Correlations between spatially resolved Raman shifts and dislocation density in GaN films

Abstract

Spatially resolved Raman spectra were measured on thick GaN samples with known dislocation density grown by hydride vapor phase epitaxy. The frequencies of the E2 (high) and E1 (transverse optical) phonons shift to lower wave number over a distance of 30 μm from the sapphire substrate/GaN interface. The shifts are linearly correlated with the dislocation density suggesting that the strain due to the lattice mismatch at the interface determines both quantities.