Growth of large-area atomically thin MoS
2
film via
ambient pressure chemical vapor deposition
Caiyun Chen,
1
Hong Qiao,
1
Yunzhou Xue,
1
Wenzhi Yu,
1
Jingchao Song,
2
Yao Lu,
1
Shaojuan Li,
1
and Qiaoliang Bao
1,2,
*
1
Institute of Functional Nano and Soft Materials (FUNSOM), Jiangsu Key Laboratory for
Carbon-Based Functional Materials and Devices, and Collaborative Innovation Center of
Suzhou Nano Science and Technology, Soochow University, Suzhou 215123, China
2
Department of Materials Engineering, Monash University, Clayton, Victoria 3800, Australia
*Corresponding author: qlbao@suda.edu.cn
Received January 12, 2015; revised March 7, 2015; accepted March 8, 2015;
posted March 11, 2015 (Doc. ID 232329); published May 7, 2015
Atomically thin MoS
2
films have attracted significant attention due to excellent electrical and optical properties.
The development of device applications demands the production of large-area thin film which is still an obstacle.
In this work we developed a facile method to directly grow large-area MoS
2
thin film on SiO
2
substrate via ambient
pressure chemical vapor deposition method. The characterizations by spectroscopy and electron microscopy
reveal that the as-grown MoS
2
film is mainly bilayer and trilayer with high quality. Back-gate field-effect transistor
based on such MoS
2
thin film shows carrier mobility up to 3.4 cm
2
V
−1
s
−1
and on/off ratio of 10
5
. The large-area
atomically thin MoS
2
prepared in this work has the potential for wide optoelectronic and photonic device
applications. © 2015 Chinese Laser Press
OCIS codes: (310.3840) Materials and process characterization; (310.6188) Spectral properties; (310.6845)
Thin film devices and applications; (310.6870) Thin films, other properties.
http://dx.doi.org/10.1364/PRJ.3.000110
1. INTRODUCTION
Atomic-layered molybdenum disulfide (MoS
2
), a new two-
dimensional (2D) material, has gained intense attention due
to its outstanding electrical and optical properties [
1–5].
When bulk MoS
2
is reduced to monolayer sheet, an indi-
rect-to-direct bandgap transition occurs, leading to extremely
high quantum efficiency for light emission [
6,7]. Compared
with graphene, MoS
2
has a visible bandgap to allow the
field-effect transistors based on this material to be effectively
switching off. Moreover, the carrier mobility is impressively
high, up to 400 cm
2
V
−1
s
−1
in theory [8] and 45 cm
2
V
−1
s
−1
demonstrated in experiments [2] for monolayer MoS
2
.
In order to fulfill the demands for device applications, sub-
stantial efforts have been devoted into synthesize atomically
thin MoS
2
film, including micromechanical exfoliation
[
4,5,9,10], liquid exfoliation [11–13], and physical vapor depo-
sition [
14]. However, MoS
2
films are often limited to their
micrometer size, which hinders large-scale device applica-
tions. Hence, it is critical to develop practical methods to grow
large-area MoS
2
thin film aiming for device fabrications.
Similar to the growth of large-area graphene film, chemical
vapor deposition (CVD) has been successfully applied to syn-
thesize large-area MoS
2
film. Zhan et al. [15] reported the pro-
duction of large-area few-layer MoS
2
film through sulfiding the
Mo∕SiO
2
substrate but the thin films possess poor quality.
Alternatively, the thermal decomposition of NH
4
2
MoS
4
[16] in the presence of mixed gas could also induce large-area
MoS
2
thin film; however, the pre-deposition of precursors by
dip-coating lacks the control of thickness. Lee et al. [
17] chose
MoO
3
powder as precursor for CVD growth of MoS
2
thin films
by seeding the substrate with reduced graphene oxides. The
resulting product may have contamination of the seeds.
Recently, Yu et al. [
18] reported a self-limiting CVD approach
to produce large-area MoS
2
thin films on various substrates
but a very low carrier mobility (0.003–0.03 cm
2
V
−1
s
−1
)
was achieved.
In this work, we report a seedless and scalable growth
method using ambient pressure CVD to produce high quality
few-layer MoS
2
thin film. Compared with previous reports
which used low-pressure CVD to grow MoS
2
[18,19], the
present method has simpler operation procedures and better
repeatabilities. The as-grown MoS
2
on SiO
2
∕Si is suitable for
following device fabrication without transfer process which
could induce defects and impurities. The scalable growth
method can be further adopted to more complicated photonic
structures such as waveguides and gratings, affording compat-
ability with integrated photonic circuits.
2. RESULTS AND DISCUSSION
Figure 1(a) schematically shows the experimental setup to
synthesize MoS
2
thin film on SiO
2
substrate. The sulfur pow-
der was located at upstream of the CVD system. The MoO
3
powder was placed in a quartz boat in the furnace and the SiO
2
substrate was next to the MoO
3
source. During the growth,
sulfur and MoO
3
were heated to 100°C and 650°C, respec-
tively. The carrying gas argon was at a flow rate of 150 sccm
and the system was kept at ambient pressure. As illustrated in
Fig.
1(a), MoO
3
is reduced by sulfur vapor to form MoO
3−x
species [17,20], which will diffuse to SiO
2
substrate and
eventually lead to nucleation and growth of MoS
2
thin film.
110 Photon. Res. / Vol. 3, No. 4 / August 2015 Chen et al.
2327-9125/15/040110-05 © 2015 Chinese Laser Press