SURFACE STRESS, MORPHOLOGICAL DEVELOPMENT, AND DISLOCATION NUCLEATIONDURING SIXGE1-X EPITAXY

Utilizing Ge marker layer experiments combined with atomic number cont rast (Z-contrast) imaging, we have studied the evolving surface morpho logy of SixGe1-x alloys during growth by molecular beam epitaxy. The m arker layers map out the instability transition between planar two-dim ensional (2D) growth and three-dimensional (3D) growth. The transition occurs via the gradual formation of a surface ripple as anticipated f rom instability theory. However, these undulations rapidly develop int o crack-like surface instabilities which we simulate and explain by th e mechanism of stress-driven surface diffusion. Finally, we model the large stresses associated with these features within a fracture mechan ics formalism. This analysis demonstrates that crack-like instabilitie s provide ideal candidate sites for the nucleation of misfit dislocati ons.