1. www.tyndall.ie Lorenzo O. Mereni Valeria Dimastrodonato Gediminas Juska Robert J. Young Emanuele Pelucchi Physical properties of highly uniform InGaAs Pyramidal Quantum Dots with GaAs barriers: the Fine Structure Splitting Epitaxy and Physics of Nanostructures Group: Tyndall National Institute University College of Cork Ireland

2. www.tyndall.ie Why Quantum Dots??? As Development Tools for novel technologies and materials As Instruments of investigation for the properties of the low dimensional solid state

3. www.tyndall.ie Characteristics of an ideal, easy-to-use QD source 1 -control over QD position and distance between QDs 2 -easy tunability of the QD electronic properties 3 -allow engineering of the coupling (i.e. allow the formation of artificial "molecules") and stacking of QDs in an easy and controllable way 4 -allow a single or stack of dots to be easily addressed and controlled electrically, and not only optically 5 -“identical” dots 6 -High optical quality

4. www.tyndall.ie SELF ASSEMBLED AND SITE CONTROLLED: TWO DIFFERENT APPROACHES Self assembled Site controlled

5. www.tyndall.ie GaAs (111)B substrate GaAs SiO 2 Resist deposited and exposed to UV light SiO 2 removal with HFResist removal Wet etching of tetrahedrical recesses Ready for growth! WET LITHOGRAPHY

6. www.tyndall.ie Easy patterning and growth process

7. www.tyndall.ie M. Baier, E. Pelucchi, S. Watanabe, and E. Kapon, “High- uniformity of site-controlled pyramidal quantum dots grown on pre-patterned substrates”, Appl. Phys. Lett. 84, 1943 (2004). M. Baier,et al...” Single photon emission from site-controlled pyramidal quantum dots”, Appl. Phys. Lett. 84, 648 (2004). M. Baier, C. Constantin, E. Pelucchi, and E. Kapon, “ Electroluminescence from a single pyramidal quantum dot in a light- emitting diode”, Appl. Phys. Lett. 84, 1967 (2004). +single photon electrically pumped …M.H..Baier et al unpublished DOs AND DONTs OF PYRAMIDAL QUANTUM DOTS

8. www.tyndall.ie InGaAs Dots with GaAs 1)Cladding Layer Al 55% Ga 45% As 2)GaAs barriers 3)Dot layer In 25% Ga 75% As – 0.5 nm nominal thickness 4)Vertical Quantum Wire σ = 1.2 meV FWHM = 2.8 meV L. O. Mereni et al., Appl. Phys. Lett. 94, 223121 (2009)

9. www.tyndall.ie CAN WE MAKE ENTANGLED PHOTONS WITH THESE DOTS?

10. www.tyndall.ie THE BIEXCITON-EXCITON CASCADE & FSS XX X 0 σ+σ+σ+σ+ σ+σ+σ+σ+ σ-σ-σ-σ- σ-σ-σ-σ- Electric fields Structural Asymmetries Structural Asymmetries Alloy Disorder H V V H FSS

11. www.tyndall.ie (111): AN IDEAL PLATFORM FOR THE DEVELOPMENT OF ENTANGLED PHOTONS (111) Surfaces show a symmetry that has been indicated as ideal by many authors K. F. Karlsson., to appear in Phys. Rev. B 81 A.Schliwa et al., Phys. Rev. B 80, 161307 (2009) (111) Surfaces show a symmetry that has been indicated as ideal by many authors K. F. Karlsson., to appear in Phys. Rev. B 81 A.Schliwa et al., Phys. Rev. B 80, 161307 (2009) The design of the dots itself is conceived to be free of structural aymmetries No Splitting is expected a priori for geometrical reasons from these dots

12. www.tyndall.ie OPTICAL SETUP HALF WAVEPLATE LINEAR POLARIZER MONOCHROMATOR CLOSED CYCLE CRYOSTAT

13. www.tyndall.ieBUT…… Mean FFS: 13 μeV σ = 4 μeV X XX

14. www.tyndall.ie PHASE (μeV)

15. www.tyndall.ie FURTHER INVESTIGATIONS In 0.25 Ga 0.65 As Mean FFS: 13 μeV σ = 4 μeV In 0.35 Ga 0.65 As Mean FFS: 20 μeV σ = 10 μeV AlGaAs barriers Mean FFS: ? σ = ? 15% (μeV)

16. www.tyndall.ie Energy tuning (eV)

17. www.tyndall.ie DOTS WITH NITROGEN DOTS WITH NITROGEN Small shift of the emission wavelenght Antibinding biexciton energy Splitting within the experimental error

18. www.tyndall.ie Thank you for your attention Slann