Improved drain lag by reduced surface current in GaN HEMT via an ultrathin HfO 2 blanket layer

This paper reports the influence of an ultrathin 1.5 nm atomic-layer-deposited HfO 2 blanket layer as a gate dielectric on GaN high-electron-mobility transistors (HEMTs) grown on a 4H-SiC substrate. Transistors with a gate length of 250 nm and a source-to-drain distance of 3 µ m were manufactured. The proposed technique involves HfO 2 deposition at 250 ∘ C prior to the gate metallization with no additional lithography steps. This approach reduced the drain lag by 83% compared to the conventional design with no gate dielectric. The HfO 2 layer suppressed the parasitic lateral conduction from the gate, reduced surface trapping, and improved gate electrostatics. The manufactured devices exhibited nearly three orders of magnitude decreased surface leakage, better turn-on behavior, and improved cut-off frequency f T linearity by 16%. High quality metal-oxide interface formation was confirmed by the conductance method. Results demonstrate that the blanket HfO 2 deposition is a promising approach to improve the current dispersion characteristics and gate electrostatics of GaN HEMTs without incurring major changes to the established fabrication techniques.