  N-type Bi100-xSbx alloys have the highest thermoelectric figure of merit (zT)
of all materials below 200K; here we investigate how filling multiple valence
band pockets at T and H-points of the Brillouin zone produces high zT in p-type
Sn-doped material. This approach, theoretically predicted to potentially give
zT>1 in Bi, was used successfully in PbTe. We report thermopower, electrical
and thermal conductivity (2 to 400K) of single crystals with 12<x<37 and
polycrystals (x=50-90), higher Sb concentrations than previous studies. We
obtain a 60% improvement in zT to 0.13.
