Fabrication of green LED.

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