Study of growth behaviour and microstructure of epitaxially grown self-assembled Ge quantum dots on nanometer-scale patterned SiO₂/Si(001) substrates

The growth behaviour and microstructure of epitaxially grown self-assembled Ge quantum dots on patterned SiO₂/Si(001) substrates by molecular beam epitaxy were studied. The hexagonally ordered Si holes with 30 nm thick SiO₂ mask layer having ~25 nm diameter, ~40 nm center-to-center distance, and density of ~7 × 10¹⁰ cm^-2, were formed using self-assembled diblock copolymer, composed of polystyrene and poly(methyl methacrylate) (PS-b-PMMA). The multiple Ge nuclei are selectively formed along the periphery of the individual Si holes and these nuclei subsequently coalesce forming single dot with an identical size of patterns. The strain of dots is relaxed up to 80%. The lattice planes of some Ge dots are found to be tilted from those of Si substrates. The Ge dots have dislocations at the interface with Si substrate even at the small size of ~25 nm, resulting from the limited elastic relaxation in the confined patterned structure.