On the understanding of the optoelectronic properties of S-doped MoO3 and O-doped MoS2 bulk systems: a DFT perspective

Abstract

First-principles calculations are carried out to understand the structure and optoelectronic properties of α-MoO₃ and 2H-MoS₂ bulk systems with anionic isovalent-atom substitutions. Density functional theory (DFT) calculations are performed by adopting the HSE06 functional to probe the optoelectronic structures and the Boltzmann transport theory to compute the DOS-averaged effective mass and mobility of the studied compounds. We show that substituting oxygen atoms by sulfur atoms in α-MoO₃, the electronic energy gap is decreased from 3.0 eV in the pristine material to around 1.6 eV in the sulfur doped material. By contrast, substituting sulfur atoms with oxygen atoms in 2H-MoS₂ does not produce any significant change in the electronic band gap. We found that α-MoO₃ with high sulfur concentrations (greater than 33%) is thermodynamically stabilized by H₂S sulfidation and exhibit improved dielectric function, optical and charge transport properties and exciton binding energy for with respect to pristine α-MoO₃. The carrier mobility is enhanced by such high sulfur concentrations induced by the delocalization of S-electronic states at the top of the valence band. For the oxygen substituted 2H-MoS₂ bulk material, the optoelectronic properties, charge mobilities and charge separation are either unaltered or even degraded with respect to 2H-MoS₂.