Two-dimensional photovoltaic detector capable of switching working modes and preparation method and application thereof

Abstract

The invention relates to a two-dimensional photovoltaic detector capable of switching working modes and a preparation method and application thereof. The two-dimensional photovoltaic detector comprises a two-dimensional material layer located on a grid electrode, a source electrode and a drain electrode, the source electrode and the drain electrode are arranged at the two ends of the two-dimensional material layer, and the drain electrode and the two-dimensional material layer are in ohmic contact; a Schottky junction is formed between the source electrode and the two-dimensional material layer; on the other hand, the insulation isolation material layer extends along the surface of the source electrode to cover a part of the surface of the two-dimensional material layer, the source electrode is in ohmic contact with the two-dimensional material layer, and a transverse PN homojunction is formed between the part, not covered by the insulation isolation material layer, of the two-dimensional material layer and the part, covered by the insulation isolation material layer, of the two-dimensional material layer; different voltages are applied between the source electrode and the drain electrode, so that the working mode of the detector is switched between the photodiode and the photoconductive tube; under the condition that a certain voltage is applied to the grid electrode, the detector shows a photovoltaic effect and a rectification behavior.

Description

Technical Field

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

[0002] Photodetectors can 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 people's daily lives. Traditional silicon and InGaAs photodetectors have reached a high level of maturity and dominate the commercial market, but they face challenges in 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 fields due to their advantages such as adjustable interlayer band gap, strong light-matter interaction, no dangling bonds on the surface, and large-scale growth. In the TMDs family, MoS2 stands out due to its excellent physical and optoelectronic properties such as high mobility and stability in air.

[0004] Photodetectors can be mainly divided into photodiodes and photoconductors according to their structure and mechanism. The former usually relies on junctions (Schottky junctions or PN junctions) and photovoltaic effects, with fast response speeds but low responsivity. The latter is based on photoactive channels and photoconductivity effects, and usually has high photoconductivity gain. Two-dimensional MoS2 photodetectors with these two structures have also been well developed, aiming to achieve both fast speed and high gain, but they usually involve complex manufacturing processes such as heterogeneous integration or transfer stacking. Therefore, it is of great significance to develop a photodetector with a simple structure and a simple method to combine the functions of photoconductors and photodiodes. Summary of the invention

[0005] In view of the technical problems existing in the prior art, the primary purpose of the present invention is to provide a two-dimensional photovoltaic detector with switchable working modes, a preparation method and application thereof, in which the photovoltaic effect and rectification behavior are realized by applying a certain voltage to the gate; the photoelectric detection mode can be switched between the photodiode and the photoconductor according to different application scenarios or requirements by applying different bias voltages between the source electrode and the drain electrode. The present invention at least provides the following technical solutions.

[0006] On one hand, the present invention provides a two-dimensional photovoltaic detector with switchable working modes, comprising 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 between the source electrode and 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] Among them, by applying different voltages between the source electrode and the drain electrode, the working mode of the detector is switched between the photodiode and the photoconductor;

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

[0010] On one hand, the present invention provides a two-dimensional photovoltaic detector with switchable working modes, comprising 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 between the drain electrode and 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 part 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] Among them, by applying different voltages between the source electrode and the drain electrode, the working mode of the detector is switched between the photodiode and the photoconductor;

[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 the 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 5nm to 100nm;

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

[0020] Furthermore, the gate comprises 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] Further, a few-layer two-dimensional material layer is obtained by mechanical stripping, 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, and then the substrate is heated at 50° C. to 100° C. for 5 to 10 minutes, which is conducive to the 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 material layer on the gate, and provides a source electrode and a drain electrode at both ends of the two-dimensional material layer, respectively, so that the drain electrode and the two-dimensional material layer are in ohmic contact, the source electrode includes a two-dimensional high work function material layer and a source electrode sublayer, and 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 working mode based on the Schottky junction; further, on the basis of the above device structure, an insulating isolation material layer extending to a part of the surface of the two-dimensional material layer is covered on the source electrode, and a solution doping method is used to dope the part of the surface not covered with the insulating isolation material layer, so that the two-dimensional high work function layer and the two-dimensional material layer are in ohmic contact, and a lateral PN homojunction is formed between the part of the two-dimensional material layer covered with the insulating isolation material layer and the part not covered with the insulating isolation material layer, thereby forming a two-dimensional photovoltaic detector with a switchable working mode based on the lateral PN homojunction; for the two-dimensional photovoltaic detectors of these two structures, the working mode of the device is switched between a photodiode and a photoconductor by applying different bias voltages between the source electrode and the drain electrode; for the photodiode mode, significant rectification and photovoltaic behavior are achieved and adjusted by the gate voltage, and a fast light response speed is achieved. 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 for different needs, enabling potential applications in photodetectors and solar cells.

[0027] In one embodiment, in the 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 the 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 invention has a simple structure and is prepared by simple thermal evaporation and chemical treatment methods. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0030] Figure 2 A schematic diagram of the structure of a two-dimensional MoS2 photovoltaic detector with switchable working modes 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) shows the device in a dark environment with different gate voltages (V g ) sd -V sd The inset shows the rectification ratio vs. V g (b) The figure shows the relationship between different V under illumination 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 responsiveness of the device and the change of light power density.

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

[0034] Figure 6 The light detection performance of the two-dimensional MoS2 photovoltaic detector with switchable working mode based on 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 responsiveness 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 creative work are all within the scope of protection of the present invention. The experimental methods described in the following embodiments 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", etc. to describe various elements, layers, regions, sections, etc. is not intended to be limiting. The use of "having", "containing", "including", "comprising", etc. is open-ended, indicating the presence of the stated elements or features, but does not exclude additional elements or features. Unless the context clearly states otherwise.

[0038] The present invention provides a two-dimensional photovoltaic detector with switchable working modes, which includes 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 a SiO2 insulating layer of about 300 nm thick on the surface, and other suitable material layers can also be used as the gate.

[0039] The two-dimensional material layer is disposed on the gate as a conductive channel layer, and the two-dimensional material layer is, for example, one of a few-layer N-type MoS2 layer, WS2, MoSe2, and InSe. In a preferred embodiment, the two-dimensional material layer uses a few-layer N-type MoS2 layer, and a mechanical stripping method is used to obtain the few-layer two-dimensional N-type MoS2. The PVA dry transfer process is used to transfer the target two-dimensional MoS2 layer to the SiO2 / Si substrate.

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

[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 to 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 rectification behavior.

[0042] In another embodiment, an insulating isolation material layer covers the surface of the source electrode, extends along the surface of the source electrode to cover part of the surface of the two-dimensional material layer, and the remaining part of the surface of the two-dimensional material layer is not covered. A chemical solution is used to dope the part of the two-dimensional material layer not covered with the insulating isolation material layer, so that a lateral PN homojunction is formed between the part not covered with the insulating isolation material layer and the part 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 in photodiode mode, V 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

[0044] First, the SiO2 / Si substrate was soaked in acetone solution, isopropanol solution and deionized water in sequence, and was placed in an ultrasonic instrument for ultrasonic cleaning after each soaking, with an ultrasonic power of 10% and an ultrasonic time of 5 minutes.

[0045] 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 a 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.

[0046] Next, the SiO2 / Si substrate was immersed in hot acetone to remove residual glue of the PVA / PDMS material, then immersed in water, and washed with deionized water and dried with a nitrogen gun.

[0047] Then, a photoresist was spin-coated on the MoS2 two-dimensional material layer at a spin-coating speed of 4000 rpm for 60 seconds, followed by baking at 100°C for 4 minutes.

[0048] 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.

[0049] Next, an atomic layer deposition (ALD) process was used to deposit an insulating isolation material layer of Al2O3 on the upper surface of the device. The deposition process was repeated 450 times, and the deposition thickness of Al2O3 was about 45nm. The Al2O3 layer covered part of the surface of the MoS2 two-dimensional material layer along the surface of the Ti / Au electrode.

[0050] 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 the 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, and 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.

[0051] 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.

[0052] The two-dimensional MoS2 photovoltaic detector with switchable detection mode based on Schottky junction obtained in Example 1 is designed with asymmetric electrodes, Ti / Au is deposited on one side of the MoS2 conductive channel for ohmic contact, and MoO3 / Au is deposited on the other side for Schottky contact. MoO3 has a high work function and forms a Schottky junction at the MoO3 / MoS2 interface. Before doping the device, there is a large Schottky barrier between the MoO3 / Au electrode and MoS2, and the electrode on the other side is an ohmic contact. Figure 3 The middle 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.

[0053] In order to further study the photodetection performance, we sd The dynamic photoresponse under 635nm light was measured at -1, 0 and 1V. sd The relationship between the photocurrent and the optical power density is as follows: Figure 4 Figure (a) shows the change of responsivity (R) with light power density under different bias voltages. sd At 0 and -1V, 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 A / W, which is nearly 3 orders of magnitude larger than that of the photodiode mode (1.8A / W). These results show that the photodetection mode can be switched between photodiode and photoconductor by applying different bias voltages, so that the operation mode can be selected according to different requirements.

[0054] The two-dimensional MoS2 photovoltaic detector with switchable detection mode based on lateral PN junction obtained in Example 1 is based on the above-mentioned Schottky device, and we chemically treat the exposed MoS2 part with P-type doping. After treatment, the MoS2 covered with Al2O3 still remains N-type, while the unprotected part is doped as P-type-MoS2. In this case, a lateral PN junction can be formed at the interface. Figure 5 Figure (a) shows the I sd -Vsd It is observed that the PN homojunction also exhibits rectification behavior, with a current rectification ratio exceeding 10 2 , and the photovoltaic effect is also observed, V oc is -0.3V, I sc is 8nA. Figure 5 As shown in Figure (b), the photovoltaic characteristics of a lateral PN diode can be controlled by the gate voltage (V g ) is modulated. As V g The reduction of power conversion efficiency (PCE) and fill factor (FF) increases. Especially in V g At −20 V, the PCE and FF can reach 5.2% and 47%, respectively, which indicates that the device has great potential in photovoltaic applications.

[0055] 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 0 and 1V V sd , the device switches to photodiode mode very quickly, about 10ms, but with a relatively low responsivity of 443mA / W.

[0056] In summary, the Schottky and PN junction detectors with bias-switchable modes of the present invention have been demonstrated to have photovoltaic characteristics and photoconductor performance, thereby enabling potential applications in photodetectors and solar cells.

[0057] 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 equivalent replacement methods and are included in the protection scope 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 two 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; Among them, by applying different voltages between the source electrode and the drain electrode, the working mode of the detector is switched between the photodiode and the photoconductor; When a certain voltage is applied to the gate, the detector exhibits photovoltaic effect and rectification behavior.

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 two 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 part 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; Among them, by applying different voltages between the source electrode and the drain electrode, the working mode of the detector is switched between the photodiode and the photoconductor; When a certain voltage is applied to the gate, the detector exhibits photovoltaic effect and rectification behavior.

3. The two-dimensional photovoltaic detector according to claim 1 or 2, characterized in that: The two-dimensional material layer is one of n-type semiconductors MoS2, WS2, MoSe2, and InSe; the thickness of the two-dimensional material layer is 1nm to 50nm.

4. The two-dimensional photovoltaic detector according to claim 3, characterized in that: The two-dimensional high work function material layer is one of MoO3, WO3, Pt, and Pd.

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

6. 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; the thickness of the insulating isolation material layer is 5nm to 100nm; Preferably, the insulating isolation material layer is Al2O3 formed by an atomic layer deposition process.

7. The two-dimensional photovoltaic detector according to claim 1, 2, 4, 5 or 6, characterized in that: The gate comprises a heavily doped Si substrate, and a SiO2 insulating layer is disposed 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 8, characterized in that: A few-layer two-dimensional material layer is obtained by mechanical stripping, 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, 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 claim 1, 2, 4, 5, 7 or 9, characterized in that: The drain electrode is a Ti / Au electrode; the source electrode sublayer is an Au layer.

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