Low-resistance and thermally stable Pd/Re ohmic contacts to p-type GaN

We have investigated a low-resistance thermally stable Pd/Re ohmic contact on moderately doped p-GaN:Mg (1.1 × 10¹⁷ cm^-3). It is shown that the I-V characteristic of the as-deposited sample is improved upon annealing at 550 °C for 1 min under N₂ ambient. However, annealing the sample at 650 °C results in the degradation of the I-V behaviour. Specific contact resistance as low as 8.7 × 10^-4 ω cm² is obtained from the Pd(20 nm)/Re(25 nm) contact annealed at 550 °C. It is also shown that the contact exhibits thermal stability during annealing at 550 °C. Auger electron microscopy and glancing angle x-ray diffraction studies are carried out to characterize interfacial reactions between the Pd/Re contacts and the GaN.