SELF-ALIGNED SOURCES FOR DISLOCATION NUCLEATION - THE KEY TO LOW THREADING DISLOCATION DENSITIES IN COMPOSITIONALLY GRADED THIN-FILMS GROWN AT LOW-TEMPERATURE

We show that, contrary to previous modeling and experiments, threading dislocation annihilation plays the dominant role in obtaining low threading dislocation densities during. low temperature growth of compositionally graded SiGe layers. This is demonstrated by measuring the number of dislocations nucleated, which together with the density of threading dislocations, provides a direct measure of the number of annihilation events. Thread annihilation happens on a much larger scale than expected because the dislocation reproduction mechanism results in the ''self-alignment'' of the sources, leading to an (almost) perfect network of zigzagging dislocations.