# Diode and doping on N and P regions

by fisico30
Tags: diode, doping, regions
 P: 374 Dear forum, in a diode semiconductor, the N region is rich in electrons. The P region is rich in holes. Is the number of extra electrons in the N region equal, larger or smaller than the number of holes in the P region? If so, why? Also, in the N region, it is said that the majority carriers are the electrons. I get that. The minority carriers are the holes....but there are no holes in the N region so how can there be any minority carriers at all? Thanks, fisico30
 Sci Advisor PF Gold P: 2,013 The number of electrons/holes is a function of doping and can be controlled by the device designer. The doping saturates at around 10^19 cc-1, which is called "extrinsic" doping. It gives the highest conductivity possible which is useful near the electrode connections. You can inject holes into the n region, where they live for a time (the mean recombination time) before meeting electrons and annihilating. Transistor action is caused by minority carriers injected across the base region into the collector.
 Sci Advisor P: 3,257 No, at non-zero temperature, even in equilibrium there are both electrons and holes present in both the n and p region. They fulfill a equilibrium constant equation ##n_en_h=K(T)##. On the n side ##n_e=n_{0e}-n_h\approx n_{0e}## and thus ##n_h\approx K/n_{0e}## where ##n_e## is the number density of electrons ##n_h## the number density of holes and ##n_{0e}## the number density of donor atoms. A similar equation holds for the p side.

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