Pn junction is a junction where p type and n type diode are joint together is called pn junction
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“A p-n diode or p-n junction is a two terminal device formed by joining a p-type and n-type semi-conductors.” A junction between p-type and n-type is formed where holes and electrons diffuse into each other thereby forming a depletion layer. The thickness of depletion layer provides a potential barrier which prevent further migration of holes and electrons through depletion layer. Thickness of depletion layer could be increased or decreased by varying the potential of the potential barrier, which increases or decreases the conductivity of diode. A p-n diode could be used in electrical circuits across a battery, as it permits the flow of current in one direction only.