Crystal growth and characterization of Mg₂Si for IR-detectors and thermoelectric applications

We have investigated the melt growth of Mg₂Si crystal and its electrical and optical properties. Progress in Mg source purity and stoichiometric control during the growth enabled the development of a high purity Mg₂Si crystal with low carrier density and a high stable Mg₂Si with good doping controllability. The Mg₂Si crystal grown by the pressure controlled Bridgman method using 5N purity or 6N purity of Mg source and purified PG crucible showed low electron density (∼10¹⁵cm^-3) and high electron mobility (485cm²V^-1 s^-1 at 300K and 21900 cm²V^-1 s^-1 at 40 K). Silver doping in the high purity crystals performed the low-hole density of p-type Mg₂Si (∼3 × 10¹⁶cm^-3). Ionization energy of residual Al donor in the high purity crystal and Ag acceptor in the Ag doped crystals was determined as 8-9meV and 26meV, respectively. Indirect band gap energy E_g of approximately 0.61 eV at 300K and 0.69 eV at 4K were estimated by the optical transmission measurements on the high purity crystals. It is also found that the Sb-doped melt grown crystal had good power factor around room temperature (26μWcm^-1K^-2 at 270 K).