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

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.