AVS 45th International Symposium
    Thin Films Division Monday Sessions
       Session TF-MoM

Paper TF-MoM4
Chemical State Effects on Doped ZnO Film Properties

Monday, November 2, 1998, 9:20 am, Room 310

Session: Transparent Conductive Oxides
Presenter: G.J. Exarhos, Pacific Northwest National Laboratory
Authors: G.J. Exarhos, Pacific Northwest National Laboratory
L.-Q. Wang, Pacific Northwest National Laboratory
C.F. Windisch, Jr., Pacific Northwest National Laboratory
Correspondent: Click to Email
Zinc oxide is representative of the class of transparent conducting oxides which exhibit high transmission at visible wavelengths and concurrent low electrical resistivity. The resident conductivity and associated long wavelength reflectivity of these II-VI semiconductor films arises from the introduction of defect levels within the bandgap generated during the deposition process itself or during subsequent processing. In this work, films are prepared by means of rf-sputter and solution deposition methods. The deposition parameters are varied in order to increase conductivity in films which incorporate multivalent cationic dopants (Ga@super +3@, In@super +2@, Cu@super +2@, Au@super +3@, Pt@super +4@,...) within the wurtzite lattice. Post deposition modification of films on silica, Si, Al, or Pt substrates involves annealing in Ar/4% H2 or cathodic reduction in an electrochemical cell. Electrochemical film modification is carried out in aqueous solution (pH 7) or in an organic solvent such as CH@sub 3@CN. As-deposited and modified films are characterized using a cadre of analytical methods including XPS, AFM, TEM, XRD, Raman spectroscopy, and Electrochemical Impedance Spectroscopy. EIS measurements enable selective characterization of polarization effects within the oxide film and localized chemistry at the film-solution interface as a function of applied potential. The defect structure of the oxide is readily probed by means of in situ Raman spectroscopy during electroreduction. Results indicate that the LO Raman E@sub 1@ mode intensity, linewidth, and resonance frequency are particularly sensitive to the nature and concentration of defect states present in the film. Based upon these studies, a surface hydroxyl species is proposed to explain the observed reversible changes in conductivity. Such measurements complement the XPS studies which probe dopant oxidation state. Insight into film properties stability is based upon the electrochemical studies and measured variations in film properties upon subsequent annealing.