Comparison of lasing characteristics of GaN microdisks with different structures

Abstract

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 8µm whispering-gallery mode (WGM) microdisks with different degrees of optical confinement. The microdisks have lasing thresholds ranging from 2.1 to 8.3 mJ/cm2 and quality factors of 1400 to 4200. The lasing characteristics are correlated to the material qualities, optical confinement as well as the overlap of the mode with the MQWs 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.

Enhancing Optical Confinement of InGaN Thin-Film Microdisk Lasers with Hybrid Omnidirectional Reflectors

“…Multimode lasing is expected for an 8-μm diameter GaN microdisk based on both theory , and our previous experimental observations. − However, single-mode lasing is observed under a low excitation power, which remains dominant until it reaches saturation. This is attributed to spatial hole burning (SHB), where the mode with the highest gain depletes all the inverted carriers near the mode’s antinodes within the resonant cavity .…”

“…To address these issues, thin-film GaN microdisks have been developed utilizing wafer bonding, substrate removal, and thinning techniques, ,− enabling optimization of the microdisk thickness without altering the growth process to maintain the high internal quantum efficiency (IQE) of InGaN/GaN multiquantum wells (MQWs). In this approach, the metallic bonding layer serves as the bottom mirror to provide optical confinement for the microdisks.…”

“…In this approach, the metallic bonding layer serves as the bottom mirror to provide optical confinement for the microdisks. However, compared to the undercut structure, the lasing threshold and Q factor of these thin-film microdisks with metallic mirrors did not improve significantly due to strong optical absorption of the metal . A previous study explored the utilization of epitaxial 25-pair AlN/AlGaN distributed Bragg reflector (DBR) instead of the undercut structure to achieve optical isolation from the substrate, realizing an optical-pumped ultraviolet GaN microdisk laser with a Q factor of approximately 400 .…”

III-Nitride Materials: Properties, Growth, and Applications

“…Microdisk lasers are promising light sources in photonic integrated circuits [47]. The threshold, quality, and other properties are gradually being improved [47][48][49][50][51][52].…”