Thin films of oxygen-deficient perovskite phases by pulsed-laser ablation of strontium titanate

An oxygen-deficient phase has been formed by pulsed-laser ablation of strontium titanate under vacuum conditions (10^-70.3em0exmbar). By the complementary use of Rutherford backscattering spectrometry and x-ray diffraction, the composition and structure of films were determined. A large oxygen deficiency is revealed in the films as the corresponding formula is SrTiO2.5. This understoichiometry means that Ti³⁺ are present in such films, while only Ti⁴⁺ is observed in stoichiometric compound (SrTiO₃). The presence of Ti³⁺ species in the SrTiO2.5 films was checked by x-ray absorption spectroscopy. The SrTiO2.5 films were found to crystallize in the cubic perovskite structure with a lattice parameter of 0.400.3em0exnm, considerably higher than that of the stoichiometric compound (0.390.3em0exnm). The SrTiO2.5 films were epitaxially grown on MgO single-crystal substrates, with a ``cube-on-cube'' in-plane orientation with the substrate. In contrary to stoichiometric SrTiO₃ films which are perfectly insulating, the SrTiO2.5 films were found to be conductor or semiconductor at room temperature, depending on the growth temperature. Resistivities at room temperature in the 10^-3--10^-20.3em0exΩ0.3em0excm range are thus obtained.