amorphoussilicon

Amorphous silicon refers to a non-crystalline form of silicon in which the atoms lack long-range order. Unlike crystalline silicon, which has a regular lattice, amorphous silicon forms a disordered network of silicon atoms. In practice, device-grade amorphous silicon is often hydrogenated (a-Si:H) to passivate dangling bonds, improving electronic quality.

The material has a larger optical band gap than crystalline silicon, typically around 1.7 to 1.8 eV for a-Si:H, and a high density of defect states near the Fermi level due to structural disorder. Hydrogen passivation reduces dangling bonds, but some defects remain, leading to lower carrier mobilities and shorter diffusion lengths compared with crystalline silicon.

Amorphous silicon is produced by thin-film deposition techniques such as plasma-enhanced chemical vapor deposition (PECVD) from silane or other silicon hydrides at low temperatures, enabling coating on glass, plastic, and metal substrates. Other methods include standard chemical vapor deposition or sputtering, often in multilayer stacks that include silicon nitride and/or microcrystalline layers.

Applications include thin-film solar cells, especially in a-Si:H and tandem devices combining amorphous and microcrystalline silicon, as well as thin-film transistors in displays and imaging sensors. A notable drawback is light-induced degradation (Staebler–Wronski effect), which reduces performance under illumination and can partially recover in darkness.

Despite limitations, amorphous silicon offers low material cost, mechanical flexibility, and the possibility to be deposited on large-area substrates, making it attractive for photovoltaics and flexible electronics.