MOCVD growth of ZnGeN2 films on sapphire

Heterovalent ternary ZnGeN2 thin films were grown on c-, r- and a-sapphire substrates using metalorganic chemical vapor deposition. The crystal structure of the films was identified by X-ray diffraction spectroscopy. It is consistent with orthorhombic Pna21 assuming perfect ordering of the cations. For a fully disordered cation sublattice, the X-ray diffraction spectra correspond to a wurtzitic crystal. The growth directions were determined to be along the c- axis for the films grown on c- and a-sapphire substrates, and along the orthorhombic [010] axis (wurtzite [11-20]) for films grown on r-sapphire substrates. The Zn/Ge atomic ratios, determined by energy dispersive X-ray spectroscopy, were observed to decrease as growth temperatures were increased. Growth rates for all substrates decreased by approximately 10% with changes in growth temperatures from 600 °C to 710 °C. Broad photoluminescence peaks at ~2.05 eV were observed at room temperature. These are associated with transitions involving deep level...