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 MOLECULESG

row

th D

irecti

on

Gro

wth

Dire

ction

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)G

aAsIn

As

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

ns

ity

(a

rb. u

nit

s)

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 (

eV

)

-6 -4 -2 0 2 41,292

1,290

1,288

1,286

1,284

1,282

1,280

1,278

Voltage (V)

E (

eV)

X0A

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

XX

X

XXX

XXX

X

XXXX

X X

XX

X

XX

X

Voltage (V)

0 2 4 6 8 10

TRP

L In

tens

ity (A

rb. U

nits

)

Time (ns)

X @ 956.3 nmXX @ 957.3 nm

V = 5.7 V

0,1 1 10 100

m = 2.0729 @ 957,3 nm

m = 0.98788 @ 960,9 nm

Int.

In

ten

sity

(ar

b.

Un

its)

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

Inte

nsi

ty (

arb

. un

its)

Photon Energy (eV)1.24 1.25 1.26 1.27 1.28 1.29 1.30 1.31 1.32

PL

Inte

ns

ity

(a

rb. u

nit

s)

Photon Energy (eV)1.24 1.25 1.26 1.27 1.28 1.29 1.30 1.31 1.32

PL

Inte

ns

ity

(a

rb. u

nit

s)

Photon Energy (eV)

m-PL m-PL

QD-A QD-B QD-C

m-PL

1.4 ML

Ensemble

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)

Ph

oto

n E

ne

rgy

(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.