Abstract-Comparison of unit cell coupling for grating‐gate and high electron mobility transistor array THz resonant absorbers

Journal of Applied Physics

Ajay Nahata, Ashish Chanana, Berardi Sensale-Rodriguez, Debdeep Jena, Hugo O. Condori Quispe, Huili Grace Xing, Jimy Encomendero, Mingda Zhu, Nicole Trometer, 

https://aip.scitation.org/doi/abs/10.1063/1.5032102

We report experimental studies on the excitation of synchronized plasmon resonances in AlGaN/GaN High Electron Mobility Transistor (HEMT) arrays. In contrast to the commonly employed grating-gate configurations, the analyzed structure contains periodically patterned ohmic contacts to the two-dimensional electron gas, which are laid-out parallel to the gate fingers. In this structure, the terahertz to plasmon coupling mechanism is fundamentally different from that in grating-gate configurations. Whereas the grating-gate configuration constitutes a coupled resonant system in which the resonance frequency depends on the grating periodicity, when periodical ohmic contacts are incorporated, the system behaves as a synchronized resonant system in which each unit cell is effectively independent. As a result, in a HEMT-array, the resonance is no longer set by the periodicity but rather by the gate and the ungated region length. Experimental results of fabricated samples compare well with numerical simulations and theoretical expectations. Our work demonstrates that the proposed approach allows: (i) more efficient excitation of high order plasmon modes and (ii) superior overall terahertz to plasmon coupling, even in configurations having less number of devices per unit area. From this perspective, our results reveal a simple way to enhance the terahertz to plasmon coupling and thus improve the performance of electron plasma wave-based devices; this effect can be exploited, for example, to improve the response of HEMT-based terahertz detectors.

Abstract-Comparison of unit cell coupling for grating‐gate and high electron mobility transistor array THz resonant absorbers

Journal of Applied Physics

Hugo O. Condori Quispe,   Ashish Chanana, Jimy Encomendero,Mingda Zhu, Nicole Trometer,  Ajay Nahata, Debdeep Jena,   Huili Grace Xing,Berardi Sensale-Rodriguez,

https://aip.scitation.org/doi/10.1063/1.5032102

We report experimental studies on the excitation of synchronized plasmon resonances in AlGaN/GaN High Electron Mobility Transistor (HEMT) arrays. In contrast to the commonly employed grating-gate configurations, the analyzed structure contains periodically patterned ohmic contacts to the two-dimensional electron gas, which are laid-out parallel to the gate fingers. In this structure, the terahertz to plasmon coupling mechanism is fundamentally different from that in grating-gate configurations. Whereas the grating-gate configuration constitutes a coupled resonant system in which the resonance frequency depends on the grating periodicity, when periodical ohmic contacts are incorporated, the system behaves as a synchronized resonant system in which each unit cell is effectively independent. As a result, in a HEMT-array, the resonance is no longer set by the periodicity but rather by the gate and the ungated region length. Experimental results of fabricated samples compare well with numerical simulations and theoretical expectations. Our work demonstrates that the proposed approach allows: (i) more efficient excitation of high order plasmon modes and (ii) superior overall terahertz to plasmon coupling, even in configurations having less number of devices per unit area. From this perspective, our results reveal a simple way to enhance the terahertz to plasmon coupling and thus improve the performance of electron plasma wave-based devices; this effect can be exploited, for example, to improve the response of HEMT-based terahertz detectors.

Abstract-Terahertz imaging employing graphene modulator arrays

Berardi Sensale-Rodriguez, Subrina Rafique, Rusen Yan, Mingda Zhu, Vladimir Protasenko, Debdeep Jena, Lei Liu, and Huili Grace Xing »View Author Affiliations

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-21-2-2324

In this paper we propose and experimentally demonstrate arrays of graphene electro-absorption modulators as electrically reconfigurable patterns for terahertz cameras. The active element of these modulators consists of only single-atom-thick graphene, achieving a modulation of the THz wave reflectance > 50% with a potential modulation depth approaching 100%. Although the prototype presented here only contains 4x4 pixels, it reveals the possibility of developing reliable low-cost video-rate THz imaging systems employing single detector.

Abstract-Efficient terahertz electro-absorption modulation employing graphene plasmonic structures

http://arxiv.org/abs/1211.4176
 Berardi Sensale-Rodriguez, Rusen Yan, Mingda Zhu, Debdeep Jena, Lei Liu, Huili Grace Xing

We propose and discuss terahertz electro-absorption modulators based on graphene plasmonic structures. The active device consists of a self-gated pair of graphene layers, which are patterned to structures supporting THz plasmonic resonances. These structures allow for efficient control of the effective THz optical conductivity, thus absorption, even at frequencies much higher than the Drude roll-off in graphene where most previously proposed graphene-based devices become inefficient. Our analysis shows that reflectance-based device configurations, engineered so that the electric field is enhanced in the active graphene pair, could achieve very high modulation-depth, even ~100%, at any frequency up to tens of THz.

Abstract-Extraordinary Control of Terahertz Beam Reflectance in Graphene Electro-absorption Modulators

 

http://pubs.acs.org/stoken/nanotation/pipe/abs/10.1021/nl3016329

Berardi Sensale-Rodriguez *†, Rusen Yan †‡, Subrina Rafique †, Mingda Zhu †, Wei Li ‡§, Xuelei Liang §,David Gundlach ‡, Vladimir Protasenko †, Michelle M. Kelly †, Debdeep Jena †, Lei Liu †, and Huili Grace Xing *†

^† Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556, United States

^‡ Semiconductor and Dimensional Metrology Division,National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States

^§ Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing, 100871, China

Nano Lett., Article ASAP

DOI: 10.1021/nl3016329

Publication Date (Web): August 3, 2012

Copyright © 2012 American Chemical Society

*E-mail address: bsensale@nd.edu; hxing@nd.edu

 

We demonstrate a graphene-based electro-absorption modulator achieving extraordinary control of terahertz reflectance. By concentrating the electric field intensity in an active layer of graphene, an extraordinary modulation depth of 64% is achieved while simultaneously exhibiting low insertion loss (2 dB), which is remarkable since the active region of the device is atomically thin. This modulator performance, among the best reported to date, indicates the enormous potential of graphene for terahertz reconfigurable optoelectronic devices.