First-principles study of thermoelectric and lattice vibrational properties of chalcopyrite CuGaTe2

Abstract

The electronic structure of CuGaTe2 has been investigated using first-principles calculations, and it was discovered that it has a mixture of heavy and light bands near the valence band maximum and a combination of electronically conducting and insulating units near the gap edges, highly desirable for good thermoelectric performance. Semi-classic Boltzmann transport theory was then used to calculate the thermoelectric properties of CuGaTe2, and the optimal p- or n-type doping concentrations have been estimated based on the predicted maximum power factors. The phonon dispersion, phonon density of states, and specific heat of CuGaTe2 were evaluated by density functional perturbation theory in combination with the quasi-harmonic approximation, and the calculated phonon frequencies at the Γ point as well as the specific heat are in agreement with experimental data. The relatively high thermal conductivity of CuGaTe2 at low temperature is attributed to the lack of low-frequency vibrational modes, suggesting that its thermal conductivity can be reduced by introducing additional phonon scattering.