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 period superlattices grown on Si have been studied by transmission electron microscopy. Relaxation occurs by the formation of 60-degrees dislocations which terminate at heterogeneous sources close to the surface of the sample. The rate of strain relaxation in the short period superlattices has been compared to the rate in homogeneous Si1-xGex layers grown in the same chamber and having equivalent effective stresses to drive the dislocations. The rate of dislocation nucleation was observed to be much higher in the short period superlattices. This was attributed to the tendency for Ge island formation during the growth of the superlattices, leading to localized strain centers which act at easy dislocation sources on annealing.