Photoluminescent silicon quantum dots in core/shell configuration: synthesis by low temperature and spontaneous plasma processing

Quantum confinement in zero-dimensional silicon nanocrystals (nC) in the quantum dot (QD) configuration has triggered a tremendous interest in nanostructured device technology. However, the formation of Si-QDs eventually proceeds through multi-step routes and involves high temperature processing that impedes preferred device configuration. The present work demonstrates the formation of nC-Si QDs of controlled size, density and distribution through one-step and spontaneous plasma processing, at a low substrate temperature (300 deg. C) compatible for device fabrication. Direct growth of nC-Si/SiOx core/shell quantum dots embedded in the a-Si matrix, 6.4-3.7 nm in diameter and with number density in the range ∼ 6 x 109-1 x 1011 cm-2 has been accomplished, following a novel route where He dilution to SiH4 in RF plasma CVD has been found instrumental. On gradual reduction in the size of QDs, splitting of the energy bands widens the optical band gap and induces visible photoluminescence that appears controllable by tuning the size and density of the dots. This low temperature and spontaneous plasma processing of nC-Si/SiOx core/shell QDs that exhibit the quantum size effect in photoluminescence is being reported for the first time.