A two-dimensional photovoltaic detector with switchable working modes and its preparation method and application

Abstract

The present invention relates to a two-dimensional photovoltaic detector with switchable working modes, as well as a preparation method and application thereof. The detector comprises a two-dimensional material layer located on a gate, a source electrode and a drain electrode arranged at both ends of the two-dimensional material layer, and an ohmic contact between the drain electrode and the two-dimensional material layer; a Schottky junction is formed between the source electrode and the two-dimensional material layer; on the other hand, an insulating isolation material layer extends along the surface of the source electrode to cover part of the surface of the two-dimensional material layer, and an ohmic contact is formed between the source electrode and the two-dimensional material layer, and a lateral PN homojunction is formed between the portion of the two-dimensional material layer not covered by the insulating isolation material layer and the portion covered by the insulating isolation material layer; by applying different voltages between the source electrode and the drain electrode, the working mode of the detector is switched between a photodiode and a photoconductor; under the condition that a certain voltage is applied to the gate, the detector exhibits a photovoltaic effect and a rectifying behavior.

Description

Technical Field

[0001] The present invention relates to the fields of photoelectric detection and photovoltaics, and in particular to a two-dimensional photovoltaic detector with switchable working modes, a preparation method thereof, and applications thereof. Background Art

[0002] Photodetectors convert incident light into electrical signals and are widely used in digital cameras, optical communications, machine vision, and industrial inspection, playing an indispensable role in today's information technology and our daily lives. Traditional silicon and InGaAs photodetectors have reached a high level of maturity and dominate the commercial market, but they face challenges in terms of low cost, transparency, and flexibility due to their epitaxial growth, bulk, and rigid properties.

[0003] In recent years, two-dimensional transition metal dichalcogenides (TMDs) have been widely used in various photodetector applications due to their advantages, including tunable interlayer band gaps, strong light-matter interactions, the absence of dangling bonds on the surface, and the ability to grow on a large scale. Among TMDs, MoS2 stands out for its excellent physical and optoelectronic properties, including high mobility and stability in air.

[0004] Photodetectors can be broadly categorized into photodiodes and photoconductors based on their structure and mechanism. The former typically relies on a junction (Schottky junction or PN junction) and the photovoltaic effect, resulting in fast response speed but low responsivity. The latter, on the other hand, utilizes a photoactive channel and the photoconductive effect, typically exhibiting high photoconductive gain. Two-dimensional MoS2 photodetectors with these two structures have also been well developed, aiming to achieve both high speed and high gain, but these typically involve complex fabrication processes such as heterojunction integration or transfer stacking. Therefore, developing a photodetector combining the functionalities of both photoconductors and photodiodes with a simple structure and facile methods is of great significance. Summary of the Invention

[0005] To address the technical issues existing in the prior art, the primary objective of the present invention is to provide a two-dimensional photovoltaic detector with switchable operating modes, as well as its preparation method and application. In this detector, the photovoltaic effect and rectification behavior are achieved by applying a certain voltage to the gate. The photodetection mode can be switched between a photodiode and a photoconductor by applying different bias voltages between the source and drain electrodes, depending on the application scenario or requirements. The present invention provides at least the following technical solutions.

[0006] In one aspect, the present invention provides a two-dimensional photovoltaic detector with switchable operating modes, comprising a gate, a two-dimensional material layer located on the gate, a source electrode and a drain electrode respectively disposed at both ends of the two-dimensional material layer, wherein the drain electrode forms an ohmic contact with the two-dimensional material layer;

[0007] The source electrode comprises a two-dimensional high work function material layer and a source electrode sublayer, the two-dimensional high work function material layer is located between the source electrode sublayer and the two-dimensional material layer, and a Schottky junction is formed between the two-dimensional high work function material layer and the two-dimensional material layer;

[0008] The working mode of the detector is switched between a photodiode and a photoconductor by applying different voltages between the source electrode and the drain electrode.

[0009] When a certain voltage is applied to the gate, the detector exhibits photovoltaic effect and rectification behavior.

[0010] In one aspect, the present invention provides a two-dimensional photovoltaic detector with switchable operating modes, comprising a gate, a two-dimensional material layer located on the gate, a source electrode and a drain electrode respectively disposed at both ends of the two-dimensional material layer, wherein the drain electrode forms an ohmic contact with the two-dimensional material layer;

[0011] The source electrode comprises a two-dimensional high work function material layer and a source electrode sublayer, the two-dimensional high work function material layer is located between the source electrode sublayer and the two-dimensional material layer, and the two-dimensional high work function material layer is in ohmic contact with the two-dimensional material layer;

[0012] an insulating isolation material layer covering the surface of the source electrode, extending along the surface of the source electrode to cover a portion of the surface of the two-dimensional material layer, and forming a lateral PN homojunction between a portion of the two-dimensional material layer not covered by the insulating isolation material layer and a portion covered by the insulating isolation material layer;

[0013] The working mode of the detector is switched between a photodiode and a photoconductor by applying different voltages between the source electrode and the drain electrode.

[0014] When a certain voltage is applied to the gate, the detector exhibits photovoltaic effect and rectification behavior.

[0015] Furthermore, the two-dimensional material layer is one of n-type semiconductors MoS2, WS2, MoSe2, and InSe; and the thickness of the two-dimensional material layer is 1 nm to 50 nm.

[0016] Furthermore, the two-dimensional high work function material layer is one of MoO3, WO3, Pt, and Pd.

[0017] Furthermore, the thickness of the two-dimensional high work function material layer is 1 nm to 20 nm.

[0018] Furthermore, the insulating isolation material layer is at least one of Al2O3, SiO2, HfO2, hBN, and AlN; the thickness of the insulating isolation material layer is 5 nm to 100 nm;

[0019] Preferably, the insulating isolation material layer is Al2O3 formed by an atomic layer deposition process.

[0020] Furthermore, the gate includes a heavily doped Si substrate, and a SiO2 insulating layer is provided on the surface of the Si substrate.

[0021] Furthermore, a chemical solution is used to dope the portion of the two-dimensional material layer not covered by the insulating isolation material layer to form a lateral PN homojunction.

[0022] Furthermore, a mechanical exfoliation method is used to obtain a few layers of two-dimensional material, and a PVA dry transfer process is used to transfer the target two-dimensional material layer to the Si substrate to form the two-dimensional material layer. Subsequently, the substrate is heated at 50°C to 100°C for 5 to 10 minutes to facilitate adhesion between the two-dimensional material and the substrate.

[0023] The source electrode and the drain electrode are prepared by photolithography and thermal evaporation processes.

[0024] Furthermore, the drain electrode is a Ti / Au electrode; and the source electrode sublayer is an Au layer.

[0025] Compared with the prior art, the present invention has at least the following beneficial effects:

[0026] The present invention provides a two-dimensional photovoltaic detector with a switchable operating mode based on the Schottky junction by disposing a two-dimensional material layer on the gate, and disposing a source electrode and a drain electrode at both ends of the two-dimensional material layer, respectively. The drain electrode forms an ohmic contact with the two-dimensional material layer, and the source electrode includes a two-dimensional high work function material layer and a source electrode sublayer. A Schottky junction is formed between the two-dimensional high work function material layer and the two-dimensional material layer, thereby forming a two-dimensional photovoltaic detector with a switchable operating mode based on the Schottky junction. Furthermore, based on the above device structure, an insulating isolation material layer is covered on the source electrode and extends to a portion of the surface of the two-dimensional material layer. The portion of the surface not covered by the insulating isolation material layer is doped using a solution doping method, so that the two-dimensional high work function layer and the two-dimensional material layer form an ohmic contact, and a lateral PN homojunction is formed between the portion of the two-dimensional material layer covered by the insulating isolation material layer and the portion not covered by the insulating isolation material layer, thereby forming a two-dimensional photovoltaic detector with a switchable operating mode based on the lateral PN homojunction. The two-dimensional photovoltaic detectors with these two structures switch the operating mode between a photodiode and a photoconductor by applying different bias voltages between the source electrode and the drain electrode. In the photodiode mode, significant rectification and photovoltaic behavior are achieved and adjusted by the gate voltage, resulting in a fast light response speed. For the photoconductor mode, the photoconductive effect leads to an optical gain mechanism and high responsivity. This switchable mode capability enables the device to be customized according to different needs, enabling potential applications in photodetectors and solar cells.

[0027] In one embodiment, in photodiode mode, the device can achieve significant rectification and photovoltaic behavior, and achieve a fast light response speed (about 10ms) by adjusting the gate voltage. In photoconductor mode, the photoconductive effect can lead to an optical gain mechanism and up to 10 3 The two-dimensional photovoltaic detector provided by the present invention has a switchable operation mode, which enables our device to be customized for photoelectric detection applications according to different needs.

[0028] The device provided by the present invention has a simple structure and is prepared by simple thermal evaporation and chemical treatment methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the structure of a two-dimensional MoS2 photovoltaic detector with switchable working mode based on Schottky junction provided in Example 1.

[0030] Figure 2 Schematic diagram of the structure of a two-dimensional MoS2 photovoltaic detector with switchable working mode based on a lateral PN junction provided in Example 1.

[0031] Figure 3 The performance test of the two-dimensional MoS2 photovoltaic detector with switchable working mode based on Schottky junction in Example 1. (a) The figure shows the device in a dark environment with different gate voltages (V g ) under I sd -V sd Curve, inset shows the rectification ratio vs. V g (b) The figure shows the relationship between different V g I sd -V sd curve, the inset shows the V g Related V oc and I sc .

[0032] Figure 4 The light detection performance of the two-dimensional MoS2 photovoltaic detector with switchable working mode based on Schottky junction in Example 1 under 635nm laser, (a) shows the relationship between the photocurrent of the device and the change of light power density; (b) shows the relationship between the responsivity of the device and the change of light power density.

[0033] Figure 5 This is the performance test of the two-dimensional MoS2 photovoltaic detector with switchable working mode based on the lateral PN junction of Example 1. (a) Figure shows the I of the device in the dark and under light. sd -V sdCurve; (b) The power conversion efficiency (PCE) and fill factor (FF) of the device are plotted as V g .

[0034] Figure 6 The light detection performance of the two-dimensional MoS2 photovoltaic detector with switchable working mode based on the lateral PN junction of Example 1 under 635nm laser, (a) is the relationship between the photocurrent of the device and the change of light power density; (b) is the relationship between the responsivity of the device and the change of light power density. DETAILED DESCRIPTION

[0035] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings of the present invention. The described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, other embodiments obtained by ordinary technicians in this field without making creative work are all within the scope of protection of the present invention. The experimental methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials, unless otherwise specified, can be obtained from public commercial channels.

[0036] Spatially relative terms such as "below," "beneath," "below," "above," "upper," etc. are used in this specification to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the device in addition to different orientations than those depicted in the figures.

[0037] In addition, the use of terms such as "first," "second," and the like to describe various elements, layers, regions, sections, and the like is not intended to be limiting. The use of "having," "containing," "including," and "comprising" are open-ended terms that indicate the presence of stated elements or features, but do not exclude additional elements or features, unless the context clearly indicates otherwise.

[0038] The present invention provides a two-dimensional photovoltaic detector with switchable operating modes, comprising a gate, a two-dimensional material layer, a source electrode, and a drain electrode. In a preferred embodiment, the gate is a heavily doped Si substrate with an approximately 300nm thick SiO2 insulating layer on its surface. Other suitable material layers may also be used as the gate.

[0039] A two-dimensional material layer is disposed on the gate as a conductive channel layer. The two-dimensional material layer can be, for example, a few-layer N-type MoS2 layer, WS2, MoSe2, or InSe. In a preferred embodiment, the two-dimensional material layer is a few-layer N-type MoS2 layer. Mechanical exfoliation is used to obtain the few-layer two-dimensional N-type MoS2 layer, and a PVA dry transfer process is used to transfer the target two-dimensional MoS2 layer to a SiO2 / Si substrate.

[0040] The source electrode and the drain electrode are respectively arranged at both ends of the two-dimensional material layer. The drain electrode forms an ohmic contact with the two-dimensional material layer, for example, a Ti / Au electrode. The thickness of the Ti layer is about 2 nm, and the thickness of the Au layer is about 50 nm.

[0041] The source electrode includes a two-dimensional high work function material layer and a source electrode sublayer. The work function of the two-dimensional high work function material layer is greater than 5.2eV, and its thickness is 1nm~20nm, for example, it is one of MoO3, WO3, Pt, and Pd; in a preferred embodiment, the two-dimensional high work function material layer is MoO3, and its thickness is 10nm. The two-dimensional high work function material layer is located between the source electrode sublayer and the two-dimensional material layer, and a Schottky junction is formed between the two-dimensional high work function material layer and the two-dimensional material layer. The source electrode sublayer is, for example, an Au layer. In a preferred embodiment, the source electrode is a MoO3 / Au electrode. A certain voltage is applied between the source electrode and the drain electrode, for example, a source-drain voltage V sd When it is 0V and -1V, it behaves like a photodiode. sd When the gate voltage is 1 V, the device behaves as a photoconductor. When a certain voltage is applied to the gate side, the device exhibits photovoltaic effect and rectifying behavior.

[0042] In another embodiment, an insulating isolation material layer covers the surface of the source electrode and extends along the surface of the source electrode to cover part of the surface of the two-dimensional material layer. The remaining surface of the two-dimensional material layer is uncovered. A chemical solution is used to dope the portion of the two-dimensional material layer not covered with the insulating isolation material layer, thereby forming a lateral PN homojunction between the portion not covered with the insulating isolation material layer and the portion covered with the insulating isolation material layer. At this time, a certain voltage is applied between the source electrode and the drain electrode, for example, a source-drain voltage V sd When it is 0V and -1V, it behaves as a photodiode mode. sd When the gate voltage is -1 V, the device behaves in photoconductor mode. When a certain voltage is applied to the gate side, the device exhibits photovoltaic effect and rectification behavior.

[0043] Example 1: First, the SiO2 / Si substrate was soaked in acetone solution, isopropyl alcohol solution, and deionized water in sequence, and after each soaking, it was placed in an ultrasonic instrument for ultrasonic cleaning, with an ultrasonic power of 10% and an ultrasonic time of 5 minutes.

[0044] Next, cut the PVA / PDMS material of appropriate size, use the mechanical stripping method to obtain a thin layer of MoS2, select a thin layer of MoS2 with a larger area and relatively flat thickness as the target two-dimensional material layer, and use the PVA / PDMS material to transfer the selected target two-dimensional material layer to the above-mentioned cleaned SiO2 / Si substrate.

[0045] Next, the SiO2 / Si substrate was immersed in hot acetone to remove the residual glue of the PVA / PDMS material, then immersed in water, washed with deionized water, and dried with a nitrogen gun.

[0046] Then, photoresist was spin-coated on the MoS2 two-dimensional material layer at a spin-coating speed of 4000 rpm for 60 seconds, and then baked at 100°C for 4 minutes.

[0047] Ti (2nm) / Au (50nm) and MoO3 (10nm) / Au (50nm) electrodes were deposited on both ends of the MoS2 two-dimensional material layer using UV lithography and thermal evaporation. Thus, a two-dimensional MoS2 photovoltaic detector based on Schottky junction was prepared. Its device structure is as follows Figure 1 shown.

[0048] Next, an atomic layer deposition (ALD) process was used to deposit an insulating isolation layer of Al2O3 on the top surface of the device. This deposition process was repeated 450 times, resulting in a thickness of approximately 45nm. The Al2O3 layer extended along the surface of the Ti / Au electrode and partially covered the MoS2 two-dimensional material layer.

[0049] Next, a chemical solution is used to dope the portion of the MoS2 layer that is not covered with the insulating isolation material layer to form a lateral PN homojunction. Specifically, 30 mg of gold chloride (AuCl3) powder is dissolved in 5 mL of nitromethane to form a 20 mM solution, and then this solution (20 mM) is ultrasonically treated at 60 ° C for 3 hours, and then filtered to remove larger Au aggregates to prepare a P-type doped AuCl3 chemical solution. 3-5 drops of 20 mM AuCl3 solution are dropped on the SiO2 / Si substrate with the MoS2 device, spin-coated at 3000 rpm for 1 minute, and then baked on a heating table at 100 ° C for 5 minutes. The MoS2 layer not covered with the Al2O3 layer is doped to P type, completing the doping treatment of the P-type chemical solution. The device structure is as shown below. Figure 2 shown.

[0050] At this point, the transformation of the two-dimensional MoS2 photovoltaic detector from Schottky junction to lateral PN junction has been completed, and a two-dimensional MoS2 photovoltaic detector with switchable detection mode based on lateral PN junction has been prepared.

[0051] The two-dimensional MoS2 photovoltaic detector with a switchable detection mode based on a Schottky junction, as obtained in Example 1, features asymmetric electrodes. Ti / Au is deposited on one side of the MoS2 conductive channel for an ohmic contact, while MoO3 / Au is deposited on the other side for a Schottky contact. MoO3 has a high work function, forming a Schottky junction at the MoO3 / MoS2 interface. Before doping, a large Schottky barrier exists between the MoO3 / Au electrode and the MoS2, leaving the other electrode in an ohmic contact. Figure 3 Figure (a) shows different gate voltages V under dark conditions g I sd -V sd The curves show a clear and gate-adjustable rectification behavior. (a) The inset shows the rectification ratio vs. V g The rectification ratio can reach an optimal value of about 10 3 . I under light sd -V sd The curve is shown in Figure (b), and the inset shows the V oc and I sc With V g , proving the gate-adjustable photovoltaic effect.

[0052] In order to further study the photodetection performance, we sd The dynamic photoresponse under 635 nm light was measured at -1, 0 and 1 V. sd The relationship between the photocurrent and the optical power density is as follows: Figure 4 As shown in Figure (a). Figure (b) shows the change of responsivity (R) with optical power density under different bias voltages. sd At 0 and -1 V, it behaves like a photodiode, with a fast response but no gain. sd When the voltage is 1V, the device behaves as a photoconductor and the photoresponsivity can reach 10 3 The A / W is nearly three orders of magnitude greater than that of the photodiode mode (1.8 A / W). These results indicate that the photodetection mode can be switched between photodiode and photoconductor by applying different bias voltages, allowing the operation mode to be selected according to different requirements.

[0053] The two-dimensional MoS2 photovoltaic detector with a switchable detection mode based on a lateral PN junction, obtained in Example 1, is based on the aforementioned Schottky device. The exposed MoS2 portion undergoes a chemical treatment to induce p-type doping. After this treatment, the MoS2 covered with Al2O3 remains n-type, while the unprotected portion is doped to p-type MoS2. In this case, a lateral PN junction can form at the interface. Figure 5 Figure (a) shows the I sd-V sd It is observed that the PN homojunction also exhibits rectification behavior, with a current rectification ratio exceeding 10 2 , and the photovoltaic effect was also observed, V oc is -0.3V, I sc is 8nA. Figure 5 As shown in Figure (b), the photovoltaic characteristics of the lateral PN diode can be adjusted by the gate voltage (V g ) is modulated. As V g The power conversion efficiency (PCE) and fill factor (FF) increase. g At −20 V, the PCE and FF can reach 5.2% and 47%, respectively, indicating that the device has great potential in photovoltaic applications.

[0054] Similar to Schottky devices, lateral PN homojunction detectors also have switchable detection modes by applying different bias voltages. Figure 6 Figures (a) and (b) show the different V sd The photocurrent and responsivity change with the light power density. sd When V is -1V, the device works in the photoconductive mode, the photocurrent is large, but the response speed is slow. Due to the existence of photoconductive gain, the response can be as high as 35.4A / W under weak light power. On the other hand, by applying V of 0 and 1V sd , the device switches to photodiode mode very quickly, about 10ms, but with a relatively low responsivity of 443mA / W.

[0055] In summary, the bias-switchable Schottky and PN junction detectors of the present invention have been demonstrated to possess photovoltaic and photoconductor properties, thus enabling potential applications in photodetectors and solar cells.

[0056] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A two-dimensional photovoltaic detector with switchable working modes, characterized in that: It includes a gate, a two-dimensional material layer located on the gate, a source electrode and a drain electrode respectively arranged at both ends of the two-dimensional material layer, and an ohmic contact is formed between the drain electrode and the two-dimensional material layer; The source electrode comprises a two-dimensional high work function material layer and a source electrode sublayer, the two-dimensional high work function material layer is located between the source electrode sublayer and the two-dimensional material layer, and a Schottky junction is formed between the two-dimensional high work function material layer and the two-dimensional material layer; The working mode of the detector is switched between a photodiode and a photoconductor by applying different voltages between the source electrode and the drain electrode. Under the condition of applying a certain voltage to the gate, the detector exhibits photovoltaic effect and rectification behavior; The two-dimensional material layer is one of n-type semiconductors MoS2, WS2, MoSe2, and InSe, and the two-dimensional high work function material layer is one of MoO3, WO3, Pt, and Pd.

2. A two-dimensional photovoltaic detector with switchable working modes, characterized in that: It includes a gate, a two-dimensional material layer located on the gate, a source electrode and a drain electrode respectively arranged at both ends of the two-dimensional material layer, and an ohmic contact is formed between the drain electrode and the two-dimensional material layer; The source electrode comprises a two-dimensional high work function material layer and a source electrode sublayer, the two-dimensional high work function material layer is located between the source electrode sublayer and the two-dimensional material layer, and the two-dimensional high work function material layer is in ohmic contact with the two-dimensional material layer; an insulating isolation material layer covering the surface of the source electrode, extending along the surface of the source electrode to cover a portion of the surface of the two-dimensional material layer, and forming a lateral PN homojunction between a portion of the two-dimensional material layer not covered by the insulating isolation material layer and a portion covered by the insulating isolation material layer; The working mode of the detector is switched between a photodiode and a photoconductor by applying different voltages between the source electrode and the drain electrode. Under the condition of applying a certain voltage to the gate, the detector exhibits photovoltaic effect and rectification behavior; The two-dimensional material layer is one of n-type semiconductors MoS2, WS2, MoSe2, and InSe, and the two-dimensional high work function material layer is one of MoO3, WO3, Pt, and Pd.

3. The two-dimensional photovoltaic detector according to claim 1 or 2, characterized in that: The thickness of the two-dimensional material layer is 1 nm to 50 nm.

4. The two-dimensional photovoltaic detector according to claim 3, characterized in that: The thickness of the two-dimensional high work function material layer is 1 nm to 20 nm.

5. The two-dimensional photovoltaic detector according to claim 2, characterized in that: The insulating isolation material layer is at least one of Al2O3, SiO2, HfO2, hBN, and AlN; and the thickness of the insulating isolation material layer is 5 nm to 100 nm.

6. The two-dimensional photovoltaic detector according to claim 5, characterized in that: The insulating isolation material layer is Al2O3 formed by an atomic layer deposition process.

7. The two-dimensional photovoltaic detector according to any one of claims 1, 2, 4, 5 and 6, characterized in that: The gate includes a heavily doped Si substrate, and a SiO2 insulating layer is provided on the surface of the Si substrate.

8. The two-dimensional photovoltaic detector according to claim 2 or 6, characterized in that: A chemical solution is used to dope the portion of the two-dimensional material layer not covered by the insulating isolation material layer to form a lateral PN homojunction.

9. The two-dimensional photovoltaic detector according to claim 7, characterized in that: A few two-dimensional material layers are obtained by mechanical exfoliation, and the target two-dimensional material layer is transferred to the Si substrate by a PVA dry transfer process to form the two-dimensional material layer, and then the substrate is heated at 50° C. to 100° C. for 5 to 10 minutes; The source electrode and the drain electrode are prepared by photolithography and thermal evaporation processes.

10. The two-dimensional photovoltaic detector according to any one of claims 1, 2, 4, 5 and 9, characterized in that: The drain electrode is a Ti / Au electrode; the source electrode sublayer is an Au layer.

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