Anistropy of the Constant-Energy Surfaces inn-Type BiTe32andBi2Se3from Galvanomagnetic Coefficients

Low-field galvanomagnetic coefficients have been measured on single crystals of ${\mathrm{Bi}}_2$ ${\mathrm{Te}}_3$ and ${\mathrm{Bi}}_2$ ${\mathrm{Se}}_3$ at 76 °K in fields to 9 kG. Using a six-valley ellipsoid model in the isotropic relaxation-time approximation, the mass parameters of the ellipsoids are calculated for both compounds. The discrepancy between previously reported galvanomagnetic data and de Haas-van Alphen data for ${\mathrm{Bi}}_2$ ${\mathrm{Te}}_3$ can be minimized by recalculating the mass parameters from the galvanomagnetic data and by not assuming complete degeneracy. The experimental data on ${\mathrm{Bi}}_2$ ${\mathrm{Te}}_3$ are in agreement with those reported earlier. There is also very good evidence of second-band effects at high electron concentrations (> ${10}^{19}$ ${\mathrm{cm}}^{-3\mathrm{}}$), as has been previously suggested. The constant-energy surfaces undergo an apparent change in shape between low- and high-concentration samples. Data on ${\mathrm{Bi}}_2$ ${\mathrm{Se}}_3$ indicate that the constant-energy surfaces are more spherical than in the case of ${\mathrm{Bi}}_2$ ${\mathrm{Te}}_3$.