V.V. Volobuev

Effect of oxidation on the thermoelectric properties of PbTe and PbS epitaxial films

We report on the thickness d dependences of the Seebeck coefficient, electrical conductivity, and Hall coefficient of PbTe and PbS epitaxial thin films (d=5–200 nm), prepared by thermal evaporation in vacuum and deposition on (001) KCl substrates. The oxidation of the films in air at 300 K leads to a sign inversion of the carrier type from n to p in films with d⩽125 and 110 nm for PbTe and PbS, respectively. The observed d dependences are interpreted in terms of compensating acceptor states created by oxygen on the film surface.

Antiferromagnetic interlayer coupling in ferromagnetic semiconductor EuS/PbS(001) superlattices

Antiferromagnetic coupling between ferromagnetic layers has been observed for the first time in an all-semiconductor superlattice structure EuS/PbS(001), by neutron scattering and magnetization measurements. Spin-dependent superlattice band structure effects are invoked to explain the possible origin and the strength of the observed coupling.

Influence of oxidation on the transport properties of IV–VI-thin films

Abstract The effect of oxidation at room temperature on the thickness dependences of transport properties of IV–VI (PbS, PbSe, PbTe) thin films was studied. The effect of charge carrier concentration on the character of these dependences in n-PbTe thin films was detected. The regularities in the behavior of IV–VI thin films exposed to air were established. The experimental results are interpreted within the framework of models taking into consideration the presence of compensating acceptor states created by oxygen on the film surface.

Effect of non-stoichiometry on oxidation processes in n-type PbTe thin films

Abstract The dependences of the galvanomagnetic and thermoelectric properties on the thicknesses d (5–200 nm) of PbTe thin films prepared by the thermal evaporation of non-stoichiometric PbTe with 2 at.% excess lead were studied, with measurements conducted in air at room temperature on freshly grown films. It was established that with decreasing film thicknesses, an inversion of the dominant charge carrier sign from n to p takes place at d ∼40 nm. A comparison of the results obtained in this work with those for PbTe films prepared from stoichiometric PbTe showed that the increase in n-type charge carrier concentration results in a shift of the inversion point to smaller d values. The observed effect is attributed to oxidation processes taking place in PbTe thin films at room temperature in air, and the effect is interpreted in terms of compensating acceptor states created by oxygen on the film surface.

Coupling of the magnetic layers and electron spin polarization in four-layer structures of amplitude and nonmagnetic semiconductors

The electron energy spectrum, the energy Em of the exchange coupling between magnetic layers, and the relative polarization β of the electron spins in semiconductor structures with two ferromagnetic barriers and nonmagnetic layers acting as potential wells for electrons are considered. For the example of EuS/PbS(001) structures it is shown that in the case of Fermi statistics Em is a sign-varying oscillatory function of the width a of the potential well between barriers, and with increasing electron density n0 in the wells and increasing thickness d of the nonmagnetic sublayers between the barrier and substrate, the extrema of Em are shifted to smaller a and their amplitudes rapidly increase. As the temperature is lowered from the Curie point, the energy Em, depending on a, n0, and d, can increase (in modulus) monotonically or nonmonotonically, change sign from positive to negative, or change sign twice. The polarization β decreases with increasing a, n0, and d, undergoing sharp jumps when Em changes sign. For Boltzmann statistics only a ferromagnetic orientation of the barrier magnetizations (Em<0) is possible.The electron energy spectrum, the energy Em of the exchange coupling between magnetic layers, and the relative polarization β of the electron spins in semiconductor structures with two ferromagnetic barriers and nonmagnetic layers acting as potential wells for electrons are considered. For the example of EuS/PbS(001) structures it is shown that in the case of Fermi statistics Em is a sign-varying oscillatory function of the width a of the potential well between barriers, and with increasing electron density n0 in the wells and increasing thickness d of the nonmagnetic sublayers between the barrier and substrate, the extrema of Em are shifted to smaller a and their amplitudes rapidly increase. As the temperature is lowered from the Curie point, the energy Em, depending on a, n0, and d, can increase (in modulus) monotonically or nonmonotonically, change sign from positive to negative, or change sign twice. The polarization β decreases with increasing a, n0, and d, undergoing sharp jumps when Em changes sign...

Electric field effect analysis of thin PbTe films on high-ε SrTiO3 substrate

Thin PbTe films (thickness 500–600A), deposited on SrTiO3, have been investigated by electric field effect (EFE). The high resistivity of such thin films warrants a high sensitivity of the EFE method. The SrTiO3 substrate serves as the dielectric layer in the gate-dielectric-PbTe structure. Due to the large dielectric constant of SrTiO3, particularly at low temperatures, the electric displacement D in the film reaches the high value of ∼108V∕cm, and the EFE introduced charge into the PbTe film amounts to ∼8μC∕cm2. The high D permits to measure the EFE resistance and Hall constant over a wide region of D, revealing the characteristic features of their D dependence. An appropriate theoretical model has been formulated, showing that, for such films, one can measure the dependence of the Fermi level on D. In fact, we demonstrate that by shifting the Fermi level across the gap by varying D, the density of states of the in-gap states can be mapped out. Our results show that the PbTe layers studied possess a mob...

Diffusion and Kirkendall effect in PbSe-EuS multilayer

Epitaxial PbSe–EuS multilayer subjected to diffusion annealing was examined by low-angle X-ray diffraction and Bragg X-ray diffraction. Multilayer profile change in the course of diffusion intermixing was determined by simulation of X-ray diffraction on the model multilayer profile and comparison of calculated patterns with experimental ones. The systematic shift of the average Bragg peak found at diffusion shows the presence of Kirkendall effect in the specimen. Matano procedure was applied to calculate the partial diffusion coefficients of the multilayer components. 2002 Elsevier Science B.V. All rights reserved.