Fabrication and quantum properties of nanostructured silicon

Physical properties of nanostructured silicon are reviewed in comparison to those of single-crystalline silicon (c-Si) and amorphous silicon (a-Si). Particular emphases are placed on low-dimensional silicon chains (e.g. polysilane) and nanocrystalline silicon (nc-Si) particles (e.g. porous silicon (PS)). These materials can be obtained by nanofabrication technology based on chemical, electrochemical, or dry-processing techniques. Due to induced strong quantum confinement effects. the optical and related properties of nanostructured silicon become free from direct- and indirect-transition regime. Then various functions appear as a novel serniconducting system. Polysilane consisting of a linear silicon backbone chain and capped organo-substituents acts as a self-assembled quantum wire. Nanocrystalline porous silicon composed of highly packed isolated or interconnected silicon nanocrystallites with an average diameter of 2-3 nm efficiently luminesces visible light, Highly efficient electroluminescent nc-Si diodes have been fabricated based on silicon substrates. In addition, nc-Si devices operate as a negative-resistance diode with an electroluminescent behavior, a light-emissive nonvolatile memory, a ballistic electron emitter, and an ultrasound generator. Scientific significance and technological potential of silicon nanostructuring are discussed from viewpoints of exploring advanced materials and developing functional integration. (C) 2003 Elsevier Science B.V. All rights reserved.