GaN-Based LEDs With GaN $\mu$ -Pillars Around Mesa, Patterned Substrate, and Reflector Under Pads

Nitride-based light-emitting diodes (LEDs) with textured sidewall, GaN mu-pillars around mesa region, patterned sapphire substrate (PSS), and highly reflective Ag-Cr-Au electrode pads were fabricated using the conventional lithography method (labeled as experimental LEDs). When a 20-mA injection current was applied, forward voltages were 3.18 and 3.4 V for the conventional and experimental LEDs, respectively. The high 20-mA V_f of LEDs with Ag-Cr-Au electrode pads could be attributed to the fact that the specific contact resistance of n⁺-GaN-Ag-Cr-Au is slightly higher than that of the n⁺ -GaN-Cr-Au contact. It was found that we could achieve much stronger LED output power with textured sidewalls, GaN mu-pillars around mesa region, PSS, and highly reflective Ag-Cr-Au electrode pads. It was also found that we could enhance LED output power by more than 80% compared with the conventional LEDs.