SUB : ELECTRONICS DEVICES & CIRCUITS (2131006)
Topics :
The Unbiased Diode, Forward Bias, Reverse Bias, Breakdown, Energy Levels, The energy
Hill, The Barrier Potential and Temperature , Reverse-Biased Diode
Created by:
Meghwal Dinesh S. 130140111041
Mistry Keyur R. 130140111043
Nakrani Pratik R. 130140111046

The Unbiased Diode
What is Diode :- A semiconductor device with two
terminals, typically allowing the flow of
current in one direction only.
What is Unbiased Diode :- when we do not apply any
source of energy or electricity than a
diode is said to be unbiased diode.

The Unbiased Diode
 FORMATION OF P-N JUNCTION
p type
semiconductor
n type
semiconductor
Anode
Cathode
Junction
P side is called as N type is called as
Holes
Electrones
Majority
Minority
Minority
Majority
Diffusion is same

Forward bias
 If p region is connected to the positive terminal of external dc source & n region is
connected to negative terminal of dc source is said to be forward biasing.
If If
Forward biasing of a diode Symbolic Representation

Operation of a Forward biased Diode

-
-
-
-
-
+
+
+
+
+
+
+
-
-
The holes Converting into
the negative ions into
neutral atomes
p n
R
Current
limiting
resister
V
Due to negative terminal of external
souce connected to n-region so
electrons are pushed towards p-side
Due to Positive terminal of external souce
connected to p-region so holes are
pushed towards n-side
The Electrones Converting
into the Positive ions into
neutral atomes Due to this The
width of deplation
region will reduce
Due to reduction in
the depletion region
width the barrier also
reduced.
Hence a large number
of electrons & holes can
cross the junction under
the influence of
externally connected
DC voltage
As we can say that the flow of electrons is current so that the current produce
in this position said to be forward Current

Reverse bias
 If p region is connected to the negative terminal of external dc source & n region is
connected to Positive terminal of dc source is said to be reverse biasing.
Ir Ir
Reverse biasing of a diode Symbolic Representation

Operation of a Reverse biased Diode

-
-
-
-
-
+
+
+
+
+
The process of widening is not take place at longer time due to
there is no steady flow of current from n-side to p-side
+
+
-
-
p n
R Current
limiting
resister
Holes in P region are attracted V
towards negative terminal of
supply
Electrones in n region are
attracted towards positive
terminal of supply.
Due to this The width
of deplation region will
incresases
Due to increases
in the depletion region
width the barrier also
increases.
Minority carrier in p-region
attracted
towards positive of
supply.
-
-
-
-
-
+
+
+
+
+
So that few electrons are flow so the current is also tiny that current states at this position
said to be reverse saturation current due to minority carrier

Breakdown
The reverse saturation current flowing in reverse biased diode is
dependent only on temperature &
independent on reverse applied voltage externally.
The breakdown in reverse biased diode can take place due to following effects.
Avalache
effect
Zener
effect
B
R
E
A
K
D
O
W
N

Breakdown due to Avalache effect
Due to large voltage
velocity of minority
carriers will increase
to great exent
Therefore Kinetic
energy also increses
While traveling
minority carriers will
collide with stable
atomes & import
some of kinetic
energy To the
valance electrons
present in co-valent
band
Due to this
additional energy
these electones will
break the covalent
bonds &jump into
the conduction
band to free for
conduction.
Now this free
electones will be
accelerated &they
knockout some
more valance
electrons by means
collisions.
THIS “CHAIN
REACTION” IS
CALLED as
“AVALANCHE
EFFECT”

Break down due to Zener effect
Due to heavy doping of
p & n side of the diode
the deplation region is
narrow in reverse biased
condition.
Therefore electrical field
which is the voltage per
unit distance is very
intense across the
deplation region
This intense electric field
can pull some of
valence electrons by
breaking the covalent
bonds these electrons
than become free
electrons.
The large number of
such electrons can
constitute through
diode this is called as
the breakdown due to
zener effect

Energy Levals
 Each electrons orbit has an energy leval associated with it. The electrons in the inner orbits are
more closely bound to the nucleus to the nucleus and posses less energy.
 As we move towards the valance shell, the bliding force between nucleus & electrons reduces
and the electrons reduces & elctrones posses higher energy.
Shell 1
Lowest energy
Energy leval increses as we move
away from the nucleus
Valance orbit has
highest energy leval

Energy Bands
First band
Formed by cluster
of energy leval in
first shell
Valence
band
Corresponds to
valance electrons
present in different
atomes of
materials
Enrgy associated is
second highest.
Conduction
band
The electrons in
conduction band
are the free
electrons.
Enrgy associated is
highest.
Concept of forbidden gap:
• Forbidden gap is energy gap that separates the conduction band & Valence bands.
• For any material the forbidden gap may be large, small , or even nonexistent. The materials
are classified as conductor , insulator, semiconductors based on relative widths of forbidden
gap.


Energy Hill
Energy
Conduction band
Valence band
The Valence &
Conduction bands
are slightly lower
energy levals
This is Due to difference
in the atomic
characteristics of the
pentavalent(n-type) &
Trivalent(p-tpye) impurity
atomes
Minority
carriers(electrons)
Majority
carriers(Holes)
Majority
carriers(electrons)
Minority
carriers(Holes)
A p-region n-region K

Barrier Potential & Temperature
 Inernal temperature of p-n junction is known as the junction temperature
 Whereas the air surrounding the device is called as ambient temprerature
For conducting
Diode
Junction Temp. > Ambient Temp.
Barrier Potential 1
junction temperature
So that Due to Incresed Temp. barrier potential decreases more electrons & hole
pair produced . These will diffuse into deplation region to narrow it down.
The barrier potential of a silicon diode decreases at 2 mV per degree Celsius rise in
junction temperature.
-2mV/◦ 퐶 =
Δ퐕
Δ퐓

Circuit Courtesy : Circuit Maker
Platformed by :- Microsoft office 2013