Enhancement in external quantum efficiency of AlGaInP red \u03bc-LED using chemical solution treatment process

Byung Oh Jung,Myungshin Choi,Hui-Youn Shin,Yoon-Ho Choi,Moon J Kim,Wonyong Lee,Minho Joo,Jeomoh Kim,Sukkoo Jung

doi:10.1038/s41598-021-83933-3

Byung Oh Jung, Myungshin Choi + Show 7 more

Open Access

https://doi.org/10.1038/s41598-021-83933-3

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Abstract

To investigate the effects of their surface recovery and optical properties, extremely small sized (12 µm × 12 µm mesa area) red AlGaInP micro light emitting diodes (upmu LED) were fabricated using a diluted hydrofluoric acid (HF) surface etch treatment. After the chemical treatment, the external quantum efficiencies (EQEs) of upmu-LED at low and high injection current regions have been improved by 35.48% and 12.86%, respectively. The different phenomena of EQEs have a complex relationship between the suppression of non-radiative recombination originating from the etching damage of the surface and the improvement of light extraction of the sidewalls. The constant enhancement of EQE at a high injection current it is attributed to the expansion of the active region’s sidewall surface area by the selective etching of AlInP layers. The improved EQE at a low injection current is related to the minimization of the surface recombination caused by plasma damage from the surface. High-resolution transmission electron microscopy (HR-TEM) revealed physical defects on the sidewall surface, such as plasma-induced lattice disorder and impurity contamination damage, were eliminated using chemical treatment. This study suggests that chemical surface treatment using diluted HF acid can be an effective method for enhancing the upmu-LED performance.

Highlights

High-brightness RGB full-color light-emitting diodes (LEDs) with low energy consumption and high efficiency are required for display devices
The epi structure of μ-LEDs consisted of a GaInP etching stop layer (ESL), n+-AlGaInP contact layer, n-cladding AlInP, AlGaInP active layers including a number of multiple quantum wells (MQWs), a thin AlInP layer with high Al content, p-cladding AlInP, AlGaInP tensile strain barrier reducing (TSBR) layer, magnesium-doped p-GaP windows layer, and p+-GaP:C ohmic contact layer
This etching behavior depending on the aluminum content can play a vital role in enhancing the light emission efficiency in μ-LEDs, which will be discussed in detail of this article

Summary

Introduction

High-brightness RGB full-color light-emitting diodes (LEDs) with low energy consumption and high efficiency are required for display devices. Several approaches have been proposed to improve the light emission efficiency of AlGaInP-based LEDs through the various designs of the chip g eometry[6], wafer bonding technique[7], surface texture with a patterned structure[8,9], and self-assembled (or embedded) nano-architecture[10,11,12] Their efforts mainly focus on the improvement of the light extraction efficiency (LEE) to enhance the external quantum efficiency (EQE) of the LEDs because it is difficult for photons to escape into the air from a semiconductor with a high-refractive-index. Surface recombination has a detrimental influence on the efficiency of AlGaInP-based μ-LEDs owing to the relatively enhanced non-radiative recombination at the sidewalls of the active region as the chip size is reduced[15] For these reasons, to achieve a high light emission efficiency, the red emission of μ-LEDs in particular must be obtained through a high LEE and minimized emission losses from the elimination of the surface recombination. The EQE of the red emission improved by over 30%

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