CRITICAL PHENOMENON AND SEGREGATION BEHAVIOR AT INTERFACES AND SUBGRAIN BOUNDARIES

Abstract
We have analyzed two important phenomena in lattice mismatched systems : (1) critical stresses, strains and thicknesses, and (2) dopant/impurity segregation at coherent, semicoherent, incoherent interfaces and subgrain boundaries. During formation of epitaxial films, the growth (pseudomorphic) occurs upto a certain thickness with planar spacing normal to the interface being essentially the same both in the substrate and the film. Above a critical thickness it becomes energetically favorable for the film to contain dislocations. This occurs usually by generating glide dislocations near the free surface because there is a lack of dislocation sources in mostly "defect-free" semiconductor materials. We present an analysis of the critical phenomena in semiconductors based upon this experimental fact. In previous work, the critical step associated with the generation of dislocations was largely neglected. We also consider finite (island) growth of thin films and its effect on critical phenomena. The experimental results clearly show the presence of glide dislocations in Ge/Si and GaAs/Si systems with extra half planes being in the silicon substrate. If the growth or processing temperature is high enough, then the diffusion and segregation phenomena at dislocation arrays and interfaces become important. The interaction of dopants and impurities with dislocation arrays and interfaces results in a drift term in the diffusion equation, which leads to enhanced segregation of dopants and impurities. Such segregation effects are analyzed for Ge/Si and GaAs/Si interfaces as well as subgrain boundaries in silicon.