Effect of preparation conditions on properties of atomic layer deposited TiO2 films in Mo–TiO2–Al stacks

TiO2 films were grown by atomic layer deposition on Mo electrodes in order to elucidate the dominating conductance mechanism and its dependence on the growth chemistry. TiCl4 and Ti(OC2H5)4 served as titanium precursors, and H2O or H2O2 as oxygen precursors. The films grown at lower temperatures were amorphous. With increasing growth temperatures the crystallization first started in the TiCl4–H2O process. The films grown in this process were clearly leakier compared to the films grown from Ti(OC2H5)4 and H2O and from Ti(OC2H5)4 and H2O2. In the Ti(OC2H5)4-based processes, the application of H2O2 instead of H2O resulted in the films with considerably lowered conductivity, although structural differences in these films were insignificant. Space–charge-limited currents were prevailing in all our amorphous Mo–TiO2–Al packages. Measurements at different temperatures suggested quite high trap densities likely due to the presence of impurities and structural disorder, while the strong differences in conductivity seemed to be due to different densities of gap states.