Synthesis and characterization of ZnGeN2 grown from elemental Zn and Ge sources

Polycrystalline ZnGeN2 was synthesized by a new method, via vapor growth from Zn and Ge with thermal cracking of NH3. Measured lattice parameters indicate a monoclinic structure with a=b=0.3157±0.0024 nm, c=0.5137±0.0021 nm, and γ=119°30′±22′, consistent with previous reports. Planar stacking faults lying on the (0 0 1) plane were identified by transmission electron microscopy. Analysis indicates that these stacking faults are bound by a prismatic dislocation loop having in-plane and out-of-plane Burgers vector components of (a/3[1 1¯ 0]) and (c/2[0 0 1]), respectively. Photoluminescence spectroscopy at low temperature (∼4 K) showed broad “yellow-band” impurity luminescence centered around 2.6 eV and a narrower near-band-edge luminescence peak at 3.40±0.01 eV. The near-band-edge luminescence peak is higher in energy by approximately 50 meV, and higher in efficiency by at least two orders of magnitude than any previously reported. These observations indicate that this material has superior optical quality than previously obtained by other growth methods. The temperature dependence of the near-band-edge luminescence efficiency is consistent with excitons bound to a shallow donor band.