Elimination of Size Effects in InGaN Quantum Dot Cyan-Green Micro-LEDs by Constructing a Full-m-Plane Hexagonal Structure

GaN-based micro-light-emitting diodes (micro-LEDs) are critical for lighting and display applications due to their high efficiency and stability. However, it has been a challenge to alleviate the reduction of the external quantum effect (EQE) of micro-LEDs with a decreasing size. This is attributed to an increase in the Shockley–Read–Hall (SRH) nonradiative recombination rate of the sidewall. Due to the size effects, it is more difficult to prepare efficient micro-LEDs with decreasing mesa size. In this work, micro-LED epi-wafers with InGaN quantum dots (QDs) as active layer materials were grown by plasma-assisted molecular beam epitaxy (PA-MBE), and full-M-sided hexagonal structure micro-LEDs were prepared. We fabricated the micro-LED array with the full-M-sided hexagonal structure and repaired etching damage on the sidewall by chemically treating with a tetramethylammonium hydroxide (TMAH) solution. Most of the surface defects caused by etching were eliminated, and the etching damage can be further reduced by using QDs as an active region. Thus, the efficiency of the micro-LED at a low injection current density is improved, and the size effect is eventually overcome. Compared with the 20 μm micro-LED array, the peak EQE of the 10 μm micro-LED array was improved by 79%, reaching 0.83% at 11 A/cm2. We demonstrate that constructing full-M-sided structures can overcome the size effect in InGaN QD-based micro-LEDs. Notably, the cyan-green micro-LEDs fabricated by this method exhibited low efficiency drop. In addition, the QD-based micro-LED exhibits excellent wavelength stability with increasing injection current density. This work provides a new way to fabricate high-efficiency micro-LEDs.