Compositional modulations in GexSi1−x heteroepitaxial layers

A study is presented of compositional modulations (i.e., so‐called banding) in heteroepitaxial strained layers of nominally uniform Ge0.1Si0.9 grown by molecular‐beam epitaxy (MBE). The oscillatory nature of the modulations is studied by transmission electron microscopy (TEM) techniques and the results show that the contrast modulations have a periodicity of ∼23 nm when 1‐μm‐thick epilayers are grown on a rotated substrate. For growth on an unrotated substrate, contrast modulations are still observed but they are less regular. It is further shown that the electron microscope image features are dominated by strain contrast and not structure factor contrast. The presence of strain is consistent with there being a small change in lattice parameter between adjacent bands of material, together with elastic relaxations afforded by the proximity of the thin‐film surfaces. It is concluded that these variations in the lattice parameter are due to the compositional modulations. Limits on the magnitude (Δx) of the c...