Study On Fabrication And Properties Of Al-doped ZnO Transparent Conductive Thin Films

At present, the transparent conductive oxide films have been widely used intransparent conductive contacts, solar cells, laser diodes, ultraviolet lasers, thin-filmtransistors and other fileds, and the demand for it is growing with the expansion ofapplication. Currently, indium tin oxide （ITO） is the most widely used for transparentconducting oxide materials. Because of the constraint supply of indium, it seems to bedifficult to meet the supply requirements. Al-doped ZnO （AZO） transparent conductivefilms become one of hot research spots and are recognized to be the best candidate toreplace ITO films in terms of its excellent optical and electrical performance, lowmanufacturing costs and environmental friendliness. This paper focuses on optimization ofperformance of AZO transparent conductive films by adjusting process parameters usingRF magnetron sputtering, and carries out research and analysis.In the experiment, Al-doped zinc oxide ceramics was taken as sputtering targets, andRF magnetron sputtering system was used to deposite AZO films on glass and Si substrateby regulating the relevant parameters（Al-doped concentration, substrate temperature,sputtering power, working pressure, hydrogen and oxygen concentration in working gas）,and some of the samples were annealed under different conditions. Then XRD, SEM,UV-vis, Hall measurement system, step profiler, four-probe resistance tester and otherequipments were used to characterize and analyze films’ microstructure, optical andelectrical properties.The results indicate that all the samples show an obvious （002） diffraction peak, andhave a good c-axis preferred orientation perpendicular to the substrate surface in hexagonalwurtzite structure. Under the same conditions, the crystal quality of AZO thin filmsdeposited on Si substrate is significantly higher than on the glass slide, but with relativelyhigher resistivity. When Al₂O₃-doped mass fraction in the zinc oxide ceramics reaches2%,the films have the highest crystallinity, the largest grain size, the lowest resistivity and thehighest transmittance towards visible light. The crystalline quality of thin films improveswith the increase of substrate temperature, and the resistivity decrease, while the transmittance increases. Appropriate sputtering power and working gas pressure canameliorate the structural, optical and electrical performance of the thin films. H₂doped inthe working atmosphere will affect adversely thin films’ each property that deteriorateswith the increase of H₂concentration, which is relevant to the reductibility of H₂; however,the incorporation of small amount of O₂gas will help to optimize the optical and electricalperformance of thin films, which is due to the reduction of the O vacancies in the film’slattice, but the excessive amount of O₂gas will affect the growth and the resistivity of films,owing to the oxidation of O₂. In a pure Ar atmosphere, the films have a relatively goodoptical and electrical property, deposited at0.8Pa,400℃,200W, and its resistivity is1.53×10^-3Ωcm，the average visible light transmittance is about83%and the optical band gapis3.52eV. The crystalline quality of AZO thin films annealed under different atmospheresis improved, but the impact on the resistivity and optical band gap is quit different. Theresistivity is reduced by annealing in N₂atmosphere, and decreases with the increase of thetemperature, while in transmittance spectrum the absorption edge carries out “bule shift”; inair the resistivity of films increases with the increase of the temperature, while theabsorption edge carries “red shit”.