| Sn-doped In2O3(ITO) film is a special class of materials combining high transparency in the visible region and low electrical resistivity, which have been widely applied in the solar cells, at panel displays and other photoelectric devices fields. Its room temperature resistivity r can be as low as 410 cm-W. Its carrier concentration, n, can reach a level as high as 2 0 21 310-10 cm-, which is two to three orders of magnitude lower than that in typical metals. ITO possesses free-carrier-like electronic properties. These features provide a good model system for studying some fundamental physical problems. In this thesis, the ultrathin ITO granular films, two-dimensional(2D) ITO films with different thicknesses, 3D homogeneous disordered ITO films, and series of In2O3 films with different thicknesses were fabricated by the standard rf sputtering method. We systematically studied the following physical problems: the influence of electron-electron interaction(EEI) on Hall coefficient and electrical conductivity in granular system, the growth process of ITO epitaxial films, the electron-electron scattering in 3D disordered conductors, as well as the effect of surface electrical state in In2O3 films, respectively.For ultrathin ITO granular films(~5-13 nm) deposited on glass substrates, we have measured systematically the Hall coefficient RH and the electrical conductivity σ between 2 and 300 K. A robust lnHDR μT law is observed in a considerably wide temperature range of 2 and ～120 K. This lnT dependence is explained as originating from the EEI effect in the presence of granularity as theoretically predicted. Meanwhile, we observed a Ds μln T law from 3 K up to several tens K, which also arose from the Coulomb interaction effect in inhomogeneous systems. In addition, we have extracted the electron dephasing time jt in homogeneous ITO films from the 2D weak-localization magnetoresistance studies. We found that the dephasing rate was governed by the small-energy-transfer electron-electron scattering process at low temperatures( /B eT < hk t), crossing over to the large-energy-transfer electron-electron scattering process at several tens of kelvins( /B eT > hk t)。For 2D ITO films deposited on YSZ substrates, we systematically study the structures and electrical transport properties of a series of ITO films with thickness t ranging from ~5 to ~53 nm. SEM and XRD results indicate that the t ￡16.8 nm films are polycrystalline, while those t 326.7 nm films are epitaxially grown along [100] direction. For t 326.7 nm films, our observed the lnT dependence of sheet conductance sWcan be well described by Altshuler and Aronov EEI theory, and the ratios of relative change of Hall coefficient /H HDR R to relative change of resistance DR/ RW Ware ?2, which is quantitatively consistent with EEI theory in homogeneous disordered system. For the t ￡16.8 nm films, the temperature behaviors of sheet conductance and Hall coefficient can only be quantitatively described by the current theory of EEI effect in the presence of granularity. In addition, we extract the intergranular tunneling conductance of each film by comparing Ds μln T data with the predication of EEI theories in granular metals. It is found that when the tunneling conductance is less than the conductance of a single ITO grain, the ITO film reveals granular metal characteristics in transport properties; conversely, the film shows transport properties of homogeneous disordered conductors.For a series of homogeneous disordered ITO films(~1 um), we have measured the low field magnetoresistances in the temperature range of 4-35 K. The electron dephasing rate1 /jt as a function of T for each film was extracted by comparing the magnetoresistance data with the 3D weak-localization theoretical predictions. We found that the extracted 1 /jt varies linearly with T3/2. Furthermore, at a given T, 1/jt varies linearly with 5/ 2 3/ 2Fk l- -, where kF is the Fermi wave number and l is the elastic mean free path of electrons. These features are well explained in terms of the small-energy-transfer electron-electron scattering time in 3D disordered conductors. This electron dephasing mechanism dominates over the electron-phonon scattering process because the carrier concentrations in our films are ~3 orders of magnitude lower than those in typical metals, which resulted in a greatly suppressed electron-phonon relaxation rate.We performed thickness-dependent conductivity and Hall measurements in epitaxial In2O3 films with thicknesses ranging from ~9.0 to ~956 nm, finding that the ultrathin film conductivity reaches up to 4000 S/m and is about 1 order of magnitude larger than that of the thicker films. The measurements of bandgap and PL spectra reveal that the surface layer has an electronic structure which differs from that of the bulk. A band model determined that surface oxygen vacancy(VO) occupied the shallow donor states, whereas the bulk oxygen defect level is too deep to produce large densities of free electrons. The surface VO is the physical origin of high conductivity in TCOs films. |
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