Introducing Boron. Of course, n-type silicon cannot form the electric field by itself; it's also necessary to have some
silicon altered to have the opposite electrical properties. So, boron, which has three valence
electrons, is used for doping p-type silicon. Boron is introduced during silicon processing,
where silicon is purified for use in PV devices. When a boron atom assumes a position in the
crystal lattice formerly occupied by a silicon atom, there is a bond missing an electron (in other
words, an extra hole).
Substituting a boron atom (with three valence electrons) for a
silicon atom in a silicon crystal leaves a hole (a bond missing an electron) that is relatively free
to move around the crystal.
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