Large Lateral Photovoltaic Effect in MoS2/GaAs Heterojunction
Hao et al. Nanoscale Research Letters
Large Lateral Photovoltaic Effect in MoS /GaAs Heterojunction 2
Lanzhong Hao 0 1
Yunjie Liu 1
Zhide Han 1
Zhijie Xu 1
Jun Zhu 0
0 State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China , Chengdu 610054 , People's Republic of China
1 College of Science, China University of Petroleum , Qingdao 266580, Shandong , People's Republic of China
Molybdenum disulfide (MoS2) nanoscaled films are deposited on GaAs substrates via magnetron sputtering technique, and MoS2/GaAs heterojunctions are fabricated. The lateral photovoltaic effect (LPE) of the fabricated MoS2/GaAs heterojunctions is investigated. The results show that a large LPE can be obtained in the MoS2/n-GaAs heterojunction. The LPE exhibits a linear dependence on the position of the laser illumination and the considerably high sensitivity of 416.4 mV mm−1. This sensitivity is much larger than the values in other reported MoS2-based devices. Comparatively, the LPE in the MoS2/p-GaAs heterojunction is much weaker. The mechanisms to the LPE are unveiled by constructing the energy-band alignment of the MoS2/GaAs heterojunctions. The excellent LPE characteristics make MoS2 films combined with GaAs semiconductors promising candidates for the application of high-performance position-sensitive detectors.
MoS2; GaAs; Photovoltaic; Heterojunction; Interface
Background
Due to its excellent properties, molybdenum disulfide
(MoS2) is being investigated as one typical kind of
twodimensional materials to develop next-generation
microelectronic devices and optoelectronic devices [
1–5
].
Unlike graphene, MoS2 has obvious band gap and its band
gap decreases with increasing layer numbers [
6
]. The
presence of the obvious band gap allows the fabrication
of the MoS2 transistors with an on/off ratio exceeding
108 and the photodetectors with high responsivity [
7, 8
].
Recently, MoS2 combined with other semiconductors
has attracted much interest, such as GaAs, Si, and GaN
[
9–13
]. These designed heterostructures supply feasible
technical route for MoS2-based materials to develop
practically applicable optoelectronic devices. Among
all these bulk semiconductors, GaAs has a suitable
direct band gap of ~ 1.42 eV and high electron
mobility (~ 8000 cm2 V−1 s−1). Lin et al. fabricated MoS2/
GaAs solar cells with a power conversion efficiency
over 9.03% [9]. Further, Xu et al. reported a MoS2/
GaAs self-driven photodetector with the extremely
high detectivity of 3.5 × 1013 Jones [
10
]. In previous
reports, the studies on MoS2/GaAs heterostructures
have been mainly focused on the application in the
area of solar cells and photodetectors. However, the
MoS2/GaAs as a position-sensitive detector (PSD)
based on the lateral photovoltaic effect (LPE) has
been reported rarely. Different from the ordinary
longitudinal photovoltaic effect, the LPE originates from
the lateral diffusion and recombination of the
photongenerated carriers in the inversion layer at the
interface [
14–18
]. In the LPE effect, a lateral photovoltage
(LPV) can be obtained and it changes linearly with
the laser spot position on the active region of the
device surface. These characteristics make LPE very
useful in developing high-performance PSDs and have
been studied widely in the area of robotics,
biomedical applications, process control, position information
systems, and so on.
In this work, MoS2 thin films with different thickness
are deposited on the surface of n-/p-GaAs substrates via
magnetron sputtering technique. A large LPE is
observed in the fabricated MoS2/n-GaAs heterojunction,
and the sensitivity reached 416.4 mV mm−1. Our results
further show that the LPE exhibits obvious dependence
on the carrier types of the GaAs substrates and the
thickness of the MoS2 films. Through the construction
of the energy-band alignment at the interface, the
mechanisms to the LPE in the devices are proposed.
Methods
MoS2 thin films were deposited on (100)-oriented GaAs
substrates using the DC magnetron sputtering
technique. The MoS2 powders (purity, ~ 99%) were
coldpressed into a disk under the pressure of 20.0 MPa. The
as-fabricated disk (Φ60.0 mm × 4.5 mm) was used as
the target during sputtering. The n-/p-GaAs substrates
were used in our experiments, respectively. Before the
deposition, the substrates were ultrasonically cleaned in
sequence by alcohol, acetone, and de-ionized water.
Subsequently, MoS2 thin films with different thickness
(dMoS2 = ~ 10, 30, 50, 90 nm) were grown on the GaAs
substrates at the temperature of 400 °C, respectively.
During the deposition, the working pressure and power
were kept at 1.0 Pa and 10.0 W, respectively. As a
reference, MoS2 thin films were also deposited on intrinsic
GaAs (i-GaAs) substrates under the same condition.
Finally, about 300-μm In pads with a diameter of 0.5 mm
as electrodes were pressed on the MoS2 film.
The MoS2 films were characterized using R (...truncated)