EFFECT OF ALLOY COMPOSITION ON DEFECT FORMATION IN GEXSI1-X SI HETEROSTRUCTURES OBTAINED BY MOLECULAR-BEAM EPITAXY

GexSi1-x/Si(001) heterostructures with thick layers were grown by mole cular beam epitaxy to study the alloy composition dependence of defect formation. The structural features of the sample were studied using o ptical microscopy and transmission electron microscopy. The character of dislocation distribution in heterostructures was found to be princi pally different for three composition ranges. The nonmonotonic change of layer plasticity is one of the basic causes of this effect. The lay er plasticity behavior proves to be most unexpected in the middle (0.0 2 < x less-than-or-equal-to 0.2) composition range. For these alloy co mpositions, it is characteristic that a three-dimensional misfit dislo cation (MD) network is formed at the interface and this process is acc ompanied by substrate plastic deformation in the near-interface region . Such a network is formed by the misfit dislocation multiplication at the interface through the Frank-Read mechanism. The dislocation multi plication is due to retard of misfit strain relaxation through the gen eration of dislocation semiloops from the layer surface because of a h igh layer strengthening. The spinodal decomposition of the alloy is th e likely cause of nonmonotonic change of layer plasticity. The results are discussed in terms of influence of spinodal decomposition of allo y on dislocation generation, moving and multiplication in layers.