【International Papers】VBr >10 kV E-Beam/Sputtered Vertical NiOx/(011) β-Ga₂O₃ HJDs with PFOM >2.3 GW/cm²

      Researchers from the University of California and United States Naval Research Laboratory (NRL) have published a dissertation titled "V_Br >10 kV E-Beam/Sputtered Vertical NiOx/(011) β-Ga₂O₃ HJDs with PFOM >2.3 GW/cm²".

Background

      The rapid expansion of data centers for artificial intelligence (AI) and charging networks for electric vehicles (EVs) have stimulated the necessity for efficient, cost-effective grid-level transmission and power conversion circuits at medium voltage level (1-35 kV). Solid states transformers (SSTs) are critical for data centers in enabling efficient, high power density distribution by replacing conventional magnetic transformers with power semiconductor-based converters. Enormous market potential is available in direct-to-rack power conversion for AI data centers that facilitate large voltage (13.5-35 kV, AC) to 800 V DC to reduce immediate power conversion steps, improving efficiencies for AI graphics processing units (GPUs) and accelerators. The high critical electric field strength (6-8 MV/cm) and availability of the shallow hydrogenic dopants in epitaxial β-Ga₂O₃ can be leveraged to demonstrate power devices with much lower differential specific on-resistance while operating at a higher blocking voltage compared to silicon carbide (SiC) and gallium nitride (GaN). Although reliable p-type doping is currently not available in β-Ga₂O₃, heterojunctions formed with p-NiO_x are able to realize multi-kV class junctions along with breakdown electric field anisotropy across various orientations.

Abstract

      Beta-gallium oxide (β-Ga₂O₃) holds enormous potential for medium voltage range power electronic applications. This work reports V_Br > 10 kV/R_on,sp = 43 mΩ•cm² class edge terminated vertical heterojunction diodes (HJDs) with e-beam/sputtered nickel oxide (NiO_x) stack on epitaxial (011) β-Ga₂O₃. The power figure of merit (PFOM) of the HJD exceeds 2.3 GW/cm². The extracted parallel plane breakdown field is > 5.3 MV/cm, which is the highest reported electric field for thick (011) β-Ga₂O₃ epitaxial drift layer.

Conclusion

      This work demonstrates >10 kV class NiO_x/(011) HVPE β-Ga₂O₃ heterojunction diodes by combining e-beam and sputtered NiO_x as the p-type layers. The field-plated HJD with mesa-isolation accomplishes a PFOM value > 2.3 GW/cm² and a parallel-plane breakdown electric field > 5.3 MV/cm. The high breakdown voltage/electric field accomplished on (011) β-Ga₂O₃ along with large PFOM value suggests this substrate orientation possesses potential for high electric field handling capability.