Abstract-Contactless graphene conductivity mapping on a wide range of substrates with terahertz time-domain reflection spectroscopy

Hungyen Lin, Philipp Braeuninger-Weimer, Varun S. Kamboj, David S. Jessop, Riccardo Degl’Innocenti, Harvey E. Beere, David A. Ritchie, J. Axel Zeitler,  Stephan Hofmann

https://www.nature.com/articles/s41598-017-09809-7?WT.feed_name=subjects_materials-science

We demonstrate how terahertz time-domain spectroscopy (THz-TDS) operating in reflection geometry can be used for quantitative conductivity mapping of large area chemical vapour deposited graphene films on sapphire, silicon dioxide/silicon and germanium. We validate the technique against measurements performed with previously established conventional transmission based THz-TDS and are able to resolve conductivity changes in response to induced back-gate voltages. Compared to the transmission geometry, measurement in reflection mode requires careful alignment and complex analysis, but circumvents the need of a terahertz transparent substrate, potentially enabling fast, contactless, in-line characterisation of graphene films on non-insulating substrates such as germanium.

Abstract-Fast room temperature detection of terahertz quantum cascade lasers with graphene loaded bow-tie plasmonic antenna arrays

Riccardo Degl'Innocenti, Long Xiao, David S. Jessop, Stephen J Kindness, Yuan Ren, Hungyen Lin, J. Axel Zeitler, Jack A. Alexander-Webber, Hannah J Joyce, Philipp Braeuninger-Weimer, Stephan Hofmann, Harvey E Beere, and David A. Ritchie

ACS Photonics, Just Accepted Manuscript

DOI: 10.1021/acsphotonics.6b00405

Publication Date (Web): September 20, 2016

Copyright © 2016 American Chemical Society

https://www.blogger.com/blogger.g?blogID=124073320791841682#editor/target=post;postID=4022381804460754923

We present a fast room temperature terahertz detector based on interdigitated bow-tie antennas contacting graphene. Highly efficient photodetection was achieved by using two metals with different work functions as the arms of a bow-tie antenna contacting graphene. Arrays of the bow-ties were fabricated in order to enhance the responsivity and coupling of the incoming light to the detector realizing an efficient imaging system. The device has been characterized and tested with a terahertz quantum cascade laser emitting in single frequency around 2 THz yielding a responsivity of ~ 34 μA/W and a noise-equivalent-power of ~1.5E-7W/Hz1/2

Abstract-Fast modulation of terahertz quantum cascade lasers using graphene loaded plasmonic antennas

Riccardo Degl'Innocenti, David S. Jessop, Christian W. O. Sol, Long Xiao, Stephen J. Kindness, Hungyen Lin, J. Axel Zeitler, Philipp Braeuninger-Weimer, Stephan Hofmann, Yuan Ren, Varun S. Kamboj, Jonathan P. Griffiths, Harvey E. Beere, and David A. Ritchie

ACS Photonics, Just Accepted Manuscript

DOI: 10.1021/acsphotonics.5b00672

Publication Date (Web): February 23, 2016

Copyright © 2016 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/acsphotonics.5b00672?journalCode=apchd5

We report the fast amplitude modulation of a quantum cascade laser emitting in single mode operation in the terahertz frequency range by employing compact, integrated devices based on the interplay between plasmonic antenna arrays and monolayer graphene. By acting on the carrier concentration of graphene the optical response of these plasmonic resonances was modified. The modulators characteristics have been studied by using both time domain spectroscopic laser systems, yielding the broad frequency response of these resonant arrays, and quantum cascade lasers, providing us with a narrow and stable laser source, a mandatory prerequisite for the determination of the modulation speed of these devices. The measured modulation speed exhibits a cut-off frequency of 5.5 MHz ± 1.1 MHz. These results represent the first step toward the realization of fast integrated circuitry for communications in the terahertz frequency range.