optical spectroscopy for nanoparticles-can

7/30/2019 Optical Spectroscopy for Nanoparticles-can

1/19

Optical SpectroscopyOptical Spectroscopyonon

Semiconductor NanostructuresSemiconductor Nanostructures


2/19

OutlineOutline

BackgroundBackground

99 Low dimensional nanostructuresLow dimensional nanostructures

From bulk to quantum dotsFrom bulk to quantum dots

99 Optical spectroscopy techniquesOptical spectroscopy techniques

ResultsResults

99 Optical spectroscopy onOptical spectroscopy on Quantum wiresQuantum wires

Quantum dotsQuantum dots


3/19

Low dimensional nanostructuresLow dimensional nanostructures

EEGG

3D

DOS

3D

DOS

2D

DOS

2D

DOS

1D

DO

S

1D

DO

S

0D

DO

S

0D

DO

S

EEGG

EEGG EEGG

EnergyEnergy EnergyEnergy

EnergyEnergyEnergyEnergy

EE11 EE22 EE33

EE1111 EE1212 EE1313 EE111111 EE112112 EE113113

(a)(a) (b)(b)

(c)(c) (d)(d)

tz

tz

ty

tz

tytx

EEGG

3D

DOS

3D

DOS

2D

DOS

2D

DOS

1D

DO

S

1D

DO

S

0D

DO

S

0D

DO

S

EEGG

EEGG EEGG

EnergyEnergy EnergyEnergy

EnergyEnergyEnergyEnergy

EE11 EE22 EE33

EE1111 EE1212 EE1313 EE111111 EE112112 EE113113

(a)(a) (b)(b)

(c)(c)

(d)(d)

tz

tz

ty

tz

ty

tz

tytx


4/19

Example: QWRExample: QWR

Return to selfReturn to self--

limited profilelimited profile

GaGa--rich VQWrich VQW

AlGaAs barrierAlGaAs barrier

GaAs QWRGaAs QWR

20 nm20 nm

(a)(a) (b)(b)

zz

xx

TT((xx))

cbcb

vbvb

Electron 1DElectron 1D

subbandssubbands

Hole 1DHole 1D

subbandssubbands

HighHigh

bandgapbandgap

LowLow

bandgapbandgap





GaAs QWRGaAs QWR

20 nm20 nm





GaAs QWRGaAs QWR

20 nm20 nm





GaAs QWRGaAs QWR

20 nm20 nm

(a)(a) (b)(b)

zz

xx

TT((xx))

cbcb

vbvb


subbandssubbands

Hole 1DHole 1D

subbandssubbands

HighHigh

bandgapbandgap

LowLow

bandgapbandgap

zz

xx

TT((xx))

cbcb

vbvb


subbandssubbands

Hole 1DHole 1D

subbandssubbands

HighHigh

bandgapbandgap

LowLow

bandgapbandgap


5/19

Example: QDsExample: QDs

S-K Growth Pyramidal QDs

22 mm22 mm

QD


6/19

Optical spectroscopy techniquesOptical spectroscopy techniques

Barrier continuumBarrier continuum

CBCB

VBVB

Non

radiative

Non

radiative

hh outouthh inin

SampleSample

Exciting lightExciting light

(a)(a) (b)(b)

MicroscopeMicroscope

objectiveobjective

(c)(c)

SNOMSNOM

tiptip(d)(d)

ElectronElectron

beambeam

SampleSample

Exciting lightExciting light

(a)(a) (b)(b)

MicroscopeMicroscope

objectiveobjective

(c)(c)

SNOMSNOM

tiptip(d)(d)

ElectronElectron

beambeam

10-100m ~1m

~100nm


7/19

PL / PLEPL / PLE

energy

PL

JDOS

det

de

t

PLE

PL: Spectroscopy of occupied levels

PLE: Spectroscopy of unocuppied levels ( ~ absorption)


8/19

Photoluminescence setupPhotoluminescence setup

DetDetSingleSingle

spectrometerspectrometer

CCD

CCD

samplesample

HeHe--flow cryostatflow cryostat

MicroscopeMicroscopeobjectiveobjective

LaserLaser TemperatureTemperaturecontrollercontroller

CutCut--offoff

filterfilter

Spatial filterSpatial filterJY HR 460JY HR 460

DetDetSingleSingle

spectrometerspectrometer

CCD

CCD

samplesample

HeHe--flow cryostatflow cryostat

MicroscopeMicroscopeobjectiveobjective

LaserLaser TemperatureTemperaturecontrollercontroller

CutCut--offoff

filterfilter

Spatial filterSpatial filterJY HR 460JY HR 460


9/19

Optical spectroscopy onOptical spectroscopy onQWRsQWRs


10/19

Photoluminescence on QWRsPhotoluminescence on QWRs

Polarisation anisotropy in

absorption spectrumSignature of 1D confinement

Black arrows:

6-band kp theoretical model


11/19

Carrier localisation in QWRsCarrier localisation in QWRs

X localisation on a ~m length scale:Chain of QDs

Monolayer fluctuation of confinementpotential along QWR axis

REALITY

DREAM

Fully delocalised 1D states


12/19

Optical spectroscopy on QDsOptical spectroscopy on QDs


13/19

Single QD spectroscopySingle QD spectroscopy

Inhomogeneous broadening in QD ensembles

cb

energy

30-80 meV

10-50meV

1-5meV

Electronic fine structure onlyvisible if single QDs are probed!

lu

minescence

vb

SK QD P id l QD


14/19

SK QDs vs. Pyramidal QDsSK QDs vs. Pyramidal QDs

QD

Typical micro-photoluminescence experiment

~1m laser spot

1 m

energy energy

Al shadow mask

QT d i l QD


15/19

Towards single QD spectroscopyTowards single QD spectroscopy

1.20 1.25 1.30 1.35 1.40

PL energy (eV)

P

Lintensity

(arb.units

)

= 130 eV1 QD

WLEnsemble

3 10 QDs5

Exci tation power 0.1 mWT=4.2 K

QD l iQD l t i t t


16/19

QD electronic structureQD electronic structure

Artificial atomElectronic propertiescan be tailored

Quantum dot2D Harmonic oscillator model

energy

emission

XX 2XX2

Xchange

A few meV

Ch d i SCh d t t i S K QDK QD


17/19

Charged states in SCharged states in S--K QDsK QDs

Energy (meV)

Ch d t t i id l QDCh d t t i id l QD


18/19

Charged states in pyramidal QDsCharged states in pyramidal QDs

1.56 1.565 1.57 1.575 1.58 1.585photon energy [eV]

PL

intensity

[a.u.]

X 10

30 pW

600 nW

2.5 nW

1.56 1.565 1.57 1.575 1.58 1.585

Energy (eV)

PL

inten

sity

X

X

X2X2

2X

SS


19/19

SummarySummary

99 Optical spectroscopy techniquesOptical spectroscopy techniques

99 Optical properties of QWRsOptical properties of QWRs

Polarisation anisotropyPolarisation anisotropy

Exciton localisationExciton localisation

99 Optical properties of QDsOptical properties of QDs

MultiMulti--charged excitonscharged excitons

QDs as artificial atomsQDs as artificial atoms

optical spectroscopy for nanoparticles-can

Documents