1. Quantum Dots in Photonic Structures Wednesdays, 17.00, SDT Jan Suffczyński Projekt Fizyka Plus nr POKL.04.01.02-00-034/11 współfinansowany przez Unię Europejską ze środków Europejskiego Funduszu Społecznego w ramach Programu Operacyjnego Kapitał Ludzki Lecture 10: QD-microcavity in weak coupling regime

2. Reminder - microdisc cavity Total internal reflection Lord Rayleigh, “The problem of the whispering gallery,” Philosophical Magazine’1910.

3. Photonic Crystal cavity formed by a point defect O. Painter et. al., Science (1999)

4. Picture: M.V.Artemyev, I. Nabiev CdSe QDs attached to a glass m-sphere

5. Here: CdSe-shell on glass  -sphere R=3.1  m Wavelength (nm) mode separation >  QD room temperature emission Nano Lett. 1, 309 (2001)

6. Coupled QD - micropillar systems

7. Motivation – enhancement of photon extraction efficiency sin  max = 1/n quantum dot Low photon extraction efficiency from unstructured crystal

8. Motivation S. Strauf, Nature Photonics 2010

9. Desired: production method of coupled QD-cavity systems „on demand” Motivation

10. For a planar microcavity: rlrl ruru Reflectivity d cav n cav Quality factor of a planar cavity

11. For a planar microcavity (GaAs/AlAs example): rlrl ruru Reflectivity Effective cavity length d cav n cav Quality factor of a planar cavity Effective refractive index of DBR Effective mirror length Effective number of mirror pairs

12. Quality factor of a planar cavity The reflectivity of a DBR consisting of m mirror pairs (n 0 equals 1 for the top mirror and n 0 = nGaAs for the bottom mirror) AlAs/GaAs planar microcavity sample with 20/24 mirror pairs in the upper/lower DBR

13. Planar cavity (top view) A condition for a sizable Purcell effect: fully 3D cavity The idea: Lateral structuring of a planar cavity D Emitter Planar cavity Impact of the cavity on the spontaneous emission rate

14. From 2D to 3D photonic crystal DBR made of ZnSSe and MgS/ZnCdSe supperlattices Lohmeyer et al. Planar microcavity = 1D confinement of the light Pillar microcavity= 3D confinement of the light

15. Quality factor of the micropillar Evolution of the microresonator resonance with diameter T. Rivera et al., APL ’1999 Two main effects of the diameter reduction:  blueshift of the fundamental mode  linewidth increase due to the higher optical losses

16. Quality factor of the micropillar  The degradation of Q below a certain critical diameter  losses due to the scattering by the roughness of the microresonators sidewalls + intrinsic losses  Q constant for large pillar diameters = close to the Q of the planar cavity Rivera et al.’1999

17. r rr Quality factor of the micropillar: loss sources  r: typically ~ 10 nm Photon Escape  Rate „Planar” losses „Sidewall” losses Scattering losses proportional to the transverse mode intensity at the microresonator edge: + Top view

18. Sidewall roughness

19. Roughness of the order of tens of nm GaAs/AlAs DBRs

20. Reitzenstein et al. Quality factor of the micropillar: loss sources Q decraese with pillar diameter - dominant contribution from egde scattering losses

21. Quality factor of the micropillar: implications for the Purcell factor Gayralet al. Non-linear dependence of F p on Q factor in the limit of small pillar diameters The same Q planar Low losses High lossses

22. Quality factor of the micropillar: implications for the Purcell factor The same Q planar Low losses High lossses

23. Q factor oscillations Lalanne et al.’2004 Prediction: The appearance of strong oscillations for high-Q micropillars in the small diameter regime

24. Q factor oscillations Lalanne et al Prediction: Lecamp et al.’2007 experiment calculation The appearance of strong oscillations for high-Q micropillars in the small diameter regime Observation:

25. Q factor oscillations Oscillations attributed to a coupling of the fundamental mode to higher-order pillar modes Basic idea: + +

26. Micropillar eigenmodes vs diameter T. Jakubczyk et al. Blueshift of the mode with decreasing diameter evidenced in photoluminescence

27. Photoluminescence - Micropillar eigenmodes ExperimentSimulation Extended transfer matrix method: Material absorption included Equal emission intensity of each line assumed T. Jakubczyk et al.

28. Purcell enhancement of spontaneous emission Purcell Factor Spontaneous emission rate

29. Reminder: Fermi’s Golden Rule Density of photon states at emitter wavelength Electric field intensity at emitter position Dipol moment of the emitter Spontaneous emission rate is not an inherent property of the emitter Sponteanous emission rate proportional to: mirror Spontaneous emission inhibited Spontaneous emission enhanced

30. - cavities

32. Purcell factor in realistic case The observation of cavity QED phenomena relies on high Q/ Veff spatial and spectral matching Quality factor Effective mode volume

33. Purcell factor in realistic case

35. QD-micropillar system – the first realization J. M. Gérard et al. ’ PRL1998 Out of cavity - reference QDs In cavity – out of resonance In cavity – on resonance Measurements on QD ensamble

36. Bayer et al 2001 Enhancement or suppression of QD spontaneous emission QD in micropillar with coated sidewalls QD in micropillar QD in planar microcavity

37. Decay rate as a function of detuning T. Jakubczyk et al.

38. Decay rate as a function of detuning Strong enhancement of the decay rate at zero-detuning

39. Decay rate as a function of detuning Strong enhancement of the decay rate at zero-detuning T. Jakubczyk et al.

40. Decay rate as a function of detuning Strong enhancement of the decay rate at zero-detuning Shortening of the decay time does not depend on temperature Far detuned QDs have similar decay time to reference QDs T. Jakubczyk et al.

41. Decay rate as a function of detuning Strong enhancement of the decay rate at zero-detuning Shortening of the decay time does not depend on temperature Far detuned QDs have similar decay time to reference QDs T. Jakubczyk et al.

42. Decay rate as a function of detuning Strong enhancement of the decay rate at zero-detuning Shortening of the decay time does not depend on temperature Far detuned QDs have similar decay time to reference QDs T. Jakubczyk et al.

43. Deterministic and scalable method for production of coupled QD-cavity devices SEM image 2  m

44. QD coupled to the mode of the micropillar microcavity: an ideal case Spatial matching: QD at the spatial maximum of the cavity optical mode Spectral matching: QD emission energy = Optical cavity fundamental mode energy QD micropillar Energy Emission M QD

45. Towards deterministic coupling - Control of the spatial positions of individual QDs? 100 nm AFM image

46. Towards deterministic coupling - Control of the spatial positions of individual QDs? - Yes.

47. ~ 50 meV ~ µeV Energy (eV) 1.321.401.48 PL  Probability of random spatial and spectral matching of the QD to the cavity mode for 2  m pillar smaller than 1/1000 Towards deterministic coupling - Control of the energy emission of individual QDs? - No. Bragg mirrors

48. Spatial matching

49. Technology so far  Many steps  Precision of spectral matching 6 meV  Only one coupled device on the sample QD in photonic crystal cavity – coupled „on demand” (Imamoglu’s group, Science’2005, Nature’2007): Quantum nature of a strongly coupled single quantum dot-cavity system K.Hennessy & al., Nature 2007

50. Deterministic and scalable method for production of coupled QD-cavity devices Spectral and spatial QD-cavity matching in a single step Many coupled systems on the same sample One or more QDs coupled to the same mode

51. sample at 10 K focus control spatial matching laser 532 nm laser 750 nm spectrometer CCD emission analysis spectral matching x y z shutter Experimental setup

52. 20 pairs 24 pairs } Photolithographic method in situ Bragg mirrors AlAs/GaAs: two dimensional optical cavity } Sample preparation: InAs/GaAs QD layer MBE grown between AlAs/GaAs Bragg mirrors Positive photoresist spin coated on the sample surface Positive photoresist Low density InAs/GaAs QD layer

53. Positive photoresist InAs/GaAs QD layer Sample at T= 10 K planar cavity x y Piezoelectric x-y stages Photolithographic method in situ

54. microskope signal Spectra acquisition Spectrometer + CCD µ-PL excitation at 750 nm Sample at T= 10 K planar cavity Positive photoresist InAs/GaAs QD layer µ-PL scanning x y Photolithographic method in situ Piezoelectric x-y stages

55. photoluminescence X- Y mapping c) QD PL intensity y ( ) x ( ) QD position determination with 50 nm accuracy 15 12 9 6 3 0  Spatial coupling Photolithographic method in situ

56. microskope signal Spectra acquisition Spectrometer + CCD µ-PL excitation at 750 nm Sample at T= 10 K planar cavity Positive photoresist InAs/GaAs QD layer Optical Lithography x y Photolithographic method in situ ‘Green’ beam co-linear with ‘red’ beam photoresist exposure at 532 nm Piezoelectric x-y stages

57. Spectral matching  =0  max planar cavity a) EXEX EXEX R  QD emission energy = Optical cavity fundamental mode energy 5 µm Photo of the sample surface: Ni masks Increasing exposure time

58. Spectral matching 2 µm pillar radius R  Pillar radius calibration  Spectral and spatial QD-cavity matching: a single step process!

59. Signal Photoresist exposured Pillar etching Nickel mask deposition Lift-off Pillar with a QD placed in the mode maximum Etching: Resist development

60. 10K 32K pillar 1 M x10 PL Intensity Selected QD Pillar radius R=0.85 µm after pillar etching during lithography QD-cavity coupling „on demand” - weak coupling A. Dousse, L. Lanco, J. Suffczyński, E. Semenova, A. Miard, A. Lemaitre, I. Sagnes, C. Roblin, J. Bloch and P. Senellart, Phys. Rev. Lett. 101, 267404 (2008)

61. Controlled Purcell efect )(  P sat X FnI C. Böckler et al., Appl. Phys. Lett., 92, 091107 (2008) PL Intensity at saturation vs QD – cavity mode detuning: Expected: F p = 9.5 (for R = 0.85µm and Q=1500) Measured: F p = 9 ± 3  Purcell factor as predicted

62. PL intensity  -PL d uring lithography After pillar etching selected QD M M M Etched mikropillars – SEM image: Many coupled systems on the same sample Scalability of the technique selected QD

63. Standard deviation: 0.6 meV Scalability of the technique - precision