Carrier Pocket Engineering to Improve Thermoelectric Transport
Dr. G. Jeffrey Snyder
(California Institute of Technology, Pasadena, USA)
14.06.2012
High Seebeck coefficient in semiconductors generally results from a high density of states (DOS) effective mass. Many unconventional electronic structures that increase effective mass are being studied or proposed for high efficiency thermoelectric materials. However high effective mass of the carriers due to flat bands results in low mobility, which leads to lower zT. Instead, high DOS effective mass due to high valley degeneracy leads to high zT. For example, utilizing the high degeneracy second valence band in PbTe leads to nearly twice the zT (zT ~ 1.4) than that of the low degeneracy first valence band. By engineering the two valence bands to converge further increases the degeneracy and zT. Using such band engineering approaches, peak zT near 1.8 and higher average ZT can be achieved making PbTe alloys most suitable for waste heat recovery applications.