Optical gain dynamics in InGaN/InGaN quantum wells

Stimulated emission dynamics in InGaN-based multiple quantum wells (MQWs) is analyzed. The lasing threshold measurements of the In0.09Ga0.91N/In0.02Ga0.98N MQWs revealed non-monotonous threshold dependence on the growth temperature of the active MQW region. The optimal growth temperature range with the lowest stimulated emission threshold (100 kW/cm2) in the active region was found to be 780 - 800°C. The influence of indium nano-clusters on stimulated emission threshold is discussed. Optical gain in InGaN MQWs was measured using variable excitation stripe length technique. The optical gain dependence on excitation stripe length and excitation power density was studied. The onset of the gain saturation was observed on the high energy side of the stimulated emission peak. The onset exhibited red-shift with increasing stripe length due to reduced electron-hole density caused by high optical transition rate. Increase of excitation power density resulted in the strong blue-shift of the optical gain spectra. The maximal optical gain coefficient values of 200 cm-1 and 300 cm-1 were obtained for the samples with the lowest and the highest stimulated emission thresholds, respectively. The calculated optical confinement factor (3.4 %) for the samples yielded the net gain coefficient of about 5900 cm-1 and 8800 cm-1, respectively