The effects of oxidant (H2O) feeding time and growth temperature on the C- and N-related impurities and Si diffusion behavior in the atomic-layer-deposition (ALD) of La2O3 films were examined using in situ Xray photoelectron spectroscopy analysis. Longer H2O pulse time assisted in a complete ligand exchange reaction during ALD, which suppressed the accumulation in the film of residual C- and N-related byproducts/impurities with low bonding energy that originated from incompletely reacted ligands and carboxyl compound intermediate phases. In addition, this phenomenon slightly increased the growth rate of the La2O3 film even under the nominal growth-saturated ALD conditions because the concentration of residual C- and N-related byproducts/impurities, which disturb the formation of the active sites, was reduced. The band gap energy of the films increased slightly with H2O feeding time due to the reduction of C impurities. The residual C- and N-related byproducts/impurities and carboxyl compound intermediate phases in the La2O3 films were effectively reduced by increased growth temperature. However, increased growth temperature enhanced the Si out-diffusion from the substrate into the films and decreased the film growth rate because the surface functional groups for sequential film growth during ALD were reduced. The enhanced Si out-diffusion increased the band gap of the film and the valence band off-set with respect to the Si substrate. (C) 2013 Elsevier B.V. All rights reserved.