Preparation and transfer methods of flexible graphene / germanium heterojunction

Abstract

The present invention discloses a method for preparing a flexible graphene / germanium heterojunction. Using high-purity Ge as a target, copper foil graphene as a substrate, and a laser as a particle excitation source, a germanium thin film is deposited on the copper foil graphene using the PLD method. The present invention also discloses a method for transferring the flexible graphene / germanium heterojunction. The prepared flexible graphene / germanium heterojunction is spin-coated with a PMMA support film, and then the copper foil is etched away with a CuSO4 solution to achieve the overall transfer of the flexible graphene / germanium heterojunction. The flexible graphene / germanium heterojunction preparation and transfer methods provided by the present invention address the issues of low light absorption, which lead to low photoresponsivity in graphene detectors and a short lifetime of photogenerated carriers in graphene itself. This allows the preparation of a graphene-based heterojunction with high near-infrared response and high speed.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor material preparation, and in particular relates to a method for preparing a flexible graphene / germanium heterojunction. The present invention also relates to a method for transferring the flexible graphene / germanium heterojunction. Background Art

[0002] Ge and Si are both Group IV semiconductor materials with the same basic properties. They are also the earliest semiconductor materials used to make transistors. The mobility of electrons and holes in Ge is very high, reaching 3900±100cm 2 ·V -1 ·s -1 and 1900±50cm 2 ·V -1 ·s -1 , significantly higher than many currently available Si compound semiconductor materials. In particular, strained Ge materials grown on relaxed SiGe substrates are subjected to biaxial compressive strain, significantly enhancing hole mobility, reaching 8-10 times that of Si. Ge single crystals have similar lattice constants to III-V materials such as GaAs, with a lattice mismatch of only 0.07%. GaAs / Ge solar cells fabricated using low-resistivity Ge single crystals exhibit reverse breakdown in localized shadows, strong solar radiation resistance, and long lifetimes, paving the way for the integration of Ge-based electronic devices with III-V optical devices. Furthermore, Ge's high absorption coefficient in the 0.8-1.55μm band and its high carrier mobility make it suitable for optical detectors and CMOS devices. As a channel material, Ge can increase the speed of integrated circuits and offers great potential for performance improvements. Germanium-based photodetectors are a key component in silicon-based photonics due to their unique response characteristics in the telecommunications band and their compatibility with CMOS processes. However, the low quantum efficiency and high surface recombination rate of ultrathin germanium films, especially in the near-infrared band, pose a huge obstacle to their application. Currently, practical applications require more nanoscale devices with lower power consumption, higher responsivity and response speed.

[0003] Graphene as a substrate for flexible photodetectors has also attracted more and more attention in the industry. The thickness of a single layer of graphene is only It is the thinnest material currently available. Its hardness is higher than that of diamond, yet it has excellent toughness and can be bent. Compared with traditional indium tin oxide (ITO) materials, graphene has higher flexibility and can be stretched 20% without breaking. Therefore, using graphene as a conductor material can make display devices that can be bent, folded, and stretched. Secondly, graphene has extremely strong conductivity, with a carrier mobility of up to 2.5×105cm 2 / V·s, is the intrinsic Si electron mobility (1400cm 2 / V·s) over 170 times faster than a typical conductor, allowing electrons to travel at 1 / 300 of their speed. Unlike many materials, graphene's electron mobility is less affected by temperature fluctuations, resulting in a correspondingly low resistivity, making it the lowest room-temperature resistivity of any known material. This makes graphene displays more sensitive to touch, making it suitable for the development of flexible touchscreens. Furthermore, graphene exhibits an ultra-wide spectral response, encompassing the entire spectrum from the ultraviolet to the terahertz band. While its excellent photoelectric properties have garnered widespread attention in the field of photodetection, graphene's use for photodetection also presents significant disadvantages and limitations. Intrinsic graphene's low light absorption (monolayer graphene absorbs only 2.3% of visible light) results in low photoresponsivity in graphene detectors. Graphene's inherently short lifetime of photogenerated carriers, measured in picoseconds, makes them difficult to collect effectively, thus limiting the detector's photosensitivity. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing a flexible graphene / germanium heterojunction, which solves the problem that graphene has low light absorption rate, resulting in low photoresponsivity of graphene detectors and short lifetime of photogenerated carriers in graphene itself.

[0005] Another object of the present invention is to provide a method for transferring a flexible graphene / germanium heterojunction.

[0006] The technical solution adopted by the present invention is: a method for preparing a flexible graphene / germanium heterojunction, using Ge as a target material, copper foil graphene as a substrate, laser as a particle excitation source, and using the PLD method to deposit a germanium film on the copper foil graphene.

[0007] The technical solution adopted by the present invention is also characterized by: a method for preparing a flexible graphene / germanium heterojunction, and the specific preparation steps are as follows:

[0008] Step 1: Place the copper foil graphene in the sample chamber and pump the pressure in the sample chamber to the same as that in the growth chamber, i.e. 1×10 -1 Below Pa;

[0009] Step 2: Send the copper foil graphene to the growth chamber and pump the pressure of the growth chamber to 1×10 -4 Pa below, heated to 500℃-590℃ for growth;

[0010] Step 3: N2 is introduced into the growth chamber and the laser is turned on for preheating for 30-50 minutes.

[0011] Step 4: Adjust the laser light path to irradiate the Ge target, with the distance between the target and the copper foil graphene being 6.2 cm to 8.6 cm, and deposit for 30 min to 60 min;

[0012] Step 5: After the deposition is completed, the vacuum is pumped until the vacuum degree of the sample chamber and the growth chamber differ by one order of magnitude, and the finished material is taken out to obtain a flexible graphene / germanium heterojunction.

[0013] The heating method in step 2 is to heat to 500°C-590°C at a rate of 15°C / min-25°C / min.

[0014] In step 4, the laser pulse frequency is 3 Hz-7 Hz, the laser energy is 530 mJ-630 mJ, and the purity of the Ge target is 99.99999%.

[0015] Place the copper foil graphene in the injection chamber first, pump the air pressure in the injection chamber to the same as that in the growth chamber, and then send it to the growth chamber to prevent it from coming into contact with air and affecting the results.

[0016] The second technical solution adopted by the present invention is a method for transferring a flexible graphene / germanium heterojunction. The flexible graphene / germanium heterojunction prepared according to the above-mentioned flexible graphene / germanium heterojunction preparation method is spin-coated with a PMMA support film, and then the copper foil is etched away with a CuSO4 solution to achieve the overall transfer of the flexible graphene / germanium heterojunction.

[0017] The second technical solution adopted by the present invention is also characterized by: a method for transferring a flexible graphene / germanium heterojunction, wherein the specific transfer steps are as follows:

[0018] Step 1: Place the flexible graphene / germanium heterojunction into a spin coater, add a drop of PMMA solution and spin coat for 16s-38s, repeating the spin coating operation until the PMMA solution completely covers the germanium film;

[0019] Step 2: heating the flexible graphene / germanium heterojunction spun in step 1 for 20-30 minutes at a temperature of 90° C. to 120° C. to solidify the PMMA to obtain a PMMA / flexible graphene / germanium heterojunction;

[0020] Step 3: Wipe the back of the copper foil in the PMMA / flexible graphene / germanium heterojunction with acetone;

[0021] Step 4: placing the PMMA / flexible graphene / germanium heterojunction in a CuSO4 solution and allowing it to stand for 12-24 hours to obtain a PMMA / flexible graphene / germanium heterojunction with the copper foil removed;

[0022] Step 5: Wash the PMMA / flexible graphene / germanium heterojunction obtained in step 4 with deionized water for 3-5 times, and then transfer the PMMA / flexible graphene / germanium heterojunction to a flexible PI substrate to obtain a PMMA / flexible graphene / germanium / PI heterojunction;

[0023] Step 6: Debonding the PMMA / germanium / graphene / PI heterojunction in a water bath to obtain a flexible graphene / germanium / PI heterojunction;

[0024] Step 7: Dry the flexible graphene / germanium / PI heterojunction to complete the transfer of the flexible graphene / germanium heterojunction.

[0025] The spin coating operation in step 1 is specifically as follows: first, spin coating at 600 r / min-800 r / min for 6s-8s, and then spin coating at 3000 r / min-5000 r / min for 10s-30s.

[0026] In step 4, the CuSO4 solution is prepared by mixing 1 g of CuSO4 powder with 120 mL of deionized water.

[0027] In step 6, the water bath temperature is 40°C-60°C, and the time is 15min-30min.

[0028] In step 7, the drying temperature is 60° C.-90° C., and the drying time is 15 min-30 min.

[0029] The beneficial effects of the present invention are:

[0030] The present invention proposes to use pulsed laser deposition (PLD) method, with copper foil graphene as substrate and germanium as target material, supplemented by wet transfer process, to prepare high-quality, portable flexible graphene-based heterojunction on flexible polyimide plastic substrate. Combining the high responsiveness of Ge film to near-infrared light, the excellent material properties of graphene such as high mechanical flexibility, high carrier mobility, and ultra-wide spectral response range, a flexible graphene / germanium heterojunction with high near-infrared responsiveness is developed.

[0031] In the present invention, flexible graphene and ultrathin germanium film form a heterojunction and are transferred as a whole to its flexible plastic substrate to prepare a flexible graphene / germanium heterojunction. Graphene has ultra-high carrier mobility, which can improve the light responsiveness and response speed of the device. The germanium film serves as the main absorption material for near-infrared light, making up for the low light absorption rate of the graphene material, thereby improving the performance of the device.

[0032] The present invention forms a heterojunction between Ge and graphene. Based on the high absorption rate of Ge to near-infrared light, the photosensitivity of the graphene material in the near-infrared light band can be improved, and the carrier lifetime of the graphene is also modulated. The photodetector based on the germanium-graphene structure provides a new idea for realizing small-scale high-performance devices in the process of silicon-based optical chip integration, and provides new opportunities for applications in imaging, sensing and other optoelectronic fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic flow chart of a method for preparing a flexible graphene / germanium heterojunction according to the present invention;

[0034] Figure 2 This is a surface morphology image of the flexible graphene / germanium heterojunction prepared in Example 2 of the present invention;

[0035] Figure 3 1 is a Raman image of the flexible graphene / germanium heterojunction prepared in Example 2 of the present invention at different growth temperatures;

[0036] Figure 4 1 is a Raman image of the flexible graphene / germanium heterojunction prepared in Example 2 of the present invention grown at different laser energies;

[0037] Figure 5 1 is a Raman image of the flexible graphene / germanium heterojunction prepared in Example 2 of the present invention grown at different laser frequencies;

[0038] Figure 6 1 is a Raman image of the flexible graphene / germanium heterojunction prepared in Example 2 of the present invention grown at different target spacings;

[0039] Figure 7 is an XRD pattern of the flexible graphene / germanium heterojunction prepared in Example 2 of the present invention;

[0040] Figure 8 is a TEM image of the flexible graphene / germanium heterojunction prepared in Example 2 of the present invention;

[0041] Figure 9 is a VIS-NIR transmittance graph of the flexible graphene / germanium heterojunction prepared in Example 2 of the present invention;

[0042] Figure 10 1 is an IV diagram of the flexible graphene / germanium heterojunction prepared in Example 2 of the present invention;

[0043] Figure 11 This is a photoresponse diagram of the flexible graphene / germanium heterojunction prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0044] The invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0045] The present invention provides a method for preparing and transferring a flexible graphene / germanium heterojunction, such as Figure 1 As shown, Ge is used as the target material, copper foil graphene is used as the substrate, and laser is used as the particle excitation source. The PLD method is used to deposit a germanium film on the copper foil graphene.

[0046] The specific preparation steps are as follows:

[0047] Step 1: Place the copper foil graphene in the sample chamber and pump the pressure in the sample chamber to the same as that in the growth chamber, i.e. 1×10 -1 Below Pa;

[0048] Step 2: Send the copper foil graphene to the growth chamber and pump the pressure of the growth chamber to 1×10 -4 Pa below, heating to 500℃-590℃ at a rate of 15℃ / min-25℃ / min for growth;

[0049] Step 3: N2 is introduced into the growth chamber and the laser is turned on for preheating for 30-50 minutes.

[0050] Step 4: Adjust the laser light path and irradiate the target. The distance between the target and the copper foil graphene is 6.2 cm to 8.6 cm. The deposition time is 30 min to 60 min. The laser pulse frequency is 3 Hz to 7 Hz. The laser energy is 530 mJ to 630 mJ. The purity of the Ge target is 99.99999%.

[0051] Step 5: After the deposition is completed, the vacuum is pumped until the vacuum degree of the sample chamber and the growth chamber differ by one order of magnitude, and the finished material is taken out to obtain a flexible graphene / germanium heterojunction.

[0052] The present invention also provides a method for transferring a flexible graphene / germanium heterojunction, wherein a PMMA support film is spin-coated on the prepared flexible graphene / germanium heterojunction, and then the copper foil is etched away with a CuSO4 solution to achieve the overall transfer of the flexible graphene / germanium heterojunction.

[0053] The specific transfer steps are as follows:

[0054] Step 1: Place the flexible graphene / germanium heterojunction into a spin coater, add a drop of PMMA solution, and spin coat it at 600-800 rpm for 6-8 seconds, then at 3000-5000 rpm for 10-30 seconds. Repeat the spin coating operation until the PMMA solution completely covers the germanium film.

[0055] Step 2: heating the flexible graphene / germanium heterojunction spun in step 1 for 20-30 minutes at a temperature of 90° C. to 120° C. to solidify the PMMA to obtain a PMMA / flexible graphene / germanium heterojunction;

[0056] Step 3: Wipe the back of the copper foil in the PMMA / flexible graphene / germanium heterojunction with acetone;

[0057] Step 4: Place the PMMA / flexible graphene / germanium heterojunction into a CuSO4 solution prepared by mixing 1 g of CuSO4 powder with 120 mL of deionized water, and allow the solution to rest for 12-24 hours to obtain a PMMA / flexible graphene / germanium heterojunction with the copper foil removed.

[0058] Step 5: Wash the PMMA / flexible graphene / germanium heterojunction obtained in step 4 with deionized water for 3-5 times, and then transfer the PMMA / flexible graphene / germanium heterojunction to a flexible PI substrate to obtain a PMMA / flexible graphene / germanium / PI heterojunction;

[0059] Step 6: Debonding the PMMA / germanium / graphene / PI heterojunction in a water bath to obtain a flexible graphene / germanium / PI heterojunction. The water bath temperature is 40° C. to 60° C., and the time is 15 min to 30 min.

[0060] Step 7: Dry the flexible graphene / germanium / PI heterojunction to complete the transfer of the flexible graphene / germanium heterojunction. The drying temperature is 60° C.-90° C. and the time is 15 min-30 min.

[0061] The preparation method and transfer method of the flexible graphene / germanium heterojunction of the present invention are further described below through specific examples.

[0062] Example 1

[0063] Preparation of flexible graphene / germanium heterojunction:

[0064] Step 1: Place the copper foil graphene in the sample chamber and pump the pressure in the sample chamber to the same as that in the growth chamber, i.e. 1×10 -1 Below Pa;

[0065] Step 2: Send the copper foil graphene to the growth chamber and pump the pressure of the growth chamber to 1×10 -4 Pa below, heating to 500 °C at a rate of 15 °C / min for growth;

[0066] Step 3: N2 was introduced into the growth chamber and the laser was turned on to preheat for 30 minutes;

[0067] Step 4: Adjust the laser light path and irradiate the target. The distance between the target and the copper foil graphene is 6.2 cm. The deposition time is 30 minutes. The laser pulse frequency is 3 Hz and the laser energy is 530 mJ.

[0068] Step 5: After the deposition is completed, the vacuum is pumped until the vacuum degree of the sample chamber and the growth chamber differ by one order of magnitude, and the finished material is taken out to obtain a flexible graphene / germanium heterojunction.

[0069] Transfer of flexible graphene / germanium heterojunctions:

[0070] Step 1: Place the flexible graphene / germanium heterojunction into a spin coater, add a drop of PMMA solution, and spin coat at 600 rpm for 6 seconds, then at 3000 rpm for 10 seconds. Repeat the spin coating operation until the PMMA solution completely covers the germanium film.

[0071] Step 2: heating the flexible graphene / germanium heterojunction spun in step 1 for 20 minutes at 90° C. to solidify the PMMA to obtain a PMMA / flexible graphene / germanium heterojunction;

[0072] Step 3: Wipe the back of the copper foil in the PMMA / flexible graphene / germanium heterojunction with acetone;

[0073] Step 4: Place the PMMA / flexible graphene / germanium heterojunction into a CuSO4 solution prepared by mixing 1 g of CuSO4 powder with 120 mL of deionized water, and allow the solution to rest for 12 hours to obtain a PMMA / flexible graphene / germanium heterojunction with the copper foil removed.

[0074] Step 5: Wash the PMMA / flexible graphene / germanium heterojunction obtained in step 4 three times with deionized water, and then transfer the PMMA / flexible graphene / germanium heterojunction to a flexible PI substrate to obtain a PMMA / flexible graphene / germanium / PI heterojunction;

[0075] Step 6: Debonding the PMMA / germanium / graphene / PI heterojunction in a water bath to obtain a flexible graphene / germanium / PI heterojunction. The water bath temperature is 40° C. and the time is 15 minutes.

[0076] Step 7: Dry the flexible graphene / germanium / PI heterojunction to complete the transfer of the flexible graphene / germanium heterojunction. The drying temperature is 60° C. and the time is 15 minutes.

[0077] Example 2

[0078] Preparation of flexible graphene / germanium heterojunction:

[0079] Step 1: Place the copper foil graphene in the sample chamber and pump the pressure in the sample chamber to the same as that in the growth chamber, i.e. 1×10 -1 Below Pa;

[0080] Step 2: Send the copper foil graphene to the growth chamber and pump the pressure of the growth chamber to 1×10 -4 Pa below, heating to 530 °C at a rate of 20 °C / min for growth;

[0081] Step 3: N2 was introduced into the growth chamber and the laser was turned on to preheat for 40 minutes;

[0082] Step 4: Adjust the laser light path and irradiate the target. The distance between the target and the copper foil graphene is 6.7 cm. Deposition is performed for 40 minutes. The laser pulse frequency is 5 Hz and the laser energy is 580 mJ.

[0083] Step 5: After the deposition is completed, the vacuum is pumped until the vacuum degree of the sample chamber and the growth chamber differ by one order of magnitude, and the finished material is taken out to obtain a flexible graphene / germanium heterojunction.

[0084] Transfer of flexible graphene / germanium heterojunctions:

[0085] Step 1: Place the flexible graphene / germanium heterojunction into a spin coater, add a drop of PMMA solution, and spin coat at 700 rpm for 7 seconds, then at 4000 rpm for 20 seconds. Repeat the spin coating operation until the PMMA solution completely covers the germanium film.

[0086] Step 2: heating the flexible graphene / germanium heterojunction spun in step 1 for 25 minutes at a heating temperature of 100° C. to solidify the PMMA to obtain a PMMA / flexible graphene / germanium heterojunction;

[0087] Step 3: Wipe the back of the copper foil in the PMMA / flexible graphene / germanium heterojunction with acetone;

[0088] Step 4: Place the PMMA / flexible graphene / germanium heterojunction into a CuSO4 solution prepared by mixing 1 g of CuSO4 powder with 120 mL of deionized water, and allow the solution to rest for 18 hours to obtain a PMMA / flexible graphene / germanium heterojunction with the copper foil removed.

[0089] Step 5: Wash the PMMA / flexible graphene / germanium heterojunction obtained in step 4 with deionized water four times, and then transfer the PMMA / flexible graphene / germanium heterojunction to a flexible PI substrate to obtain a PMMA / flexible graphene / germanium / PI heterojunction;

[0090] Step 6: Debonding the PMMA / germanium / graphene / PI heterojunction in a water bath to obtain a flexible graphene / germanium / PI heterojunction. The water bath temperature is 50° C. and the time is 25 min.

[0091] Step 7: Dry the flexible graphene / germanium / PI heterojunction to complete the transfer of the flexible graphene / germanium heterojunction. The drying temperature is 80° C. and the time is 25 min.

[0092] Example 3

[0093] Step 1: Place the copper foil graphene in the sample chamber and pump the pressure in the sample chamber to the same as that in the growth chamber, i.e. 1×10 -1 Below Pa;

[0094] Step 2: Send the copper foil graphene to the growth chamber and pump the pressure of the growth chamber to 1×10 -4 Pa below, heating to 590 °C at a rate of 25 °C / min for growth;

[0095] Step 3: N2 was introduced into the growth chamber and the laser was turned on to preheat for 50 minutes;

[0096] Step 4: Adjust the laser light path and irradiate the target. The distance between the target and the copper foil graphene is 8.6 cm. The deposition time is 60 min. The laser pulse frequency is 7 Hz and the laser energy is 630 mJ.

[0097] Step 5: After the deposition is completed, the vacuum is pumped until the vacuum degree of the sample chamber and the growth chamber differ by one order of magnitude, and the finished material is taken out to obtain a flexible graphene / germanium heterojunction.

[0098] Transfer of flexible graphene / germanium heterojunctions:

[0099] Step 1: Place the flexible graphene / germanium heterojunction into a spin coater, add a drop of PMMA solution, and spin coat at 800 rpm for 8 seconds, then at 5000 rpm for 30 seconds. Repeat the spin coating operation until the PMMA solution completely covers the germanium film.

[0100] Step 2: heating the flexible graphene / germanium heterojunction spun in step 1 for 30 minutes at a heating temperature of 120° C. to solidify the PMMA to obtain a PMMA / flexible graphene / germanium heterojunction;

[0101] Step 3: Wipe the back of the copper foil in the PMMA / flexible graphene / germanium heterojunction with acetone;

[0102] Step 4: Place the PMMA / flexible graphene / germanium heterojunction into a CuSO4 solution prepared by mixing 1 g of CuSO4 powder with 120 mL of deionized water, and allow the solution to rest for 24 hours to obtain a PMMA / flexible graphene / germanium heterojunction with the copper foil removed.

[0103] Step 5: Wash the PMMA / flexible graphene / germanium heterojunction obtained in step 4 with deionized water five times, and then transfer the PMMA / flexible graphene / germanium heterojunction to a flexible PI substrate to obtain a PMMA / flexible graphene / germanium / PI heterojunction;

[0104] Step 6: Debonding the PMMA / germanium / graphene / PI heterojunction in a water bath to obtain a flexible graphene / germanium / PI heterojunction. The water bath temperature is 60° C. and the time is 30 min.

[0105] Step 7: Dry the flexible graphene / germanium / PI heterojunction to complete the transfer of the flexible graphene / germanium heterojunction. The drying temperature is 90° C. and the time is 30 min.

[0106] Experimental verification

[0107] Figure 2 This is a surface morphology image of the flexible graphene / germanium heterojunction prepared in Example 2 of the present invention. The results show that the film prepared in the present invention grows uniformly and has a smooth surface.

[0108] Figure 3 This is a Raman image of the flexible graphene / germanium heterojunction prepared in Example 2 of the present invention grown under different temperature conditions. The results show that 530° C. is the optimal growth temperature in the present invention.

[0109] Figure 4 This is a Raman image of the flexible graphene / germanium heterojunction prepared in Example 2 of the present invention grown under different laser energy conditions. The results show that 530mJ is the optimal laser energy for thin film growth in the present invention.

[0110] Figure 5 This is a Raman image of the flexible graphene / germanium heterojunction prepared in Example 2 of the present invention grown under different laser frequency conditions. The results show that 5 Hz is the optimal laser frequency for thin film growth in the present invention.

[0111] Figure 6 This is a Raman image of the flexible graphene / germanium heterojunction prepared in Example 2 of the present invention grown under different target spacing conditions. The results show that 7.7 cm is the optimal target spacing for thin film growth in the present invention.

[0112] Figure 7 TEM image of the flexible graphene / germanium heterojunction prepared in Example 2 of the present invention. The results show that the germanium film on the graphene prepared in the present invention has a polycrystalline structure.

[0113] Figure 8 The XRD pattern of the flexible graphene / germanium heterojunction prepared in Example 2 of the present invention shows that the germanium film on the graphene prepared in the present invention has a polycrystalline structure and <111> Crystal orientation preferential growth.

[0114] Figure 9 This is a VIS-NIR transmittance graph of the flexible graphene / germanium heterojunction prepared in Example 2 of the present invention. The results show that the graphene / germanium heterojunction prepared in the present invention can be used to prepare VIS-NIR light-controlled devices.

[0115] Figure 10 This is an IV test graph of the flexible graphene / germanium heterojunction prepared in Example 2 of the present invention. The graphene / germanium heterojunction prepared in the present invention has good rectification characteristics and responds to VIS-NIR.

[0116] Figure 11This is a switching characteristic diagram of the flexible graphene / germanium heterojunction prepared in Example 2 of the present invention. The graphene / germanium heterojunction prepared in the present invention has good light response and good repeatability.

Claims

1. A method for preparing a flexible graphene / germanium heterojunction, characterized in that: Using Ge as target, copper foil graphene as substrate, and laser as particle excitation source, PLD method was used to deposit germanium thin film on copper foil graphene. The specific preparation steps are as follows: Step 1: Place the copper foil graphene into the sample chamber and pump the pressure of the sample chamber to the same as that of the growth chamber, i.e., below 1×10-1Pa; Step 2: Send the copper foil graphene to the growth chamber and pump the pressure of the growth chamber to 1×10 -4 Pa below, heated to 500℃-590℃ for growth; The heating method in step 2 is to heat to 500°C-590°C at a rate of 15°C / min-25°C / min; Step 3: N2 is introduced into the growth chamber and the laser is turned on for preheating for 30-50 minutes. Step 4: Adjust the laser light path to irradiate the Ge target, with the distance between the target and the copper foil graphene being 6.2 cm to 8.6 cm, and deposit for 30 min to 60 min; In step 4, the laser pulse frequency is 3 Hz-7 Hz, the laser energy is 530 mJ-630 mJ, and the purity of the Ge target is 99.99999%; Step 5: After the deposition is completed, the vacuum is pumped until the vacuum degree of the sample chamber and the growth chamber differ by one order of magnitude, and the finished material is taken out to obtain a flexible graphene / germanium heterojunction.

2. A method for transferring a flexible graphene / germanium heterojunction, characterized in that: The flexible graphene / germanium heterojunction prepared by the method for preparing the flexible graphene / germanium heterojunction according to claim 1 is spin-coated with a PMMA support film, and then the copper foil is etched away with a CuSO4 solution to achieve the overall transfer of the flexible graphene / germanium heterojunction; The specific transfer steps are as follows: Step 1: Place the flexible graphene / germanium heterojunction into a spin coater, add a drop of PMMA solution and spin coat for 16s-38s, repeating the spin coating operation until the PMMA solution completely covers the germanium film; The spin coating operation in step 1 is specifically as follows: first, spin coating at 600 rpm to 800 rpm for 6 s to 8 s, and then spin coating at 3000 rpm to 5000 rpm for 10 s to 30 s; Step 2: heating the flexible graphene / germanium heterojunction spun in step 1 for 20-30 minutes at a temperature of 90° C. to 120° C. to solidify the PMMA to obtain a PMMA / flexible graphene / germanium heterojunction; Step 3: Wipe the back of the copper foil in the PMMA / flexible graphene / germanium heterojunction with acetone; Step 4: placing the PMMA / flexible graphene / germanium heterojunction in a CuSO4 solution and allowing it to stand for 12-24 hours to obtain a PMMA / flexible graphene / germanium heterojunction with the copper foil removed; In step 4, the CuSO4 solution is prepared by mixing 1 g of CuSO4 powder with 120 mL of deionized water. Step 5: Wash the PMMA / flexible graphene / germanium heterojunction obtained in step 4 with deionized water for 3-5 times, and then transfer the PMMA / flexible graphene / germanium heterojunction to a flexible PI substrate to obtain a PMMA / flexible graphene / germanium / PI heterojunction; Step 6: Debonding the PMMA / germanium / graphene / PI heterojunction in a water bath to obtain a flexible graphene / germanium / PI heterojunction; In step 6, the water bath temperature is 40°C-60°C and the time is 15min-30min; Step 7: drying the flexible graphene / germanium / PI heterojunction, thereby completing the transfer of the flexible graphene / germanium heterojunction; In step 7, the drying temperature is 60° C.-90° C., and the drying time is 15 min-30 min.

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