Si/Ge-nanocrystals in SiC(0001)

Different SiC-surfaces were coated with thin layers of Si or Ge and subsequently annealed to 900 °C respective 600 °C. According to AFM results, Si- or Ge-clusters, respectively, are formed whose number, size distribution and shape depend on the process parameters. Such samples were investigated with synchrotron x-ray diffraction on the ROBL-beamline at the ESRF. The /2 - scans show for all samples (111)- and (220)-reflections of Si or Ge, respectively. This reveals unambiguously that the clusters grow preferentially in two different orientations (<111>, <110>). Interestingly, for the Ge-samples those reflections are shifted towards the angular position of the corresponding Si-reflection. Such a peak shift could be explained by a lattice distortion due to the lattice mismatch or by the change in the lattice constant due to the formation of a Si/Ge solid solution. The lateral orientation of the (111)- and (110)-clusters was investigated by comparison of the -scans of a cluster-reflection (220-reflection for (111)-clusters and 111-reflection for (110)-clusters) with an appropriate substrate-reflection. This comparison showed that the (111)-clusters as well as the (110)-clusters grow coherently with respect to the substrate.