【Domestic Papers】Ultrahigh-Performance Photovoltaic Ga₂O₃ Solar-Blind Ultraviolet Detectors via Two-Dimensional Step-Flow Growth and Drift Region Optimization

      Researchers from the Fuzhou University have published a dissertation titled "Ultrahigh-Performance Photovoltaic Ga₂O₃ Solar-Blind Ultraviolet Detectors via Two-Dimensional Step-Flow Growth and Drift Region Optimization" in ACS Applied Materials & Interfaces.

Project Support

      This work was financially supported by the National Natural Science Foundation of China (Grant No. 62204270), the Major Science and Technology Special Project of Fujian Province (Grant No. 2022HZ027006), the Quanzhou Municipal Science and Technology Major Project (Grant No. 2022GZ7), the Department of Science and Technology of Fujian Province (Fujian Provincial Industry-University Cooperation Project, Grant No. 2023H6030), and the Fujian Provincial Natural Science Foundation General Program (Grant No. 2024J01251).

Background

      The solar-blind ultraviolet (SBUV) band offers a particularly “clean” detection window for various applications such as fire detection, ozone-hole monitoring, missile warning, and corona discharge observation. Nowadays, there is a growing demand for photovoltaic solar-blind ultraviolet photodetectors (SBPDs) that exhibit selective response, high quantum efficiency, and zero power consumption, especially for applications operating without a power supply. Wide-bandgap semiconductor materials that exhibit selective response to SBUV include Ga₂O₃, the AlₓGa₁₋ₓN system, and the MgₓZn₁₋ₓO system. The latter two material systems face significant challenges in producing high-performance photovoltaic SBPDs due to issues such as precise bandgap tuning, lattice mismatch with the substrate, and phase separation. In comparison, Ga₂O₃ exhibits a direct bandgap of 4.8 eV corresponding to the SBUV band, eliminating the need for bandgap tuning by doping or alloying. Furthermore, numerous studies emphasize its exceptional operational performance under extreme irradiation and high-temperature conditions. These characteristics position Ga₂O₃ as an ideal material for high-performance SBPDs.

Abstract

      Photovoltaic solar-blind ultraviolet photodetectors (SBPDs) operate independently of an external power source, addressing critical demands in extreme environments, such as forest fire detection and atmospheric ozone layer monitoring. Gallium oxide (Ga₂O₃) offers significant potential for extreme applications due to its radiation resistance and high-temperature stability. Here, we present a novel homoepitaxy strategy to produce an “atomic smooth” step-flow Ga₂O₃ photosensitive layer, successfully fabricating device-grade Ga₂O₃/n⁺-Ga₂O₃ homojunctions for photovoltaic SBPDs. These devices exhibit a maximum open-circuit voltage of 1.0 V, an ultrahigh external quantum efficiency of 59.5%, and an ultrafast response time of 100 ns under zero bias, maintaining consistent performance even at 390 K. By implementing a 2D step-flow growth mode, both bulk and interface defects were effectively suppressed, achieving the desired band alignment. Furthermore, the optimized high-quality depletion region formed by the Ga₂O₃ layer facilitates enhanced carrier drift, resulting in an efficient carrier collection. This work fully explores the potential of Ga₂O₃ SBPDs for extreme applications and provides an effective design strategy for achieving photovoltaic detectors characterized by zero power consumption, high responsivity, and rapid response.

Conclusion

      In conclusion, we successfully fabricated vertical Schottky photodiodes based on high-quality Ga₂O₃ thin films grown homoepitaxially on n⁺- Ga₂O₃ substrates via MOCVD. Operating in zero-power mode, the device exhibits high responsivity (118 mA/W) and EQE (59.5%) at 246 nm, indicating its potential for applications in extreme environments without external power supply. Additionally, it features a low dark current of 0.31 pA, a rectification ratio exceeding 10⁷ at ±5 V, a PDCR of 1.53×10⁴, and rise and decay times of 100 ns and 320 μs, respectively, showcasing exceptional performance. These characteristics are attributed to the excellent step-flow morphology of the Ga₂O₃ epitaxial layer, which has a low defect density. Furthermore, the thin layer and low carrier concentration facilitate complete depletion under the influence of the top Pt electrode and the bottom n-type conductive substrate, forming a wide space-charge region that optimizes carrier separation and collection efficiency, thus achieving near-optimal performance without external bias. The Ga₂O₃ photovoltaic SBPD developed in this study exhibits significant potential for application in extreme environments, such as remote ozone hole monitoring, forest fire detection, and corona discharge monitoring.