Red micro-light-emitting diodes (μLEDs) have been generated significant interest for the next generation μLEDs displays. It has been shown that the external quantum efficiency (EQE) of AlInGaP red μLEDs markedly decreases as the size goes to very small dimension. Here, we demonstrate size-independent peak EQE of 611 nm InGaN red μLEDs. Packaged μLEDs show a peak EQE varied from 2.4% to 2.6% as the device area reduces from 100 × 100 to 20 × 20 μm2. These results demonstrate the promising potential for realizing high efficiency red μLED with very small size using InGaN materials.
We study the high-temperature electroluminescence properties of 600 nm InGaN red 40 × 40 μm2 micro-light-emitting diodes (μLEDs) with a peak external quantum efficiency (EQE) of 3.2%. Temperature-dependent peak wavelength measurements show a low redshift of 0.05 nm/K. The injection efficiency improves with increasing temperature. The hot/cold (HC) factor is used to quantify the thermal droop: at 400 K, the EQE and wall-plug efficiency HC factors at 50 A/cm2 reach high values of 0.72 and 0.85, respectively. This demonstrates the robustness of InGaN red μLEDs up to high temperature, with a much-improved stability over conventional AlInGaP red μLEDs.
III-nitrides based light-emitting diodes and laser diodes (LDs) have shown great success as solid-state lighting sources, but the development of common c-plane (0001) polar GaN emitters is facing limitations due to quantum-confinement Stark effect, efficiency drop, low efficiency at green range, and peak wavelength blue-shift. Efficient semipolar or nonpolar GaN light emitting diodes and LDs have been successfully demonstrated by growing on semipolar or nonpolar free-standing GaN substrates. The small size and high cost of high crystal quality semipolar or nonpolar free-standing GaN substrates, which are sliced from hydride vapor phase epitaxy grown c-plane bulk GaN substrate, have severely limited their commercial development and application. Achieving scalable heteroepitaxial semipolar GaN materials with a very low density of basal-stacking faults (BSFs) on a foreign substrate remains very challenging. The recent breakthrough in the demonstration of continuous-wave (CW) semipolar (202¯1) LDs at room-temperature on semipolar GaN/sapphire template marks a milestone in exploring high crystal quality heteroepitaxial semipolar GaN materials and low-cost semipolar emitters. Here, we review the key progress through the past years about the development of heteroepitaxial semipolar GaN materials including epitaxial lateral overgrowth, orientation controlling epitaxy, BSFs burying by neighboring Ga-polar (0001) GaN with air voids, facet-engineering orientation control epitaxy, resulting in a low density or free of basal stacking faults. Furthermore, we discuss the heteroepitaxially grown pulsed semipolar (112¯2) blue LDs and CW semipolar (202¯1) LDs.
Red micro-size light-emitting diodes (μLEDs) less than 10 × 10 μm2 are crucial for augmented reality (AR) and virtual reality (VR) applications. However, they remain very challenging since the common AlInGaP red μLEDs with such small size suffer from a dramatic reduction in the external quantum efficiency. In this work, we demonstrate ultra-small 5 × 5 μm2 607 nm amber μLEDs using InGaN materials, which show an EQE over 2% and an ultra-low reverse current of 10−9 A at −5 V. This demonstration suggests promising results of ultra-small InGaN μLEDs for AR and VR displays.
We present efficient red InGaN 60 × 60 μm2 micro-light-emitting diodes ( μLEDs) with an epitaxial tunnel junction (TJ) contact. The TJ was grown by metal-organic chemical vapor deposition using selective area growth. The red TJ μLEDs show a uniform electroluminescence. At a low current density of 1 A/cm2, the emission peak wavelength is 623 nm with a full-width half maximum of 47 nm. The peak external quantum efficiency (EQE) measured in an integrating sphere is as high as 4.5%. These results suggest a significant progress in exploring high efficiency InGaN red μLEDs using TJ technology.
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