A graphene / lead sulfide infrared detector and its preparation method

Abstract

The present invention discloses a graphene / lead sulfide infrared detector and its preparation method. The graphene / lead sulfide infrared detector comprises a substrate, which is sequentially covered with a graphene film, a metal electrode, a lead sulfide seed layer, and a lead sulfide nanocrystal film layer. The graphene film is provided with one of the metal electrodes at each end. The present invention introduces a lead sulfide seed layer onto the surfaces of the graphene and metal electrodes, using the seed layer to assist in the growth of lead sulfide nanocrystals, resulting in a dense, smooth, uniform, high-quality lead sulfide nanocrystal film layer, ultimately realizing a highly responsive infrared detector.

Description

Technical Field

[0001] The invention belongs to the field of semiconductor optoelectronic devices and relates to a graphene / lead sulfide infrared detector and a preparation method thereof. Background Art

[0002] An infrared detector is a device that converts infrared light signals into electrical signals. Depending on how the device responds to infrared radiation, infrared detectors can be divided into photoconductive, built-in electric field photovoltaic, photothermoelectric, and bolometer types. Infrared detectors are a crucial technology in modern national defense and military affairs, facilitating observation and combat operations at night, in smoke, and in fog. Currently, widely used infrared detector technologies include cooled and uncooled. Cooled infrared imaging requires complex cooling equipment, making the system bulky and unsuitable for soldiers in combat. Uncooled infrared imaging technology started later but has developed rapidly. Lead sulfide infrared detectors are a typical example of uncooled infrared detectors.

[0003] In existing technologies, by combining graphene with a lead sulfide light-absorbing layer to form a composite structure, electrons in the graphene are transferred to the proximal light-absorbing layer, filling the vacant states in the lead sulfide valence band generated by photon absorption. This suppresses the recombination of electron-hole pairs generated by photoexcitation in the lead sulfide, and the electrons in the lead sulfide remain in the conduction band without decay. Furthermore, the heterojunction formed by graphene and lead sulfide effectively separates photogenerated carriers, increasing carrier lifetime and leading to a synergistic increase in device gain and responsivity.

[0004] However, the lead sulfide preparation method for the above-mentioned composite structure is typically a spin coating method, which repeatedly repeats the following steps: spin coating, ligand replacement, and washing to achieve the target lead sulfide film thickness. This method is complex, inefficient, and has poor experimental reproducibility. The chemical water bath method is an extremely simple and reproducible method for preparing lead sulfide. However, the lead sulfide prepared by this method on graphene and metal electrode surfaces has poor film quality due to the different growth rates of lead sulfide on different material surfaces, resulting in almost no response from the resulting detector. Summary of the Invention

[0005] In view of this, one of the objects of the present invention is to provide a graphene / lead sulfide infrared detector, which obtains a dense, flat, uniform, high-quality lead sulfide nanocrystal thin film layer by adding a lead sulfide seed layer, thereby ultimately realizing a high-responsiveness infrared detector.

[0006] To achieve the above object, the technical solution of the present invention is:

[0007] A graphene / lead sulfide infrared detector comprises a substrate, wherein the substrate is sequentially covered with a graphene film, a metal electrode, a lead sulfide seed layer, and a lead sulfide nanocrystal film layer; wherein one metal electrode is laid at each end of the graphene film.

[0008] Preferably, the substrate comprises a silicon wafer with a silicon dioxide layer.

[0009] Furthermore, 1-3 layers of graphene film are laid between the metal electrode and the substrate.

[0010] Furthermore, the metal electrode includes gold, silver, chromium / gold, and chromium / silver; wherein, in the composite metal electrode containing chromium, the chromium is located on the graphene film, and the gold or silver film is located on the chromium.

[0011] Furthermore, the lead sulfide seed layer is a thin film composed of quantum dots with a size of 1-10 nm, and the thickness of the lead sulfide seed layer is 8-16 nm.

[0012] Furthermore, the lead sulfide nanocrystal thin film layer is a thin film composed of nanocrystals with a particle size of 50-500 nm, and the thickness of the lead sulfide nanocrystal thin film is 70-150 nm.

[0013] Preferably, the ligands of the quantum dots include EDT and octylamine.

[0014] In view of this, the second object of the present invention is to provide a method for preparing a graphene / lead sulfide infrared detector. By using this preparation method, a dense, flat, uniform, high-quality lead sulfide nanocrystalline thin film layer can be obtained, and ultimately a high-responsivity infrared detector can be realized.

[0015] To achieve the above object, the technical solution of the present invention is:

[0016] A method for preparing a graphene / lead sulfide infrared detector, characterized by comprising the following steps:

[0017] (1) Prepare a graphene film and transfer it to a clean substrate;

[0018] (2) Depositing metal on the surface of the graphene film and patterning it to form a metal electrode;

[0019] (3) Patterning of graphene films;

[0020] (4) preparing a lead sulfide seed layer on the surface of the graphene film and the surface of the metal electrode;

[0021] (5) With the assistance of the lead sulfide seed layer, a lead sulfide nanocrystalline thin film layer is prepared.

[0022] Furthermore, in the step (1), a graphene film is prepared on copper by chemical vapor deposition, and the graphene film is transferred from the copper foil to the substrate by PMMA.

[0023] Furthermore, in step (2), a continuous metal film is obtained by magnetron sputtering, and the metal electrode is obtained by structuring based on a double-layer adhesive stripping process. The specific steps are as follows:

[0024] First, a double layer of photoresist is spin-coated on the graphene film, and the resist structure is left after exposure and development. Then, a metal film is sputtered and deposited. The photoresist is removed with acetone, and the metal on the surface of the photoresist is also peeled off, finally forming a metal electrode.

[0025] Furthermore, in the step (3), a double-layer resist process is used for photolithography, followed by plasma etching of the graphene film, and finally the resist is removed to complete the patterning of the graphene film.

[0026] Furthermore, the method for preparing the lead sulfide seed layer in step (4) includes: spin coating, invasion coating, and drop coating.

[0027] Furthermore, the specific method for preparing the lead sulfide nanocrystalline thin film layer in step (5) is as follows:

[0028] Lead acetate, thiourea, sodium citrate and sodium hydroxide are dissolved in water to prepare a precursor solution, and then the precursor solution is transferred into a water bath to prepare a lead sulfide nanocrystalline film through a chemical water bath method.

[0029] Beneficial effects

[0030] This invention designs a graphene / lead sulfide infrared detector. By introducing a lead sulfide seed layer onto the graphene and metal electrode surfaces, the seed layer assists in the growth of lead sulfide nanocrystals, resulting in a dense, flat, uniform, high-quality lead sulfide nanocrystal thin film. This ultimately creates a highly responsive infrared detector. The invention also provides a method for preparing the graphene / lead sulfide infrared detector, which features simple process steps, good experimental reproducibility, and the ability to implement a parallel structure, making it suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0032] Figure 1 This is a flow chart of an embodiment of a method for preparing a graphene / lead sulfide infrared detector according to the present invention;

[0033] Figure 2 This is a schematic cross-sectional view of an embodiment of a graphene / lead sulfide infrared detector of the present invention;

[0034] Figure 3 This is a scanning electron microscope image of a lead sulfide nanocrystal thin film layer in a graphene / lead sulfide infrared detector according to an embodiment of the present invention. DETAILED DESCRIPTION

[0035] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, 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, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0036] The examples are provided to better illustrate the present invention, but are not intended to limit the present invention to the examples. Therefore, non-essential improvements and adjustments to the embodiments made by those skilled in the art based on the above-mentioned invention still fall within the scope of protection of the present invention.

[0037] Example 1

[0038] refer to Figure 1 and Figure 2 , respectively, are a flow chart of an embodiment of a method for preparing a graphene / lead sulfide infrared detector according to the present invention and a schematic cross-sectional structure diagram of an embodiment of a graphene / lead sulfide infrared detector. Specifically, a method for preparing a graphene / lead sulfide infrared detector comprises the following steps:

[0039] S10: preparing a graphene film and transferring it to a clean substrate; then performing step S20;

[0040] In this embodiment, a silicon wafer with a silicon dioxide layer on its surface is selected as the substrate 1 .

[0041] In this embodiment, before using the substrate 1, it is ultrasonically cleaned with acetone, alcohol, and deionized water for 10 minutes respectively, and then blown dry with nitrogen for standby use; then, a single-layer graphene film 2 is prepared on a copper foil base using chemical vapor deposition.

[0042] In this embodiment, the prepared graphene film 2 is transferred from the copper foil to the substrate 1 by PMMA (polymethyl methacrylate). Specifically, the graphene film 2 is cut into 3 cm x 3 cm sizes and taped to the silicon wafer under the copper foil. The PMMA solution is spin-coated onto the surface of the graphene film 2 at a speed of 4000 RPM, and then baked in an oven at 100 degrees for 10 minutes. The graphene film 2 and copper foil spun with PMMA are removed from the silicon wafer, and the graphene on the back is first etched with oxygen plasma, and then the copper foil is removed by wet etching with HCl+H2O2 solution (3:1) as the etching solution for 3 hours. After the copper is dissolved, it is repeatedly rinsed with deionized water, and the graphene film 2 is fished out with the substrate 1, placed in the air to dry naturally, and then placed in acetone to remove the PMMA glue to complete the transfer of the graphene film 2.

[0043] S20: depositing metal on the surface of the graphene film and patterning it to form a metal electrode; then executing step S30;

[0044] In this embodiment, the metal electrode 3 is formed by magnetron sputtering to form a 100nm continuous gold film, which is then structured using a double-layer resist stripping process. Specifically, a double layer of photoresist is spin-coated on the graphene film 2. Exposure and development leave the resist structure. A gold film is then sputtered and deposited. The photoresist is then removed using acetone, stripping away the gold on the photoresist surface. Finally, the metal electrode 3 is formed. At this point, a metal electrode 3 is located at each end of the graphene film 2.

[0045] S30: Patterning of the graphene film; then executing step S40;

[0046] In this embodiment, a double-layer resist process is used to photolithography the remaining surface of the graphene film 2 after step S20, and then the graphene film 2 is etched by plasma, and finally the resist is removed to complete the patterning of the graphene film 2, thereby obtaining graphene strips with a length and width of micrometer level.

[0047] S40: Preparing a lead sulfide seed layer on the surface of the graphene film and the surface of the metal electrode; then performing step S50;

[0048] In this embodiment, a 10 nm thick lead sulfide quantum dot film is deposited on the surface of the graphene strips and the metal electrode surface on the graphene film by spin coating, which is the lead sulfide seed layer 4; wherein the ligand of the lead sulfide quantum dots is octylamine, the concentration of the lead sulfide quantum dot solution is 25 mg / ml, and the rotation speed is 3000 RPM.

[0049] S50: With the assistance of the lead sulfide seed layer, a lead sulfide nanocrystalline thin film layer is prepared on its surface.

[0050] In this embodiment, lead acetate, thiourea, sodium citrate, and sodium hydroxide were dissolved in water to prepare a precursor solution. A 120 nm thick lead sulfide nanocrystalline thin film layer 5 was prepared by a chemical water bath method in a water bath (40 degrees). The surface morphology of the thin film layer is shown in FIG. Figure 3 As shown, the detector preparation is then completed.

[0051] According to the above preparation method, the following can be obtained: Figure 2 The graphene / lead sulfide infrared detector of the structure shown specifically includes a substrate 1, on which a graphene film 2, a metal electrode 3, a lead sulfide seed layer 4, and a lead sulfide nanocrystal film layer 5 are laid in sequence from substrate 1 upward; wherein, a metal electrode is laid at each end of the graphene film.

[0052] After testing, the graphene / lead sulfide infrared detector obtained in this embodiment has a device responsivity of 10 under 635nm wavelength incident light. 3 A / W. Under 1550nm wavelength incident light, the device's responsivity was measured to be 10 2 mA / W.

[0053] Example 2

[0054] In this embodiment, a graphene / lead sulfide infrared detector having a double-layer graphene film 2 is prepared, and its structure is similar to Figure 2 , the difference is that, in this embodiment, the graphene film 2 has two layers.

[0055] In this embodiment, the preparation method can refer to Example 1, except that:

[0056] In this embodiment, the graphene film transfer step in step S10 needs to be repeated once to obtain a double-layer graphene film 2;

[0057] The ligand of the lead sulfide quantum dots used in preparing the lead sulfide seed layer 4 is EDT;

[0058] Furthermore, the other steps are the same as those in Example 1, and finally a graphene / lead sulfide infrared detector having two layers of graphene films 2 is prepared.

[0059] After testing, the graphene / lead sulfide infrared detector with two layers of graphene film 2 obtained by the steps in this embodiment has a device responsivity of 10 under 635nm wavelength incident light. 4 A / W. Under 1550nm wavelength incident light, the device's responsivity was measured to reach 1A / W.

[0060] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are protected by the present invention.

Claims

1. A method for preparing a graphene / lead sulfide infrared detector, characterized in that: The graphene / lead sulfide infrared detector includes a substrate, which is sequentially covered with a graphene film, a metal electrode, a lead sulfide seed layer, and a lead sulfide nanocrystal film layer; wherein, one metal electrode is laid on each end of the graphene film; The lead sulfide seed layer is a thin film composed of quantum dots with a size of 1-10 nm, and the thickness of the lead sulfide seed layer is 8-16 nm; The lead sulfide nanocrystal thin film layer is a thin film composed of nanocrystals with a particle size of 50-500 nm, and the thickness of the lead sulfide nanocrystal thin film is 70-150 nm; The following steps are involved: (1) Prepare graphene film and transfer it to a clean substrate; (2) Depositing metal on the surface of the graphene film and patterning it to form a metal electrode; (3) Patterning of graphene films; (4) preparing a lead sulfide seed layer on the surface of the graphene film and the surface of the metal electrode; (5) preparing a lead sulfide nanocrystalline thin film layer with the assistance of the lead sulfide seed layer; The specific method for preparing the lead sulfide nanocrystalline thin film layer in step (5) is as follows: Lead acetate, thiourea, sodium citrate and sodium hydroxide are dissolved in water to prepare a precursor solution, and then the precursor solution is transferred into a water bath to prepare a lead sulfide nanocrystalline film through a chemical water bath method.

2. The preparation method according to claim 1, characterized in that One to three layers of graphene film are laid between the metal electrode and the substrate.

3. The preparation method according to claim 1, characterized in that The metal electrodes include gold, silver, chromium and gold or chromium and silver; wherein, for the metal electrodes containing chromium and gold or chromium and silver, the chromium is located on the graphene film, and the gold or silver film is located on the chromium.

4. The preparation method according to claim 1, characterized in that In the step (1), a graphene film is prepared on copper by chemical vapor deposition, and the graphene film is transferred from the copper foil to the substrate by PMMA.

5. The preparation method according to claim 1, characterized in that In step (2), a continuous metal film is obtained by magnetron sputtering, and the metal electrode is obtained by structuring based on a double-layer adhesive stripping process. The specific steps are as follows: First, a double layer of photoresist is spin-coated on the graphene film, and the resist structure is left after exposure and development. Then, a metal film is sputtered and deposited. The photoresist is removed with acetone, and the metal on the surface of the photoresist is also peeled off, finally forming a metal electrode.

6. The preparation method according to claim 1, characterized in that The method for preparing the lead sulfide seed layer in step (4) includes: spin coating, dip coating or drop coating.

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