Imaging conduction band electrons in gated monolayer TMDC using µARPES

Understanding of electric field induced doping effects in the electronic structure of direct band gap single-layer (SL) semiconductors is crucial for developing electronic and optoelectronic applications of the materials. However, direct visualization of the electronic structure remains experimentally challenging for in situ gated 2D material devices. Here, we apply in operando micrometer scale angle-resolved photoemission spectroscopy at the ASTRID2 light source in order to characterize the electronic structure of a SL WS₂ gateable device. Using micromechanical cleaving and transfer methods, the SL WS₂ is partially contacted to a graphene top electrode and placed on a boron nitrite dielectric on a graphite back-gate. We directly visualize distinct conduction band populations, band gap renormalization and charge transfer processes across the bare WS₂ and graphene/WS₂ interface. Our observations provide a better understanding of band renormalization and carrier doping in two-dimensional heterostructure devices combining direct gap semiconductors and graphene electrodes.