It has been shown that the strain in the device changes the spatial geometry of the wave functions, and that considering this effect offers a possible explanation of the current-voltage characteristics of the device. Several applications have been proposed for quantum dot devices including field effect transistors, quantum memory devices, and solid state lasers. However, reliable fabrication of these devices remains an issue. A particularly challenging aspect of this fabrication problem is management of the large stresses and strains associated with the lattice mismatch between the constituent materials. It has been found that when SiGe is grown on Si , pyramidal islands begin to nucleate when the film thickness reaches 25A. The density increases rapidly until the thickness reaches approximately 35A and from that point on the islands increase in size.
Elastic interactions cause the islands to order along specific crystallographic directions.
The islands also change in morphology, and computer simulations show that this transition is strongly affected by elastic interactions between the islands. The effects of surface energy and the kinetics of the transition have also been modeled. The accompanying graphics show an experiment image of these islands, the results of a finite element calculation that models their growth, and calculations of the strain associated with an island.