Optical properties of nonpolar aa-plane GaN layers

We have studied optical properties of nonpolar aa-plane GaN layers grown on rr-plane sapphire by metalorganic chemical vapor deposition and hydride vapor phase epitaxy using different nucleation schemes. Several emission bands, which are not typical for cc-plane GaN, are observed in the photoluminescence spectra and their excitation-intensity, temperature, and polarization dependencies are examined. In addition, the spatial distribution of the emissions was examined by cathodoluminescence imaging and relations of the different emissions with particular structural features in the layers are revealed. The results are discussed with emphasis on the origin of the emission line and particular recombination mechanisms.