Transport properties and microstructures of polycrystalline In₂O₃–ZnO thin films

We prepared polycrystalline In₂O₃–ZnO films by post annealing the amorphous films (1.0 wt % ZnO) at 200 °C with various annealing times t_a 0≤t_a≤20 h. We have measured the electric resistivity and Hall mobility and also observed film structures by not only the x-ray diffraction but also scanning transmission electron microscopy (STEM) with electron energy-loss spectroscopy (EELS). We have found the following: (1) Hall mobility takes the maximum with respect to the carrier density and the annealed films clearly show the superconductivity of which transition temperature increases with increase in t_a. (2) The data on EELS spectra mapping of indium plasmon indicate that droplets of the pure indium phase exist on grain boundaries and near the interface between the film and the glass substrate. However, it seems that these droplets do not form an electrical conducting path but contribute to the scattering centers for carrier electrons, from the dispersed distribution of these droplets in STEM-EELS spectra mapping and the relationship between the electron mean free path and the grain size.