PN junction diode and its applications

PN junction diode

A PN junction is an interface between two types of semiconductor material, p-type and n-type. The "p" (positive) side contains an excess of holes while the "n" (negative) side contains an excess of electrons in the outer shells of the electrically neutral atoms there. This allows electrical current to pass through the junction only in one direction. The p-n junction is created by doping, for example by ion implantation, diffusion of dopants, or by epitaxy. If two separate pieces of material were used, this would introduce a  between the semiconductors that would severely inhibit its utility by scattering the electrons and holes. P-N junctions are the elementary building blocks of semiconductor electronic devices such as diodes, transistors, solar cells, and integrated circuits. They are the active sites where the electronic actions of devices take place.

PN junction diode

Forward biased 

When the p-type is connected to the positive terminal of the battery and the n-type to the negative terminal then the p-n junction is said to be forward-biased. In the case of the forward-biased junction, the built-in electric field at the p-n junction and the applied electric field are in opposite directions. When both the electric fields add up, the resultant electric field has a lower magnitude than the built-in electric field. The potential barrier is almost eliminated and the current starts flowing in the circuit. results in a less resistive and narrow depletion layer or region. The depletion region’s resistance becomes negligible when the applied voltage is large. 

Forward biased function 

Reverse biased

When the p-type is connected to the negative terminal of the battery and the n-type is connected to the positive side then the p-n junction is said to be reverse biased. In this case, the built-in electric field and the applied electric field are in the same direction. When the two fields are added, the resultant electric field is in the same direction as the built-in electric field creating a more resistive, thicker depletion region. The depletion region becomes more resistive and thicker if the applied voltage increases and the junction resistance becomes very high and as a result, practically no current flows through the circuit.

Reverse biased function 

Application of a junction diode

• PN junction diode can be used as a photodiode as the diode is sensitive to the light when the configuration of the diode is reverse-biased.

• It is used as a rectifier in many electric circuits and as a voltage-controlled oscillator in varactors.

• It can be used as a solar cell and used in switches digital design.

•  The forward-biased diode is used in LED lighting applications.

• It is used in wave shaping circuits in radar, computers, and other electronic devices.