puneesh makhija is wrong.
Zener breakdown is due to the high electric field present
at the junction.Because of the high E , a sufficiently
strong force exerted on a bound electron by the field to
tear it out of its covalent bond . The new holeelectron pair
created increases the reverse current.(for highly doped
Avalanche breakdown is due to collisions . A thermally
generated carrier falls down the junction barrier and
acquires energy from the applied potential . This carrier
collides with a crystal ion and imparts sufficient energy
to disrupt a covalent bond . In addition to original carrier
a new electron-hole pair is generated . This cumulative
process is referred to as avalanche multiplication .
When in a normally doped p-n juction diode, a high
potential in reverse bias configuration is introduced, the
minority charge carriers(let us take electrons in p type Si
material for explanation)get high Kinetic Energy due to
which they collide with the covalent bonds of Si atoms. The
reaction takes place like an avalanche an one electron
excites two others of the covalent bond. Due to the fast
moving electrons from p to n and holes from n to p in the
avalanche, the potential barrier between the p and n type
material is destroyed. Ths point of time at which the
avalanche takes place is called the AVALANCHE BREAKDOWN.
Also there is a hysteresis effect,once avalanche breakdown
has occurred, the material will continue to conduct if the
voltage across it drops below the breakdown voltage.
Whereas this is not the case in Zener diode.
Zener Diode has a special configuration. It is a heavily
doped p-n junction diode. In zener diode when we increase
the voltage in reverse bias configuration, a point comes
when a high electric field developes at the junction with
positive polarity on the p side and negative polarity at
the n side. This electric field attracts the minority
charge carriers on either side(take electrons on p side) to
move to the other side. Thus electrons on p side move to n
side with high velocity but due to heavy doping, the
electron jumps the juntion. Although the high speed breaks
the boundries of the junction. This point is known as the
ZENER BREAKDOWN. As we know that in Zener breakdown, the
junction does not breaks, it leads to the result that when
the voltage is decreased(less than the zener voltage) in
reverse bias, the zener diode stops acting as a conductor.
In heavily doped diode if we apply a reverse voltage
then it increase the electric field at the junction
and this high electric field leads to the breakdown of the
covalent bonds at the junction, this is called the zener
In a normally doped diode when a high reverse voltage is
appilied then the minority charge carrier get kinetic
energy and recive a high velocity. when electrons with high
kinetic energy colloides with covalent bond knock out the
electron from the bond.The newly generted ele. reapete the
same process.it leads to a chain reaction which makes the
diode highly conducting.
in zener breakdown the breakdown of the covalent bond is
due to the high electric field but in the avalanche
breakdown the breakdown of the covalent bond is due the
colloision of the electron.
suggetions are wellcomed :firstname.lastname@example.org
Nondestructive breakdown in a semicoductor,occuring when
the electric field across the barrier region becomes high
enough to produce a form fo field emission the suddenly
increase the number of carrier in this region.Also known as
Zener breakdown and Avalanche breakdown both are under
reverse bias.which are responsible for such large reverse
Avalanche:-It takes place due to the drift of thermally
generated minority carriers through the junction under the
influence of external field.
Zener breakdown:-It takes place due to presence of strong
electric field and presence of large reverse bias voltage
When doping is heavy then in reverse bias even before the
minority charge carriers aquire sufficient velocity the
breakdown occurs. This kind of breakdown is called Zener
When the reverse voltage is increased the width of the
depletion layer increases at the same time due to the force
of attraction and aquire high velocity. During their motion
inside the diodethey collide with the electrons which are
in covalent bonds of the crystaland bring them out of the
bond. Now these two charges again gain sufficient velocity
an da gain collide with the electrons in the covalent bonds
and bring them out. Due to this multiplication process a
large current flows and this kind of breakdown is called
Avalanche multiplication or Avalanche breakdown.
I just want to know if anyone can explain that why is zener
breakdown reversible and why not avalanche breakdown
although the depletion region width is more in normal pn
junction diode and less in zener diode. This also means
that the junction at zener diode is more easily breakable.
zener breakdown is occur in thin junction which is heavily
doped.when there is an increase in reverse current there is
a strong electric field which is due to the electrons come
across the junction and enough to exert the force on
covalent bonds than there is a inc in electrons&holes pair
are produced which inc the zener current or reverse
saturation current which is independent of applied voltage.
ZenerBreakdown===If the Diode is Heavliy dopped,the depletion
layer will be narrow. As a result very high electric field
exists across the depletion layer.Near the zener breakdown
voltage the field is very intense enough to pull electrons
from the covalant bond directly and create current
Avalanche break down:-
If both p-side and n-side of the diode are lightly doped,
depletion region at the junction widens. Application of a very large electric field at the
junction may rupture covalent bonding between electrons. Such rupture leads to the
generation of a large number of charge carriers resulting in avalanche multiplication.
Zener break down:-
If both p-side and n-side of the diode are heavily doped,
depletion region at the junction reduces. Application of even a small voltage at the
junction ruptures covalent bonding and generates large number of charge carriers.
Such sudden increase in the number of charge carriers results in zener mechanism