Development of a Au-free process using Mo-based metallization for high-power AlGaN/GaN-on-Si heterostructure field-effect transistors

Abstract

A Au-free ohmic contact process for fabricating AlGaN/GaN heterostructure field-effect transistors (HFETs) on Si substrates was developed by using Mo-based metallization. We investigated Si/Ti/Al/Mo metal stacks for ohmic metallization where the Ti/Al thickness ratio and the annealing temperature were varied. The optimized metal stack and annealing conditions were a Si/Ti/Al/Mo stack with 5/40/60/50 nm thicknesses and rapid thermal annealing in a N-2 ambient at 900 A degrees C for 30 sec, which resulted in a contact resistance of 1.24 Omega A center dot mm, a sheet resistance of 410 Omega/sq and a specific contact resistivity of 3.76 x 10(-5) Omega A center dot cm(2). Devices fabricated using the optimized Mo-based, Au-free ohmic contact process exhibited comparable characteristics with higher breakdown voltage to those of devices fabricated using a conventional Au-based ohmic contact process.