Freezing shape and composition of Ge∕Si(001) self-assembled islands during silicon capping

Abstract

We use atomic force microscopy, x-ray photoemission spectroscopy, and x-ray absorption spectroscopy to study the effect of the deposition of a Si cap layer by chemical vapor deposition on the morphology and composition of a Ge island layer grown at 600°C. We found that the capping of self-assembled Ge islands under a silicon layer results in high-quality, atomically flat layer only at deposition temperature above 700°C. On the other hand at this temperature Ge–Si intermixing and island coarsening are greatly enhanced, resulting in an increased average island volume. Here we show that the predeposition at low temperature of a thin cap layer preserves island shape, size, and composition when the capped islands undergo a subsequent process at higher temperature up to 750°C. It is shown, therefore, that with a two-step capping process it is possible to combine the benefit of a low temperature capping, which reduces island alloying and coarsening, with that of a high temperature capping which is needed to recover a flat surface.