Tuning band alignment at a semiconductor-crystalline oxide heterojunctionvia electrostatic modulation of the interfacial dipole*

Charge transfer across semiconductor heterojunctions and the electric fields that arise therefrom underpin the functionality of virtually all device technologies. In conventional semiconducting heterojunctions, band alignments are rigid under doping and charge transfer. In contrast, here we demonstrate that band alignment can be altered through charge transfer at hybrid heterojunctions comprised of crystalline oxides and semiconductors. The interfacial dipole associated with bonding across the SrTiO3/Si heterojunction can be tuned through space charge, thereby enabling band offsets and ultimately band alignment to be altered via doping. Oxygen impurities in Si act as donors that create space charge by transferring electrons across the interface into SrTiO3. The space charge induces an electric field that modifies the interfacial dipole, thereby tuning the band alignment from type II to III. The transferred charge, accompanying built-in electric fields, and change in band alignment are manifested in electrical transport and hard x-ray photoelectron spectroscopy measurements. Ab initio models reveal the interplay between polarization and band offsets. We find that band offsets can be tuned by modulating the density of space charge across the interface. Modulating the interface dipole to enable electrostatic altering of band alignment opens additional pathways to realize functional behavior in semiconducting hybrid heterojunctions.