Silicon Laser

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Silicon Laser

• Shyam Sabanathan
• Chenjing Li
• Thannirmalai

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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.

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• 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.

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Concentration of the dopant vs Resistivity
inSilicon
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Introduction to Lasers

• 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.

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Silicon Laser

• Raman Laser
• Hybrid Silicon Laser

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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.

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Applications of Raman laser

• Laser guide star
• RGB source in TV
• Molecular researches

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Hybrid Silicon Laser Demonstration

• http//www.youtube.com/watch?vf0XTK_a4v9c

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Hybrid Silicon Laser

• 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.

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Fabrication of Hybrid Silicon Laser

• 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

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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 100s 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.

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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
  carriersnegative electrons and positive holesdo
  not match, and when they combine they are more
  likely to produce a vibration than a photon.

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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"
  .

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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.