Scanning tunneling microscopy and ab initio studies of precursor states of Ga-induced cluster on Si(001) surface

The growth processes and structures of Ga layers formed on a Si(0 0 1) surface have been studied by scanning tunneling microscopy (STM) and ab initio calculation. The precursor states of the Ga clusters that compose the Si(0 0 1) 8 X n-Ga (n = 4, 5, 6) structures are observed in addition to the 2 X 2- and 4 X 2-Ga structures at a Ga coverage of 0.55 ML at 300 deg C. There are two types of precursor clusters whose protrusions are observed as different shapes in filled-state STM images. We compare the observed STM images with the simulated ones to identify the possible structural models. From the results, we determine the structure of each precursor cluster. On the basis of the results, the formation processes of the cluster are discussed.