An upright graphene heterostructure and its preparation method, a photodetector and its usage and application

Abstract

This invention relates to an upright graphene heterostructure and its preparation method, a photodetector and its usage and application, comprising: placing a substrate in a quartz tube and then evacuating it; introducing a protective gas into the quartz tube and heating it to a set temperature; turning off the protective gas and evacuating it again; first introducing methane into an ethanol solution, and then introducing methane gas containing ethanol vapor into the quartz tube to grow upright graphene on the substrate surface.

Description

Technical Field

[0001] This invention relates to the field of photoelectric detection, and in particular to an upright graphene heterostructure and its preparation method, a photodetector and its usage and application. Background Technology

[0002] As an important component of modern optoelectronic information technology, the main function of photodetectors is to efficiently convert optical signals into electrical signals. They are widely used in cutting-edge fields such as optical communication, lidar, infrared imaging, and quantum detection.

[0003] Graphene photodetectors primarily rely on mechanisms such as the photovoltaic effect, photothermal electron effect, and photothermal effect of photogenerated carriers to achieve photo-to-electric signal conversion. The main optimization method for graphene photodetectors is to increase the specific surface area and porosity of graphene, thereby enhancing its light absorption. However, current technologies offer relatively limited means to improve the specific surface area and porosity of graphene, making it difficult to achieve significant improvements. Therefore, graphene's light absorption capacity is currently at a bottleneck. Summary of the Invention

[0004] Therefore, it is necessary to address the problem of insufficient light absorption capacity of graphene by providing an upright graphene heterostructure, its preparation method, a photodetector, its usage method, and its application.

[0005] A method for preparing an upright graphene heterostructure, characterized by comprising:

[0006] The substrate was placed in a quartz tube, and then a vacuum was drawn.

[0007] A protective gas is introduced into the quartz tube and heated to the set temperature;

[0008] Turn off the protective gas and evacuate again;

[0009] First, methane is passed into an ethanol solution, and then methane gas containing ethanol vapor is passed into a quartz tube to grow vertical graphene on the substrate surface.

[0010] In some embodiments, the set temperature is 850℃-950℃, the power of the radio frequency plasma source is 200W-300W, and the growth time of the upright graphene is 4h-6h.

[0011] In some embodiments, the pressure inside the quartz tube is 10 Pa to 40 Pa during the growth of upright graphene.

[0012] In some embodiments, the flow rate of methane into the ethanol solution is 0.5 sccm-1.5 sccm.

[0013] In some embodiments, the pressure inside the quartz tube is 15 Pa to 25 Pa during the growth of upright graphene.

[0014] An upright graphene heterostructure is prepared using the method described above.

[0015] A photodetector includes a power source and the vertical graphene heterojunction, wherein the vertical graphene on the substrate is connected to the positive terminal of the power source, and the substrate is connected to the negative terminal of the power source.

[0016] A method of using the aforementioned photodetector, wherein when the photodetector performs light detection, the ambient pressure of the photodetector is controlled to be lower than 100 Pa.

[0017] In some embodiments, when the photodetector performs light detection, the ambient pressure of the photodetector is controlled to be below 10 Pa to allow the photodetector to detect light at 2200 nm.

[0018] An apparatus for preparing upright graphene heterostructures includes a liquid tank, a gas tank, a radio frequency plasma source, a quartz tube, and a vacuum pump;

[0019] The liquid tank is used to hold ethanol, the input end of the liquid tank is used to connect to a methane cylinder, the input end of the gas tank is used to connect to a protective gas, the output ends of the liquid tank and the gas tank are connected in parallel to the inlet end of the quartz tube, the radio frequency plasma source is installed on the quartz tube, and the outlet end of the quartz tube is connected to the vacuum pump.

[0020] An application of the aforementioned photodetector in signal encoding.

[0021] The beneficial effects of this invention are as follows:

[0022] This invention provides a method for preparing upright graphene heterostructures, which uses both methane and ethanol as carbon sources, resulting in upright graphene with a unique morphological structure of rolled-up sheets.

[0023] The vertical graphene heterojunction of this invention contains a natural nanocavity within the vertical graphene and exhibits high porosity. This morphological structure helps to increase the specific surface area and multiple scattering capability, thereby inducing multiple reflections and scatterings of light within or near the surface of the vertical graphene. This effectively extends the light propagation path within the vertical graphene, enhances the interaction strength between light and the vertical graphene, improves light absorption efficiency, and reduces the recombination probability of charge carriers, effectively improving the photoelectric response performance of the device. Attached Figure Description

[0024] Figure 1a and Figure 1bThe image shows the IV curves of the photodetector in Embodiment 2 of the present invention under different wavelengths of light (optical power is 0.4 W / cm²). 2 (The test environment was at normal pressure).

[0025] Figure 2 The frequency-dependent noise current curve of the photodetector in Embodiment 2 of the present invention;

[0026] Figure 3 The Nyquist plot of the photodetector in Embodiment 2 of the present invention (the inset is an equivalent circuit model);

[0027] Figure 4 This is a stability test diagram of the photodetector in Embodiment 2 of the present invention;

[0028] Figure 5 The photocurrent amplitude attenuation curves of the photodetector at different switching frequencies in Embodiment 2 of the present invention are shown.

[0029] Figure 6 The following are the response curves of the photodetector in Embodiment 2 of the present invention at different switching frequencies;

[0030] Figure 7 The photocurrent rise and fall time test curve of the photodetector in Embodiment 2 of the present invention;

[0031] Figure 8 The above are the response curves of the photodetector in Embodiment 2 of the present invention after being placed in a normal temperature and humidity environment for different times.

[0032] Figure 9a This is a SEM image of the upright graphene heterostructure in Example 1 of the present invention;

[0033] Figure 9b This is a SEM image of the upright graphene heterostructure in Example 2 of the present invention;

[0034] Figure 9c This is a SEM image of the upright graphene heterostructure in Example 3 of the present invention;

[0035] Figure 10 This is the AFM image of the upright graphene heterostructure in Example 2 of the present invention;

[0036] Figure 11 This is a normalized electric field distribution diagram of the upright graphene heterojunction in Embodiment 2 of the present invention;

[0037] Figure 12 The absorption spectrum of the upright graphene heterojunction in Example 2 of this invention;

[0038] Figure 13 The IV curves of the photodetectors in Examples 1-4 of this invention under 1550nm illumination are shown.

[0039] Figure 14 are AFM images of the vertical graphene heterojunctions in Examples 1 to 4 of the present invention (wherein a corresponds to Example 1, b corresponds to Example 2, c corresponds to Example 3, d corresponds to Example 4);

[0040] Figure 15 is an SEM image of the vertical graphene heterojunction in the comparative example of the present invention;

[0041] Figure 16 are I-V curves of the photodetector in Example 2 of the present invention under 1550 nm illumination with different optical power densities (test environment: 5 Pa);

[0042] Figure 17 are change curves of responsivity and specific detectivity corresponding to the photodetector in Example 2 of the present invention under 1550 nm illumination with different optical power densities (test environment: 5 Pa);

[0043] Figure 18 are I-V curves of the photodetector in Example 2 of the present invention under 1850 nm and 2200 nm illumination, with an optical power of 45 mW / cm 2 , and the test environment is 5 Pa);

[0044] Figure 19 are I-V curves of the photodetector in Example 2 of the present invention at different temperatures, with an optical power of 90 mW / cm 2 , and the test environment is 5 Pa);

[0045] Figure 20 is a comparison table of Unicode codes and ASCII codes corresponding to the Chinese characters "海", "纳", "百" and "川";

[0046] Figure 21 is an information encryption output signal of the photodetector in Example 2 of the present invention under zero bias;

[0047] Figure 22 is a schematic structural diagram of an apparatus for preparing a vertical graphene heterojunction in Example 1 of the present invention;

[0048] Figure 23 is a graph of the dependence of temperature and pressure inside a quartz tube obtained by simulation using the finite-difference time-domain method. DETAILED DESCRIPTION

[0049] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0050] Example 1:

[0051] See Figure 22 This embodiment first provides an apparatus for preparing upright graphene heterostructures, specifically including a liquid tank 1, a gas tank 2, a radio frequency plasma source 3, a quartz tube 4, and a vacuum pump 5.

[0052] Liquid tank 1 contains liquid ethanol, and its input is connected to methane cylinder 6. Gas tank 2 has two inputs, one connected to argon cylinder 7 and the other to hydrogen cylinder 8. The outputs of liquid tank 1 and gas tank 2 are connected in parallel to the inlet of quartz tube 4, and the outlet of quartz tube 4 is connected to vacuum pump 5. Radio frequency plasma source 3 is mounted on quartz tube 4. Corresponding valves are installed at the input and output ends of liquid tank 1 and gas tank 2.

[0053] This embodiment further provides a method for preparing upright graphene heterostructures, which includes the following steps in sequence:

[0054] Step 101: Place the substrate in the quartz tube 4, and then evacuate the inside of the quartz tube 4 to below 1 Pa.

[0055] For example, in this embodiment, the substrate material is Si.

[0056] Step 102: Pass protective gas into the quartz tube 4 and heat it to the set temperature.

[0057] For example, in this embodiment, the protective gas includes hydrogen and argon, provided by argon cylinder 7 and hydrogen cylinder 8, respectively. The flow rate of argon is 10 sccm, the flow rate of hydrogen is 1 sccm, and the set temperature is 900°C. In other embodiments, the set temperature can be set between 850°C and 950°C.

[0058] Step 103: Turn off the protective gas and evacuate the inside of the quartz tube 4 again to below 1 Pa.

[0059] Step 104: First, methane gas in methane cylinder 6 is passed into ethanol solution to generate bubbles, which promotes the evaporation of ethanol. Then, methane gas containing ethanol vapor is passed into quartz tube 4 to grow vertical graphene on the substrate surface.

[0060] In this embodiment, the flow rate of methane is 1 sccm, the power of the radio frequency plasma source 3 is 250W during the growth of vertical graphene, the pressure inside the quartz tube 4 is maintained at 10Pa, and the growth time of vertical graphene is 5h.

[0061] Once the upright graphene is prepared on the substrate, the upright graphene heterostructure can be obtained.

[0062] This embodiment further provides a photodetector, including a power source and the upright graphene heterojunction. The upright graphene is connected to the positive terminal of the power source, and the substrate is connected to the negative terminal of the power source.

[0063] Example 2:

[0064] The difference between this embodiment and Embodiment 1 is that, in step 104, the pressure inside the quartz tube 4 is maintained at 20 Pa.

[0065] Example 3:

[0066] The difference between this embodiment and embodiment 1 is that in step 104, the pressure inside the quartz tube 4 is maintained at 30 Pa.

[0067] Example 4:

[0068] The difference between this embodiment and embodiment 1 is that in step 104, the pressure inside the quartz tube 4 is maintained at 40 Pa.

[0069] Comparative Example:

[0070] This comparative embodiment also provides a method for preparing upright graphene heterostructures, which includes the following steps in sequence:

[0071] Step 101a: Place the silicon substrate in the quartz tube 4, and then evacuate the inside of the quartz tube 4 to below 1 Pa.

[0072] Step 102a: Introduce hydrogen and argon gas into quartz tube 4 and heat it to 900°C. The flow rate of argon gas is 10 sccm and the flow rate of hydrogen gas is 1 sccm.

[0073] Step 103a: Turn off the protective gas and evacuate the inside of the quartz tube 4 again to below 1 Pa.

[0074] Step 104a: Heat ethanol to form ethanol vapor, and pass the ethanol vapor into quartz tube 4 to grow vertical graphene on the substrate surface.

[0075] In this comparative embodiment, the power of the radio frequency plasma was 250W, the pressure inside the quartz tube 4 was maintained at 20Pa, and the growth time of the vertical graphene was 3h.

[0076] Firstly, as Figure 1a As shown, under normal temperature and pressure testing conditions, the photodetector in Example 2 exhibits excellent response capability to excitation light in the 440nm-1550nm range. However, on the other hand, as the excitation light wavelength gradually increases from 440nm, the photocurrent of the photodetector gradually decreases. Further as... Figure 1b As shown, under normal temperature and pressure testing conditions, when the excitation wavelength is 2200nm, the photocurrent and dark current of the photodetector are almost equal. In other words, the photodetector cannot detect 2200nm light at this time. Therefore, under normal temperature and pressure testing conditions, the photodetector in Example 2 has a light detection range of 440nm-1550nm.

[0077] like Figure 2 As shown, the noise current of the photodetector in Example 2 is The noise level is low, in other words, the signal-to-noise ratio is high. This proves that the photodetector in Example 2 can achieve high-precision detection of weak light signals.

[0078] like Figure 3 As shown, the photodetector in Example 2 has a large charge transfer resistance, in other words, it has a strong ability to capture photogenerated carriers. Therefore, it can suppress the recombination of electron-hole pairs, improve the separation efficiency of electron-hole pairs, and thus enhance the photoresponse performance of the device.

[0079] like Figure 4 As shown, in Example 2, under 1550 nm illumination and zero bias detection conditions, the photocurrent of the photodetector did not show significant attenuation during 200 consecutive switching cycles, demonstrating the excellent cyclic reliability of the photodetector in self-powered operation mode.

[0080] like Figure 5 As shown, the photodetector in Example 2 has a -3 dB cutoff frequency as high as 1 kHz, demonstrating that the photodetector has a fast dynamic response capability and can efficiently modulate optical signals. Further as... Figure 6 As shown, under a bias voltage of -3 V and illumination of 1550 nm, the normalized photocurrent at a switching frequency of 250 Hz, 500 Hz and 1000 Hz is very stable.

[0081] like Figure 7 As shown, the rise time and fall time of the photocurrent in the photodetector in Example 2 are 130μs and 154μs, respectively. The shorter rise time and fall time indicate that the photodetector can quickly capture the optical signal and convert it into an electrical signal, which is beneficial to meet the application requirements of high-speed optical communication and real-time monitoring.

[0082] like Figure 8 As shown in Example 2, after the photodetector was placed under normal temperature and humidity conditions for 1 month, 2 months, 3 months and 4 months respectively, the photocurrent did not decrease significantly, which proves that the photodetector has good physical stability and optical inertness.

[0083] Based on the above test results, it is fully demonstrated that the photodetector and the upright graphene heterostructure in Example 2 possess excellent photoelectric detection performance. Furthermore, the photodetectors in Examples 1, 3, and 4 also exhibit excellent photoelectric detection performance. This indicates that the upright graphene in Examples 1-4 possesses relatively unique morphological characteristics.

[0084] Specifically, such as Figures 9a-9c and Figure 10 As shown, the upright graphene in Examples 1-3 exhibits a rolled-up sheet structure with a natural nanocavity inside. This morphology helps to improve the specific surface area and multiple scattering capability. Further... Figure 11 As shown, when light is incident on the surface of upright graphene, the rolled-up sheet structure and nanocavity of the upright graphene can induce multiple reflections and scatterings of light inside or near the surface of the upright graphene. This effectively extends the propagation path of light within the upright graphene, enhances the interaction strength between light and the upright graphene, and the resulting photolocalization effect significantly improves the light absorption efficiency. This helps to efficiently excite photogenerated carriers in the locally enhanced electric field region, promotes their separation and transport, reduces the recombination probability of carriers, and thus effectively improves the photoelectric response performance of the device. As supporting evidence, such as... Figure 12 As shown, the photodetector in Example 2 has a light absorption rate of up to 89% at a wavelength of 1550 nm.

[0085] See further Figure 13 As the pressure environment during the growth of upright graphene increased from 10 Pa to 40 Pa, the photocurrent of the photodetector first increased and then decreased, reaching a maximum at 20 Pa. The power density was 0.4 W / cm². 2 The effective light-illuminated area is 1.256 × 10⁻⁶. -5 cm 2 In the case of Example 1-Example 3, the responsivity and specific detectivity data are shown in Table 1.

[0086] Table 1

[0087] Based on the data in Table 1, it can be demonstrated that for the vertical graphene of this application, the pressure environment during its growth process will inevitably have a significant impact on the final morphology, and when the pressure is 20 Pa, the morphology of the vertical graphene is most conducive to photoelectric detection.

[0088] See details Figures 9a-9c as well as Figure 14 In Example 1, the height of the upright graphene was 0.6 μm and the porosity was 68%; in Example 2, the height was 4.8 μm and the porosity was 73%; in Example 3, the height was 1.3 μm and the porosity was 71%; and in Example 4, the porosity was 70%. This demonstrates that, for the upright graphene of this application, the pressure environment during growth has a significant impact on the final height and porosity of the upright graphene, thereby causing differences in the photoresponsivity and specific detectivity of the photodetector. Furthermore, increasing the height and porosity of the upright graphene also plays a crucial role in increasing the final photoresponsivity and specific detectivity.

[0089] The unique morphological characteristics of the upright graphene in this application are mainly due to the following factors:

[0090] 1. Both methane and ethanol were selected as carbon sources in the growth process of upright graphene, with the ethanol content being greater than that of methane.

[0091] In this case, if only methane is introduced to maintain the internal pressure of 20 Pa in the quartz tube 4, the methane flow rate needs to be as high as 10 sccm, which is significantly different from the methane flow rate of 1 sccm in Examples 1-4. This proves that the carbon source in the vertical graphene growth process of this application mainly comes from ethanol, and methane plays a supplementary role in the carbon source. On the other hand, as... Figure 15 As shown, in the comparative examples where only ethanol was used as the carbon source, the vertical graphene not only grew slowly with a height of only 400 nm (far lower than the 4.8 μm in Example 2), but also had a relatively small pore size. This demonstrates that the combined use of methane and ethanol as carbon sources plays a crucial role in forming the unique morphology of the vertical graphene of this application.

[0092] 2. In the plasma environment of PECVD, the activation energy barrier required for precursor molecular bond breaking can be lowered, allowing ethanol and methane molecules to decompose under high-energy electron bombardment, generating a large number of active carbon radicals and a small number of H and OH radicals. Under low pressure conditions, as plasma density and electron temperature increase, the frequency of collisions between electrons and ethanol and methane molecules increases, further reducing the activation energy of ethanol and methane during decomposition, increasing the concentration of carbon radicals, and simultaneously, H radicals continuously etch the defect regions on the graphene thin film surface, inhibiting thick film deposition. It is worth noting that if the pressure is too low, it indicates insufficient carbon source supply, which will also affect the growth of vertical graphene.

[0093] 3. For example Figure 23As shown, analysis using the finite-difference time-domain method revealed that the low-pressure environment enhances the thermal accumulation effect inside the quartz tube 4, increasing the local temperature on the substrate surface. This effectively reduces the surface diffusion activation energy for carbon free radical migration and directional nucleation on the substrate surface, promoting the directional nucleation of carbon atoms in regions with lower energy barriers, such as defects and steps. Furthermore, combined with the non-equilibrium plasma-assisted CVD growth mode under PECVD conditions, the vertical growth rate of upright graphene is much greater than the surface diffusion rate, achieving diffusion-limited conditions. The active carbon source rapidly deposits locally on the substrate, causing the graphene sheets to curl, overlap, and self-organize within microscale regions, forming the unique morphology of this application.

[0094] Further as Figure 16 As shown, under a 5Pa test environment, the photocurrent of the photodetector in Example 2 increases with the increase of excitation light power density. Furthermore, under the same excitation light power density, the photocurrent of the photodetector under a 5Pa test environment is significantly greater than the photocurrent under a normal pressure test environment. Figure 17 As shown, the test environment is 5Pa and the excitation light power density is... Effective light area Under the conditions, the responsivity of the photodetector in Example 2 The detection rates were 82 A / W and 82 A / W, respectively. In contrast, the ambient pressure testing environment and the excitation light power density... (Minimum power with light response), effective illumination area Under these conditions, the responsivity and specific detectivity of the photodetector in Example 2 are only 28 A / W and A significant decline occurred.

[0095] The improvement in photocurrent, responsivity, and detectivity of the device by reducing the atmospheric pressure of the detection environment is mainly attributed to the fact that the low-pressure environment reduces the adsorption of air molecules and water vapor on the graphene surface, decreasing the number of recombination centers on the graphene surface. This suppresses nonradiative recombination of photogenerated carriers, improves carrier lifetime and collection efficiency, and allows more photogenerated carriers to participate in the conduction process. Furthermore, the reduced number of interface defect states and adsorbed states under low pressure significantly reduces carrier recombination losses, thereby effectively improving the device's photoelectric conversion efficiency and weak signal detection capability.

[0096] like Figure 18As shown, in Example 2, when the photodetector is tested in a test environment of 5 Pa, its spectral response range is extended from 1550 nm (tested under atmospheric pressure) to 2200 nm (tested at 5 Pa). This is also attributed to the fact that the low-pressure environment reduces the trap state density on the surface of the vertical graphene, and reduces the recombination probability of low-energy carriers generated by long-wave photon excitation on the surface of vertical graphene, so that the photodetector can achieve excitation response to photons with longer wavelengths (lower energy), thereby expanding the response band of the detector.

[0097] By reducing the air pressure of the detection environment from atmospheric pressure to 5 Pa, the performance of the photodetector in Example 2 is significantly improved, which indirectly reflects that the vertical graphene in Example 2 has a large specific surface area and strong adsorption capacity for impurities in air.

[0098] As Figure 19 shown, as the temperature increases, the thermal excitation of carriers in vertical graphene is enhanced, the mobility is improved, and the recombination probability is reduced at the same time, thereby increasing the collection efficiency of photogenerated carriers, and further significantly increasing the photocurrent.

[0099] Four Chinese characters "Hai", "Na", "Bai" and "Chuan" are selected as the encrypted information carriers, and their corresponding Unicode codes and 8-bit ASCII codes are shown in Figure 20 . The encoded binary signal is loaded onto a modulated laser via a signal generator to regulate the laser pulse, where "1" represents laser on and "0" represents laser off. Under the modulation of 1550 nm laser, the self-driven photoelectric detection based on the vertical graphene heterojunction in Example 2 does not require an external bias voltage, and can generate photogenerated carriers through incident light excitation. Driven by the built-in electric field at the heterojunction interface, efficient carrier separation and fast signal output are realized. Specifically as shown in Figure 21 , the photodetector in Example 2 can respond in real time and accurately reproduce the binary signal encoded by the modulated laser, and convert the optical signal into a corresponding electrical signal through a semiconductor analyzer, completing information encryption and decoding transmission of complex binary optical signals. Relying on its excellent photoelectric conversion capability and built-in electric field assisted separation mechanism, the device realizes highly sensitive, stable and passive information encrypted transmission.

[0100] Various technical features of the embodiments described above can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the various technical features in the above embodiments are described. However, as long as there is no contradiction between the combinations of these technical features, they should all be considered as falling within the scope recorded in this description.

[0101] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing an upright graphene heterostructure, characterized in that, include: The substrate was placed in a quartz tube, and then a vacuum was drawn. A protective gas is introduced into the quartz tube and heated to the set temperature; Turn off the protective gas and evacuate again; First, methane is introduced into an ethanol solution, and then methane gas containing ethanol vapor is introduced into a quartz tube to grow vertical graphene on the substrate surface. During the growth of vertical graphene, the pressure inside the quartz tube is 10 Pa to 40 Pa.

2. The method for preparing upright graphene heterostructures according to claim 1, characterized in that, The set temperature is 850℃-950℃, the power of the radio frequency plasma source is 200W-300W, and the growth time of the upright graphene is 4h-6h.

3. The method for preparing upright graphene heterostructures according to claim 1, characterized in that, The flow rate of methane into the ethanol solution is 0.5 sccm-1.5 sccm.

4. The method for preparing upright graphene heterostructures according to claim 1, characterized in that, During the growth of upright graphene, the pressure inside the quartz tube is 15 Pa to 25 Pa.

5. An upright graphene heterostructure, characterized in that, It is prepared by the preparation method described in any one of claims 1-4.

6. A photodetector, characterized in that, It includes a power source and an upright graphene heterojunction as described in claim 5, wherein the upright graphene on the substrate is connected to the positive terminal of the power source, and the substrate is connected to the negative terminal of the power source.

7. A method of using the photodetector as described in claim 6, characterized in that, When the photodetector performs light detection, the ambient pressure of the photodetector is controlled to be below 100 Pa.

8. The method of using the photodetector according to claim 7, characterized in that, When the photodetector performs light detection, the ambient pressure of the photodetector is controlled to be lower than 10 Pa to allow the photodetector to detect light at 2200 nm.

9. An apparatus for preparing upright graphene heterojunctions capable of implementing the preparation method according to any one of claims 1-4, characterized in that, It includes a liquid tank (1), a gas tank (2), a radio frequency plasma source (3), a quartz tube (4), and a vacuum pump (5); The liquid tank (1) is used to hold ethanol. The input end of the liquid tank (1) is used to connect to the methane cylinder (6). The input end of the gas tank (2) is used to connect to the protective gas. The output ends of the liquid tank (1) and the gas tank (2) are connected in parallel to the gas inlet of the quartz tube (4). The radio frequency plasma source (3) is installed on the quartz tube (4). The gas outlet of the quartz tube (4) is connected to the vacuum pump (5).

10. An application of the photodetector as described in claim 6 in signal encoding.

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