The continuing trend to miniaturization of devices in modern technology faces fundamental physical
limits of applied materials. The search for novel structures with new functionalities has brought
atomically thin two-dimensional (2D) materials into the focus of current research. The most prominent respresentatives of this class of materials are graphene and transition metal dichalcogenides (TMDs).
They show a wide range of exceptional optical and electronic properties suggesting technological application in next-generation of optoelectronic devices including lasers, photodetectors, and solar cells.
The rapidly growing research on these materials has revealed many fascinating features, however, most of the underlying many-particle phenomena have not been entirely understood yet. The main goals of the proposed project are (i) to provide fundamental insights into the coupled dynamics of electrons, phonons, and photons in graphene and TMDs under the influence of an external electrical field and (ii) to exploit the gained knowledge to concretely model photodetectors based on these materials.
After an optical excitation, electrons are lifted from the valence up into the conduction band. These non-equilibrium electrons interact among each other as well as with the lattice transferring parts of their excess energy into lattice vibrations (phonons). On their way to an equilibrium distribution, they can accumulate close to the band minimum, however the probability for radiative recombination is very high resulting in light emission (photons). Now, turning on an electrical field to model the dynamics in a typical photodetector, makes the scattering dynamics between electrons, phonons, and photons more complicated, since it accelerates electrons in the momentum space giving rise to a strong non-equilibrium distribution.
Based on a quantum mechanic theory, we will investigate electron-electron, electron-phonon, and electron-photons interactions in graphene and selected TMD materials on a consistent theoretical footing. The core of the theoretical model are Bloch equations, a couples system of differential equations allowing us to to resolve the non-equilibrium dynamics of optically excited electrons in time and energy. With the gained insights, we will be able to investigate the possibility to design highly efficient and ultrafast photodetecotors operating in a wide spectral range. As a result, the proposed project is of great interest for both fundamental and application-oriented research