Used as semiconductor material for a-Si solar cells, or thin-film silicon solar cells, it is deposited in thin films onto a technology and Applications of Amorphous Silicon PDF of flexible substrates, such as glass, metal and plastic. Amorphous silicon differs from other allotropic variations, such as monocrystalline silicon—a single crystal, and polycrystalline silicon, that consists of small grains, also known as crystallites.
Författare: Robert A. Street.
Amorphous silicon has enabled a new technology for large-area electronics, with major applications in liquid crystal displays, image sensing and solar power conversion. This book presents a broad description of the current technology and its future potential, so that the reader can understand how the particular properties of amorphous silicon lead to unique applications. Topics covered include the design of the amorphous silicon transistor and sensor devices, the range of matrix-addressed arrays and other systems that can be fabricated, and the performance of the various application areas.
Silicon is a fourfold coordinated atom that is normally tetrahedrally bonded to four neighboring silicon atoms. In amorphous silicon this long range order is not present. Rather, the atoms form a continuous random network. Moreover, not all the atoms within amorphous silicon are fourfold coordinated. Due to the disordered nature of the material some atoms have a dangling bond. Physically, these dangling bonds represent defects in the continuous random network and may cause anomalous electrical behavior. The material can be passivated by hydrogen, which bonds to the dangling bonds and can reduce the dangling bond density by several orders of magnitude.
Introduction of carbon atoms adds extra degrees of freedom for control of the properties of the material. The film could also be made transparent to visible light. This can potentially increase the light efficiency of solar cells made with amorphous silicon carbide layers. Several studies are found in the scientific literature, mainly investigating the effects of deposition parameters on electronic quality, but practical applications of amorphous silicon carbide in commercial devices are still lacking. The density of amorphous Si has been calculated as 4.
Silicon is one of the few elements that expands upon cooling and has a lower density as a solid than as a liquid. Unhydrogenated a-Si has a very high defect density which leads to undesirable semiconductor properties such as poor photoconductivity and prevents doping which is critical to engineering semiconductor properties. By introducing hydrogen during the fabrication of amorphous silicon, photoconductivity is significantly improved and doping is made possible. While a-Si suffers from lower electronic performance compared to c-Si, it is much more flexible in its applications. For example, a-Si layers can be made thinner than c-Si, which may produce savings on silicon material cost.
One further advantage is that a-Si can be deposited at very low temperatures, e. This allows deposition on not only glass, but plastic as well, making it a candidate for a roll-to-roll processing technique. Another advantage is that a-Si can be deposited over large areas by PECVD. Si photodiodes on glass are used as visible-light image sensors in some flat panel detectors for fluoroscopy and radiography.