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(Color online) EL images of 20 × 20 μm² LED pixel under injection current density of 10 A cm⁻² for (a) reference sample (b) with hydrogen passivation applied.
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We investigated the effect of the sidewall passivation by hydrogen plasma on the InGaN green micro-LED performance. Hydrogen passivation deactivates the surface region of p-GaN around the perimeter of the device mesa. Thus, hole injection is suppressed in this region, where etching-caused material degradation results in leakage current, decreasing...
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Citations
... Hang and Zhang et al. employed the resistive ITO/p-GaN junction and Ta 2 O 5 high-k insulator to modulate the band structure and reduce hole concentration near damaged regions 23,24 . Kirilenko et al. utilized H 2 plasma to passivate Mg acceptors of p-type layers near the sidewall and formed an insulating region to suppress carrier non-radiative recombination 25 . ...
The traditional plasma etching process for defining micro-LED pixels could lead to significant sidewall damage. Defects near sidewall regions act as non-radiative recombination centers and paths for current leakage, significantly deteriorating device performance. In this study, we demonstrated a novel selective thermal oxidation (STO) method that allowed pixel definition without undergoing plasma damage and subsequent dielectric passivation. Thermal annealing in ambient air oxidized and reshaped the LED structure, such as p -layers and InGaN/GaN multiple quantum wells. Simultaneously, the pixel areas beneath the pre-deposited SiO 2 layer were selectively and effectively protected. It was demonstrated that prolonged thermal annealing time enhanced the insulating properties of the oxide, significantly reducing LED leakage current. Furthermore, applying a thicker SiO 2 protective layer minimized device resistance and boosted device efficiency effectively. Utilizing the STO method, InGaN green micro-LED arrays with 50-, 30-, and 10-µm pixel sizes were manufactured and characterized. The results indicated that after 4 h of air annealing and with a 3.5-μm SiO 2 protective layer, the 10-µm pixel array exhibited leakage currents density 1.2 × 10 ⁻⁶ A/cm ² at −10 V voltage and a peak on-wafer external quantum efficiency of ~6.48%. This work suggests that the STO method could become an effective approach for future micro-LED manufacturing to mitigate adverse LED efficiency size effects due to the plasma etching and improve device efficiency. Micro-LEDs fabricated through the STO method can be applied to micro-displays, visible light communication, and optical interconnect-based memories. Almost planar pixel geometry will provide more possibilities for the monolithic integration of driving circuits with micro-LEDs. Moreover, the STO method is not limited to micro-LED fabrication and can be extended to design other III-nitride devices, such as photodetectors, laser diodes, high-electron-mobility transistors, and Schottky barrier diodes.
... 75 Hydrogen passivation can reduce non-radiative recombination at the sidewall by preventing the injection current from flowing into the sidewall region. 94,95 In a previous study, p-GaN was passivated with hydrogen by intentionally exposing the sidewall to hydrogen. This process significantly improved LED performance by blocking current injection into the mesa-etch-induced sidewall defects. ...
... For Hpassivated InGaN-based green lLEDs (20 Â 20 lm 2 ), the reverse leakage current was reduced more than 10-fold and the EQE was enhanced by 140% compared to the reference sample [ Fig. 6(c)]. 94 Furthermore, a nitrogen ion implantation process has been adopted to modify sidewall surface defects. 96 The PL intensity of InGaN-based green lLEDs was enhanced sevenfold after passivation. ...
Display technology has developed rapidly in recent years, with III-V system-based micro-light-emitting diodes (uLEDs) attracting attention as a means to overcome the physical limitations of current display systems related to their lifetime, brightness, contrast ratio, response time, and pixel size. However, for uLED displays to be successfully commercialized, their technical shortcomings need to be addressed. This review comprehensively discusses important issues associated with uLEDs, including the use of the ABC model for interpreting their behavior, size-dependent degradation mechanisms, methods for improving their efficiency, novel epitaxial structures, the development of red uLEDs, advanced transfer techniques for production, and the detection and repair of defects. Finally, industrial efforts to commercialize uLED displays are summarized. This review thus provides important insights into the potential realization of next-generation display systems based on uLEDs.
... But it is worth noting that as the size of micro-LEDs decreases, the quantum efficiency decreases significantly and is still present. The previous reports of sidewall defects in micro-LEDs mainly depend on current leakage increase and EQE reduction [5,6,15]. The other parameters such as current spreading and electrode distribution are also size dependent [16,17], which will affect the evaluation of sidewall defects on non-radiative recombination of micro-LEDs with various sizes. ...
Sidewall defects play a key role in determining the efficiency of GaN-based micro-light emitting diodes (LEDs) for next generation display applications, but there still lacks direct observation of defects-related recombination at the affected area. In this Letter, we proposed a direct technique to investigate the recombination mechanism and size effect of sidewall defects for GaN blue micro-LEDs. The results show that mesa etching will produce stress release near the sidewall, which can reduce the quantum confinement Stark effect (QCSE) to improve the radiative recombination. Meanwhile, the defect-related non-radiative recombination generated by the sidewall defects plays a leading role under low-power injection. In addition, the effective area of the mesas affected by the sidewall defects can be directly observed according to the fluorescence lifetime imaging microscope (FLIM) characterization. For example, the effective area of the mesa with 80 µm is affected by 23 ${\% }$ % while the entire area of the mesa with 10 µm is almost all affected. This study provides guidance for the analysis and repair of sidewall defects to improve the quantum efficiency of micro-LEDs display at low current density.
... 15,16 Various mesa sidewall passivation methods, such as dielectric (e.g., SiO 2 , Al 2 O 3 ) deposition using plasma-enhanced chemical vapor deposition (PECVD) and atomic layer deposition (ALD), acid-base etching, hydrogen plasma, and sulfur treatments, are suggested ways to minimize non-radiative recombination and improve the external quantum efficiency. [258][259][260][261] Progress toward improving the extraction efficiency of LEDs using photonic crystals and beam shaping using microlenses has been made, but challenges related to reliable integration with microLEDs remain to be addressed. The most common microlens fabrication technique (as the reflow method) faces uniformity and control challenges that need to be improved. ...
MicroLEDs offer an extraordinary combination of high luminance, high energy efficiency, low cost, and long lifetime. These characteristics are highly desirable in various applications, but their usage has, to date, been primarily focused toward next-generation display technologies. Applications of microLEDs in other technologies, such as projector systems, computational imaging, communication systems, or neural stimulation, have been limited. In non-display applications which use microLEDs as light sources, modifications in key electrical and optical characteristics such as external efficiency, output beam shape, modulation bandwidth, light output power, and emission wavelengths are often needed for optimum performance. A number of advanced fabrication and processing techniques have been used to achieve these electro-optical characteristics in microLEDs. In this article, we review the non-display application areas of the microLEDs, the distinct opto-electrical characteristics required for these applications, and techniques that integrate the optical and electrical components on the microLEDs to improve system-level efficacy and performance.
... Hydrogen plasma treatment has been shown to enhance the peak EQE by 1.4 times in InGaN-based green micro-LEDs. This was attributed to the deactivation of Mg acceptors around the device mesa, which inhibited the injection of charge carriers along the region with a high density of surface defects [56]. Surface treatments ACCEPTED ARTICLE PREVIEW immediately after mesa etching have been studied, including using atomic layer deposition (ALD) for depositing a dielectric Al2O3, or an (NH4)2S treatment, which can effectively passivate surface states [57,118]. ...
... free pixelization of InGaN LED [11,13] and micro-LED sidewall passivation [14]. Here, we used hydrogen passivation to suppress the current injection underneath the metal p-pad of the LED chip. ...
... After plasma exposure, the p-GaN sheet resistance increases up to ten-fold [11,12]. We previously applied hydrogen passivation to achieve mesa etching-free pixelization of InGaN LED [11,13] and micro-LED sidewall passivation [14]. Here, we used hydrogen passivation to suppress the current injection underneath the metal p-pad of the LED chip. ...
... A reduced leakage current along the device's sidewalls leads to improvements in the injection efficiency. An efficiency gain with the same order of magnitude was reported in the case of the standard-size LED sidewall passivation via a dielectric layer deposition on the mesa sidewall [22] and a micro-LED sidewall passivation by hydrogen plasma [14]. We assume that the great improvement in the device's light output density, and, therefore, its efficiency, was brought about by the reduction in the non-radiative recombination that occurred on the device sidewalls [23]. ...
We report p-GaN passivation via hydrogen plasma used to create current blocking regions (CBRs) in InGaN-based green LEDs with standard dimensions of 280 × 650 μm2. The CBRs are created before mesa etching in two variants: underneath the opaque metal p-pad and both underneath the p-pad and along the device’s mesa perimeter. The peak EQE increased by 13% and 23% in the first and the second cases, respectively, in comparison to the reference LED with no CBR. With a high injection current of 50 A/cm2, the EQE value increased by 2% in the case of CBRs underneath the p-pad as well as by 14% in the case of CBRs both underneath the p-pad and along the mesa perimeter (relative to the reference sample with no CBR).
UV‐ranged micro‐LEDs are being explored for numerous applications due to their high stability and power efficiency. However, previous reports have shown reduced external quantum efficiency (EQE) and increased leakage current due to the increase in surface‐to‐volume ratio with a decrease in the micro‐LED size. Herein, the size‐related performance for UV‐A micro‐LEDs, ranging from 8 × 8 to 100 × 100 μm ² , is studied. These devices exhibit reduced leakage current with the implementation of atomic layer deposition‐based sidewall passivation. A systematic EQE comparison is performed with minimal leakage current and a size‐independent on‐wafer EQE of around 5.5% is obtained. Smaller sized devices experimentally show enhanced EQE at high current density due to their improved heat dissipation capabilities. To the best of authors’ knowledge, this is the highest reported on‐wafer EQE demonstrated in <10 μm dimensioned 368 nm UV LEDs.
Direct-gap semiconductors are the basic materials of many light-emitting devices (LEDs) and laser-diodes (LDs) found in our daily life. We give here some fundamental physical properties of these materials and how they are implemented in such devices. We start with a description of the emitted spectrum of LEDs using a generalized Kirchhoff law and introduce emitter characteristics like efficiency and efficacy. In particular, the properties of various ternary and quaternary semiconductor alloys are discussed with focus on the achievable tunability of the emission wavelength. Also energy quantization in colloidal quantum dots and its application in full-color displays is illustrated. We then turn to the realization and optimization of optical gain and lasing in LDs. Finally the electron relaxation dynamics in quantum cascade lasers is described.
