Answer / geethu

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
breakdown.


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.

Answer / rigzin namgyal nit kkr

"'Zener diode' and 'avalanche diode' are terms often used
interchangeably, with the former much more common. Both
refer to breakdown of a diode under reverse bias.
Specifically, when a diode is reverse biased, very little
current flows, and the diode is to a first order
approximation an open circuit. As the reverse voltage is
increased, though, a point is reached where there is a
dramatic increase in current. Equivalently, there is a
dramatic reduction in the dynamic resistance (slope of the
V-I curve) that can be as low as 1- 2 W in this region.ÝThis
voltage is called the reverse breakdown voltage and it is
fairly independent of the reverse current flowing.ÝThis
property makes it ideal as a voltage reference.Ý

"Avalanche breakdown is caused by impact ionization of
electron-hole pairs.ÝWhile very little current flows under
reverse bias conditions, some current does flow.ÝThe
electric field in the depletion region of a diode can be
very high. Electron/holes that enter the depletion region
undergo a tremendous acceleration.Ý As these accelerated
carriers collide with the atoms they can knock electrons
from their bonds, creating additional electron/hole pairs
and thus additional current.ÝAs these secondary carriers are
swept into the depletion region, they too are accelerated
and the process repeats itself.ÝThis is akin to an avalanche
where a small disturbance causes a whole mountainside of
snow to come crashing down.Ý The efficiency of the avalanche
effect is characterized by a so-called multiplication factor
M that depends on the reverse voltage (Equation 1).


Equation 1: Multiplication Factor

"Here n is in the range 2 - 6, V is the applied (reverse)
voltage, and Vbr is the breakdown voltage.ÝThis is an
empirical relationship, as are many of the relationships
used to describe both Zener and avalanche breakdown.Ý

"Avalanche breakdown occurs in lightly-doped pn-junctions
where the depletion region is comparatively long.ÝThe doping
density controls the breakdown voltage.ÝThe temperature
coefficient of the avalanche mechanism is positive.ÝThat is,
as the temperature increases, so does the reverse breakdown
voltage.ÝThe magnitude of the temperature coefficient also
increases with increasing breakdown voltage. For example,
the temperature coefficient of a 8.2 V diode is in the range
3 - 6 mV/K while the temperature coefficient of an 18 V
diode is in the range ofÝ 12 - 18 mV/K.

"Zener breakdown occurs in heavily doped pn-junctions.ÝThe
heavy doping makes the depletion layer extremely thin. So
thin, in fact,Ýcarriers canít accelerate enough to cause
impact ionization.ÝWith the depletion layer so thin,
however, quantum mechanical tunnelingÝ through the layer
occurs causing current to flow.ÝThe temperature coefficient
of the Zener mechanism is negativeóthe breakdown voltage for
a particular diode decreases with increasing
temperature.ÝHowever, the temperature coefficient is
essentially independent of the rated breakdown voltage, and
on the order ofÝ -3 mV/K.

"In a 'Zener' diode either or both breakdown mechanisms may
be present. At low doping levels and higher voltages the
avalanche mechanism dominates while at heavy doping levels
and lower voltages the Zener mechanism dominates.ÝAt a
certain doping level and around 6 V for Si, both mechanism
are present with temperature coefficients that just cancel.
It is possible to make Zener diodes with quite small
temperature coefficients.Ý

"Neither Zener nor avalanche breakdown are inherently
destructive in that the crystal lattice is damaged.ÝHowever,
the heat generated by the large current flowing can cause
damage, so either the current must be limited and/or
adequate heat sinking must be supplied."

Answer / debi prasan das

zener breakdown occurs due tos strong electric field across
the diode.when a lower voltage is given ,higher electric
field is generated .due to strong electric field ,the
covalent bonds breakdown and free electrons are generated
when they are sufficient there is sharp rise in current and
breakdown occurs.


avalanche breakdown occurs due to higher velocity of
minority carriers.due to less doping the width of depeletion
region is more.so when a high voltage is given,velocity of
minority carriers increases towards opposite type
semiconductor.when they collide with the walls of
semiconductor,free electrons are generated.when free
electrons are sufficient ,then there is sharp rise in
currents and breakdown occurs.

Answer / kannu

breakdown is the process in which the reverse current increases the depletion layer width, then after a optimum level the reverse electric field or the increase in thermal energy due to increase in temprature make the electron from the valence shell of the atom to get out of it thus creating a electron hole pair whic increases current...zener breakdown occurs due to increase in electric field and avlanche brealdown accurs due to increase in thermal energy of the bonds...

Answer / gyanendu

"Answer:
"'Zener diode' and 'avalanche diode' are terms often used
interchangeably, with the former much more common. Both
refer to breakdown of a diode under reverse bias.
Specifically, when a diode is reverse biased, very little
current flows, and the diode is to a first order
approximation an open circuit. As the reverse voltage is
increased, though, a point is reached where there is a
dramatic increase in current. Equivalently, there is a
dramatic reduction in the dynamic resistance (slope of the
V-I curve) that can be as low as 1- 2  in this region.ÝThis
voltage is called the reverse breakdown voltage and it is
fairly independent of the reverse current flowing.ÝThis
property makes it ideal as a voltage reference.Ý
"Avalanche breakdown is caused by impact ionization of
electron-hole pairs.ÝWhile very little current flows under
reverse bias conditions, some current does flow.ÝThe
electric field in the depletion region of a diode can be
very high. Electron/holes that enter the depletion region
undergo a tremendous acceleration.Ý As these accelerated
carriers collide with the atoms they can knock electrons
from their bonds, creating additional electron/hole pairs
and thus additional current.ÝAs these secondary carriers are
swept into the depletion region, they too are accelerated
and the process repeats itself.ÝThis is akin to an avalanche
where a small disturbance causes a whole mountainside of
snow to come crashing down.Ý The efficiency of the avalanche
effect is characterized by a so-called multiplication factor
M that depends on the reverse voltage (Equation 1).


Equation 1: Multiplication Factor
"Here n is in the range 2 - 6, V is the applied (reverse)
voltage, and Vbr is the breakdown voltage.ÝThis is an
empirical relationship, as are many of the relationships
used to describe both Zener and avalanche breakdown.Ý
"Avalanche breakdown occurs in lightly-doped pn-junctions
where the depletion region is comparatively long.ÝThe doping
density controls the breakdown voltage.ÝThe temperature
coefficient of the avalanche mechanism is positive.ÝThat is,
as the temperature increases, so does the reverse breakdown
voltage.ÝThe magnitude of the temperature coefficient also
increases with increasing breakdown voltage. For example,
the temperature coefficient of a 8.2 V diode is in the range
3 - 6 mV/K while the temperature coefficient of an 18 V
diode is in the range ofÝ 12 - 18 mV/K.
"Zener breakdown occurs in heavily doped pn-junctions.ÝThe
heavy doping makes the depletion layer extremely thin. So
thin, in fact,Ýcarriers canít accelerate enough to cause
impact ionization.ÝWith the depletion layer so thin,
however, quantum mechanical tunnelingÝ through the layer
occurs causing current to flow.ÝThe temperature coefficient
of the Zener mechanism is negativeóthe breakdown voltage for
a particular diode decreases with increasing
temperature.ÝHowever, the temperature coefficient is
essentially independent of the rated breakdown voltage, and
on the order ofÝ -3 mV/K.
"In a 'Zener' diode either or both breakdown mechanisms may
be present. At low doping levels and higher voltages the
avalanche mechanism dominates while at heavy doping levels
and lower voltages the Zener mechanism dominates.ÝAt a
certain doping level and around 6 V for Si, both mechanism
are present with temperature coefficients that just cancel.
It is possible to make Zener diodes with quite small
temperature coefficients.Ý
"Neither Zener nor avalanche breakdown are inherently
destructive in that the crystal lattice is damaged.ÝHowever,
the heat generated by the large current flowing can cause
damage, so either the current must be limited and/or
adequate heat sinking must be supplied."

Answer / jackkkk

In silicon diodes up to about 5.6 volts, the Zener effect is
the predominant effect and shows a marked negative
temperature coefficient. Above 5.6 volts, the avalanche
effect becomes predominant and exhibits a positive
temperature coefficient.

In a 5.6 V diode, the two effects occur together and their
temperature coefficients neatly cancel each other out, thus
the 5.6 V diode is the component of choice in
temperature-critical applications

Answer / james bani legei

zener breakdown is the breaking of the zener diode due to
its breakdown voltage being exceeded .it is cause by high
energy from the current supplied.this energy is used to
break the covalent bonds setting electrons free in large
numbers hence high current conduction in the reverse direction.

avalanche breakdown is caused by current that set few
electrons free,this eletrons starts moving freely hence
colliding and breaking the bonds setting more electrons free

Answer / rahul

avalanche breakdown occurs in low doped junction.
Breakdownvoltage is greater than 5v. Since it is lightly
doped so, width of depletion layer more therefore

Answer / navdeep

zener breakdown occurs under the influence of strong
electric field.By the strong E.F,more breakage of covalent
bonds take place.Due to which more e-hole pairs come to
play. Then the reverse current rises abruptly and
breaakdown takes place known as zener breakdown.

Under the low influence of electric field in the
junction,the covalent bonds break and more charge carriers
are formed.and under the more reverse voltage,the reverse
current flows and the breakdown due to ore voltage is known
as avlanche breakdown.

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Answer / shameem ahmed

Apropert dop cristal Diode which has a sharp breackdown voltage is known as Zener Diode

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