Charge Transfer and Built-in Electric Fields between a Crystalline Oxide and Silicon

We report charge transfer and built-in electric fields across the epitaxial SrNb_{x}Ti_{1-x}O_{3-δ}/Si(001) interface. Electrical transport measurements indicate the formation of a hole gas in the Si and the presence of built-in fields. Hard x-ray photoelectron measurements reveal pronounced asymmetries in core-level spectra that arise from these built-in fields. Theoretical analysis of core-level spectra enables built-in fields and the resulting band bending to be spatially mapped across the heterojunction. The demonstration of tunable charge transfer, built-in fields, and the spatial mapping of the latter, lays the groundwork for the development of electrically coupled, functional heterojunctions.