Aluminum doped zinc oxide AZO has been studied for 20 years. It can improve thin films¡¦ thermal stability and transparency in visible range .However AZO is not as good as ITO in conductivity and transparency, that¡¦s why the application of AZO is only limited in few fields. This is because the nature limit of ZnO. Because part of doped Al forms Al2O3 instead of sits on Zn sites, that enhances light and carriers scattering and suppresses the optical transparency and electric conductivity. This study is plane to take advantage of amorphous properties, that may be achieved try grown films at liquid Nitrogen temperature, in which the distribution of Al and Zn will be very uniform and the solubility of Al will be high. ZnO:Al thin films is grown on glass substrates at low temperature by Radio frequency magnetron sputtering system. Low-temperature deposition is done in order to deposit amorphous thin films (ceramic targets ZnO contained 2wt.% Al2O3). The Al3+ in place of Zn2+ should be uniformly distributed in the thin films because of amorphous structure. It expects to find the best deposition condition under a fixed target-to-substrate distance (10cm) by varying growth, such as the deposition mode, PF plasma power and working pressure. AFM, XRD (grazing incident x-ray diffraction) and N&K analyzer were used to measure the thin surface morphology, structure, thickness and transmittance, respectively. The colors of the thin films are very different dependent on the modes of deposition. The low sputtering rate by lower RF power and high working pressure is the key to successfully grow amorphous ZnO:Al films. The amorphous ZnO:Al thin films (a-5) are deposited under 100W of RF power and 50mTorr of working pressure. The transmittance of the assembly of ZnO:Al thin films/glass substrate is the same as glass substrates which inducates the transmittance of films is far above 90%. However, the amorphous ZnO:Al thin films are poor conductor . We also tried to improve it by the post-annealing of ZnO:Al thin films in 2% hydrogen atmosphere. It is found to be not successful.

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 97-109). Also available on the World Wide Web.

Thesis (Ph. D.)--University of California, Riverside, 2009. / Includes abstract. Available via ProQuest Digital Dissertations. Title from first page of PDF file (viewed March 12, 2010). Includes bibliographical references. Also issued in print.

Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Deng,Yulin; Committee Member: Hsieh, Jeffery S.; Committee Member: Nair, Sankar; Committee Member: Singh, Preet; Committee Member: Yao, Donggang. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Zinc Oxide (ZnO)is a wide band gap semiconductor which has attracted great attention because of its wide applicability. In order to obtain semiconductor devices with stable and reproducible properties further study of deep level defects is essential. DLTS (Deep level Transient Spectroscopy) is a direct and straightforward techniqueto determine the energy level of the deep level defects. Other information such as activation energy and capture cross section of the defect can also be obtained through this method. In our study ZnO single crystal samples were implanted by oxygen with the energy of 150keV. After the pretreatment of hydrogen peroxide, Schottky contacts were fabricated with Au film deposited by thermal evaporation. Deep level defects were studied by deep level transient spectroscopy (DLTS). Single peak spectra were observed in the as-implanted sample and samples anneal at 350oC, 650oC and 750oC with the corresponding activation energy decreasing with the annealing temperature from ~0.29eV as found in theas-implanted sample. Three peaks were identified in the DLTS spectra of the 900oC sample, with the activation energies of 0.11eV, 0.16eV and 0.37eV respectively.After analysis in detail we found some peaks in the DLTS spectra were the combination of two other peaks, dominated in different temperature range. The thermal evolutions of the deep levels up to the temperature of 1200oC were also investigated. / published_or_final_version / Physics / Master / Master of Philosophy

published_or_final_version / Physics / Master / Master of Philosophy

Zinc oxide (ZnO) is a wide band-gap semiconductor that is of interest for application in dye sensitized solar cells (DSSCs) because of similarity of its properties to TiO2. Unlike TiO2, ZnO can readily be grown in a wide variety of morphologies, using inexpensive, simple, and low temperature methods. Recent research on ZnO-based DSSCs focuses on modifying the ZnO layer morphology in order to maximize surface area, and enhance the electron collection by providing fast electron transport. It is expected that the improvement in cell performance by morphology modification is due to higher dye loading, increased electron lifetime and fast electron transport. However, ZnO properties may be affected by various synthesis methods. It is difficult to make a conclusion whether the change of performance are attributed to change of morphology or a change in the defect types and/ or defect concentrations. In this study, the influence of ZnO nanoparticle properties on cell performance has been investigated. Commercial ZnO nanoparticles with different sizes and optical properties were utilized. It was found that there is a complex relationship between native defects, dye loading, charge transport and photovoltaic performance. In particular, the presence of non-radiative defects was found to be detrimental to photovoltaic performance. In addition, with the similar defect emission intensities, sample exhibiting orange-red defect emission showed better performance than the samples emitting green defect emission. Nanoparticle properties and their relationship between dye adsorption, electron injection, electron lifetime and electron transport, and photovoltaic performance will be discussed. / published_or_final_version / Physics / Master / Master of Philosophy

In this dissertation, I present the results of my research regarding hybrid semiconductor interfaces between organic and inorganic semiconductors. Using photoemission spectroscopy, I elucidate the important role of defect-induced electronic states within the inorganic semiconductor phase. These states significantly affect both the energy level alignment and the charge carrier dynamics at the hybrid interface. I demonstrate that the behavior of these hybrid semiconductor interfaces is complex and not well characterized by current models for organic semiconductor interfaces. Specifically, I show that hybrid interfaces host unique electronic phenomena that depend sensitively on the surface structure of the inorganic semiconductor. I also demonstrate new applications of photoemission spectroscopies that enable the direct analysis of important properties of inorganic semiconductors, including charge carrier behavior near hybrid interfaces and the electronic character of defect-induced energy levels. The research presented here focuses on two different n-type inorganic semiconductors, tin disulfide (SnS₂) and zinc oxide (ZnO). SnS₂ is a layered transition metal dichalcogenide that presents an atomically flat and inert surface, ideal for sensitively probing electronic interactions at the hybrid interface. To probe the electronic structure of the SnS₂ surface, I used a variety of organic molecules, including copper phthalocyanine, vanadyl naphthalocyanine, chloro-boron subphthalocyanine, and C₆₀. ZnO has a complex surface structure that can be modified by simple experimental procedures; it was therefore used as a tunable semiconductor substrate where the effects of altered electronic structure can be observed. By carefully studying the origin of hybrid interfacial interactions, these research projects provide a first step in explicitly elucidating the fundamental mechanisms that determine the electronic properties of hybrid interfaces.

Quantum-scale semiconductors embedded in an electrically-active matrix have the potential to improve photovoltaic (PV) device power conversion efficiencies by allowing the solar spectral absorption and photocarrier transport properties to be tuned through the control of short and long range structure. In the present work, the effects of phase assembly on quantum confinement effects and carrier transport were investigated in CdTe - ZnO nanocomposite thin films for use as a spectrally sensitized n-type heterojunction element. The nanocomposites were deposited via a dual-source, sequential radio-frequency (RF) sputter technique that offers the unique opportunity for in-situ control of the CdTe phase spatial distribution within the ZnO matrix. The manipulation of the spatial distribution of the CdTe nanophase allowed for variation in the electromagnetic coupling interactions between semiconductor domains and accompanying changes in the effective carrier confinement volume and associated spectral absorption properties. Deposition conditions favoring CdTe connectivity had a red shift in absorption energy onset in comparison to phase assemblies with a more isolated CdTe phase. While manipulating the absorption properties is of significant interest, the electronic behavior of the nanocomposite must also be considered. The continuity of both the matrix and the CdTe influenced the mobility pathways for carriers generated within their respective phases. Photoconductivity of the nanocomposite, dependent upon the combined influences of nanostructure-mediated optical absorption and carrier transport path, increased with an increased semiconductor nanoparticle number density along the applied field direction. Mobility of the carriers in the nanocomposite was further mediated by the interface between the ZnO and CdTe nanophases which acts as a source of carrier scattering centers. These effects were influenced by low temperature annealing of the nanocomposite which served to increase the crystallinity of the phases without modification of the as-deposited phase assembly and associated absorption properties. Integration of the nanocomposite as an n-type heterojunction element into a PV device demonstrated the ability to tune device response based on the spectral absorption of the nanocomposite sensitizer film as dictated by the phase assembly. Overall the various phase assemblies studied provided increased opportunity for optimization of the absorption and carrier transport properties of the nanocomposite thin films.

Τα νανοϋλικά, τα υλικά δηλαδή που οι διαστάσεις τους είναι στην νανοκλίμακα, έχουν διαφορετικές ιδιότητες από τα αντίστοιχα υλικά σε μεγαλύτερη κλίμακα. Για αυτό το λόγο, τα νανοϋλικά παρουσιάζουν ιδιαίτερο ενδιαφέρον για περαιτέρω μελέτη και έρευνα. Σε αυτά τα υλικά ανήκει και το οξείδιο του ψευδαργύρου (ZnO). Το οξείδιο του ψευδαργύρου είναι ένας σύνθετος ημιαγωγός τύπου II-IV με άμεσο ενεργειακό χάσμα (Eg=3.37 eV) σε θερμοκρασία δωματίου και με μεγάλη ενέργεια σύνδεσης εξιτονίου (60 meV). Σκοπός της παρούσας διπλωματικής εργασίας είναι η σύνθεση, ο χαρακτηρισμός και η μελέτη ιδιοτήτων νανοσύνθετων υλικών οξειδίου του ψευδαργύρου-πολυμερικής μήτρας. Το υλικό που θα χρησιμοποιήσουμε ως πολυμερική μήτρα είναι η πολυβινυλική αλκοόλη (PVA). Αρχικά, θα δώσουμε τον ορισμό της νανοτεχνολογίας και των νανοϋλικών, και θα παρουσιάσουμε και διάφορους τρόπους παρασκευής νανοϋλικών. Στο δεύτερο κεφάλαιο, θα ασχοληθούμε με το οξείδιο του ψευδαργύρου (ZnO). Στο κεφάλαιο αυτό, γίνεται εκτενής περιγραφή της δομής, των ιδιοτήτων και των νανοδομών του οξειδίου του ψευδαργύρου. Στην συνέχεια, θα περιγράψουμε τις βασικές αρχές που αφορούν τις πειραματικές τεχνικές που θα χρησιμοποιήσουμε για τoν χαρακτηρισμό των δειγμάτων. Ενώ στο τέταρτο κεφάλαιο, θα παρουσιάσουμε την πειραματική διαδικασία που θα ακολουθήσουμε για την σύνθεση του οξειδίου του ψευδαργύρου, καθώς και για την παρασκευή των μεμβρανών PVA-ZnO. Στο ίδιο κεφάλαιο, θα παρουσιάσουμε τα αποτελέσματα από το χαρακτηρισμό των νανοσωματιδίων του ZnO και των μεμβρανών PVA-ZnO. Στο τελευταίο κεφάλαιο, θα αναφέρουμε τα συμπεράσματα μας σχετικά με την παρούσα διπλωματική εργασία. / Nanomaterials, materials on the scale of a few nanometers, have different properties in comparison with larger-scale materials. For this reason, nanomaterials are of particular interest for further study and research. Zinc Oxide (ZnO) belongs to these materials. ZnO is a complex II-VI semiconductor with a direct band-gap energy (Eg = 3.37 eV) at room temperature and a large exciton binding energy (60 meV). The aim of the present diploma thesis is the preparation, the characterisation and the study of properties of ZnO particles in a polymer matrix. A polyvinyl alcohol (PVA) matrix has been used. Firstly, nanotechnology and nanomaterials are defined and various synthetic methods of nanomaterials are presented. The second chapter deals with ZnO. This chapter comprehensively describes the structure, the properties and the nanostructures of zinc oxide particles. Thereafter, in chapter three, the basic principles concerning the experimental techniques of characterization which have been used are described. The forth chapter describes the experimental process followed for preparing ZnO nanoparticles and PVA-ZnO nanocomposites. The results from the characterization of the ZnO nanoparticles and PVA-ZnO membranes are then presented. In the last chapter, we make our conclusions about this diploma thesis.