1 Group Assignment Prepared by: 1. Wilson Teng Yisheng (1104947 ) 2. Bong Wilson (1104987 ) 3. Teoh Kheng Hwa (1103790) 4. Lee Le Yu (1104890) 5. Ng Wei Zhang (1105014) 6. Cheok Kah Guan (1105017) Programme Bachelor of Engineering (Hons) Mechanical Engineering Course UEME 1122 Material Science Year One Semester One Prepared for: Dr. Yap Yeow Hong Date August 18, 2012 UNIVERSITI TUNKU ABDUL RAHMAN (UTAR) FACULTY OF ENGINEERING AND SCIENCE (FES)
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1
Group Assignment
Prepared by: 1. Wilson Teng Yisheng (1104947 )
2. Bong Wilson (1104987 )
3. Teoh Kheng Hwa (1103790)
4. Lee Le Yu (1104890)
5. Ng Wei Zhang (1105014)
6. Cheok Kah Guan (1105017)
Programme Bachelor of Engineering (Hons) Mechanical Engineering
Course UEME 1122 Material Science
Year One
Semester One
Prepared for: Dr. Yap Yeow Hong
Date August 18, 2012
UNIVERSITI TUNKU ABDUL RAHMAN (UTAR)
FACULTY OF ENGINEERING AND SCIENCE (FES)
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Introduction
A light-emitting diode (LED) is a semiconductor light source made from a combination
of chemically polarized semiconductors. The chemical composition is chosen to define
the energy of the electrons that pass across the boundary between the two types of
semiconductor. This electron energy is converted to light as electrons flow though the
device. The electron energy defines the wavelength of the resultant coloured light.
Early development:
1907:
first experimenter H. J. Round (British)
1927:
first researcher to publish journal Oleg Vladimirovich Losev (Russian)
1955:
Rubin Braunstein reported on infrared emission from gallium arsenide (GaAs) in
simple diode structures.
1961:
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Robert Biard and Gary Pittman (American experimenter) found that GaAs emitted
infrared radiation when electric current was applied and received the patent for
the infrared LED.
First visible spectrum LED:
1962:
develop by Nick Holonyak (father of the light-emitting diode)
1960’s:
red LEDs became commercially available.
1970’s – 2000’s:
1972:
Nick Holonyak invented yellow LED and improved the brightness of red and red-
orange LEDs by a factor of ten.
1976:
T. P. Pearsall created high-brightness, high-efficiency LEDs for optical fiber
telecommunications.
1993:
Shuji Nakamura (Japanese) demonstrated first high-brightness blue LED.
1995:
Alberto Barbieri investigated the efficiency and reliability of high-brightness LED.
These developments produce white LED.
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Chemical Structure of LED
There are several types of semiconductor of LED. The chemical structure includes
molecular geometry, electronic structure and crystal structure of molecules.
1. Gallium Arsenide (GaAs) - has molecular shape of linear shape.
-has crystal structure of zincblende.
-has formula weight of 144.64.
-has lattice constant of 0.56533nm.
-produce red and infrared light.
2. silicon carbide (SiC) –has electron mobility of 900cm2/V.s(all polytypes)
-can doped n-type by nitrogen or phosphorus
-can doped p-type y aluminium, boron or beryllium.
-produce blue light.
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Structure of major SiC polytypes.
(β)3C-SiC
crystal structure :Zinc
blende(cubic)
4H-SiC
crystal structure:hexagonal
(α)6H-SiC
crystal structure:hexagonal
3. Gallium Nitride-has coordination geometry of tetrahedral.
-has band gap of 3.4 eV.
-has electron mobility of 440 cm2/ (V·s) at temperature 300 K.
-has crystal structure of Wurtzite.
-emitting green, pure green or emerald green and blue light.