Shape transformation of Ge quantum dots due to Si overgrowth

The optimisation of the opto-electronic properties of Ge dots embedded in Si requires the precise control of their structural properties. In the present study we investigated the initial stages of overgrowth using transmission electron microscopy (TEM), energy resolved TEM and in situ scanning tunnelling microscopy. It is found that Ge dome clusters and Ge hut clusters behave differently during the overgrowth by Si. Ge domes transform back into hut clusters after the deposition of 5 Monolayers of Si, thus they decrease in height and increase in diameter. Ge hut clusters increase in height and diameter during Si overgrowth. The changes in shape are accompanied by local changes in the strain and composition of the dot. The presented data give detailed insights into the shape and composition of Ge quantum dots before and after embedding in Si.