Papers by Author: V.A. Kulbachinskii

Abstract: The influence of the Co doping on the properties of zinc oxide films was investigated. The films were grown by oxygen and water assisted metal organic chemical vapor deposition (MOCVD). The large positive magnetoresistance (PMR) was observed in Co doped films at low temperatures while the negative magnetoresistance was observed in undoped ZnO films deposited under the same conditions. The relative variation of resistivity was comparable in the films grow by oxygen and water assisted MOCVD although the resistivity and its temperature dependence were significantly different. The magnitude of PMR increases with an increase of the Co content and with the decrease of temperature.

Abstract: Transport and magnetic properties of δ-Mn doped GaAs/InGaAs/GaAs quantum wells (QW) with various In content were studied at temperatures 4.2K≤T≤300K. Fluctuation potential (FP) appeared to be crucial for transport characteristics of structures under investigation. The magnetic percolation transition was observed at temperature T_p in the range 20 - 40K. The T_p dependence on the In content is nonmonotonic due to the peculiarities of free-carrier mediated exchange interaction mechanisms. The change of the anomalous Hall effect (AHE) sign with decreasing temperature was detected at temperatures close to the T_p. The main reason of the AHE sign change is the variation of contributions of different AHE mechanisms (intrinsic and side-jump) caused by the reduction of spin-dependent scattering intensity with temperature decrease. We believe that our results are the experimental observation of the AHE intrinsic mechanism in 2D.

Abstract: Transport, magnetotransport and magnetic properties of structures GaAs/InAs/GaAs with a InAs quantum dot (QD) layer have been investigated in the temperature interval 4.2<T<300 K. The structures were delta-doped by Mn from a one side to provide magnetic properties and by carbon from the other side to enhance a p-type conductivity. The ferromagnetic phase up to 400 K was detected by SQUID magnetometer. Anomalous Hall-effect was observed at low T. The role of additional disorder in conducting channel due to the QD layer was investigated. It is shown a principal role of a fluctuation potential of Mn layer separated from conducting QD layer by a spacer in anomalous transport properties of structures. The negative magnetoresistance was observed at low T due to the reduction of the spin-flip scattering by aligning spins by magnetic field.

Abstract: Temperature dependencies of the Seebeck coefficient, electrical conductivity, heat conductivity and the dimensionless thermoelectric figure of merit ZT of p-Bi₂Te₃, n-Bi₂Se₃ and Sb₂Te₃ doped by Fe or Cr have been investigated in the temperature interval 7 < T < 300 K. At T=4.2 K the Shubnikov-de Haas and Hall effects have been measured. By increasing the Fe content, the hole concentration decreases in p-Bi_2-xFe_xTe₃, while the electron concentration increases in n-Bi_2-xFe_xSe₃. The hole concentration decreases in Sb_2-xCr_xTe₃ with Cr doping. This demonstrates that Fe or Cr act as donors. The Seebeck coefficient increases in p-Bi_2-xFe_xTe₃ and Sb_2-xCr_xTe₃ with increasing Fe or Cr content, while it decreases in n-Bi_2-xFe_xSe₃.

Abstract: We have investigated the thermodynamic, transport and magnetotransport properties of free charge carriers in a diluted magnetic semiconductor with a quantum well InGaAs in the GaAs with δ-doped by C and Mn. In order to determine the density of the holes in a quantum well, we carried out thermodynamic calculations of the system of free holes, atoms Mn0 and ions Mn–. We calculated the temperature dependence of resistance and magnetoresistance of holes in the quantum well. The contributions of various scattering mechanisms of holes to the resistance were analyzed. The negative magnetoresistance are explained as the reduction of spin-flip scattering by aligning spins of the magnetic field.