Enhanced thermoelectric figure-of-merit of p-type SiGe through TiO2 nanoinclusions and modulation doping of boron

Abstract

The thermoelectric performance of p-type SiGe is usually inferior as compared to the n-type SiGe. In this work, we demonstrate that by in-situ creation of coherent TiO2 nanoinclusions and boron rich regions in p-type SiGe, a high figure-of-merit of ∼1.3 is achieved at 1100 K, which is 29% higher than pristine p-type SiGe. Such a composite material (SiGe-TiO2) with improved performance was synthesized through vacuum hot pressing of p-type SiGe and TiB2 nanopowders. The phonon scattering and energy filtering of charge carriers at the TiO2/SiGe coherent interface together resulted in lowering of thermal conductivity and enhancement of the Seebeck coefficient. Modulation doping of boron along with improved densification maintain high electrical conductivity. Such a unique combinations of low thermal conductivity, high Seebeck coefficient, and high electrical conductivity of SiGe-TiO2 composite are responsible for the improvement of the thermoelectric figure-of-merit.