Crystallization amorphous silicon

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. 

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. 

Single crystal silicon (sc-Si), polyciystalline silicon (p-Si), and amorphous silicon (a-Si) can all be used to make solar cells, with fabrication cost and device photoconversion efficiencies decreasing as one moves from single-crystal to amorphous materials. Various properties of these materials are summarized in Table 8.1. Other relatively common solar cell materials include gallium arsenide (GaAs), copper indiirm diselenide (CIS), copper indium-gallium... 

The short-range order in a material is important in determining optoelectronic properties. For instance, x-ray and electron diffraction experiments performed on amorphous silicon ( -Si) and germanium (d-Ge) have revealed that the nearest neighbor environments are approximately the same as those found in their crystalline counterparts (6) photoemission experiments performed on -Si show that the DOS in valence and conduction bands are virtually identical to the corresponding crystal with the exception that the singularities (associated with periodicity) present in the latter are smeared out in the former. 

With materials of this type FIM finds its limitations. Several attempts have been made to use field ion microscopy to study amorphous materials such as metallic glasses and amorphous silicon or hydrogenated amorphous silicon thin films deposited on metal tip surfaces.96"98 100-102 Since there is no well defined crystal lattice, the structure of an amorphous material is usually described by the pair distribution function of the... 

Although conventional solar cells based on silicon are produced from abundant raw materials, the high-temperature fabrication routes to single-crystal and polycrystalline silicon are energy intensive and expensive. The search for alternative solar cells has therefore focused on thin films composed of amorphous silicon and on other semiconductor heterojunction cells (e.g., cadmium telluride and copper indium... 

Transmission electron microscopy (tern) is used to analyze the structure of crystals, such as distinguishing between amorphous silicon dioxide and crystalline quartz. The technique is based on the phenomenon that crystalline materials are ordered arrays that scatter waves coherently. A crystalline material diffracts a beam in such a way that discrete spots can be detected on a photographic plate, whereas an amorphous substrate produces diffuse rings. Tern is also used in an imaging mode to produce images of substrate grain structures. Tern requires samples that are very thin (10—50 nm) sections, and is a destructive as well as time-consuming method of analysis. 

Microsystems can be built on various substrates with a range of materials crystalline silicon, amorphous silicon, glass, quartz, metals, and organic polymers. Single-crystal silicon substrates have been used in most areas of microfabrication for a range of excellent reasons ... 

T. Tsukada, Active-Matrix Liquid-Crystal Displays in Technology and Applications of Amorphous Silicon, R. A. Street (Ed), Springer Verlag, Heidelberg, 2000. 

Work with a-sexithienyl TFTs yielded more promising values The field-effect mobility reaches 3 x 10"2 cm2/V s, with currents and voltages similar to those with CPs [227,254]. For comparison, amorphous silicon FETs [256] usually have x 0.1 to 0.3 cm2/V s, sometimes nearly reaching 1 cm2/V s [257], with /D 1 to 100 xA at voltages of about 10 V, and such devices are used in liquid-crystal display panels [234]. 

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