Evolution of the strain relaxation in a Ge layer on Si(001) by reconstruction and intermixing

The periodicity of the $(2\mathrm{}\times N)$ reconstruction of two-dimensional Ge layers on Si(001) is measured as a function of the Ge coverage with a high-temperature scanning tunneling microscope during growth. The strain energy, which increases with increasing coverage, is the driving force for the formation of the strain relieving $(2\mathrm{}\times N)$ reconstruction trenches and Si/Ge intermixing. A quantitative comparison to total-energy calculations predicting the periodicity of the $(2\mathrm{}\times N)$ reconstruction with the experimental results is used to estimate the amount of Si-Ge intermixing near the surface.