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Prathul Nath P P, Subin C P,15PH62R06, 15PH62R08,IIT KHARAGPUR IIT KHARAGPURBLUE LED: The greatest Benefit to Mankind

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 wideBandgap SCs like GaN (3.4 eV) and InGaN (2.6 eV).

Credit: Consolidatedconsultants.com

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

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ChallengesNo 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

GaN powered Blue LEDNakamura 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.

GaN growth techniquesVapor 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

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.

Blue LED Design

Credit: Bryan Christie Design, IEEE

Historical evolution of Blue LEDs. PC white- Phosphor converted White light.

Credit : Royal Swedish Academy of SciencesIn 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

White LEDThere 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

Applications of Blue LEDWhite LED Lamps

Digital Displays

Water Purification

Enhancing Plant growth

Commercial decoration

White LEDBlue 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

Digital DisplaysAble 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.

Blu-ray Players, use blue LED lasers to read data off a digital optical disc.

Credits: Retrevo.com

A 4K TV

Credits: QDvisionThe 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.

Water PurificationCurrently, purification plants use mercury lamps to kill any microbes in drinking water, but these lamps consume a lot of electricity.LED, Requires very little energyUV light destroys bacteria, fungi and viruses, by scrambling their DNA structure.20,000 times more efficient than boiling. Chemical FreeTaste & Odor Free

Credits: earthuntouched.com

Other ApplicationsTo enhance plant growth : It has been observed that the plant growth can be stimulated by light wavesCommercial decoration

Credits: lifescience.com

ConclusionBlue 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, the2014 physics Nobel prizewas 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 for its extreme benefits.

Reference1) http://www.popsci.com2) http://www.pbs.org/wgbh/nova/blogs/physics/20143) Nakamura lecture Blue LED invention4) Popular Physics Prize, Royal Swedish Academy of Sciences5) http://www.bbc.com/news/science-environment6) http://www.livescience.com/7) http://spectrum.ieee.org/semiconductors/optoelectronics8) http://earthuntouched.com/relevance-blue-leds/9) Wikipedia.org

THANK YOUThanks a lot for making our lives better.

Thanks Amreesh sir for giving this opportunity.

Thanks Rounak Kumar and Suman Mandal for valuable suggestions.