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

Research paper by M. Omprakash, M. Arivanandhan, M. Sabarinathan, T. Koyama, Y. Momose, H. Ikeda, H. Tatsuoka, D.K. Aswal, S. Bhattacharya, Y. Inatomi, Y. Hayakawa

Indexed on: 14 Mar '16Published on: 02 Mar '16Published in: Journal of Crystal Growth


Compositionally homogeneous Sb-doped (5×1018 and 1×1019 cm−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 1×1019 cm−3) Si0.73Ge0.27 bulk crystals were 18.3 and 15.1 mm, respectively. Grain distribution was investigated by electron backscattered diffraction spectrum (EBSD). The Seebeck coefficients (−440 and −426 μV/K) of Sb-doped (5×1018 and 1×1019 cm−3) Si0.73Ge0.27 were higher than the reported value (−211 μV/K) of P-doped (5×1019 cm−3) Si0.8Ge0.2 at room temperature. Thermal conductivity of Ga and Sb-doped SiGe were decreased with temperature due to scattering of phonon at the temperature range between 313 and 913 K. The maximum ZT values of Ga and Sb-doped SiGe were 0.34 and 0.44 at 820 K, 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 (5×1019 cm−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.

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