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

Thin polycrystalline zinc-doped indium oxide (In2O3–ZnO) films were prepared bypost-annealing amorphous films with various weight concentrations x of ZnO in the range06x60.06. We have studied the dependences of the resistivityρand Hall coefficient on temperature T and magnetic field H in the range 0.56T6300 K,H66 Tfor 350 nm filmsannealed in air. Films with 06x60.03 show the superconducting resistive transition.The transition temperature Tc is below 3.3 K and the carrier densitynis about 1025–1026m−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 fieldHc2(T)for the film with x=0.01. From the slope of dHc2/dT, we obtain the coherence lengthξ(0)≈10 nm at T=0 K and a coefficient of electronic heat capacity that is small compared with those of other oxide materials.