Effect of point defects on the optical and transport properties of MoS2 and WS2

Imperfections in the crystal structure, such as point defects, can strongly modify the optical and transport properties of materials. Here, we study the effect of point defects on the optical and dc conductivities of single layers of semiconducting transition metal dichalcogenides with the form MS2, where M = Mo or W. The electronic structure is considered within a six band tight-binding model, which accounts for the relevant combination of d orbitals of the metal M and p orbitals of the chalcogen S. We use the Kubo formula for the calculation of the conductivity in samples with different distributions of disorder. We find that M and/or S defects create midgap states that localize charge carriers around the defects and which modify the optical and transport properties of the material, in agreement with recent experiments. Furthermore, our results indicate a much higher mobility for p-doped WS2 in comparison to MoS2.