When semiconductor materials, such as silicon, are artificially dopedvalence electronLess impurity atoms, such as boron, replace the position of silicon atoms in the lattice. The impurity atoms lack electrons to form covalent bonds with silicon. It is necessary to seize a valence electron from silicon atoms elsewhere to form holes and negative centers. Such doped impurity elements are called acceptor impurities.
Taking boron doped into silicon crystal as an example to illustrate the role of the acceptor impurity, a boron atom occupies the position of the silicon atom, and the boron atom has three valence electrons. When it forms a covalent bond with the surrounding four silicon atoms, it still lacks an electron, and it must seize a valence electron from the silicon atom elsewhere, so a hole is generated in the covalent bond of silicon crystal.The boron atom receives an electron and becomes a negatively charged boron ion (B-）, called negative center.The negative center has less binding on the hole, and the hole can break free with less energy, which is called free moving conductive hole.Because impurities can accept electrons in silicon and germanium to generate conductive holes and form negative centers.Therefore, they are called acceptor impurities or p-type impurities.[1]
Doping result
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After the pure semiconductor is doped with the acceptor impurity, the acceptor impurity ionizes, which increases the conductive holes in the valence band and enhances the conductivity of the semiconductor. Generally, the semiconductor that mainly relies on hole conduction is called hole type or p-type semiconductor.[1]
