Transcript Transistor Lasers Constantine Kapatos Moses Farley Vicki Kaiser

Transistor Lasers
Courtesy hispamp3.com
Constantine Kapatos
Moses Farley
Vicki Kaiser
Philip Furgala
Melroy Machado
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
today’s light emitting diode and laser diodes.
Light was detected at the base of the transistor and the
creation of the transistor laser had occurred.
• 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.
Courtesy photonics.com
L.A.S.E.R.: Light Amplification by Stimulated Emission of Radiation
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)
Base
(trigger)
Photon
Emission
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.
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)….
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.
Courtesy ieee.spectrum.org
Electrons that don’t recombine
with holes in the well or the base
go into the collector, which
exhibits a current gain.
The device can be switched
on and off rapidly (billions of
switches per second), and
produces optical and electrical
signals.
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.
Courtesy falstad.com
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.
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.
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
• In this device the quantum well is a layer of Indiumgallium-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.
• 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
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
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 signal—while
simultaneously delivering an electrical
signal with gain.
Future Uses of Transistor Lasers
Courtesy www.spectrum.ieee.org
- ultra-fast transistor lasers
could extend the modulation
bandwidth of a semiconductor
light source from 20 gigahertz to
more than 100 gigahertz
Courtesy www.earthsky.org
-more precise plasma-etching
techniques
- can output both an electrical
and optical signal
simultaneously at possibly 100
billion bits per second
Courtesy www.earthsky.org
- faster internet connections and
high definition video on cell
phones
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
• Supercomputer grids
would be able to crunch
test data from the world's
most advanced particle
accelerators in minutes
instead of days.
Acknowledgments:
Holonyak, Nick Jr. and Feng, Milton. The Transistor Laser. February 2006. Spectrum, IEEE. 25 April 2006.
<http://www.spectrum.ieee.org/feb06/2800/1>
Kloeppel, James E. Hidden Structure Revealed in Characteristics of Transistor Laser. 10 April 2006. Science Daily,
Science Daily LCC. April 25 2006. <http://www.sciencedaily.com/releases/2006/04/060410164025.htm>
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. <http://www.photonics.com/content/news/2006/April/7/82059.aspx>