We report on self-assembled formation of spherically shaped voids in MBE grown SiGe alloy layers implanted in-situ at elevated temperature with low-energy Ge ions, followed by thermal annealing. The voids are of nanometer size and are e xclusively assembled in thin SiGe quantum wells. The voids only appear in the layers after heat treatment at a temperature higher than 700°C, and they are stable up to 950°C. The results are discussed in terms of the separation of the vacancies and interstitials induced by the strain situation around the SiGe quantum wells.
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