Weimin Chan

Absorption of light by excitons and trions in monolayers of metal dichalcogenideMoS2: Experiments and theory

We measure the optical absorption spectra and optical conductivities of excitons and trions in monolayers of metal dichalcogenide MoS

Ultrafast response of monolayer molybdenum disulfide photodetectors

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Fast exciton annihilation by capture of electrons or holes by defects via Auger scattering in monolayer metal dichalcogenides

and compare the results with theoretical models. Our results show that the Wannier-Mott model for excitons, with modifications to account for small exciton radii and large exciton relative wavefunction spread in momentum space, phase space blocking due to Pauli exclusion in doped materials, and wavevector dependent dielectric constant, gives results that agree well with experiments. The measured exciton optical absorption spectra are used to obtain experimental estimates for the exciton radii that fall in the

Coupling of plasmon modes in graphene microstructures

7-10\AA

Radiative and nonradiative exciton energy transfer in monolayers of two-dimensional group-VI transition metal dichalcogenides

range and agree well with theory. The measured trion optical absorption spectra are used to obtain values for the trion radii that also agree well with theory. The measured values of the exciton and trion radii correspond to binding energies that are in good agreement with values obtained from first principles calculations.

Ultrafast Two-Pulse Photocurrent Correlation Measurements of Single Atomic Layer MoS2 Photodetectors

The strong light emission and absorption exhibited by single atomic layer transitional metal dichalcogenides in the visible to near-infrared wavelength range make them attractive for optoelectronic applications. In this work, using two-pulse photovoltage correlation technique, we show that monolayer molybdenum disulfide photodetector can have intrinsic response times as short as 3 ps implying photodetection bandwidths as wide as 300 GHz. The fast photodetector response is a result of the short electron–hole and exciton lifetimes in this material. Recombination of photoexcited carriers in most two-dimensional metal dichalcogenides is dominated by nonradiative processes, most notable among which is Auger scattering. The fast response time, and the ease of fabrication of these devices, make them interesting for low-cost ultrafast optical communication links.

Very Fast Capture of Electrons and Holes of Excitons by Defects via Auger Scattering in Monolayer Metal Dichalcogenides

The strong Coulomb interactions and the small exciton radii in two-dimensional metal dichalcogenides can result in very fast capture of electrons and holes of excitons by mid-gap defects from Auger processes. In the Auger processes considered here, an exciton is annihilated at a defect site with the capture of the electron (or the hole) by the defect and the hole (or the electron) is scattered to a high energy. In the case of excitons, the probability of finding an electron and a hole near each other is enhanced many folds compared to the case of free uncorrelated electrons and holes. Consequently, the rate of carrier capture by defects from Auger scattering for excitons in metal dichalcogenides can be 100-1000 times larger than for uncorrelated electrons and holes for carrier densities in the

Graphene Plasmo-Mechanical Structures and Devices

10^{11}

Graphene micro- and nano-plasmonics

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Far-IR Spectroscopy and FDTD Simulations of Graphene Plasmonic Structures

10^{12}