A photodetector with a composite structure of noble metal nanowires and two-dimensional molybdenum disulfide and its preparation method

Abstract

The present invention provides a photodetector of a composite structure of noble metal nanowires and two-dimensional molybdenum disulfide and a preparation method thereof. First, a first noble metal nanowire array consisting of a plurality of parallel noble metal nanowires is prepared on an oxidized silicon wafer; a monolayer molybdenum disulfide film is then transferred to the top of the first noble metal nanowire array on the oxidized silicon wafer by a micromechanical peeling method; finally, a second noble metal nanowire array and a noble metal electrode are constructed on the monolayer molybdenum disulfide film, and the nanowires of the second noble metal nanowire array and the nanowires of the first noble metal nanowire array are perpendicular to each other to form a noble metal nanogrid, thereby obtaining a photodetector based on a composite structure. The preparation method makes the width and spacing of the noble metal nanowires more controllable, and can realize flexible modulation of the optical properties of two-dimensional materials. The structure can firmly localize and enhance the light field, improve the light absorption capacity and sensitivity of the photodetector, and has strong light detection performance.

Description

Technical Field

[0001] The present invention relates to the technical field of optoelectronic devices, and more specifically to a photoelectric detector having a composite structure of noble metal nanowires and two-dimensional molybdenum disulfide and a preparation method thereof. Background Art

[0002] Photodetectors can convert light signals in a certain wavelength band into electrical signals, and therefore have a wide range of applications in fields such as communications and sensing. Studies have shown that two-dimensional MoS2 photodetectors have the advantages of small size, high responsiveness, wide wavelength band, and ultra-sensitivity, but due to the atomic-level thickness of two-dimensional MoS2, its light absorption capacity is poor. Summary of the invention

[0003] In view of the shortcomings of traditional two-dimensional MoS2 photodetectors with weak light absorption performance, the present invention proposes a photodetector with a composite structure of noble metal nanowires and two-dimensional MoS2 and a preparation method thereof, which utilizes the noble metal nanowires to generate surface plasmons under the excitation of a light field, and utilizes the surface localization and near-field enhancement properties of the surface plasmons to enhance the light field near the two-dimensional MoS2 and concentrate it on the two-dimensional MoS2, thereby overcoming the problem of weak light absorption ability of a single two-dimensional MoS2 photodetector, improving the sensitivity of the photodetector to light, and achieving optimization of detection performance.

[0004] The present invention adopts the following technical solution:

[0005] A method for preparing a photoelectric detector having a composite structure of noble metal nanowires and two-dimensional molybdenum disulfide, characterized in that it comprises the following steps:

[0006] Step 1: preparing a first noble metal nanowire array consisting of a plurality of noble metal nanowires arranged in parallel on an oxidized silicon wafer;

[0007] Step 2: Transferring a monolayer of molybdenum disulfide film onto the first noble metal nanowire array on the silicon oxide wafer by micromechanical peeling;

[0008] Step 3: Construct a second noble metal nanowire array and a noble metal electrode on the single-layer molybdenum disulfide film. The second noble metal nanowire array is also composed of a plurality of parallel noble metal nanowires, and the nanowires of the second noble metal nanowire array and the nanowires of the first noble metal nanowire array are perpendicular to each other to form a noble metal nanogrid, thereby obtaining a photodetector based on a composite structure.

[0009] Furthermore, the noble metal nanowires are gold nanowires or silver nanowires.

[0010] Furthermore, the spacing between the noble metal nanowires is 100-250 nm, and the width and thickness of the noble metal nanowires are both 30-80 nm.

[0011] Furthermore, the noble metal nanowires in step 1 and step 3 are prepared by electron beam lithography and evaporation technology:

[0012] First, a photoresist is coated on a silicon oxide wafer or a molybdenum disulfide film using a coating machine. After the photoresist is baked, an electron beam lithography machine is used to photolithograph parallel nanometer-sized strip patterns and positioning patterns on the silicon oxide wafer, and then development and fixing treatment are performed to obtain a patterned substrate.

[0013] Then evaporate or deposit a layer of precious metal film on the patterned substrate, and then place the silicon oxide wafer in a degumming solution to remove excess photoresist and precious metal film; after the degumming is completed, soak the silicon oxide wafer in acetone, IPA and deionized water in turn for cleaning, and then dry the silicon oxide wafer after cleaning.

[0014] Furthermore, the photoresist is PMMA A5 positive photoresist, and the oxidized silicon wafer is preheated to 70°C before coating the photoresist; during the photoresist coating process, the process parameters of the photoresist spreader are: first gear speed 500r / min, photoresist spreading time 5s; second gear speed 2500r / min, photoresist spreading time 60s; third gear speed 1000r / min, photoresist spreading time 10s; gear shift acceleration is 2500r / min / s; photoresist baking temperature is 150°C, and baking time is 2min.

[0015] Furthermore, the process parameters of the electron beam lithography machine during lithography are: acceleration voltage 125kV, electron beam current 1nA, exposure dose 1600μC / cm 2 / Vs; The photolithography process also includes the step of photolithography of a cross mark pattern.

[0016] Furthermore, during the development and fixing processes, a solution of methyl isobutyl ketone (MIBK) / isopropyl alcohol (IPA) = 1 / 3 was selected as a developer, and IPA was selected as a fixer. The time for the development and fixing processes was 60 seconds and 15 seconds, respectively.

[0017] Furthermore, when removing the excess photoresist and precious metal film, N-methylpyrrolidone (NMP) is selected as the degumming liquid. First, the silicon oxide wafer to be stripped is immersed in a sealed container containing NMP and soaked at 80°C for 3 to 4 hours until the photoresist expands significantly. The silicon oxide wafer is clamped and the photoresist is lifted up by the flowing liquid and stripped off by blowing air.

[0018] Furthermore, the preparation method of the first noble metal nanowire array and the second noble metal nanowire array in step 1 and step 3 is to first prepare a layer of noble gold film by electrochemical deposition, ion sputtering, magnetron sputtering or vacuum deposition, and then etch out a plurality of parallel arranged nanowires by chemical etching or laser etching.

[0019] The preparation method is a photoelectric detector with a composite structure of noble metal nanowires and two-dimensional molybdenum disulfide.

[0020] Surface plasmons refer to surface waves formed by collective coherent oscillations of surface electrons of precious metal nanostructures such as gold and silver under the excitation of light. They have the characteristics of local and near-field enhancement, and can greatly enhance the light field near the metal surface. Surface plasmons can be used to manipulate light at the nanoscale, breaking through the limits of optical diffraction. By rationally designing the composite structure of precious metal nanostructures and two-dimensional materials, flexible modulation of the optical properties of two-dimensional materials can be achieved. In addition, under appropriate excitation conditions, when the surface plasmons of multiple nanostructures work together, the electromagnetic fields between the nanostructures will be coupled, and the light field will be concentrated in the gaps of the nanostructures, that is, the gap mode surface plasmons, which generate electromagnetic field intensity much higher than the electromagnetic field intensity of a single nanostructure surface plasmon.

[0021] Noble metal nanowires can simultaneously excite two forms of surface plasmons under light fields. One is the conductive surface plasmon that propagates along the long axis, which can form a stable waveguide; the other is the localized surface plasmon generated in the nanoscale short axis direction, which will lead to strong local field enhancement. By constructing a composite structure of noble metal nanowires and two-dimensional MoS2, the external optical environment of two-dimensional MoS2 can be enhanced, thereby improving the light absorption of two-dimensional MoS2 and optimizing the detection performance of photodetectors.

[0022] The present invention constructs two layers of mutually perpendicular noble metal nanowire arrays on a base material to form a noble metal nanowire network structure, and places a monolayer of molybdenum disulfide between the two layers of noble metal nanowire arrays, that is, the monolayer of molybdenum disulfide is located in the grid gap. Under the excitation of light, the free electrons on the surface of molybdenum disulfide oscillate collectively, and couple with photons to produce surface plasmon resonance. Under the joint action of surface plasmons of multiple nanostructures, the light field will be confined to a very small range on the surface of molybdenum disulfide and enhanced, greatly enhancing the light field near molybdenum disulfide. The present invention uses the surface plasmons excited by the noble metal nanowire array under the light field and the gap mode surface plasmons at the intersection of the noble metal nanowire grid to firmly localize and enhance the light field, which can greatly improve the light absorption of the monolayer of molybdenum disulfide, thereby improving the sensitivity of the photodetector to light and optimizing the detection performance.

[0023] At the same time, since the present invention is a structural improvement based on the traditional two-dimensional molybdenum disulfide photodetector, it retains the original advantages of small size, high responsiveness, wide band and ultra-sensitivity.

[0024] Furthermore, since the present invention uses electron beam lithography technology to construct the noble metal nanowire array, the width and spacing of the noble metal nanowires have greater controllability, and the optical properties of the two-dimensional material can be flexibly modulated. With the continuous breakthroughs in the preparation of high-quality two-dimensional molybdenum disulfide, this method provides a technical solution for the development and application of new two-dimensional molybdenum disulfide photodetectors. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the structure of photolithography of the first layer of noble metal nanowire array and positioning pattern on the substrate;

[0026] Figure 2 It is a schematic diagram of the structure after transferring a single layer of MoS2 film;

[0027] Figure 3 It is a schematic diagram of the structure of a photodetector with a composite structure of a noble metal nanowire grid and a single-layer molybdenum disulfide.

[0028] Figure 4 This is the transfer characteristic curve of the Ag / MoS2 / Ag composite structure photodetector under 532nm excitation light.

[0029] Figure 5 This is the light switch and response speed test curve of Ag / MoS2 / Ag composite structure photodetector under 532nm excitation light.

[0030] Figure 6 This is the transfer characteristic curve of a single-layer MoS2 phototransistor under 532nm excitation light.

[0031] Figure 7 This is the light switching and response speed test curve of the single-layer MoS2 phototransistor under 532nm excitation light.

[0032] In the figure: 1-silicon oxide wafer; 2-first noble metal nanowire array; 3-positioning pattern; 4-molybdenum disulfide film; 5-electrode; 6-second noble metal nanowire array. DETAILED DESCRIPTION

[0033] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

[0034] The method for preparing the photoelectric detector of the composite structure of noble metal nanowires and two-dimensional molybdenum disulfide of the present invention comprises the following steps:

[0035] Step 1: Use acetone, anhydrous ethanol and deionized water in sequence to ultrasonically clean the surface of the 300nm thick silicon oxide wafer 1 for 5 to 10 minutes, with an ultrasonic power of 30 to 50W. After cleaning, blow dry with a nitrogen gun.

[0036] Step 2: PMMA A5 positive photoresist was selected. Before coating, the silicon oxide wafer 1 was preheated on a hot plate at 70°C for 2 minutes. The coating machine was set as follows: the first gear speed was 500r / min, the coating time was 5s; the second gear speed was 2500r / min, the coating time was 60s; the third gear speed was 1000r / min, the coating time was 10s; the gear shift acceleration was 2500r / min / s; after coating, the silicon oxide wafer 1 was placed on a hot plate at 150°C for 2 minutes; then, the silicon oxide wafer 1 was placed on the electron beam lithography machine for photolithography. The nanometer-sized strip patterns and cross mark patterns are arranged in rows. The process parameters of the electron beam lithography machine are: acceleration voltage 125kV, electron beam current 1nA, exposure dose 1600μC / cm2 / Vs, the spacing between the photolithographic silver nanowires is 100nm, and the width and thickness of the silver nanowires are both 50nm; after the photolithography is completed, development and fixing operations are performed, and methyl isobutyl ketone (MIBK) / isopropyl alcohol (IPA) = 1 / 3 solution is selected as the developer, and IPA is used as the fixer. The development and fixing times are 60s and 15s, respectively.

[0037] Step 3: Use electron beam evaporation equipment to evaporate a 50nm thick silver film on the patterned substrate. Immediately after the evaporation is completed, place the silicon oxide wafer 1 in the degumming solution. Select N-methylpyrrolidone (NMP) as the degumming solution. First, immerse the silicon oxide wafer 1 to be stripped in NMP, seal the container and place it on a hot plate at 80°C for 3 to 4 hours. When the photoresist on the silicon oxide wafer 1 is soaked until it is obviously expanded, use tweezers to clamp and fix the silicon oxide wafer in the solvent, and use a straw inserted into the solution to blow the upper surface of the silicon oxide wafer horizontally from the four sides of the silicon oxide wafer 1, so that the photoresist is lifted by the flowing liquid and peeled off. When the stripping is completed, immerse the silicon oxide wafer 1 in acetone, IPA and deionized water in turn for cleaning. After blowing dry with a nitrogen gun, place the silicon oxide wafer 1 on a hot plate at 60°C to dry, and obtain Figure 1 The structure shown.

[0038] Step 4: Use a blue film tape to tear the molybdenum disulfide sample 5 to 8 times by micromechanical peeling method and then transfer it to the PDMS film. In the two-dimensional material transfer platform, dry transfer the monolayer molybdenum disulfide film 4 to the first silver nanowire array 2 of the silicon oxide wafer 1 to obtain Figure 2 The structure shown.

[0039] Step 5: Coat PMMA A5 type photoresist on the molybdenum disulfide film 4 again. Before coating, preheat the silicon oxide wafer 1 on a hot plate at 70°C for 2 minutes. The process parameters of the coating machine are the same as those of the first coating. After coating, the silicon oxide wafer 1 is placed on a hot plate at 150°C and baked for 2 minutes; after baking, the silicon oxide wafer 1 is placed in an electron beam lithography machine for overlay, and the cross mark pattern in the electronic layout is first overlapped with the cross mark pattern generated by the first photolithography to ensure that the electrode pattern falls accurately in the predetermined area. On the monolayer of molybdenum disulfide, parallel nano-sized strip patterns and electrode 5 patterns are photolithographically arranged, and the nanowires of the second silver nanowire array 6 and the nanowires of the first silver nanowire array 2 are perpendicular to each other to form a silver nano-grid. The spacing between the photolithographic silver nanowires is 100nm, and the width and thickness of the silver nanowires are both 50nm. After the photolithography is completed, the same development and fixing operations as before are performed again.

[0040] Step 6: Use electron beam evaporation equipment to evaporate a 50nm thick silver film on the patterned substrate. NMP is selected as the degumming liquid to complete the stripping process, and the stripping steps are the same as those in step 3. Then, the silicon oxide wafer is sequentially soaked in acetone, IPA and deionized water for cleaning, and after being blown dry with a nitrogen gun, the silicon oxide wafer 1 is placed on a hot plate at 60°C for drying to obtain a photodetector based on a composite structure.

[0041] The performance of photodetectors can be evaluated by the following indicators: responsivity, external quantum efficiency, detection rate and response speed. The present invention uses a composite structure of Ag nanowires and MoS2 for testing. In the photoelectric test, a suitable laser power is set and an excitation light with a wavelength of 532nm is selected to irradiate the surface of the single-layer MoS2 channel of the back-gate phototransistor.

[0042] The responsivity R reflects the photoelectric conversion efficiency of the photodetector, which is defined as the photocurrent I generated by the photodetector. P With the incident light power P in The ratio of is:

[0043]

[0044] In the formula, I ill is the source-drain current of the device under light field, I d is the dark current of the device, I P is the photocurrent of the device, P in is the optical power of the incident light.

[0045] From formula (1), we can see that the factors that determine the responsivity R are the incident light intensity P in and photocurrent I P , and the photocurrent I P The size of the source-drain voltage V dsand gate voltage V g About. Figure 4 As shown in the figure, the transfer curve of the device under the light field shows that when V g =60V, V ds =500mV, P in =100μW, the source-drain current of the device is ill =80nA, while the dark current I d =24nA. Therefore, the device responsivity R at this time can be calculated to be approximately 0.56mA / W.

[0046] External quantum efficiency EQE refers to the ratio of the number of photoelectrons generated by a photodetector per second to the number of incident light quanta. It describes the efficiency of the device in utilizing photons. The corresponding formula is:

[0047]

[0048] In the formula, Planck constant h is 6.62607015×10 -34 J·s, the speed of light c is 3×10 8 m / s, υ is the frequency of light, and λ is the wavelength of light.

[0049] From formula (2), we can know that the external quantum efficiency is proportional to the responsivity and inversely proportional to the wavelength of light. In this experiment, the wavelength λ is 532nm. Substituting it and the previously obtained responsivity R into formula (2), we can obtain the external quantum efficiency EQE of this device, which is about 1.30×10 -3 .

[0050] Detection rate D * It is an important parameter to describe the detection capability of photodetectors, which is used to reflect the device's ability to detect weak light. When the noise in the phototransistor mainly comes from the dark current I d When the detection rate D * It can be expressed as:

[0051]

[0052] Where A is the area of ​​the channel.

[0053] The length and width of the channel of the device measured in the experiment are both about 4μm. Substituting into equation (3) we can get the detection rate D of the device. * About 3.13×10 4 Jones.

[0054] In the light response speed test, a 532nm excitation light with a power of 100μW is selected, and a signal generator is used to digitally modulate the laser switch. Under the periodic switching light, the source-drain current I dsWhen the on and off time of the light is 10s, the device obtains a stable switching response current, such as Figure 5 (a) shown.

[0055] In the high-frequency optical response speed test, the rising edge t r =5μs, falling edge t f = 8μs, such as Figure 5 (b) The rising and falling edges of the device both reach the microsecond level, showing a very high light response speed.

[0056] Under the same experimental conditions, Figure 6 , Figure 7 , the responsivity of the single-layer MoS2 photodetector can be obtained as R = 0.1 mA / W, and the external quantum efficiency EQE = 2.3×10 -4 , detection rate D * =2.5×10 4 Jones, the rising edge of the device t r =6ms, falling edge t f =7ms.

[0057] The test results of the Ag / MoS2 / Ag photodetector and the single-layer MoS2 photodetector prepared by the present invention are shown in Table 1. The performance parameters of the Ag / MoS2 / Ag photodetector are improved compared with those of the single-layer MoS2 phototransistor. In particular, in terms of light response speed, the rising and falling edges are improved by three orders of magnitude compared with the single-layer MoS2 phototransistor.

[0058] Table 1 Performance parameters of Ag / MoS2 / Ag photodetector and single-layer MoS2 photodetector

[0059]

[0060] In the above specific embodiment, the precious metal nanowires are silver nanowires. In addition, precious metal nanowires such as gold nanowires and platinum nanowires also have the same surface plasmon effect as silver nanowires. Therefore, precious metal nanowires such as gold nanowires and platinum nanowires can also be used to replace the above silver nanowires to achieve the same effect.

[0061] The spacing between the noble metal nanowires can be 100-250nm, and the width and thickness of the noble metal nanowires can be 30-80nm. In addition to being prepared by the above-mentioned electron beam lithography and evaporation technology, the metal nanowires can also be prepared by other methods, such as first preparing a layer of noble gold film by electrochemical deposition, ion sputtering, magnetron sputtering or vacuum deposition, and then etching a plurality of parallel nanowires by chemical etching or laser etching.

[0062] The above embodiments are only preferred embodiments of the present invention and are not limitations of the technical solutions of the present invention. Any technical solution that can be implemented on the basis of the above embodiments without creative work should be deemed to fall within the scope of protection of the patent of the present invention.

Claims

1. A method for preparing a photoelectric detector of a composite structure of noble metal nanowires and two-dimensional molybdenum disulfide, characterized in that: The steps include: Step 1: preparing a first noble metal nanowire array (2) consisting of a plurality of noble metal nanowires arranged in parallel on an oxidized silicon wafer (1); Step 2: transferring the monolayer molybdenum disulfide film (4) onto the first noble metal nanowire array (2) on the oxidized silicon wafer (1) by a micromechanical peeling method; Step 3: constructing a second noble metal nanowire array (6) and a noble metal electrode (5) on the monolayer molybdenum disulfide film (4), wherein the second noble metal nanowire array (6) is also composed of a plurality of parallel noble metal nanowires, and the nanowires of the second noble metal nanowire array (6) and the nanowires of the first noble metal nanowire array (2) are perpendicular to each other to form a noble metal nanogrid, thereby obtaining a photodetector based on a composite structure; The spacing between the noble metal nanowires is 100-250nm, and the width and thickness of the noble metal nanowires are both 30-80nm.

2. The method for preparing a photoelectric detector of a composite structure of noble metal nanowires and two-dimensional molybdenum disulfide according to claim 1, characterized in that: The noble metal nanowires are gold nanowires or silver nanowires.

3. The method for preparing a photoelectric detector of a composite structure of noble metal nanowires and two-dimensional molybdenum disulfide according to any one of claims 1 to 2, characterized in that: The noble metal nanowires in step 1 and step 3 are prepared by electron beam lithography and evaporation technology: First, a photoresist is coated on a silicon oxide wafer (1) or a molybdenum disulfide film (4) by using a coating machine, and after the photoresist is baked, a parallel-arranged nanometer-sized strip pattern and a positioning pattern (3) are photoetched on the silicon oxide wafer (1) by using an electron beam lithography machine, and then a development and fixing process is performed to obtain a patterned substrate; Then, a layer of noble metal film is evaporated or deposited on the patterned substrate, and then the silicon oxide wafer (1) is placed in a degumming solution to remove excess photoresist and the noble metal film; After the degumming is completed, the oxidized silicon wafer (1) is sequentially immersed in acetone, IPA and deionized water for cleaning, and then the oxidized silicon wafer (1) is dried after cleaning.

4. The method for preparing a photoelectric detector of a composite structure of noble metal nanowires and two-dimensional molybdenum disulfide according to claim 3, characterized in that: The photoresist is PMMA A5 type positive photoresist. Before coating the photoresist, the oxidized silicon wafer (1) is preheated to 70° C.; during the photoresist coating process, the process parameters of the coating machine are as follows: first gear speed 500 r / min, coating time 5 s; second gear speed 2500 r / min, coating time 60 s; third gear speed 1000 r / min, coating time 10 s; gear shift acceleration is 2500 r / min / s; photoresist baking temperature is 150° C., baking time is 2 min.

5. The method for preparing a photoelectric detector of a composite structure of noble metal nanowires and two-dimensional molybdenum disulfide according to claim 3, characterized in that: The process parameters of electron beam lithography are: acceleration voltage 125kV, electron beam current 1nA, exposure dose 1600μC / cm 2 / Vs; the photolithography process also includes the step of photolithography positioning pattern (3).

6. The method for preparing a photoelectric detector of a composite structure of noble metal nanowires and two-dimensional molybdenum disulfide according to claim 3, characterized in that: During the development and fixing processes, a solution of methyl isobutyl ketone (MIBK) / isopropyl alcohol (IPA) = 1 / 3 was selected as a developer and IPA was selected as a fixer. The time for the development and fixing processes was 60 seconds and 15 seconds respectively.

7. The method for preparing a photoelectric detector of a composite structure of noble metal nanowires and two-dimensional molybdenum disulfide according to claim 3, characterized in that: When removing the excess photoresist and precious metal film, the degumming liquid is N-methylpyrrolidone (NMP). First, the silicon oxide wafer (1) to be stripped is immersed in a sealed container containing NMP and soaked at 80° C. for 3 to 4 hours until the photoresist swells significantly. The silicon oxide wafer (1) is clamped and the photoresist is lifted up by the flowing liquid and stripped off by blowing air.

8. The method for preparing a photoelectric detector of a composite structure of noble metal nanowires and two-dimensional molybdenum disulfide according to any one of claims 1 to 2, characterized in that: The preparation method of the first noble metal nanowire array and the second noble metal nanowire array in step 1 and step 3 is to first prepare a layer of noble gold film by electrochemical deposition, ion sputtering, magnetron sputtering or vacuum deposition, and then etch out a plurality of parallel arranged nanowires by chemical etching or laser etching.

9. A photoelectric detector having a composite structure of noble metal nanowires and two-dimensional molybdenum disulfide prepared by the preparation method according to any one of claims 1 to 8.

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