This letter reports a novel Al2O3-passivated graded-barrier (GB) AlxGa1-xN/AlN/GaN/Si heterostructure field-effect transistor (HFET) formed by using hydrogen peroxide (H2O2) oxidization method. Different from the Al0.26Ga0.74N conventional barrier (CB), a compositionally graded AlxGa1-xN (x = 0.22∼0.3) barrier was devised to increase the Schottky-barrier height (B) and improve the interfacial quality at the same time. Reduced gate leakage and enhanced device gain are further achieved by the Al2O3 passivation. The present Al2O3-passivated/unpassivated GB-HFETs (unpassivated CB-HFET) has demonstrated improved maximum drain-source current density (IDS, max) of 708/699 (654) mA/mm at VDS = 7 V, maximum extrinsic transconductance (gm, max) of 139/126 (113) mS/mm, subthreshold swing (SS) of 176/253 (274) mV/dec, on/off-current ratio (Ion/Ioff) of 3.8 × 106/1.4 × 104 (7.1 × 103), two-terminal off-state gate-drain breakdown voltage (BVGD) of −126.4/−96.8 (−89.3) V, turn-on voltage (Von) of 1.1/0.7 (0.3) V, and three-terminal on-state drain-source breakdown voltage (BVDS) of 109/89 (71) V.
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