Temperature dependence of resistance and thermopower of thin indium tin oxide films

We have measured the resistance and thermopower of a series of RF sputtered and annealed indium tin oxide (ITO) thin films from 300 K down to liquid-helium temperatures. Thermal annealing was performed to modulate the levels of disorder (i.e., resistivity) of the samples. The measured resistances are well described by the Bloch–Grüneisen law between 150 and 300 K, suggesting that our thin films are metallic. At lower temperatures, a resistance rise with decreasing temperature was observed, which can be quantitatively ascribed to the two-dimensional electron–electron interaction and weak-localization effects. The thermopowers in all samples are negative and reveal fairly linear temperature dependence over the whole measurement temperature range, strongly indicating free-electron like conduction characteristics in ITO thin films. As a result, the carrier concentration in each film can be reliably determined. This work demonstrates that ITO films as thin as 15 nm thick can already possess high metallic conductivity.