Defect-controlled electronic, magnetic, and optical tunability in monolayer SiC: A first-principles study of vacancy and dopant engineering

Defect engineering provides an effective route for tailoring the electronic, magnetic, and optical functionality of two-dimensional semiconductors without changing their host framework. In this work, first-principles density functional theory calculations are performed to investigate the structural stability, mechanical response, electronic structure, magnetic behavior, charge-transfer mechanism, and optical properties of pristine and defect-engineered monolayer Two-dimensional (2D) silicon carbide (SiC). Four representative defect configurations were investigated: a carbon vacancy (V_C), a silicon vacancy (V_Si), nitrogen substitution at the carbon site (N_C), and boron substitution at the carbon site (B_C). The pristine monolayer exhibits a stable honeycomb structure with an optimized lattice constant of 3.09 Å , Si–C bond length of 1.79 Å, high cohesive energy, and a wide indirect band gap of 3.41 eV. Phonon dispersion and elastic-constant analysis confirm the dynamical and mechanical stability of pristine, defective, and doped configurations. Vacancy defects strongly reconstruct the local bonding environment and introduce defect states inside or near the band gap. In particular, V_Si produces spin-polarized mid-gap states and a magnetic moment of 2.00 μB, mainly localized on neighboring C atoms, whereas V_C generates near-Fermi defect bands and drives the system toward quasi-metallic behavior. Substitutional doping provides controlled carrier-type engineering: N substitution introduces donor-like impurity states near the conduction-band edge, resulting in n-type semiconducting behavior with a calculated band gap of 2.25 eV. While B doping shifts the Fermi level downward, producing p-type character with a band gap of 2.10 eV and a finite magnetic moment of 1.00 μB. Charge-density difference, Bader charge, electron localization function, and spin-density analyses reveal that vacancy- and dopant-induced electronic and magnetic states originate from local charge redistribution, orbital rehybridization, and dangling-bond-like states around the defect centers. Optical calculations show that pristine monolayer SiC is mainly active in the near-UV region, while vacancies and dopants red-shift the absorption edge and enhance visible/near-UV optical activity. These results demonstrate that defect engineering can transform monolayer SiC from a wide-band-gap non-magnetic semiconductor into a tunable multifunctional material with controllable electronic, magnetic, and optical states for nanoelectronic, spintronic, and optoelectronic applications.