Deep levels of single vacancies and antisite defects in the structure of the ZnGeP2 compound were investigated using the pseudopotential method and an extended unit cell. The data obtained were compared with those for the GaP iso-electronic analogue. It was demonstrated that, in the case of the ZnGeP2 crystal, deep levels (degenerate in the GaP structure) were substantially split as a result of lowering the lattice symmetry and anisotropy of the chemical bonding. In particular, the splitting of the VP0 (t2) level was equal to 1.58eV. The averaged levels of defects in the ZnGeP2 compound were in close agreement with the levels of defects in the GaP compound. The absorption coefficients for polarized light were calculated with allowance made for the neutral and charged states of the defects. The optical transitions responsible for the absorption peaks in the IR range of the spectrum of the ZnGeP2 compound were revealed. It was shown that the first peaks were associated with the transitions of electrons from the valence band states located deep in the Brillouin zone to the VZn-1 and VP0 deep levels. This leads to a considerable shift (by about 0.3eV) of these peaks toward the high-energy range as compared to the energy positions of the deep levels in the band gap with respect to the top of the valence band. The experimental data on the photo-induced electron paramagnetic resonance spectra of post-growth and electron-irradiated ZnGeP2 crystals were consistently interpreted by analyzing the electron density.

Deep Levels of Intrinsic Point Defects and the Nature of “Anomalous” Optical Absorption in ZnGeP2. V.N.Brudnyĭ, V.G.Voevodin, S.N.Grinyaev: Physics of the Solid State, 2006, 48[11], 2069-83