Core Level Photoemission Measurements of Heterojunction Valence Band Offsets in Highly Strained Systems

The binding energy separation between the Si2p and Ge3d 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 heterojunction. 

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 Si2p- Ge3d energy difference on strained heterojunctions, allows 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.