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An Introduction to
Quantum Dot Spectrometer
Amir Dindar
ECE Department, University of Massachusetts, Lowell
An Introduction to Quantum Dot Spectrometer
University of Massachusetts, Lowell ECE Department
Regular Photodetectors
An Introduction to Quantum Dot Spectrometer
University of Massachusetts, Lowell ECE Department
Regular Photodetectors
Rela
tive in
ten
sit
y
wavelength
Carrier concentration
An Introduction to Quantum Dot Spectrometer
University of Massachusetts, Lowell ECE Department
Electron Confinement
Bulk material Quantum Well Quantum Dot
An Introduction to Quantum Dot Spectrometer
University of Massachusetts, Lowell ECE Department
Quantum Dots; A Tunable Range of Energies
-Size
-Addition or subtraction of just a few atoms
-Changing the geometry of the surface
-Composition
DimensionEgEgEgEg
20x20x100.1590.1940.2760.45
10x10x 50.6050.7411.021.57
5 x 5 x 2.52.1522.653.354.74
Images and data form Nanohub.org, QDot software
An Introduction to Quantum Dot Spectrometer
University of Massachusetts, Lowell ECE Department
Absorption
Absorption versus Energy for Pyramid Quantum Dot 10x10x5 nm (Eg = 1.57)
Ab
sorp
tion
Energy (eV)
An Introduction to Quantum Dot Spectrometer
University of Massachusetts, Lowell ECE Department
Same Material in Various Sizes
Images and data form http://www.EvidentTech.com
Quantum Dot Materials SystemDiameterEmission (absorption)
CdSe Core Quantum Dot1.9nm - 6.7nm465nm-640nm
CdSe/ZnS Core Shell Quantum Dot2.9nm - 6.1 nm490nm-620nm
CdTe/CdS Core Shell Quantum Dot3.7nm - 4.8nm620nm-680nm
PbS Core Quantum Dot2.2nm - 9.8nm850nm - 2100nm
PbSe Core Quantum Dot3.5nm - 9nm1200nm-2340nm
An Introduction to Quantum Dot Spectrometer
University of Massachusetts, Lowell ECE Department
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 !
An Introduction to Quantum Dot Spectrometer
University of Massachusetts, Lowell ECE Department
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…
An Introduction to Quantum Dot Spectrometer
University of Massachusetts, Lowell ECE Department
Read-Out Mechanism
Obvious solution:
- The second plane of quantum dots coupled to the first plane through a tunnel barrier
Two requirements:
1) The second layer should be uniform enough
2) 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
An Introduction to Quantum Dot Spectrometer
University of Massachusetts, Lowell ECE Department
Solution: Resonance Tunneling
Tra
nsm
issio
n
Energy (eV)
- 1.0
- 0.5
Barrier
Thi
ckne
ss
En
erg
y
En
erg
y
An Introduction to Quantum Dot Spectrometer
University of Massachusetts, Lowell ECE Department
Capture and Read-Out
Q.D.Q.W.
Capture
Read-Out
)/(1
))(/(
2
2
12
2121
2
22
2
1
22
1
mm
VEmmVEE
m
kVEE
m
kVEE
QWQWDot
llQWDot
llQWDot
This equation relates the energy of a QD to a specific voltage, so:
Setting V, sets the spectral channel read be the detector
An Introduction to Quantum Dot Spectrometer
University of Massachusetts, Lowell ECE Department
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).
E
Optical transition energy oE
Excited states difference
E Number of channels =
E
Eo
An Introduction to Quantum Dot Spectrometer
University of Massachusetts, Lowell ECE Department
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
An Introduction to Quantum Dot Spectrometer
University of Massachusetts, Lowell ECE Department
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