Defect characterization in ZnGeP2 by time-resolved photoluminescence
The native defect-related optical properties of ZnGeP2 are studied by steady-state and time-resolved photoluminescence. ZnGeP2 crystals grown from the vapor phase by high pressure physical vapor transport (HPVT) and from the melt by gradient freezing (GF) show a broad infrared emission with peak position at 1.2 eV with a decay time constant of a few micro-s and a faster recombination center peaked at 1.68 eV. The decay transient for the emission at 1.2 eV exhibits features of classical donor-acceptor recombination and is linked to close-pairs that are tentatively associated with germanium-on-zinc antisite donors and zinc vacancy acceptors. Higher energetic luminescence structures at 1.6eV and 1.7eV are revealed after annealing of the ZnGeP2 crystals and are associated with the formation zinc and phosphorous vacancies in the near surface region. ZnGeP2 crystals grown by HPVT from zinc and phosphorus supersaturated vapor compositions show additional emission structure at 1.8 eV and a sharp donor-acceptor emission at 1.778 eV that is related to the presence of additional donor states.