Silicon Nanocrystals: Size Matters

This paper reviews new approaches to size‐controlled silicon‐nanocrystal synthesis. These approaches allow narrowing of the size distribution of the nanocrystals compared with those obtained by conventional synthesis processes such as ion implantation into SiO 2 or phase separation of sub‐stoichiometric SiO x layers. This size control is realized by different approaches to introducing a superlattice‐like structure into the synthesis process, by velocity selection of silicon aerosols, or by the use of electron lithography and subsequent oxidation processes. Nanocrystals between 2 and 20 nm in size with a full width at half maximum of the size distribution of 1 nm can be synthesized and area densities above 10 12  cm –2 can be achieved. The role of surface passivation is elucidated by comparing Si/SiO 2 layers with superlattices of fully passivated silicon nanocrystals within a SiO 2 matrix. The demands on silicon nanocrystals for various applications such as non‐volatile memories or light‐emitting devices are discussed for different size‐controlled nanocrystal synthesis approaches.