Adsorption Induced Indirect-to-Direct Band Gap Transition in Monolayer Blue Phosphorus

In this work, we systematically studied adsorption induced indirect-to-direct band gap transition in monolayer blue phosphorus from first-principles calculations by combining one-shot GW approximation and the Bethe-Salpeter equation. Our results revealed that surface adsorption (i.e., O 2, −OH, −COOH, and −CN) strongly modifies the conduction and valence band edges, resulting in an indirect-to-direct band gap transition. More importantly, the direct band gap can be dramatically tuned by either the in-plane strain or the coverage ratio of adsorbates, which enables monolayer blue phosphorus to efficiently adsorb visible light. The mechanism of strain effect and surface adsorption on band gap tuning was deeply discussed. Moreover, our results clearly showed that the adsorbates have an important influence on the exciton binding energies (EBE), while the coverage of adsorbates play a crucial role in the linear scaling behavior between EBE and quasi-particle band gap. Our findings suggest that monolayer blue phosphorus has potential applications in electro-optical devices.