1ST STAGES OF GE ADSORPTION ON THE SI(111)7X7 SURFACE - EXPERIMENTAL AND THEORETICAL-STUDIES

We present both experimental and theoretical studies of the adsorption of germanium on the reconstructed Si(111)7 x 7 surface. Catalytically decomposed germane (GeH) has been used as the primary gas source. Ge adsorption on Si(111)7 x 7 has been experimentally characterized by s urface analysis techniques such as low energy electron diffraction (LE ED) and angle resolved ultraviolet photoelectron spectroscopy (ARUPS). The exposure of the Si(111)7 x 7 surface to 10(4) L GeH4 leads to th e formation of a Ge:Si(111)7 x 7 surface; the electronic structure has been determined by ARUPS spectra recorded along the [121BAR] azimutha l direction corresponding to the GAMMABAR-MBAR line in the 1 x 1 surfa ce Brillouin zone of Si(111). Various Ge adsorption mechanisms are the oretically investigated in the framework of the crystalline extension of the extended Huckel theory (EHT). Our results show that the substit ution of surface Si atoms by Ge atoms is hardly possible, while the ad dition of Ge atoms seems to be more acceptable. We consider the possib ility of Ge adsorption on threefold filled sites (T4), threefold hollo w sites (H3), on top of comer - and center - adatoms, as well as rest atoms and comer atoms. The faulted and unfaulted parts of the 7 x 7 un it cell have been distinguished.