Raman Scattering Study of InGaN Grown by Metalorganic Vapor Phase Epitaxy on (0001) Sapphire Substrates

We have studied the asymmetric broadening of the Raman spectra of In x Ga 1- x N grown on sapphire substrates with the aid of the spatial correlation model. The asymmetric broadening of the E 2 phonon mode is enhanced in the region of immiscibility by increasing the indium molar fraction. The correlation length, which corresponds to the decay length of the E 2 phonon mode, was estimated for the first time. It was on the order of 6–10 nm, which is on the same order of magnitude as the size of the columnar structure suggested by transmission electron microscope analyses.