Improvement of photoluminescence efficiency in stacked Ge/Si/Ge quantum dots with a thin Si spacer

Abstract

AbstractIn this work, two successive layers of Ge quantum dots separated by a thin Si spacer grown by ultra‐high‐vacuum chemical vapor deposition were demonstrated. With an optimal thickness of the thin Si spacer, the sandwiched Ge (13.1 ML)/Si (28 ML)/Ge (13.1 ML) quantum dots suppress the coarsening of Ge quantum dots and efficiently increase the uniformity of the quantum dots. Cross‐sectional transmission electron microscopy shows that the Si/Ge underlayers provide preferred nucleation sites for the overlayer Ge deposition. Such a modification avoids the formation of Ge superdomes and prevents the occurrence of threading dislocations even at such a thin Si spacer thickness. A stronger photoluminescence intensity of these sandwich Ge/Si/Ge quantum dots was observed compared with that of 26.2 eq‐ML Ge quantum dots without using any intermediate Si layer. Furthermore, the narrower width of the photoluminescence spectra indicates that the Ge/Si/Ge dots are more uniform compared with the 13.1 and 26.1 eq‐ML Ge quantum dots. Five‐fold bilayers of Ge/Si/Ge/Si(150 ML) have been achieved to enhance the photo‐emission efficiency. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)