Growth And Characterization Of Wide Gap Semiconducting Oxide And Chalcogenide Thin Films By Pulsed Laser Deposition

The preparation and characterization of thin film oxides and chalcogenides by pulsed laser deposition (PLD) is presented. An overview of fundamental PLD concepts are presented and are followed by a description implementation and development of the PLD systems at OSU. We present the results of thin film growth of high electron mobility In2O3:W in which we have prepared films exhibiting □ > 100 cm2/Vs on vitreous SiO2 substrates. The growth of Cu3TaQ 4 (Q = S, Se) films is outlined as a two step process consisting of PLD of ceramic targets followed by ex-situ annealing in chalcogenide vapor. Also, BiCuOSe thin films have been prepared in-situ and exhibit a high hole mobility up to 4 cm2/Vs. A discussion of their electronic structure is presented which explains the nature of the low band gap energy on the basis of deep Bi 6p level at the conduction band minimum. Finally, the results of BaBiO3 thin film preparation are presented in which both polycrystalline and highly (00l) oriented samples were grown.

Oxides form a broad subject area of research and technology development which encompasses different disciplines such as materials science, solid state chemistry, physics etc. The aim of this book is to demonstrate the interplay of these fields and to provide an introduction to the techniques and methodologies involving film growth, characterization and device processing. The literature in this field is thus fairly scattered in different research journals covering one or the other aspect of the specific activity. This situation calls for a book that will consolidate this information and thus enable a beginner as well as an expert to get an overall perspective of the field, its foundations, and its projected progress.

In order to fabricate layered electrochromic devices capable of reversibly changing color in response to applied voltage, pulsed laser deposition was used to deposit thin films of tungsten oxide on fluorine doped tin oxide substrates.The thin films were deposited at room temperature in an O2 atmosphere of the order of 10−1 mbar on FTO/glass substrates using a KrF pulsed laser source. XRD analysis confirmed the resulting films to be amorphous and UV-Vis spectroscopy confirmed transparency. Raman shift confirms non-crystalline WO3 presence. Electrochromic devices were connected to a cyclic voltammetry system to regulate voltage sweeps, investigate charge transport, response time and reversibility of color/bleached states. Scanning electron microscopy was performed on the films post device operation to examine the surface topography and composition. Raman spectroscopy and XRD was performed post device films to investigate any changes in the films. Li+ ion conducting glasses of composition xLi2SO4 - (1-x)[0.50Li2O-0.5(2NH4H2PO2)) were characterized using resistivity measurements and neutron diffraction experiments to evaluate them as suitable substitutes for the electrolyte in the electrochromic devices. Formation of crystallites above 400°C has been observed which is understood to hamper Li+ ion mobility, resulting in reduced performance of the electrolyte. The acid based electrochromic devices have exhibited superior reversibility.

Pulsed ultraviolet light from a XeF excimer laser was used to grow thin films of zinc oxide and tin dioxide on (111) p-type silicon wafers within a versatile high vacuum laser deposition system. This pulsed laser deposition system was self-designed and self-built. Parameters such as pressure, target temperature, and distance from the target to the substrate can be adjusted in the system. Scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction spectroscopy, Raman spectroscopy and ellipsometry were used to analyze the structures and properties of ZnO and SnO2 thin films. The critical temperature required to fabricate a crystalline ZnO thin film by pulsed laser deposition was found and has been confirmed. For the SnO2 thin film, the critical temperature required to generate a crystalline structure could not be found because of the temperature limit of the substrate heater used in the experiment. In SnO2 thin films, thermal annealing has been used to convert into crystalline structure with (110), (101) and (211) orientations. After fabricating the amorphous SnO2 thin films, they were put into an oven with specific temperatures to anneal them. The minimum annealing temperature range was found for converting the amorphous SnO2 thin films into SnO2 thin films with a crystalline structure. Thermal annealing has also been applied to some amorphous ZnO thin films which were fabricated under the critical temperature required to produce crystalline ZnO thin films. The minimum annealing temperature range for amorphous ZnO thin films was found and only one orientation (002) shown after annealing. Laser annealing technology has also been applied for converting both amorphous ZnO and SnO2 thin films, and results show that this method was not well suited for this attempt. ZnO thin films and SnO2 thin films with a crystalline structure have inportant widely used in industry, for example, application in devices such as solar cells and UV or blue-light-emitting devices. The aim of this research is to help improving the manufacturing process of ZnO and SnO2 thin films.

Oxides form a broad subject area of research and technology development which encompasses different disciplines such as materials science, solid state chemistry, physics etc. The aim of this book is to demonstrate the interplay of these fields and to provide an introduction to the techniques and methodologies involving film growth, characterization and device processing. The literature in this field is thus fairly scattered in different research journals covering one or the other aspect of the specific activity. This situation calls for a book that will consolidate this information and thus enable a beginner as well as an expert to get an overall perspective of the field, its foundations, and its projected progress.

Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.

The electronic, optical and luminescent properties of europium doped wide band gap oxide thin films and the electronic properties of indium gallium zinc oxide (IGZO), a novel amorphous oxide semiconductor were investigated. The thin films of europium doped gallium and gadolinium oxides and indium gallium zinc oxide were deposited on c-axis oriented sapphire substrates by Pulsed Laser Deposition at various conditions of temperature, pressure and doping concentration. Europium doped gallium oxide was found to be in beta phase with monoclinic crystal structure and the films exhibited intense red emission under cathode ray excitation with a peak wavelength of emission at 611 nm which corresponds to the transitions from 5D0 to 7F2 levels in europium. Europium doped gadolinium oxide thin films were found to exhibit two different phases (cubic and monoclinic) with the one of the phases being dominant depending on the growth conditions. The peak wavelength of emission was either 611 nm or 613 nm depending on the phase of the films. The amorphous indium gallium zinc oxide thin films were found to exhibit very high hall mobilities of the order of ̃15 cm2∙V−1∙s−1 and the conductivity could be controlled over several orders of magnitude from 5 x 10−3 S∙cm−1 to 10 S∙cm−1 in the amorphous phase. Annealing the films in presence of air was found to decrease the carrier concentration of the films due the incorporation of oxygen in the films thereby filling up the oxygen vacancies. Applications of amorphous indium gallium zinc oxide include Transparent Thin Film Transistors and use as transparent conducting oxide for optoelectronic devices.