Roughness analysis of Si_1-xGe_x films

The morphology of Si1-xGex films is studied using atomic force microscopy (AFM) and scanning tunneling microscopy (STM). Depending on growth temperature and Ge content, growth proceeds in either a layer-by-layer mode or by the growth of 3-dimensional coherent islands. In the former case strain relaxation occurs by formation and multiplication of misfit dislocations, leading to a cross-hatched surface morphology. In the latter case the rough morphology leads to a higher density of nucleation sites, and reduced glide efficiency, for the dislocations. A Fourier transform based method for analyzing the morphology is introduced, and is compared with other, existing roughness analysis methods.