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P-N JUNCTION/a>
p n Junction when a ptype semiconductor is suitably joined to n type semiconductor the contact surface is called PN Junction consider two types of materials one p type and the other n type as shown in diagram left side material is a ptype semiconductor having negative acceptor ions and positively charged holdes the right side material is n type semiconductor having positive donor ions and free electrons suppose the two pieces are suitably treated to form p and Junction keep in mind that n type material has a high concentration of free electrons while ptype material has a high concentration of holes therefore at the junction there is a tendency for the free electrons to diffuse over to the P side and holds to the inside as the free electrons move across the junction from n type to P type positive donor ions are uncovered and they are robbed of free electrons hence a positive charge is built on inside of The Junction at the same time the free electrons cross the junction and uncover the negative acceptor ions by filling in the holes therefore a net negative charge is established on P side of the junction when a sufficient number of donor and acceptor ions is uncovered further diffusion is prevented it is because positive charge on ins side repels holes to cross from P type to n type a negative charge on P side repels free electron to enter from n type to P type thus a barrier is set up against further movement of charge carrier that is holes and electrons this is called potential barrier or Junction barrier V not the layer name the PN Junction in which no free electrons or holes are available is called the depletion layer
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