Showing papers on "Photoconductivity published in 1981"
TL;DR: In this paper, a study of the sources and control of residual impurities in GaAs grown by metalorganic chemical vapor deposition (MOCVD) is presented, and the effects of source purity, growth temperature, and reactor pressure upon residual impurity incorporation are detailed.
178 citations
TL;DR: In this paper, a direct way to obtain the spectra dependence of the optical absorption coefficient in the low-absorption region (10−1−103cm−1) on thin amorphous silicon films is presented.
163 citations
TL;DR: In this paper, the properties of amorphous hydrogenated silicon are reviewed, with special emphasis placed on results obtained by the method of reactive sputtering in an argon-hydrogen plasma.
158 citations
TL;DR: In this article, the authors used ion implantation to control the carrier lifetime in silicon-on-sapphire (SOS) films and found that the carrier mobility was at least an order of magnitude higher than amorphous silicon materials with similar relaxation times.
Abstract: Radiation damage caused by ion implantation is used to control the carrier lifetime in silicon‐on‐sapphire (SOS) films. Photoconductivity measurements show the relaxation time changes by several orders of magnitude and can be as short as 8 ps. The carrier mobility is found to be at least an order of magnitude higher than amorphous silicon materials with similar relaxation times. A photodetector is described that demonstrates the high‐speed capability of these high‐defect‐density films.
158 citations
TL;DR: In this paper, the photoluminescence, optical properties and photoconductivity of amorphous Si : C : H alloys prepared from the plasma decomposition of silane and ethylene are presented.
Abstract: Results on the photoluminescence, optical properties and photoconductivity of amorphous Si : C : H alloys prepared from the plasma decomposition of silane and ethylene are presented. Films deposited at substrate temperatures of 30 and 300°C have been studied with compositions ranging from 100 to 10% silicon. The photoluminescence spectra measured at 77 and 300 K show considerable discrepancies with respect to previously reported results. The emission is in the form of a single band which broadens and shifts towards higher photon energies as the carbon concentration is increased. The highest emission-peak energy of 2·05 eV is achieved for samples with 90 at.% C. The temperature quenching of the luminescence is reduced with increasing carbon concentration. For 90% C specimens there is less than a factor of 2 reduction in emission intensity between 77 and 300 K. As a consequence visible (yellow–orange) room-temperature luminescence can be clearly observed with the naked eye. The luminescence efficie...
144 citations
TL;DR: Amorphous silicon films prepared by a discharge of 10% SiH4•90% H2 mixture are shown to have properties comparable to those prepared from 100%SiH4.
Abstract: Amorphous silicon films prepared by a discharge of 10% SiH4‐90% H2 mixture are shown to have properties comparable to those prepared from 100% SiH4. These films are found to be quite stable against prolonged light exposure.
133 citations
TL;DR: In this paper, the electrical and optical properties of a-sixn1-x:H prepared by the glow discharge of a SiH4-NH3-H2 gas mixture have been systematically investigated as a function of the ammonia-to-silane molar fraction.
Abstract: The electrical and optical properties of a-SixN1-x:H prepared by the glow discharge of a SiH4-NH3-H2 gas mixture have been systematically investigated as a function of the ammonia-to-silane molar fraction. The optical bandgap increases smoothly from 1.75 eV to 5.5 eV as the molar fraction increases. A normalized photoconductivity ηµτ larger than 10-6 cm2V-1 is easily obtained in the ammonia fraction range 3.3×10-3 to 0.60, and it has a maximum (ηµτ4.8 ×10-5 cm2V1) around a fraction of 0.1.
97 citations
TL;DR: In this paper, the authors used the coherent potential approximation to calculate the electronic densities of states for a model of hydrogenated amorphous silicon, and demonstrated the restoration and widening of the band gap with increasing hydrogen content.
Abstract: We have used the coherent potential approximation to calculate the electronic densities of states for a model of hydrogenated amorphous silicon. The results demonstrate the restoration and widening of the band gap with increasing hydrogen content. In the valence band, excellent agreement with photoemission experiments is obtained. In the conduction band Si-H antibonding states are predicted that can be inferred from photoconductivity measurements.
91 citations
TL;DR: In this article, the influence of the incident photon energy, of the applied electric field strength, and of the concentration of two electron scavengers (carbon tetrachloride and perfluoromethylcyclohexane) was studied.
Abstract: Measurements of the photoconductivity of liquid n‐pentane, n‐hexane, cyclopentane, cyclohexane, neopentane, neohexane, and tetramethylsilane induced by far UV radiation (7⩽hν⩽10 eV) have been performed. We have studied the influence of the incident photon energy, of the applied electric field strength, and of the concentration of two electron scavengers (carbon tetrachloride and perfluoromethylcyclohexane). Our results show that in going from the gas phase to the liquid phase, the ionization energy threshold values of these low dielectric constant liquids are lowered by about 1.6 eV. The introduction of an electron scavenger reduces drastically the solvent photocurrent. Our results are consistent with the quenching, by the scavenger, of a solvent expanded excited state, precursor of the geminate ion pair, and not with an epithermal electron scavenging as in high energy photon irradiation.
82 citations
TL;DR: In this article, the temperature and flux dependences of photoconductivity have been investigated for plasma-deposited hydrogenated amorphous silicon alloys produced under a variety of processing conditions.
Abstract: The temperature and flux dependences of photoconductivity have been investigated for plasma‐deposited hydrogenated amorphous silicon alloys produced under a variety of processing conditions. In undoped films, new features such as thermal quenching and supralinearity are observed. Such behavior is critically dependent on the position of the Fermi level, and is not observed in alloys doped by the addition to the plasma of PH3, B2H6, O2+N2 mixtures, or air. Interpretation of the data is based on a model of competing recombination centers.
82 citations
TL;DR: In this paper, the results of steady state photoconductivity experiments on cis- and trans-(CH)x are interpreted in terms of charged solitons, photogenerated either directly (threshold hv = 4Δ/π) or indirectly through coupling of the lattice to electron-hole pair excitations (hv ⩾ 2Δ).
TL;DR: In this article, the effects of the additional selenium on the properties of the films were investigated by structural investigations and photoconductivity measurements, and it was found from the results of the present measurements that compositional changes occur in the films with increasing Selenium/InSe ratio and that single-phase films containing only InSe are obtained at a certain critical ratio.
TL;DR: In this article, the effect of thermal annealing or Li-diffusion on the behavior of the energy levels of residual acceptors is investigated to ascertain the nature of doubly ionizable acceptors.
Abstract: Hall effect, photoluminescence, and photoconductivity measurements on residual acceptors in GaSb grown by the Bridgman method, are presented and discussed with emphasis on the determination of energy level positions. The effect of thermal annealing or Li-diffusion on the behavior of the energy levels of residual acceptors is investigated to ascertain the nature of doubly-ionizable acceptors. Photoluminescence data on the Au-GaSb Schottky barrier give additional results confirming that the rediual acceptor is doubly ionizable. Direct evidence for the defect configuration is also presented.
TL;DR: Anodic oxide films on bismuth are amphoteric semiconductors with n -type and p -type behavior and an optical band gap of 28 eV at room temperature as mentioned in this paper.
TL;DR: In this paper, the effect of introducing oxygen to a certain partial pressure into the vacuum system during deposition and of the further sensitization of the films by a thermal treatment in air was studied by transmission electron microscopy and by mobility and carrier concentration measurements.
TL;DR: In this paper, the photoconductivity action spectrum showed a steep rise of the photo carrier generation efficiency in the range 345-290 nm and a plateau at shorter wavelengths, and the lower limit of the photogeneration quantum yield was estimated as 6 × 10−3 charge carriers/photon with an applied field of 1 × 104 V/cm.
Abstract: Steady state photoconduction in iodoform has been studied between 210–400 nm. The photoconduction threshold is at 345 nm whereas the crystal absorption extends up to 480 nm. The photoconductivity action spectrum shows a steep rise of the photo carrier generation efficiency in the range 345–290 nm and a plateau at shorter wavelengths. Current-voltage characteristics measured under steady illumination show a square dependence of the photocurrent on applied voltage showing the influence of space charge effects. Electron photocurrents are three orders of magnitude lower than hole photocurrents. The lower limit of the photogeneration quantum yield is estimated as 6 × 10−3 charge carriers/photon with an applied field of 1 × 104 V/cm.
Patent•
15 Apr 1981TL;DR: In this paper, an electrophotographic member employing an amorphous silicon photoconductive layer, a part which is at least 10 nm thick inwardly of the ammorphous silicon layer from the surface (or interface) of the polysilicon layer is made of amorphously silicon which has an optical forbidden band gap of at least 1.6 eV and a resistivity of 10 10 Ωcm.
Abstract: In an electrophotographic member employing an amorphous silicon photoconductive layer, a part which is at least 10 nm thick inwardly of the amorphous silicon layer from the surface (or interface) of the amorphous silicon layer is made of amorphous silicon which has an optical forbidden band gap of at least 1.6 eV and a resistivity of at least 10 10 Ω.cm. The electrophotographic member exhibits a satisfactory resolution and good dark-decay characteristics. Further, a region which has an optical forbidden band gap narrower than that of the amorphous silicon forming the surface (or interface) region is disposed within the amorphous silicon layer to a thickness of at least 10 nm, whereby the sensitivity of the electrophotographic member to longer wavelengths of light can be enhanced.
TL;DR: In this article, the authors present the low-temperature deep-level photoconductivity spectra of a wide range of n-type and semi-insulating Fe-doped InP crystals.
Abstract: Presents the low-temperature deep-level photoconductivity spectra of a wide range of n-type and semi-insulating Fe-doped InP crystals. The results differ in important respects from some recently reported photoconductivity work and conclusively demonstrate that Fe2+ rather than Fe+ is the stable charge state in n-type material. The electron ionisation threshold energy from the Fe2+ state to the lowest conduction band at 0.65 eV is found in all the samples studied. Only the semi-insulating show a strong photoconductivity threshold at 1.15 eV. This feature is absent in n-type InP(Fe). The authors tentatively assign this structure to an Fe-related level (Fe3+) 1.15 eV below the conduction band-edge.
TL;DR: In this article, it was shown that the photoconductivity in polycrystalline semiconductors can be principally a majority carrier phenomenon, where the majority carrier dark current is limited by transport across the grain boundaries, and the only effect of the minority carriers is in the modification, by the optical illumination, of the barrier height at these boundaries, through Shockley-Read-Hall capture/emission processes.
Abstract: It is shown that, unlike in crystalline semiconductors, the photoconductivity in polycrystalline semiconductors can be principally a majority carrier phenomenon. This occurs when the majority carrier dark current is limited by transport across the grain boundaries, and the only effect of the minority carriers is in the modification, by the optical illumination, of the barrier height at these boundaries, through Shockley‐Read‐Hall capture/emission processes. The photoconductivity is predicted to be proportional to Gphd2, where Gph is the (uniform) photogeneration rate and d is the (cubic) grain size, over a considerable range of d.
TL;DR: In this article, a picosecond photodetector based on a new photoconductive material, called ρ•Ge, is described, which is capable of operation to wavelengths of 1.7 μm.
Abstract: A picosecond photoconductive detector based on a new photoconductive material, ρ‐Ge, is described. Photoconductivity measurements show relaxation times less than 50 ps and sensitivities greater than 0.1 mA/mW with 25‐μm electrode spacings. A comparison is made with similar devices through the introduction of a merit‐figure Fi, which we propose as being particularly suited to evaluating picosecond photodetectors. The device is capable of operation to wavelengths of 1.7 μm.
TL;DR: In this paper, a two-carrier model under illumination assuming that Δn=Δp, where Δn and Δp are the photogenerated carrier concentration of electrons and holes, respectively, was used to measure photoconductivity and photo-Hall effect on Zn-doped p-type InSe.
Abstract: Measurements of photoconductivity and photo-Hall effect have been made on Zn-doped p-type InSe in the temperature range from 220 to 330 K. The results are interpreted by a two-carrier model under illumination assuming that Δn=Δp, where Δn and Δp are the photogenerated carrier concentration of electrons and holes, respectively. The obtained mobility ratio b is determined as 9.5×10-2T0.7, and the temperature dependence of the hole mobility can be well fitted by the model developed by Schmid (Nuovo Cimento B21 (1974) 258).
TL;DR: In this article, a series of hydrogenated amorphous Si1−xGex alloy films prepared by cathodic sputtering were used to explore to what extent the addition of Ge in aSi:H could change the gap state distribution, the recombination process, and the lifetime for photogenerated carriers.
Abstract: The dark conductivity and photoconductivity have been measured for a series of hydrogenated amorphous Si1−xGex alloy films prepared by cathodic sputtering. The primary aim of the work has been to explore to what extent the addition of Ge in a‐Si:H could change the gap state distribution, the recombination process, and the lifetime for photogenerated carriers. Whereas the composition dependence of the mobility gap is expected to be linear, we show evidence for the existence of a critical concentration of Ge xc, between 0.25 and 0.30 above which the electronic properties of the films change profoundly. At xc the photoconductivity decreases significantly and there occurs a transition from monomolecular to bimolecular recombination. Experimental data also suggest that above xc the range of tail states below Ec is gradually broadened with increasing the Ge amount. Films with xc are found to be highly photosensitive. In this group of samples, slight phosphorus doping leads to considerable increase in photocondu...
TL;DR: In this article, the authors describe the various theoretical considerations, which need to be taken into account during any analysis to this phenomenon, and point out that the conductive and dielectric properties of the photo-induced plasma can be used to control the wave propagation depending on the wavelength of the electromagnetic waves.
Abstract: Phenomenon of picosecond photoconductivity has gained importance recently due to ultrafast optoelectronic switching. We describe the various theoretical considerations, which need to be taken into account during any analysis to this phenomenon. It is also pointed out that the conductive as well as dielectric properties of the photo-induced plasma can be used to control the wave propagation depending on the wavelength of the electromagnetic waves. Various possible applications of this phenomenon are discussed.
TL;DR: In this paper, the binding energies of the ground state and excited state are 1.1 and 0.34 eV, respectively, and a model for the electronic structure of the dominant copper related center is discussed.
Abstract: Schottky diodes of copper doped CdS have been studied using photocapacitance techniques. Copper doping of CdS gives rise to deep hole states in the lower half of the band gap. The binding energies of the ground state and excited state are 1.1 and 0.34 eV, respectively. Optical emission of both holes and electrons as well as internal transitions followed by thermal emission of holes have been studied and absolute values of photoionization cross sections have been measured. The results are related to previous measurements of luminescence, absorption, photoconductivity, and photo‐Hall effect. A model for the electronic structure of the dominant copper related center is discussed.
TL;DR: In this paper, the effect of irradiation damage on the electrical properties of amorphous Si deposited by the glow discharge technique was studied and it was shown that the accumulation of radiation damage is similar in a-Si to that in c-Si.
Abstract: We have studied the effect of irradiation damage on the electrical properties of amorphous Si deposited by the glow-discharge technique. The irradiations were performed with chemically inactive ion species. Although the results show obvious differences between c-Si and a-Si in their dependence on ion mass and the sample temperature during irradiation, there are nevertheless many similarities and these are particularly apparent in the behaviour of the room temperature electrical conductivity with increasing ion dose. The results suggest that as far as changes in transport properties are concerned the accumulation of radiation damage is similar in a-Si to that in c-Si. A comparison of photoconductivity results with earlier data for implantations with chemically active ions suggests that non-doping configurations of the latter produce additional states in the gap which act as recombination centres.
TL;DR: The photoconductivity of DCHD displays a maximum near 3.6 eV coinciding with the maximum of the S o → S 1 absorption of the carbazole group as mentioned in this paper.
Patent•
17 Jun 1981TL;DR: In this paper, a composite photo-sensitive material for electrophotography is presented, which comprises a conductive substrate on which there is laminated a first photoconductive layer having a sensitivity to at least a part (Light A) of the chromatic light of visible light region and a second photoconductor layer capable of transmitting said Light A as well as having an additional sensitivity to another chromatic color (Light B), characterized in that said photoconductor layers are each capable of holding the electric charge of a polarity opposite to each other.
Abstract: A composite photosensitive material for use in electrophotography which comprises a conductive substrate on which there is laminated a first photoconductive layer having a sensitivity to at least a part (Light A) of the chromatic light of visible light region and a second photoconductive layer capable of transmitting said Light A as well as having a sensitivity to another chromatic light (Light B), characterized in that said photoconductive layers are each capable of holding the electric charge of a polarity opposite to each other and additionally accepting as well as retaining a surface potential enough to develop an electrostatic latent image, which is formed by said electric charge, with a toner.
TL;DR: In this article, the photoreceptors of amorphous silicon prepared by rf glow discharge of silane were investigated for charging and photodischarging characteristics, and a range-limited photocurrent flow was observed in a photoreceptor with a thick Si:H layer and the value of 2×10−8 cm2/V was estimated as μτ product of photoholes.
Abstract: Charging and photodischarging characteristics were investigated for the photoreceptors of amorphous silicon prepared by rf glow discharge of silane. For the positive corona, a sufficient charge retention was attained in the photoreceptor providing a thin layer of a‐silicon doped with boron between the photosensitive Si:H film and the conductive substrate to prohibit the injection of carriers from the substrate. The photoconductivity gain of unity was attained in the photoreceptor when it was illuminated with visible light. A range‐limited photocurrent flow was observed in the photoreceptor with a thick a‐Si:H layer and the value of 2×10−8 cm2/V was estimated as μτ product of photoholes. The space‐charge perturbed photocurrent was observed in the photoreceptor for the negative corona. The structure of the photoreceptor is intrinsic a‐Si:H/n‐type of a‐silicon on a conductive substrate. In this case, the photocurrent flow was effectively perturbed by a space charge that accumulated in the photoconductor owin...
TL;DR: Vacuum-evaporated pure amorphous silicon films have been successfully hydrogenated in a Theta-pinch plasma source to give high photoconductivity.
Abstract: Vacuum‐evaporated pure amorphous silicon films have been successfully hydrogenated in a Theta‐pinch plasma source to give high photoconductivity. Unlike films produced by glow discharge of silane gas, these films are highly stable against heat, intense light illumination, moisture, and other atmospheric contamination. Structural change in the bulk Si matrix being absent, a comparison of properties of films before and after plasma treatment can provide valuable information on pure hydrogenation effects.