Thermal annealing effects on Ni/Au contacts to p type GaN in different ambient

Abstract

Current–voltage ( I– V) characteristics, contact resistance, and optical transmittance measurements are performed to investigate the effects of different annealing ambient conditions on properties of contacts of Ni/Au/p-GaN. With increasing annealing temperature in the range from room temperature to 600 °C in air, I– V characteristics become linear, and the specific contact resistance ( ρ c) reduces continually. ρ c of Ni (20 nm)/Au (50 nm) contact to p-GaN annealed in air at 600 °C is obtained as 2.76×10 −2 Ω cm 2. However, in N 2 ambient, ρ c is higher and shows a more complex evolution with increasing annealing temperature. The optical transmittance of the specimens increases and maintains a high value with the annealing temperature in air while it increases first, and then decreases monotonically in N 2 atmosphere. We suggest that formation of low-resistance and high optical transmittance p-type Ohmic contact may be attributed to the oxidized Ni layer. The mechanism of Ohmic contact formation under different ambient conditions is also discussed.