【Member Papers】Boosting the responsivity of β-Ga₂O₃ metal–semiconductor–metal solar-blind photodetectors through oxygen-related defect states

      Researchers from the Southern University of Science and Technology have published a dissertation titled "Boosting the responsivity of β-Ga₂O₃ metal–semiconductor–metal solar-blind photodetectors through oxygen-related defect states" in Scientific Reports.

Project Support

      This work was supported by the National Key Research and Development Program of China under Grant (Grant No. 2022YFA1405200), Shenzhen Science and Technology Program (Grant No. JCY20240813100810014), Natural Science Foundation of Shandong province (Grant No. ZR2025ZD32 and ZR2022ZD05), the Instrument Improvement Funds of Shandong University Public Technology Platform (Grant No. ts20230207), and Shenzhen Key Laboratory of Deep Sub-wavelength Scale Photonics (ZDSYS20220527171201003).

Background

      Solar-blind photodetectors (SBPDs) offer unique advantages, including all-weather operability and high sensitivity, owing to the negligible background noise in the solar-blind spectral region (190-280 nm). These features make them highly desirable for a wide range of civilian and defense applications, such as flame detection, optical communication, and missile warning systems. However, conventional Si-based SBPDs exhibit limited response in this wavelength range and typically rely on costly optical filters to suppress visible and near-UV light. Wide-bandgap semiconductor materials have emerged as promising candidates for next-generation SBPDs. Among these, Ga₂O₃ has attracted considerable attention owing to its ultra-wide direct bandgap (4.4-5.3 eV), which naturally corresponds to the solar-blind region and eliminates the need for complex alloying to achieve bandgap tuning. Moreover, Ga₂O₃ exhibits a large ultraviolet-absorption coefficient, remarkable radiation and thermal stability, and chemical robustness under harsh environmental conditions. The feasibility of large-scale Ga₂O₃ single-crystal growth via melt-based techniques further enhances its cost-effectiveness and industrial potential.

Abstract

      Achieving high responsivity is essential for advancing solar-blind photodetectors (SBPDs) in applications such as wireless communication and fire warning systems. In this study, we investigate metal-semiconductor-metal SBPDs based on β-Ga₂O₃ epitaxial films grown on sapphire substrates by metal-organic chemical vapor deposition at different temperatures. Structural and spectroscopic analyses indicate that growth temperature modulates oxygen-related defect states in β-Ga₂O₃ films, which correlate with changes in responsivity through defect-assisted photoexcitation processes. Notably, the SBPD fabricated from a Ga₂O₃ film grown at 900 °C exhibited a responsivity of 4.2⋅10⁴ A/W, a detectivity of 1.2⋅10¹³ Jones, and an exceptional external quantum efficiency of 2.1⋅10⁷%. These findings highlight the important role of oxygen-related defect states in optimizing the photoresponse of β-Ga₂O₃ based SBPDs.

Conclusions

      In summary, SBPDs based on β-Ga₂O₃ epilayers grown at different temperatures were fabricated and characterized. The optimized device, employing a β-Ga₂O₃ epilayer grown at 900ºC, exhibited a high R of 4.2´10⁴ A/W, an EQE of 2.1´10⁷%, and a D* of 1.2´10¹³ Jones under 254 nm illumination at a power density of 64 µW/cm². Comprehensive structural and compositional analysis, including XRD and XPS, revealed that the defect-related state concentration in β-Ga₂O₃ epilayers increases with growth temperature. These defect states act as photoionization centers, contributing additional charge carriers and thereby enhancing the device responsivity. The results demonstrate that growth temperature acts as a tuning parameter for defect-related states in β-Ga₂O₃, thereby influencing the electrical and ultraviolet photodetection characteristics. This study demonstrates that defect-related states play a key role in determining the responsivity and response dynamics of solar-blind photodetectors, providing useful guidance for future device optimization.