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MICRO-PHOTOLUMINISCENCE FROM InAs/GaAS QUANTUM DOT MOLECULES GROWN BY DROPLET
EPITAXY
G. Muñoz-Matutano1, J. Canet-Ferrer1, D. Fuster1, J. Martínez-Pastor1
P. Alonso-González2, B. Alén2, I. Fernández-Martínez2, Y. González2, F. Briones2, L. González2
1UMDO (unidad asociada al IMM-CSIC), Instituto de Ciencias de los
Materiales, Universitat de València.2IMM-CNM-CSIC: Instituto de Microelectrónica de Madrid.
MICRO-PHOTOLUMINISCENCE FROM InAs/GaAs QUANTUM DOT MOLECULES GROWN BY DROPLET EPITAXY
OUTLOOK:1. Introduction: Quantum Dot Molecule.
2. Droplet Epitaxy Growth: optical features.
3. Sample and Experimental Set-Up.
4. Lateral QD molecule results.
i) Voltage Features.
ii) Molecular Coupling.
5. Vertical QD molecule preliminar results.
6. Conclusions.
1. INTRODUCTION: QD MOLECULESGr
owth
Dire
ction
Grow
th D
irecti
on
VERTICAL MOLECULES LATERAL MOLECULESe-
h+
1. Electron states coupling (e- Tunneling )
2. Hole states coupling (h+ Tunneling )
3. Excitonic state couplin ( Föster copling (virtual photon))
1. INTRODUCCIÓN: DEL QD AISLADO AL CRISTAL DE QDs
E.A. Stinaff et al, Science 311, 636 (2006)
H.J. Krenner et al, PRL 94, 57402 (2005)C.J. Beirne et al, PRL 96, 137401 (2006)
VERTICAL MOLECULES
LATERAL MOLECULES
TUNNING QD STATES WITH ELECTRIC FIELD
2. DROPLET EPITAXY GROWTH:
ADVANTAGES :
• Localized nanostructures.
• Low density samples.
• Growth by QD pairs.
P. Alonso-González et al, Crystal Growth and Design 9, 2525 (2009)
L.Wang et al, New Journal of Physics 10, 045010 (2008)
• Density ≈ 2.5 x 108 cm-2
• Negative excitonic complex.
• Arsenic Vacancies.
P. Alonso-González et al, APL 91, 163104 (2007)
HIGH OPTICAL QUALITY
2. DROPLET EPITAXY GROWTH:
3. SAMPLE AND EXP. SET UP: Lateral Molecules.
110
1-10
• InAs Droplets Pairs.
• Schottky Diode.
• Field on 110
1 - 1,5 µm
Au-Cr
ΔV
E (110)Ga
AsInAs
3. SAMPLE AND EXP. SET-UP: Vertical Molecules.
P. Alonso-González et al, APL 93, 183106 (2008)
• First layer:
QDs grown by Droplet Epitaxy
• Second layer:
4 nm of GaAs
• Tercera capa:
Self assembled QDs localized on first
layer QDs.
1.20 1.24 1.28 1.32
Photon energy (eV)
PL
Inte
nsity
(arb
. uni
ts)
1.2 ML
1.4 ML
1.6 ML
3. SAMPLE AND EXP: SET-UP: Vertical Molecules.
3. SAMPLE AND EXP. SET-UP: Confocal Microscope.
Laser
μPL Signal
LATERAL MOLECULERESULTS
4. RESULTS: Lateral Molecules
QDs DROPLET PAIRS: Voltage Features.
Journal of Physics: Conference Serires 210, 012015 (2010)
-6 -5 -4 -3 -2 -1 01.3350
1.3325
1.3300
1.3275
1.3250
Voltage (V)
E (e
V)
-6 -4 -2 0 2 41,292
1,290
1,288
1,286
1,284
1,282
1,280
1,278
Voltage (V)
E (e
V)X0
A
X-1A
X-2T, A
X0B
X-1B
X-2T, B
Type I: Isolated Type II: Decoupled pair
4. RESULTS: Lateral Molecules
QDs DROPLET PAIRS: Voltage Features.
Journal of Physics: Conference Serires 210, 012015 (2010)
Type III: Coupled pair
4. RESULTS: Lateral Molecules
QDs DROPLET PAIRS: Coupling (optical signatures)
-3 -2 -1 0 1 2 3 4 5 6
954
956
958
960
962
964
966
968
Wav
elen
ght (
nm)
X
XX
X
X
XXX
XXX
XXX
X
XXXX
X XXX
X
XX
X
Voltage (V)
0 2 4 6 8 10
TRPL
Inte
nsity
(Arb
. Uni
ts)
Time (ns)
X @ 956.3 nmXX @ 957.3 nm
V = 5.7 V
0,1 1 10 100
m = 2.0729 @ 957,3 nmm = 0.98788 @ 960,9 nm
Int.
Inte
nsity
(arb
. Uni
ts)
Power (W)
V = 5,7 v
4. RESULTS: Lateral Molecules
QDs DROPLET PAIRS: CouplingPositive Sweep
4,0 4,5 5,0 5,5 6,0
1,292
1,291
1,290
1,289
X
X
E (e
.V.)
Voltage (V)
• Identified some examples of anticrossing
μPL evolution.
ZOOM 1 ZOOM 2
VERTICAL MOLECULE RESULTS
4. RESULTS: Vertical Molecules Preliminary Results
1.20 1.24 1.28 1.32
Photon Energy (eV)
1.23 1.24 1.25 1.26 1.27 1.28 1.29
PL In
tens
ity (a
rb. u
nits
)
Photon Energy (eV)1.24 1.25 1.26 1.27 1.28 1.29 1.30 1.31 1.32
PL In
tens
ity (a
rb. u
nits
)
Photon Energy (eV)1.24 1.25 1.26 1.27 1.28 1.29 1.30 1.31 1.32
PL In
tens
ity (a
rb. u
nits
)Photon Energy (eV)
-PL -PL
QD-A QD-B QD-C
-PL
1.4 MLEnsemble
QD Droplet (QD1) + SAQD (QD2)
4. RESULTS: Vertical Molecules Preliminary results
0.6 0.3 0.0 -0.3 -0.61.280
1.285
1.290
1.295
1.300
Gate Voltage (V)
Phot
on E
nerg
y (e
V)
E.A. Stinaff et al, Science 311, 636 (2006)
Anomalous stark shifts (Blue y Red Shifts)
MICRO-PHOTOLUMINISCENCE FROM InAs/GaAs QUANTUM DOT MOLECULES GROWN BY DROPLET EPITAXY
Conclusions:
1. Lateral Molecules:
• Different Voltage features.
• Optical anticrossings as signatures of molecular coupling.
2. Vertical Molecules:
• Optical evidences from two different QDs.
• Anomalous QCSE shifts.