Electrical properties of layered FeGaInS<Subscript>4</Subscript> single crystals

The temperature dependence of conductivity and current-voltage characteristics of a layered FeGaInS₄ single crystal have been studied in various conditions. It is shown that the nonlinearity of the current-voltage characteristic is due to the space-charge-limited current. The activation energies of impurity levels in FeGaInS₄ single crystals are determined.     

Dielectric properties of MnGa2S4 single crystals in an alternating electric field

The results of studies of the frequency and temperature dependences of dielectric conductance and the tangent of the angle of dielectric losses for MnGa₂S₄ single crystals in a varying electric field are presented. Their values are determined experimentally. An increase in the dielectric conductivity is related to an increase in the defect concentration as temperature is increased. At the temperatures under study, a resonance peak is observed for ? and tanδ in the frequency range of 435–500 kHz. It is found that, in the frequency range of 25?2 × 10⁵ kHz, the tangent of the angle of dielectric losses decreases in reverse proportion to the frequency (～1/ω).     

Frenkel thermal-field effect in MnGaInS<Subscript>4</Subscript> layered single crystals

The I–V characteristics are investigated in the region of high electric fields in MnGaInS₄ single crystals. It is shown that the current in the nonlinear portion of the I–V characteristic is caused by the Frenkel thermal-field effect. The permittivity, trap concentration, and potential-well shape are determined.     

Electrical properties of FeIn<Subscript>2</Subscript>Se<Subscript>4</Subscript> single crystals

The temperature dependence of electrical conductivity and current-voltage characteristics of FeIn₂Se₄ single crystals were studied. It is shown that the current in the nonlinear range of the current-voltage characteristic is caused by the field effect. The activation energy of charge carriers, the concentration of traps, and the shape of a potential well in the region of a trap are determined.     

Effect of a high electric field on the conductivity of MnGa<Subscript>2</Subscript>S<Subscript>4</Subscript>, MnIn<Subscript>2</Subscript>S<Subscript>4</Subscript>, and MnGaInS<Subscript>4</Subscript> single crystals

The results of studying the effect of a high electric field on the conductivity of MnGa₂S₄, MnIn₂S₄, and MnGaInS₄ single crystals are reported. The activation energy is determined in high and low electric fields. It is established that the decrease in the activation energy with increasing the external voltage is associated with decreasing the depth of the potential well, in which the electron is located.     

Electrical properties of layered FeGaInS4 single crystals with an alternating current

The frequency and temperature dependences of the permittivity and conductivity of FeGaInS₄ single crystals in an ac current have been investigated. The permittivities of single crystals and activation energies of permittivity and conductivity are determined. It is established that the conduction of these crystals in the temperature range under study has an activation nature. A frequency dependence of the activation energy is observed, which is related to the decrease in the relaxation time of blocking layers with an increase in frequency.     

Photoconductivity of the Pb<Subscript>0.75</Subscript>Sn<Subscript>0.25</Subscript>Te:In alloy in an alternating electric field

Kinetics of variations in the components of total impedance for single-crystal Pb_0.75Sn_0.25Te:In samples is investigated upon switching on and switching off of the illumination source at temperature 4.2 K and frequency 10⁶ Hz. The calculation carried out in the context of representation of equivalent circuits showed that the parameters of a parallel R _p C _p chain, which approximates the sample behavior, correlate strictly. In the region of low resistances R _p , the values of C _p increase abruptly following the law C _p ∝ R _p ^?2 . It is of no importance what method of decreasing the resistance is used—heating of the sample or its illumination at low temperature. The obtained results were analyzed taking into account the contribution of the impurity subsystem to conductivity and the possible manifestation of Maxwell-Wagner-type effects.     

Optical properties of CuIn<Subscript>5</Subscript>Se<Subscript>8</Subscript> single crystals

Single crystals of the CuIn₅Se₈ ternary compound are grown by the Bridgman-Stockbarger method (with the vertical layout of the procedure). The composition and structure of the crystals are determined. The spectra of transmittance and photoluminescence are studied in the temperature range from 10 to 300 K. The transmittance spectra and the photoluminescence spectra are used to determine, correspondingly, the band gap and the energy of donor-acceptor transitions in the CuIn₅Se₈ crystals. The temperature dependences of these parameters are obtained.     

Current-voltage characteristics of MnGa<Subscript>2</Subscript>Se<Subscript>4</Subscript> single crystals

The current-voltage characteristics of MnGa₂Se₄ single crystals have been investigated. The measurements were performed in the range of electric fields from the level at which the Ohm law is satisfied to 10 V/cm, and in the temperature range 300–400 K. The data obtained are interpreted within the theory of injection-contact phenomena and the theory of field ionization of traps due to the Poole-Frenkel effect.     

Fabrication and properties of photosensitive structures based on ZnIn<Subscript>2</Subscript>S<Subscript>4</Subscript> single crystals

Photosensitive structures based on single crystals of the ZnIn₂S₄ ternary compound were fabricated and studied for the first time. The optoelectronic properties of this compound and corresponding structures were analyzed using the results of measurements of the optical-absorption spectra of ZnIn₂S₄ crystals, steady-state current-voltage characteristics, and photosensitivity of the structures at T=300 K. It is concluded that surface-barrier structures and heterojunctions based on ZnIn₂S₄ can be used as wide-band photodetectors of natural optical radiation.     

Photosensitive structure on CdGa<Subscript>2</Subscript>S<Subscript>4</Subscript> single crystals

Single crystals of the CdGa₂S₄ ternary compound were grown either from melt or by chemical-vapor deposition. The crystal-lattice parameters and some physical properties of homogeneous crystals having defect chalcopyrite structure with the point symmetry group \(I\bar 4(S_4^2 )\) are determined. A number of photosensitive structures—Schottky barriers, heterostructures, photoelectrochemical cells, and natural-protein-CdGa₂S₄ barriers—were formed for the first time on the basis of the single crystals under investigation. The photoelectric properties of the structures obtained were studied using natural and linearly polarized light at T=300 K. The main parameters of these structures are determined, and it is concluded that they can be used in photodetectors.     

Photosensitive structures based on HgGa<Subscript>2</Subscript>S<Subscript>4</Subscript> single crystals: Preparation and properties

Photosensitive structures based on n-HgGa₂S₄ single crystals were prepared and investigated. It was concluded that HgGa₂S₄ crystals are promising for the fabrication of photodetectors of natural and linearly polarized light in the short-wavelength spectral region.     

Fabrication and properties of ZnFe<Subscript>2</Subscript>S<Subscript>4</Subscript> single crystals and structures based on them

A new class of ternary semiconductor compounds has been proposed and synthesized. ZnFe₂S₄ single crystals, which belong to this class, have been grown for the first time; and their structural, electrical, and optical properties have been investigated. The first photosensitive structures have been fabricated, and their photoelectric characteristics have been studied. A conclusion was made that heterostructures and surface-barrier structures based on ZnFe₂S₄ single crystals are promising for practical applications.     

Photosensitive structures based on ZnIn<Subscript>2</Subscript>Se<Subscript>4</Subscript> single crystals

Photosensitive structures of surface-barrier and homojunction types have been fabricated for the first time on the basis of ZnIn₂Se₄ single crystals. The spectral dependence of the quantum efficiency of photoconversion has been studied and discussed. It is concluded that the structures are promising for commercial applications.     

Magnetic properties of the FeIn<Subscript>2</Subscript>S<Subscript>4</Subscript> ternary-compound crystals

Crystals of the ternary compound FeIn₂S₄ are grown by directional crystallization of a melt (the horizontal Bridgman method). Composition of the crystals and their crystal structure are determined. Magnetic properties of the FeIn₂S₄ crystals are studied in the temperature range 4–310 K in magnetic fields of 0–140 kOe. It is shown that the crystals under study are paramagnets up to ∼12 K and their specific magnetic moment monotonically increases with decreasing temperature. The antiferromagnetic character of indirect interactions between Fe²⁺ cations is established. The most probable causes and the mechanism of the formation of the magnetic state in the FeIn₂S₄ crystals are discussed.     

Temperature dependence of the band gap of FeIn<Subscript>2</Subscript>S<Subscript>4</Subscript> single crystals

Single crystals of the FeIn₂S₄ ternary compound are grown by the Bridgman method. The composition and structure of the crystals are established. The transmittance spectra of the crystals in the region of the fundamental absorption edge are studied in the temperature range of T = 20–300 K. The band gap E _g and its temperature dependence E _g (T) are determined from the transmittance spectra. It is shown that the shape of the dependence E _g (T) is typical of complex compounds.     

Features of the charge-transport mechanism in layered Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> single crystals doped with chlorine and terbium

The temperature dependences (T = 5−300 K) of the resistivity in the plane of layers and in the direction perpendicular to the layers, as well as the Hall effect and the magnetoresistance (H < 80 kOe, T = 0.5−4.2 K) in Bi₂Te₃ single crystals doped with chlorine and terbium, are investigated. It is shown that the doping of Bi₂Te₃ with terbium atoms results in p-type conductivity and in increasing hole concentration. The doping of Bi₂Te₃ with chlorine atoms modifies also the character of its conductivity instead of changing only the type from p to n. In the temperature dependence of the resistivity in the direction perpendicular to layers, a portion arises with the activation conductivity caused by the hopping between localized states. The charge-transport mechanism in Bi₂Te₃ single crystals doped with chlorine is proposed.     

Photovoltaic effects in CdV<Subscript>2</Subscript>S<Subscript>4</Subscript> single crystals and structures based on them

Single crystals of the CdV₂S₄ ternary compound are grown, and their crystal structure, electrical properties, and optical absorption are studied. The substitution of vanadium for Group III element in A^IIB ₂ ^III C ₄ ^VI compounds results in the formation of crystals of n-type conduction with an electron density of ～10¹⁸ cm^?3 and a Hall mobility U_n≈150 cm²/(V s) at T=300 K, which is limited by scattering on lattice vibrations. Rectifying photosensitive structures based on CdV₂S₄ single crystals are fabricated for the first time, their photoelectric properties are studied, and a conclusion is made on their applicability in the design of wide-spectral-range photodetectors of unpolarized light.     

Electrical properties of FeIn2Se4 layered single crystals for alternating current

Results of investigations of temperature and frequency dependences of the permittivity and conductivity of FeIn₂Se₄ layered single crystals on alternating current are presented. The permittivity of single crystals and the activation energies of charge carriers are determined. In the temperature range under investigation, the conductivity is caused by the activation mechanism.     

Conductivity of Hg<Subscript>3</Subscript>In<Subscript>2</Subscript>Te<Subscript>6</Subscript> crystals in high electric fields

The effect of electric field and temperature on the conductivity of bulk Hg₃In₂Te₆ crystals is investigated. It is shown that the I–V characteristics in high electric fields are of the S type with the effect of switching into a low-resistance state. The critical voltage of transition from the Ohm law to the exponential dependence of the current (I) on the voltage (U) and the threshold voltage of transition into the region of negative differential resistance dU/dI = s< 0 linearly depend on the sample thickness. The activation energies of conductivity in low and high electric fields are determined. It is established that the superlinear portion of the I–V characteristic with dU/dI > 0 is described by the dependence of the type I = I ₀ exp(U/U ₀) and caused by the electron transitions from the local centers with the energy level E _t = 0.19 eV.