PN Junction Diode
Basically, PN junction diode is two-terminal semiconductor device that control flow of electric current in a circuit. In case P-type semiconductor holes are majority carriers and electrons are minority carrier and in n-type of semiconductor electrons are majority carries & holes are minority carriers. They individually act like resistor. But when they joined together by the method of doping the junction is form between them.
When a p-n junction is formed, some of the electrons which are present in n-region diffuse across the junction and combine with holes to form negative ions. Similarly, the positive charges or holes from the p-side are diffused to the n region and they form a layer of positive charge on the n-side. The region between these two layers is the depletion region.
About unbiased p-n junction, due to presence of immobile positive and negative ions on opposite side of junction, an electric field is created across the junction this is nothing but barrier potential. For Si= 0.7 & for Ge= 0.3 volts. Due to the electric field which is created around junction, the minority carriers near the junction gets attracted towards junction and swapped across the depletion region. In this case no external voltage is applied so flow of majority carrier as well as flow of minority carrier balances each other so net current in the circuit is zero.
There are two types of p-n junction namely Forward biased and Reversed biased junction.
In case of forward biased junction, the positive terminal of the battery is connected to the n-side and negative terminal of battery is connected to the p-side of the battery. When we apply more external voltage, the width of the depletion layer decreases and current start flowing due to majority carriers from p-side to n-side.
In case of Reverse Biased, the positive terminal of battery connected to the p-side and negative to the n-side. When voltage is applied across a diode, the potential barrier at the junction increases as well as resistance at junction also increases. Due to this, It prevents current flow but the minority carriers are accelerated by the reverse voltage resulting a very small current that current is called reverse current.