Resonant raman scattering as a selective probe for compositional inhomogeneity in low In content (InGa)N

Raman spectroscopy has been used to study compositional inhomogeneity in MOCVD grown In(x)Ga(1-x)N with x about 0.1, taking advantage of the selective enhancement of Raman scattering by the A1 (LO) phonon from regions with different alloy composition. A clear high- frequency shift of the A1(LO) mode relative to the E2 mode is observed, when the experimental conditions are varied from excitation below the fundamental energy gap of the (InGa)N to above band gap excitation. This frequency shift is taken as direct evidence for compositional inhomogeneity, which results in localised regions with different In content, and thus different gap energies and A1(LO) phonon frequencies.