Effect of the active-layer growth temperature on optical gain and lasing threshold power density in AlGaN-based UV-B lasers

Herein, we investigate the effect of active-layer growth temperature on the optical and lasing characteristics of AlGaN-based ultraviolet (UV)-B laser diodes using a scanning electron transmission electroscope and a photoexcitation method. The results show that when the active-layer growth temperature of the multiquantum well is reduced from 1000 °C to 750 °C, significant improvements in interface steepness, emission linewidth, and optical gain are observed. Specifically, the full width at half maximum value of spontaneous emissions decreases by ∼40%, and the lasing threshold power density exhibits its minimum value at a 775 °C growth temperature, indicating an ∼40% reduction compared with the reference value. However, at 750 °C, the threshold power density value exhibits a slight increase, indicating that an optimal growth window exists near 775 °C. Variable stripe length measurements showed improved gain performance at low excitation power densities. These results demonstrate that optimizing low temperatures for sample growth is an effective strategy for improving the performance of AlGaN-based UV laser diodes.