Theoretical Investigation on the Effect of Transition-Metal Doping on Seebeck Coefficient of SiGe Alloy*

To improve the efficiency of thermoelectric materials for advanced energy conversion technologies, numerous ways of modifying their electronic and structural properties have been proposed. One of the strategies is to enhance their Seebeck coefficient by impurities doping. For silicon-germanium (SiGe) alloy, the efficiency has been improved experimentally by doping iron [1]. Here, by using first-principles calculations, a systematic search is performed to investigate the effect of various transition-metals on the Seebeck coefficient of the alloy. The electronic structures of pure SiGe alloy and 3d-, 4d-, 5d-transition-metal-doped alloy systems were analyzed to compare the change in band gap energy as well as the modification of electronic density of states before and after doping. We found, among investigated transition-metals, Ti-, V-, Ru- and Os-doped SiGe alloy behave similarly to the case of Fe doping as in previous study [2]. The doping of those metals makes large improvement to the Seebeck coefficient, especially for p-type SiGe alloy in the temperature range of 300 to 900K. This enhancement is mainly attributed to the appearance of intense, sharp peaks at the bottom of conduction band contributed by the d states of transition-metals.