Investigations on In_0.12Al_0.88N/AlN/Al_xGa_1-xN/ In_0.12Al_0.88N MOS-HFETs With Symmetrically-Graded Wide-Gap Channel and Drain Field-Plate Design

Novel In0.12Al0.88N/AlN/AlxGa1-xN/In0.12Al0.88N 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 AlxGa1-xN (x = 0.32 -> 0.1 -> 0.32) wide-gap channel with an In0.12Al0.88N back-barrier was devised to enhance the carrier confinement, channel conductivity, and breakdown characteristics. The MOS-gate structure, employing high-k Al2O3 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 Al0.21Ga0.79N 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,I-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 x 10(8) (1.3 x 10(8)), two-terminal off-state gate-drain breakdown voltage (BVGD) of -530 (-490) V, three-terminal on-state drain-source breakdown voltage (BVDS) 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.