Electronic structure of the C defects of Si(001) measured by scanning tunneling spectroscope at room and low temperature (80 K)

We have studied the electronic characteristics of the C defects of Si(001) by scanning tunneling microscopy (STM) and spectroscopy at 80 K and room temperature. At room temperature, the C defects had a metallic feature as reported before. However, at 80 K, the C defects that do not act as phase shifters were found to have a metallic feature similar to those at room temperature, while the C defects that act as phase shifters have a semiconductive feature with a band gap of −0.5 V. This indicates that the buckled dimers surrounding the C defects influence and change the electronic structure of the C defects at low temperature. When compared with the buckled dimers, the semiconductive C defects have a state with strong intensity located 0.5 V above the Fermi level and the metallic C defects have a prominent state just above the Fermi level. These states are the origin of the appearance of the C defects as bright protrusions in the empty state STM images.