Structure amorphous silicon

Biswas, R., Grest, G. S., and Soukoulis, C. M., Generation of amorphous silicon structures with use of molecular-dynamics simulations. Phys. Rev. B 36,7437-7441 (1987). 

Work on the stability and efficiency characteristics of amorphous silicon structures for direct water splitting systems clearly showed that it is feasible to utilize amorphous silicon devices in direct contact with aqueous electrolytes without additional protective coatings. 

In developing PEC hydrogen systems that will meet these requirements, research efibrts are focused in two areas (1) chemical modification of the semiconductor electrode surface material to improve system energetics, and (2) evaluation of triplejunction amorphous silicon structures as low-cost thin-film water splitting systems. 

Fig. 1.18 Radial distribution functions (RDFs) and bond-angle distribution functions (BADFs) of four amorphous silicon structures shown in Fig. 1.17 (from Demkowicz and Argon (2005a) courtesy of the APS).

The chemistry of silicon in very low oxidation states is one of the most fascinating research areas, which can be located between molecular compounds of silicon and elemental (perhaps amorphous) silicon [190-194]. Most interesting results have recently been obtained by structural investigations of siliddes in Zintl phases. However, compounds of silicon with negative oxidation states and very low coordination numbers of 1, 2, and 3 are so far only known in the composite of a crystal lattice. 

Amorphous Silicon (a-Si). Amorphous silicon is considered a promising new material.As mentioned above, only a very thin coating is necessary, since the amorphous structure is much better at absorbing sunlight than is the crystalline material. The most common process to produce a-Si is the decomposition of silane by plasma CVD (see Ch. 8). Thicknesses of a few micrometers can be deposited and,... 

Material Aspects of Hydrogenated Amorphous Silicon 1.1.2.1. Atomic Structure... 

The refractive index of amorphous silicon is. within certain limits, a good measure for the density of the material. If we may consider the material to consist of a tightly bonded structure containing voids, the density of the material follows from the void fraction. This fraction / can be computed from the relative dielectric constant e. Assuming that the voids have a spherical shape, / is given by Bruggeman [61] ... 

Hydrogenated amorphous silicon is not a homogeneous material. Its structure is thought to consist of voids embedded in an amorphous matrix [62, 63]. The size and number density of the voids depend on the deposition conditions. Poor-quality material can have a void fraction around 20%, while device quality a-Si H has been shown to contain fewer voids, 1%. with a diameter of 10 A [64-66]. The surfaces of the voids may be partly covered with hydrogen atoms [62, 67],... 

Figure 16 (Street et al., 1986) shows the typical sample structure, consisting of three layers of a-Si H. Results using this technique have been reported for samples grown by the rf glow discharge of silane and by rf sputtering (Shinar et al., 1989). The first layer is hydrogenated amorphous silicon, deposited under conditions that yield high quality films (i.e., deposition temperature of 230°C, low growth rate) and is typically two microns thick. Next a layer of approximately 1000 A is deposited, whereby...

The experimental observations of red shifts of the UV absorptions tails with increase in silicon dimensionality were corroborated by ZINDO-calculated spectra comparing linear polysilane, network polysilyne, crystalline cluster, and amorphous cluster structures, which showed respectively lowest absorption transition energies of 5.38 eV (230.4 nm), 4.60eV (269.5nm), 4.57eV (271.2nm), and 2.46eV (503.9nm), as shown in Figure 57.362... 

M. Khayyat, G. Banini, D. Hasko, and M. Chaudhri, Raman microscopy investigations of structural phase transformations in crystalline and amorphous silicon due to indentation with a Vickers diamond at room temperature and at 77 K, J. Phys. D—Appl. Phys. 36, 1300-1307 (2003). 

FIGURE 12.3 Segment of amorphous silicon dioxide (Si02) structure. 

Tsu DV, Chao BS, Ovshinsky SR, Guha S, Yang J (1997). Effect of hydrogen dilution on the structure of amorphous silicon alloy. Appl Phys Lett 71 1317-1319... 

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