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Transmission Electron Microscopy of semiconductor quantum...
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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]
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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
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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
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Energy gap and lattice parameters of compound semiconductors
Ban
d ga
p(e
V)
Lattice parameter (Å)
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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)
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Publications on quantum structures
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Publications on quantum dots
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Publications on semiconductor QDs
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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
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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
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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
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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
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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
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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
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TEM preparationof QD samples
Planar view Cross sectional view
3 mm
sample thickness: 5..200 nm
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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
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020 040000
002 220
004
Schematic diffraction pattern
Sample
Objective aperture
Image plane
Back focal plane
Phase contrast imaging –HRTEM
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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
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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
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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
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Z-contrast imaging
HAADF detectorI ~ Z3/2
Electron probe
Sample
Z contrast image
position y
posit
ion x
intensity
y
x
r
Z↑
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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
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Energy gap and lattice parameters of compound semiconductors
Ban
d ga
p(e
V)
Lattice parameter (Å)
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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
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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
Humboldt-Universität zu Berlin, Institut für Physik, AG Kristallographie, AG Elementaranregungen und Transport in Festkörpern
InP
InAs
View along steps View perpendicular to stepsH. Kirmse et al., EMC 2004, Antwerp, Vol. II: p. 211
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Humboldt-Universität zu Berlin, Institut für Physik, AG Kristallographie, AG Elementaranregungen und Transport in Festkörpern
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
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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
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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 onseed QDs
5. Summary
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Energy gap and lattice parameters of compound semiconductors
Ban
d ga
p(e
V)
Lattice parameter (Å)
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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
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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
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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
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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
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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
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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)
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⎥⎦
⎤⎢⎣
⎡)()(
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)
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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
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[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
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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
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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
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Summary
Z-contrast
EFTEMEELS
FEM simulation
CTEMBF + DF
Computer simulation
STRUCTURE DEFORMATION COMPOSITION
HRTEM qHRTEM
HRTEM +simulation
CTEMDF
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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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Thank you for your attention!