Du fait de ses propriétés intéressantes, le domaine de fréquence térahertz (THz) du spectre électromagnétique peut avoir de nombreuses applications technologiques, de l'imagerie à la spectroscopie en passant par les télécommunications. Toutefois, les contraintes technologiques empêchant l'émission et la détection efficaces de ces ondes par des systèmes conventionnels ont valu à cette partie du spectre électromagnétique le nom de gap THz. Au cours des deux dernières décennies, plusieurs solutions novatrices sont apparues. Parmi elles, l'utilisation de transistors à effet de champ s'est imposée comme une solution originale, bon marché, avec un fort potentiel d'intégration. Le mécanisme identifié fait intervenir l'interaction entre les ondes THz et des ondes de courant (dites ondes plasma) dans le canal du transistor. Le canal du transistor agit tel une cavité pour ces ondes plasma. Le dispositif peut alors se comporter de manière résonante ou non-résonante en fonction de divers paramètres. Dans ce manuscrit, nous étudions numériquement ces différents régimes à l'aide de modèles hydrodynamiques. Les modèles utilisés élargissent les phénomènes pris en compte dans de précédentes études théoriques. Les résultats portent sur la détection d'ondes THz par des transistors et dans une moindre mesure sur leur émission. Dans le régime non-résonant, nous étudions dans quelle mesure la plage de linéarité de détection peut être étendue. Dans le régime résonant, nous montrons l'existence de nouvelles fréquences de résonance, permettant d'élargir le spectre d'intérêt de ces détecteurs.

Thermal decomposition of silicon carbide (SiC) provides transfer free and wafer-scale homogeneous graphene forming on a semi-insulating substrate. Large-area monolayer graphene growth was initially developed at the atmospheric pressure (around 900 mbar) in an argon ambient and at high temperature (>1650°C). However, it remains challenging to obtain films with different and controlled characteristics such as the number of graphene layers or the doping by tuning the growth parameters. In this work, we optimized the epitaxial growth of monolayer graphene (1LG) on 4H-SiC (0001) under a low argon pressure of 10 mbar. This intermediate pressure allows growing a continued 1LG in a short process time of ~1h30. Here, we discuss the initial growth stages from buffer layer to 1LG as a function of annealing temperature (same heating rate). The combined Raman spectroscopy and atomic force microscopy (AFM) analyses show that a buffer layer, fully covering the Si-face of SiC, forms as the first step of growth (1600°C). Subsequently, 1LG starts to grow at step edges (1700°C) and continue to cover the buffer layer with a step-flow growth mechanism, as shown in the literature. Eventually, continued large-scale graphene films were achieved at 1750°C with a reproducible process. These graphene films were characterised by Raman, STM and electrical measurement. The integrated intensity of G-band in Raman spectra normalized with respect to a HOPG reference, AG/AG-HOPG, of each spectrum in Raman map is very close to the experimental value reported for a 1LG. Atomically resolved scanning tunnelling microscopy evidences a (6x6) superstructure, indicative of 1LG covering a reconstructed interface layer. Moreover, quantum Hall plateau values observed in our graphene layers confirmed both continuity and thickness of the 1LG film. The carrier density of pHall~1010 - 1011 cm-2 in 1LG films can be achieved at 1.7K in helium atmosphere. Thus, our as-grown 1LG graphene films with low p-type carrier density provide perspectives for further studies and applications on graphene.

An electromagnetic wave detector comprises a field effect transistor, an antenna 601 connected to a first end of a gate 608 of the field effect transistor for receiving incident electromagnetic waves, and a biasing connection pad 605 connected to a second end of the gate 608 for applying a bias voltage to the transistor. The antenna may have a first part 601b connected to the first end of the gate 608 and a second part 601a connected to a source 602 of the transistor. The detector may further comprise a virtual ground element 607 connected to the second end of the gate 608. A control module may control the bias voltage applied on the biasing connection pad 605 according to the electromagnetic power received by the detector. The transistor may be a high electron mobility transistor (HEMT).

At least one electronic device, system and method of manufacturing an electromagnetic wave detector are provided herein. The electronic device for receiving at least one electromagnetic wave of a given frequency may comprise at least one first field effect transistor, and at least one antenna configured to receive the at least one electromagnetic wave and connected to a gate of the at least one first field effect transistor, wherein a length of the gate is in a same order of magnitude as an oscillation length of an oscillation regime of the at least one first field effect transistor at the given frequency, and a width of the gate is such that an impedance presented by the at least one first field effect transistor in the oscillation regime is adapted to an impedance of the at least one antenna.