PN Junction Diode in forward and reverse biasing

The PN juntion diode is the basic electronic device after which large number of electronic devices were invented. PN junction diode normally used under the forward bias as it allows current to flow through it only under this condition, while in reverse bias also a minute amount of current flows through the device but it is negligible and is not used in reverse bias. Special types of diodes are used to work under the reverse bias condition for specific application such as Zener Diode.

When we consider the forward bias we consider

1) Ideal case

2) Practical case

Ideal case in which there will not be any resistance or any junction voltage under zero biasing and when a forward voltage is applied the current will suddenly raise.But ideal cases are never true in the field of electronics.

In practical case there will already be a voltage across the junction. Now the forward biasing the PN means P connected to positive side and N is connected to the negative side, the junction voltage will be opposite direction of forward bias. So initially there will not be any current passing through the junction. Increase a bit forward voltage still no current, continue this at a particular voltage called as the cutin voltage of the diode which is approximately equal value to the junction voltage current starts to flow through the diode.  While increasing the voltage under forward biasing the the charge carriers which are separated by the junction voltage will start moving towards the junction due to the potential applied now when the potential applied is slightly greater than the junction potential then the carriers will cross the junction leading to current. As we further increase the forward voltage the current  increases in exponential manner.

Under the reverse biasing condition , the P side is connected to the negative terminal and N side connected to the positive terminal which leads to the carriers moving away from the junction and the current produced will always be zero in ideal case and practically a reverse saturation current exist.