Modulation of anisotropic crystalline in a-plane GaN on HT-AlN buffer layer

(image) a-plane gallium nitride has been investigated by Raman spectroscopy and X-ray diffraction. Strains of a-plane GaN grown on LT-GaN nucleation layer were both compressive along [image] and [0 0 0 2] orientations. However, strains of GaN epitaxied on HT-AlN buffer were tensile along [0 0 0 2] and compressive along [image] GaN orientation. The crystalline anisotropy and quality were also improved by the HT-AlN layer. Atomic force microscopy was utilized for analyzing the HT-AlN buffer layer. We ascribed this divergence of strain and improvement of crystalline to the thermal expansion and lattice mismatch effects of HT-AlN buffer during the metalorganic vapor phase epitaxy.