Bandgap renormalization and band offset in 2D materials caused by dielectric screening

Modifying the external dielectric environment of a 2D semiconductor monolayers offers a new approach to bandgap engineering [1]. While Rydberg spectroscopy using optical absorption can provide access to the quasiparticle bandgap, and its variation with the surrounding dielectric environment, the distribution of the energy offset of valence and conduction bands across the lateral junction induced in a 2D semiconductor by a change in the external dielectric has not yet been examined experimentally. Here, we present measurements of the influence of dielectric screening on the band structure of WS₂ monolayers by employing angle-resolved photoemission spectroscopy with micrometer resolution (μ-ARPES). We visualize the valence bands of the semiconductor WS₂ on different substrates and determine their energy with respect to atomic core levels. In addition, we determine the bandgap of the samples by measuring ground and excited exciton transitions with optical spectroscopy, which are extrapolated to yield the quasiparticle bandgap and, thus, the energy of the conduction band. We discuss the influence of dielectric screening on the valence bands in different parts of the Brillouin zone.

[1] A. Raja et al., Nat. Comm. 8, 15251 (2017)