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