MOCVD-grown β-Ga₂O₃ as a Gate Dielectric on AlGaN/GaN-Based Heterojunction Field Effect Transistor

Abstract

We report the electrical properties of Al0.3Ga0.7N/GaN heterojunction field effect transistor (HFET) structures with a Ga2O3 passivation layer grown by metal–organic chemical vapor deposition (MOCVD). In this study, three different thicknesses of β-Ga2O3 dielectric layers were grown on Al0.3Ga0.7N/GaN structures leading to metal-oxide-semiconductor-HFET or MOSHFET structures. X-ray diffraction (XRD) showed the (2¯01) orientation peaks of β-Ga2O3 in the device structure. The van der Pauw and Hall measurements yield the electron density of ~ 4 × 1018 cm−3 and mobility of ~770 cm2V−1s−1 in the 2-dimensional electron gas (2DEG) channel at room temperature. Capacitance–voltage (C-V) measurement for the on-state 2DEG density for the MOSHFET structure was found to be of the order of ~1.5 × 1013 cm−2. The thickness of the Ga2O3 layer was inversely related to the threshold voltage and the on-state capacitance. The interface charge density between the oxide and Al0.3Ga0.7N barrier layer was found to be of the order of ~1012 cm2eV−1. A significant reduction in leakage current from ~10−4 A/cm2 for HFET to ~10−6 A/cm2 for MOSHFET was observed well beyond pinch-off in the off-stage at -20 V applied gate voltage. The annealing at 900° C of the MOSHFET structures revealed that the Ga2O3 layer was thermally stable at high temperatures resulting in insignificant threshold voltage shifts for annealed samples with respect to as-deposited (unannealed) structures. Our results show that the MOCVD-gown Ga2O3 dielectric layers can be a strong candidate for stable high-power devices.

Keywords

• GaN
• MOSHFET
• Ga₂O₃
• MOCVD
• gate dielectric