Research On Prepareation And Optical And Electrical Properties Of SnO₂ Low Emission Films

With the increased situation of Energy Crisis, the low-emssion glass, which can save energy and reduce pollution, becomes one of hot topics in research. The low-emission glass can reflect infrared ray emmitted from sunshine and body indoor, without the losing the transittance in visible. It can prevent the heat exchange between both sides of glass and decrease the buliding energy comsumption. However, the current low-emission glass is composed by Ag films, which has high cost, high reflectance in visible. The SnO₂ films prepared by ultrasonic spray pyrolysis can overcome the disadvantages of the Ag films. There are also some problems in low emission film of SnO₂, such as weak reflectivity in near infrared, high cutoff wavelength of infrared reflectivity etc. Moreove, the mechanism of refectivity in SnO₂ films and the releation betweent the film structure and optical-electrical properties needs more research work. The probe into the preparation parameters and the modified SnO₂ films may be the key point of the research work. In the paper, we investigated the proper preparation parametes in ultrasonic spray pyrolysis and the releation betweent the structure and optical-electrical properties in SnO₂ films. The fluorine doped SnO₂ film, boron doped SnO₂ films and lithium doped SnO₂ films also have been studied.The preparation parameters showed that droplet flux and carrier gas flux decided the deposition process; drying rate and permeabitiy affected the transformaiton of particles; the effect of thickness on the electrical properties was not obvious when the thickness was more than1.1μm; the temperature of 350℃was suitable for deposition.The results of fluorine doped SnO₂ films showed that, at low fluorine doping levels, the fluorine ions substituted the oxide ions in SnO₂ lattice to form the defect of FO·and release the electrons, that in turn, leading to the splitting of O-Sn-O vibration and increasing of carrier concentration in films; at high fluorine doping levels, fluorine ions became to fill the intersitital site, forming the defect of Fi′, which could decrease the carrier concentration in films and move the vibration frequency of Sn-O. The optical reflectivity showed the similar rule with carrier concentration at different doping levels, which could be explained by Drude theory. The main scattering mechanism in SnO₂:F films is the impurity ions scattering.The results of SnO₂ films prepared from SnCl₂ and SnCl₄ showed the oxygen vacancy existed in fluorine doped SnO₂ films. With the increased fluorine concentrations, the contribution of oxygen vacancy became weak; the results of SnO₂ films prepared from NH4F and HF showed the activity of HF was not as good as NH4F at the same fluorine doping level.The results of SnO₂:Sb films showed that when antimony doping concentration was less than 2.0%, the antimony ions in SnO₂ lattice behaved +5 valence state and substituted tin ions forming the donor defect and increase of carrier concentration; when antimony concentration was more than 2.0%, the antimony showed +3 valence state and substituted tin ions forming acceptor defect and decrease of carrier concentration, which had a negetive effect on the reflectivity of SnO₂:Sb films. The results of SnO₂:B films showed that a small quantitiy of bonor ions in SnO₂ lattice would fill the intersitital site to form Bi′′′and increase the carrier concentration and reflectivity; too much bonor ions in SnO₂ lattice could make bonor ions to substitute tin ions and decrease the reflectivity and carrier concentration. The results of SnO₂:Li films showed lithium ions in SnO₂ lattice would substitute the tin ions, that in turn to the disappear of optical reflectivity and electrical properties.