Highly low resistance and transparent NiÕZnO 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 (5310 cm). 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 °C for 2 min in air ambient results in linear current–voltage characteristics, giving a specific contact resistance of 1.01 310 and 8.46310 V cm, respectively. It is further shown that annealing the contact at 550 °C for 5 min produces a specific contact resistance of 6.23310 V cm. The light transmittance of the contacts annealed at 550 °C 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. © 2003 American Institute of Physics. @DOI: 10.1063/1.1591236#