Supplementary Information
Metal-Semiconductor Barrier Modulation for
High Photoresponse in Transition Metal Dichalcogenide
Field Effect Transistors
Hua-Min Li, Dae-Yeong Lee, Min-Sup Choi,
Deshun Qu, Xiaochi Liu, Chang-Ho Ra, and Won Jong Yoo *
Samsung-SKKU Graphene Center (SSGC)
SKKU Advanced Institute of Nano Technology (SAINT)
Department of Nano Science and Technology
Sungkyunkwan University
300 Cheoncheon-dong, Jangan-gu, Suwon 440-746, Korea
* Corresponding email: yoowj@skku.edu
1. Raman spectrum and AFM characterizations
Thin MoS2 and WSe2 flakes are obtained by mechanical exfoliation from the bulk
crystals by using a Scotch tape. The MoS2 flake has the thickness of ~3 nm measured by
AFM, and its Raman spectrum (532 nm wavelength) shows two typical peaks (E2g1 at 384
cm–1 and A1g at 407cm–1) with a large separation of 23 cm–1. The WSe2 flake has the
thickness of ~9 nm, and only shows a single peak at around 250 cm–1. Those suggest the fewlayer structure of both MoS2 and WSe2 flakes, as shown in Fig. S1.
2. Hysteresis of MoS2 and WSe2 FETs
The electrical characterizations of MoS2 and WSe2 FETs are performed in a vacuum
condition (10 mTorr) at the room temperature. The hysteresis is induced by the traps, which
origin could be the defects and/or fixed charges on the dielectric surface, or the remained
residuals on the TMDC surface. The voltage shift has the value of 2 and 10 V in MoS2 and
WSe2 FETs, suggesting the equivalent trap density (ntrap) of 4.79×1011 and 2.40×1012 cm–2,
respectively. The ntrap is approximated as CoxΔV [S1], where Cox is the oxide capacitance
equaling to 3.83×10–8 F/cm2 for 90-nm-thick SiO2.
References
S1 Wang, H., Wu, Y., Cong, C., Shang, J. and Yu, T. Hysteresis of electronic transport in graphene transistors.
ACS Nano 4, 7221–7228 (2010).
2
Figures
(a)
(c)
20 um
20 um
Intensity (a.u)
Intensity (a.u)
A1g
E2g1
MoS2
WSe2
532 nm
350
400
450
500
532 nm
550
Raman Shift (cm-1)
200
6
300
350
400
Raman Shift (cm-1)
12
(b)
MoS2
(d)
WSe2
4
8
Height (nm)
Height (nm)
250
2
~3 nm
0
4
~9 nm
0
-2
0
2
4
6
8
Scan Length (um)
FIG. S1.
10
0
2
4
6
8
10
Scan Length (um)
(a, b) Raman spectrum and AFM characterizations for MoS2 flake on 90-nm-thick SiO2
substrate. Inset of (a): Optical microscopic images of MoS2 flake on SiO2 substrate. (c,
d) Raman spectrum and AFM characterizations for WSe2 flake on 90-nm-thick SiO2
substrate. Inset of (c): Optical microscopic images of WSe2 flake on SiO2 substrate.
3
10-3
10
ID (A)
10
1 to 5 V
Step: 2V
-6
MoS2 FET
Laser of f
-7
-50
-25
0
VG (V)
FIG. S2.
Forward
Reverse
10-4
-4
10-5
10
10-2
(b)
Forward
Reverse
25
50
10-6
ID (A)
(a)
1 to 5 V
Step: 2 V
10-8
10-10
10-12
WSe2 FET
Laser of f
-50
-25
0
25
50
VG (V)
(a) Hysteresis in transfer characteristic of MoS2 FET for various VD levels in dark
environment. (b) Hysteresis in transfer characteristic of WSe2 FET for various VD levels
in dark environment.
4