Characteristics of T_c and ρ(T) of polycrystalline (In ₂O₃)-(ZnO) films with low carrier density

For the polycrystalline (In₂O₃)-(ZnO) prepared by annealing in air, we investigated the relation among superconductivity, ρ(T) characteristics and preparation conditions. To clarify the distribution of elements, we studied the microstructure by scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS). It was found that 1) The films annealed at restricted regions of annealing temperature T _a and time t_a show the superconductivity. Transition temperature T_c and carrier density n are T_c<3.3K and n ≈10²⁵/m³∼10²⁶/m³, respectively. 2) The data on EELS spectra mapping of indium plasmon indicate that droplets of the pure indium phase distribute discretely on grain boundaries and near the interface between the film and the glass substrate. 3) Although data in the T_c - T_a relation are scattered, the T _c shows relatively good correlation with n, taking a convex form.