First stages of Ge adsorption on the Si(111)7 × 7 surface: experimental and theoretical studies

Abstract

We present both experimental and theoretical studies of the adsorption of germanium on the reconstructed Si(111)7 × 7 surface. Catalytically decomposed germane (GeH∗ 4) has been used as the primary gas source. Ge adsorption on Si(111)7 × 7 has been experimentally characterized by surface analysis techniques such as low energy electron diffraction (LEED) and angle resolved ultraviolet photoelectron spectroscopy (ARUPS). The exposure of the Si(111)7 × 7 surface to 10 4 L GeH∗ 4 leads to the formation of a Ge : Si(111)7 × 7 surface; the electronic structure has been determined by ARUPS spectra recorded along the [1̄21̄] azimuthal direction corresponding to the \\ ̄ gG-M̄ line in the 1 × 1 surface Brillouin zone of Si(111). Various Ge adsorption mechanisms are theoretically investigated in the framework of the crystalline extension of the extended Hückel theory (EHT). Our results show that the substitution of surface Si atoms by Ge atoms is hardly possible, while the addition of Ge atoms seems to be more acceptable. We consider the possibility of Ge adsorption on threefold filled sites (T4), threefold hollow sites (H3), on top of corner — and center — adatoms, as well as rest atoms and corner atoms. The faulted and unfaulted parts of the 7×7 unit cell have been distinguished.