Fir photoconductivity in epitaxial InP

FIR photoconductivity from shallow donors in n-type InP was studied using Fourier transform spectroscopy. The ls → 2p transition frequency was found to be 45.5 ± 0.2 cm⁻¹ in zero magnetic field. Spectral response measurements made in magnetic fields from 0 to 40 kG reveal Zeeman transitions of the ls → 2p (m = 0, ±1) states. Laser magnetospectroscopy was also investigated, employing an optically-pumped FIR laser. There is excellent agreement between the results obtained by the two experiments. From the transition energies, an effective mass of 0.077 ± 0.003 m₀ is obtained. With the experimentally-determined ls → 2p transition energy and the effective mass, the static dielectric constant of InP at 4.2 K was found to be 11.8 ± 0.2.     

Electron-mediated ferromagnetism in Fe-doped InP: Theory and experiment

We report on the electron-mediated ferromagnetism in Fe-doped InP from both first-principles calculations and experiments. Theoretically, based on the spin-polarized density functional theory within the Heyd-Scuseria-Ernzerhof (HSE03) approach, we systematically investigate the magnetic properties of Fe-doped InP and predict the existence of electron-mediated ferromagnetism. Experimentally, by diffusing Fe into the n-type InP wafer with thermal annealing at 800 C, we observe room-temperature ferromagnetism in InP:Fe, which is in agreement with the theoretical prediction.     

Fano resonance in the impurity photoconductivity spectrum of InP doped with shallow donors

The Fano resonances in the impurity photoconductivity spectra of n-InP are investigated theoretically and experimentally. It is shown that the calculations describe the experimental data with an accuracy of up to 20%.     

Infrared absorption of n- and p-type Fe-doped InP and mapping of the Fe distribution

The near-IR absorption spectra of n- and p-type Fe-doped InP were measured at room temperature in a wide range of Fe concentrations. A clear correlation was found between the Fe content in the InP samples which were only Fe-doped and the optical IR absorption. The absorption coefficient at 1000 nm depends linearly on the chemical Fe concentration. The same dependence was observed for Te/Fe (n-type) as well as for Zn/Fe (p-type) co-doped InP. This effect is used for a quantitative evaluation of the Fe distribution across whole wafers (mapping). The results are compared to those of other characterization techniques, e.g. selective etching, showing an excellent agreement.     

Transient photoconductivity in EuSe

Transient photoconductivity measurements in EuSe have been made in order to distinguish between mobility and lifetime effects in steady state photoconductivity. The results show that in the paramagnetic region the decay time is constant while the mobility is thermally activated. The data are explained by a magnetic impurity state model including both charged and neutral defects. In this model both hopping and quasi-thermally activated band conduction may occur.     

Transient photoconductivity in NiO

Extensive experimental observations have failed to confirm reported observations of transient photoconductivity in single crystal NiO. The negative results are due either to rapid deep trapping, low quantum efficiency for carrier photogeneration, or to carrier drift mobilities μ < 4 × 10^?5 cm²/V sec at 300K.     

Photorefractive effect in Fe-doped GaN

The photorefractive effect was observed in Fe-doped semi-insulating GaN. We measured the two-beam coupling constant and the grating formation time as a function of pump intensity at a wavelength of 458 nm in reflection geometry. The photorefractive gain coefficient was 0.39 cm⁻¹, and the grating formation time was 7 ms at a pump intensity of 1.0 W/cm². Besides the refractive index grating, the contribution of an absorption grating was also observed in a two-wave mixing experiment. The coupling constant of the absorption grating was negative and increased with the pump intensity. The origin of the absorption grating was attributed to light-intensity-dependent photochromism.     

Frozen photoconductivity in PbTe films

We have studied PbTe films of thicknessd=200/10000 A made with telluride vapour deposition on glass substrate at room temperature. The estimate of the donor concentration ～10¹⁹ cm^?3 of the fresh-deposited film compared with the impurity content in the bulk raw material ～10¹⁷ cm^?3 shows that the donors were mainly film defects or nonstoichiometric Pb atoms. Electrical conductivity of the freshly deposited film increased with lowering of the temperature. After deposition the donors were compensated with an oxidation in the laboratory air. Transition to the thermally activated conductivity resulted from oxidation. At temperatures belowT≈100 K the resistance of the compensated films followed Mott’s ruleR=R ₀ exp(T ₀/T)^1/3. The square film value 1 Mohm andT ₀≈100 K ford=1000 A. At low temperatures an exposure to light resulted in sharp decrease of the film resistance. At liquid helium temperatures the resistance dropped 10³–10⁶ times and stayed at the low value for an indeterminate time. The heating of the film aboveT=100 K gave rise to an initial high resistive state. The critical temperatureT _c, when the frozen photoconductivity became negligible, varied with samples in the temperature region 90–120 K. Near the critical temperature we could measure the time dependence of the film resistance after the light exposure, which followed the equationR=A+B.lnt fort>1 sec with the empirical constantsA andB. After a time intervalτ the resistance gained the initial “dark” value and remained stationary. The value lnτ≈α.(T _c?T), where the factorα approximately wasα≈0.5 K^?1. Some results of these experiments were published earlier (Krylov and Nadgorny 1982; Krylov and Pojarkov 1984).     

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.     

Persistent photoconductivity in sulfur-diffused silicon

A large persistent photoconductivity effect is found in single-crystal p-type bulk silicon covered by an n-type surface layer produced by a sulfur diffusion. Recombination of carriers is precluded by their spatial separation in the n-p junction. The photogenerated holes exceed the relatively few remaining acceptor-introduced holes at our measurement temperature of 45 K, while the corresponding electrons are captured at the sulphur donors.     

Space-charge-limited transient photoconductivity in polymers

Space-charge-limited (SCL) photoconductivity in transient regime and its modification, T-SCLC (transient space-charge-limited currents), are readily observed in high resistivity materials with mobile carriers and thus may be with advantage used as a tool for the study of the density of localized states (DOS) in organic molecular semiconductors. The only prerequisite for the experimental observation of SCL photoconductivity is a reasonably long Maxwell relaxation time. This paper presents the new possibilities of the T-SCLC method for elucidation of the DOS in organic molecular solids with practical examples of modeling, reconstruction of post-transit data and its application for a typical polymer — poly(methylphenylsilyene). Presented at the 1st Czech-Chinese Workshop “Advanced Materials for Optoelectronics”, Prague, Czech Republic, June 13–17, 1998. The support of the Grant Agency of the Academy of Sciences of the Czech Republic by the grant No. A 1050901 and the COST 518 project are acknowledged.     

Impurity photoconductivity in n-type InSb

Photoconductivity is observed when sufficiently pure n-type InSb is illuminated by radiation of wavelengths between 0.2 and 8.6 mm. The time constant of this effect has been found to be not greater than 1 μsec.The electrical characteristics of the material showing this effect and the strong dependence of both the photoconductive and electrical properties upon a magnetic field are described.     

Light-induced absorption change in Fe-doped GaN

The properties of a light-induced absorption (LIA) change were investigated in a semi-insulating Fe-doped GaN crystal. The temporal profile and a spectrum of the LIA were measured in the temperature range from 15 K to 300 K. The LIA was almost proportional to the light intensity and showed slight saturation behavior. The relaxation time constant, in the range of milliseconds, was equal to the lifetime of infrared photoluminescence related to the Fe³⁺ internal transition Fe³⁺(⁴T₁)→Fe³⁺(⁶A₁). The LIA was attributed to an excited-state absorption from Fe³⁺(⁴T₁). Some of the peak energies observed in the LIA spectrum showed good agreement with transition energies expected from an energy diagram of Fe-doped GaN crystal.