The optoelectronics industry continues to demand improved materials, devices and systems for the generation, transmission, detection, amplification and processing of optical signals. Heterojunction phototransistors (HPTs), in recent years, have attracted considerable interest for optical detection due to their intrinsic gain, low noise performance, high-frequency operation and process and the device layer compatibility with heterojunction bipolar transistors for high-speed optoelectronic monolithic microwave/millimetre-wave integrated circuit (OEMMIC) photoreceivers. A key performance parameter of HPTs is their spectral response (SR) which is critical in their usage in optical applications. The SR depends on several inherent factors including material absorption coefficient, refractive index, device structure, doping and temperature of operation along with the external factors such as bias voltage and the energy of incident radiation. The spectral response and optical characteristics of GaAs-based and InP-based sHPTs have been successfully predicted for the first time through an advanced absorption theoretical model. The model is based on the accurate prediction of photocarriers in the active layers of the phototransistor which, when related to the base current of the transistor in forward active mode, enables the prediction of optical characteristics. The importance of collection efficiency in accurate SR modelling is highlighted and the layer dependence of the optical flux absorption profile at near-band gap wavelengths is also investigated and its generalisation as a single-exponential has been refuted for GaAs-based HPTs. Analytical modelling of the spectral response has also been developed from the resolution of continuity equations that govern the excess optically generated minority carrier variation in the active layers of the HPT, taking into account the related physical parameters. Realistic boundary conditions have been considered for efficient device operation and a detailed optical flux absorption profile is constructed for accurate device modelling. This analytical model provides insight into the direct influence of various parameters (such as base width and carrier concentration) on the device performance, thus, providing a valuable optimization tool for the future design of HPTs in optical receivers. The measured results at 635 nm, 780 nm 808 nm and 850 nm for AlGaAs/GaAs HPTs and 980 nm, 1310 nm and 1550 nm for InP/InGaAs HPTs show good agreement with the predicted data, validating the proposed theoretical model. Finally, a detailed absorption model and photoresponse of double heterojunction phototransistors in a top/surface-illuminated orientation has been analyzed with a modified small-signal model. The effect of incident optical illumination on intrinsic small-signal parameters such as resistances and capacitances has been discussed and analyzed for photoresponse modelling.

Layered Van der Waals solids, due to their highly anisotropic structure as well as their availability in mono, few and multi-layer form constitute a perfect playground, where a variety of possibility in structural variation as well as functionalities are expected. This potentially gives rise to a library of unique and fascinating 2D materials systems. These systems appear to demonstrate some spectacular variety of fundamental physics as well as indicate that some of these systems can be beneficial for several niche applications directly or indirectly resulting from their electrical and optical properties.

Ce travail de thèse présente le développement de phototransistors bipolaires à hétérojonction (HPT) SiGe/Si mis en œuvre dans une technologie de processus 80GHz SiGe bipolaire pour des applications de transmission Radio-sur-Fibre. Le cas particuliers d'un réseau domestique sans fil à infrastructure optique est considéré pour lequel le critère de coût est prépondérant. Le fonctionnement des ce HPT SiGe/Si est étudié sous une longueur d'onde optique de 850 nm en exploitant des fibres optique multimode (MMF) suffisantes pour les besoins de bande passante dans un environnement de réseau domestique. Le HPT SiGe/Si est également développé dans l'objectif de permettre une intégration combiné du photorécepteur et circuit intégré monolithiquement, conduisant à des structures de type Opto-electronic Microwave Monolithically Integrated Circuit (OE-MMIC), visant à poursuivre l'intégration et la réduction des cours. Deux topologies ont été explorées principalement: 1) une topologie avec élargissement de la base et du collecteur (xBC HPT) et 2) une topologie avec élargissement des trois régions de base, émetteur et collecteur simultanément (xEBC HPT). Des variations technologies ont été réalisées et analysées en détail, à la fois en terme de couches verticales que de dessin de masque (layout). Les mesures ont démontré la validité technologique de chacune de ces approches, et permis d'isoler l'impact sur les performances statiques et dynamiques de chacune de ces couches. Une solution de type xEBC se montre ainsi préférable pour le cas de composants de petites dimensions inférieure à 50x50µm², dans la bande du GHz. Les phototransistors sont développés dans une configuration à trois terminaux (3T-HPT). Le type de polarisation de la base du HPT influe également sur la responsivité du phototransistor. Une polarisation de courant constant (CC) démontre une plus grande responsivité par rapport au cas d'une polarisation en tension ( CV). Une analyse détaillée montre aussi les différences de responsivité mesurées en continue et celles mesurées en basse fréquence à 50MHz. La connexion de base permet également de varier l'impédance de charge présentée sur celle-ci. La théorie de l'adaptation des phototransistors est rappelée. L'effet de différentes impédances de base sont étudiées par la simulation et la mesure des circuits réalisés technologiquement. L'intégration du phototransistor au sein d'un circuit élémentaire est enfin explorée. Différentes configurations de paires HPT - HBT sont étudiées, formant des circuits élémentaires. Des caractérisations expérimentales permettent de vérifier l'amélioration apportées par ces topologies par rapport au phototransistor unique. Enfin, un phototransistor SiGe en configuraiton 2T-HPT est utilisé et intégré avec succès pour la première fois au sein d'un module de type Receiving Optical Sub Assembly (ROSA) pour la mise au point d'une transmission Radio-sur-Fibre multiGigabit par seconde pour un réseau domestique / This research is focused on the study of silicon germanium based heterojunction bipolar phototransistors (SiGe HPTs) implemented in an 80GHz SiGe Bipolar process technology. It's application in a radio over fiber system for home area networks are investigated. RoF for Home area networks are envisioned to implemented with a minimal system cost. Operation at 850nm is identified as a critical parameter to achieve this goal. Low cost off the shelf optical components are readily available at this wavelength. The use of multi mode fibers (MMF) as opposed to higher cost single mode fiber (SMF) is sufficient for the bandwidth requirements in a home network environment. A monolithically integrated OE receiver chip would help in the overall reduction of the system cost by having the optical detector in the same chip with the electronic circuits. We have designed and implemented three terminal HPT (3T-HPT) structures. The two main groups of the HPT structures are: 1) HPTs with extended Base and Collector regions (xBC HPT) and 2) HPTs with extended Emitter, Base and Collector regions (xEBC HPT). Variations to improve optical coupling the though optimizations in the vertical stack and lateral size of the HPT. The measurements and characterization showed that all the structures are compatible with the process technology. The type of biasing used in the base of the HPT also influences the HPT performance. A constant current (CC) bias has higher extracted DC responsivity as compared to a constant voltage (CV) bias. The effects of the different passive base loads on the HPT responsivity are studied through simulation and measurement of fabricated circuits. The impedance presented on the base has a great influence on the HPT responsivity. The performance of an HPT as circuit component is studied using different HPT-HBT pair configurations. Tests and measurements verify that improvement in the classical transistor pair configurations are also present in the opto microwave response of the HPT-HBT pair. Finally, SiGe hpt is used in the development of a ROSA module for a radio over fiber systems for home area network

Organic phototransistors (OPTs) can enable essential applications, such as nonvolatile memory, artificial synapses, and photosensors in next-generation optical communication and wearable electronics. Among these applications, nonvolatile OPT memories are particularly promising, as they can retain captured visual information for extended periods, making them valuable for data storage, image and video processing applications. The capability of storing multi-bit information, which provides a low-cost way to increase the memory density per unit cell area, is one of the most critical challenges of memory products. In this work, we explore different solution-processible electrets to obtain highly sensitive phototransistor memory devices. Different planar heterojunctions, including small molecule/small molecule and small molecule/polymer, are used to fabricate OPT memories. Additionally, we explore the feasibility of producing polymer/polymer planar heterojunctions through printing processes. Firstly, OPT memories that can be programmed with white light and erased by applying a negative voltage are fabricated with a planar heterojunction of a nonconductive nanographene layer and a semiconducting layer of 2,9-didecyldinaphtho[2,3-b:2’,3’-f]thieno[3,2-b]thiophene (C10-DNTT). We systematically study the optical and memory characteristics of devices with an 8 nm nanographene (NG) layer. The photosensitivity of such devices can be as high as 3.4×105. The memory also shows quite good endurance and data-storing stability; an endurance of 100 write-read-erase-read (WRER) cycles and 1.5×105 s retention time are obtained. The thickness of the NG layer has a considerable influence on the performance of fabricated devices. The results suggest that devices with a thicker NG layer are more sensitive to weak light. In comparison, devices with a relatively thin NG layer are found to be promising for multi-bit photo memory devices. Secondly, we fabricate OPT memories by replacing the nanographene layer with a commercially available semiconducting polymer, namely Poly(2,5-bis(2-octyldodecyl)-3,6-di(pyridin-2-yl)-pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-2,2’-bithiophene) (PDBPyBT). This polymer possesses a narrow bandgap and exhibits a broad range of light absorption, spanning from ultraviolet (UV) to red light wavelengths. As a result, the fabricated devices are capable of responding to a broad spectrum of light colors. The light response of these devices is investigated in terms of their reaction to different colors of light. Also, devices with varying thicknesses of the PDBPyBT layer are fabricated and studied. The results indicate that all of the fabricated devices demonstrate multi-bit programming properties, and the devices incorporating a thin, ribbon-structured PDBPyBT layer are particularly well-suited for applications as light dosimeters. Moreover, the results highlight that both the C10-DNTT and the PDBPyBT layer function as photo exciton generation and charge-trapping layers. Last, we seek to fabricate cost-effective organic multilayer devices through a solution-processing approach, eliminating the need for orthogonal solvents. We observe a crosslinking effect in the thin films caused by thermal annealing without using any crosslinker. Remarkably, this effect is found to be universal for several commercial semiconducting polymers investigated in our study. Following annealing at 200 ºC or higher temperatures, the thin films exhibit enhanced stability against the original solvent. Various analytical techniques are employed to examine the thin films to gain insights into the microstructural changes. Our results suggest that the observed crosslinking effect is predominantly attributed to a physical transformation, whereby the films became more crystalline after annealing at relatively high temperatures. To further explore the feasibility of fabricating multilayer devices, we simulate the construction of multilayer devices by top-gate-bottom-contact (TGBC) devices using the same solvent for the polymer dielectric layer and the semiconducting layer. We also fabricated planar polymer/polymer heterojunction via this method. Encouragingly, this approach demonstrated that thermal annealing could work as a straightforward and promising method for producing cost-effective organic multilayer devices, e.g., fully solution-processed diodes, functional transistors, and solar cells.:Abstract iii Contents vii 1 Introduction 1 1.1 Motivation 1 1.2 Organic semiconductor 2 1.2.1 Atom orbitals and molecular orbitals 2 1.2.2 Energy levels in solid 5 1.2.3 Fermi level 6 1.2.4 Band bending 7 1.2.5 From orbital to states 8 1.2.6 Organic semiconductor materials 9 1.2.7 Nanographene 10 1.2.8 Charge carrier transport in organic semiconductors 11 1.3 Organic field-effect transistors (OFET) 11 1.3.1 OFET architectures 12 1.3.2 OFET operation principle 12 1.3.3 OFET performance parameters 14 1.3.4 OFET memory 17 1.4 Optical electronics 20 1.4.1 Exciton pair generation. 20 1.4.2 Photoelectronic devices 21 1.4.3 Phototransistor devices 22 1.5 Phototransistor memories 23 1.5.1 Working mechanism of phototransistor memories 23 1.5.2 Phototransistor memory architecture 24 1.5.3 State-of-the-art organic phototransistor memory 25 1.6 Objective and outline 27 2 Materials and methods 29 2.1 Materials 29 2.2 Device fabrication 30 2.2.1 Substrate cleaning 30 2.2.2 Solution shearing 30 2.2.3 Thermal vapor deposition 31 2.3 Characterization 31 2.3.1 Thin film characterization 31 2.3.2 Current voltage characteristics 35 2.3.3 Capacitance 36 3 C10-DNTT/NG planar heterojunction phototransistor memories 37 3.1 Introduction 37 3.2 Thin films 39 3.2.1 Film and device fabrication 39 3.2.2 Characterization of thin films 39 3.3 Transfer characteristics under light 41 3.3.1 Writing process 41 3.3.2 Erasing process 48 3.3.3 C10-DNTT-only devices 51 3.4 Summary of working principle 52 3.5 Output characteristics and evaluation of the optical properties 52 3.6 Memory properties of NG-based OPT memory devices 55 3.7 Devices with different NG thicknesses 56 3.7.1 The impact of NG thickness 56 3.7.2 Devices fabricated from 0.05 mg ml-1 NG solution 60 3.8 Conclusion 64 4 C10-DNTT/PDBPyBT heterojunction phototransistor memories 67 4.1 Introduction 67 4.2 Device Architecture 68 4.3 Physical characterization of PDBPyBT and C10-DNTT thin films 69 4.4 Performance of devices with a thick PDBPyBT layer 72 4.4.1 Erasing and programming process 72 4.4.2 Response to different colors of light 78 4.5 Variation of PDBPyBT thickness 80 4.5.1 Transfer characteristics 80 4.5.2 Morphology of C10-DNTT 85 4.5.3 Output characteristics 86 4.5.4 Multi-level programming test 86 4.6 Comparison of the devices 92 4.7 Summary 93 5 Organic multilayer devices fabricated via thermal annealing 95 5.1 Introduction 95 5.2 Film Fabrication 97 5.3 Study on thin films 97 5.3.1 Thickness changes 97 5.3.2 Characterization of the thin films 99 5.3.3 Impact of re-annealing 107 5.3.4 Other semiconducting polymers 108 5.4 Discussion of the working mechanism 110 5.5 Impact of thermal annealing on devices’ performance 111 5.5.1 BGTC devices fabrication 111 5.5.2 TGBC devices fabrication 113 5.6 Planar heterojunction devices via solution processing 116 5.7 Conclusion 117 6 Conclusions and outlook 119 6.1 Conclusions 119 6.2 Outlook 120 Bibliography 123 List of Figures 143 List of Tables 155 List of abbreviations 157 Appendix A 159 Appendix B 165 B1.1 Introduction 165 B1.2 Devices with a 7 nm shear coated Al2O3 dielectric 166 B1.2.1 Normal-sized channel devices 166 B1.2.2 Ultra-wide channel devices 167 B1.3 Devices with a 30 nm ALD Al2O3 dielectric 169 B1.3.1 Normal-sized channel devices 169 B1.3.2 Ultra-wide channel devices 170 B1.4 Ferroelectric organic phototransistor devices 172 B1.4.1 Dielectric layer 172 B1.4.2 Devices with 10 nm HZO 173 B1.4.3 Devices with 30 nm HZO 175 Conclusion 176 Publications 177 Acknowledgment 179

Mon travail de thèse porte sur l’assemblage supramoléculaire et le transport de charge des multi-composants utilisés dans le domaine de l’électronique à base organique. En particulier, l’étude et l’optimisation des transistors organiques à effet de champ (OFETs), des phototransistors, et des inverseurs organiques. Nous avons démontré que la température de recuit des dispositifs OFETs améliore les performances électriques d’un dérivé de fullerène (ICBA). Ces dispositifs dont les surfaces de SiO2 sont fonctionnalisées par OTS ou HMDS ont montrés des mobilités d’électrons de 0.1cm2V-1s-1, qui est la plus élevée par rapport à la littérature. Aussi, nous avons fabriqué des phototransistors à base de mono- et multifibres de PDIF-CN2 qui ont été optimisés par traitements de surfaces du diélectrique (HMDS ou OTS). Les propriétés optoélectroniques de ces dispositifs ont été comparées à ceux des dispositifs à base des couches minces déposés par spin-coating (éduction centrifuge). Nos dispositifs mono-fibres ont montré des valeurs de mobilité plus élevées (supérieure à 2 cm2V-1s-1) par rapport à ceux des multifibres et couches minces. Une telle efficacité de transport d’électrons est le résultat d’une cristallinité très élevée des fibres, qui permet une collecte efficace des excitons photo-générés qui se traduit par la plus haute sensibilité à la lumière (R) et photosensibilité (P) rapportées pour les phototransistors à base de mono-fibre supérieure à 2 × 103 AW-1, et 5 × 103 AW-1. Enfin, un polymère ambipolaire (DPPT-TT) a été utilisé lors de la fabrication de nouveaux dispositifs multifonctionnels par l’addition des molécules diaryléthènes (DAE_tBu et ou DAE_F), dont les propriétés électriques sont contrôlées par la lumière. Cette approche a permis un contrôle optique de gain en tension des inverseurs organiques, ces dispositifs multi-composants sont caractérisés par des gain en tensions très élevées (jusqu’au 504) comparés à ceux reportés dans la littérature (86). Ces travaux réalisés durant cette thèse offrent de nouvelles perspectives dans le domaine de l’optoélectronique et la conception des mémoires optiques. / This thesis is focused on the investigation of supramolecular assemblies and the charge carriers transport across organic single, bi- and three-component materials, used as the active layer in organic field-effect transistors (OFET), phototransistors (OPT) and complementary inverters. We demonstrated that thermal annealing and duration has high impact in OFET performances based on a fullerene derivative called ICBA. The devices electron mobility enhanced upon HMDS and OTS treated SiO2 surface and reached 0.1 cm2V-1s-1, which is the highest reported value in literature. We have provided evidence for the influence of the order at the supramolecular level in the semiconducting material (PDIF-CN2) on the performance of OPTs. We compared solution processed single crystalline PDIF-CN2 fibers and multifiber assemblies with spin-coated thin films, which revealed that the former exhibited good electron mobility up to 2 cm2s-1V-1. The improved fiber crystallinity allows efficient collection of photogenerated excitons, results in the highest reported responsivity R (>5 × 103 AW-1), and photoswitching ratio P (>2 × 103), which are to date the highest reported in literature for PDI-single crystal OPTs. Finally, we have performed for the first time new multifunctional devices combining an ambipolar polymer (DPPT-TT) with inserted diarylethene molecules in its matrix. The fabricated OFET and organic complementary inverters were optically controlled. The resultant inverters gain values are tuned by ultraviolet and visible light irradiation, reaching 504, which is higher than those reported in literature (86). These findings qualify them as promising potential candidates for the construction of high-performance integrated logic circuits and memory chips.

Dans cette thèse, nous présentons des outils de modélisation destinés à l'étude des composants optoélectroniques et des méthodes d'optimisation permettant d'en tirer encore plus de profit. Afin de modéliser différents composants optoélectroniques sur InP, nous avons mis au point un logiciel fondé sur la méthode des faisceaux propagés (BPM) afin d'étudier la propagation et l'absorption de la lumière, et un modèle hydrodynamique afin de modéliser leur comportement électronique. Nous avons réalisé une recherche bibliographique pour regrouper les données matériaux nécessaires. Le premier composant que nous avons étudié et optimisé est un phototransistor à hétérojonction InP/InGaAs pour les applications hyperfréquences. Nous avons exposé son fonctionnement et montré ses possibilités et limites. Sa structure optique de type guide d'onde peut être améliorée par l'ajout d'une couche de quaternaire. On peut envisager la réalisation de phototransistors à double hétérojonction pour les applications de puissance. Nous avons ensuite étudié des photodiodes PIN-guide à très fort coefficient de couplage et grande tolérance d'alignement. Différentes solutions ont été envisagées. Nous avons montré l'intérêt des « structures lentillées », comportant plusieurs couches de confinement d'indices optiques progressifs, et étudié leurs performances optiques et électriques. Pour optimiser ces structures, nous avons mis au point un algorithme Monte Carlo couplé à une BPM-2D, qui permet de tester des milliers de structures aléatoires. Enfin, nous avons réalisé un Algorithme Génétique couplé à une BPM-2D et avons montré son intérêt pour l'optimisation de composants optoélectroniques avec de nombreux paramètres et des objectifs multiples. Ce type d'algorithme est fondé sur la théorie de l'évolution de Darwin. Nous l'avons appliqué à l'optimisation de commutateurs optique à réflexion interne totale et de commutateurs cascade.