Core-level photoemission measurements of valence-band offsets in highly strained heterojunctions: Si-Ge system

The binding-energy separation between the Si 2p and Ge 3d core levels has been measured on pseudomorphically strained heterojunctions consisting of Si on Ge(100) and Ge on Si(100) using x-ray photoemission. Analysis shows that the core-level binding energies referenced to the top of the valence band depend explicitly on strain. As a consequence, the use of core-level data from unstrained materials is inappropriate for determining valence-band offsets in highly strained heterojunctions. Our data have been supplemented by calculations of the relative core–valence-band deformation potentials. These results, together with the calculated uniaxial component of the valence-band splitting and the measured $E_{\mathrm{Si}2\mathrm{p}\mathrm{-}{E}_{\mathrm{Ge}3\mathit{d}}}$ energy difference on strained heterojunctions, allow us to estimate valence-band offsets of 0.74±0.13 and 0.17±0.13 eV for Ge on Si(100) and Si on Ge(100), respectively.