  Strontium titanate, SrTiO3, a widely used substrate material for electronic
oxide thin film devices, has provided many interesting features. In a
combination with a similar oxide material, LaAlO3, it has recently received
great interest. It was suggested that two-dimensional electron gas is formed at
the interface between SrTiO3 and LaAlO3, resulting in high electrical
conductivity and mobility. In this report we demonstrate that the transport
properties in those heterostructures are very sensitive to the deposition
parameters during thin film growth. Using cathode- and photoluminescence
studies in conjunction with measurements of electrical transport properties and
microstructure we show that the electronic properties observed at a
LaAlO3/SrTiO3 interface can be explained by oxygen reduced SrTiO3. In addition,
we demonstrate that oxygen can be pushed in and out of the sample, but that
re-oxygenation of an initially oxygen depleted LaAlO3/SrTiO3 heterostructure is
partly prevented by the presence of the film.
