Effect of the growth rate on the morphology and structural properties ofhut-shaped Ge islands in Si(001)

The effect of Ge deposition rate on the morphology and structural properties of self-assembled Ge/Si(001) islands was studied. Ge/Si(001) layers were grown by solid-source molecular-beam epitaxy at 500 ◦C. We adjusted the Ge coverage, 6 monolayers (ML), and varied the Ge growth rate by a factor of 100, R = 0.02–2 ML s−1, to produce films consisting of hut-shaped Ge islands. The samples were characterized by scanning tunnelling microscopy, Raman spectroscopy, and Rutherford backscattering measurements. The mean lateral size of Ge nanoclusters decreases from 14.1 nm at R = 0.02 ML s−1 to 9.8 nm at R = 2 ML s−1. The normalized width of the size distribution shows non-monotonic behaviour as a function of R and has a
minimum value of 19% at R = 2 ML s−1. Ge nanoclusters fabricated at the highest deposition rate demonstrate the best structural quality and the highest Ge content (∼0.9).