【Domestic Papers】Theoretical study on interfacial tuning via Ga/Zn mutual cation doping: Mechanism in Ga₂O₃/ZnO heterojunctions

      Researchers from the Inner Mongolia University of Technology have published a dissertation titled "Theoretical study on interfacial tuning via Ga/Zn mutual cation doping: Mechanism in Ga₂O₃/ZnO heterojunctions" in Chemical Engineering Journal.

Project Support

      This work was supported by the National Natural Science Foundation of China (Grant No. 12164031), the Natural Science Foundation of Inner Mongolia (Grant Nos. 2023LHMS01004, NJZY22376 and JY20250043).

Background

      β-Ga₂O₃ possesses a wide range of applications in photodetectors due to the wide band-gap of 4.9 eV, high breakdown electric field of 6–8 MV/cm, short absorption cutoff edge, excellent stability, ease of preparation, and low loss. The desirable band-gap of β-Ga₂O₃ enhances its absorption properties in the solar-blind ultraviolet (UV) region, where solar-blind UV light is absorbed by the ozone layer and is almost absent at the Earth's surface. Therefore, β-Ga₂O₃ exhibits unique characteristics of low background noise and high sensitivity, making it widely used in applications such as environmental monitoring, space communication, missile tracking, and biomedical research Currently, Metal-Semiconductor (MS) and Metal-Semiconductor-Metal (MSM) structures are much commonly used for β-Ga₂O₃-based solar-blind UV detectors, with MSM β-Ga₂O₃ detectors already in commercial operation. However, these detectors suffer from continuous photoconductivity, slow response times, and the need for an external power supply to operate. The response speed of optoelectronic devices is primarily affected by the mobility and recombination rates of charge carriers. Therefore, improving the mobility and recombination speed of charge carriers is a key challenge in optimizing β-Ga₂O₃ based optoelectronic devices.

      Therefore, in this work, the photoelectric properties of g-ZnO/β-Ga₂O₃ heterojunctions were systematically investigated. In particular, the mechanism by which the introduction of intrinsic defects such as V_O, Ga_Zn, and Zn_Ga modulate the photoelectric behavior of the heterojunctions were examined. This doping strategy enabled the fabrication of heterojunction optoelectronic devices with enhanced performance, thereby providing a theoretical foundation for the design of high-efficiency optoelectronic systems.

Abstract

      The ultra-wide band-gap of β-Ga₂O₃ makes it highly suitable for solar-blind UV detection. However, intrinsic oxygen vacancies (V_O) hinder its performance by acting as recombination centers and obstructing carrier transport. We demonstrate that g-ZnO/β-Ga₂O₃ heterojunctions, with controlled Ga_Zn (Ga → Zn) and Zn_Ga (Zn → Ga) doping, can mitigate these limitations. Ga_Zn doping reduces the n-type conductivity of g-ZnO, reduces the Schottky barrier height, and increases the dielectric response, while Zn_Ga doping improves the n-type conductivity of β-Ga₂O₃ and lowers interfacial barriers, resulting in an 80.8 % tunneling probability, an increase in charge transfer, and a more than 7-fold improvement in mobility. Co-doping establishes an S-shaped charge transfer pathway through HOMO electron-valence band hole recombination, enhancing conductivity compared to undoped structures. The heterostructure exhibits strong UV absorption in the 200–300 nm range, along with improved responsivity. These results present a doping strategy for high-performance β-Ga₂O₃ photodetectors, particularly for solar-blind applications that demand fast response time and low dark current.

Highlights

      ● Interfacial barrier control (Φ_B↓) suppresses V_O recombination.

      ● Novel S-path carrier injection mechanism

      ● High-speed UV detection in solar-blind region

Conclusion

      This study elucidates the critical role of oxygen vacancies (V_O) and dopants (Ga_Zn, Zn_Ga) in modulating the optoelectronic properties of g-ZnO/β-Ga₂O₃ heterostructures. The presence of V_O introduces mid-gap states that impede carrier separation, while Ga/Zn doping effectively adjusts the Fermi level and alters the built-in electric field, thereby reducing interface barriers and enhancing charge transport. Notably, the g-ZnO-V_O:Ga_Zn/β-Ga₂O₃-V_O system forms an ohmic contact, enabling unimpeded carrier flow . In contrast, the g-ZnO-V_O:Ga_Zn/β-Ga₂O₃-V_O:Zn_Ga configuration establishes an S-type heterojunction that facilitates efficient charge separation. These findings underscore the potential of controlled defect engineering in optimizing interfacial properties, providing valuable insights for the design of high -performance, self-powered solar-blind photodetectors.