Direct Measurement of Band Edge Profiles at Epitaxial Oxide/Semiconductor Heterojunctions*

Band edge profiles for semiconductor heterojunctions can be approximated using transport data and/or calculated from first principles, assuming an atomistic materials structure. However, direct and accurate experimental measurement has not been possible by traditional means. We have used hard x-ray photoelectron spectroscopy (HAXPES) to extract band edge profiles from core-level spectra by developing an effective algorithm that fits experimental heterostructure spectra to sums of flat-band spectra, measured for pure reference materials, in which the binding energies are exhaustively varied to sample the phase space of physically reasonable potential profiles over all layers within the HAXPES probe depth. We apply this method to heterojunctions of n-SrNb_xTi_1-xO₃ and intrinsic Si(001), prepared by molecular beam epitaxy. Heterojunction formation results in a Si hole gas and a surface depleted dead layer in the SrNb_xTi_1-xO₃. The band edge profiles resulting from the HAXPES fitting reveal both of these features, and match what is expected based on Hall data remarkably well. In this talk, we present highlights of this analysis.