Interfacial reaction and surface morphology of Pd/Re contact schemes to <i>p</i>-type GaN

Abstract

The interfacial reactions between the Pd (20 nm) / Re (25 nm) contacts and <i>p</i>-GaN(1.13×10¹⁷cm^-3) have been investigated using glancing angle XRD and Auger depth profiling. The samples are annealed at temperatures of 550 ºC and 650 ºC for 1 min in a nitrogen ambient. The I-V measurements show that the as-deposited sample is ohmic with a contact resistance of 1.4×10^-3 Ω cm². However, the annealing of the sample at 550 ºC results in much better ohmic behaviour with a specific contact resistance of 8.7×10^-4 Ω cm². Further, increase in annealing temperature (650 ºC) causes the degradation of the ohmic property. Based on AES and XRD results, the formation of Ga-Pd reaction phases results in the generation of Ga vacancies at the GaN surface region, which plays a role in reducing contact resistivity. The AFM results show that the surface morphology of the as-deposited contact is fairly smooth (with a rms roughness of 1.7 nm) and when annealed at 550 °C, contact has become somewhat degraded with a root-mean-square roughness of 6.5 nm.