Ultra-low resistance Au-free V/Al/Ti/TiN ohmic contacts for AlGaN/GaN HEMTs

We report on the electrical and microstructural characterization of an Au-free V/Al/Ti/TiN ohmic contact for AlGaN/GaN heterostructures. Ultra-low contact resistance and specific contact resistivity of R<inf>c</inf> < 0.1 Ω mm and ρ<inf>c</inf> < 2.4 × 10⁻⁷ Ω cm² have been achieved with very low RMS surface roughness. This was accomplished at a comparably low annealing temperature of 800 °C and without applying any contact recess, regrowth, or implantation process. High electron mobility transistors were fabricated and a comparison of the electrical performance with state-of-the-art Ti/Al/Ti/TiN and Ti/Al/Ni/Au contacts was made. The contact formation mechanism is discussed on the basis of microstructural features.