In a pn junction, why does current flow in the forward-bias direction but not in the reverse-bias direction?
PN-Junction:
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.