Structural and Magnetotransport Study of SrTiO$_{3-\delta}$/Si Films Grown by Molecular Beam Epitaxy

SrTiO$_{3}$ (STO) films were grown on p-Si (001) substrates using molecular beam epitaxy (MBE). Oxygen vacancies were introduced by controlling the Oxygen resulting in SrTiO$_{3-\delta}$ with $\delta$ $\sim$ 0.02{\%} for the lowest pressure. The single phase STO/Si films were of high crystalline quality as verified by x-ray diffraction, transmission electron microscopy, and had an rms roughness of less than 0.5nm measured by atomic force microscopy. Transport measurements were performed on the STO/Si structures in a Van der Pauw configuration. We measured resistance as a function of temperature, T $=$ 3K-300K and as a function of an applied magnetic field , H$=$0 to $\pm$ 9T. The resistivity decreased from 1 Ohm cm to 3x10$^{-2}$ Ohm cm as the film thickness increased (3nm-60nm) for all temperatures. The magnetoresistance (MR) shows a reproducible trend for all films, the MR is positive at 300K, becomes negative between 200K and 100K and at low temperatures T$=$3-20K the MR is positive at low H$=$0 to $\pm$ 2T but at high fields, it starts decreasing again. The MR behavior combined with the Hall effect data indicates the presence of localized electrons that delocalize with H and T.