Stability of semiconductor strained-layer superlattices

The criteria for strained-layer growth of semiconductor superlattices are discussed. It is shown that to avoid misfit dislocations, careful attention has to be paid to the composition, geometry, and dimensions of the quantum well structure. Two critical thicknesses are found to apply to strained-layer superlattice growth, one relating to the thickness of individual layers and one relating to the overall thickness of the superlattice. We derive the relationship between these two critical values. Experimental studies of the GexSi1−x/Si on Si and GexSi1−x/Ge on Ge systems using electron microscopy, Raman scattering, and ion channeling show that exceeding the critical superlattice thickness results in a network of dislocations between the substrate and first superlattice layer.