Effect of the bimodal size distribution on the optical properties of self-assembled Ge/Si(001) quantum dots

In situ reflection high-energy electron diffraction, atomic force microscop y and photoluminescence spectroscopy have been combined to investigate the effects of a bimodal size distribution and of the pyramid/dome transition o n the optical properties of related Ge/Si lavers. it is shown that the wett ing layers are inhomogeneous in thickness due to the lateral diffusion of G e from 2D layers towards islands, while no change is observed in the island -related photoluminescence. These results indicate that 3D islands are, in their early nucleation stages, formed by consuming Ge from 2D layers, and t hat island luminescence energy is not sensitive to the vertical confinement inside islands. (C) 2000 Elsevier Science B.V. All rights reserved.