Electrical study of antiferroelectric NaNbO3 thin films integrated directly on 4H-SiC
Introduction
Integration of multifunctional perovskite oxides with semiconductors has attracted tremendous attention because of their potential ability to herald some new functionalities and applications. For example, integrating ferroelectric (FE) perovskite oxides with GaN-based semiconductors can have access to a cloud of applications such as smaller and faster electronic, optoelectronic, and memory devices [[1], [2], [3], [4]]. As the cousin of FE, antiferroelectric (AFE) has many analogous features including bulk photovoltaic effect [5], memory effect [6], energy storage [7], and solid-state cooling [8]. In this respect, coupling AFE perovskite oxides with semiconductors can obviously enrich the family of the integration of multifunctional oxides with semiconductors. Moreover, due to the unique properties of AFE like field-induced antipolar-to-polar transition [9], such integration can also provide more probabilities for hybrid devices.
Sodium niobate (NaNbO3, NNO), being a lead-free AFE material, is widely known for its complicated temperature-dependent phase transitions [[10], [11], [12]] and fascinating applications including photocatalysis, energy storage, and electrothermal energy conversion [[13], [14], [15], [16]]. To date, significant efforts have been dedicated to the growth of NNO thin films on substrates that are usually coated with metal or oxide electrodes [[17], [18], [19], [20]]. However, less attention has been paid to the direct growth of NNO thin films on semiconductors, especially SiC. As known, SiC is one of the third-generation wide-bandgap semiconductor materials, and it exhibits many intriguing properties such as large breakdown fields, high electron saturation velocity, and excellent thermal conductivity and stability [21]. Accordingly, SiC was extensively used as the promising technology platform (e.g., metal-oxide-semiconductor-based devices [21], single-photon sources [22]) in the semiconductor industry. Additionally, the availability of large area, highly-conducting bulk SiC substrates is also advantageous as the conducting electrode for NNO thin films to form vertical device structures. In this work, therefore, NNO thin films were directly deposited on 4H-SiC substrates by a sol-gel route. It is a low-cost, low-temperature deposition method, and that makes it suitable for industrial applications [23]. And, the leakage mechanism in Pt/NNO/4H-SiC devices was investigated, which is of importance for promising applications.
Section snippets
Experimental
NNO thin films were deposited on n-type 4H-SiC single-crystalline substrates by a sol-gel route, and more details of the sol-gel route have been described in our previous work [24]. The n-type 4H-SiC substrates, which were purchased from HeFei Crystal Technical Material Co., Ltd., have the resistivity of <0.02 Ω cm.
The phase structure and surface topography of NNO thin films were investigated by grazing incidence X-ray diffraction (GIXRD) (PANalytical Empyrean) and atomic force microscope (AFM)
Results and discussion
Fig. 1 (a) shows the GIXRD spectrum of NNO thin film. Except the peaks from 4H-SiC substrate, all the other peaks match well with NaNbO3 (JCPDS No: 74–2454), indicating that the prepared NNO thin film exhibits a polycrystalline orthorhombic perovskite structure without visible secondary phases. It is also mentioned that the orthorhombic structure was widely accepted as AFE phase in NNO [17,25].
Fig. 1 (b) presents the surface morphology and the corresponding cross-section profile of NNO thin
Conclusions
In summary, polycrystalline sodium niobate (NaNbO3, NNO) thin films with orthorhombic perovskite structure were grown on wide-bandgap semiconductor 4H-SiC substrates by sol-gel method. The ‘‘slanted’’ P–V hysteresis loop was observed. Both the dielectric constant and dielectric loss decreased with frequency. Modeled analysis of the current-voltage characteristics indicated that the leakage current in the Pt/NNO/4H-SiC device was controlled by trap-related space-charge-limited-current mechanism.
CRediT authorship contribution statement
Huijuan Dong: Formal analysis. Bingcheng Luo: Writing - original draft, Writing - review & editing, Formal analysis. Zhengyuan Liu: Formal analysis. Kexin Jin: Writing - review & editing, Formal analysis.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work is supported by “the Fundamental Research Funds for the Central Universities (No: 310201911cx024)”
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