Comparison of lasing characteristics of GaN microdisks with different structures

The lasing characteristics of optically-pumped GaN microdisks of different configurations, including microdisks with undercuts, microdisks with cladding layers and thin-film microdisks are investigated in this paper. The microdisks, fabricated from a range of epitaxial structures containing blue-light emitting InGaN/GaN multi-quantum wells grown on Si, sapphire or GaN substrates, undergo different processes to form 8 mu m diameter whispering-gallery mode microdisks with different degrees of optical confinement. The microdisks have lasing thresholds ranging from 2.1-8.3 mJ cm(-2) and quality factors of 1400-4200. The lasing characteristics are correlated to the material qualities, optical confinement as well as the overlap of the mode with the multi-quantum wells in the microdisk structures. The undercut microdisks benefit from high optical confinement factors but poor overlap factor, while the thin film structures have high overlap factors but low confinement due to absorption by the metallic bonding layers. The findings provide useful insight on ways to optimize GaN microdisk for improving lasing performances.