Mechanism of thermopower maximum of Bi-Sb semiconducting alloys

Temperature dependence of the Seebeck coefficient of Bi-Sb alloy, which is known to be an efficient thermoelectric material, is investigated in terms of the multi-carrier Boltzmann transport theory. The chemical potential is calculated self-consistently with the measured Hall coefficient, by solving an integral equation. The calculated chemical potential shows a clear indication of the extrinsic-to-intrinsic transition, and determines the temperature dependence of all the transport properties. In particular, maximum thermopower is bound to occur in the vicinity of the transition temperature. It is confirmed that the electrons in the L-point conduction band act as dominant carriers, whereas the valence bands at the L, T and H points serve primarily as carrier reservoirs. The electrons are sufficiently degenerate that the conventional analysis is misleading, corresponding to the unphysical solution of the equation.