【International Papers】>3kV NiO/Ga₂O₃ Heterojunction Diodes With Space-Modulated Junction Termination Extension and Sub-1V Turn-On

      Researchers from the Arizona State University have published a dissertation titled ">3kV NiO/Ga₂O₃ Heterojunction Diodes With Space-Modulated Junction Termination Extension and Sub-1V Turn-On" in IEEE Journal of the Electron Devices Society.

Background

      Over the past decade, β-Ga₂O₃ has emerged as a prime candidate for next generation power electronics, owing to the high critical electric field (8 MV/cm), ease of n-type doping, and availability of large-area single crystal substrates. The availability of high quality, low defect density β-Ga₂O₃ drift-layers grown on bulk β-Ga₂O₃ substrates coupled with advanced damage-free etching techniques are paving the way for high-performance Ga₂O₃ power devices. In particular, two-terminal vertical β-Ga₂O₃ devices have shown great improvements in performance over the past few years, exceeding the unipolar FOM of both SiC and GaN. Majority of these reports employ p-NiO/Ga₂O₃ heterojunctions that have demonstrated superior breakdown performance. However, a key limitation with these HJDs is the much larger turn on voltage (V_ON) of ~2V. A higher VON results in significantly higher conduction losses (~I_ON² V_F, where V_F=V_ON+ I_ON× R_on,sp), degrading device efficiency. Therefore, achieving high breakdown voltage while maintaining low V_ON is critical for enabling low-loss β-Ga₂O₃ rectifiers.

Abstract

      This work demonstrates high-performance vertical NiO/Ga₂O₃ heterojunction diodes (HJDs) with a 2-step space-modulated junction termination extension. Distinct from the current state-of-the-art Ga₂O₃ HJDs, we achieve breakdown voltage exceeding 3 kV with a low turn on voltage (V_ON) of 0.8V, estimated at a forward current density (I_F) of 1 A−cm^-2. The measured devices exhibit excellent turn-on characteristics achieving 100 A−cm^-2 current density at a forward bias of 1.5 V along with a low differential specific on-resistance (R_on,sp) of 4.4 m Ω -cm². The SM-JTE was realized using concentric NiO rings with varying widths and spacing that approximates a gradual reduction in JTE charge. The unipolar figure of merit (FOM) calculated exceeds 2 GW-cm² and is among the best reported for devices with a sub-1V turn-on. The fabricated devices also displayed minimal change in forward I-V characteristics post reverse bias stress of 3 kV applied during breakdown voltage testing.

Conclusion

      In conclusion, we demonstrate p-NiO/Ga₂O₃ HJDs with space-modulated junction termination extension (SM-JTE) enabling a gradual reduction in JTE charge. We simultaneously obtain excellent forward and reverse performance including a low V_ON of 0.8 V, V_BR of 3 kV and R_on of 4.4 mΩ -cm^-2 resulting in a power figure of merit exceeding 2 GW-cm^-2. We also report a record low effective R_on of 14.5mΩ-cm^-2 for NiO/Ga₂O₃ HJDs. The high-voltage reverse blocking capacity with sub-1V turn-on voltage showcases the great promise of Ga₂O₃ HJDs for low-loss kilovolt class power electronics.