STRESS-RELAXATION IN SIGE LAYERS GROWN ON OXIDE-PATTERNED SI SUBSTRATES

Silicon-germanium layers with Ge concentrations up to 14% are grown by liquid phase epitaxy on oxide-patterned (111) Si substrates. Strains and defect formation are studied by transmission electron microscopy. Below Ge concentrations of 10% strain relaxation occurs via heterogene ous nucleation of dislocation loops at edges of the oxide mask. Cross- slip leads to pinning points from where Frank-Read sources eject dislo cations into the substrate. These dislocations relax strain induced by misfit and oxidation. At Ge contents above 10% misfit dislocations ar e observed at the Si/SiGe interface. Only a few threading dislocations occur and are confined to the seed areas where the SiGe layer grows d irectly on the Si substrate. Because edges of the oxide mask act as ob stacles for dislocation propagation, SiGe layers growing laterally on the oxide-covered Si substrate are almost dislocation free. (C) 1996 A merican Institute of Physics.