Thermoelectric Properties of CuIn1—xGaxTe2 Single Crystals

Abstract

In this paper we report on crystal growth and the electrical characterization of the compounds CuGaTe2, CuInTe2 and their solid solutions CuIn1—xGaxTe2. Single crystals were obtained by zone melting and a vertical Bridgman technique. From resistivity and Hall effect measurements in the temperature range of 35 to 400 K the carrier concentrations and mobilities were determined. All samples showed p-type conductivity. The hole densities at room temperature were approximately p = 1020 cm—3, which indicates that these materials are degenerate semiconductors. For thermoelectric applications weakly degenerate semiconductors are required. In order to investigate whether these materials are suitable for thermoelectric applications we measured the Seebeck coefficient between 90 and 400 K and the thermal conductivity in the range of 80 to 360 K. From the analysis of the obtained data we were able to calculate the temperature dependence of the Fermi level, the density-of-states effective mass of holes, the electronic contribution to the thermal conductivity and the figure of merit for a thermoelectric material. With a theoretical estimation it is shown that there is a optimum doping concentration which leads to a maximum figure of merit Z for this material group. Further possibilities to improve Z are discussed.