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HL: Fachverband Halbleiterphysik

HL 7: "New" Materials and New Physics in "Old" Materials I

HL 7.8: Vortrag

Montag, 26. März 2012, 11:15–11:30, EW 015

Atomically thin layers of transition metal dichalcogenides investigated by ab initio methods — •Kerstin Hummer and Georg Kresse — University of Vienna, Computational Materials Physics, Vienna, Austria

The advances in the fabrication of atomically thin layered materials has enabled investigations of new physical properties inherent to low dimensional structures. Transition metal dichalcogenides (TMX₂) crystallize in a quasi-two-dimensional structure that allows for low dimensional structuring. Among them, the prototype material molybdenum disulfide (MoS₂), has attracted intense interest because of its distinct electronic and optical properties that enable its application in photovoltaics and photocatalysis. A key issue regarding the applicability in efficient opto-electronic devices is the energy gap that should match the solar spectrum (1-3 eV). Bulk TMX₂ with TM = Mo, W and X = S, Se, Te have band gaps between 1 and 1.5 eV, but their fundamental gaps are indirect and thus optically forbidden. However, a transition from an indirect to an direct gap semiconductor was achieved in MoS₂, when going from bulk to atomically thin layers.

In this work, we present density functional theory studies of thin layer TMX₂ with TM = Mo, W and X = S, Se, and Te. Accurate band structures are obtained with the modified Becke-Johnson exchange potential in combination with LDA correlation. Particular emphasis is put on the variation of the band gap with layer thickness as well as the influence of the substrate present in experiment.