title: Exciton radiative lifetimes in two-dimensional transition metal dichalcogenides.
abstract: Light emission in two-dimensional (2D) transition metal dichalcogenides (TMDs) changes significantly with the number of layers and stacking sequence. While the electronic structure and optical absorption are well understood in 2D-TMDs, much less is known about exciton dynamics and radiative recombination. Here, we show first-principles calculations of intrinsic exciton radiative lifetimes at low temperature (4 K) and room temperature (300 K) in TMD monolayers with the chemical formula MX2 (X = Mo, W, and X = S, Se), as well as in bilayer and bulk MoS2 and in two MX2 heterobilayers. Our results elucidate the time scale and microscopic origin of light emission in TMDs. We find radiative lifetimes of a few picoseconds at low temperature and a few nanoseconds at room temperature in the monolayers and slower radiative recombination in bulk and bilayer than in monolayer MoS2. The MoS2/WS2 and MoSe2/WSe2 heterobilayers exhibit very long-lived (∼20-30 ns at room temperature) interlayer excitons constituted by electrons localized on the Mo-based and holes on the W-based monolayer. The wide radiative lifetime tunability, together with the ability shown here to predict radiative lifetimes from computations, hold unique potential to manipulate excitons in TMDs and their heterostructures for application in optoelectronics and solar energy conversion.
authors: †Dipartimento di Fisica, Università di Roma Tor Vergata, and European Theoretical Spectroscopy Facility (ETSF), Via della Ricerca Scientifica 1, 00133 Roma, Italy.
authors: Maurizia
authors: M
authors: Palummo
authors: ‡Department of Physics, University of California, Berkeley, California 94720, United States.
authors: Marco
authors: M
authors: Bernardi
authors: §Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, United States.
authors: Jeffrey C
authors: JC
authors: Grossman
mesh_terms: D004220:Disulfides / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry*; D008982:Molybdenum / Q000737:chemistry*; D012993:Solar Energy; D028561:Transition Elements / Q000737:chemistry
chemical_list: D004220:Disulfides; D028561:Transition Elements; D008982:Molybdenum
keywords: Monolayer materials; excitons; luminescence; optoelectronics; radiative lifetime; transition metal dichalcogenides