Terahertz plasmonic devices
A terahertz (THz) source is the crucial part of all active systems. The task of THz generation, however, has proven to be exceedingly difficult, and the existing sources have a number of limitations. I am developing THz sources based on plasmon instabilities in semiconductors. My work is theoretical, but I am also collaborating with experimental groups.
The basic idea is based on the analogy between dc currents flowing in semiconductors and electron beams in vacuum. The electron beam devices rely of the transfer of the kinetic energy of the electrons into electromagnetic waves for wave amplification and generation. It should also be possible to transfer the kinetic energy of electrons flowing in a semiconductor into the energy of THz plasmons, thus creating a solid-state THz source. The ideas from the vacuum electronics cannot be, however, translated directly into solid state, because of differences in electron velocities, densities, and collision rates. A solid-state source requires novel approaches.
I have recently shown that plasmon amplification and generation can be achieved in two-dimensional semiconductors when plasmons reflect from the ohmic contacts.
The figure below shows a basic geometry (a) and the computed gain (b). In the presence of a dc current, the plasmons propagating along a two-dimensional electron system (2DES) have different field distributions. As a result, plasmon reflection from an ohmic contact is no longer a simple process with a unity reflection coefficient. At the contact, the transverse z-component of the electric field must vanish, which cannot be satisfied by the incident and reflected plasmons alone. As a result, the reflection coefficient is no longer equal to unity, as in the case without a dc current. It exceeds unity (gain) when the plasmon is incident on the contact against the direction of the dc current.The above theoretical calculations are based on a technique called 'mode matching', which I have adopted and developed for the THz plasmonic waveguides supporting dc currents. The technique is based on expanding the fields at junctions and contacts into the waveguide eigenmodes, which include plasmons, radiation and evanescent modes, and then matching the fields, as required by Maxwell's equations.
Together with my collaborators from the University of Leeds, I have recently verified the model by comparing its predictions to the measurements made by the collaborators. The figure below shows agreement between the theory and the measurements.
Sydoruk O, Wu JB, Mayorov A, et al., 2015, Terahertz plasmons in coupled two-dimensional semiconductor resonators, PHYSICAL REVIEW B, Vol: 92, ISSN: 1098-0121
Sydoruk O, Choonee K, Dyer GC, 2015, Transmission and Reflection of Terahertz Plasmons in Two-Dimensional Plasmonic Devices, IEEE TRANSACTIONS ON TERAHERTZ SCIENCE AND TECHNOLOGY, Vol: 5, Pages: 486-496, ISSN: 2156-342X