C-induced Ge dots: a versatile tool to fabricate ultra-small Ge nanostructures

Epitaxial growth of a submonolayer amount of C, followed by 2-4 monolayers (ML) Ge results in the formation of extremely small C-induced Ge (CGe) quan tum dots. Different stacks of CGe islands combined with pure Ge island laye rs are fabricated. We present vertical coherent quantum dot stacks, consist ing of an initial 0.2 ML C/3 ML Ge dot layer, followed by five layers of 4 ML Ge. Each layer is separated by 1 nm of Si. The islanding process is init iated before the critical thickness for planar Ge growth is reached and res ults in only 20 nm wide and 2 nm high vertically aligned Ge dots. However, if we substitute the pure Ge layers by CGe dot layers, no vertical correlat ion is observed. We explain this phenomenon by the: kinetically limited pro cess of CGe island formation. itself. (C) 1998 Elsevier Science S.A. All ri ghts reserved.