Defect-Polarization Coupling in 3D-Graphene/β-Ga₂O₃ Heterostructures for Self-Powered and Multifunctional Solar-Blind...

Solar-blind ultraviolet photodetectors are promising for secure communication, early warning systems, and information security. Monoclinic phase gallium oxide (β-Ga₂O₃) is an ideal candidate due to its ultrawide bandgap. Unavoidable oxygen vacancies in β-Ga₂O₃ have been viewed as detrimental defects that degrade performance. However, this study introduces an innovative approach that reinterprets these oxygen vacancies as beneficial for optoelectronic enhancement, accomplished through a 3D-graphene/β-Ga₂O₃ heterojunction. Oxygen vacancies cause localized lattice symmetry breaking, generating dipole fields and local polarization. This interacts with the optical resonance of 3D-graphene, enhancing optical and electrical fields in the heterojunction, which improves the separation and transport of photogenerated carriers. Experimental investigations, along with DFT and TCAD calculations, reveal that oxygen-vacancy-induced local polarization reduces the interfacial barrier, enhances electron injection, and increases photoconductive gain through a trap-assisted mechanism. The photodetector achieves weak-light detection at 255 nm (0.002 µW/mm²) with a responsivity of 3740 A/W and specific detectivity of 6.85 × 10¹³ Jones, a response of 140 µs, and enabling zero-bias self-powered operation. The 8 × 8 array allows for ultraviolet imaging and optical encrypted communication. This study reframes oxygen vacancies as functional mechanisms for enhancing polarization, paving the way for advanced wide-bandgap optoelectronic device design.