Keywords: self-assembly, MBE, Ge islands, heterostructures, germanium islands, nanotechnology, molecular beam epitaxy, annealing, stability, coarsening
Properties of self-assembled Ge islands grown by molecular beam epitaxy
Self-assembled germanium islands have been grown on Si (001) substrates using solid source molecular beam epitaxy. A series of annealing experiments have been performed at a temperature 650°C in order to clarify some issues related to island stability and coarsening mechanism. The shape and size distribution of Ge islands as a function of annealing time up to 90 min have been studied through atomic force microscopy. Foot-prints of the annealed and etched islands have demonstrated that the coarsening is dominated by coalescence mechanisms rather than the Ostwald ripening. A detailed Raman characterisation, using optical phonons as efficient probes in analysing self-organised Si1-xGex islands, is reported. The alloy composition has been determined from the Raman intensities. The experimental results are in good agreement with the strain relaxation obtained from X-ray rocking curve and data from AFM topographic images. The generic mechanisms for the growth of self-assembled Ge islands as a function of growth parameters and post-growth treatment are also reviewed.