Structure and energetics of segregated and non-segregated H : Ge(001)/Si and Cl : Ge(001)/Si

The equilibrium atomic geometry, energetic stability and chemical bonding f or H and Cl passivation of the Si/Ge(001)-(2 x 1) surface have been studied by applying the ab initio pseudopotential method. In a recent theoretical work, a segregated structure in which Si occupies the second layer while Ge floats to the surface was found to be energetically favourable by 0.38 eV per dimer compared with the non-segregated Si-capped structure. Upon hydrog en passivation, the situation is reversed: the non-segregated structure bec omes energetically favourable by 0.08 eV per dimer compared with the segreg ated structure. For chlorine passivation, this energy difference is 0.3 eV per dimer. For the non-segregated H(Cl):Ge(001)/Si system, the Si dimer bec omes symmetric with the bond length elongated from 2.26 Angstrom to 2.39 An gstrom (2.42 Angstrom). For the segregated H(Cl):Ge(001)/Si system, the Ge dimer also becomes symmetric with the bond length elongated from 2.39 Angst rom to 2.45 Angstrom (2.46 Angstrom). (C) 2000 Elsevier Science B.V. All ri ghts reserved.