Sn doping in thermoelectric Bi ₂ Te ₃ films by metal-organic chemical vapor deposition

Sn-doped Bi ₂ Te ₃ films were grown on vicinal GaAs (0 0 1) substrates by metal-organic chemical vapor deposition at 360 °C. Trimethylbismuth and diisopropyltellurium, which are alkyl-based, were used as the Bi and Te sources, respectively. Tetrakis(dimethylamino)tin (TDMASn) and tetramethyltin (TMSn) were used as the Sn precursors. Both Sn precursors successfully converted the carrier type of the Bi ₂ Te ₃ films from n- to p-type and achieved a high Seebeck coefficient. In the case of the Sn-doped Bi ₂ Te ₃ films with TDMASn, however, the Sn concentration could not be monotonically controlled by the amount of the precursor, and even the hole concentration was almost invariant despite the drastic increase in the amount of the precursor. In the case of the Sn-doped Bi ₂ Te ₃ films grown with TMSn, on the other hand, the Sn and hole concentrations could be easily controlled by the variation in the flow rate of the H ₂ carrier gas. In particular, the hole concentration varied over a range of 1-5 × 10 ¹⁹ /cm ³ in which a thermoelectric power factor can be maximized despite a very high vapor pressure of TMSn. The growth of high-quality Sn-doped Bi ₂ Te ₃ films was possible using all alkyl-based precursors.