Thermoelectric performance of non-degenerate and degenerate semiconductors

Abstract

Thermoelectric generators have been used for space probe mission by NASA and other space agencies for a long time. These are absolutely indispensable for missions for Jupiter and beyond, where there is no solar radiation or no alternate source that could provide energy for these missions. Thermoelectrics convert heat directly into electricity. Seebeck coefficient is extremely important parameter in thermoelectric devices. On one hand it determines the open circuit voltage developed for thermoelectric generator, on the other hand, it also controls the magnitude of the Peltier coefficient responsible for thermoelectric cooling applications. When operating at wide range of temperature, not only the Fermi level changes, which needs to be taken into account, but the band gap changes with temperature, and therefore, causes the band edge to move and produces additional force on the carriers. The relations for Seebeck have a simpler form for non-degenerate semiconductor but become more complex for degenerate case. Besides, in small band gap materials (such as BiTe) as well as when operating over wide temperature range, the carrier of both signs (electrons and holes) may be present and therefore, bipolar effects need to be considered in these devices. Apart from traditional combination of parameters to solve for bipolar effects, we have developed our own algorithm, based on Landauer approach that can solve for seebeck coefficient for real band structure, any dimension (1D, 2D and 3D) at any Fermi energy and temperature. The simulation tool also incorporates various scattering mechanisms.