Ti-based nonalloyed Ohmic contacts for Al_0.15 Ga_0.85 N/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 AlGaNGaN high electron mobility transistors (HEMTs). With the regrown n⁺-GaN layers and recessed drain/source, a low contact resistance of 0.6 Ω mm was obtained for TiAu contacts to AlGaN. The peak drain current (I_DS,max) and maximum transconductance (g_m,max) of the AlGaNGaN HEMTs with nonalloyed Ohmic contacts were 573 mAmm and 60 mSmm, 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.