Direct Epitaxial Approach to Achieve a Monolithic On-Chip Integration of a HEMT and a Single Micro-LED with a High-Modulation Bandwidth.

Visible light communications (VLC) require III-nitride visible micro-light-emitting diodes (μLEDs) with a high-modulation bandwidth. Such μLEDs need to be driven at a high injection current density on a kA/cm2 scale, which is about 2 orders of magnitude higher than those for normal visible LED operation. μLEDs are traditionally fabricated by dry-etching techniques where dry-etching-induced damages are unavoidable, leading to both a substantial reduction in performance and a great challenge to viability at a high injection current density. Furthermore, conventional biasing (which is simply applied across a p–n junction) is good enough for normal LED operation but generates a great challenge for a single μLED, which needs to be modulated at a high injection current density and at a high frequency. In this work, we have proposed a concept for an epitaxial integration and then demonstrated a completely different method that allows us to achieve an epitaxial integration of a single μLED with a diameter of 20 μm and an AlGaN/GaN high-electron-mobility transistor (HEMT), where the emission from a single μLED is modulated by tuning the gate voltage of its HEMT. Furthermore, such a direct epitaxial approach has entirely eliminated any dry-etching-induced damages. As a result, we have demonstrated an epitaxial integration of monolithic on-chip μLED-HEMT with a record modulation bandwidth of 1.2 GHz on industry-compatible c-plane substrates.

可见光通信（VLC）需要具有高调制带宽的III - 族氮化物可见微发光二极管（μLED）。这种μLED需要在千安/平方厘米量级的高注入电流密度下驱动，这比普通可见发光二极管的工作电流密度大约高两个数量级。μLED传统上是通过干法蚀刻技术制造的，其中干法蚀刻造成的损伤不可避免，这导致性能大幅下降，并且在高注入电流密度下的可行性面临巨大挑战。此外，传统的偏置（简单地施加在p - n结上）对于普通发光二极管的工作来说足够好，但对于单个μLED却带来了巨大挑战，因为单个μLED需要在高注入电流密度和高频下进行调制。在这项工作中，我们提出了一种外延集成的概念，并展示了一种完全不同的方法，该方法使我们能够实现直径为20μm的单个μLED与AlGaN / GaN高电子迁移率晶体管（HEMT）的外延集成，其中单个μLED的发光通过调节其HEMT的栅极电压来调制。此外，这种直接外延方法完全消除了任何干法蚀刻造成的损伤。结果，我们在工业兼容的c面衬底上展示了单片片上μLED - HEMT的外延集成，其调制带宽达到了创纪录的1.2 GHz。