DIODES
Applications
EE314
Diodes applications
1.LED – Light Emitting
Diodes
2.LD – Laser Diodes
3.Fiber optics
4.Optical switching MEMS
5.Nanotechnology
6.Solar Cells
7.Light Detection
8.Future Technologies
Green electroluminescence from a point
contact on a crystal of SiC recreates H. J.
Round's original experiment from 1907.
Light Spectrum
Light Spectrum
Red, green and blue LEDs
LED - Light Emitting Diodes
When a light-emitting diode is
forward biased, electrons are
able to recombine with holes
within the device, releasing
energy in the form of photons.
This effect is called
electroluminescence and the
color of the light (corresponding
to the energy of the photon) is
determined by the energy gap of
the semiconductor.
Source http://en.wikipedia.org/wiki/Light-emitting_diode
LED - Light Emitting Diodes
UV – AlGaN
Blue – GaN, InGaN
Red, green – GaP
Red, yellow – GaAsP
IR- GaAs
LED - Colors & voltage drop
Color
Wavelength
(nm)
Voltage (V)
Semiconductor Material
Infrared
λ > 760
ΔV < 1.9
Gallium arsenide (GaAs) Aluminium gallium arsenide (AlGaAs)
Red
610 < λ < 760
1.63 < ΔV < 2.03
Aluminium gallium arsenide (AlGaAs) Gallium arsenide phosphide
(GaAsP) Aluminium gallium indium phosphide (AlGaInP) Gallium(III)
phosphide (GaP)
Orange
590 < λ < 610
2.03 < ΔV < 2.10
Gallium arsenide phosphide (GaAsP) Aluminium gallium indium
phosphide (AlGaInP)Gallium(III) phosphide (GaP)
Yellow
570 < λ < 590
2.10 < ΔV < 2.18
Gallium arsenide phosphide (GaAsP) Aluminium gallium indium
phosphide (AlGaInP) Gallium(III) phosphide (GaP)
Green
500 < λ < 570
1.9 < ΔV < 4.0
Indium gallium nitride (InGaN) / Gallium(III) nitride (GaN) Gallium(III)
phosphide (GaP)Aluminium gallium indium phosphide (AlGaInP)
Aluminium gallium phosphide (AlGaP)
Blue
450 < λ < 500
2.48 < ΔV < 3.7
Zinc selenide (ZnSe), Indium gallium nitride (InGaN), Silicon carbide
(SiC) as substrate, Silicon (Si)
Violet
400 < λ < 450
2.76 < ΔV < 4.0
Indium gallium nitride (InGaN)
Purple
multiple types
2.48 < ΔV < 3.7
Dual blue/red LEDs,blue with red phosphor,or white with purple plastic
Ultraviolet
λ < 400
3.1 < ΔV < 4.4
diamond (235 nm), Boron nitride (215 nm) , Aluminium nitride (AlN)
(210 nm) Aluminium gallium nitride (AlGaN) (AlGaInN) — (to 210 nm)
White
Broad
spectrum
ΔV = 3.5
Blue/UV diode with yellow phosphor
Wireless telemedicine
The PillCam is a ‘swallow’
diagnostic device, taking
high-quality, high-speed
photos as it passes through
the esophagus.
PillCam transmits 14
pictures/sec. to a receiver
worn by the patient.
This enables diagnosis of
throat disease and related
ailments.
http://www.three-fives.com/latest_features/feature_articles/250205medical.html
pn-junction laser
Light
Amplification by
Stimulated
Emission of
Radiation
Diode Lasers are Small!
http://faculty.uml.edu/carmiento/Special%20Lectures/Intro%20to%20EE%20Lecture.pdf
Radar/Laser Detectors
A radar/laser detector is a combination of a radar detector, which
senses radar in the air, and a laser detector, which looks for laser
beams directed at your car.
A laser beam is a very focused
beam of light that does not
separate out from its beam path.
Fortunately, there is a lot of dust
and fine particles in the air, which
causes the laser beam to separate
enough that the beams can be seen
by a proper detector.
Optical Fiber Communications
What is it?
Transmission of information using light over
an optical fiber
Why use it?
–Extremely high data rate and wide
bandwidth
–Low attenuation (loss of signal strength)
–Longer distance without repeaters
–Immunity to electrical interference
–Small size and weight
–Longer life expectancy than copper or
coaxial cable
–Bandwidth can be increased by adding
wavelengths
Information Capacities in Optical Fiber
•Each wavelength can carry a signal at 10 gigabits/sec (1010 bits/sec)
•A fiber can transport up to 64 different wavelengths
–Each wavelength can carry 10 Gb/s
–Unlike electrical signals, optical signals inside the same fiber at
different wavelengths don’t interfere with each other
•Each fiber can have an aggregate data rate of 640 Gb/s
–This is 640,000,000,000 bits per second!
•This rate translates to:
–10 million simultaneous telephone calls (64 kb/s each)
–Download the contents of the Library of Congress takes:
•84 years using a 56 kb/s modem
•0.22 seconds using the aggregate fiber rate
•These rates can go much higher!
–Researchers have developed operation of 40 Gb/s per wavelength
–A fiber cable can contain as much as a hundred fibers
Cable Size Comparison: Copper vs. Fiber
This is a standard
copper cable used for
telephone service. This
carries about 300 phone
calls
One of these fibers can
carry up to 10 million
telephone calls
Optical Switching
Where electrical and mechanical engineering meet
Route optical communication signals
without conversion to the electronic
domain using microscopic mirrors
based on MEMS technology
MEMS: Miniature Motors
Human hair
Nanotechnology
Small and
getting smaller
Video 2:30 min
Micro and nanotechnologies are
revolutionizing medicine
Almost invisible' tools are being developed by
European researchers to discover diseases earlier and
to treat patients better.
The miniaturization of instruments to micro and nano
dimensions promises to make our future lives safer and
cleaner.
In the "Adonis"-project, nano-sized gold particles are
used to detect prostate cancer cells at an early stage.
Video 7:30 min
http://www.zangani.com/node/2763
Photovoltaics
The word Photovoltaic is a combination of the Greek
word for Light and the name of the physicist
Allesandro Volta.
It identifies the direct conversion of sunlight into
energy by means of solar cells. The conversion process
is based on the photoelectric effect discovered by
Alexander Bequerel in 1839.
The photoelectric effect describes the release of
positive and negative charge carriers in a solid state
when light strikes its surface.
http://www.solarserver.de/wissen/photovoltaik-e.html
Photovoltaics
How Does a Solar Cell Work?
Solar cells are composed of
various semiconducting materials.
Semiconductors become
electrically conductive when
supplied with light or heat.
Over 95% of all the solar cells
are composed of the Si.
How Does a Solar Cell Work?
Photo generated current
The equivalent circuit of a solar cell
The usable voltage from solar cells depends on the semiconductor
material. In silicon it amounts to approximately 0.5 V.
Terminal voltage is only weakly dependent on light radiation, while
the current intensity increases with higher luminosity.
A 100 cm² silicon cell, for example, reaches a maximum current
intensity of approximately 2 A when radiated by 1000 W/m².
Characteristics of a Solar Cell
oThe output power of a solar cell
is temperature dependent.
oHigher cell temperatures lead
to lower output, and hence to
lower efficiency.
oEfficiency indicates how much
of the radiated quantity of light
is converted into useable
electrical energy.
Today on the order of 15-25%
Light Detectors
Optical detectors,
Chemical detectors,
Photoresistors or Light Dependent Resistors
(LDR)
Photovoltaic cells or solar cells
Photodiodes
Phototransistors
Optical detectors that are effectively
thermometers, responding to the heat by the
incoming radiation, such as pyroelectric
detectors, Golay cells, thermocouples and
thermistors,
Cryogenic detectors are sufficiently sensitive
to measure the energy of single x-ray
Charge-coupled devices (CCD),
CCD Detectors
An image is projected by a lens on the
capacitor array causing each capacitor
to accumulate an electric charge
proportional to the light intensity at
that location.
A charge-coupled device (CCD) is an
analog shift register that transports
electric charges through successive
capacitors, controlled by a clock signal.
CCDs are used in digital photography,
digital photogrammetry, astronomy,
sensors, electron microscopy, medical
fluoroscopy, optical and UV
spectroscopy,etc.
CCD used for ultraviolet imaging
in a wire bonded package.
CCD color sensor
CCD Detectors
Testing an LED
Never connect an LED directly to a battery or a power supply!
It will be destroyed almost instantly because too much current
will pass through and burn it out.
LEDs must have a resistor in series to limit the current to a safe
value, for quick testing purposes a 1kΩ resistor is suitable for
most LEDs if your supply voltage is 12V or less.
Remember to connect the LED the correct way!
Tri-color LEDs
The most popular type of tri-color LED has
a red and a green LED combined in one
package with three leads.
They are called tri-color because mixed
red and green light appears to be yellow.
The diagram shows the organization of a
tri-color LED. Note the different lengths
of the three leads.
The central lead (k) is the common
cathode for both LEDs, the outer leads (a1
and a2) are the anodes to the LEDs
allowing each one to be lit separately, or
both together to give the third color.
Calculating an LED resistor value
An LED must have a resistor connected in series
to limit the current through the LED. The
resistor value, R is given by:
R = (VS - VL) / I
VS = supply voltage
VL = LED voltage (usually 2V, but 4V for blue and white LEDs)
I = LED current (e.g. 20mA), this must be less than the maximum permitted
If the calculated value is not available, choose the nearest standard resistor value which
is greater, to limit the current. Even greater resistor value will increase the battery life
but this will make the LED less bright.
For example
If the supply voltage VS = 9V, and you have a red LED (VL = 2V), requiring a current
I = 20mA = 0.020A,
R = (9V - 2V) / 0.02A = 350, so choose 390 (the nearest greater standard value).
Connecting LEDs in series
If you wish to have several LEDs on at the same
time, connect them in series.
This prolongs battery life by lighting several
LEDs with the same current as just one LED.
The power supply must have sufficient voltage to
provide about 2V for each LED (4V for blue and
white) plus at least another 2V for the resistor.
To work out a value for the resistor you must
add up all the LED voltages and use this for VL.
Connecting LEDs in series
Example
A red, a yellow and a green LED in series need a
supply voltage of at least 3×2V + 2V = 8V,
so choose a 9V battery. Adjust the resistor R to
have current I=15 mA.
Connecting LEDs in series
Example
A red, a yellow and a green LED in series need a
supply voltage of at least 3×2V + 2V = 8V,
so choose a 9V battery. Adjust the resistor R to
have current I=15 mA.
VL = 2V + 2V + 2V = 6V (the three LED voltages
added up).
If the supply voltage VS is 9V and the current I
must be 15mA = 0.015A,
Resistor R = (VS - VL) / I = (9 - 6) / 0.015 = 3 /
0.015 = 200,
so choose R = 220Ω (the nearest standard value
which is greater).
Avoid connecting LEDs in parallel!
Connecting several LEDs in parallel with
just one resistor shared between them is a
bad idea.
If the LEDs require slightly different
voltages only the lowest voltage LED will
light and it may be destroyed by the larger
current flowing through it.
If LEDs are in parallel each one should have
its own resistor.
LED Displays
It is a common anode display since
all anodes are joined together and
go to the positive supply.
The cathodes are connected
individually to resistors limiting the
current through each diode to a
safe value.
LED displays are packages of many LEDs arranged in a pattern, the
most familiar pattern being the 7-segment displays for showing
numbers (digits 0-9).
Using Varicap Diode
When the junction diode is reverse
biased, the insulating barrier widens
reducing diode capacitance.
The barrier forms the dielectric, of
variable width, of a capacitor.
The N and P type cathode and anode are the two plates of the capacitor.
In the diagram, the diode and coil form a resonant circuit.
The capacitance of the diode, and thereby the resonant frequency, is
varied by means of the potentiometer controlling the reverse voltage
across the varicap.
The capacitor prevents the coil shorting out the voltage across the
potentiometer.
Diode Capacitance as a Funcion of VD
•
Ideality factor (m) depends on junction gradient
Nanotechnology 101
Nanotechnology is the art and
science of manipulating matter at
the nanoscale (down to 1/100,000
the width of a human hair) to create
new and unique materials and
products.
Nanotechnology has enormous
potential to change society.
An estimated global research and development investment of nearly $9
billion per year is anticipated to lead to:
 new medical treatments and tools;
more efficient energy production, storage and transmission;
better access to clean water;
more effective pollution reduction and prevention;
and stronger, lighter materials and many other uses.
Nanotechnology 101
So what?
The nanoscale is the scale of atoms
and molecules.
At the nanoscale, scientists can
start affecting the properties of
materials directly, making them
harder or lighter or more durable.
In some cases, simply making things smaller changes their properties:
a chemical might take on a new color, or
start to conduct electricity.
nanoscale particles are more chemically reactive with more surface area
nanotubes made of carbon, can be up to thirty times stronger than steel,
yet is one sixth the weight.
http://www.nanotechproject.org/topics/nano101/introduction_to_nanotechnology/
Nanotechnology 101
nanotubes
Dollars and Sense
In 2007, $60 billion worth of nano-enabled
products were sold.
Nanotechnology will produce an anticipated 7
million jobs in the next decade.
By 2014, $2.6 trillion in manufactured goods
will incorporate nanotechnology
.
Carbon nanotubes make bicycle frames and tennis rackets lighter and stronger.
Nano-sized particles of titanium dioxide and zinc oxide are used in sunscreens.
Nanoscale silver is antimicrobial and prevents food stored in plastic bags from
going bad.
Clothes treated with nano-engineered coatings are stain-proof or static-free.
Computer chips using nanoscale components are used anywhere from computers
to mp3 players, digital cameras to video game consoles
Future Technologies
Future technology
videos
Part1: 7:00 min
Part2: 7:50 min
Part3: 7:22 min
Part4: 8:24 min
Part5: 7:30 min