Coalescence of domes and superdomes at a low growth rate or during annealing: Towards the formation of flat-top superdomes

We investigate the morphology of islands obtained by epitaxial growth of Ge on Si(0 0 1). During a low growth rate or during annealing and depending of the quench method, we observe the formation of a new type of superdomes, which exhibit additional {15 3 23} facets, an increase of their {0 0 1} and {1 0 5} facet area on their top and a smaller aspect ratio compared to known superdomes. This flat-top superdome shape results from the complex evolution of domes and superdomes: coalescence, intermixing and ripening. Dome or superdome coalescence which results in the newly observed shape appears as a dominant pathway towards dislocation nucleation for the investigated temperature range.