Anistropy of the constant-energy surfaces in n-type Bi2Te3 and Bi2Se3 from galvanomagnetic coefficients

Low-field galvanomagnetic coefficients have been measured on single crystals of Bi2Te3 and Bi2Se3 at 76 degrees 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 Bi2Te3 can be minimized by recalculating the mass parameters from the galvanomagnetic data and by not assuming complete degeneracy. The experimental data on Bi2Te3 are in agreement with those reported earlier. There is also very good evidence of second-band effects at high electron concentrations (>10(19) cm(-3)), as has been previously suggested. The constant-energy surfaces undergo an apparent change in shape between low- and high-concentration samples. Data on Bi2Se3 indicate that the constant-energy surfaces are more spherical than in the case of Bi2Te3.