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+/-0.0024nm, c=0.5137+0.0021nm, and gamma = 119 degrees 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) over bar0]) and (c/2[001]), respectively. Photoluminescence spectroscopy at low temperature (similar to 4 K) showed broad yellow-band impurity luminescence centered around 2.6eV 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. (C) 2008 Elsevier B.V. All rights reserved.