Structural, electrical and optical properties of p-type transparent conducting SnO2:Al film derived from thermal diffusion of Al/SnO2/Al multilayer thin films

doi:10.1016/j.actamat.2010.07.042

Acta Materialia

Volume 58, Issue 19, November 2010, Pages 6243-6248

https://doi.org/10.1016/j.actamat.2010.07.042 Get rights and content

Abstract

Highly transparent, p-type conducting SnO₂:Al films derived from thermal diffusion of a sandwich structure Al/SnO₂/Al multilayer thin films deposited on quartz substrate have been prepared by direct current and radio-frequency magnetron sputtering using Al and SnO₂ targets. The deposited films were annealed at various temperatures for different durations. The effect of thermal diffusing temperature and time on the structural, electrical and optical performances of SnO₂:Al films has been studied. X-ray diffraction results show that all p-type conducting films possessed polycrystalline SnO₂ with tetragonal rutile structure. Hall-effect results indicate that 450 °C for 4 h were the optimum annealing parameters for p-type SnO₂:Al films, resulting in a relatively high hole concentration of 7.2 × 10¹⁸ cm⁻³ and a low resistivity of 0.81 Ω cm. The transmission of the p-type SnO₂:Al films was above 80%.

Introduction

Tin oxide (SnO₂) is one of the most important transparent conductive oxide (TCO) materials, and has numerous applications in modern technologies, such as flat panel displays, solar cells, light emitting diodes and gas sensors [1], [2], [3], [4], due to its attractive properties of a wide band gap (E_g = ∼3.6 eV), high electrical conductivity, high transmittance in the ultraviolet–visible (UV–vis) region and high infrared (IR) reflectance, abundance in nature and absence of toxicity [1], [5]. Conventional transparent conductors such as SnO₂ are n-type (electron) conductors and because their conductivity varies inversely with the oxygen partial pressure, it has been commonly attributed to the presence of native point defects; in particular, to oxygen vacancies [6], [7].

Recently, Singh et al. [8] found that the incorporation of group-IIIA atoms (In, Ga, and Al) in the Sn site produces shallow acceptors that exhibit good solubility and a low degree of self-compensation. Different dopants such as Al [9], [10], Sb [11], In [12], Ga [13] and Li [14], and techniques such as sputtering [11], [13], sol–gel [9], [12] and spray pyrolysis [10], [14], have been used to obtain p-type doping SnO₂. Among various possible acceptor dopants, Al has been evaluated as an efficient one to produce p-type SnO₂. Ahmed et al. [9] described p-type Al doped SnO₂ thin films synthesized by a sol–gel dip coating technique. The synthesis of p-type Al doped SnO₂ thin films via a spray pyrolysis process have been reported by Mehdi et al. [10].

However, there is no report available on the systematic study of p-type SnO₂:Al thin films obtained by magnetron sputtering. The sputtering and evaporation techniques are the commonly used methods for industrial applications. The magnetron sputtering technique has been effectively adapted for production because of its high throughput and controllable thickness, as well as high uniformity and flexibility. In the present study, the p-type SnO₂:Al thin films were prepared from the thermal diffusion of a sandwich structure of Al/SnO₂/Al multilayer thin films deposited on quartz substrates which were obtained using a direct current (DC) and radio-frequency (RF) magnetron sputtering process. X-ray diffraction (XRD), Raman spectrometry, field-emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) spectroscopy, Hall-effect measurements, and UV–vis spectrometry were used to characterize the films. The effects of annealing temperature and time on the structural, electrical and optical properties of the SnO₂:Al thin films were investigated and discussed in detail.

Section snippets

Sample preparation

The sandwich structure of Al/SnO₂/Al multilayer thin films was deposited layer by layer on quartz substrates with a conventional DC and RF magnetron sputtering system. An Al (99.99% in purity) disk was used as the DC magnetron sputtering target, while an SnO₂ ceramic plate with a diameter of 5.6 cm and thickness of 5 mm sintered at ∼1250 °C for 5 h at a slow ramping and cooling rate produced from the SnO₂ powder (99.9% in purity) was used as the RF sputtering target. The quartz substrates were

Crystal structure and morphology of thin films

Fig. 1 illustrates the XRD patterns of the as-deposited Al/SnO₂/Al multilayer thin films annealed at various temperatures and times in air. It reveals that all the patterns of the thin films annealed between 400 and 500 °C were SnO₂ with a tetragonal rutile structure (JCPDS card No. 41-1445), without other phases being detected. When annealing at 650 °C for 4 h, a broad peak appearing around 2θ ≈ 22° is attributed to the quartz substrate (JCPDS card No. 51-1379) which, because the structure of the

Conclusions

In summary, the p-type transparent conductive SnO₂:Al thin films were prepared from the thermal diffusion of a sandwich structure Al/SnO₂/Al multilayer thin films which were deposited on quartz substrates by DC and RF magnetron sputtering using Al and SnO₂ targets. Room temperature Hall measurements revealed that the SnO₂:Al films showed p-type conductivity within a certain annealing temperature range of 450–500 °C, while the films annealed below 400 °C and above 500 °C (duration longer than 4 h)

Acknowledgements

The authors gratefully acknowledge the financial support by the National Basic Research Program of China (2009CB939704), and the Fundamental Research Funds for the Central Universities (Wuhan University of Technology), and the helpful discussion from Prof. Moo-Chin Wang, Kaohsiung Medical University, during the manuscript preparation.

References (20)

D.S. Ginley et al.
MRS Bull
(2000)
D.L. Young et al.
J Appl Phys
(2003)
M.G. McDowell et al.
Appl Phys Lett
(2008)
B. Thangaraju
Thin Solid Films
(2002)
T. Minami
MRS Bull
(2000)
Z.M. Jarzebski et al.
J Electrochem Soc
(1976)
S. Samson et al.
J Appl Phys
(1973)
A.K. Singh et al.
Phys Rev Lett
(2008)
S.F. Ahmed et al.
J Sol-Gel Sci Technnol
(2006)
M. Mehdi et al.
J Appl Phys
(2004)

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

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Structural, electrical and optical properties of p-type transparent conducting SnO2:Al film derived from thermal diffusion of Al/SnO2/Al multilayer thin films

Abstract

Introduction

Section snippets

Sample preparation

Crystal structure and morphology of thin films

Conclusions

Acknowledgements

MRS Bull

J Appl Phys

Appl Phys Lett

Thin Solid Films

MRS Bull

J Electrochem Soc

J Appl Phys

Phys Rev Lett

J Sol-Gel Sci Technnol

J Appl Phys

Structural, electrical and optical properties of p-type transparent conducting SnO₂:Al film derived from thermal diffusion of Al/SnO₂/Al multilayer thin films