Investigation of structural and optical anisotropy of m-plane InN films grown on γ-LiAlO2(1 0 0) by metal organic chemical vapour deposition

Abstract

In this paper a systematic investigation of structural and optical anisotropy of m-plane InN film grown on γ-LiAlO2(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 ω/2θ 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 ∥ [0 1 0]LAO and [1 1 − 2 0]InN ∥ [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 ∼0.7 eV 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.