Thermal stability study of Cr/Au contact formed on n-type Ga-polar GaN, N-polar GaN, and wet-etched N-polar GaN surfaces

The electrical characteristics and thermal stability of a Cr/Au contact formed on n-type Ga-polar (0 0 0 1) GaN, N-polar    GaN, and wet-etched N-polar GaN were investigated. As-deposited Cr/Au showed a nearly ohmic contact behavior for all samples, i.e., the specific contact resistance was 3.2 × 10−3, 4.3 × 10−4, and 1.1 × 10−3 Ω cm2 for the Ga-polar, flat N-polar, and roughened N-polar samples, respectively. However, thermal annealing performed at 250 °C for 1 min in a N2 ambient led to a significant degradation of contact, i.e., the contact resistance increased by 186, 3260, and 2030% after annealing for Ga-polar, flat N-polar, and roughened N-polar samples, respectively. This could be due to the different disruption degree of Cr/Au and GaN interface after annealing, i.e., the insignificant interfacial reaction occurred in the Ga-polar sample, while out-diffusion of Ga and N atoms was clearly observed in N-polar samples.