Pulsed Laser Deposition And Performance Of The ATO Thin Films

Due to the prominent advantages as abundant resources, low cost, non-toxicity, radioresistance and thermal stability, ATO (SnO2:Sb) thin films have been one of the potential substitutes for ITO (In2O3:Sn) thin films which have high cost and toxicity. The complex factors of ATO thin films involing the valence state distribution of Sb element, crystallinity, homogeneity, carrier trasportation will have negative effects on the optical and electrical properties. The effect of procssing parameters on the phase, composition and microstructure and the relationship between Sb doping content, valence state distribution and the physical properties has been investigated. The difficulity to obtain the ATO thin films with high performance is the main problem for the preparation of the ATO thin films. In the thesis, ATO thin films were prepared by pulsed laser deposition (PLD) techinique on quartz substrate. It is significant to prepare the ATO thin films with high optical transmittance and high conductivity by optimizing the processing parameters and annealing treatment. The effect of processing parameters on the structure, composition and microstructure and the relationship between Sb doping content, valence state distribution and the physical properties has been investigated.Firstly, the effect of deposition temperature, annealing temperature and oxygen pressure on the structure, composition, optical and electrical properties has been investigated. It is observed that the ATO thin films deposited under low temperature and annealed at high temperature show high optical transmittance (92.0%) and resistivity of2.7×10-3Ω·cm. The bad crystallinity contributes to low Hall mobility, resulting in the electrical properties of the ATO thin films mainly influenced by carrier concentration. The increase of annealing temperature and oxygen pressure will promote the transition of Sb3+to Sb5+, contributing to the increase of carrier concentration and decrease of resistivity. However, when the oxygen pressure exceeds8Pa, the decrease of oxygen vacancies and the severe competition between Sb3+and Sb5+will decrease carrier concentration, resulting in the resistivity increasing to1.40×10-2Ω·cm. Carrier concentration of the ATO thin films can be controlled by Sb5+/Sb3+ratio.Secondly, the effect of Sb doping content on the structure, composition, optical and electrical properties has been explored. It is suggested When the Sb doping content is less than12at.%, there is no obvious variation of optical properties and the increase of Sb doping content will promote the transition of Sb3+to Sb5+to increase the Sb5+/Sb3+ratio and decrease the resistivity. Nevertheles, when Sb doping content exceeds12at.%, the optical properties begins to decrease obviously and Sb3+begins to occupy the domain position, contributing to the decrease of Sb5+/Sb3+ratio. The corresponding carrier concentration and conductivity both increase firstly and then decrease. The optimal Sb doping content is12at.%。There is certain limitation to control the performance of the ATO thin films simply by adjusting the carrier concentration. Hence, the enhancement of Hall mobility is an effective way to further improve the optical and electrical properties of the ATO thin films. It shows that the ATO thin films deposited directly under high temperature show good crystallinity and perfect growth of grains, contributing to obviously enhancement of Hall mobility and conductivity of the ATO thin films. Moreover, the growth orientation of the thin films will also affect Hall mobility. The (101) orientation will block the transportation of carriers. It is suggested that the ATO thin films with the lowest resistivity of6.60×10-4Ω·cm, highest hall mobility of6.15cm2V-1s-1and optical transmittance of82.0%are obtained when the deposition temperature of550℃, oxygen pressure of8Pa, laser energy density of5.4J/cm2and the thickness of380nm.