Low leakage GaN HEMTs with sub-100 nm T-shape gates fabricated by a low-damage etching process

This paper demonstrates a new fabrication process for gallium nitride high-electron mobility transistors (HEMTs) free of plasma damages in the sub-100 nm T-shape gate area. The common peeling-off problems of electron beam resists during gate metal deposition process were solved by introducing a fluorine plasma treatment process before gate metal deposition. By combining dry and wet etching processes appropriately, an on/off ratio of 10 at a drain-to-source voltage of 1 V was achieved. This work also investigated the short channel effect in devices with gate lengths from 70 to 440 nm. Reducing gate length results in decrease of threshold voltage due to the drain-induced barrier-lowering effect. Current gain cut-off frequency f and maximum oscillation frequency f increase while gate length reduces till 250 nm. However, below 250 nm, f and f no longer increase while gate length reduces till sub-100 nm, which reflect the short channel effect.