Size reduction of the Ge islands by utilizing the strain fields from the lower-temperature-grown hut-clusters buried in the Si matrix

The growth mode of the self-assembled Ge islands on a Si (001) substrate was studied when the Si substrate contained the buried Ge islands grown at the lower temperature. The drastic reduction of the island sizes and the increase of the island density in the upper layer were observed in the presence of the buried islands. From the observations of the atomic force microscopy (AFM) and the photoluminescence (PL) spectroscopy, the islands in the upper layer were found to possess very similar properties to those of the buried islands. These results are explained as that the strain fields from the buried islands drastically modified the growth mode of the Ge islands in the upper layer.