Bipolar response photoelectric detector and preparation method thereof

Abstract

The present invention relates to the field of optical communication, and provides a bipolar response photoelectric detector and a preparation method thereof, wherein the bipolar response photoelectric detector comprises: a heavily doped P-type silicon substrate, a silicon oxide layer attached to the surface of which; polymethyl methacrylate modified graphene, including graphene and polymethyl methacrylate adsorbed on the surface of the graphene, attached to the silicon oxide layer; and two electrodes, respectively attached to the set positions of the polymethyl methacrylate modified graphene. The detector is low-cost and easy to process. Through the composite structure design of graphene and polymethyl methacrylate, the responsiveness and stability of the detector are significantly improved. It can also detect multiple optical signals of different wavelengths at the same time to meet the needs of different application scenarios. In addition, the time-dependent characteristics of the positive response current and the negative response current of the detector are significantly different, which solves the problem of bit errors caused by the offset of positive and negative responses in the previous bipolar response detector in optical communication applications.

Description

Technical Field

[0001] The present invention relates to the field of optical communication technology, and in particular to a bipolar response photoelectric detector and a preparation method thereof. Background Art

[0002] As a key component for information acquisition and processing, photodetectors are widely used in communications, medical imaging, environmental monitoring, security surveillance, and autonomous driving. Their performance directly affects the progress of related technologies. However, traditional photodetectors based on semiconductor materials have limitations in spectral response range and responsivity. Existing silicon and indium gallium arsenide detectors can only perform intensity detection and cannot distinguish light signals of different wavelengths, which limits their development in applications such as multi-dimensional information transmission and encryption.

[0003] In order to overcome these limitations, wavelength-dependent bipolar response photodetectors have attracted much attention in recent years. This type of photodetector can distinguish between positive and negative current responses through the conductivity changes of light signals of different wavelengths, thereby simplifying the structure of optical communication systems and expanding the performance and application areas of detectors.

[0004] At present, researchers have constructed bipolar response detectors using different perovskite layers, p-AlGaN / n-GaN pn heterojunction nanowires, two-dimensional materials and other materials, and have achieved some results. However, there are still some challenges in the existing bipolar response photodetector technology. For example, the complex preparation process, low responsiveness, and similar time-dependent characteristics of positive and negative current responses have seriously restricted the promotion of bipolar response photodetectors in practical applications.

[0005] Therefore, developing a bipolar response photodetector with simple preparation process, high responsiveness, stable response polarity change and wide spectral response is a current scientific research hotspot. Summary of the invention

[0006] The present invention provides a bipolar response photodetector and a preparation method thereof, which are used to overcome the defects of the existing bipolar response photodetector, such as complex preparation process and operation, low responsiveness, and the similar time-dependence characteristics of positive and negative current responses, which easily cancel each other out and cause bit errors. The present invention can reduce the preparation cost, significantly improve the responsiveness and stability of the detector, and the time-dependence characteristics of the positive and negative response currents have obvious differences, so there is no problem of bit errors caused by the positive and negative response currents canceling each other out.

[0007] On the one hand, the present invention provides a bipolar response photodetector, comprising: a heavily doped P-type silicon substrate, a silicon oxide layer attached to the surface of which; polymethyl methacrylate modified graphene, comprising graphene and polymethyl methacrylate adsorbed on the surface of the graphene, adhered to the silicon oxide layer; two electrodes, respectively adhered to set positions of the polymethyl methacrylate modified graphene.

[0008] Furthermore, the two electrodes are both gold electrodes.

[0009] In a second aspect, the present invention also provides a method for preparing a bipolar response photodetector, which is used to prepare the bipolar response photodetector described in any of the above items, comprising: growing a single layer of graphene and transferring it to a heavily doped P-type silicon substrate, the surface of the heavily doped P-type silicon substrate being attached with a silicon oxide layer; placing the graphene transferred to the heavily doped P-type silicon substrate in an acetone solution dissolved with polymethyl methacrylate, evaporating and vacuum annealing to obtain polymethyl methacrylate-modified graphene; preparing two electrodes by thermal evaporation, and the two electrodes are respectively attached to the set positions of the polymethyl methacrylate-modified graphene.

[0010] Furthermore, the growth of a single layer of graphene and its transfer to a heavily doped P-type silicon substrate comprises: growing a single layer of graphene on a copper foil substrate by chemical vapor deposition; spin coating a polymethyl methacrylate solution on the graphene on the copper foil substrate, and placing it in an etching solution after heating until the copper foil substrate is completely dissolved to obtain a polymethyl methacrylate-graphene sample; placing the polymethyl methacrylate-graphene sample in a deionized water solution, and replacing the deionized water solution multiple times to clean the residual etching solution on the polymethyl methacrylate-graphene sample; taking out the polymethyl methacrylate-graphene sample from the deionized water solution through a heavily doped P-type silicon substrate; when the surface water of the polymethyl methacrylate-graphene sample is fully evaporated and the graphene in the polymethyl methacrylate-graphene sample is attached to the heavily doped P-type silicon substrate, placing the polymethyl methacrylate-graphene sample in an acetone solution to dissolve the polymethyl methacrylate on its surface and clean it to complete the transfer of the graphene to the heavily doped P-type silicon substrate.

[0011] Furthermore, the spin coating of the polymethyl methacrylate solution on the graphene on the copper foil substrate includes: spin coating the polymethyl methacrylate solution by a spin coating machine, during which the spin coating is firstly performed at a first rotation speed for a first time period, and then at a second rotation speed for a second time period; wherein the first rotation speed is lower than the second rotation speed, and the first time period is shorter than the second time period; the polymethyl methacrylate solution uses anisole or chloroform as a solvent, and the mass fraction is 3%-8%.

[0012] Furthermore, the graphene transferred to the heavily doped P-type silicon substrate is placed in an acetone solution dissolved with polymethyl methacrylate, and polymethyl methacrylate-modified graphene is obtained through evaporation and vacuum annealing, including: evaporating the acetone solution, polymethyl methacrylate is adsorbed on the surface of the graphene to form a discontinuous film; and vacuum annealing at a set temperature to enhance the chemical bond contact between polymethyl methacrylate and graphene, thereby obtaining polymethyl methacrylate-modified graphene.

[0013] Furthermore, the preparation of the two electrodes by thermal evaporation includes: attaching a pre-designed electrode mask plate to polymethyl methacrylate modified graphene, and preparing two gold electrodes by thermal evaporation under set vacuum conditions; when the thickness of the two gold electrodes reaches the set thickness, stopping the thermal evaporation to obtain the two gold electrodes.

[0014] Furthermore, after the bipolar response photoelectric detector is prepared, the method further includes: performing a vacuum annealing treatment at 145° C. to 160° C. on the bipolar response photoelectric detector to improve the contact characteristics between the polymethyl methacrylate modified graphene and the two electrodes.

[0015] In a third aspect, the present invention also provides a modified graphene material, the preparation method of which comprises: (1) growing a single-layer graphene on a metal foil substrate by chemical vapor deposition; (2) transferring the single-layer graphene to a heavily doped P-type silicon substrate by wet transfer technology; (3) placing the single-layer graphene transferred to the heavily doped P-type silicon substrate obtained in step (2) on a 4×10 -6 -1×10 -5 (4) annealing at 145°C to 160°C in a vacuum oven to obtain a modified graphene material.

[0016] In a fourth aspect, the present invention also provides an application of the modified graphene material in preparing a photodetector, especially in preparing a bipolar response photodetector.

[0017] In a fifth aspect, the present invention also provides a bipolar response light detection method, comprising: irradiating the bipolar response photodetector described in any one of the above texts with the light to be detected to generate a positive response current signal and a negative response current signal; drawing a first curve of the positive response current signal changing with time, and a second curve of the negative response current signal changing with time; and determining, based on the first curve and the second curve, whether there is a difference between the time dependence characteristics of the positive response current signal and the time dependence characteristics of the negative response current signal.

[0018] The bipolar response photoelectric detector provided by the present invention comprises a heavily doped P-type silicon substrate, a silicon oxide layer attached to the surface of which; polymethyl methacrylate modified graphene, comprising graphene and polymethyl methacrylate adsorbed on the graphene surface, attached to the silicon oxide layer; and two electrodes, respectively attached to the set positions of the polymethyl methacrylate modified graphene. The detector is low-cost and easy to process. Through the composite structure design of graphene and polymethyl methacrylate, the responsiveness and stability of the detector are significantly improved. It can also detect multiple optical signals of different wavelengths at the same time to meet the needs of different application scenarios. In addition, the time dependence characteristics of the positive response current and the negative response current of the detector are significantly different, which solves the problem of bit errors caused by the offset of positive and negative responses in previous bipolar response detectors. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 It is a schematic diagram of the structure of a bipolar response photodetector provided in an embodiment of the present invention.

[0021] Figure 2 It is a schematic diagram of the mechanism of the bipolar response photodetector provided in an embodiment of the present invention.

[0022] Figure 3 It is a schematic flow chart of a method for preparing a bipolar response photodetector provided in an embodiment of the present invention.

[0023] Figure 4 It is a schematic diagram of the preparation process of polymethyl methacrylate modified graphene provided in an embodiment of the present invention.

[0024] Figure 5 It is a flow chart of a bipolar response light detection method provided in an embodiment of the present invention.

[0025] Figure 6 It is a curve diagram showing the change of negative response current and positive response current of the bipolar response photodetector provided by an embodiment of the present invention under the irradiation of light of different wavelengths over time.

[0026] Figure 7 It is a curve diagram showing the change of the responsivity of the negative response current and the positive response current of the bipolar response photodetector provided by an embodiment of the present invention with the wavelength.

[0027] Reference numerals: 110: heavily doped P-type silicon substrate; 120: silicon oxide layer; 130: polymethyl methacrylate modified graphene; 140: electrode. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are 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 creative work are within the scope of protection of the present invention.

[0029] With the rapid development of modern science and technology, photodetectors, as key components for information acquisition and processing, are widely used in fields such as communications, medical imaging, environmental monitoring, security monitoring, and autonomous driving. Photodetectors based on traditional semiconductor materials generate photogenerated carriers through illumination, thereby improving the conductivity of semiconductor materials and realizing the conversion of light intensity signals into electrical signals. However, traditional photodetectors often have a limited response range to the spectrum, and the responsivity is usually less than 1A / W, which makes it difficult to meet the requirements of high sensitivity and wide spectral response. Especially in the visible to near-infrared spectral range, the performance of existing detectors is often restricted by material bandgap limitations and preparation processes. In addition, traditional silicon and indium gallium arsenide detectors can only perform intensity detection and cannot distinguish light signals of different wavelengths. This limitation limits their applicability in applications such as multidimensional information transmission and encryption.

[0030] In recent years, wavelength-dependent bipolar response detectors have attracted widespread attention. The conductivity of bipolar response detectors will increase or decrease under the excitation of light of different wavelengths, generating a positive response current higher than the dark current or a negative response current lower than the dark current, thereby achieving the distinction of light signals of different wavelengths. This feature not only simplifies the structure of the optical communication system without adding additional filters for wavelength distinction, but also greatly expands the performance and application areas of the detector, such as low-power all-optical switches, reconfigurable optical synapse systems, and high-precision optical network computing.

[0031] However, there are many technical challenges in the existing bipolar response detectors. For example, some studies have prepared photodetection devices with different perovskite layers through a two-step method, integrating semiconductor materials with different bandgap widths in different directions of the substrate, and using the difference in the direction of electron transmission under different wavelengths to achieve the change of current polarity. This method requires the incident direction of light to be on both sides, which is complicated to operate. At the same time, there is no response gain, and the response is low, less than 1A / W.

[0032] Another study has prepared a bipolar response detector by growing vertically arranged p-AlGaN / n-GaN pn heterojunction nanowires and covering the top of the nanowires with platinum nanoparticles. Due to the carrier transport in a single pn junction and the redox reaction on the surface of the nanowire, the detector generates positive response current and negative response current under light of different wavelengths (254nm and 365nm). However, the response of this method is low, only 0.2A / W.

[0033] In addition, there are studies using two-dimensional materials such as graphene and transition metal chalcogenides to construct detectors through stacking and bandgap control to achieve changes in response polarity at different wavelengths. However, this type of method has problems such as complex preparation process and similar time-dependent characteristics of positive and negative responses.

[0034] In view of this, the present invention proposes a new bipolar response photodetector, specifically, Figure 1 A schematic structural diagram of a bipolar response photodetector provided in an embodiment of the present invention is shown.

[0035] like Figure 1 As shown, the bipolar response photodetector includes: a heavily doped P-type silicon substrate 110, with a silicon oxide layer 120 attached to its surface; a polymethyl methacrylate modified graphene 130, including graphene and polymethyl methacrylate adsorbed on the surface of the graphene, adhered to the silicon oxide layer 120; two electrodes 140, respectively adhered to the set positions of the polymethyl methacrylate modified graphene 130.

[0036] The structure of the bipolar response photodetector will be described in detail below.

[0037] Regarding the heavily doped P-type silicon substrate 110 (P++ Si).

[0038] The heavily doped P-type silicon substrate 110 refers to a silicon material doped with a relatively high concentration of acceptor impurities (usually boron, B), so that the material has a relatively high hole concentration and thus exhibits a strong P-type semiconductor characteristic.

[0039] “Heavy doping” refers to the addition of high concentrations of impurity atoms into a relatively pure silicon substrate. High concentration usually refers to a doping concentration of 10 19 to 10 21 cm −3 This high concentration of doping will significantly change the electrical properties of silicon materials, greatly enhancing their conductivity.

[0040] In this embodiment, a layer of silicon oxide (SiO2) is attached to the surface of the heavily doped P-type silicon substrate 110, which helps to maintain a high resistivity. The silicon oxide layer 120 can be formed by thermal oxidation. Specifically, thermal oxidation refers to placing the heavily doped P-type silicon substrate 110 in an oxygen or water vapor environment at a high temperature (usually 900 degrees Celsius to 1200 degrees Celsius) so that the silicon surface reacts with oxygen to generate a dense layer of silicon oxide. The silicon oxide layer 120 formed by this method has good interface quality and is tightly bonded to the heavily doped P-type silicon substrate 110.

[0041] Of course, the silicon oxide layer 120 may also be deposited by chemical vapor deposition, which is not specifically limited here.

[0042] About polymethyl methacrylate modified graphene 130 (PMMA-modified Graphene).

[0043] Graphene has become a research hotspot for the new generation of optoelectronic materials due to its high mobility, good optical properties and chemical stability. The bandgap width of graphene is close to zero, which enables it to effectively absorb photons of different wavelengths in a wide spectral range, making it an important material for preparing photodetectors. At the same time, graphene has a layered structure and a large specific surface area, which is easily affected by surface photogenerated carriers, and produces high gain through the optical gating effect, which is expected to realize a highly responsive photodetector.

[0044] Poly(methyl methacrylate) (PMMA) is an excellent organic polymer, which is often used as a substrate material for optoelectronic materials due to its good optical transparency (over 90%) and high mechanical strength. The polar ester group in PMMA can produce localized trap states, which can interact with semiconductors to cause carrier migration, extend carrier lifetime, and produce high-gain enhanced light response in detectors.

[0045] The polymethyl methacrylate modified graphene 130 in this embodiment is prepared based on a composite structure of graphene and PMMA. Specifically, the polymethyl methacrylate modified graphene 130 includes graphene and PMMA adsorbed on its surface. The thickness of PMMA is about 10 nm. The polymethyl methacrylate modified graphene 130 is entirely attached to the silicon oxide layer 120 .

[0046] This embodiment can significantly improve the responsiveness and stability of the photodetector through the composite structure design of graphene and PMMA. Specifically, the responsiveness of the photodetector under positive and negative responses exceeds 1000A / W, and the normalized gain characteristic is one order of magnitude higher than that of the existing bipolar response detector. High responsiveness means that the photodetector can detect light signals more sensitively and can achieve effective detection of weak light signals.

[0047] Regarding electrode 140 .

[0048] Electrode 140 is a conductive component in the photodetector for introducing or extracting current.

[0049] In this embodiment, the photodetector includes two electrodes 140 , and the electrodes 140 are attached to the upper surface of the polymethyl methacrylate modified graphene 130 . The specific attachment position can be set according to actual conditions and is not specifically limited here.

[0050] For example, in one specific embodiment, Figure 1 As shown, two electrodes 140 are respectively attached to two ends of the polymethyl methacrylate-modified graphene 130 .

[0051] The three electrodes 140 in this embodiment may be metal electrodes (such as gold, silver, platinum, copper, etc.), and the specific materials may depend on actual needs.

[0052] In this embodiment, the bipolar response photodetector includes a heavily doped P-type silicon substrate 110, on the surface of which a silicon oxide layer 120 is attached; polymethyl methacrylate modified graphene 130, including graphene and polymethyl methacrylate adsorbed on the surface of graphene, is attached to the silicon oxide layer 120; two electrodes 140 are respectively attached to the set positions of the polymethyl methacrylate modified graphene 130. The detector is low-cost and easy to process. By optimizing the composite ratio and structural design of graphene and polymethyl methacrylate, the responsiveness and stability of the detector are significantly improved. It can also detect multiple optical signals of different wavelengths at the same time to meet the needs of different application scenarios. In addition, the time dependence characteristics of the positive response current and the negative response current of the detector are significantly different, which solves the problem of bit errors caused by the offset of positive and negative responses in previous bipolar response detectors.

[0053] On the basis of the above embodiment, optionally, both electrodes 140 in the bipolar response photodetector are gold electrodes, and the thickness of the gold electrode is 100 nm. It is easy to understand that gold electrodes have many unique advantages over electrodes of other materials. Specifically, on the one hand, gold electrodes have excellent electrical conductivity, can effectively transmit current, and reduce resistance loss; on the other hand, gold electrodes have strong corrosion resistance and oxidation resistance, and have good chemical stability.

[0054] In some other embodiments, Figure 2 A schematic diagram showing the mechanism of a bipolar response photodetector provided by an embodiment of the present invention is shown.

[0055] like Figure 2As shown in (a), the polar ester group of PMMA produces local trap states at around -4.2 eV, and its distribution width is about 0.4 eV. When the energy of the photogenerated electron carriers in graphene is higher than the trap state, the electrons are transferred to PMMA. Through the photogate effect of the electron carriers trapped in PMMA, more hole carriers are induced, and the conductivity of p-type graphene increases. Therefore, compared with the original graphene, a more significant positive response current is achieved in the range of 405nm to 1650nm. At the same time, the PMMA on the surface enhances the adsorption of air molecules (such as oxygen).

[0056] like Figure 2 As shown in (b), these oxygen molecules capture electrons and become negatively charged ions. Under short-wavelength light, the release of oxygen leads to electron-hole recombination, thereby increasing the Fermi level position. The hole photoconductivity then decreases to below the dark current along with the photocurrent. The bipolar response photodetector provided by the present invention exhibits a significant negative response current in the range of 405nm to 580nm.

[0057] In addition to the bipolar response photodetector described in the above embodiments, the present invention also provides a method for preparing a bipolar response photodetector, which is used to prepare the bipolar response photodetector described in the above embodiments.

[0058] Specifically, Figure 3 The figure shows a flow chart of a method for preparing a bipolar response photodetector provided in an embodiment of the present invention.

[0059] like Figure 3 As shown, the method includes steps S310-S330, and steps S310-S330 and related steps will be described in detail below.

[0060] S310, growing a single layer of graphene and transferring it to a heavily doped P-type silicon substrate, wherein a silicon oxide layer is attached to the surface of the heavily doped P-type silicon substrate.

[0061] It is easy to understand that a single layer of graphene is first grown on a copper foil substrate by chemical vapor deposition (CVD) and then transferred to a heavily doped p-type silicon substrate by wet transfer technology.

[0062] Growing a single layer of graphene on a copper foil substrate by chemical vapor deposition specifically includes the following steps S311-S314.

[0063] S311, preparing a copper foil substrate.

[0064] High-purity copper foil (e.g. 99.99% purity) is usually used, with a thickness of 25μm to 100μm. In order to ensure good nucleation and growth conditions, the copper foil needs to undergo a rigorous cleaning process to remove surface oxides and other contaminants.

[0065] S312, preheating and annealing.

[0066] The cleaned copper foil substrate is placed in the CVD reaction chamber and gradually heated to the required temperature (usually around 1000°C). Hydrogen is introduced during the heating process to reduce the oxide on the copper surface while maintaining the active state of the copper foil surface.

[0067] S313, carbon source introduction and graphene growth.

[0068] When the temperature reaches the set value, the hydrogen is turned off and methane is introduced as the carbon source gas. The ratio of methane can be adjusted according to the number of graphene layers required; for single-layer graphene, a lower concentration of methane is usually used (for example, a ratio of methane to hydrogen of 1:100 to 1:1000).

[0069] The temperature is kept constant for a period of time (e.g., 10 to 30 minutes), during which the carbon atoms diffuse on the surface of the copper foil and form graphene nuclei, which gradually expand into a continuous single-layer structure.

[0070] S314, cooling and transfer.

[0071] After the carbon source gas supply is stopped, the surface is cooled naturally to room temperature. In order to prevent the graphene from reacting with the copper surface during the cooling process, an inert gas (such as argon Ar) or hydrogen is usually continued to be introduced.

[0072] Since copper foil is not suitable for direct use in most applications, the grown graphene needs to be transferred from the copper foil to a target substrate (such as the heavily doped P-type silicon substrate in this embodiment).

[0073] The grown single-layer graphene is transferred to a heavily doped p-type silicon substrate by a wet transfer technique, which specifically includes the following steps S315-S319.

[0074] S315, coating a support layer.

[0075] A polymer support layer, such as polymethyl methacrylate (PMMA) solution, is coated on the surface of the grown graphene. This layer of polymer plays a protective role and helps maintain the integrity of the graphene in subsequent steps.

[0076] Specifically, in one embodiment, a PMMA solution is spin-coated onto the graphene on the copper foil substrate by a spin coater, wherein the PMMA solution uses anisole or chloroform as a solvent, and the mass fraction thereof is 3%-8%.

[0077] During the spin coating process, the coating is firstly performed at a first rotation speed (such as 500 r / min) for a first time (such as 10 s), and then the coating is performed at a second rotation speed (such as 2000 r / min) for a second time (such as 30 s); wherein the first rotation speed is lower than the second rotation speed, and the first time is shorter than the second time.

[0078] Subsequently, the graphene on the copper foil substrate spin-coated with the PMMA solution was placed on a hot plate at 120 degrees Celsius and heated for three minutes.

[0079] S316, etching the metal substrate.

[0080] Put the graphene with polymer support layer and copper foil substrate into the etching solution, with PMMA facing upward, and ensure that the copper foil substrate is in contact with the etching solution until the copper foil substrate is completely dissolved and the graphene with polymer support layer floats on the liquid surface, thereby obtaining a polymethyl methacrylate-graphene sample. Among them, the commonly used etching solution includes FeCl3 solution.

[0081] S317, cleaning of two-dimensional materials (graphene coated with a polymer support layer, i.e., polymethyl methacrylate-graphene samples).

[0082] To remove residual etching solution and other contaminants, graphene is usually cleaned in a range of solvents, such as deionized water, ethanol, etc. Ensuring that graphene is clean is critical to maintaining its performance.

[0083] Specifically, in one embodiment, the polymethyl methacrylate-graphene sample is transferred into a deionized water solution through a glass sheet, and the deionized water solution is replaced multiple times to clean the residual etching solution on the polymethyl methacrylate-graphene sample.

[0084] S318, transfer to the target substrate.

[0085] The polymethyl methacrylate-graphene sample floating on the liquid surface was carefully fished out through a heavily doped P-type silicon substrate and placed in a ventilated and dry environment to evaporate the residual moisture.

[0086] S319, removing the polymer support layer.

[0087] The polymer support layer is removed in a suitable solvent (such as acetone solution) to expose clean graphene, i.e., graphene on a heavily doped P-type silicon substrate.

[0088] Specifically, in one embodiment, when the surface moisture of the polymethyl methacrylate-graphene sample is fully evaporated and the graphene in the polymethyl methacrylate-graphene sample is adhered to the heavily doped P-type silicon substrate, the polymethyl methacrylate-graphene sample is placed in an acetone solution to dissolve the polymethyl methacrylate (i.e., the polymer support layer) on its surface, and is cleaned with alcohol and deionized water solution to complete the transfer of graphene from the copper foil substrate to the heavily doped P-type silicon substrate.

[0089] Based on the above steps, a single layer of graphene can be grown and transferred to a heavily doped P-type silicon substrate, and then step S320 is performed.

[0090] S320, placing the graphene transferred to the heavily doped P-type silicon substrate in an acetone solution containing polymethyl methacrylate, and obtaining polymethyl methacrylate-modified graphene through evaporation and vacuum annealing.

[0091] Figure 4 A schematic diagram of the preparation process of polymethyl methacrylate-modified graphene provided in an embodiment of the present invention is shown.

[0092] like Figure 4 As shown, after completing the transfer of graphene from the copper foil substrate to the heavily doped P-type silicon substrate, the graphene together with the heavily doped P-type silicon substrate is placed in an acetone solution containing a small amount of PMMA. At room temperature, as the acetone solution evaporates, PMMA will be adsorbed on the surface of the graphene to form a discontinuous film with a thickness of about 10 nm.

[0093] Subsequently, by vacuum annealing at a set temperature (such as 150 degrees Celsius), the chemical bond contact between PMMA and graphene is enhanced, thereby obtaining PMMA-modified graphene, namely polymethyl methacrylate-modified graphene.

[0094] Next, execute step S330.

[0095] S330, preparing two electrodes by thermal evaporation, and the two electrodes are respectively attached to the set positions of the polymethyl methacrylate modified graphene.

[0096] It is easy to understand that two electrodes are prepared by thermal evaporation on polymethyl methacrylate-modified graphene with the help of a mask with a fixed pattern.

[0097] Regarding thermal evaporation, the polymethyl methacrylate-modified graphene on a heavily doped P-type silicon substrate close to a mask is placed in a thermal evaporation system, and metals (such as gold Au, silver Ag, aluminum Al, etc.) are evaporated under high vacuum conditions to deposit metal atoms on the graphene areas not covered by the photoresist.

[0098] During thermal evaporation, the vacuum condition of the equipment needs to be below 5 mbar, and the deposition rate is controlled at 1.5 Å / s using a suitable current, and the evaporation is stopped when the metal thickness reaches 100 nm. In a specific embodiment, both electrodes prepared are gold electrodes.

[0099] Based on the above steps, a preliminary bipolar response photodetector can be prepared.

[0100] In order to further optimize the device performance, the prepared bipolar response photodetector is subjected to vacuum annealing at a set temperature (e.g., 150 degrees Celsius) at high temperature. The annealing treatment can improve the contact characteristics between the polymethyl methacrylate-modified graphene and the two electrodes. The set temperature is 145°C to 160°C.

[0101] In this embodiment, a single layer of graphene is grown and transferred to a heavily doped P-type silicon substrate, and then the graphene transferred to the heavily doped P-type silicon substrate is placed in an acetone solution dissolved with polymethyl methacrylate, and polymethyl methacrylate-modified graphene is obtained by evaporation and vacuum annealing, thereby preparing two electrodes by thermal evaporation, and the two electrodes are respectively attached to the set positions of the polymethyl methacrylate-modified graphene to prepare a bipolar response photodetector. The detector prepared by this method is low-cost and easy to process. The composite structure design of graphene and polymethyl methacrylate significantly improves the responsiveness and stability of the detector, and can also detect multiple optical signals of different wavelengths at the same time to meet the needs of different application scenarios. In addition, the time-dependent characteristics of the positive response current and the negative response current of the detector are significantly different, which solves the problem of bit errors caused by the offset of positive and negative responses in previous bipolar response detectors.

[0102] In addition, the present invention also provides a modified graphene material, the preparation method of which comprises: (1) growing a single-layer graphene on a metal foil substrate by chemical vapor deposition; (2) transferring the single-layer graphene to a heavily doped P-type silicon substrate by wet transfer technology; (3) placing the single-layer graphene transferred to the heavily doped P-type silicon substrate obtained in step (2) on a 4×10 -6 -1×10 -5 A culture dish with an inner diameter of 9 cm and a depth of 2 cm is placed in an acetone solution of polymethyl methacrylate with a high concentration. After the acetone solution evaporates, the polymethyl methacrylate is adsorbed on the surface of graphene to form a discontinuous film; (4) vacuum annealing at 145°C to 160°C to obtain a modified graphene material.

[0103] At the same time, the present invention also provides the application of the modified graphene material in the preparation of a photoelectric detector, especially in the preparation of a bipolar response photoelectric detector.

[0104] In addition, the present invention also proposes a bipolar response light detection method, specifically, Figure 5 The figure shows a flow chart of a bipolar response light detection method provided by an embodiment of the present invention.

[0105] like Figure 5 As shown, the method includes steps S510-S530, and steps S510-S530 and related steps will be described in detail below.

[0106] S510, irradiating the bipolar response photodetector with the light to be detected to generate a positive response current signal and a negative response current signal.

[0107] S520, plotting a first curve showing the positive response current signal changing with time, and a second curve showing the negative response current signal changing with time.

[0108] S530: Determine, according to the first curve and the second curve, whether a time dependence characteristic of the positive response current signal is different from a time dependence characteristic of the negative response current signal.

[0109] It is easy to understand that the bipolar response photodetector can generate a positive response current signal and a negative response current signal when illuminated by the light to be detected.

[0110] Specifically, when the photon energy is greater than the band gap of the semiconductor material, the photon can excite electrons to jump from the valence band to the conduction band, forming electron-hole pairs. These carriers move under the action of the electric field and generate a positive photocurrent, that is, a positive response current signal.

[0111] In some cases, the detector will generate a negative response current signal. For example, in the highly doped area, there may be deep energy level trap states, which can capture carriers and release them under certain conditions, generating a negative response current signal. In addition, dark current may also cause reverse current, generating a negative response current signal.

[0112] Figure 6 The graph shows the change of negative response current and positive response current of the bipolar response photodetector provided by the embodiment of the present invention under the irradiation of light of different wavelengths over time.

[0113] exist Figure 6 In the figure, the upper curve graph is a first curve showing that the negative response current signal changes with time, and the lower curve graph is a second curve showing that the positive response current signal changes with time.

[0114] according to Figure 6 It can be seen that, for the negative response current signal, the current continues to decrease when the light is turned on, and the current slowly recovers when the light is turned off; for the positive response current signal, the current rises and then remains stable when the light is turned on, and the current drops rapidly when the light is turned off.

[0115] It can be seen that there is an obvious difference in the time dependence of the positive response current signal and the negative response current signal. In this case, the problem of bit errors caused by the cancellation of the positive and negative responses of the previous bipolar response detector will not occur.

[0116] Finally, it is worth mentioning that compared with existing solutions, the bipolar response photodetector and preparation method, as well as the bipolar response light detection method provided by the present invention have the following four advantages.

[0117] First, low cost and easy processing. The present invention uses chemical vapor deposition to grow graphene and transfers it to a heavily doped P-type silicon substrate through wet transfer technology. The preparation process is simple and low cost, and it is suitable for large-scale production. Compared with existing commercial detector technology, the present invention does not require complex equipment and expensive materials, which significantly reduces the preparation cost.

[0118] The second point is high responsiveness. By optimizing the composite ratio and structural design of graphene and PMMA, the responsiveness and stability of the detector are significantly improved.

[0119] Figure 7 A curve diagram showing the change in the responsivity of the negative response current and the positive response current of the bipolar response photodetector provided by the embodiment of the present invention with the wavelength.

[0120] like Figure 7 As shown in the figure, the detector has a positive response current and a negative response current responsivity of more than 1000A / W at a certain wavelength, and the normalized gain characteristic is one order of magnitude higher than the existing bipolar response detector. High responsivity means that the detector can detect optical signals more sensitively and can effectively detect weak optical signals.

[0121] The third point is wide spectral response. The detector's spectral response range is from 400nm to 1650nm, covering the visible to near-infrared bands. It can detect optical signals of multiple wavelengths at the same time to meet the needs of different application scenarios, especially suitable for optical communications, imaging systems and environmental monitoring.

[0122] Fourth, the time-dependent characteristics are different. The time-dependent characteristics of the positive and negative response currents are significantly different, which breaks through the problem of the offset of the positive and negative responses of the previous bipolar response detectors, resulting in bit errors. It is more conducive to signal recovery in secure optical communications and can improve the accuracy and security of information transmission.

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A bipolar response photodetector, characterized in that: include: A heavily doped P-type silicon substrate with a silicon oxide layer attached to its surface; Polymethyl methacrylate modified graphene, comprising graphene and polymethyl methacrylate adsorbed on the surface of the graphene, adhered to the silicon oxide layer; Two electrodes are respectively attached to the set positions of the polymethyl methacrylate modified graphene; Wherein, the preparation method of the polymethyl methacrylate modified graphene comprises: (1) Growing a single layer of graphene on a metal foil substrate by chemical vapor deposition; (2) Transferring a single layer of graphene onto a heavily doped P-type silicon substrate using a wet transfer technique; (3) The single-layer graphene transferred to the heavily doped P-type silicon substrate obtained in step (2) was placed on a 4×10 -6 -1×10 -5 In an acetone solution of polymethyl methacrylate with a concentration of 1.5, polymethyl methacrylate is adsorbed on the surface of graphene to form a discontinuous film; (4) annealing at 145° C. to 160° C. in vacuum to obtain the polymethyl methacrylate modified graphene.

2. The bipolar response photodetector according to claim 1, characterized in that: The two electrodes are both gold electrodes.

3. A method for preparing a bipolar response photodetector, used for preparing the bipolar response photodetector according to claim 1 or 2, characterized in that: include: Growing a single layer of graphene and transferring it to a heavily doped P-type silicon substrate, wherein a silicon oxide layer is attached to the surface of the heavily doped P-type silicon substrate; The graphene transferred to the heavily doped P-type silicon substrate is placed in an acetone solution containing polymethyl methacrylate, and the polymethyl methacrylate-modified graphene is obtained by evaporation and vacuum annealing. Two electrodes are prepared by thermal evaporation method, and the two electrodes are respectively attached to the set positions of the polymethyl methacrylate modified graphene.

4. The method for preparing a bipolar response photodetector according to claim 3, characterized in that: The method of growing a single layer of graphene and transferring it to a heavily doped P-type silicon substrate comprises: Growing a single layer of graphene on a copper foil substrate by chemical vapor deposition; Spin-coating a polymethyl methacrylate solution on the graphene on the copper foil substrate, and placing the solution in an etching solution after heating until the copper foil substrate is completely dissolved, thereby obtaining a polymethyl methacrylate-graphene sample; Placing the polymethyl methacrylate-graphene sample in a deionized water solution, and replacing the deionized water solution several times to clean the residual etching solution on the polymethyl methacrylate-graphene sample; Taking out the polymethyl methacrylate-graphene sample in the deionized water solution through the heavily doped P-type silicon substrate; When the surface moisture of the polymethyl methacrylate-graphene sample is fully evaporated and the graphene in the polymethyl methacrylate-graphene sample is adhered to the heavily doped P-type silicon substrate, the polymethyl methacrylate-graphene sample is placed in an acetone solution to dissolve the polymethyl methacrylate on its surface and clean it to complete the transfer of the graphene to the heavily doped P-type silicon substrate.

5. The method for preparing a bipolar response photodetector according to claim 4, characterized in that: The method of spin coating polymethyl methacrylate solution on the graphene on the copper foil substrate comprises: Spin coating the polymethyl methacrylate solution by a spin coating machine, during which the coating is firstly continuously spun at a first rotation speed for a first time, and then continuously spun at a second rotation speed for a second time; Wherein, the first speed is lower than the second speed, and the first duration is shorter than the second duration; The polymethyl methacrylate solution uses anisole or chloroform as solvent, and the mass fraction is 3%-8%.

6. The method for preparing a bipolar response photodetector according to claim 4, characterized in that: The graphene transferred to the heavily doped P-type silicon substrate is placed in an acetone solution containing polymethyl methacrylate, and the polymethyl methacrylate-modified graphene is obtained by evaporation and vacuum annealing, comprising: The acetone solution is evaporated, and polymethyl methacrylate is adsorbed on the surface of graphene to form a discontinuous film; By vacuum annealing at a set temperature, the chemical bond contact between polymethyl methacrylate and graphene is enhanced to obtain polymethyl methacrylate modified graphene.

7. The method for preparing a bipolar response photodetector according to claim 4, characterized in that: The method of preparing two electrodes by thermal evaporation method comprises: The pre-designed electrode mask was attached to the polymethyl methacrylate-modified graphene, and two gold electrodes were prepared by thermal evaporation under set vacuum conditions; When the thickness of the two gold electrodes reaches the set thickness, the thermal evaporation is stopped to obtain two gold electrodes.

8. The method for preparing a bipolar response photodetector according to any one of claims 3 to 7, characterized in that: After the bipolar response photodetector is prepared, the method further comprises: The bipolar response photoelectric detector is subjected to vacuum annealing treatment at 145° C. to 160° C. to improve the contact characteristics between the polymethyl methacrylate-modified graphene and the two electrodes.

9. A bipolar response light detection method, characterized in that: include: Irradiating the bipolar response photodetector according to claim 1 or 2 with light to be detected to generate a positive response current signal and a negative response current signal; Draw a first curve showing that the positive response current signal changes with time, and a second curve showing that the negative response current signal changes with time; According to the first curve and the second curve, it is determined that there is a difference between the time dependence characteristic of the positive response current signal and the time dependence characteristic of the negative response current signal.

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