A photodetector based on ultrashort channel graphene and its preparation method

Abstract

The present invention belongs to the field of semiconductor optoelectronic devices, and specifically relates to a photodetector based on ultrashort channel graphene and a method for preparing the same. The photodetector structure comprises an insulating substrate, a metal electrode, a graphene conductive channel, and a semiconductor light-absorbing layer. The proposed photodetector based on ultrashort channel graphene utilizes a focused helium ion beam to process a sub-10 nanometer graphene conductive channel, which can improve the graphene carrier mobility and achieve an ultrashort transit time. At the same time, the graphene / semiconductor composite structure effectively improves the carrier separation efficiency and increases the carrier lifetime. By fully leveraging the advantages of graphene's high mobility and the composite structure's effective carrier separation, a high-gain photodetector is achieved. The photodetector provided by the present invention has the advantages of being light and thin, having high gain, high responsiveness, good process repeatability, and easy integration. It can be applied to weak light detection and is a highly practical photodetector structure.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor optoelectronic devices, and in particular relates to a photodetector based on ultrashort channel graphene and a preparation method thereof. Background Art

[0002] A photodetector is a device that converts light signals into electrical signals. Depending on how the device responds to light radiation, photodetectors can be classified as photoconductive, built-in electric field photovoltaic, photothermoelectric, and bolometer types. Based on the wavelength of light they can detect, photodetectors can be categorized as ultraviolet, visible, and infrared. Photodetectors have a wide range of applications in various fields, including military and economics. Ultraviolet photodetectors are primarily used in ultraviolet communications, ozone monitoring, open flame detection, and biomedical analysis. Visible photodetectors can be used for radiation measurement and detection, industrial automation, and photometry. Infrared photodetectors are primarily used in missile warning and guidance, infrared remote sensing, and infrared thermal imaging.

[0003] Semiconductor nanomaterials such as cadmium sulfide, perovskite, lead sulfide, and lead selenide are widely used as light-absorbing materials in photoconductive photodetectors due to their high light absorption efficiency. However, these photodetectors lack effective separation of electrons and holes and stable charge capture. Photoinduced electron-hole pairs in the light-absorbing layer rapidly recombine within a few picoseconds, resulting in a short carrier lifetime and low device gain. Graphene is a two-dimensional material composed of a single-layer sheet of carbon atoms, arranged in a hexagonal honeycomb lattice structure with sp2 hybridized orbitals. Graphene films exhibit excellent properties such as low resistivity, high carrier mobility, a broad absorption spectrum, and fast response time. Researchers combined graphene with semiconductor light-absorbing materials to form a composite structure. Electrons in the graphene transfer to the proximal light-absorbing layer, filling the vacant states in the valence band of the light-absorbing material generated by photon absorption. This suppresses the recombination of photoexcited electron-hole pairs in the light-absorbing layer, allowing electrons in the light-absorbing material to remain in the conduction band without decaying. At the same time, the heterojunction formed by graphene and semiconductor light-absorbing materials can achieve effective separation of photogenerated carriers, thereby increasing the carrier lifetime and leading to a synergistic increase in device gain and responsiveness.

[0004] Graphene combined with semiconductor light-absorbing materials can effectively suppress electron-hole pair recombination, but the transit time is still long, limiting the performance of photodetectors. Therefore, finding new solutions to shorten carrier transit time is crucial for the development of composite structure photodetectors. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a photodetector based on ultrashort channel graphene and a preparation method thereof. By constructing a sub-10 nanometer graphene conductive channel, the high carrier mobility characteristics of graphene are stimulated, and the carrier transit time is reduced, thereby obtaining a high-gain, high-responsivity photodetector.

[0006] The present invention provides a photodetector based on ultrashort channel graphene. The device comprises, from bottom to top, an insulating substrate; a metal electrode built on the insulating substrate, the metal electrode comprising a large metal electrode and a channel electrode, wherein the large metal electrode contacted by a probe during testing is connected to the channel electrode that determines the channel line width; a graphene conductive channel layer covering the channel electrode; and a semiconductor light absorption layer located above the conductive channel.

[0007] Furthermore, the insulating substrate includes: a silicon wafer with a silicon dioxide layer.

[0008] Furthermore, the metal large electrode in the metal electrode includes: chromium / gold, chromium / silver, chromium / aluminum, wherein the chromium is located on the insulating substrate, and the gold, silver, and aluminum films are located on the chromium.

[0009] Furthermore, the thickness of the chromium film is 10 nm, and the thickness of the gold, silver and aluminum films is 100-150 nm.

[0010] Furthermore, the metal electrode comprises a channel electrode material including gold and silver. Since the electrode spacing, which determines the channel line width, is at the nanometer scale, the thickness of the channel electrode must be significantly smaller than that of the surrounding metal electrode to achieve the desired aspect ratio of the channel processing. Furthermore, to ensure continuity of the ultra-thin metal film, the thickness of the gold and silver electrodes is 5-10 nm. This channel electrode is patterned to achieve a sub-10 nm electrode spacing.

[0011] Furthermore, the number of layers of the graphene conductive channel layer is 1-3.

[0012] Furthermore, the semiconductor light-absorbing layer includes: cadmium sulfide, perovskite, lead sulfide, and lead selenide.

[0013] The present invention also provides a method for preparing a photodetector based on ultrashort channel graphene, which is characterized by comprising the following steps:

[0014] (1) Cleaning of insulating substrate;

[0015] (2) depositing metal on the substrate surface to form a metal electrode;

[0016] (3) Preparation, transfer and patterning of graphene films;

[0017] (4) A semiconductor light-absorbing layer is provided on the graphene layer.

[0018] Furthermore, the substrate cleaning process in step (1) is as follows: ultrasonic cleaning with acetone, alcohol, and deionized water for 10 minutes respectively, and then drying with nitrogen.

[0019] Furthermore, the metal electrode formation described in step (2) includes: obtaining a large metal electrode by electron beam evaporation, structuring it based on a double-layer resist stripping process, first spin-coating a double-layer photoresist, exposing and developing to leave the resist structure, then evaporating and depositing a metal thin film, removing the photoresist with acetone, and stripping off the metal film on the surface of the photoresist, ultimately forming a large metal electrode. Ultra-thin metal is prepared by sputtering, and a sub-10 nanometer electrode spacing is achieved based on pA-level small-beam focused helium ion beam processing technology, ultimately forming a channel electrode.

[0020] Furthermore, the step (3) includes: preparing graphene on copper by chemical vapor deposition, transferring the graphene from the copper foil to a silicon / silicon dioxide / metal target substrate by PMMA, and patterning the graphene by a double-layer glue process.

[0021] Furthermore, the preparation methods of the semiconductor light-absorbing layer in step (4) include: chemical water bath method, spin coating method, vacuum evaporation method, etc.

[0022] The basic principle of the present invention is that the photodetector gain is determined by the carrier lifetime and the transit time (G = T lifetime / T transit ), responsiveness is positively correlated with gain. Therefore, the higher the carrier lifetime and the shorter the transit time, the greater the device gain and responsiveness. Based on the graphene composite structure, a sub-10 nanometer graphene conductive channel is constructed. On the one hand, the composite structure can achieve effective carrier separation, avoid the recombination of electrons and holes, and achieve an increase in carrier lifetime. On the other hand, a sub-10 nanometer channel is constructed using a focused helium ion beam method. The ultrashort channel is conducive to improving the graphene carrier mobility and reducing the carrier transit time. Through the coordinated regulation of carrier lifetime and transit time, a high-gain, high-responsiveness photodetector is obtained.

[0023] The ultrashort channel graphene photodetector proposed in the present invention has a simple structure, good process repeatability, can realize a parallel structure, and can be produced on a large scale. It is a very practical photodetector structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 3D structure diagram of the photodetector according to an embodiment of the present invention;

[0025] Figure 2 is a cross-sectional view of a photodetector according to an embodiment of the present invention;

[0026] Figure 3 2 is a plan view of a photodetector according to an embodiment of the present invention. DETAILED DESCRIPTION

[0027] 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.

[0028] Example 1

[0029] The structure of the ultra-short channel graphene photodetector proposed in the present invention is as follows: Figure 1-3 As shown, from bottom to top, it includes: a silicon substrate 1, a silicon dioxide insulating layer 2, a metal electrode (including a large metal electrode 3 and a channel electrode 4), a graphene conductive channel layer 5, and a semiconductor light absorption layer 6. The insulating substrate in this embodiment is a heavily doped P-type silicon 1 substrate covered with thermally oxidized silicon dioxide 2. The large metal electrode 3 is a chromium / gold film with a chromium thickness of 10nm and a gold thickness of 100nm. The channel electrode 4 is 8nm thick gold, and after patterning, an electrode spacing of 6 nanometers is obtained. The graphene conductive channel layer 5 is a single-layer film. The semiconductor light absorption layer is 100nm thick lead selenide.

[0030] The main process steps for preparing silicon / silicon dioxide / chromium / gold / graphene / lead selenide photodetectors include:

[0031] (1) Before use, the silicon / silicon dioxide substrate was ultrasonically cleaned with acetone, alcohol, and deionized water for 10 minutes respectively, and then dried with nitrogen gas for later use.

[0032] (2) Chromium / gold is prepared by electron beam evaporation and structured based on a double-layer resist stripping process. First, a double layer of photoresist is spin-coated, and the resist structure is left after exposure and development. Then, a chromium / gold thin film is deposited by evaporation. The photoresist is removed using acetone, and the metal film on the surface of the photoresist is also stripped off, ultimately forming a large metal electrode.

[0033] (3) A gold film was prepared by sputtering, and the target electrode spacing was achieved based on pA-level small beam focused helium ion beam processing technology, ultimately forming a channel electrode.

[0034] (4) On a copper substrate, a single layer of graphene was prepared using chemical vapor deposition. The graphene was transferred from the copper foil to a silicon / silicon dioxide / metal target substrate using PMMA. The graphene transfer process was as follows: the graphene was cut into 3cm x 3cm pieces and taped to a silicon wafer. The PMMA solution was spin-coated onto the graphene surface at a speed of 4000RPM, and then baked in an oven at 100 degrees for 10 minutes. The graphene and copper foil with PMMA spin-coated on them were removed from the silicon wafer. The graphene on the back was first etched away using oxygen plasma, and then the copper foil was removed using wet etching with HCl+H2O2 solution (3:1) as the etching solution for 3 hours. After the copper was dissolved, it was repeatedly rinsed with deionized water, and the graphene was fished out using a silicon / silicon dioxide / metal target substrate. It was then air-dried and placed in acetone to remove the PMMA glue. The graphene transfer was completed. Finally, the graphene was patterned using a double-layer glue process.

[0035] (5) Prepare a 10mg / ml lead selenide solution and spin-coat the lead selenide light-absorbing layer at 3000RPM to complete the detector preparation. After testing, the photodetector has a response of 10 at an incident light wavelength of 3um. 2 A / W.

[0036] Example 2

[0037] The structure of the ultra-short channel graphene photodetector proposed in the present invention is as follows: Figure 1-3 As shown, from bottom to top, it includes: a silicon substrate 1, a silicon dioxide insulating layer 2, a metal electrode (including a large metal electrode 3 and a channel electrode 4), a graphene conductive channel layer 5, and a semiconductor light absorption layer 6. The insulating substrate in this embodiment is a heavily doped P-type silicon 1 substrate covered with thermally oxidized silicon dioxide 2. The large metal electrode 3 is a chromium / gold film with a chromium thickness of 10nm and a gold thickness of 100nm. The channel electrode 4 is 8nm thick gold, and after patterning, an electrode spacing of 6 nanometers is obtained. The graphene conductive channel layer 5 is a double-layer film. The semiconductor light absorption layer is 100nm thick lead sulfide.

[0038] The main process steps for preparing silicon / silicon dioxide / chromium / gold / graphene / lead sulfide photodetectors include:

[0039] (1) Before use, the silicon / silicon dioxide substrate was ultrasonically cleaned with acetone, alcohol, and deionized water for 10 minutes respectively, and then dried with nitrogen gas for later use.

[0040] (2) Chromium / gold is prepared by electron beam evaporation and structured based on a double-layer resist stripping process. First, a double layer of photoresist is spin-coated, and the resist structure is left after exposure and development. Then, a chromium / gold thin film is deposited by evaporation. The photoresist is removed using acetone, and the metal film on the surface of the photoresist is also stripped off, ultimately forming a large metal electrode.

[0041] (3) A gold film was prepared by sputtering, and the target electrode spacing was achieved based on pA-level small beam focused helium ion beam processing technology, ultimately forming a channel electrode.

[0042] (4) On a copper substrate, a single-layer graphene was prepared using chemical vapor deposition. The graphene was transferred from the copper foil to a silicon / silicon dioxide / metal target substrate using PMMA. The graphene transfer process was as follows: the graphene was cut into 3cm x 3cm pieces and taped to a silicon wafer. The PMMA solution was spin-coated onto the graphene surface at a speed of 4000RPM, and then baked in an oven at 100 degrees for 10 minutes. The graphene and copper foil with PMMA spin-coated on them were removed from the silicon wafer. The graphene on the back was first etched away using oxygen plasma, and then the copper foil was removed using wet etching with HCl:H2O2 (3:1) as the etching solution for 3 hours. After the copper was dissolved, it was repeatedly rinsed with deionized water, and the graphene was removed from the silicon / silicon dioxide / metal target substrate. It was air-dried and then placed in acetone to remove the PMMA glue. The transfer was repeated twice to obtain a double-layer graphene. Finally, the graphene was patterned using a double-layer glue process.

[0043] (5) Prepare a 25mg / ml lead sulfide solution and spin coat the lead sulfide light absorbing layer at 3000RPM to complete the detector preparation. The test showed that the photodetector has a responsivity of 10 at an incident light wavelength of 980nm. 7 A / W. At an incident light wavelength of 1550nm, the photodetector's responsivity reaches 10 3 A / W.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a photodetector based on ultrashort channel graphene, characterized in that: The ultrashort channel graphene-based photodetector comprises, from bottom to top, an insulating substrate; a metal electrode built on the insulating substrate, the metal electrode comprising a metal macroelectrode and a sub-10 nanometer channel electrode, wherein the metal macroelectrode contacted by a probe during testing is connected to the sub-10 nanometer channel electrode that determines the channel line width; a graphene conductive channel layer covering the channel electrode; and a semiconductor light absorption layer located above the conductive channel. The preparation method comprises the following steps: (1) Depositing metal on the substrate surface to form a metal electrode; (2) Preparation, transfer and patterning of graphene films; (3) providing a semiconductor light-absorbing layer on the graphene film; The formation of the metal electrode described in step (1) includes: obtaining a large metal electrode by electron beam evaporation, structuring based on a double-layer glue stripping process, first spin-coating a double-layer photoresist, exposing and developing to leave the glue structure, then evaporating and depositing a metal film, using acetone to remove the photoresist, and stripping off the metal film on the surface of the photoresist, finally forming a large metal electrode, preparing ultra-thin metal by sputtering, achieving a sub-10 nanometer electrode spacing based on pA-level small beam focused helium ion beam processing technology, and finally forming a channel electrode.

2. The method for preparing a photodetector according to claim 1, wherein: The insulating substrate includes a silicon wafer with a silicon dioxide layer.

3. The method for preparing a photodetector according to claim 1, wherein: The metal large electrode in the metal electrode includes: chromium / gold, chromium / silver or chromium / aluminum, wherein the chromium is located on the insulating substrate, and the gold, silver or aluminum film is located on the chromium.

4. The method for preparing a photodetector according to claim 3, wherein: The thickness of chromium in the metal macroelectrode in the metal electrode is 10 nm, and the thickness of the gold, silver or aluminum film is 100-150 nm.

5. The method for preparing a photodetector according to claim 1, wherein: The sub-10 nanometer channel electrode material in the metal electrode includes: gold or silver; the thickness of the gold or silver is 5-10 nm; the channel electrode is patterned to achieve a sub-10 nanometer electrode spacing.

6. The method for preparing a photodetector according to claim 1, wherein: The number of layers of the graphene conductive channel layer is 1-3.

7. The method for preparing a photodetector according to claim 1, wherein: The semiconductor light-absorbing layer includes: cadmium sulfide, perovskite, lead sulfide or lead selenide.

8. The method for preparing a photodetector according to claim 1, wherein: The step (2) comprises: preparing graphene on copper by chemical vapor deposition, transferring the graphene from the copper foil to a silicon / silicon dioxide / metal target substrate by PMMA, and patterning the graphene by a double-layer glue process.

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