AVS 46th International Symposium
    Thin Films Division Wednesday Sessions
       Session TF-WeA

Paper TF-WeA9
Mott-Schottky Analysis of Thin ZnO Films

Wednesday, October 27, 1999, 4:40 pm, Room 615

Session: Transparent Conductive Oxides
Presenter: C.F. Windisch, Pacific Northwest National Laboratory
Authors: C.F. Windisch, Pacific Northwest National Laboratory
G.J. Exarhos, Pacific Northwest National Laboratory
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Thin ZnO films have been prepared in our laboratory using both rf-sputtering and solution deposition routes. Processing parameters were found to have a marked effect on film conductivity. In addition, measured conductivity and infrared reflectivity could subsequently be enhanced by either chemical treatment in hydrogen gas at 400°C or cathodic electrochemical treatment in a neutral (pH = 7) phosphate buffer solution. While film conductivity and free carrier content usually are determined by Hall measurements, the present study focused on whether a conventional Mott-Schottky analysis could be used to monitor the change in concentration of free carriers in these films before and after chemical and electrochemical reduction. The Mott-Schottky approach is particularly promising for electrochemically modified films since the measurements could be made in the same electrolyte used for post-deposition electrochemical processing. Results of studies on sputtered pure ZnO films in ferricyanide solution were encouraging. Mott-Schottky plots were linear and gave free carrier concentrations typical for undoped semiconductors. Film thicknesses estimated from the Mott-Schottky data agreed with values calculated from reflectance measurements and confirmed by spectroscopic ellipsometry. However, studies on solution-deposited films yielded anomalous results. Mott-Schottky plots were nonlinear, apparently due to film porosity. A combination of dc polarization and AFM measurements confirmed this conclusion. The results suggest that Mott-Schottky analysis would be suitable for characterizing the dielectric response of solution-deposited ZnO films only if the effects of film porosity on the characteristics of the space charge region of the semiconductor were included in the analysis. This work was sponsored by the Office of Materials Science of the Office of Basic Energy Science, U. S. Department of Energy, under contract DE-AC06-76RLO 1830.