First-Principles Study on Doping of Copper Halides

We investigate the doping behavior of copper halides CuX (X = Cl, Br, and I) by using density functional theory calculations. We evaluate the formation energies of Cu and X vacancies, which reveal the formation of Cu vacancies to be energetically favorable when the Fermi level is near the valence band maximum, leading to the p-type conductivity of CuX. The possible hole concentration of CuX due to the formation of vacancies is predicted to decrease from CuI to CuBr and CuCl, consistent with experiments. We also study hydrogen interstitials, which show that the p-type conductivity of CuX, especially CuCl, can be undermined due to compensation of holes by hydrogen interstitials. By inspecting the band offset of CuX, we provide fundamental insights into the X dependence of p-type doping in CuX.