Schottky Barrier Height Modulation Using Interface Characteristics of

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Functional Inorganic Materials and Devices

Schottky Barrier Height Modulation Using Interface Characteristics of MoS Interlayer for Contact Structure 2

Seung-Hwan Kim, Kyu Hyun Han, Gwang-Sik Kim, Seung-Geun Kim, Jiyoung Kim, and Hyun-Yong Yu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b18860 • Publication Date (Web): 21 Jan 2019 Downloaded from http://pubs.acs.org on January 24, 2019

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ACS Applied Materials & Interfaces

Schottky Barrier Height Modulation Using Interface Characteristics of MoS2 Interlayer for Contact Structure Seung-Hwan Kim,1 Kyu Hyun Han,1 Gwang-Sik Kim,1 Seung-Geun Kim,2 Jiyoung Kim,3 and Hyun-Yong Yu1,2,* 1School

of Electrical Engineering, Korea University, Seoul 02841, Korea

2Department

of Semiconductor Systems Engineering, Korea University, Seoul 02841, Korea

3Department

of Materials Science and Engineering, The University of Texas at Dallas,

Richardson, Texas 75080, United States

*corresponding author: [email protected]

KEYWORDS: Schottky barrier height, Fermi-level pinning, molybdenum disulfide, metalinduced gap state, III–V semiconductor, germanium, source/drain contact.

ACS Paragon Plus Environment

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ABSTRACT

Schottky barrier height (SBH) engineering of contact structures is a primary challenge to achieve high performance in nanoelectronics and optoelectronics applications. Although the SBH can be lowered

through

various

Fermi-level

(FL)

unpinning

techniques,

such

as

a

metal/interlayer/semiconductor (MIS) structure, the room for contact metal adoption is too narrow because the work function of the contact metals should be near conduction band edge (CBE) of the semiconductor to achieve low SBH. Here, we propose a novel structure, the metal/transition metal dichalcogenide (TMD)/semiconductor (MTS) structure, as a contact structure that can effectively lower the SBH with wide room for contact metal adoption. A perpendicularly integrated molybdenum disulfide (MoS2) interlayer effectively alleviates the FL pinning by reducing metal-induced gap states (MIGS) at the MoS2/semiconductor interface. Additionally, it can induce strong FL pinning of the contact metals near its CBE at the metal/MoS2 interface. The technique using the FL pinning and unpinning at the metal/MoS2/semiconductor interfaces is firstly introduced in the MIS scheme for allowing the use of various contact metals. Consequently, significant reductions of the SBH from 0.48 eV to 0.12 eV for GaAs and from 0.56 eV to 0.10 eV for Ge are achieved with several different contact metals. This work significantly reduces the dependence on contact metals with the lowest SBH and proposes a new way of overcoming current severe contact issues for future nanoelectronics and optoelectronics applications.


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1. INTRODUCTION As silicon-based nanoelectronics have been scaled down, diverse problems inducing severe device performance degradation have emerged due to these physical limits.1,2 Some alternatives, III–V compound semiconductors and germanium (Ge), have been widely studied because of their excellent electrical properties, which are promising for a new generation of nanoelectronic.2-4 Specially, two-dimensional (2D) layered materials have recently been reported for their attractive properties.5-10 However, even those promising materials have serious problems in the source/drain (S/D) contact because the effect of severe Fermi-level (FL) pinning has impeded their promise for metal contact.11-14 Although FL unpinning techniques, such as metal/interlayer/semiconductor (MIS) structures and 2D-based heterostructures, have been presented, they cannot effectively optimize the Schottky barrier height (SBH), a key factor in determining the contact resistance.15-19 Because the increased contact resistance by scaled regions, accounting for the majority of the total resistance, induces drastic degradation of device performance, finding new strategies is essential to further improve device performance.20,21 Most contacts have severe FL pinning at the metal/semiconductor (MS) interfaces, disturbing the control of their S/D contact characteristics.11-14 The SBH is fixed regardless of the contact metal work function due to strong FL pinning to the charge neutrality levels (CNL) of semiconductors. Because the CNLs of GaAs and Ge are 0.8 eV22 and 0.55 eV23 below each conduction band edge (CBE), large SBHs are formed even though contact metals with small work functions, such as Ti, are adopted. The severe FL pinning at the MS interface is mainly induced by metal-induced gap states (MIGS) in the bandgap of the semiconductor, as shown in Figure 1a.24 Wide-bandgap materials, such as zinc oxide (ZnO), titanium dioxide (TiO2), and aluminum oxide (Al2O3), are mostly applied to the MIS structure as an interlayer (IL) to


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effectively reduce the MIGS at the semiconductor surface.3,4,11-13,16 Even if the FL is fully unpinned at the IL/semiconductor interface by reducing the MIGS, the low SBH is only achieved with small work function contact metals because the FL at the metal/IL interface is almost unpinned due to the wide bandgap of the IL, as shown in Figure 1b. Thus, the room for contact metal adoption of the MIS contact becomes significantly narrow, which means that only a few metals with small work functions should be adopted as contact metals without any consideration for other properties of the metals, such as cost, fabrication compatibility, and conductivity. To allow the use of various contact metals with low SBH, not only is the FL at the IL/semiconductor interface effectively unpinned, but also the FL of the metal should be strongly pinned to CBE of the IL. Therefore, it is necessary to seek alternative ILs that can better enable contact metal adoption and achieve very low SBH for the extensive research of various nanoelectronics applications. Herein, we introduce a new technique by using the metal/transition metal dichalcogenides (TMDs)/semiconductor (MTS) contacts with molybdenum disulfide (MoS2) IL on the n-GaAs and the n-Ge to achieve low SBH, despite values of the contact metal work function. The SBH modulation on n-GaAs and n-Ge substrates by controlling the MoS2 IL thickness is well demonstrated. Furthermore, the SBH reduction of the MTS contact is investigated by comparing to typical MIS contacts adopting widely used material, ZnO. In particular, three different metals, Ti, Cu, and Pt, are used as contact metals to verify the effective reduction in the SBH of the MTS contacts, regardless of their work function values. Furthermore, we theoretically analyzed the MTS contacts with respect to the MoS2 thickness, in comparison with calculated results from universal MIS model. Our work demonstrates the importance of the reduction in contact metal


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dependency and low SBH achievement in next-generation S/D contact techniques for diverse nanoelectronics applications by using the proposed MTS contacts.


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2. RESULTS AND DISCUSSION 2.1 Structures of MTS Contacts. Figure 2a presents a three-dimensional (3D) schematic diagrams of our MTS structure. To define the same top contact region and avoid direct contact between the metal and semiconductor, a silicon dioxide (SiO2) IL dielectric (ILD) was deposited on the MoS2/n-GaAs and n-Ge heterostructures. Because the MoS2 ILs were exfoliated on the semiconductor surface, it is difficult to analyze the electrical characteristics as a function of MoS2 IL thickness through only the exfoliation process. Therefore, an SF6 plasma-etching process using inductively coupled plasma-reactive ion etching (ICP-RIE) were used to modulate MoS2 IL thickness. The details of the fabrication process flow are shown in the Supporting Information. A cross-sectional schematic diagram of the MTS structure is shown in Figure 2b. The current–voltage (I–V) characteristics are vertically measured to verify the reverse current, which can indicate the FL pinning characteristics, and to extract the SBHs of the MTS structures. Top-view optical microscopy images exhibit the active regions of the Au/Ti/MoS2/n-GaAs and n-Ge contacts, as shown in Figure 2c and e, respectively. Transmission electron microscopy (TEM) images of the MTS structure, as shown in Figure 2d and f, demonstrate the uniformly etched MoS2 ILs on the GaAs and Ge substrates, respectively. 2.2 Effect of SBH Lowering Using MoS2 IL on GaAs Substrate. Figure 3a, b, and c show the band diagrams of the Ti/n-GaAs, the Ti/thin MoS2/n-GaAs and the Ti/thick MoS2/n-GaAs structures, respectively. When the metal directly contacts the GaAs surface, as shown in Figure 3a, a large SBH is induced by several causes that induce FL pinning, such as the MIGS, dipole, and interface states.25-28 The main cause is the MIGS induced by electron penetration from the metal to the semiconductor surface. To lower the SBH by reducing the MIGS at the GaAs surface, MoS2 ILs with various thicknesses are inserted between the metal and GaAs. Figure 3b


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shows the MTS structure with thin MoS2, which cannot sufficiently reduce the MIGS, so the FL is not fully unpinned. The decay of the electron wavefunction depends exponentially on the bandgap of the dielectric material.29,30 This is why wide-bandgap materials have been widely used as MIS contacts. However, because the bandgap of the multi-layered MoS2 is 1.2 eV,31 the MIGS cannot be fully alleviated with a thin MoS2 IL. Therefore, a thicker MoS2 IL, rather than a wide-bandgap material, is needed to achieve low SBH, as shown in Figure 3c. It is well known that the metal FL is attached near the CBE of the MoS2, regardless of the work function.10,32 Thus, the FL of Ti is fixed near the CBE of the MoS2, which indicates the MoS2 IL induces nearly zero barrier at the metal/IL interface, as shown in Figure 3b and c. Finally, the near-zero barrier between the metal and GaAs is formed and provides ultralow tunneling resistance. Figure 3d exhibits the current density–voltage (J–V) characteristics of the MTS contacts on the n-GaAs. The MS contact and the MTS contacts with thin MoS2 IL (< 10 nm) show rectifying characteristics due to their large SBH. As mentioned above, the MIGS at the GaAs surface with thin MoS2 IL cannot be fully alleviated due to narrow band gap of MoS2. The MTS contact with 20-nm-thick MoS2 IL exhibits Ohmic behavior and the highest reverse current density, which indicates that the SBH of the MTS contact is effectively lowered. The electrical properties of the MTS contact with a thicker MoS2 IL than 20 nm are slightly reduced, because the series resistance between the metal and n-GaAs is increased as the IL thickness increases. In addition, the contact behavior transition from the Ohmic to Schottky characteristic is observed for the MTS contacts with 42-nm- and 48-nm-thick MoS2 IL, which indicates that their SBHs are increased. Figure 3e shows the reverse current densities at -1 V and the extracted electron SBHs of the MTS contacts on n-GaAs. Although the work function value of Ti is 4.33 eV, which indicates that the ideal SBH of the MS contact is 0.26 eV, the extracted SBH is 0.48 eV due to


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the effect of FL pinning. When the MoS2 IL is inserted between Ti and n-GaAs, the SBH values of the MTS contacts are reduced as the thickness of the MoS2 IL increases. The MTS contact with 20-nm-thick MoS2 IL presents the lowest SBH value (~0.12 eV). As the thickness of the MoS2 IL further increases beyond the optimum thickness, a turn-around effect is observed. The capacitance of the IL is reduced, because the MoS2 IL thickness increases, whereas the total charge at the MoS2 IL/semiconductor interface is almost constant. As a result, the increased total dipole voltage induces an increase in the SBH, whose details are shown in the Supporting Information.33 It is also confirmed that the SBH values of the MTS contacts are inversely proportional to their reverse current densities. Moreover, the vertical transport properties of the MoS2 IL are shown in the Supporting Information. Because it is known that the MoS2 has poor vertical transport properties due to weak van der Waals interaction, thick MoS2 ILs can degrade the conductivities of the MTS contacts. However, it is well demonstrated that the series resistance of the MoS2 IL thickness much less affects than the resistance of the SBH as shown in the Supporting Information. Although the thick MoS2 ILs (~ 6, 12, 20, and 58 nm) are inserted between the metals, their current levels are almost same with that of the M-M structure. Figure 3f shows the Raman spectra of the MoS2/GaAs heterostructures with respect to the MoS2 IL thickness, where the measured area is the active region between the metal contacts, as shown in Figure 2c. The Raman peaks of all the MTS contacts are observed at near 382 and 406 cm-1, related to the E12g and A1g mode, respectively, which indicate that the MoS2 ILs used in this work are bulk.34,35 The thicknesses of the MoS2 ILs are modulated by the plasma-etching process to obtain the optimum electrical characteristics. It can be possible that the 1T-2H phase transition occurs after plasma-etching process.36 However, the phase transition does not happen in this work, because signature peaks of the 1T MoS2, J1, J2, and J3, are not observed near 167 cm-1, 227


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cm-1, and 334 cm-1, respectively, as shown in Figure 3f.37,38 Moreover, the difference in the electrical characteristics between the MTS contacts with and without the etching process is confirmed, as shown in the Supporting Information. 2.3 Effect of SBH Lowering Using MoS2 IL on Ge Substrate. Figure 4a, b, and c show the band diagrams of the Ti/n-Ge, the Ti/thin MoS2/n-Ge, and the Ti/thick MoS2/n-Ge contacts. It is well known that Ge has severe FL pinning and that its CNL is near the valence band edge (VBE).23 Therefore, a large SBH is induced for the Ti/n-Ge contact. When a thin MoS2 IL is inserted between the Ti and the n-Ge, the SBH of the MTS contact is slightly lowered. However, similar to the MTS contact on GaAs, a thick MoS2 IL is needed to sufficiently reduce the MIGS at the Ge surface. The J–V characteristics of the MTS contact on Ge are shown in Figure 4d. Schottky behavior is observed for the MS and MTS contacts with thin MoS2 ILs (< 10 nm). However, the MTS contacts with 17-nm-, 20-nm-, and 25-nm-thick MoS2 ILs exhibit Ohmic behavior because the SBH is lowered by MIGS reduction. The MTS contacts with thicker MoS2 ILs than 30 nm present degradation of the current densities due to their high series resistance and increased SBH. The inverse proportion between the reverse current densities and the extracted electron SBHs of the MTS contacts on the n-Ge is shown in Figure 4e. For the MS contact, it is confirmed that the FL is strongly pinned to the CNL (0.55 eV) of Ge, which indicates that a large SBH is induced. The optimum SBH value (~0.10 eV) is observed for ~17-nm-thick MoS2 IL. In contrast to the MTS contacts on GaAs, the SBHs of those on Ge are slightly increased because Ge has zero conduction band offset (CBO) to MoS2, which induces higher tunneling probability than GaAs. Ge also generally has a low interface state density, which yields little increase in the total dipole voltage at the MoS2/n-Ge interface.33 Figure 4f shows the Raman spectra of the MoS2/Ge heterostructures as a function of MoS2 IL thickness. The Raman peaks of the MoS2 ILs


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are observed near 382 and 406 cm-1, related to the E12g and A1g mode, respectively. The Raman peaks of Ge are also verified near 301 cm-1, and their intensities are reduced as the MoS2 IL thickness increases. For MoS2 (43 nm)/Ge heterostructure, the Raman peak of Ge is not observed due to the thick MoS2 IL. The phase transition of the MoS2 IL also is not observed for the MTS contacts on the Ge substrate. 2.4 Contact Metal Dependency on SBH Modulation. To verify the SBH difference of the MTS contacts with respect to contact metal work function, three different contact metals, Ti (4.33 eV), Cu (4.7 eV), and Pt (5.12 eV), are used as the MTS contacts. Figure 5a, b, and c show the band diagrams of the MS, MIS, and MTS contacts on GaAs with three different contact metals, which demonstrate the effects of the FL pinning and SBH lowering. First, the SBH difference between the three different contact metals for the MS contact is very small, as shown in Figure 5a, because a large amount of the MIGS at the GaAs surface induces strong FL pinning. Thus, all FLs of the three contact metals are attached to near the CNL of GaAs. However, for the MIS contact, a thin IL can effectively unpin the FLs by reducing the MIGS at the semiconductor surface. Although the MIS contact can achieve effective FL unpinning, the SBH significantly depends on the work function value of the contact metal, as shown in Figure 5b. Because the effect of the FL pinning at the metal/IL interface is very weak due to wide bandgap of the ILs, the SBH value changes according to the work function value of contact metal. When the Ti (4.33 eV) and Pt (5.12 eV) contact metals are used for the MIS contact while assuming a fully unpinned condition, the value of the SBHTi-MIS is ~0.26 eV (|𝜒𝐺𝑎𝐴𝑠 ― Φ𝑇𝑖|) and the value of the SBHPt-MIS is ~1.05 eV (|𝜒𝐺𝑎𝐴𝑠 ― Φ𝑃𝑡|). Therefore, to achieve further reduction of the SBH value than 0.26 eV, a contact metal with a lower work function value than Ti must be used. As a result, the room for contact metal adoption of the conventional MIS contact becomes


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extremely narrow. To solve this problem, the material, which can induce strong FL pinning at the metal/IL interface and effective FL unpinning at the IL/semiconductor interface, should be applied as IL, and the MoS2 fulfills these conditions as shown in Figure 5c. When the metals directly contact the MoS2 surface, the FLs of the metals are strongly pinned to near its CBE.32 Furthermore, the MoS2 effectively unpins the FL at the MoS2/semiconductor interface by reducing the MIGS. Thus, this MTS contact can achieve low SBH with various contact metals. Figure 5d shows the SBH vs. MoS2 IL thickness with three different contact metals for GaAs. The thicknesses of the MoS2 ILs are modulated by the etching process to confirm the contact metal dependency on SBH modulation under the same conditions. It is verified that there are few differences among the MTS contacts using three different contact metals with similar MoS2 ILs thicknesses, which means the electrical properties of the MTS contacts are not affected by the work function values of the contact metals. These results indicate FLs of the contact metals are strongly pinned to near CNL of the MoS2, so that low SBH is achieved with various contact metals. The results of the SBH modulation are in good agreement with the strong FL pinning to near CBE of the MoS2 IL, as shown in band diagrams of Figure 3, 4, and 5. The SBHs of the MTS contacts on Ge with three different contact metals are shown in the Supporting Information. Also, few differences of the SBH values among the MTS contacts on Ge using three different contact metals are observed. Figure 5e shows the SBH values of the metal/nGaAs, metal/ZnO (~3 nm)/n-GaAs, and metal/MoS2 (~20 nm)/n-GaAs contacts for differing contact metal work functions. The slope of each structure corresponds with the pinning factor (S), which indicates the severity of the FL pinning.24,32,39 A maximum value of dimensionless S is 1, meaning ideal contact and a minimum value of that is 0, meaning perfect FL pinning. The S values of the MS, MIS, and MTS contacts are ~0.06, ~0.54, and ~0.001, respectively. Because


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the S value of the MS contact is near 0 and its SBH is large, the Ohmic contact cannot be formed using any contact metal for the MS contact. In case of the MIS contacts, although the S value is very high because of the FL unpinning effect at the ZnO/GaAs interface, their SBHs heavily depend on the work function value of the contact metals. However, the S value of the MTS contacts exhibits almost 0 with the lowest SBH values, meaning the SBH can be significantly lowered with wide room for contact metal adoption, caused by the strong FL pinning at the metal/MoS2 interface and effective FL unpinning at the MoS2/GaAs interface. The comparison of the current densities between the MTS and the MIS contacts is shown in Supporting Information. 2.5 Analytical Study of MTS Contact Based on MIS Model. To analytically study and prove physical validity of the MTS contacts, calculated SBH values are compared to our experimental values based on the MIS model using MoS2 properties as IL.40-42 Figure 6a shows the SBHs of the MTS contacts obtained by the experimental results (symbols) and the MIS model (lines) as a function of the MoS2 IL thickness. The pinning factor of the MTS contacts (SMTS) is expressed as follows:30 1

𝑆𝑀𝑇𝑆 = 1+

, 𝑞2𝐷𝑖𝑡(𝜀𝐼𝐿 ∙ 𝛿 + 𝜀𝑆 ∙ 𝑑𝐼𝐿)

(1)

𝜀𝑆 ∙ 𝜀𝐼𝐿

where Dit is the total interface states density, composed of the MIGS (intrinsic) and the interface trap states (extrinsic); q is the electron charge; dIL is MoS2 IL thickness, εIL is dielectric constant of the MoS2 IL, and εS and δ are dielectric constant at the semiconductor interface and decay length of the electron wave function, respectively. Using the SMTS values via eq 1, 𝜓𝑆, band bending of the semiconductor, is calculated, which is related to the SBH calculation. The SBH of MTS contact is calculated as follows:39


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Φ𝐵𝑛 = Φ𝑆 ― 𝜒𝑆 ― 𝜓𝑆,

(2)

where ΦS is the semiconductor work function and χS is electron affinity of the semiconductor. Details of the MIS models are given in the Supporting Information. The values of the contact metals work function are used as effective work function values, which are 4.05 eV for Ti, 4.072 eV for Cu, and 4.087 eV for Pt, because the FLs of the contact metals are strongly pinned to near CBE of the MoS2 IL when the metal/MoS2 IL interface is formed.32 The calculated SBH values of the MTS contacts well correspond to the experimental results as shown in Figure 6a. The comparison plot between the measured and the calculated SBH of the MTS contacts on Ge is also shown in the Supporting Information. Moreover, to compare the effect of SBH lowering using the MIS contact with that using the MTS contact, the SBHs of the Ti/ZnO/n-GaAs contacts are also obtained by electrical measurement (symbol) and MIS model (line), as shown in Figure 6b. Four different ZnO IL thicknesses, 1, 2, 3, and 4 nm, are deposited on GaAs to verify optimum SBHs of the MIS contacts. Optimum SBH of the MIS contact is exhibited with the 3nm-thick ZnO IL and its value is 0.25 eV. Although the MoS2 IL for optimum SBH is thick, optimum SBH value of the MTS contact is significantly lower than that of the MIS contact, which shows a good agreement with our discussion.


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3. CONCLUSIONS We have demonstrated the novel MTS contact structures on GaAs and Ge to achieve the lowest SBH with wide room for contact metal adoption. Thick MoS2 IL, near 20 nm, can make the FL of the contact metal strongly pinned to near its CBE at the metal/MoS2 interface and effectively induce FL unpinning at the MoS2/GaAs and Ge interfaces. These results indicate low SBH can be achieved and values of the contact metal work function hardly affect the electrical properties, which cannot be obtained by conventional MIS contacts. The lowest SBH for the MTS contact on GaAs, 0.12 eV, is achieved, whereas that for the MIS contact with ZnO IL is 0.25 eV. Also, the SBH of Ge is decreased from 0.56 eV for the MS contact to 0.10 eV for the MTS contact. Furthermore, few differences of the SBH values among the three different contact metals are observed by inserting the MoS2 IL on both GaAs and Ge. The physical validity of the proposed structure is also investigated by comparing experimentally extracted SBH values with those calculated by the MIS model. The proposed structure, well applying the interface characteristics of the MoS2 IL, can be a new technique for solving serious contact issues and a promising contact scheme for future nanoelectronics application.


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4. METHODS 4.1. MTS and MIS Contacts Fabrication. The Si-doped GaAs (Nd = 4 × 1017 cm–3) and the As-doped Ge (Nd = 1 × 1015 cm–3) were cleaned with acetone, 2-propanol, and deionized water. The GaAs substrate was cleaned with 20% HCl solution and Ge substrate was cleaned with 2% HF solution to remove each native oxide. The MoS2 flakes were immediately transferred onto the GaAs and Ge substrates by a polydimethylsiloxane (PDMS) stamp. The active region was defined by using patterned SiO2 ILD to form same area of the MTS contacts. The MoS2 IL thickness was controlled by using SF6 plasma, which is created under source power of 50 W and bias power of 15 W with SF6 flow rate of 20 sccm and plasma pressure of 50 mTorr in the ICPRIE chamber. To form the MIS contact, an atomic layer deposition (ALD) was used to deposit ZnO on GaAs. The ZnO IL was formed by using a diethyl zinc (DEZ) precursor with an H2O gas reactant under a process temperature of 150 °C. The Au/Ti, Cu, and Pt contacts were deposited by electron-beam evaporation. 4.2. Electrical Characterization. The J–V characteristics of the MS, the MIS, and the MTS contacts were measured by electrical measurement setup (Keithley 4200-SCS). The SBH values are extracted by using temperature-dependent forward-current characterization, detailed in the Supporting Information. 4.3. Raman and HR-TEM analyses. Raman spectra were obtained by a Raman microscopic system with a 532-nm laser, whose spot size is ~1 μm in diameter. A focused ion beam (FIB) milling process (Nova 200, FEI) were implemented for preparing the TEM specimen. The MTS structures on GaAs and Ge were scanned by a field emission TEM (JEM-2100F, JEOL LTD.) at 200 kV.


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ASSOCIATED CONTENT Supporting Information Schematic illustration and fabrication process flow of the MTS contact, Schematic and band diagram to explain why the SBH increases beyond optimum IL thickness, J-V characteristics of the M-M and M-I-M structures to verify the vertical transport properties of the MoS2 IL, J–V characteristics of the Ti/Etched-MoS2 (10 nm)/n-GaAs and the Ti/As-transferred-MoS2 (10 nm)/n-GaAs contacts, Extracted SBH values of the MTS contact on the Ge with three different contact metals, J–V characteristics of the Ti/MoS2 (10 nm and 20 nm)/n-GaAs and Ti/ZnO (1, 2, 3, and 4 nm)/n-GaAs contacts, Extracted and calculated SBH values of the metal/MoS2/n-Ge contacts with three different contact metals, Calculation of the SBH using temperature dependent forward current characterization, Details of MIS model.

AUTHOR INFORMATION Corresponding Author Hyun-Yong Yu School of Electrical Engineering, Korea University, 145, Anam-ro, Seongbuk-gu, Seoul, 02841, Korea (E-mail: [email protected], Tel: +82-2-3290-4830, Fax: +82-2-921-0544). ACKNOWLEDGMENTS This work was supported in part by the Technology Innovation Program within the Ministry of Trade, Industry and Energy, Korea, under Grant 10052804, in part by the Basic Science


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Research Program within the Ministry of Science, ICT, and Future Planning through the National Research Foundation of Korea under Grant 2017R1A2B4006460, and in part by Samsung Electronics.


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Figure 1. Band diagrams of (a) the MS contact, which shows a large SBH regardless of the contact metal work function values, and (b) the MIS contacts, which show different SBHs with respect to the contact metal work function values.


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Figure 2. (a) 3D and (b) cross-sectional schematics of the MTS contacts. (c) Top-view optical microscopy image of the Au/Ti/MoS2/n-GaAs contact and (d) cross-sectional TEM image of the Ti/MoS2/n-GaAs contact. (e) Top-view optical microscopy image of the Au/Ti/MoS2/n-Ge contact and (f) cross-sectional TEM image of the Ti/MoS2/n-Ge contact.


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Figure 3. Band diagrams of the (a) MS contact, (b) MTS contact with thin MoS2 IL, and (c) MTS contact with thick MoS2 IL on GaAs. (d) J–V characteristics of the MS and MTS contacts on GaAs. (e) Reverse current density at -1 V and extracted SBH values of the MTS contacts. (f) Raman spectra for the MoS2/n-GaAs heterostructures.


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Figure 4. Band diagrams of (a) the MS contact, (b) the MTS contact with thin MoS2 IL, and (c) the MTS contact with thick MoS2 IL on Ge. (d) J–V characteristics of the MS and the MTS contacts on Ge. (e) Reverse current density at -1 V and extracted SBH values of the MTS contacts. (f) Raman spectra for the MoS2/n-Ge heterostructures.


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Figure 5. Band diagrams of (a) metal/n-GaAs, (b) metal/ZnO/n-GaAs, and (c) metal/MoS2/nGaAs contacts with three different contact metals. (d) Extracted SBH values of the MTS contact on GaAs with three different contact metals as a function of MoS2 thickness. (e) Extracted SBH values of the metal/n-GaAs, metal/ZnO (~3 nm)/n-GaAs, and metal/MoS2 (~20 nm)/n-GaAs contacts for differing contact metal work functions.


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Figure 6. Extracted and calculated SBH values of (a) the metal/MoS2/n-GaAs contacts with three different contact metals and (b) the Ti/MoS2/n-GaAs and the Ti/ZnO/n-GaAs contacts.


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Table of Contents Graphic


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Schottky Barrier Height Modulation Using Interface Characteristics of

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