In a basic semiconductor, a junction is formed due to the interaction between p-type and n-type. This junction can be dope heavily or lightly based on circumstances. As it is already known that a basic diode that is of junction p-n can conduct during forward bias.
Once the stage of reverse bias entered it cannot conduct and some breakdowns arise. These are mainly due to the multiplication of the carriers as well as due to the doping concentration made high at the junction. There are two types of breakdown
(1) Avalanche Breakdown
(2) Zener Breakdown
What is Avalanche Breakdown?
- As the functionality of the basic diode is already known in reverse bias condition the diode gets affected as it is non-conducting mode. But still there is the movement noticed and that is due to minority carriers.
- The current generated because of the minority charge is referred to as reverse saturation current and this is responsible for the occurrence of avalanche breakdown.
- However in a diode, if p-type and n-type material is utilized the interacted part of it is termed as the junction. At this junction there exist depletion region.
- Both p and n types have some majority and minority carriers in it. As the reverse bias is considered the focus is on minority carriers. P-type has electrons and n-type has holes for this purpose.
- As the width of the depletion region at the junction is variable. It is dependent on the type of bias is supplied to the diode.
- In the case of the reverse bias, the width of the region will be more. This can affect the working condition of the diode. But in this condition, the minority charges gets sufficient kinetic velocity so that it can overcome the barrier of the junction.
- Due to this, collisions in between occurs. These are responsible for the generation of free charges. As this process goes on the further generation of carriers takes place resulting in the formation of more number of free carriers. This phenomenon is referred to as carrier multiplication.
- Hence the flow of reverse current is noticed. This leads to the condition in the diode breakdown referred to an avalanche breakdown. This can damage the junction completely and it is non-refundable.
What is Zener Breakdown?
- In the basic diode, a junction is formed due to the interaction of p-type and n-type. This has the depletion region at the junction.
- The width of this region is also the factor of the doping concentration. The doping at the junction can be done lightly or heavily.
- The width of the depletion and the doping levels are inversely related to each other. It means if the junction is heavily doped then the width will be minimum and vice-versa.
- If the considered junction is of high doping value then undergoes the phenomena of zener breakdown.
- If it has a minimum width of depletion region it suggests that it has the number of free charges present. These tend to cross the junction. Because it has the highest electric intensity of the field the rapid movement in the carriers is noticed.
- Hence it results in the formation of free carriers and the flow of reverse current can be seen. This eliminates the depletion region. This type of phenomena is known as zener breakdown.
- But in zener breakdown, the depletion region will retain back once the reverse voltage has been removed.
In this way, the types of breakdowns in the basic diode due to the reverse biasing condition has been discussed.
What is an Avalanche Diode?
A diode that is designed to operate in the reverse biasing condition and it’s junction is lightly doped. But it comes under the special category of the diode. The symbolic representation for both zener and avalanche diodes are the same.
What is a Zener Diode?
A basic diode with a normal junction of p-n cannot operate in reverse bias. In order to make this one possible a special diode has to be designed, that has the normal characteristics during forward bias but during reverse bias, it can operate and tolerate the currents.
Hence this is referred to as zener diode. This type of diode is having good doping concentration at its junction.
Difference between Zener and Avalanche Breakdown
Both the zener and the avalanche breakdowns occur in the reverse biasing stage. The zener breakdown’s voltage is comparatively lesser than the breakdown of an avalanche. The basic differences of both the breakdowns can be listed as follows
(1) The reason behind the occurrence of this breakdown is mainly due to the collision that takes place between the carriers.
(1) The reason here behind this breakdown is due to the high intensity of the electric field.
(2) The region of the depletion region is thick enough.
(2) The width of the region of depletion is thin.
(3) The concentration of doping at the junction is at the minimum.
(3) The concentration level of doping is high at the junction.
(4) Focused on the production of a pair of electrons and holes.
(4) Mainly the production of electrons focused here.
(5) The intensity of the electric field is low.
(5) The intensity of the electric field is strong enough.
(6) The coefficient of temperature is of positive value.
(6) The coefficient of temperature is of negative value.
(7) The ionization occurred here is due to the influence of collision effect.
(7) The ionization in this breakdown is due to the strong intensity of the electric field.
(8) The breakdown voltage and the temperature are directly related to each other.
(8) The breakdown voltage and the temperature are inversely related to each other.
(9) Once the breakdown has occurred the voltage tend to vary.
(9) The occurrence of breakdown doesn’t affect the voltage.
(10) Once it undergoes the breakdown the junction gets destroyed completely it cannot retain back its position.
(10) As the reverse voltage is removed from the diode the junction gets back to its normal position.
Hence in this way, the analysis for the types of breakdown is done. Both the breakdowns have their own standards. Now based on the above analysis can determine which type of diode either avalanche or zener is used in protection circuitry?