【Member Papers】Enhanced performance of solar-blind UV photodetectors based on β-Ga₂O₃/SiO₂/Si nBn heterojunction with varied thicknesses of SiO₂ blocking layer

      Researchers from the Northeast Normal University have published a dissertation titled "Enhanced performance of solar-blind UV photodetectors based on β-Ga₂O₃/SiO₂/Si nBn heterojunction with varied thicknesses of SiO₂ blocking layer" in Applied Surface Science.

Project Support

      This work was supported by the National Natural Science Foundation of China (NO. 62274027 and 62404039), the Open Research Fund of Song Shan Lake Materials Laboratory (2023SLABFK03), 111 Center (B25030) and the Funding from Jilin Province (NO. 20220502002 GH), the Postdoctoral Fellowship Program of CPSF (GZC20230416), the Fundamental Research Funds for the Central Universities (2412024QD010).

Background

      Due to absorption by the atmospheric ozone layer, deep ultraviolet (UV) light in the solar-blind wavelength range of 200–280 nm is almost non-existent at the Earth's surface. Solar-blind UV photodetectors have been widely used in various applications such as satellite communications, flame detection, and missile guidance due to their high detection sensitivity and low background noise. Gallium oxide (Ga₂O₃) is an ultrawide bandgap semiconductor material (Eg:4.5 ∼ 5.5 eV) that has emerged as an ideal material for solar-blind UV photodetectors because of its unique band structure. Ga₂O₃ has five polymorphs, among which monoclinic β-Ga₂O₃ exhibits the most stable physicochemical properties.

      In this study, we prepared n-Ga₂O₃/Barrier/n-Si (nBn) heterojunction photodetectors by inserting SiO₂ layers of different thicknesses as a barrier between n-Si and Ga₂O₃. Devices based on the nBn structure were compared with those based on β-Ga₂O₃/n-Si heterojunctions. The introduction of the SiO₂ barrier layer significantly reduced the dark current, improved the signal-to-noise ratio, and greatly suppressed persistent photoconductivity. This provides a practical and cost-effective new approach for β-Ga₂O₃/Si heterojunction UV photodetectors.

Abstract

      In this paper, solar-blind UV photodetectors based on β-Ga₂O₃/SiO₂/n-Si nBn heterojunctions were fabricated by introducing a SiO₂ blocking layer of varying thickness to suppress the dark current and increase the I_photo/I_dark. The β-Ga₂O₃ thin films were deposited by metal–organic chemical vapor deposition. Due to the blocking effect of the SiO₂ barrier layer, the device’s dark current was significantly reduced. Compared to the device based on a β-Ga₂O₃/n-Si heterostructure without SiO₂, the dark current was reduced by five orders of magnitude after introducing the SiO₂ layer. Under 254 nm UV light irradiation, the photo-to-dark current ratio of the device with a 50 nm SiO₂ layer reached 1.1 × 10³ at a bias voltage of −6.5 V, which is two orders of magnitude higher than that of the device without the SiO₂ barrier. At a bias of −10 V, a peak responsivity of 39.2 mA/W and a detectivity of 4.8 × 10¹² cm·Hz^1/2/W were achieved for the device with the 50 nm SiO₂ barrier layer. Meanwhile, the persistent photoconductivity effect was significantly suppressed, and the decay time decreased with increasing barrier layer thickness, reaching 9.4 ms in the device with a 300 nm SiO₂ barrier layer.

Highlights

      ● The introduction of the SiO₂ barrier layer significantly suppressed the reverse leakage current of the heterojunction device.

      ● The variation in the thickness of the SiO₂ barrier layer can significantly affect the optoelectronic performance of heterojunction devices.

      ● The SiO₂ barrier layer suppresses the persistent photoconductivity phenomenon by blocking the slowly released trapped carriers.

Conclusion

      In this work, high-performance solar-blind ultraviolet photodetectors were fabricated by introducing a SiO₂ barrier layer into the β-Ga₂O₃/n-Si structure. The SiO₂ layer forms a potential barrier that impedes carrier transport, resulting in a significant reduction in dark current. The dark current of the β-Ga₂O₃/SiO₂/n-Si photodetector was reduced by five orders of magnitude compared to the β-Ga₂O₃/n-Si device. Under 254 nm UV illumination, the photo-to-dark current ratio of the device with a 50 nm SiO₂ layer reached 1.1 × 10³ at a bias voltage of − 6.5 V, a substantial improvement over the device without the barrier layer. The responsivity and detectivity were measured at 39.2 mA/W and 4.8 × 10¹² cm⋅Hz^1/2/W, respectively. Furthermore, the persistent photoconductivity was significantly suppressed. With increasing SiO₂ thickness, the response speed of the device improved. The decay time for the device with a 300 nm SiO₂ layer was as low as 9.4 ms. These high-performance, Si-based β-Ga₂O₃/SiO₂/n-Si heterojunction photodetectors offer a cost-effective approach for solar-blind UV detection and provide flexibility for potential integration with Si-based electronic circuits.