On the formation of self-assembled Ge/Si(001) quantum dots

In situ refection high-energy electron diffraction (RHEED) along with atomi c force microscopy (AFM) and photoluminescence spectroscopy (PL) have been used to investigate the Ge/Si(0 0 1) growth process in an ultrahigh-vacuum chemical-vapor deposition (UHV-CVD) system. The existence of an intermediat e phase between entirely pseudomorphic 2D layers and 3D macroscopic islands is established. This phase is found to occur before the onset of the 2D to 3D growth mode transition determined from RHEED. It consists of square bas ed pyramidal clusters, and is found to be metastable against the formation of 3D macroscopic islands. The formation of this phase can be explained by a local strain relaxation of the Ge wetting layer surface before reaching t he equilibrium critical thickness. (C) 1999 Elsevier Science B.V. All right s reserved.