Effect of Ultraviolet Irradiation on Surface Doping and Strain Properties of Chemical Vapor Deposition-Grown MoS ₂

Molybdenum disulfide (MoS₂) monolayers are promising candidates for next-generation nanoelectronics, yet ultraviolet (UV) irradiation during device fabrication induces surface defects that compromise device reliability. This study systematically investigates the wavelength-dependent effects of 365 nm (UV-365) and 193 nm (UV-193) irradiation on the strain and doping characteristics of chemical vapor deposition (CVD)-grown monolayer MoS₂. Raman spectroscopy analysis reveals that UV-365 irradiation (1000-3000 mJ) consistently induces ∼0.1% tensile strain with minimal variation in doping levels (Δn ∼ -1 × 10¹² cm⁻²). In contrast, UV-193 irradiation at identical energies generates compressive strain (∼0.2-0.3%) and pronounced p-type doping, with carrier density reaching Δn ∼ -3.5 × 10¹² cm⁻² at 3000 mJ. X-ray photoelectron spectroscopy (XPS) elucidates distinct mechanisms: UV-365 promotes oxygen adsorption via photothermal effects, inducing tensile strain and weak p-type doping, and UV-193 (photon energy > Mo-S bond energy) cleaves Mo-S bonds, enabling oxygen passivation of sulfur vacancies to form MoO₃. This process causes lattice compression (compressive strain) and enhances p-type doping through defect-mediated charge transfer. These findings underscore that UV-193 irradiation significantly alters critical electrical parameters (strain and doping), whereas UV-365 irradiation primarily modulates the strain. Mitigating such wavelength-specific surface modifications is essential for enhancing the reliability of wafer-scale MoS₂ field-effect transistors.