Thermoelectric properties of heavily GaP- and P-doped Si0.95Ge0.05

The Seebeck coefficient S, the electrical resistivity rho and the thermal c onductivity kappa of Si0.95Ge0.05 samples doped with 0.4 at. % P and/or 0.5 -2.0 mol % GaP, which were prepared by a conventional arc melting method, w ere measured as functions of GaP content and temperature T in the range fro m 323 to 1208 K. When multidoped with P and GaP, Ga tends to segregate more strongly with Ge to the grain boundaries than P, while when doped with GaP alone, both P and Ga segregate equally strongly with Ge. For multidoped sa mples, the S values at 323 K have a minimum at 1.0 mol % GaP and then incre ase with additional GaP, while the values of rho and kappa decrease monoton ically with increasing GaP content. The optimum additional content of GaP t hat gives the largest thermoelectric figures of merit (ZT=(ST)-T-2/kappa rh o) for multidoped n-type Si0.95Ge0.05 samples was 1.5 mol %, which is sligh tly less than the 2.0 mol % of GaP added to Si0.8Ge0.2 alloy by hot pressin g. The ZT value for multidoped Si0.95Ge0.05 with an optimum content of GaP increases linearly with temperature, and at 1073 K is 18% higher than that obtained previously for Si0.95Ge0.05 doped with only 0.4 at. % P. At 1173 K the ZT value is 1.16, which corresponds to 95% of that obtained previously at the corresponding temperature for Si0.8Ge0.2 alloy doped with 2.0 mol % GaP. (C) 2001 American Institute of Physics.