Editing Silicon (section)

====Electrical====
At standard temperature and pressure, silicon is a shiny [[semiconductor]] with a bluish-grey metallic lustre; as typical for semiconductors, its resistivity drops as temperature rises. This arises because silicon has a small energy gap ([[band gap]]) between its highest occupied energy levels (the valence band) and the lowest unoccupied ones (the conduction band). The [[Fermi level]] is about halfway between the [[valence and conduction bands]] and is the energy at which a state is as likely to be occupied by an electron as not. Hence pure silicon is effectively an insulator at room temperature. However, [[Doping (semiconductor)|doping]] silicon with a [[pnictogen]] such as [[phosphorus]], [[arsenic]], or [[antimony]] introduces one extra electron per dopant and these may then be excited into the conduction band either thermally or photolytically, creating an [[Extrinsic semiconductor#N-type semiconductors|n-type semiconductor]]. Similarly, doping silicon with a [[boron group|group 13 element]] such as [[boron]], [[aluminium]], or [[gallium]] results in the introduction of acceptor levels that trap electrons that may be excited from the filled valence band, creating a [[Extrinsic semiconductor#P-type semiconductors|p-type semiconductor]].{{sfn|Greenwood|Earnshaw|1997|p=331}} <!-- this could be moved to electronic applications --> Joining n-type silicon to p-type silicon creates a [[p–n junction]] with a common Fermi level; electrons flow from n to p, while holes flow from p to n, creating a voltage drop. This p–n junction thus acts as a [[diode]] that can rectify alternating current that allows current to pass more easily one way than the other. A [[transistor]] is an n–p–n junction, with a thin layer of weakly p-type silicon between two n-type regions. Biasing the emitter through a small forward voltage and the collector through a large reverse voltage allows the transistor to act as a [[triode]] amplifier.{{sfn|Greenwood|Earnshaw|1997|p=331}}