Ti-based nonalloyed Ohmic contacts for Al0.15Ga0.85N∕GaN high electron mobility transistors using regrown n+-GaN by plasma assisted molecular beam epitaxy

Abstract

A technique for regrowing n+-GaN layers has been developed to realize nonalloyed Ohmic contacts using plasma assisted molecular beam epitaxy. The contact resistance and device performance were measured of a recessed-gate with the regrowth and of recessed-source/drain AlGaN∕GaN high electron mobility transistors (HEMTs). With the regrown n+-GaN layers and recessed drain/source, a low contact resistance of 0.6Ωmm was obtained for Ti∕Au contacts to AlGaN. The peak drain current (IDS,max) and maximum transconductance (gm,max) of the AlGaN∕GaN HEMTs with nonalloyed Ohmic contacts were 573mA∕mm and 60mS∕mm, respectively. These results demonstrate that the regrowth of highly doped GaN layers is crucial in achieving low-resistance nonalloyed Ohmic contacts for the HEMT structures.