Properties Of Ta-doped TiO₂Thin Films Prepared By Pulsed Laser Deposition

Transparent conductive oxide (TCO) thin film has broad application prospects in the field of Solarphotovoltaic (PV) cells，flat panel display，heat reflecting mirror，Transparent p-n junction，Gassensitive components, transparent electrodes and so on. Tantalum doped titanium dioxide is a newkind of transparent conductive oxide which has great potentials in applications. As it was discoveredin recent years, understanding of this material does not go far enough. Exploring the preparationprocess and investigating its physics mechanism become particularly important. Our previousresearch of tantalum-doped TiO2thin films lacks analysis of the internal electric transport mechanism.In this thesis, we prepare tantalum-doped TiO2(Ta:TiO2) thin films by pulsed laser deposition (PLD)and perform detailed studies in the structure, morphology, optical properties, and electrical transportproperties of the films. The main contents of the dissertation are as follows:1. Tantalum-doped TiO2thin films were deposited on quartz glass substrates by PLD technology.The structure and surface morphology were tested and characterized by X-ray Diffraction (XRD) andAtomic Force Microscope (AFM). Films are all with (101) preferred orientation and anatasepolycrystalline structure when the energy density of pulsed laser is about6.5J/cm2, repetitionfrequency is5Hz, substrate temperature is300℃, oxygen pressure ranges from0.3pa to0.7pa. Thepeak to valley roughness of the films are around10nm, which meets the requirements of a variety ofoptoelectronic devices on the market.2. The average transmittance of the films in the visible spectra was measured byultraviolet-visible spectrophotometry. The visible light transmittance of the prepared films were allabove80%. And the transmission peak of the films has a tendency of red-shift and blue-shift when theoxygen pressure changes because of their band gap’s change.3. The electrical properties of tantalum-doped TiO2thin films were investigated by Hall effectmeasurement system.The results show that the Resistivity, carrier concentration and mobility of thefilms are very sensitive to the oxygen partial pressure. This can be explained by the energy loss ofparticles when they approach to the surface of the substrate, which gives rise to a low mobility.4. The electrical property dependence on temperature of the films was measured to identify thedominant conduction mechanism. It was found that thermally activated band conduction is thedominant conduction mechanism in the temperature range from150K to210K.Whereas, in thetemperature region from10K to150K,the dependence of conductivity on temperature follows Mott’svariable range hopping (VRH) model. Moreover, the temperature dependence of resistivity for thefilms can be described by~exp(b/T)1/2at temperatures from210K to300K, belongs to hoppingconduction mechanism.