Graphene / PbS heterojunction photoelectric detector with wide spectral response and preparation method thereof

Abstract

The invention discloses a graphene / PbS heterojunction photoelectric detector with wide spectral response and a preparation method thereof, and belongs to the technical field of semiconductor photoelectric integration. According to the method, a lead sulfide nano-film is synthesized on a substrate through a chemical bath method, and a graphene / lead sulfide heterojunction structure is successfully constructed by optimizing process conditions. The heterostructure effectively prolongs the service life of photon-generated carriers through a built-in electric field which is spontaneously formed, and enhances the response performance of the photoelectric detector. The high carrier mobility of the graphene is combined with the excellent infrared absorption characteristic of the lead sulfide, so that the photoelectric detection function with high response rate is realized. The test result shows that the response rates of the device are 72 A / W and 5.8 A / W respectively under the irradiation of 792 nm laser and 1550 nm laser. The optimized detector has a wide spectral response range of 265 nm to 2200 nm, and the response time is less than 10 milliseconds. The photoelectric detector provided by the invention has relatively high performance, does not need a selective substrate, and has a relatively good application prospect.

Description

Technical Field

[0001] The present invention proposes a process preparation method for a graphene / PbS heterojunction detector without a selective substrate, which can achieve high response in a wide band, and specifically involves the growth of lead sulfide nanofilms and the process integration of graphene lead sulfide, and belongs to the field of semiconductor optoelectronic integration. Background Art

[0002] Graphene has attracted widespread attention from researchers due to its high carrier mobility, superb mechanical properties, good thermal conductivity, and high light transmittance. Based on these properties, graphene has broad application potential in sensing, imaging, spin electronics, and flexible wearable devices. Since graphene is a zero-bandgap material, it has a certain light absorption in the ultraviolet to terahertz band. Although graphene has a very wide absorption spectrum range, the absorption rate of light of different wavelengths varies greatly.

[0003] The existing graphene-based photodetectors are often only sensitive to incident light of a certain wavelength or a few wavelengths, which limits the application range of the device to a certain extent. In addition to the narrow detectable wavelength range, since the single-layer graphene itself is only one atomic layer thick, the absorption rate of incident light is only 2.3%. At the same time, although the light response speed of graphene is very fast, the time for graphene to generate electron holes when light enters graphene does not exceed 50fs. Therefore, in some cases, the basic indicators required by photodetectors cannot be achieved. The response rate of graphene photodetectors with ordinary structures is usually only in mAW. -1 Order of magnitude. This greatly limits its application. In order to enhance light absorption, microcavities, metal nanostructures and silicon optical waveguides are integrated on graphene, but these structures can only enhance the absorption of graphene in a narrow spectral range, and the process is complicated, which may cause interface contamination and affect device performance. Prolonging the lifetime of photogenerated carriers in graphene can effectively improve the responsiveness of graphene devices. Therefore, other new nanomaterials, such as quantum dots, two-dimensional materials, carbon nanotubes, etc., are introduced to construct heterojunctions with graphene. Due to its mature manufacturing process, the wafer surface of traditional semiconductors has nanoscale flatness, which is conducive to forming a uniform and flat contact with graphene. Heterojunction structures such as graphene-silicon and graphene-gallium arsenide have been reported.

[0004] For the above methods, graphene has been combined with GaAs, PbS QDs, nanowires, etc. to form photoconductive graphene detectors, and remarkable results have been achieved. However, whether it is the synthesis of quantum dots or the growth of nanowires and GaAs epitaxial wafers, the synthesis of materials has a certain complexity. And although relatively high responses can be achieved in certain bands, the response wavelength is narrow. Summary of the invention

[0005] The present invention provides a graphene / lead sulfide heterojunction photoelectric detector that does not require a selective substrate, and its manufacturing process does not rely on a silicon substrate. The detector successfully realizes the photoelectric detection function of the graphene / lead sulfide heterojunction structure by synthesizing a lead sulfide nanofilm on a substrate using a chemical water bath method and optimizing the process conditions.

[0006] A graphene / lead sulfide photodetector with wide spectrum and high response, the specific structure is to deposit a layer of lead sulfide film on the substrate by chemical water bath method, then a SiO2 dielectric layer is formed on the surface of the lead sulfide film, a titanium / gold electrode is formed on the SiO2 dielectric layer, and graphene is mounted on the titanium / gold electrode; the graphene is in contact with the lead sulfide film only in the middle area of ​​the channel. There is no current in the lead sulfide film, and the lead sulfide film only forms a built-in electric field with the graphene to capture holes generated by light.

[0007] The preparation method of the graphene / lead sulfide photoelectric detector comprises the following steps:

[0008] Step 1, cleaning a designated substrate;

[0009] Step 2, depositing a lead sulfide film on the substrate: at a constant temperature of 30°C and a rotation speed of 180r / min, a chemical water bath method is used to deposit a lead sulfide film about 500nm thick on the specified substrate. The chemical raw materials are: Pb(NO3), NaOH and SC(NH3). The concentrations are: 0.33M, 1.5M and 0.33M respectively. And in an atmosphere of N2:O2=50sccm:50sccm and a temperature of 450°C, the lead sulfide film is annealed in a rapid annealing furnace for 20min;

[0010] Step 3, depositing a layer of SiO2 as a dielectric layer on the upper surface of lead sulfide by PECVD, and patterning the SiO2 by a photolithography stripping process;

[0011] Step 4, sputtering a layer of titanium / gold electrode on the SiO2 dielectric layer using a photolithography process, and peeling off to obtain a metal pattern;

[0012] Step 5, using a mixed solution of copper sulfate pentahydrate: 37% hydrochloric acid: H2O = 10g: 50ml: 50ml as an etching solution, etching away the copper metal catalytic thin layer of CVD copper foil graphene, and obtaining and patterning graphene by photolithography; thereby obtaining a graphene / lead sulfide heterojunction detector;

[0013] In the graphene patterning process, conventional methods usually use oxygen plasma to remove the unnecessary graphene part so as to retain only the channel area. However, since lead sulfide is highly sensitive to oxygen ions, it is susceptible to oxidation, which seriously reduces the photosensitivity. In order to solve this problem, the present invention reduces the concentration of oxygen plasma by optimizing process parameters, thereby avoiding excessive oxidation of lead sulfide, but also to ensure the effective treatment of graphene. Further, through process adjustment, while using photoresist to protect graphene during the patterning process, the lead sulfide layer can also be protected to avoid it being affected by oxidation during the patterning process. This method enables the graphene patterning process and the protection of the photosensitivity of lead sulfide to be achieved simultaneously, thereby effectively improving the performance and stability of the device.

[0014] Compared with the prior art, the present invention has the following technical advantages:

[0015] 1. The use of chemical water bath method to prepare lead sulfide thin film has significant process advantages, and the substrate material has wide applicability. This method has no strict requirements on the selection of substrate, and a variety of materials can be used as substrates, such as silicon wafers, glass or other common glass slides. This feature makes the preparation process more flexible, and can significantly reduce production costs, facilitate large-scale manufacturing, and has high economic benefits and application prospects.

[0016] 2. Lead sulfide has excellent infrared light absorption properties. Combining it with graphene materials with high electron mobility can effectively improve the response performance of photodetectors. This innovative material combination can not only significantly enhance the sensitivity of the detector in the infrared band, but also optimize the overall response speed of the device, providing a new technical path for the research and development of high-performance graphene-based photodetectors, with broad application prospects.

[0017] 3. The graphene / lead sulfide photodetector can effectively cover the spectrum in the wavelength range of 365nm to 2200nm, and has a wide range of light detection capabilities. At the same time, the device's responsivity reaches or exceeds 1A / W, showing excellent photoelectric conversion efficiency. This feature enables the device to maintain high response performance in multiple wavelength ranges, further enhancing its application potential in the field of photoelectric detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 : A glass substrate sheet on which lead sulfide has been deposited;

[0019] Figure 2 : One-step photolithography on the lead sulfide surface;

[0020] Figure 3 : PECVD deposits a layer of SiO2;

[0021] Figure 4: Peel off to obtain patterned SiO2;

[0022] Figure 5 :One-step photolithography on the silicon dioxide surface;

[0023] Figure 6 : Magnetron sputtering of a titanium electrode;

[0024] Figure 7 : Peel off to obtain a patterned titanium electrode;

[0025] Figure 8 : Transfer graphene to the surface;

[0026] Fig. 9 :One-step photolithography on the graphene surface;

[0027] Fig.10 : Oxygen plasma bombards the surface to obtain patterned graphene;

[0028] Fig.11 : XRD pattern of lead sulfide after degradation;

[0029] Fig.12 :Raman spectrum test chart of graphene;

[0030] Fig.13 : The responsivity of the device at different wavelengths;

[0031] Among them, 1 is a glass substrate, 2 is lead sulfide, 3 is SiO2, 4 is a titanium / gold electrode, and 5 is graphene. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with examples, but the present invention is not limited to the following examples.

[0033] There are many substrates that can be deposited by the chemical water bath method. In the present invention, a glass substrate of 1 cm×1 cm is taken as an example. The specific device manufacturing process steps are as follows:

[0034] (a) Preparation of lead sulfide thin film by chemical water bath method;

[0035] (1) Glass substrate cleaning. First, immerse the glass substrate in a mixed solution of potassium caseinate, concentrated sulfuric acid and deionized water in a mass ratio of 20 g: 360 ml: 40 ml for 4 hours. Then,

[0036] The substrate was placed in acetone, ethanol and deionized water in sequence and ultrasonically cleaned for 10 minutes in each step.

[0037] Finally, the cleaned substrate was placed in an oven at 100°C and baked for 5 minutes until completely dry.

[0038] (2) Preparation of chemical solutions. Weigh appropriate amounts of Pb(NO3)2, NaOH, and SC(NH2)2, respectively, and place them in three 100ml beakers. Add deionized water until the volume of each solution reaches 30ml, 20ml, and 30ml, respectively. Stir evenly to ensure that the concentrations of Pb(NO3)2, NaOH, and SC(NH2)2 are 0.33M, 1.5M, and 0.33M, respectively. Then, heat the solution in a 30℃ constant temperature oven.

[0039] (3) Preparation of lead sulfide film. Place the beaker containing SC(NH2)2 solution at a constant temperature of 30°C, stir it in a magnetic stirrer at a speed of 180r / min, and immerse the cleaned glass substrate vertically in the SC(NH2)2 solution. Then, slowly add the NaOH solution to the Pb(NO3)2 solution, stir evenly and let it stand until the upper layer of the solution becomes clear. Subsequently, use a glass rod to carefully drain the clarified liquid into the SC(NH2)2 solution, and add an appropriate amount of deionized water to finally make the reaction solution volume reach about 100ml.

[0040] Keep the reaction solution still for 1 hour until a uniform lead sulfide film is deposited. Figure 1 .

[0041] (4) Annealing of the lead sulfide film: The prepared lead sulfide film was first placed in ethanol for ultrasonic cleaning for 10 minutes. Then, it was placed in a rapid annealing furnace and annealed at 450°C for 20 minutes in a mixed atmosphere of nitrogen and oxygen (N2:O2=50sccm:50sccm). This annealing process is intended to optimize the photosensitivity of the lead sulfide film by controlling the grain size. XRD tests were also performed on it. See Appendix Fig.11 .

[0042] (ii) growing SiO2 dielectric layer using PECVD;

[0043] (5) Growth of SiO2 dielectric layer. Figure 2 ) is placed in the reaction chamber of a plasma enhanced chemical vapor deposition (PECVD) device, and a 300nm thick SiO2 dielectric layer is deposited on the surface of the substrate using appropriate gas sources and process parameters. The deposition process is carried out under a specific atmosphere to ensure the uniformity and stability of the SiO2 layer. Figure 3 .

[0044] (6) Stripping of SiO2 layer. Since the deposition stability of lead sulfide film is low, the traditional stripping solution cannot effectively strip the film, so the acetone ultrasonic cleaning method is used for stripping. The substrate is immersed in acetone and treated with ultrasonic cleaning equipment to remove the unstable lead sulfide film, and finally a SiO2 dielectric layer with a patterned structure is obtained. See Appendix Figure 4 .

[0045] (iii) growing source and drain electrodes;

[0046] (7) Magnetron sputtering. Figure 5 ) substrate was placed in a magnetron sputtering instrument to sputter a layer of titanium / gold source and drain electrodes with a thickness of 15 / 150nm. Figure 6 .

[0047] (8) Stripping of metal electrodes. Use acetone to strip off the photoresist on the substrate to obtain sputtered patterned titanium source and drain electrodes. Figure 7 .

[0048] (iv) Tubular furnace thermal CVD growth of graphene;

[0049] (9) Growth of graphene: Single crystal copper foil was selected as the substrate, and graphene was grown under specific conditions using a tube furnace thermal chemical vapor deposition (CVD) method. The flow ratio of the reaction gas was set to H2:CH4=5sccm:10sccm, the gas pressure was maintained at 1300Pa, and the growth temperature was 1000℃. The graphene obtained by this process showed a low defect density and was confirmed to be a single-layer graphene by Raman spectroscopy. See Appendix Fig.12 .

[0050] (10) Etching of copper foil substrate. To ensure the transfer of graphene, a PMMA protective layer is first coated on the graphene surface and heated in an oven at 100°C to complete the drying of PMMA. Subsequently, the copper foil substrate is placed in a mixed etching solution containing copper sulfate pentahydrate, 37% hydrochloric acid and deionized water to dissolve the copper foil. After etching, the graphene is repeatedly washed with deionized water and transferred to the substrate on which the metal has been sputtered. Finally, acetone is used to remove the PMMA protective layer to complete the graphene transfer process.

[0051] (V) Patterned graphene;

[0052] (11) On the graphene layer that has been transferred to the substrate, a photolithography process (see Appendix Figure 8 ) to etch the desired pattern. Fig. 9 .

[0053] (12) The substrate is treated with oxygen plasma, and the residual photoresist on the surface is removed with acetone to obtain a patterned graphene structure. A graphene / lead sulfide photodetector is obtained. Fig.10 .

[0054] The electrical and optoelectronic properties of the device were measured at room temperature using an Agilent B1500A semiconductor characterization system, and a probe station was used during the test. To avoid interference from ambient light, the test was carried out in a black shielding box. The test results are shown in Figure (13), and the response rates of the device under 792nm and 1550nm laser irradiation were 72A / W and 5.8A / W, respectively. The optimized device exhibits a wide spectral response in the range of 265nm to 2200nm, and the response time is less than 10 milliseconds. It is believed that this hybrid structure will play an important role in the development of high-performance photodetectors in the future.

Claims

1. A graphene / PbS heterojunction photodetector with a wide spectral response, characterized in that: A lead sulfide film is deposited on a substrate using a chemical water bath method, and then a SiO2 dielectric layer is formed on the upper surface of the lead sulfide film, a titanium / gold electrode is formed on the SiO2 dielectric layer, and graphene is mounted on the titanium / gold electrode; the graphene is in contact with the lead sulfide film only in the middle area of ​​the channel; there is no current in the lead sulfide film, and the lead sulfide film only forms a built-in electric field with the graphene to capture holes generated by light.

2. A method for preparing a graphene / PbS heterojunction photodetector with a wide spectral response as claimed in claim 1, characterized in that: The steps include: Step 1, cleaning a designated substrate; Step 2, depositing a lead sulfide film on a substrate: at a constant temperature of 30°C and a rotation speed of 180 r / min, a lead sulfide film with a thickness of about 500 nm is deposited on a specified substrate using a chemical water bath method; the chemical raw materials are: Pb(NO3), NaOH and SC(NH3); the concentrations are: 0.33M, 1.5M and 0.33M respectively; and the lead sulfide film is annealed for 20 minutes in an atmosphere of N2:O2=50sccm:50sccm and a temperature of 450°C using a rapid annealing furnace; Step 3, depositing a layer of SiO2 as a dielectric layer on the upper surface of lead sulfide by PECVD, and patterning the SiO2 by a photolithography stripping process; Step 4, sputtering a layer of titanium / gold electrode on the SiO2 dielectric layer using a photolithography process, and peeling off to obtain a metal pattern; Step 5, using a mixed solution of copper sulfate pentahydrate: 37% hydrochloric acid: H2O = 10g: 50ml: 50ml as an etching solution to etch away the copper metal catalytic thin layer of CVD copper foil graphene, and obtain and patterned graphene through photolithography; thereby obtaining a graphene / lead sulfide heterojunction detector.

3. The method for preparing a graphene / PbS heterojunction photodetector with a wide spectral response according to claim 2, characterized in that: Through process adjustment, while photoresist is used to protect graphene during the patterning process, the lead sulfide layer can also be protected to prevent it from being affected by oxidation during the patterning process; the patterning processing of graphene and the protection of the photosensitivity of lead sulfide are achieved simultaneously, thereby effectively improving the performance and stability of the device.

4. The method for preparing a graphene / PbS heterojunction photodetector with a wide spectral response according to claim 2, characterized in that: The glass substrate was immersed in a mixed solution of potassium caseinate, concentrated sulfuric acid and deionized water in a mass ratio of 20g:360ml:40ml, and the treatment was continued for 4 hours; then, the substrate was placed in acetone, ethanol and deionized water in turn, and ultrasonic cleaning was performed for 10 minutes each step; finally, the cleaned substrate was placed in an oven at 100°C and baked for 5 minutes until it was completely dry.

5. The method for preparing a graphene / PbS heterojunction photodetector with a wide spectral response according to claim 2, characterized in that: Weigh appropriate amounts of Pb(NO3)2, NaOH and SC(NH2)2 respectively, and place them in three 100ml beakers, add deionized water until the volume of each solution reaches 30ml, 20ml, and 30ml respectively; stir evenly to ensure that the concentrations of Pb(NO3)2, NaOH and SC(NH2)2 are 0.33M, 1.5M, and 0.33M respectively; then, heat the solution in a constant temperature oven at 30℃.

6. The method for preparing a graphene / PbS heterojunction photodetector with a wide spectral response according to claim 2, characterized in that: A beaker containing SC(NH2)2 solution is placed at a constant temperature of 30°C, stirred in a magnetic stirrer at a speed of 180r / min, and a cleaned glass substrate is vertically immersed in the SC(NH2)2 solution; then, NaOH solution is slowly added to the Pb(NO3)2 solution, stirred evenly and allowed to stand until the upper layer of the solution becomes clear; then, the clarified liquid is carefully drained into the SC(NH2)2 solution with a glass rod, and an appropriate amount of deionized water is added to eventually make the volume of the reaction liquid reach about 100ml; the reaction solution is kept standing for 1 hour until a uniform lead sulfide film is deposited; for the annealing treatment of the lead sulfide film, the prepared lead sulfide film is first placed in ethanol for ultrasonic cleaning for 10 minutes; then, it is placed in a rapid annealing furnace and annealed at 450°C for 20 minutes in a mixed atmosphere of nitrogen and oxygen (N2:O2=50sccm:50sccm).

7. The method for preparing a graphene / PbS heterojunction photodetector with a wide spectral response according to claim 2, characterized in that: Growth of SiO2 dielectric layer: placing the photolithographically processed lead sulfide film substrate into the reaction chamber of a plasma enhanced chemical vapor deposition (PECVD) device, and using appropriate gas source and process parameters to deposit a 300nm thick SiO2 dielectric layer on the substrate surface; The deposition process is carried out under a specific atmosphere to ensure the uniformity and stability of the SiO2 layer; The SiO2 dielectric layer is stripped; the stripping is performed by using an acetone ultrasonic cleaning method; the substrate is immersed in acetone and treated with an ultrasonic cleaning device to remove an unstable lead sulfide film, and finally a SiO2 dielectric layer with a patterned structure is obtained.

8. The method for preparing a graphene / PbS heterojunction photodetector with a wide spectral response according to claim 2, characterized in that: Growth of source and drain electrodes; magnetron sputtering; placing the photolithographic substrate into a magnetron sputtering instrument to sputter a layer of titanium / gold source and drain electrodes with a thickness of 15 / 150nm; stripping of the metal electrode; stripping off the photoresist on the substrate with acetone to obtain sputtered patterned titanium / gold source and drain electrodes.

9. The method for preparing a graphene / PbS heterojunction photodetector with a wide spectral response according to claim 2, characterized in that: Tube furnace thermal CVD growth of graphene; Growth of graphene: Select single crystal copper foil as substrate, and use tube furnace thermal chemical vapor deposition CVD method to grow graphene under specific conditions; The flow ratio of the reaction gas is set to H2:CH4=5sccm:10sccm, the gas pressure is maintained at 1300Pa, and the growth temperature is 1000℃; The graphene obtained by this process shows a low defect density and is confirmed to be a single-layer graphene by Raman spectroscopy test; Corrosion of copper foil substrate: To ensure the transfer of graphene, a PMMA protective layer is first coated on the surface of the graphene, and heated in an oven at 100℃ to complete the drying of the PMMA; Subsequently, the copper foil substrate is placed in a mixed corrosion solution containing copper sulfate pentahydrate, 37% hydrochloric acid and deionized water to dissolve the copper foil; After corrosion, the graphene is repeatedly washed with deionized water and transferred to the substrate on which the metal has been sputtered; Finally, acetone is used to remove the PMMA protective layer to complete the graphene transfer process.

10. The method for preparing a graphene / PbS heterojunction photodetector with a wide spectral response according to claim 2, characterized in that: Patterning graphene; etching a desired pattern on the graphene layer transferred to a glass substrate by a photolithography process; treating the substrate with oxygen plasma and removing the photoresist remaining on the surface with acetone to obtain a patterned graphene structure; and obtaining a graphene / lead sulfide photodetector.

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