Research On The Preparation And Properties Of B And Ga Co-doped ZnO Thin Films

Zinc oxide(ZnO), as a Ⅱ-VI compound semiconductor with a wide direct bandgap of 3.37 eV at room temperature, has excellent electrical and optical properties. Compared with GaN, ITO and SnO2, ZnO has many advantages, such as abundant raw material, low cost, non-toxicity, relatively low deposition temperature and high chemical and thermal stability. As a transparent conductive oxide(TCO),ZnO films has been widely used in many applications such as flat panel display devices, thin-film solar cells, light-emitting diodes, surface acoustic wave, gas sensors and detectors due to its unique properties.So far great efforts have been introduced for improving the performance of ZnO films, and the experimental results show that ZnO TCO with excellent electrical and optical properties can be fabricated by doping with appropriate metal elements such as B, Al, Ga, In, etc. In recent years, attentions have been paid to the co-doping process in which the two or more elements are doped into ZnO simultaneously in order to get further improvements in electrical, optical properties and thermal stability. This thesis disscussed the preparation technology and properties of B Ga co-doped ZnO(BGZO) thin film in detail. The main research contents were as follows:In this thesis, B and Ga co-doped ZnO films(BGZO) were deposited by radio frequency magnetron sputtering method. Effects of deposition parameters such as sputtering power, thickness, and substrate temperature on the electrical, optical, structural and morphological properties of BGZO were investigated. The surface morphology of the as-deposited films was analyzed by scanning electron microscopy(SEM) and atomic force microscopy(AFM). The structural properties including crystal orientation, grain size and stress of the films were determined with a powder X-ray diffractometer. The optical transmittance of the films was measured using a UV-Visible spectrophotometer and the optical bandgap(Eg) was evaluated. Furthermore, the electrical properties including resistivity, mobility and carrier concentration of the films were analyzed by Hall measurement system.(1)With different parameters mentioned above, all the films showed highly c-axis orientation perpendicular to the substrate and structure of hexagonal wurtzite. Average optical transmittance of all the BGZO films is greater than 85% in the visible wavelength range.(2)With sputtering power of 150 W, the films showed higher mobility and lower resistivity. With further increasing in sputtering power, the grain size decreased, resulting in the increase of resistivity. The carrier concentration and optical band gap(Eg) increased with the increasing sputtering power.(3)Film thinckness can affect the properties of the films. With an increase in film thickness, the crystal quality of the films was improved, the resistivity was decreased, and the mobility was increased and tended to be stable.(4)The BGZO film grown at 200℃ showed larger crystallite size, lower resistivity, higer Hall mobility and wider band gap.