Amorphous silicon and carbon

Discovery of amorphous silicon and its dopability has already had a tremendous impact on industrial applications of amorphous materials. Amorphous Si is now used fairly extensively as a photovoltaic material. In photovoltaic applications, solar photons excite the electrons across the gap and the resulting electron-hole pairs, are driven towards the respective electrodes in order to prevent their recombination. Electron is driven through an external resistance to generate the electrical power. The efficiency of conversion of solar energy to electrical power is characterized by an efficiency factor, r, which is given by. 

Elliott, S.R., 1984, Physics of Amorphous Materials (Longman, London). 

in Physics of Structurally disordered Solids, ed. S.S. Mitra (Plenum Press, New York). 

Joannopoulos, J.D., and M.L. Cohen, 1976, Solid State Physics, Vol. 31, eds. H. Ehrenreich, F. Seitz and D. Turnbull (Academic Press, New York) p. 71. 

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Chalcogenides of group IV and V elements form glasses, which constitute a major class of amorphous semiconductors. As a class of semiconductors, hydrogenated amorphous silicon and carbon constitute a... 

The preparation, manufacture, and reactions of SiC have been discussed in detail in Gmelin, as have the electrical, mechanical, and other properties of both crystalline and amorphous of SiC. Silicon carbide results from the pyrolysis of a wide range of materials containing both silicon and carbon but it is manufactured on a large scale by the reduction of quartz in the presence of an excess of carbon (in the form of anthracite or coke), (Scheme 60), and more recently by the pyrolysis of polysilanes or polycarbosUanes (for a review, see Reference 291). Although it has a simple empirical formula, silicon carbide exists in at least 70 different crystalline forms based on either the hexagonal wurtzite (ZnS) structme a-SiC, or the cubic diamond (zinc blende) structme /3-SiC. The structmes differ in the way that the layers of atoms are stacked, with Si being fom-coordinate in all cases. 

R. M. Laine, F. Babonneau, K. Y. Blohowiak, R. A. Kennish, J. A. Rahn, and G. J. Exharos, The evolutionary process during pyrolytic transformation of poly(n-methylsilazane) from a preceramic polymer into an amorphous silicon nitride/carbon composite, J. Am. Ceram. Soc. 1995, 78, 137-145. 

Silicon is prepared commercially by heating silica and carbon in an electric furnace, using carbon electrodes. Several other methods can be used for preparing the element. Amorphous silicon can be prepared as a brown powder, which can be easily melted or vaporized. The Gzochralski process is commonly used to produce single crystals of silicon used for solid-state or semiconductor devices. Hyperpure silicon can be prepared by the thermal decomposition of ultra-pure trichlorosilane in a hydrogen atmosphere, and by a vacuum float zone process. 

Metallic Glasses. Under highly specialized conditions, the crystalline structure of some metals and alloys can be suppressed and they form glasses. These amorphous metals can be made from transition-metal alloys, eg, nickel—zirconium, or transition or noble metals in combination with metalloid elements, eg, alloys of palladium and silicon or alloys of iron, phosphoms, and carbon. 

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