Thermally Grown TiO 2 and Al 2 O 3 for GaN-Based MOS-HEMTs

We have demonstrated the potential use of thermally grown TiO 2 and Al 2 O 3 oxides as gate dielectrics for GaN-based high-electron-mobility-transistors. TiO 2 and Al 2 O 3 are found to provide negative and positive band offsets with AlGaN, respectively. A significant performance improvement on various device characteristics provides evidence for its potential use. The oxides are formed by a combination of predeposition of a thin film and followed by oxidation in pure O 2 environment. The formation and thickness of the oxides are confirmed through the X-ray photoelectron spectroscopy and the transmission electron microscopy. The performance improvement for TiO 2 - and Al 2 O 3 -based oxide gates have been identified in terms of a ideality factor and a reduction in the gate leakage current in comparison with that of control devices. This is further augmented by an increase in the ${n}_{s}\times \mu $ product. The ON/OFF current ratio and turn-ON voltage increase by 2–3 orders of magnitude and 0.3–0.6, respectively, for the Schottky diodes. The negative shift on the capacitance–voltage characteristics is also found to be minimal, indicating higher gate coupling with thermally grown oxides.