Quantitative electron microscopy studies of silicon germanium/silicon(001).

摘要

Over the last decade, much progress has been made in understanding the thermodynamic and kinetic properties of self-assembled quantum dot structures. These structures form as a result of the strain energy in mismatched epitaxial systems. Ge/Si(001) has been investigated for its potential importance technologically, as well as serving as a model system. However, it has been difficult to obtain data on how the strain in these islands effects the island's thermodynamic properties and kinetic evolution. In this work, we investigate the thermodynamics and kinetics of the Ge/Si(001) system. We have applied the new Abrupt Displacement Approximation using transmission electron microscopy (TEM) to measure the average island strain, and have coupled this with the Suppressed Diffraction condition to measure the size and the shape of the islands. By these techniques, as well as some more traditional TEM methods, we directly show the energetic pathway of the island shape reverse transition. We show how the thermodynamic island diameter is ∝1/32r , where 3r is the strain reduction in an island. We also use these methods to understand the kinetic properties of the island formation and growth. We show that Ge does segregate out of Si1-xGe x alloy films to create islands with higher Ge concentration than the deposited film. We also show that the coarsening of the island diameter growth that occurs during a 650°C anneal obeys a power law which suggests that adatoms detach from the perimeter of the islands contact line with the substrate and diffuse via surface diffusion between islands.