Simultaneous edge and surface stimulated emission from AlGaN-based deep ultraviolet laser bars

Simultaneous edge stimulated emission (ESE) and surface stimulated emission (SSE) are reported in AlGaN-based deep ultraviolet (DUV) laser bars under a sufficiently high optical pumping power density. The optical pumping properties of SSE are independent of the cavity length of laser bars and similar to those obtained in a surface-emitting measurement setup for unprocessed laser wafers. The SSE is deduced to stem from the vertical optical resonance within the epilayers. Furthermore, as the growth temperature of the n-cladding layer was increased from 1035 to 1115 ℃, the onset threshold of SSE was reduced by 41%, and the linewidth after stabilization marginally decreased from 1.38 nm to 1.28 nm; while the lasing threshold of ESE in the laser bar with a 1-mm cavity length was reduced by 46%, and the linewidth shrank from 1.15 nm to 0.87 nm. The improved lasing performance is attributed to the lowered internal loss caused by the smoother surface morphology and lower concentration of C_N-related defects in the n-AlGaN cladding layer. The positive correlation between SSE and ESE inspires an efficient approach to improve the performance of DUV lasers by empirically assessing the optical pumping properties of SSE from unprocessed laser wafers.