Effect of surface intermixing on the morphology of Sb-terminated Ge(100) surfaces - art. no. 195309

The interaction of Sb with Ge(100) was investigated as a function of substr ate temperature and Sb coverage using temperature programmed desorption, lo w energy electron diffraction, ion scattering, and scanning tunneling micro scopy. An Sb desorption peak associated with multilayer physical adsorption was observed at 550 K while a second desorption peak at 980 K was attribut ed to Sb bound to the Ge surface. Four basic types of Sb clusters were iden tified at 320 K: a three-dimensional tetramer; a square, flat tetramer; dim ers running perpendicular to the substrate dimer rows; and dimers running p arallel to the dimer rows. The three-dimensional tetramer was observed to c onvert irreversibly to the flat tetramer, while the flat tetramer reversibl y split to form the dimers. Diffusion of both the flat tetramers and the pe rpendicular dimers led to the formation of asymmetric (2 x 1) reconstructed islands. At 520 K, Sb started to displace Ge in the top layer creating pit s at low Sb coverage. As the Sb coverage was increased, both islands and pi ts were observed. Intermixing between Sb and Ce was found in both the islan ds and the original surface layer. Intermixing, however, was limited betwee n 520 K and 620 K when the Ge surface was covered with 1 monolayer or more of Sb, resulting in the smoothest Sb-terminated Ge surfaces. Regardless of how the Sb layer was prepared, annealing at 800 K roughened the surface sev erely and increased the amount of exposed Ge, even though no Sb desorbed at this temperature. The surface roughening was attributed to the increased s urface area enabling Sb-Ge exchange without burying the lower surface tensi on Sb beneath the surface. Antimony is used as a surfactant to promote the growth of flat Ge films. The results demonstrate, however, that intermixing can lead to the surfactant severely roughening the surface if the growth o f the surfactant layer is not carefully controlled.