Field Effect Transistors for Terahertz Detection: Physics and First Imaging Applications

Resonant frequencies of the two-dimensional plasma in FETs increase with the reduction of the channel dimensions and can reach the THz range for sub-micron gate lengths. Nonlinear properties of the electron plasma in the transistor channel can be used for the detection and mixing of THz frequencies. At cryogenic temperatures resonant and gate voltage tunable detection related to plasma waves resonances, is observed. At room temperature, when plasma oscillations are overdamped, the FET can operate as an efficient broadband THz detector. We present the main theoretical and experimental results on THz detection by FETs in the context of their possible application for THz imaging.Comment: 22 pages, 12 figures, review pape

Détection et Emission Terahertz par les ondes de plasma dans des transistors HEMT à base d'hétérostructures GaN/AlGaN et InGaAs/InAlAs

We report on detection of terahertz radiation by high electron mobility nanometer transistors. The photovoltaic type of response was observed at the 1.8–3.1 THz frequency range, which is far above the cut-off frequency of the transistors. The resonant response was observed and was found to be tunable by the gate voltage. The resonances were interpreted as plasma wave excitations in the gated two-dimensional electron gas. The minimum noise equivalent power was estimated, showing possible application of these transistors in sensing of terahertz radiation. Also, we report on the demonstration of room temperature, tuneable terahertz detection obtained by 50 nm gate length InGaAs/InAlAs High Electron Mobility Transistors (HEMT). We show that the physical mechanism of the detection is related to the plasma waves excited in the transistor channel and that the increasing of the drain current leads to the transformation of the broadband detection to the resonant and tuneable one. In addition we report on terahertz emission by two-dimensional electron plasma oscillations in nanometric transistors at room temperature. We observe the room temperature emission for transistors based on two types of heterostructures- InGaAs/InAlAs and AlGaN/GaN. For both types we obtain a well-defined source-drain voltage threshold for the integrated emission, which depends on the gate bias. For InGaAs/InAlAs, we observe only emission signal integrated over the total frequency range (0.1 – 10 THz). High intensity of the Thz emission from GaN/AlGaN structures allowed analysing its spectral content. The emission is interpreted as resulting from a current driven plasmainstability leading to oscillations in the transistor channel (Dyakonov–Shur instability)Les détecteurs et émetteurs travaillant dans la gamme dite Terahertz sont très coûteux et onctionnent généralement à basse température. Les Professeurs Dyakonov et Shur ont proposé en 1993 une théorie sur l'instabilité des ondes de plasma dans un gaz d'électrons bidimensionnel. Cette théorie énonce qu'un transistor peut fonctionner comme détecteur ou source Terahertz quand la longueur de grille est de taille nanométrique. Dans ce manuscrit, nous présentons une source de radiation Terahertz par un Transistor HEMT à base de l'hétérostructures GaN/AlGaN, (cohérente), accordable à température ambiante, relativement intense (0.1 NW), de taille nanométrique et peu coûteuse. En second lieu, nous proposons des détecteurs Terahertz basés sur la technologie GaN/AlGaN et InGaAs/InAlAs et accordables à température ambiante. Notre étude, d'intérêt pluridisciplinaire, vise à explorer les limites physiques et technologiques des performances des transistors HEMT sur l'Emission et la Détection de radiation Terahertz. L'estimation du NEP (Noise Equivalent Power) a également été réalisée. D'un point de vue fondamental, cette étude nous permettra de mieux connaître les propriétés de la détection et de l'émission par un gaz d'électrons bidimensionnel par le biais des ondes de plasma

Détection et Emission Terahertz par les ondes de plasma dans des transistors HEMT à base d'hétérostructures GAN/AlGaN et InGaAs/InAlAs

Les détecteurs et émetteurs travaillant dans la gamme dite Terahertz sont très coûteux et fonctionnent généralement à basse température. Les Professeurs Dyakonov et Shur ont proposé en 1993 une théorie sur l instabilité des ondes de plasma dans un gaz d électrons bidimensionnel. Cette théorie énonce qu un transistor peut fonctionner comme un détecteur ou un émetteur des radiations Terahertz quand la longueur de grille est de taille nanométrique. Dans ce manuscrit, nous présentons une source de radiation Terahertz par un Transistor HEMT à base de l hétérostructures GaN/AlGaN, cohérente et potentiellement accordable à température ambiante, intense avec une puissance de 0.1 W, de taille nanométrique et peu coûteuse. En second lieu, nous proposons des détecteurs Terahertz à base de la technologie GaN/AlGaN et InGaAs/InAlAs, accordable à température ambiante. Notre étude, d intérêt pluridisciplinaire, vise à explorer les limites physique et technologique sur les performances des transistors HEMT sur l Emission et la Détection de radiation Terahertz, l estimation du NEP (Noise Equivalent Power) a été réalisée. D un point de vue fondamental, cette étude nous permettra de mieux connaître les propriétés de la détection et de l émission par un gaz d électrons bidimensionnel par le biais des ondes de plasmaWe report on detection of terahertz radiation by high electron mobility nanometer InGaAs/InAlAs transistors. The photovoltaic type of response was observed at the 1.8 3.1 THz frequency range, which is far above the cut-off frequency of the transistors. The experiments were performed in the temperature range from 10 to 80 K. The resonant response was observed and was found to be tunable by the gate voltage. The resonances were interpreted as plasma wave excitations in the gated two-dimensional electron gas. The minimum noise equivalent power was estimated, showing possible application of these transistors in sensing of terahertz radiation. Also, we report on the demonstration of room temperature, tuneable terahertz detection obtained by 50 nm gate length InGaAs/InAlAs High Electron Mobility Transistors (HEMT). We show that the physical mechanism of the detection is related to the plasma waves excited in the transistor channel and that the increasing of the drain current leads to the transformation of the broadband detection to the resonant and tuneable one. We also show that the cap layer regions significantly affect the plasma oscillation spectrum in HEMT by decreasing the resonant plasma frequencies. In addition we report on terahertz emission by two-dimensional electron plasma oscillations in nanometric transistors at room temperature. Previously, the THz emission was reported only at 4,2 K in a 60 nm InGaAs high electron mobility transistor. We observe the room temperature emission for transistors based on two types of heterostructures- InGaAs/InAlAs and AlGaN/GaN. For both types we obtain a well defined source drain voltage threshold for the integrated emission, which depends on the gate bias. For InGaAs/InAlAs, we observe only emission signal integrated over the total frequency range (0.1 10 THz). High intensity of the Thz emission from GaN/AlGaN structures allowed analysing its spectral content. The emission is interpreted as resulting from a current driven plasma instability leading to oscillations in the transistor channel (Dyakonov Shur instability)MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Extreme rainfall events in Morocco: Spatial dependence and climate drivers

The history of Morocco is replete with tragic natural disasters related to floods that led to numerous casualties and significant material losses. An important driver of these floods is extreme precipitation. Understanding the spatial characteristics of extreme precipitation events is critical to accurately predicting, assessing, and mitigating the risks they pose. Yet, the physical drivers of extreme precipitation events (EPEs) in Morocco remain poorly known. To address this gap, we apply a clustering method to divide Morocco into regions that are spatially consistent in terms of extreme precipitation. We then determine the drivers of extreme precipitation by analyzing atmospheric circulation anomalies during the occurrence of some well chosen EPEs in each region. Our findings suggest that Morocco can be subdivided into 5 spatially coherent regions. Extreme precipitation in the northwestern regions is associated with patterns similar to the negative phase of the North Atlantic Oscillation (NAO) with strong upper-level flow anomalies enhanced by Greenland blocking and/or Rossby wave breaking (RWB) episodes. By contrast, the southern regions are associated with relatively weak upper air troughs but strong water vapor transport anomalies from the tropics

Broadband terahertz imaging of documents written with lead pencils

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Plasma wave field effect transistor as a resonant detector for 1 terahertz imaging applications

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Adjustment of Terahertz Properties Assigned to the First Lowest Transition of (<i>D</i>⁺, <i>X</i>) Excitonic Complex in a Single Spherical Quantum Dot Using Temperature and Pressure

This theoretical study is devoted to the effects of pressure and temperature on the optoelectronic properties assigned to the first lowest transition of the (D+,X) excitonic complex (exciton-ionized donor) inside a single AlAs/GaAs/AlAs spherical quantum dot. Calculations are performed within the effective mass approximation theory using the variational method. Optical absorption and refractive index as function of the degree of confinement, pressure, and temperature are investigated. Numerical calculation shows that the pressure favors the electron-hole and electron-ionized donor attractions which leads to an enhancement of the binding energy, while an increasing of the temperature tends to reduce it. Our investigations show also that the resonant peaks of the absorption coefficient and the refractive index are located in the terahertz region and they undergo a shift to higher (lower) therahertz frequencies when the pressure (temperature) increases. The opposite effects caused by temperature and pressure have great practical importance because they offer an alternative approach for the adjustment and the control of the optical frequencies resulting from the transition between the fundamental and the first excited state of exciton bound to an ionized dopant. The comparison of the optical properties of exciton, impurity and (D+,X) facilitates the experimental identification of these transitions which are often close. Our investigation shows that the optical responses of (D+,X) are located between the exciton (high energy region) and donor impurity (low energy region) peaks. The whole of these conclusions may lead to the novel light detector or source of terahertz range

Terahertz imaging with GaAs field-effect transistors

Imaging at 0.6 THz is tested with a commercial GaAs high-electron-mobility transistor (HEMT) operated at room temperature. The results allow the assessment of the potential of future antenna-fitted HEMT arrays for real-time imaging