PN junction diode is a unidirectional device (conduct only in one direction)
PN junction diode is also called as semiconductor device. It is made up of joining p-type semiconductor and n-type semiconductor together. Due to this there is an electron from n-type combines with holes in the p-type and becomes neutral forming a depletion region.
No Biasing:
No biasing means when a diode is not connected with any external voltages.
Biasing:
- Forward biasing
- Reverse biasing
Forward biasing:
Forward biasing means positive terminal of the battery is connected to p-type and negative terminal of the battery is connected to n-type . When battery is switched on due to forward bias the depletion layer reduces and after some voltage current reduces as shown in the figure.
For germanium — 0.3
For silicon — 0.7
Reverse biasing:
Reverse biasing means negative terminal of the battery is connected to p-type and positive terminal of the battery is connected to n-type . When battery is switched on due to reverse bias the depletion layer increases. Due to this no current flow occurs.
Ideal condition:
At ideal condition diode act as a switch at forward bias diode act as a close circuit at reverse bias diode act as a open circuit .
VI characteristics of forward and reverse bias:
Engineer's class 