Time-evolution of low-temperature photoconductivity and hall mobility in semi-insulating GaAs

The time-evolution of photo-Hall mobility, μ_H, during low-temperature illumination with 1.55 eV photons is presented as determined experimentally. At first μ_H decreases gradually during illumination, dropping almost to zero, and then increases back to high values, reaching an equilibrium value. The same behavior of μ_H is predicted from calculations of time-evolutions of free electrons and holes, derived from the time-evolution of independently measured thermoelectric effect signal and photoconductivity. Results are compatible with the model in which the dynamics of trap filling and changes of relative occupancies of traps with different sign are responsible for transient phenomena observed in photoconductivity, Hall mobility and thermoelectric signal during low-temperature, low-intensity illumination.     

Some photoeffects on the semiconductor surface under sub-bandgap illumination

Surface photovoltage as well as surface photoconductivity response on the light intensity under sub-bandgap illumination is treated. The influence of the surface barrier height, the density of surface traps, the bulk electron density as well the temperature on the surface photovoltage (surface photoconductivity) is analysed. The detectability conditions are included. The consequences of detectability conditions are discussed.     

High-resolution positron lifetime spectrometer with BaF2 scintillators

A transient negative photoconductivity phenomenon observed in silicon doped with gold atoms by an appropriate diffusion condition has been investigated. The transient negative photoconductivity could be observed with a diode doped with gold atoms under intrinsic light-pulse illumination. In the recovery process of the transient negative photoconductivity to a steady-state dark level, two kind of time constants were observed, which may be related with the emission of electrons from gold level. A dependence of the magnitude of the peak value on the ambient temperature was observed; a qualitative explanation is given.     

Defect-Related Photoresponse and Polarization-Sensitive Photodetection of Single ZnO Nanowires

Defect-related photoconductivity of single ZnO nanowires is investigated. The photoconductivity shows powerlaw dependence with incident green laser intensity due to the defect mechanisms including both recombination centres and traps. The device based on single ZnO nanowire shows a sensitive photoresponse to green light with significant on/off ratios. In addition, the photocurrent ＆ highly sensitive to the polarization of the incident illumination. Therefore, the nanowire may act as a polarized photodetector.     

Far infrared photoconductivity from majority and minority impurities in high purity Si and Ge

The effects of intrinsic illumination on the far infrared photoconductivity of high purity Si and Ge are studied. Such illumination permits the observation of both the majority and minority impurities. One of the donors in Ge is highly sensitive to heat treatment, a result suggesting that it arises from lattice defects rather than chemical impurities.     

ВЛИЯНИЕ ПРЕДВАРИТЕЛ ЬНОГО ОСВЕЩЕНИЯ НА ПР ОВОДИМОСТЬ И ФОТОПРОВОДИМОСТЬ З АКИСИ МЕДИ

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The effect of preliminary illumination on conductivity and photoconductivity of cuprous oxide

     

The effect of illumination on dark conductivity and photoconductivity of hydrogenated amorphous silicon layered films

It is established that both the amplitude and temperature dependence of dark conductivity and photoconductivity of preilluminated high-sensitivity layered films of amorphous hydrogenated silicon (a-Si:H) prepared by cyclic deposition with layer-by-layer annealing in hydrogen plasma depend on illumination temperature. The relaxation kinetics of the dark conductivity of these films after illumination is shut off is found to be nonmonotonic. The observed effects can be explained by fast and slow changes in the distribution of energy state density below the midgap during and after illumination.     

Photoconductivity and the structural phase transition in SrTiO3

Detailed photoconductivity measurements have been performed in nominally pure SrTiO₃ in order to elucidate the effect of the antiferrodistorsive cubic-tetragonal phase transition. Small features in the photoconductivity’s temperature dependence in the phase transition region were found using low intensity interband UV or 514 nm light illumination. Such features are associated with a transformation of the defect system controlling the photoconductivity. At the same time, the temperature behavior of the photoconductivity spectral maximum reveals a rather unusual feature which is connected with changes in the absorption band edge structure in the phase transition region.     

Photoelectricity of β-Agl under sub-bandgap illumination

An experimental study of the spectral, intensity and temperature dependences of the photoconductivity and contact photovoltage of β-AgI single crystals under sub-bandgap illumination is carried out. Both dc and ac photoconductivity experiments are performed and dark-to-light relaxation characteristics of the contact photovoltage are investigated. It is found that the processes under consideration are of a unified character in the spectral region below 2.20 eV, in which the photoconductivity spectrum follows Urbach's rule, temperature behaviour is opposite to that of dark conductivity and dependence on exciting light intensity is linear. A simple model is proposed to explain qualitatively the results obtained, based on the assumption for photoexcited ionic-type conductivity.     

Photostimulated phenomena in relaxors

The action of illumination on the conducting and dielectric properties of lead magnoniobate was investigated. The photostimulated currents were examined and the spectral dependence of photoconductivity in the region of diffuse phase transition was obtained. It was found that the illumination affects the dielectric properties and that its action is memorized at temperatures below room temperature. The role of defect states in the formation of relaxor properties is discussed on the basis of the obtained data.     

Zur lichtelektrischen Leitfähigkeit von KCl

The transient photoconductivity of additively coloured KCl crystals has been measured between 10 and 90°K using zone refined KCl single crystals, air grown KCl, and KCl+SrCl₂. Crystals with various impurity contents differ both in the amount and the temperature dependence of photoconductivity. Pure crystals after previous illumination at various temperatures show the same behaviour. The observed differences may be explained by trapping processes. From electrical glow curves it is concluded that all crystals contain a large number of traps.     

Effect of IR illumination on photocurrent spectra in CdS crystals

Low-temperature near-band-edge photoconductivity (PC) spectra of CdS crystals were studied as a function of IR illumination intensity in the PC quenching interval. The photocurrent quenching by IR light of the PC response profile has been investigated. An analysis of these relationships permitted establishing a direct connection between the r photoconductivity centers and the near-band-edge structure of the spectrum. The effect of “pinning” of majoritycarrier lifetime on the semiconductor surface has been discovered and interpreted. It is proposed that surface-acceptor states in CdS crystals play the part of surface photoconductivity centers. Fiz. Tverd. Tela (St. Petersburg) 41, 1181–1184 (July 1999)     

Luminescence and photoconductivity properties of porous polycrystalline silicon

In recent years, the photoluminescence and the photoconductivity of porous silicon were comprehensively studied. But the photoluminescence and the photoconductivity of porous polycrystalline silicon have not been wholely studied. In this paper, the results showed that luminescent property of the samples prepared by poly-crystal silicon wafers may be related to the defects on Si complexes surface, which can be proved by microwave-detected photoconductivity decay measurements. Furthermore, the luminescence of samples was disappeared under the external illumination, which may be related to the elimination of luminescent-centers. In addition, the conductivities of the samples were dependent on etched time and current density, and the large porosity of samples led to isotropic photoconductivity, which may be related to the change of energy band structure of the devices.     

Long lifetime photoconductivity in semi-insulating bulk GaAs

We report a new photomemory effect in semi-insulating bulk GaAs. Persistent illumination with 1.15 eV photons induces a photosensitivity state in GaAs, which is characterized by a slow decay of the photoconductivity, after the light is switched-off. The most relevant phenomenological aspects of this effect are summarized in this communication.     

Dark electrical conductivity and photoconductivity of Ga4Se3S layered single crystals

Ga₄Se₃S layered crystals were studied through the dark electrical conductivity, and illumination- and temperature-dependent photoconductivity in the temperature region of 100-350 K. The dark electrical conductivity reflected the existence of two energy states located at 310 and 60 meV being dominant above and below 170 K, respectively. The photoconductivity measurements revealed the existence of another two energy levels located at 209 and 91 meV above and below 230 K. The photoconductivity was observed to increase with increasing temperature. The illumination dependence of photoconductivity was found to exhibit linear and supralinear recombination above and below 280 K, respectively. The change in recombination mechanism was attributed to the exchange in the behavior of sensitizing and recombination centers.     

Photoconductivity on europium oxyde single crystals and thin films

In this paper, results of photoconductivity measurements on four EuO samples are given. Low frequency photoconductivity versus temperature (10°K < T < 300°K) and magnetic field H is investigated for two wavelengths: 6600 Å and 9000 Å. The photoconductivity kinetic is also described, and is characterized by a distribution in decay times. Temperature, magnetic field and carrier concentration have small effects on this kinetic. Quenching effect is obtained by adding a continuous illumination (λ₂) to the weak modulated light (λ₁). The kinetic is strongly affected by quenching and becomes more simple. Quenching effect is maximum for the wavelength associated to the 4?⁷–4?⁶ 5d, transition. In contrast to the Penney-Kasuya[1] model we propose another one in which the conduction of equilibrium carriers as photo-excited carriers takes place in a broad band. The variation of low frequency photoconductivity versus temperature is attributed to the mobility variation. This variation agrees well with the model of mobility controlled by spin-disorder. The photoconductivity kinetic is interpreted by a three levels recombination model: the conduction band, the 4f levels and a distribution of trap levels. The lack of variation of photoconductivity decay in the range of metal-semiconductor transition is discussed.     

Persistence in photoconductivity and optical property of nanostructured copper (II) phthalocyanine thin films

The optical and photoconductive properties of nanostructured copper (II) phthalocyanine (CuPc) surface cells have been studied at room temperature (30 °C). The change in the conductivity of the surface type sample cells under illumination of light was studied as a function of duration and wavelength of photoexcitation. The photoconductivity spectrum of a film of CuPc surface cell does not agree with the absorption spectrum. Particularly for the photoexciting wavelengths in the region 400–500 nm, the photoconductivity shows an appreciable value (or comparatively higher value), although the absorbance in this region is minimum or very less. The change in current under illumination of light and after turning it off has indicated that photoinduced effects persist for a longer period of time even after turning off the illumination of light of various wavelengths and duration. An increase in persistence in photocurrent was noticed with the repeated exposure within a short interval of time. Such studies are important for searching new types of electrically conducting systems (semiconductors) in the form of nanostructured thin films for use as photoactive materials in optoelectronic and memory devices.     

Photoconductivity and chemisorption kinetics in sintered zinc oxide semiconductor*

Decay kinetics of the photoconductivity of zinc oxide are measured as a function of previous intensity of illumination and ambient oxygen pressure. The analysis of the measured kinetics is carried out in terms of a model wherein the basic process is the penetration of a surface barrier by the photoconduction electrons and the consequent formation of adions. The model is used to derive a generalized Elovich equation.     

Negative photoconductivity in low-dimensional materials

In recent years,low-dimensional materials have received extensive attention in the field of electronics and optoelectronics.Among them,photoelectric devices based on photoconductive effect in low-dimensional materials have a broad development space.In contrast to positive photoconductivity,negative photoconductivity(NPC)refers to a phenomenon that the conductivity decreases under illumination.It has novel application prospects in the field of optoelectronics,memory,and gas detection,etc.In this paper,we review reports about the NPC effect in low-dimensional materials and systematically summarize the mechanisms to form the NPC effect in existing low-dimensional materials.     

Ferroelectric,magnetoelectric and photoelectric properties of BiFeO3 /LaNiO3 heterostructure

BiFeO₃/LaNiO₃ (BFO/LNO) heterostructure was fabricated on quartz substrate via RF sputtering method. The microstructure and surface morphology of the BFO/LNO heterostructure was demonstrated. BFO layer shows good ferroelectric and weak ferromagnetic characters at room temperature. The dielectric constants of the heterostructure under an applied magnetic field 1.2T and zero field are both decreased with increasing frequency at room temperature and the dielectric constant under the applied magnetic field is larger, which is attributed to the coupling between the electric and magnetic dipoles, and further demonstrated in the framework of the Ginzburg-Landau theory for second phase transition. Additionally, the photoconductivity of the heterostructure under blue-laser illumination was observed, and the photoconductivity increase with the enhanced power of the blue-laser.