Experimental evidence of improved thermoelectric properties at 300K in Si/Ge superlattice structures

Abstract

The authors have found that it may be possible to obtain significant enhancement in ZT at 300 K, over conventional bulk SiGe alloys, through the use of Si/Ge Superlattice (SL) structures. The Seebeck coefficient in Si/Ge SL structures was observed to increase rapidly with decreasing SL period with no loss of electrical conductivity. The carrier mobilities in Si/Ge SLs were higher than in a comparable thin-film Si/Ge alloy. The best power factor of the short-period Si/Ge SLs is 112.2 {micro}W/K{sup 2} cm, over five-fold better than state-of-the-art n-type, bulk SiGe alloys. Approximately a two to four-fold reduction in thermal conductivity in short-period SL structures, compared to bulk SiGe alloy, was observed. The authors estimate at least a factor of five improvement over current state-of-the-art SiGe alloys, in several Si/Ge SL samples with periodicity of {approximately}45 to 75 {angstrom}. The results of this study are promising, but tentative due to the possible effects of substrate and the developmental nature of the thermoelectric property measurements.