Abstract

The fabrication of nanoporous (NP) GaN is proposed as a generic technique to create out-of-plane index guiding for nitride microcavities. Compared to the conventional undercut technique, the proposed technique forms uniformly a low-index NP-GaN layer beneath the entire microcavity. Therefore, it supports all cavity modes (with different cavity geometries), while the undercut technique only supports the modes that reside at the circumference of a circular microcavity. As a proof of concept, GaN microdisk cavities were fabricated with the NP-GaN as the bottom low-index medium. A cold cavity with $Q>\mathrm{2,000}$ was reported under continuous-wave pumping. Lasing was demonstrated with threshold optical pumping power $P_{\mathrm{th}}\sim 60\mathrm{kW}/{\mathrm{cm}}^2$ for the $r=10\mathrm{\mu m}$ microdisk and $P_{\mathrm{th}}\sim 7\mathrm{kW}/{\mathrm{cm}}^2$ for the $r=50\mathrm{\mu m}$ microdisk. A rate equation analysis was performed to estimate the spontaneous coupling factor $\beta \sim 1\mathrm{E}\text{-}3$, which was one order of magnitude higher than the previous report of a nitride microdisk laser with an InGaN quantum well active region. Therefore, NP GaN was proven to be a suitable replacement of the undercut technique for future nitride microcavities applications.

© 2018 Optical Society of America

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