Recent advancements in photodetection using 2D materials suggest significant improvements in the performance of photodetectors. Among these, graphene field-effect transistors (GFETs) have demonstrated promising enhancements in photodetection, characterized by low noise, broad-spectrum response, high responsivity, and fast response [46, 126]. These photodetectors utilize graphene as the active channel, with graphene deposited on an insulating layer and semiconductor substrate. The contact of graphene with an insulator/semiconductor structure induces an interfacial potential to trap one type of photo-generated carrier at the interface. The trapped charge carriers induce opposite carriers in the graphene channel through the capacitive coupling effect. Due to a long lifetime of trapped carriers, the induced carriers in the graphene channel circulate multiple times under a given bias between the source and drain contacts, generating a photocurrent with high gain. Here, we explore GFET photodetectors fabricated on p-GaAs and p-Si wafers at room temperature. The photodetectors achieve a high gain. The photocurrent is generated due to the photogating effect. In this work, we explore GFET photodetectors fabricated on p-GaAs and p-Si wafers at room temperature. The photodetectors achieve a high gain and high responsivity of 106 (A/W) under the above bandgap excitation and can detect light below the bandgap illumination for both p-doped substrates. NEP and D* values of these detectors have been characterized along with response time characteristics. The NEP and D∗ values for both detectors are around 10−15 W/√ and 1012 Jones respectively, indicating a sensitive photodetection. The response time characterization suggests the rise and decay time depends on incident power. These results provide us with a deeper insight into the photodetection of the GFETs from the ultraviolet to near-infrared region. / Master of Science / Photodetectors have numerous applications in our daily lives, such as optical sensors in mobile phones, telecommunications, and biological imaging. However, current photodetection technologies often struggle to meet the increasing demands of modern equipment. These technologies require improving the existing photodetectors so that they can operate at exceptionally high speeds with low noise. Graphene is a highly sensitive material, that has shown significant potential for photodetection due to its fascinating optoelectronic and mechanical properties. In this study, we fabricated two field effect transistors on two semiconductor materials of different bandgaps with a single layer of graphene added on top of the substrate/insulator layer for photodetection. Specifically, we investigate the performance of GaAs and Si substrates to understand how varying the substrate can affect photodetection so that it can open up possible routes to future applications.

Ce travail expérimental traite de la détection de radiations Térahertz (THz) par des transistors à base de silicium. Après avoir exposé le contexte de l'étude et les bases théoriques des modèles nécessaires à la compréhension du sujet, le manuscrit débute par une comparaison des transistors de haute mobilité électronique (HEMTs à base de matériaux III-V), aux transistors à base de silicium (Si-MOSFETs). Cette étude permet une meilleure compréhension du mécanisme physique responsable de la détection de radiations THz par les transistors à effet de champ de manière générale. La seconde partie de ce travail est consacrée à l'étude théorique et expérimentale de la longueur critique du canal Lc, liée à la distance d'amortissement des ondes de plasma et à partir de laquelle le signal de détection sature. Par ailleurs, le signal de détection THz de différents types de Si-MOSFETs a été étudié en fonction du champ magnétique, de la température et de la fréquence de l'onde THz incidente. Des raies inattendues et extrêmement marquées sont observées, jusqu'à la température ambiante, dans le signal de détection et dans la résistance du canal en champ magnétique. Celles-ci semblent être liées à une résonance de spin de facteur gyromagnétique égal à 2. L'allure générale du signal THz en champ magnétique est également discutée. Enfin, l'une des premières générations de détecteurs optimisés pour le THz et conçue dans le cadre d'un partenariat avec le CEA-LETI est présentée. Il s'agit notamment d'une matrice de pixels composés de Si-MOSFETs connectés à des antennes adaptées, à des amplificateurs de signaux, et à une première ébauche de circuit de lecture. La sensibilité, la puissance équivalent bruit (NEP) et la polarisation de ces détecteurs, est également étudiée en fonction de la fréquence incidente. Les résultats de cette étude mettent en exergue le potentiel de ces transistors nanométriques à base de Silicium entant que détecteur dans un système d'imagerie THz performant à température ambiante. / The experimental study reported here, deals with Therahertz (THz) radiation detection with silicon based transistors. After a brief overview of the context and the basics of the theory necessary to understand the subject, the report starts with a comparison betwen high mobility transistors (HEMTs based on III-V technolgies), and silicon transistors (Si-MOSFETs). This study allows a better understanding of the physical phenomenom responsible for THz radiation detection with field effect transistors in general. The second part is focalized on theoretical and experimental study of the critical chanel length (Lc), correlated to the distance of the plasma waves damping, from which the detection signal saturates. Beside, this THz detection signal, from diffrent kind of Si-MOSFETs, has been studied in magnetic field, in temperature, and in the frequency of the incomming radiation. Very pronounced and odd peaks are observed and studied, up to the ambiant temperature, inside the THz signal and the resistance of the MOS submited to magnetic field. These peaks seems to be linked by some way to a spin resonnance with a gyromagnetic factor of 2. The global tendancy of the evolution of the signal in magnetic field is also studied. Finally, one of the first generation of THz optimized detectors, develloped in partnership with CEA-LETI, is presented. Indeed, matrixes of pixels, composed of Si-MOSFETs connected to specific antennas, integrated amplifiers, and a basic reading circuit are studied. Sensitivity, noise equivalent power (NEP), polarization, of these detectors are caracterized. This study demonstrates the whole potential of these silicon based transistors as efficient THz imagery detectors for room temperature.

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