Improved light output power of GaN-based ultraviolet light-emitting diode using a mesh-type GaN/SiO_2/Al omnidirectional reflector

摘要

We investigated the effect of a mesh-type GaN/SiO_2/Al omnidirectional reflector (ODR) on the light output power of AlGaN/InGaN-based ultraviolet (365 nm) LEDs and compared their performance with that of LEDs with a GaN/ITO/Al reflector. Using the scattering matrix method, the normal incidence reflectance was calculated to be 93.7% for the GaN/SiO_2 (62 nm)/Al ODR and 79% for the GaN/ITO (30 nm)/Al reflector. The Ag/Ni/Al/Ni (52 nm/10 nm/200 nm/20 nm) contact showed a specific contact resistance of 3.2 × 10~(−5) Ω cm~2 after annealing at 500 °C for 1 min. The forward-bias voltages at 20 mA of LEDs with ODR were in the range of 3.49-3.54 V, which were similar to that of LEDs with an ITO/Al reflector (3.51 V). The LEDs with ODR had series resistances in the range of 14.8-12.5 Ω, whereas the LED with an ITO/Al reflector showed 11.7 Ω. The LEDs with ODR yielded 9.3-19.9% higher light output power at 20 mA than the LED with an ITO/Al reflector. The improved light output power was attributed to the optimization of the high reflectance of the ODR (reflective area) and contact area.