Charge carrier transport mechanisms in nanocrystalline indium oxide

The charge transport properties of nanocrystalline indium oxide (In2O3) are studied. A number of nanostructured In2O3 samples with various nanocrystal sizes are prepared by sol-gel method and characterized using various techniques. The mean nanocrystals size varies from 7-8 nm to 18-20 nm depending on the conditions of their preparation. Structural characterizations of the In2O3 samples are performed by means of transmission electron microscopy and X-ray diffraction. The analysis of dc and ac conductivity in a wide temperature range (T = 50-300 K) shows that at high temperatures charge carrier transport takes place over conduction band and at low temperatures a variable range hopping transport mechanism can be observed. We find out that the temperature of transition from one mechanism to another depends on nanocrystal size: the transition temperature rises when nanocrystals are bigger in size. The average hopping distance between two sites and the activation energy are calculated basing on the analysis of dc conductivity at low temperature. Using random barrier model we show a uniform hopping mechanism taking place in our samples and conclude that nanocrystalline In2O3 can be regarded as a disordered system. (C) 2014 Elsevier B. V. All rights reserved.