SHI-Induced Sulfur Vacancies Driven Photoconductivity in CVD-Grown MoS ₂ for Optoelectronic Applications

Layered MoS2 films were synthesized via chemical vapor deposition (CVD), and controlled sulfur vacancies were introduced using swift heavy ion (SHI) irradiation. These SHI-induced vacancies present a promising strategy for tailoring the optical, electrical, and optoelectrical characteristics of MoS2. Following exposure to 70 MeV Si4+ ions at different fluences, X-ray photoelectron spectroscopy (XPS) results show the generation of S-vacancies, while Raman spectroscopy of the irradiated films exhibited a redshift in the A1g out-of-plane vibrational mode, signifying the development of tensile strain and enhanced n-type conductivity. Furthermore, as defect concentration increased, a gradual reduction in the overall photoluminescence (PL) intensity was observed. The strain-induced n-type behavior also contributed to a rise in the formation of defect-bound negative trions with increasing ion fluence. Photoconductive results show that the trion-based nonradiative decay dominates over the exciton-based radiative decay, which leads to the quenching of the photocurrent in irradiated MoS2 sheets. Also, the switching on and off of the pulse of light shows the biexponential trend in decay current. The relaxation times associated with the fast and slow components of the current decay dynamics also became lower as the irradiation of the SHI dose increased. Our detailed experiments and thorough quantitative analysis offer fresh insights into the underlying mechanism of photoconductivity in monolayer SHI-irradiated MoS2 film.