NATIVE DEFECT RELATED OPTICAL-PROPERTIES OF ZNGEP2

We present photoluminescence, photoconductivity, and optical absorptio n spectra for ZnGeP2 crystals grown from the melt by gradient freezing and from the vapor phase by high pressure physical vapor transport (H PVT). A model of donor and acceptor related subbands in the energy gap of ZnGeP2 is introduced that explains the experimental results. The e mission with peak position at 1.2 eV is attributed to residual disorde r on the cation sublattice. The lower absorption upon annealing is int erpreted in terms of both the reduction of the disorder on the cation sublattice and changes in the Fermi level position. The n-type conduct ivity of ZnGeP2 crystals grown under Ge-deficient conditions by the HP VT is related to the presence of additional donor states. (C) 1994 Ame rican Institute of Physics.