External Quantum Efficiency Enhancement of InGaN-Based Quantum Dot Green Micro-Light-Emitting Diode Arrays by Fabricating Full-A-Sided Triangular Mesa
Peng Zhang, Ying Gu, Yi Gong, Haowen Hua, S. Jin, Wenxian Yang, Jianjun Zhu, Shibing Long, Shulong Lu
Abstract
Efficient GaN-based green micro light-emitting diodes (micro-LEDs) are critical for novel full-color displays. In this work, triangular-mesa micro-LED arrays with full-A-side (sample A) and full-M-side (sample M) were fabricated using InGaN-based quantum dot green LED epitaxial wafers grown by plasma-assisted molecular beam epitaxy. The two samples were soaked in a tetramethylammonium hydroxide solution to remove the damage caused by dry etching on their sidewalls. The effect of the crystallographic orientations of device sidewalls on the optoelectronic performance of micro-LEDs was investigated. The result indicates that the external quantum efficiency (EQE) of the as-prepared micro-LEDs with both structures has been greatly improved compared with the normal-structured micro-LEDs. The peak EQE of sample A is 43% higher than that of sample M. Most importantly, the peak EQE of sample A is 80% higher than that of conventional quadrilateral devices. The efficiency improvement of sample A is attributed to the increasing light extraction efficiency because zigzagged sidewalls are performed after the sidewall repair process in sample A, while flat sidewalls are in sample B. However, the zigzagged sidewalls simultaneously bring about a larger leakage current because more surface defects are formed on larger equivalent sidewall surface areas. In addition, the two samples exhibit excellent wavelength stability due to the weakened polarization field in quantum dots. Therefore, it is a promising method for improving the luminous efficiency of InGaN QD-based micro-LEDs by adopting a full-A sidewall structure.