Density-functional electronic structure calculations for native defects and Cu impurities in CdS

We performed density-functional electronic structure calculations for wurtzite CdS with native defects and Cu impurity. We investigate formation energies and ionization levels of the defects in various charge states. Our results reveal that the S vacancy is a double donor with the strongly localized orbital at the defect site, and could act as an intrinsic compensation defect under p-type doping. On the other hand, the interstitial S at the tetrahedral site is a double acceptor which forms into a dumbbell-like atomic configuration with the nearest S atom. The impurity Cu substituting Cd produces a single acceptor state, while the interstitial Cu generates a single donor state. The calculated formation energies imply that the donor state could also cause the compensation in the Cu doped CdS.