ELECTRICAL-CONDUCTIVITY OF SPUTTERED FILMS OF STRONTIUM-TITANATE

Among the most critical parameters in the fabrication of rf-sputtered SrTiO3 films is the argon/oxygen ratio in the sputter gas and the substrate temperature, both during sputtering and during postannealing. After sputtering at 500 °C, SrTiO3 layers on Al2O 3 substrates are partially crystalline. In this case the SrTiO 3 lattice is enlarged compared to the bulk material. With increasing temperatures of postannealing, the crystallites grow and the lattice shrinks. In particular, films that are sputtered with a sputter gas containing oxygen show an additional phase of TiO2 when they are annealed at temperatures of more than 1000 °C. This paper shows for the first time results of the investigation of sputtered SrTiO3 films on Al2 O 3 substrates as a function of oxygen partial pressure P(O 2). The measurements performed on the sputtered films indicate semiconducting properties in agreement with the bulk material: At temperatures between 700 and 1100 °C the electrical conductivity of sputtered layers changes from p-type to n-type as the oxygen partial pressure decreases from 1 to 10-15 bar. The enthalpy of oxidation in the SrTiO3 films is 1.24 eV, and the energy gap is 3.30 eV. These values are in agreement with those reported for bulk materials.