Recent Studies of Bismuth Telluride and Its Alloys

This paper reviews the work which has been carried out in these Laboratories during the past two years on single crystals of bismuth telluride and its alloys. The combination of experiments on Faraday rotation with those performed previously on galvanomagnetic effects has established that there are 3- and 6-valley band structures associated with p- and n-type Bi2Te3, respectively. However, observations of the anisotropy ratio for the electrical conductivity and of the galvanomagnetic coefficients for heavily doped n-type material have shown that the shape of the equal-energy surfaces is dependent on carrier concentration. Similar conclusions have been drawn from the behavior of the Seebeck coefficient at low temperatures. Measurements on Bi2Te3 at low temperatures and on alloys of Bi2Te3 have shown that the lattice thermal conductivity is particularly sensitive to the substitution of atoms of I, Se, or S for those of Te. It has also been shown that the anisotropy ratio for the lattice thermal conductivity is almost the same for the alloys as for pure Bi2Te3.