Crystals with various dislocation densities were characterized by micro-Raman spectroscopy. Defects and strain for the GaN layer were examined via measurements of the Raman shift and the width of the TO phonon bands. The broadening of Raman bands in GaN crystals occurred as the dislocation density increased. The up-shift of the peak frequencies corresponding to compressive strain was observed for the hetero-epitaxial samples grown by metal organic chemical vapour deposition and molecular beam epitaxy. The in-plane distribution of defects and strain in epilayers with various dislocation densities was also examined by Raman mapping. The Raman maps showed that the examined phonon frequency and band width in samples fluctuated spatially. The increase of dislocation density in GaN epilayers induced not only the broadening of Raman bands but also increase of fluctuation.

Raman Scattering Analysis of GaN with Various Dislocation Densities. T.Kitamura, S.Nakashima, N.Nakamura, K.Furuta, H.Okumura: Physica Status Solidi C, 2008, 5[6], 1789-91