単斜晶WO3薄膜抵抗率の熱処理依存性
Resistivity dependence of Monoclinic Thin Tungsten Oxide Film on
Annealing Processes
東工大フロンティア研1，東工大総理工2, 東芝マテリアル3 ○李 蔚1, 佐々木亮人3, 大図秀行3, 青木克明3, 角嶋邦之2, 片岡好則2, 西山彰2, 杉井信之2,
若林整2, 筒井一生2, 名取研二1, 岩井洋1
Tokyo Tech. FRC 1, Tokyo Tech IGSSE 2, Toshiba Material Co., LTD3, ○W. Li1, A. Sasaki3, H. Oozu3, K. Aoki3, K. Kakushima2, Y. Kataoka2, A.
Nishiyama2, N. Sugii2, H. Wakabayashi2, K. Tsutsui2, K. Natori1, H. Iwai1
Introduction
Tungsten oxide (WO3) as a promising candidate for visible light-driven photocatalyst, has attracted a strong interest
owing to its narrow band gap (about 2.6eV), strong light absorption, deep valence band, easy synthesis, and nontoxicity .
For the application of photocatalyst, WO3 needs high electron transport which can suppress the recombination of
photogenerated electron-hole pairs thus improve the performance of photocatalyst . In this study, we measured the
resistivities of monoclinic WO3 thin film after different annealing processes and gave a proposal of how to obtain high
electron transport in WO3.
Results and Discussion
10
Experiment
5
Device Fabrication
104
104
103
103
No annealing
N2 annealing
5% O2 annealing
102
101
2.0
2.5
3.0
3.5
4.0
4.5
1000/T (K-1)
Fig.1 the nature logarithm resistivity versus
1000/T at different annealing atmospheres
Spray coating
Resistivity(cm)
• Monoclinic WO3 nanopowder
•BET Specific surface area: about 37m2/g
•Porosity: about35%
Resistivity(cm)
Material parameters:
105
as-received
N2 300oC 5min
N2 400oC 5min
N2 500oC 5min
102
101
N2 600oC 5min
100
N2 700oC 5min
10-1
N2 750oC 5min
10-2
2.0
2.5
3.0
0
Nearest neighbor hopping
n-Si
o
450 C
WO3(100nm)
annealing
for 30 min
EC
ED
700oC in N2
-3
=0.015eV
750oC in N2
-5
1
 1

1
 E1 
  
 T   
exp   
exp 
 kT 
 kT 
 qrNd 
 q1  r N d h
SiO2(400nm)
-2
-4
  
 T   exp 
 kT 

Ea=0.23eV
-1
ln  (cm)
SiO2(400nm)
4.5
Fig.2 the nature logarithm resistivity versus 1000/T at
different nitrogen annealing temperatures
 E1 
 T   0 exp 
 kT 
E1  EC  ED
ED
4.0
1000/T (K-1)
Band conduction
EC
3.5
Band conduction
Hopping conduction
-6
0.002
1 1



0.0025
0.003
1/T
0.0035
(K-1)
0.004
0.0045
Fig.3 Resistivity fitting of mixture of band
conduction and NNH conduction at 700 0C
and 7500C
0  r  1
n-Si
W sputtering
(50nm)
W
SiO2(400nm)
1.0E+00
1.0E+21
Hopping conduction
1.0E+20
Mobility (cm2/Vs)
WO3(100nm)
Carrier density (cm-3)
1.0E+22
1.0E+19
1.0E+18
Band conduction
1.0E+17
1.0E+16
WO3(100nm)
Top view
SiO2(400nm)
n-Si
200
400
600
800
Annealing temperature(oC)
W
#1#2 #3 #4
Band
conduction
バンド伝導
1.0E-02
1.0E-03
0
1. Lithography
2. W etching (H2O2)
3. Resist removal
1.0E-01
1.0E+15
1.0E+14
n-Si
Hopping
conduction
ホッピング伝導
Fig.4a carrier density of band conduction and
hopping conduction
0
200
400
600
800
Annealing
temperature(
熱処理温度
(oC) oC)
Fig.4b mobility of band conduction and hopping
conduction
Conclusion
◎It clearly showed that the oxygen vacancies were generated by the N2 annealing.
◎Moreover, hopping conduction should be increased since it can give lower resistivity and
higher carrier mobility.
◎Amount of oxygen vacancies should be increased in order to increase hopping conduction.
The possible methods are such as high temperature annealing, metal doping and so on.
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