Prof. Dr. Cem Sevik
“Intrinsic Control of Interlayer Exciton Generation in Van der Waals Materials via Janus Layers”
In this presentation, we explore the pivotal role of Janus transition metal dichalcogenide layers in tuning the properties of interlayer excitons, quasiparticles essential for advancing optoelectronic device applications. The lifetime of an exciton, influenced by annihilation and dissociation, depends significantly on the binding energy and spatial separation of its constituent electron and hole. Historically, modifying the exciton separation in bulk semiconductors has presented considerable challenges. However, recent developments in interlayer excitons – layer-separated bound states of electrons and holes – within stacked van der Waals semiconductors, especially in transition metal dichalcogenide heterostructures, have opened new avenues for easier manipulation of these parameters.
Our focus is on the innovative engineering of optical properties in transition metal dichalcogenide hetero-bilayers, particularly those where one layer possesses a Janus structure. We employ first-principles methods to investigate various MoS2@Janus layer combinations, accounting for exciton and exciton-phonon coupling effects. Our research reveals that the intrinsic electric field from the Janus layer alters the electronic band alignments, impacting the energy gap between dark interlayer and bright in-plane exciton states.
We discover that in-plane lattice vibrations significantly facilitate the coupling between these exciton states, suggesting exciton-phonon scattering as a potential pathway for generating interlayer excitons upon light absorption. Notably, in MoS2@WSSe hetero-bilayers, the energy difference between low-lying interlayer excitons and in-plane excitons aligns resonantly with the transverse optical phonon modes (40 meV), identifying this structure as a particularly promising candidate for efficient generation of charge-separated electron-hole pairs.
Dr. Cem Sevik has been a distinguished member of the Physics Department at Antwerp University since May 2022, serving in a senior academic staff role. Prior to this, he enhanced his research skills as a faculty member in the Mechanical Engineering Department at Eskisehir Technical University from 2012 to 2022 and as a postdoctoral researcher at Texas A&M University’s Department of Chemical Engineering from 2012 to 2018. Dr. Sevik’s academic journey started at AIBU in Turkey, where he earned his bachelor’s degree in physics. He then obtained his master’s degree from Bilkent University, where he specialized in the ensemble Monte Carlo simulation of solid-state devices. In 2008, he was awarded his PhD from the same institution, with a dissertation on carrier dynamics in nanocrystals.
Date: January 17, 2024 Wednesday