Study of the electrical, structural and surface morphological characteristics of Pt/Re/Au ohmic contacts on p-type GaN

We have investigated the electrical, structural and surface morphological characteristics of Pt/Re/Au ohmic contacts to moderately doped p-type GaN (1.13 × 1017 cm−3) before and after annealing. It is shown that the current–voltage (I–V) characteristics of the as-deposited contacts is improved upon annealing at 600 °C for 1 min under N2 ambient. Pt (20 nm)/Re (30 nm)/Au (80 nm) contact produces a specific contact resistance (ρc) of 1.4 × 10−3 Ω cm2 when annealed at 600 °C. However, annealing the sample at 800 °C results in the degradation of the I–V behavior. Auger electron microscopy and glancing angle XRD are used to investigate interfacial reactions between the Pt/Re/Au and p-GaN layers. It is shown that Ga-related phases such as Ga3Pt5, GaPt2, Ga3Re, GaAu2 and GaAu are formed upon annealing at 600 °C. The AFM results showed that the surface morphology of the as-deposited contact is improved (with a RMS roughness of 2.2–1.4 nm) with increasing temperature up to 600 °C and degraded when the contact annealed at 800 °C (with RMS roughness of 8.6 nm).