Alloyed 2D metal-semiconductor atomic layer junctions · Alloyed 2D metal-semiconductor atomic layer junctions ... because the MF is nonlinear filtering based on the order-static

1

Supporting Information

Alloyed 2D metal-semiconductor atomic layer

junctions

Ah Ra Kim1†, Yonghun Kim1,2†, Jaewook Nam3†, Hee-Suk Chung4, Dong Jae Kim3, Jung-Dae

Kwon1, Sang Won Park1, Jucheol Park5, Sun Young Choi1, Byoung Hun Lee2, Ji Hyeon Park6,

Kyu Hwan Lee7, Dong-Ho Kim1, Sung Mook Choi7, Pulickel M. Ajayan8*, Myung Gwan

Hahm9†* and Byungjin Cho1*

1Department of advanced Functional Thin Films, Surface Technology Division, Korea

Institute of Materials Science, 797 Changwondaero, Sungsan-Gu, Changwon, Gyeongnam

51508, Korea, 2School of Materials Science and Engineering, Gwanju Institute of Science

and Technology (GIST), 261 Cheomdan-gwangiro, Buk-Gu, Gwangju 61005, Republic of

Korea, 3School of Chemical Engineering, Sungkyunkwan University, 300 Cheongcheon-

dong, Suwon, Gyeonggi-do 16419, Republic of Korea, 4Jeonju Center, Korea Basic Science

Institute, Jeonju, Jeollabuk-do 54907, Republic of, 5Structure Analysis Group, Gyeongbuk

Science & Technology Promotion Center, Future Strategy Research Institute, 17

Cheomdangieop 1-ro, Sangdong-myeon, Gumi, Gyeongbuk 39171, Republic of Korea,

6Department of Electricity and Electronic Engineering, University of Ulsan, 93 Daehak-ro,

Nam-gu, Ulsan 44610, Republic of Korea, 7Electrochemistry Department, Surface

Technology Division, Korea Institute of Materials Science (KIMS), 797 Changwondaero,

Sungsan-gu, Changwon, Gyeongnam 51508, Republic of Korea, 8Department of Materials

2

Science and NanoEngineering, Rice University, 6100 Main Street, Houston, Texas 77005,

USA, 9School of Materials Science and Engineering, Inha University, 100 Inharo, Nam-Gu,

Incheon 22212, Korea

†These authors contributed equally to this work.

3

Materials and Methods CVD synthesis of semiconducting WSe2 and metallic NbSe2

Semiconducting WSe2 and metallic NbSe2 were synthesized with thermal chemical vapor

deposition (CVD) technique. First of all, using a thermal evaporator, WO3 and Nb2O5 thin

films were deposited onto SiO2/Si wafers for WSe2 and NbSe2, respectively. The thickness of

WO3 and Nb2O5 thin films is 3 and 5 nm, respectively. The metal oxide deposition samples

were placed on the center of furnace and evacuated with rotary pump. Then, the furnace was

heated to desired temperature (900 ~ 1000 °C) with 5% hydrogen-balanced Ar gas and at the

same time, selenium source on inlet of the furnace was heated to 500 °C to evaporate. After 1

hour selenization, the furnace was cooled down to room temperature. Cross-sectional images

of the resulting as-grown WSe2 and NbSe2 film are shown in Figure S1.

Synthesis of WxNb1-xSe2 transition layers

Firstly, WO3 thin film was deposited onto SiO2/Si wafer using thermal evaporator.

Secondly, for precise control of Nb element percentage on WxNb(1-x)Se2 transition layers,

Nb2O5 was deposited by plasma-enhanced atomic layer deposition (PEALD) technique.

Niobium pentafluoride (NbF5) was maintained at 50°C and supplied in Ar gas at a flow rate

of 50 sccm using a bubbling system. The stainless-steel feed line was heated to 100°C to

prevent precursor condensation in the line. In the mixed gas consisting of H2 and O2 gas, the

H2 gas served as the reducing agent for NbF5, the O2 gas served as the oxygen source of the

Nb2O5 thin films. The H2 gas flow rate of 100 sccm and O2 gas flow rate of 50 sccm were

supplied to the reaction chamber continuously. One deposition cycle is as follows: an

exposure to NbF5, a purge period, an exposure to mixed gas plasma, and another purge period.

A parallel-plate PEALD reactor was used for deposition. A wafer was loaded on the bottom

electrode, which was grounded. The upper electrode was a showerhead-type electrode to

4

distribute the reactant gas uniformly, and was operated at an electrical power of 150 W

coupled with a radio-frequency 13.56 MHz power generator capacitively. The thickness of

Nb2O5 thin film was controlled by the number of cycles of PEALD. The thicknesses of

Nb2O5 deposited by 1, 3, and 5 cycles were 0.8, 1.2, and 1.8 nm, respectively, as shown in

Figure S4 and Table S1. XPS measurements validated that the deposited oxide thin film has

the stoichiometry of Nb2O5 as shown in Figure S5. After the selenization process (the same as

CVD conditions for WSe2 and NbSe2 formation) of the Nb2O5-deposited WO3, WxNb1-xSe2

transition layer was obtained as shown in Figure S6 (the case of 1 cycle).

Process of image analysis

Figure S9 displays the sequence of processed image snapshots during the image analysis

performed in the manuscript. The algorithm flow chart (Figure S10) summarizes the overall

image analysis explained in what follows. Note that the boxes in the chart denote the

operations or methods and the labels above the arrows correspond to the resultant images in

Figure S9.

Figure S9A show the raw images of different cycles obtained from STEM with ADF. As

shown in Figure S9A, the image suffers not only from noise but also from non-uniform

background luminance. Here, the noise can be interpreted as random variations of intensity

superimposed on a gray-scale image; these variations are not associated with the objects in

the material under investigation. The non-uniform luminance yields images with uneven

contrasts. For example, the original gray scale image obtained after the 5 cycles of for the

Nb2O5 deposition in Figure S9A bright left and dark right parts.

To enhance the image, we applied two pre-processing methods: “median filtering (MF)”1

for eliminating the intensity variations and “morphological top-hat (MTH) operation”2 for

5

background luminance equalization. Note that the MF method tends to conserve the image

edges as well as not to cause blurring compared with linear filters such as the average filter,

because the MF is nonlinear filtering based on the order-static method.1 Herein, we used a

7×7 kernel in MF and disk-shaped structural elements with radii of 12 pixels in MTH. Figure

S9B shows the results for each cycle.

However, pixel intensities from the processed image cannot be used for the classification

of atoms directly. Furthermore, in this atomic scale image, the boundaries between the atoms

and the background cannot be determined easily. To overcome these difficulties, we enhance

the image by taking full advantage of the atomic lattice structure, which remains almost

regular even with the introduction of Nb, to detect the regions associated with the atoms.

This structural periodicity can be easily seen in the frequency domain. Figure S9C shows

center part of the Fourier spectrum, which includes low frequencies that is relative to outline

of the image. Herein, standard logarithmic intensity amplification1 is used to emphasize the

details. Due to the nearly periodic structure, the bright spots in the frequency domain, namely

the energy explosion spots, are located in grid-like patterns. Note that the coefficients of the

Fourier transform, or the intensities of the Fourier spectrum in Figure S9C, were estimated by

discrete Fourier transform (DFT).1 Therefore, these energy explosion spots can be interpreted

as the dominant frequencies or pattern in Figure S9B.

As explained in the main text, six or more energy explosion spots were chosen to enhance

intensities of the atoms. Since arrangement of atoms in original image (Figure S9A) has

hexagonal pattern, it can be enhanced if we choose dominant frequency like hexagonal as red

boxes in Figure S9C and then adding the inverse DFT (IDFT) of those patterns to the pre-

processed spatial domain image. Figure S9D show the extracted pattern from result of IDFT

of the spots, whose size is 5 by 5 pixels for each, in Figure S9C. The resulting enhanced

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image is shown in Figure S9E. The enhancement is done by adding 1.5 times pixel values of

IDFT images (Figure S9D) to the pre-processed images (Figure S9B).

It should be emphasized that the pixel values of the IDFT images ranges from negative to

positive ones. As a result, the difference between intensities of pixels associated with atoms

and background become larger by this enhancement, and the positions of atoms can be easily

recognized. Compare Figure S9A with Figure S9E.

For the 3 cycles and 5 cycles cases, blue boxes, whose size are also 5 by 5 pixels, are also

used to enhance the corresponding images 5 cycles in addition to red boxes. This additional

usage of explosion spots is due to the fact that the most of atoms in such cases are not bright

enough. Therefore, additional frequencies are helpful to enhance such images.

In this enhanced image, the regions can be detected by using the size-invariant circle

detection method (SICD) implemented in MATLAB built-in function “imfindcircles”.3 In

this study, the radii of the circles were set to 9 pixels (approximate sizes of atoms in the

image) and the sensitivity and edge threshold value were 0.99 and 0.1, respectively. Although

the SICD efficiently detects the regions, it is possible that their locations are slightly off from

the actual locations of atoms, which mainly due to severely blurred area or too weak

intensities. To correct the locations of the circles, we propose a correction algorithm. The

idea is to shift the location based on the pixel intensities of the original image. The algorithm

can be summarized as:

1. Select one of the circles detected using SICD,

2. Collect the pixels from the image in Figure S9B that are located inside the circles,

3. Sort the intensity values in the collected pixels and choose pixel coordinates that

rank above 70% in terms of the intensity,

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4. Evaluate the central points of the chosen pixels by averaging the coordinates of the

chosen pixels,

5. Move the circle to the evaluated center,

6. Repeat steps 2 to 4 for other circles obtained using SICD,

7. Iterate steps 1 to 5 5 times.

Here, we choose to collect intensity values inside the circles that rank above 70% and

perform five iterations, because this choice of parameters yielded reasonable results

comparing with the original images. The algorithm reasonably detects the approximated

positions of atoms as shown in Figure S9F.

Once the approximated positions are determined, the classification of atoms can be done

by considering the average intensity of the pixels inside the red circles. Here, a statistical

approach, the Otsu method4, was used to classify the atoms. The method evaluates optimal

intensity thresholds based on a given intensity histogram. In this study, a tri-class

segmentation was used. Pixels with intensity lower than the lowest threshold intensity and

higher than the highest threshold intensity were classified as background and W atoms,

respectively. Pixels with intensity in between those two threshold values were classified as

collections of Se and Nb atoms. Herein, we assigned the circle as W when average intensity

of circle is greater than 180. That is because oversaturated intensities may hamper to find

threshold value in Otsu method. Therefore, the threshold values are determined between 0 to

179.

After segmentation, classification of Nb and Se atoms could be performed by exploiting the

fact that Nb atoms can be only located in place of W atoms. Therefore, Se atoms can be

simply identified when they are not in the rows of W atoms. The remaining are Nb atoms.

Figure S9G show the classification results for which W, Nb, and Se were assigned to bright

8

gray, dark blue and brown circles, respectively.

Additional Figures I. CVD synthesis of semiconducting WSe2 and metallic NbSe2

Figure S1. Cross-sectional transmission electron microscopy (TEM) images of as-grown (A)

WSe2 and (B) NbSe2. The thicknesses of WSe2 and NbSe2 is 2.5 and 3.2 nm, respectively.

The scale bars are 5 nm.

Figure S2. (A) Planar annular dark-field scanning transmission electron microscopy (ADF-

STEM) image of as-synthesized WSe2 and (B) its color-rendered image. The scale bars are

2nm.

2 nm

2 nm

A B

9

Figure S3. XPS spectra showing (A) W 4f and (B) Se 3d peaks of as-grown WSe2

semiconducting layer and (C) Nb 3d and (D) Se 3d peaks of as-synthesized metallic NbSe2.

The doublet with components at 203.7 and 206.5 eV is attributed to Nb4+ in NbSe2. The peak near

210.5 eV corresponds with Nb5+ in the oxidized species. However, it is so negligible, indicating that

surface of NbSe2 is not much oxidized.

40 38 36 34 32 30*WO3

Inte

nsity

(a.u

.)

Binding Energy (eV)

W 4f5/2

W 4f7/2

*

58 56 54 52

Inte

nsity

(a.u

.)

Binding Energy (eV)

Se 3d3/2

Se 3d5/2

212 210 208 206 204 202 200

Inte

nsity

(a.u

.)

Binding Energy (eV)

Nb 3d3/2

Nb 3d5/2

58 56 54 52

Inte

nsity

(a.u

.)

Binding Energy (eV)

Se 3d3/2 Se 3d5/2

A

C

B

D

10

II. Synthesis of WxNb1-xSe2 transition layers

Figure S4. Atomic force microscopy (AFM) morphology and height profile of Nb2O5

deposited with (A, D) 1, (B, E) 3, and (C, F) 5 cycles of PEALD technique.

Table S1. Thicknesses confirmation of Nb2O5 deposited with by 1, 3, and 5 cycles.

(unit: nm)

Thickness analysis tool Nb2O5 1 cycle Nb2O5 3 cycles Nb2O5 5 cycles

Ellipsometer 0.8 1.3 1.6

AFM N/A 1.2 ~ 1.4 1.6 ~ 1.8

0 1 2 3 4 5 6 7 8 9 10-1

0

1

2

3

H

eigh

t (nm

)

Distance (µm)0 1 2 3 4 5 6 7 8 9 10

-4-3-2-1012345

H

eigh

t (nm

)

Distance (µm)0 1 2 3 4 5 6 7 8 9 10

-1

0

1

2

3

H

eigh

t (nm

)

Distance (µm)

A

D

B

E

C

F

ALD 1 cycle

Nb2O5Nb2O5

Nb2O5

ALD 3 cycles ALD 5 cycles

11

Figure S5. XPS spectra of (A) Nb 3d and (B) O 1S region peaks on Nb2O5 deposited with

PEALD technique.

Figure S6. (A) Planar ADF-STEM image of as-synthesized WxNb1-xSe2 (1 cycle) and (B) its

color-rendered image.

214 212 210 208 206 204

Nb 3d3/2

Nb 3d5/2

Inte

nsity

(a. u

.)

Binding Energy (eV)

Nb2O5

530 535

O 1s

Inte

nsity

(a. u

.)

Binding Energy (eV)

Nb2O5

A B

2 nm 2 nm

A BWxNb1-xSe2 (1 cycle)

12

Figure S7. XPS spectra of (A) W 4f, (B) Nb 3d, and (C) Se 3d peaks recorded from three

WxNb1-xSe2 transition layers. Amount of Nb doping clearly increases as number of ALD

cycles increases from 1 to 5.

40 38 36 34 32 30 28

1 cycle

3 cycles

Nb2O

5

5 cycles

WxNb1-xSe2

W 22.5%

W 25.2%

W 31.7%

Inte

nsity

(a.u

.)

Binding Energy (eV)

W 4f

58 56 54 52 50

Se 66.7%

Se 66.7%

Se 65.3%

Se 3d

Inte

nsity

(a.u

.)

Binding Energy (eV)

1 cycle

3 cycles

Nb2O

5

5 cycles

WxNb1-xSe2

213 210 207 204 201 198

Nb 1.6%

Nb 8.1%

Inte

nsity

(a.u

.)

Binding Energy (eV)

Nb 3d

Nb 12.2%

1 cycle

3 cycles

Nb2O

5

5 cycles

WxNb1-xSe2B

C

A

13

III. Hall measurement method

Hall measurements were performed using LakeShore Model 8404 AC/DC Hall Effect

Measurement System (HMS) with homemade helium atmosphere-based cryostat. LakeShore

Model 8404 AC/DC Hall Effect Measurement System (HMS) is composed of 2182A

nanovoltmeter, 6220 precision current source, 776 HMS matrix, 7230 DSP lock-in amplifier,

and 336 temperature controller. Atomic-layered TMDs were patterned to clover leaf

geometry that edge-to-edge distances of the central square were 10 mm by all sides, as shown

in Figure S8A and S8B.

Figure S8. (A) Schematic drawing, (B) optical image of a Hall measurement sample, and (C)

hall voltages as function of magnetic field on m-vdW: 5 cycles transition film

Except for 1 cycled WxNb1-xSe2 film, all samples were measured under DC magnetic field

which was swept between ±8 kG under a constant excitation current with the magnitude

depending on the sample resistivity. Hall voltage as function of magnetic field was also

checked on the m-vdW: 5 cycles transition film (Figure S8C). The hall coefficient value

calculated from the slope of hall voltage versus magnetic field was 2.14 × 10-3 cm3C-1. The 1

cycled film had higher resistivity than other samples. Therefore, the magnitude of excitation

current was limited. It made Hall voltage low (VH = RHIB/t), and a misalignment voltage was

dominant. So, in the case of 1 cycled sample, Hall effect measurements were performed

under AC magnetic field. The magnitude of AC magnetic field was 6107.6G. A misalignment

A B

2 mm

C

14

voltage is reduced in AC Hall effect measurements. For estimation of resistivity (1),

conductivity (2), carrier density (3), and mobility (4), following equations were used.

Resistivity, 𝜌 = !"!"!

!!",!"!!!",!"!

𝑓 !!",!"!!",!"

- (1)

, where d is thickness.

Conductivity, σ = 1/ρ - (2)

Hall voltage, 𝑉! =!!!"!

, where t is thickness and RH is Hall coefficient.

Carrier density (n), n = !!!!

- (3)

, where RH is Hall coefficient.

Mobility (µH), µ! =!!!

- (4)

15

IV. Cross-sectional images of WxNb1-xSe2 (1, 3, and 5 cycles) transition layers

Figure S9. Cross-sectional TEM images and energy dispersive spectroscopy (EDS) line

profiles of WxNb1-xSe2 transition layers with (A) 1, (B) 3, and (C) 5 cycles. (D) Normalized

intensity profile of Nb element along the vertical scan region (white dash arrows from Figure

S6A-C) The scale bars are 5 nm.

16

V. Process of image analysis

Figure S10. Image processing procedure. (A) original image obtained from ADF-STEM. (B)

Noise reduction by MF and illuminance equalization by MTH. (C) Fourier spectrum of result

from DFT of (B). (D) IDFT of (C). (E) Enhanced image by adding 1.5-folded (D) to (B), (F)

Applying SICD to find atoms. (G) Final results by classifying three atoms that W, Nb, and Se

are assigned to bright gray, dark blue and brown circles, respectively.

17

Figure S11. Flow chart for image analysis

18

VI. Fabrication process of WSe2-based FET array devices

Figure S12. Atomic crystal structures of (i) Pd–WSe2 MS, (ii) NbSe2–WSe2 vdW, and (iii)

NbSe2–WxNb1–xSe2–WSe2 m-vdW junctions.

A

19

Figure S13. Fabrication flow chart of MS (Pd-WSe2) and vdW (NbSe2-WSe2) junction FET

array devices.

MS Junction(Pd-WSe2)

1. WSe2 CVD synthesis

old SiO2/Si

WSe2

2. WSe2 channel patterning

old SiO2/Si

WSe2

3. WSe2 transfer

new SiO2/SiWSe2

Pd

4. Pd electrode deposition

new SiO2/SiPMMA-coated WSe2

- Photolithography - Ar RIE etching- PR removal

- WO3 thermal evaporation - CVD selenization

- PMMA coating - SiO2 etching using HF- Transfer- PMMA removal

- Photolithography - Pd thermal evaporation- Lift-off

1. WSe2 & NbSe2 CVD synthesis

WSe2

WSe2

2. NbSe2 transfer on WSe2

WSe2

WSe2


WSe2

NbSe2

4. NbSe2/WSe2 transfer on new SiO2

new SiO2/Si

NbSe2

WSe2

#01 old SiO2/Si

#02 old SiO2/Si

#01 old SiO2/Si

#01 old SiO2/Si


- Photolithography- Nb2O5 thermal evaporation- PR removal - CVD selenization




PMMA-coated NbSe2

vdW Junction(NbSe2-WSe2)

WSe2

Pd/WSe2

NbSe2

NbSe2

NbSe2/WSe2

NbSe2/WSe2

20

Figure S14. Fabrication flow chart of m-vdW (NbSe2-WxNb1-xSe2-WSe2) junction FET array

devices.

m-vdW Junction(NbSe2-WxNb1-xSe2-WSe2)

1. WSe2 , NbSe2, & WxNb1-xSe2 synthesis

WSe2

#01 old SiO2/Si

WSe2

SiO2/SiNbSe2

NbSe2WxNb1-xSe2

WxNb1-xSe2

2. NbSe2 transfer on WxNb1-xSe2

NbSe2

3. NbSe2/WxNb1-xSe2 patterning

NbSe2

4. NbSe2/WxNb1-xSe transfer on WSe2

WSe2


SiO2/SiWSe2

NbSe2WSe2

NbSe2

6. NbSe2/WxNb1-xSe/WSe2 transfer on new SiO2

new SiO2/Si

#02 old SiO2/Si #03 old SiO2/Si

#03 old SiO2/SiWxNb1-xSe2

NbSe2

WxNb1-xSe2

WxNb1-xSe2

#03 old SiO2/Si

#01 old SiO2/Si

WSe2

WxNb1-xSe2

NbSe2

WSe2

WxNb1-xSe2

#01 old SiO2/Si


- Nb2O5 thermal evaporation - CVD selenization

- WO3 thermal evaporation - ALD Nb2O5 deposition- CVD selenization


- Photolithography - O2/CF4 RIE etching- PR removal



- PMMA coating - HF etching of SiO2- Transfer- PMMA removal

PMMA-coated NbSe2/WxNb1-xSe/WSe2

7. NbSe2/WxNb1-xSe/WSe2 FET device

NbSe2

WSe2

WxNb1-xSe2

new SiO2/Si

NbSe2/WxNb1-xSe2

NbSe2/WxNb1-xSe2/WSe2

21

VII. WSe2-based FET array devices

Figure S15. Optical images of (A) MS, (B) vdW, and (C) m-vdW junction devices. Right

insets: zoom-in images of single device

WSe2

NbSe2

NbSe2/WxNb1-xSe2

Pd

WSe2

WSe2

Pd/WSe2

NbSe2/WSe2

NbSe2/WxNb1-xSe2/WSe2

A

B

C

22

VIII. AFM morphologies of vdW and m-vdW junction

Figure S16. AFM morphologies of (A) vdW and (B) m-vdW junctions for 10 µm channel

devices.

A B

NbSe2 WSe2 NbSe2NbSe2/WxNb1-xSe2

WSe2

vdW junction m-vdW junction

23

IX. Junction-dependent electrical properties of WSe2 FET devices

Figure S17. Drain-source current vs. drain voltage (IDS-VDS) curves of WSe2 FET devices

with each different junction. The channel length tested is 50 µm. The m-vdW: 1 cycle

junction devices exhibit relatively symmetric and linear IDS–VDS behaviors.

-4 -2 0 2 4-3n

-2n

-1n

0

1n

2n

3n MS vdW m-vdW: 1 cycle m-vdW: 3 cycles m-vdW: 5 cycles

I DS (A

)

VDS (V)

50 µm channel

24

X. Channel-length-dependent electrical properties for each junction

Figure S18. Transfer characteristics of IDS-VBG curves of (A) MS, (B) vdW, (C) m-vdW: 1

cycle, (D) m-vdW: 3 cycles, and (E) m-vdW: 5 cycles. (F) Summary of ON (IDS @ VBG = -

60 V and VDS = -5 V) and OFF states (IDS @ VBG = 30 V and VDS = -5 V) for each junction

as a function of channel length. 10 devices were evaluated for each junction.

25

XI. Output characteristics dependent on junction properties

Figure S19. Output characteristics of IDS-VDS curves of (A) MS and vdW, and (B) m-vdW: 1,

3, and 5 cycles. The Channel length tested is 50 µm.

-4 -2 00

20n

40n

60n

80n

100n

MS vdW

I DS (

A)

VDS (V)

VBG

= 20 to -60 V, step: -20 V

-4 -2 00

100n

200n

300n VBG

= 20 to -60 V, step: -20 V

m-vdW: 1 cycle m-vdW: 3 cycles m-vdW: 5 cycles

I DS (

A)

VDS (V)

A B

26

XII. Contact resistance of 2D TMD junction devices

Figure S20. Contact resistances of MS, vdW, and m-vdW: 1 cycle devices at (A) Vg = 0 V

and (B) Vg = -60 V employing transfer line methods.

Table S2. Comparison of contact, channel, and total resistance extracted from Figure S20

above

Vg = 0 V Rc (MΩ·µm) Rch (MΩ·µm) Rtot (MΩ·µm) MS 8.2 6.8 23.2

vdW 3.1 0.9 7.1 m-vdW: 1 cycle 1.6 1 4.2

Vg = -60 V Rc (kΩ·µm) Rch (kΩ·µm) Rtot (kΩ·µm) MS 71.8 169.5 313

vdW 37.2 42.4 116.8 m-vdW: 1 cycle 14.7 23.5 52.9

Compared with the MS device, the contact resistance values of vdW and m-vdW: 1 cycle

devices were reduced, leading to the improvement of FET performance on the 2D vdW

junction devices.

10 20 30 40 50

0

50

100

m-vdW junction (1 cycle)

vdW junction

MS junction

Rto

tal (

MΩ⋅µ

m)

Lg (µm)

@ Vg = 0 VA B

0 10 20 30 40 50-200

0

200

400

600

800

2Rc = 29.4 kΩ⋅µm


vdW junction

MS junction

Rto

tal (

kΩ⋅µ

m)

Lg (µm)

@ Vg = -60 V

27

XIII. Physical parameters of 2D WSe2-based FET devices

Figure S21. Statistical distribution of (A) subthreshold swing and (B) mobility for MS, vdW,

and m-vdW: 1 cycle junction devices.

A B

0 5 10 15 20 25 300

2

4

Subthreshold swing (V/dec)

0

2

Cou

nts

0

2

11.7 ± 0.7

16.4 ± 3.9


vdW junction

MS junction16.4 ± 4.2

0.0 0.2 0.4 0.6 0.8 1.00

1

Mobility (cm2/Vs)

0

2

Cou

nts

MS junction

vdW junction


0.08 ± 0.06

0.11 ± 0.03

0.38 ± 0.14

0

2

4

28

XIV. Contact stability of 2D TMD junction devices

Figure S22. Contact stabilty of (A) vdW, (B) m-vdW: 1 cycle, (C) m-vdW: 3 cycles, and (D)

m-vdW: 5 cycles junction devices. Any serious electrical degradation was not observed on

transfer characteristics (IDS–VBG) of vdW, and m-vdW: 1, 3, and 5 cycle junction devices

even after 75 days. Stable electrical and physcial contact properties on 2D metal-

semiconductor atomic layer junctions were achieved.

-60 -40 -20 0 20 4010-10

10-9

10-8

10-7

10-6

pristine after 75 days

I DS (A

)

VBG (V)

vdW junctionA B

-60 -40 -20 0 20 4010-10

10-9

10-8

10-7

10-6


I DS (A

)

VBG (V)

m-vdW: 1 cycle junction

-60 -40 -20 0 20 4010-11

10-10

10-9

10-8

10-7

10-6


I DS (A

)

VBG (V)

m-vdW: 3 cycles junction

-60 -40 -20 0 20 4010-11

10-10

10-9

10-8

10-7

10-6


I DS (A

)

VBG (V)

m-vdW: 5 cycles junctionC D

29

XVI. Temperature-variable hall measurement

Figure S23. Temperature dependence of (A) sheet carrier concentration and (B) hole

mobility of NbSe2 and WxNb1-xSe2: 1, 3, and 5 cycle devices. WxNb1-xSe2: 1 cycle film shows

only positive slope dµ/dT (i.e., thermally activated transport) while all other films exhibit

negative slopes or negligible temperature dependences (i.e., band-like transport). (C)

Arrhenius plot of mobility against 1/KT for m-vdW (1 cycle) film where the slope

corresponds to thermal activation energy (Ea). (D) Conductivity for Nb-controlled WxNb1-

xSe2 films and NbSe2 film under the range of 10 ~ 300 K.

0 100 200 300

1014

1015NbSe2

WxNb1-xSe2 (5 cycles)


WxNb1-xSe2 (1 cycle)

T (K)

n she

et (c

m-2)

0 100 200 30010-1

100

101

102

103

WxNb1-xSe2 (1 cycle) WxNb1-xSe2 (3 cycles) WxNb1-xSe2 (5 cycles) NbSe2

σ (S

cm

-1)

T (K)

A

C

B

0.0 0.1 0.2 0.3 0.4 0.5

0.1

1 @ WxNb1-xSe2 (1 cycle)

µ (c

m2 V-1

s-1)

1/kT (meV-1)

Ea: 2.9 meV

0.0 0.1 0.2 0.3 0.4 0.5

0.1

1 @ WxNb1-xSe2 (1 cycle)

µ (c

m2 V

-1s-1

)

1/kT (meV-1)

Ea: 2.9 meV

0 100 200 300

1014

1015NbSe2



WxNb1-xSe2 (1 cycle)

T (K)

n she

et (c

m-2)

A

C

B

0 100 200 300

0.1

1

NbSe2

W xNb1-xSe2 (1 cycle) W xNb1-xSe2 (3 cycles) W xNb1-xSe2 (5 cycles)

µ (c

m2 V

-1s-1

)

T (K)

D

30

XVII. Effect of NbSe2 top layer on m-vdW: 1 and 3 cycles junction FET device

Figure S24. Comparison of IDS–VBG characteristics of (A) m-vdW: 1 cycle junction devices

and (B) m-vdW: 3 cycle junction devices with and without final top NbSe2 electrodes,

respectively. 10 devices were evaluated each.

-60 -40 -20 0 20 4010-11

10-10

10-9

10-8

10-7

10-6

without NbSe2

with NbSe2

@ m-vdW: 3 cycles

I DS (A

)

VBG (V)-60 -40 -20 0 20 40

10-11

10-10

10-9

10-8

10-7

10-6

@ m-vdW: 1cycle

without NbSe2

with NbSe2

I DS (A

)

VBG (V)

A B

31

XVIII. Channel length dependence of m-vdW: 1 cycle junction devices

Figure S25. (A) Variable transfer IDS-VBG curves of m-vdW: 1 cycle junction devices with

different channel length. (B) Summary of ON and OFF states. 16 devices were evaluated for

each channel.

10 20 30 40 5010-10

10-9

10-8

10-7

10-6

m-vdW: 1 cycle

I DS (A

)

Channel length (µm)-60 -40 -20 0 20 40

10-10

10-9

10-8

10-7

10-6m-vdW: 1 cycle VDS = -5 V

10 µm 20 µm 30 µm 40 µm 50 µm

I DS (A

)

VBG (V)

A B

32

XIX. Two conditions for barrier height extraction

Table S3. Contact and channel resistance for MS, vdW, and m-vdW: 1cycle devices

Vg = 0 V 2Rc (MΩ·µm) Rch (MΩ·µm) Rtot (MΩ·µm) MS 22.1 1.1 23.2

vdW 6.2 0.9 7.1 m-vdW: 1 cycle 3.2 1 4.2

Figure S26. (A) Transfer curves showing threshold voltages and charge transport regions. (B)

Representative temperature-variable transfer curves of m-vdW: 1 cycle device displaying

charge transport regions (tunneling and thermionic regions)

The first condition that contact resistance out of total resistance should be dominant part was

met. The second condition that thermionic emission current should be dominant at the VBG =

0 V was acceptable. Thus, it is sure that the calculated barrier heights are reasonable since

two conditions are met on our devices.

-60 -40 -20 0 20 4010-10

10-9

10-8

10-7

10-6

MS vdW m-vdW: 1cycle

I DS (A

)

VBG (V)

Tunnelingregion

Thermionic region

Vth (MS)Vth (vdW)Vth (M-vdW: 1c)

-60 -40 -20 0 20 4010-9

10-8

10-7

10-6

10-5

I DS (

A)

VBG (V)

m-vdW : 1 cycle junctiion

temp. : 318 - 413 K (step: 15K)A BVth region (M-vdW: 1c)

Tunnelingregion

Thermionicregion

33

XX. Temperature-variable electrical properties

Figure S27. Arrhenius plots of ln(IDS/T3/2) against 1000/T for (A) MS, (B) vdW, and (C) m-

vdW: 1 cycle junction devices. The drain currents were obtained at the back gate voltage of 0

V. (D) Summary of Arrhenius plots at a fixed drain voltage of 0.5 V. Temperature range was

293–393 K. The absolute value of the slope is proportional to the Schottky barrier height. The

slopes are linearly proportional to Schottky barrier height based on the following equation:

The drain current through a Schottky barrier can be described by the 2D thermionic emission

equation: 5,6

𝐼!" = 𝐴!!∗ 𝑆𝑇!/!𝑒𝑥𝑝 −𝑞𝐾!𝑇

𝛷! −𝑉!"𝑛

where A*2D is the 2D equivalent Richardson constant, S is the contact area, T is the

temperature, q is the electron charge, KB is the Boltzmann constant, Φ! is the Schottky

barrier height, and n is the ideality factor. The slopes, obtained by fitting the Arrhenius plots

2.6 2.8 3.0 3.2 3.4

-30

-29

-28

0.5 to 1V

m-vdw: 1 cycle junction

ln(I D

S/T3/

2 )

1000/T (1/K)

2.6 2.8 3.0 3.2 3.4-33

-32

-31

-30

-29

0.5 to 1V

ln(I D

S/T3/

2 )

1000/T (1/K)

MS junction

2.6 2.8 3.0 3.2 3.4

-28

-27

-26

0.5 to 1V

vdw junction

ln(I D

S/T3/

2 )

1000/T (1/K)

2.6 2.8 3.0 3.2-3

-2

-1

0 VDS = 0.5 V

MS(slope: -3.6)vdw(slope: -2.3)m-vdw:1 cycle (slope: -2.0)

Δln

(I DS/T

3/2 )

1000/T (1/K)

A

C

B

D

34

of ln(IDS/T3/2) vs. 1000/T, are plotted as a function of VDS (0.5 to 1 V) and then can be

extrapolated. Consequently, the Schottky barrier height values were calculated from the y-

intercepts as S! = − !!!!"""#!

.

35

XXI. Barrier height of m-vdW: 3 and 5 cycles junction devices

Figure S28. Schottky barrier heights of m-vdW: 3 and 5 cycle junction devices.

0.0 0.3 0.6 0.9

-3.2

-3.0

-2.8

-2.6m-vdW: 3 cycles (qΦ = 238 meV)

m-vdW: 5 cycles (qΦ = 272 meV)

Slo

pe

VDS (V)

36

References

1. Gonzalez, R.C.; Woods, R.E.; Eddins, S.L. Eddins, Pearson Education India Digital image

processing using MATLAB. 2004.

2. Jackway, P. Electronics Letters 2000, 36, 1194-1195.

3. Atherton, T.J.; Kerbyson, D.J. Image and Vision computing 1999, 17, 795-803.

4. Otsu, N. Automatica, 1975, 11, 23-27.

5. Anwar, A.; Nabet, B.; Culp, J.; Castro, F. J. Appl. Phys. 1999, 85, 2663.

6. Wang, W.; Liu, Y.; Lei, T.; Jin, Y.; Zhao, T.; Xiu, F. Sci. Rep. 2014, 4, 6928.

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