NON-PARABOLICITY OF THE CONDUCTION-BAND AND ANISOTROPY OF THE ELECTRON EFFECTIVE MASS IN N-BI2SE3 SINGLE-CRYSTALS

Single crystals of n-Bi2Se3 were prepared with free-carrier concentration N in the range 5×1018<N<2×1020 cm-3. Results of the measurements of infrared reflectance, Seebeck coefficient, and Hall voltage are interpreted using the nonparabolic two-band approximation under the assumption of isotropic relaxation time. Good agreement between the experimental and theoretical values of the Seebeck coefficient is obtained provided the scattering of free carriers by the optical branch of the lattice vibrations is taken into account. The values of the perpendicular component of the effective mass m0=0.07m0 and the density-of-states effective mass md,O=(0.160.01)m0 were obtained for the bottom of the band. Taking into account the inequality m,0<m,0m0 and making use of the assumptions discussed in the paper it is concluded that, in the crystals studied, the value of the m ratio decreases with increasing concentration of free carriers. © 1979 The American Physical Society.