Atomic layer deposition (ALD) of Al2O3 is of interest for a wide range of micro-nanoelectronic applications, where the electrical properties of the deposited layers can be strongly affected by deposition conditions and post-deposition treatments. In this work, a mercury-probe capacitance-voltage characterization is carried out on Al2O3 films deposited on silicon by ALD at different temperatures and subjected to various thermal treatments in N-2 ambient. Effective positive charges located at the semiconductor/dielectric interface are encountered for the films deposited at the lowest temperature (100 degrees C). Positive V-fb shifts are always registered after the different thermal annealing conditions studied; however, the impact of the thermal treatments is found to be different depending on the deposition temperature. A significant negative charges build-up is observed after a 30 min anneal at 450 degrees C, where improved surface passivation properties are achieved. Interestingly, the hysteresis, as well as the V-fb shifts, clearly diminish for higher deposition temperatures or after a thermal anneal. However, the highest temperature treatments (>= 800 degrees C) result in significant interface states generation. Finally, exploratory experiments about the stability of the Al2O3 layers under UV-light irradiation (in the 200-300 nm wavelengths range) show that this can be responsible for a significant degradation of their electrical characteristics. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3559458] All rights reserved.