ELECTRICAL PROPERTIES AND BAND STRUCTURE IN Pb1-xSnxTe

Abstract

Strong evidence for the existence of two valence bands in Pb0.7Sn0.3Te and Pb0.5Sn0.5Te is inferred from the observation of a kink in the variation of the Hall ratio R300 °K/R100 °K, as a function of hole concentration. This existence is also supported by the fact that the variation of the Seebeck coefficient as a function of hole concentration exhibits a minimum. Moreover, non parabolic bands are expected from our Hall mobility data, which indicate µH ~ p-1 instead of µH ~ p-1/3 for a parabolic band. According to the existence of two valence bands, the thermal energy gap behavior in Pb-rich alloys (x ⩽ 0.3) is discussed. From electrical results in the intrinsic regions, the thermal energy gaps for different compositions ranging from PbTe to x = 0.3 were found to be of the same order. Taking into account the interpretation for PbTe, and in correlation with the observed behavior of the energy gap Eg, the energy separation Ev between the two valence bands V1 and V2 is expected to increase with increasing Sn content and to decrease with increasing temperature. Data on Sn-rich alloys would lead to a better appreciation of a possible shift of V2 relatively to V1 and to the conduction band with increasing Sn content.