Near-infrared photodetector based on upconversion nanoparticles and preparation method thereof

Abstract

The present invention relates to the field of optical communication, and provides a near-infrared photodetector based on upconversion nanoparticles and a preparation method thereof, wherein the near-infrared photodetector comprises: a low-doped P-type silicon substrate, a silicon oxide layer attached to the surface thereof; graphene, attached to the silicon oxide layer; a first electrode, a second electrode and a third electrode, wherein the first electrode, the second electrode and the third electrode are attached to the graphene in sequence according to a preset channel distance; upconversion nanoparticles, which are spin-coated on the graphene with a preset channel distance between the first electrode and the second electrode, and the concentration of rare earth ions doped in the upconversion nanoparticles is greater than or equal to a set concentration. The detector has a simple structure, can effectively improve the upconversion efficiency and absorption capacity, generates high photoconductivity gain when performing near-infrared light detection, and converts the upconversion luminescence of the upconversion nanoparticles into a prominent light response current; in addition, it also has wavelength selectivity, and can distinguish different wavelengths by using the difference in the response current state at different wavelengths.

Description

Technical Field

[0001] The present invention relates to the field of optical communication technology, and in particular to a near-infrared photodetector based on up-conversion nanoparticles and a preparation method thereof. Background Art

[0002] In recent years, with the rapid development of optical communications, national defense security, lidar, communication remote sensing and biomedical imaging, the demand for near-infrared (NIR) photodetectors has increased.

[0003] The most widely used silicon detectors can only respond to wavelengths below 1100nm and cannot detect the 1.5μm band. Although traditional near-infrared photodetectors (such as InGaAs) can detect 1.5μm light, their high cost, complex growth technology and the need for low-temperature refrigeration limit their application. In addition, most of the current near-infrared photodetectors can only measure the intensity of the detection light and cannot achieve wavelength-selective detection alone.

[0004] To solve this problem, researchers have explored many new materials and structures to achieve high-performance near-infrared photodetectors, but they still face many challenges. For example, regulating the size of quantum dots can achieve low-cost near-infrared detection, but the presence of heavy metals inevitably brings environmental and health risks. Although second harmonic up-conversion technology can achieve 1.5μm light detection through nonlinear crystals, it has extremely high requirements for the excitation light power and extremely low up-conversion efficiency. There are also some methods that can achieve 1.5μm light detection, but the device response intensity is low and there is a lack of high-gain near-infrared photodetector structures. In addition, in order to enhance the up-conversion process, it is easy to cause the device structure to be complex and large in size.

[0005] Therefore, how to solve the problems of low upconversion efficiency, low device responsiveness, lack of wavelength selectivity, complex device structure and large size in existing near-infrared photodetectors is an important issue that needs to be urgently addressed in the field of optical communications. Summary of the invention

[0006] The present invention provides a near-infrared photodetector based on upconversion nanoparticles and a preparation method thereof, so as to overcome the defects of the existing near-infrared photodetectors such as low upconversion efficiency, low device responsiveness, lack of wavelength selectivity, complex device structure and large size, improve the upconversion efficiency and device responsiveness, simplify the device structure design and have wavelength selectivity.

[0007] On the one hand, the present invention provides a near-infrared photodetector based on upconversion nanoparticles, comprising: a low-doped P-type silicon substrate, a silicon oxide layer attached to the surface of which; graphene, bonded to the silicon oxide layer; electrodes, comprising a first electrode, a second electrode and a third electrode, the first electrode, the second electrode and the third electrode being sequentially bonded to the graphene according to a preset channel distance; upconversion nanoparticles, spin-coated on the graphene at a preset channel distance between the first electrode and the second electrode, the concentration of rare earth ions doped in the upconversion nanoparticles being greater than or equal to a set concentration.

[0008] Furthermore, the upconversion nanoparticles include one or more combinations of erbium-containing nanoparticles, ytterbium-containing nanoparticles, holmium-containing nanoparticles, thulium-containing nanoparticles and neodymium-containing nanoparticles, and the surface of the upconversion nanoparticles is coated with an inert protective layer.

[0009] Furthermore, the first electrode, the second electrode and the third electrode are all gold electrodes.

[0010] Furthermore, the near-infrared photodetector includes a first semiconductor and a second semiconductor; the first semiconductor includes a low-doped P-type silicon substrate, a silicon oxide layer, graphene and up-conversion nanoparticles arranged between the first electrode and the second electrode, and the second semiconductor includes a low-doped P-type silicon substrate, a silicon oxide layer and graphene arranged between the third electrode and the second electrode; when near-infrared light of different wavelengths irradiates the near-infrared photodetector, the first semiconductor responds to the light signal of the first wavelength and generates a first current; the second semiconductor responds to the light signal of the second wavelength and generates a second current; the second wavelength is shorter than the first wavelength.

[0011] Further, the first wavelength includes 1.5 microns, and the second wavelength is shorter than 1.1 microns.

[0012] In the second aspect, the present invention also provides a method for preparing a near-infrared photodetector based on upconversion nanoparticles, which is used to prepare the near-infrared photodetector based on upconversion nanoparticles as described in any of the above items, comprising: growing a single layer of graphene and transferring it to a low-doped P-type silicon substrate; preparing a first electrode, a second electrode and a third electrode based on the graphene transferred to the low-doped P-type silicon substrate; the first electrode, the second electrode and the third electrode are sequentially attached to the graphene according to a preset channel distance; spin coating a pre-synthesized upconversion nanoparticle solution on the graphene with a preset channel distance between the first electrode and the second electrode; the rare earth ion concentration in the upconversion nanoparticle solution is greater than or equal to the set concentration.

[0013] Furthermore, the preparation of the first electrode, the second electrode and the third electrode based on the graphene transferred to the low-doped P-type silicon substrate includes: spin coating photoresist on the graphene on the low-doped P-type silicon substrate, and performing photolithography, thermal evaporation and lift-off operations to obtain the first electrode, the second electrode and the third electrode.

[0014] Furthermore, the synthesis step of the upconversion nanoparticle solution specifically includes: synthesizing the upconversion nanoparticle solution by thermal decomposition method, and increasing the rare earth ion concentration in the upconversion nanoparticle solution to a set concentration; wherein the surface of the upconversion nanoparticles in the upconversion nanoparticle solution is coated with an inert protective layer.

[0015] Furthermore, the upconversion nanoparticle solution includes one or more combinations of an erbium-containing nanoparticle solution, an ytterbium-containing nanoparticle solution, a holmium-containing nanoparticle solution, a thulium-containing nanoparticle solution, and a neodymium-containing nanoparticle solution.

[0016] In a third aspect, the present invention also provides a near-infrared light detection method, comprising: irradiating the near-infrared photodetector based on up-conversion nanoparticles as described in any of the above items with light to be detected of different wavelengths; generating a first current in response to a light signal of the light to be detected of a first wavelength; generating a second current in response to a light signal of the light to be detected of a second wavelength; and distinguishing light to be detected of different wavelengths based on the difference in the ratio of the first current to the second current.

[0017] The near-infrared photodetector based on upconversion nanoparticles provided by the present invention comprises a low-doped P-type silicon substrate, a silicon oxide layer attached to the surface of the substrate; graphene, attached to the silicon oxide layer; electrodes, comprising a first electrode, a second electrode and a third electrode, the first electrode, the second electrode and the third electrode being attached to the graphene in sequence according to a preset channel distance; and upconversion nanoparticles, which are spin-coated on the graphene with a preset channel distance between the first electrode and the second electrode. The detector has a simple structure, and by increasing the concentration of rare earth ions doped in the upconversion nanoparticles to a set concentration, the upconversion characteristics thereof are fully utilized, and the upconversion efficiency and absorption capacity are effectively improved; at the same time, by utilizing the optical gating effect of graphene with high mobility, a high photoconductivity gain can be generated during near-infrared light detection, and the upconversion luminescence of the upconversion nanoparticles can be converted into a prominent photoresponse current; in addition, the detector also has wavelength selectivity, and the difference in the response current state at different wavelengths is utilized to achieve the distinction of different wavelengths. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] 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.

[0019] Figure 1 It is a schematic structural diagram of a near-infrared photodetector based on up-conversion nanoparticles provided in an embodiment of the present invention.

[0020] Figure 2 It is a schematic diagram of the energy level structure of rare earth erbium ions provided in an embodiment of the present invention.

[0021] Figure 3 It is a schematic diagram of the mechanism of a near-infrared photodetector based on upconversion nanoparticles provided in an embodiment of the present invention.

[0022] Figure 4 It is a schematic flow chart of a method for preparing a near-infrared photodetector based on up-conversion nanoparticles provided in an embodiment of the present invention.

[0023] Figure 5 It is a schematic diagram of the overall process of the method for preparing a near-infrared photodetector based on up-conversion nanoparticles provided in an embodiment of the present invention.

[0024] Figure 6 It is a flow chart of the near-infrared light detection method provided by an embodiment of the present invention.

[0025] Figure 7 It is a schematic diagram of the difference in current response of a near-infrared photodetector based on upconversion nanoparticles under different states provided by an embodiment of the present invention.

[0026] Reference numerals: 110: low-doped P-type silicon substrate; 120: silicon oxide layer; 130: graphene; 140: electrode; 141: first electrode; 142: second electrode; 143: third electrode; 150: up-conversion nanoparticles. DETAILED DESCRIPTION

[0027] 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.

[0028] In recent years, with the rapid development of optical communications, national defense security, lidar, communication remote sensing and biomedical imaging, the demand for near-infrared photodetectors has increased. In particular, the detection of the 1.5μm band has important research significance. For example, in optical communications, the 1.5μm wavelength of light signals is the most commonly used transmission wavelength; in the field of biological imaging, 1.5μm light has become an ideal choice for non-invasive imaging due to its good biocompatibility and penetration ability. In addition, 1.5μm light can also be used for night imaging, food inspection, and target identification through scattering media such as fog, haze, and smoke.

[0029] However, the most widely used silicon detectors are limited in their response band to 1100nm due to the band gap of silicon, and cannot respond to longer bands. At the same time, traditional near-infrared photodetectors (such as InGaAs) usually require low-temperature refrigeration due to their high cost, complex epitaxial growth technology, and thermal noise, and cannot meet the needs of the next generation of high-performance, low-cost near-infrared photodetectors. In addition, traditional photodetectors can only detect light intensity and cannot independently realize detectors with wavelength selection capabilities.

[0030] To solve this problem, researchers began to explore new materials and new structures to achieve high-performance near-infrared photodetectors. Some researchers proposed to achieve low-cost near-infrared light detection by adjusting the size of II-VI quantum dots, but because they contain heavy metals, they are not friendly to the environment and human health. Other researchers proposed that the second harmonic up-conversion process relies on the frequency doubling effect of nonlinear crystals and combines commercial silicon detectors to achieve 1.5μm near-infrared detection, but the excitation light power requirement is very high (>10 6 W / cm 2 ), the conversion efficiency is extremely low.

[0031] In addition, some researchers have proposed the use of low-cost, large-scale, bio-friendly upconversion nanoparticles to achieve wavelength conversion of near-infrared light, relying on the multi-photon upconversion process of rare earth erbium ions to convert light near 1.5μm into visible light for detection. At the same time, the upconversion nanoparticles have sharp absorption peaks, and it is easy to construct narrow-band response detectors without filters, which is expected to design wavelength-selective detectors. However, the upconversion detectors based on erbium materials currently reported have low responses. Due to the low erbium concentration of the nanoparticles, the absorption is limited, the upconversion efficiency is low, and there is a lack of high-gain detector structures. In addition, in order to enhance the upconversion process, it is easy to cause the device structure to be complex and large in size.

[0032] In view of this, the present invention proposes a new near-infrared photodetector based on upconversion nanoparticles, specifically, Figure 1 A schematic structural diagram of a near-infrared photodetector based on up-conversion nanoparticles provided in an embodiment of the present invention is shown.

[0033] like Figure 1 As shown, the near-infrared photodetector includes a low-doped P-type silicon substrate 110, on the surface of which a silicon oxide layer 120 is attached; a graphene 130, which is attached to the silicon oxide layer 120; an electrode 140, including a first electrode 141, a second electrode 142 and a third electrode 143, wherein the first electrode 141, the second electrode 142 and the third electrode 143 are sequentially attached to the graphene 130 according to a preset channel distance; and an upconversion nanoparticle 150, which is spin-coated on the graphene 130 at a preset channel distance between the first electrode 141 and the second electrode 142.

[0034] The structure of the near-infrared photodetector based on upconversion nanoparticles will be described in detail below.

[0035] Regarding the low-doped P-type silicon substrate 110 .

[0036] Low-doped P-type silicon substrate 110 (P+ Si) refers to a silicon material doped with a small amount of acceptor impurities (usually boron, B), so that the material as a whole exhibits P-type semiconductor characteristics. In this type of silicon, holes are the majority carriers, and electrons are the minority carriers.

[0037] "Low doping" refers to a relatively low doping concentration. The doping concentration directly affects the electrical properties of silicon materials, such as resistivity, conductivity type, etc. Low doping can provide higher resistivity, which is beneficial for the preparation of near-infrared photodetectors. The high resistivity substrate has a long carrier lifetime, which helps to increase the photoconductivity gain and improve the device performance.

[0038] In this embodiment, a layer of silicon oxide (SiO2) is attached to the surface of the low-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 low-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 low-doped P-type silicon substrate 110.

[0039] Of course, the silicon oxide layer 120 may also be deposited by chemical vapor deposition, which is not specifically limited here.

[0040] About Graphene 130.

[0041] Graphene 130 is a two-dimensional honeycomb lattice structure material composed of carbon atoms in sp² hybrid orbitals, each carbon atom is bonded to three other carbon atoms to form a hexagonal planar network structure. Graphene 130 is a single layer of graphite, only one atom thick, with very unique physical, chemical and electronic properties.

[0042] It is worth mentioning that the preparation cost of graphene 130 is lower, the responsivity in the visible band is higher, and the optical gating effect of graphene 130 can generate high photoconductivity gain. Specifically, the optical gating effect of graphene 130 refers to the use of light to regulate the conductivity characteristics in the graphene 130 field effect detector. This effect mainly stems from the fact that when light is irradiated on the low-doped P-type silicon substrate 110, the photogenerated electrons are localized at the interface between the low-doped P-type silicon substrate 110 and the silicon oxide layer 120, and the hole carriers in the graphene are changed through the gate control effect. Due to the high carrier mobility in graphene and the long lifetime of the localized electrons in silicon, the optical gating effect can generate high conductivity gain, so that the detector can achieve a high response current. In this embodiment, the graphene 130 is attached to the silicon oxide layer 120 on the surface of the low-doped P-type silicon substrate 110 to make full use of the excellent electrical and optical properties of the graphene 130 and the good insulation and stability of silicon oxide.

[0043] Regarding electrode 140 .

[0044] Electrode 140 is a conductive component in the photodetector for introducing or extracting current.

[0045] In this embodiment, each near-infrared photodetector includes three electrodes 140, namely Figure 1 In the figure, the first electrode 141, the second electrode 142 and the third electrode 143 are sequentially attached to the graphene 130 from left to right. There are channels between the first electrode 141 and the second electrode 142, and between the second electrode 142 and the third electrode 143. The channel length is the preset channel distance. The preset channel distance can be set according to actual needs and is not specifically limited here.

[0046] It should be noted that the channel distance between the first electrode 141 and the second electrode 142 and the channel distance between the second electrode 142 and the third electrode 143 may have the same setting value or different setting values, which is not specifically limited herein.

[0047] For example, in a specific embodiment, the channel distance between the first electrode 141 and the second electrode 142 and the channel distance between the second electrode 142 and the third electrode 143 are both preset channel distances, and the value is 3 μm.

[0048] The three electrodes in this embodiment can be metal electrodes (such as gold, silver, platinum, copper, etc.) or carbon-based electrodes (such as graphite, activated carbon, carbon nanotubes, graphene 130, etc.), depending on actual needs.

[0049] Regarding upconversion nanoparticles 150.

[0050] The upconversion nanoparticles 150 are a special type of luminescent material that can absorb low-energy long-wavelength photons (such as near-infrared light) and accumulate the energy of these photons through a multi-photon absorption process, ultimately emitting high-energy short-wavelength photons (such as visible light or ultraviolet light).

[0051] The upconversion nanoparticles 150 are usually composed of a certain matrix material and doped rare earth ions, the matrix material is such as fluoride, oxide, phosphate, etc., and the doped rare earth ions are such as rare earth elements: ytterbium (Yb 3+ ), Erbium 3+ ), Thulium (Tm 3+ ), Neodymium (Nd 3+ )wait.

[0052] In a specific embodiment, Figure 2 FIG. 1 is a schematic diagram showing the energy level structure of the rare earth erbium ion provided by an embodiment of the present invention. Figure 2 The left vertical axis represents energy (unit: 10³cm -1 ), the horizontal lines represent different energy levels, marked as 4 I 15 / 2 , 4 I 13 / 2 , 4 I 11 / 2 , 4 I 9 / 2 , 4 F 9 / 2 , 4 S 3 / 2 and 2 H 11 / 2 . In the ground state 4 I 15 / 2 The ions can transition to higher energy levels by photon absorption. The blue arrows represent the photon absorption process, the wavy arrows represent the non-radiative transition, and the red arrows represent the photon emission process.

[0053] according to Figure 2 It can be seen that the energy level transition of rare earth erbium ions in the up-conversion luminescence process can transition from the ground state to a high energy level through multiple photon absorption and non-radiative transitions, and finally return to the ground state by emitting photons of different wavelengths.

[0054] In this embodiment, the upconversion nanoparticles 150 are only spin-coated on the graphene 130 at a preset channel distance between the first electrode 141 and the second electrode 142 , and there are no spin-coated upconversion nanoparticles 150 between the second electrode 142 and the third electrode 143 .

[0055] It is worth mentioning that in order to improve the up-conversion efficiency, the concentration of rare earth ions doped in the up-conversion nanoparticles 150 in this embodiment should be increased as much as possible. For example, the concentration of erbium ions in this embodiment reaches 10 22 cm -3 And above.

[0056] Based on the above, reference Figure 1 The near-infrared photodetector provided in this embodiment comprises, from bottom to top, a low-doped P-type silicon substrate 110, a silicon oxide layer 120 attached to the surface of the low-doped P-type silicon substrate 110, graphene 130, electrodes, and up-conversion nanoparticles 150 between the two electrodes on the left.

[0057] In this embodiment, the near-infrared photodetector includes a low-doped P-type silicon substrate 110, on the surface of which a silicon oxide layer 120 is attached; graphene 130 is adhered to the silicon oxide layer 120; electrodes include a first electrode 141, a second electrode 142 and a third electrode 143, and the first electrode 141, the second electrode 142 and the third electrode 143 are sequentially adhered to the graphene 130 according to a preset channel distance; upconversion nanoparticles 150 are spin-coated on the graphene 130 at a preset channel distance between the first electrode 141 and the second electrode 142. The detector has a simple structure. By increasing the concentration of rare earth ions doped in the upconversion nanoparticles 150 to a set concentration and making full use of its upconversion characteristics, the upconversion efficiency and absorption capacity can be effectively improved. At the same time, by utilizing the light gating effect of the high-mobility graphene 130, high photoconductivity gain can be generated during near-infrared light detection, and the upconversion luminescence of the upconversion nanoparticles 150 can be converted into a prominent light response current. In addition, the detector also has wavelength selectivity, and different wavelengths can be distinguished by utilizing the difference in response current states at different wavelengths.

[0058] Based on the above embodiment, optionally, the upconversion nanoparticles 150 include one or more combinations of erbium-containing nanoparticles, ytterbium-containing nanoparticles, holmium-containing nanoparticles, thulium-containing nanoparticles and neodymium-containing nanoparticles, and the surface of the upconversion nanoparticles 150 is coated with an inert protective layer.

[0059] It is easy to understand that the upconversion nanoparticles 150 are usually composed of a certain matrix material and doped rare earth ions, the matrix material is such as fluoride, oxide, phosphate, etc., and the doped rare earth ions are such as rare earth elements: ytterbium (Yb 3+ ), Erbium 3 +), Thulium (Tm 3+ ), Neodymium (Nd 3+ )wait.

[0060] Considering the difference of rare earth ions doped in the up-conversion nanoparticles 150, the up-conversion nanoparticles 150 can be divided into erbium-containing nanoparticles, ytterbium-containing nanoparticles, holmium-containing nanoparticles, thulium-containing nanoparticles and neodymium-containing nanoparticles. The up-conversion nanoparticles 150 in this embodiment can be any one of erbium-containing nanoparticles, ytterbium-containing nanoparticles, holmium-containing nanoparticles, thulium-containing nanoparticles and neodymium-containing nanoparticles, or can be a combination of two or more of erbium-containing nanoparticles, ytterbium-containing nanoparticles, holmium-containing nanoparticles, thulium-containing nanoparticles and neodymium-containing nanoparticles, which are not specifically limited here.

[0061] It should be emphasized that, in this embodiment, no matter what kind of rare earth ions the upconversion nanoparticles 150 contain, the concentration of the doped rare earth ions must be increased to a set concentration to promote effective absorption of the 1.5 μm band, thereby improving the upconversion efficiency.

[0062] In a specific embodiment, the concentration is set to 10 22 cm -3 Compared with the existing upconversion detectors based on erbium materials, the rare earth ion concentration is increased by an order of magnitude, greatly improving the absorption capacity and upconversion efficiency of 1.5μm light.

[0063] It is also worth mentioning that the surface of the upconversion nanoparticle 150 is coated with an inert protective layer to form a core-shell structure, which can prevent surface state quenching of rare earth ion concentration and improve the upconversion efficiency.

[0064] On the basis of the above embodiment, optionally, the three electrodes in the near-infrared photodetector are all gold electrodes. 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 good chemical stability.

[0065] Based on the above embodiment, optionally, when near-infrared light of different wavelengths illuminates the near-infrared photodetector, the first semiconductor responds to the light signal of the first wavelength to generate a first current; the second semiconductor responds to the light signal of the second wavelength to generate a second current.

[0066] Among them, the first semiconductor includes a low-doped P-type silicon substrate 110, a silicon oxide layer 120, a graphene 130 and up-conversion nanoparticles 150 arranged between the first electrode 141 and the second electrode 142, and the second semiconductor includes a low-doped P-type silicon substrate 110, a silicon oxide layer 120 and a graphene 130 arranged between the third electrode 143 and the second electrode 142; the second wavelength is shorter than the first wavelength.

[0067] It is easy to understand that still refer to Figure 1 When the near-infrared photodetector is irradiated with near-infrared light, the first electrode 141, the second electrode 142, the low-doped P-type silicon substrate 110, the silicon oxide layer 120, the graphene 130 and the up-conversion nanoparticles 150 between the first electrode 141 and the second electrode 142 form a current loop, and the second electrode 142, the third electrode 143, the low-doped P-type silicon substrate 110, the silicon oxide layer 120 and the graphene 130 between the second electrode 142 and the third electrode 143 form another current loop. These two loops respond to light signals of different wavelengths and generate currents of different directions and magnitudes, and the currents can be read by the correspondingly designed ammeters in the loops.

[0068] The current loop on the left is called the first loop, and the current loop on the right is called the second loop.

[0069] In the first circuit, since the upconversion nanoparticles 150 are spin-coated on the graphene 130 with a preset channel distance between the first electrode 141 and the second electrode 142, and the concentration of rare earth ions doped in the upconversion nanoparticles 150 is greater than or equal to the set concentration, the first circuit can respond to optical signals within the wavelength range of 1.5μm by utilizing the wavelength conversion effect of the upconversion nanoparticles 150.

[0070] In the second loop, there is only graphene 130 between the second electrode 142 and the third electrode 143 , and through the light gate control effect of the low-doped P-type silicon substrate 110 , only light signals with a wavelength less than 1.1 μm can be responded to.

[0071] Therefore, under near-infrared light of different wavelengths, there is a large difference in the current generated by the first circuit and the second circuit.

[0072] In some other embodiments, Figure 3 A schematic diagram of the mechanism of a near-infrared photodetector based on up-conversion nanoparticles provided in an embodiment of the present invention is shown.

[0073] like Figure 3As shown, under the excitation of 1.5μm light, erbium nanoparticles generate light with a wavelength below 1.1μm through a multiphoton upconversion process. Low-doped silicon absorbs short-wavelength upconverted photons to generate electron-hole pairs. The built-in electric field at the interface of low-doped silicon and silicon oxide promotes the accumulation of photogenerated electrons on the silicon surface. Due to the gating effect of localized electrons, induced holes are generated in graphene 130, which is the photogate effect. The photoconductivity gain generated by this effect is proportional to the ratio τ m / τ t Proportional to, where τ m represents the lifetime of localized electrons in silicon, τ t represents the transit time of holes in graphene 130. Due to the long electron lifetime in low-doped silicon and the high hole mobility in graphene 130, the detector has a high photoconductive gain. By utilizing the efficient upconversion emission of erbium nanoparticles and the photogate effect of graphene 130, high-responsivity detection can be finally achieved at 1.5 μm.

[0074] In addition to the near-infrared photodetectors based on upconversion nanoparticles described in the above embodiments, the present invention also proposes a method for preparing a near-infrared photodetector based on upconversion nanoparticles, which is used to prepare the near-infrared photodetectors based on upconversion nanoparticles described in the above embodiments.

[0075] Specifically, Figure 4 A schematic flow chart of a method for preparing a near-infrared photodetector based on up-conversion nanoparticles provided in an embodiment of the present invention is shown.

[0076] like Figure 4 As shown, the method includes steps S410-S430, and steps S410-S430 and related steps will be described in detail below.

[0077] S410, growing a single layer of graphene and transferring it to a low-doped P-type silicon substrate.

[0078] 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 low-doped p-type silicon (resistivity 1-10Ω / cm) substrate by wet transfer technology.

[0079] Growing a single layer of graphene on a copper foil substrate by chemical vapor deposition specifically includes the following steps S411-S414.

[0080] S411, prepare a copper foil substrate.

[0081] 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.

[0082] S412, preheating and annealing.

[0083] 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.

[0084] S413, carbon source introduction and graphene growth.

[0085] 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).

[0086] 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.

[0087] S414, cooling and transfer.

[0088] 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.

[0089] 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 a low-doped P-type silicon substrate in this embodiment).

[0090] The wet transfer technology is used to transfer the silicon to a low-doped p-type silicon (resistivity 1-10Ω / cm) substrate, which specifically includes the following steps S415-S419.

[0091] S415, coating a support layer.

[0092] A polymer support film, such as polymethyl methacrylate (PMMA), 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.

[0093] S416, etching the metal substrate.

[0094] The graphene with a polymer support layer is placed in an etching solution together with a copper foil substrate. Common etching solutions include FeCl3 solution to etch the copper foil substrate. The etching process dissolves the copper foil substrate, separating the graphene from the copper foil and floating on the liquid surface.

[0095] S417, cleaning of two-dimensional materials.

[0096] 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.

[0097] S418, transfer to the target substrate.

[0098] Use tweezers or special tools to carefully scoop out the graphene floating on the liquid surface together with the polymer support layer through the target substrate (low-doped P-type silicon substrate).

[0099] S419, removing the polymer support layer.

[0100] The polymer support layer is removed in a suitable solvent (such as acetone solution) to expose clean graphene, i.e., graphene on a low-doped P-type silicon substrate.

[0101] Based on the above steps, a single layer of graphene can be grown and transferred to a low-doped P-type silicon substrate, and then step S420 is performed.

[0102] S420, preparing a first electrode, a second electrode and a third electrode based on the graphene transferred to the low-doped P-type silicon substrate; the first electrode, the second electrode and the third electrode are sequentially attached to the graphene according to a preset channel distance.

[0103] It is easy to understand that a photoresist is spin-coated on the graphene on the low-doped P-type silicon substrate, and the first electrode, the second electrode and the third electrode are prepared in sequence through processes such as photolithography, thermal evaporation and lift-off. The channel distance between the first electrode and the second electrode and the channel distance between the second electrode and the third electrode are both preset channel distances, which can be set according to actual conditions, for example, a value of 3 μm. The thickness of the first electrode, the second electrode and the third electrode are all 100 nm.

[0104] Regarding photolithography. A photolithography machine can be used to project the designed pattern through a mask plate onto the photoresist layer on the graphene of the low-doped P-type silicon substrate, and the appropriate ultraviolet intensity and exposure time can be set to ensure that the photoresist reacts fully, thereby achieving accurate pattern replication.

[0105] About thermal evaporation. The graphene on the low-doped P-type silicon substrate after photolithography is placed in a thermal evaporation system, and metals (such as gold Au, silver Ag, aluminum Al, etc.) are evaporated under high vacuum conditions, so that metal atoms are deposited on the graphene area not covered by the photoresist.

[0106] Regarding lift-off. Use a special stripping solution (such as acetone, NMP, etc.) to soak the sample after thermal evaporation to dissolve the remaining photoresist and the metal layer above it, and thoroughly clean the sample to remove all residual substances. After rapid drying, the prepared electrode can be obtained.

[0107] Then, step S430 is executed.

[0108] S430, spin coating a pre-synthesized upconversion nanoparticle solution on the graphene with a preset channel distance between the first electrode and the second electrode; the rare earth ion concentration in the upconversion nanoparticle solution is greater than or equal to a set concentration.

[0109] It is easy to understand that the upconversion nanoparticle solution is pre-synthesized in this embodiment. Specifically, the upconversion nanoparticle solution can be prepared by thermal decomposition, and the rare earth ion concentration in the upconversion nanoparticle solution is increased by one order of magnitude to a set concentration, for example, 10 22 cm -3 The surface of the upconversion nanoparticles in the synthesized upconversion nanoparticle solution is coated with an inert protective layer to form a core-shell structure, which can prevent the surface state quenching of rare earth ion concentration and improve the upconversion efficiency.

[0110] Due to the increase in rare earth ion concentration, the absorption in the 1.5μm band is greatly enhanced. At the same time, since the upconversion energy transfer process is inversely proportional to the sixth power of the distance between ions, the upconversion process is greatly improved.

[0111] The upconversion nanoparticle solution in this embodiment includes one or more combinations of erbium-containing nanoparticle solution, ytterbium-containing nanoparticle solution, holmium-containing nanoparticle solution, thulium-containing nanoparticle solution and neodymium-containing nanoparticle solution, which are not specifically limited here.

[0112] In a specific embodiment, the upconversion nanoparticle solution is an erbium-containing nanoparticle solution.

[0113] According to the above steps S410-S430, a near-infrared photodetector based on up-conversion nanoparticles can be prepared.

[0114] In another embodiment, Figure 5 The overall process diagram of the method for preparing a near-infrared photodetector based on up-conversion nanoparticles provided in an embodiment of the present invention is shown.

[0115] like Figure 5As shown, the process specifically includes transferring the grown single-layer graphene to a low-doped P-type silicon substrate, and then spin-coating photoresist, and then undergoing processes such as photolithography, thermal evaporation, and lift-off to obtain the first electrode, the second electrode, and the third electrode bonded to the graphene. Subsequently, the mask plate designed in advance is placed close to the electrode surface (the specific placement position can be found in Figure 5 ), and spin-coat the prepared up-conversion nanoparticle solution, such as erbium-containing nanoparticle solution, on the mask plate. After the spin coating is completed, the mask plate is removed to obtain the prepared near-infrared photodetector based on up-conversion nanoparticles.

[0116] In this embodiment, a single layer of graphene is grown and transferred to a low-doped P-type silicon substrate, and then based on the graphene transferred to the low-doped P-type silicon substrate, a first electrode, a second electrode and a third electrode are prepared; the first electrode, the second electrode and the third electrode are sequentially attached to the graphene according to a preset channel distance; thus, a pre-synthesized upconversion nanoparticle solution is spin-coated on the graphene with a preset channel distance between the first electrode and the second electrode; the rare earth ion concentration in the upconversion nanoparticle solution is greater than or equal to a set concentration. The detector prepared by this method has a simple structure, and by increasing the concentration of rare earth ions doped in the upconversion nanoparticles to a set concentration and making full use of their upconversion characteristics, the upconversion efficiency and absorption capacity can be effectively improved; at the same time, by utilizing the optical gating effect of graphene with high mobility, a high photoconductivity gain can be generated during near-infrared light detection, and the upconversion luminescence of the upconversion nanoparticles can be converted into a prominent photoresponse current; in addition, the detector also has wavelength selectivity, and the difference in the response current state at different wavelengths can be used to distinguish different wavelengths.

[0117] In addition, the present invention also provides a near-infrared light detection method, specifically, Figure 6 A schematic flow chart of a near-infrared light detection method provided in an embodiment of the present invention is shown.

[0118] like Figure 6 As shown, the method includes steps S610-S640, and steps S610-S640 and related steps will be described in detail below.

[0119] S610, irradiating the near-infrared photodetector based on up-conversion nanoparticles described in any of the above embodiments with light to be detected of different wavelengths.

[0120] S620, generating a first current in response to an optical signal of the light to be detected having a first wavelength.

[0121] S630, generating a second current in response to an optical signal of the light to be detected having a second wavelength.

[0122] S640: Distinguish to-be-detected light of different wavelengths according to a difference in ratio between the first current and the second current.

[0123] It is easy to understand that when light to be detected of different wavelengths is irradiated onto the light receiving surface of the near-infrared photodetector, a first circuit formed by the first electrode, the second electrode, and the low-doped P-type silicon substrate, silicon oxide layer, graphene and up-conversion nanoparticles between the first electrode and the second electrode will respond to the light to be detected of the first wavelength and generate a first current; a second circuit formed by the second electrode, the third electrode, and the low-doped P-type silicon substrate, silicon oxide layer and graphene between the third electrode and the second electrode will respond to the light to be detected of the second wavelength and generate a second current.

[0124] According to the response difference between the first current and the second current at different wavelengths, it is possible to distinguish between different wavelengths of light to be detected.

[0125] Contrary, Figure 7 A schematic diagram showing the difference in current response of a near-infrared photodetector based on upconversion nanoparticles provided in an embodiment of the present invention under different states is shown.

[0126] exist Figure 7 Including Figure 7 (a) Figure 7 (b) and Figure 7 (c), I1 represents the first current, and I2 represents the second current. Figure 7 (a) Different lighting states (including 633nm light source and 1520nm light source), where 0 means off and 1 means on. Figure 7 (b) is the curve of current response changing with time. Figure 7 (c) shows the difference in current response ratios calculated under different lighting conditions, and the difference is obvious.

[0127] It is worth mentioning that compared with existing solutions, the near-infrared photoelectric detector based on upconversion nanoparticles and its preparation method, as well as the near-infrared photoelectric detection method provided by the present invention have the following four advantages.

[0128] First, the detection responsivity at 1.5 μm is improved. On the one hand, the concentration of rare earth ions doped in upconversion nanoparticles is increased by an order of magnitude to 10 22 cm -3 , improving the 1.5μm absorption capacity and upconversion energy transfer efficiency of the material. On the other hand, the light gating effect of graphene is used to generate high photoconductivity gain. Therefore, the near-infrared photodetector provided by the present invention has a responsivity of more than 50A / W.

[0129] Second, it reduces production costs. Considering that graphene has lower preparation costs and higher responsivity in the visible band, a graphene detector was prepared and combined with an upconversion film (spin-coated upconversion nanoparticles) to achieve a low-cost, high-responsivity near-infrared photodetector.

[0130] Third, the device size is reduced. Compared with the reported A / W up-conversion detectors, the near-infrared photodetector provided by the present invention has a simple preparation process and a smaller size. At the same time, taking advantage of the simple preparation of graphene, it is easy to design an array structure, which provides strong support for the large-scale production and application of high-performance near-infrared photodetectors.

[0131] Fourth, wavelength-selective detection is achieved. By utilizing the narrowband response characteristics of upconversion nanoparticles, especially erbium-containing nanoparticles, a near-infrared photodetector with wavelength selectivity is proposed, which can realize wavelength recognition without additional modulation of the incident light source. Compared with traditional detectors, it can expand more application areas, such as multi-wavelength imaging, secure optical communications, multi-modal autonomous driving, etc.

[0132] Through the description of the above implementation methods, those skilled in the art can clearly understand that each implementation method can be implemented by means of software plus a necessary general hardware platform, and of course, can also be implemented by hardware. Based on this understanding, the above technical solution is essentially or the part that contributes to the prior art can be embodied in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a disk, an optical disk, etc., including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or some parts of the embodiments.

[0133] 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 near-infrared photodetector based on upconversion nanoparticles, characterized in that: include: A low-doped P-type silicon substrate having a silicon oxide layer attached to its surface; Graphene, attached to the silicon oxide layer; Electrodes, including a first electrode, a second electrode and a third electrode, wherein the first electrode, the second electrode and the third electrode are sequentially attached to the graphene according to a preset channel distance; Upconversion nanoparticles are spin-coated on the graphene at a preset channel distance between the first electrode and the second electrode, wherein the concentration of rare earth ions doped in the upconversion nanoparticles is greater than or equal to a set concentration; The near-infrared photodetector includes a first semiconductor and a second semiconductor; The first semiconductor includes a low-doped P-type silicon substrate, a silicon oxide layer, graphene and up-conversion nanoparticles disposed between the first electrode and the second electrode, and the second semiconductor includes a low-doped P-type silicon substrate, a silicon oxide layer and graphene disposed between the third electrode and the second electrode; When near-infrared light of different wavelengths illuminates the near-infrared photodetector, the first semiconductor responds to the light signal of the first wavelength and generates a first current; the second semiconductor responds to the light signal of the second wavelength and generates a second current; the second wavelength is shorter than the first wavelength.

2. The near-infrared photodetector based on upconversion nanoparticles according to claim 1, characterized in that: The up-conversion nanoparticles include one or more combinations of erbium-containing nanoparticles, ytterbium-containing nanoparticles, holmium-containing nanoparticles, thulium-containing nanoparticles and neodymium-containing nanoparticles, and the surface of the up-conversion nanoparticles is coated with an inert protective layer.

3. The near-infrared photodetector based on upconversion nanoparticles according to claim 1, characterized in that: The first electrode, the second electrode and the third electrode are all gold electrodes.

4. The near-infrared photodetector based on upconversion nanoparticles according to claim 1, characterized in that: The first wavelength includes 1.5 microns and the second wavelength is shorter than 1.1 microns.

5. A method for preparing a near-infrared photodetector based on upconversion nanoparticles, used for preparing the near-infrared photodetector based on upconversion nanoparticles according to any one of claims 1 to 4, characterized in that: include: Grow a single layer of graphene and transfer it to a low-doped P-type silicon substrate; Based on the graphene transferred to the low-doped P-type silicon substrate, a first electrode, a second electrode and a third electrode are prepared; the first electrode, the second electrode and the third electrode are sequentially attached to the graphene according to a preset channel distance; A pre-synthesized up-conversion nanoparticle solution is spin-coated on the graphene with a preset channel distance between the first electrode and the second electrode; the rare earth ion concentration in the up-conversion nanoparticle solution is greater than or equal to the set concentration.

6. The method for preparing a near-infrared photodetector based on upconversion nanoparticles according to claim 5, characterized in that: The method of preparing the first electrode, the second electrode and the third electrode based on the graphene transferred to the low-doped P-type silicon substrate comprises: The first electrode, the second electrode and the third electrode are obtained by spin coating the graphene on the low-doped P-type silicon substrate with photoresist, and performing photolithography, thermal evaporation and lift-off operations.

7. The method for preparing a near-infrared photodetector based on upconversion nanoparticles according to claim 5, characterized in that: The synthesis steps of the upconversion nanoparticle solution specifically include: synthesizing the upconversion nanoparticle solution by thermal decomposition, and increasing the rare earth ion concentration in the upconversion nanoparticle solution to a set concentration; Wherein, the surface of the upconversion nanoparticles in the upconversion nanoparticle solution is coated with an inert protective layer.

8. The method for preparing a near-infrared photodetector based on upconversion nanoparticles according to any one of claims 5 to 7, characterized in that: The up-conversion nanoparticle solution includes one or more combinations of an erbium-containing nanoparticle solution, an ytterbium-containing nanoparticle solution, a holmium-containing nanoparticle solution, a thulium-containing nanoparticle solution, and a neodymium-containing nanoparticle solution.

9. A near-infrared light detection method, characterized in that: include: Irradiating the near-infrared photodetector based on upconversion nanoparticles according to any one of claims 1 to 4 with light to be detected of different wavelengths; In response to an optical signal of a light to be detected having a first wavelength, generating a first current; generating a second current in response to an optical signal of the light to be detected having a second wavelength; Light to be detected of different wavelengths is distinguished according to the difference in ratio between the first current and the second current.

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