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 verticaltype 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 °C to 900 °C by using a rapid thermal process for 1 min ~ 30 min to optimize the transmittance; then, the Al reflector with an optimized transmittance was deposited on indium-tinoxide 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 °C for 20 min in an oxygen ambient.