A photodetector based on bottom metal regulation and a preparation method thereof

Abstract

The application discloses a kind of photodetector based on bottom metal regulation and preparation method thereof, comprising the following steps: substrate surface photoetching two electrode area patterns and metal regulation layer area pattern, electrode and metal regulation layer are evaporated simultaneously in electrode area pattern and metal regulation layer area pattern and remove photoresist, MoS2 film is transferred to electrode and metal regulation layer, after annealing, photodetector based on bottom metal regulation is obtained.The metal regulation layer of the application forms Schottky barrier after contacting with MoS2 film, and built-in electric field perpendicular to channel is introduced through metal regulation layer, to promote the separation of photo-generated carriers in MoS2 device channel; Bottom electrode is protruding compared to substrate, MoS2 channel does not contact with substrate, optimize the bottom interface of MoS2 channel, improve carrier transport efficiency and response speed, compared with original MoS2 device, rise / fall time reaches 7.3 / 47 μs, to realize superfast response.

Description

Technical Field

[0001] This invention relates to the field of photodetector technology, and more specifically to a photodetector based on bottom metal modulation and its fabrication method. Background Technology

[0002] Photodetectors are fundamental components in modern information transmission. However, with continuous technological innovation, the power consumption, response performance, manufacturing cost, and size of silicon-based optoelectronic devices are becoming increasingly problematic, limiting their further development. Therefore, finding new optoelectronic devices that can replace or supplement silicon-based optoelectronic devices has become a research focus for the scientific community.

[0003] Two-dimensional materials, with their broad spectral response, high sensitivity, and flexibility, combined with breakthroughs in heterogeneous integration and large-scale fabrication technologies, are gradually replacing silicon-based materials and becoming a new paradigm in photoelectric detection. MoS2, a typical two-dimensional transition metal dichalcogenide (TMDC), possesses atomic-level thickness, high carrier mobility, a tunable bandgap (approximately 1.2-1.9 eV), and strong light-matter interactions. These properties give it advantages in photoelectric detection that are difficult for traditional materials to match.

[0004] However, due to the relatively complex electronic structure of MoS2 and the limitations of its intrinsic properties, it suffers from problems such as low carrier mobility, high exciton binding energy, low separation efficiency, and large dark current and noise. Without any improvement design, the intrinsic photoelectric performance of MoS2 is very poor, often with a light response time of tens or hundreds of seconds, which contradicts the original intention of fast response of photodetectors.

[0005] In recent years, significant progress has been made in the research of MoS2-based photodetectors, one approach being the introduction of heterojunction engineering. This heterojunction design optimizes carrier separation efficiency through band matching, thereby fabricating high-performance, low-power MoS2 photodetectors. Heterojunctions are further divided into out-of-plane and in-plane heterojunctions. In-plane heterojunctions exhibit self-driven effects and high carrier transport efficiency, but their band matching range is limited, making them susceptible to lattice mismatch and requiring more complex operation. Out-of-plane heterojunctions, on the other hand, offer a large band matching range, have potential for large-scale fabrication, and are easy to integrate into multifunctional devices, but they introduce impurity scattering centers, limiting device response speed. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by providing a bottom-metal-controlled photodetector and its fabrication method. A protruding bottom electrode and a non-connected metal control layer are fabricated on a substrate. After a MoS2 thin film is transferred onto the electrode, the metal control layer forms a Schottky barrier upon contact with the MoS2 film, simultaneously generating a built-in electric field pointing from MoS2 to Au, which accelerates the separation of photogenerated carriers in the MoS2 channel. Furthermore, because the bottom electrode protrudes relative to the substrate, the MoS2 sheet in the region between the metal control layer and the electrode is suspended, improving interface contact and enhancing carrier transport efficiency and response speed.

[0007] To address the aforementioned technical problems, this invention provides a method for fabricating a photodetector based on bottom metal modulation, comprising the following steps:

[0008] S1. After coating the substrate surface with photoresist, photolithographically pattern the two electrode regions and the metal control layer region pattern located between the two electrode regions.

[0009] S2. Simultaneously deposit electrodes and metal control layers in the electrode area pattern and the metal control layer area pattern, and remove the photoresist.

[0010] S3. The MoS2 thin film is transferred to the electrode and the metal control layer by PDMS dry transfer, and after annealing, the photodetector based on bottom metal control is obtained.

[0011] This invention fabricates a bottom electrode protruding relative to the substrate and a non-connected metal control layer located between the two electrodes on a substrate. A MoS2 thin film is then transferred onto the electrodes. The metal control layer forms a Schottky barrier upon contact with the MoS2 thin film, and a built-in electric field perpendicular to the channel is introduced through the metal control layer. This promotes the separation of photogenerated carriers within the MoS2 device channel, improving the response speed. Compared to the original MoS2 device, the rise / fall time reaches 7.3 / 47 μs, achieving an ultrafast response. Simultaneously, because the bottom electrode protrudes relative to the substrate, the MoS2 channel does not contact the substrate, and the MoS2 sheet in the region between the metal control layer and the electrode is in a suspended state, reducing interface state scattering, optimizing the bottom interface of the MoS2 channel, and improving carrier transport efficiency and response speed. The MoS2 thin films are stacked using a dry transfer technique, offering strong controllability and enabling large-scale fabrication. Both the bottom electrode and the metal control layer are fabricated using a one-step photolithography method, simplifying the operation and facilitating the integration of multiple devices.

[0012] Furthermore, in S2, the electrodes and the metal control layer are arranged parallel to each other along the length direction and spaced apart. The distance between the two electrodes and the metal control layer is independently 2-20 μm, and the distance is less than the width of the metal control layer.

[0013] Furthermore, in S2, both the electrode and the metal control layer include an adhesion layer and a conductive layer. The adhesion layer is made of one of Au, Ni, Cr, Ti, and Pt, and the conductive layer is made of Au. First, the adhesion layer is deposited by vapor deposition, and then Au is subsequently deposited by vapor deposition based on the temperature of the adhesion layer.

[0014] Furthermore, the thickness of the adhesive layer is 4-6 nm, and the thickness of the electrode and metal control layer is >30 nm.

[0015] Furthermore, the adhesion layer is prepared by electron beam evaporation, and the conductive layer is prepared by thermal evaporation.

[0016] Furthermore, in S1, the substrate is SiO2.

[0017] Furthermore, in S3, the MoS2 film is a multilayer MoS2 film obtained by mechanical exfoliation.

[0018] Furthermore, in S3, the thickness of the MoS2 thin film is 10-200 nm.

[0019] Furthermore, in S3, the annealing conditions are a vacuum environment, a temperature of 180-220°C, and a time of 50-70 minutes.

[0020] Furthermore, in S2, the removal of the photoresist specifically involves ultrasonic cleaning with acetone, ethanol, and deionized water in sequence, followed by drying.

[0021] The second aspect of the present invention provides a photodetector prepared by the preparation method described in the first aspect.

[0022] The beneficial effects of this invention are:

[0023] In this invention, a Schottky barrier is formed after the metal control layer comes into contact with the MoS2 thin film, and a built-in electric field perpendicular to the channel is introduced through the metal control layer to promote the separation of photogenerated carriers in the channel of the MoS2 device and improve the response speed. Compared with the original MoS2 device, the rise / fall time of the device reaches 7.3 / 47μs, achieving an ultrafast response.

[0024] In this invention, the bottom electrode protrudes relative to the substrate, the MoS2 channel does not contact the substrate, and the MoS2 sheet in the region between the metal control layer and the electrode is in a suspended state, which reduces interface state scattering, optimizes the bottom interface of the MoS2 channel, and improves carrier transport efficiency and response speed.

[0025] In this invention, the MoS2 thin films are stacked using a dry transfer technique, which offers strong controllability and allows for large-scale fabrication. The bottom electrode and the metal control layer are fabricated using a one-step photolithography method, which is simple to operate and facilitates the integration of multiple devices. Attached Figure Description

[0026] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a flowchart illustrating the fabrication process of the optoelectronic device in Example 1;

[0028] Figure 2 This is an optical mirror image of the optoelectronic device in Example 1;

[0029] Figure 3 This is a flowchart of the fabrication process of the optoelectronic device in Comparative Example 1;

[0030] Figure 4 This is an optical mirror image of the optoelectronic device in Comparative Example 1;

[0031] Figure 5 This is a flowchart of the fabrication process of the optoelectronic device in Comparative Example 2;

[0032] Figure 6 This is a light mirror image of the optoelectronic device in Comparative Example 2;

[0033] Figure 7 This is the light response time diagram of the photodetector in Example 1, where a is the rise time and b is the fall time;

[0034] Figure 8 This is a diagram showing the light response time of the photodetector in Comparative Example 1.

[0035] Figure 9 This is a diagram showing the light response time of the photodetector in Comparative Example 2. Detailed Implementation

[0036] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] This embodiment relates to a method for fabricating a photodetector based on bottom metal modulation, comprising the following steps:

[0038] S1. After coating the substrate surface with photoresist, photolithographically pattern the two electrode regions and the metal control layer region pattern located between the two electrode regions.

[0039] S2. Simultaneously deposit electrodes and metal control layers in the electrode area pattern and the metal control layer area pattern, and remove the photoresist.

[0040] S3. The MoS2 thin film is transferred to the electrode and the metal control layer by PDMS dry transfer, and after annealing, the photodetector based on bottom metal control is obtained.

[0041] In a preferred embodiment, in S2, the electrodes and the metal control layer are arranged parallel to each other along their length and spaced apart. The distance between the two electrodes and the metal control layer is independently 2-20 μm, and the distance is less than the width of the metal control layer. Both the electrodes and the metal control layer include an adhesion layer and a conductive layer. The adhesion layer is made of one of Au, Ni, Cr, Ti, and Pt, and the conductive layer is made of Au. First, the adhesion layer is deposited by vapor deposition, and then Au is deposited by subsequent vapor deposition based on the temperature of the adhesion layer. The thickness of the adhesion layer is 4-6 nm, and the thickness of the electrodes and the metal control layer is >30 nm. The adhesion layer is prepared by electron beam vapor deposition, and the conductive layer is prepared by thermal vapor deposition.

[0042] In a preferred embodiment, in S3, the MoS2 film is a multilayer MoS2 film obtained by mechanical exfoliation; the thickness of the MoS2 film is 10-200 nm.

[0043] In a preferred embodiment, in S3, the annealing conditions are a vacuum environment, a temperature of 180-220°C, and a time of 50-70 minutes.

[0044] In a preferred embodiment, in S1, the substrate is SiO2; in S2, the removal of the photoresist specifically involves ultrasonic cleaning with acetone, ethanol, and deionized water in sequence, followed by drying.

[0045] Another embodiment provides a photodetector prepared by the preparation method described in the above embodiments.

[0046] Example 1

[0047] This embodiment relates to a method for fabricating a photodetector based on bottom metal modulation, referring to... Figure 1 As shown, it includes the following steps:

[0048] (1) Place the SiO2 silicon substrate in acetone and ultrasonically clean it for 5 min. Then place the silicon substrate in ethanol and ultrasonically clean it for 5 min. After that, ultrasonically clean it in deionized water for 5 min. Then dry it with a nitrogen gun and finally bake it on a heating platform at 300°C for 10 min.

[0049] (2) The photoresist AZ5214E ​​is uniformly spin-coated on the empty substrate in step (1). The spin-coating speed is 600 rpm for 10 s and 3000 rpm for 30 s. Then it is baked at 100℃ for 90 s. The bottom electrode pattern and the metal control layer pattern are photolithographically etched in the center of the substrate using a maskless lithography machine to obtain a substrate with a partial photoresist mask. The substrate with the bottom electrode pattern and the metal control layer pattern area is exposed to the environment, while the other parts are still isolated from the environment by photoresist.

[0050] (3) The substrate is placed in the evaporation machine, and metal is deposited in the electrode pattern and metal control layer pattern; first, nickel metal is deposited by electron beam evaporation: vacuum conditions 6×10 -4 Below Pa, the evaporation rate is A nickel adhesion layer with a thickness of 5 nm was obtained after a 3-minute time; then gold was thermally deposited under vacuum conditions of 6 × 10⁻⁶. -4 Below Pa, the evaporation rate is The time was 30 min, and the thickness of the gold conductive layer was 50 nm. Electrodes and metal control layers were obtained. The electrodes and metal control layers were deposited simultaneously with the same material and thickness and were set in parallel and spaced apart. The distance between the metal control layer and the two electrodes was 10 μm.

[0051] (4) Place the vapor-deposited substrate in acetone and ultrasonically clean it until the photoresist is removed from the substrate without any residue. Then soak it in ethanol for 2 minutes, then soak it in deionized water for 2 minutes, then dry it with a nitrogen gun, and finally bake it on a heating platform at 100°C for 1 minute.

[0052] (5) Preparation of MoS2 thin film by mechanical peeling method: First, a part of the sample is attached to the surface of MoS2 crystal with 3M tape. Then, the tapes are peeled off one by one. The process is repeated until the sample left on the tape is gray (about 60 nm thick), and then the MoS2 film is obtained. Then, the MoS2 film is transferred to the electrode by PDMS dry transfer technology: The tape containing MoS2 is attached to the PDMS surface. After standing for 2 hours, the tape is peeled off, leaving the MoS2 sample on the surface of polydimethylsiloxane (PDMS). Then, the treated bottom electrode substrate is aligned with a microscope and attached to the PDMS surface. After standing for 2 hours again, the silicon substrate is peeled off, and the MoS2 sample is transferred to the electrode and metal control layer on the substrate surface. The PDMS substrate used is self-prepared. When preparing, Dow Corning SYLGARD 184 silicone rubber and curing agent are mixed at a weight ratio of 10:1 and stirred evenly. After all the bubbles disappear, it is placed in a refrigerator at 4°C for 48 hours to solidify and form a transparent film.

[0053] (6) The transferred substrate was placed in a vacuum annealing furnace, and a low vacuum of 7 Pa was maintained by evacuation using a mechanical pump. The annealing temperature was 200℃ and the time was 60 min. After completion, a MoS2 photodetector was obtained, such as... Figure 2 As shown.

[0054] Comparative Example 1

[0055] The difference between this comparative example and Example 1 is that a MoS2 thin film is first transferred onto the substrate, and then the top electrode is deposited by evaporation. Specific parameters remain unchanged. (Refer to Example 1 for details.) Figure 3 As shown, specifically:

[0056] (1) Place the SiO2 silicon substrate in acetone and ultrasonically clean it for 5 min. Then place the silicon substrate in ethanol and ultrasonically clean it for 5 min. After that, ultrasonically clean it in deionized water for 5 min. Then dry it with a nitrogen gun and finally bake it on a heating platform at 300°C for 10 min.

[0057] (2) MoS2 thin films were prepared by mechanical exfoliation and then MoS2 sheets were transferred to a substrate by PDMS dry transfer technology;

[0058] (3) Spin coat the photoresist uniformly onto the substrate of step (2) at a spin speed of 600 rpm for 10 s and 3000 rpm for 30 s, and then bake at 100°C for 90 s; use a maskless lithography machine to photolithographically etch the top electrode pattern in the center of the substrate to obtain a substrate with a partial photoresist mask, wherein the top electrode pattern area is exposed to the environment, and the other parts are still isolated from the environment by photoresist;

[0059] (4) Place the substrate in the evaporation machine and evaporate the metal in the electrode pattern; first, electron beam evaporation of nickel metal: vacuum conditions 6×10 -4 Below Pa, the evaporation rate is A nickel adhesion layer with a thickness of 5 nm was obtained after a 3-minute time; then gold was thermally deposited under vacuum conditions of 6 × 10⁻⁶. -4 Below Pa, the evaporation rate is The time was 30 minutes, the thickness of the gold conductive layer was 50 nm, and the top electrode was obtained;

[0060] (5) Place the vapor-deposited substrate in acetone and ultrasonically clean it until the photoresist is removed from the substrate without any residue. Then soak it in ethanol for 2 minutes, then soak it in deionized water for 2 minutes, then dry it with a nitrogen gun, and finally bake it on a heating platform at 100°C for 1 minute.

[0061] (6) In a vacuum annealing furnace, a low vacuum of 7 Pa was maintained by evacuation using a mechanical pump. The annealing temperature was 200℃ and the time was 60 min to obtain a MoS2 photodetector, such as... Figure 4 As shown.

[0062] Comparative Example 2

[0063] The difference between this comparative example and Example 1 is that plasma etching is added between steps (2) and (3) to etch grooves for the electrode and metal control layer on the substrate. Subsequently, the electrode and metal control layer are deposited in the grooves. The depth of the grooves is the same as the thickness of the electrode and metal control layer. Figure 5 The etching step specifically involves: placing the substrate into a plasma reaction chamber and using a mild plasma etching technique, employing N2 and SF6 gases to etch the exposed SiO2 on the substrate within the plasma reaction chamber, resulting in a 55nm deep groove. The plasma treatment parameters are set as follows: RF power 300W and reflection power within 80W, the chamber pressure of the mild plasma reaction chamber maintained at 31-34 Pa, and the reaction time 1 min 30 s. The purity of SF6 and N2 is 5N, and their gas flow rates are 15 sccm and 7 sccm, respectively. Other steps and parameters remain unchanged, resulting in the fabrication of a MoS2 photodetector, such as... Figure 6 As shown.

[0064] The response rate of the MoS2 photodetectors obtained in Example 1 and Comparative Examples 1-2 was tested. The samples were placed under the optical mirror of the probe stage, and the probes were connected to the source and drain electrodes respectively. A bias voltage of 1V was applied, but no gate voltage was applied. A 532nm laser emitter was used as the emission source and connected to the signal generator to perform rapid laser pulse testing to test the photoresponse speed. The current was collected using a Keithley 4200 test source meter.

[0065] Figure 7 The image shows the photoresponse speed test image of the photodetector obtained in Example 1, where a is the rise time and b is the fall time. It can be seen that the rise time of the photodetector is 7.3 μs and the fall time is 47 μs.

[0066] Figure 8 The photoresponse speed test image of the optoelectronic device obtained in Comparative Example 1 shows that the rise time of this device is 38.9 s and the fall time is 151.5 s. Comparing the rise and fall times of the device in Example 1, it is found that the response speed of the MoS2 optoelectronic device based on the bottom metal control layer in Example 1 is improved by about 8 orders of magnitude. Figure 9The image shows the photoresponse speed test results of the optoelectronic device obtained in Comparative Example 2. The results show that the rise time of the device is 207.5 ms and the fall time is 1.41 s. Compared with the rise and fall times of the device in Comparative Example 1, the response speed of the device in Comparative Example 2 is improved by two orders of magnitude, but the improvement effect is still not as good as that of the device in Example 1. This is because the electrode and metal control layer used in Comparative Example 2 are embedded, and theoretically and technically, the metal control layer cannot be allowed to cover the entire channel. After the MoS2 sheet is transferred to the electrode, the MoS2 sheet above the gap between the electrode and the metal control layer comes into contact with the SiO2 substrate. The surface defects, surface charge, and surface impurity adsorption characteristics of the SiO2 substrate make its interface interaction with the two-dimensional material strong, affecting the photoelectric performance of the MoS2 photodetector. Therefore, it can be seen from Example 1, Comparative Example 1, and Comparative Example 2 that the MoS2 optoelectronic device based on the bottom metal control layer proposed in this invention can effectively improve the performance of MoS2 optoelectronic devices.

[0067] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for fabricating a photodetector based on bottom metal modulation, characterized in that, Includes the following steps: S1. After coating the substrate surface with photoresist, photolithographically pattern the two electrode regions and the metal control layer region pattern located between the two electrode regions. S2. Electrodes and metal control layers are simultaneously deposited in the electrode region pattern and the metal control layer region pattern, and the photoresist is removed; wherein, the electrodes and metal control layers are parallel to each other along the length direction and spaced apart, the spacing between the two electrodes and the metal control layer is independently 2-20μm, and the spacing is less than the width of the metal control layer; both the electrodes and the metal control layer include an adhesion layer and a conductive layer, the adhesion layer is made of one of Au, Ni, Cr, Ti, and Pt, and the conductive layer is made of Au; S3. The MoS2 thin film is transferred to the electrode and the metal control layer by PDMS dry transfer, and after annealing, a photodetector based on bottom metal control is obtained; wherein, after the metal control layer contacts the MoS2 thin film, a Schottky barrier is formed, and a built-in electric field perpendicular to the channel is introduced through the metal control layer.

2. The fabrication method of the photodetector based on bottom metal modulation as described in claim 1, characterized in that, The thickness of the adhesive layer is 4-6 nm, and the thickness of the electrode and metal control layer is >30 nm.

3. The method for fabricating a photodetector based on bottom metal modulation as described in claim 1, characterized in that, The adhesion layer is prepared by electron beam evaporation, and the conductive layer is prepared by thermal evaporation.

4. The method for fabricating a photodetector based on bottom metal modulation as described in claim 1, characterized in that, In S3, the MoS2 film is a multilayer MoS2 film obtained by mechanical exfoliation.

5. The method for fabricating a photodetector based on bottom metal modulation as described in claim 4, characterized in that, In S3, the thickness of the MoS2 thin film is 10-200 nm.

6. The method for fabricating a photodetector based on bottom metal modulation as described in claim 1, characterized in that, In S3, the annealing conditions are a vacuum environment, a temperature of 180-220℃, and a time of 50-70 minutes.

7. The method for fabricating a photodetector based on bottom metal modulation as described in claim 1, characterized in that, In S2, the removal of the photoresist specifically involves ultrasonic cleaning with acetone, ethanol, and deionized water in sequence, followed by drying.

8. A photodetector prepared by the preparation method according to any one of claims 1-7.

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