La-silicate of (La2O3)(0.6)(SiO2)(0.4) was prepared by e-beam evaporation of mixed oxides target to control the chemical bonding state and band structure of La2O3 film on n-GaAs (001). Prior to deposition of La-silicate film, sulfur passivation was performed on the surface of GaAs. The composition and uniformity of La-silicate film were simulated from the ratio of photoelectron intensity, I-La (4d)/I-Si (2p), using angle resolved X-ray photoelectron spectroscopy. The formation of hydroxide phase was effectively prohibited when La-silicate is formed. Energy band gap of La2O3 and La-silicate were estimated as similar to 5.6 eV and similar to 6.5 eV, respectively, by combining valence band and absorption spectra. The change in the energy band structure with regard to n-GaAs was correlated with electrical properties. An enhanced conduction band offset of La-silicate is evidenced by Fowler-Nordheim tunneling mechanism. (c) 2005 Elsevier B.V. All rights reserved.