Séminaire (15-05-2014)

SEMINAIRE Département Photonique et Ondes- Groupe TéHO

Plasma Oscillations in a Submicron Planar Gunn Diode

Ata KHALID Research Fellow
MicroSystem Technology Research Group
School of Engineering, University of Glasgow

Jeudi 15 mai 2014, 14 heures
Salle des séminaires, bâtiment 21, 4è étage
Contact : This email address is being protected from spambots. You need JavaScript enabled to view it.

The Gunn diode was first demonstrated in 1963 using a GaAs bar-like structure with electrical contacts on its opposing faces [1]. Early research work demonstrated the difficulties of achieving planar structures for several reasons. However, as material quality has continuously improved, new attempts have been made to make Gunn devices in a planar layout that would enable integrated diodes for on chip applications such as high frequency radar and security imaging [2]. Early theoretical investigations show that the high-energy relaxation time of GaAs might limit Gunn oscillation to 60 GHz [3].

Monte-Carlo simulations showed that ultrafast quasi-ballistic electrons in the Γ-valley would, under the influence of a high electric field caused by an etched recess, achieve a velocity of up to 10⁸ cm/s leading to terahertz operation [4]. Moreover, plasma oscillations up to several THz have been observed in highly doped semiconductor material. In_xGa_1-xAs displays significant improvements in mobility compared to GaAs with increasing indium content, and Monte-Carlo modelling and experimental data has consequently shown the potential for much higher frequency operation of In_xGa_1-xAs channel planar Gunn diodes compared to GaAs channel diodes [6].

In this background of extensive research to develop solid state THz source, I will discuss the development of planar Gunn diode technology and various technology issues needed to be resolved to keep the progress towards a THz source technology. Recent development of submicron planar Gunn diode has shown oscillations above 300GHz for the first time. Agreement with theory and experiment is reasonably good for Gunn oscillations, though with the simulations systematically recording frequencies about 10% higher than those observed experimentally. It was very interesting that Monte Carlo simulations show 450GHz and 688GHz plasma oscillations for our submicron device at lower applied basis, while higher biases were needed in the simulation to maintain accumulation layer Gunn oscillations. There was no plasma oscillation observed during the simulations for devices longer than 750nm. At present we are unable to experimentally verify the predicted plasma wave oscillations due to lack of available experimental set-up. However, it is interesting to note that a 475GHz experimentally measured signal was reported recently in InGaAs channel of a HEMT device [6].

References

[1] J. B. Gunn, “ Microwave oscillation of current in III–V semiconductors,” Solid State Commun. 1(4), 88–91 (1963). http://dx.doi.org/10.1016/0038-1098(63)90041-3

[2]. A. Förster, J. Stock, S. Montanari, M. I. Lepsa, and H. Luth, “ Fabrication and characterisation of GaAs Gunn diode chips for applications at 77 GHz in automotive industry,” Sensors 6(4), 350–360 (2006). http://dx.doi.org/10.3390/S6040350

[3]. G. S. Hobson, “ The transferred-electron effect and space-charge instabilities,” in The Gunn Effect (Clarendon Press, 1974), pp. 3–20.

[4]. S. Perez, T. González, D. Pardo, and J. Mateos, “ Terahertz Gunn-like oscillations in InGaAs/InAlAs planar diodes,” J. Appl. Phys. 103(9), 094516 (2008). http://dx.doi.org/10.1063/1.2917246

[5]. Ata Khalid, G. M. Dunn, R. F. Macpherson, S. Thoms, D. Macintyre, C. Li, M. J. Steer, V. Papageorgiou, I. G. Thayne, M. Kuball, C. H. Oxley, M. Montes Bajo, A. Stephen, J. Glover, and D. R. S. Cumming, "Terahertz oscillations in an In0.53Ga0.47As submicron planar Gunn diode", J. Appl. Phys. 115, 114502 (2014); http://dx.doi.org/10.1063/1.4868705

[6]. P. Nouvel, J. Torres,S. Blin, H. Marinchio, T. Laurent, C. Palermo, L. Varani, P. Shiktorov, E. Starikov, V. Gruzinskis, F. Teppe, Y. Roelens, A. Shchepetov and S. Bollaert,"Terahertz emission induced by optical beating in nanometer-length field-effect transistors" J. Appl. Phys. 111, 103707 (2012); http://dx.doi.org/10.1063/1.4718445

L'IES à La Chapelle (01-04-2014)

Dans le cadre des cafés LAB, qui sont organisés les mardis soirs à la Chapelle, les membres de la partie acoustique du groupe M2A présentent le 1er avril "Jeux acoustiques dans l'espace et l'image sonore". Les jeux et démonstrations qui vont être présentés seront accompagnés ce soir-là par des musiciens du conservatoire de Montpellier.

Depuis Pythagore, les scientifiques se sont amusés, parfois fort sérieusement, à comprendre la musique des ondes sonores. Les applications de leurs travaux trouvent aujourd'hui résonance dans des domaines nombreux et variés : musique, architecture, industries ou médecine.
IES l'institut d'électronique, à travers l'équipe M2A, Matériaux Micro-capteurs et Acoustique, est spécialiste de caractérisation de matériaux industriels et biologiques par méthodes acoustiques. Ses membres sont aussi fortement impliqués dans les formations de l'Université Montpellier 2 : Licence Professionnelle "Acoustique et Environnement Sonore" ou Masters.
Se basant sur des analogies musicales ou naturelles, ils exposeront, au cours de cette soirée, les principes de base de l'acoustique et présenteront des résultats et images issus d'activités de recherches internationales. A travers des jeux acoustiques, ils nous proposent une immersion dans l'espace et l'imagerie sonore dévoilant les liens existants entre Science et Esthétisme.

LES JEUDIS DE L'IES (27-02-2014)

SEMINAIRE de Luis ESPINOSA
Master Student in Industrial Automation
Teaching assistant
National University of Colombia

Travaux en collaboration avec
César Polanco, Professor, District University
Flavio Prieto, Professor, Department of Mechanical and Mechatronics Engineering, National University of Colombia
Loïc Brancheriau, Scientist, AMAP, RU 51, CIRAD-Montpellier
Computer vision techniques for wood characterisation

Wood industry is one of the most important around the world, related to the use of natural resources. Deforestation rates and forest loss for natural reasons are worrying factors in local governments. Therefore, different techniques are available to do wood managing according to the species. Wood species identification could be achieved through the study of macroscopic and microscopic characteristics. At microscopic level, one approach is the use of characteristics that are related to the anatomical structure, mainly composed by 4 differents elements in hardwoods : pores, rays, fibers and parenchyma.
In this talk, we will present some results on the application of different computer vision techniques for wood characterisation from microscopic images. We will also present some outlook work related to the interpretation of acoustic tomography images.

Jeudi 27 février 2014 à 13h45
Salle des séminaires de l'IES, bât 21, 4è étage
Contact : Emmanuel Le Clézio