First-Principles Study on Electronic and Optical Properties of Li, Na, Mg, Al, Ca, and Y-Doped Si₂N₂O

This study systematically investigates the effects of metal doping (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{Li}, \text{Na}, \text{Mg}, \text{Al}, \text{Ca}, \mathrm{Y}$</tex>) on the structural stability, electronic properties, and optical performance of silicon oxynitride (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{Si}_{2}\ \mathrm{N}_{2} \mathrm{O}$</tex>) through first-principles calculations. The results reveal that dopants modulate dielectric response, absorption characteristics, and band structures through mechanisms involving atomic radius, electronegativity, and orbital hybridization. Li and Na act as donor dopants, inducing metallic behavior through free electron injection and continuous density of states in the conduction band. Mg and Al retain semiconducting properties due to weak hybridization effects from their small atomic radii and higher electronegativity. Ca and Y exhibit enhanced polarization via p/d orbital hybridization, with Mg-doped models achieving the highest static dielectric constant (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\varepsilon_{\infty}=7.6$</tex>), demonstrating potential for high-<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\varepsilon$</tex> applications. <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$Y$</tex> doping shows the lowest absorption coefficient within the 14.5 – 15.5 eV range, suggesting suitability for wave-transparent materials. The modulation mechanisms are elucidated through binding energy, formation energy, band structure and projected density of state analysis.