Notre recherche se base sur la structuration des polymères conjugués qui présentent des propriétés optiques et électroniques intéressantes en raison de leur structure moléculaire intrinsèque. En effet, la structure des polymères conjugués se compose d’une alternance de simples et de doubles liaisons donnant lieu à une délocalisation des électrons le long des chaînes. Cette conjugaison est à l’origine de leurs propriétés de luminescence et de leur caractère semi-conducteur. Ces polymères sont couramment utilisés dans des dispositifs électroniques où ils jouent le rôle de composant actif. Le fonctionnement de ces dispositifs repose sur la capacité des charges à se déplacer le long des chaînes (processus intramoléculaire) et d'une chaîne à l'autre (processus intermoléculaire) et par conséquent, ces propriétés de transport dépendent de l’arrangement des chaînes polymères dans le solide, qui lui-même découle des interactions supramoléculaires. Il est donc impératif de maîtriser ces interactions et d’étudier l’influence qu’elles ont sur les performances de tels dispositifs électroniques. C’est précisément sur ce point que porte notre travail : étudier et contrôler la formation de nanostructures en termes de dimensions, de forme et de localisation, en appliquant une contrainte physique extérieure à un film de polymère conjugué. Le polymère conjugué sur lequel notre étude se base principalement est le poly(3-hexylthiophène), P3HT. Ce polymère est semi-cristallin et possède une mobilité de charge élevée (0.18 cm2/V.s), ce qui en fait un très bon candidat en tant que composant actif dans les transistors à effet de champ. Nous avons, dans le cadre de notre recherche, étudié la structuration de films minces de P3HT, réalisée par l’application de contraintes physiques extérieures. L’utilisation d’une pointe de microscope à force atomique travaillant en mode contact permet de déformer plastiquement la surface polymère en créant des structures périodiques en surface des films mais elle permet, en outre, d’orienter les chaînes polymères dans la direction de passage de la pointe. Différents paramètres expérimentaux ont été étudiées comme par exemple, la résolution choisie pendant l’expérience, le nombre de passage effectués par la pointe ou encore l’angle avec lequel la pointe structure le film polymère. Nous avons également démontré que cette technique, appliquée au canal polymère d’un transistor à effet de champ, permet d’améliorer les propriétés électriques du P3HT et par conséquent, d’augmenter les performances du dispositif électronique. Nous avons utilisé une autre méthode, dite de « lithographie douce », afin de structurer le P3HT. Cette technique présente l’avantage de « façonner » le polymère lorsqu’il se trouve en solution et ne nécessite donc pas la formation préalable d’un film. Elle consiste à déposer une goutte de solution polymère sur un substrat, à l’entrée de canaux micrométriques de PDMS; l’écoulement de la solution polymère, qui se fait par capillarité dans les canaux, est donc confiné. Le solvant va ensuite s’évaporer et il reste alors, sur le substrat, un dépôt polymère qui est la réplique négative des canaux de PDMS. L’analyse du dépôt polymère formé grâce à cette méthode révèle, comme c’était le cas pour la technique précédente, une orientation des chaînes polymères au sein des canaux. Dans la dernière partie de ce travail, nous avons étudié le dopage de films fibrillaires de P3HT. L'étude de la morphologie des films dopés montre que la structure fibrillaire est conservée, avec une légère augmentation de la largeur des fibrilles. Cette augmentation résulte d'un déplacement des chaînes polymères les unes par rapport aux autres dans l'axe du squelette conjugué afin de laisser des espaces vacants pour accueillir les contre-ions dans le réseau polymère. Les mesures électriques des films dopés montrent un accroissement très important de la conductivité du polymère. On observe une augmentation de six ordres de grandeur entre les conductivités d'un film neutre et dopé.

This thesis reports on the growth and characterization of p-type pseudomorphic A1GaAs /InGaAs /GaAs modulation doped field effect transistor (MODFET) structures. A series of different p-type MODFET structures were grown with a systematic variation of the indium mole fraction and quantum well width of the InGaAs channel region. Extensive characterization of these samples using van der Pauw Hall and photoluminescence measurements showed clear trends in carrier mobility and quantum well quality with respect to the structure of the InGaAs region. From this an optimal indium mole fraction and quantum well width were obtained. Subsequent to material characterization, MODFET devices were fabricated and characterized. The measured DC device performance was reasonable and suggests that high quality p-type MODFETS should be obtainable with a properly optimized device structure and fabrication process. / Graduation date: 1993

The purpose of this work is to develop a new model for LDD n-MOSFET degradation in drain current under long-term AC use conditions for lifetime projection which includes a self-limiting effect in the hot-electron induced device degradation. Experimental results on LDD n-channel MOSFETs shows that the maximum drain current degradation is a function of the AC average substrate current under the various AC stress conditions but not a function of frequency or waveforms or different measurement configurations. An empirical model is constructed for circuit applications. It is verified that the self-limiting in drain current is due to the thermal re-emission of a trapped-hot-electron in the oxide. Results show that self-heating during AC stress releases trapped electrons, which in turn limits the maximum amount of drain current degradation. Moreover, tunneling to and from traps model is employed to visualize the internal mechanism of thermal recovery of electrons under different bias conditions. Although the LDD device structure can reduce the hot electron effect, various processing technologies can also affect the device reliability. A carbon doped LDD device with the first and the second level metal and passivation layer but without any final anneal shows that a significant reduction in the shifts of the threshold voltage of MOSFETs with time can be achieved. However, the long-term reliability projection of nMOSFETs based on DC stress tests alone is shown to be overly pessimistic. / Graduation date: 1992

The semiconductor gallium arsenide (GaAs) has many potential advantages over the more widely used semiconductor silicon (Si). These include higher low field mobility, semi-insulating substrates, a direct band-gap, and greater radiation hardness. All these advantages offer distinct opportunities for implementation of new circuit functions or extension of the operating conditions of similar circuits in silicon based technology. However, full exploitation of these advantages has not been realized. This study examines the limitations imposed on conventional GaAs metal-semiconductor field effect transistor (MESFET) technology by deviations of the semi-insulating substrate material from ideal behavior. The interaction of the active device with defects in the semi-insulating GaAs substrate is examined and the resulting deviations in MESFET performance from ideal behavior are analyzed. A p-well MESFET technology is successfully implemented which acts to shield the active device from defects in the substrate. Improvements in the operating characteristics include elimination of drain current transients with long time constants, elimination of the frequency dependence of g[subscript ds] at low frequencies, and the elimination of sidegating. These results demonstrate that control of the channel to substrate junction results in a dramatic improvement in the functionality of the GaAs MESFET. The p-well MESFET RF characteristics are examined for different p-well doping levels. Performance comparable with the conventional GaAs MESFET technology is demonstrated. Results indicate that optimization of the p-well MESFET doping levels will result in devices with uniform characteristics from DC to the highest operating frequency. / Graduation date: 1991

A complete Gallium Arsenide Metal Semiconconductor Field Effect Transistor (GaAs MESFET) model including deep-level trap effects has been developed, which is far more accurate than previous equivalent circuit models, for high-speed applications in linear integrated circuit design. A new self-backgating GaAs MESFET model, which can simulate low frequency anomalies, is presented by including deep-level trap effects which cause transconductance reduction and the output conductance and the saturation drain current to increase with the applied signal frequency. This model has been incorporated into PSPICE and includes a time dependent I-V curve model, a capacitance model, a subthreshold current model, an RC network describing the effective substrate-induced capacitance and resistance, and a switching resistance providing device symmetry. An analytical approach is used to derive capacitances which depend on Vgs and Vds and is one which also includes the channel/substrate junction modulation by the self backgating effect. A subthreshold current model is analytically derived by the mobile charge density from the parabolic potential distribution in the cut-off region. Sparameter errors between previous models and measured data in conventional GaAs MESFET's have been reduced by including a transit time delay in the transconductances, gm and gds, by the second order Bessel polynomial approximation. As a convenient extraction method, a new circuit configuration is also proposed for extracting simulated S-parameters which accurately predict measured data. Also, a large-signal GaAs MESFET model for performing nonlinear microwave circuit simulations is described. As a linear IC design vehicle for demonstrating the utility of the model, a 3-stage GaAs operational amplifier has been designed and also has been fabricated with results of a 35 dB open-loop gain at high frequencies and a 4 GHz gain bandwidth product by a conventional half micron MESFET technology. Using this new model, the low frequency anomalies of the GaAs amplifier such as a gain roll-off, a phase notch, and an output current lag are more accurately predicted than with any other previous model. This new self-backgating GaAs MESFET model, which provides accurate voltage dependent capacitances, frequency dependent output conductance, and transit time delay dependent transconductances, can be used to simulate low frequency effects in GaAs linear integrated circuit design. / Graduation date: 1991

This thesis includes elementary introductions to nuclear quadrupole resonance (NQR) detection and fieldeffect transistors (PET). The construction and operation of the FET-NQR detector, as originally designed by Viswanathan, Viswanathan and Sane and published in Rev. Sci. Instr. 39,472 (1968), is discussed extensively. The thesis also contains a step by step discussion of the construction of an alternate PET-N'QP detector. Although the alternate detector never functioned properly, the information gathered would aid anyone desiring to design and construct a new NQR detector.Ball State UniversityMuncie, IN 47306

This thesis provides the study of graphene’s electrostatic interaction with the substrate surrounding it. Mathematical models based on current experimental configurations of graphene field-effect transistors (FET) are developed and analyzed. The conductivity and mobility of charge carriers in graphene are examined in the presence of impurities trapped in the substrate near graphene. The impurities encompass a wide range of possible structures and parameters, including different types of impurities, their distance from graphene, and the spatial correlation between them. Furthermore, we extend our models to analyze the influence of impurities on the fluctuations of the electrostatic potential and the charge carrier density in the plane of graphene. The results of our mathematical models are compared with current experimental results in the literature.

Thesis (Ph. D.)--Lehigh University, 2000. / Includes vita. Includes bibliographical references (leaves 132-136).

Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Electrical and Computer Engineering." Includes bibliographical references (p. 151-156).

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 129-145). Available also in a digital version from Dissertation Abstracts.