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

Systematic designs to achieve normally-off operation and improved device performance for A(10.26)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 CF4 plasma treatment, (3) growing the Al2O3 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 Al2O3 gate dielectric. Devices with four different evolutionary gate structures have been compared and studied. Variations of threshold voltage (V-th), Hooge coefficients (alpha(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 (BVGD/V-on), on/off current ratio (I-on/I-off), and high-temperature characteristics up to 450 K are also investigated.