Andreas Klein Surface Science (D3)
Karsten Albe Materials Modelling (C2)
Do TCOs contribute to electrical
fatigue of organic LEDs
5.5
5.0
4.5
wo
rk f
un
cti
on
[eV
]
4.0 3.8 3.6 3.4 3.2 3.0
ECB
SnO
2:F
EF-EVB [eV]
SnO2
SnO2:Sb
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 2
What is a TCO
VB
CB
energ
y
Eg >~3eV
EF
k
Optical transparent material by large band gap
Highly conducting material by degenerate doping
Doped ZnO, SnO2, In2O3
undoped high doping higher doping
n~ 1021 cm-3
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 3
In2O3:Sn (ITO)
Highest conductivity and transparency of TCO materials
Good structurability by chemical etching
Surface properties modified by oxidation treatments (increase of work
function)
Bixbyite crystal structure with 80 atom unit cell and plenty interstitial
positions
Typically 10 mole% SnO2 doping
Sn dopants mainly compensated by interstitial oxygen
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 4
Self-compensation
Compensating defects (Oi in ITO) are formed spontaneously only
when the Fermi energy is deep in the conduction band
• The formation of defects requires a certain amount of energy DHdef
Example: Donor type defect (VO)
EVB
ECB
ED
eDD
EF ED
EF
occupied unoccupied
D0 D+
d
E
• The charge state of the defect depends on the Fermi level position
DH
def
EF
donor ED
EF
acceptor
EA
J Am Ceram Soc 96 (2013) 331
CB VB only n-type
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 5
Oxygen vacancies
Indium oxide and tin oxide are truly intrinsically n-type semiconductors
The behavior is more complex for ZnO
Phys Rev Lett 103 (2009) 245501
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 6
Compensating acceptors
Charged oxygen interstitials are very unfavorable in SnO2
Oxygen transport only via oxygen vacancies in SnO2
Stability of acceptor defects increases with increasing Fermi energy
J Appl Phys 108 (2010) 053511
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 7
The TCO electrode in OLEDs
grain orientation determined by
surface energy & deposition
Workfunction determined by
surface orientation and
termination
Hole injection determined
by workfunction
Oxygen exchange
determined by surface
properties
Defect concentration (e.g. Oi) and mobility
determined by material properties and doping
cathode
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 8
Possible contributions to fatigue
Change of injection barrier during operation
Change of work function
surface termination
Fermi level position (oxygen concentration)
Interfacial reaction
Release of oxygen
Chemical decomposition of organic
Change of TCO conductivity
Oxygen exchange surface vs. diffusion limitation
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 9
Performed work
Experimental
Systematic determination of TCO work functions
Interfaces between ITO and organic semiconductors
Conductivity relaxation experiments (oxygen exchange)
Building test OLEDs and study fatigue behaviour ( D4)
Theoretical
Thermodynamics of point defects in ZnO, In2O3 and SnO2
Anion and cation diffusion in ZnO and In2O3
Thermodynamics of surface structures of In2O3 and SnO2
Defect at (101) twin boundary in SnO2
Adsorption behaviour of organic compounds
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 10
DAISY-MAT (XPS/UPS + preparation)
electron analyser
UV-source Ion-source
monochromated X-ray source
sample handler
load lock
magnetron sputtering
MBE organics, metals
MOCVD ALD
Preparation
Analysis
magnetron sputtering
evaporation
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 11
TCO work functions
5.5
5.0
4.5
4.0 3.8 3.6 3.4 3.2 3.0
SnO
2:F
EF-EVB [eV]
SnO2:Sb
SnO2
3.6 3.2 2.8 2.4 2.0
EF-EVB [eV]
5.5
5.0
4.5
4.0
ITO
5.0
4.5
4.0
3.5
3.6 3.2 2.8 2.4
work
function [
eV]
EF-EVB [eV]
ZnO
ZnO:Al
Thin Solid Films 518 (2009) 1197
Large variation of work function due to changes in
Fermi level position, surface orientation and termination
ZnO SnO2 In2O3
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 12
Types of surfaces
In2O3 (110) In2O3 (111) In2O3(100)
non-polar polar - stable polar - unstable
stoichiometric stoichiometric non-stoichiometric
stable composition stable composition variable composition
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 13
In2O3 surfaces
oxygen chemical potential [eV]
Surf
ace e
nerg
y [
eV/Å
2]
(110) stoichiometric
(111) stoichiometric
stoichiometric
(100)
UPS of epitaxial In2O3 films
Calculated ionization potentials
100-perox 100-met 100-st 111
7.7 eV 6.8 eV 8.6 eV 7.1 eV
J Phys CM 23 (2011) 334203
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 14
ITO/Al2O3 interface
strong increase in work function initial dipole formation
binding energy [eV]
18 14
SEC
12 8 4 0
VB
65Å
41Å
25Å
14Å
8.5Å
4.7Å
1.4Å
0.7Å
2 0
EF
6.4eV
4.5eV
5.9eV
thickness [Å]
9
8
7
6
5
IP
f
4
3
2
60 50 40 30 20 10 0
In 3d
Sn 3d
Al 2p
EF-E
VB [
eV
]
f /
IP [
eV
]
Change to anion-terminated surface ?
Phys Chem Chem Phys 11 (2009) 3049
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 15
ITO/organic interface
O O O O
O O O O O
O
ITO ITO + O2
EVB
ECB
EF
HOMO
ZnPC
energ
y
292 288 284
0.4Å
536 532 528
binding energy [eV]
-1 1
O1s C1s UPS
0.8Å
0Å
536 532 528 1 -1 292 288 284
C-O
binding energy [eV]
O1s C1s UPS
FB
J Phys Chem B 110 (2006) 4793
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 16
O-intersticialcy diffusion in ZnO
Phys Rev B 73 (2005) 115207
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 17
Oxygen diffusion in ZnO
Interstitialcy mechanism, neutral and positive charge states
Dependence of diffusivity on Fermi level and chemical potential
Phys Rev B 73 (2005) 115207
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 18
Zn diffusion in ZnO
Hierarchy of mobilities:
zinc interstitials
oxygen interstitials
zinc vacancies
oxygen vacancies
Appl Phys Lett 88 (2006) 201918
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 19
EB(A) =0.99 eV
EB(B) =1.28 eV
EB(G) =3.82 eV
VO••
Combined DFT+KMC Ansatz
Diffusion in In2O3
Phys Rev B 81 (2010) 195205
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 20
EM(V
O) = 1.01 eV
EM(O
i) = 1.40 eV
G. P. Wirtz and H. P. Takiar, J. Am. Ceram. Soc. 64, 748 (1981).
Diffusion in In2O3
Phys Rev B 81 (2010) 195205
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 21
Conductivity relaxation
glass
TCO
contacts
van der Pauw
conductivity measurement
gas flow gas flow
pO2
time
pO
2
conductivity s
O2,g
O2,ad
+𝑒 O2,ad
− +𝑒 O2,ad
2− 2Oad
− +2𝑒+2VO 2Os
2−
2O2−
Surface oxygen exchange reaction
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 22
Conductivity relaxation of ITO (1 bar)
6 ppm 16 ppm
1010 ppm
0.97 %
9.94 %
97.6 %
Conductivity depends on oxygen pressure
Slope related to dominant defect species
Log (pO2)
Log (
co
nductivity)
-1/8
T=590°C
d=400nm
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 23
Hall effect and conductivity relaxation
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 24
Hall effect measurement of ITO
Changes much slower than expected from oxygen diffusion
Changes not monotonic
Cation diffusion is also involved
Agrees with pO2 dependent Sn segregation from XPS
Solid State Ionics 262 (2014) 636
PRB 73 (2006) 245312
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 25
Enhancement of exchange by In2O3
Exchange at SnO2 possible with 1nm In2O3 on surface
1440 1200 960 720 480 240 0
time [min]
400
300
200
100
0
tem
peratu
re [
°C
]
0.01
0.1
1
10
con
du
cti
vit
y [
S/
cm
]
960 720 480 240 0
time [min]
s
T
0.6 Pa O 2 0.6 Pa O 2
SnO2 SnO2/In2O3
ITO conductivity during OLED operation
1st step: new contacting
method in order to assure
reproducibility
2nd step: remeasure, also
with ITOs with different
oxygen content:
ITO Conductivity
[S/cm]
concentration
[1/cm³]
Mobility µ
[cm²/Vs]
Commercial ITO 7400 1E+21 40
Commercial ITO
after lithography
5800 1E+21 35
most reduced
ITO 100% Ar
7700 1E+21 41
ITO 1% O2 1900 3E+20 36
ITO 10% O2 70 3E+19 17
30.09.2013 | Mareike Hohmann | SFB Meeting Bad Orb | 26
?
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 27
Summary
Carrier concentration in TCOs determined by doping and
intrinsic defects (self-compensation)
Work function determined by doping, surface orientation
and surface termination
Inhomogeneous work function (charge injection)
Oxygen exchange at ITO limited by bulk diffusion and not
by surface exchange coefficient in contrast to SnO2
Oxygen exchange in principle also at T < 200°C
No dominant influence of ITO electrode on OLED fatigue
identified
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 28
Contributors
Ph.D. students
Paul Erhart, Péter Ágoston, Arno Fey, Yvonne Gassenbauer,
André Wachau, Mareike Frischbier (Hohmann)
Bachelor, Master, Diploma students
Péter Ágoston, Arno Fey, Thorsten Bayer, Kai Kühne, André
Wachau, Mareike Hohmann, Karsten Rachut, Hans Wardenga,
Robert Schafranek, Mirko Weidner, Timo Noll, Jonas
Deuermeier
International cooperations
T.O. Mason (Northwestern University), R.G. Egdell (Oxford),
Y. Shigesato (Yokohama), R. Nieminen, K. Nordlund (Helsinki)
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 29
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 30
Publication Highlights
7 joint publications with 432 citations
34 publication of project D3 with 1253 citations
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 31
Relaxation setup
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 32
Discussing the carrier concentration
Gassenbauer, Y., et al. (2006).
Physical Review B 73: 245312. 30.09.2013 | Mareike Hohmann | SFB Meeting Bad Orb | 32
Effects affecting carrier concentration n:
1. oxygen incorporation n ↓
2. Sn segregation n ↓
3. T↑ µo ↓ n ↑
0
0 ln+=p
pRTµµ
O
O
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 33
Discussing the carrier concentration
30.09.2013 | Mareike Hohmann | SFB Meeting Bad Orb | 33
Effects affecting carrier concentration n:
1. oxygen incorporation n ↓
2. Sn segregation n ↓
3. T↑ µo ↓ n ↑
0
0 ln+=p
pRTµµ
O
O
seg
i
SnO
eSnO
SnO
In
In
2+2
1
2+2+2
1
2+
2
'•
2
•"
First ideas on
complex interplay
of several effects
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 34
In2O3 – work function
Almost no change of surface termination with oxygen
Work function depends on surface orientation
Differences between In2O3 and ITO explained by
texture of films
Surface oxidation (e.g. via ozone) only possible for
(100) orientation
(100)
(111)
DFT
J. Phys. CM 23 (2011) 334203
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 35
Doping limit of ITO (In2O3:Sn)
Self-compensation provides a natural explanation for the
transition from electronic to ionic compensation of SnIn
1 eV
In O2 3
EF
DHd (Oi)
EF (max)
ECB
EVB log [Sn]
log c
Mostly electronic compens.
Mostly ionic
compens.
n
[Sn]
[Oi] O-p
oor
O-r
ich
J Am Ceram Soc 96 (2013) 331
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 36
Fermi level of TCO films
J. Am. Ceram. Soc. 96 (2013) 331
energ
y
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 37
Work function and ionisation potential
doping
wo
rk f
un
cti
on
EF-EVB [eV]
Evac-E
F [
eV
] Evac
ECB
EVB
EF
IP
IP= constant
Work function affected by Fermi level and ionisation
potential
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 38
Band gap of In2O3 and ITO
In2O3
Eg,opt Eg
0.8 eV
Forbidden
transitions
DEF (XPS) ~ DEF (optic)
Fundamental gap Eg ~ 2.8 eV
3.4
3.2
3.0
2.8
4.4 4.2 4.0 3.8
0% Sn
2% Sn
10% Sn
Eg,opt –
1.04 eV
EF-E
VB [
eV]
Eg,opt [eV]
XPS vs. Optik Theorie ITO = In2O3:Sn
PRL 100 (2008) 167402
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 39
organic
TCO (ITO)
structurestoichiometry
surfacedefects
exchangekinetics
concentration, type and charge of point defects
mobility of defects
dopant distribution
and mobility
orientationtermination
charge injectionwork function
grain orientation
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 40
Conductivity and carrier concentration
CBE
dEEfEDn )()(
Non-degenerate semiconductors
ECB-EF > 3 kBT
kT
EENn FCB
C exp
Electron concentration
Electrical conductivity determined by carrier concentration
Carrier concentration determined by Fermi level position
n [
cm
-3]
EF-ECB [eV]
1020
0.8 0.4 0.0 -0.4
D(E)
E
VB
CB
log n
log p EF
1018
1016
1014
1012
Conductivity he epen s
RT
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 41
Optical properties
data: K. Orgassa, IPE Stuttgart
transm
issio
n [
%]
wave length [nm]
400 600 800 1000 1200 1400 1600 1800 2000 0
20
40
60
80
100
I II
I: Burstein-Moss shift
II: Free-carrier induced infrared absorption
increase of carrier
concentration
Plasmon energy (Drude theory): eVm
en5.0~
0
22
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 42
TCO applications
Energy band alignment at interfaces important for function
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 43
Topics
Transparent conducting oxides
Basic electrical and optical properties
Applications and importance of surfaces and interfaces
Experimental Approach
Surface Properties
Work function and ionization potential
Oxygen exchange
Interface properties
Energy band alignment
Redox processes at interface
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 44
Photoemission (XPS, UPS) – Basics
Electron analyser
Light source:
•X-ray (Mg, Al)
•Gas discharge (He)
•Synchrotron
Vacuum chamber UHV (p=10-10 mbar)
e-
sample
Electron detector
schematics
Count
rate
590 585 580 575 570
Te 3d5/2 Te 3d3/2
CdTe
TeO2
Binding energy [eV]
CdTe
TeO2
Chemical shift
Chemical analysis Elemental analysis
Count
rate
Binding energy [eV]
1200 800 400 0
Cd Te
O
C
Mean f
ree p
ath
[Å]
5 10 100 1000 2
kinetic energy of electrons [eV]
Surface sensitivity
100
50
10
5
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 45
Surface vs. Bulk Fermi level
Fermi level in bulk corresponds with Fermi level at surface
J. Am. Ceram. Soc. 96 (2013) 331
EF
EVB
ECB
EF
EVB
ECB
or ?
In2O3(:Sn)
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 46
Photoemission – Semiconductors
Evac
f
ECB
EVB
EF hn – workfunction
counts
binding energy [eV] 0=EF
EF-EVB
valence band
core level secondary electrons
DEB
DEB
Df
EF-EVB
f
DEB
l
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 47
In-situ vs. ex-situ
Spectral shape and
binding energies (Fermi
level position in band
gap) are affected by
contact with air
J. Am. Ceram. Soc. 96 (2013) 331
EF
EVB
ECB
in situ ex situ
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 48
Topics
Transparent conducting oxides
Basic electrical and optical properties
Applications and importance of surfaces and interfaces
Experimental Approach
Surface Properties
Work function and ionization potential
Oxygen exchange
Interface properties
Energy band alignment
Redox processes at interface
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 49
Preferred orientation
J. Phys. D 43 (2010) 055301
• Change of stable surface
orientation with oxygen
pressure
norm
iert
e I
nte
nsitä
t [w
illk.
Ein
h.]
908070605040302010
2
11
0
10
1
11
1
21
1
11
2
22
2
22
00
02
32
1
100% Ar
1% O2
2% O2
5% O2
10% O2
25% O2
(110)
(101) xO
2 [
%]
XRD
norm
alized inte
nsity
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 50
ZnO – work function
Change of ionisation potential due
to different surface orientation
Single crystal ZnO
(wurtzite)
IP = 7.0eV (0001)
IP = 7.8eV (000-1)
IP = 7.8eV (10-10)
5.0
4.5
4.0
3.5
3.6 3.2 2.8 2.4
work
function [
eV]
EF-EVB [eV]
ECB
ZnO
ZnO:Al
(1
10
)
(100)
-q
-q
+q
+q
cation anion
GaAs
TSF 518 (2009) 1197
Ranke (1983)
Swank (1967)
Jacobi (1984)
Materials 3 (2010) 4892
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 51
SnO2 – work function
5.5
5.0
4.5
wo
rk f
un
cti
on
[eV
]
4.0 3.8 3.6 3.4 3.2 3.0
ECB
SnO
2:F
EF-EVB [eV]
SnO2
SnO2:Sb
pO2
Change of ionization potential with surface termination
Change of surface termination with oxidation/reduction
Evac
ECB
EVB
EF
IP
TSF 518 (2009) 1197 Materials 3 (2010) 4892
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 52
Post deposition treatment
After O2 annealing
SnO2 (100% Ar)
In
ten
sit
y [
a.u
.]
15 10 5 0
(001)
(110)
binding energy [eV]
Large change of work
function and ionization
potential independent on
orientation
ionis
ation p
ote
ntial [e
V]
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 53
Conductivity relaxation of SnO2 (1 bar)
Almost no change of s with pO2 at 400°C
Equilibrium carrier concentration not achieved
time [h]
co
nd
ucti
vit
y [
S/
cm
]
oxyg
en
pressu
re [
Pa]
400°C 8
6
4
2
0
30 24 18 12 6 0
10 -1
10 0
10 1
10 2
10 3
10 4
10 5
time [h] co
nd
ucti
vit
y [
S/
cm
]
oxyg
en
pressu
re [
Pa] 600°C
3.0
2.5
2.0
1.5
1.0
0.5
0.0
36 30 24 18 12 6 0
10 -1
10 0
10 1
10 2
10 3
10 4
10 5
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 54
Relaxation at low pressure
Relaxation observed when starting from reduced surface
Saturated conductivity does not correlate with pO2
PCCP 13 (2011) 3223
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 55
Oxygen exchange of SnO2
Surface properties are crucial for oxygen exchange
reduced-SnO2 SnO2/In2O3 oxidized-SnO2
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 56
Relaxation measurements
Kinetics of oxygen exchange not accessible
contact failure
10% O2
100% Ar
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 57
Mobility and carrier concentration
Carrier concentration
(defect concentration) in
equilibrium
Carrier mobility different
for differently prepared
samples
Possible influence of
microstructure (texture,
grain size, segregation)
Necessary to understand
the evolution and the
control of microstructure
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 58
Topics
Transparent conducting oxides
Basic electrical and optical properties
Applications and importance of surfaces and interfaces
Experimental Approach
Surface Properties
Work function and ionization potential
Oxygen exchange
Interface properties
Energy band alignment
Redox processes at interface
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 59
Band alignment
Type I alignment before contact Type II alignment
ECB
EVB
Energy band alignment described by band discontinuities
Each material combination has characteristic alignment
Semiconductor I Semiconductor II
Eg,1 Eg,2
DECB DECB
DEVB
DEVB
DECB: conduction band discontinuity (offset)
DEVB: valence band discontinuity (offset)
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 60
Interface ITO/Al2O3
Pinning in ALD-Al2O3 leads to modified band alignment
PCCP 11 (2009) 3049, Chem. Mater. 24 (2012) 4503
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 61
SnO2/Pt – interface chemistry
Reversible oxidation/reduction of Sn
Sn 3d
490 488 486 484
binding energy [eV]
co
un
t ra
te [a
rb. u
nits]
oxygen p
ressure
T=150°C
oxidation @ 150°C reduction @ 150°C
490 488 486 484
binding energy [eV]
Sn4+ Sn0
• 150°C: Sn0 <-> Sn4+
with intermediate
Sn2+ state
• 100°C: Sn0 <-> Sn2+
•Oxidation/reduction
not observable for
- large Pt islands
- bare SnO2 surface
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 62
Chemistry at buried interface
SnO2
EF
Pt
EVB
ECB
SnO2
EF
Pt
EVB
ECB
Reducing environment Oxidizing environment
H
O H
O
O O
SnO2 Pt SnO2 Pt
Sn0 Sn4+
Oxygen is reversibly transported to/from the interface
Barrier changes with oxidation/reduction
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 63
Summary
Transparent Conducting Oxides are important
technological materials
Surface and Interface properties can be systematically
adressed using photoelectron spectroscopy with in-situ
sample preparation
Work function and oxygen exchange determined by
doping, surface orientation and surface termination
Energy band alignment governed by orbital contribution
to the valence band density of states
Defects limit dopability and can modify the energy band
alignment
16.09.2014 | SFB Symposium Sellin | Andreas Klein | 64
Acknowledgement
Frank Säuberlich, Yvonne Gassenbauer, Christoph Körber, André
Wachau, Jürgen Gassmann, Mareike Hohmann, Thorsten Bayer, Jonas
Deuermeier, Mirko Weidner, Anne Fuchs, Sebastian Siol
Paul Erhart, Péter Ágoston, Karsten Albe (TUD – Modelling)
Steven P. Harvey, Diana E. Proffit, E. Mitch Hopper, Thomas O. Mason
(Northwestern University)
German Science Foundation (SFB 595) MWN program)
BMBF (ZnO network project)
State of Hessen (LOEWE center AdRIA)
Work summarized in: J. Am. Ceram. Soc. 96, 331-345 (2013) Transparent Conducting Oxides: Electronic Structure – Property Relationship from
Photoelectron Spectroscopy with in-situ Sample Preparation
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