Tuning band alignment at a semiconductor-crystalline oxide heterojunction via electrostatic modulation of the interfacial dipole

TL;DR

This study shows how doping-induced space charge can electrostatically tune the band alignment at a SrTiO3/Si heterojunction by modifying the interfacial dipole, enabling control over electronic properties.

Contribution

It introduces a method to tune band alignment via electrostatic modulation of the interfacial dipole using doping-induced space charge.

Findings

Band alignment can be switched from type-II to type-III.

Doping controls the interfacial dipole and band offsets.

Electrical and spectroscopic measurements confirm the tuning.

Abstract

We demonstrate that the interfacial dipole associated with bonding across the SrTiO3/Si heterojunction can be tuned through space charge, thereby enabling the 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 type-III. The transferred charge, resulting in 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. Functionalizing the interface dipole to enable electrostatic altering of band alignment opens new pathways to realize novel behavior in semiconducting heterojunctions.