Au-free AlGaN/GaN heterostructure field-effect transistor with recessed overhang ohmic contacts using a Ti/Al bilayer

Abstract

We have developed a low-temperature ohmic contact process with a recessed overhang configuration for Au-free (complementary metal-oxide semiconductor) CMOS-compatible AlGaN/GaN heterostructure field effect transistors (HFETs). The recessed overhang configuration has a Ti/Al bilayer directly in contact with the AlGaN/GaN heterojunction interface at the recessed sidewall overlaid with the AlGaN barrier layer, which allows good and reproducible ohmic formation with low-temperature annealing. The optimum Ti/Al thickness was 40/200 nm, which resulted in an R-c of 0.76 Omega mm with excellent surface morphology when annealed at 550 degrees C for 1 min. The device fabricated with a Ni/Mo gate exhibited a maximum drain current density of similar to 500 mA mm(-1), a specific on-resistance of 1.35 m Omega cm(2) and a breakdown voltage of >1 kV.