Two-band model of the electron spectrum in n-Bi/sub 2/Te/sub 2.7/Se/sub 0.3/

The Hall factor and thermoelectric properties of n-Bi/sub 2/Te/sub 2.7/Se/sub 0.3/ solid solution with the room-temperature Seebeck coefficient S = 212 /spl mu/V/K have been studied in the temperature range 77-350 K. The observed temperature dependences demonstrate some specific features, which were found earlier in samples with lower electron density N. The effect of these specific features on the thermoelectric figure of merit Z appears to be more favorable for the sample under study: this sample is most efficient in the temperature range 120-340 K, the average value of ZT is 0.71. It is found that the rise of density N enhances the factor responsible for the effective mass decreasing as temperature increases; this effect appears when the analysis is made in terms of a single-band parabolic model with N = const(T). We believe that the most probable reason for the unusual behavior of properties is a complex structure of the electron spectrum. Calculations have been made, and the obtained temperature dependences of transport coefficients show a good agreement with the experimental data for two samples of the mentioned composition with different electron densities. The calculations were performed in terms of a two-band model and acoustic scattering, with the account for anisotropy and nonparabolicity of the light-electron spectrum.