MICRO-PHOTOLUMINISCENCE FROM InAs/GaAs QUANTUM DOT MOLECULES
GROWN BY DROPLET EPITAXY
Growth Direction
VERTICAL MOLECULES
QD MOLECULES
eh+
LATERAL MOLECULES
Growth Direction
1. INTRODUCTION:
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
TUNNING QD STATES WITH ELECTRIC FIELD
LATERAL MOLECULES
VERTICAL
MOLECULES
C.J. Beirne et al, PRL 96, 137401 (2006)
H.J. Krenner et al, PRL 94, 57402 (2005)
E.A. Stinaff et al, Science 311, 636 (2006)
2. DROPLET EPITAXY GROWTH:
ADVANTAGES :
• Localized nanostructures.
• Low density samples.
• Growth by QD pairs.
L.Wang et al, New Journal of Physics 10, 045010 (2008)
P. Alonso-González et al, Crystal Growth and Design 9, 2525 (2009)
2. DROPLET EPITAXY GROWTH:
HIGH OPTICAL QUALITY
• Density ≈ 2.5 x 108 cm-2
• Negative excitonic complex.
• Arsenic Vacancies.
P. Alonso-González et al, APL 91, 163104 (2007)
3. SAMPLE AND EXP. SET UP: Lateral Molecules.
E (110)
• InAs Droplets Pairs.
Au-Cr
GaAs
InAs
• Schottky Diode.
• Field on 110
ΔV
110
1 - 1,5 µm
1-10
3. SAMPLE AND EXP. SET-UP: Vertical Molecules.
PL Intensity (arb. units)
1.2 ML
1.4 ML
1.6 ML
1.20
1.24
• First layer:
1.28
1.32
Photon energy (eV)
QDs grown by Droplet Epitaxy
• Second layer:
4 nm of GaAs
• Tercera capa:
Self assembled QDs localized on first
layer QDs.
P. Alonso-González et al, APL 93, 183106 (2008)
3. SAMPLE AND EXP: SET-UP: Vertical Molecules.
3. SAMPLE AND EXP. SET-UP: Confocal Microscope.
μPL Signal
Laser
LATERAL
MOLECULE
RESULTS
4. RESULTS: Lateral Molecules
QDs DROPLET PAIRS: Voltage Features.
Type I: Isolated
Type II: Decoupled pair
1.3250
1,278
1,280
1.3275
-2
XT, A
E (eV)
E (eV)
1,282
1.3300
1,284
1,290
1.3350
-5
-4
-3
-2
Voltage (V)
-1
0
1,292
-6
-2
XT, B
-1
XB
1,286
1,288
1.3325
-6
-1
XA
0
XB
0
XA
-4
-2
0
Voltage (V)
Journal of Physics: Conference Serires 210, 012015 (2010)
2
4
4. RESULTS: Lateral Molecules
QDs DROPLET PAIRS: Voltage Features.
Type III: Coupled pair
Journal of Physics: Conference Serires 210, 012015 (2010)
4. RESULTS: Lateral Molecules
QDs DROPLET PAIRS: Coupling (optical signatures)
968
TRPL Intensity (Arb. Units)
966
X
XX
XX
962
X
960
958
XX
X
X
X
0
X
XX
X
XX
X
X
XX
954
-2
-1
0
4
1
2
3
Voltage (V)
4
6
8
10
Time (ns)
X
-3
2
XX
XX
X
956
V = 5.7 V
5
6
m = 0.98788 @ 960,9 nm
Int. Intensity (arb. Units)
Wavelenght (nm)
964
X @ 956.3 nm
XX @ 957.3 nm
m = 2.0729 @ 957,3 nm
V = 5,7 v
0,1
1
10
Power (W)
100
4. RESULTS: Lateral Molecules
QDs DROPLET PAIRS: Coupling
Positive Sweep
ZOOM 1
ZOOM 2
E (e.V.)
1,289
X
1,290
X
1,291
1,292
4,0
4,5
5,0
Voltage (V)
5,5
6,0
• Identified some
examples of anticrossing
μPL evolution.
VERTICAL
MOLECULE
RESULTS
4. RESULTS: Vertical Molecules
Preliminary Results
1.4 ML
Ensemble
1.20
1.24
1.28
1.32
Photon Energy (eV)
QD-A
1.23
1.24
1.25
1.26
1.27
Photon Energy (eV)
1.28
1.29
-PL
QD-B
PL Intensity (arb. units)
-PL
PL Intensity (arb. units)
PL Intensity (arb. units)
QD Droplet (QD1) + SAQD (QD2)
-PL
QD-C
1.24 1.25 1.26 1.27 1.28 1.29 1.30 1.31 1.32
1.24 1.25 1.26 1.27 1.28 1.29 1.30 1.31 1.32
Photon Energy (eV)
Photon Energy (eV)
4. RESULTS: Vertical Molecules
Preliminary results
Photon Energy (eV)
1.300
1.295
1.290
1.285
1.280
0.6
0.3
0.0
-0.3
-0.6
E.A. Stinaff et al, Science 311, 636 (2006)
Gate Voltage (V)
Anomalous stark shifts (Blue y Red Shifts)
MICRO-PHOTOLUMINISCENCE FROM InAs/GaAs QUANTUM DOT MOLECULES
GROWN BY DROPLET EPITAXY