Investigations of TiO2–AlGaN/GaN/Si-Passivated HFETs and MOS-HFETs Using Ultrasonic Spray Pyrolysis Deposition

Comparative studies for TiO₂-passivated Al_0.25Ga_0.75N/GaN heterostructure FETs (HFETs) and TiO₂-dielectric MOS-HFETs using nonvacuum ultrasonic spray pyrolysis deposition technique are made. Optimum device performances are obtained by tuning the layer thickness of TiO₂ to 20 nm. High relative permittivity (k) of 53.6 and thin effective oxide thickness of 1.45 nm are also obtained. Pulse-IV, Hooge coefficient (α_H), Transmission Electron Microscopy, and atomic force microscope have been performed to characterize the interface, atomic composition, and surface flatness of the TiO₂ oxide. Superior improvements for the present TiO2dielectric MOS-HFET/TiO₂-passivated HFETs are obtained, including 47.6%/23.8% in two-terminal gate-drain breakdown voltage (BV_GD), 111%/22.2% in two-terminal gate-drain turnON voltage (V_ON), 47.9%/39.4% in ON-state breakdown (BV_DS), 12.2%/10.2% in drain-source current density (I_DS) at V_GS = 0 V (I_DSS0), 27.2%/11.7% in maximum I_DS (I_DS,max), 3/1-order enhancement in ON/OFF current ratio (I_ON/I_OFF), 58.8%/17.6% in gate-voltage swing linearity, 25.1%/13.2% in unity-gain cutoff frequency (f_T), 40.6%/24.7% in maximum oscillation frequency (f_max), and 33.8%/15.6% in power-added efficiency with respect to a Schottky-gated HFET fabricated on the identical epitaxial structure. The present MOS-HFET has also shown stable electrical performances when the ambient temperature is varied from 300 to 450 K.