Instability-driven SiGe island growth

Three-dimensional islanding is generally assumed to proceed through nucleation and growth. Here we present studies showing the growth of Si1-xGex islands (0.2

New mechanism for dislocation blocking in strained layer epitaxial growth

Dislocation interactions play a critical role in plasticity and heteroepitaxial strain relaxation. We use real time transmission electron microscopy observations of the interaction between threading and misfit dislocations in SiGe heterostructures to investigate interactions quantitatively. In addition to the expected long-range blocking of threading segments, we observe a new short-range mechanism which is significantly more effective. Simulations show that this reactive blocking occurs when two dislocations with the same Burgers vector reconnect.

Thermal roughening of a thin film: A new type of roughening transition

The equilibrium thermal roughening of thin Ge layers (one and two monolayers) deposited on Si(001) has been investigated with low-energy electron microscopy. A Ge-coverage-dependent roughening is observed. For two monolayers, the temperature at which imaging contrast is lost due to surface roughness is 900+/-25 degrees C, between the roughening temperatures of Ge(001) and Si(001). Lower Ge coverages move this temperature closer to that of Si(001). The roughening is confined to the Ge overlayers. It is believed that this phenomenon represents a new type of surface roughening transition that should be generally applicable for heteroepitaxial films.

Ostwald Ripening of Self-Assembled Germanium Islands on Silicon(100).

: We describe here real-time, in situ observations of the formation of nanosize germanium (Ge) islands on silicon (Si). The deposition of Ge onto electron-transparent Si(100) takes place in a UHV transmission electron microscope that has been modified to allow chemical vapor deposition to be carried out in the polepiece. We recorded the growth process at video rate and were therefore able to follow the evolution of individual islands. As the islands grew, we observed a coarsening process similar to classical Ostwald ripening, but which leads at certain times to a bimodal distribution of island sizes. We show that this phenomenon can be understood using a model in which a conventional coarsening process is modified by a transition between two different island shapes.