Vertical gradient solution growth of N-type Si0.73Ge0.27 bulk crystals with homogeneous composition and its thermoelectric properties

Abstract

Compositionally homogeneous Sb-doped (5×1018 and 1×1019cm−3) Si0.73Ge0.27 bulk crystals were grown by a vertical gradient solution growth method. The sandwich sample Si (seed)/Sb-doped Ge/ Si(feed) was set up inside a furnace under a mild temperature gradient 0.57°C/mm for homogeneous growth. The Si composition was analyzed by electron probe micro- analysis (EPMA). It revealed that the Si composition was homogeneous and the lengths of the Sb-doped (5×1018 and 1×1019cm−3) Si0.73Ge0.27 bulk crystals were 18.3 and 15.1mm, respectively. Grain distribution was investigated by electron backscattered diffraction spectrum (EBSD). The Seebeck coefficients (−440 and −426μV/K) of Sb-doped (5×1018 and 1×1019cm−3) Si0.73Ge0.27 were higher than the reported value (−211μV/K) of P-doped (5×1019cm−3) Si0.8Ge0.2 at room temperature. Thermal conductivity of Ga and Sb-doped SiGe was decreased with temperature due to scattering of phonon at the temperature range between 313 and 913K. The maximum ZT values of Ga and Sb-doped SiGe were 0.34 and 0.44 at 820K, respectively. The ZT values of Ga and Sb-doped SiGe were higher (0.07 and 0.13) than the reported value of Ga-doped Si0.81Ge0.19 (0.05) and P-doped (5×1019cm−3) Si0.8Ge0.2 bulk crystals at room temperature. The improvement in ZT value was caused by a decrease of thermal conductivity which related to a composition of the alloy and doping concentration in the crystal.