Diffraction Anomalous Fine Structure study and atomistic simulation of Ge/Si nanoislands

We applied Grazing Incidence Diffraction Anomalous Fine Structure to the study of the structure of Ge dome-shaped nanoislands, grown by Molecular Beam Epitaxy on Si (0 0 1) substrates at a temperature of 650 °C. We determined the vertical composition of the islands showing the presence of a strong Ge/Si intermixing that is nearly constant from bottom to top. In particular, an abrupt change is found at the substrate interface where the composition switches from pure Si to Ge0.6Si0.4. The analysis of the Diffraction Anomalous Fine Structure oscillations of the spectra is crucial to obtain the true composition profile. We performed atomistic simulations to investigate the role of the strained substrate underneath the dome on the diffraction results and to quantify the resolution of our method. Anomalous Diffraction spectra and Diffraction Anomalous Fine Structure oscillations have been simulated for a real size and real shape cluster including faceting, giving a more detailed data interpretation and understanding of the Ge-Si intermixing mechanism.