【Member Papers】Interface-engineered Ga₂O₃ photodetectors with quantum-dot-assisted band modulation for spectrum-selective UVC detection

      Researchers from the Xidian University, Fudan University and Northwestern Polytechnical University have published a dissertation titled " Interface-engineered Ga₂O₃ photodetectors with quantum-dot-assisted band modulation for spectrum-selective UVC detection" in Materials Today Electronics.

Background

      Ultraviolet-C (UVC, 200–280 nm) photodetectors are widely used in flame detection, environmental monitoring, secure optical communication, solar-blind imaging, quantum photonics and autonomous sensing. With the development of related fields, UVC detectors are required to achieve high responsivity and millisecond-level temporal response under ultra-weak illumination. However, traditional wide-bandgap semiconductors such as ZnO, AlGaN and diamond have problems such as complex epitaxy, high defect density and limited carrier transport, which restrict the simultaneous optimization of sensitivity and response speed. As an emerging wide-bandgap semiconductor material, Ga₂O₃ has a band gap of 4.9–5.2 eV, good thermal and chemical stability, and intrinsic solar-blind response characteristics, making it an ideal material for UVC photodetectors. Nevertheless, the intrinsic n-type conductivity and doping asymmetry of Ga₂O₃ hinder the fabrication of high-efficiency p-n junctions, resulting in low carrier extraction efficiency in Schottky and MSM photodetectors. Constructing heterojunctions with p-type semiconductors can introduce built-in electric fields and adjustable band offsets, which is an effective way to solve the above problems. However, the existing Ga₂O₃-based heterojunction photodetectors still have high dark current and slow photoresponse due to interface recombination and trap-assisted carrier dynamics.

Abstract

      Achieving fast and highly sensitive ultraviolet-C (UVC) detection under ultra-weak illumination remains challenging due to inefficient carrier separation and severe interfacial recombination in wide-bandgap semiconductors. Here, the team reports an interface-engineered Ga₂O₃-based photodetector by integrating p-type NiO quantum dots (p-NQDs) onto an n-type Ga₂O₃ channel to form a surface-type heterojunction. The introduction of the p-NQDs modifies the interfacial energy landscape, leading to enhanced built-in electric fields and suppressed recombination at the Ga₂O₃ surface. Benefiting from the type-II band alignment and interfacial modulation, the heterojunction device achieves an ultralow dark current of ~10⁻¹⁴ A, a high responsivity of 4.66 A/W, and a detectivity of 5.56 × 10¹⁴ Jones under 254 nm illumination. Time-resolved measurements reveal a significantly accelerated photoresponse with rise and decay times down to tens of milliseconds, indicating improved carrier transport dynamics compared with pristine Ga₂O₃ devices. Furthermore, a proof-of-concept single-pixel UVC imaging demonstration confirms high-contrast spatial mapping capability under weak illumination. These results suggest that quantum-dot-assisted interfacial engineering provides an effective strategy for modulating carrier dynamics in oxide semiconductors, offering insights for the development of high-sensitivity solar-blind UVC photodetectors.

Highlights

      Propose a quantum-dot-mediated surface heterojunction strategy for Ga₂O₃-based UVC photodetectors by selectively integrating p-type NiO quantum dots onto n-type Ga₂O₃ channel.

      Realize type-II band alignment at p-NQDs/n-Ga₂O₃ interface, which enhances built-in electric field, suppresses interfacial recombination and improves carrier separation efficiency.

      Obtain ultra-low dark current (~10⁻¹⁴ A), high responsivity (4.66 A/W), high detectivity (5.56 × 10¹⁴ Jones) and millisecond-level response speed (rise time 24 ms, decay time 8 ms) under 254 nm illumination.

      Complete proof-of-concept single-pixel UVC spatial mapping with high contrast under weak illumination, verifying the imaging application potential.

Conclusion

      The team reports an interface-engineered p-NQDs/n-Ga₂O₃ photodetector that achieves enhanced performance in the solar-blind UVC region through interface modulation enabled by type-II band alignment. The incorporation of p-NQDs modifies the interfacial electronic structure and provides defect passivation, facilitating carrier separation and suppressing recombination losses. As a result, the device exhibits a high responsivity of 4.66 A/W, a specific detectivity of 5.56 × 10¹⁴ Jones, and a fast response with rise and decay times of 24 ms and 8 ms, respectively, under 254 nm illumination. Furthermore, a proof-of-concept single-point UVC spatial mapping demonstration reveals clear pattern recognition with high contrast under low-intensity illumination, highlighting the potential of the device for spatial light discrimination. These results underscore the effectiveness of interface engineering using quantum dots as an approach for tuning carrier dynamics in Ga₂O₃-based heterostructures. This work provides insights into the design of low-dark-current, high-sensitivity solar-blind UVC photodetectors and suggests a promising pathway toward advanced deep-UV sensing and imaging applications.

Project Support

      National Natural Science Foundation of China (Grant No. 62404176, 62293522, 12175298), National Key R&D Program of China (No. 2024YFF1504400), Zhejiang Provincial Natural Science Foundation of China (LDT23F0402, LDT23F04024F04), Leading innovation and entrepreneurship Project of Zhejiang Province (2023R01014), the key program of Shannxi Provincial Department of science and technology support (2024CY2-GJHX-81).