1. An Introduction to Quantum Dot Spectrometer Amir Dindar ECE Department, University of Massachusetts, Lowell

2. An Introduction to Quantum Dot Spectrometer University of Massachusetts, LowellECE Department Regular Photodetectors

3. An Introduction to Quantum Dot Spectrometer University of Massachusetts, LowellECE Department Regular Photodetectors Relative intensity wavelength Carrier concentration

4. An Introduction to Quantum Dot Spectrometer University of Massachusetts, LowellECE Department Electron Confinement Bulk materialQuantum WellQuantum Dot

5. An Introduction to Quantum Dot Spectrometer University of Massachusetts, LowellECE Department Quantum Dots; A Tunable Range of Energies -Size -Addition or subtraction of just a few atoms -Changing the geometry of the surface -Composition Eg Dimension 0.450.2760.1940.15920x20x10 1.571.020.7410.60510x10x 5 4.743.352.652.1525 x 5 x 2.5 Images and data form Nanohub.org, QDot software

6. An Introduction to Quantum Dot Spectrometer University of Massachusetts, LowellECE Department Absorption Absorption versus Energy for Pyramid Quantum Dot 10x10x5 nm (Eg = 1.57) Absorption Energy (eV)

7. An Introduction to Quantum Dot Spectrometer University of Massachusetts, LowellECE Department Same Material in Various Sizes Images and data form http://www.EvidentTech.com Emission (absorption)DiameterQuantum Dot Materials System 465nm-640nm1.9nm - 6.7nmCdSe Core Quantum Dot 490nm-620nm2.9nm - 6.1 nmCdSe/ZnS Core Shell Quantum Dot 620nm-680nm3.7nm - 4.8nmCdTe/CdS Core Shell Quantum Dot 850nm - 2100nm2.2nm - 9.8nmPbS Core Quantum Dot 1200nm-2340nm3.5nm - 9nmPbSe Core Quantum Dot

8. An Introduction to Quantum Dot Spectrometer University of Massachusetts, LowellECE 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 !

9. An Introduction to Quantum Dot Spectrometer University of Massachusetts, LowellECE 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…

10. An Introduction to Quantum Dot Spectrometer University of Massachusetts, LowellECE 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

11. An Introduction to Quantum Dot Spectrometer University of Massachusetts, LowellECE Department Solution: Resonance Tunneling Transmission Energy (eV) - 1.0 - 0.5 Barrier Thickness Energy

12. An Introduction to Quantum Dot Spectrometer University of Massachusetts, LowellECE Department Capture and Read-Out Q.D. Q.W. 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

13. An Introduction to Quantum Dot Spectrometer University of Massachusetts, LowellECE 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). Optical transition energy Excited states difference Number of channels =

14. An Introduction to Quantum Dot Spectrometer University of Massachusetts, LowellECE 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

15. An Introduction to Quantum Dot Spectrometer University of Massachusetts, LowellECE 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