Photovoltaic properties of BiFeO3 thin film capacitors by using Al-doped zinc oxide as top electrode

doi:10.1016/j.matlet.2012.10.031

Materials Letters

Volume 91, 15 January 2013, Pages 359-361

https://doi.org/10.1016/j.matlet.2012.10.031 Get rights and content

Abstract

We demonstrate using Al-doped zinc oxide films as electrode materials to form ferroelectric thin film capacitors. The photocurrent density and open circuit voltage for the capacitor with an Al-doped zinc oxide/BiFeO₃/Fluorine doped tin oxide structure are measured to be 0.13 mA/cm² and 0.63 V, respectively, much higher than the reported values for traditional BFO based capacitors. To clarify the contribution of Al-doped zinc oxide to the photovoltaic effect, Au top electrode was used as a comparison group. The Al-doped zinc oxide based capacitors show a more than 3 times larger photovoltaic output than that of the Au counterpart, which indicates that the Al-doped zinc oxide makes a major contribution to the high photovoltaic effect. The comparison shows that the larger photovoltaic effect may be attributed to the larger build-in-electric field, depolarization electric field and higher transparency of top electrode. Our results suggest that the transparent Al-doped zinc oxide film can be a promising electrode material in ferroelectric film capacitors and could be a potential replacement of indium tin oxide materials.

Highlights

► AZO was used as electrode in ferroelectric capacitors for the first time. ► AZO film has high transmittance of more than 80% in the visible range. ► AZO based capacitors provide comparable photovoltaic effect with that of ITO ones. ► EQE of 7% was obtained in polycrystalline BFO based capacitor for the first time.

Introduction

Transparent conducting oxide (TCO) semiconductors that are used as transparent electrodes play an important role in most optoelectronic devices. Though indium tin oxide (ITO) thin films have been in practical use for transparent electrode applications, it may be faced with high cost and scarcity of indium. It is crucial to find out appropriate TCO materials to replace ITO. Some other TCO materials have been reported [1], [2]. Doped zinc oxide thin films have been widely studied for their use as alternative to ITO [3], [4], [5], [6]. Impurity-doped zinc oxide (ZnO) was proposed to be a potential alternative to ITO [3], [4]. Among the doped zinc oxide films, aluminum-doped zinc oxide (AZO) films with a band gap of about 3.3 eV show the lowest electrical resistivity 2–4×10⁻⁴ Ω cm [5], [6], which is similar to that of ITO films [7], [8], [9]. Unlike the more commonly used indium tin oxide (ITO), zinc oxide (ZnO) is a non-toxic and inexpensive material. It is chemically and thermally stable under hydrogen plasma processes commonly used for the production of solar cells [10] and light emitting diodes [11], [12]. Thus, AZO is expected to be a promising material for fabricating transparent electrodes in optoelectronic devices.

Recently, the photovoltaic effect in ferroelectric materials has gained much attention [13] due to the high output photovoltage and control of the photocurrent induced by mechanisms, such as electric field, magnetism and heat. Among the ferroelectric materials, multiferroic BiFeO₃ (BFO) with narrow band gap and high remnant polarization exhibit appreciable photovoltaic output in the visible light region. Chen et al. [14] used ITO and Au as top electrode to investigate the photovoltaic effect of BFO thin films and suggest that the electrode plays an important role in determining the photovoltaic effect of ferroelectric thin films. Zang et al. [13] obtained improved photovoltaic properties with a carbon nanotube/BFO/Pt as top electrode, with the open circuit voltage reaching as high as 0.47 V. However, most of the heterojunction structures are based on using metal and ITO electrodes, and the traditional process derived polycrystalline BFO with perovskite structure [13], [14] still show limited photovoltaic effect.

In this paper, we demonstrate the ferroelectric film based capacitors using AZO as the top electrode for the first time. The heterojunction structure consists of AZO/BFO/Fluorine tin oxide (FTO). BFO with rhombohedral structure belongs to the R3c space group was prepared as reported earlier [15]. An Au top electrode was used for comparison to further indicate the function of AZO in improving the photovoltaic effect of BFO based capacitors.

Section snippets

Experimental

Polycrystalline BFO thin films were deposited on the commercial FTO glass substrates through a modified chemical solution deposition [15]. The optical properties were investigated using an UV–visible spectrophotometer in the wavelength range of 330–900 nm. AZO electrodes of 0.5 mm×1 mm were deposited on the surface of BFO by the RF magnetron method [11] at room temperature in Ar gas with 2 wt% Al₂O₃-doped ZnO sintered sheet as the target. Au top electrodes of 0.5 mm×1 mm were prepared using a DC

Results and discussions

The photovoltaic properties of the as-prepared polycrystalline BFO thin films are shown in Fig. 1(a). The open circuit voltage (V_OC) and the photocurrent density (J_SC) of the capacitor can reach up to 0.63 V and 0.13 mA/cm², respectively, much higher than the reported values for traditional polycrystalline BFO based capacitors. They are comparable with those of the ITO/BFO/FTO structure (V_OC=0.65 V, J_SC=0.13 mA/cm²) [15]. To clarify the effect of AZO electrode on improving the photovoltaic effect

Conclusions

In summary, AZO was used to investigate the photovoltaic properties of ferroelectric film based capacitors for the first time. The open circuit voltage and photocurrent density for the AZO/BFO/FTO structure are measured to be 0.13 mA/cm² and 0.63 V, respectively, much higher than the reported values for traditional polycrystalline BFO based capacitors. They are comparable with those of the ITO/BFO/FTO structure (J_SC=0.13 mA/cm², V_OC=0.65 V) previously reported [15]. A comparison with Au/BFO/FTO

Acknowledgments

This work is supported by the National Nature Science Foundation of China (no. 11074165).

References (21)

H. Kim et al.
Appl Phys Lett
(2000)
J.Q. Zhao et al.
Synth Met
(2000)
W. Dong et al.
Mater Lett
(2012)
R.G. Gordon
Mater Res Bull
(2000)
T.J. Coutts et al.
Mater Res Bull
(2000)
T. Minami
Mater Res Bull
(2000)
T. Minami et al.
Appl Phys Lett
(1982)
Y. Igasaki et al.
J Appl Phys
(1991)
H. Kim et al.
Appl Phys Lett
(1999)
H. Kim et al.
J Appl Phys
(1999)

There are more references available in the full text version of this article.

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Photovoltaic properties of BiFeO3 thin film capacitors by using Al-doped zinc oxide as top electrode

Abstract

Highlights

Introduction

Section snippets

Experimental

Results and discussions

Conclusions

Acknowledgments

Appl Phys Lett

Synth Met

Mater Lett

Mater Res Bull

Mater Res Bull

Mater Res Bull

Appl Phys Lett

J Appl Phys

Appl Phys Lett

J Appl Phys

Photovoltaic properties of BiFeO₃ thin film capacitors by using Al-doped zinc oxide as top electrode