Erbium oxide (Er2O3) films have been deposited by metal organic chemical vapor deposition on Si(001) using tris(isopropylcyclopentadienyl)erbium. The impact of Si surface passivation by the metal organic prior growth initiation was investigated. The correlation between the Er2O3 films structure, the optical response, the static dielectric constant (K), and density of interface traps is discussed. An Er-silicate interfacial layer with a thickness of 1.5 nm, a static dielectric constant of 10-12.4, and a density of interface traps of 4.2x10(10) cm(2) eV(-1) measured for a film with a physical thickness of 8.2 nm (with an equivalent oxide thickness of 2.7 nm) render Er2O3 an interesting candidate as a high-K dielectric.(c) 2007 American Institute of Physics.