When the diode is in forward bias phase and suddenly we apply a reverse bias voltage, the diode takes time to be fully blocked because of the excess of minority charges that are stored in P and N region. Thus a reverse current appears in the diode for a short time before it is blocked. My question is, is this current a diffusion of the excess of minority carriers that are stocked? If yes, why does this happen physically speaking? How does the current suddenly become negative?
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In transient conditions you also need to consider the displace current which flows in response to a time varying electric field. This will happen as you reverse the bias applied across the diode,
$$J = j_e + j_h + \epsilon_0 \frac{\partial\bf{E}}{\partial t}$$
where $j_e$ and $j_h$ are the currents due to flow of particles (the drift and diffusion of electrons (e) and holes (h)) and the third term is the displacement current.
boyfarrell
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