Thesis (Ph.D.) - University of Glasgow, 1979. / Ph.D. thesis submitted to the Faculty of Engineering, University of Glasgow, 1979. Print version also available.

The electronic g-tensor in halogen-doped cadmium sulfide has been measured at 1.7°K, and its dependence upon uniaxial pressures parallel and perpendicular to the c-axis has been investigated. A sample doped with iodine to a room temperature resistivity of ≈ 0.7Ω cm exhibited an anisotropic g-tensor with gǁ = 1.785 and g⊥ = 1.767. The anisotropy in a heavily bromine-doped sample [formula omitted] was the same, but gǁ was slightly larger, 1.789. When some of the cadmium is replaced by zinc, the alloy acquires properties intermediate between those of CdS and ZnS. This was shown to apply to the g-tensor by measuring it in CdS(10%Zn):I. It was found to have a smaller anisotropy and a larger absolute value than that of CdS:I, thus having changed towards that of ZnS. The pressuredependence of the g-tensor and the change in the optical bandgap under hydrostatic pressure could be reasonably well explained in terms of two deformation potential constants for the bandgap, D₁-C₁-C₃ ≈ 6.3 eV/unit strain and D₂-C₂-C₄ ≈ 1.8 eV/unit strain. It is therefore concluded that although the bandstructure of CdS is not sufficiently well known to predict the g-tensor correctly, the interaction of the conduction band with the valence bands appears to be dominant. Further experiments to study the conduction band edge are proposed. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Cadmium sulfide and cadmium selenide are important materials for applications such as photoconductive cells, photovoltaic cells and other electrooptical devices. Generally, these devices use single crystals. However, reasonable efficiencies have been observed by using polycrystalline films on conducting substrates, which are easier to make and provide considerable savings on materials and energy. Polycrystalline CdS/CdSe films have been made by sputtering and solution spraying, compound evaporation, chemical vapor deposition, and many others. A recent technique involves the electrochemical deposition of CdS and CdSe from nonaqueous solvents. Preparation of these films is based upon the cathodic deposition from a nonaqueous solution of a cadmium salt and elemental sulfur and/or selenium. Although the technique is simple, no mechanistic information is known to optimize the conditions in which films of controlled stoichiometry, doping and crystallinity are made. This research has the purpose to understand the mechanism of the formation of polycrystalline films of CdS and CdSe by electrochemical deposition in dimethylsulfoxide. This approach to the problem makes use of electrochemical techniques such as rotating ring disc electrode, linear scan voltammetry, high pressure liquid chromatography coupled with ultraviolet and electrochemical detection. By the rotating ring disc electrode technique, we have studied the kinetic parameters for the reduction of sulfur, selenium, cadmium, and the electroChemical formation of CdS and CdSe for temperatures from 25 - lOO°C. The results show that rates of initie.l electron transfer for the reduction of these species are moderately rapid, and secondly, that the reverse reaction is irreversible and involves additional steps. Studies of solubility of selenium with temperature reveal that its solubility is enhanced by the addition of sulfur. Understanding the electrochemical behavior of sulfur-selenium mixtures is of great importance to produce mixed semiconductive films with more adequate bandgaps for use with solar spectrum. Electrochemistry of sulfur-selenium mixtures are no different from that of sulfur alone. High pressure liquid chromatography separations with spectroscopic and electrochemical detectors have shown that sulfur solutions contain 86 and 87 fractions which are not electrochemically active.

This work has analyzed the complex interfaces of GaN and InGaN grown by sputter deposition and GaN grown by metal-organic chemical vapor deposition (MOCVD) with CdTe and CdS. First, the GaN and InGaN films were characterized by AFM and XRD, and it has been shown that the MOCVD samples have a very smooth surface and are single crystalline with growth in the (002) direction. On the other hand, the sputter deposited samples have rougher surfaces and are polycrystalline. Furthermore, complete interface studies have been performed using in-situ XPS and deposition between GaN grown by sputter deposition and MOCVD and CdTe and CdS to determine the band alignments, conduction and valence band offsets, and Fermi level positions. These interface studies will help determine basic properties to see if these GaN films can be incorporated in a CdTe solar cell to improve its efficiency. It was determined that all the interfaces between the sputtered GaN/InGaN and CdTe/CdS have small conduction band offsets of less than 0.1 eV that do not significantly prevent electron flow across the interface. However, the valence band offsets were much more significant, as they ranged from 0.43 eV to over 1.8 eV. For purposes of the desired positions of the GaN in the CdTe solar cell, the conduction band offsets are much more crucial, and very small conduction band offsets are desired. An interesting effect was that the interfaces between InGaN/CdTe and InGaN/CdS showed In migration into the CdTe and CdS, causing a rise in the Fermi level for the CdTe and CdS, which has been known to worsen the performance of the CdTe solar cell. The MOCVD GaN/CdTe and CdS interfaces showed a slightly higher conduction band offset of about 0.15 eV, but this barrier still should not significantly prevent current flow. / Master of Science

No description available.

CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior / This research describes the process of obtaining a photovoltaic cell, since getting electrical conductor glasses used for the flow of electrons coming from the photovoltaic effect until the deposition of thin films of semiconductor titanium dioxide (TiO2) and cadmium sulfide (CdS) at each of these glasses. The use of natural or synthetic dyes deposited on titanium dioxide layer has the objective to increase the absorption spectrum of the TiO2, since sunlight emits most of its energy in the frequency range of visible light. After joining the two glasses with thin films deposited over TiO2 plus dye and CdS, it was used a potassium triiodide electrolyte for regeneration and consequently the activation of photovoltaic solar cell. After mounting the cell concerned, tests of photoactivity have been performed by exposing the cells to sunlight collected for specified periods and the values of voltage and photocurrent generated. Theoretical studies have been conducted to mathematical modeling of the behavior of the solar cell mounted, and then we have analyzed the efficiency of converting solar energy into electrical energy. The constituents of the cell have been characterized by the techniques of X-ray diffraction (XRD) and scanning electron microscopy (SEM) for analyzing the porosity, uniformity and other physical parameters of thin films. / O presente trabalho descreve o processo de obtenÃÃo de uma cÃlula fotovoltaica, desde a obtenÃÃo de vidros condutores elÃtricos utilizados para o fluxo dos elÃtrons oriundos do efeito fotovoltaico, atà a deposiÃÃo dos filmes finos dos semicondutores diÃxido de titÃnio (TiO2) e sulfeto de cÃdmio (CdS) em cada um dos vidros. O uso de corantes naturais ou sintÃticos na camada depositada de diÃxido de titÃnio possuiu como objetivo aumentar o espectro de absorÃÃo do mesmo, uma vez que a luz solar emite uma grande parte de sua energia na faixa de frequÃncia da luz visÃvel. Depois de unir os dois vidros com os filmes finos depositados de TiO2 mais corante e o CdS, utilizou-se o eletrÃlito de tri-iodeto de potÃssio para a regeneraÃÃo e consequentemente a ativaÃÃo da cÃlula solar fotovoltaica. ApÃs a montagem da cÃlula em questÃo, foram realizados testes de fotoatividade, expondo as cÃlulas ao sol por perÃodos determinados e coletados os valores da fotocorrente gerada e a tensÃo, alÃm disso, foram realizados estudos teÃricos para modelagem matemÃtica do comportamento da cÃlula solar montada e em seguida analisou-se a eficiÃncia de conversÃo de energia solar em energia elÃtrica. Os constituintes da cÃlula foram caracterizados pelas tÃcnicas de difraÃÃo de raios-X (DRX) e microscopia eletrÃnica de varredura (MEV) para analisar a porosidade, uniformidade e outros parÃmetros fÃsicos dos filmes finos.

In this study , we investigate the relationship between growth condition and thin film quality of cadmium sulfide (CdS) thin films grown by chemical bath deposition (CBD) method. Thin film structures are analyzed by X-ray diffraction , morphology and grain size are obtained by scanning electronic microscopy , and film thickness measured by reflectance spectroscopy . In medium pH value ( pH=10.5) , 20 min deposition can achieve 450 nm film thickness . At lower pH (pH=8.5), low hydrolysis rate of thiourea limits the concentration of sulfur anion , film thickness is only 49 nm after one hour deposition at 70 ¢J , and the obtained thin film can not fully cover the substrate to have a pin-hole free film . At higher pH (pH=11), 40 min only deposites 100 nm film thickness. Strong binding between the cadmium ion and the complexing agent causes low free cadmium cation concentration in the solution, which limits the growing rate. By varying the growth pH condition, the difference in thickness is more than one order of magnitude. In contrast to the film thickness relationship, grain size distribution suffers less influence from the pH consition. Our results indicate no explicitly relation between the grain size and solution pH condition. 20 minutes depositions result cadmium sulfide grain sizes to be 70¡Ó10nm , and 40 minutes result grain size to be 75¡Ó15nm . The results indicate that film thickness increases mainly due to the increasing of grain number, rather than the increasing of grain size . By summarized the results, we propose that the deposition of cadmium sulfide film is initially formed homogeneous nucleation in the solution. The nuclea diffuse and adhere to the substrate. Intristic electric dipole momentum of the cadmium sulfide nano-particle provides an attractive force for the adhesion, and results preferred orientation. Meanwhile, the grain keeps growing up until the size saturated .

This work aims to study the variation in electrical and optical properties of nanoscale Schottky diodes by varying their dimensions in the nanoscale. Experimental conditions for fabricating porous alumina with varying pore diameters and inter-pore distances were first optimized by anodizing Aluminum tape with variable currents. Cadmium Sulfide nanowires were then synthesized inside the membranes by dc electrodeposition. Finally a high work function metal was deposited on top as a contact for the metal-semiconductor Schottky diode junction. As a comparative study, Schottky diodes fabricated using the same metals and Cadmium Sulfide thin films deposited on conducting glass substrates using electro-deposition and annealed in different ambient were also studied. Device characterizations were carried out by field-emission scanning electron microscopy (FESEM), current voltage (I-V) measurements, ultraviolet-visual (UV-Vis) absorption spectroscopy and X-Ray diffraction.

Thesis (M.S.)--University of Delaware, 2008. / Principal faculty advisor: Robert W. Birkmire, Dept. of Materials Science & Engineering. Includes bibliographical references.

Thesis (M.S.)--University of Nevada, Reno, 2008. / "December, 2008." Includes bibliographical references (leaves 69-76). Online version available on the World Wide Web.