Elsevier

Materials Letters

Volume 285, 15 February 2021, 128995
Materials Letters

A high performance self-powered heterojunction photodetector based on NiO nanosheets on an n-Si (1 0 0) modified substrate

https://doi.org/10.1016/j.matlet.2020.128995Get rights and content

Highlights

  • A high-performance NiO/Si(1 0 0) photodetector was fabricated by interface modulation.

  • The detectors exhibited excellent self-powered performance.

  • The EQE and switch ratio are characterized and the results are satisfying.

Abstract

A self-powered ultraviolet–visible photodetector based on NiO/Si heterojunctions made from NiO nanosheets on a Si (1 0 0) modified substrate was successfully manufactured via a facile hydrothermal method and subsequent calcination process. The fabricated detectors not only response to ultraviolet (UV) and visible light, but also possess excellent photocurrents and a lower dark current. The good performance, i.e., the external quantum efficiency (EQE) of ~22.4% and 33.1% under 350 nm and 600 nm, respectively, at zero bias, superior to most reported NiO/Si photodetectors, could be ascribed to the good crystalline NiO nanosheets and the suitable n-Si (1 0 0) substrate. Therefore, as-fabricated self-powered broadband detectors have a great potential application in wearable and portable devices.

Graphical abstract

A self-powered broadband photodetector based on NiO/Si heterojunction made from NiO nanosheets on a Si (1 0 0) modified substrate demonstrates an EQE as high as ~33.1% at zero bias.

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Introduction

Nowadays, photodetectors, are considered as one of the most attractive candidates for energy conversion systems, especially the detectors made by wide band gap metal oxides (such as TiO2, ZnO, NiO, etc.), due to their good thermal and chemical stability, low cost and environmental friendliness [1]. However, the characteristics of the rapid recombination of photogenerated carriers and almost no response to visible light, seriously reduce the lifetime of photogenerated carriers and affect the performance of the devices. Therefore, researchers built a heterojunction to promote the separation of carriers by the built-in electric field formed at the heterojunction interface [2], [3], [4], [5]. Nevertheless, most of the reported high performances heterojunctions are acquired by doping methods [6]. It inevitably changes the electronic structure and increases the state defects on the crystal surface, thereby destroying the surface atomic structure and introducing new defect energy levels, then, increasing the probability of electron hole recombination [7]. Therefore, constructing an appropriate PN junction, which can promote the separation of carriers and improve the performance of the detector without changing the electronic structure, becomes the motivation and the direction of the researchers.

NiO, because of its higher resistance and ionization energy, excellent electrical and optical properties, and natural p-type property, is widely used in various fields [8]. However, there are few reports about heterojunction photodetectors based on NiO with high performance. In recent years, it has been found that the detection performance can be further improved by selecting suitable substrate materials [9]. N-Si (1 0 0) substrate has lower crystal densities, higher bond densities, and higher electron mobility, which are beneficial to the growth of crystal and the formation of strong valence bond. [10]. Therefore, a photodetector based on NiO with higher performance can be realized by building a NiO/n-Si(1 0 0) heterojunction.

In this work, we successfully prepared NiO nanosheets on a n-Si(1 0 0) substrate via a facile hydrothermal method. The synthesized devices display outstanding photoelectric detection behaviors, that is, an EQE of ~22.4% (350 nm) and 33.1% (600 nm) at 0 V, and a switch ratio of ~1942% (350 nm) and ~5392% (600 nm) at −0.5 V. Hence, as-fabricated device is proven to be a great potential in the fields of self-powered or energy-saving optoelectronic devices.

Section snippets

Devices preparation

All chemicals were analytical grade and used without further purification. The NiO nanosheets were prepared via a simple hydrothermal route. First, NiO nano seeds was obtained by sputtering with Ni (99.99%) target on a cleaned n-type Si (1 0 0) (1–10 Ω cm) substrate. Second, 1 mmol of Ni(NO3)2·6H2O and 16 mmol of urea were fully dissolved in deionized water (48 mL). Then put the pre-treated Si substrate into the solution and maintained at 120 °C for 2 h to obtain NiO precursor. Third, annealing

Experimental results and analysis

The preparation process and the structure of NiO/n-Si (1 0 0) devices are shown in Fig. 1(a). Fig. 1(b) exhibits the XRD spectrum of the obtained samples. The diffraction peaks match well with the cubic structure of NiO (JCPDS: 65–2901) [1]. Fig. 1(c) reveals the SEM images of NiO nanosheets obtained by hydrothermal growth, in which NiO nanosheets are uniformly and densely distributed on the Si substrates. The insert in Fig. 1(c) shows the corresponding high-magnification SEM image, demonstrating

Conclusions

In summary, a photodetector based on NiO/n-Si (1 0 0) heterojunction was fabricated using a simple hydrothermal method. The detectors exhibited excellent properties including good rectification characteristics (the rectification ratio ~100 at ± 2 V), higher photocurrent (~100 μA cm−2 (350 nm) and 266 μA cm−2 (600 nm) at −0.5 V), outstanding switch ratio (~1942% (350 nm) and ~5392% (600 nm) at −0.5 V), especially the prominent self-powered properties (EQE: ~22.4% (350 nm) and 33.1% (600 nm) at

CRediT authorship contribution statement

Yongfang Zhang: Conceptualization, Investigation, Data curation, Formal analysis, Writing - review & editing. Tao Ji: Data curation, Supervision. Jinqi Zhu: Investigation. Rujia Zou: Project administration, Supervision. Junqing Hu: Project administration, Supervision, Writing - review & editing.

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 was financially supported by the National Natural Science Foundation of China (Grant No.: 51972055, 11974074, 51672044).

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