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Lorenzo O. MereniLorenzo O. Mereni

Valeria DimastrodonatoValeria Dimastrodonato

Gediminas JuskaGediminas Juska

Robert J. YoungRobert J. Young

Emanuele PelucchiEmanuele Pelucchi

Physical properties of Physical properties of highly uniform InGaAs highly uniform InGaAs Pyramidal Quantum Pyramidal Quantum

Dots with GaAs barriers: Dots with GaAs barriers: the Fine Structure the Fine Structure

SplittingSplitting

Epitaxy and Physics of Epitaxy and Physics of Nanostructures Group:Nanostructures Group:

Tyndall National Institute Tyndall National Institute University College of Cork University College of Cork

IrelandIreland

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Why Quantum Dots???Why Quantum Dots???

As Development Tools for novel technologies and materialsAs Development Tools for novel technologies and materials

As Instruments of investigation for the properties of the low As Instruments of investigation for the properties of the low dimensional solid state dimensional solid state

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Characteristics of an ideal, easy-to-use QD Characteristics of an ideal, easy-to-use QD sourcesource

1 -1 - control over QD control over QD positionposition and distance between QDs and distance between QDs

2 -2 - easy easy tunability of the QD electronic propertiestunability of the QD electronic properties

3 -3 - allow allow engineering of the coupling (i.e. allow the formation engineering of the coupling (i.e. allow the formation of artificial of artificial "molecules") "molecules") and stacking of QDs in an easy and and stacking of QDs in an easy and controllable way controllable way

4 -4 - allow a single or stack of dots to be easily allow a single or stack of dots to be easily addressed and addressed and controlled controlled electricallyelectrically, and not only optically, and not only optically

5 -5 - “identical” dots“identical” dots

6 -6 - High optical qualityHigh optical quality

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SELF ASSEMBLED AND SITE CONTROLLED: SELF ASSEMBLED AND SITE CONTROLLED: TWO DIFFERENT APPROACHESTWO DIFFERENT APPROACHES

Self assembledSelf assembled Site controlledSite controlled

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GaAs (111)B substrate

GaAs

SiO2

Resist deposited and exposed to UV light

SiO2 removal with HF

Resist

removal

Wet etching of tetrahedrical recesses

Ready for growth!

WET LITHOGRAPHYWET LITHOGRAPHY

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Easy patterning and growth processEasy patterning and growth process

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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 DOs AND DONTs OF PYRAMIDAL QUANTUM DOTSDOTS

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InGaAs Dots with GaAsInGaAs Dots with GaAs

1) Cladding Layer Al55%Ga45%As

2) GaAs barriers3) Dot layer In25%Ga75%As – 0.5

nm nominal thickness4) Vertical Quantum Wire

σ = 1.2 meVFWHM = 2.8 meV

L. O. Mereni et al., Appl. Phys. Lett. 94, 223121 (2009)

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CAN WE MAKE ENTANGLED

PHOTONS WITH THESE DOTS?

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THE BIEXCITON-EXCITON CASCADE & FSSTHE BIEXCITON-EXCITON CASCADE & FSS

XXXX

XX

00

σσ++

σσ++

σσ--

σσ--

Electric fields

Structural Asymmetries

Alloy Disorder

HH

VV

VV

HH

FSS

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(111): AN IDEAL PLATFORM FOR THE (111): AN IDEAL PLATFORM FOR THE DEVELOPMENT OF ENTANGLED PHOTONSDEVELOPMENT 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 81A.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

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OPTICAL SETUPOPTICAL SETUP

HALF WAVEPLATE LINEAR

POLARIZER MONOCHROMATOR

CLOSED CYCLE CRYOSTAT

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BUT……BUT……

Mean FFS: 13 μeV σ = 4 μeV

X

XX

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PHASEPHASE

(μeV

)

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FURTHER INVESTIGATIONSFURTHER INVESTIGATIONS

In0.25Ga0.65As Mean FFS: 13 μeVσ = 4 μeV

In0.35Ga0.65As Mean FFS: 20 μeVσ = 10 μeV

AlGaAs barriers

Mean FFS: ?

σ = ?

15%(μeV

)

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Energy tuningEnergy tuning

15 20 25 30 35 40 45 50 55 601.30

1.35

1.40

1.45

1.50

0.5 nm 0.5 nm

Em

iss

ion

En

erg

y

Indium concentration

(eV

)

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DOTS WITH NITROGENDOTS WITH NITROGEN

Small shift of the emission wavelenght

Antibinding biexciton energy Splitting within the experimental error

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Thank you for your Thank you for your attentionattention

SlannSlann