Among various polymorphic phases of gallium oxide (Ga₂O₃), α-phase Ga₂O₃ has clear advantages such as its heteroepitaxial growth as well as wide bandgap, which is promising for use in power devices. In this work, we demonstrate α-Ga₂O₃ MOSFETs with hybrid Schottky drain (HSD) contact, comprising both Ohmic and Schottky electrode regions. In comparison with conventional Ohmic drain (OD) contact, a lower on-resistance (R_on) of 2.1 kΩ mm is achieved for variable channel lengths. Physics-based TCAD simulation is performed to validate the turn-on characteristics of the Schottky electrode region and the improved R_on. Electric-field analysis in the off-state is conducted for both the OD and HSD devices. Furthermore, a record breakdown voltage (BV) of 2.8 kV is achieved, which is superior to the 1.7 kV of the compared OD device. Our results show that the proposed HSD contact with a further optimized design can be a promising drain electrode scheme for α-Ga₂O₃ power MOSFETs.

AlGaN/GaN metal-oxide semiconductor high electron mobility transistors (MOS-HEMTs) with undoped ferroelectric HfO₂ have been investigated. Annealing is often a critical step for improving the quality of as-deposited amorphous gate oxides. Thermal treatment of HfO₂ gate dielectric, however, is known to degrade the oxide/nitride interface due to the formation of Ga-containing oxide. In this work, the undoped HfO₂ gate dielectric was spike-annealed at 600 °C after the film was deposited by atomic layer deposition to improve the ferroelectricity without degrading the interface. As a result, the subthreshold slope of AlGaN/GaN MOS-HEMTs close to 60 mV/dec and on/off ratio>10⁹ were achieved. These results suggest optimizing the HfO₂/nitride interface can be a critical step towards a low-loss high-power switching device.

Various high-k dielectrics have been proposed for AlGaN/GaN MOSHEMTs for gate leakage and drain-current collapse suppression. Hafnium oxide (HfO₂) is particularly interesting because of its large bandgap, high dielectric constant, and ferroelectricity under specific phase and doping conditions. However, defects and surface scattering caused by HfO₂ dissimilarity and degraded HfO₂/GaN interface quality still leave the challenge of reducing the SS and R_on. In this study, we investigated the effects of the first spike-annealed HfO₂ (6 nm) layer, compared with the conventional ALD-HfO₂ (6 nm) layer in the HfO₂ bilayer gate dielectric structure on AlGaN/GaN HEMTs. Both devices exhibit negligible hysteresis and near-ideal (~60 mV/dec) subthreshold slopes of more than three orders of magnitude. The device with the first annealed HfO₂ layer exhibited a reduced R_on with notably less gate bias dependency and enhanced output current. On the other hand, the capacitance–voltage and conductance methods revealed that the border and interface trap densities of the device were inferior to those of the conventional HfO₂ layer. The trade-off between enhanced electrical performance and oxide traps is discussed based on these results.