Electronic properties at the interface in oxide BiFeO$_{3}$/Nb-doped SrTiO$_{3}$ semiconductor

In oxide systems, the interface of the heterojunctions had attracted much attention due to the interesting properties of the low-dimensional electron confinement. In this work, by using cross-sectional scanning tunneling microscopy, the direct and local information of structural and electronic properties across the$ p-n$ heterojunction in the multiferroic BiFeO$_{3}$ films grown on Nb-doped SrTiO$_{3}$ substrate was investigated. Spectroscopy analysis of the point-to-point electronic properties allows us to realize how the asymmetrically electronic band alignment is formed at the interface. Further analysis of the evolution of the potential field across the interface also reveals that surface charge states, spontaneous polarization, and the $p-n$ contact contribute to the formation of the build-in field pointing from BiFeO$_{3}$ films to Nb-SrTiO$_{3}$ semiconductors.