Simple synthesis of ultra-high quality In
2
S
3
thin films on InAs
substrates
Yumin Sim
1
, Jinbae Kim
1
, Maeng-Je Seong
*
Department of Physics, Chung-Ang University, Seoul 06794, South Korea
article info
Article history:
Received 8 March 2016
Received in revised form
26 May 2016
Accepted 29 May 2016
Available online 30 May 2016
Keywords:
Indium-sulfide
Thin films
X-ray diffraction (XRD)
Scanning electron microscopy (SEM)
Raman spectroscopy
abstract
We report a simple and reliable technique to synthesize high-quality In
2
S
3
films on InAs substrates by
using thermal sulfurization in a hot-wall tube furnace. X-ray diffraction and energy dispersive X-ray
spectroscopy data confirmed that the synthesized films were cubic b-In
2
S
3
or tetragonal b-In
2
S
3
,
depending on growth conditions. Field emission scanning electron microscopy analysis and Raman
spectroscopy showed that the In
2
S
3
films are of remarkable crystal quality. Especially, by optimizing the
growth conditions, we have grown an extremely high-quality tetragonal b-In
2
S
3
thin film firmly
remained on the InAs substrate, for the first time.
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
In
2
S
3
attracted tremendous attention for solar cell, display,
water splitting, and photocatalyst applications due to its environ-
mental friendliness, high photosensitivity, photoconductivity, and
stable chemical composition [1e 12]. In
2
S
3
, a typical III-VI chalco-
genide semiconductor with its band gap ranging from 1.65 eV up to
2.95 eV depending on the synthesis technique reported in the
literature [13], can exist in a few crystalline phases at atmospheric
pressure, namely cubic a-In
2
S
3
, cubic b-In
2
S
3
, tetragonal b-In
2
S
3
,
and hexagonal g-In
2
S
3
[14]. Among these, the tetragonal b-In
2
S
3
,a
spinel tetragonal structure as shown in Fig. 1(a) (JCPDS #25-0390
[15]), is stable up to 420
C. Above 420
C, two new modifications
appear: the cubic a-In
2
S
3
shown in Fig. 1(b) (JCPDS #05-0731 [16])
and the cubic b-In
2
S
3
, whose lattice constant is twice that of a-
In
2
S
3
, shown in Fig. 1(c) (JCPDS #32-0456 [17]). A layered hexag-
onal structure g-In
2
S
3
appears above 750
C, which is stable up to
the melting point of 1050
C [18]. In addition to these, an ε-In
2
S
3
with a rhombohedral cell can be prepared at high-pressure of
35 Kbar and 500
C [18]. Generally, the tetragonal b-In
2
S
3
crystal
structure is the most stable phase at room temperature. However,
the cubic In
2
S
3
crystal structure can be made stable at room tem-
perature by controlling the stoichiometry or by introducing certain
impurities during the growth process [14]. A mixture of cubic and
tetragonal phases of In
2
S
3
at room temperature was also reported
in the literature [18,19].
Until now, In
2
S
3
crystals have been grown by using various
growth techniques such as metalorganic chemical vapor deposition
(MOCVD) [20], chemical bath deposition [21e23], spray pyrolysis
[24e26], successive ionic layer adsorption and reaction technique
[27,28], RF sputtering [29], hydrothermal process [30,31], slurry
painting [32], and aerosol assisted CVD [33]. However, preparing
uniform In
2
S
3
films of high crystalline quality by using a simple
technique is still a great challenge. Especially, for useful device
applications, it is highly desired for high quality In
2
S
3
thin films to
be grown on device-ready substrates, such as commercially avail-
able InAs wafers.
In this work, we report a simple and reliable technique to syn-
thesize high-purity In
2
S
3
films of remarkable crystal quality on InAs
substrates by using thermal sulfurization in a hot-wall tube
furnace. The crystal structure, composition, morphology, and
vibrational modes of the synthesized In
2
S
3
crystals were studied by
using X-ray diffraction (XRD), energy dispersive X-ray (EDX), field
emission scanning electron microscopy (FE-SEM), and Raman
spectroscopy. Especially, by optimizing the growth conditions, we
have grown an extremely high-quality tetragonal b-In
2
S
3
thin film
firmly remained on the InAs substrate, for the first time.
* Corresponding author.
E-mail address: mseong@cau.ac.kr (M.-J. Seong).
1
These authors contributed equally.
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: http://www.elsevier.com/locate/jalcom
http://dx.doi.org/10.1016/j.jallcom.2016.05.327
0925-8388/© 2016 Elsevier B.V. All rights reserved.
Journal of Alloys and Compounds 685 (2016) 518e522