First-principles calculations were presented for the VZn and VGe cation vacancies and the ZnGe and GeZn antisites in ZnGeP2, using full-potential linearized muffin-tin orbital method super-cell calculations in the local-density approximation to density-functional theory. Under Zn-poor conditions, the lowest Gibbs energy defects were found to be the GeZn and VZn defects, leading to a compensated p-type material in agreement with experimental evidence. The occupation energy levels of the defects were determined and compared with available experimental information. As expected, the GeZn was found to be a donor while the other three were acceptors. Good agreement was obtained with optical quenching and activation of electron paramagnetic resonance signal studies if a direct transfer of electrons from VZn2- to GeZn2+ was assumed rather than a process via the conduction band. This suggested a close association of the dominant acceptors and donors. This was further confirmed by showing that the formation of complexes consisting of two VZn- with a single GeZn2+ antisite were favorable in energy. The VGe on the other hand was found to have high energy of formation under any chemical potential conditions and was found to be unstable toward formation of a VZn and ZnGe pair. Structural relaxation of all defects was performed but no symmetry breaking distortions were found. As a result, the defect wave functions of the unpaired electron in the VZn- was found to be spread equally over the four neighboring P atoms, in disagreement with electron nuclear double resonance data which indicated primary localization on a pair of P atoms.

Theoretical Study of Cation-Related Point Defects in ZnGeP2. X.Jiang, M.S.Miao, W.R.L.Lambrecht: Physical Review B, 2005, 71[20], 205212 (12pp)