Effects of substrate temperature on the resistivity of non-stoichiometric sputtered NiOx films

doi:10.1016/S0257-8972(02)00037-3

Surface and Coatings Technology

Volume 155, Issues 2–3, 17 June 2002, Pages 231-235

https://doi.org/10.1016/S0257-8972(02)00037-3 Get rights and content

Abstract

Thin films of nickel oxide (NiO) were deposited on Corning 7059 glass substrates by RF magnetron sputtering. The relationship between substrate temperature and resistivity and the microstructural defects of the NiO films were investigated. Crystalline NiO film with (111) orientation was obtained in this study. A resistivity of 0.22 Ω cm and a hole concentration of 4.4×10¹⁹ cm⁻³ were obtained for non-doped NiO films prepared at a substrate temperature of 300 °C in pure oxygen sputtering gas. As the substrate temperature was increased from 300 to 400 °C, the resistivity changed from 0.22 to 0.70 Ω cm. The mechanism of electrical conductivity for the NiO films is discussed from the viewpoint of defect chemistry and was confirmed by X-ray photoelectron (XPS) and energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD) data.

Introduction

Nickel oxide (NiO) films have a wide range of applications due to their excellent chemical stability, as well as optical, electrical and magnetic properties. They have been used as antiferromagnetic materials [1], materials for electrochromic display devices [2], p-type transparent conducting films [3] and functional layer materials for chemical sensors [4]. There are several methods to prepare nickel oxide films, such as sputtering [5], [6], [7], electron beam evaporation [8], [9] and sol–gel deposition [10]. Among these methods, reactive sputtering has been most widely used. The properties of the films depend on various sputtering parameters, including the sputtering gas, sputtering pressure and substrate temperature. However, little research has been carried out concerning the dependence of film properties on substrate temperature. Therefore, the purpose of this study was to investigate the effects of substrate temperature on electrical properties of nickel oxide films. From the experimental results, we also attempt to discuss the mechanism of electrical conductance of NiO film based on defect chemistry.

Section snippets

Experimental method

In this study, nickel oxide films were prepared by an RF magnetron sputtering system with a NiO target of 99.99% purity. Glass substrates of Corning 7059 were placed at a distance of 7 cm from the target with a diameter of 7.62 cm and thickness of 0.64 cm. Sputtering deposition was performed at a gas pressure of 0.01 torr and the target was kept at a constant RF power of 50 W. Pure oxygen gas was used as the reactive sputter gas. The range of substrate temperatures investigated was from 250 to

Results and Discussions

Fig. 1 shows the diffraction patterns of samples that were prepared at different substrate temperatures. In the 2θ range under investigation, only the (111) diffraction peak was observed. Diffraction peaks corresponding to Ni, NiOOH, Ni₂O₃ and Ni(OH)₂ cannot be found, regardless of substrate temperature. From XRD spectra of the as-deposited NiO films, it was found that the NiO films prepared at a substrate temperature of 200 °C had weak and broadened (111) diffraction peaks, which implies poor

Conclusion

NiO films with a preferred orientation of (111) have been deposited by RF reactive magnetron sputtering using a nickel oxide target at different substrate temperatures. A minimal resistivity of 0.22 Ω cm was obtained at a substrate temperature of 300 °C. Variation in resistivity is strongly related to changes in crystalline imperfection, which induces electrical carriers. In this study, non-stoichiometric nickel oxide films exhibit p-type extrinsic semiconductor behavior, and electron holes act

Acknowledgements

The authors are grateful to the National Science Council in Taiwan for financially supporting this research under Grant NSC-89-2216-E-168-005.

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Effects of substrate temperature on the resistivity of non-stoichiometric sputtered NiOx films

Abstract

Introduction

Section snippets

Experimental method

Results and Discussions

Conclusion

Acknowledgements

Thin Solid Films

Sol. Energy Mater.

Jpn. J. Appl. Phys.

Jpn. J. Appl. Phys.

J. Mater. Sci. Lett.

J. Appl. Phys.

J. Vac. Sci. Technol

Effects of substrate temperature on the resistivity of non-stoichiometric sputtered NiO_x films