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

We have investigated the melt growth of Mg 2 Si 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 Mg 2 Si crystal with low carrier density and a high stable Mg 2 Si with good doping controllability. The Mg 2 Si 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 (∼10 15 cm −3 ) and high electron mobility (485 cm 2 V −1 s −1 at 300 K and 21900 cm 2 V −1 s −1 at 40 K). Silver doping in the high purity crystals performed the low-hole density of p-type Mg 2 Si (∼3 × 10 16 cm −3 ). Ionization energy of residual Al donor in the high purity crystal and Ag acceptor in the Ag doped crystals was determined as 8–9 meV and 26 meV, respectively. Indirect band gap energy E g of approximately 0.61 eV at 300 K and 0.69 eV at 4 K 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 (26 µW cm −1 K −2 at 270 K).