Size effect on electronic transport in nC–Si/SiOx core/shell quantum dots

Electronic transport in silicon quantum dots (Si-QDs) in core/shell configuration was studied. The nC–Si cores encapsulated by protective SiOx shells embedded in a-Si matrix were obtained from one-step and spontaneous plasma processing, at low substrate temperature (300 °C) compatible for device fabrication. The size, density and distribution of nC–Si QDs were controlled by optimizing the plasma parameters. Very high electrical conductivity, σ ∼ 4 × 10−2 S cm−1, was achieved at a total number density of Si-QDs, N ∼ 4.8 × 1011 cm−2, corresponding to the lowering in its average core size, d ∼ 3.7 nm, to the order of the bulk Si exciton Bohr radius and the associated quantum confinement effects. The electrical conductivity was demonstrated to exhibit quantum size (3 < d (nm) < 10) effect in zero dimensional quantum dots. The underlying electronic transport was explained using heteroquantum-dot model, the nC–SiOx:H QDs possess hetero-junction like band structure in the interface regions, due to their different band gaps.

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► Electrical conductivity (σ) demonstrated to exhibit quantum size effect for Si-QDs.
► High σ ∼ 4 × 10−2 S cm−1 for Si-QDs of average size ∼3.7 nm, number density ∼4.8 × 1011 cm−2.
► Heterojunction-like band-structure at the QD interface controls electronic transport.