Enhanced Surface-Emitting Vertical InGaN Light-Emitting Diodes by Self-Aligned Sidewall Electrodes and Optical Cavity Length Modulation

A technique to enhance the light extraction of InGaN-based micro-light-emitting diodes (LEDs) using an etch-back and a self-aligned sidewall electrode structure was demonstrated. By removing the sapphire substrate, the backside of the micro-LEDs was selectively processed to remove the highly defective backside and allowed passivation of the LED sidewalls. The etch-back process enhanced the light coupling of photons emitting through the top p-contact by 2×. An Al n-contact, surrounding the passivated LED structure, was used to deplete carriers away from the interface defects along the LED sidewalls when the diode is forward biased, minimizing carrier recombination and reducing the leakage current by 10×. This structure effectively reduced contact series resistance from 0.12 to 5.6 × 10–4 Ω. Optically, the LEDs showed a light extraction efficiency improvement by >200% and the combination of optical and electrical enhancements resulted in a >400% increase in the electroluminescence efficiency.