Theoretical study of cation-related point defects inZnGeP2

Abstract

First-principles calculations are presented for the V Zn and V Ge cation vacancies and the Zn Ge and Ge Zn antisites in ZnGeP 2 , using full-potential linearized muffin-tin orbital method supercell calculations in the local-density approximation to density-functional theory. Under Zn-poor conditions, the lowest Gibbs energy defects are found to be the Ge Zn and V Zn defects, leading to a compensated p-type material in agreement with experimental evidence. The occupation energy levels of the defects are determined and compared with available experimental information. As expected, the Ge Zn is found to be a donor while the other three are acceptors. Good agreement is obtained with optical quenching and activation of electron paramagnetic resonance signal studies if a direct transfer of electrons from V Zn 2− to Ge Zn 2+ is assumed rather than a process via the conduction band. This suggests a close association of the dominant acceptors and donors. This is further confirmed by showing that the formation of complexes consisting of two V Zn − with a single Ge Zn 2+ antisite are favorable in energy. The V Ge on the other hand is found to have high energy of formation under any chemical potential conditions and is found to be unstable toward formation of a V Zn and Zn Ge pair. Structural relaxation of all defects is performed but no symmetry breaking distortions are found. As a result, the defect wave functions of the unpaired electron in the V Zn − is found to be spread equally over the four neighboring P atoms, in disagreement with electron nuclear double resonance data which indicate primary localization on a pair of P atoms. Several possible origins for this discrepancy are discussed.

Study on annealing of infrared nonlinear optical crystal ZnGeP2

“…Both the absorption spectra and photo-induced absorption spectra studies in [5][6][7] and the computer simulation using the pseudo-potential method reached the conclusion that the absorption nearby 2 mm is mainly contributed by Zinc vacancy absorption [18]. Our annealing results also agree with such a conclusion.…”

“…Many studies on the near-infrared absorption have been performed to understand its origin. The defects that result in such absorption in ZGP crystals are probably the zinc vacancy V Zn À , the phosphorus vacancy V P 0 , as well as of group IV anti-site Ge zn þ [5][6][7]. Post thermal annealing experiments have been carried out by several research groups to reduce the near-band-edge absorption [8][9][10][11][12][13][14].…”

Photoluminescence properties of ZnSnP2 single crystals

“…We can tentatively assign the shallower level (50 meV) as an acceptor level and the deeper level (110 meV) as a donor level. Candidates for the donor and acceptor are Sn at Zn sites (Sn Zn ) and Zn vacancy levels (V Zn ), respectively, with an analogy of the defects and impurity levels of ZnGeP 2 reported by Jiang et al [7,8]. However, further studies are required to clarify the origins of the DAP transition.…”

Growth and characterization of ZnGeP2 single crystals by the modified Bridgman method

“…Secondly, ZGP contains toxic and volatile components with high vapor pressure at the melting point (1027 1C) [6], which can lead to deviations from stoichiometry. Thirdly, it is susceptible to stress-induced twinning and cracking during crystal growth process [7,8]. Therefore, it is a challenging work to obtain high-quality ZGP single crystals.…”