Light Emitting Diode
Contents
1.History
2.Application
3.Epitaxy
4.Fabrication
5.Packaging
6.OLED
7.Future
The history of lighting and LED
In ancient times , there were no lamps,
so people could only use fire for lighting.
People stepped into the world of light .
The first generation of lighting
kerosene lamp
candle
Incandescent lamps were widely used
because of the extensive application of electricity.
The second generation of lighting
incandescent lamps
Now, fluorescent lamps are the most widely used.
The third generation of lighting
fluorescent lamps
compact fluorescent lamp
LED is the fourth generation of lighting.
The development of LEDs
The application of LED
LED signal lights
Street Lights
A—LED Street Lights
B—Metal Halide Street Lights
C—Sodium Street Lamps
Solar Street
Lamps
Airport runway lighting and LED tunnel lamps
Automotive Application with LEDs
LED interior lighting
Bar Landscape
Lighting
Mobile Application With LEDs
LED Screen Display
The painted scroll is
made up of 44,000 LEDs.
The Olympic rings
are made up of 2,000
blue and 44,794 white
LEDs.
Epitaxy
The first generation materials:
Si, Ge ;
 The second generation materials:
GaAs, InP, GaP, InAs, AlAs;
 The third generation materials:
SiC, ZnAs, GaN, diamond.

Epitaxial growth technology
(GaN-based materials )
MOCVD (the most widely used)
(metal organic chemical vapor deposition )
 MBE
(molecular beam epitaxy)
 HVPE
(hydride vapor phase epitaxy)

The choice of substrate materials

Sapphire
common used, fabrication maturity, low price;
large lattice dismatch, poor electric conductivity,
poor thermal conductivity.

SiC
small lattice dismatch, good electric conductivity; high price.

Si
low price, big area, high quality, good electric conductivity;
large lattice dismatch.
The epitaxial structure of GaN-based LED
p-type Mg-doping GaN
Multi-quantum wells
n-type Si-doping GaN
AlN suffer layer
Substrate (silicon or sapphire)
vertical structure of LED epitaxial wafer
Fabrication
Hundreds of thousands of LED chips
are produced on one epitaxial wafer.
silicon epitaxial wafer
sapphire epitaxial wafer
LED chips
1 mm2
Multi-quantum wells (MQW)
Blue light comes
from MQW, which is
also called active
region.
vertical structure of LED epitaxial wafer
Can we make LED electrodes with vertical structure?
1.The answer depends on the
buffer and substrate.
2.The vertical structure will
cause high resistance.
3.It is not easy for fabrication
when the two electrodes are
at different sides.
Photoetching and ICP etching
ICP :
Inductively Coupled Plasma
P-electrode and n-electrode
are made at the same side
to form lateral structure.
Transparent electrode evaporation
Since p-GaN layer is in high
resistance, we need to evaporate
transparent electrode to improve
current spreading.
The electrode is as thin as
about 12 nm, so it is transparent.
LED chip
VS
lateral structure LED chip
vertical structure LED chip
Different p-electrode structures
To improve current spreading and luminous efficiency
LED chips in our lab
(Semiconductor Lighting Research Center)
The mechanism of LED
balanced state
The mechanism of LED
Forward voltage is applied.
Electrons and holes
recombine to emit light.
LED Packaging
The development of LED packaging
Purpose for packaging



To get the input signal
To protect the LED chips
To get the output of visible light
Two main methods of LED packaging
1.Pin type packaging
2. Planar packaging
How to make white LED?
LED is single color, such as red, yellow, green,
blue and so on.
However, white is mixed color. We need to mix
colors to make white LED.
Two main methods of making white LED
1. blue LED + yellow phosphor = white LED
2. red + green + blue = white
OLED
OLED = Organic Light Emitting Diode
Its light-emitting mechanism is similar to LED.
the structure of OLED
Classification
According to light-emitting materials :
Small molecular OLED:Alq3
Polymer OLED (PLED)：PPV,MEH-PPV
 According to display models :
Passive Matrix(PM-OLED) :
Acitive Matrix (AM-OLED):TFT
 FOLED:Flexible OLED

Comparison
Advantages






Thickness can be less than 1 mm.
Simple process; Low cost(30~40%of LCD).
Self-luminous; Highly efficient and kind to
environment.
Low drive voltage and low power
consumption.
Microsecond response time(1000
times)and wide view angle(>170°).
High brightness(100~14000 cd/m2 ), wide
temperature range(-30~80 ℃)
Disadvantages




Life is usually only 5,000 hours, less than that
of LCD at least 1 million hours.
Color purity is not enough to show bright and
rich color.
Large-size OLED panel production has very low
yield(<30%), compared with LCD’s(>99%).
High patent fees.
Application
Compared with IPhone
First OLED wireless digital
photo frame of KODAK
View from side(LG‘s first OLED television)
First OLED notebook in
the world(SUMSUNG)
Application
3D-movie
head-mounted
display
Bracket lights
TV and display
Military display
Folding E-book;
Rollable E-newspaper
The future of LED





I’M CUTE!

My name is LED .
Firstly, I am smaller .
Secondly，I need less
power.
Thirdly，I enjoy longer life.
At the same time，you
can call me energy saving
lamp .
It’s last but not the least,
I’m a faddish girl .
My weakness
When it comes to my weakness, my price is too
high.
 And then, my luminous flux is low.
 Stroboscopic phenomenon.
 Strong stimulation.

My future is bright!
With the development of technology
and the reduction of cost, I will be the
most popular in the world!