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

Comparative studies for TiO2-passivated Al0.25Ga0.75N/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 ( \alpha _{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 TiO2-dielectric MOS-HFET/TiO2-passivated HFETs are obtained, including 47.6%/23.8% in two-terminal gate–drain breakdown voltage (BV _{\rm GD}) , 111%/22.2% in two-terminal gate-drain turn-ON voltage ( V\mathrm{{\scriptscriptstyle ON}}) , 47.9%/39.4% in ON-state breakdown (BV DS) , 12.2%/10.2% in drain–source current density ( IDS) at VGS = 0 V ( IDSS0) , 27.2%/11.7% in maximum IDS ( IDS, max) , 3/1-order enhancement in on/off current ratio ( I\mathrm{{\scriptscriptstyle ON}} / I\mathrm{{\scriptscriptstyle OFF}}) , 58.8%/17.6% in gate-voltage swing linearity, 25.1%/13.2% in unity-gain cutoff frequency ( fT) , 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. [ABSTRACT FROM AUTHOR]