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First-principles calculations have been performed to study the structural features of the monolayer MoS2(1-x)Se2x (x = 0.25) alloy and its electronic properties. We studied the effects of the relative positions of Se atoms in a real monolayer alloy. It was demonstrated that the distribution of the Se atoms between the top and bottom chalcogen planes was most energetically favorable. For a more probable distribution of Se atoms, a MoS2(1-x)Se2x (x = 0.25) monolayer alloy is a direct semiconductor with a fundamental band gap equal to 2.35 eV (calculated with the GVJ-2e method). We also evaluated the optical band gap of the alloy at 77 K (1.86 eV) and at room temperature (1.80 eV), which was in good agreement with the experimentally measured band gap of 1.79 eV. [ABSTRACT FROM AUTHOR]

The formation and diffusion of intrinsic defects in bulk and monolayer MoS2 are studied. For the first time, the formation energy of a split sulfur and molybdenum Frenkel pair in bulk (6.56 and 12.6 eV) and monolayer (3.95 and 12.1 eV) MoS2 is determined without using chemical potential. For the intrinsic defects, a complete calculation of the diffusion coefficient (pre‐exponential factor and activation barrier) is performed and the effect of the defect charge state on the diffusion coefficient is studied. [ABSTRACT FROM AUTHOR]