Enhancement Mode β-(AlxGa1-x)2O3/Ga2O3 Heterostructure FET (HFET) With High Transconductance and Cutoff Frequency

This letter reports $\beta $ -(Al _x Ga _1-x ) ₂ O ₃ /Ga ₂ O ₃ (AlGaO/GaO) heterostructure FETs (HFETs) with significant improvement of peak transconductance (g _m ), current and power gain cutoff frequencies. A modulation doping scheme is used to form a two dimensional electron gas in AlGaO/GaO heterostructures. Highly scaled transistors (gate lengths of 160–200 nm) were fabricated on these wafers with source/drain regrowth, scaled source access lengths and Pt Schottky gates. The fabricated HFETs show an enhancement-mode operation with high transconductance and a peak current density of 74 mA/mm. Small signal measurements show a peak current gain cut off frequency (f _T ) and power gain cutoff frequency (f _max ) of 30 and 37 GHz respectively at 10 V drain voltage. While the cutoff frequencies are highest to date, they are limited by high source resistance at the regrowth interface. We observed a moderate off state breakdown at V _GS = −2 V, limited by gate leakage and Schottky gate breakdown with an average field strength of 1.35 MV/cm. The f _T .L _G product 4.8 GHz- ${\mu }\text{m}$ reported for this device is higher than any other current generation $\beta $ -Ga ₂ O ₃ transistors which paves the way for future RF device applications.