P-N JUNCTION DIODE

 P-n junction diode

An unbiased PN junction is a built in potential will be potential  will be developed at the junction. When PN junction is formed,the resulting two terminal device is called as junction diode.

The P terminal is called as anode and N terminal is called cathode. Under unbiased condition,there is no conduction,that is no current exists in the device.for the current to flow the device must be biased suitably by baiasing it means the application of an external voltage.there are two methods of biasing a junction diode.

1.forward bias

2.reverse bias

Forward bias

The forward bias junction diode is as shown in below.by forward bias,it means that the positive terminal of external sources is connected to the P terminal and the negative terminal to the N material, respectively. By doing  so, the externally connected DC voltage established an electric field opposite to the potential barrier,there by reducing the potential barrier.the potential barrier is typically 0.1 ev for Ge and 0.5 for Si. As such, a small external voltage is enough to eliminate the barrier,and the junction resistance becomes almost zero.now aided by this external voltage,the free electrons in the N material cross the junction and move into P region.the free electrons combines with holes near the junction .since a holes is the Covalent bond,where a free electrons combines with a hole,it becomes a valence electrons and in the P region the electrons travel as valence and enter the positive terminal. So this is a forward bias.

               Forward bias circuit diagram 

Reverse bias

When the positive terminal and negative terminal of the battery are connected to the N type material and the P type material.  Then the type of biasing is called reverse bias.

Electrons in N region and holes in previous moves away from the junction. And therefore is no connected increase the potential barrier,which prevent the flow the no combination of Electron and holes  prati ally the reverse bias current is zero,and whatever little current is present.

In this two methods forward bias having a small resistance, resulting in an appreciable forward current. When the reverse bias having no current.

                     Reverse bias circuit diagram