(a) Emission spectra of the semi-polar overgrown GaN measured as a function of an optical pumping density from 130 to 1100 kW/cm²; (b) Integrated intensity and line-width of the stimulated emission as a function of an optical pumping density. Inset of (b): Integrated intensity of a stimulated emission as a function of an optical pumping density measured on a standard c-plane GaN sample grown on sapphire for comparison.