We fabricated high forward and low leakage current trench MOS-type Schottky barrier diodes (MOSSBDs) in combination with a field plate on a 12 μm thick epitaxial layer grown by halide vapor phase epitaxy on β-Ga2O3 (001) substrate. The MOSSBDs, measuring 1.7 × 1.7 mm2, exhibited a forward current of 2 A (70 A cm−2) at 2 V forward voltage and a leakage current of 5.7 × 10–10 A at −1.2 kV reverse voltage (on/off current ratio of > 109) with an ideality factor of 1.05 and wafer-level specific on-resistance of 17.1 mΩ · cm2.

β-Ga2O3 (001) Schottky barrier diodes (SBDs) fabricated on a halide vapor phase epitaxy-grown epilayer showed anomalous reverse leakage characteristics, which could not be explained through thermionic field emission theory. A systematic investigation through the measurements and simulations of capacitance-voltage and current density-voltage characteristics suggested the presence of a thin surface layer on the epilayer with high density of oxygen vacancy states. This thin surface layer allowed the tunneling of electrons and caused anomalous reverse leakage properties (Thin surface barrier model). Annealing of the epilayer in an oxidative environment passivated the surface oxygen vacancy states and reduced the reverse leakage current enormously.

Electrical characteristics of vertical Schottky barrier diodes (SBDs) fabricated on as-grown and oxygen annealed β-Ga 2 O 3 (001) epilayers were investigated. SBDs on as-grown epilayer showed anomalous reverse leakage characteristics. Annealing of β-Ga 2 O 3 epilayers in an oxygen-containing environment up to 40 min immensely reduced the reverse leakage current. The specific onresistance (R on ) of the SBD remained very close to that of the as-grown sample for annealing up to 20 min and increased almost by 25 times for annealing up to 40 min. Simulations of reverse tunneling characteristics, assuming oxygen vacancy type surface states, explained both the magnitude and the shape of anomalous reverse leakage. The diffusion of oxygen during annealing passivated the oxygen vacancy type surface states at first (for 20 min annealing)-resulting in two orders of reduction in leakage with minimal change in R on . Further annealing (up to 40 min) subsequently reduced the epilayer net carrier concentration from 3.3 × 10 16 to 2.9 × 10 15 cm −3 -resulting in immense change in both reverse leakage and R on . Thus, oxygen annealing proved to be a vital technique for the passivation of surface states and to reduce the net carrier concentration, which allows the modulation of reverse leakage of β-Ga 2 O 3 SBDs.

UMOSFET is theoretically suitable to decrease the on-resistance of the MOSFET. In this study, in order to determine the cell structure of the SiC UMOSFET with extremely low on-resistance, influences of the orientation of the trench and the off-angle of the wafer on the MOS properties are investigated. The channel resistance, gate I-V curves and instability of threshold voltage are superior on the {11-20} planes as compared with other planes. On the vicinal off wafer, influence of the off-angle disappears and the properties on the equivalent planes are almost the same. The obtained results indicate that the extremely low on-resistance with the high stability and high reliability is possible in the SiC UMOSFET by the hexagonal cell composed of the six {11-20} planes on the vicinal off wafer, and actually an extremely low channel resistance was demonstrated on the hexagonal UMOSFET with the six {11-20} planes on the vicinal off wafer.

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