In a pn junction, why does current flow in the forward-bias direction but not in the reverse-bias direction?
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Solution
PN-Junction:
P-n junctions are produced by connecting n-type and p-type semiconductor materials. Electrons diffuse from the n-type side to the p-type side because the n-type has a high electron concentration and the p-type has a high hole concentration.
A diode (PN junction) permits the current to flow more freely in one direction than the other. When a voltage is applied to a diode that permits current to flow freely is termed forward biasing, whereas reverse biasing is when a voltage is applied in the opposite direction to a diode.
An electric current will flow in the forward-bias direction due to the majority of carriers' migration over the p-n junction, which is known as forwarding current. When forward biased, the p-n junction has a low resistance to current flow.
4. When the p-type is connected to the battery’s positive terminal and the n-type to the negative terminal, then the P-N junction is said to be forward-biased. 5. When the P-N junction is forward biased, the built-in electric field at the P-N junction and the applied electric field are in opposite directions.
6. When both the electric fields add up, the resultant electric field has a magnitude lesser than the built-in electric field. This results in a less resistive and thinner depletion region.
In the reverse bias case, the built-in electric field and the applied electric field are in the same direction. When the two fields are added, the resultant electric field is in the same direction as the built-in electric field, creating a more resistive, thicker depletion region. The depletion region becomes more resistive and thicker if the applied voltage becomes larger.
Hence, the current flows in the forward-bias direction as a result of a less resistive and thinner depletion region.
