Weak Localization and Correlation Effects in Indium-Tin-Oxide Films. II. Two-to-Three Dimensional Transition and Competition between Localization and Superconductivity

A study was made of the temperature and magnetic field dependence of the conductivity in indium-tin-oxide (ITO) films for two and for three dimensional electron systems. Clear evidence of a three dimensional localization as well as Coulomb interaction effects is observed above 15 K in relatively thick samples (≥400 Å). On application of a magnetic field, a two-to-three dimensional transition is observed above a critical field, that depends on the sample thickness. From the temperature dependence of conductivity for the thickest film (20000 Å), it was found that ITO shows a superconducting nature below 3.5 K. For the sample with an intermediate thickness (1000 Å), temperature and magnetic field dependence of conductivity is discussed from the view-point of the competition between electron localization and superconductivity.