<P> (Note: When discussing periodic table groups, semiconductor physicists always use an older notation, not the current IUPAC group notation . For example, the carbon group is called "Group IV", not "Group 14".) </P> <P> For the Group IV semiconductors such as diamond, silicon, germanium, silicon carbide, and silicon germanium, the most common dopants are acceptors from Group III or donors from Group V elements . Boron, arsenic, phosphorus, and occasionally gallium are used to dope silicon . Boron is the p - type dopant of choice for silicon integrated circuit production because it diffuses at a rate that makes junction depths easily controllable . Phosphorus is typically used for bulk - doping of silicon wafers, while arsenic is used to diffuse junctions, because it diffuses more slowly than phosphorus and is thus more controllable . </P> <P> By doping pure silicon with Group V elements such as phosphorus, extra valence electrons are added that become unbonded from individual atoms and allow the compound to be an electrically conductive n - type semiconductor . Doping with Group III elements, which are missing the fourth valence electron, creates "broken bonds" (holes) in the silicon lattice that are free to move . The result is an electrically conductive p - type semiconductor . In this context, a Group V element is said to behave as an electron donor, and a group III element as an acceptor . This is a key concept in the physics of a diode . </P> <P> A very heavily doped semiconductor behaves more like a good conductor (metal) and thus exhibits more linear positive thermal coefficient . Such effect is used for instance in sensistors . Lower dosage of doping is used in other types (NTC or PTC) thermistors . </P>

How doping alters the atomic structure of silicon
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