ABSTRACT
This chapter describes the band structure engineering tools used to create a favorable density of states (DOS). The use of electron energy bands that have a high DOS over a very narrow energy range is obviously advantageous. A plot of the DOS as a function of energy for a given impurity in a solid, as is often found in the literature, can therefore give only a necessary but not a sufficient condition for an impurity level to be resonant. The band structure distortions can work either by the excess DOS they induce or at low temperature by inducing resonant scattering. The resonant levels of interest in thermoelectric (TE) materials are those that exist in semiconductors. Alloys of the group IVVI compound semiconductors that crystallize in the rocksalt structure are the mainstay of TE technology aimed at operating near 500°C, where combustion processes typically provide the heat.
