| Indium oxide thin films doped with different niobium concentrations, 0.7%--9.1%, were grown epitaxially on yttria-stabilized zirconia (001) substrates by concurrent magnetron sputtering using In2O 3 and Nb targets with a substrate temperature of 550°C. X-ray diffraction corroborated the existence of a single epitaxial phase, except for x=9.1% Nb sample. X-ray photoelectron spectroscopy revealed that Nb charge state varies between +2 to +5. Introduction of Nb can decrease resistivity down to rho(300K)=4.1x10-4 Ohm-cm for x=3.2% Nb, which in addition to its transparency >97% in the visible range makes this transparent conductor a possible candidate for industrial applications. Low-temperature magneto-transport measurements show an anomalous increase of resistivity at low temperatures which, in addition to the negative magnetoresistance found at low temperatures, is interpreted as a signature of weak localization and its analysis show that electron interaction effects dominate low temperature scattering. Optical absorption analysis in the UV-Vis and mid-IR range reveals the bands curvature deviates from parabolic, as judged by the change in effective mass with doping level. Additionally, band tails are found for all samples, qualitatively explaining the discrepancy of absorption VS emission energies for indium oxide as a tail to tail transition. Low-temperature photoluminescence show effects of negative thermal quenching for all Nb-doped samples and this phenomenon is interpreted as the existence of energy barriers which carriers have to surpass in order to recombine at low temperatures. |
