Berlin 2018 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 38: 2D materials: Chalcogenides II (joint session HL/DS)
HL 38.1: Talk
Thursday, March 15, 2018, 09:30–09:45, A 151
Excitation-induced transition from direct to indirect band gaps in monolayer TMDCs — •Daniel Erben1, Alexander Steinhoff1, Tim Wehling1,2, Christopher Gies1, and Frank Jahnke1 — 1Insitute for Theoretical Physics, University of Bremen, Germany — 2Bremen Center for Computational Materials Science, University of Bremen, Germany
Monolayer transition metal dichalcogenides (TMDCs) are atomically thin semiconductors with a direct band gap, which allows their use as active material in optoelectronic devices. Often photoluminescence or photoemission spectroscopy experiments are employed for the characterization of TMDCs. Via laser pulse excitation these methods provide excited charge carriers that populate the valleys of the band structure. The Coulomb interaction of these excited carriers causes strong many-body renormalizations in the band structure, which consequently shift the valleys and the excitonic resonances by several hundred meV.
In this talk we give detailed insight into the many-body effects in monolayer MoS2, MoSe2, WS2 and WSe2 by evaluating the semiconductor Bloch equations including DFT-band structures and interaction-matrix elements. This provides a precise description for the interplay of the Coulomb interaction with the electron and hole populations. We describe the impact of these effects on the K- and Σ-valley in the band structure. Our calculations show a clear tendency to a direct-to-indirect band gap transition due to the renormalizations. Being reminiscent of the effect of strain on monolayers, this transition should also lead to a quenching of the photoluminescence.