Zener Breakdown and Avalanche Breakdown

The main point of difference between the two is the way they occur. Both these breakdowns may happen at the same time. Zener breakdown happens when there is a high electric field while avalanche breakdown occurs due to the collision of free electrons and atoms  

AVALANCHE BREAKDOWN                                                                                                                    ZENER BREAKDOWN

 ZENER DIODE- 

A Zener diode is a PN junction that works in a reverse-biased state. When a normal PN junction is connected reversely, it is termed as Zener diode. A Zener diode is heavily doped. When forward biased, it functions as an ordinary diode. On reversing, the depletion layer of the diode gets broader along with minority carriers due to which, a constant reverse saturation current occurs. The minority carriers acquire kinetic energy due to the strong intensity of the electric field. The stationary ions of the depletion layer collide with free electrons to produce more free electrons. These new electrons acquire enough kinetic energy resulting in the generation of more free electrons. This constant loop results in a large number of electrons which make the diode conductive. 

ZENER BREAKDOWN-

Application of a reverse-biased voltage on the ends of highly doped PN junctions results in the expansion of the depletion region of the diode. Due to this, a large number of electrons is produced and holes are generated. There are holes and electrons on either side of the depletion region. These carrier electrons create a high electric field. A force is exerted by this electric field which is present in the valence band. These valence electrons will be forced into the conduction band. This phenomenon is known as the Zener effect. High doping is the main reason for Zener’s breakdown. 

Applications of Zener diode-

1. Acts as a voltage regulator- the constant reverse voltage makes it a good source to regulate the output voltage. 
2. Zener- controlled output switch- the Zener diode is used to switch the output between voltages when the input voltage difference is detected. The Zener regulator present switches the output circuit from one Zener voltage to another on transition. 
3. Zener limiter- one side of a sinusoidal wave can be limited by a single Zener diode while the other side is fixed to zero. 
4. Zener role in power supply- the ability of Zener diodes to maintain constant voltage over a large current range makes it a valuable voltage regulator. 

AVALANCHE DIODE-

It is primarily designed to cause an avalanche breakdown at a set reverse bias

voltage. The PN junction of this type of diode is structured in such a way that the concentration of current is prevented to protect the diode from being damaged by the avalanche breakdown. The Zener diode and avalanche diode are made similarly. Unlike Zener diodes, a voltage higher than the breakdown voltage is maintained by avalanche diodes. 

AVALANCHE BREAKDOWN- 

The electrons move across the depletion region which is the reason for the velocity and kinetic energy possessed by them. The velocity of minority carriers makes them move in the semiconductor band. The collision of tightly bonded stationary atoms and free electrons takes place. The stationary is tightly held due to the covalent bond which is broken by the bound electrons. The stationary electrons travel towards the conduction band which in turn increases the kinetic energy. The reverse bias voltage is also increased. More electrons will keep on colliding which will result in a high-intensity current generation. This will cause the breakdown of the diode. This phenomenon is known as avalanche breakdown. 

MAJOR DIFFERENCES BETWEEN ZENER & AVALANCHE BREAKDOWN:

1. Zener breakdown occurs in the thin region while avalanche breakdown occurs in the thick region.
2. Zener breakdown occurs in highly doped junctions while avalanche breakdown has lightly doped junctions.
3. The electric field is stronger in Zener diodes than an avalanche breakdown. 
4. Zener breakdown produces electrons while avalanche breakdown produces both electrons and holes in pairs. 
5. The avalanche breakdown voltage is higher than the Zener breakdown. 
6. The Zener breakdown is irreversible while avalanche breakdown is irreversible. 
7. The coefficient of temperature is positive and negative in avalanche breakdown and Zener breakdown respectively. 
8. The temperature and voltage are directly proportional in avalanche breakdown while in Zener breakdown they are indirectly proportional.

CONCLUSION-

Zener breakdown and avalanche breakdown differ mainly by their mechanism of occurrence. The Zener breakdown is not reversible while the avalanche breakdown is.