Modeling the electrically tunable optical properties of monolayer MoS2

Student thesis: Master thesis (including HD thesis)

  • Mads-Peter Verner Christiansen
  • Jannick Kjær Jørgensen
4. term, Nanotechnology, Master (Master Programme)
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 of
this phenomenon a quantum mechnical description is required. The tunability of the optical properties
is 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 dielectric
screening has been developed which predicts intrinsic properties in fair agreement with experiments. The
inclusion of doping by electrostatic gating requires including the effect in the DFT calculation and two
models of doping have been proposed and compared. G0W0 calculations have been performed to study
the effect of doping on bandgap renormalization and it has been found that doping also significantly
reduces the effective electron mass in the case of n-doping. Importantly the effect of doping must also be
included in the dielectric screening which is done through an analytical model. The fully developed model
qualitatively reproduces the tunability of the optical properties. Reflection spectroscopy measurements
have been carried out on intrinsic MoS2 showing the excitonic transitions. Gates have been deposited
on the MoS2 sample in order to electrically dope during reflectance measurements, however more work
is required to obtain definitive results.
SpecialisationNanophysics and -materials
Publication date1 Jun 2018
Number of pages86
ID: 280210880