Thesis (M.S.)--Rochester Institute of Technology, 1992. / Typescript. Includes bibliographical references (leaves 65-68).

Organic field-effect transistors (OFET) have attracted considerable interests as a promising technology for the next-generation flexible electronics. Thioacenes have recently emerged as potential semiconducting materials for OFETs. On the other hand, Photovoltaic (PV) technology is regarded as a prospective alternative for green and renewable energy source. Recently, dye sensitized solar cells (DSSCs) have drawn intensive attention and showed great potential for practical application. Herein, the research in this thesis would include the synthesis and characterization of novel thioacene-based semiconductors for OFET and DSSC applications. To begin with, a general review on the current status of organic semiconductors for OFET and DSSC applications was presented in Chapter 1. In chapter 2, a series of novel benzodithieno[3,2-b]thiophene derivatives (BDTT-n) with different lateral alkyloxy groups were designed and synthesized. In addition, alkyloxy-substituted benzo[2,1-b:3,4-b’]bis-[1]benzothiophenes derivatives (BBBT-n) were also synthesized. The performances of OFETs based on BDTT-n and BBBT-n have been fully investigated. Among them, BDTT-4 based OFET exhibited the highest hole mobility of 1.74 cm 2 /(Vs) with a current on/off ratio above 10 7 without annealing. In chapter 3, a novel series of naphthodithiophene-based oligomers with D-A- D-A- D structure motif were designed and synthesized. All these oligomers have 2 been fully characterized by NMR and mass spectrometry. The hole mobility properties of these oligomers were determined in OFETs as fabricated by drop- coating technique. These oligomers exhibited typical p-type semiconducting behavior. A mobility of 1.6x10 -2 cm 2 /(Vs) was demonstrated by ENBT based OFET with a current on/off ratio in the range of 10 5-7 after annealing at 160ºC. Besides, in chapter 4, a novel [pi]-bridge, namely naphthodithienothiophene was developed and employed to explore photosensitizers for DSSC application. In this work, four novel photosensitizers with D-A-[pi]-A or D-[pi]-A structure motif were designed and synthesized in which the carbazole or triphenylamine derivative was used as a donating group and benzothiadiazole was applied as auxiliary accepting group. The performances of DSSCs based on these photosensitizers have been fully investigated. Among them, CB-NDTT- CA based device exhibited the highest power conversion efficiency (PCE) of 7.29%. Meanwhile, the interfacial properties of these photosensitizers anchored on TiO 2 have also been studied by ab-initio simulation and Gaussian calculations. In chapter 5, another novel series of photosensitizers with benzodithienothiophene as the [pi]-bridge would be presented, in which different donors, auxiliary acceptors, and structures were incorporated into the frameworks of D-[pi]-A motif to investigate the relationship between the structure and properties. The performances of DSSCs based on these photosensitizers have been fully investigated, and BD-5 based device exhibited the best power conversion efficiency (PCE) of 4.66%. Furthermore, it was demonstrated that molecular engineering was an efficient way to modulate the performance of the DSSCs in 3 which benzothiadiazole was used as an effective auxiliary accepting group in constructing photosensitizers with D-A-[pi]-A structure motif. The di-anchoring approach was also found to be a promising method to design photosensitizers with improved performance.

abstract: This thesis describes several experiments based on carbon nanotube nanofludic devices and field-effect transistors. The first experiment detected ion and molecule translocation through one single-walled carbon nanotube (SWCNT) that spans a barrier between two fluid reservoirs. The electrical ionic current is measured. Translocation of small single stranded DNA oligomers is marked by large transient increases in current through the tube and confirmed by a PCR (polymerase chain reaction) analysis. Carbon nanotubes simplify the construction of nanopores, permit new types of electrical measurement, and open new avenues for control of DNA translocation. The second experiment constructed devices in which the interior of a single-walled carbon nanotube field-effect transistor (CNT-FET) acts as a nanofluidic channel that connects two fluid reservoirs, permitting measurement of the electronic properties of the SWCNT as it is wetted by an analyte. Wetting of the inside of the SWCNT by water turns the transistor on, while wetting of the outside has little effect. This finding may provide a new method to investigate water behavior at nanoscale. This also opens a new avenue for building sensors in which the SWCNT functions as an electronic detector. This thesis also presents some experiments that related to nanofabrication, such as construction of FET with tin sulfide (SnS) quantum ribbon. This work demonstrates the application of solution processed IV-VI semiconductor nanostructures in nanoscale devices. / Dissertation/Thesis / Ph.D. Physics 2011

In today's "silicon age" in which we live, field-effect transistors (FET) are the workhorse of virtually all modern-day electronic gadgets. Although silicon currently dominates most of these electronics, layered 2D transition metal dichalcogenides (TMDCs) have great potential in low power optoelectronic applications due to their indirect-to-direct band gap transition from bulk to few-layer and high on/off switching ratios. TMDC WSe2 is studied here, mechanically exfoliated from CVT-grown bulk WSe2 crystals, to create a few-layered ambipolar FET, which transitions from dominant p-type behavior to n-type behavior dominating as temperature decreases. A high electron mobility μ>150 cm2V-1s-1 was found in the low temperature region near 50 K. Temperature-dependent photoconduction measurements were also taken, revealing that both the application of negative gate bias and decreasing the temperature resulted in an increase of the responsivity of the WSe2 sample. Besides TMDCs, Group III-VI van der Waals structures also show promising anisotropic optical, electronic, and mechanical properties. In particular, mechanically exfoliated few-layered InSe is studied here for its indirect band gap of 1.4 eV, which should offer a broad spectral response. It was found that the steady state photoconduction slightly decreased with the application of positive gate bias, likely due to the desorption of adsorbates on the surface of the sample. A room temperature responsivity near 5 AW-1 and external quantum efficiency of 207% was found for the InSe FET. Both TMDC’s and group III-VI chalcogenides continue to be studied for their remarkably diverse properties that depend on their thickness and composition for their applications as transistors, sensors, and composite materials in photovoltaics and optoelectronics.

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology. / Front-end power converters for nanosatellite applications demand better performance in accurate reference tracking because of the wide-range input voltage of the solar panels. The very tight output voltage requirements demand a robust, reliable, and high-efficiency converter. The control of such a converter is very complex and time consuming to design. Two commonly used control modes are current and voltage control. The design and implementation of a voltage controller for DC–DC power converter is simpler but compared to current mode controller, does not do provide for overcurrent protection. A single-ended primary inductance converter (SEPIC) was selected for this research work because of its ability to buck or boost the input voltage coupled with the ability to provide noninverting polarity with respect to the input voltage. Parameter values for the converter studied are used to analyse and design both the voltage and the current mode controllers for the nanosatellite front-end power converter. Output voltage reference tracking with step and ramp changes in the input voltage is evaluated in terms of the time taken to reach steady-state after the induced disturbances and either the overshoot or undershoot of the output voltage reference. The design of analogue pulse width modulation (PWM) study was carried out in order to drive the metal-oxide-semiconductor field-effect transistor (MOSFET) switch. For the two controllers, changes in the reference output voltage in response to load changes are also studied. An examination of the effects of solar radiation on the MOSFET switch was conducted; this switch is the main component of the front-end DC–DC power converter for a nanosatellite. At the more general level the examination also provided information on the response of the semiconductor technology in space application. The overall purpose of studying the MOSFET switch was to investigate the mechanisms that will facilitate its ability of switching ‘on’ and ‘off’ without failure as a result of solar radiation. The effects of solar radiation on MOSFET device in space, has resulted in more malfunctions of these devices in the past five years than over the preceding 40 years.

abstract: Silicon (Si) solar cells are the dominant technology used in the Photovoltaics industry. Field-effect passivation by means of electrostatic charges stored in an overlying insulator on a silicon solar cell has been proven to be a significantly efficient way to reduce effective surface recombination velocity and increase minority carrier lifetime. Silicon nitride (SiNx) films have been extensively used as passivation layers. The capability to store charges makes SiNx a promising material for excellent feild effect passivation. In this work, symmetrical Si/SiO2/SiNx stacks are developed to study the effect of charges in SiNx films. SiO2 films work as barrier layers. Corona charging technique showed the ability to inject charges into the SiNx films in a short time. Minority carrier lifetimes of the Czochralski (CZ) Si wafers increased significantly after either positive or negative charging. A fast and contactless method to characterize the charged overlying insulators on Si wafer through lifetime measurements is proposed and studied in this work, to overcome the drawbacks of capacitance-voltage (CV) measurements such as time consuming, induction of contanmination and hysteresis effect, etc. Analytical simulations showed behaviors of inverse lifetime (Auger corrected) vs. minority carrier density curves depend on insulator charge densities (Nf). From the curve behavior, the Si surface condition and region of Nf can be estimated. When the silicon surface is at high strong inversion or high accumulation, insulator charge density (Nf) or surface recombination velocity parameters (Sn0 and Sp0) can be determined from the slope of inverse lifetime curves, if the other variable is known. If Sn0 and Sp0 are unknown, Nf values of different samples can be compared as long as all have similar Sn0 and Sp0 values. Using the saturation current density (J0) and intercept fit extracted from the lifetime measurement, the bulk lifetime can be calculated. Therefore, this method is feasible and promising for charged insulator characterization. / Dissertation/Thesis / M.S. Electrical Engineering 2014

Orientador: José Antonio Siqueira Dias / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-17T22:39:39Z (GMT). No. of bitstreams: 1 Garcia_AlexandreDavidRinco_M.pdf: 2843880 bytes, checksum: ecc88d93aeb48f3dad51bc6b4d4fe6f4 (MD5) Previous issue date: 2011 / Resumo: Neste trabalho é apresentado um estudo que visa otimizar os sistemas de ripple counter mediante a utilização de relés de estado sólido (FET). Com a utilização de relés de estado sólido para ripple counter é possível não apenas economizar recursos com a montagem do circuito, mas também inserir proteções inerentes ao FET. Este trabalho também mostra que é possível compensar as variações de camada devidas ao aumento da temperatura. Os sistemas atuais utilizam relés comuns e circuitos agregados; este trabalho demonstra que o uso de relés de estado sólido em aplicações de ripple counter, considerando as variações de temperatura da junção, é, não apenas viável, como também uma solução que agrega maior valor ao produto / Abstract: In this work a deep study to optimize ripple counter systems utilizing solid state relays (FET) is presented. The usage of solid relay for ripple counter will be possible not only saving money on external circuits but also inserting inherent protection's FET. This work shows that is possible to compensate the layer variations due to temperature's increasing. The currently systems use common relays and aggregates circuits, but the description above demonstrates that the usage of solid-state relay in ripple counter applications considering the junction temperature variations is not only feasible but also a better solution / Mestrado / Eletrônica, Microeletrônica / Mestre em Engenharia Elétrica

M.Ing. (Electrical and Electronic Engineering) / The possibilities and technology of converters with an alternating voltage link are investigated for high specific power conversion at high frequencies. With a view to the functional description of these power converters, s i muLat i on techniques are considered for both system and circuit analysis. A thorough investigation is made into the design of high frequency power transformers, which play an important role in this class of power circuits. This includes a theoretical analysis in conjunction with the 'practical implementation of a design procedure for minimal eddy current losses in the windings as well as experimental work on losses in ferrite cores. For the remainder of the study, attention is focussed on the two pulse inverter which is responsible for the generation of the alternating voltage in the high frequency link. The suitability of bipolar and field effect transistors for power switching, is critically examined and a voltage compensation on the bipolar Darlington, which reduces on-state losses, yielded good results upon application. A study on the feasibility of non-dissipative snubber techniques on the centre tapped inverter is presented, thus supplying a practical way of reducing switching losses without affecting the efficiency of the system. An additional, yet simple, network is added to the snubber circuits of the two pulse inverter which is operational during low load conditions.' in order also to have low switching losses under these circumstances. Finally a 50 k~v, 10 kHz centre tapped inverter was developed and built.

The current temperature operating range of semiconducting materials is given to be between -10°C and 105°C. Current plans are to increase this range due to an industry demand for semiconducting materials able to operate outside these bounds. Wide bandgap semiconductor materials have been researched for some time in an effort to manufacture commercially viable controlled semiconductor switches. Samples of such a controlled switch have been obtained and promises to be close to commercial rollout. This controlled switch takes on the form of a Junction Field Effect Transistor (JFET), which is a depletion mode component. Depletion mode switches are normally-on, and have thus far not been used in the power electronics field. Due to difficult switching and availibility of component which are switched more easily, these components were quicklier and easierly adopted for use. The Silicon Carbide JFET promises to circumvent these cons with the ability to block higher voltages, at higher temperatures and at higher speeds. Lower on resistance and smaller size of substrates are other benefits that the use of Silicon Carbide semiconducting material promises. A variety of properties of the Silicon Carbide JFET are investigated. Some of these properties include the component on-resistance, gate charge, breakthrough voltage of the gate and leakage current of the channel. Switching performance is also investigated as well as the reverse recovery of the body diode. All properties were measured as a function of temperature in an effort to describe the difference in performance at high temperatures. / Prof. Ivan Hofsajer

Les supraconducteurs à haute température critique (HTS) sont des systèmes fortement corrélés. Dans ces matériaux, une petite modification du nombre de porteurs peut avoir de grandes conséquences sur leurs propriétés physiques. C'est le cas lorsqu'un matériau ferroélectrique est à proximité immédiate d'un HTS : de manière locale et rémanente, la polarisation ferroélectrique modifie par effet de champ électrostatique le nombre d'électrons dans le HTS, au voisinage de l'interface avec le ferroélectrique. Cet effet peut être exploité dans le but de définir des structures à géométrie variable : dans un premier cas, des jonctions qui consistent en deux électrodes supraconductrices, séparées par une zone où la supraconductivité a été affaiblie par effet de champ. Dans un second cas, des jonctions tunnel ferroélectriques - à nouveau avec des électrodes supraconductrices - où l'épaisseur de la barrière est modulable par effet de champ ferroélectrique. Les travaux menés au cours de cette thèse visent à développer les matériaux et les technologies de lithographie pour fabriquer de telles structures, et à caractériser les propriétés de transport de ces dernières. / In this experimental thesis, we fabricated ferroelectric field-effect devices based on high-Tc superconductors. We grew high-quality epitaxial heterostructures consisting of an ultra-thin (2 to 6 unit cells) film of YBCO and a thin ferroelectric film (BFO-Mn). We fabricated transport measurement microbridges and used a CT-AFM tip to polarise the BFO-Mn outwards or towards the BFO-Mn/YBCO interface. Due to the ferroelectric field-effect, the superconducting properties of the underlying YBCO film were consequently modified. We then used this effect locally in order to design weak links within the microbridges: two regions where the superconducting properties are enhanced are separated by a narrow region where they are depressed. We explored the conditions of existence of a Josephson coupling across this weak link. In parallel, we fabricated ferroelectric junctions. The barrier is an ultra-thin BFO-Mn film sandwiched between a high-Tc superconducting YBCO bottom electrode and a low-Tc superconducting top electrode. Both at room temperature and at low temperature, we characterised the transport properties across the barrier and the resistive switching resulting from the polarisation of the ferroelectric barrier.