Silicon nanocrystals electronic properties

In a Si zero-dimensional system the strong quantum confinement can increase the optical infrared gap of bulk Si and consequently shift the optical transition energies towards the visible range [65,66]. This is the reason for which silicon nanocrystals (Si-NCs) with a passivated surface are used as the natural trial model for theoretical simulations on Si based light emitting materials, such as porous Si or Si nanocrystals dispersed in a matrix. In this section we present a comprehensive analysis of the structural, electronic and optical properties of Si-NCs as a function of size, symmetry and surface passivation. We will also point out the main changes induced... 

Wilcoxon JP, Samara GA, Provencio PN (1999) Optical and electronic properties of Si nanoclusters synthesized in inverse micelles. Phys Rev B 60 2704-2714 Wilson WL, Szajowski PF, Brus LE (1993) Quantum confinement in size-selected surface-oxidized silicon nanocrystals. Science 262 1242-1244... 

Most of the semiempirical tight-binding methods for nanostructures are based on the parametrization of bulk systems. It consists of an iterative fitting procedure, performed on the tight-binding parameters, to match the bulk silicon band structure calculated using the most advanced techniques [21]. The as-calculated parameters are then applied to the study of the electronic properties of silicon nanostructures. When the nanostructures are well passivated, the surface is expected to play a minor role, and the main electronic and optical properties are determined by the nanocrystal core. 

This chapter summarizes the main theoretical approaches to model the porous silicon electronic band structure, comparing effective mass theory, semiempirical, and first-principles methods. In order to model its complex porous morphology, supercell, nanowire, and nanocrystal approaches are widely used. In particular, calculations of strain, doping, and surface chemistry effects on the band structure are discussed. Finally, the combined use of ab initio and tight-binding approaches to predict the band structure and properties of electronic devices based on porous silicon is put forward. 

One of the most important physical parameters of any material is its thermal conductivity (see handbook chapter Thermal Properties of Porous Silicon ). Bulk crystalline Si, the material that is widely used in today s electronics and sensors, shows moderate thermal conductivity at room temperature (Slack 1964). On the other hand, highly porous Si, which is a complex nanostructured Si material, composed of interconnected nanowires and nanocrystals, shows a much lower thermal conductivity than that of bulk crystalline Si, which depends strongly on its structure and morphology. The voids within the porous Si layer and the low dimensionality of the highly porous Si skeleton serve to inhibit thermal transport within the layer. 

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