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Quantum Dots: Photon Interaction Applications. Brad Gussin John Romankiewicz 12/1/04. Semiconductor Structures. Bulk Crystal (3D)  3 Degrees of Freedom (x-, y-, and z-axis). Quantum Well (2D)  2 Degrees of Freedom (x-, and y-axis). Quantum Wire (1D) 

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quantum dots photon interaction applications

Quantum Dots: Photon Interaction Applications

Brad Gussin

John Romankiewicz



Semiconductor Structures

Bulk Crystal (3D) 

3 Degrees of Freedom (x-, y-, and z-axis)

Quantum Well (2D) 

2 Degrees of Freedom (x-, and y-axis)

Quantum Wire (1D) 

1 Degree of Freedom (x-axis)

Quantum Dot (0D) 

0 Degrees of Freedom

(electron is confined in all directions)


Structure vs. Energy

Quantum Dots are sometimes called “artificial atoms”


Infrared Photodetection QWIP

Quantum Well IP

Bulk Crystal









QWIP Drawbacks

  • High Intensity / Low Temp
  • Polarization scatter grating
      • Detector only works when photon hits semiconductor perpendicularly to the two unconfined axis



Quantum Dots

(Structure and Formation)

Self-Assembly (a.k.a Stranski-Krastanow Method): Mismatched lattice constants cause surface tension which results in Qdot formation with surprisingly uniform characteristics.

GaAs  5.6533 Å InAs  6.0584 Å



  • 3D e- Confinement: Sharper wavelength discrimination
  • E = n / R2  E controlled by dimensional parameter R
  • No need for Polarization
  • “Photon Bottleneck” : e- stays excited for a longer time (i.e. less recombination), resulting in a more efficient detector and resistance to temperature.
  • Higher temperatures and lower intensity.

The Future of QDIPs

  • Self-assembly techniques still unstable: tune photodetection properties by manipulating the shape and size of Qdots
  • Possible Solutions:
  • Different Material Combinations
  • More precise control of parameters (T, pressure, physical setup)
  • Combine self-assembly with lithography and etching techniques
      • For example: create crevices or pre-etched holes to encourage qdot growth in specified positions.
  • * Dr. Bijan Movaghar estimates 5-10 years before commercially practical QDIPs are in use.

QDIP Applications

Increase detectivity  Increase number of applications


(Thermal Imaging)



Astronomy: Infrared Image of the Milky Way

solar cell applications
Solar Cell Applications
  • Currently, quantum wells and quantum dots are being researched for use in solar cells.
  • Factors that affect solar cell efficiency:
    • Wavelength of light
    • Recombination
    • Temperature
    • Reflection
    • Electrical Resistance

On an I-V curve characterizing the output of a solar cell, the ratio of maximum power to the product of the open-circuit voltage and the short circuit current is the fill factor. The higher the fill factor, the “squarer” the shape of the I-V curve.

quantum well application
Quantum Well Application
  • Photocurrent and output voltage can be individually optimized
    • Absorption edge and spectral characteristics can be tailored by the width and depth of QWs.
  • In GaAs/AlxGa1-xAs p – i – n structure with inserted QWs, researchers have observed enhancement in the short-circuit current and thus efficiency in comparison with control samples that are identical except without the QWs.
quantum dot application
Quantum Dot Application
  • Have potential to improve efficiency
    • Reducing recombination
      • Channeling the electrons and holes through the coupling between aligned QD’s
      • Photon bottleneck
    • Increasing the amount of usable incident light
    • Can be used at higher temperatures
  • Drawbacks
    • Size is harder to control
      • Thus harder to control the light absorption spectrum
  • Solutions for quantum dot solar cells are similar to QDIP solutions
structure and energy diagram
Structure and Energy Diagram
  • P-type, intrinsic, n-type structure
  • Based on a self-organized InAs/GaAs system
  • Quantum dots used in active regions
  • Qdot technology will help optimize the photon detection and photovoltaic industries by making devices more efficient and functionally effective.
  • Possible other areas for commercial development include use in the automobile or robotics industries
      • Detect object or humans in the vicinity of the device.
      • Power generation for device.
  • Interview with Dr. Bijan Movaghar, visiting professor (November 19, 2004).
  • Aroutounian, V. et al. Journal of Applied Physics. Vol. 89, No. 4. February 15, 2001.
  • Razeghi, Manijeh. Fundamentals of Solid State Engineering. Kluwer: Boston. 2002.
  • Center For Quantum Devices. <http://cqd.ece.northwestern.edu/>
  • Quantum Dots Introduction <http://vortex.tn.tudelft.nl/grkouwen/qdotsite.html>