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

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 degrees 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 degrees 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 degrees 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. (c) 2006 American Institute of Physics.