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欧姆接触制造用聚焦离子束技术和电气特性的半导体层的纳米结构

Published: December 05, 2015
doi:
10.3791/53200
, , ,
1Graduate Institute of Applied Science and Technology,National Taiwan University of Science and Technology, 2Department of Electronic Engineering,National Taiwan University of Science and Technology

Summary

We describe the approaches for the device fabrication and electrical characterization of molybdenum diselenide (MoSe2) layer semiconductor nanostructures with different thicknesses. In addition, the fabrication of ohmic contacts for MoSe2-layer nanocrystals by the focused-ion beam deposition method using platinum (Pt) as a contact metal is described.

Abstract

层半导体用容易加工的二维（2D）结构表现出间接到直接带隙跃迁和优越的晶体管性能，这表明用于下一代超薄和灵活的光子和电子设备的发展的新方向。增强发光量子效率得到了广泛的观察，这些原子薄的二维晶体。然而，除了量子限制厚度或甚至微米尺度尺寸效应预计不会与很少被观察到。在这项研究中，钼二硒化物（摩西2）层晶体纳米被制造为两个或四个终端设备的厚度范围的6-2,700。欧姆接触的形成，成功通过使用铂（Pt）作为接触金属的聚焦离子束（FIB）沉积方法来实现的。层的晶体具有各种厚度通过简单的机械剥离通过使用切割带制备。电流 – 电压曲线measuremenTS进行，以确定层纳米晶体的电导率值。此外，高分辨率透射电子显微镜，选择区域电子衍射仪和能量色散X射线光谱进行了表征的金属-半导体的FIB-制造MOSE 2设备的接触界面。施加的方法之后，在很宽的厚度范围为摩西2 -layer半导体实质厚度依赖性的导电性进行了观察。电导率增加从4.6以上两个数量级到1500Ω – 1厘米– 1，从2700至6nm的降低的厚度。另外，温度依赖性的导电性表明，薄摩西2多层膜表现出与3.5-8.5兆电子伏的活化能，其中比大部分（36-38兆电子伏）小得多相当弱半导体行为。普罗巴竹叶提取表面主导的运输性质和在摩西2的高表面电子浓度的存在下提出。类似的结果可以为其他层的半导体材料，例如二硫化钼和WS 2来获得。

Introduction

过渡金属二硫属化物（TMDS），诸如二硫化钼，摩西2，WS 2，和WSE 2，有一个有趣的二维（2D）层结构和半导体性能1-3。科学家最近发现， 二硫化钼的单层结构示出了由于量子限制效应基本上提高发光效率。的新的直接带隙半导体材料的发现已引起大量关注4-7。此外，TMDS的易剥离层结构是研究二维的材料的基本性质的一个很好的平台。不像无带隙的金属石墨烯，TMDS具有固有半导体的特性，并具有在1-2电子伏特1,3,8的范围内的带隙。 TMDS 9的三元化合物和这些化合物与石墨烯的一体化的可能性的2D结构提供了前所未有的奥普ortunity开发超薄和柔性电子器件。

不像石墨烯，2D TMDS的室温的电子迁移率的值是在中等水平（1-200厘米2 V – 1秒- 1 二硫化钼十月十七号 ;大约50厘米2 V – 1秒- 1 MOSE 2 18 ）。石墨烯的最优迁移率值已被报道为高于10,000个厘米2 V – 1秒 – 1 19-21日然而，半导体的TMD单层表现出优良的器件性能。例如， 二硫化钼和摩西2单层或多层场效应晶体管显示出极高的开/关比，高达10 6 -10 9 10,12,17,18,22。因此，关键的是要了解的2D TMDS和的基本电性能的IR散装物料。

然而，该层材料的电性能的研究已部分地是由于在形成在层的结晶良好的欧姆接触的困难的阻碍。三种方法，阴影掩模沉积（SMD）23，电子束光刻（EBL）24,25，和聚焦离子束（FIB）沉积，26,27已被用于形成纳米材料电触头。因为贴片通常涉及使用一个铜栅作为掩模，两个接触电极之间的间隔是大多大于10μm。不同于EBL和FIB的沉积，而没有目标或选择在SMD方法的兴趣进行纳米材料在基片上的电极阵列的金属沉积。这种方法不能保证金属图案被正确地沉积在纳米材料个体作为电极。在SMD方法的结果具有偶然性的因素。所述EBL和FIB淀积方法在所使用的扫描电子显微镜（SEM）的系统;纳米材料可以直接观察和选择用于电极沉积。此外，EBL可以用来容易地制造金属电极与线宽度和接触电极间隔小于100nm。然而，残留的抗蚀剂上期间光刻不可避免地导致在金属电极和纳米材料之间的绝缘层的形成左纳米材料表面上。因此，EBL导致高接触电阻。

通过FIB淀积电极制造的主要优点是，它会导致低的接触电阻。因为金属沉积是由有机金属前体的分解通过使用离子束在所规定区域进行的，金属的沉积和离子轰击同时发生。这可能会破坏金属 – 半导体界面和防止的肖特基接触的形成。离子轰击也可以消除表面杂质如烃的丝宝和原生氧化物，从而降低接触电阻。通过FIB沉积欧姆接触的制造已经证明了不同的纳米材料27-29。此外，在FIB淀积方法的整个制造过程比在EBL简单。

作为半导体层通常显示高度各向异性导电，在层与层方向的电导率是几个数量级小于在面内方向30,31更低。这个特性增加制造欧姆接触，并确定导电率的难度。因此，在此研究中，FIB沉积用于研究层半导体纳米结构的电性能。

Protocol

莫塞的2层晶体（见第1步中的图1）1.结构表征 X射线衍射测量程序装入摩西2层晶体（具有5×5×0.1-10×10×0.5毫米3大小范围）或晶体粉末在支架上（该混合有石英粉末和粘合剂，并涂抹在载玻片）。 按保持器由一个载玻片以确保层晶面平行于托面。 样品架装载到衍射仪。 关闭衍射仪的门。 因此校准光束线制造商的说明。 输入?…

Representative Results

纳米材料层具有不同厚度的电导（G）和电导率（σ）的所确定的值是高度依赖于电触点的质量。的FIB-沉积制造的双端摩西的欧姆触点 2的设备的特征在于测量电流-电压（I – V）的曲线。室温我 – V曲线为具有不同厚度的二端摩西2纳米片的设备示于图2a。 该 I – V曲线遵循线性关系。这证实了摩西2器件的欧姆?…

Discussion

准确测定的σ值的和它在该层中纳米晶体尺寸的依赖是高度依赖于电触点的质量。用于金属电极沉积的FIB沉积法在整个研究过程中发挥了至关重要的作用。根据电气，结构和组成分析，稳定和高度可再现的欧姆触点的制造中，使用FIB淀积法，在摩西2或二硫化钼的设备提供了便利的非晶态导电性合金的铂金属和摩西2之间形成层的半导体。有缺陷的合金结构在摩西2…

Declarações

The authors have nothing to disclose.

Acknowledgements

RSC thanks the support of the National Science Council (NSC) of Taiwan under Project NSC 102-2112-M-011-001-MY3. YSH acknowledges the support of the NSC of Taiwan under Project NSC 100-2112-M-011-001-MY3.

Materials

HRTEM&SEAD FEI (http://www.fei.com/products/tem/tecnai-g2/?ind=MS) Tecnai™ G2 F-20
SEM&EDS HITACHI (http://www.hitachi-hitec.com/global/em/sem/sem_index.html) S-3000H
FIB FEI (http://www.fei.com/products/dualbeam/versa-3d/) Quanta 3D FEG
AFM BRUKER (http://www.bruker.com/products/surface-analysis/atomic-force-microscopy/dimension-icon/overview.html) Dimension Icon
XRD Bruker (https://www.bruker.com/products/x-ray-diffraction-and-elemental-analysis/x-ray-diffraction/d2-phaser/learn-more.html) D2 PHASER X-ray Diffractometer
Raman Renishaw (http://www.renishaw.com/en/renishaw-enhancing-efficiency-in-manufacturing-and-healthcare–1030) inVia Raman microscope system
Keithley-4200 keithley (http://www.keithley.com.tw/products/dcac/currentvoltage/4200scs) 4200scs
ultralow current leakage cryogenic probe station Lakeshore Cryotronics (http://www.lakeshore.com/) TTP4
copper foil tape 3M (http://solutions.3m.com/wps/portal/3M/en_US/Electronics_NA/Electronics/Products/Product_Catalog/~/3M-Copper-Foil-Shielding-Tape-1182?N=4294300025+5153906&&Nr=AND%28hrcy_id%3A8CQ27CX0WMgs_F2LMWMM6M6_N2RL3FHWVK_GPD0K8BC31gv%29&rt=d) 1182
Ag paste Well-Being (http://www.gredmann.com/about.htm) MS-5000
Cu wire Guv Team (http://www.guvteam.com) ICUD0D01N
dicing tape Nexteck (http://www.nexteck-corp.com/tw/product-tape.html) contact vender
mica Centenary Electronic (http://100y.diytrade.com/sdp/307600/4/pl-1175840/0.html) T0-200
enamel wire Light-Tech Electronics (http://www.ltc.com.tw/product_info.php/products_id/57631) S.W.G #38
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Tags

Keywords: Ohmic ContactFocused-ion BeamLayer SemiconductorMoSe2Electrical CharacterizationThickness-dependent ConductivitySurface-dominant TransportTwo-dimensional Materials
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Chen, R., Tang, C., Shen, W., Huang, Y. Ohmic Contact Fabrication Using a Focused-ion Beam Technique and Electrical Characterization for Layer Semiconductor Nanostructures. J. Vis. Exp. (106), e53200, doi:10.3791/53200 (2015).
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