Amorphous silicon

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Amorphous silicon (a-Si) is the non-crystalline allotropic form of silicon. Silicon is a four-fold coordinated atom that is normally tetrahedrally bonded to four neighboring silicon atoms. In crystalline silicon this tetrahedral structure is continued over a large range, forming a well-ordered lattice (crystal). In amorphous silicon this long range order is not present and the atoms form a continuous random network. Not all the atoms within amorphous silicon are four-fold coordinated. Due to the disordered nature of the material some atoms have a dangling bond. These dangling bonds are defects in the continuous random network, which cause undesired (electrical) behaviour. 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. Hydrogenated amorphous silicon has a sufficiently low amount of defects to be used within devices. However, the hydrogen is unfortunately associated with light induced degradation of the material, termed the Staebler-Wronski Effect.

Stanford R. Ovshinsky holds a number of patents in the area of amorphous semiconductor materials, semiconductors, and solar electricity generation via amorphous silicon solar cells, which are much cheaper to produce than solar cells made of crystalline silicon.

Amorphous silicon is one of the materials used for microbolometer arrays for uncooled thermal cameras.

[edit] See also

• Nanocrystalline silicon
• Polycrystalline silicon
• Stanford R. Ovshinsky

[edit] External links

• Amorphous Silicon Devices group at the University of Waterloo, Ontario, Canada
• Theory and Simulation at Ohio University, Athens Ohio
• National (U.S.) Renewable Energy Laboratory Information on Amorphous Silicon
• How electronic inks will work
• Xsunx - A company which has developed a manufacturing technique for transparent solar cells