Blue LED as we all know is the discovery of the century. Its applications spans most of our needs in day to day life and it is one of the greatest innovations in the history of mankind for which it was given nobel.

1. Seminar by,
Prathul Nath P P, Subin C P,
15PH62R06, 15PH62R08,
IIT KHARAGPUR IIT KHARAGPUR
BLUE LED: The greatest Benefit to
Mankind

2. What is a Blue LED?
 Light Emitting Diodes which can emit Blue light
(Energy around 2.7 eV).
 Was possibly the missing link to produce LeD Lamps.
 Current bright blue LEDs are based on the
wide Bandgap SC’s like GaN (3.4 eV) and InGaN (2.6
eV).
Credit: Consolidatedconsultants.com

3. Akasaki, Amano, and Nakamura, worked on their two
separate efforts for years on the problem to create GaN which
theoretically could be used to create a blue LED, but which in
practice proved to be very uncooperative.
 Professors
Akasaki, Amano
and Nakamura
made the first
blue LEDs using
GaN in the early
1990s.
Credit: BBC

4. Challenges
 No one was able to grow gallium nitride (III-V class )
crystals of high enough quality, since it was difficult
to find a fitting surface to grow the GaN crystal on.
 Difficult to get native substrates in high quality and
large quantities Even the slight lattice mismatch
induce misfit dislocations at the interface, which
could develop cracks in crystals that degrade the
performance of devices.
Credit: wikipedia.org

5. GaN powered Blue LED
 Nakamura grew his own GaN crystals and developed a
simpler method for making the p-type layers using careful
heating. He was also the first to understand why the
electron beam boosted the light output of LEDs: it was
removing hydrogen, just as his own heating technique
did.
 Modern blue LEDs require a more sophisticated
approach, including varying the amount of indium and
gallium. Further, with the introduction of aluminum, it is
possible to make even bluer LEDs, even ultraviolet ones.

6. GaN growth techniques
 Vapor phase
Epitaxy(HVPE) Molecular
beam Epitaxy (MBE)
Metal organic chemical
vapor
deposition(MOCVD).
 Highly suitable for GaN
films due to high growth
rate and bandgap
engineering in near-UV
spectral range is
possible.
Schematic drawing of the inverted
vertical HVPE growth reactor BOSAN
Credit: Frederik Karlsson, Linkoping
Uniersity

7. Blue LED
Credit: Johan Jamestad, Swedish Academy of Science
The metallic crystals needed to be of extremely high quality
and the alloy was very prone to poisoning by hydrogen, so
making p-layers of adequate purity was not easy, and the
use of electron beams to make the diodes was difficult and
expensive.

8. Blue LED Design
Credit: Bryan Christie Design, IEEE

9. Historical evolution of Blue LEDs. PC white- Phosphor converted
White light.
Credit : Royal Swedish Academy of Sciences
In 1994, Nakamura and co-workers achieved a
quantum efficiency of 2.7% using a double
heterojunction InGaN/AlGaN With these important first
steps, the path was cleared towards the development
of efficient blue LEDs and their application was open.
Wallplug
Efficiency

10. White LED
 There are three main methods
of mixing colors to produce
white light from an LED:
1)Blue LED + green LED + red
LED (color mixing; can be used
as backlighting for displays.
2)Near-UV or UV LED +
RGB phosphor
(an LED producing light with a
wavelength shorter than blue's is
used
to excite an RGB phosphor).
3) blue LED + yellow phosphor
(two complementary colors
combine to form white light). Credit: Wikipedia.org

11. Applications of Blue LED
 White LED Lamps
 Digital Displays
 Water Purification
 Enhancing Plant growth
 Commercial decoration

12. White LED
 Blue or UV LED, and a yellow phosphor coating gives
White colour.
 LED lamps give out light at up to 300 (lm/W)- 5% of
the power of an incandescent lamp.
 LED combined with rechargeable battery and solar
cell, Can be used as lamps in rural areas.
Credits: Johan Jamstad, Royal swedish academy

13. Digital Displays
 Able to create Smartphone, TV and
computer screens, as well as light
bulbs that last longer and use less
electricity.
 Blue, red and green LEDs could be
combined to make white or any other
color light. This development led to
the power-efficient screens for cell
phones, TVs, etc.
 Blue LEDs are used in High
resolution TV displays like 4K to
enhance the light.
Credits: Retrevo.com

14. A ‘4K TV’
Credits: QDvision
 The blue LED light drives
the blue light for the
picture, but red and green
light is created by the
quantum dots.
 When a quantum dot is
struck by light, it glows
with a very specific color
that can be finely tuned.
When those blue LEDs
shine on the quantum
dots, the dots glow with
very high intensity.

15. Water Purification
 Currently, purification plants
use mercury lamps to kill any
microbes in drinking water,
but these lamps consume a
lot of electricity.
 LED, Requires very little
energy
 UV light destroys bacteria,
fungi and viruses, by
scrambling their DNA
structure.
 20,000 times more efficient
than boiling.
 Chemical Free
Credits: earthuntouched.com

16. Other Applications
 To enhance plant growth : It
has been observed that the
plant growth can be
stimulated by light waves
 Commercial decoration
Credits: lifescience.com

17. Conclusion
 Blue LEDs already started a big revolution with
scientists claiming 21st century will be lit by LED
Lamps.
 Expected to reduce the power consumption to 40%
by 2040.
 Blue LEDs can also provide clean and environment
friendly light with no toxic waste.
 For the invention of blue LEDs, the 2014 physics
Nobel prize was awarded to Japanese scientists
Isamu Akasaki, Hiroshi Amano and Shuji Nakamura ,
first time for a practical invention.
 Research in this field have already led to great
inventions and with the invention of a cost effective
method to produce Blue LED, whole world will bow

18. Reference
1) http://www.popsci.com
2) http://www.pbs.org/wgbh/nova/blogs/physics/2014
3) Nakamura lecture Blue LED invention
4) Popular Physics Prize, Royal Swedish Academy of
Sciences
5) http://www.bbc.com/news/science-environment
6) http://www.livescience.com/
7)
http://spectrum.ieee.org/semiconductors/optoelectronic
s
8) http://earthuntouched.com/relevance-blue-leds/
9) Wikipedia.org

19. THANK YOU
 Thanks a lot for making our lives better.
 Thanks Amreesh sir for giving this opportunity.
 Thanks Rounak Kumar and Suman Mandal for
valuable suggestions.