Comparative studies of normally-off Al0.26Ga0.74N/AlN/GaN/Si high electron mobility transistors with different gate structures

Abstract Systematic designs to achieve normally-off operation and improved device performance for Al 0.26 Ga 0.74 N/AlN/GaN high electron mobility transistors (HEMTs) grown on a Si substrate are investigated in this work. The step-by-step approach includes: (1) devising a thin AlGaN/AlN composite barrier, (2) introducing fluoride ions within the active region by using CF 4 plasma treatment, (3) growing the Al 2 O 3 oxide passivation layers within gate-drain/source regions by using a cost-effective ozone water oxidization technique, and (4) integrating a metal-oxide-semiconductor gate (MOS-gate) design with high- k Al 2 O 3 gate dielectric. Devices with four different evolutionary gate structures have been compared and studied. Variations of threshold voltage ( V th ), Hooge coefficients ( α H ), maximum drain-source current density ( I DS, max ), maximum extrinsic transconductance ( g m, max ), gate-voltage swing ( GVS ) linearity, two-terminal gate-drain breakdown/turn-on voltages ( BV GD / V on ), on/off current ratio ( I on / I off ), and high-temperature characteristics up to 450 K are also investigated.