Dissertations / Theses on the topic 'Polycrystalline semiconductors'
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1
Burg, Tristan Kevin Materials Science & Engineering Faculty of Science UNSW. "Semiconducting properties of polycrystalline titanium dioxide." Publisher:University of New South Wales. Materials Science & Engineering, 2008. http://handle.unsw.edu.au/1959.4/41262.
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Titanium dioxide, TiO2, has potential applications as a photoelectrode for photoelectrochemical generation of hydrogen by splitting water using solar energy and as a photocatalyst for water purification. This study is part of the UNSW research program to process TiO2-based oxide semiconductors as high-performance photoelectrodes and photocatalysts. This study investigates the effect of defect disorder on semiconducting properties of polycrystalline TiO2. This study involved the processing of high-purity polycrystalline TiO2 and determination of its semiconducting properties through measurement of electrical conductivity and thermoelectric power at elevated temperatures (1073-1323K) in controlled oxygen activities [1x10-13 Pa < p(O2) < 75 kPa]. The study included two types of experiments: Determination of electrical properties under conditions of gas/solid equilibrium. The data obtained was used to derive defect disorder and related semiconducting properties Monitoring of electrical properties during equilibration. This data was used to determine the chemical diffusion coefficient. The data obtained under equilibrium conditions indicates that oxygen may be used as a dopant to impose controlled semiconducting properties. In reduced conditions TiO2 is an n-type semiconductor and under oxidizing conditions TiO2 is a p-type semiconductor. The n-type behaviour is associated with oxygen vacancies as the predominant defects and titanium interstitials as the minority defects. The p-type behaviour is closely related to titanium vacancies that are formed during prolonged oxidation. Charge transport at elevated temperature was shown to involve substantial contribution from ions. Analysis of electrical properties enabled determination of several defect-related quantities including the activation enthalpy for oxygen vacancy formation, and the activation energy of the electrical conductivity components related to electrons, holes and ions. The kinetic data obtained during gas/solid equilibration enabled determination of the chemical diffusion coefficient which exhibited a complex dependence on nonstoichiometry. In addition, prolonged oxidation showed that equilibration occurred in two kinetic regimes. One for highly mobile oxygen vacancies and titanium interstitials which quickly reached an ??operational equilibrium?? within hours and another slow kinetic regime for equilibration of titanium vacancies over many thousand hours. The determined chemical diffusion coefficient data may be used to select the processing conditions required to impose uniform concentration of defects within a TiO2.
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Karbasi, Hossein. "Deep level transient spectroscopy of heteroepitaxial polycrystalline diamond and aluminum nitride /." free to MU campus, to others for purchase, 1998. http://wwwlib.umi.com/cr/mo/fullcit?p9901245.
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Judson, Elizabeth Ann. "An analysis of preferred orientation in YBa₂ Cu₃ O₇ ₋ ₓ superconducting films deposited by CVD on single and polycrystalline substracts." Thesis, Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/8562.
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Golego, Nickolay. "Thin-film polycrystalline titanium-oxygen semiconductors prepared by spray pyrolysis." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ33300.pdf.
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Armstrong, Jeffrey Lee. "Reaction of carbonyl-and nitrogen-containing molecules on Si(100) and fluxless solder re-flow on polycrystalline Cu surfaces /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
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Murphy, Robert Clayton. "Effects of material inhomogeneity on the terminal characteristics of polycrystalline silicon solar cells /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
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Song, Dengyuan Centre for Photovoltaic Engineering UNSW. "Zinc oxide TCOs (Transparent Conductive Oxides) and polycrystalline silicon thin-films for photovoltaic applications." Awarded by:University of New South Wales. Centre for Photovoltaic Engineering, 2005. http://handle.unsw.edu.au/1959.4/29371.
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Transparent conductive oxides (TCOs) and polycrystalline silicon (poly-Si) thin-films are very promising for application in photovoltaics. It is extremely challenging to develop cheap TCOs and poly-Si films to make photovoltaic devices. The aim of this thesis is to study sputtered aluminum-doped ZnO TCO and poly-Si films by solid-phase crystallization (SPC) for application in low-cost photovoltaics. The investigated aspects have been (i) to develop and characterize sputtered aluminum-doped ZnO (ZnO:Al) films that can be used as a TCO material on crystalline silicon solar cells, (ii) to explore the potential of the developed ZnO:Al films for application in ZnO:Al/c-Si heterojunction solar cells, (iii) to make and characterize poly-Si thin-films on different kinds of glass substrates by SPC using electron-beam evaporated amorphous silicon (a-Si) [referred to as EVA poly-Si material (SPC of evaporated a-Si)], and (iv) to fabricate EVA poly-Si thin-film solar cells on glass and improve the energy conversion efficiency of these cells by post-crystallization treatments. The ZnO:Al work in this thesis is focused on the correlation between film characteristics and deposition parameters, such as rf sputter power (Prf), working gas pressure (Pw), and substrate temperature (Tsub), to get a clear picture of film properties in the optimized conditions for application in photovoltaic devices. Especially the laterally non-uniform film properties resulting from the laterally inhomogeneous erosion of the target material are investigated in detail. The influence of Prf, Pw and Tsub on the structural, electrical, optical and surface morphology properties of ZnO:Al films is discussed. It is found that the lateral variations of the parameters of ZnO:Al films prepared by rf magnetron sputtering can be reduced to acceptable levels by optimising the deposition parameters. ZnO:Al/c-Si heterojunction solar cells are fabricated and characterized to demonstrate the feasibility of the fabricated ZnO:Al films for application in heterojunction solar cells. In this application, expensive indium-tin oxide (ITO) is usually used. Under the standard AM1.5G spectrum (100 mW/cm2, 25 ??C), the best fabricated cell shows an open-circuit voltage of 411 mV, a short-circuit current density of 30.0 mA/cm2, a fill factor of 66.7 %, and a conversion efficiency of 8.2 %. This is believed to be the highest stable efficiency ever reported for this type of cell. By means of dark forward current density-voltage-temperature (J-V-T) measurements, it is shown that the dominant current transport mechanism in the ZnO:Al/c-Si solar cells, in the intermediate forward bias voltage region, is trap-assisted multistep tunneling. EVA poly-Si thin-films are prepared on four types of glass substrates (planar and textured glass, both either bare or SiN-coated) based on evaporated Si, which is a cheaper Si deposition method than the existing technologies. The textured glass is realized by the UNSW-developed AIT process (AIT = aluminium-induced texture). The investigation is concentrated on finding optimized process parameters and evaluating film crystallization quality. It is found that EVA poly-Si films have a grain size in the range 0.8-1.5 ??m, and a preferential (111) orientation. UV reflectance and Raman spectroscopy measurements reveal a high crystalline material quality, both at the air-side surface and in the bulk. EVA cells are fabricated in both substrate and superstrate configuration. Special attention is paid to improving the Voc of the solar cells. For this purpose, after the SPC process, the samples receive the two post-crystallization treatments: (i) a rapid thermal anneal (RTA), and (ii) a plasma hydrogenation. It is found that two post-crystallization treatments more than double the 1-Sun Voc of the substrate-type cells. It is demonstrated that RTA improves the structural material quality of the cells. Furthermore, a hydrogenation step is shown to significantly improve the electronic material quality of the cells. Based on the RTA???d and hydrogenated EVA poly-Si material, the first mesa-type EVA cells are fabricated in substrate configuration, by using sputtered Al-doped ZnO as the transparent front contact. The investigation is focused on addressing the correlation between the type of the substrate and cell performance. Optical, electrical and photovoltaic properties of the devices are characterized. It is found that the performance of EVA cells depends on the glass substrate topography. For cells on textured glass, the AIT texture is shown to have a beneficial effect on the optical absorption of EVA films. It is demonstrated that a SiN barrier layer on the AIT-textured glass improves significantly both the crystalline quality of the poly-Si films and the energy conversion efficiency of the resulting solar cells. For cells on planar glass, a SiN film between the planar glass and the poly-Si film has no obvious effect on the cell properties. The investigations in this thesis clearly show that EVA poly-Si films are very promising for poly-Si thin-film solar cells on glass.
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Al-Ahmadi, Ahmad Aziz. "Fabrication and characterization of ZnO film by spray pyrolysis and ZnO polycrystalline sintered pellets doped with rear earth ions." Ohio : Ohio University, 2003. http://www.ohiolink.edu/etd/view.cgi?ohiou1175017625.
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Khadilkar, Unmesh. "Modeling and Characterization of Polycrystalline Mercuric Iodide Radiation Detectors." [Tampa, Fla. : s.n.], 2003. http://purl.fcla.edu/fcla/etd/SFE0000088.
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Albin, David Scott. "Fabrication and structural, optical, and electrical characterization of multisource evaporated copper-gallium-selenide polycrystalline thin films." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184745.
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Theoretical considerations for the use of chalcopyrite ternary I-III-VI₂ compounds in heterojunction photovoltaic conversion devices are presented, followed by an in-depth study of the structural, optical, and electrical characteristics of multi-source evaporated CuGaSe₂ thin films as determined by processing. Film composition was identified as the primary variable for affecting the microstructure and optical-electrical behavior of the films. Film composition was in turn dependent upon elemental flux rates and substrate related effects. Films deposited on glass and bare alumina substrates were richer in selenium than films deposited on molybdenum coated substrates. Cu-poor, near stoichiometeric, and Cu-rich compositions were obtained by varying the Cu/Ga flux ratio. Cu-poor films deposited on bare ceramic substrates were characterized by secondary impurity phase content and a tendency for cubic CuGaSe₂ formation. The cubic nature of optically thin films deposited on glass was substantiated by a lack of crystal field splitting of the valence band as observed by optical absorption measurements. Cubic-tetragonal phase behavior was monitored on optically opaque samples by observation of intensity-independent (112)/(111) x-ray diffraction peak shifts. Cu-poor films on glass were also characterized by surfaces pitting at substrate temperatures in excess of 450°C which may be related to the high surface energy of gallium. Cu-poor films deposited on molybdenum coated alumina substrates exhibited less impurity phase formation and were largely single-phase tetragonal CuGaSe₂. Cu-rich films on all substrates contained CuₓSe impurities and tetragonal CuGaSe₂.
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Shi, Lei Photovoltaics & Renewable Energy Engineering Faculty of Engineering UNSW. "Contact resistance study on polycrystalline silicon thin-film solar cells on glass." Publisher:University of New South Wales. Photovoltaics & Renewable Energy Engineering, 2008. http://handle.unsw.edu.au/1959.4/41425.
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Thin-film solar cells are widely recognised to have the potential to compete with fossil fuels in the electricity market due to their low cost per peak Watt. The Thin-Film Group at the University of New South Wales (UNSW) is engaged in developing polycrystalline silicon (poly-Si) thin-film solar cells on glass using e-beam evaporation technology. We believe our solar cells have the potential of significantly lowering the manufacturing cost compared to conventional, PECVD-fabricated thin-film solar cells. After years of materials research, the focus of the Group??s work is now moving to the metallisation of evaporated solar cells. Minimising various kinds of losses is the main challenge of the cell metallisation procedure, within which the contact resistance is always a big issue. In this thesis, the contact resistance of aluminium contacts on poly-Si thin-film solar cells on glass is investigated. To the best of the author??s knowledge, this is the first ever contact resistance investigation of Al contacts on evaporated poly-Si material for photovoltaic applications. Various transmission line models (TLM) are employed to measure the contact resistance. An improved TLM model is developed to increase the measurement precision and, simultaneously, to simplify the TLM pattern fabrication process. In order to accommodate the particular requirements of poly-Si coated glass substrates, a TLM pattern fabrication process using photolithography is established. Furthermore, a Kelvin sense tester is set up to ensure an accurate measurement of the contact resistance. After establishment of the TLM technique at UNSW, it is successfully tested on singlecrystalline silicon wafer samples. The thermal annealing process of the contacts is also optimised. Then, the general behaviour of Al contacts on uniformly doped poly-Si films (i.e., no p-n junction) is investigated using the verified TLM technique. The long-term stability of the contacts is also studied. This is followed by an investigation of the contact resistance of the back surface field and emitter layers of different types of poly-Si thin-film solar cells. Finally, a novel contact resistance measurement model is proposed that is believed to be able to overcome the measurement bottleneck of the transmission line models.
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Baier, Robert [Verfasser]. "Electronic grain boundary properties in polycrystalline Cu(In,Ga)Se2 semiconductors for thin film solar cells / Robert Baier." Berlin : Freie Universität Berlin, 2012. http://d-nb.info/1027815618/34.
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Mackay, Ian. "Thin film electroluminescence /." Online version of thesis, 1989. http://hdl.handle.net/1850/10551.
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Ho, Kang Jin. "Studies on Amorphous Silicon Thin Films Doped with Aluminium." Thesis, Indian Institute of Science, 1995. https://etd.iisc.ac.in/handle/2005/157.
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Amorphous Silicon(a-Si) films have attracted the attention of several investigators as it is an economical material for devices. One of the problems that is addressed is the doping of these films after they are prepared.
In this thesis, we investigated the effects of doping amorphous Silicon films(prepared by r.f. sputtering) with Aluminium(Al) by thermal diffusion. Amorphous Silicon films have been prepared on glass substrates at optimal process parameters. Then, the a-Si films are coated with Al by vacuum evaporation and subjected to heating in N2 atmosphere in the temperature range 300°C to 600°C for different durations.
After etching Al layer, it has been found that some of the films which are heated around 550°C contain filament like polycrystalline regions surrounding islands of a-Si.
This structure has been confirmed through Scanning Electron Mi-croscope(SEM) photographs and electrical conductivity measurements. SEM photographs indicate that, bright regions of amorphous material are surrounded by dark regions of relatively higher conducting
boundaries.
The electrical conductivity study shows that there is sharp increase in conductivity of Al doped films, which is attributed to the conducting polycrystalUne filament.
A simple model has been proposed to explain the variation of conductivity of these transformed films, with process parameters and with temperature.
Schottky barrier diodes have been fabricated using these transformed materials and their characteristics explained.
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Ho, Kang Jin. "Studies on Amorphous Silicon Thin Films Doped with Aluminium." Thesis, Indian Institute of Science, 1995. http://hdl.handle.net/2005/157.
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Amorphous Silicon(a-Si) films have attracted the attention of several investigators as it is an economical material for devices. One of the problems that is addressed is the doping of these films after they are prepared.
In this thesis, we investigated the effects of doping amorphous Silicon films(prepared by r.f. sputtering) with Aluminium(Al) by thermal diffusion. Amorphous Silicon films have been prepared on glass substrates at optimal process parameters. Then, the a-Si films are coated with Al by vacuum evaporation and subjected to heating in N2 atmosphere in the temperature range 300°C to 600°C for different durations.
After etching Al layer, it has been found that some of the films which are heated around 550°C contain filament like polycrystalline regions surrounding islands of a-Si.
This structure has been confirmed through Scanning Electron Mi-croscope(SEM) photographs and electrical conductivity measurements. SEM photographs indicate that, bright regions of amorphous material are surrounded by dark regions of relatively higher conducting
boundaries.
The electrical conductivity study shows that there is sharp increase in conductivity of Al doped films, which is attributed to the conducting polycrystalUne filament.
A simple model has been proposed to explain the variation of conductivity of these transformed films, with process parameters and with temperature.
Schottky barrier diodes have been fabricated using these transformed materials and their characteristics explained.
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Lee, Shih-Chung. "Physically-based modelling of polycrystalline semiconductor devices." Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394408.
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Garcia, Victoria. "Effect of dislocation density on residual stress in polycrystalline silicon wafers." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22621.
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St, Omer Ingrid L. J. "The pressure response of synthetic polycrystalline diamond f ilms /." free to MU campus, to others for purchase, 1996. http://wwwlib.umi.com/cr/mo/fullcit?p9737861.
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Знаменщиков, Ярослав Володимирович, Ярослав Владимирович Знаменщиков, Yaroslav Volodymyrovych Znamenshchykov, Володимир Володимирович Косяк, Владимир Владимирович Косяк, Volodymyr Volodymyrovych Kosiak, Анатолій Сергійович Опанасюк, Анатолий Сергеевич Опанасюк, Anatolii Serhiiovych Opanasiuk, and P. M. Fochuk. "Effect of Laser Annealing on the Properties of the Surface of Polycrystalline CdZnTe Thick Film." Thesis, Sumy State University, 2015. http://essuir.sumdu.edu.ua/handle/123456789/42798.
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In this work effect of laser annealing on properties of surface of CdxZn1-xTe (CZT) films was studied. CZT layers were deposited by co-evaporation of CdTe and ZnTe using close-spaced vacuum sublimation (CSVS) method. Structural properties and chemical composition of films were studied by X-ray Diffraction (XRD) and Energy Dispersive Spectroscopy (EDS). The annealing of the sample was carried out with the
help of micro-Raman infrared laser of 785 nm wavelength at maximal 100x magnification. It was established that laser annealing of the surface substantially causes redistribution of Zn atoms. More detailed study of the sample by the scanning of surface with the micro-Raman method allows to determine trend in this process and to detect Te-rich zones. Improvement of the crystal quality near annealed area of the thick
film was achieved.
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JAYASEELAN, VIDHYA SAGAR. "STUDY OF POLYCRYSTALLINE DIAMOND THIN FILMS GROWN IN A CUSTOM BUILT ECR PE-CVD SYSTEM." University of Cincinnati / OhioLINK, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=ucin975513169.
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Golestanian, Hassan. "Chemical vapor deposited boron doped polycrystalline diamond thin film growth on silicon and sapphire growth, doping, metallization, and characterization /." free to MU campus, to others for purchase, 1997. http://wwwlib.umi.com/cr/mo/fullcit?p9841292.
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Zhang, Fengguo. "Determination of the stress field in polycrystalline materials by Laue microdiffraction." Thesis, Paris, ENSAM, 2015. http://www.theses.fr/2015ENAM0020/document.
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La microdiffraction Laue permet l'estimation des déformations élastiques à l'échelle du micron. La procédure d'analyse standard, bien établie, utilisée pour extraire les déformations élastiques des images de Laue est limitée par deux sources d'erreurs : la détermination de la positions des taches de Laue sur le détecteur, et la sensibilité aux paramètres de calibration du montage. Pour améliorer la procédure, nous avons développé une procédure appelée Laue-DIC qui utilise la très bonne résolution de la technique de corrélation d'images numériques (DIC). Cette méthode utilise, pour la détermination de l'incrément de déformation élastique et de rotation, le déplacement des pics entre deux configurations mécaniques, estimé par DIC, au lieu de leur position. Nous montrons que cette méthode donne un profil de contrainte en meilleur accord avec les solutions analytiques et numériques, pour des échantillons monocristallins déformés en flexion 4-points. Nous proposons également une méthode Laue-DIC améliorée, dans laquelle les paramètres de calibration sont estimés à chaque point de mesure, simultanément à la déformation élastique.En parallèle à la formulation de la méthode Laue-DIC (améliorée), nos efforts ont porté sur l'estimation de l'incertitude obtenue sur les déformations élastiques. Nous avons développé un modèle de bruit pour les images de Laue mesurées en rayonnement synchrotron, qui a été validé sur des séries de données, et qui nous a permis d'estimer les erreurs statistiques de la DIC, à partir d'images de Laue synthétiques. Ces erreurs ont ensuite été propagées dans la méthode Laue-DIC afin d'estimer les incertitudes sur les déformations élastiques, que l'on trouve en bon accord avec la fluctuation des contraintes locales estiméesLaue microdiffraction is a powerful technique to characterize the intragranular elastic strain field at the scale of micrometer. Although a standard procedure extracting elastic strain and crystal orientation from Laue image has been well-established, it can suffer from two sources of uncertainties: the determination of peaks' positions and the sensitivity to calibration parameters. In light of the high accuracy of digital image correlation (DIC), we developed the so-called Laue-DIC method which used the peaks' displacements measured by DIC instead of peaks' positions to determine the elastic strain increment and rotation between two mechanical configurations. This method has been proved more efficient than the standard procedure in terms of stress profiles of bended beam. We also developed the enhanced version of Laue-DIC. By using the term “enhanced”, we mean that we attempt to obtain both lattice matrices and calibration parameters of two configurations rather than solely the elastic strain increment and rotation from peaks' displacements.Aside from the formulation of Laue-DIC, we also developed a procedure of statistically estimating the errors of elastic strain/stress resulted from DIC errors and calibration accuracy. We have first validated a classical noise model, Poissonian-Gaussian model, from diffraction images acquired at synchrotron radiation facility. With the noise model, we could statistically estimate the DIC errors by synthesizing artificial spots. The estimated DIC errors were further transmitted into the errors of Laue-DIC through statistical tests
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Turcu, Mircea Cassian. "Defect energies, band alignments, and charge carrier recombination in polycrystalline Cu(In,Ga)(Se,S)2 alloys." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2004. http://nbn-resolving.de/urn:nbn:de:swb:14-1086247686828-95497.
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This work investigates the defect energies, band alignments, and charge carrier recombination in polycrystalline Cu(In1-xGax)(Se1-ySy)2 chalcopyrite thin films and the interrelationship with the alloy composition. Photoluminescence spectroscopy of investigated Cu-poor Cu(In,Ga)(Se,S)2 layers generally shows broad emission lines with the corresponding maxima shifting towards higher energies under decreasing temperature or under increasing excitation power. Admittance spectroscopy of Cu-poor ZnO/CdS/Cu(In,Ga)(Se,S)2 chalcopyrite devices shows that the activation energies of the dominant defect distributions involving donors at the CdS/absorber interface and deep acceptors in the chalcopyrite bulk, increase upon alloying CuInSe2 with S. The band alignments within the Cu(In1-xGax)(Se1-ySy)2 system are determined using the energy position of the bulk acceptor state as a reference. The band gap enlargement under Ga alloying is accommodated almost exclusively in the rise of the conduction band edge, whereas the increase of band gap upon alloying with S is shared between comparable valence and conduction band offsets. The extrapolated band discontinuities [delta]EV(CuInSe2/CuInS2) = -0.23 eV, [delta]EC(CuInSe2/CuInS2) = 0.21 eV, [delta]EV(CuInSe2/CuGaSe2) = 0.036 eV, and [delta]EC(CuInSe2/CuGaSe2) = 0.7 eV are in good agreement with theoretical predictions. Current-voltage analysis of Cu-poor ZnO/CdS/Cu(In,Ga)(Se,S)2 devices reveals recombination barriers which follow the band gap energy of the absorber irrespective of alloy composition, as expected for dominant recombination in the chalcopyrite bulk. In turn, the recombination at the active junction interface prevails in Cu-rich devices which display substantially smaller barriers when compared to the band gap energy of the absorber. The result indicates that the Cu-stoichiometry is the driving compositional parameter for the charge carrier recombination in the chalcopyrite heterojunctions under investigations.
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Turcu, Mircea Cassian. "Defect energies, band alignments, and charge carrier recombination in polycrystalline Cu(In,Ga)(Se,S)2 alloys." Doctoral thesis, Technische Universität Dresden, 2003. https://tud.qucosa.de/id/qucosa%3A24342.
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This work investigates the defect energies, band alignments, and charge carrier recombination in polycrystalline Cu(In1-xGax)(Se1-ySy)2 chalcopyrite thin films and the interrelationship with the alloy composition. Photoluminescence spectroscopy of investigated Cu-poor Cu(In,Ga)(Se,S)2 layers generally shows broad emission lines with the corresponding maxima shifting towards higher energies under decreasing temperature or under increasing excitation power. Admittance spectroscopy of Cu-poor ZnO/CdS/Cu(In,Ga)(Se,S)2 chalcopyrite devices shows that the activation energies of the dominant defect distributions involving donors at the CdS/absorber interface and deep acceptors in the chalcopyrite bulk, increase upon alloying CuInSe2 with S. The band alignments within the Cu(In1-xGax)(Se1-ySy)2 system are determined using the energy position of the bulk acceptor state as a reference. The band gap enlargement under Ga alloying is accommodated almost exclusively in the rise of the conduction band edge, whereas the increase of band gap upon alloying with S is shared between comparable valence and conduction band offsets. The extrapolated band discontinuities [delta]EV(CuInSe2/CuInS2) = -0.23 eV, [delta]EC(CuInSe2/CuInS2) = 0.21 eV, [delta]EV(CuInSe2/CuGaSe2) = 0.036 eV, and [delta]EC(CuInSe2/CuGaSe2) = 0.7 eV are in good agreement with theoretical predictions. Current-voltage analysis of Cu-poor ZnO/CdS/Cu(In,Ga)(Se,S)2 devices reveals recombination barriers which follow the band gap energy of the absorber irrespective of alloy composition, as expected for dominant recombination in the chalcopyrite bulk. In turn, the recombination at the active junction interface prevails in Cu-rich devices which display substantially smaller barriers when compared to the band gap energy of the absorber. The result indicates that the Cu-stoichiometry is the driving compositional parameter for the charge carrier recombination in the chalcopyrite heterojunctions under investigations.
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Mih, Thomas Attia. "A novel low-temperature growth method of silicon structures and application in flash memory." Thesis, De Montfort University, 2011. http://hdl.handle.net/2086/5183.
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Flash memories are solid-state non-volatile memories. They play a vital role especially in information storage in a wide range of consumer electronic devices and applications including smart phones, digital cameras, laptop computers, and satellite navigators. The demand for high density flash has surged as a result of the proliferation of these consumer electronic portable gadgets and the more features they offer – wireless internet, touch screen, video capabilities. The increase in the density of flash memory devices over the years has come as a result of continuous memory cell-size reduction. This size scaling is however approaching a dead end and it is widely agreed that further reduction beyond the 20 nm technological node is going to be very difficult, as it would result to challenges such as cross-talk or cell-to-cell interference, a high statistical variation in the number of stored electrons in the floating gate and high leakage currents due to thinner tunnel oxides. Because of these challenges a wide range of solutions in form of materials and device architectures are being investigated. Among them is three-dimensional (3-D) flash, which is widely acclaimed as the ideal solution, as they promise the integration of long-time retention and ultra-high density cells without compromising device reliability. However, current high temperature (>600 °C) growth techniques of the Polycrystalline silicon floating gate material are incompatible with 3-D flash memory; with vertically stacked memory layers, which require process temperatures to be ≤ 400 °C. There already exist some low temperature techniques for producing polycrystalline silicon such as laser annealing, solid-phase crystallization of amorphous silicon and metal-induced crystallization. However, these have some short-comings which make them not suitable for use in 3-D flash memory, e.g. the high furnace annealing temperatures (700 °C) in solid-phase crystallization of amorphous silicon which could potentially damage underlying memory layers in 3-D flash, and the metal contaminants in metal-induced crystallization which is a potential source of high leakage currents. There is therefore a need for alternative low temperature techniques that would be most suitable for flash memory purposes. With reference to the above, the main objective of this research was to develop a novel low temperature method for growing silicon structures at ≤ 400 °C. This thesis thus describes the development of a low-temperature method for polycrystalline silicon growth and the application of the technique in a capacitor-like flash memory device. It has been demonstrated that silicon structures with polycrystalline silicon-like properties can be grown at ≤ 400 °C in a 13.56 MHz radio frequency (RF) plasma-enhanced chemical vapour deposition (PECVD) reactor with the aid of Nickel Formate Dihydrate (NFD). It is also shown that the NFD coated on the substrates, thermally decomposes in-situ during the deposition process forming Ni particles that act as nucleation and growth sites of polycrystalline silicon. Silicon films grown by this technique and without annealing, have exhibited optical band gaps of ~ 1.2 eV compared to 1.78 eV for films grown under identical conditions but without the substrate being coated. These values were determined from UV-Vis spectroscopy and Tauc plots. These optical band gaps correspond to polycrystalline silicon and amorphous silicon respectively, meaning that the films grown on NFD-coated substrates are polycrystalline silicon while those grown on uncoated substrates remain amorphous. Moreover, this novel technique has been used to fabricate a capacitor-like flash memory that has exhibited hysteresis width corresponding to charge storage density in the order of 1012 cm-2 with a retention time well above 20 days for a device with silicon films grown at 300 °C. Films grown on uncoated films have not exhibit any significant hysteresis, and thus no flash memory-like behaviour. Given that all process temperatures throughout the fabrication of the devices are less than 400 °C and that no annealing of any sort was done on the material and devices, this growth method is thermal budget efficient and meets the crucial process temperature requirements of 3-D flash memory. Furthermore, the technique is glass compatible, which could prove a major step towards the acquisition of flash memory-integrated systems on glass, as well as other applications requiring low temperature polycrystalline silicon.
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Pavlov, Marko. "Modélisation numérique du couplage thermique-photoélectrique pour des modules photovoltaïques sous faible concentration." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS361/document.
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La faible exploitation de l'irradiation inter-rangée limite la production des modules photovoltaïques (PV). Le projet "Aleph" explore l'intérêt d'ajouter des réflecteurs plans entre les rangées pour augmenter la production, et dégage des règles claires permettant l'optimisation géométrique de l'ensemble. Ce travail présente une modélisation multiphysique du système, des simulations numériques de son comportement, et la comparaison avec des données expérimentales. Deux technologies de module PV sont considérées : silicium amorphe (a-Si) et silicium polycristallin (p-Si). Les mesures montrent des gains énergétiques importants grâce aux réflecteurs. Les gains sont plus importants pour les modules a-Si que p-Si. La modélisation associe un modèle optique de lancers de rayons par méthode Monté-Carlo sous EDStaR, un modèle photoélectrique sous SPICE, et un modèle thermique empirique. Le modèle complet est calibré avec des données expérimentales en utilisant un algorithme évolutif. Une fois calibré, le modèle démontre une bonne performance en simulant la puissance générée par les modules en fonction des données atmosphériques et radiativesThe poor utilisation of the inter-row irradiation limits the production of photovoltaic (PV) modules. The "Aleph" project explores the potential of adding inter-row planar reflectors to increase the system yield, and defines clear rules for optimal settings of such systems in a given location and under a given climate. This work presents a multiphysics model of the system, numerical simulations of its behaviour, and the comparison with experimental data. Two PV module technologies are tested: amorphous silicon (a-Si) and polycrystalline silicon (p-Si). The experimental data show significant gains in produced energy brought by the reflectors. The gains are higher for a-Si modules compared to p-Si. The modelling work combines a Monte-Carlo ray-tracing optical model (EDStaR), a photo-electric model (SPICE), and an empirical thermal model. The complete model is calibrated with measurements using an evolutionary algorithm. Once calibrated, the model demonstrates good performance in predicting the module power output as a function of atmospheric and irradiance data
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Said-Bacar, Zabardjade. "Elaboration et caractérisations de silicium polycristallin par cristallisation en phase liquide du silicium amorphe." Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00680303.
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L'objectif de ce travail de thèse est l'élaboration du silicium polycristallin en phase liquide, sur substrat de verre borosilicate, en utilisant l'irradiation par laser continu de forte puissance d'un film de silicium amorphe. Des simulations numériques modélisant l'interaction laser-silicium amorphe ont été effectuées grâce à un modèle que nous avons développé sur l'outil COMSOL. Nous avons ainsi pu suivre l'évolution des transferts thermiques dans les différentes structures Si/verre irradiées par laser et ainsi pu évaluer l'impact des paramètres expérimentaux tels que la vitesse de balayage, la puissance du laser, la température du substrat sur les seuils de transition de phase du Si amorphe (fusion, cristallisation, évaporation). Ces résultats de simulation ont été confrontés à des données réelles obtenues en réalisant différentes expériences d'irradiation de films Si amorphe. Les résultats de cette comparaison ont été largement discutés. Dans une deuxième partie, nous avons étudié les propriétés structurales et morphologiques de films Si polycristallin obtenus par l'irradiation laser de films Si amorphe. En particulier, nous avons mis en évidence les effets de la présence d'impuretés tels que l'hydrogène ou l'argon présent dans les couches Si amorphe préalablement au traitement laser. Nous avons également montré que la croissance des cristaux silicium s'opère par épitaxie à partir d'un effet de gradient thermique latéral et longitudinal, produit respectivement par le profil énergétique du faisceau laser et la diffusion thermique par conduction, et par convection thermique dans la direction de balayage. L'optimisation des conditions opératoires nous a permis de réaliser des films Si polycristallin à larges grains, jusqu'à plusieurs centaines de µm de long sur plusieurs dizaines de µm de large. Ces structures sont très intéressantes pour des applications en électronique et en photovoltaïque.
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"Phosphorous diffusion and hydrogen passivation of polycrystalline silicon for photovoltaic cells." Thesis, 2012. http://hdl.handle.net/10210/5415.
Full textAbstract:
M.Sc.Techniques for the fabrication of polycrystalline silicon solar cells have advanced in recent years with efficiencies exceeding 17%. The major advantage of polycrystalline silicon is its low cost relative to single-crystalline silicon. The disadvantage is the significantly smaller minoritycarrier bulk diffusion length and inhomogeneous nature of the material. These two drawbacks are due to the presence of grain boundaries as well as high concentrations of dislocations and other physical and chemical defects. In this study the experimental conditions were determined to fabricate solar cells on polycrystalline silicon substrates. The controlled diffusion of phosphorous into silicon and subsequent evaluation of the doped layers (by spreading resistance profiling and chemical staining) were important aspects of this study. From these results the diffusion parameters (i.e. temperature and reaction times) could be optimized in order to improve the solar cell output parameters. Additional material improvement (increase in surface- and bulk minority carrier lifetimes) was demonstrated by the hydrogen passivation of electrically active defects in polycrystalline silicon. However. measurements on hydrogenated silicon samples also indicated that excess passivation can result in surface damage and subsequent reduction in the minority carrier lifetimes. Preliminary solar cells were fabricated on polycrystalline silicon with efficiencies ranging between 0.5 and 6% (total area = 16 cm2).
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Langa, Dolly Frans. "Comparison of the structural properties of a-Si:H and CulnSe₂ on glass and flexible substrates." Thesis, 2012. http://hdl.handle.net/10210/4540.
Full textAbstract:
M.Sc.Thin film solar cells based on polycrystalline indium diselenide (CulnSe₂) and amorphous silicon (a-Si:H) are promising candidates for the efficient conversion of sunlight into useable, cheap electrical energy. However, typical device structures are rather complex and consists of semiconductor/metal contacts as well as complicated p - n and p - i - n heterojunctions. In this study, CulnSe₂ absorber layers with excellent material properties were prepared by the selenization of metallic alloys. The a-Si:H thin films were deposited by radio frequency (RF) glow discharge in vacuum. The polycrystalline and amorphous absorber layers were deposited on glass and flexible substrates. In each case, a systematic study was conducted in which all the relevant processing parameters were varied over a broad range. These studies indicated that the structural features of the substrate significantly influence the structural features of the semiconductor thin films. The flexible substrate (kapton) was characterized by the presence of ridges, which distorted the growth behavior of the films. Deposition of ln/Cu/ln metallic alloys onto Mo coated glass (kapton) resulted in discontinuous metallic alloys, which were characterized by the presence of separated elongated island structures. The structural features of the precursors were maintained in the absorber film after selenization in elemental Se vapor. The morphological features of the CulnSe₂ absorber films were also critically influenced by the reaction temperature And reaction period to Se. The structural features on a-Si:H was significantly influenced by the structural features of the particular substrate used. Atomic force microscopy (AFM) imaging in combination with statistical analysis revealed higher roughness values when the amorphous semiconductor materials were deposited onto kapton, which negatively impacts on the device properties of solar cell devices.
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Carpenter, Derrick Todd. "Improvements in the characterization of polycrystalline thin films : microchemistry, microtexture and microstructure /." Diss., 1998. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:9919140.
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Bekker, Willem Johannes. "Structural analysis of polycrystalline CuInSe₂ thin films." Thesis, 2010. http://hdl.handle.net/10210/3525.
Full textAbstract:
M.Sc.CuInSe2 (CIS) is considered to be one of the most promising candidates for high efficiency thin film solar cells. The reaction of metallic alloys to a reactive selenium atmosphere (H2Se/Ar or elemental Se vapour) is a promising growth technique to produce CIS thin films of high crystalline quality. However, up to now, the control of the final film quality has been critically influenced by the loss of material and subsequent formation of detrimental binary phases during the high temperature selenization stages. In this study, it is shown that this phenomenon is strongly related to the selenization temperature and, in particular, the ramping procedure followed to the final selenization temperature. Metallic alloys which were selenized in H2Se/Ar at 400°C or slowly heated in 20 minutes to temperatures around 400°C were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) to have nonuniform surface morphologies, highly defected 0.8-2 !lm sized grains and to contain Cuselenide binary phases. Energy dispersive X-ray spectroscopy (EDS) analysis confirmed the generally reported sharp increase in the Cu/In atomic ratio for these classes of samples. In contrast, rapid heating (in 2 minutes) of identical metallic alloys to temperatures above 400°C, resulted in uniform, dense films with low defect density 1 !lm sized grains void of any evidence of secondary phases. X-ray fluorescence (XRF) Kal,2 measurements of metallic alloys at different stages of selenization revealed no evidence of material losses. XRF depth profiles, however, explained this discrepancy by revealing a pronounced segregation of In towards the Mo back contact when the samples were selenized at 400°C, or slowly heated to temperatures around 400°C. This segregation was dramatically reduced in films rapidly heated and selenized at temperatures above 400°C. For the purpose of comparison, metallic alloys were also reacted to elemental Se vapour. The structural features (grain size and preferred orientation) ofthese films differed significantly from those selenized under similar conditions in H2Se/Ar. The results from this study, including photoluminescence (PL) measurements obtained from these films, were used to affect the fabrication of CIS absorbers with excellent material properties and solar cell devices with moderate conversion efficiencies.
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Van, der Merwe Johan Petrus. "Elektriese eienskappe van aluminium kontakte op polikristallyne silikon." Thesis, 2012. http://hdl.handle.net/10210/6737.
Full textAbstract:
M.Sc.The efficiency of commercial polycrystalline silicon solar cells is currently 12% and 15% in the case of single crystalline cells. It is possible to lose about half of the open circuit voltage due to inferior contacts on the cell. It is thus clear that inferior contacts can seriously impede the relative low efficiency and care should be taken to make good ohmic contacts. Experiments were done to evaluate the influence of several factors on the quality and stability of the contacts. 1 C2•cm p-type polycrystalline silicon and 3 52.cm n-type single crystalline silicon were primarily used for these experiments. Results of molybdenum contacts on n-type silicon are also presented and the problems with silver epoxy contacts are discussed. It was found that aluminium contacts on p-type polycrystaline silicon improve with temperature and time, while those on single crystaline n-type degrade with temperature and time. These changes are already present at room temperature and are attributed to solid state diffusion of the aluminium into the silicon. This results in a p + layer. In the case of contacts on p-type, the behaviour is that of a Schottky diode. After the solid state diffusion, it becomes possible for the charges to quantum mechanically tunnel through the p+ layer. This results in an improvement of the contact. The contacts on n-type however, are ohmic just after evaporation. Similar to the p-material, the p+ layer causes a p+-n-junction with the depletion layer primarily in the n-type material. This causes a degradation in the contact quality. It is possible to achieve good quality contacts on polycrystaline p-type material, by annealing the contacts above 500°C for one minute. These contacts however, are non-ideal. SEM photographs show that the silicon surface is crated by pits due to solid state diffusion. It is only at these pits that conduction through the Schottkybarrier is possible. Since the area of the pits constitutes only a portion of the total area, only a portion of the surface will partake in conduction. Contact resistance is always present. For pm sized contacts on integrated circuits, the spesific resistance is of the order of 10 -6 Q.cm2. Contacts on solar cells, however, are of millimetre dimensions and the spesific resistance can be four orders of magnitude larger. The conduction through the surface can be modelled as conduction through a surface that is constituted of a mixture of minute ohmic and diode surfaces.
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"The effect of temperature, time and gas flow rate on the growth and characterization of Cu(In,Ga)Se₂ (CIGS) absorbers for thin film solar cells." Thesis, 2008. http://hdl.handle.net/10210/1361.
Full textAbstract:
M.Sc.Current solar cell research programmes in general aim to develop a high conversion efficiency photovoltaic (PV) module from high quality thin films. In this study, Cu (In,Ga)Se2 (CIGS) thin films were grown and characterized. These films were grown by selenization of Cu-In-Ga precursors. These precursors were prepared by co-sputtering In and (Cu, Ga). All the precursors were grown on Mo coated soda lime glass substrates. The selenization was conducted under different conditions in Ar/H2Se atmosphere, i.e. taking different values of flow rate of H2Se (5.00, 1.00, 0.25 mol%) in Ar, temperature (350, 450, 550 ºC) and time (10, 20, 30, 40, 50, 60 min). At each selenization condition, two samples were placed at different positions in the chamber. The structural properties of the produced films were analyzed by the techniques of X-ray Diffraction (XRD) for phases, Scanning Electron Microscopy (SEM) for morphology and Energy Dispersive Spectroscopy (EDS) for the bulk composition. The effect of temperature variation, the effect of flow rate variation and the effect of time variation were analyzed by comparing the structural properties as analyzed by the techniques mentioned. All in all this specific study delivers important information about the sensitivity of Cu(In,Ga)Se2 (CIGS) thin films to the temperature, gas flow rate and exposure time of the selenization step.
Doctor C.A. Engelbrecht Professor Vivian Alberts
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Marques, Miguel João Bolacha. "New insights into perovskite semiconductors for electronic applications." Master's thesis, 2019. http://hdl.handle.net/10362/94397.
Full textAbstract:
Transparent semiconductors are a type of materials distinguished by high transmission of light in visible region and relatively high electrical conductivity. These materials show diverse applications in the fields of solar energy and optoelectronics, being considered one of the most successful everyday products as they’re installed everywhere, like window electrodes in smartphones and solar panels. For n-type semiconductors is easy to obtain high carrier mobility, which is not the case for p-types. Developing p-type high mobility devices proves to be difficult given the nature of valence bands in most oxides, generally leading to large hole effective mass and poor charge conductivity. This current situation limits advances on thin-films technology, restraining materials band matching possibilities and unfulfilling goal creation of devices with both p- and n-type materials, hence denying improvements in transparent electronics. However, in recent studies, p-type perovskite-structured semiconductors with low fabrication cost and several applications have shown to possess excellent transparent semiconductor qualities, thus being a potential for the future of electronics and photovoltaics. In this work, mixed halide – iodine and bromine – organolead-based perovskite semiconductor thin-films (𝐹𝐴𝑃𝑏𝐵𝑟𝑥𝐼3−𝑥) were subjected to absorbance, thickness and structural characterizations, and then, dielectric and conductive layers were added to analyze semiconductor carrier properties, metal-oxide-semiconductor (MOS) capacitance and thin-film transistor (TFT) output. As a result, p-type and n-type hall mobilities of 20.2𝑐𝑚2/𝑉𝑠 and 38.1𝑐𝑚2/𝑉𝑠, respectively, were achieved by 𝐹𝐴𝑃𝑏𝐵𝑟𝑥𝐼3−𝑥 polycrystalline thin-films, negative capacitance and ion migration were identified in MOS capacitors, and relatively high field-effect mobility was estimated for the fabricated TFTs. These analyses show one thing in common, more ambipolar characteristics confirmed by increasing bromine contents.
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Egilmez, Mehmet. "Magnetotransport and magnetoresistive anisotropy in perovskite manganites." Phd thesis, 2009. http://hdl.handle.net/10048/421.
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Thesis (Ph. D.)--University of Alberta, 2009.Title from pdf file main screen (viewed on July 13, 2009). "A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy, Department of Physics, University of Alberta." Includes bibliographical references.
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Hemati, Azadeh. "LAYER BY LAYER NANOASSEMBLY OF COPPER INDIUM GALLIUM SELENIUM (CIGS) NANOPARTICLES FOR SOLAR CELL APPLICATION." 2011. http://hdl.handle.net/1805/2923.
Full textAbstract:
Indiana University-Purdue University Indianapolis (IUPUI)In this research thesis, copper indium gallium selenium (CIGS) nanoparticles were synthesized from metal chlorides, functionalized to disperse in water, and further used in layer by layer (LbL) nanoassembly of CIGS films. CIGS nanoparticles were synthesized through the colloidal precipitation in an organic solvent. The peak and average sizes of the synthesized particles were measured to be 68 nm and 75 nm in chloroform, and 30 nm and 115 nm in water, respectively. Two methods were used to disperse the particle in water. In the first method the stabilizing agent oleylamine (OLA) was removed through multiple cleaning processes, and in the second method ligand exchange was performed with polystyrene sulfonate (PSS). Zeta potential of CIGS nanoparticles dispersed in water was measured to be +61 mV. The surface charge of the nanoparticles was reversed by raising the pH of the solution, which was measured to be −43.3 mV at 10.5 pH. In a separate process, the CIGS nanoparticles dispersed in water were coated with PSS. The resulting dispersion was observed to be stable and the surface charge was measured to be −56.9 mV. The LbL deposition process of CIGS nanoparticles was characterized by depositing thin films on quartz crystal microbalance (QCM). LbL depositions was conducted using (i) oppositely charged CIGS nanoparticles, (ii) positively charged CIGS nanoparticles and PSS, and (iii) PSS-coated CIGS (CIGS-PSS) and polyethyleneimine (PEI). The average thickness of each bi-layer of the above mentioned depositions were measured to be 2.2 nm, 1.37 nm, and 10.12 nm, respectively. The results from the QCM have been observed to be consistent with the film thickness results obtained from atomic force microscopy (AFM). Various immersion times versus thickness of the film were also studied. For electrical characterization, the CIGS films were deposited on indium tindioxide (ITO)-coated glass substrates. Current versus voltage (I/V) measurements were carried out for each of the films using the Keithley semiconductor characterization instruments and micromanipulator probing station. It was observed that the conductivity of the films was increased with the deposition of each additional layer. The I/V characteristics were also measured under the light illumination and after annealing to study the photovoltaic and annealing effects. It was observed that under light illumination, the resistivity of a 12-layer CIGS film decreased by 93% to 0.54 MΩ.m, and that of the same number of layers of PSS-coated CIGS and PEI film decreased by 60% to 0.97 MΩ.m under illumination. The resistivity of an 8-layer CIGS and PSS film decreased by 76.4% to 0.1 MΩ.m, and that of the same layers of PSS-coated CIGS and PEI decreased by 87% to 0.07 MΩ.m after annealing. The functionalized nanoparticles and the LbL CIGS films were implemented in the solar cell devices. Several configurations of CIGS films (p-type), and ZnO and CdS films (n-type) were considered. Poly(3,4-ethylenedioxythiophene) (PEDOT), molybdenum (Mo), and ITO were used as back contacts and ITO was used as front contact for all the devices. The devices were characterized the Keithley semiconductor characterization instruments and micromanipulator probing station. For a CIGS and n-ZnO films device with PEDOT as back contact and ITO as front contact, the current density at 0 V and under light illumination was measured to be 60 nA/cm2 and the power density was measured to be 0.018 nW/cm2. For a CIGS and CdS films device with ITO as both back and front contact, the current density at 0 V and under light illumination was measured to be 50 nA/cm2 and the power density was measured to be 0.01 nW/cm2. For a drop-casted CIGS and CdS films device with Mo as back contact and ITO as front contact, the current density of 50 nA/cm2 at 0 V and power density of 0.5 nW/cm2 under light illumination was measured. For the LbL CIGS and chemical bath deposited CdS films device with ITO as both back and front contact, the current density of 0.04 mA/cm2 at 0 V and power density of 1.6 μW/cm2 under light illumination was measured. Comparing to Device-III, an increase by 99% in the power density was observed by using the CIGS LbL film in the device structure. The novel aspects of this research include, (i) functionalization of the CIGS nanoparticles to disperse in water including coating with PSS, (ii) electrostatic LbL deposition of CIGS films using oppositely charged nanoparticles and polymers, and (iii) the utilization of the fabricated LbL CIGS films to develop solar cells. In addition, the n-type cadmium sulfide film (CdS) and zinc oxide (ZnO) buffer layer were also deposited through LbL process after the respective particles were functionalized with PSS coating in separate experiments.
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Mugdur, Prakash. "Continuous flow microreactor for chemical bath deposition : a novel approach to the deposition of polycrystalline semiconductor thin films." Thesis, 2005. http://hdl.handle.net/1957/32160.
Full textAbstract:
Over the years, chemical bath deposition (CBD) is being widely used in the
fabrication of Cu (In, Ga) Se��� and CdTe based solar cells and photovoltaics. Many
chalcogenides have been successfully deposited by this technique and it has
received a great deal of attention owing to its low temperature and low-cost nature.
CdS, an important layer in heterojunction solar cells and other optoelectronic
devices, has been successfully deposited by this technique, which is normally
carried out as a batch process. But a major disadvantage of batch CBD is the
formation of particles and also unwanted deposition generating a lot of waste and
thus resulting in defective devices.
In this study, we have developed a continuous flow microreactor for CBD
to overcome the drawbacks of batch process. This novel microreactor setup makes
use of a micromixer for efficient mixing of the reactant streams and helps in
controlling the particle size and distribution before the solution impinges on the
hot substrate.
CdS semiconductor thin films were successfully deposited on oxidized
silicon substrates using the microreactor setup and a batch reactor as well.
Comparisons of nanostructured thin films were performed by various
characterization techniques. The surface morphology of the deposited films,
carried out by AFM, SEM and Dektak surface profiler, clearly indicated an
improved film quality in case of microreactor. This setup can also be used to
deposit various other compound semiconductor thin films with improved film
quality and minimum waste production.Graduation date: 2005
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Chang, Fang-Long, and 張芳龍. "Analyses of High-Performance Integrated Power Lateral Double-Diffused Metal-Oxide-Semiconductor Field-Effect-Transistors Fabricated on Single Crystalline and Low Temperature Polycrystalline Silicon Materials." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/g2etmd.
Full textAbstract:
博士國立交通大學
電子工程系所
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In this dissertation, for the sake of system-on-a-chip (SOC), silicon-on-insulator (SOI) and Bipolar-CMOS-DMOS (BCD) technology have been studied because of its superior isolation characteristics and mixture of the analog functions of bipolar, digital design of CMOS and high-voltage elements of DMOS on the same chip. In order to improve breakdown voltage from less reduced-surface-field (RESURF) effect of SOI devices, the step doping profile are investigated instead of complicated linearly graded doping profile by the distinct doping region along lateral direction. In order to stride forward the future integrations on any substrates, the LTPS LDMOS using excimer laser crystallization has been demonstrated by combination of the thin film technology and power device architecture. The LTPS LDMOS at 400 C substrate heating during excimer laser annealing will be used to expect to be a future driver device in system-on-a-panel (SOP) and three-dimensional (3-D) circuit integrations. Additionally, in order to comprehend heat dissipation in 3-D integration circuits, analyses of thermal problems in 3-D circuits are necessary. First, traditional Bipolar-CMOS-DMOS (BCD) technology, which is designed for only lateral bipolar (Bipolar, 12 V BVCEO and 25 V BVCBO), complementary metal oxide semiconductor (CMOS, 1.2 V threshold voltage) and double diffused metal oxide semiconductor (DMOS, 40 V breakdown voltage) transistors on the bulk silicon wafer, has been successfully utilized directly to fabricate silicon-on-insulator lateral-double -diffused-metal-oxide-semiconductor (SOI LDMOS) for the first time without changing any trial parameters. To simultaneously display the characteristics of high-power, high-speed and high-frequency, the results of output characteristics, switch and microwave performance must be moderate instead of individual optimum. Finally, according to the experimental results, it is proved that Bulk-BCD technology simultaneously enables high speed, high frequency and high blocking voltage applications�osuch as those in high-voltage integrated circuit switches (ns-range) and RF power amplifiers (MHz range to GHz range)�ousing a SOI wafer. In the study of step doping profile, a partition method is proposed to analyze the high-voltage step-doping silicon on insulator lateral insulated gate bipolar transistor (Step-Doping SOI-LIGBT) structure. The on-state characteristics will be present with the similar forward voltage drop (Vce) value between the step doping and linearly graded doping devices. The breakdown voltage can be deduced by the partition mid-point method and the corresponding breakdown electric field will also be fingered out in the step drift region. Furthermore, in order to reduce the undesirable additional masks, the degraded factor (D) is developed to evaluate the minimum number of frames with the better performance. Eventually, a 660 V step analytical results will be exemplified to compare with a 606.6 V MEDICI simulation, which shows very good agreement by this proposed method. In the study of future SOP and 3-D integrations, a new low-temperature polycrystalline silicon high-voltage LDMOS (LTPS HVLDMOS) using excimer laser crystallization has been proposed for the first time. However, in order to enhance LTPS HVLDMOS characteristics, there are two starting points: 1) integrate the thin film technology with the power device, 2) clarify the requirement of excimer laser treatment for low temperature power devices. As a result, the ON/OFF current ratio after laser treatment is improved over 106 times than that before laser treatment at Ldrift=15-�慆 and Vds=25 V. The LTPS HVLDMOS after laser treatment also demonstrates the better trade-off between the specific on resistance and breakdown voltage against the previous HVTFTs by solid phase crystallization�osuch as semi-insulating (SI), metal-field-plated (MFP), and offset-drain (OD) HVTFTs. In order to further improve the quality of crystallized poly-Si thin films and the performance of LTPS LDMOS, low-temperature poly-Si lateral double diffused metal oxide semiconductor (LTPS LDMOS) with high voltage and very low on-resistance has been achieved using excimer laser crystallization at 400 �aC substrate heating for the first time. The ON/OFF current ratios were exhibited with 2.96 × 10^5 and 6.72 × 10^6 while operating at Vds=0.1 V and 10 V, respectively. The maximum current limit was up to 10 mA and maximum power limit could be enhanced over 1 Watt at Vds=90 V and Vgs=20 V. The Ron,sp with dimensions of W/Lch=600-um/12-um could be significantly decreased 6.67 × 102 times in the magnitude as compared with the traditional offset drain (OD) TFTs. At last part of this thesis, the issue of heat dissipation will be discussed because many potential applications require operation at elevated temperatures. The effects of a high temperature ambient are exacerbated by power dissipation which causes additional temperature rise within the device. Power devices are often expected to run hotter than other component, but the excessive temperature rise of an inherently problem device will often lead to catastrophic failure. Failure of a single power device can shut down a computer, bring to halt a motor-driven system, or stop a vehicle dead in its tracks. This problem is anticipated to be exacerbated in 3-D circuit integration because the same power generated in a 2-D chip will now be generated in a smaller 3-D chip size resulting in a sharp increase in the power density. Therefore, accurate characterization of the thermal properties of power transistors is critical to the reliability of the systems using these devices. In order to understand this problem, the different electrical characteristics between crystalline and polycrystalline high voltage devices will be studied and the thermal stability of the LTPS LDMOS between the room temperature and 400 C irradiation will also be discussed over the ambient temperatures of 300 K�{400 K. The results of ambient temperature variation in LTPS LDMOS at 400 C irradiation are demonstrated the less sensitivity than the LTPS LDMOS before laser irradiation and at room temperature irradiation. Hence, the LTPS LDMOS at 400 C irradiation is very suitable for future system-on-a-panel (SOP) applications with higher temperature reliability.