INSTITUTE UIE
DEPARTMENT ACADEMIC UNIT-1
Bachelor of Engineering (Computer Science & Engineering)
Subject Name Semi Conductor Physics
Subject Code 23SPH-143
Prepared By
Dr.Anuj Kumar Goel
Lecture-2.2.3
Visible Light Emitting Diodes and Displays.
DISCOVER . LEARN . EMPOWER
Lecture
Objectives
S. No. Objectives
To make student aware about the basic concept of Light emitting
1 diodes.
2 To aware about working principle of LED.
3 To provide knowledge about types and construction of LED.
4 To make familiar with the features of LEDs.
https://library.automationdirect.com/basic-el
ectrical-theory/
5 To give brief knowledge about applications of LEDs.
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Course
Objectives
S. No. Objectives
1 To understand the basic materials and properties of semiconductors.
Understand the basic of semiconductor and components like diode, transistor, FET,
2
MOSFET and Energy Sources.
To give knowledge about semiconductor physics and discus working and
3
applications of basic devices, including p-n junctions, BJTs and FETs.
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ectrical-theory/
3
Course Outcomes
CO
Title Level
Number
To apply the knowledge of basic semiconductor material
CO1 physics and understand fabrication processes. Remember
To understand the characteristics of different electronic
CO2 devices such as diodes, transistors. Understand
To derive the relationships between the parameters in diode,
CO3 FET, configurations of Transistor and MOSFETs. Analyze
To describe the working and design considerations for the
CO4 various photonic devices like photo detectors, solar-cells and Evaluate
LEDs.
To provide problem solving experience and learning of
CO5 concepts through it in semiconductor physics. Create https://library.automationdirect.com/basic-el
ectrical-theory/
4
Content
Introduction to visible LEDs.
What is an LED?
How LED works.
Energy band diagram of LED.
Construction of LED.
Electrical characteristics of LED.
What determines the color of LED.
How much light do LEDs produce.
What makes LEDs suitable for illumination applications?
Features and Benefits of LED.
Applications of LEDs.
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Introduction to LEDs
LEDs are promising light source whose efficiency was 10 times
greater than the incandescent lighting.
Long operating life and reliability has made LEDs as a potential
choice for next generation lighting systems, including automotive,
emergency, backlight, indoor and outdoor.
LED lighting can also be referred to as solid-state lighting (SSL)
because an LED is solid-state technology.[Solid State
Semiconductor Device]
LEDs were first developed in 1960s and its characteristics decides
this light source is suitable for indication not illumination.
Introduction to LEDs
Indication:
Indication – refers – use of light source – viewed directly – self
luminous object.
Ex: Signs, signals, indicator lights in electronic equipments.
Illumination:
Illumination – refers – use of light source – view other object by the
light reflected from those object.
Ex: Lightings found in rooms and Task lightings in desk.
LED - Indicator LED - Illuminator
Introduction to LEDs
LEDs are quite effective and efficient for colored light applications.
Unlike conventional signs and signals which use a nominally white
light source and a colored glass or plastic filter or lens to create the
sign or signal, colored LEDs require no filtering.
The light absorbed by the filters in the conventional products is
essentially wasted, and because of this waste, the luminous efficacy
of LED signs and signals is often higher than those using
conventional white light sources.
Introduction to LEDs
• The development of white light LEDs in the mid-1990s, have made
LED illumination systems feasible for some applications, and a
number of products are now available on the market.
• At present, typical indicator LEDs have light outputs on the order of
one to several lumens, whereas LEDs for illumination produce on the
order of tens to hundreds of lumens.
[lumens - (denoted by lm) are a measure of the total amount of visible
light (to the human eye) from a lamp or light source. The higher
the lumen rating the “brighter” the lamp will appear.]
• As the LED technology revolutionize the lighting industry so it’s important
to understand how an LED light source works.
What is an LED?
LEDs are semiconductor diodes, electronic devices that permit
current to flow in only one direction.
The diode is formed by bringing two slightly different materials
together to form a PN junction .
In a PN junction, the P side contains excess positive charge ("holes,"
indicating the absence of electrons) while the N side contains excess
negative charge (electrons).
How LED Works?
How LED Works?
When current flows across a
diode.
Negative electrons move one way
and positive holes move the other
way
How LED Works?
The holes exist at a lower energy
level than the free electrons.
Therefore when a free electrons
falls it losses energy
How LED Works?
• This energy is emitted in a form of a
photon, which causes light.
• The color of the light is determined
by the fall of the electron and hence
energy level of the photon.
Energy band diagram of LED
Electron – Hole recombination
LED Construction
How to Connect a LED?
• Requires 1.5~2.5V and 10 mA
• To prevent overloading, use resistor 470 Ω
Electrical characteristics of LEDs
- Individual LEDs are low voltage devices.
- Single indicator LEDs require 2 to 4 volts of direct current, with
current in the range from 1 to 50 milliamperes.
- An illumination-grade LED containing a single semiconducting
element requires the same voltage, but operating currents are much
higher, typically several hundred milliamperes.
- A device containing multiple elements connected in series will
require higher voltage corresponding to the larger number of
individual elements in the device.
- Reverse polarity destroys an LED.
- Manufacturers provide specifications about the maximum reverse
voltages acceptable for LED devices; 5 volts is a typical maximum
rating.
What Determines the color of the LED
The material used in the semiconducting element of an LED determines its color.
The two main types of LEDs presently used for lighting systems are aluminum gallium
indium phosphide (AlGaInP, sometimes rearranged as AlInGaP) alloys for red, orange
and yellow LEDs.
Indium gallium nitride (InGaN) alloys for green, blue and white LEDs. Slight changes in
the composition of these alloys changes the color of the emitted light.
How much light do LEDs produce?
How much light do LEDs produce?
V-I Characteristics of LED
What now makes LEDs suitable for
illumination applications?
LED construction has also changed to
make them more efficient.
The crystals forming early LED junctions
were grown on light-absorbing
substrate materials.
Using transparent substrates and
optimizing the shape of the semiconducting
element have increased the amount of light
able to leave the device
Kinds of LEDs
How are LEDs packaged into systems for
lighting applications?
Features & Benefits of LED
LED’s are extremely efficient low energy light sources.
In 2005 white LED’s had reached outputs of over 30 lumens/Watt
and coloured versions 50 lumens/Watt.
The light gains continue to grow, doubling about every two years.
Long operational life of up to 50,000 hours.
Compact light source, no other lamp possesses such small
dimensions for a comparative light output.
Features & Benefits of LED
LED’s do not emit ultraviolet (UV) or infrared (IR) radiation. They do not radiate heat
in the direction of the illuminated object, they can therefore be used to illuminate
materials that fade easily, food, works of art etc.
LED’s are durable against impact and vibration.
LED’s can be dimmed.
Coloured light can be produced effectively - over 16 million colours.
Common Application
- Display lighting - compact displays are possible with low operating
temperatures
- Display case, museum and shop lighting - illumination of sensitive objects
at close range with ultraviolet (UV) and infrared(IR) free light
- Underwater lighting - low voltage supply for safety and low maintenance
- Outside lighting - coloured effects to enhance outdoor spaces
- Sign lighting - strips of LED’s can be used to light signage in many
different colours
- Low level lighting - LED luminaires are cool to touch and are therefore
suitable for us in domestic situations where children may come into contact
with them
- Architectural detail lighting.
- LED’s can be used in applications which traditionally used neon or cold
cathode.
Summary
Introduction to Visible LEDs.
Various types of LEDs.
Electrical and V-I Characteristics of visible LED.
How to connect a LED.
Features and Applications of Visible LEDs and Displays.
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Frequently Asked Questions
What is the working principle of LED?
Give the example of different colored LEDs.
How to make 7 segment display?
Define construction of LED.
What are the applications of LEDs?
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To make students understand
• Concepts of visible LED and relate
LEARNING them to practical engineering
OUTCOMES systems.
• Importance of light spectrum.
• Understanding of electrical
characteristics of LEDs.
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Course Outcome to Program Outcome
Relationship
(21ELH-101) BEEE
PO→
CO↓ PO PO2 PO3 PO4 PO5 PO6 PO7 PO8 PO9 PO10 PO11 PO12 PSO1 PSO2 PSO3
1
CO1 3 2 0 0 1 0 0 0 0 0 0 0 2 0 0
CO2 3 2 0 0 1 0 0 0 0 0 0 0 2 0 0
CO3 3 2 0 0 1 0 0 0 0 0 0 0 2 0 0
CO4 3 2 0 0 1 0 0 0 0 0 0 0 2 0 0
CO5 3 2 0 0 1 0 0 0 0 0 0 0 2 0 0
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Assessment Pattern
A B C D E F G
Assignment Time Bound Quiz (each Mid Semester Homework Discussion Attendance
(each Surprise Test quiz) Test(one per Forums and
assignment) (each test) test) engagement
Score on BB
10 12 4 20 NA NA 2
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References
Text Books
1. Semi-Conductor Physics & devices- Basic Principles, Donald.A. Maemen,4 th Edition,
MacGraw Hill,2021.
2. Physics of Semiconductor Devices By Pearson, M.Shur, 4 th Edition , Pearson.
3. Principles Of Physics, Robert Resnick Jearl Walker, David Holliday 10 th Edition 2015.
4. Battery Reference book, Thomas Crompton, Newnes, 3rd edition,2000.
Reference Books
5. Semiconductor Devices, S.Szee,Ming-Kwel Lee,3 rd Edition,Wiley,2021.
6. Semiconductor Devices, Physics and Tech.S.Szee Ming-Kwel Lee,3 rd Edition,Wiley, 2015.
7. Principles of Electronics, VK Mehta, Rohit Mehta, 12th Edition, S. Chand Publishing, 2014.
8. Solid State Electronic Devices, Ben Streetman and Sanjay Banerjee, Seventh Edition,
Pearson Education India, 2015.
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