【Domestic Papers】Fabrication of porous Ga₂O₃/GaN heterojunction for ultraviolet photodetector application

      Researchers from the Taiyuan University of Technology have published a dissertation titled "Fabrication of porous Ga₂O₃/GaN heterojunction for ultraviolet photodetector application" in Optics Express.

Project Support

      Shanxi Provincial Key Research and Development Project (202302150101001); Shanxi-Zheda Institute of Advanced Materials and Chemical Engineering (2021SX-AT002, 2022SX-TD018); National Natural Science Foundation of China (21972103, 61904120).

Background

      UV photodetectors are widely used in both military and civilian applications such as astronomical imaging systems, chemical/biological analysis, bioaerosol detection, ozone hole monitoring, and secure communications. Among the photodetectors reported to date, p-n junction-type UV photodetectors have attracted considerable research interest owing to their many advantages, which include a low dark current (I_dark), low power consumption, and high responsivity (R). As a significant fourth-generation semiconductor material, Ga₂O₃ is a promising candidate for UV-detection applications because of its wide band gap (4.4–5.2 eV), high UV transmittance (over 80%), large edge absorption coefficient (up to 10⁵cm⁻¹), and excellent chemical and thermal stability. Ga₂O₃ is generally considered an n-type semiconductor owing to its inherent oxygen deficiency. However, due to the self compensation effect of oxygen vacancies and the deep energy level of acceptors, the p-type Ga₂O₃ is difficult to obtain , which greatly limits the development of Ga₂O₃-based p-n junction-type photodetectors. In response to this challenge, researchers have proposed the integration of Ga₂O₃ with p-type semiconductors such as NiO, SnO₂ , and GaN, to construct heterojunction photodetectors. In particular, GaN has received increased attention because of its high carrier mobility, wide direct band gap (3.4 eV), and good chemical and thermal stability; moreover, when combined with Ga₂O₃, it shows minimal lattice mismatch and a low conduction band shift.

Abstract

      Ga₂O₃/GaN heterojunction has important applications in optoelectronic devices. Understanding optoelectronic performance and interface relationships of the heterojunction is the key to designing optimal devices. Herein, a porous Ga₂O₃/GaN heterojunction is systematically investigated. Porous GaN is initially fabricated via ultraviolet-assisted electrochemical etching and porous Ga₂O₃ is subsequently converted from porous GaN by thermal oxidation. Compared with planar Ga₂O₃/GaN heterojunction, porous Ga₂O₃/GaN heterojunction has higher crystal quality. Porous Ga₂O₃/GaN heterojunction exhibits a light/dark current ratio of 10520, a responsivity of 0.108 A/W, an external quantum efficiency of 52.9%, a detectivity of 1.36 × 10¹² Jones, and the response time of 0.35 s/0.13 s under 254 nm UV irradiation (0.33 mw/cm²) at 0 V bias. Additionally, the operating mechanism of the device is further explored through energy band structure and carrier-transport process diagrams. This study provides valuable insights and paves the way for developing next-generation optoelectronic devices based on Ga₂O₃/GaN heterojunction.

Conclusion

      In summary, a porous Ga₂O₃​/GaN heterojunction was designed, and its morphology, structure, and crystal plane alignment relationship were investigated using SEM, Raman spectroscopy, and TEM. Subsequently, the heterojunction was used to construct a UV photodetector. The device achieved an I_dark of 0.22 nA, R of 0.108 A/W, D* of 1.36 × 10¹² Jones, EQE of 52.9%, τ_r /τ_d of 0.35 s/0.13 s and I_light/I_dark of 10520 under 254 nm UV irradiation (0.33 mw/cm² ) at 0 V bias. It also demonstrated good repeatability and stability. The above data indicate that the porous Ga₂O₃​/GaN heterojunction photodetector can efficiently absorb UV light. The results demonstrate a new and effective method for developing high-performance photodetectors.