Sputter epitaxy of step-graded Si1−xGex/Si(001): evolution of defects and surface morphology

A series of step-graded Si1−xGex films have been grown by magnetron sputter epitaxy at a substrate temperature TS = 550°C and under conditions of only partial thermalization of sputtered atoms, with average impact kinetic energies of the order of 1 eV. The evolution of dislocations in these films was studied by transmission electron microscopy, and the simultaneous development of the surface morphology was imaged by contact atomic force microscopy. The defect arrangement is characterized by the formation of pile-ups of dislocations, injected deep into the Si substrate. Dislocations in the SiGe alloy are confined to layers close to the SiGe/Si interface, so that regions close to the surface always contain a low density of defects. With progressive relaxation, a transition is observed in the surface morphology from a shallow texture to a cross-hatch pattern.