Photoluminescence of carbon-induced Ge islands in silicon

Reducing the size of germanium islands improves their optical properties. T he spatially strong localised holes in the islands are more uncertain in mo mentum and thereby the probability of direct optical transitions is enhance d. Carbon predepositon onto Si has been shown to reduce the size of germani um islands. We have studied such islands grown by molecular beam epitaxy. T he germanium islands show an intense PL-signal, which is typically more tha n one order of magnitude larger in intensity than the PL from silicon-germa nium quantum wells. Reducing the amount of Ge from 3.4 monolayer (ML) to 1. 0 hit results in a PL blueshift from 0.81 to 1.08 eV in conjunction with a narrowing of the PL peak. The blueshift indicates a reduction in the size o f the germanium islands, which was confirmed by TEM. increasing the C cover age from 0.2 to 0.3 ML leads to a red shifted FL. This is attributed to a c hange in the aspect ratio of the islands with the result of an increased ve rtical island height. (C) 2000 EIsevier Science B.V. All rights reserved.