137 research outputs found
Graphene Terahertz Plasmon Oscillators
In this paper we propose and discuss coherent terahertz sources based on
charge density wave (plasmon) amplification in two dimensional graphene. The
coupling of the plasmons to interband electron-hole transitions in population
inverted graphene layers can lead to plasmon amplification through stimulated
emission. Plasmon gain values in graphene can be very large due to the small
group velocity of the plasmons and the strong confinement of the plasmon field
in the vicinity of the graphene layer. We present a transmission line model for
plasmon propagation in graphene that includes plasmon dissipation and plasmon
interband gain due to stimulated emission. Using this model, we discuss design
for terahertz plasmon oscillators and derive the threshold condition for
oscillation taking into account internal losses and also losses due to external
coupling. The large gain values available at terahertz frequencies in graphene
can lead to integrated oscillators that have dimensions in the 1-10 micron
range.Comment: To appear in IEEE Transactions on Nanotechnology (TNANO
High Intrinsic Mobility and Ultrafast Carrier Dynamics in Multilayer Metal Dichalcogenide MoS2
The ultimate limitations on carrier mobilities in metal dichalcogenides, and
the dynamics associated with carrier relaxation, are unclear. We present
measurements of the frequency-dependent conductivity of multilayer
dichalcogenide MoS2 by optical-pump terahertz-probe spectroscopy. We find
mobilities in this material approaching 4200 cm2/Vs at low temperatures. The
temperature dependence of scattering indicates that the mobility, an order of
magnitude larger than previously reported for MoS2, is intrinsically limited by
acoustic phonon scattering at THz frequencies. Our measurements of carrier
relaxation reveal picosecond cooling times followed by recombination lasting
tens of nanoseconds and dominated by Auger scattering into defects. Our results
provide a useful context in which to understand and evaluate the performance of
MoS2-based electronic and optoelectronic devices.Comment: 13 pages, 8 figure
- …