Elsevier

Thin Solid Films

Volume 602, 1 March 2016, Pages 68-71
Thin Solid Films

Evaluation of field emission properties from multiple-stacked Si quantum dots

https://doi.org/10.1016/j.tsf.2015.10.070Get rights and content

Highlights

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    Electron field emission from 6-fold stack of Si-QDs has been evaluated.

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    AFM measurements show the local electron emission from individual Si-QDs.

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    Impact of applied bias on the electron emission energy distribution was investigated.

Abstract

Multiple-stacked Si quantum dots (QDs) with ultrathin SiO2 interlayers were formed on ultrathin SiO2 layers by repeating a process sequence consisting of the formation of Si-QDs by low pressure chemical vapor deposition using a SiH4 gas and the surface oxidation and subsequent surface modification by remote hydrogen and oxygen plasmas, respectively. To clarify the electron emission mechanism from multiple-stacked Si-QDs covered with an ultrathin Au top electrode, the energy distribution of the emitted electrons and its electric field dependence was measured using a hemispherical electron energy analyzer in an X-ray photoelectron spectroscopy system under DC bias application to the multiple-stacked Si-QD structure. At − 6 V and over, the energy distributions reached a peak at ~ 2.5 eV with a tail toward the higher energy side. While the electron emission intensity was increased exponentially with an increase in the applied DC bias, there was no significant increase in the emission peak energy. The observed emission characteristics can be interpreted in terms of field emissions from the second and/or third topmost Si-QDs resulting from the electric concentration there.

Introduction

Nanometer-scale silicon structures have been attracting attention for their unique functionalities including multiple-valued charge storage [1], [2], single-electron transfer [3], [4], luminescence [5], [6], and electron field emission [7], [8], [9]. In terms of application to electron emitting devices using Si nanostructures, size uniformity and the increasing density of Si nanostructures are major technological concerns when it comes to improving power efficiency and dimensional stability. So far, we have demonstrated the formation of Si quantum dots (QDs) on thermally-grown SiO2 by controlling the early stages of low pressure chemical vapor deposition using a SiH4 gas [10]. Recently, we have succeeded in fabricating multiple-stacked Si-QDs embedded in a SiO2 matrix by repeating a process sequence consisting of the formation of Si-QDs and the surface oxidation and subsequent surface modification by remote plasmas. In the present work, to get a better understanding of the electron field emission mechanism from multiple-stacked Si-QD structures, we evaluated the energy distribution of electron emissions and its electric field dependence by using an electron energy analyzer in an x-ray photoelectron spectroscopy system.

Section snippets

Experimental

After conventional wet-chemical cleaning steps, ~ 3.5-nm-thick SiO2 was grown on n-Si(100) by dry O2 oxidation at 1000 °C. The SiO2 surface was exposed to remote Ar plasma and then to remote H2 plasma for termination with OH bonds, where a 60-MHz power source was used to generate the remote plasmas. Subsequently, Si-QDs were formed from the thermal decomposition of pure SiH4 under 66.6 Pa at 560 °C and followed by radical oxidation of 1% O2 diluted with He under 13.3 Pa at 560 °C to cover the dot

Results and discussions

Fig. 2 shows the topographic and corresponding current images of the 6-fold stack of Si-QDs with and without applied bias to the Al back contact with respect to the Au top electrode. The topographic image taken in contact mode shows a bumpy surface with a bump density of ~ 1011 cm− 2 and an average size of 30 nm in diameter (Fig. 2(a)). We confirmed that there was no change in the surface roughness before and after Au layer formation. This result indicates that observed nano-scale bumps correspond

Conclusions

The 6-fold stack of a Si-QD structure was fabricated and its local electron emission properties were characterized by AFM non-contact measurements in which current images were taken using an Au-coated Si cantilever. Non-uniform contrast of current images reflecting the spatial distribution of electron emission was observed at negative biases of − 6 V and over applied to the Al back contact with respect to the Au top electrode. The kinetic energy of emitted electrons shows a peak at ~ 2.5 eV and

Acknowledgments

This work was supported in part by Grant-in Aids for Scientific Research (A) No. 24246054 and Young Scientists (A) No. 25709023 from the Ministry of Education, Culture, Sports, Science and Technology, Japan and by the Japan Society for the Promotion of Science (JSPS) Core-to-Core Program of International Collaborative Research Center on Atomically Controlled Processing for Ultralarge Scale Integration. In addition, the authors deeply appreciate that the samples were fabricated by utilizing the

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