Explain the formation of potential barrier and depletion region in a p-n junction diode. What is effect of applying forward bias on the width of depletion region ?
Formation of the depletion region
Due to concentration gradient hole diffuses from p to n region leaving behind immobile negative charges (ionized acceptor). And electron diffuses from n to p region leaving behind immobile positive charges (ionized doner). Thus a space of positive charge on n side and negative charge on p side is created. This space charge junction on either side is known as the depletion region
Barrier Potential
Due to the depletion region an electric field develops. Due to this electric field, the electron on p side moves to n side and hole an n side of the junction moves to p side. This motion of the charge is called drift current. At some point of time, the diffusion current equals drift current and p-n junction under equilibrium is formed and there is no net current.
Now there is a difference of potential between p and n region and the polarity of potential is such that there is no further flow of carriers
This is known as barrier potential
When a forward bias is applied, the width of the depletion region
decreases.