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

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 beta-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) over bar 01) orientation peaks of beta-Ga2O3 in the device structure. The van der Pauw and Hall measurements yield the electron density of similar to 4 x 10(18) cm(-3) and mobility of similar to 770 cm(2)V(-1)s(-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 similar to 1.5 x 10(13) 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 similar to 10(12) cm(2)eV(-1). A significant reduction in leakage current from similar to 10(-4) A/cm(2) for HFET to similar to 10(-6) A/cm(2) for MOSHFET was observed well beyond pinch-off in the off-stage at -20 V applied gate voltage. The annealing at 900 degrees 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.