The effect of mesa shape upon the threading dislocation density in Ge epilayers on Si was studied. Etch-pit counting at the surfaces showed that post-growth annealing reduced the threading dislocation densities in Ge mesa structures on Si, and in the blanket Ge layers. Dry-etched mesas with vertical side-walls exhibited dislocation densities which were identical to those for the blanket layers; indicating that the reduction in threading dislocation density in dry-etched mesas was due mainly to the annihilation of dislocations having opposite Burgers vectors, and that the motion of dislocations to the mesa-edges did not contribute. However, selective-grown mesas with inclined (311) facet side-walls exhibited lower dislocation densities than those of blanket layers; indicating that the dislocations could glide beyond the mesa edges. Shear stresses, thermally introduced into the Ge, were responsible for dislocation glide motion, and so the present results suggested that selective-grown mesas should be different to dry-etched mesas in terms of the shear stresses which accumulated during annealing. Strain simulations of these mesa structures showed that the magnitudes and distributions of thermally induced shear stresses were quite different near to the top edges between the mesa structures.

Effect of Mesa Shape on Threading Dislocation Density in Ge Epitaxial Layers on Si after Post-Growth Annealing. Y.Takada, J.Osaka, Y.Ishikawa, K.Wada: Japanese Journal of Applied Physics, 2010, 49, 04DG23