Characterization of HVPE GaN layers by atomic force microscopy and Raman spectroscopy

GaN layers were deposited on (0001) sapphire by hydride vapour phase epitax y (HVPE) and then extensively characterized by Raman spectroscopy and atomi c force microscopy. It was observed that the GaN epilayers directly deposit ed on sapphire generally have rough surfaces, mostly made of pyramids. The Raman scattering technique was found to be a powerful tool for quick and no n-destructive assessment of the crystallographic quality of HVPE GaN, altho ugh care must be taken in the spectra analysis as the surface morphology ca n affect the spectra structure. The absence of forbidden modes indicate tha t the surface is planar and smooth and the material is of good crystalline quality. A discussion on the observed red-shift of the A(1) (LO) mode frequ ency is presented.