Sidewall Repair Improves Optical Power Density of 237 nm AlGaN-Based Micro-LEDs

doi:10.16553/j.cnki.issn1000-985x.2024.0274

Abstract

Abstract: AlGaN-based deep ultraviolet Micro-LEDs have important applications in maskless lithography， deep ultraviolet non-line-of-sight communication and other fields. However， the sidewall effect and current crowding effect seriously restrict the optical power density of Micro-LEDs under high current density. In this work， 237 nm deep ultraviolet Micro-LEDs with mesa radiuses of 12.5， 25.0 and 50.0 μm were prepared， and the effects of sidewall repair on different sized and different arrayed Micro-LEDs were systematically studied. It is revealed that KOH solution effectively reduces the sidewall defect density of AlGaN-based deep ultraviolet Micro-LEDs， and contributes to a lower reverse leakage current density and Shockley-Read-Hall （SRH） non-radiative recombination caused by these sidewall defects. For single mesa devices， a smaller sized device owns a higher maximum optical power density， but the sidewall effect seriously restricts the optical power density of the smaller sized device， resulting in the lowest optical power density of the 12.5 μm sized device at low current density. After sidewall repair， the peak optical power density of the 12.5 μm sized device increases by 186%， and the optical power density is the highest at all current density range. For arrayed devices with an identical mesa area， after the sidewall repair， a bigger matrix contributes to a higher optical power density. The peak optical power density of the 4×4 arrayed 12.5 μm sized Micro-LED increases by 116% compared to the 50 μm sized device. The underlying reason is that a bigger matrix can improve the uniformity of current density distribution and the light efficiency while maintaining low sidewall defects. This study is helpful to improve the optical power density of Micro-LEDs and will promote the practical application of short-wavelength deep ultraviolet Micro-LEDs.

Key words: sidewall effect; current crowding effect; AlGaN micro-LED; sidewall repair; array engineering

CLC Number:

TN312⁺.8

HAO Jialong, LI Hongbo, LYU Shunpeng, ZHU Licai, SUN Wenchao, ZHANG Ruojia, LIU Zhongxu, JIANG Ke, BEN Jianwei, ZHANG Shanli, SUN Xiaojuan, LI Dabing. Sidewall Repair Improves Optical Power Density of 237 nm AlGaN-Based Micro-LEDs[J]. Journal of Synthetic Crystals, 2025, 54(6): 970-978.

Figures/Tables 6

Fig.1 （a） Schematic diagram of the epitaxial layer structure；（b）~（d） schematic diagrams of Micro-LED structures；（e） optical microscope image of Micro-LED；（f） electroluminescence （EL） spectra of the epitaxial layers

Table 1 Basic information of Micro LED

Sample	Mesa radius/μm	Matrix	p-contact radius/μm
S1	12.5	1×1	7.5
S2	25.0	1×1	20.0
S3	50.0	1×1	45.0
S4	25.0	2×2	20.0
S5	12.5	4×4	7.5

Fig.2 Current density-voltage characteristic curves of S1， S2， S3 before （a） and after （b） the sidewall repair； optical power density-current density characteristic curves of S1， S2， S3 before （c） and after （d） the sidewall repair

Fig.3 Simulation results of Micro-LEDs of different sizes （without considering sidewall effects）. （a） Current density-voltage characteristic curves；（b） optical power density-current density characteristic curves；（c） relationship curves between IQE and current density；（d） lateral distribution of carrier concentration in the quantum wells （the small inset in the figure is a schematic diagram of the data extraction position）

Fig.4 Schematic diagram of the device current path. （a） Single mesa；（b） arrayed mesa

Fig.5 Current density-voltage characteristic curves of S3， S4， S5 before （a） and after （b） sidewall repair； optical power density-current density characteristic curves of S3， S4， S5 before （c） and after （d） sidewall repair

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