Influence of doping and solid solution formation on the thermoelectric properties of chalcopyrite semiconductors

We have investigated the influence of zinc doping on the thermoelectric properties of CuInTe2-CuGaTe2 solid solution alloys. Undoped end-member compounds display typical p-type semiconducting behavior, with a negative temperature coefficient of resistivity and large Seebeck coefficient. With zinc substituting for indium or gallium, the hole concentration is increased and the electrical transport behavior evolves into that of a degenerate semiconductor, with both electrical resistivity and Seebeck coefficient increasing with temperature up to the highest temperature measured. For undoped samples the thermoelectric power factor is maximized close to 750 K, while in doped specimens the maximum occurs at much lower temperature. Substitution of gallium for indium induces significant phonon scattering and thermal conductivity reduction below 500 K. The dimensionless figure of merit rises to above unity over a range of compositions in these chalcopyrite compounds, with optimized samples reaching a figure of merit of 1.3.