Recent Developments in Scanning Tunneling Spectroscopy of Semiconductor Surfaces

Several recent developments in scanning tunneling spectroscopy (STS) of semiconductor surfaces are reviewed. First, the normalization of spectra is discussed, which for the Si(111)2x1 surface is found to produce a small shift in the apparent position of band edges. With this correction, the surface band gap measured by STS is found to be in good agreement with that obtained by other experimental and theoretical techniques. Second, it is shown for the SiC(0001) root(3) x root(3) surface that the tunneling spectra show a remarkable evolution with decreasing current, and at pA levels they reveal a Mott-Hubbard gap for the surface states, in agreement with that seen by other methods. Finally, a detailed discussion is presented on the absence of electronic effects for the tunnel current into empty states of III-V (110) cleaved surfaces. From this result it is demonstrated that one can use observed strain induced displacements of such surfaces to yield information on the chemical composition of the underlying material.