Superconductivity in transparent zinc-doped In₂O₃films having low carrier density

Thin polycrystalline zinc-doped indium oxide (In 2 O 3 -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 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 10 25 -10 26 m -3 . The annealed In 2 O 3 -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 (0) 10 nm at T = 0 K and a coefficient of electronic heat capacity that is small compared with those of other oxide materials.