الفهرس 
Electronic Band StructureOnly 14 pages are availabe for public view
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Abstract
This thesis is devoted to produce transparent conducting oxide (TCO) thin film oxides with improved electrical and optical properties. The structure of the prepared materials as well as its optical and electrical properties are studied and correlated with the transparent conducting phenomena. The need for these oxides stems from the difficulty of achieving high transparency and high conductivity simultaneously. The demand for new materials is also amplified by a variety of potential new uses for TCOs; these include novel applications in more demanding environments than those currently and new heterostructure applications as part of the rapid emergence of all-oxide electronics. Extended solid-solution phases afford tailorable TCO properties, such as optical gap and/or work function, in addition to electronic conductivity.
The most promising multi-cation TCO materials share common chemical and structural features and possess similar carrier-generation mechanisms
Cadmium Oxide pure and, doped with Fluorine, Cadmium-Zinc oxide, and Cadmium-Zinc-Oxide doped with Fluorine thin films were deposited on glass substrates using spray pyrolsis technique to form transparent conducting materials.
Deposition conditions such as deposition time, deposition temperature, flow rate and nozzle to substrate distance necessary to produce CdO films with high conductivity and optical transparency over a wide spectral range were studied and optimized. The transmission and reflectance were measured for all films by double beam spectrophotometer from 200 nm to 2500 nm. from the transmission data the refractive index n and the absorption coefficient ⍺ were calculated. Applying Drude’s theory and Frensel equations the real and imaginary part of the dielectric constant along with the plasma frequency ωp were obtained for films having high conductivity. Obtaining the plasma frequency ωp it became possible to compute the optical carrier concentration Nopt, optical resistivity ρopt., and optical mobility opt..
CdO films were deposited at different deposition times (5 min to 45 min) at deposition temperature 350 ºC. It was found that a sharp increase in thickness observed with the increase in deposition time up to td=20 min. The growth rate then decreased at td>20 min. It was found that the roughness of CdO thin films increases with thickness up to a certain limit then it decreases once again. This was attributed to change in growth mode from perpendicular to the substrate surface to parallel to the substrate surface. It was observed from the XRD measurements the change in the preferred orientation from the (111) plane (perpendicular to the substrate) to the (200) (parallel to the substrate). The average grain size increased as a function of deposition.
It was found that CdO thin films are stable in the deposition temperature range from 300 ºC to 400 ºC. For deposition temperatures Td> 450 ºC the Cadmium re-evaporates. The surface topography of some of the CdO thin film samples deposited under different conditions were studied using atomic force microscopy (AFM). It was found that Nopt. was relatively higher for deposition temperatures Td<450 ºC than for deposition temperatures Td≥450 ºC. The ρopt. increased significantly from 2.64 x 10-3 Ω cm at Td=350 ºC to 3 x 10-2 Ω cm at at Td=450 ºC. The same trend was also observed for electrical resistivity. This behavior can be explained in terms of the change of conduction mechanism from degenerate at low deposition temperature to non-degenerate at high deposition temperatures.
Cadmium Oxide thin films doped with different Fluorine concentrations at deposition temperature 350 ºC deposited on glass substrates was studied. The samples compositions were checked by elemental analysis (EDAX). The EDAX was an effective tool in detecting F atoms at high concentrations (F≥0.07). Concentrations of Fluorine were varied in order to produce CdO:F thin films with high conductivity and optical transparency. It was found that Nopt. increased as the F concentration increased. The ρopt. decreased significantly from F=0 to F=0.035 and then for F> 0.035 it reached a steady state. This trend was also observed for electrical resistivity. The best figure of merit Fh=3.04 x 10-6 Ω-1 was obtained for F concentration 0.035.
The best deposition conditions were taken into consideration when multi-component Cd(1-x)ZnxO thin films were deposited at different Zinc concentrations at different deposition temperatures. The electrical and optical as well as the structural effect of changing the Zinc concentration and deposition temperature on the deposited films was studied. The aim was to find the best films fulfilling the criteria of good transparent conducting oxide. Cd0.75Zn0.25O thin film deposited at deposition temperature 350 ºC had the best figure of merit (3.95x10-6 Ω-1) with relatively low resistivity as compared to pure CdO but with improved transparency in the visible region as a result of the band gap widening from 2.54 eV at x = 0 to 2.66 eV at x = 0.25. The Nopt. DROPped by a factor of 10 from x=0 (pure CdO) to x=0.333. The electrical measurements showed the same trend. The ρopt. increased significantly (tripled) as the Zn concentration x got closer to the phase separation region.
Making the use of the results from studying the Cd(1-x)ZnxO thin film systems, we choose the Cd0.75Zn0.25O thin film deposited at 350 ºC as a base material to study the effect of adding the Fluorine with different concentrations as a way of mixing between conventional and non-conventional doping. Though, the direct energy band gap remained the same around 2.72 eV for all deposited Cd0.75Zn0.25O: F the transparency improved by a factor 1.69 at Fluorine concentration 0.1. The best figure of merit among these films reached 1.66 x 10-5 Ω-1 at Fluorine concentration 0.05