Meng Qin, 1,2 Kui Yao, 2,* and Yung C. Liang 1
1 Institute of Materials Research and Engineering (IMRE), A*Star (Agency for Science, Technology and
Research), 3 Research Link, Singapore 117602
2 Department of Electrical and Computer Engineering, National University of Singapore, Kent Ridge,
Singapore 119260
A. The effect of dielectric constant of electrode on screening charge distribution
Our theoretical analyses showed that the dielectric constant of the electrode significantly
influenced the screening charge distribution and the photovoltaic output. Figure 1 presents
the simulation results of the screening charge distribution in the electrodes with different dielectric constants (
ε e 1
and
ε e 2
) in a 400-nm-thick PLZT film. The low-dielectric-constant electrode (e.g. metal electrode, ε
Au
≈ 6, ε
Pt
≈ 8) tends to have the screening charges more concentrated near the ferroelectric-electrode interface and thus polarization is screened more severely; On the contrary, the high-dielectric-constant electrode (e.g. conductive oxide electrode,
ε
LSMO
≈ 800, and ε
Nb:STO
≈ 1000) tends to have the screening charges more extensively distributed away from the interface and consequently the polarization screening effect is weakened.
10
23
10
22
10
21
10
20
(a) Top electrode dielectric constant
 e1
= 10
 e1
= 100
 e1
= 1000
10
19
10
18
-5 -4 -3 x (nm)
-2 -1 0
* Corresponding author. Email: k-yao@imre.a-star.edu.sg, Tel: 65-68745160, Fax: 65-68720785.
1

10
23
10
22
10
21
10
20
10
19
(b) Bottom electrode dielectric constant
 e2
= 10
 e2
= 100
 e2
= 1000
10
18
400 401 402 x (nm)
403 404 405
Figure 1 . Simulation results of the screening charge distribution in the top (x < 0 nm) (a) and bottom
(x > 400 nm) electrodes (b) of a PLZT film with a thickness of L=400 nm with electrodes of different dielectric constant.
B. Parameters and data for numerical simulation
Table 1 Parameters and data for the numerical simulations for PLZT thin films
LSMO /PLZT/
Nb:STO
Au /PLZT/
Nb:STO
300 (experimental)
Au /PLZT/ Pt
Temperature T (K)
Relative dielectric constant of ferroelectric film ε r
Relative dielectric constant of top electrode
ε e 1
Relative dielectric constant of bottom electrode
ε e 2
Space charge density of top
Schottky barrier N eff 1
(cm
-3
)
Space charge density of bottom
Schottky barrier N eff 2
(cm
-3
)
800 [1]
1000 [3]
2×10
1×10
20
20
[5]
[5]
1200 (experimental)
6 [2]
1000 [3]
2×10
1×10
20
20
[5]
[5]
6 [2]
8 [4]
2×10
3×10
20
20
[5]
[5]
Remnant polarization P r
(µC/cm
2
)
SCR width of top Schottky barrier w
1
(nm)
SCR width of bottom Schottky barrier ( w
2
) (nm)
Thickness of top electrode
(0 – L
1
) (nm)
Thickness of bottom electrode
30
(experimental)
30
(experimental)
20
(experimental)
5×10 5
5
5
[5]
[5]
200 (experimental)
5×10 5
500 (Pt layer)
2

( L
2
– L ) (nm)
Quantum efficiency β
Absorption coefficient α (cm -1 )
Incident UV intensity (mW/cm
2
)
Top electrode transmittance
T transmit
Carrier lifetime τ n
(ps)
Carrier mobility
μ n
(cm
2
/Vs)
(Nb:STO substrate)
(Nb:STO substrate)
(experimental) (experimental)
90% [6, 7]
4×10 4 [8, 9]
(experimental)
0.26 (experimental)
30%
200 [10]
100 [11, 12]
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