transmission electron microscopy of semiconductor quantum...

Transmission Electron Microscopy of semiconductor

quantum structures

Autumn School on Materials Science and Electron Microscopy 2005 "Microscopy of Tomorrow’s Industrial Materials"

Berlin, October 4th – October 7th , 2005

Holm Kirmse

Humboldt-Universität zu Berlin, Institut für Physik, AG KristallographieNewton-Str. 15, 12489 Berlin, Germany

http://crysta.physik.hu-berlin.deEmail: [email protected]

Outline

1. Motivation

2. Instrumentation and Methods

3. Self-organized InAs QWRs on vicinal In(P,As)

4. Self-organized Ga(Sb,As) / GaAs QDs on seed QDs

5. Summary

Energy gap and lattice parameters of compound semiconductors

Ban

d ga

p(e

V)

Lattice parameter (Å)

Correlation of dimension of structures and density of electronic states

Quantum WellBulk

ρ(E)

E

EC

Quantum Wire Quantum Dot

ρ(E) – density of electronic statesE – energy (EC – energy of conduction band)

Publications on quantum structures

Publications on quantum dots

Publications on semiconductor QDs

Stranski-Krastanov growth

Pseudomorphic layer Island formation Cap layer growth

Formation of semiconductor quantum dots (QDs)

Formation via strain induced self-organization during epitaxial growth

Driving force for self-organization process: minimization of energy

Z-contrast

EFTEMEELS

FEM simulation

CTEMBF + DF

Computer simulation

STRUCTURE DEFORMATION COMPOSITION

HRTEM qHRTEM

HRTEM +simulation

CTEMDF

Analysis of structural and chemical properties of quantum structures by TEM

Outline

1. Motivation




5. Summary

TEM / STEM JEOL JEM-2200FS

Field-emission gun

Electron biprism

Energy dispersive X-ray detector (EDXS)

High angle annular dark-field (HAADF) detector

In-column energy filter

Energy resolution: 0.7 eV

Probe size STEM: < 0.5 nm

Point resolution: 1.9 Å

Accelerating voltage: 200 kV

TEM / STEM HITACHI H-8110

Accelerating voltage: 200 kVPoint resolution: 2.3 ÅEnergy resolution: 2 eV

Gatan imaging filter (GIF)Energy dispersive X-ray detector (EDXS)Scanning TEM BF/DF detectorSecondary electron detector

thin crystallinespecimen

EELS / EFTEM / Z CONTRAST

primary electrons

DIFFRACTION ← diffracted beamCONTRAST IMAGING

backscatteredelectrons

secondaryelectrons

Augerelectrons X-rays → EDXS

Cathodoluminescence

direct beam

elastically and inelastically scattered electrons

→ HRTEMqHRTEM

Interaction between electrons and sample

TEM preparationof QD samples

Planar view Cross sectional view

3 mm

sample thickness: 5..200 nm

Objective aperture

Back focal plane

Sample

Amplitude contrast imaging Back focal plane / diffraction pattern

400

Kikuchi lines

220

040

220Sample

Objective aperture

Image plane

Back focal plane

Bright-field image

400

040

220

220000

Objective aperture

Image plane

Dark-field image

020 040000

002 220

004

Schematic diffraction pattern

Sample

Objective aperture

Image plane

Back focal plane

Phase contrast imaging –HRTEM

Crystal structure – diffraction pattern

[Sphalerite]e.g.: GaAs,

ZnSe

Electron diffraction pattern taken along [001]

[Diamond]e.g.: Si, Ge

220220

040040

400400

220220

200200

020020

040040

400400

F002 = 4·[fIII – fV]composition sensitive

F004 = 4·[fIII + fV]strain sensitive

F - Structure amplitude, f - Atomic scattering factor

Post-column Filter(GATAN Imaging Filter)

Experimental set up for energy-filtered TEM (EFTEM)

In-column Filter(JEOL and ZEISS )

magnetic prism

slit

slit

Ω-Filter

Series of single energy-filtered images (above),procedure of background extrapolation and subtraction (below)

Cr-L23 mapPost-edge imagePre-edge 2 imagePre-edge 1 image

200 nm

γ‘ phase

γ phase

Energy loss in eV Energy loss in eV

Cr-L23 edgeCr-L23 edge

Net signal

Post edge1 2

By courtesy of R. Schneider (MLU Halle)

EFTEM imaging

Z-contrast imaging

HAADF detectorI ~ Z3/2

Electron probe

Sample

Z contrast image

position y

posit

ion x

intensity

y

x

r

Z↑

Outline

1. Motivation




5. Summary


Ban

d ga

p(e

V)


Humboldt-Universität zu Berlin, Institut für Physik, AG Kristallographie, AG Elementaranregungen und Transport in Festkörpern

300 nm In(P,As)

d

QWR

l

Growth parameters:In(P,As) substrate[001], 2° off towards [110]l = 16 nmdIn(P,As) = 5, 10, 20 nmTGrowth = 450 °C

Aims of TEM investigations:Vertical correlation of QWRsGeometry of QWRsElemental distribution As, P

15 x 4 ML InAs

100 nm (In,Al)As

Self-organized InAs quantum wires on vicinal In(P,As) Sample structure

Self-organized InAs quantum wires on vicinal In(P,As) Cross sectional TEM, 002 dark field images

HU#1513_o_cs/2, links: hu#1513_o_2_05_002df_c.jpg, rechts: hu#1513_o_2_08_002df_c.jpg


InP

InAs

View along steps View perpendicular to stepsH. Kirmse et al., EMC 2004, Antwerp, Vol. II: p. 211


Self-organized InAs quantum wires on vicinal In(P,As) Cross sectional TEM, 004 dark field images

HU#1513_o_cs/2, links: hu#1513_o_2_17_004df_c.jpg, rechts: hu#1513_o_2_27_004df_c.jpg

InP

InAs

View along steps View perpendicular to steps

InAs QWRs elongated InAs QWRs

H. Kirmse et al., EMC 2004, Antwerp, Vol. II: p. 211

Self-organized InAs QWRs on vicinal In(P,As) Energy filtered TEM

HU#1513_p_cs/1, links: EFTEM3_c.jpg, rechts: EFTEM6_c.jpg

TU Graz, FELMIHumboldt-Universität zu Berlin

Elemental map: P L2,3 (∆E = 132 eV) Maximum of 1st plasmon peak

Outline

1. Motivation



4. Self-organized Ga(Sb,As) / GaAs QDs onseed QDs

5. Summary


Ban

d ga

p(e

V)


Metal organic chemical-vapor deposition

(L. Müller-Kirsch, D. Bimberg, TU Berlin)

Application: Storage devices

♦ (In,Ga)As seed layer for provision of favorable locations for the formation of Ga(Sb,As) QDs

♦ Thickness of GaAs spacer: 3.5 or 4.5 nm

Aims of TEM characterization:

♦ Size

♦ Defects

♦ Strain state

♦ Vertical correlation

♦ Composition

GaAs

GaAs

(In,Ga)As

Ga(Sb,As)

GaAs

Ga(Sb,As) / GaAs Quantum Dots on (In,Ga)As Seed QDs

TEM diffraction contrast of Ga(Sb,As)/GaAs QDsplan view diffraction contrast imaging

TU#5169pv/a: 7_c.jpg, TU#5170pv/c: 1355_c.jpg, TU#5174pv/a: 1332_c.jpg, TU#5176pv/a: 1313_c.jpg,

Humboldt-Universität zu Berlin, Institut für Physik, AG KristallographieTechnische Universität Berlin, Institut für Festkörperphysik

Growth interruption time: 5 s

3.6 ML

4.0 ML

5.0 ML

5.4 MLdefect

1⋅1010 cm-2

3⋅1010 cm-2

4⋅1010 cm-2

L. Müller-Kirsch et al., Appl. Phys. Lett. 79 (2001) 1027

Diffraction contrast imaging of Ga(Sb,As)/GaAs QDs on (In,Ga)As/GaAs seed layer

Humboldt-Universität zu Berlin, Institut für Physik, AG KristallographieTU Berlin, Institut für Festkörperphysik

links: TU#5294cs/2, 1533_d.jpg, rechts: 1534_d.jpg

F002 = 4·[fIII – fV]composition sensitive

F004 = 4·[fIII + fV]strain sensitive

H. Kirmse. et al., Proc. 15th Int. Conf. Electr. Microsc., Durban 2002

Z-contrast Diffraction contrast

BA

A

B

A

B

BA (In,Ga)AsGa(Sb,As)(In,Ga)As

Ga(Sb,As)

Ga(Sb,As)/GaAs QD on (In,Ga)As seed QD Humboldt-Universität zu Berlin, Institut für Physik, AG Kristallographie

TU Berlin, Institut für Festkörperphysik

TU#5293; links oben: 1505_2_c.jpg, rechts oben: GaAsHAADF5_e.jpg

H. Kirmse et al., Proc. 15th Int. Conf. Electr. Microsc., Durban 2002

Aims of qHRTEM:♦ Visualization of the

strain field of the QDs♦ Quantification of the

local chemical composition

HRTEM of Ga(Sb,As) QD on (In,Ga)As seed QD(cS-corrected Philips CM200, FZ Jülich, IFF)

Humboldt-Universität zu Berlin, Institut für Physik, AG KristallographieForschungszentrum Jülich GmbH, Institut für Festkörperforschung

TU#5294cs/2, qdot5_012c[1] Kopie2.jpg

Chemical compositionLattice parameters / strain

Atomic structure

- Peak Finding Procedure

- Geometrical Phase Methode

- Computer-aided HRTEM image simulations

- Computer-aided HRTEM image simulations

- Peak Finding Procedure

- Composition evaluation by lattice fringe analysis(CELFA)

- Jülich Chemical Mapping Package (JCMP)

By courtesy of I. Häusler (IKZ Berlin)

⎥⎦

⎤⎢⎣

⎡)()(

ruru

y

xr

rDisplacement field

Geometrical Phase MethodPeak Finding Procedure

Perfect periodic crystal:

rgiHrIg

grrr⋅= ∑ π2exp)(

ggg PiAH exp=

)(rurr rrrr−→ )(rPP gg

r→Lattice distortion: &

[ ][ ][ ])()(2)(

)()(2)(

)(2)(

222

111

rugrugrP

rugrugrP

rugrP

yyxxg

yyxxg

g

rrr

rrr

rrrr

+⋅−=

+⋅−=

⋅⋅−=

π

π

π

g1

g2

⎥⎦

⎤⎢⎣

⎡⎥⎦

⎤⎢⎣

⎡−=⎥

⎦

⎤⎢⎣

⎡−

1

11

22

11

21

)()(

g

g

yx

yx

y

x

PP

gggg

ruru

πr

v

M.J. Hÿtch, et.al., Ultramicroscopy 74 (1998) 131

1. Find the maxima of the HRTEM image

2. Find the nearest neighbourand generate the grid

3. Define the reference lattice in a non-distorted region

4. Measure local deviation from lattice positions

A. Rosenauer, et. al., Ultramicroscopy 72 (1998) 121.

e.g.: DALI(Digital Analysis of Lattice Images)

Local lattice parameter in [001] direction as revealed by peak finding algorithm

position in nm

posi

tion

in n

m

Strain state analysis of stacked QD structureGa(Sb,As) on (In,Ga)As seed QD

[001] lattice parameter by geometric phase method

Strain state analysis of stacked QD structure Ga(Sb,As) on (In,Ga)As seed QD

R. Otto et al., Appl. Phys. Lett., 85 (2004) 4908

Line profiles of the [001] lattice parameter across QD system

Strain state analysis of stacked QD structureGa(Sb,As) on (In,Ga)As seed QD

R. Otto et al., Appl. Phys. Lett., 85 (2004) 4908

Outline

1. Motivation




5. Summary

Summary

Z-contrast

EFTEMEELS

FEM simulation

CTEMBF + DF

Computer simulation

STRUCTURE DEFORMATION COMPOSITION

HRTEM qHRTEM

HRTEM +simulation

CTEMDF

AcknowledgementI. Häusler, I. Hähnert, E. Oehlschlegel, W. Neumann

HU Berlin, Institute of Physics, CrystallographyFormer co-workers: R. Otto, R. Schneider

Cooperations:

InAs QWRs:O. Bierwagen, R. Pomraenke, W.T. MasselinkHU Berlin, Institute of Physics, Semiconductor PhysicsB. Schaffer, F. HoferFELMI Graz

Ga(Sb,As) QDs:L. Müller-Kirsch, D. Bimberg(Institute of Solid State Physics, TU Berlin)

Cs corrected TEM:M. Lentzen, K. Urban(Ernst-Ruska-Centre at the Research Centre Jülich)

Financial support:German Research Foundation

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