14.16.6 Thermoelectric Refrigeration Thermoelectricity is the direct or spontaneous conversion of heat into electrical energy. In 1834, Jean Charles Peltier (1785–1845) observed that, when an electric current was passed through two different metallic conductors connected in a loop, one of the two junctions between the conductors cooled while the other warmed. When the direction of the current was reversed, the effect was reversed, with the first junction warming and the second cooling. Thermoelectric cooling remained a laboratory curiosity until after 1950, when semiconductors were developed. Semiconductor materials were formulated to produce much more efficient thermoelectric cooling than pure metals. They were used effectively in the U.S. space program in the 1960s and have a growing market today.

We briefly review the thermal conductivity and thermoelectricity of semiconductors. This subject has more than a 100-year history since Drude established his kinetic theory of electron gas in 1900. We focus on recent developments, particularly shedding light on energy conversion and nanotechnology. We begin with the Boltzmann equations for electrons and phonons, and review thermal conductivities of various semiconductors. Then, we discuss the thermoelectric effects – cross-correlation phenomena between electrical and thermal currents.