Berlin 2018 – scientific programme

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DS: Fachverband Dünne Schichten

DS 20: 2D materials: Chalcogenides I (joint session HL/DS)

DS 20.8: Talk

Wednesday, March 14, 2018, 11:30–11:45, A 151

Thermal annealing effects on optical properties of 2D MoS₂ — •Oleg Gridenco, Kathrin Sebald, Christian Tessarek, Martin Eickhoff, and Jürgen Gutowski — Institute of Solid State Physics, University of Bremen, Germany

Mechanically exfoliated monolayers obtained by using natural crystals and deposited by a polymer transfer process on substrates suffer from residues on the surface which are hard to be removed. The residues as well as absorbed O₂ and H₂O at the surface of a monolayer are known to modify the optical and electrical properties resulting in a quenching of the photoluminescence (PL) and a reduction of the carrier mobility. We present a systematic thermal annealing study conducted by heating and laser annealing in order to remove such residues. The results show that the PL energy is blue-shifted and the PL intensity is enhanced by a factor of 1.8 after a thermal annealing cycle. The blue-shift points to a reduction of the trion contribution and a relative increase of free-exciton recombination. In addition, the overall PL enhancement can be related to a decrease of non-radiative recombination processes. A similar behaviour of the PL is observed after MoS₂ monolayers were exposed to UV laser irradiation for several seconds. The study provides a low-cost, large scale and effective route to enhance the PL efficiency which is important for the device performance.