Spatially resolved Raman spectra were measured for thick samples, having known dislocation densities, which had been grown by means of hydride vapor phase epitaxy. The frequencies of the E2 (high) and E1 (transverse optical) phonons shifted to a lower wave-number over a distance of 30µm from the substrate(sapphire)/GaN interface. The shifts were linearly correlated with the dislocation density, and it was suggested that the strain due to lattice mismatch at the interface governed both quantities.

Correlations between Spatially Resolved Raman Shifts and Dislocation Density in GaN Films. G.Nootz, A.Schulte, L.Chernyak, A.Osinsky, J.Jasinski, M.Benamara, Z.Liliental-Weber: Applied Physics Letters, 2002, 80[8], 1355-7