Superconductivity in In₂O₃-ZnO crystalline films

Thin In₂O₃-ZnO (IZO) films were prepared by DC-magnetron sputtering with changing the weight concentration x of ZnO, 0 ≤ x ≤ 0.07. As-grown amorphous IZO films show the metallic characteristic but do not show superconductivity. We have investigated the T and H dependence of the resistivity ρ and Hall coefficient for annealed films with thickness d 350 nm in air. It is found that the films with 0 ≤ x ≤ 0.03 show superconductivity. Transition temperature T_c and the carrier density n of these films are 2.0 K and 10²⁵ -10²⁶ m^-3, respectively. The annealed In₂O₃-ZnO films were examined by a high resolution transparent electron microscopy. This investigation reveals that films annealed at 300 °C are sufficient crystalline. There is a difference of crystal structures between the superconducting film and normal film. We studied the upper critical magnetic field H_C2 (T) for the film with x 0.005. From the slope of dH_c2/dT, we obtain the coherent length ζ(0) 100 A at T 0 K and the coefficient of the electronic heat capacity γ 3.2 (J/m³K²) which is small compared with that of other oxide materials.