Transcript Silicon and its properties

Silicon Laser
Shyam Sabanathan
Chenjing Li
Thannirmalai
Silicon and its properties
It is semiconductor
which is used in most
of the electronic
devices. It is found
abundant in nature.
• The silicon atom gas
the following electronic
configuration
[Ne].3s2.3p2. It has
four electrons in its
valence shell. They are
insulators in pure state.
•
• It can be converted to a conductor by doping.
• N-type doping: phosphorus or arsenic is added to
the silicon in small quantities. Phosphorus and
arsenic each have five outer electrons. The fifth
electron has nothing to bond to, so it's free to move
around. N-type silicon is a good conductor. Electrons
have a negative charge, hence the name N-type.
• P-type doping: doping, boron or gallium is the
dopant. Boron and gallium each have only three
outer electrons. They form "holes" in the silicon
lattice where a silicon electron has nothing to bond
to. The absence of an electron creates the effect of
a positive charge, hence the name P-type. P-type
silicon is a good conductor.
Concentration of the dopant vs Resistivity in
Silicon
Introduction to Lasers
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Light Amplification by
Simulated Emission of Radiation
Laser light is monochromatic,
coherent, and moves in the
same direction
In 1916, Albert Einstein, laid
the foundation for the
invention of the laser and its
predecessor, the maser, in a
ground-breaking rederivation of
Max Planck's law of radiation
based on the concepts of
probability coefficients for the
absorption, spontaneous and
stimulated emission.
Silicon Laser
Raman Laser
Hybrid Silicon Laser
Raman Laser
• Raman Scattering effect: When light is
scattered from an atom or a molecule, most
of the photons are scattered elastically
(same energy, frequency and wavelength).
• Light collides with Si atoms. Collision
produces secondary light of different energy.
This secondary light is coherent,
monochromatic and unidirectional.
Applications of Raman laser
• Laser guide star
• RGB source in TV
• Molecular
researches
Hybrid Silicon Laser
Demonstration
http://www.youtube.com/watch?
v=f0XTK_a4v9c
Hybrid Silicon Laser
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It is a semiconductor laser
fabricated from both silicon and
group III-V semiconductor
materials.
The hybrid silicon laser was
developed to address the lack of a
silicon laser to enable fabrication
of low-cost, mass-producible silicon
optical devices.
The hybrid approach takes
advantage of the light-emitting
properties of III-V semiconductor
materials combined with the
process maturity of silicon to
fabricate electrically driven lasers
on a silicon wafer that can be
integrated with other silicon
photonic devices.
Fabrication of Hybrid Silicon
Laser
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The hybrid silicon laser is fabricated by
a technique called plasma assisted wafer
bonding.
Silicon waveguides are first fabricated
on a silicon on insulator (SOI) wafer.
This SOI wafer and the un-patterned III-V
wafer are then exposed to an oxygen
plasma before being pressed together at
a low (for semiconductor manufacturing)
temperature of 300C for 12hours.
This process fuses the two wafers
together.
The III-V wafer is then etched into mesas
to expose electrical layers in the
epitaxial structure.
Metal contacts are fabricated on these
contact layers allowing electrical
current to flow to the active region
Applications of Hybrid Silicon
Laser
 Intel suggests this light source could be used for optical
communications when integrated with silicon photonics.
 Silicon manufacturing and fabrication is widely used in the
electronic industry to mass-produce low-cost electronic devices.
 Silicon photonics uses these same electronic manufacturing
technologies to make low cost integrated optical devices.
 By using this wafer bonding technique many hybrid silicon lasers
can be fabricated simultaneously on a silicon wafer, all aligned to
the silicon photonic devices.
 Potential uses cited in the references below include fabricating
many, possibly 100’s of hybrid silicon lasers on a die and using
silicon photonics to combine them together to form high
bandwidth optical links for personal computers, servers or back
planes.
Problems in making silicon lasers:
Unlike the III-V compounds, such as gallium arsenide,
generally used to make semiconductor lasers, silicon has an
indirect bandgap. That means the momentum of the charge
carriers—negative electrons and positive holes—do not
match, and when they combine they are more likely to
produce a vibration than a photon.
Using Raman Effect
Intel researchers used an external light
source to "pump" light into their chip. The
natural atomic vibrations in silicon amplify
the light as it passes through the chip. This
amplification is called the Raman effect.
But, increasing the light pump power beyond
a certain point no longer increased
amplification and eventually even decreased
it. The reason was a physical process called
"Two-Photon Absorption" .
Solution
To integrate a semiconductor structure, PIN
(P-type - Intrinsic - N-type) device into the
waveguide. When a voltage is applied to the
PIN, it acts like a vacuum and removes most
of the excess electrons from the light's path.
The PIN device combined with the Raman
effect produces a continuous laser beam.