Fabrication and Characterization of p-Type SnO Thin Film
with High c-Axis Preferred Orientation
YANLI PEI,
1,2
WUGUANG LIU,
1
JINGTAO SHI,
1
ZIMIN CHEN,
1,3
and GANG WANG
1
1.—State Key Lab of Optoelectronics Materials and Technologies, School of Electronics and
Information Technology, Sun Yat-Sen University, Guangzhou 510006, People’s Republic of China.
2.—e-mail: peiyanli@mail.sysu.edu.cn. 3.—e-mail: chenzim8@mail.sysu.edu.cn
p-Type tin monoxide (SnO) thin films with high c-axis preferred orientation
have been fabricated on quartz substrate via electron-beam evaporation at
280C. Subsequently, rapid thermal annealing (RTA) was performed in N
2
atmosphere at 400C to 800C. Their structural, chemical, optical, and elec-
trical properties were investigated by x-ray diffraction analysis, ultraviolet–
visible spectroscopy, scanning electron microscopy, x-ray photoelectron spec-
troscopy, and Hall-effect measurements. The c-axis-oriented films of Sn-rich
SnO presented excellent thermal stability up to RTA at 700C. Both the
crystallization and the hole Hall mobility were enhanced with increasing RTA
temperature, with Hall mobility of 16 cm
2
V
1
s
1
being obtained after RTA at
700C. It was considered that the presence of defects and low scattering from
grain boundaries contributed to this high Hall mobility. RTA annealing tem-
perature above 700C induced chemical reaction between SnO and the quartz
substrate, with a change of the film to amorphous state with Sn
4+
formation.
Key words: p-Type tin monoxide (SnO), high c-axis orientation, thermal
stability
INTRODUCTION
Recently, n-type oxide-semiconductor-based thin-
film transistors (TFTs) such as amorphous In-Ga-
Zn-O (a-IGZO) TFTs have been applied in next-
generation active-matrix liquid-crystal displays
(AMLCDs) and active-matrix organic light-emitting
diode (AMOLED) displays, owing to their merits
including high mobility, excellent on/off ratio, low
processing temperature, and high uniformity.
1–5
However, compared with the rapid progress of
development of n-type oxide TFTs, development of
p-type oxide TFTs has been relatively slow, and
their electrical performance remains inferior to that
of n-type devices.
6
This restricts implementation of
complementary logic-based circuits using oxide
TFTs. In general, the hole transport paths and
valence-band maximum (VBM) of oxide semicon-
ductors are composed of 2p orbitals of oxygen ions.
7
These are strongly anisotropic and localized, limit-
ing the hole mobility. Tin monoxide (SnO) with
spherical Sn 5s orbitals has been suggested as a
promising p-type oxide semiconductor. The spheri-
cal Sn 5s orbitals with energy nearly equal to O 2p
orbitals can hybridize with and delocalize O 2p
orbitals.
7,8
The resulting isotropic extended orbitals
correspond to cation wavefunctions with large over-
lap, forming an effective hole conduction path.
However, SnO can easily decompose to SnO
2
with
expulsion of Sn atoms at high processing tempera-
ture.
8
Most reported mobilities of SnO films are
lower than 4 cm
2
V
1
s
1
.
9–11
The properties of
p-type SnO films are still far from levels required
for practical applications.
12,13
Tetragonal litharge
SnO with layered crystal structure can form a
strong anisotropic film.
10,14
The (001) surface has
the lowest surface energy,
15
indicating that high
thermal stability may be obtained for SnO thin films
with c-axis preferred orientation. Therefore, it is
interesting to prepare SnO thin films with preferred
(Received December 29, 2015; accepted July 18, 2016)
Journal of ELECTRONIC MATERIALS
DOI: 10.1007/s11664-016-4816-7
2016 The Minerals, Metals & Materials Society