This document discusses green LEDs and the challenges in manufacturing pure green LEDs. It provides background on why LEDs were developed, how they work internally, and the electromagnetic spectrum. Manufacturing a pure green LED is difficult as traditional methods produce light by aiming blue light at a phosphor. Newer methods using metal-organic chemical vapor deposition can produce high quality gallium nitride to potentially enable pure green LEDs. The document outlines the traditional fabrication process involving crystal growth, epitaxial layers, and packaging. It also discusses potential applications of green LEDs and answers some frequently asked questions.

1. GREEN LED
Presentation by,
P. Venkata Sai Vamsi,
B.Tech 4th year, E.E,
1100224

2. • Why LED? • Why Green LED?
Reference:- http://arstechnica.com/science/2014/10/blue-leds-given-nobel-prize-in-physics/
Motivation

3. Introduction
Reference:- http://en.wikipedia.org/wiki/Light-emitting_diode,

4. Inside the LED
Reference:- http://www.electroschematics.com/5104/light-emitting-diode-how-it-works/

5. EM Spectrum
Reference:- http://www.cyberphysics.co.uk/topics/light/emspect.htm
Do you know?
Voltage drop in a green
LED is 2.1V, in contrast to
1.7V in a Red LED

6. Difficulty in creating green LED
• Manufacturing a pure green LED is very difficult.
• The LED-based lights available today circumvent the problem by aiming the blue light at a
phosphor, which then emits green light.
• In this way, we can produce white light, but it is still wasteful compared to a white light that makes
use of three distinct, all-LED components.
Reference:- http://www.gizmag.com/first-green-led-light-manufactured/14761/

7. Traditional LED Fabrication
• Raw materials:
Traditional green:
Gallium(III) phosphide (GaP)
Aluminium gallium indium phosphide (AlGaInP)
Aluminium gallium phosphide (AlGaP)
Pure green:
Indium gallium nitride (InGaN) / Gallium(III) nitride (GaN)

8. Semiconductor die
• By using Czochralski crystal growth (or liquid
encapsulation) method, semiconductor wafer of
Gallium(III) phosphide (GaP) is made.
• Additional layers of semiconductor crystal are
grown on the surface of the wafer. The crystal
layers are grown this time by a process
called Liquid Phase Epitaxy (LPE)
Reference:- http://www.wafertech.co.uk/technology/crystal-growth/

9. Semiconductor die
• LPE creates an exceptionally uniform layer of material, which makes it a preferred growth and
doping technique. The layers formed are several microns thick
• After depositing epitaxial layers, Nitrogen is added to the top layer of the diode to make the light
more green.
Demerit:- This fabrication process doesn’t allow us to fabricate a pure green LED, as growing Indium
gallium nitride (InGaN) / Gallium(III) nitride (GaN) using Czochralski crystal growth is
difficult.

10. Mounting and Packaging
• Individual dies are mounted on the appropriate
package
• Finally, the entire assembly is sealed in plastic.
The wires and die are suspended inside a mold that
is shaped according.
Reference:- http://www.madehow.com/Volume-1/Light-Emitting-Diode-LED.html

11. LED Using MOCVD
• By using Metal-Organic Chemical Vapor Deposition (MOCVD), we can produce
high quality gallium nitride.
• This led to the creation of Blue LEDs.
• With the addition of indium, blue LED can be converted into Green LED
• Initially in traffic lights, we used filter the green light from a light source emitting
at the full spectrum of the visible light.
• With these new LEDs we can cut down the power consumption by half.
Reference:- http://iopscience.iop.org/1347-4065/34/7A/L797
Proposed in 2000

12. National Renewable Energy Laboratory
• LED can be thought of as the reverse of a solar panel.
• Reversing the process of absorbing sunlight in the green
spectral region in order to manufacture a green LED.
• Mascarenhas's idea was to reverse the process that is,
making a current flow between appropriately spaced
layers of lattice to obtain green light and reportedly
managed to produce a radiant deep green light on the
very first try.
Reference:- http://www.nrel.gov/news/features/feature_detail.cfm/feature_id=1545
Proposed in 2010

13. Application of Green LEDs
Reference:- https://images.google.com/
RGB LED

14. Few FAQs
• Why people are trying to build Green LEDs, can’t they just coat green color upon a white LED?
Ans:- Pure white LED is difficult to create. We need to combine Red, Blue, Green colors to get
white light.
• Why a Green LED appears brighter than a Red LED even though both use same current?
Ans:- Human eye has maximum sensitivity to light near 550 nm region of yellow - green part of
the visible spectrum
• Does a typical Diode produces light? How the LED is different from a Diode?
Ans:- Yes, it produces light. But we can’t observe it, as most of the light produced fall in either IR
or UV region. The materials and the dopants used differentiate the LED from a diode.

15. THANK YOU