Morphology and microstructure of tensile-strained SiGe(001) thin epitaxial films

Tensile-strained Si_0.6Ge_0.4 alloys are deposited on Ge(001) by molecular beam epitaxy. The morphology and microstructure of as-deposited (6.5-130 nm thick deposited at 325-500 °C) and annealed (2 min at 625 or 700 °C) epitaxial films are studied by in situ scanning tunneling microscopy, ex situ atomic force microscopy, and transmission electron microscopy. 6.5 nm thick films deposited at 325 and 410 °C are atomically flat with low densities of partial dislocations: stress relaxation of 6.5 nm thick films is limited by dislocation blocking. The surface morphology of thicker films grown at 410 °C is strongly influenced by the interactions of stacking faults and surface steps. Annealing of 13 nm thick films at 700 °C produces a severe roughening with the formation of a regular pattern of 50 nm deep surface pits bounded by {113} facets.