| Depletion Zone |
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CONCEPTUAL OVERVIEW The depletion region forms across the P-N Junction when the junction is in thermal equilibrium, ''i.e.'' things are in a steady state. Electron s and Hole s will diffuse into regions with lower concentrations of electrons and holes, much as ink will diffuse into water until it is uniformly distributed throughout. N-type semiconductor has an excess of free electrons, and P-type has an excess of holes. Therefore when N-doped and P-doped pieces of semiconductor are placed together to form a junction, electrons will diffuse into the P side and holes will diffuse into the N side. However when a hole and an electron come into contact, they eliminate each other through Recombination . This bares the Donor atoms adjacent to the depletion region, which are now Charge d Ion s. The ions are positive on the N side and negative on the P side, creating an Electric Field that counteracts the continued diffusion of charge carriers. When the electric field is sufficient to repel incoming holes and electrons, the depletion region reaches its equilibrium width. Integrating the electric field in the depletion region gives what is known as the built-in potential (also called the junction voltage or barrier voltage). Under reverse bias (P negative with respect to N) this potential is increased, further widening the depletion zone. Forward bias (P positive with respect to N) narrows the zone and eventually reduces it to nothing, making the junction conductive and allowing free flow of charge carriers. The depletion region area is void of all majority carriers. |
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