Abstract
The photogating effect based on the vertical structure of a two-dimensional material allows high-sensitivity and broad-spectrum photodetector. A high-sensitivity photodetector based on the vertical heterostructure of indium selenide (InSe)/molybdenum ditelluride (MoTe2) is reported, which exhibits excellent broad-spectrum detection capability from 365 to 965 nm. The top layer of InSe was used as the grating layer to regulate the channel current, and MoTe2 was used as the transmission layer. By combining the advantages of the two materials, the photodetector has a fast response time of 21.6 ms and achieves a maximum detectivity of 1.05 × 1
Two-dimensional (2D) materials, such as graphene, BP, and transition metal dichalcogenides (TMDCs), the research of 2D materials has become a top priority in the field of optoelectronics due to their excellent optical and electrical propertie
2D van der Waals (vdW) heterojunctions offer an ideal platform to overcome the limitations of single materials and enhance device performance. In vdW heterojunctions, the individual components are stacked using weak vdW forces between the layer
In this paper, a photodetector based on InSe/MoTe2 vertical heterojunction is fabricated, in which MoTe2 serves as the transmission layer and InSe serves as the grating layer to regulate the channel current. The photodetector exhibits excellent photodetection performance due to its vertical structure and high-quality interface. The detectivity of the photodetector shows an ultrahigh value of over 1.05×1
The vertically structured InSe/MoTe2 heterojunction was fabricated using a deterministic dry transferred technique. First, 300 nm silicon oxide insulation layer was deposited on a silicon wafer by plasma-enhanced chemical vapor deposition. The BN thin layer was removed by mechanical stripping and placed on the SiO2/Si substrate to provide a clean and flat interface. Then MoTe2 nanoflakes were mechanically exfoliated from the bulk crystals to the polydimethylsiloxane (PDMS) films and transferred onto the SiO2/Si substrate. Next, several layers of mechanical peeling InSe flakes were artificially stacked on the MoTe2 flakes under the optical microscope (OM, BX51, OLMPUS) assisted by an aligned transfer system. The two-dimensional materials mentioned in the text are commercially available bulk crystals. Finally, multiple electrode patterns were defined by standard electron beam lithography (EBL, Raith eLine Plus), then Ti/Au (10 nm/60 nm) metal stacks were deposited by electron beam evaporation (Ulvac Ei-5z) to form source and drain electrodes. The thickness of the photodetector was determined by AFM (Dimension ICON, American Bruker). Raman spectra were carried out using a Raman spectrometer system (Raman, LABRAM HR, Japan Horriba-JY) with a 532 nm laser source. The atomic structure features of the heterojunction were examined using HRTEM (Talos). The composition and element distribution of the heterojunction were analyzed via EDS mapping on the HRTEM. Before the HRTEM test, the photodetector’s surface was coated with a conductive layer of elemental Cr to facilitate the positioning of the cut sample and the deposition of the protective layer under the focused ion beam (FIB) microscope. The electrical transport properties of the photodetector were carried out by Keithley 2612B and 2400 at room temperature.
The vertically stacked heterostructure based on InSe/MoTe2 is shown in

Fig. 1 Characterization of InSe/MoTe2 heterostructure: (a) Schematic diagram of the InSe/MoTe2 heterostructure; (b) The AFM image of MoTe2 flakes. Inset: morphological characteristics of the InSe/MoTe2 heterojunction; (c) The AFM image of InSe flakes; (d) HRTEM image; (e) EDS of the corresponding elements of the photodetector; (f) Raman spectra of pristine InSe, MoTe2 and overlapped region.
图1 InSe/MoTe2 异质结构的表征:(a) InSe/MoTe2 异质结构示意图;(b) MoTe2 材料的 AFM 图像,插图:InSe/MoTe2 异质结的形貌特征图;(c) InSe 材料的AFM 图像;(d) HRTEM 图像;(e) 光电探测器各层元素的EDS图像;(f) 原始 InSe、MoTe2 和重叠区域的拉曼光谱
The electrical properties of the InSe/MoTe2 heterojunction photodetector were tested under dark conditions.

Fig. 2 Electrical I-V characteristics of the device based on InSe/MoTe2 heterostructure under non-illumination condition: (a) Ids-Vds output characteristics under various back gate voltages; (b) Ids-Vg transfer curves at various drain voltages.
图2 基于InSe/MoTe2异质结构器件在无光照条件下的电学I-V特性:(a) 不同背栅电压下的Ids-Vds输出特性曲线;(b) 不同漏极电压下的Ids-Vg转移特性曲线
To investigate the optoelectronic performance of InSe/MoTe2 heterojunction photodetectors under the illumination, we measured the Ids-Vds curves (

Fig. 3 (a) Schematic structure of the device under laser irradiation; (b)Photo-response of the Ids-Vds output characteristics with different incident light power under 365 nm illumination (Vg = 0 V) ;(c) Photo-response of the Ids-Vg transfer characteristics with different incident light power under 365 nm illumination (Vds = 6 V) ;(d) The Iph as a function of incident light power at Vds = 6 V
图3 (a)激光照射下的器件结构示意图;(b) 在365 nm光照下不同入射光功率的Ids-Vds输出特性曲线(Vg = 0 V) ;(c) 在365 nm光照下 不同入射光功率下Ids-Vg转移特性曲线(Vds = 6 V) ;(d) Vds = 6 V 时,Iph与入射光功率的函数关系
The non-linear relationship between the photocurrent and optical power density can be well fitted with the power law equatio
, | (1) |
where is a constant for a certain wavelength, P is the incident power density and the exponent determines the photoelectric conversion efficiency.
To evaluation the performance of the heterojunction photodetector, the responsivity (R), detectivity (
, | (2) |
, | (3) |
, | (4) |
, | (5) |
where is the incident optical power density, A is the effective illumination area, c is the speed of light, is the incident light wavelength and h is Planck's constant.

Fig.4 (a) Responsivity as a function of the gate voltage under different incident light powers (Vds=6 V); (b) Detectivity as a function of incident light power density (Vds=6 V, Vg=-15 V) ; (c) EQE as a function of the gate voltage under different incident light powers (Vds=6 V) ; (d) Noise equivalent power (NEP) as a function of illumination power intensity (Vg = -15 V, Vds=6 V); (e) Time-dependent photocurrent response under switched-on/off light irradiation with different power intensities at Vds=1 V, Vg=0 V; (f) The rise and decay times of the photocurrent under the power intensity of 16.75 mW/c
图4 (a) 不同入射光功率下的响应度与栅极电压的关系 (Vds=6 V);(b) 探测率与入射光功率密度的函数关系(Vds=6 V,Vg=-15 V);(c) 外量子效率在不同入射光功率下与栅极电压的函数关系 (Vds=6 V);(d) 噪声等效功率与入射光功率密度的函数关系(Vg = -15 V, Vds=6 V);(e)不同功率强度下的光开关特性(Vds=1 V,Vg=0 V);(f)光功率密度为 16.75 mW/cm2 时光电流的上升和衰减时间(Vds = 1 V)
The band gaps of MoTe2 and InSe materials can be adjusted depending on their thickness, which extends the light detection range of the InSe/MoTe2 heterojunction photodetector to the near-infrared.

Fig. 5 (a) Photo-response of the Ids-Vds output characteristics (Vg = 0 V); (b) Photo-response of the Ids-Vg transfer characteristics (Vds = 6 V) under different incident light wavelengths.
图5 (a) 不同光照波长下的Ids-Vd输出特性(Vg = 0 V);(b) 不同光照波长下Ids-Vg转移特性曲线(Vds = 6 V)
The optical switching characteristics of InSe/MoTe2 heterojunction photodetectors under different laser wavelengths are shown in

Fig. 6 (a) Time-dependent photocurrent response with different wavelengths at Vds = 2 V; (b) 2D plot of responsivity as a function of incident light wavelength and gate voltage at Vds=6 V; (c)
图 6 (a)不同波长照射下的光开关特性(Vds = 2 V);(b)响应度随入射光波长和栅极电压变化的二维函数图像;(c) 探测率和外量子效率与入射光波长的函数关系(Vds=6 V, Vg=0 V);(d) 噪声等效功率与不同入射光波长的函数关系
In summary, the vertically stacked InSe/MoTe2 heterojunction photodetector has been fabricated and systematically investigated, where InSe serves as the grating layer to regulate the channel photocurrent through localized or released holes. In terms of photoelectric performance, the InSe/MoTe2 heterojunction photodetector has a fast response time of 21.6 ms at 365 nm, and by modulating the gate voltage and incident optical power, it can achieve a response rate of 300.57 A/W, a maximum detectivity of 1.05 × 1
Acknowledgements
The authors would like to thank the Nano Fabrication Facility, Vacuum Interconnected Nanotech Workstation at Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, and Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences for their technical supports.
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