Amphoteric doping and thermoelectric transport in the CuInTe2–ZnTe solid solution

Abstract

The chalcopyrite CuInTe₂ is a promising thermoelectric material; here, optimal carrier concentrations can be achieved through careful stoichiometric control or the introduction of extrinsic dopants such as Zn. However, CuInTe₂ is challenging to rationally dope: Zn can expected to substitute on either cation site, and there are a large number of competing low energy native defects. Zn doping is further complicated by the complete solid solution formed between CuInTe₂ and ZnTe, which creates uncertainty in the experimental elemental chemical potentials. In this work, first principles calculations are united with experimental synthesis and transport measurements to predict the formation energies of defects in Zn-doped CuInTe₂. This is a challenging task: within Zn-doped CuInTe₂, we face an expansive four-dimensional single phase region in chemical potential space. To render this space tractable, we present how native and extrinsic defects evolve when: (i) varying Cu, In, and Te chemical potentials for fixed Zn chemical potential, and (ii) adjusting Zn chemical potential for fixed Cu, In, and Te chemical potential. Computationally, we predict that the introduction of Zn significantly alters the native defect landscape, generates large concentrations of Zn_Cu–Zn_In defect complexes, and serves as an ambipolar dopant. These predictions are supported by electronic transport measurements on bulk, polycrystalline samples that further demonstrate the broad range of charge carrier concentrations achievable in the space. These results come together in a unified workflow to account for the interplay between native defects, ambipolar extrinsic dopants, and solid solution behavior in Zn-doped CuInTe₂.