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

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.

InGaN-based red light-emitting diodes: from traditional to micro-LEDs

“…76,77) Also, a bottom-up selective growth method to form μLED mesas was able to avoid the generation of non-radiative recombination centers on the sidewalls. 78) As a result, InGaN blue μLEDs are demonstrated to have remarkable performance even when the device dimension decreases to 10 μm or less. 79,80) However, extending the emission wavelength to the red region to realize InGaN red μLEDs is still challenging.…”

Investigation of InGaN-based red/green micro-light-emitting diodes

“…This method can easily integrate RGB colors into matrices on the same substrate [7], yet the colorconversion efficiency of hybrid devices must be improved [8]. Another approach chooses to fabricate red and green µLEDs using different materials, AlInGaP for red µLEDs [9] and InGaN for green µLEDs [10]. This material difference causes a mismatched angular distribution between the red and green µLEDs [11], leading to a noticeable color shift at different observed angles.…”

606-nm InGaN Amber Micro-Light-Emitting Diodes With an On-Wafer External Quantum Efficiency of 0.56%

“…reliability, many studies have reported that the external quantum efficiency (EQE) of InGaN µLEDs decreases with chip size [3][4][5]. This size dependence of the EQE was caused by the non-radiative recombination at the edge of the device active region [6][7][8], which could be eliminated or avoided by using a combination of chemical treatment and atomic-layer deposition sidewall passivation [9] or the bottom-up growth method to form µLED mesas [10].…”