Structural studies of ITO thin films with the Rietveld method

Tin doped indium oxide (ITO) films of different tin concentrations were deposited by e-beam evaporation onto glass substrates. These ITO films were investigated using grazing incidence X-ray diffractometry (GIXRD). The application of the Rietveld refinement to GIXRD patterns provides information about the crystallographic structure of the films. Lattice constants, atomic positions and bond lengths were calculated for different doping concentrations. From the shifting and broadening of X-ray line profiles domain sizes and microstrains were calculated. Small tin amounts cause decreasing lattice constants and also a decrease in In/Sn1-In/Sn2 bond lengths. The In/Sn1-O bond length increases and the distortion of the asymmetric In/Sn2-O octahedron becomes stronger. At larger doping concentrations both lattice constants and In/Sn1-In/Sn2 lengths increase. The In/Sn1-O bond length and the distortion of the In/Sn2 octahedron first decrease, but with further tin insertion an increase of these parameters is observed. The microstrains calculated from X-ray line profile analysis correlate with the distortion behaviour of the In/Sn2-O octahedrons. With increasing domain sizes the resistivity of the films decreases. Therefore it can be concluded that the conductivity of tin doped In2O3 films is not dominated by grain boundaries. Some mechanisms of the tin insertion into the In2O3 lattice are discussed. (C) 1998 Elsevier Science S.A. All rights reserved.