Comparison of strain relaxation in epitaxial Si0.3Ge0.7 films grown on Si(001) and Ge(001)

Epitaxial Si1−xGex films of thickness ∼200 nm have been grown on Si(100) and Ge(100) substrates using chemical vapor deposition. Both X-ray diffraction and Raman studies show that the films are Ge rich (x=0.7) with no residual strain. Cross-sectional transmission electron microscopy studies have been used to demonstrate that the films relax by different mechanisms leading to different surface morphology and interface structure. Films in tension (SiGe/Ge) were seen to relax through the creation of misfit dislocations, whereas those in compression (SiGe/Si) formed islands without dislocations. Consideration of the misfit dislocation formation mechanism in these materials has been used to explain this behavior phenomenologically.