Studies Of The Influence Of Defects On The Electrical And Optical Properties Of ZnO:Al(H) Films By Magnetron Sputtering

Transparent conductive oxides films(TCOs) are kind of photoelectric materials combining with optical properties and electrical properties. TCOs can offer high carrier concentrations(~1020cm-3) and posses optical selectivity at different frequency range(reflecting infrared light, absorbing ultraviolet light and high transparent at visible light). Due to these excellent photoelectrical properties, it has been widely used in the field of thin films solar cells, liquid crystal display, gas sensor and thermal conductive glass at planes and automobile.ZnO:Al(AZO) transparent conductive oxide films has been considered as the optimum choice for substituting In2O3(ITO) films because of rich resource, low cost and stability in hydrogen atmosphere. The AZO films have been put into production for industry application as the electrode of solar cell. The resistivity of AZO films is still inferior and is unstable in ambient comparing to ITO films. In addition, which kind of defects dominating the photoelectrical properties is still under dispute. Based on these problems, this thesis is mainly devoted to the work as follows:1. Chapter 1 gived a brief overview of the basic properties of ZnO-based materials as well as the intrinsic and doped defects. We also summarized the H-realted defects in ZnO. In addition, the usual TCOs films, the methods how to prepare AZO films, the status and potential application of AZO films had been introduced. The main researches in this dissertation were shown in the end.2. In Chapter 2, we firstly introduced the work principle of magnetron sputtering instrument and annealed process. Then several main methods used in characterizing the microstructure and physical properties of AZO films were given, such as X-ray diffraction(XRD), Scanning Electron Microscopy(SEM), Transmission Electron Microscopy(TEM), Raman spectrum and et al.3. In Chapter 3, the main work is about how to reduce the bombardment of energetic oxygen negative ions on the AZO films. It is concluded that the increase in Argon flow or target-to-substrate distance can decrease the bombardment of energetic oxygen negative ions. The AZO films with the lowest resistivity of 2.68×10-3?cm and transmittance more than 85% were deposited. In addition, the effect of the bombardment of energetic oxygen negative ions on the microstructure and physical properties of AZO films fixed in the front of the targets are also investigated. It is proved that the bombardment of energetic oxygen negative ions dominated the physical properties of AZO films at erosion area while the number of active oxygen governed the physical properties of AZO films at non-erosion area. The AZO films with the lowest resistivity of 5.8×10-4?cm can be gained.4. In the Chapter 4, we briefly focoused on the technical study of preparing H doped AZO transparent conductive films. The effect of hydrogen exsiting at molecular or radicals during sputtering process on the electrical, optical properties and microstructrue of AZO films had been studied. The resistivity of AZO films could be improved by hydrogen incorporation because that hydrogen existing as hydrogen interstials is donated as shallow donor. Besides, the hydrogen can occupy oxygen vacancies forming HO, which is responsible for the improvement in transmittance of visable light(especially in 400-500nm). The lowest resistivity of hydrogenated AZOfilms is 1.54×10-3 ?cm.5. In Chapter 5, the change of defects in AZO films due to annealed process has been discussed and the effect of defects on the microstructure and photoelectric properties had been discussed. The absorbates at grain boundary of AZO films could increase the resistivity, decrease the optical band gap, enhance the intensity of visable light in PL spectrum and produce single ionic oxygen vacancies in depletion region. The trends of temperature-dependent resistivity in hydrogen atmosphere inidicated that the metal-like behavior of AZO films can be observed during the temperature range from RT to 350°C.In addition, the resistivity trends of AZO films on drums not only displayed metal-like behavior but also showed hysteresis loop. The reason of hysteresis loop can be attributed to the decomposition of complex defects *2()OH during heating process and the formation of *2()OH again during cooling process. By further analysising the influence of hydrogen annealing on the spatial distribution of electrical properties of AZO films, it is concluded that hydrogen annealed can reconcile the grain boundary barrier of AZO films in the front of the targets. However, the mobility of annealed AZO films in the front of the targets still showed spatial distribution due to different grain size.6. In Chapter 6, the summary of this dissertation is presented and future research has been suggested.