【Member Papers】A deep ultraviolet photodetector based on n-ε-Ga₂O₃/p-diamond heterojunction

      Researchers from the Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences have published a dissertation titled "A deep ultraviolet photodetector based on n-ε-Ga₂O₃/p-diamond heterojunction" in Applied Surface Science.

Background

      Deep-ultraviolet (DUV) detectors have significant potential applications in fields such as optical communications, environmental monitoring, and military early warning systems. Diamond, with an ultra-wide bandgap of 5.47 eV, exhibits intrinsic DUV photoresponse characteristics, coupled with an exceptional high thermal conductivity of 2200 W/m·K and fantastic electrical properties. Compared to conventional Si DUV detectors, the wide bandgap of diamond promises low solar-blind background noise for DUV detection. However, the difficulty in achieving n-type doping severely restricts its application in bipolar device architectures. As another ultra-wide bandgap semiconductor, Ga₂O₃ possesses a bandgap of 4.8 eV, and a breakdown field strength of up to 8 MV/cm. In contrast to diamond, Ga₂O₃ exhibits excellent n-type doping capability while lack effective p-type doping ability. Considering the doping complementary, the combination of diamond and Ga₂O₃ will pave a new way for the integration of Ga₂O₃ on diamond, and the fabrication of bipolar devices. Nevertheless, the current integrated fabrication processes for n-type gallium oxide and p-type diamond remain insufficiently developed.

Abstract

      Diamond-based deep-ultraviolet photodetectors have significant potential in communications, sensing, and imaging. However, the challenge of n-type doping restricts the fabrication of diamond pn structural photodetectors. In this work, a photodetector based on n-ɛ-Ga₂O₃/p-diamond heterojunction was fabricated by depositing n-type ɛ-Ga₂O₃ on p-type diamond substrate via pulsed laser deposition (PLD). X-ray photoelectron spectroscopy (XPS) analysis indicated the ɛ-Ga₂O₃/diamond heterojunction possesses a Type II band structure, with valence and conduction band offsets of approximately 2.23 eV and 3.10 eV, respectively. The fabricated detector exhibits an ultra-low dark current of 1.16 × 10⁻¹² A and a high photo-to-dark current ratio (PDCR) of 10⁶. The detector also showed excellent spectral selectivity in the deep-ultraviolet range. Moreover, the detector exhibits self-powered operation under DUV illumination because of the built-in electric field at the hetero p-n junction. This study demonstrates the feasibility of integrating ɛ-Ga₂O₃ with diamond and provides guidance for designing future deep-ultraviolet photodetectors based on ɛ-Ga₂O₃/diamond heterojunctions.

Highlights

      ε-Ga₂O₃/p-diamond heterojunction：n-type ε-Ga₂O₃film was deposited on p-type diamond substrate, and a deep ultraviolet photodetector was fabricated based on this hetero pn junction.

      Type-II Band Alignment: Precise interfacial engineering achieved a staggered band offset, with valence band (VBO) and conduction band (CBO) offsets of 2.23 eV and 3.10 eV, respectively.

      Ultralow Dark Current: The device demonstrated exceptional noise suppression, exhibiting a dark current as low as 1.16×10^-12A and a high light-to-dark current ratio of 10⁶.

      Self-Powered Capability: The photodetector operates autonomously, delivering a short-circuit current (I_SC) of 5.04×10^-12 A and an open-circuit voltage (V_OC) of 0.19 V.

Conclusion

      In this study, a DUV photodetector based on anε-Ga₂O₃/diamond heterojunction was fabricated by depositing n-type ε-Ga₂O₃ on a p-type diamond substrate. The band structure of the n-ε-Ga₂O₃/p-diamond heterojunction was determined to be a staggered type (Type II), with VBO and CBO values of 2.23 eV and 3.10 eV, respectively. The fabricated detector features an ultra-low dark current of 1.16 × 10⁻¹² A (at −3 V) and an ultra-high light-to-dark current ratio of 10⁶, with responsivity and specific detection sensitivity of 7.79×10⁻³ A/W and 1.61×10¹² Jones, respectively. Meanwhile, the detector also showed self-power ability, with the open-circuit voltage (V_OC) of 0.19 V, short current (ISC) of 5.04×10⁻¹² A, and maximum output power density of 0.69 W/cm². Structural and interface defects (grain boundaries, twins, dislocations, oxygen vacancies, Ga⁺ defects) exist in the ε-Ga₂O₃ film. These defects increase recombination and weaken the builtin field via Fermi-level pinning. Thus, breakdown voltage (4.75–7.25 V) and VOC (≈0.19 V) are low. Still, this study shows the feasibility of epitaxial ε-Ga₂O₃/diamond heterojunctions. It also offers guidance for improvement through defect engineering and interface optimization.

Project Support

      This research was funded by the National Natural Science Foundation of China (52302202), in part by the Yongjiang Talent Introduction Programme of Ningbo (2021A-037-C, 2021A-108-G), Ningbo Science & Technology Bureau under program grant No. 2022-DST-001.