Superconductivity in transparent zinc-doped In₂O₃ films having low carrier density

Thin polycrystalline zinc-doped indium oxide (In₂O₃-ZnO) films were prepared by post-annealing amorphous films with various weight concentrations x of ZnO in the range 0⩽x ⩽0.06. We have studied the dependences of the resistivity ρ and Hall coefficient on temperature T and magnetic field H in the range 0.5⩽T ⩽300 K, H⩽6 Tfor 350 nm films annealed in air. Films with 0⩽x⩽0.03 show the superconducting resistive transition. The transition temperature T_c is below 3.3 K and the carrier density n is about 10²⁵-10²⁶ m^-3. The annealed In₂O₃-ZnO films were examined by transmission electron microscopy and x-ray diffraction analysis revealing that the crystallinity of the films depends on the annealing time. We studied the upper critical magnetic field H_c2 (T) for the film with x = 0.01. From the slope of dH_c2 /dT, we obtain the coherence length ξ (0) ≈ 10 nm at T = 0 K and a coefficient of electronic heat capacity that is small compared with those of other oxide materials.