Multi-band analyses of the conductivity, the Hall coefficient, and the Seebeck coefficient of single crystal p-type β-FeSi2

Abstract β-FeSi2 is called the “environment-friendly thermoelectric semiconductor” but the origin of its high thermoelectromotive power is still unknown. In the present study, the temperature-dependence data of the electrical conductivity, the Hall coefficient, and the Seebeck coefficient on bulk single crystal p-type β-FeSi2 samples reported in literature have been analyzed in a multi-band model. In the model, the effects of the 2nd maximum of the valence band, the 2nd minimum of the conduction band, and an acceptor impurity band are included and are proved to be important. Through the simultaneous fits to the temperature-dependence data of the three transport coefficients, the effective masses of holes at the 1st and the 2nd maximum of the valence band and those of electrons at the 1st and the 2nd minimum of the conduction band are deduced together with the energy separations among the bands. In addition, by including the temperature-dependent Hall factor for impurity hopping conduction, impurity concentrations have been significantly corrected from those previously estimated in a simple two-band model.