C-induced Ge Research Articles

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) quantum dots. Different stacks of CGe islands combined with pure Ge island layers are fabricated. We present vertical coherent quantum dot stacks, consisting 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 2 nm of Si. The islanding process is initiated before the critical thickness for planar Ge growth is reached and results 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 correlation is observed. We explain this phenomenon by the kinetically limited process of CGe island formation, itself.

Photoluminescence and band edge alignment of C-induced Ge islands and related SiGeC structures

Growth of less than 2 monolayers Ge on a submonolayer amount of predeposited C on Si results in the formation of very small Ge quantum islands. In a photoluminescence study, we compare these C-induced Ge (CGe) dots with carefully chosen reference structures incorporating the same total amount of C and Ge but with different deposition orders and with varied C distribution below the Ge islands. Our investigations imply that the special combination of pregrown low surface mobility C and post-grown high surface mobility Ge constitutes a distinct microstructure within the SiGeC material system, causing dot formation at a very early stage and showing particularly intense photoluminescence signal. Moreover, structures combining CGe dots with Si1−yCy quantum wells are well explained by the model of spatially indirect type-II recombination within the CGe islands.