Abstract-Graphene Terahertz Plasmon Oscillators

Farhan Rana

https://ieeexplore.ieee.org/document/4362685/

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 threshold condition is shown to depend on the ratio of the external impedance and the characteristic impedance of the plasmon transmission line. The large gain values available at terahertz frequencies in graphene can lead to integrated oscillators that have dimensions in the 1-10 mum range.

Abstract-High intrinsic mobility and ultrafast carrier dynamics in multilayer metal-dichalcogenide MoS2

Jared H. Strait, Parinita Nene, and Farhan Rana

https://journals.aps.org/prb/accepted/2e07dO93Jc91692ff2019f21feb79d6d9cfee0aea


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 cm2V-1s-1 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.