Al₂O₃/AlN/Al-based backside diffuse reflector for high-brightness 370-nm AlGaN ultraviolet light-emitting diodes

We report an Al₂O₃/AlN/Al-based backside diffuse reflector for near-ultraviolet light-emitting diodes (NUV LEDs), and its superiority compared with conventional reflectors. After fabrication of LEDs, a sapphire (Al₂O₃) surface was UV-irradiated to utilize the diffuse reflection effect by roughening the surface. Then, a thermally treated AlN layer was deposited on it, to obtain a mirror-like surface, before deposition of Al. The reflectance increased by 1.3% and 3.9% for these Al₂O₃/AlN/Al reflectors without and with surface treatment, respectively, compared with an Al reflector. These reflectors were then used with 370 nm AlGaN NUV LEDs, and the performances of LEDs without and with an Al reflector were compared. As a result, the NUV LED with both thermally and UV-treated AlN/Al reflector exhibited the best performance, and its output power and electroluminescence intensity were higher by 82.7% and 41.9%, respectively, than those of the LED without a reflector.