| Strain relaxation in SiGe thin film heteroepitaxy has been investigated. Layers with 30% Ge were grown on Si substrates with unique surface orientations. Characterized by the surface normals, these substrates have surface normals which are rotated off of the [001] axis [111] crystalographic direction by up to 22 degrees. Specifically, we used surfaces rotated by 0 degrees, the (001) surface, 10 degrees, approximately the (118) surface, and 22 degrees, which lies about midway between the (114) and (113) surfaces. These could be considered high index or highly vicinal substrates. We have derived relationships which allow us to determine the amount of strain relaxation in a film grown on these off-axis substrates using Raman spectroscopy. Documentation of these data has demonstrated an approximate linear relationship between relaxation and film thickness. Transmission electron microscopy (TEM) was used to examine the dislocation structure at the interface. Misfit dislocations were found in regular arrays lined up with the intersection of the {lcub}111{rcub} planes with the individual surfaces forming a triangular pattern. A cataloging of the possible Burgers vectors for these dislocations has led to useful relations for determining strain relief caused by dislocation formation. The surface topography was determined using atomic force microscopy (AFM). For thin layers, tens of nanometers, images show a smooth corrugation with features on the order of 100 nm having no long-range order. For thick layers, 100 to 200 nm, images show the corrugation aligning over large ranges, greater than tens of micrometers. These long range corrugations were determined to be roughly aligned with the pattern of dislocations in the interface. These arrays of surface corrugations form unique patterns that change as a function of off-axis angle. A discrepancy between the amount of relaxation measured with Raman and that measured by counting dislocations in TEM has been attributed to organization of the surface morphology. |
