Study On Preparation And Properties Of Al-doped ZnO Thin Films

In recent years, the transparent conductive oxide films have been widely used in solar cells, liquid crystal display, Laser diode, gas sensor and other fileds. Nowadays, indium tin oxide (ITO) occupies the main market.As a result of the lack of resources, expensive price, poisonous and other problems, the indium seems to be difficult to meet the needs of requirements. Among those oxdie films, Al-doped ZnO (AZO) as for its high transmittance in the visible light region, good conductivity, rich source, inexpesive, environment-friendly and high thermal and chemical stability when exposed to hydrogen plasma proves to be the appropriate placer for ITO. In this article, we use R.F magnetron sputtering method to deposit AZO thin films. We system study on the film quality by controlling deposition conditions (such as substrate temperature,oxygen and argon proportion, working pressure, sputtering power,target to substrate distance), getting the optimized conditions. Using X Ray Diffraction (XRD), Scanning Electron Microscope (SEM),Ultraviolet-visible spectrum (UV-Vis) and Four-Point Probes analytic technique to study the change rule of micro-structre and optical-electro properties of the films. Using annealing, utilizing homo-buffer layer technique achieve the property optimization.The results indicate that all the films show an obvious (002) diffraction peak, have high transmittance (80～87%) in the visible light range (390～780nm),the lowest sheet resistance reaches11Ω/□.The higher substrate temperature gets the lower resistance in certain rang, but too high temperature goes against the films’ preferred growth. When introducing oxygen into the sputtering atmosphere, the conductivity of thin films will reduce. Working pressure and sputtering power have similar influence on the film electrical properties, when the pressure or power enhanced, conductivity of thin films derived from enhanced. Appropriate target-substrate distance improves the growth and electrical properties of thin films. All films prepared by different conditions show good transmittance in light rang, the transmittance reaches above80%.The annealing for thin films have nearly no changes on films’ transmittance, but has great effects on the electrical properties. When the films in an oxidizing atmosphere annealing treatment may cause serious deterioration in electrical properties, instead, the electrical properties will be improved in reductive atmosphere which vacuum anneal improves the best. The insertion of AZO homo-buffer layer and hetero-buffer layer can effectively improve the electrical properties when controlling the layer thickness. Using argon atmosphere, pressure4Pa, sputtering power100w,target to substrate50mm, and time for sputtering is0.5h,SiO2hetero-buffer layer (thickness20nm) and annealed in vacuum at the temperature400℃for1h.We achieve the best properties for AZO thin films, which the sheet resistance is16Ω/□and the transmittance is85.5%, performance index is1304.8×10-5Ω-1.