Influence of surface roughness on the lasing characteristics of optically pumped thin-film GaN microdisks

Optically pumped whispering-gallery mode (WGM) lasing is observed from a thin-film GaN microdisk processed from GaN-on-Si InGaN/GaN multi-quantum well wafers by selective wet-etch removal of the substrate. Compared with thin-film microdisks processed from GaN-on-sapphire wafers through laser lift-off of the sapphire substrate, the exposed surface is significantly smoother as laser-induced damage is avoided, with a root-mean-square roughness of 1.3 nm compared with 5.8 nm of the latter wafer. The similar to 8-mu m diameter microdisks, fabricated by pattern transfer from a silica microsphere and dry etching, benefit from the surface smoothness to offer superior optical confinement within the cavity. WGM lasing thresholds of similar to 2.9 mJ/cm(2) and similar to 3.5 mJ/cm(2) with quality (Q)-factors of similar to 3100 and similar to 1700 are observed at the peak lasing wavelengths of similar to 453 nm and similar to 532 nm, respectively, which are significantly better than thin-film microdisks processed from GaN-on-sapphire wafers despite lower internal quantum efficiency, highlighting the importance of surface smoothness in such optical cavities. (C) 2022 Optica Publishing Group

Automated summary

Optically pumped whispering-gallery mode (WGM) lasing is observed from a thin-film GaN microdisk processed from GaN-on-Si InGaN/GaN multi-quantum well wafers by selective wet-etch removal of the substrate. The surface smoothness of the microdisk is significantly improved compared to those processed from GaN-on-sapphire wafers through laser lift-off. The improved surface smoothness contributes to superior optical confinement and better lasing performance.