for the first time. A horn antenna was used to allow cooling of samples to 77 K outside the waveguide and testings of large‐size samples. A good agreement was established between lifetime results from the contactless microwave reflection technique and the standard photoconductivity decay method using two ohmic contacts. The feasibility of lifetime mapping by moving the pulsed light beam to different locations on the samples was also demonstrated.
TL;DR: In this paper, the theory of recombination at dangling bonds and band tails is developed and the statistics for correlated defects are included and the Shockley-Read formalism is extended to asymmetric exponential distributions of tail states.
Abstract: The theory of recombination at dangling bonds and band tails is developed. The statistics for correlated defects are included and the Shockley-Read formalism is extended to asymmetric exponential distributions of tail states. Parametrical representations of the photoconductivity and the charge densities are obtained. A comparison of the results explains the thermal quenching of the photoconductivity experimentally observed. At low temperatures, the photoconductivity is determined by the balance between the two band- tail charge densities. At higher temperatures, one band-tail density becomes negligible compared with the dangling-bond charge density and the photoconductivity is controlled by the latter. Finally, the variations in photoconductivity with the density-of-states parameters are discussed. The agreement between the model and experimental results on undoped hydrogenated amorphous silicon is excellent for temperature above 150K. The divergence observed below 150K can be interpreted with ca...
TL;DR: In this paper, the optical absorption and photoconductivity measurements were carried out at the temperature region 20-300 K and the photoacoustic spectrum was done at 292 K, respectively, and the results showed that the structural defects of the β⋅In2S3 single crystal decreased as cobalt was introduced into the samples and that the cobalt atoms were located at the Td symmetry site of the host lattice as Co2+ ion.
Abstract: β⋅In2 S3 and β⋅In2S3 :Co2+ single crystals were grown by the chemical transport reaction method. The optical absorption and photoconductivity measurements carried out at the temperature region 20–300 K and the photoacoustic spectrum was done at 292 K. The results showed that the structural defects of the β⋅In2 S3 single crystal decreased as cobalt was introduced into the samples and that the cobalt atoms were located at the Td symmetry site of the β⋅In2 S3 host lattice as Co2+ ion.
Patent•
30 Dec 1988
TL;DR: A fiber optic dosimeter in which an electron trapping material is held in a probe on the tip of an optical fiber is used to measure the amount of ambient radiation in this article, where the probe is placed in a region with the radiation to be measured, and the opposite end of the optical fiber, from which radiation readings are measured, is located in a location remote from the radiation source.
Abstract: A fiber optic dosimeter in which an electron trapping material is held in a probe on the tip of an optical fiber The probe is placed in a region with the radiation to be measured, and the opposite end of the optical fiber, from which radiation readings are measured, is placed in a location remote from the radiation source When radiation impinges upon the electron trapping material, electrons in the material are raised to a higher state where they are trapped and stay indefinitely When infrared light strikes the material, the stored electrons are released from their traps and, upon falling to a lower energy level, emit visible light which can be detected and measured Thus, to measure the amount of ambient radiation, the electron trapping material is stimulated with infrared light from an infrared source at the opposite end of the optical fiber This infrared stimulation releases trapped electrons and causes the emission of visible light, at least a portion of which is collected and directed back down the optical fiber to the visible light detector, where it is converted into an electrical signal and measured The infrared stimulation is modulated to allow for measurement of background fluorescence during radiation exposure when infrared stimulation is not applied This background fluorescence is then substracted from the gross signal under infrared stimulation to yield a signal which changes linearly with radiation input
TL;DR: In this paper, the authors analyzed the effect of alloying on diffusion lengths and photoconductivity of a-SiGe:H and showed that changes in photoconductivities by generation of defects (light soaking) result in noticeable changes in diffusion lengths.
Abstract: Ambipolar diffusion lengths in a-SiGe:H and a-SiC:H have been analyzed by Steady State Photocarrier Grating Technique. Diffusion lengths and photoconductivity of a-Si:H are considerably affected by alloying. Photoconductivity in a-SiGe:H can be improved by special deposition methods, diffusion lengths, however turn out to remain nearly unchanged. The comparison of diffusion lengths and -ho~oconductivity yields hole mobilities in a-Si 1-x Ge x :H of 10 -2 cm 2 /Vs for O≤×≤O.2. For a-Si:H changes in photoconductivity by generation of defects (light soaking) result in noticeable changes in diffusion lengths, whereas different photoconductivities in a-SiGe:H caused by different deposition methods end up in the same diffusion lengths. Consequently the improvement of a-SiGe:H photoconductivity by changes in deposition condition is by far a much more complex process than only decrease of density of midgap states.
TL;DR: In this article, Si:H films were deposited by direct photochemical vapor deposition using vacuum ultraviolet lights emitted from deuterium (161 nm) and Xe (147 nm) discharge lamps.
Abstract: a‐Si:H films were deposited by direct photochemical vapor deposition using vacuum ultraviolet lights emitted from deuterium (161 nm) and Xe (147 nm) discharge lamps. A source gas of Si2H6 was effectively decomposed, and a high deposition rate of 7.5 nm/min could be achieved in the case of the Xe lamp. The films had excellent electrical and photoelectric properties similar to ordinary films deposited by glow discharge, and showed very little degradation of photoconductivity under illumination.
TL;DR: In this article, time-resolved photoconductivity measurements for pulsed excitation of highly oriented poly(p-phenylenevinylene) (PPV) films are reported, revealing a large, short-lived photoconductive response separate from the long-lived component.
Abstract: Time-resolved photoconductivity measurements are reported for pulsed excitation of highly oriented poly(p-phenylenevinylene) (PPV) films. These measurements reveal a large, short-lived photoconductive response separate from the long-lived component that has been investigated by several other groups. The authors report the dependence of this short-lived photocurrent upon the sample temperature, upon the polarisation, energy and intensity of the excitation light and upon the magnitude and orientation of the applied DC bias field.
TL;DR: In this article, the dark and photoconductivity characteristics of a thin crystalline film of epindolidione, sandwiched between indium tin oxide coated glass and indium, have been investigated.
TL;DR: A spatial light modulator with a thin (1-microm) amorphous silicon (PIN) photoconductor has been demonstrated with a threshold sensitivity of <3 microw/cm(2) and a novel compound electrode design greatly increases the efficiency allowing the use of a photoconductive layer thin enough to achieve good transmission.
Abstract: A spatial light modulator with a thin (1-microm) amorphous silicon (PIN) photoconductor has been demonstrated with a threshold sensitivity of <3 microw/cm(2). A novel compound electrode design greatly increases the efficiency allowing the use of a photoconductive layer thin enough to achieve good transmission. The performance characteristics are reported and compared to the predictions of a theoretical model of the device.
TL;DR: In this article, the effect of incorporation of 10 at.% of Sb and Ge on the steady state transient photoconductivity in vacuum evaporated amorphous thin films of Se80Te20 was investigated.
Abstract: The present paper reports the effect of incorporation of 10 at.% of Sb and Ge on the steady state transient photoconductivity in vacuum evaporated amorphous thin films of Se80Te20. The photosensitivity at room temperature decreases after incorporating these elements with the decrease being greater in the case of Ge. The transient photoconductivity is also affected quite appreciably after incorporating these elements in the binary Se80Te20 alloy.
TL;DR: In this paper, the effects of TiO2 on the CdS photoconductance or conductivity after illumination were investigated under vacuum or under various O2 pressures, at room temperature for the powders Cs, TiO 2, mixtures of Cs with a small amount of SiO2, and a Cs-TiO2 double pellet.
Abstract: Photoconductance measurements have been carried out in the visible and/or ultraviolet spectral region, under vacuum or under various O2 pressures, at room temperature for the powders CdS, TiO2, mixtures of CdS with a small amount of TiO2(or SiO2 for comparison) and a CdS–TiO2 double pellet. Under vacuum, regardless of the spectral range, the effects of TiO2 on the CdS photoconductance or conductivity after illumination are interpreted by electron transfer from TiO2 to CdS. In the presence of O2, this transfer is limited by oxygen species adsorbed on TiO2, which deplete this material of its free electrons (pressure dependence) and which can also capture free electrons of CdS to an extent which depends on the number and areas of the interfaces between particles of the two semiconductors.
Patent•
27 Jan 1988TL;DR: An amorphous silicon photosensor is described in this article, which comprises a photoconductive layer which comprises three or four polysilicon layers formed on a substrate, each layer containing at least one kind of atom selected from the group consisting of hydrogen, heavy hydrogen, and halogen atoms, and having two heterojunctions, in which the optical band gap of an amomorphous silicon layer lying between the two heterjunctions is in the range of 1.6 to 1.8 eV, and at least part of the layer indicates an i-type or p
Abstract: An amorphous silicon photosensor is disclosed, which comprises a photoconductive layer which comprises three or four amorphous silicon layers formed on a substrate, each layer containing at least one kind of atom selected from the group consisting of hydrogen, heavy hydrogen, and halogen atoms, and having two heterojunctions, in which the optical band gap of an amorphous silicon layer lying between the two heterojunctions is in the range of 1.6 to 1.8 eV, a first end amorphous silicon layer, to which light is applied, contains oxygen, has an optical band gap of 1.9 eV or more, and at least part of the layer indicates an i-type or p-type conductivity, and a second end amorphous silicon layer, to which light is not applied, contains oxygen, having an optical band gap of 1.9 eV or more, and at least part of the layer indicates an i-type or n-type conductivity.
TL;DR: In this paper, photoluminescence and photoconductivity measurements on single InAs quantum wells under a 3.4% biaxial compression were reported, which is interpreted as recombination between electrons and holes distributed over a range of confined energy states associated with quantum well width fluctuations.
Abstract: We report photoluminescence and photoconductivity measurements on single InAs quantum wells under a 3.4% biaxial compression. The photoluminescence line, which is in the 1.2–1.6 μm wavelength range depending on well thickness, is interpreted as recombination between electrons and holes distributed over a range of confined energy states associated with quantum well width fluctuations. Photoconductivity is found to provide spectroscopic measurements of the optical transitions even for single, extremely thin quantum wells. We find excellent agreement between the measured transition energies and the result of an envelope function calculation taking into account the effect of both strain and quantum confinement.
Patent•
22 Apr 1988TL;DR: A light receiving member for electrophotography made up of an aluminum support and a multilayered light receiving layer exhibiting photoconductivity formed on the aluminum support is described in this article.
Abstract: A light receiving member for electrophotography made up of an aluminum support and a multilayered light receiving layer exhibiting photoconductivity formed on the aluminum support, wherein the multilayered light receiving layer consists of a lower layer in contact with the support and an upper layer, the lower layer being made of an inorganic material containing at least aluminum atom (Al), silicon atoms (Si) and hydrogen atoms (H), and having portion in which the aluminum atoms (Al), silicon atoms (Si), and hydrogen atoms (H) are unevenly distributed across the layer thickness, the upper layer being made of a non-single-crystal material composed of silicon atoms (Si) as the matrix and at least either of hydrogen atoms (H) or halogen atoms (X) and containing at least one of carbon atoms, nitrogen atoms (N) and oxygen atoms (O) in the layer region in adjacent with the lower layer. The light receiving member for electrophotography can overcome all of the foregoing problems and exhibits extremely excellent electrical property, optical property, photoconductivity, durability, image property and circumstantial property of use.
TL;DR: In this article, the inplane sheet resistance can be increased by a factor of more than 60 with illumination of less than 1 W/cm2, and the effect is mainly due to hole trapping in the potential minima of AlGaAs and subsequent recombination of minority electrons.
Abstract: In p‐modulation‐doped quantum wells of GaAs/AlGaAs extremely high negative photoconductivity is observed at low temperatures. The in‐plane sheet resistance can be increased by a factor of more than 60 with illumination of less than 1 W/cm2. Spectral analysis shows that the effect is mainly due to hole trapping in the potential minima of AlGaAs and subsequent recombination of minority electrons.
TL;DR: In this article, a GaAs/AlGaAs multiple quantum well pin modulator with sub-picosecond optical pulses was used to achieve a limiting rise time of 170 ps for establishing crosswell photoconductivity.
Abstract: Excite and probe measurements on a GaAs/AlGaAs multiple quantum well pin modulator using sub-picosecond optical pulses are reported. The quantum confined Stark effect allows measurement of a limiting rise time of 170 ps for establishing crosswell photoconductivity.
TL;DR: In this paper, a simple and economic but versatile time-of-flight (TOF) transient photoconductivity apparatus which enables RC transient-free interrupted transit time (ITT), as well as delayed and advanced photoexcitation mode measurements, to be carried out on high resistivity solids was described.
Abstract: The authors describe a simple and economic but versatile time-of-flight (TOF) transient photoconductivity apparatus which enables RC transient-free interrupted transit time (ITT), as well as delayed and advanced photoexcitation mode measurements, to be carried out on high resistivity solids. The apparatus uses a short (130 ns) intense light pulse from a xenon flash bulb for photogeneration and high voltage complementary HEXFETS to apply the bias voltage. The ITT method was applied to examine charge trapping kinetics in vacuum-deposited amorphous Se layers suitable for X-ray medical imaging. It is shown that the ITT technique was successful in identifying two species of traps and extracting the hole trapping and release times, which are much longer than the transit times, even when the conventional TOF signal showed very little evidence of trapping.
TL;DR: In this article, power limiting and self-switching caused by the field shielding effects of charge created by photoconductivity at 1.06 μm in CdTe have been demonstrated.
Abstract: Power limiting and self‐switching which is caused by the field shielding effects of charge created by photoconductivity at 1.06 μm in CdTe have been demonstrated. The effect has a relatively low threshold of ∼100 μW/cm2, an extrapolated switching time of microseconds, and can be used over the wavelength band of approximately 0.9–1.3 μm.
TL;DR: The saturation effect of optical degradation in hydrogenated amorphous silicon films (a-Si:H) deposited at various temperatures Ts has been studied by means of photoconductivity measurements.
Abstract: The saturation effect of the optical degradation in hydrogenated amorphous silicon films (a-Si:H) deposited at various temperatures Ts has been studied by means of photoconductivity measurements. It was confirmed that the saturation is mainly related to the simultaneous annealing at a higher light-soaking temperature T1 (?20?C) as well as the depletion of the weak Si-Si bonds at lower T1 (?0?C). The weak bond density (1016?1018/cm3) estimated from the low-temperature saturation effect decreases with increasing Ts corresponding to the growth of Si clusters.