Low-resistance Ohmic contacts for high-power GaN field-effect transistors obtained by selective area growth using plasma-assisted molecular beam epitaxy

Abstract

Selective area growth (SAG) has been demonstrated using plasma-assisted molecular beam epitaxy (PAMBE) resulting in vastly improved Ohmic contacts for GaN-based high-power field-effect transistors (FETs). A heavily doped n-GaN layer was grown only in the Ohmic contact region and the resulting nonalloyed Ti∕Al∕Ti∕Au metal contacts exhibited linear Ohmic behavior. Through rapid thermal annealing, very low specific contact resistivity (1.8×10−8Ωcm2) was obtained at 850°C. Furthermore, contact resistances below 0.8Ωmm were obtained by annealing at a wide range of temperatures (750–950°C). GaN metal-semiconductor FETs were fabricated to investigate the effect of the PAMBE-SAG on device performance, producing great improvement in the dc characteristics.