Depletion and enhancement mode β-Ga₂O₃ MOSFETs with ALD SiO₂ gate and near 400 v breakdown voltage

As a next generation wide bandgap semiconductor for power electronics, β-Ga₂O₃ (Ga₂O₃) has shown a lot of potential in recent studies. It has been reported to have high Baliga's Figure of Merit (BFoM), a figure of merit for power devices, next only to diamond among wide bandgap semiconductor materials [1]. Moreover, a mature growth technology for large area substrates is a major practical advantage for cost effectiveness and rapid adaptation by industry [2]. Because of the advantages of this material, depletion mode MOSFETs and Schottky diodes based on Ga₂O₃ with high breakdown voltages have been recently demonstrated [3][4]. However, enhancement mode MOSFETs are preferred in power electronics applications. All the previous work incorporated ALD Al₂O₃ as gate barrier due to its high dielectric constant. However, a recent study reported that SiO₂/Ga₂O₃ interface has a much bigger conduction band offset than that of Al₂O₃/Ga₂O₃ [5] which is preferred in MOSFET. In addition, SiO₂/Ga₂O₃ interface has a relatively low interface states density according to our recent data. These properties make SiO₂ an attractive gate dielectric for Ga₂O₃ power MOSFETs. Here, we first report depletion mode MOSFET on MBE grown Ga₂O₃ with an ALD SiO₂ gate. We also report the first successful enhancement mode MOSFET on β-Ga₂O₃. Both depletion mode and enhancement mode MOSFETs show near 400 V off state drain source breakdown voltage.