Relaxation of strained Si layers grown on SiGe buffers

Thin strained Si layers grown on SiGe layers graded to 20% Ge were studied for resistance to relaxation. It was observed that in the presence of simil ar to 10(5)/cm(2) threading dislocations from the underlying graded layers, the barrier to misfit dislocation formation is sufficiently reduced to ind uce relaxation in Si layers even when the layer thickness is less than the predicted critical thickness. Raman spectroscopy revealed that elastic stra in accumulation in the uniform SiGe layers is a significant contributor to strain relaxation in the Si cap layers. Upon annealing, thermal mismatch ca uses the Si layers to relax further, but most of the strain relaxation is a ccommodated by elastic strain increase in the SiGe layers. This prevents th e rampant increase in defect density that would otherwise accompany the str ain relaxation. Annealing in an oxidizing ambient appears to pin pre-existi ng threading dislocations causing nucleation of new threading dislocations and short misfit segments to relieve the thermal mismatch stresses. (C) 199 9 American Vacuum Society. [S0734-211X(99)04204-3].