Investigation of structural and optical anisotropy of m-plane InN films grown on gamma-LiAlO(2)(100) by metal organic chemical vapour deposition

In this paper a systematic investigation of structural and optical anisotropy of m-plane InN film grown on gamma-LiAlO(2)(1 0 0) substrate by metal organic chemical vapour deposition, which is believed to be much more difficult than molecular beam epitaxy, is presented. The InN film showed pure m-plane phase as confirmed by x-ray diffraction omega/2 theta scan together with polarized Raman spectroscopy. The epitaxial relationship between the m-plane InN and the substrate was found to be [0 0 0 1](InN) parallel to [0 1 0](LAO) and [1 1 - 2 0](InN) parallel to [0 0 1](LAO). The inherent film mosaic anisotropy was studied by x-ray rocking curve analysis. Atomic force microscopy revealed that stripe-like features appear on the surface of the m-plane InN film, which originated from the replication of the surface morphological anisotropy of the substrate. Scanning electron microscopy showed blocky surface structures that were indicative of three-dimensional growth mode, which was related to the anisotropic structural mismatch of the film and the foreign substrate. A small direct band gap of similar to 0.7eV of the m-plane InN film was confirmed by low-temperature photoluminescence spectra, which showed evident polarization anisotropy in terms of both intensity and peak energy. Finally, a blue-shift of absorption edge as compared with the photoluminescence peak energy was observed and fully accounted for by the Burstein-Moss effect.