Ultrasmall, Ultracompact and Ultrahigh Efficient InGaN Micro Light Emitting Diodes (μLEDs) with Narrow Spectral Line Width

Jie Bai,Tao Wang,Peter Fletcher,Ye Tian,Chenqi Zhu,Yuefei Cai,Peng Feng

doi:10.1021/acsnano.0c01180

Abstract

Augmented reality and visual reality (AR and VR) microdisplays require micro light emitting diodes (μLEDs) with an ultrasmall dimension (≤5 μm), high external quantum efficiency (EQE), and narrow spectral line width. Unfortunately, dry etching which is the most crucial step for the fabrication of μLEDs in current approaches introduces severe damages, which seem to become an insurmountable challenge for achieving ultrasmall μLEDs with high EQE. Furthermore, it is well-known that μLEDs which require InGaN layers as an emitting region naturally exhibit significantly broad spectral line width, which becomes increasingly severe toward long wavelengths such as green. In this paper, we have reported a combination of our selective overgrowth approach developed very recently and epitaxial lattice-matched distributed Bragg reflectors (DBRs) embedded in order to address all these fundamental issues. As a result, our μLEDs with a diameter of 3.6 μm and an interpitch of 2 μm exhibit an ultrahigh EQE of 9% at ∼500 nm. More importantly, the spectral line width of our μLEDs has been significantly reduced down to 25 nm, the narrowest value reported so far for III-nitride green μLEDs.

Highlights

Augmented reality and visual reality (AR and VR) microdisplays require micro light emitting diodes with an ultrasmall dimension (≤5 μm), high external quantum efficiency (EQE), and narrow spectral line width
This is important for AR/VR microdisplays which require μLEDs with an ultrasmall diameter (≤5 μm), high external quantum efficiency (EQE), and narrow spectral line width
A standard photolithography technique combined with subsequent dry-etching processes remains a typical approach to the fabrication of μLEDs, in particular μLEDs with a small diameter (≤50 μm).[6−11] this approach unavoidably introduces severe damage induced during dry-etching and follow-up processes, significantly enhancing nonradiative recombination and severely degrading the optical performance.[12−17] This issue becomes increasingly severe with decreasing the dimension of μLEDs.[13,14,18,19]

Summary

Introduction

Augmented reality and visual reality (AR and VR) microdisplays require micro light emitting diodes (μLEDs) with an ultrasmall dimension (≤5 μm), high external quantum efficiency (EQE), and narrow spectral line width. Dry etching which is the most crucial step for the fabrication of μLEDs in current approaches introduces severe damages, which seem to become an insurmountable challenge for achieving ultrasmall μLEDs with high EQE It is well-known that μLEDs which require InGaN layers as an emitting region naturally exhibit significantly broad spectral line width, which becomes increasingly severe toward long wavelengths such as green. There is a significant growing interest in developing IIInitride microLEDs (μLEDs), the key components for microdisplays which are crucial for smart phones, smart watches, and augmented reality and visual reality (AR and VR) devices.[1−5] These kinds of devices are typically utilized in small spaces or at close proximity to the eye, and it requests that μLEDs exhibit high resolution and high luminance This is important for AR/VR microdisplays which require μLEDs with an ultrasmall diameter (≤5 μm), high external quantum efficiency (EQE), and narrow spectral line width. The intrinsically broad spectral line width of μLEDs will have to be significantly reduced

Methods

Results

Conclusion