In this Letter, high-performance β-Ga2O3 vertical heterojunction barrier Schottky (HJBS) diodes have been demonstrated together with the investigation of reverse leakage mechanisms. In HJBS configurations, NiO/β-Ga2O3 p-n heterojunctions and p-NiO field limiting rings (FLRs) are implemented by using a reactive sputtering technique at room temperature without intentional etching damages. Determined from the temperature-dependent current-voltage characteristics, the reverse leakage mechanism of the HJBS diode is identified to be Poole-Frenkel emission through localized trap sates with an energy level of EC-0.72 eV. With an uniform FLR width/spacing of 2 μm in HJBS, a maximum breakdown voltage (BV) of 1.89 kV and a specific on-resistance (Ron,sp) of 7.7 mΩ·cm2 are achieved, yielding a high Baliga's figure-of-merit (FOM, BV2/Ron,sp) of 0.46 GW/cm2. The electric field simulation and statistical experimental facts indicate that the electric field crowding effect at device edges is greatly suppressed by the shrinkage of p-NiO FLR spacing, and the capability of sustaining high BV is enhanced by the NiO/β-Ga2O3 bipolar structure, both of which contribute to the improved device performance. This work makes a significant step to achieve high performance β-Ga2O3 power devices by implementing alternative bipolar structures to overcome the difficulty in p-type β-Ga2O3.

Epitaxial film quality is critical to the success of high-performance a-Ga 2 O 3 vertical power devices. In this work, the origins of threading dislocation generation and annihilation in thick a-Ga 2 O 3 films heteroepitaxially grown on sapphire by the mist-CVD technique have been examined by means of high-resolution X-ray diffraction and transmission electron microscopies. By increasing the nominal thickness, screw dislocations exhibit an independent characteristic with a low density of about 1.8 Â 10 6 cm À2 , while edge dislocations propagating along the c-axis are dominant, which decrease down to 2.1 Â 10 9 cm À2 in density for an 8 lm-thick a-Ga 2 O 3 layer and exhibit an inverse dependence on the thickness. In the framework of the glide analytical model, parallel edge dislocations are generated at the interface due to the misfitinduced strain relaxation, while the dislocation glide and coalescence result in the annihilation and fusion behaviors. The optimal thick a-Ga 2 O 3 with low dislocation densities may provide a prospective alternative to fully realize a-Ga 2 O 3 power devices.

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Integration of intriguing ferroelectric κ-Ga2O3 on other oxide semiconductors opens an exciting avenue to invoke emergent transport phenomena and enable rational design of advanced device architectures, whereas the fundamental growth dynamics and physical properties of metastable κ-Ga2O3 are still far unexplored. In this work, we report on the heterostructure construction of single crystalline metastable orthorhombic κ-Ga2O3 epilayers and cubic In2O3(111) by means of laser molecular beam epitaxy. Elements of Sn and In are found to segregate to the growth surface and serve as surfactants to reduce the total surface energy and diffusion barrier of oxygen adatoms, hence producing Ga-rich conditions on the growth front, which in turn facilitates the stabilization of κ-phase Ga2O3. Depth-profiled X-ray photoemission spectral (XPS) analysis identified a type-I band alignment with a conduction band offset (CBO) of 0.45 eV and a valence band offset (VBO) of −1.15 eV for a κ-Ga2O3/In2O3 heterostructure. Determined by the analysis of Hall results with a double-layer model, a two-dimensional electron gas (2DEG) with a sheet carrier concentration of 1.2 × 1014 cm–2 and an enhanced mobility of 192 cm2/(V s) is confined at the heterostructure interface. The self-consistent Poisson–Schrödinger calculations indicate that the enhanced interfacial conductivity is a result of the combination of polarization manipulation and band discontinuity, well-supported by the characteristics of piezoelectric force microscopy and depth-profiled XPS. Integrating κ-Ga2O3 on other hexagonal polar semiconductors may open a possibility to manipulate the interfacial conductivity through polarization engineering and deliver advanced devices with multiple functionalities.