Scanning Tunneling Spectroscopy Investigation of the Strained Si_1−xGe_x Band Structure

The band offsets and band gap are the most important parameters that determine the electrical and optical behavior of a heterojunction. In situ scanning tunneling spectroscopy was employed to measure the valence-band offset of strained Si_1−xGe_x-on-Si (100) for the first time. The valence-band offsets of the strained Si_0.77Ge_0.23 and Si_0.59Ge_0.41 on Si(100) were found to be 0.21 and 0.36 eV, respectively. The results were in good agreement with theory and with results from other experimental methods. Due to band bending and surface states, it was difficult to determine the conduction band edge at the interface of the Si_1−xGe_x/Si exactly but we found that the conduction band offset is much smaller than the valence-band offset.