Tuning the Electrical Properties of NiO Thin Films by Stoichiometry and Microstructure

Peng Zhang,Xiao-Yan Liu,Yu-He Liu,Yong Wang,Hui Sun,Bo Dai

doi:10.3390/coatings11060697

Peng Zhang, Xiao-Yan Liu + Show 4 more

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https://doi.org/10.3390/coatings11060697

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Abstract

Here, the electrical properties of NiO thin films grown on glass and Al2O3 (0001) substrates have been investigated. It was found that the resistivity of NiO thin films strongly depends on oxygen stoichiometry. Nearly perfect stoichiometry yields extremely high resistivity. In contrast, off-stoichiometric thin films possess much lower resistivity, especially for oxygen-rich composition. A side-by-side comparison of energy loss near the edge structure spectra of Ni L3 edges between our NiO thin films and other theoretical spectra rules out the existence of Ni3+ in NiO thin films, which contradicts the traditional hypothesis. In addition, epitaxial NiO thin films grown on Al2O3 (0001) single crystal substrates exhibit much higher resistivity than those on glass substrates, even if they are deposited simultaneously. This feature indicates the microstructure dependence of electrical properties.

Highlights

As one of the most interesting oxides with strong correlations, nickel oxide (NiO)has been extensively studied during the past two decades [1,2,3,4]
NiO thin films grown with the oxygen flow rates of 4–7 sccm seemed to exhibit the preferred orientation
We have shown that the phase structure, preferred orientation, and microstructure of thin films are independent of glass or Si (100) substrates, because the amorphous SiO2 layer on single-crystal Si (100) substrate was not removed [29,30,31]

Summary

Introduction

As one of the most interesting oxides with strong correlations, nickel oxide (NiO)has been extensively studied during the past two decades [1,2,3,4]. A major resurgence of interest has been paid to NiO due to its variety of potential applications, such as p-type transparent semiconductors [5,6,7], gas sensors [8], electrochromic devices [9,10]. Recent investigations have shown that NiO could be a good p-type semiconductor [5,15,16], which makes it attractive as a transparent hole-transport layer in photovoltaics [11,12,17]. It is conventionally speculated that such a transition from an insulator to a semiconductor with lower resistivity is attributed to the introduction of Ni3+ ions via increasing the density of nickel vacancies [18,19,20,21,22]. The additional satellite shoulder peaks at about a 1.5 eV higher bonding energy, with respect to the main line in the Ni 2p edge, have generally been assigned to Ni3+ species [18,21,22]

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