| Transparent conductive oxides (TCOs) thin films have high electrical conductivity and high optical transparency. So they become the key research projects of academe and industry. The emphasis was reflected in TCOs as transparent conductive electrodes have lots of applications in photoelectron solar, flat panel display, organic light emitting diode, etc. Among them, tin-doped indium oxide (ITO) is the most widely used material. However, it has severe limitations due to the scarcity and high price of indium needed for ITO. So we need to find a new alternative material and its electrical resistivity (p) should be less than～10-3Ωcm, and with a transmittance higher than 80% in the near-UV-VIS range. At present, doped CdO and ZnO semiconductors thin films are the best choice to replace ITO, because they have a low resistivity, e.g. in the order of 10-4Ωcm, high optical transmittance in visible range, and their raw materials are inexpensive for mass production. CdO and ZnO-based thin films can be widely used in the areas of displays, sensors, anti-reflective coating, gas sensors, photovoltaic, electro-chromic devices, etc. Therefore, the study of optical and electrical properties of CdO and ZnO-based transparent conductive oxides films has great significance.To sum up, this thesis has two research purposes:Firstly, how to further reduce the resistivity of the film; Secondly, how to effectively change the optical band gap of thin film. Structure, morphology, electrical and optical properties of the In, Sn doped CdO thin film were studied. In addition, ZnO and CdO have similar semiconductor properties, so the alloy and mixture thin films of ZnO and CdO were also thoroughly studied and explored in this article. X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and X-ray photoelectron spectroscopy (XPS) were used to observe and analyze the microstructure and composition of the thin film. And the optical and electrical properties were studied by UV-visible spectrophotometer, photoluminescence and Hall Effect device.1. Transparent indium-doped cadmium oxide (In-CdO) thin films were deposited on quartz glass substrates by pulse laser deposition (PLD) from ablating Cd-In metallic target at a fixed pressure 10 Pa and a fixed substrate temperature 300℃. The influences of indium concentrations in target on the microstructure, optical and electrical performances were studied. When the indium concentration reaches to 3.8 at%, the as-deposited In-CdO film shows high optical transmission in visible light region, obviously enhanced direct band gap energy (2.97 eV), higher carrier concentration and lower electrical resistivity compared with the un-doped CdO film. With a further increase of indium concentration to 5.5 at% induces the formation of In2O3, which reverse the variation of these parameters and performance.2. Transparent tin-doped cadmium oxide (Sn-CdO) thin films with different Sn concentration were deposited on quartz glass substrates by pulse laser deposition (PLD) at 300℃. The film's crystallographic structure, optical and electrical properties were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), UV-VIS spectrophotometer and Hall system. Results show that doping of Sn enhances the film's [111] preferred orientation and causes slight shift in the (200) Bragg angle towards higher value. The optical band gaps (Eg) of the Sn-doped films were increase with the increase of Sn doping concentration. In addition, proper doping of Sn evidently improves the electrical properties of CdO, such as the resistivity of the CdO film with 2.9 at% Sn doping is about one-twelfth of that of the CdO film, while the carrier concentration is about 13 times of that of the undoped.2.9 at% Sn doped CdO film has the best performance figure of merit, reached 3.5×10-3Ω-1, this value is very close to the performance of ITO (4.2×10-3Ω-1). Therefore, the improvements both in optical and electrical properties endow that the Sn-CdO thin films have potential application as TCOs material for different optoelectronic device applications.3. Ternary polycrystalline Zn1-xCdxO semiconductor films with cadmium content (x) ranging from 0 to 0.23 were obtained on quartz substrate by pulse laser deposited (PLD) technique. X-ray diffraction measurement revealed that all the films were single phase of wurtzite structure grown on c-axis orientation with its c-axis lattice constant increasing as the Cd content x increasing. Atomic force microscopy observation revealed that the grain size of Zn1-xCdxO films decreases continuously as the Cd content x increases. Both photoluminescence and optical measurements showed that the band gap decreases from 3.27 to 2.78 eV with the increasing the Cd content x. Increasing the Cd content x also leads to the broadening of the emission peak. The resistivity of Zn1-xCdxO films decreases evidently for higher values of Cd content x. The shift of PL emission to visible light as well as the decrease of resistivity makes the Zn1-xCdxO films potential candidate for optoelectronic device. 4. Zn0.86Cd0.11In0.03O alloy semiconductor film was deposited on quartz substrate by pulsed laser deposition technique. Cd is used to change the optical band gap and In is used to increase carrier concentration of the ZnO film. XRD studies confirm that the structure of Zn0.86Cd0.11In0.03O is hexagonal wurtzite structure without CdO phase appeared. FE-SEM shows that the grain size of Zn0.86Cd0.11In0.03O film is smaller than that of ZnO. These films are highly transparent (～85% ) in visible region. Most importantly, the electrical properties of Zn0.86Cd0.11In0.03O film highly improved with In doped. It has low resistivity (4.42×10-3Ωcm) and high carrier concentration (5.50×1019cm-3) that enable this film a promising candidate for window layer in solar cells and other possible optoelectronic applications.5. ZnO/CdO composite films with different CdO content were obtained by pulse laser deposition technique. The structural, optical and electrical properties of the composite films were investigated by XRD, photoluminescence and electrical resistivity measurements, respectively. Results show that the UV emission was with constant peak position in their photoluminescence spectra. In meantime, their electrical resistivity decreased to very low level approaching to the value of CdO film, which can be explained by the Matthiessen composite rule for resistivity. Compared with the conventional doping methods, ZnO/CdO composite films prepared in this experiment have optical properties of ZnO and the electrical properties of CdO, thus obtain the properties which a single TCO materials doesn't possess in order to meet some special requirement.
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