Shape, facet evolution and photoluminescence of Ge islands capped with Si at different temperatures

We investigate the embedding of Ge islands in a Si matrix by means of atomic force microscopy and photoluminescence (PL) spectroscopy. The Ge islands were grown between 360degreesC and 840degreesC and subsequently capped with Si at different temperatures. For the highest Ge growth temperature (840degrees), we show that the surface flattens at high Si capping temperatures while new facets can be identified at the island base for intermediate capping temperatures (650-450degreesC). At low capping temperatures (300-350degreesC), the island morphology is preserved. In contrast to the observed island shape changes, the decreasing Si capping temperature causes only a small redshift of the island related PL signal for islands grown on high temperatures. This redshift increases for Ge islands grown at lower temperatures due to an increased Ge content in the islands. By applying low-temperature capping (300degrees) on the different island types, we show that the emission wavelength can be extended up to 2.06 mum for hut clusters grown at 400degreesC. Further decreasing of the island growth temperature to 360degreesC leads to a PL blueshift, which is explained by charge carrier confinement in Ge quantum dots. (C) 2004 Elsevier B.V. All rights reserved.