This document discusses light emitting diodes (LEDs). It explains that LEDs are semiconductors that emit light of a single color when electrically biased in the forward direction. LEDs work by converting electrical energy into light energy as electrons move between energy levels and release photons. The color of the light depends on the energy level difference of the electrons. Common LED materials include gallium arsenide and gallium phosphide alloys. The document also outlines some applications of LEDs and notes that they must have resistors in series to limit current.

1. LED-Electrical Properties-Hetero junctions
LIGHT EMITTING
DIODES
From Light-Emitting Diodes, Fred Schubert.

2. In this Lectures..
Applications of LED
LED Configuration
How does LED
Works?
P-n diode,
radiative transmission
Materials for LED
LED GaAsP
GaAsP:N
UV,
VIS,IR LED
Band-gap
engineering
Definition of LED
Group III-V
Group II-V

3. What is an LED?
• Light-emitting diode
• Semiconductor
• Has polarity

4. A light emitting diode (LED) is essentially a PN junction opto-semiconductor
that emits a monochromatic (single color) light when
operated in a forward biased direction.
LEDs convert electrical energy into light energy. They are
frequently used as "pilot" lights in electronic appliances to indicate
whether the circuit is closed or not.

5. LED: How It Works
• When current flows
across a diode
• Negative electrons move one way
and positive holes move the other
way

6. LED: How It Works
• The wholes exist at
a lower energy level
than the free
electrons
• Therefore when a free electrons
falls it losses energy

7. LED: How It 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

8. Inside a Light Emitting Diode
1. Transparent Plastic
Case
2. Terminal Pins
3. Diode

9. Testing LEDs
Never connect an LED directly to a
battery or power supply! It will be destroyed
almost instantly because too much current will
pass through and burn it out.
LEDs must have a resistor in series to
limit the current to a safe value, for quick
testing purposes a 1k resistor is suitable for
most LEDs if your supply voltage is 12V or less.
Remember to connect the LED the
correct way round!

10. How Much Energy Does
an LED Emit?
The energy (E) of the light emitted by an LED is related to
the electric charge (q) of an electron and the voltage (V)
required to light the LED by the expression: E = qV Joules.
This expression simply says that the voltage is proportional
to the electric energy, and is a general statement which applies
to any circuit, as well as to LED's. The constant q is the electric
charge of a single electron, -1.6 x 10-19 Coulomb.
10

11. Kinds of LEDs

12. Some Types of LEDs
Bargraph 7-segment Starburst Dot matrix
12

13. Applications
• Sensor Applications
• Mobile Applications
• Sign Applications
• Automative Uses
• LED Signals
• Illuminations
• Indicators

14. Sensor Applications

15. Mobile Applications

17. LED MATERIALS
 IT must have an energy gap of appropriate
width.
 Both p and n types must exist with low
resistivities.
 Efficient radiative path must present.
 Ga,As,GaP and the tertiary alloy
GaAs(1+x) Px are most important
compounds used.

20. Dis-Advantages Of LED
 Consumes more energy when compared to
LCD’s.
 Relatively costlier.

21. For Your Attention
By:Naseeruddin