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 ESi2p-EGe3d 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.