How is the structure of silicon


Silicon (Si) is a chemical element with semiconductor properties that is used in microelectronics in a highly pure, monocrystalline form. The silicon atoms are arranged in a regular lattice. In the valence band, the silicon atoms have four electrons that are firmly connected to the electrons of the neighboring atom.

The band gap between the conduction band and the valence band is relatively small and is 1.1 electron volts (eV). If an electron is torn out of the electron compound by the supply of energy, it can be used for charge transport and leaves a hole in its previous position. The charge transport can be increased by further released electrons and by additionally added electrons. These additional electrons are introduced through targeted contamination, known as doping.

The different forms of silicon

Silicon can be manufactured in a highly pure form with a monocrystalline structure, but also in a polycrystalline and non-crystalline, amorphous structure. Monocrystalline silicon (c-Si) is high-purity silicon in which the atomic structures are arranged in a regular, directed crystal lattice. Monocrystalline silicon is drawn into monocrystalline silicon cylinders, called ingots, in a silicon melt and form the basic material for the wafers. For this purpose, the silicon cylinders are sawn into thin silicon wafers, which are used for the production of integrated circuits and solar cells. However, pure silicon only absorbs wavelengths up to 1,100 nm. Polycrystalline silicon (p-Si), also known as polysilicon, has a multicrystalline structure and consists of many individual crystals. The crystals are about 10 ┬Ám in size and have a regular structure, although they are arranged irregularly in the silicon block. During production, it is poured into silicon blocks that are sawn into thin slices. The molecular structure of polycrystalline silicon is coarser than that of monocrystalline silicon. This semiconductor material can be manufactured more cheaply and is used, among other things, in photovoltaics.

Sharp has further developed the polycrystalline silicon by means of Low Temperature Poly Silicon (LTPS) to Continuous Grain Silicon (CG-Si). Continuous Grain Silicon is characterized by larger, regular crystal structures of uniform size and expansion. The electron mobility is many times - approx. 600 times - higher than that in amorphous silicon. This allows displays to be developed whose pixels have shorter response times.

Amorphous silicon (a-Si) does not have a regular crystal structure and also has no crystal face. This material, which can be synthetic resin or glass, does not have a solid structure. It has a high absorption capacity, can be manufactured inexpensively, but has poorer electronic properties than poly- and monocrystalline silicon. In photovoltaics, it is used with an optimized microstructure. The non-crystalline semiconductors also include cadmium sulfide, cadmium telluride (CdTe) and copper indium diselenide (CIS). The efficiency of amorphous silicon is around 7%, only about half that of pure silicon.