Investigation on reliability of red micro-light emitting diodes with atomic layer deposition passivation layers

Abstract

In this study, AlGaInP red light emitting diodes with sizes ranging from 5 to 50 micrometers were fabricated and characterized. The atomic layer deposition technology is applied to coat a layer of silicon dioxide for passivation and protection. The top emission area is covered by ITO layer to maximize the optical output. From the optical measurement, the linewidth and emission peaks shift very little among different current levels (from 30 to 150 A/cm2). High current level lifetests are performed and a 15 µm ALD device can last 27 hours of continuous operation at 100 A/cm2 before their diode junction failed. A much shorter lifetime of 5.32 hours was obtained when the driving current is raised to 400 A/cm2. When the same condition was applied to 15 µm PECVD devices, 25 hours and 4.33 hours are registered for 100 A/cm2 and 400 A/cm2 tests, respectively. The cross-sectional SEM reveals the voids, defects, and dark lines developed during the aging tests, and most of them are caused by top contact failure. The surface layers of ITO and SiO2 were melted and the dark lines which were originated from the top surface propagated through the device and led to the eventual failure of the diode. The optical intensity degradation slopes of different sizes of devices indicate a large device can last longer in this accelerated aging test. The efficiencies of the devices are also evaluated by the ABC model and the fitted bimolecular coefficient ranges from 1.35 to 3.40×10−10 cm3/s.

Advanced Atomic Layer Deposition Technologies for Micro-LEDs and VCSELs

“…Considering the influence of the passivation protection layer grown by PECVD and ALD on the leakage current, Fig. 3 shows the leakage current diagrams of the red μ-LED after PECVD and ALD passivation protection [ 66 – 68 ]. The average leakage current of the device using ALD is observed to be much lower than that obtained using PECVD.…”

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Fig. 4 Integrated spectral intensity between ALD and PECVD samples under high/low current densities [ 68 ]

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Analysis of Size-Dependent Quantum Efficiency in AlGaInP Micro–Light-Emitting Diodes With Consideration for Current Leakage

“…Thus, several aspects, such as microassembly, mass transfer, epitaxial growth, and electronic circuitry, must be substantially improved [1,2]. A full-color micro-LED display requires red, green, and blue subpixels on the same backplane and various active materials to generate these colors: InGaN for blue and green and AlGaInP or high-In content InGaN for red [3][4][5][6][7][8]. When the resolution of the display is increased for augmented and virtual reality, the size of the red, green, and blue subpixels must be lowered.…”

“…For example, a monochromatic screen with a 2000-pixel-per-inch resolution would require a 12-μm pixel array. For the same resolution in a full-color screen, a sub-10-μm device would be required [6,9]. For InGaN-and GaN-based blue and green materials, devices Yi-Yang Li, Fang-Zhong Lin, Kuo-Lin Chi, Shao-Yi Weng, Guan-Ying Lee are with Institute of Photonic System, College of Photonics, National Yang Ming Chiao Tung University, Tainan City 71150, Taiwan.…”

Colloidal Quantum Dot Enhanced Color Conversion Layer for Micro LEDs

“…One of the key concerns rises from the difficulties for smaller chip transfer. Although it is possible to fabricate micro LED chips with sizes smaller than 5 m [6,7] these days, it is difficult to mass-transfer tiny devices onto different substrates, not to mention the high precision that requires in this job. In the past, 8 m by 15m devices have been demonstrated with an estimated array size of 100 by 100 [8].…”