Effect of surface intermixing on the morphology of Sb-terminated Ge(100) surfaces

Abstract

The interaction of Sb with Ge(100) was investigated as a function of substrate temperature and Sb coverage using temperature programmed desorption, low energy electron diffraction, ion scattering, and scanning tunneling microscopy. An Sb desorption peak associated with multilayer physical adsorption was observed at 550 K while a second desorption peak at 980 K was attributed to Sb bound to the Ge surface. Four basic types of Sb clusters were identified at 320 K: a three-dimensional tetramer; a square, flat tetramer; dimers running perpendicular to the substrate dimer rows; and dimers running parallel to the dimer rows. The three-dimensional tetramer was observed to convert irreversibly to the flat tetramer, while the flat tetramer reversibly split to form the dimers. Diffusion of both the flat tetramers and the perpendicular dimers led to the formation of asymmetric $(2\mathrm{}\times 1)$ reconstructed islands. At 520 K, Sb started to displace Ge in the top layer creating pits at low Sb coverage. As the Sb coverage was increased, both islands and pits were observed. Intermixing between Sb and Ge was found in both the islands and the original surface layer. Intermixing, however, was limited between 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 severely and increased the amount of exposed Ge, even though no Sb desorbed at this temperature. The surface roughening was attributed to the increased surface area enabling Sb-Ge exchange without burying the lower surface tension 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 of the surfactant layer is not carefully controlled.