Sb-Mediated Si heteroepitaxial growth on Ge(0 0 1)

Silicon heteroepitaxial growth on Ge(0 0 1) was studied with and without an Sb surfactant using scanning tunneling microscopy. Growth was studied at 570 K where Ge segregation was kinetically inhibited but Sb segregation was not. Without Sb, elongated rectangular 2D islands were initially observed. As the 2D islands grew they left behind long, straight trenches in the first layer that paralleled the island dimer rows. Second layer islands grew until they reached the trenches and formed double height steps. A barrier to descend the double height steps along with nucleation at domain boundaries in the second layer islands then caused 3D pyramids followed by more rounded 3D mounds to form. The 3D features caused the surface roughness to rapidly increase with Si coverage. In contrast, Si growth on Sb-terminated Ge(0 0 1) led to a high density of smaller, more isotropic islands. The growth was still not layer-by-layer, however, the surface roughness increased only very slowly with coverage. The smoother growth was attributed to the change in island shape. Because diffusion along dimer rows is much faster than across them, for the same island area, the downward flux is enhanced on square islands compared to islands elongated along their dimer row direction. In addition, the shape change prevents the long straight trenches from forming in the first layer that subsequently caused the 3D pyramids and mounds to form. The results for Si are compared with previous data for Ge homoepitaxy with and without Sb.