Quasi-vertical GaN heterojunction diodes with p-NiO anodes deposited by sputtering and post-annealing

Quasi-vertical GaN heterojunction diodes were fabricated with p-NiO anodes deposited by radio frequency magnetron sputtering. The influence of sputtering gas ratio on the quality of the NiO films was investigated and the crystalline quality of the NiO film is better at a lower oxygen ratio. The crystal structure, electrical and optical properties of the NiO thin films after post-deposition annealing (PDA) at various temperatures in oxygen ambient were evaluated. X-ray diffraction and optical results showed that the crystallinity of the NiO films was improved after annealing. With increasing PDA temperature, the carrier concentrations of the NiO films decreased and the bandgap became larger, which is ascribed to the out-diffusion of oxygen interstitial atoms. Moreover, high-performance NiO/GaN heterojunction PN diodes (HJPNDs) were obtained. The ideality factor and reverse voltage characteristics of the HJPNDs were enhanced with increasing PDA temperature. The hard breakdown voltage of the HJPND with PDA at 500 °C was 698 V without optimized termination techniques. •Post-deposition annealing (PDA) at various temperatures was conducted on magnetron sputtered NiO films.•The crystal structure, electrical and optical properties of the NiO thin films after PDA were evaluated.•Quasi-vertical GaN heterojunction diodes were fabricated with p-NiO anodes.•The breakdown voltage was enhanced dramatically with increasing PDA temperature.