【Member Papers】Synergistic work function modulation and interface traps suppression in CuCrO₂/β-Ga₂O₃ p-n heterojunction diodes through oxygen vacancy passivation

      A research team led by Prof. Weifeng Yang from Xiamen University has published a paper in the international journal Journal of Alloys and Compounds, entitled:Synergistic work function modulation and interface traps suppression in CuCrO₂/β-Ga₂O₃ p-n heterojunction diodes through oxygen vacancy passivation.

Background

      Gallium oxide (Ga₂O₃), as an emerging ultra-wide bandgap semiconductor, features a wide bandgap of 4.9 eV and a high critical breakdown field of 8 MV/cm, showing great potential for next-generation high-power electronic devices. In addition, it supports melt growth of large-size wafers, offering advantages for low-cost industrial-scale production. However, due to the strong localization of holes, achieving effective p-type doping remains a key bottleneck. To overcome this limitation, integrating p-type materials such as Cu₂O, SnO, and NiO with n-type β-Ga₂O₃ to form heterojunction diodes (HJDs) has become a mainstream strategy. Among them, delafossite-structured CuCrO₂ is considered a highly promising p-type transparent oxide due to its high transparency, excellent thermal stability, and tunable carrier concentration.  However, CuCrO₂ films prepared by magnetron sputtering typically contain a high density of intrinsic defects, especially oxygen vacancies (V_O). These oxygen vacancies act as donor states, compensating acceptors and suppressing p-type conductivity. In addition, V_O-related traps in both the bulk and interface capture carriers, enhance recombination, and increase leakage current, thereby degrading device performance. Currently, the trap-limited transport mechanisms in CuCrO₂/β-Ga₂O₃ heterojunctions remain insufficiently understood. Therefore, developing effective interface and bulk optimization strategies is crucial for high-efficiency and high-reliability Ga₂O₃-based power devices.

Abstract

      This work reports a vertical p–n heterojunction diode based on CuCrO₂/β-Ga₂O₃, with oxygen plasma treatment used to achieve synergistic control of both interface and bulk properties. Experimental results show that oxygen plasma effectively passivates oxygen vacancies in CuCrO₂ and promotes the oxidation of Cu⁺ to Cu²⁺. With reduced oxygen vacancies and increased hole concentration, the contact resistance of Ni/CuCrO₂ decreases, and the specific on-resistance is reduced from 6.4 mΩ·cm² to 5.2 mΩ·cm². In terms of reverse characteristics, the breakdown voltage increases from 1110 V to 1785 V. KPFM measurements show that the work function increases from 4.99 eV to 5.18 eV, and the built-in potential rises from 2.04 V to 2.16 V. The interface trap density decreases from 7.98×10¹² cm⁻²·eV⁻¹ to 6.02×10¹² cm⁻²·eV⁻¹. Leakage paths associated with SRH recombination and Poole–Frenkel emission are effectively suppressed. 

Key Innovations

      A synergistic oxygen vacancy passivation strategy enables simultaneous optimization of interface and bulk properties.

      Device performance is significantly improved, with PFOM increased by 221%.

      The work function and built-in potential are simultaneously enhanced, strengthening the rectification barrier.

      Trap-related transport mechanisms are suppressed, reducing leakage current.

Conclusion

      This study demonstrates that O₂ plasma-induced oxygen vacancy passivation provides a synergistic approach to simultaneously improve the interface and bulk electronic properties of CuCrO₂/β-Ga₂O₃ heterojunction diodes. The treatment enhances the p-type conductivity of CuCrO₂, increases the work function (Φ) and built-in potential , and improves Ni/CuCrO₂ ohmic contact by increasing hole concentration and reducing contact resistivity , thereby lowering the on-resistance. Band alignment analysis shows that the increased conduction band offset  strengthens the barrier against electron injection, effectively suppressing reverse leakage. Meanwhile, trap-related mechanisms are mitigated through passivation, reducing dominant leakage paths associated with PF emission and SRH recombination. TCAD simulations further confirm that the O₂ plasma treatment alleviates electric field crowding near the anode by simultaneously increasing hole concentration and reducing interface trap density (D_it), resulting in a more uniform electric field distribution. These results highlight oxygen vacancy passivation as a practical and scalable strategy for simultaneous interface and bulk optimization, offering strong potential for next-generation wide bandgap oxide power electronic devices.