Investigation of Pd∕Ti∕Al and Ti∕Al Ohmic contact materials on Ga-face and N-face surfaces of n-type GaN

Pd ∕ Ti ∕ Al and Ti∕Al Ohmic contact materials on Ga-face and N-face surfaces of n-type GaN were investigated by measuring the contact resistivities with respect to annealing temperatures. Pd∕Ti∕Al contact showed good Ohmic property in contrast to Ti∕Al contact on N-face surface of n-type GaN. Cross-sectional transmission electron microscopy results on samples of as-deposited and annealed at 450°C for 30s indicated that Pd played an important role in changing the surface state of N-face surface of n-type GaN and less than 50Å of Pd was required to obtain the best Ohmic contact property.