INITIAL-STAGES OF MISFIT DISLOCATION FORMATION IN COMPRESSIVELY STRAINED SI-GE SHORT-PERIOD SUPERLATTICES

The initial stages of strain relaxation in two (Si(m)Ge(n))p short per iod superlattices grown on Si have been studied by transmission electr on microscopy. Relaxation occurs by the formation of 60-degrees disloc ations which terminate at heterogeneous sources close to the surface o f the sample. The rate of strain relaxation in the short period superl attices has been compared to the rate in homogeneous Si1-xGex layers g rown in the same chamber and having equivalent effective stresses to d rive the dislocations. The rate of dislocation nucleation was observed to be much higher in the short period superlattices. This was attribu ted to the tendency for Ge island formation during the growth of the s uperlattices, leading to localized strain centers which act at easy di slocation sources on annealing.