Substrate screening effects on the quasiparticle band gap and defect charge transition levels in MoS₂.

Monolayer MoS₂ has emerged as an interesting material for nanoelectronic and optoelectronic devices. The effect of substrate screening and defects on the electronic structure of MoS₂ are important considerations in the design of such devices. We find a giant renormalization to the free-standing quasiparticle band gap in the presence of metallic substrates, in agreement with recent scanning tunneling spectroscopy and photoluminescence experiments. Our sulfur vacancy defect calculations using the DFT+GW formalism, reveal two CTLs in the pristine band gap of MoS₂. The (0/-1) CTL is significantly renormalized with the choice of substrate, with respect to the pristine valence band maximum. The (+1/0) level, on the other hand, is pinned 100 meV above the pristine VBM for the different substrates. This opens up a pathway to effectively engineer defect charge transition levels in 2D materials through choice of substrate.