A Seminar report on the topic
P.N JUNCTION
Presented by :- Seema
Guided by :- Manjushree Dash Panda
Class :- +3 2nd Year (Sc.)
Roll No. :– BP20-005
CONTENT
Introduction
Formation of p-n junction
Working principle of p-n junction
Characteristics
Application of p-n junction
Types of diode
Advantages and disadvantages
Conclusion
INTRODUCTION
The p-n junction diode was invented by an American physicist
RUSSEL.S.OHL at bell laboratory.
The p-n junction is a junction formed together by p-type semiconductor
and n-type semiconductor material.
It is commonly used in transistor, solar cell and integrated circuit.
FORMATION OF P-N JUNCTION
Diode consists of two electrode i.e cathode and anode.
ANODE CATHODE
When a p-type semiconductor joined with n-type semiconductor suitably
then p-n junction is formed.
P-n junction can be formed in various way. Those are
Grown junction method; Method in which p and n type impurity are
alternatively added to the molten semiconductor
Alloying method; Placing a n-type crystal over the wafer of p– type impurity in
the presence of heat until liquefaction occurs
Diffusion method ; Diffusion of n-type impurity into p-type crystal.
WORKING OF P-N JUNCTION
ELECTRON
N-TYPE DIFFUSION
HOLE
P-TYPE
DIFFUSION
Due to the concentration difference, the electron from n-region
diffuse into the p-region.
After diffusion a layer of positive charge develop on the n-side and
negative charge develop on p-side.
The region of +ve charge and –ve charge on either side of the
junction is termed as the depletion region.
P type N type
Material Material
- +
- + Free
Empty - +
Hole Electron
- +
- +
Depletion
Region
Due to this +ve and negative space charge region an electric field is
developed from n-side towards p-side.
Due to electric field an electron on the p-side of the junction move to the n-
side of the junction .This motion is termed as the drift .
Diffusion Current
Drift Current
BIASING CONDITIONS ;
Biasing means the way of connecting EMF source to p-n junction diode.
Based on voltage applied we can bias the p-n junction in two ways;
Eb
1. Forward biasing E
2. Reverse biasing - + +
Forward biasing; - +
- +
- +
- +
P N
+ -
a) In forward bias p-type is connected with positive terminal while negative terminal
is connected with n-type.
b) The applied electric field acts against the barrier field
c) Hence the resultant field at the junction is weakened and the barrier width
deceases.
d) As applied forward voltage is grater than barrier potential a forward current is
setup across the junction.
REVERSED BIASING; Eb
E
- - + +
+
- - + +
- - + +
- - + +
- - + +
P N
- +
a) Here p-type is connected with –ve and n-type is connected with positive terminal .
b) In this case the barrier electric field and the applied electric field are in same
direction.
c) When both electric field add up the depletion region increases and become more
resistive.
d) The width of depletion layer increases .
e) Reversed bias supports the potential barrier and no current flows across the
junction.
CHARACTERISTICS;
It is the curve between voltage and
current.
When p-n junction is unbiased there is
no current flow due to barrier
potential.
In forward biased condition, the
potential barrier decreases and there is
a flow of current.
When large amount of voltage is
applied the current increases rapidly.
Forward Current (in mA)
The voltage at which the current starts
to increase is called cut in voltage. For
Ge =0.3v ,si=0.7v
Forward Voltage
Knee
Voltage
A very small current of the order of
microampere flows through the circuit due to
the minority carriers known as saturation
current.
If reverse voltage is increased then minority
charge carrier increases , this energy is the
reason to knockout electron from
semiconductor . This voltage is known as
break down voltage.
After breakdown voltage the reverse
current increases and a sudden fall of
resistance of barrier region noticed.
This may destroy the junction
permanently.
APPLICATION;
RECTIFIER
SOLAR CELL,PHOTODIODE
LED
LOGICAL GATES
LASER DIODE
VOLTAGE REGULATOR
TYPES OF DIODE
1. LIGHT EMITING DIODE;
A LED is a semiconductor that emits light when current flows through it.,
Light colour depends on the energy gap of the semiconductor used.
It is used in traffic signals automotive head lamp , t.v backlight ,smart phone
back light and infrared LEDs are used in remote control circuits.
1. LASER DIODE;
A laser diode is a semiconductor that uses p-n junction for producing coherent
radiation with the same frequency .
It is used in laser printer c.ds and dvd players.
It is also used for cutting , drilling, welding in industry.
AVALANCHE DIODE;
It works in reverse biased.
It is used to protect the circuit against unwanted voltage.
It is used for photo detection.
ZENER DIODE;
It is designed to operate in the reversed biased.
As it gives stable reference voltage it is widely used.
SCHOTTKY DIODE;
1. It is a diode having a low forward
voltage drop and a very fast
switching speed.
2. It is highly used in rectification.
3. The change from ON to OFF state
is fast by using the diode.
PHOTO DIODE:
a. A photo diode is a p-n junction
diode that consumes light energy
to produce an electric current.
b. It works in reversed bias .
c. It is used in solar cell panels and
photometer. Also used for smoke
and fire detection.
Advantages;
1. As a rectifier it converts A.C to D.C.
2. Operate very fast and does not need any warm up time.
3. It is very cheap .
4. It works at low voltage and consumes less power .
5. Small in size and light in weight.
6. It has long life.
DISADVANTAGES:
7. Semiconductor diode cannot withstand very high reverse voltage.
8. Poor response.
9. At high frequency its noise level is high.
CONCLUSION;
1) P-N junction can conduct current only in forward biased .
2) During reversed bias it breaks down.
3) As it used in conversion of A.C into D.C its practical application is rectification.
4) The p-n junction is the basic building block for other semiconductor devices.
5) Modern p-n junction are fabricated using “planar technology” .
