The electro-optical properties of the ZnO/Si heterojunction embedded with self-assembled gold nanoparticles on patterned silicon substrate are investigated in this master thesis. High quality n-type ZnO film is deposited on patterned p-type silicon substrate by radio-frequency sputtering to form a ZnO/Si pn junction. The patterned silicon substrates are prepared by ICP-RIE using self-assembled nickel metal dot and silicon dioxide as etching mask. The optimum ICP process conditions of silicon nanopillars are CF4/Ar ~ 40/40 sccm and bias/RF power 400/400 W. Silicon nanopillars of diameter ~ 50 nm and height 100~400 nm are formed on the substrate surface. ZnO film is then deposited of a growth rate ~ 12 nm/min at the substrate temperature = 200oC. The plasmonic effects on the electro-optical properties, including photoluminescence (PL), reflection, and electrical characteristics, are studied by adding self-assembled gold nanoparticles within the ZnO film. The self-assembled gold nanoparticles are formed by thermal deposition and rapid thermal annealing at 700oC. The gold nanoparticles are observed by scanning electron microscopy (SEM) and particles of diameter about 100 nm. The PL intensity of ZnO is enhanced more than ten times at the peak wavelength = 380 nm by adding the gold nanoparticles and silicon nanopillars. Strong blue emission light could be saw with the naked eyes. For the electric characteristics, self-assembled gold nanoparticles in patterned ZnO/Si heterojunction show photoelectric conversion phenomenon because of high electromagnetic absorption and plasmonic effects.

Silicon is the most important semiconducting material for optoelectronics owing to its suitable and tunable physical properties. Even though there are several alternatives, silicon based solar cells are still the most widely produced and commercially feasible system. Extensive efforts have been spent in order to increase the efficiency and decrease the cost of these systems. The studies that do not focus on replacement of the semiconducting material, mostly concentrate on the developments that could be brought by nanotechnological approaches. In this aspect, utilization of silicon nanowires has been predicted to improve the efficiency of the silicon based solar cell technology. Moreover, besides solar cells, silicon nanowires have been investigated for many other electronic systems such as thermoelectrics, light emitting diodes, biological/chemical sensors, photodetectors and lithium ion v batteries. Therefore, production of silicon nanowires through a cost-effective and well controlled method could make important contributions to many fields. In this thesis, electroless etching method, which is a novel and solution based method enabling vertically aligned silicon nanowire array fabrication over large areas, is investigated. A detailed parametric study resulting in a full control over the resultant nanowire morphology is provided. The parameters affecting the structure have been determined as etching time, solution temperature, solution concentration, pressure and starting wafer characteristics. The results show that electroless etching method could replace the conventional silicon nanowire fabrication methods. It was shown that specific nanowire lengths for any application, can be obtained simply by adjusting the parameters of electroless etching system. One of the most crucial features of vertically aligned silicon nanowire arrays is their remarkable antireflective properties. The optical reflectivity measurements showed that 42% reflectivity of pristine polished silicon wafer decreases down to 1% following fabrication of silicon nanowire arrays on their surface. This unique characteristic reveals that these nanowires could be used as antireflective surfaces in solar cells. Moreover, it was determined that p-n heterojunctions that are formed by silicon nanowires, namely radial heterojunctions, would yield higher efficiencies compared to planar heterojunctions because of the dramatic increase in the charge carrier collection efficiency and orthogonal photon absorption. On this subject, n-type silicon nanowire arrays were fabricated by electroless etching followed by drop casting Poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) (PEDOT:PSS) organic layer on these nanowires as the complementary layer, forming the radial heterojunction. The energy conversion efficiency of silicon nanowire / PEDOT: PSS device was found as 5.30%, while planar silicon / PEDOT: PSS control device displayed only 0.62% efficiency. Developments and optimizations in both the electroless etching method and solar cell models could lead to important developments in photovoltaic industry.

This thesis researchs the design of quadrature modulator consists of 120MHz quadrature modulator that is fabricated using hybrid elements and print circuit board (PCB) technology for digital signal generator and quadrature modulator monolithic-microwave integrated-circuit (MMIC) that is fabricated using GaAs heterojunction bipolar transistor (HBT) technology for Personal Communication Service (PCS) applications. The 120MHz quadrature modulator incorporates power divider/combiner, phase shifter and doubly balanced mixer; the design architecture, principle and measurement results of division are presented in this thesis. A quadrature modulator is implemented by combining every division and measures specifications accurately, comparing with that of Agilent ESG-D series digital signal generator with the same carrier frequency and digital modulation. The quadrature modulator MMIC for PCS applications incorporates phase shifter, Gilbert cell mixer, differential to single-ended converter and RF amplifier at output; the design architecture, principle and simulation results of division are presented in this thesis. A quadrature modulator is integrated by combining every division and simulates parameters strictly.For troublesome specification measurement of quadrature modulator, this thesis also presents measurement method and instrument setup detailedly.

This thesis proposes a modified inductively degenerated common-emitter low-noise amplifier. To add a series-shunt feedback capacitance in series to the base of the cascode transistor for increasing the load impedance of the common-emitter transistor and enhancing the Miller effect, it is applied to improve the circuit¡¦s performance. By thoroughly studying the Miller effect for the input matching, noise, and linearity analysis and derivation of the modified structure, the theoretical analysis and experiments demonstrate the improved linearity and well noise performance. In addition, the proposed method is presented with the good figure of merit. The proposed method is presented in a hybrid circuit with the NEC 2S5010 NPN transistor for 900 MHz applications. It demonstrates that this method improves the linearity and the figure of merit has been increased by 50 to 70 percent. Moreover, the novel low noise amplifier is designed with a 0.35£gm SiGe BiCMOS process supported by the TSMC for 5.7 GHz WLAN band applications. It is found that the circuit has the characteristic of IM3 nonlinearity cancellation because the cascode transistor eliminates the third-order intermodulation genaerated by the common-emitter transistor. This thesis establishes a realizable method for high-linearity low-noise amplifier.

Thesis--Auburn University, 2009. / Abstract. Vita. Includes bibliographic references (p.64-66).

For more than 20 years, scientists have studied solar cells made from organic semiconductors. Throughout this time, device structures have evolved from bilayer devices to bulk heterojunction (BHJ) devices and even though efficiencies are approaching 10%, scientists still know relatively little about the transport of charge carriers and recombination mechanisms in these materials. Novel structures, based on lateral BHJ solar cells, have proven to be versatile tools to study transport and recombination mechanisms. In addition, these structures can easily be employed by researchers and solar cell manufacturers to determine the quality and measure the improvement of their materials. For these studies, poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C61-butyric acid methyl ester (PCBM) has been employed due to its wide use among researchers as well as potential for commercialization. DC photocurrent measurements as a function of device length have yielded the mobility-lifetime product and the generation rate of free carriers within these BHJ devices. In addition to these parameters, the recombination rate as a function of light intensity provides information about the mechanisms of recombination. For example, by measuring the recombination rate as a function of applied electric field and light intensity we have found that recombination is unimolecular in nature and shifts to bimolecular at increased electric field strengths. Additionally, the mobility-lifetime product, generation rate, and recombination mechanism have been studied as a function of applied electric field, illumination spectrum, illumination intensity, etc. This information has provided much insight on physics of the P3HT:PCBM material system which did not exist before these studies. / text

Milimetrinių bangų sritis yra perspektyvi daugelyje sričių, nuo kasdienio vartojimo įtaisų tokių, kaip telekomunikacijų tinklų įranga iki specifinių taikymų kariuomenėje, bei diagnostinėje medicinoje. Milimetrinių bangų imtuvuose dažniausiai naudojamas netiesinis elementas yra Šotkio (Schottky) diodas. Nors jo veikimo dažnių ruožas yra iki terahercų srities, tokie trūkumai kaip jautrio priklausomybė nuo temperatūros, neatsparumas elektrinėms perkrovoms, bei jo parametrų blogėjimas laikui bėgant verčia ieškoti naujų alternatyvų. Disertacijoje pristatomi dviejų tipų mikrobangų diodai, pagaminti naudojant įvairiatarpius GaAs/AlGaAs darinius. Puslaidininkinių darinių sluoksnių kokybė buvo eksperimentiškai įvertinta naudojant nuostoviosios fotoliuminescencijos ir laike koreliuoto fotonų skaičiavimo metodus. Aprašytas mikrobangų diodų gamybos procesas. Elektrinės savybės buvo įvertintos išmatavus mikrobangų diodų voltamperines charakteristikas, o detekcinės jų savybės ištirtos plačiame dažnių ruože. / Spectrum region of millimeter wave is extensively used in various areas: from consumer devices in telecommunication networks, to specific applications in military and diagnostic medicine. Schottky diode is the most commonly used two terminal device in microwave receivers. Although the operational frequency of Schottky diode is reaching the terahertz frequency range it has several drawbacks such as sensitivity dependence on temperature, long-term instability and sensitivity to overloads. These drawbacks impelled one to search new type of devices. Two types of microwave diodes fabricated using GaAs/AlGaAs heterostructures are presented in the thesis. The quality of semiconductor epitaxial layers was experimentally estimated using photoluminescence and time correlated single photon counting techniques. The process of microwave diode fabrication is described. Electrical properties of microwave diodes were estimated from current-voltage characteristics and properties of microwaves detection were investigated in wide frequency range.

Spectrum region of millimeter wave is extensively used in various areas: from consumer devices in telecommunication networks, to specific applications in military and diagnostic medicine. Schottky diode is the most commonly used two terminal device in microwave receivers. Although the operational frequency of Schottky diode is reaching the terahertz frequency range it has several drawbacks such as sensitivity dependence on temperature, long-term instability and sensitivity to overloads. These drawbacks impelled one to search new type of devices. Two types of microwave diodes fabricated using GaAs/AlGaAs heterostructures are presented in the thesis. The quality of semiconductor epitaxial layers was experimentally estimated using photoluminescence and time correlated single photon counting techniques. The process of microwave diode fabrication is described. Electrical properties of microwave diodes were estimated from current-voltage characteristics and properties of microwaves detection were investigated in wide frequency range. / Milimetrinių bangų sritis yra perspektyvi daugelyje sričių, nuo kasdienio vartojimo įtaisų tokių, kaip telekomunikacijų tinklų įranga iki specifinių taikymų kariuomenėje, bei diagnostinėje medicinoje. Milimetrinių bangų imtuvuose dažniausiai naudojamas netiesinis elementas yra Šotkio (Schottky) diodas. Nors jo veikimo dažnių ruožas yra iki terahercų srities, tokie trūkumai kaip jautrio priklausomybė nuo temperatūros, neatsparumas elektrinėms perkrovoms, bei jo parametrų blogėjimas laikui bėgant verčia ieškoti naujų alternatyvų. Disertacijoje pristatomi dviejų tipų mikrobangų diodai, pagaminti naudojant įvairiatarpius GaAs/AlGaAs darinius. Puslaidininkinių darinių sluoksnių kokybė buvo eksperimentiškai įvertinta naudojant nuostoviosios fotoliuminescencijos ir laike koreliuoto fotonų skaičiavimo metodus. Aprašytas mikrobangų diodų gamybos procesas. Elektrinės savybės buvo įvertintos išmatavus mikrobangų diodų voltamperines charakteristikas, o detekcinės jų savybės ištirtos plačiame dažnių ruože.

The investigation carried out in this project allowed for the development of eleven regioregular π-conjugated alternating copolymers and their implementation in organic solar cells. The eleven synthesized polymers, poly[(2,7-(9-(heptadecan-9-yl)-9H-carbazole))-alt-(4,7-dithien-2-yl-2,1,3-benzothiadiazole)] (CB), poly[(2,7-(9,9-dioctyl-9H-fluorene-2,7-diyl))-alt-(1,6-pyrene)] (LP), poly[(2,7-(9-(heptadecan-9-yl)-9H-carbazole))-alt-(5,5’’’-(3,3’’’-dihexyl-2,2':5',2'':5'',2'''-quarterthiophene))] (CT), poly[(2,7-(9-(heptadecan-9-yl)-9H-carbazole))-alt-(2,7-9H-fluoren-9-one)] (CF), poly[(2,7-(9-(heptadecan-9-yl)-9H-carbazole))-alt-(1,6-pyrene)] (CP), poly[(2,7-(9,9-dioctyl-9H-fluorene-2,7-diyl))-alt-(4,7-dithien-2-yl-2,1,3-benzothiadiazole)] (LB), poly[(2,7-(9,9-dioctyl-9H-fluorene-2,7-diyl))-alt-(2,7-9H-fluoren-9-one)] (LF), poly[(5,5’’’-(3,3’’’-dihexyl-2,2':5',2'':5'',2'''-quarterthiophene))-alt-(2,7-9H- fluoren-9-one)] (TF), poly[(2,7-(9,9-dioctyl-9H-fluorene-2,7-diyl))-alt-(4,4'-dioctyl-2,2'-bithiophene)] (oTLT), poly[(2,7-(9-(heptadecan-9-yl)-9H-carbazole))-alt-(4,4'-dioctyl-2,2'-bithiophene)] (oTCT), poly[(2,7-(9-(heptadecan-9-yl)-9H-carbazole))-alt-(4,4'-dihexyl-2,2'-bithiophene)] (TCT), were investigated using theoretical methods that included semi-empirical geometry optimizations, density functional theory (DFT) energy calculations, and time-dependent density functional theory (TD-DFT) optical absorption predictions. The absorption predictions gave credence to our experimental results in which the absorption of the longer polymer chains underwent a redshift from the monomer absorption. With several of the prepared polymers, bulk-heterojunction photovoltaic cells were fabricated and their photovoltaic activity was investigated. Several of the fabricated cells exhibited photovoltaic efficiencies including polymer/PCBM composites with an aluminum back electrode (CF, CT, P3HT, and MEH-PPV), and also inverted cells with a silver back electrode (CT, P3HT, and MEH-PPV). Several polymers (CF, CT, TCT, LP, oTCT, oTLT, P3HT, and MEH-PPV) were used to solubilize single-walled carbon nanotubes (SWNTs). The solubility of the nanotubes occurred by the polymers’ ability to wrap the tubes, disrupt the bundles (ropes of tubes), and allow for the creation of a homogeneous mixture. Polymer:PCBM:SWNT mixtures were prepared and utilized as the active layer in BHJ solar cells. Some of the inverted cells (with a silver back electrode) that incorporated the nanotube composites (CT, oTCT, oTLT, P3HT, and MEH-PPV) displayed photovoltaic activity. These preliminary results illuminate the photovoltaic behavior of the polymer and provide evidence for their future use in polymer solar cells. / Thesis (Master, Chemistry) -- Queen's University, 2011-02-13 22:09:00.464

The arrangement of soft materials through solution processing techniques is a topic of profound importance for next generation solar cells; the resulting morphology has a major influence on construction, performance and lifetime. This thesis investigates the connections between the soft matter physics of colloidal systems and solid state dye sensitised (SSDS) and bulk heterojunction (BHJ) solar cells. A study of aqueous titanium dioxide nanoparticulate suspensions was carried out in order to observe how suspension structure can be controlled by altering the inter-colloid potential via pH-induced electrostatic charging. Measurements were performed at volume fractions between 0.025% and 8.2% with the solution pH set to 3.1, 3.5 or 4.5 before mixing. Suspensions with a volume fraction above 4% formed self-supporting gels regardless of the set pre-mix pH. These gels displayed shear thinning behaviour with a power law exponent of 0.8, a yield stress of 11(1) Pa and rheological response consistent with an aggregated fractal network. At lower volume fractions, suspensions exhibited consolidation interpreted as the collapse of a gel of fractal clusters with a fractal dimension of 2.36. The velocity of the suspension/supernatant interface exhibited delayed sedimentation behaviour, as well as further fractal-based power law scalings with volume fraction. Lower volume fraction suspensions were explored using dynamic light scattering. Limited aggregation of ‘stable’ suspensions was observed when compared to primary aggregate radii measured from electron microscopy images. To connect suspension structure and cell manufacture, the behaviour of more concentrated suspensions was observed during the drying of thin films, a process which forms an essential part of a SSDS solar cell. Lowering the pH of the suspension after mixing from 4 to 3 resulted in an ordering of observed crack domains. An increase in film delamination was also observed. Rates of mass loss during drying followed the expected three phase process, although there was an unexpected increase in rate during the initial phase (where rate is usually constant in time). Dynamic light scattering was found to be a useful but demanding technique for studying cluster formation in titanium dioxide suspensions. A non-linear fitting technique utilising the method of moments was thoroughly explored using computer simulated datasets. The algorithm reduced the systematic error in fitted parameters for moderately polydisperse (0:2 < < 0:4) datasets as compared to the commonly applied linear algorithm. The fitting algorithm was also robust to bad initial estimates of parameters. Finally, test solar cells have been built using blends of titanium dioxide and poly-3-hexylthiophene. Device performance was reduced with blend standing time after mixing but could be improved by remixing the blend before spin coating, implicating a reversible process (e.g. aggregation of titanium dioxide or crystallisation of P3HT) in the loss of performance. Addition of a titanium dioxide hole blocking layer before spin coating reduced cell performance. Combining the above studies and these device designs provides a future platform for continuation of this work in the context of real devices.