Logarithmic Temperature-Dependent Resistance of an indium tin oxide thin film from 300 K down to dilution refrigerator temperatures

Indium tin oxide (ITO) is a technologically relevant transparent conducting oxide, with a wide range of applications such as electrodes in organic light emitting diodes, solar cells, and transparent gates for photonic devices. We measured the resistance of a 20 nm thick ITO film over four orders of magnitude in temperature from 300 K down to dilution refrigerator temperatures. Three regions are distinguishable in the resistance as a function of temperature: (i) 300 K – 140 K, where the resistance decreases with decreasing temperature consistent with electron-phonon scattering, (ii) 140 K – 0.1 K where the resistance increases with rising temperature, and (iii) less than 0.1 K, where the temperature dependence weakens, possibly due to thermal decoupling of the charge carriers. In region (ii) we observe a logarithmic rise of the resistance with decreasing temperature with a significant contribution from weak localization (WL), consistent with previous reports. We also measured the temperature evolution of the magnetoresistance and Hall resistance. We observed a strong WL peak at lower temperatures, which broadens and decreases with increasing temperatures until it disappears at about 120 K, while the carrier concentration remains constant. Our results, together with microstructural analysis, give us insight into the quantum-coherent transport in these (possibly granular) materials.