CRITICAL NUCLEI SHAPES IN THE STRESS-DRIVEN 2D-TO-3D TRANSITION

We investigate the kinetic pathways to coherent island formation durin g the stress-driven roughening of strained films, and specifically exa mine the role of facets during island nucleation. Despite the ubiquito us appearance of {501} facets in the Si-Ge system, we show that for Ge 0.5Si0.5 strained layers, the initial islanding pathway does not invol ve discrete {501} facets. A kinetic model based on interacting surface steps is developed, which explains the observed pathway and is consis tent with the sensitive dependence of the 2D-3D transition on temperat ure and the sign of misfit.