X-ray photoelectron spectroscopic evaluation of valence band offsets for strained Si1-xGex, Si1-yCy, and Si1-x-yGexCy on Si(001)

The crucial parameters which determine the electrical and optical behavior of a heterojunction are the valence and conduction band offsets. We demonstrate that carefully performed in situ x-ray photoelectron spectroscopic measurements allow the evaluation of valence band offsets in strained heteroepitaxial systems on Si(001). The result obtained for a Si0.75Ge0.25 alloy layer agrees very well with the known value, indicating the reliability of the used method. For Si0.977C0.023 alloy layers tensily strained on Si(001), we could not find any significant valence band offset to Si. The observed band gap narrowing is mainly dominated by a conduction band offset. Ternary strained Si0.727Ge0.25C0.023 alloy layers show the same valence band offset to Si as the appropriate binary Si0.75Ge0.25 alloy layers, that is, the valence band offset is dominated by Ge effects. (C) 1997 American Institute of Physics.