Mechanisms for spontaneous and stimulated recombination in multiple quantum wells of InGaN/GaN heterostructures on silicon substrates

With the aim of establishing the mechanisms for spontaneous recombination and lasing, we have studied InGaN/GaN multiple quantum well heterostructures emitting in the 450 nm region and grown by organometallic vapor-phase epitaxy on silicon substrates using several mechanical stress-reducing AlN/AlGaN inserts. Photoluminescence (PL) excitation spectroscopy, the non-monoexponential nonequilibrium carrier relaxation kinetics, and x-ray diffractometry data indicate significant inhomogeneity of the InGaN solid solution in quantum wells of these structures. The dependences of the position of the photoluminescence spectra on the excitation level and the temperature, the large shift in the photoluminescence, gain, and lasing spectra relative to the absorption edge allow us draw the conclusion that the dominant contribution to spontaneous and stimulated recombination comes from nonequilibrium charge carriers localized in indium-rich InGaN clusters.