Transparent And Conductive Films Of Zinc Tin Oxides Obtained By Using Sol-gel Method And Their Applications

Transparent and conductive oxide (TCO) films are widely used as transparent electrodes for optoelectronic devices such as touch panels, flat panel displays, liquid crystal display (LCD), semiconductor/ insulator/ semiconductor (SIS) hetero-conjunction, and thin-film solar cells, since they have high transmittance in visible range, high reflectance in infrared range and semiconductor's characteristics and their electrical conductivities are similar to those of metals. Recently, ZnO and SnO₂ films have received much attention because of their possibility for TCO films with excellent chemical and thermal stability in addition to high electrical conductivity and optical transparency.Comparing to other methods, sol-gel is a new method to make TCO for its simplicity, easy doping and large area deposition on the substrates. As-prepared phosphors have intrinsic drawbacks in application, surface coatings have proved an efficient solution against agglomeration of powders, unstable surface electrical and chemical performances.In this thesis, we have investigated the method to obtain transparent and conductive zinc tin oxide films and their application to coat phosphors. The main results are as follow:1. SnO₂:Sb film, ZnO:Al film and alternate multi-layer films of SnO₂-ZnO were obtained respectively, by using sol-gel method. The electrical characterization of the films was basically conducted by conventional four probe technique and current-voltage (I-V) measurements. An phenomenon of deviating from ohmic law based I-V relation has been observed when the multi-layer films were measured at higher temperature. X-ray photoelectron spectroscopy (XPS), Ultraviolet (UV)-visible spectra and scanning electron microscopy (SEM) have been used to investigated the composition , visible light transmittance and morphology of the samples, respectively.2. It has been found that partially sublimating tin xerogel occurs during oxidization. The matter of tin xerogel sublimating has been deposited on quartz and silicon wafers to form transparent and conductive flms. The experimental conditions were controlled as follow: 0.8g tin xerogel was used as the sublimating source, 5cm from the source to the substrate, oxidizing for 1h under flux pure oxygen (99.9%). The results of XRD and XPS show that the film has stoichiometry of SnO₂ with tetragonal rutile crystal structure. The average transmittance of the film was above 80% in visible range. SEM and atomic force microscope (AFM) have been used to analyze the morphology of the film. It shows that the nanocrystal is compact and uniform in size and the films is smooth with equal thickness basically. The thickness and resistitvity of the film obtained as above is 70nm from deduction of absorption coefficient and 2.86×10^-2Ω·cm from four-probe measurements.3. Partial sublimation of SnO₂:Sb xerogel during oxidation was utilized to treat the as-prepared ZnS:Mn phosphor. The mass ratio of SnO₂:Sb xerogel to ZnS:Mn phosphors changed from 0.5 to 4.0 and the range of the oxidation temperature was 300-600℃under the given oxygen flux (0.2 L·min-1) and oxidation duration (30 min).The treated phosphors were characterized by X-ray diffraction (XRD), photoluminescence (PL), transmittance electron microscopy (TEM), and electrical resistance measurements. The results showed that the conductivity of the treated ZnS:Mn phosphors was obviously improved when the mass ratio of SnO₂:Sb xerogel to ZnS:Mn phosphors and the oxidation temperature were 3.0 and 500℃, respectively. The photoluminescence characteristics and crystal structure of the treated ZnS:Mn phosphors remained the same as the as-prepared phosphors.