Atomic-force-microscopy investigation of the formation and evolution of Ge islands on GexSi1−x strained layers

A constant amount of Ge was deposited on strained ${\mathrm{Ge}}_x{\mathrm{Si}}_{\text{1−x}}$ layers of approximately the same thickness but with different alloy compositions, ranging from $\text{x=0.06}$ to $\text{x=0.19.}$ From their atomic-force-microscopy images, we found that both the size and density of Ge islands increased with the Ge composition of the strained layer. By conservation of mass, this implies that these islands must incorporate material from the underlying strained layer.