Theoretical design of 2D Pca2₁ SiNOX (X = H, F, and Cl) phases: a new family of flexible wide bandgap semiconductors

By first-principles calculations, a new family of two-dimensional (2D) Pca2₁ SiNOX (X = H, F, and Cl) phases were rationally designed by theoretical exfoliation of bulk layered α-LiSiON compounds, taking advantage of the in- and out-of-plane bonding anisotropy of the bulk parental compound. It is found that 2D Pca2₁ SiNOX phases have wide direct and quasi-direct bandgaps of 4.99-6.33 eV using the HSE06 functional with good thermodynamic, mechanical, dynamic, and thermal stabilities. In addition, the flexibility of 2D Pca2₁ SiNOX structures was evidenced with moderate in-plane Young's moduli of 133.27-141.87 N m⁻¹, ideal strength of 6.06-6.56 N m⁻¹, and out-of-plane bending strength of 1.41-1.57 eV. What is more, the stronger anharmonicity of 2D Pca2₁ SiNOH leads to lower lattice thermal conductivities, in comparison with 2D Pca2₁ SiNOF and SiNOCl. Finally, isovalent elemental substitutions are adopted to tune the bandgaps of 2D Pca2₁ SiNOX phases within the range of 0.54-6.64 eV with the HSE06 functional and ten wide bandgap semiconductors (2D Pca2₁ CNOH, GeNOH, CNOF, GeNOF, CNOCl, SiNOCl, GeNOCl, SiPOCl, SiNSH, and SiNSeH) were unveiled with bandgaps larger than 3.5 eV. Our findings enrich the family of 2D wide bandgap semiconductors, and also highlight the promising multi-functional electronic applications of 2D Pca2₁ SiNOX phases.