利用应变增强MoS2光探测器性能
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"通过在多层MoS2上采用原子层沉积技术生长Al2O3应力层，实现对MoS2-GaN光电探测器的应变增强。研究显示，这种应变调控能有效提升二维（2D）过渡金属二硫化物的光电器件性能。"
在标题"Strain enhancement for a MoS2"中，提到的核心知识点是应变增强（Strain enhancement），这主要针对的是二维材料MoS2（二硫化钼）。MoS2是一种重要的二维过渡金属二硫化物，因其独特的电子结构和优异的光电器件性能，在光电子学、光伏器件等领域有着广泛应用。应变工程是改变材料物理特性的有效手段，尤其是通过施加拉伸应变（tensile strain），可以显著调整MoS2的能带结构，进而优化其光吸收和电荷传输性能。
描述部分进一步指出，应变调控被广泛用于提高2D过渡金属二硫化物的光电性质，以提升光伏设备的性能。这里，研究人员采用了在多层MoS2上沉积3nm Al2O3的方法引入应变。Al2O3作为一种应力层，不仅能够稳定MoS2（由温度依赖的拉曼光谱证实了MoS2的热稳定性提高），还可能通过与MoS2的相互作用，改变了材料的机械特性，进而实现应变的引入。
理论模拟（theoretical simulations）证实了Al2O3应力层的存在，并且很可能通过改变MoS2的晶格常数来调控其电子结构。这表明，通过这种应变调控策略，可以精确地控制MoS2的光电响应，从而提高光电探测器的灵敏度和响应速度。
此外，Al2O3的生长方法是原子层沉积（Atomic Layer Deposition, ALD），这是一种精密的薄膜沉积技术，能够确保膜层的均匀性和控制精度，对于实现精细的应变调控至关重要。ALD的使用还有助于避免对MoS2层的损伤，保持其原有的优异性质。
该研究展示了应变工程在优化二维材料性能上的潜力，特别是在提升MoS2基光电设备性能方面，同时强调了ALD技术在实现这一目标中的关键作用。这对于设计高性能、稳定的2D材料光电器件提供了新的思路和实验依据。
Strain enhancement for a MoS
2
-on-GaN
photodetector with an Al
2
O
3
stress liner grown
by atomic layer deposition
ZHIWEN LI,
1,†
JIANGLIU LUO,
1
SHENGQUN HU,
1
QIANG LIU,
2,†
WENJIE YU,
2
YOUMING LU,
1
AND XINKE LIU
1,
*
1
College of Materials Science and Engineering, Shenzhen University, Shenzhen 518060, China
2
State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology,
Chinese Academy of Sciences, Shanghai 200050, China
*Corresponding author: xkliu@szu.edu.cn
Received 19 December 2019; revised 29 February 2020; accepted 29 February 2020; posted 16 March 2020 (Doc. ID 385885);
published 6 May 2020
Strain regulation as an effective way to enhance the photoelectric properties of two-dimensional (2D) transition
metal dichalcogenides has been widely employed to improve the performance of photovoltaic devices. In this
work, tensile strain was introduced in multilayer MoS
2
grown on GaN by depositing 3 nm of Al
2
O
3
on the
surface. The temperature-dependent Raman spectrum shows that the thermal stability of MoS
2
is improved
by Al
2
O
3
. Theoretical simulatio ns confirmed the existence of tensile strain on MoS
2
covered with Al
2
O
3
,
and the bandgap and electron effective mass of six layers of MoS
2
decreased due to tensile strain, which resulted
in an increase of electron mobility. Due to the tensile strain effect, the photodetector with the Al
2
O
3
stress liner
achieved better performance under the illumination of 365 nm wavelength, including a higher responsivity of
24.6 A/W, photoconductive gain of 520, and external quantum efficiency of 8381%, which are more than twice
the corresponding values of photodetectors without Al
2
O
3
. Our work provides an effective technical way for
improving the performance of 2D material photodetectors.
© 2020 Chinese Laser Press
https://doi.org/10.1364/PRJ.385885
1. INTRODUCTION
Two-dimensional (2D) transition metal dichalcogenid es
(TMDs) have important research value in the fields of optoelec-
tronic devices, energy storage, catalysis, etc., due to their special
structure and excellent properties [1–7]. MoS
2
, as a typical
representative of TMDs, possesses a bandgap ranging from
1.80 eV (monolayer) to 1.20 eV (bulk), high mobility
(∼500 cm
2
· V
−1
· s
−1
), high light absorptivity, and thermal sta-
bility (∼1100°C), which facilitate its applications in field effect
transistors (FETs), photodetectors, and sensors [8–11].
Furthermore, its excellent mechanical property makes it useful
in the application of related flexible and wearable devices.
Although the carrier mobility for MoS
2
transistors is estimated
to be 410 cm
2
· V
−1
· s
−1
at room temperature by theoretical
calculation [12], the experimental value is normally 1 or 2 or-
ders lower, which significantly limits the performance of the
transistors. Then many efforts, e.g., phase engineering [13], di-
electric passivation [14], and boron nitride as back-gate dielec-
tric [15], have been implemented to improve performance.
Current research indicates that the properties of 2D
TMD materials, such as bandgap [16,17], effective carrier mass
[18], conductivity [19], exciton–phonon coupling [20], and
spin-orbit coupling [21] can be changed by strain through
changing the lattice structure (such as bond length, bond angle,
and relative position of atoms) [22] and lattice symmetry [17].
Therefore, the strain regulation of 2D TMDs has aroused great
interest from researchers. In the band structure of TMDs, the
conduction band mainly comes from the contribution of the d
2
z
orbital of M , while the valence band mainly comes from the
contribution of the d
xy
, d
22
x−y
orbital of M and hybridization
of P
x
, P
y
of X [23] [here, MX
2
represents TMDs, M is a tran-
sition metal element, and X is the VI main group element (S,
Se, Te)]. When 2D TMDs have in-plane tensile strain, the
band structure is changed, which in turn affects the properties
of the material due to lattice being stretched, the distance be-
tween M and X being increased, the X−M−X bond angle being
decreased, the relative position between the atoms being
changed, and the state of the orbital overlap being changed.
Li et al. calculated the relationship between the biaxial strain
and the absorption spectrum with a strain range of 0%–9%,
and found that the excitation energy decreased from 2.0 eV
in the unstrained state to 1.1 eV under 9% biaxial strain
[24]. It was found using density functional theory (DFT) that
as the tensile strain on MoS
2
increases, the bandgap decreases,
Research Article
Vol. 8, No. 6 / June 2020 / Photonics Research 799
2327-9125/20/050799-07 Journal © 2020 Chinese Laser Press
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