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Quantum Dots in Photonic Structures

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1 Quantum Dots in Photonic Structures
Lecture 14: Implemenatations, perspeectives Jan Suffczyński Wednesdays, 17.00, SDT Projekt Fizyka Plus nr POKL /11 współfinansowany przez Unię Europejską ze środków Europejskiego Funduszu Społecznego w ramach Programu Operacyjnego Kapitał Ludzki

2 Plan for today Reminder 2. QD lasers 3. Other…

3 The source of polarization entangled photons
Linear polarizer V H V

4 Enangled photons from a QD
The method: biexciton – exciton cascade Obstacle: anisotropy Biexciton Exciton Empty dot The energy carries the information on the polarization of the photon

5 Entangled photons from a QD
The method: biexciton – exciton cascade An obstacle: anisotropy Biexciton Exciton The energy carries the information on the polarization of the photon Empty dot (in circular polarization basis:)

6 Fine structure of neutral exciton
( + )/ 2 X δ1~0.1meV ( – )/ 2 X Anisotropic exchange δ0~1meV Isotropic exchange ( + )/ 2 δ2 ≈0 Xdark ( – )/ 2

7 Entanglement test XX-X cascade time START (H) STOP (H) XX X START
XX-X cascade

8 Influence of the in-plane electric field on the photoluminescence of individual QDs
Kowalik et al., APL’2005 InAs/GaAs Quantum Dots

9 Evolution of the anisotropy exchange splitting with the applied voltage
Kowalik et al., APL’2005

10 Influence of the in-plane magnetic field on the photoluminescence of individual QDs
Magnetic field [T] AES [meV] 2 4 6 0.10 0.14 0.18 1.8904 1.891 Energy [eV] m -PL B=0 experiment model 2 4 6 8 10 Magnetic Field [T] [meV] 0.45 p Angle J-2f [rad] Increase or decrease of the anisotropy splitting, depending on the magnetic field direction K. Kowalik et al., PRB 2007


12 QD in a pillar molecule:
an ultrabright source of entangled photons

13 QD as an entangled photons source
The idea: obtain polarization entangled photon pairs from biexciton-exciton cascade Main obstacle: anisostropy of the QD  exciton level splitting Hindrance: low collection efficiency (a few %) Energy XX X Ground state The solution: coupling of the X and XX to the modes of the photonic molecule When exciton level homogeneous linewidth larger than exciton anisotropy splitting: polarization entangled photons emitted in XX-X cascade  Increased extraction efficiency due to photon funneling into cavity mode

14 Pillar molecules Photon Energy (meV) R Distance Electronic lithography
1,315 1,320 1,325 1,330 1,335 PL Intensity (arb. units) Energy (eV) Electronic lithography Radius Distance

15 Experimental realization
Purcell effect evidenced on X and XX transitions  The proof of entanglement: polarization resolved second order XX-X crosscorrelations A. Dousse, at al. Nature 2010

16 Characterization of the source - entanglement
Density matrix of the two-photon state  67 % degree of entanglement  Entanglement criteria fullfilled

17 Quantum Dot Lasers

18 A laser – basic characteristics
mirror mirror cavity

19 A laser – basic characteristics
Active material mirror mirror cavity

20 A laser – basic characteristics
pumping Active material emission mirror mirror cavity

21 A laser – basic characteristics
Components of a laser An energy pump source An active medium to create population inversion by pumping mechanism: - photons at some site stimulate emission at other sites while traveling Two reflectors: to reflect the light in phase multipass amplification


23 Potential Advantages for Quantum Dot Semiconductor Lasers
Wavelength of light determined by the energy levels not by bandgap energy: improved performance & increased flexibility to adjust the wavelength

24 Potential Advantages for Quantum Dot Semiconductor Lasers
Wavelength of light determined by the energy levels not by bandgap energy: improved performance & increased flexibility to adjust the wavelength

25 Potential Advantages for Quantum Dot Semiconductor Lasers
Wavelength of light determined by the energy levels not by bandgap energy: improved performance & increased flexibility to adjust the wavelength Small volume: low power high frequency operation large modulation bandwidth small dynamic chirp small linewidth enhancement factor Superior temperature stability of I threshold I threshold (T) = I threshold (T ref).exp ((T-(T ref))/ (T 0)) High T 0  decoupling electron-phonon interaction by increasing the intersubband separation. Undiminished room-temperature performance without external thermal stabilization

26 QDs as an active medium in lasers: the first theoretical predictions
Extremely low current treshhold Increased gain Przewidywania teoretyczne dotyczące zastosowania kropek kwantowych w obszarze aktywnym lasera półprzewodnikowego; (A) zaleŜność funkcji wzmocnienia od wymiarowości układu fizycznego w obszarze aktywnym15; (B) zaleŜność prądu progowego od wymiarowości obszaru aktywnego16: (a) materiał lity, (b) studnia kwantowa, (c) drut kwantowy, (d) kropka kwantowa. 15 M. Asada et al., IEEE J. Quantum Electron. 22, 1915 (1986) 16 Y. Arakawa et al., Appl. Phys. Lett. 40, 939 (1982) A new type of semiconductor laser is studied, in which injected carriers in the active region are quantum mechanically confined in two or three dimensions (2D or 3D). Effects of such confinements on the lasing characteristics are analyzed. Most important, the threshold current of such laser is predicted to be far less temperature sensitive than that of conventional lasers, reflecting the reduced dimensionality of electronic state. In the case of 3D-QW laser, the temperature dependence is virtually eliminated. Jth – current treshhold To są zewidywanie teoretyczne – w 1982 roku jeszcze nie istniały metody produkcji kropek kwantowych Praca cytowana 1900 razy M. Asada et al., IEEE J. Quantum Electron. 22, 1915 (1986). Y. Arakawa et al., Appl. Phys. Lett. 40, 939 (1982).


28 Increased maximum material gain

29 Potential Advantages for Quantum Dot Semiconductor Lasers
Lower Threshold Higher Modulation Speed Smaller Linewidth Less Temperature Sensitivity Reduced Auger Recombination → Mid-Infrared Semiconductor Lasers

30 Q. Dot Laser vs. Q. Well Laser
In order for QD lasers compete with QW lasers: A large array of QDs since their active volume is small An array with a narrow size distribution has to be produced to reduce inhomogeneous broadening Array has to be without defects may degrade the optical emission by providing alternate nonradiative defect channels The phonon bottleneck created by confinement limits the number of states that are efficiently coupled by phonons due to energy conservation Limits the relaxation of excited carriers into lasing states Causes degradation of stimulated emission Other mechanisms can be used to suppress that bottleneck effect (e.g. Auger interactions)

31 QDL – Application Requirements
Same energy level Size, shape and alloy composition of QDs close to identical Inhomogeneous broadening eliminated  real concentration of energy states obtained High density of interacting QDs Macroscopic physical parameter  light output Reduction of non-radiative centers Nanostructures made by high-energy beam patterning cannot be used since damage is incurred Electrical control Electric field applied can change physical properties of QDs Carriers can be injected to create light emission

32 Electrically pumped Quantum Dot Laser
Fujitsu Temperature Independent QD laser (2004)

33 Temperature Independent QD laser
Fujitsu (2004)


35 QD laser already on the market

36 Stable operation up to 60C without a cooler
Modulation rates up to 500MHz 2VDC operation 532nm output ( mW power level, with frequency doubling) Tiny TO-56 package (5.6mm diameter)

37 Lasing in a QD-microdisc system
InAs/GaAs QDs cavity Q exceeds

38 Lasing in a QD-microdisc system
„In most of our samples lasing persists when the sample is tuned from 6 to 55 K (a QD tuning range of 1.5 nm). This indicates the lasing is not based exclusively on observable QD states resonantly coupled to the mode.”

39 Lasing in a QD-microdisc system
Because the QDs are randomly distributed throughout the disk, spectral alignment between the cavity mode and QD state does not guarantee coupling „However, the relative spectral tuning of observed QDs emission states and cavity modes does influence the L-I curve.” Z. G. Xie et al., PRL’2007

40 A recipy for a good QD laser
„To achieve single state lasing the processes associated with the loss must be suppressed and more efficient lasing via the single-emitter state (i.e., higher effective oscillator strength and higher Q), must be implemented.” Z. G. Xie et al., PRL’2007 + … a good QD-cavity mode spatial matching

41 The investigations clearly visualize a smooth transition from spontaneous to predominantly stimulated emission which becomes harder to determine for high beta. With increasing , the steplike ‘‘threshold’’ in the output intensity of conventional 1 laser devices gradually disappears up to the so-called thresholdless laser [8] in the limit 1 S. M. Ulrich et al., PRL’2007

42  = t2 – t1 t1 = 0 t2 = 20 Karta do pomiaru korelacji
Od źródła fotonów Karta do pomiaru korelacji  = t2 – t1 Dioda „STOP” Liczba skorelowanych zliczeń n() Dioda „START” t1 = 0 wejście STOP t2 = 20 wejście START

43 Increased g(2) (t) at lasing treshold
S. M. Ulrich et al., PRL’2007

44 b of a mode = the ratio of SE into that mode divided by the total SE into all modes
S. M. Ulrich et al., PRL’2007

45 Measured second-order photon correlation function at zero delay
time (top) and output intensity versus input pump power, Pexc (bottom), for three different microcavity lasers. Q = 1850 20 QDs Q = 9000 30 QDs Q = 19000 15 QDs Wiersig et al., Nature’2009

46 k-space imaging Fourier plane

47 k-space imaging Fourier plane imaging

48 Real-space imaging

49 Angle resolved emission from QDs in planar cavity
GaAs/InGaAs planar cavity Photon Energy

50 Angle resolved emission from QDs in planar cavity

51 QD in micropillar microcavity– angular dependences
Each mode characterizied by a specific emission pattern

52 QD in micropillar microcavity – angular dependences


54 Mode 01 Mode 21

55 Mode 01 Mode 21

56 QDs in bio-physics Foto: Felice Frankel

57 Zalety QD jako źródeł światła: Duża wydajność kwantowa
Duża wartość molowego współczynnika ekstynkcji (przekroju czynnego na oddziaływanie ze światłem) Szerokie pasmo wzbudzenia Wąskie pasmo emisji (FWHM ~25-40 nm) Duże przesunięcie Stokesa Duża odporność na fotowybielanie Długi czas życia stanu wzbudzonego Remigiusz Worch, IF PAN

58 Porównanie z „klasycznymi” fluoroforami
Związek organiczny: rhodamine red Białko fluorescencyjne: DsRed2 QDs: Medintz et al., 2005, Nature Materials Remigiusz Worch, IF PAN

59 Przykład obrazowania komórek
Medintz et al., 2005, Nature Materials Barwienie organelli komórkowych za pomocą QD: Cyan- 655 nm- jądra komórkowe Magenta- 605 nm- białko Ki-67 (obecne w jądrze, marker proliferacji) Pomarańczowy- 525 nm- mitochondria Zielony- 565 nm – mikrotubule Czerwony – 705 nm – filamenty aktynowe Remigiusz Worch, IF PAN

60 INVITROGEN: Qdot Nanocrystal
Multicolor immunofluorescence imaging with Qdot® secondary antibody conjugates. Laminin in a mouse kidney section was labeled with an anti-laminin primary antibody and visualized using green-fluorescent Qdot® 565 IgG. PECAM (platelet/endothelial cell adhesion molecule; CD31) was labeled with an anti–PECAM-1 primary antibody and visualized using red-fluorescent Qdot® 655 IgG. Nuclei were stained with blue-fluorescent Hoechst

61 INVITROGEN: Qdot Nanocrystal

62 W „bio-aplikacjach” QD stosowane są jako koloidy (najczęściej core-shell CdSe-ZnS).
Pasywacja ZnS służy stabilności, jak również tworzy „platformę” do dalszych modyfikacji chemicznych . „Kapowanie” molekułami bi-funkcyjnymi zapewnia rozpuszczalność w środowisku wodnym, jak również różne grupy chemiczne umożliwiają dołączanie biomolekuł. Medintz et al., 2005, Nature Materials Remigiusz Worch, IF PAN

63 Istnieje potrzeba sprawdzania stabilności tak uzyskanych struktur koloidalnych oraz znajomości promienia hydrodynamicznego w roztworze. E. P. Petrov and P. Schwille, Springer Ser Fluoresc (2008) Jedną z technik wykorzystywanych w tym celu jest spektroskopia korelacji fluorescencji (Fluorescence Correlation Spectroscopy, FCS) Remigiusz Worch, IF PAN

64 FCS – idea techniki Monitorujemy natężenie fluorescencji F(t) w objętości utworzonej przez skupione światło laserowe. Obserwowane fluktuacje są, w najprostszej sytuacji, wynikiem, swobodnej dyfuzji fluorescencyjnych (luminescencyjnych) obiektów. Stosujemy formalizm autokorelacji. F(t) -> G(tau) Remigiusz Worch, IF PAN

65 FCS – funkcja autokorelacji
Dla swobodnie dyfundujących cząstek w 3-D funkcja ma postać: Z dopasowania dostajemy: tau_d (charakterystyczny czas dyfuzji przez ognisko) , a z amplitudy G(0)-1=<N> średnią liczbę cząstek Przy znanej wielkości ogniska, możemy obliczyć współczynnik dyfuzji D oraz stężenie. W przypadku kropek, z D można oszacować promień hydrodynamiczny (z relacji Einsteina-Stokesa). Remigiusz Worch, IF PAN

66 FCS i QD – przykład zastosowania
Różne związki chemiczne dołączone do ZnS – wpływ na wielkość i stabilność koloidalną Murcia et al., 2008, Optics Commun Remigiusz Worch, IF PAN

67 FCS i QD – przykład zastosowania – IF PAN (R. Worch)
QD z dołączonym białkiem roślinnym o własnościach enzymatycznych (FNR) Technika FCS użyta do oceny zmian promienia hydrodynamicznego: QD ,7±1,3 nm QD 550+FNR 10,4±2,1 nm QD ,1±4,1 nm QD 650+FNR 19,8±4,2 nm Szczepaniak, Worch, Grzyb, J. Phys.: Condens. Matter, w recenzji Remigiusz Worch, IF PAN

68 Nanoparticles of cadmium selenide (quantum dots) glow when exposed to ultraviolet light. When injected, they seep into cancer tumors. The surgeon can see the glowing tumor, and use it as a guide for more accurate tumor removal.

69 February 2003 The Industrial Physicist Magazine
Quantum Dots for Sale                      Nearly 20 years after their discovery, semiconductor quantum dots are emerging as a bona fide industry with a few start-up companies poised to introduce products this year. Initially targeted at biotechnology applications, such as biological reagents and cellular imaging, quantum dots are being eyed by producers for eventual use in light-emitting diodes (LEDs), lasers, and telecommunication devices such as optical amplifiers and waveguides. The strong commercial interest has renewed fundamental research and directed it to achieving better control of quantum dot self-assembly in hopes of one day using these unique materials for quantum computing. Semiconductor quantum dots combine many of the properties of atoms, such as discrete energy spectra, with the capability of being easily embedded in solid-state systems. "Everywhere you see semiconductors used today, you could use semiconducting quantum dots," says Clint Ballinger, chief executive officer of Evident Technologies, a small start-up company based in Troy, New York...



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