Annealed Ti/Cr/Al contacts on n-GaN

• n-GaN/Ti/Cr/Al were annealed at 400, 700 and 900 °C for 10 min in vacuum.
• Cr appeared in the top part of the GaN epitaxial layer at 700 °C.
• Ti2AlN MAX phase formed in the interface at 900 °C.
• Al2O3, Cr3GaN and CrN phases were found at 900 °C, too.
• After annealing at 700 °C contacts exhibited linear I–V characteristics.

In this study we report on the micro-, and nanostructural, morphological and electrical properties of Ti(20 nm)/Cr(120 nm)/Al(50 nm) contacts to n-GaN by electron microscopy, X-ray diffraction and I–V measurements. Tested contacts were annealed at the temperature of 400, 700 and 900 °C for 10 min in vacuum. It was found that Cr appeared in the top part of the GaN epitaxial layer at 700 °C. High resolution electron microscopy (HREM) revealed Ti2AlN MAX phase as well as Al2O3 phase at the interface of n-GaN/Ti/Cr/Al contact at 900 °C. X-ray diffraction examinations showed that new Ti2AlN MAX phase formed and Cr3GaN as well as CrN phases developed at 900 °C. I–V characterizations exhibited that while the as-deposited and annealed Ti/Cr/Al contacts are rectifying up to 700 °C the diffusion of Cr into the epi GaN layer led to ohmic behaviour at 700 °C.