P. P. Khokhlachev

Properties of CuInSe2 films obtained by methods of selenization and quasi-equilibrium deposition

The CuInSe2 films obtained by selenization and quasi-equilibrium deposition are investigated by elemental, X-ray phase, and chemical analyses. Temperature dependences of electric parameters are determined and photoelectric measurements are performed. It is shown that high-quality p-type films can be obtained by both methods. More uniform n-type films are obtained by selenization at lower temperatures. The strongest photoresponse was observed for the CuInSe2/CdS structures deposited under quasi-equilibrium conditions. Dispersion and sizes of polycrystalline grains are studied.

Effect of deviations from stoichiometry on electrical conductivity and photoconductivity of CuInSe2 crystals

The results of studying the photoelectric properties of bulk CuInSe2 crystals grown at various deviations from the stoichiometry are reported. The crystals were grown by the Bridgman method. The concentration and mobility of charge carriers were measured. The dependence of the properties of CuInSe2 crystals with n-and p-type conductivities on the deviation of composition from the stoichiometry is discussed.

Effects of the preparation procedure and In2O3 thickness on the electrical and photovoltaic properties of In2O3/CuInSe2 heterostructures

In2O3 /CuInSe2 heterostructures were produced by growing indium oxide layers on bulk single-crystal and polycrystalline p-type CuInSe2 substrates using thermal oxidation and magnetron sputtering. The substrates were prepared by cleaving or abrasive polishing and chemical etching. The resistivity of the In2O3 layers was measured as a function of temperature and layer thickness, and the current–voltage characteristics and spectral response of the heterostructures were analyzed. The results indicate that the structures exhibit reduced reflection losses at oxide thicknesses below 0.5 μm. The reduced thickness of interfacial layers owing to the low process temperature in the case of magnetron sputtering makes it possible to extend the spectral region of photosensitivity of the heterostructures.

Temperature dependence of electrical resistivity of composite films based on multi-walled carbon nanotubes

The temperature dependence of the electrical resistivity (ρ) and current-voltage characteristics of composite films based on multi-walled carbon nanotubes and a 95/5 wt % polymer have been investigated in the temperature range of 300–450 K. An unstable behavior of the composite film structure upon cyclic heating has been observed. It has been found that the resistivity ρ has maxima at T ≈ 340 and ≈420 K, which are responsible for intrinsic defects. The current-voltage characteristics have been studied in the stationary and pulsed modes at different temperatures. They prove to be purely linear and correlate with temperature variations in ρ.

Properties of AgInSe2 films grown by magnetron sputtering

Abstractn-Type AgInSe2 films 0.5 to 0.9 μm thick were grown by dc magnetron sputtering. As targets, we used AgInSe2 crystals grown by a modified Bridgman process using high-purity precursors. The crystal structure, morphology, electrical conductivity, and Hall coefficient of the films were studied at various temperatures. We determined the optimal growth and annealing temperatures of the films (500 and 250°C, respectively). Using structures based on the films, we obtained the spectral dependences of their photoresponse, established the nature of interband transitions in the films, and evaluated their band gap. The ability to vary electrical and optical properties with no changes in stoichiometry is of interest for concentrated solar power applications.

Electrical and thermoelectric properties of ZnO under atmospheric and hydrostatic pressure

Temperature (for T = 77–400 K) and pressure (for P ≤ 8 GPa) dependences of conductivity σ(T,P). Hall coefficient RH(T, P), and Seebeck coefficient Q(T) were studied in single-crystal n-ZnO samples with the impurity concentration Ni = 1017 − 1018 cm−3 and free-electron concentration n = 1013−1017 cm−3. Single crystals were grown by the hydrothermal method. Dependence of the ionization energy of a shallow donor level on the impurity concentration Ed1(Nd) is determined, along with the pressure coefficients for the ionization energy ∂Ed1/∂P and static dielectric constant ∂x/∂P. A deep defect level with the energy Ed2 = 0.3 eV below the bottom of the conduction band is found. The electron effective mass is calculated from the obtained data on the kinetic coefficients RH(T) and Q(T).

Preparation and Properties of Metal/CuInSe2 Diode Structures

The current–voltage characteristics of M/CuInSe2 (M = In, Sn, Cd, Ag, Au) structures were measured. The structures were found to have rectification ratios in the range k= 1.6–33 and to contain an interfacial oxide layer (M/n-In2O3/p-CuInSe2). The spectral response of the structures was studied at 300 K and photon energies from 0.8 to 1.3 eV. The photovoltaic effect was shown to be due not to electron photoemission from the metal to the semiconductor but to photocarrier separation at the interfacial barrier between n-In2O3 and p-CuInSe2.

Thermoelectric and photoelectric properties of the p-n CuInSe2/CdS heterostructures obtained by the quasi-equilibrium deposition method

Through deposition of CuInSe2 films on CdS substrates in a quasi-closed-circuit “hot-wall” reactor, p-n CuInSe2/CdS heterostructures were obtained. The thermoelectric power, current-voltage characteristics, and photosensitivity spectra of the structures were investigated.

Nanocomposite based on modified multiwalled carbon nanotubes: Fabrication by an oriented spinning process and electrical conductivity

We have produced nanocomposite films consisting of modified multiwalled carbon nanotubes (MWCNTs) and a polymer (MWCNT/polymer weight ratio of 95/5). The nanocomposite has been applied to a paper substrate by an oriented spinning process from a liquid phase. The resistivity of the films has been measured as a function of temperature in the range 20–140°C along and across the preferential orientation direction of the nanotubes in the nanocomposite. The results point to an irreversible transition from semiconducting to metallic behavior of the conductivity of the films.

Effect of thermal oxidation on the electrical conductivity and photoresponse of In2O3/CuInSe2 structures

Thermal annealing in oxygen has been used to produce photosensitive, rectifying In2O3/CuInSe2 structures. The optimal annealing temperature and time are 600–650 K and 40–60 min, respectively.