Electrically injected whispering-gallery mode InGaN/GaN microdisks

The combination of high-quality factors and small mode volumes in whispering-gallery-mode (WGM) resonators promotes significantly enhanced light-matter interactions, making them excellent cavities for achieving compact semiconductor lasers with low threshold and narrow linewidth. However, success in developing GaN-based WGM lasers has been extremely limited due to the complicated design and fabrication of both high-finesse optical cavities and effective efficient injection schemes. Here, we report on WGM emission from vertical-injection blue-light emitting InGaN/GaN thin-film microdisks achieved by wafer bonding and laser liftoff removal of the sapphire substrate. The observed WGMs, identified as a combination of first order and higher order modes with the aid of finite-difference time-domain simulations, have Q-factors as high as 3700. This work presents a viable approach toward the practical implementation of compact InGaN/GaN microdisk lasers through a simple and scalable process.