Suppression mechanism of optical gain formation in InxGa1−xN quantum well structures due to localized carriers

We have studied the optical gain and its suppression mechanism of InxGa1−xN multiple quantum well structures with different indium compositions. The variable stripe length method and the up-conversion method were employed in this research. It was found that the optical gain spectra became broad and the differential gain decreased with increasing the indium composition. These results indicated that inhomogeneous broadening affected not only spontaneous emission but also stimulated emission. The rise time of photoluminescence under a strong excitation condition was changed from 0.95 ps to 12.4 ps depending on the indium composition. Assuming the rise time reflects the relaxation lifetime from the absorption edge energy to population inversion levels, our calculation suggested that long rise times led to gain suppression in InxGa1−xN laser diodes with larger indium compositions.