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Improvement on electrical conductivity and electron field emission properties of Au-ion implanted ultrananocrystalline diamond films by using Au-Si eutectic substrates K. J. Sankaran, B. Sundaravel, N. H. Tai, and I. N. Lin Citation: Journal of Applied Physics 118, 085306 (2015); doi: 10.1063/1.4929431 View online: http://dx.doi.org/10.1063/1.4929431 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/118/8?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Bias-enhanced post-treatment process for enhancing the electron field emission properties of ultrananocrystalline diamond films Appl. Phys. Lett. 106, 111602 (2015); 10.1063/1.4915488 Origin of graphitic filaments on improving the electron field emission properties of negative bias-enhanced grown ultrananocrystalline diamond films in CH4/Ar plasma J. Appl. Phys. 116, 163102 (2014); 10.1063/1.4899245 Enhancing electrical conductivity and electron field emission properties of ultrananocrystalline diamond films by copper ion implantation and annealing J. Appl. Phys. 115, 063701 (2014); 10.1063/1.4865325 Gold ion implantation induced high conductivity and enhanced electron field emission properties in ultrananocrystalline diamond films Appl. Phys. Lett. 102, 061604 (2013); 10.1063/1.4792744 Microstructure evolution and the modification of the electron field emission properties of diamond films by gigaelectron volt Au-ion irradiation AIP Advances 1, 042108 (2011); 10.1063/1.3651462

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JOURNAL OF APPLIED PHYSICS 118, 085306 (2015)

Improvement on electrical conductivity and electron field emission properties of Au-ion implanted ultrananocrystalline diamond films by using Au-Si eutectic substrates K. J. Sankaran,1,2 B. Sundaravel,3 N. H. Tai,1,a) and I. N. Lin4,a) 1

Department of Materials Science and Engineering, National Tsing Hua University, Hsin-Chu Taiwan 300, Taiwan 2 Institute for Materials Research (IMO), Hasselt University, 3590 Diepenbeek, Belgium 3 Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, India 4 Department of Physics, Tamkang University, Tamsui, Taiwan 251, Taiwan

(Received 19 May 2015; accepted 11 August 2015; published online 26 August 2015) In the present work, Au-Si eutectic layer was used to enhance the electrical conductivity/electron field emission (EFE) properties of Au-ion implanted ultrananocrystalline diamond (Au-UNCD) films grown on Si substrates. The electrical conductivity was improved to a value of 230 (X cm)1, and the EFE properties was enhanced reporting a low turn-on field of 2.1 V/lm with high EFE current density of 5.3 mA/cm2 (at an applied field of 4.9 V/lm) for the Au-UNCD films. The formation of SiC phase circumvents the formation of amorphous carbon prior to the nucleation of diamond on Si substrates. Consequently, the electron transport efficiency of the UNCD-to-Si interface increases, thereby improving the conductivity as well as the EFE properties. Moreover, the salient feature of these processes is that the sputtering deposition of Au-coating for preparing the Au-Si interlayer, the microwave plasma enhanced chemical vapor deposition process for growing the UNCD films, and the Au-ion implantation process for inducing the nanographitic phases are standard thin film preparation techniques, which are simple, robust, and easily scalable. The availability of these highly conducting UNCD films with superior EFE characteristics may open up a pathway for the development of high-definition flat panel displays and plasma C 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4929431] devices. V

I. INTRODUCTION

Cold cathode materials with admirable electron field emission (EFE) properties, such as low turn-on field and high EFE current density, have been very useful for vacuum electronic devices, namely, electron source for traveling wave tubes, terahertz sources, and x-ray sources.1–4 Among the field emitting materials, including semiconductor nanowires, carbon nanotubes, and diamond thin films, diamond is one of the most fascinating electronic materials because of its negative electron affinity (NEA) surface and chemical inertness that can survive harsh environments such as plasmas.5–12 On the other hand, ultrananocrystalline diamond (UNCD) is a special form of diamond, which has attracted significant attention from researchers, because of its outstanding EFE behavior compared to that of micron-sized diamond films.13 The grains are of ultra-small size of 2–5 nm with sp3 bonded diamond, and the grain boundaries contain amorphous carbon (a-C), which help transport electrons.14 The main requirement for the UNCD films to be concluded as a promising material for the fabrication of cold cathode or other electron emitting devices is that the films must be conductive. Ion implantation has long been used to manipulate the properties of materials through controlled doping with a variety of dopants.15–17 Recent reports showed that nitrogena)

Authors to whom correspondence should be addressed. Electronic addresses: [email protected] and [email protected]

0021-8979/2015/118(8)/085306/9/$30.00

ion,18 oxygen-ion,19 and phosphorous-ion20 implantations on UNCD films provide n-type conductivity, which is mediated by current paths supplied to the films by the a-C grain boundaries. However, the electrical conductivity of a-C phases contained in the grain boundaries of UNCD films is not sufficiently high and therefore limits the EFE properties of UNCD films.21 Recently, we observed that Au-ion22 or Cuion23 implantation can directly induced graphitic phases in the grain boundaries of the UNCD films that improve markedly the EFE behavior. But the achieved electrical conductivity and EFE properties are still not satisfactory because of the high resistance in the diamond-to-substrate interface, which hinders the transport of electrons from the substrate to the diamond. On the other hand, it has been reported that the deep depletion layer formed in the vicinity of heterogeneous interfaces can result in recombination and injection of minority carriers24 when the field emission electrons are supplied via an interface conduction channel.25,26 Previously, Aucoating on Si substrates has been proved to enhance the EFE properties of MCD,27 UNCD,21,28 and diamond-like-carbon29 films due to the diffusion of Au into the interface layer; but, whether the diffusion of Au into Au-ion implanted UNCD films will also enhance the transport of electrons across the film to substrate interface and the mechanism behind such an enhancement is not clear. Here, we report the utilization of a Au-Si eutectic layer on Si-substrates to enhance the transport of electrons from the substrates to the diamond films that resulted in the

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C 2015 AIP Publishing LLC V

[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP: 193.190.11.206 On: Wed, 26 Aug 2015 14:06:59

085306-2

Sankaran et al.

improved EFE properties for Au-ion implanted UNCD films grown on Si substrates. The microstructural modifications of these films were investigated in detail using transmission electron microscopy (TEM), and the key role played by the Au-Si eutectic layer to enhance the electrical conductivity and the EFE properties of Au-ion implanted UNCD films is discussed. II. EXPERIMENTAL DETAILS

In this work, 100 nm Au was deposited on n-type Si substrates by dc sputter deposition (Helix Co., Taiwan) using a power of 50 W in Ar partial pressure of 5 mTorr. Prior to Au deposition, a thin layer of Cr (5 nm) was deposited on Si using the same deposition system to achieve strong adhesion of Au on Si. The bare Si and Au-coated Si (Au-Si) substrates were ultrasonicated for 45 min in methanol solution containing the mixture of diamond powder (about 4 nm in size) and Ti powder (SIGMA-ALDRICH) (365 mesh) to facilitate the nucleation process. The Au coatings adhered strongly on the Si substrates even after the ultrasonication process due to the presence of the Cr-interlayer between Au and Si. UNCD films were deposited by microwave plasma enhanced chemical vapor deposition (MPECVD; IPLAS, Cyrannus) using CH4(1%)/Ar(99%) gas at 1200 W and 120 Torr for 3 h. The growth process of UNCD films on bare Si and Au-Si substrates was carried out without any intentional heating of the substrate. The low growth temperature of

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