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.

中文翻译：

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纳米多孔GaN覆层实现的InGaN / GaN微盘

提出了纳米孔（NP）GaN的制造方法，以创建用于氮化物微腔的面外折射率引导的通用技术。与传统的底切技术相比，所提出的技术在整个微腔下方均匀地形成了低折射率的NP-GaN层。因此，它支持所有腔模式（具有不同的腔几何形状），而底切技术仅支持驻留在圆形微腔周围的模式。作为概念证明，以NP-GaN作为底部低折射率介质制造了GaN微盘腔。冷腔$问>\mathrm{2,000}$据报道是在连续波抽水下。通过阈值光泵浦功率演示了激光发射$P_{日}〜60\mathrm{千瓦}/{\mathrm{厘米}}^{\mathrm{2个}}$ 为了 $\mathrm{[R}=10\mathrm{微米}$ 微型磁盘和 $P_{日}〜7\mathrm{千瓦}/{\mathrm{厘米}}^{\mathrm{2个}}$ 为了 $\mathrm{[R}=50\mathrm{微米}$微型磁盘。进行速率方程分析以估计自发耦合因子$\beta 〜\mathrm{1个}\mathrm{E}\text{--}3$，比先前报道的具有InGaN量子阱有源区的氮化物微盘激光器高一个数量级。因此，对于未来的氮化物微腔应用，已证明NP GaN是底切技术的合适替代品。