Quantum Dot Infrared Photodetector

1
Quantum Dot Infrared Photo-detector

• 16.508 Quantum Electronics for Engineer
• Present by Chintana Keo
• Date May 3, 2006

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Agenda

• What is a Photo-detector?
• What is the different between Quantum Dot
  Infrared Photo-detector (QDIP) and Quantum Well
  Infrared Photo-detector (QWIP)?
• Sample sketch or diagram of QDIP
• How does the device work?
• Advantage of QDIP
• Dark current calculation Why?
• Detection energy calculation
• Some possible applications
• Conclusion

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What is a photo-detector?

• A photo-detector is a semi-conductor photodiode
  device that generate electrical current or
  electrons excitation when light source is shine
  onto its surface or when light source is
  entering a diode semiconductor device made from
  such material as GaAs InGaAs.
• A photo-detector is an opto-electronics device
  that allow us to produce an image of an object as
  a result of the electrical current produced by
  shining a light source within a given wavelength
  range depending on what materials is used.

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What is a photo-detector? (Continues)

• A photo-detector is basically a photodiode in
  principle. When struck by light source, the
  electrons within become stimulated and create
  current across a diode resulting in an exact
  duplicated image as the source.

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The different between quantum well quantum dot

• There similarities and different characteristics
  of photo detectors
• Quantum Well Infrared Photo-Detector (QWIP)
• Quantum Dot Photo-Detector (QDIP).
• Figure shows the different between quantum dot
  and quantum well
• Left is quantum well infrared photo-detector
• Well between barriers
• Right is quantum dot infrared photo-detector
• Dots between barriers

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Schematic Sample of Quantum Dot

• Boron doped Ge quantum dots growth sample
• Producing using molecular-beam epitaxy (MBE)
  method in a thin layer of semi-conductor
  materials.

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Basic Device

• Both device has an emitter and a collector
• The detection mechanism in both devices is by
  intraband photo excitation of electrons between
  energy levels

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The Advantage of QDIP

• QDIP allow direct incident normal to wafer
  surfaces.
• Avoid fabricating grate coupler as in QWIP.
• In producing QWIP, a grating coupler required
  which yield in extra fabrication steps.
• It has lower dark current high detection
  sensitivity than QWIP.
• Better Radiant sensitivity and Efficiency
  resulting in better detection.
• Dominant in normal direction response to growth
  direction.

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Dark Current Calculation

• Dark current is the current produce internal to
  the photodetector resulting as noise
• Simplest way to calculate dark current density is
  to count mobile carrier barrier and carrier
  velocity
• Jdark is a dark current
• ? is a drift velocity
• n3d is current density
• Can be calculate using the second formula at
  left.
• mb is a barrier effective mass
• Ea is thermal activation energy

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Radiant Sensitivity and Quantum Efficiency

• Current produce when light hitting a
  semi-conductor radiating electrons excitation.
• This can be calculate using the following formula
• QE ((S x 1240) / ? ) x 100
• Where S is the radiant sensitivity
• Long exited electron lifetime lead to high
  responsivity, higher temp and higher dark current
  which will limited detectivity

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Responsivity

• Responsivity can be calculated using the formula
  at left, where
• ? - a phonon frequency
• ? - the absorption efficiency
• g - photoconductive gain
• Higher absorption efficiency have better
  detection.

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Possible Applications

• High speed infrared detection
• Infrared image applicationpossible use in
  security systems to produce image of various
  objects.
• Possible use in IR Spectrophotometer
• Possible use in Cell Sorter
• Could be use in Infrared Camera

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Conclusion

• There are still many challenges to overcome such
  fabrication or manufacturing process that will
  produce quantum dot to meet design requirement
• Current manufacturing process limit to size and
  dot density that it is impractical for commercial
  used
• Due to complex fabrication process and limited
  size it is expensive to manufacture
• Still in its infancyneeds better doping control

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Question?

• Thank You

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Credit Reference

• Prof Joel TherrienUMass Lowell.
• American Science EngineeringBillerica, Ma
• Prof Sam MilshteinUMass Lowell
• PhotodiodesHamamatsu Photonics K.K. Solid State
  Division
• The Photonics Dictionary, 42nd Ed 1996The Tropel
  Spectrum
• Growth Study of Surfactant-Mediate SiGe graded
  layersThin Solid Film 380 (2000) 54-56
• Photoluminescence of multi-layer of SiGe dot
  growth on SiJ. Wa, H LouDevice research
  laboratory, Electrical Engineering
  Department---University of California at Los
  Angeles
• Reshifting and broadening of quantum well
  infrared photo-detectorIEEE Journal of selected
  topic in quantum electronics, vol 4 No 4
  July/August 1998
• Intersuband absorption in boron dope multiple Ge
  Quantum DotApplied Physic Letter Vol. 74, Number
  2, January 11, 1998
• Normal Incidence Mid-Range Ge Quantum dot
  photo-detectorFei Lou, Song Tong, Jianlin Liu
  Kang L. Wang--Journal of Electronics materials,
  vol. 33, Number 8, 2004
• Zhen Yang, Yi Shi, Jianlin Liu, Bo Yan, Rang
  Zhang, Youdou Zhen Kanglong WangOptical
  Properties of Ge/Si quantum dot
  superlaticesDepartment of Physic and National
  Laboratory of Solid State Microstructure, Nanjing
  University University of California. Science
  DirectMaterial Letters 58 (2004) 3765-3768