Advances in III-nitride semiconductor microdisk lasers

This paper reviews the recent progress in the design and fabrication strategies of III-nitride semiconductor microdisk lasers on sapphire or Si substrates. Involving more accurate lithography methods in the fabrication boosts quality factors (Q-factors) due to the improved optical confinement of whispering-gallery modes (WGMs) at the rim of the microdisks with smooth sidewalls and perfect circularity. Quantum dots (QDs) as gain medium within the microdisks are investigated and promising for the demonstration of micro-lasers with super-high Q-factors and ultra-low thresholds. And these QD-cavity systems are also facilitating the research of cavity quantum electrodynamics (QED) in the strong coupling regime and cavity-enhanced single photon emission (SPE) for quantum computing. In this paper, we also report successful fabrication of transferred GaN free-standing microdisks with InGaN quantum wells (QWs) on conductive substrates, which achieves a significant step forward to realize electrically pumped high-quality microdisk lasers on target substrates. Strategies of applying flexible transparent electrodes such as graphene and metallic nanowires are potential effective solutions for realizing current-injection of nitride-based microdisks.