An Introduction to Quantum Dot spectrometer

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An Introduction to Quantum Dot Spectrometer
Amir Dindar ECE Department, University of
Massachusetts, Lowell
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An Introduction to Quantum Dot Spectrometer
Regular Photodetectors

• University of Massachusetts, Lowell ECE Department

3
An Introduction to Quantum Dot Spectrometer
Regular Photodetectors
Carrier concentration
Relative intensity
wavelength

• University of Massachusetts, Lowell ECE Department

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An Introduction to Quantum Dot Spectrometer
Electron Confinement
Bulk material
Quantum Well
Quantum Dot

• University of Massachusetts, Lowell ECE Department

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An Introduction to Quantum Dot Spectrometer
Quantum Dots A Tunable Range of Energies

• Size
• Addition or subtraction of just a few atoms
• Changing the geometry of the surface
• Composition

Eg Eg Eg Eg Dimension
0.45 0.276 0.194 0.159 20x20x10
1.57 1.02 0.741 0.605 10x10x 5
4.74 3.35 2.65 2.152 5 x 5 x 2.5
Images and data form Nanohub.org, QDot software

• University of Massachusetts, Lowell ECE Department

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An Introduction to Quantum Dot Spectrometer
Absorption
Absorption
Energy (eV)
Absorption versus Energy for Pyramid Quantum Dot
10x10x5 nm (Eg 1.57)

• University of Massachusetts, Lowell ECE Department

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An Introduction to Quantum Dot Spectrometer
Same Material in Various Sizes
Emission (absorption) Diameter Quantum Dot Materials System
465nm-640nm 1.9nm - 6.7nm CdSe Core Quantum Dot
490nm-620nm 2.9nm - 6.1 nm CdSe/ZnS Core Shell Quantum Dot
620nm-680nm 3.7nm - 4.8nm CdTe/CdS Core Shell Quantum Dot
850nm - 2100nm 2.2nm - 9.8nm PbS Core Quantum Dot
1200nm-2340nm 3.5nm - 9nm PbSe Core Quantum Dot
Images and data form http//www.EvidentTech.com

• University of Massachusetts, Lowell ECE Department

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An Introduction to Quantum Dot Spectrometer
Size Distribution and Excitation
We always have a distribution of different sizes
A Specific Wavelength of light (Ideal case)
But it is not the real case !

• University of Massachusetts, Lowell ECE Department

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An Introduction to Quantum Dot Spectrometer
Capturing the Spectral Information
We always have a distribution of different sizes
A Range of Wavelengths of light (real case)
Again! No spectral information! Like a bulk
material

• University of Massachusetts, Lowell ECE Department

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An Introduction to Quantum Dot Spectrometer
Read-Out Mechanism

• Obvious solution
• - The second plane of quantum dots coupled to the
  first plane through a tunnel barrier
• Two requirements
• The second layer should be uniform enough
• It would have to be made of wider bandgap
  material
• The first requirement is presently not feasible!
• The more realistic approach
• Resonant-tunneling structure formed by two wells
  of different materials

• University of Massachusetts, Lowell ECE Department

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An Introduction to Quantum Dot Spectrometer
Solution Resonance Tunneling
Energy
Energy
Energy (eV)
Barrier Thickness
- 1.0
Transmission
- 0.5

• University of Massachusetts, Lowell ECE Department

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An Introduction to Quantum Dot Spectrometer
Capture and Read-Out
Capture
Read-Out
This equation relates the energy of a QD to a
specific voltage, so Setting V, sets the
spectral channel read be the detector
Q.W.
Q.D.

• University of Massachusetts, Lowell ECE Department

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An Introduction to Quantum Dot Spectrometer
Optical Channel Capability
Definition The number of independent
wavelengths it will be capable of detecting
Limiting factor Two QDs of different size, even
with the same optical transition energy, can have
different excited energies (in CB).
Optical transition energy
Number of channels
Excited states difference

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An Introduction to Quantum Dot Spectrometer
Problems and Considerations

• scattering effects
• Increasing the width of first barrier
• Decreasing the width of barrier between two
  quantum wells
• Low Responsivity
• Because of
• - Having one QD layer
• - At any time only a fraction of dots are
  active
• Solution
• - Using more sophisticated structures like
  Bragg reflectors
• - Repeating the layer over several periods

• University of Massachusetts, Lowell ECE Department

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An Introduction to Quantum Dot Spectrometer
References

1. J. L. Jimenez,a) L. R. C. Fonseca, D. J. Brady,
   and J. P. Leburton, The Quantum Dot
   Spectrometer, Appl. Phys. Lett. 71 (24),
2. John H. Davies, The Physics of Low Dimensional
   Semiconductors, Cambridge University Press,
   ISBN 0521481481
3. A. F. J. Levi, Applied Quantum Mechanics,
   Cambridge University Press, ISBN 052152086x
4. S.O.Kasap, Optoelectronics and Photonics
   principles and practices, Prentice Hall, ISBN
   0201610876
5. Andreas Scholze, A. Schenk, and Wolfgang
   Fichtner, Single Electron Device Simulation,
   IEEE Transactions on electron devices, Vol. 47,
   No. 10, 2000
6. JAMES H. LUSCOMBE, JOHN N. RANDALL, Resonant
   Tunneling Quantum Dot Diodes Physics,
   Limitations and Technological Prospect,
   PROCEEDINGS OF THE IEEE, VOL. 79, NO 8, 1991
7. Xiaohua Su, Subhananda Chakrabarti, Pallab
   Bhattacharya, A Resonant Tunneling Quantum Dot
   Infrared Photodetector, IEEE journal of quantum
   electronics, Vol. 41, No. 7, 2005

• University of Massachusetts, Lowell ECE Department