Photoluminescence of self-assembled Ge dots grown by ultra-high-vacuum chemical vapor deposition

We have investigated the photoluminescence of self-assembled Ge clusters de posited on Si(001) by chemical vapor deposition. The formation of precursor clusters is observed both by microscopy and photoluminescence before the o nset of the 2D layer-by-layer to 3D island growth mode transition. These pr ecursor clusters which are observed at different growth temperatures are fo und to be metastable. They have a square base shape with a height approxima te to 1-2 nm and a base width approximate to 30-15 nm. They exhibit strong three-dimensional confinement. Beyond the 2D-3D growth transition, we obser ve the formation of islands with a dome shape which exhibit photoluminescen ce at lower energies as compared to the precursor clusters. The photolumine scence energy is compared to the one deduced from a simulation which accoun ts for the three-dimensional confinement of the holes. (C) 1998 Elsevier Sc ience S.A. All rights reserved.