Van der waals heterojunction self-powered photodetector and preparation method and application thereof

Abstract

The application belongs to the technical field of two-dimensional material optoelectronic devices, and relates to a van der Waals heterojunction self-powered photodetector and a preparation method and application thereof. The van der Waals heterojunction self-powered photodetector comprises a substrate, a pair of electrodes and a two-dimensional material heterojunction structure. The substrate comprises a Si layer and a SiO2 layer arranged on the upper surface of the Si layer. The pair of electrodes are arranged on the upper surface of the SiO2 layer at intervals to form an electrode channel. The two-dimensional material heterojunction structure is arranged in the electrode channel and comprises a van der Waals heterojunction formed by n WSe2 layers and n MoWSe4 layers. The WSe2 layers and the MoWSe4 layers are alternately stacked along the thickness direction, the WSe2 layers and the MoWSe4 layers locally overlap in the electrode channel, and the overlapping region forms the van der Waals heterojunction. The built-in electric field formed at the overlapping region of the van der Waals heterojunction is used to realize effective separation, directional transport and stable output of photo-generated carriers under the condition of no external bias, so as to realize self-powered photodetection.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional material optoelectronic device technology, and relates to a van der Waals heterojunction self-powered photodetector, its preparation method and application. Background Technology

[0002] Photodetectors are widely used in optical communication, environmental monitoring, bioimaging, intelligent sensing, and integrated optoelectronic systems. Most existing photodetectors require an external bias voltage to operate. While they can achieve a certain light response output, they generally suffer from high power consumption, complex system structure, limited long-term stability, and limitations in portable, miniaturized, and integrated applications. With the rapid development of low-power electronic devices, wearable systems, and self-powered sensing technologies, self-powered photodetectors capable of outputting photoelectric signals without an external bias voltage are gradually becoming an important research direction in this field.

[0003] Two-dimensional materials, due to their atomic-level thickness, absence of dangling bonds, clean interfaces, ease of transfer and stacking, and excellent photoelectric properties, show promising application prospects in novel optoelectronic devices. In particular, van der Waals heterojunctions composed of two different two-dimensional materials can utilize the differences in work function and band structure between the materials to form a built-in electric field at the interface. This built-in electric field can drive the separation and transport of photogenerated electrons and holes without external bias voltage, thus providing a foundation for the realization of self-powered photodetectors. Therefore, compared to single-material devices, two-dimensional van der Waals heterojunctions have significant advantages in low power consumption, self-powering capabilities, and high-sensitivity photodetection.

[0004] Existing photodetectors based on single two-dimensional materials typically suffer from limited photogenerated carrier separation efficiency, high recombination probability, and weak output signal under zero bias conditions, thus limiting their self-powered performance. Therefore, how to construct a heterojunction device with high interface quality, a significant built-in electric field, and effective photoresponse output under zero bias conditions is a technical problem that urgently needs to be solved in this field.

[0005] MoWSe4, a two-dimensional layered alloyed selenide material, possesses a narrow bandgap of approximately 1.01 eV, which is beneficial for extending the optical response of devices from the visible to the near-infrared band. Multilayer WSe2, with a bandgap of approximately 1.2 eV, is a typical two-dimensional transition metal chalcogenide, exhibiting good carrier transport capability, stability, and interface compatibility. By constructing a MoWSe4 / WSe2 van der Waals heterojunction, not only can zero-bias self-powered detection be achieved using the built-in electric field at the heterojunction interface, but the device also possesses the potential to extend its optical response from the visible to the near-infrared band. Furthermore, this structure combines the advantages of easy integration, low power consumption, and scalability of two-dimensional materials, demonstrating promising application prospects.

[0006] Therefore, there is an urgent need to propose a self-powered photodetector based on MoWSe4 / WSe2 van der Waals heterojunction to solve the problems of existing photodetectors relying on external bias voltage, as well as the low efficiency of photogenerated carrier separation, weak output photocurrent, and difficulty in achieving stable self-powered detection under zero bias voltage conditions for single two-dimensional material devices. Summary of the Invention

[0007] While existing photodetectors are widely used in optical communication, environmental monitoring, bioimaging, and intelligent sensing, they still have the following shortcomings: 1) Most photodetectors rely on external bias voltage for driving. Traditional photodetectors typically require a certain external voltage to operate and obtain a significant photocurrent output. This not only increases device power consumption but also raises system complexity, hindering low-power, miniaturized, and portable integrated applications. 2) Single-material devices have limited performance in self-powered mode. Although two-dimensional materials possess excellent photoelectric properties, photodetectors built based on a single material often suffer from low efficiency in separating photogenerated electron-hole pairs, severe carrier recombination, and weak output signals under zero bias conditions, making it difficult to meet the practical requirements of self-powered detection. 3) Existing two-dimensional material photodetectors struggle to balance wide-band response and stable photocurrent output in low-power detection applications in the visible to near-infrared bands. Although some devices can achieve photoresponse at specific wavelengths, their response range is limited, and their response capability to changes in light intensity is insufficient, failing to meet the needs of various application scenarios.

[0008] The purpose of this invention is to construct a van der Waals heterojunction of MoWSe4 / WSe2, forming a built-in electric field at the interface, enabling the device to achieve effective separation and directional transport of photogenerated carriers under zero bias conditions, thereby outputting a stable photoelectric signal. It also has the application potential to extend from the visible band to the near-infrared band. The aim is to provide a two-dimensional heterojunction device solution with a simple structure, easy integration, and stable output of photoelectric signals under zero bias for applications such as low-power intelligent visual sensing, distributed environmental monitoring, and portable photoelectric identification.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows:

[0010] On one hand, the present invention provides a van der Waals heterojunction self-powered photodetector, comprising: The substrate includes a Si layer and a SiO2 layer disposed on the upper surface of the Si layer; A pair of electrodes are spaced apart on the upper surface of the SiO2 layer to form an electrode channel; A two-dimensional material heterojunction structure, disposed within the electrode channel, comprises a van der Waals heterojunction formed by n WSe2 layers and n MoWSe4 layers; wherein... The WSe2 layer and the MoWSe4 layer are stacked alternately along the thickness direction, such that the materials of any two adjacent layers in the stacking sequence are different from each other; The WSe2 layer and the MoWSe4 layer partially overlap within the electrode channel, and the overlapping region forms a van der Waals heterojunction. The WSe2 layer covers the upper surface of an electrode and extends into the electrode channel, then covers the upper surface of the SiO2 layer; The MoWSe4 layer covers the upper surface of the other electrode and extends into the electrode channel, then covers the upper surface of the WSe2 layer.

[0011] Furthermore, the van der Waals heterojunction forms a built-in electric field in the overlapping region to separate photogenerated electrons and holes under zero bias conditions.

[0012] In this invention, the van der Waals heterojunction interface can form a built-in electric field. This built-in electric field is used to achieve effective separation and directional transport of photogenerated carriers under zero bias conditions, thereby outputting photocurrent and realizing self-powered photoelectric detection.

[0013] Furthermore, the number of WSe2 layers is equal to the number of MoWSe4 layers.

[0014] Furthermore, n is an integer greater than or equal to 1.

[0015] Furthermore, the thickness of the WSe2 layer is 8-20 nm, and the thickness of the MoWSe4 layer is 5-15 nm.

[0016] Furthermore, the Si layer is a p-type highly doped silicon layer (thickness of 650 μm, resistivity of 0.001 Ω·cm), and the SiO2 layer is an insulating dielectric layer (thickness of 285 nm).

[0017] Furthermore, the electrode has a double-layer metal structure.

[0018] Furthermore, the dual-layer metal structure includes a nickel layer (5 nm thick) as an adhesion layer and a gold layer (50 nm thick) as the main conductive layer.

[0019] On the other hand, a method for fabricating the van der Waals heterojunction self-powered photodetector described in this invention is provided, comprising the following steps: S1. A SiO2 layer is formed on the upper surface of the Si layer to obtain a substrate; S2. A pair of electrodes are spaced apart on the upper surface of the SiO2 layer to form an electrode channel; S3. Transfer the WSe2 layer into the electrode channel and cover the upper surface of one electrode; S4. Transfer the MoWSe4 layer over the WSe2 layer and cover the upper surface of the other electrode, so that the overlapping area covered by the MoWSe4 layer and the WSe2 layer forms a van der Waals heterojunction.

[0020] The invention also provides the application of the van der Waals heterojunction self-powered photodetector in zero-bias self-powered optical detection and / or dynamic optical signal detection.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention realizes self-powered photodetection under zero bias conditions. Compared with traditional photodetectors that rely on external bias driving, the present invention is beneficial to improve the light response output capability of the device and demonstrates good self-powered detection capability.

[0022] (2) The present invention has good photoresponse stability and repeatability. Under illumination conditions of different wavelengths and different light power densities, it can produce clear, stable and repeatable photocurrent changes, indicating that the van der Waals heterojunction self-powered photodetector of the present invention has good response consistency and working stability, and is suitable for practical photodetection scenarios.

[0023] (3) The present invention has the potential to further expand the multifunctional photodetector. Since MoWSe4 has a narrow band gap (1.01eV) and WSe2 (band gap 1.2eV) has good carrier transport characteristics, the van der Waals heterojunction self-powered photodetector of the present invention can achieve zero bias self-powered photoresponse and also has the potential to extend from the visible band to the near-infrared band, which is beneficial to wide-band low-power photodetector applications.

[0024] (4) The present invention improves the separation efficiency of photogenerated carriers. Due to the band difference at the heterojunction interface and the effect of the built-in electric field, the electron-hole pairs generated under illumination can be quickly separated and transported in a directional manner, thereby reducing the carrier recombination probability. Compared with single two-dimensional material devices, it can improve photoelectric conversion efficiency and photoresponse output capability. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of a van der Waals heterojunction structure.

[0026] Figure 2 Optical image of a van der Waals heterostructure.

[0027] Figure 3 (a) Optical response characteristics of the van der Waals heterojunction; (b) Switching response of the van der Waals heterojunction at different wavelengths; (c) Switching response of the van der Waals heterojunction at different optical powers.

[0028] Figure 4 This is the frequency response diagram of a van der Waals heterojunction under zero bias.

[0029] Figure label: Figure 1 In the diagram: 100: substrate; 200: electrode; 300: two-dimensional material heterojunction structure. Detailed Implementation

[0030] The technical solution of the present invention will be described below with reference to embodiments. However, the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental methods and detection methods described in each embodiment are conventional methods; unless otherwise specified, the reagents and materials are all commercially available.

[0031] In this embodiment of the invention, the thickness direction refers to the direction perpendicular to the upper surface of the substrate (i.e., the upper surface of the SiO2 layer), which is the direction in which the two-dimensional material layers are stacked sequentially from bottom to top. Since the two-dimensional material has atomic-level thickness, its thickness direction is the longitudinal direction of the vertical stacking of each material layer.

[0032] A stacked sequence refers to the order in which WSe2 and MoWSe4 layers are arranged alternately along the thickness direction. In this stacked sequence, any two adjacent layers are different materials, meaning that WSe2 and MoWSe4 layers alternate. When n=1, the stacked sequence is WSe2 / MoWSe4; when n≥2, the stacked sequence is WSe2 / MoWSe4 / WSE2 / MoWSe4 / … and so on. This alternating stacked structure allows for the formation of multiple built-in electric fields at various heterojunction interfaces, further enhancing the separation, directional transport, and stable output efficiency of photogenerated carriers.

[0033] Example 1 This embodiment provides a van der Waals heterojunction self-powered photodetector and its fabrication method. (1) Device structure This embodiment provides a van der Waals heterojunction self-powered photodetector, including: The substrate 100 includes a Si layer and a SiO2 layer disposed on the upper surface of the Si layer; A pair of electrodes 200 are spaced apart on the upper surface of the SiO2 layer to form an electrode channel; A two-dimensional heterojunction structure 300 is disposed within an electrode channel, comprising a van der Waals heterojunction formed by n WSe2 layers and n MoWSe4 layers. The WSe2 and MoWSe4 layers are alternately stacked along the thickness direction, such that the materials of any two adjacent layers in the stacking sequence are different. The WSe2 and MoWSe4 layers locally overlap within the electrode channel, forming a van der Waals heterojunction in the overlapping region, serving as the main photoelectric response region of the device. The WSe2 layer covers the upper surface of one electrode 200, extends into the electrode channel, and then covers the upper surface of the SiO2 layer. The MoWSe4 layer covers the upper surface of the other electrode 200, extends into the electrode channel, and then covers the upper surface of the WSe2 layer. The van der Waals heterojunction forms a built-in electric field in the overlapping region, used to separate photogenerated electrons and holes under zero bias conditions. In this embodiment of the invention, the van der Waals heterojunction interface can form a built-in electric field. This built-in electric field is used to achieve effective separation and directional transport of photogenerated carriers under zero bias conditions, thereby outputting photocurrent and realizing self-powered photoelectric detection.

[0034] The number of WSe2 layers and MoWSe4 layers are equal; n is an integer greater than or equal to 1; the thickness of the WSe2 layer is 8-20 nm, and the thickness of the MoWSe4 layer is 5-15 nm; the Si layer is a p-type highly doped silicon layer (thickness 650 μm, resistivity 0.001 Ω·cm), and the SiO2 layer is an insulating dielectric layer (thickness 285 nm); silver paste is coated on the back of the silicon to improve the back conductive contact conditions and enhance the stability of the test connection; the electrode 200 is a double-layer metal structure, which includes a nickel layer (thickness 5 nm) as an adhesion layer and a gold layer (thickness 50 nm) as the main conductive layer. The nickel (Ni) layer is used to enhance the adhesion performance between the electrode 200 and the substrate 100; the gold (Au) layer is used to achieve stable electrical contact and signal output of the van der Waals heterojunction self-powered photodetector; the width of the electrode 200 is 5 μm, and the electrode channel spacing is 5 μm.

[0035] (2) Acquisition of two-dimensional materials and construction of heterogeneous structures like Figure 1 As shown, WSe2 and MoWSe4 sheets were obtained by mechanical exfoliation (obtained from the corresponding bulk crystal materials respectively by mechanical exfoliation), and suitable sheets were selected. WSe2 was then transferred to the channel region, and MoWSe4 was transferred over WSe2 to form an overlap region, thereby constructing a MoWSe4 / WSe2 van der Waals heterojunction. The bulk WSe2 and bulk MoWSe4 crystals were gradually thinned using repeated tape peeling. The resulting thin layers were then transferred to an intermediate carrier or target substrate. Sheets with complete morphology and suitable thickness were selected using optical microscopy as the two-dimensional materials required for device fabrication. Figure 2[Bright corresponds to laser irradiation on the material, generating photocurrent in the device; dark corresponds to the state where the light source is off (no light)] The bottom WSe2 region and the upper MoWSe4 region are marked. The heterojunction overlap region is located in the center of the device and is connected to the electrodes 200 on both sides for subsequent electrical and optoelectronic performance testing. Since the two-dimensional materials are mainly bonded by van der Waals forces, heterojunction structures can be formed by transfer stacking. This structure not only reduces the fabrication difficulty but also improves the flexibility of material combination and device design.

[0036] (3) Working principle The core of this invention lies in the built-in electric field formed at the MoWSe4 / WSe2 heterojunction interface. Before MoWSe4 and WSe2 come into contact, the two materials have different Fermi level positions. After they come into contact and form a van der Waals heterojunction, charge redistribution occurs at the interface due to carrier diffusion, establishing a built-in electric field at the heterojunction interface pointing from the n-type MoWSe4 side to the p-type WSe2 side, resulting in band bending and the formation of a heterojunction barrier. Under illumination, the heterojunction region absorbs incident photons, generating electron-hole pairs. Photogenerated carriers undergo directional separation under the influence of the built-in electric field, with electrons migrating towards the MoWSe4 side and holes towards the WSe2 side, thus forming a photocurrent in the external circuit. Due to the presence of the built-in electric field, the device of this invention can still achieve effective photoresponse under zero bias conditions, possessing self-powered detection potential. Furthermore, this heterojunction structure can effectively reduce the recombination probability of photogenerated carriers, which is beneficial to improving the device's photoresponse output capability.

[0037] Figure 3 Figure (a) shows the photoresponse test results of the device (van der Waals heterojunction self-powered photodetector) of the present invention under a 0V external bias condition, with test wavelengths of 635nm, 650nm, and 785nm. As can be seen from the figure, under each wavelength of illumination, when the light source is turned on, the device can quickly generate a significant photocurrent response; when the light source is turned off, the current returns to its initial state, exhibiting good periodic switching characteristics. Figure 3 Figure (b) shows the time response curves of the device under 650nm illumination and 0V bias conditions for different optical power densities. As the incident light power density gradually increases, the amplitude of the output photocurrent of the device also increases, indicating that the device of the present invention can generate a stable response to changes in external light intensity under zero bias conditions and has a clear self-powered detection characteristic. Figure 4The frequency response diagram of the van der Waals heterojunction under zero bias is shown. By periodically modulating the incident light and testing the output response of the device at different modulation frequencies, it can be seen that the heterojunction device has a good tracking ability for time-varying optical signals. This indicates that the device can not only achieve stable static optical detection under zero bias, but also meet the requirements of certain dynamic optical signal detection.

[0038] The above results demonstrate that the MoWSe4 / WSe2 van der Waals heterojunction constructed in this invention can achieve effective photoresponse output without external bias voltage, verifying the promoting effect of the built-in electric field at the heterojunction interface on the separation and transport of photogenerated carriers, and also proving that the device possesses the basic functions of a self-powered photodetector. Furthermore, the device exhibits clear switching response characteristics under illumination conditions of different wavelengths and optical power densities, indicating that it has good response stability and repeatability.

[0039] (4) Preparation method This embodiment provides a method for fabricating a van der Waals heterojunction self-powered photodetector, including the following steps: S1. A SiO2 layer is formed on the upper surface of the Si layer to obtain substrate 100; S2. A pair of electrodes 200 are spaced apart on the upper surface of the SiO2 layer to form an electrode channel; S3. Transfer the WSe2 layer into the electrode channel and cover the upper surface of one electrode; S4. Transfer the MoWSe4 layer over the WSe2 layer and cover the upper surface of the other electrode, so that the overlapping area covered by the MoWSe4 layer and the WSe2 layer forms a van der Waals heterojunction.

[0040] Specifically, two-dimensional materials are first obtained from WSe2 and MoWSe4 crystals through mechanical exfoliation. Then, the WSe2 material is transferred to the electrode channel region as the lower layer. Next, the MoWSe4 material is transferred on top of the WSe2, causing them to overlap in a localized area, thus constructing a MoWSe4 / WSe2 van der Waals heterojunction (MoWSe4 and WSe2 are obtained as two-dimensional sheets through mechanical exfoliation, and a van der Waals heterojunction region is constructed between adjacent electrodes using a transfer stacking method). In this embodiment, the MoWSe4 material is located on the upper layer with a thickness controlled at 5-15 nm; the WSe2 material is located on the lower layer with a thickness controlled at 8-20 nm. By controlling the overlap position and coverage area of ​​the two materials, the heterojunction region is located between adjacent electrodes, ensuring that the test current can pass through this heterojunction region. Finally, silver paste is coated on the back side of the silicon substrate to enhance the back contact of the substrate and improve the connection stability during testing.

[0041] It should be understood that the disclosed invention is not limited to the specific methods, schemes, and substances described, as these are all subject to variation. It should also be understood that the terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the scope of the invention, which is limited only by the appended claims.

Claims

1. A van der Waals heterojunction self-powered photodetector, characterized in that, include: The substrate includes a Si layer and a SiO2 layer disposed on the upper surface of the Si layer; A pair of electrodes are spaced apart on the upper surface of the SiO2 layer to form an electrode channel; A two-dimensional material heterojunction structure, disposed within the electrode channel, comprises a van der Waals heterojunction formed by n WSe2 layers and n MoWSe4 layers; wherein... The WSe2 layer and the MoWSe4 layer are stacked alternately along the thickness direction, such that the materials of any two adjacent layers in the stacking sequence are different from each other; The WSe2 layer and the MoWSe4 layer partially overlap within the electrode channel, and the overlapping region forms a van der Waals heterojunction. The WSe2 layer covers the upper surface of an electrode and extends into the electrode channel, then covers the upper surface of the SiO2 layer; The MoWSe4 layer covers the upper surface of the other electrode and extends into the electrode channel, then covers the upper surface of the WSe2 layer.

2. The van der Waals heterojunction self-powered photodetector according to claim 1, characterized in that, The van der Waals heterojunction forms a built-in electric field in the overlapping region to separate photogenerated electrons and holes under zero bias conditions.

3. The van der Waals heterojunction self-powered photodetector according to claim 1, characterized in that, The number of WSe2 layers is equal to the number of MoWSe4 layers.

4. The van der Waals heterojunction self-powered photodetector according to claim 1, characterized in that, The n is an integer greater than or equal to 1.

5. The van der Waals heterojunction self-powered photodetector according to claim 1, characterized in that, The thickness of the WSe2 layer is 8-20 nm, and the thickness of the MoWSe4 layer is 5-15 nm.

6. The van der Waals heterojunction self-powered photodetector according to claim 1, characterized in that, The Si layer is a p-type highly doped silicon layer, and the SiO2 layer is an insulating dielectric layer.

7. The van der Waals heterojunction self-powered photodetector according to claim 1, characterized in that, The electrode has a double-layer metal structure.

8. The van der Waals heterojunction self-powered photodetector according to claim 7, characterized in that, The dual-layer metal structure includes a nickel layer as an adhesion layer and a gold layer as the main conductive layer.

9. The method for fabricating a van der Waals heterojunction self-powered photodetector according to any one of claims 1-8, characterized in that, Includes the following steps: S1. A SiO2 layer is formed on the upper surface of the Si layer to obtain a substrate; S2. A pair of electrodes are spaced apart on the upper surface of the SiO2 layer to form an electrode channel; S3. Transfer the WSe2 layer into the electrode channel and cover the upper surface of one electrode; S4. Transfer the MoWSe4 layer over the WSe2 layer and cover the upper surface of the other electrode, so that the overlapping area covered by the MoWSe4 layer and the WSe2 layer forms a van der Waals heterojunction.

10. The application of the van der Waals heterojunction self-powered photodetector according to any one of claims 1-8 in zero-bias self-powered optical detection and / or dynamic optical signal detection.

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