Misfit strain relaxation and dislocation formation in supercritical strained silicon on virtual substrates

Relaxation of strained silicon on 20% linear graded virtual substrates was quantified using high resolution x-ray diffraction and a defect etching technique. The thickness of strained silicon was varied between 10 and 180nm. Relaxation was observed in layers below the critical thickness but increased to only 2% relaxation in the thickest layers even with annealings up to 950°C. Cross-sectional transmission electron microscopy revealed stacking faults present in layers thicker than 25nm, and nucleated 90° Shockley partial dislocations forming microtwins in the thickest layer. These features are implicated in the impediment of the relaxation process.