Scanning tunneling spectroscopy on the 6H-SiC(0001)(3 x 3) surface

Surface topographic (STM) and spectroscopic (STS) studies have been performed on the Si-terminated 6H-SiC(0001)(3 x 3) surface using a scanning tunneling microscope (STM) in ultrahigh vacuum. High-quality (3 x 3) overstructures have been prepared as observed by LEED and STM. The regular (3 x 3) surface sites revealed much weaker I(V) dependences as compared to the defect sites when measured using the constant tip-surface gap technique. The normalized (dI/dV)/(I/V) vs. V spectra exhibit distinct bands of empty and filled states, which are separated by 1.2 eV for both surface sites, respectively. The results thereby support a Mott-Hubbard-type model as used for the calculation of the density of states. However, the STS spectra become completely featureless in the range of small tip-surface distances and reveal a metallic-like Ohmic I-V dependence.