Opt Lett. 2018 Nov 15;43(22):5567-5570. doi: 10.1364/OL.43.005567.
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>2,000 was reported under continuous-wave pumping. Lasing was demonstrated with threshold optical pumping power P∼60 kW/cm for the r=10 μm microdisk and P∼7 kW/cm for the r=50 μm microdisk. A rate equation analysis was performed to estimate the spontaneous coupling factor β∼1E-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.
提出了纳米多孔（NP）GaN 的制造方法，作为在氮化镓微腔中产生面外折射率引导的通用技术。与传统的刻蚀技术相比，所提出的技术可以在整个微腔下方均匀形成低折射率的 NP-GaN 层。因此，它支持所有腔模式（具有不同的腔几何形状），而刻蚀技术仅支持位于圆形微腔圆周上的模式。作为概念验证，使用 NP-GaN 作为底部低折射率介质制造了 GaN 微盘腔。在连续波泵浦下，报道了具有 Q>2000 的冷腔。对于 r=10 μm 的微盘，阈值光泵浦功率 P∼60 kW/cm 下实现了激光激射，对于 r=50 μm 的微盘，阈值光泵浦功率 P∼7 kW/cm 下实现了激光激射。进行了速率方程分析以估计自发耦合因子 β∼1E-3，这比具有 InGaN 量子阱有源区的氮化镓微盘激光器的先前报告高一个数量级。因此，NP GaN 被证明是未来氮化镓微腔应用中刻蚀技术的合适替代品。
