Highly low resistance and transparent Ni/ZnO ohmic contacts to p-type GaN

We report on a promising Ni (5 nm)/Al-doped ZnO (AZO) (450 nm) metallization scheme for low resistance and transparent ohmic contacts to p-GaN (5x10(17) cm(-3)). It is shown that the as-deposited Ni/AZO contact shows a nonohmic characteristic due to the insulating nature of the as-deposited AZO. However, annealing the contacts at 450 and 550 degreesC for 2 min in air ambient results in linear current-voltage characteristics, giving a specific contact resistance of 1.01x10(-5) and 8.46x10(-6) Omega cm(2), respectively. It is further shown that annealing the contact at 550 degreesC for 5 min produces a specific contact resistance of 6.23x10(-6) Omega cm(2). The light transmittance of the contacts annealed at 550 degreesC for 2 min is measured to be higher than 76% at wavelengths in the range of 400-550 nm. It is shown that the Ni/AZO contact could be a suitable scheme for high-performance optical devices. (C) 2003 American Institute of Physics.