Transcript Слайд 1 - uran.ru

Structure and Electrophysical
Properties of the Transparent
Conducting Zinc and Indium Oxides
Films
V.A. Kulbachinskii
V.G. Kytin, O.V. Reukova, D.S. Glebov, D.D. Melnik, A.R. Kaul, L.I. Burova
M.V. Lomonosov Moscow State University, Moscow, Russia
Yu.M. Galperin, A.G. Ulyashin
University of Oslo, Oslo, Norway
Outline
1) Transparent conducting oxides
2) Zinc oxide:
- crystal structure; - electronic structure; - defects and dopants
- MOCVD grown undoped
- Ga doped ZnO films
- Co doped ZnO films
3) Indium oxide (In2O3):
- crystal structure
- electronic structure
- properties of Sn doped In2O3
4) Summary
2
Transparent conducting oxides and their applications
3
Crystal structure of ZnO
Basic structures of ZnO*
Zinc blende
O
Wurtzite
Rocksalt
Zn
a=3.250 Å
c=5.206 Å
4
Band structure of ZnO wurzite
Band structure of ZnO calculated by non-local
(solid lines) and local (dashed lines) empirical
pseudo potential method*
Brillouin zone of wurtzite ZnO
Electron effective mass: mII≈m┴≈(0.25-0.3)m0*
5
Defects in ZnO
Native donor defects:
- Oxygen vacancies VO
- Zinc interstitials Zni
Native acceptor defects:
- Zn vacancies ZnV
- O interstitials Oi
Calculated formation energies of native defects in ZnO*
Zn rich conditions
O rich conditions
6
Structure of undoped ZnO films grown on R-Al2O3 and
ZrO2(Y2O3)(111) substrates by oxygen assisted MOCVD
XRD data of ZnO films grown on R-Al2O3 and ZrO2(Y2O3) (111) substrates: a) and b) on R-Al2O3
θ-scan and φ-scan; c) and d) on ZrO2(Y2O3)(111) θ-scan and φ-scan
Epitaxial films with orientation determined by substrate
7
Structure of undoped ZnO films grown on MgAl2O4 (111) substrates
by oxygen assisted MOCVD
XRD data of ZnO films grown on MgAl2O4(111) substrates: a) θ-scan; b) φ-scan
a
b
Epitaxial films with 2 in-plain orientations of ZnO with respect to
substrate
8
Structure of undoped ZnO films grown by water assisted MOCVD
XRD θ-scans of ZnO films grown on r-Al2O3 and ZrO2(Y2O3) (111) substrates at 300 0C by water
assisted MOSVD
*
r-Al2O3
* - ZnO
*
*(101)
*
(110)
(100)(002)
20
25
30
35
YSZ
(111)
40
45
50
55
YSZ
(222)
log (Intensity), a.u.
lg(Intensity), a.u.
r-Al2O3
60
ZnO
(002)
ZnO
(101)
CuK

20
25
30
35
40
2degrees
45
50
55
60
65
70
2deg.
No visible structure from ZnO in φ-scans
Polycrystalline films with chaotic orientation of crystallites
9
Surface morphology of undoped ZnO films grown by oxygen and
water assisted MOCVD
AFM images of the surface of ZnO films grown on ZrO2(Y2O3) (111) substrates at 600 0C
H2O assisted MOCVD
rms 4.68 nm
O2 assisted MOCVD
rms 40.78 nm
Surface of ZnO films grown by water assisted MOCVD is smoother
than by oxygen assisted MOCVD
10
Surface morphology of undoped ZnO films grown by water assisted
MOCVD at different temperatures
SEM image ZnO film grown on
R-Al2O3 at 300 0C
SEM image ZnO film grown on
R-Al2O3 at 500 0C
11
Magnetic properties of undoped ZnO films grown by water assisted
MOCVD at different temperatures
M(H) at room temperature for the films deposited by water-assisted CVD on
r-sapphire substrates at 300 °C (R_W_300) and at 500 °C (R_W_500).
12
Resistivity of undoped ZnO films grown by oxygen assisted MOCVD
100000000
deposited at 500 0C
1000000
10000000
deposited 600 0C
100000
100000
substrate MgAl2O4 (111)
10000
1000
substrate MgAl2O 4(111)
10000
1000
substrate C-Al2O3
100
substrate R-Al2O3
substrate C-Al2O3
100
10
substrate R-Al2O 3
10
1
0
ρ, mOhm cm
ρ, mOhm cm
1000000
50
1
0
substrate ZtO 2(Y2O 3)(111)
50
100 150 200 250 300 350
100 150 200 250 300 350
T, K
T, K
Lowest resistivity have the most ordered films grown on R-Al2O3 and ZrO2(Y2O3)(111) substrate
Highest resistivity have the films with 2 different orientation of crystallites grown on MgAl2O4(111)
substrates
13
Hopping conductivity in undoped ZnO films grown by oxygen
assisted MOCVD
11 substrate MgAl O (111)
2 4
T0=2500 K
0
ln(r, mOhmcm)
deposited at 600 C
9
7
Mott's law:
[( ) ]
T0
ρ= ρ
T
T0=260 K
substrate C-Al2O 3
1/4
deposited at 500 0C
5
3
0.2
T 0≈
0.3
0.4
0.5
0.6
21.2
3
k B r 0 g (E F )
0.7
T-1/4, K-1/4
14
Resistivity of undoped ZnO films grown by water assisted MOCVD
10000
deposition temperature 600 0C
8
substrate ZrO 2(Y2O3)(111)
substrate ZrO2(Y2O3)(111)
ln(r, mOhm cm)
1000
ρ, mOhm cm
9
deposition at 600 0C
100
substrate R-Al2O3
T0=899000 K
7
6
T0=207000 K
5
10
4
1
50
100
150
200
T, K
250
300
350
3
0.22
substrate R-Al2O 3
0.24
0.26
0.28
0.3
0.32
0.34
0.36
T-1/4, K-1/4
Variable range hopping conductivity in a wide temperature range
15
Magnetoresistance of undoped ZnO films grown by oxygen assisted
MOCVD
0.01
0.000
deposition temperature 600 0C
0
-0.005
-0.01
substrate MgAl2O4(111)
-0.010
0
Dep. temp. 600 C
Dr/r(0)
Δρ/ρ(0)
-0.02
substrate R-Al2O 3
-0.03
-0.04
-0.015
-0.020
substrate R-Al2O 3
-0.05
-0.06
-0.07
0
0
Dep. temp. 600 C
substrate R-Al2O 3
substrate ZrO 2(Y2O3)(111)
-0.025
Dep. temp. 500 0C
1
2
3
4
B, T
5
6
7
8
-0.030
0
0.1
0.2
0.3 0.4
B, T
0.5
0.6
0.7
0.8
16
Intensity, a.u.
ZnO:Ga films
2θ, degree
X-ray data of ZnO:Ga films deposited at 600 0C on ZrO2(Y2O3)(111) substrate by oxygen assisted
MOCVD: a) 1.7 at. % Ga; b) 3.6 at. % Ga.
Shift of ZnO peak positions correspond to increase of lattice constant
with increase of Ga content
17
Resistivity of ZnO:Ga films grown by oxygen assisted MOCVD
ZnO:Ga on ZrO2(Y2O3)(111)
16 substrate
ZnO:Ga on R-Al2O3 substrate
35
14
30
12
0 at. % Ga
ρ,mOhm cm
ρ, mOhm cm
25
20
15
10
10
1.7 at. % Ga
8
6
6.8 at. % Ga
4
5
0
0
0 at. % Ga
5 at. % Ga
50
100
7.2 at. % Ga
150 200 250
T, K
2
300
350
0
0
50
100 150 200 250 300 350
T, K
Resistivity decreases first with an increase of Ga content
18
0.000
0.000
substrate R-Al2O 3
substrate ZrO2(Y2O 3)(111)
-0.005
-0.005
-0.010
-0.010
0 at. % Ga
-0.015
7.2 at. % Ga
-0.020
5 at. % Ga
-0.025
Dr/r(0)
Dr/r(0)
Magnetoresistance of ZnO:Ga films grown by oxygen assisted
MOCVD
6.8 at. % Ga
-0.015
0 at. % Ga
-0.020
-0.025
1.7 at. % Ga
-0.030
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
B, T
-0.030
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
B, T
19
Resistivity of ZnO:Ga films grown by water assisted MOCVD
r, Ohm cm
100
10
1
0.1
0.01
0
subsrate ZrO2 (Y2 O3)(111)
7 at. % Ga
subsrate ZrO2(Y2 O3 )(111)
25 at. % Ga
subsrate R-Al2O3
21 at. % Ga
50 100 150 200 250 300 350
Т, К
[( ) ]
T0
ρ= ρ
T
ln(r, Ohm cm
1000
7
6
5 subsrate ZrO2 (Y2 O3 )(111)
4 7 at. % Ga
3
2
subsrate ZrO 2(Y2 O3 )(111)
1
25 at. % Ga
0
-1
subsrate R-Al2 O3
-2
21 at. % Ga
-3
0.2
0.3
0.4
0.5
0.6
Т -1/4 , К -1/4
1/ 4
T 0≈
0.7
21.2
3
k B r 0 g (E F )
Variable range hopping conductivity in investigated temperature range
20
0.060
0.059
0.058
0.057
0.056
0.055
0.054
0.053
0.052
0.051
0.050
0
substrate R-Al2 O3
21 at. % Ga
5.545
5.540
5.535
5.530
5.525
5.520
5.515
5.510
5.505
5.500
5.495
0
substrate ZrO2 (Y2 O3)(111)
7 at % Ga
r, Ohm m
r, Ohm m
Magnetoresistance of ZnO:Ga films grown by water assisted
MOCVD
1
2
3
B, T
4
5
6
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
B, Т
 ρ B  
5 e 2 r04 B 2  T0 
0 =
ln
 
2
ρ
T 

 2016 
3/ 4
Estimate of r0 and g(EF) from positive magnetoresistance and ρ(T)
Substrate
Ga content, at. %
r0, nm
g(EF), 1019 cm-3eV-1
R-Al2O3
25
7
13
ZrO2(Y2O3)(111)
7
8
3.8
ZrO2(Y2O3)(111)
21
7
25
21
ZnO:Co films deposited by oxygen assisted MOCVD
ZnO:Co (7,7 at. % Co)
ZnO
(002)
20
25
30
35
Intensity, a.u.
lg(Intensity), a.u.
ZnO:Co (7,7 at. % Co)
c-Al2O3
(006)
40
45
50
2deg.
55
60
65
70
с-Al2O3
0
60
120
180
, deg.
240
300
Epitaxial films with oriention determined by substrate
22
Structure of ZnO:Co films deposited by water assisted MOCVD
ZnO
(101)
ZnO
(002)
ZnO
(100)
20
25
30
35
Al2O3 (006)
Al2O3 (006)
ZnO
(102)
40
45
grad.
50
lg (Intensity), a.u.
lg (Intensity), a.u.
ZnO:Co
(1,5 at. % Co)
ZnO
(110)
55
60
12,4 at. % Co
ZnO
(101)
ZnO
(002)
ZnO
(100)
20
25
30
ZnO
(102)
35
40
45
deg.
50
ZnO
(110)
55
60
No peaks in φ-scans. Polycrystalline structure with chaotic orientation of
crystallites.
23
EXAFS (extended X ray absorption fine structure ) spectra and Co state in
ZnO:Co films
Cobalt substitutes Zn up to 33 at. %
content
EXAFS-спектроскопия —
новый метод исследования
вещества, позволяющий
определять структурные
параметры ближнего
окружения атомов
с выбранным Z, спектры
которых изучаются. Среди
этих параметров —
межатомные расстояния,
координационные числа,
амплитуды тепловых
колебаний. Существование
дальнего порядка
в исследуемых образцах
не требуется.
В зависимости
от применяемой методики
получения спектров можно
анализировать ближнее
окружение атомов,
расположенных либо
в объеме образца, либо
на его поверхности.
24
Magnetic properties of ZnO:Co film
1,5
Zn0.985Co0.015O
0,5
Zn0.937Co0.063O
M, 10
-12
.
2
(A m )
1,0
0,0
-0,5
-1,0
-1,5
-1,0
-0,5
0,0
0,5
1,0
B (T)
25
Magnetoresistance of ZnO:Co films
-4
2.6x10
ZnO
-4
2.6x10
-4
2.5x10
-4
Zn 0.985Co 0.015O
Dr/r(0)
ρ, Ohm cm
rОмм 
2.5x10-3
1.0x10
-4
8.0x10
0.08
Zn 0.937Co 0.063O
0.06
0.04
0
1
2
3
BT
(Тл)
B,
4
5
6
0.5
0.45
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
0
substrate R-Al2O3
oxygen assisted MOCVD
1.5 at. % Co
water assisted MOCVD
1.9 at. % Co
1
2
3
B,T
4
5
6
7
Value of positive magnetoresistance increases with an increase of Co content
Value of positive magnetoresistance is larger for the films grown by oxygen assisted
MOCVD
Possible origin of positive magnetoresistance: reduction of the density of states at Fermi
energy in magnetic field
26
In2O3
Ia3
.
Кубическая структура типа
биксбита пространственной
группы Ia3
Two inequivalent positions of In cations
27
Band structure of In2O3
Band structure of In2O3
Brillouin zone of In2O3
28
Investigated In2O3:Sn films
Deposition method: magnetron sputtering
Targets: 1) Oxide target (baked In2O3 and SnO2 9:1); 2) metal target In-Sn alloy
Substrate: glass
Target
Deposition
temperature, 0C
Film thickness
oxide
RT
80
oxide
230
80
oxide
230
75
Valence band XPS spectra of In2O3:Sn films
Bandgap states in films deposited
from metal target
29
X-ray phoemission data about O state in In2O3:Sn films
High resolution O 1s spectra acquired after slight sputtering using low energy (500 eV) Ar+
30
XPS spectra of In and Sn states in In2O3:Sn films
High resolution In 3d XPS spectra of ITO films
deposited at different conditions
High resolution Sn 3d XPS spectra of ITO films
deposited at different conditions
Estimate of the film composition determined from XPS data
Target
Deposition
temperature
In content, at. %
Sn content, at. %
O content, at. %
oxide
RT
47.41
3.65
0.96
oxide
230 0C
47.66
3.50
0.95
metal
230 0C
47.93
4.04
0.92
31
Resistivity of In2O3:Sn films deposited from oxide target
0.8
0.7
deposited at RT
0.6
r, mOhm.cm
0.5
0.4
deposited at 230 0C
0.3
deposited at 230 0C 30 min H plasma
0.2
deposited at 230 0C 5 min in H plasma
0.1
0
0
50
100
150
T, K
200
250
300
The conductivity of the films deposited at 230 0C is higher than the conductivity
of the films deposited at room temperature. This correlates with the better
crystallinity of the film deposited at 230 0C
Treatment in H plasma leads to the increase of conductivity. The Effect is larger
for 5 min treatment than for 30 min treatment
32
Magnetoresisitance of In2O3:Sn films deposited from oxide target
0.0000
5
-0.0005
4.5
deposited at 230 0C
L = 360 nm
4
-0.0010
3.5
deposited at 230 0C
3
-0.0020
Δσs/G0
Dr/r(0)
-0.0015
-0.0025
-0.0030
2.5
deposited at RT
L = 230 nm
2
1.5
deposited at RT
1
-0.0035
-0.0040
0
0.5
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
0
-5
1
-4
-3
-2
-1
0
1
ln(B, T)
B, T
Δ σ2D
4 Lφ
≈ − ln
− 1.96
G0
lB
( )
l B=
√
ℏ
eB
Negative magnetoresistance is explained by weak localization theory
33
Resistivity and magnetoresistance of In2O3:Sn films deposited from
metal target in oxygen deficit conditions
2D variable range hopping conductivity. Large localization length r0>35 nm. Negative
magnetoresistance could be caused by increase of localization length in magnetic field
34
Summary
- Electron mobility in ZnO and In2O3:Sn films correlates with degree of
crystallinity: the better is the crystallinity the larger is the electron mobility.
- Electron transport in highly crystalline ZnO, ZnO:Ga and films is bandlike.
- Electron transport in polycrystalline ZnO, ZnO:Ga films and oxygen deficient
In2O3:Sn films is hopping.
- Electron concentration in ZnO:Ga films is essentially smaller than concentration
of Ga atoms.
- Electron transport in ZnO:Co films is hopping at low temperatures.
-Increase of Co content in ZnO films leads to increase of paramagnetic
susceptibility and large positive magnetoresistance at low temperatures. This
magnetoresistance could be explained by Zeemann splitting of electronic energy
levels in magnetic filed.
- Conductivity of In2O3:Sn films deposited from oxide target is larger than
conductivity of ZnO:Ga films grown by oxygen assisted MOCVD due to larger
electron concentration.
-The increase of substrate temperature from RT to 230 °C leads to essential
increase of the electron mobility and film conductivity.
35