Optical Properties of a NiO/Al-based Reflector for High-power Ultraviolet Light-emitting Diodes

We report the optical properties of a nickel oxide (NiO)/Al-based p-type reflector for vertical-type ultra-violet (UV) light-emitting diodes. The NiO film, a p-type transparent conductive oxide material, has been used as p-type Ohmic materials for wide bandgap materials; however, its optical properties have not yet been optimized for applications in the UV range. In this work, we first deposited a 10-nm-thick NiO films on AlGaN epilayers and then annealed them at temperature from 500 degrees C to 900 degrees C by using a rapid thermal process for 1 min similar to 30 min to optimize the transmittance; then, the Al reflector with an optimized transmittance was deposited on indium-tin-oxide films. Finally, we obtained an 84% transmittance from the NiO film and a 51% reflectance from the NiO/Al reflector at 365 nm after annealing at 800 degrees C for 20 min in an oxygen ambient.