Evolution of Ge/ S (001)islands during Si capping at high temperature

We discuss the effect of the deposition of a Si cap layer on the composition and morphological properties of GeSi/Si001 self-assembled islands deposited by chemical vapor deposition at 750 ° C. The morphological evolution of the island shape was investigated by means of atomic force microscopy and the actual island composition has been measured by means of x-ray photoemission spectroscopy and x-ray absorption spectroscopy techniques. At an early stage of Si capping, Si atoms are incorporated in the island layer. As a consequence, we observe a reverse Stranski-Krastanov growth dynamics in agreement with the volume-composition stability diagram proposed for domes, pyramids, and prepyramids in the Gex Si1-x /Si100 system. We find that the island burying begins when the Ge average composition reaches the valuex= 0.28. Once the islands are buried under a thin silicon layer their composition is unaffected by subsequent silicon deposition. We conclude that strain relief, rather than thermal diffusion, is the main driving force for the observed Ge-Si alloying.