Theoretical study of defect impact on two-dimensional MoS₂

Abstract

Our theoretical findings demonstrate for the first time a possibility of band-gap engineering of monolayer MoS 2 crystals by oxygen and the presence of vacancies. Oxygen atoms are revealed to substitute sulfur ones, forming stable MoS 2 x O x ternary compounds, or adsorb on top of the sulfur atoms. The substituting oxygen provides a decrease of the band gap from 1.86 to 1.64 eV and transforms the material from a direct-gap to an indirect-gap semiconductor. The surface adsorbed oxygen atoms decrease the band gap up to 0.98 eV depending on their location tending to the metallic character of the electron energy bands at a high concentration of the adsorbed atoms. Oxygen plasma processing is proposed as an effective technology for such band-gap modifications.

Impact of Defects on Electronic Properties of Heterostructures Constructed From Monolayers of Transition Metal Dichalcogenides

“…The value of such underestimation depends on the shift of eigenvalues in the energy range analyzed due to the so‐called correlation effects. Nevertheless, we have previously obtained a good agreement between experimental data and our theoretical findings for TMDs employing the fact that the corresponding eigenfunctions at the extrema points of the band structure are mainly composed of d ‐electron states of the metal atoms . So, they undergo an almost equal shift.…”

“…4 p ‐ (5 p ‐) electronic states of Mo (W) were considered as valence states. A similar approach has been already successfully tested in the calculations for individual layers of MoS 2 , MoSe 2 , WS 2 , and WSe 2 …”

“…Experimentally observed indirect energy gap ( E g ) in bulk MoS 2 ranges from 1.23 to 1.29 eV and E g in WS 2 is of about 1.35 eV while monolayers of MoS 2 and WS 2 have direct gaps of about 1.8 eV and 2.4 eV, respectively. Theoretical calculations give gaps of 0.90–1.52 eV (indirect gap) for the bulk of MoS 2 and 1.72–1.86 eV (direct gap) in a MoS 2 monolayer, respectively . For WS 2 the gaps are 1.63 eV in the bulk material and 2.53 eV in one monolayer …”

“…A similar approach has been already successfully tested in the calculations for individual layers of MoS 2 , MoSe 2 , WS 2 , and WSe 2 . [16,17,27] It should be noted here that calculations within the DFT approaches without using the electronic self-energy corrections usually underestimate band gaps with respect to the experimental ones. The value of such underestimation depends on the shift of eigenvalues in the energy range analyzed due to the so-called correlation effects.…”

“…Theoretical calculations give gaps of 0.90-1.52 eV (indirect gap) for the bulk of MoS 2 and 1.72-1.86 eV (direct gap) in a MoS 2 monolayer, respectively. [16][17][18][19][20] For WS 2 the gaps are 1.63 eV in the bulk material and 2.53 eV in one monolayer. [21] Combination of the layers of different TMDs gives a possibility to obtain a directgap hybrid two-dimensional crystal.…”