Atomic Resolution and First Principles Study of the Electronic Structure at SrTiO$_{3}$/GaAs Hetero-interfaces

We examined ultra-thin SrTiO$_{3}$ films deposited on As-terminated GaAs (001) using molecular beam epitaxy under various O$_{2}$ partial pressures. Atomic-resolution Z-contrast images of different SrTiO$_{3}$ films were obtained using the aberration-corrected JEOL JEM-ARM200CF operated at 80 kV. Using atomic-column resolved EELS, our analysis of the Ti and O near-edge fine structure reveals different bonding configurations at the interface resulting from different growth methods. These results strongly suggest that a Ti pre-layer deposition alleviates the oxidation of the substrate and consequently the Fermi level pinning at the interface, as reported before. We also examined BaTiO$_{3}$ thin films grown on GaAs (001) with an ultrathin SrTiO$_{3}$ buffer layer. Interfacial charge distribution related to the polarization of BaTiO$_{3}$ thin film will be studied using atomic-resolution Z-contrast images, annular bright field images and EELS. Using first-principles DFT calculations, we analyze the formation energies of Ti-related impurity defects in different GaAs surface reconstructions to help interpret the electron microscopy experiments.