Optical properties of InGaN grown by MOCVD on sapphire and on bulk GaN

Experimental data on photoluminescence of various bulk and quantum-well epitaxial InGaN/GaN structures grown by MOCVD are interpreted in terms of a band-tail model of inhomogeneously broadened radiative recombination. The anomalous temperature-induced blue spectral is shown to result from band-tail recombination under non-degenerate conditions. Significant differences are observed between epilayers grown on sapphire substrates and on GaN substrates prepared by the sublimination method, with no apparent evidence of band tails in homoepitaxial structures, indicating their higher crystalline quality.