Metallization contacts to nonpolar a-plane n-type GaN

We have investigated the electrical characteristics of metallization contacts to nonpolar a-plane and polar c-plane n-type GaN. Pd Schottky diodes and x-ray photoemission spectroscopy measurements show that the Schottky barrier height of the a-plane GaN is lower than that of the c-plane GaN by 0.24 and 0.30eV, respectively. Ti∕Al Ohmic contacts to the a-plane n-GaN produce lower contact resistivity than that of the c-plane samples when annealed at 500°C. However, Ti∕Al contacts to the c-plane and a-plane GaN show opposite electrical behavior when annealed at temperatures above 500°C, which is attributed to the absence of polarization-induced surface charges for a-plane GaN.