SrTiO3 (100) epitaxial films with thicknesses of 3, 1 m, and 250 nm were prepared on MgO (100) substrates by pulsed-laser deposition. The electrical conductivities of the thin films were systematically investigated as a function of temperature and ambient oxygen partial pressure. This was made possible by using a specially designed measurement setup, allowing the reliable determination of resistances of up to 25 GΩ in the temperature range of 600°–1000°C under continuously adjustable oxygen partial pressures ranging from 10−20 to 1 bar. The capabilities of the measurement setup were tested thoroughly by measuring a SrTiO3 single crystal. The well-known characteristics, e.g., the decline of the conductivity with a slope of –1/4 under reducing conditions and the opposite +1/4 behavior in oxidizing atmospheres, are found in the log()–log(pO2) profiles of the epitaxial films. However, the p-type conductivity decreases, and the n-type conductivity increases with decreasing film thickness. This phenomenon is attributed to the charge carrier redistribution in the surface space charge layers. Owing to the high surface-to-volume ratio, the space charge layers play an important role in thin films.
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Document Type: Research Article
Institut für Festkörperforschung and Center of Nanoelectronic Systems for Information Technology, Forschungszentrum Jülich, 52425 Jülich, Germany
Institut für Schichten und Grenzflächen and Center of Nanoelectronic Systems for Information Technology, Forschungszentrum Jülich, 52425 Jülich, Germany
Publication date: 2006-09-01