Thermally Grown TiO2 and Al2O3 for GaN-Based MOS-HEMTs

We have demonstrated the potential use of thermally grown TiO2 and Al2O3 oxides as gate dielectrics for GaN-based high-electron-mobility-transistors. TiO2 and Al(2)O(3 )are found to provide negative and positive band offsets with AIGaN, 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 TiO2- and Al2O3-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) x 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.