Near‐Complete Elimination of Size‐Dependent Efficiency Decrease in GaN Micro‐Light‐Emitting Diodes

Abstract

Herein, a successful elimination of the size-dependent efficiency decrease in GaN micro-light-emitting diodes (micro-LEDs) is achieved using damage-free neutral beam etching (NBE). The NBE technique, which can obtain ultralow-damage etching of GaN materials, is used in place of the conventional inductively coupled plasma to form the micro-LED mesa. It is found that all the fabricated micro-LEDs with sizes ranging from 40 to 6 μm show external quantum efficiency (EQE) versus current density characteristics similar to those of large-area GaN LEDs, with a maximum in EQE curves at a current density of as low as about 5 A cm À2 . Furthermore, all the fabricated micro-LEDs, even the 6 μm one, show a similar value of maximum EQE with a variation of less than 10%, clearly indicating a negligible size dependence of emission efficiency of micro-LEDs fabricated by the NBE technique at least down to the size of 6 μm. These results suggest that the NBE process is a promising method of fabricating high-efficiency sub-10 μm GaN

Micro‐Light‐Emitting Diodes Based on InGaN Materials with Quantum Dots

“…[62,63] Surface passivation via atomic layer deposition, wet chemical etching with KOH or (NH 4 ) 2 S, and neutral beam etching have been shown to be efficient methods for suppressing leakage current and surface defects, leading to size-independent peak EQE. [60,[63][64][65][66][67][68] As a result, blue InGaN Micro-LEDs demonstrated >40% EQE in the size range of 10-100 µm, [60] while the peak EQEs of AlGaInP Micro-LEDs remained less than 12%. Thus, for the optimal design of full-color Micro-LED displays, different size chips should be used for each color, leading to highly complex drive circuit designs.…”

Role of Intrinsic Surface States in Efficiency Attenuation of GaN‐Based Micro‐Light‐Emitting‐Diodes

“…Recently, it has been reported that chemical treatment and sidewall passivation eliminate the size‐dependent efficiency decrease for μ‐LEDs with a size down to 10 μm. [ 7,8 ] However, μ‐LEDs with a size smaller than 10 μm still suffer severe efficiency loss even with chemical treatments and passivation. [ 6 ] The previous studies have shown that the decreased EQE of μ‐LEDs with size was attributed to the increased nonradiative surface recombination with decreasing size.…”

Investigation of Electrical Properties of InGaN‐Based Micro‐Light‐Emitting Diode Arrays Achieved by Direct Epitaxy

“…[18,19] So far, a few methods have been attempted for removing the sidewall damage induced by the dry-etching, such as neutral beam etching and KOH chemical treatment. [25,26] Though they have demonstrated to be effective in mitigating the etching damage, the etching approach to fabrication of μLEDs still requires a sidewall passivation and isolation, which can bring about extra processing and performance issues as well. [20,21] Recently, we have developed a different approach to fabrication of InGaN/GaN multiquantum wells (MQWs) μLEDs: a selective overgrowth on patterned templates instead of mesa-etching.…”

“…The green μLEDs have demonstrated high external quantum efficiency and high luminescence. [3,25] We have also grown InGaNbased HEMT-μLEDs to take advantage of higher driving current densities expected of μLEDs for VLC. [7] In this work, currentvoltage and capacitance-voltage characteristics have been investigated systematically on the overgrown μLEDs with different sizes, which have also been compared with those μLEDs fabricated by means of using a conventionally dry-etching approach.…”