Atomic and electronic structure of the cleaved 6H-SiC(1120) surface

We present a combined cross-section scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) and ab initio simulations study of the nonpolar (11 (2) over bar0) cleaved surface of 6H-SiC. The experimental results show an unreconstructed surface in agreement with theory. Upon truncation, two surface bands appear inside the semiconductor band gap: one empty band localized on the Si atoms and one filled band on the C atoms. According to the STS experimental results on n-doped samples, the Fermi energy is pinned at the surface inside the band gap. By comparison of STM filled and empty states topographies we propose that on the fresh cleaved surface the Fermi level lies at the bottom of the Si-like band. The calculated STM images reproduce the experimental contrast of the 6H stacking sequence and its bias dependence very well.