Successful shape-preservation of Ge-clusters during Si-coverage at low temperature

Coherently strained Ge-clusters on Si(001) were overgrown with Si at temperatures between 300 and 620 °C. Using high-resolution transmission electron microscopy the clusters were found to strongly flatten during Si-coverage at temperatures above about 400 °C. By contrast, a good preservation of the original morphology of the Ge-clusters was achieved by Si-capping at low temperature (300 °C). A flat Si surface finally recovered if the low-temperature overgrowth was followed by Si-deposition ramping the temperature up to growth temperatures typical for the SiGe-system.