(Current flow in a pn-junction diode under forward bias.)
Under the forward bias (p-side is more positive w.r.t. n-side, or n-side is more negative w.r.t. p-side), holes are injected from the p-side (red), across the depletion region (around the junction, a region depleted of mobile carriers) into the n-side (blue). The holes injected into the n-side are minority carriers. Near the depletion region boundary, the minority-carrier hole concentration is above the thermal equilibrium concentration because of these electrically injected holes. In the neutral region (red-region) there are two processes going on for the injected minority holes: (1) diffusion and (2) recombination.
(1)Diffusion: There are more holes near the depletion boundary than deeper into the n-region. Therefore they undergo a thermal diffusion, resulting in a net flux of holes (red) away from the depletion boundary.
(2)Recombination: The Nature dictates that the hole concentration try to recover its thermal equilibrium value, and thus try to get rid of the excess holes (dp). These excess holes thus undergo a recombination with a majority-carrier electron which process annihilates holes and electrons in pairs (the vertical flow of red dots). Any of the lost (majority-carrier) electrons are quickly re-supplied from farther-into the n-side, through the Ohmic-contact and metal wire at far side of the n-type region.
The same argument applies to the injected minority electrons.
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