Tantalum pentoxide (Ta2O5) thin layers were grown on Si(100) by evaporation of Ta in an atomic oxygen plasma. The physical and electrical properties of 1000 Angstrom-thick as-deposited films were evaluated. Films grown at 650 degrees C without the presence of the plasma (molecular oxygen) were oxygen-deficient and poorly crystallized, whereas layers grown in the plasma (atomic oxygen) were stoichiometric (within 5%) and crystallized in the beta-Ta2O5 phase. A minimum flux of atomic oxygen during deposition, more than that required for growing films within 5% correct stoichiometry, was crucial for the suppression of the film leakage current. The electrical characterization of amorphous Ta2O5 films grown at 400 degrees C resulted in I-V curves exhibiting an ohmic behaviour at low electric fields, <2 MV cm(-1) (resistivity 10(14) Omega cm), and a leakage current density less than 10(-8) A cm(-2) at 1 MV cm(-1). The measured relative dielectric constant of amorphous Ta2O5 films was 26.