Martinez de Arriba Guillem, Feng Peng, Xu Ce, Zhu Chenqi, Bai Jie, Wang Tao
Department of Electronic and Electrical Engineering, The University of Sheffield, Sheffield S1 3JD, United Kingdom.
ACS Photonics. 2022 Jun 15;9(6):2073-2078. doi: 10.1021/acsphotonics.2c00221. Epub 2022 May 27.
III-nitride semiconductors and their heterojunctions exhibit intrinsic polarization due to the asymmetry of their wurtzite structure, which determines all the fundamental properties of III-nitride optoelectronics. The intrinsic polarization-induced quantum-confined Stark effect leads to an emission wavelength shift with increasing injection current for III-nitride visible LEDs, forming an insurmountable barrier for the fabrication of a full color display. For instance, a yellow LED designed to produce yellow light emits green or blue light at an elevated current, while a green (blue) LED gives off blue (violet) light with increasing current. This color instability becomes a serious issue for a microdisplay such as the displays for augmented reality (AR)/virtual reality (VR) typically utilized at proximity to the eye, where human eyes are sensitive to a tiny change in light color. It is well-known that an optical mode wavelength for a microcavity is insensitive to injection current. In this work, we have demonstrated an approach to epitaxially integrating microLEDs (green microLEDs as an example, one of the key components for a full color microdisplay) and a microcavity. This allows the emission from the microLEDs to be coupled with the microcavity, leading to a negligible emission wavelength shift with increasing injection current. In contrast, identical microLEDs but without a microcavity show a large emission wavelength shift from 560 nm down to 510 nm, measured under identical conditions. This approach provides a simple solution to resolving the 30-year issue in the field of III-nitride optoelectronics.
由于纤锌矿结构的不对称性，III族氮化物半导体及其异质结表现出固有极化，这决定了III族氮化物光电子学的所有基本特性。固有极化诱导的量子限制斯塔克效应导致III族氮化物可见光发光二极管的发射波长随注入电流增加而发生偏移，这对全彩色显示器的制造形成了一个无法克服的障碍。例如，设计用于发出黄光的黄色发光二极管在电流升高时会发出绿光或蓝光，而绿色（蓝色）发光二极管随着电流增加会发出蓝色（紫色）光。这种颜色不稳定性对于诸如增强现实（AR）/虚拟现实（VR）显示器这类通常在人眼附近使用的微型显示器来说是一个严重问题，因为人眼对光颜色的微小变化很敏感。众所周知，微腔的光学模式波长对注入电流不敏感。在这项工作中，我们展示了一种将微型发光二极管（以绿色微型发光二极管为例，它是全彩色微型显示器的关键组件之一）和微腔进行外延集成的方法。这使得微型发光二极管的发射能够与微腔耦合，从而在注入电流增加时发射波长偏移可忽略不计。相比之下，在相同条件下测量，相同的但没有微腔的微型发光二极管显示出发射波长从560纳米大幅偏移至510纳米。这种方法为解决III族氮化物光电子学领域长达30年的问题提供了一个简单的解决方案。
