Crack formation in strained SiGe grown on Ge-on-Si (111) and its suppression by patterning substrates

We study surface morphologies, defect structures and strain states in tensile-strained SiGe layers grown on Ge-on-Si(111) or Ge(111) substrates. It is found that at the initial stage of partial strain relaxation, cracks are generated on the equivalent (111) slip planes and followed by formation of surface ridge roughness along the intersections of the slip planes and the surface. These cracks and resultant ridge roughness can be avoided by the patterning of the Ge-on-Si(111) substrate presumably owing to stress relief at the edges of the patterns, indicating that this method is promising for strained SiGe-based spintronics and high mobility device applications.