Electrons in Bi-Sb Alloys

Galvanomagnetic and thermoelectric measurements have been performed on doped and undoped ${\mathrm{Bi}}_{85}$ ${\mathrm{Sb}}_{15-}$ alloy single crystals. The thermal gap, obtained from the temperature variation of resistivity on high-purity $n$- and $p$-type samples, is 0.024±0.003 eV, a significantly larger value than the previously measured maximum gap (0.014 eV) for this system. Hall data on Te-doped samples indicate that two Te atoms must be added to the crystal to add one additional free electron. Transport properties have been analyzed for Tedoped samples at 20°K, using a multivalley conduction band. The magnitudes of the Seebeck and Hall coefficients indicate that most of the electrons must reside in three (not six) bismuth-like tilted ellipsoids. However, the lack of agreement between experiment and calculations based on the three-ellipsoid model for the ratio ${\rho }_{33,11}:{\rho }_{33,33}$ suggests the possible existence of a small number of electrons in an additional electron ellipsoid along the trigonal axis.