Diode a nonlinear device that is used to control the direction of current in a circuit. It is made by combining a piece of p-type and a piece of n-type semiconductor. The layer between p-type and n-type semiconductors is called the depletion region which is made of immobile carriers. A diode has two terminal pins; the pin connected with the p-type material is called Anode and the pin connected with the n-type material is called Cathode.
A diode has two biasing modes – forward bias and reverses bias. In forward bias, i.e., when the anode is more positive biased than the cathode, the diode conducts, and in reverse bias, i.e., when the cathode is more positive biased than the anode, the diode acts as an open circuit (ideally). But when the reverse bias voltage reaches a certain value, the diode breaks down and a large reverse bias current flows through it.
Now depending on the mechanism of breakdown diode can be classified into two categories – PN junction diode and Zener Diode. In this article, we are going to discuss the difference between PN junction diode and Zener diode.
Difference between PN junction Diode and Zener Diode
In the following table, we have pointed out some key differences between the PN junction diode and Zener diode.
| PN junction diode | Zener Diode |
| The diode is made of comparatively lightly doped semiconductor materials. | The diode is made of highly doped semiconductor materials. |
| When the reverse bias voltage reaches breakdown voltage, the junction is destroyed. | When the reverse bias voltage reaches breakdown, the junction is not destroyed. |
| This type of diode has a positive temperature coefficient i.e., the value of the breakdown voltage increases if the temperature is increased. | Zener diode has a negative temperature coefficient i.e., the value of the breakdown voltage decreases when the temperature is increased. |
| The breakdown of the diode is not desired as it destroys the diode. | One of the reasons to use Zener diode is Zener breakdown. |
| It is used in rectifier, clipper, clammer circuits. | It is used in the over-voltage protection circuit. |
PN junction Diode
A PN junction diode is made by combining p-type and n-type semiconductors. When a diode is forward biased the width of this depletion region reduces and current can flow through the diode. But when the diode is reverse biased the width of the depletion region increases and the diode does not conduct. Though a very small amount of current flows in the reverse direction called reverse bias current.
When reverse bias voltage reaches breakdown voltage, the free electrons in the p-region move into the depletion region and collide with the valence band electrons of the atoms, and create more free electrons. Thus, a large reverse bias current is generated.
Zener Diode
Zener diode is also created using p-type and n-type semiconductors but in this case, the semiconductors are heavily doped. The forward bias and reverse bias situations are the same for both diodes. But the primary difference between a PN junction diode and a Zener diode is the mechanism of breakdown. In the case of the Zener diode, when the reverse bias voltage reaches the breakdown voltage, the valance band electrons in the depletion region come to the conductance band due to the applied electric field and a large amount of current flow through the diode in the reverse direction.
Conclusion
As the breakdown of the normal PN junction diode is not desired as this destroys the diode. But in the case of the Zener diode, the breakdown does not destroy the diode. That is why there are different applications. PN junction diodes are used in rectifiers, clippers, limiters, etc., and Zener diodes are primarily used in the voltage-protection circuit.
Author
Subhrajyoti Choudhury
