Investigations on In₀.₁₂Al₀.₈₈N/AlN/AlₓGa₁−ₓN/In₀.₁₂Al₀.₈₈N MOS-HFETs With Symmetrically-Graded Wide-Gap Channel and Drain Field-Plate Design

Novel In _0.12 Al _0.88 N/AlN/Al _x Ga _1-x N/In _0.12 Al _0.88 N metal-oxide-semiconductor heterostructure field-effect transistors (MOS-HFETs) grown on a SiC substrate with a drain field-plate (DFP) were investigated. A symmetrically-graded Al _x Ga _1-x N (x = 0.32 → 0.1 → 0.32) wide-gap channel with an In _0.12 Al _0.88 N back-barrier was devised to enhance the carrier confinement, channel conductivity, and breakdown characteristics. The MOS-gate structure, employing high-k Al ₂ O ₃ gate dielectric and surface passivation deposited by the non-vacuum ultrasonic spray pyrolysis deposition (USPD) technique, has resulted in enhanced gate modulation and decreased gate leakage current. A control MOS-HFET (sample A) with an equivalent Al _0.21 Ga _0.79 N channel and DFP was fabricated in comparison with the present design without/with DFP (samples B1/B2). The present sample B2 (A) has demonstrated a superior maximum drain-source current density ( I_{DS, max} ) of 937.4 (838.8) mA/mm, maximum extrinsic transconductance ( g_{m, max} ) of 89.6 (80.6) mS/mm, on/off-current ratio ( I_on / I_off ) of 1.8 × 10 ⁸ (1.3 × 10 ⁸ ), two-terminal off-state gate-drain breakdown voltage ( BV_GD ) of -530 (-490) V, three-terminal on-state drain-source breakdown voltage ( BV_DS ) of 520 (465) V at 300 K, and the corresponding Baliga's figure-of-merit (BFOM) of 79.5 (39.3) MW/cm ² . The present design is promising for high-voltage power-switching circuit applications.