Ultralow contact resistance of 0.058 Ω mm achieved by pulsed sputtering deposition of regrown degenerately doped GaN contacts for AlGaN/GaN high-electron-mobility transistors

Regrown nonalloyed ohmic contacts for AlGaN/GaN high-electron-mobility transistors (HEMTs) were fabricated using low-temperature pulsed sputtering deposition (PSD) of highly Si-doped degenerate GaN (d-GaN) onto inductively coupled plasma-etched recesses. The regrown d-GaN (thickness: 250 nm) shows a sheet resistance of 7.2 Ω/sq. with a carrier concentration and mobility of 3.4×1020 cm−3 and 100 cm2 V−1 s−1, yielding a total contact resistance of 0.058±0.004 Ω mm. The inherent interface resistance between the PSD-regrown d-GaN and two-dimensional electron gas was estimated using the transfer length method to be 0.033±0.005 Ω mm, which is close to the single-interface quantum injection limit (0.026 Ω mm). The fabricated HEMT devices with 2 μm gate length exhibited good characteristics (maximum drain current density = 850 mA mm−1, maximum transconductance = 0.2 S mm−1, and on-resistance = 2.1 Ω mm). These results indicate that the low-temperature regrowth of nonalloyed d-GaN contacts with ultralow resistance using PSD is a scalable and low-thermal-budget route for future radio frequency transistors.