PNNL

Abstract

The epitaxial n-STO/p-Ge(001) interface shows considerable promise for harvesting visible sunlight to drive the hydrogen evolution reaction (HER) associated with water splitting [1]. The Ge band gap is small (0.66 eV) and band alignment with STO is favorable for electron-hole pair creation and separation. Moreover, the conduction band minimum of STO is above the HER half-cell potential, allowing for energetically favorable electron transfer across the heterojunction/liquid interface and coupling to the HER. In determining the band alignment for n-STO/p-Ge by XPS, we have previously noted a curious broadening in the Ge 3d core-level line shape relative to that for pure, clean p-Ge(001)-(2x1) [2]. In principle, such broadening could come from a chemically shifted feature resulting from an interface formation product, or from the presence of a built-in potential within the Ge. Data taken on heterostructures with thinner (