Influence of Si interdiffusion on carbon-induced growth of Ge quantum dots: a strategy fortuning island density

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We have studied the epitaxial growth of self-assembled Ge quantum dots when a submonolayerof carbon is deposited on a Ge wetting layer (WL) prior to the growth of the dots. Usingatomic-force microscopy combined with optical techniques like Raman and ellipsometry, weperformed a systematic study of the role played by thermally activated Si interdiffusion ondot density, composition and morphology, by changing only the growth temperatureTWL of the WL. Strikingly, we observe that higher dot densities and a narrowersize distribution are achieved by increasing the deposition temperatureTWL, i.e. by enhancing Si interdiffusion from the substrate. We suggest a two-stage growthprocedure for fine tuning of dot topography (density, shape and size) useful for possibleoptoelectronic applications.