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I learned that in a p type semiconductor there are impurities with holes and the holes are majority carriers . What is puzzled me is the reason of appearing diffusion current actually . I've read this current occures because of negative ions but I don't understand how these negative ions appear !!

My actual question is about how negative ions appear in a single p type semi conductor(not doped with n type one ) . Thanks

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P-type silicon us doped with group III atoms., for example boron. Boron has one less electron than silicon. Yet it us energetically favorable to have four Si-B bonds, creating a negatively charged site. This leaves a hole in the valence band. This hole is weakly bound to the B ion and is dissociated at room temperature. This hoke contributes to the conductivity. B is therefore a shallow acceptor, whereas P is a shallow donor.

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