NUCLEATION OF DISLOCATIONS IN SIGE LAYERS GROWN ON (001)SI

A comprehensive x-ray-diffraction study of the variation of the tilt a ngle between a Si1-xGex layer and the (001) Si substrate is presented. Such measurements provide the basis of a new method for determining t he nucleation activation energy of misfit dislocations. A detailed mod el, independent of the particular relaxation mechanism, is derived whi ch relates the tilt angle to the nucleation activation energy on the d ifferent slip systems and to the density of misfit dislocations. The m odel has been applied to the modified Frank-Read mechanism observed in graded samples. Relaxation occurs in such samples for strain in the r ange 0.002 less-than-or-equal-to epsilon less-than-or-equal-to 0.006 w ith an activation energy of about 4 eV. The critical thickness for gro wth of a strained layer is shown to be smaller when the substrate is m iscut than when it is well oriented.