Defect-free AlGaInP micro-LEDs by wet chemical etching

Micro-LED is known as the best display technology for the next generation displays, however real commercialization has been repeatedly delayed due to lack of advanced process technologies. Besides the mass transfer, RGB integration and enhancing efficiency of the small LED die appears more critical to be resolved. The biggest hurdle for RGB integration is making small red LED die having comparable efficiency to the blue and green. AlGaInP native red, quantum dot, and InGaN reds have been widely attempted. While AlGaInP red appears to be a strong contender, however, fatal disadvantage is an outrageously low efficiency due to sidewall defects formed by mesa dry etching, thus, defect-free mesa etching technology has been highly sought. Recently, we have achieved a crucial breakthrough in developing mesa etching of the AlGaInP native red micro-LED by “defect-free” wet chemical etching. In the past most of the efforts have been focused on the post dry etching recovery, However, they are helpful for partial recovery only. More importantly, they are not effective for the small die because sidewall defect penetration depth is close to or excess of the micro-LED die. According to our cathodoluminescence results, the sidewall defect penetration depth of the dry etched micro-LED is more than 7 m, while it is less than 0.2 m for the wet etched micro-LED. Thus, effective mesa area of the dry etched red micro-LED is only 28% of the wet etched, which implies that almost no or negligible number of defects exist in the wet etched red micro-LED. Further, our wet etching is capable to etch thicker than 6 m AlGaInP epi layers with etch rate similar to dry etching. In particular, it is one-step etching for any combination of binary, trinary, and quaternary compound semiconductor alloys without need for multiple photo-lithography processes. The chip sidewall is highly vertical and anisotropic; thus, no undercuts are observed after mesa etching. Both defect-free etching and promising etch profile results indicate that our wet etching technology is ready to apply for mass production process for mesa etching of the phosphide-base native red micro-LEDs.