Process and defect-induced surface morphology of relaxed GexSi1-x films

We have investigated the surface morphology of relaxed, compositionally graded GexSi1-x structures to study the influence of defect-related strain fields on film growth. Quantitative topographic measurements via scanning force microscopy show that the roughness associated with the cross-hatch patterns, due to underlying misfit dislocations beneath the surface, increases as the final Ge concentration or the grading rate increases. We further show that strain fields arising from the termination of threading dislocations at the surface result in shallow depressions. In addition to the as grown samples, we have also studied the morphology of processed Si, Ge, and GexSi1-x surfaces. Protrusions are observed on top of the long-wavelength morphology when the Ge0.75Si0.25 films are annealed at 900 degree(s)C for as short as 1 minute. These protrusions are unique to the alloy films and not seen in pure Si or Ge. We offer an explanation of this process induced morphological change and discuss the effect of tip shape on images.