STM STUDY OF GEOMETRIC AND ELECTRONIC-STRUCTURES OF GE DIMERS ON SI(001)

The surface topography of an isolated Ge dimer row on the Si(001) surface traced by a scanning tunneling microscope (STM) was examined by calculating the electronic distribution above a cluster of a Ge dimer and several Si atoms with the semi-empirical molecular orbital method. The Ge layer of 0.1 ML thick was deposited on the Si(001) surface at 300-degrees-C. Then the STM images of the Ge-deposited Si surface exhibited few symmetric and many asymmetric dimer rows. It was also noticed that the Ge dimers induced the buckling of the substrate Si dimer rows. The observed traces of a scanning tip and the present simplified calculation of the electronic distribution suggest the small tilt angle of the buckled Ge dimers 4-6-degrees. However, the calculated difference in the orbital energies between the Si and Ge dimers on the Si(001) surface clearly suggests a buckling susceptibility of Ge dimers higher than of Si dimers.