Photoluminescence study of a bimodal size distribution of Ge/Si(001) quantum dots

This work presents a study on the effect of a bimodal size distribution and of the pyramid/dome transition to the optical properties of self-assembled Ge/Si quantum dots. The wetting layers are shown to be inhomogeneous in thickness due to lateral diffusion of Ge from two-dimensional (2D) layers towards islands of bimodal sizes, while the island-related photoluminescence remains unchanged. The results indicate that three-dimensional islands, at their early stages of nucleation, are formed by consuming Ge from 2D layers and that the island luminescence energies are more sensitive to Ge/Si interdiffusion than the confinement effect inside the islands as currently believed.