Abstract-Optically thin hybrid cavity for terahertz photo-conductive detectors

R. J. Thompson1,2, T. Siday1, S. Glass1, T. S. Luk3,4, J. L. Reno3,4, I. Brener3,4, and O. Mitrofanov

http://aip.scitation.org/doi/abs/10.1063/1.4974482

The efficiency of photoconductive (PC) devices, including terahertz detectors, is constrained by the bulk optical constants of PC materials. Here, we show that optical absorption in a PC layer can be modified substantially within a hybrid cavity containing nanoantennas and a Distributed Bragg Reflector. We find that a hybrid cavity, consisting of a GaAs PC layer of just 50 nm, can be used to absorb >75% of incident photons by trapping the light within the cavity. We provide an intuitive model, which describes the dependence of the optimum operation wavelength on the cavity thickness. We also find that the nanoantenna size is a critical parameter, small variations of which lead to both wavelength shifting and reduced absorption in the cavity, suggesting that impedance matching is key for achieving efficient absorption in the optically thin hybrid cavities.

Abstract-An electrically driven terahertz metamaterial diffractive modulator with more than 20 dB of dynamic range

N. Karl¹, K. Reichel¹, H.-T. Chen², A. J. Taylor², I. Brener³, A. Benz³, J. L. Reno³, R. Mendis¹ and D. M. Mittleman¹

 HIDE AFFILIATIONS
1 Department of Electrical and Computer Engineering, Rice University, MS 378, Houston, Texas 77251-1892, USA
2 Center for Integrated Nanotechnologies, Los Alamos National Laboratory, P. O. Box 1663, MS K771, Los Alamos, New Mexico 87545, USA
3 Center for Integrated Nanotechnologies, Sandia National Laboratories, P. O. Box 5800, MS 1082, Albuquerque, New Mexico 87185, USA
Appl. Phys. Lett. 104, 091115 (2014); http://dx.doi.org/10.1063/1.4867276

http://scitation.aip.org/content/aip/journal/apl/104/9/10.1063/1.4867276

We design and experimentally demonstrate a switchable diffraction grating for terahertz modulation based on planar active metamaterials, where a Schottky gate structure is implemented to tune the metamaterial resonances in real-time via the application of an external voltage bias. The diffraction grating is formed by grouping the active split-ring resonators into an array of independent columns with alternate columns biased. We observe off-axis diffraction over a wide frequency band in contrast to the narrow-band resonances, which permits operation of the device as a relatively high-speed, wide-bandwidth, high-contrast modulator,with more than 20 dB of dynamic range.

© 2014 AIP Publishing LLC

Abstract-Inducing an incipient terahertz finite plasmonic crystal in coupled two dimensional plasmonic cavities

 http://prl.aps.org/accepted/d9078Yf3F7815522c9fd50b390b44fda4c68daae4

 G. C. Dyer, G. R. Aizin, S. Preu, N. Q. Vinh, S. J. Allen, J. L. Reno, and E. A. Shaner

Accepted Thursday Aug 23, 2012

We measured a change in the current transport of an antenna-coupled, multi-gate, GaAs/AlGaAs field-effect transistor when terahertz electromagnetic waves irradiated the transistor and attribute the change to bolometric heating of the electrons in the two-dimensional electron channel. The observed terahertz absorption spectrum indicates coherence between plasmons excited under adjacent biased device gates. The experimental results agree quantitatively with a theoretical model we developed that is based on a generalized plasmonic transmission line formalism and describes an evolution of the plasmonic spectrum with increasing electron density modulation from homogeneous to the crystal limit. These results demonstrate an electronically induced and dynamically tunable plasmonic band structure.