Abstract: The transparent semiconductor γ-CuI is a highly promising material for next-generation optoelectronic devices. To further enhance its electrical and optical performance, intentional doping with alkali metals has been identified as a critical and effective strategy. In this study, the defect properties induced by doping with alkali metals (Na, K, and Cs) in CuI are systematically investigated using first-principles calculations. It is found that Na doping tends to form point defects and defect clusters, whereas the larger atomic radii of K and Cs promote the formation of more complex defect clusters. Furthermore, Na doping can result in defect concentrations higher than those of intrinsic defects, thereby significantly enhancing p-type conductivity. In contrast, the defect concentrations introduced by K and Cs doping are much lower than those of the intrinsic defects, and their effect on enhancing p-type conductivity is limited. Regarding the infrared absorption, high-concentration defects do not possess in-bandgap defect energy levels capable of absorbing infrared photons, whereas certain low-concentration defect clusters exhibit such absorption. Carrier absorption through defect energy levels has a negligible effect on the infrared transmittance of γ-CuI. This work predicts that alkali metal doped CuI is advantageous that p-type conductivity can be improved without causing uncontrollable infrared photon absorption caused by defect energy levels. This provides a theoretical basis for developing CuI-based devices that require simultaneous optimization of electrical and optical properties.

Key words: γ-CuI, alkali metal doping, first-principles calculations, defect properties, infrared transmittance