Direct observation of strained substrate in graded Si1-xGex/Si heterostructures

Cross-sectional scanning tunneling microscopy is used to study strain relax ation in a graded Si1-xGex/Si heterostructure. Two strain relaxation mechan isms are observed on the (111) cleaved surface. One is through stressing th e substrate, and the strained region in the substrate can extend several hu ndred Angstroms from the interface. The other strain relaxation mechanism i s through defect formation, i.e., atomic steps, on the cleaved surface. Thi s is analogous to misfit dislocations in bulk strain relaxation. Interactio n between these two strain relaxation mechanisms is also observed, with the presence of atomic steps reducing the strained region in the substrate. (C ) 1999 American Institute of Physics. [S0003-6951(99)02814-4].