Stable Si-based pentagonal monolayers: high carrier mobilities and applications in photocatalytic water splitting

Abstract

A new family of Si-based pentagonal monolayers is constructed on the basis of the okayamalite structure by means of first principles calculations. Phonon spectra and ab initio molecular dynamics simulations provide eloquent examinations for the dynamical and thermal stabilities of p-SiX (X = B, C, and N) monolayers. Electronic structures show that p-SiC and p-SiN are indirect semiconductors with band gaps of 2.35 and 4.98 eV by HSE hybrid functional, respectively. The carrier mobilities up to 2500 cm² V⁻¹ s⁻¹ are quantitatively investigated by using deformation potential theory with effective mass approximation. And the band structures can be modulated monotonically under proper isotropic strains. This indicates that p-SiX can be used as field effect transistors or other electronic devices. More intriguingly, the band gap of p-SiC corresponds to the wavelength of 528 nm, showing a semiconducting character absorption in the green region of the visible spectra. Enlightened by prominent photocatalytic behavior of g-C₃N₄, we demonstrate that both band gap and band edges of p-SiC can meet the requirement of the reduction and oxidation levels in water splitting. The new type of Si-based nanomaterial offers an interesting alternative to diverse nanodevices and paves way for new metal-free photocatalysts.