Transistor Lasers Constantine Kapatos Moses Farley Vicki Kaiser Philip Furgala Melroy Machado

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Transistor LasersConstantine KapatosMoses
FarleyVicki KaiserPhilip FurgalaMelroy Machado
Courtesy hispamp3.com
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The History of the Laser Transistor

• Two years ago on a hunch the professors decided
  to try using indium phosphide and indium
  gallium arsenide based transistors, the same
  sort of compound used in todays light emitting
  diode and laser diodes.
• Light was detected at the base of the
  transistor and the creation of the transistor
  laser had occurred.

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• The transistor that was created puts out an
  electrical signal and a laser beam, which can be
  modulated to send an optical signal at a rate of
  10,000,000,000 bits per second.

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How They Work
Transistor Lasers
Courtesy photonics.com
L.A.S.E.R. Light Amplification by Stimulated
Emission of Radiation
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The transistor laser combines the functions of
both a transistor and a laser by converting
electrical input signals into two output signals,
one electrical and one optical. Photons for the
optical signal are generated when electrons and
holes recombine in the base, an intrinsic feature
of transistors. The structure for the transistor
laser is a Bipolar Junction Transmitter (BJT),
which is a solid-state, semiconductor device
which uses electrons and holes to carry the main
electric current, and is often used in
amplifying/switching applications like this
laser. It is essentially two back-to-back diodes
separated by a thin, connecting base-layer.
Collector(output)
Emitter(input)
Photon Emission
Base(trigger)
Courtesy inovacaotecnologica.com
When voltage is applied to the base-emitter
junction, injected electrons from the emitter
diffuse across the base. The base is thin enough
that most of the electrons can pass through to
the collector before recombining with holes in
the p-type base.
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The semiconductor compounds in the transistor
laser are Gallium-Arsenide (GaAs) and
Indium-Gallium-Phosphide (InGaP), III-VI
compounds (from the periodic table).
Courtesy sciencedaily.com
GaAs and InGaP are direct band-gap materials, an
electron that has been excited into the
conduction band can easily fall back to the
valence band through the creation of a photon (of
little momentum) whose energy matches the
band-gap energy.
Courtesy sciencedaily.com
The transistor laser light beam with a infrared
wavelength labeled "hv" at the top is captured by
CCD camera. The contact probes (dark shadow) on
the Emitter, Base and Collector.
So, these materials will readily produce light
(photons).
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A voltage at the emitter injects electrons into
the base. In the well, more electrons combine
with holes, a process which emits light.
The light is reflected off mirrors around the
inside of the well to form a resonant cavity.
Light is increasingly stimulated until a beam of
laser light escapes.
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The device can be switched on and off rapidly
(billions of switches per second), and produces
optical and electrical signals.
Courtesy ieee.spectrum.org
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Electrons that dont recombine with holes in the
well or the base go into the collector, which
exhibits a current gain.
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The quantum well in the transistor laser
acts as a recombination center that governs the
flow of charge from the emitter to the collector.
The quantum well takes in electrons from the
base as they move from emitter(input) to
collector(output), thus trapping the electrons
and quantizing energy levels.
This process decreases the current gain of the
transistor by approximately 90, but as seen in
the previous figure, the recombination of
electrons and holes is increased, thus increasing
the photon production, thus increasing the
strength of the outputted light from the base, as
well as the electrical signal from the collector.
Courtesy falstad.com
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To turn this light into a laser beam, the edges
of the transistor are modified The crystal is
cut to make the opposite ends of the
recombination region reflective, creating a
resonant cavity, so the photons bounce between
the reflective ends,
stimulating the
emission
of additional photons that
are
in phase with the others
generated in the region.

Courtesy ieee.spectrum.org
When the light-emitting transistor begins
operating as a laser at a near-infrared
wavelength of 1006 nm, the spontaneous signal
scattered about in the crystal shifts to an
intense directed signal - a coherent laser beam
that can be toggled on and off 10 billion times
per second. The point at which lasing (coherent
radiation emission by the laser) begins, called
the lasing threshold, depends on several factors,
including current and ambient temperature. And
only recently has the technology evolved such
that we can operate transistor lasers at room
temperature thus making them possible for
commercial usage.
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How the Transistor laser is made

• The Transistor laser can be thought as two back
  to back diode separated by a thin connection
  layer, a base layer

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• In this device the quantum well is a layer of
  Indium-gallium-arsenide no more than 10
  nanometers thick. Inserted into the HBT
  (heterojunction bipolar transistor) base region,
  the quantum well acts like a special
  recombination center that governs the flow of
  charge from emitter to collector.

• The development of the transistor laser has been
  going on for over twenty five years, but only
  recently two professors from University of
  Illinois named Milton Feng and Nick Holonyak were
  able to create a transistor that switched on and
  off faster than 700,000,000,000 times per second.
  

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• The development of the transistor laser has been
  going on for over twenty five years, but only
  recently two professors from University of
  Illinois named Milton Feng and Nick Holonyak were
  able to create a transistor that switched on and
  off faster than 700,000,000,000 times per second.
  

courtesy 1115.org
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Advantages and Disadvantages of Transistor lasers

• Advantages
• Process data with light instead of electricity.
• Faster broadband communication
• Input electrical signals ? output electrical
  optical
• Integrate transistor lasers into devices and
  route out signals
• Ways to exploit fast transistors that output
  signals in two different modes simultaneous
• Disadvantages
• Potential Radiation Exposure

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Transistor Laser Transistor Laser

• A transistor with a laser diode to fashion a
  device that could produce both electrical signals
  and laser beams simultaneously
• Generating an output laser signalwhile
  simultaneously delivering an electrical signal
  with gain.

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Future Uses of Transistor Lasers
Courtesy www.spectrum.ieee.org
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• ultra-fast transistor lasers could extend the
  modulation bandwidth of a semiconductor light
  source from 20 gigahertz to more than 100
  gigahertz
• more precise plasma-etching techniques
• can output both an electrical and optical signal
  simultaneously at possibly 100 billion bits per
  second
• faster internet connections and high definition
  video on cell phones

Courtesy www.earthsky.org
Courtesy www.earthsky.org
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courtesy aliensurgeon.com
courtesy aliensurgeon.com

• -Used as optoelectronic interconnects
• transistor lasers could facilitate faster signal
  processing
• higher speed devices
• large-capacity seamless communications
• as well as a new generation of higher performance
  electrical and optical integrated circuits

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• Supercomputer grids would be able to crunch test
  data from the world's most advanced particle
  accelerators in minutes instead of days.

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Acknowledgments
Holonyak, Nick Jr. and Feng, Milton. The
Transistor Laser. February 2006. Spectrum,
IEEE. 25 April 2006. lthttp//www.spectrum.ieee.o
rg/feb06/2800/1gt Kloeppel, James E. Hidden
Structure Revealed in Characteristics of
Transistor Laser. 10 April 2006. Science Daily,
Science Daily LCC. April 25 2006.
lthttp//www.sciencedaily.com/releases/2006/04/0604
10164025.htmgt Kloeppel, James E. New transistor
laser could lead to faster signal processing. 15
November 2004. News Bureau, University of
Illinois at Urbana-Champaign. 25 April 2006.
lthttp//www.photonics.com/content/news/2006/April/
7/82059.aspxgt