The document explains the mechanisms of breakdown in diodes, specifically focusing on avalanche and zener breakdown. Avalanche breakdown occurs in lightly/moderately doped diodes at reverse voltages of 6V or more, while zener breakdown occurs in heavily doped diodes at voltages of 4V to 6V. Key differences include their doping levels, breakdown mechanisms, and temperature coefficients.

1. Diodes
Zener and Avalanche Breakdown

3. AVALANCHE BREAKDOWN
 When the Reverse voltage increases, Velocity of the carriers increases
which leads to higher kinetic energy of the carriers .
 These carriers moving with high kinetic energy collide with other atoms to
break their covalent bonds thus generating more carriers .
 This cumulative effect therefore results in multiplication of carriers called
Avalanche multiplication.
 The process thus creates a large number of carriers & thus a large amount
of current which eventually leads to break down of the diode.This is called
Avalanche breakdown .
 It happens at about 6V or more reverse voltage

5. Avalanche breakdown
 Impact ionisation
 Multiplication of carriers
 For Lightly/Moderately
doped diodes
 Occurs for Higher
voltages(6V)

6. ZENER BREAKDOWN
 ZENER Breakdown occurs in heavily doped junctions(high impurity).
 With high reverse voltage Electric field at the junction increases .
 This High electric field is strong enough to break the covalent bonds of
the other atoms
 This results in breaking up of more covalent bonds resulting in higher
number of charge carriers & eventually a large amount of current leading
to breakdown

7. Difference between Zener and Avalanche breakdown
ZENER BREAKDOWN
 Heavily doped diodes
 Occurs at a voltage in the range of 4V to 6V.
 Field Ionisation
 High electric field results in breaking up of covalent bonds
resulting in many free carriers.
 Zener diodes exhibit negative temperature coefficient
(Breakdown voltage decreases with temperature)
AVALANCHE BREAKDOWN
 Lightly/moderately doped diodes
 Occurs at a high voltage -6V or more.
 Impact Ionisation
 High reverse voltage leads to avalanche
multiplication resulting in many free carriers.
 Avalanche diodes exhibit positive
temperature coefficient (Breakdown voltage
increases with temperature)

9. Comparison PN Junction Diode Zener Diode
Definition
Symbol
It is a semiconductor diode which
conducts only in one direction, i.e., in
forward direction.
The diode which allows the current to
flow in both the direction i.e., forward
and reverse, such type of diode is
known as the Zener diode.
VI Characteristics
Reverse Current Effect Damage the junction. Do not damage the junction.
Doping Level Low/Moderate doping Heavy doping
Breakdown Occurs in higher voltage. Occur in lower voltage.
Ohms Law Obey Do not obey.

10. VI characteristics Comparison
 PN Junction Diode  Zener Diode

11. Thankyou