Christiansen, Mads-Peter Verner

Jørgensen, Jannick Kjær

The motivation of this thesis is the experimental realization of highly tunable optical properties of transition metal dichalcogenides as reported in recent literature. In order to understand the root cause ofthis phenomenon a quantum mechnical description is required. The tunability of the optical propertiesis controlled by excitons which require including the electron-hole interaction responsible for their existence. A framework based on ab-initio DFT wave functions and an analytical expression for the dielectricscreening has been developed which predicts intrinsic properties in fair agreement with experiments. Theinclusion of doping by electrostatic gating requires including the effect in the DFT calculation and twomodels of doping have been proposed and compared. G0W0 calculations have been performed to studythe effect of doping on bandgap renormalization and it has been found that doping also significantlyreduces the effective electron mass in the case of n-doping. Importantly the effect of doping must also beincluded in the dielectric screening which is done through an analytical model. The fully developed modelqualitatively reproduces the tunability of the optical properties. Reflection spectroscopy measurementshave been carried out on intrinsic MoS2 showing the excitonic transitions. Gates have been depositedon the MoS2 sample in order to electrically dope during reflectance measurements, however more workis required to obtain definitive results

Modeling the electrically tunable optical properties of monolayer MoS2

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