Electronic and optical properties of hydrogen-passivated in orthorhombic BaSi₂: First-principles study

Hydrogenation is a critical strategy for modulating the defects and electronic properties of Barium Disilicide (BaSi₂). In this work, spin-polarized density functional theory is studied to investigate the structural, electronic, dielectric, and optical properties of silicon-vacancy (V_Si) in orthorhombic BaSi₂ by varying degrees of hydrogen passivation. Three hydrogenation scenarios: single (V_Si+H), double (V_Si+2H) and triple (V_Si+3H) hydrogenation systems are systematically investigated. It is found that hydrogen atoms preferentially occupy the tetrahedral V_Si site. By increasing hydrogen concentration, mid-gap states near the Fermi levels are suppressed. At the same time, the V_Si introduces mid-gap levels, V_Si+3H transforms the system into an n-type semiconductor, as it shifts the conduction band close to the Fermi levels. The imaginary part of the dielectric function, ɛ₂(ω), exhibits prominent optical transition at 0.33-2.45 eV, which indicates enhanced infrared and visible-light absorption for hydrogenated systems. The absorption coefficients (α(ω)) reveal intense hydrogen-induced changing spectral behavior by multiple peaks appearing in the V_Si+3H system and reach up to 2.05×10⁵cm⁻¹ at 1.5 eV. This study confirms that hydrogen plays an important role in tailoring the optoelectronics functionality of orthorhombic structure BaSi₂ through effective passivation of V_Si.