Effects of Thermal Annealing on Al-Doped ZnO Films Deposited on p-Type Gallium Nitride

In this study, Al-doped ZnO (AZO) and Ni ∕ AZO films were deposited on p-type GaN films followed by thermal annealing to form ohmic contacts. After thermal annealing, the resistivities of AZO films reduced from 5 × 10 − 3 to 4 – 6 × 10 − 4 Ω cm . Both as-deposited AZO and Ni ∕ AZO contacts on p-GaN displayed a non-ohmic characteristic. Only the 800°C-annealed Ni ∕ AZO contacts exhibited a linear current–voltage characteristic, showing a specific contact resistance of around 1.2 × 10 − 2 Ω cm 2 . After undergoing the annealing in nitrogen ambience, the light transmittance of the Ni ∕ AZO films increased from 70% to higher than 90% in the visible range. These results revealed that the Ni ∕ AZO contact can serve as a suitable transparent current spreading layer for the fabrication of GaN-based light-emitting devices.