【International Papers】Over 3 kV and Ultra-Low leakage Vertical (011) β-Ga₂O₃ Power Diodes with Engineered Schottky Contact and High-permittivity Dielectric Field Plate

      Researchers from the Iowa State University have published a dissertation titled " Low leakage Vertical (011) β-Ga₂O₃ Power Diodes with Engineered Schottky Contact and High-permittivity Dielectric Field Plate ". This work utilized (011) substrates provided by Novel Crystal Technology, Japan.

Background

      β-Ga₂O₃ has attracted widespread attention for compact and high-power semiconductor devices due to its ultrawide bandgap (~4.8 eV), controllable shallow dopants, and high critical breakdown field (~8 MV/cm). The availability of melt-grown β-Ga₂O₃ native substrates offers a unique opportunity for cost-effective, large-scale production of ultrawide bandgap (UWBG) power devices. Although various field management techniques—such as field plates, trench structures, guard rings, deep etching, and ion implantation—have been employed to improve the performance of vertical β-Ga₂O₃ power diodes, most reported devices still rely on HVPE-grown ~10 μm-thick (001)-oriented epilayers with relatively high background doping. Moreover, (001) β-Ga₂O₃ epitaxy tends to generate line-shaped dislocations that serve as killer defects, forming leakage paths and degrading breakdown performance, thus limiting voltage scalability. To overcome these issues, homoepitaxial growth of β-Ga₂O₃ in alternative orientations, particularly (011), has been explored since it can reduce dislocation-induced leakage by aligning traps parallel to the (011) plane. However, fundamental studies on the electronic properties and Schottky barrier characteristics of vertical (011) β-Ga₂O₃ Schottky diodes remain limited. Achieving high-voltage operation in such devices requires effective edge field management and engineered Schottky contacts to suppress tunneling leakage and premature breakdown. In this work, vertical (011) β-Ga₂O₃ Schottky barrier diodes were developed by integrating a high-permittivity (ZrO₂) field plate and optimized composite Pt cap/PtOx/Pt (1.5 nm) anode contacts, achieving ultra-low leakage, multi-kilovolt breakdown voltage, and low turn-on voltage—demonstrating the strong potential of (011) β-Ga₂O₃ for next-generation high-voltage power devices.

Abstract

      We report (011) β-Ga₂O₃ power devices with over 3 kV breakdown voltage and ultra-low leakage, achieved through Schottky barrier engineering and high-permittivity (κ) dielectric (ZrO₂) field plates. The (011) orientation of β-Ga₂O₃ enables low background doping and thick drift layers, making it promising for kV-class vertical β-Ga₂O₃ power switches. Schottky barrier engineering was implemented using a composite Pt cap/PtO_x/Pt (1.5 nm) anode contact. This structure takes advantage of the enhanced reverse-blocking capabilities of PtO_x while maintaining low turn-on voltage through the thin interfacing Pt layer. A systematic study was conducted on co-processed Pt/(011) β-Ga₂O₃ Schottky barrier diodes (SBDs) on the same wafer. The bare SBDs exhibited a breakdown voltage of ~1.5 kV, whereas field-plate Pt/(011) β-Ga₂O₃ SBDs showed an increased breakdown voltage of 2.75 kV due to edge-field management. Further enhancement was achieved with the composite Pt cap/PtO_x/Pt (1.5 nm) contacts, effectively managing tunneling leakage and resulting in a breakdown voltage of 3.7 kV for the field-plate diodes. Remarkably, the Pt cap/PtO_x/Pt (1.5 nm) Schottky contacts maintained similar turn-on voltage compared to Pt/(011) β-Ga₂O₃ SBDs. The combination of efficient tunneling leakage suppression, edge-field reduction via the high-κ ZrO₂ field plate, and the intrinsic advantages of (011) β-Ga₂O₃ demonstrates a promising strategy for developing ultra-low leakage, multi-kV-class vertical (011) β-Ga₂O₃ power devices.

Conclusion

      In summary, we report (011) vertical β-Ga₂O₃ high-power Schottky diodes fabricated with high-permittivity (κ) dielectric ZrO₂ field-plate and Schottky barrier engineering with composite Pt cap/PtO_x/Pt (1.5 nm) contacts. The devices enabled excellent reverse bias performance with over 3 kV breakdown voltages with ultra-low leakage current. Moreover, compared to the conventional Pt Schottky contacts, the composite Pt cap/PtO_x/Pt (1.5 nm) allowed significant improvement in reverse blocking capabilities with similar turn-on voltage and lower leakage, which offers opportunities of low-loss, high-voltage power devices. Thus, our work demonstrates the potential of (011) β-Ga₂O₃, benefitted from the thick drift regions with low background doping as well as tailored device fabrication strategies that will be promising for efficient multi-kV class vertical power switches.