T. E. Svechnikova

Physical properties of Bi2Te2.85Se0.15 single crystals doped with Cu, Cd, In, Ge, S, or Se

Bi2Te2.85Se0.15 crystals doped with Cu, Cd, In, Ge, S, or Se were grown by the floating-crucible technique. The effective segregation coefficients for the dopants were determined. The thermoelectric power, electrical conductivity, and thermal conductivity of the samples were measured in the temperature range from 77 to 350 K. The effects of the dopants studied on the temperature dependences of the electrical properties and thermoelectric figure of merit were examined. The bending strength of the doped crystals was measured.

Structural and Transport Properties of Sn-Doped Bi2Te3 – xSe x Single Crystals

The transport properties of Bi2 – ySnyTe3 – xSex solid solutions are studied. The results demonstrate that doping with Sn has a strong effect on the temperature dependences of the thermoelectric power and electrical conductivity of the crystals. This suggests that the valence band of the crystals contains Sn-related resonance states. The point defects and dislocation system in Bi2Te3 and Bi2 – ySnyTe3 – xSex solid solutions are studied by transmission electron microscopy. It is shown that the predominant defects in the crystals studied, grown by the Czochralski technique, are dislocations lying in the (0001) plane. The estimated dislocation density is 108 to 109 cm–2, and the primary slip plane is (0001). Electron-microscopic examination indicates the presence of stacking faults and very small dislocation loops in both Bi2Te3 and Bi2 – ySnyTe3 – xSex single crystals. Since all of the crystals are highly degenerate semiconductors, it is reasonable to assume that structural defects have an insignificant effect on their electrical properties.

Anisotropic thermoelectric properties of the layered compounds PbSb2Te4 and PbBi4Te7

Single crystals of the ternary layered compounds PbSb2Te4 (p-type) and PbBi4Te7 (n-type) have been grown by Czochralski pulling with melt supply through a floating crucible. The in-plane and out-of-plane thermoelectric power, electrical conductivity, and thermal conductivity of the PbSb2Te4 and PbBi4Te7 crystals and related alloys have been measured in the temperature range 85–340 K. The results attest to a significant thermoelectric anisotropy in the crystals, especially in the p-type material PbSb2Te4.

Specific features of Bi2Te3 doping with Sn

The effect of doping bismuth telluride with tin, on its electrophysical properties, has been studied. It is shown that the main features in the transport coefficients of Bi2Te3:Sn can be explained by the existence of resonant Sn states within the valence band. The existence of resonant Sn states was confirmed by codoping Bi2Te3:Sn with the electroactive impurity I.

Effect of cadmium, silver, and tellurium doping on the properties of single crystals of the layered compounds PbBi4Te7 and PbSb2Te4

We have studied the effects of doping and excess Te on the thermoelectric properties of single crystals of the layered ternary compounds PbBi4Te7 and PbSb2Te4. X-ray diffraction characterization has shown that the crystals have highly disordered structures. The nature of the possible point defects in the compounds has been analyzed. The silver atoms in Ag-doped PbBi4Te7 seem to reside in the van der Waals gaps between the slabs. The introduction of excess Te is shown to markedly reduce the lattice thermal conductivity of both compounds.

On the hole scattering anisotropy in the PbSb2Te4 layered compound from data on the Nernst-Ettingshausen coefficient

Three independent components of the Nernst-Ettingshausen coefficient tensor Qikl are experimentally measured for an anisotropic single crystal of the p-PbSb2Te4 layered compound. The components Q123 and Q132 are found to be negative, whereas the component Q321 is positive. The experimental data on the anisotropy of the Nernst-Ettingshausen coefficient are discussed together with the available data on the thermopower, the Hall effect, and the electrical conductivity. The analysis demonstrates that the experimental data on the transport effects in p-PbSb2Te4 can be explained within a one-band model of the band spectrum and a mixed mechanism of hole scattering under the assumption that scattering from acoustic phonons and scattering from impurity ions are dominant in the cleavage plane and along the c3 trigonal axis, respectively.

Thermopower anisotropy in the layered compound PbSb2Te4

The possible origin of the considerable anisotropy of the Seebeck coefficient in crystals of the multicomponent layered compound p-PbSb2Te4 is analyzed. It is shown that the experimental data on the thermopower anisotropy in p-PbSb2Te4, together with the temperature dependences of the electrical conductivity along the trigonal axis and in the cleavage plane, can be explained by in terms of a one-band spectrum model and a mixed mechanism of hole scattering under the assumption that scattering from acoustic phonons and impurity ions is dominant in the cleavage plane and along the C3 trigonal axis, respectively.

Thermal conductivity of Bi2Te3: Sn and the effect of codoping by Pb and I atoms

The variation of the lattice thermal conductivity of Bi2Te3 induced either by alloying it with tin alone or by codoping the lattice with an acceptor or donor impurity was studied. The experimental data obtained at room and liquid nitrogen temperatures argue for the validity of the model of quasi-local impurity states associated with tin atoms.

Properties of Bi2Te3 single crystals doped with Sn

The effect of doping with Sn on the properties of Czochralski-grown Bi2Te3 crystals was studied. The effective segregation coefficient for Sn was determined to be 0.6. The thermoelectric power, electrical conductivity, and Hall coefficient of the doped crystals were measured at room temperature. Doping with low Sn concentrations (0.2-0.5 at. %) was found to have only a weak effect on the electrical properties ofp- type Bi2Te3. Doping with 0.7-1 at. % Sn reduces the thermoelectric power and increases the electrical conductivity and hole concentration. Lattice thermal conductivity is a nonmonotonic function of Sn concentration. The thermoelectric figure of merit of Bi2Te3 doped with less than 0.6 at. % Sn exceeds that of undoped Bi2Te3.

Influence of Sn resonance states on the electrical homogeneity of Bi2Te3 single crystals

An unusually high homogeneity of electrical properties was found in Sn-doped Bi2Te3 single crystals. The Seebeck coefficient, which is sensitive to fluctuations in charge carrier concentration, remains unchanged even when the amount of introduced Sn impurity is increased. This fact is explained in terms of the model of resonance impurity states.