A method for preparing a two-dimensional MoS2 / Re-MoS2 lateral heterojunction on a GaN substrate

Abstract

The present invention discloses a method for preparing a two-dimensional MoS2 / Re-MoS2 lateral heterojunction on a GaN substrate, comprising the following steps: (1) growing a MoS2 layer on a SiO2 substrate; (2) placing the SiO2 substrate on the left side of a new quartz boat, covering the top with a clean substrate; placing a rhenium source, a molybdenum source and a flux mixture on the right side of the quartz boat, and pushing them all into the downstream of a new quartz tube; placing sulfur powder in a quartz crucible and pushing it into the upstream of the quartz tube; exhausting the air, growing a Re-MoS2 layer on the side of the MoS2 layer, and obtaining a SiO2 substrate with a two-dimensional MoS2 / Re-MoS2 heterojunction; and (3) transferring the two-dimensional MoS2 / Re-MoS2 heterojunction to the surface of the GaN substrate. The heterojunction obtained by the present invention has a low potential barrier at the heterojunction interface, alleviates the pinning effect, and improves the tunneling mode provided for carriers to cross the potential barrier. The preparation method is simple to operate and has good controllability and safety.

Description

Technical Field

[0001] The present invention relates to the field of preparation of semiconductor materials, and in particular to a method for preparing a two-dimensional MoS2 / Re-MoS2 lateral heterojunction on a GaN substrate. Background Art

[0002] Since the 21st century, two-dimensional materials have sparked a wave of research in fields such as chemical catalysis, optoelectronic communications, and information storage, thanks to their excellent physical and chemical properties and unique low-dimensional optoelectronic properties. Molybdenum disulfide (MoS2), a representative example of two-dimensional transition metal disulfides (TMDs), exhibits high intrinsic carrier mobility and exhibits distinct electronic bulk properties as the number of layers changes, showing potential for application in high-performance optoelectronic devices.

[0003] Group III nitride materials, with their excellent optoelectronic and structural properties, have been applied in a wide range of optoelectronic devices. GaN, a representative of these third-generation semiconductors, boasts high bandwidth, high breakdown voltage, and excellent physical and chemical stability, making it the preferred raw material for high-performance optoelectronic devices.

[0004] Type II heterojunctions formed by two-dimensional monolayer MoS2 and GaN have the property of significantly promoting the separation of photogenerated carriers and can be used to prepare high-performance optoelectronic devices. However, the poor functional specificity of conventional MoS2 / GaN heterostructures, high heterojunction interface barriers, and strong Fermi pinning effects in the "metal-semiconductor" contact have limited the further application of MoS2 / GaN heterostructures. Summary of the Invention

[0005] In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, the purpose of the present invention is to provide a method for preparing a two-dimensional MoS2 / Re-MoS2 lateral heterojunction on a GaN substrate. The resulting heterojunction has a low potential barrier and alleviates the pinning effect to a certain extent, while also improving the tunneling mode provided for carriers to cross the potential barrier. The preparation method is simple to operate, has strong repeatability when the process parameters are determined, and has good controllability and safety.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A method for preparing a two-dimensional MoS2 / Re-MoS2 lateral heterojunction on a GaN substrate comprises the following steps:

[0008] (1) Growth of MoS2 layer on SiO2 substrate:

[0009] Place the clean SiO2 substrate on the left side of the quartz boat, mix the raw material MoO3 and the flux NaCl and place them on the right side of the quartz boat, and push them into the downstream of the quartz tube; put the sulfur powder into the quartz crucible and push it into the upstream of the quartz tube;

[0010] The air in the quartz tube is exhausted, and a MoS2 layer is grown on the SiO2 substrate to obtain a SiO2 substrate with a MoS2 layer grown thereon;

[0011] (2) Growing a Re-MoS2 layer on the side of the MoS2 layer prepared in step (1):

[0012] Place the SiO2 substrate with the MoS2 layer on the left side of a new quartz boat, and cover the clean substrate on top of the SiO2 substrate with the MoS2 layer. Mix the raw materials rhenium source ReO3, molybdenum source MoO3 and flux NaCl and place them on the right side of the quartz boat, and push them all into the downstream of the new quartz tube; put sulfur powder into a quartz crucible and push it into the upstream of the quartz tube;

[0013] The air in the quartz tube was exhausted, and a Re-MoS2 layer was grown on the side of the MoS2 layer to obtain a SiO2 substrate with a two-dimensional MoS2 / Re-MoS2 heterojunction:

[0014] (3) Transferring the two-dimensional MoS2 / Re-MoS2 heterojunction to the GaN substrate surface:

[0015] PMMA is spin-coated on the surface of the SiO2 substrate on which the two-dimensional MoS2 / Re-MoS2 heterojunction is grown, obtained in step (2), and the SiO2 substrate is etched in a hydrofluoric acid etchant. After observing that the PMMA layer floats above the etchant liquid surface, the GaN substrate is controlled to sink below the PMMA layer liquid surface, and the GaN substrate is pulled up to realize substrate transfer, thereby obtaining a two-dimensional MoS2 / Re-MoS2 lateral heterojunction on the GaN substrate.

[0016] Preferably, in step (1), the mass ratio of the molybdenum source MoO3 to the flux NaCl is 1:(0.9-1.1).

[0017] Preferably, the mass ratio of the molybdenum source MoO3 to sulfur powder is 1:(70-80).

[0018] Preferably, the step (1) of growing a MoS2 layer on a SiO2 substrate comprises:

[0019] The growth temperature is 780-800° C., the heating rate is 35-40° C. / min, the growth time is 20-25 min, the ambient pressure is 145-150 Torr, and the carrier gas Ar flow rate is 65-70 sccm.

[0020] Preferably, the distance between the SiO2 substrate and the raw material is 2.8 to 3.0 cm, and the distance between the upstream and downstream vessels is 15 to 20 cm.

[0021] Preferably, the mass ratio of the rhenium source ReO3, the molybdenum source MoO3 and the flux NaCl in step (2) is: 1: (0.9-1.1): (0.9-1.1).

[0022] Preferably, the mass ratio of the molybdenum source MoO3 to sulfur powder is 1:(240-260).

[0023] Preferably, the step (2) of growing a Re-MoS2 layer on the side of the MoS2 layer is specifically as follows:

[0024] The growth temperature is 550-560° C., the heating rate is 25-30° C. / min, the growth time is 8-10 min, the ambient pressure is 0.01-0.02 Torr, and the carrier gas Ar flow rate is 70-80 sccm.

[0025] Preferably, in step (2), the distance between the SiO2 substrate on which the MoS2 layer is grown and the raw material is 2.5 to 3.0 cm, and the distance between the upstream and downstream vessels is 15 to 20 cm.

[0026] Preferably, in step (3), the SiO2 substrate is placed in a hydrofluoric acid etching solution and etched for 45 to 60 minutes.

[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0028] (1) The method for preparing a two-dimensional MoS2 / Re-MoS2 lateral heterojunction on a GaN substrate of the present invention utilizes two-step CVD combined with wet transfer to realize the construction of a MoS2 / Re-MoS2 lateral heterostructure on the surface of a GaN material. The potential barrier of the heterojunction interface is low, which alleviates the pinning effect to a certain extent, and at the same time improves the tunneling mode provided for carriers to cross the potential barrier, and the response to the excitation light is also stronger.

[0029] (2) The method for preparing a two-dimensional MoS2 / Re-MoS2 lateral heterojunction on a GaN substrate of the present invention is simple to operate, has strong repeatability when the process parameters are determined, and has good controllability and safety.

[0030] (3) The method for preparing a two-dimensional MoS2 / Re-MoS2 lateral heterojunction on a GaN substrate of the present invention can be used in transistors, photodetectors, optical communications, chemical catalysis and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of a CVD device for preparing single-layer MoS2 and epitaxial Re-MoS2 in an embodiment of the present invention.

[0032] Figure 2This is a temperature-programmed curve diagram for preparing a single-layer MoS2 in an embodiment of the present invention.

[0033] Figure 3 1. A programmed temperature rise curve diagram of a schematic diagram of a CVD device for lateral epitaxial Re-MoS2 in an embodiment of the present invention.

[0034] Figure 4 This is an optical microscope image of high-quality single-layer MoS2 in an embodiment of the present invention.

[0035] Figure 5 This is a Raman characterization test image of high-quality single-layer MoS2 in an embodiment of the present invention.

[0036] Figure 6 This is an optical microscope image of the lateral epitaxial growth of Re-MoS2 in an embodiment of the present invention.

[0037] Figure 7 In the embodiment of the present invention Figure 6 Comparison of Raman characterization of regions A and B shown inside.

[0038] Figure 8 In the embodiment of the present invention Figure 6 Re 4f XPS characterization test pattern of the inner B region.

[0039] Figure 9 Calculation diagram of the heterojunction interface barrier of MoS2 / GaN (a) and Re-MoS2 / GaN (b) in the embodiments of the present invention.

[0040] Figure 10 Calculation diagram of the tunneling probability of Pt / MoS2 (a) and Pt / Re-MoS2 (b) in the embodiments of the present invention.

[0041] Figure 11 Schematic diagram of the structure of a two-dimensional MoS2 / Re-MoS2 lateral heterojunction on a GaN substrate prepared in an embodiment of the present invention. DETAILED DESCRIPTION

[0042] The present invention will be further described in detail below with reference to the examples, but the embodiments of the present invention are not limited thereto.

[0043] Example

[0044] An embodiment of the method for preparing a two-dimensional MoS2 / Re-MoS2 lateral heterojunction on a GaN substrate of the present invention is as follows:

[0045] 1. Take a SiO2 wafer (p-type, <100> Crystal orientation), cut it into multiple independent substrates of 1cm×1cm in size. At the same time, take a polar GaN wafer (n-type, c-plane crystal orientation) with a thickness of about 250nm and cut it into multiple independent substrates of 2cm×2cm in size;

[0046] 2. Clean the SiO2 and GaN substrates from step 1 separately as follows: First, place them in acetone at 85°C for 30 minutes, then transfer them to containers containing anhydrous ethanol and deionized water, and clean them in an ultrasonic cleaner (100kHz, 25°C) for 30 minutes. Finally, blow dry any remaining liquid on the surface with nitrogen gas, and then dry them naturally at 60°C for 15 minutes.

[0047] 3. Use a fine electronic balance to weigh 2.0 mg of MoO3 and NaCl, mix them evenly, weigh 150 mg of sulfur powder, and place it in a quartz crucible. Then take a clean quartz boat (5 cm long, 1.5 cm wide, 0.5 cm high, 1 mm thick), place the cleaned SiO2 substrate in step 2 on the left side of the quartz boat, and place the MoO3-NaCl mixture on the right side of the quartz boat, with a distance of about 3.0 cm between the two. Figure 1 As shown;

[0048] 4. Take a clean quartz tube (size 60×1400) and install it into the tube furnace. Push the quartz boat carrying the substrate in step 3 downstream and the quartz crucible containing sulfur powder upstream, with a distance of 20 cm between them. After confirming that the airtightness is good, turn on the vacuum pump until the pressure in the tube is about 0.01 Torr, and pass 200 sccm of argon gas to purge for 30 minutes. Finally, set the vacuum pump to increase the pressure in the tube to 150 Torr without stopping the ventilation. After completion, stop the argon gas flow;

[0049] 5. Follow Figure 2 The temperature rise program is set as shown and started. The downstream is heated to 780℃ within 20 minutes and then kept warm for 20 minutes. The upstream is delayed for 20 minutes and then heated to 200℃ within 20 minutes. 70sccm of carrier gas argon is introduced after 20 minutes of the program. After the program is completed, the temperature is naturally lowered to 600℃ without opening the top cover of the tubular furnace. After that, the top cover is opened and the temperature is quickly lowered to about 90℃ and the carrier gas is stopped. The prepared MoS2 is as shown in FIG. Figure 4 shown. Figure 5 Raman characterization showed that the distance between the two characteristic peaks was 18.24 cm -1 , which is a high-quality single-layer sample;

[0050] 6. Carefully weigh 1.0 mg of MoO₃, ReO₃, and NaCl and mix them evenly. Weigh 250 mg of sulfur powder and place it in a quartz crucible. Take another quartz boat, the same one used in step 3, and place the substrate prepared in step 5 on the left side of the boat. Cover its surface with the polished surface of a clean SiO₂ substrate. Place the MoO₃-ReO₃-NaCl mixture approximately 3.0 cm to the right of the substrate.

[0051] 7. Take the same clean quartz tube as in step 4 and install it in the tube furnace. Push the quartz boat containing the substrate downstream and the quartz crucible containing the sulfur powder upstream, 15 cm apart. After confirming that the tube is airtight, turn on the vacuum pump to a pressure of approximately 0.01 Torr inside the tube. Then, purge the tube with 200 sccm of argon gas for 30 minutes. Maintain this pressure and stop adding argon.

[0052] 8. Follow Figure 3 The temperature program is set up and started as shown. The downstream temperature is raised to 550℃ within 20 minutes and then kept at this temperature for 10 minutes. The upstream temperature is raised to 350℃ within 20 minutes and then kept at this temperature for 10 minutes. 100 sccm of carrier gas argon is introduced after 20 minutes of the program. After the program is completed, the temperature is naturally lowered to 400℃ without opening the top cover of the tube furnace. After that, the top cover is opened and the temperature is rapidly lowered to about 90℃, and the carrier gas is stopped. The results obtained are shown in the figure. Figure 6 As shown, regions A and B represent Re-MoS2 and MoS2 regions respectively. Figure 7 The Raman test shown shows that the characteristic peak in region A has a significant red shift compared to region B, indicating that Re atoms may be embedded in region A. Figure 8 The XPS test shown further illustrates the presence of Re atoms;

[0053] Take the sample substrate obtained in step 8, and use a coating machine to spin-coat a layer of PMMA on its surface (500 rpm for 6 s and then 3700 rpm for 30 s). Then transfer the substrate to a hydrofluoric acid solution and etch it naturally for 45 min. After the SiO2 substrate is completely etched, a clear PMMA layer is suspended on the surface. Use the clean GaN substrate obtained in step 2 to remove the PMMA layer from the hydrofluoric acid, transfer it to acetone, anhydrous ethanol and deionized water respectively, and let it stand for 30 min. After removal, dry it with a nitrogen gun, and the wet transfer of the substrate is completed, and a two-dimensional MoS2 / Re-MoS2 lateral heterojunction on the GaN substrate is obtained. Its structural diagram is shown as follows. Figure 11 As shown, (a) is a side view; (b) is a top view.

[0054] The first principles analysis of the two-dimensional MoS2 / Re-MoS2 lateral heterojunction on the GaN substrate prepared by the present invention is carried out, and the specific steps are as follows:

[0055] S1 constructed bulk GaN, Pt metal, single-layer MoS2 models and single-layer Re-MoS2 models in Material Studio software, where the concentration of Re atoms was 8.33 At%. To further describe the two-dimensional properties of the materials, a single-layer MoS2 and single-layer Re-MoS2 model was added in the c-plane direction. Vacuum layer;

[0056] S2 used the VASP program to optimize the structures of bulk GaN, Pt metal, single-layer MoS2 model, and single-layer Re-MoS2 model. The plane wave cutoff energy used was 400 eV, 240 eV, 260 eV, and 450 eV, respectively. The convergence criteria for both the electron step and the ion step were uniformly 1×10 6 eV and The sizes of the K grid points were 5 × 5 × 5, 5 × 5 × 5, 7 × 7 × 1, and 7 × 7 × 1, and the exchange-correlation functional used was the LDA function;

[0057] In step S3, the MoS2 / GaN and Re-MoS2 / GaN heterostructures are constructed in Material Studio using the optimized structure from step S2. The atomic positions of the GaN part are fixed, and pseudohydrogen is added to the bottom of the GaN to eliminate the effect of dangling bonds. When optimizing the two heterostructures in this step, the plane wave cutoff energy used is 350 eV, and the convergence criteria for both the electron step and the ion step are uniformly 1×10 5 eV and The size of the K grid points is 5 × 5 × 1, and the exchange-correlation functional uses the LDA function;

[0058] In step S4, the Pt / MoS2 and Pt / Re-MoS2 metal-semiconductor contact structures are constructed in Material Studio using the optimized structures from step S2. Prior to construction, the Pt unit cell basis vectors need to be modified to accommodate the hexagonal lattices of MoS2 and Re-MoS2. For the optimization of the two heterostructures in this step, a plane wave cutoff energy of 260 eV is used, and the convergence criteria for both the electron and ion steps are uniformly 1×10 5 eV and The size of the K grid points is 5 × 5 × 1, and the exchange-correlation functional uses the LDA function;

[0059] S5 uses the structure optimized in step S3 to calculate the barrier height of the MoS2 / GaN and Re-MoS2 / GaN heterojunctions. First, the electrostatic potential energy of MoS2, Re-MoS2 and the heterojunction along the c-axis is calculated using the VASP program and calculated according to the following formula:

[0060]

[0061] Where ΔV is the difference in the average electrostatic potential energy between A and B in the A / B heterostructure; and is the average electrostatic potential energy in the independent structures of A and B; E c and E F is the conduction band minimum of A and the Fermi level of B. The calculation diagram is as follows Figure 9 As shown in the results, the barrier heights of MoS2 / GaN and Re-MoS2 / GaN heterojunctions are 13.67eV and 13.20eV, respectively, which indicates that the introduction of Re atoms can reduce the heterojunction barrier height to a certain extent;

[0062] S5 uses the structure optimized in step S4 to calculate the interface barrier tunneling probability of the Pt / MoS2 and Pt / Re-MoS2 metal-semiconductor contact structures. First, the electrostatic potential energy of the MoS2, Re-MoS2 and metal-semiconductor contact structures along the c-axis is calculated using the VASP program and calculated according to the following formula:

[0063]

[0064] Among them, W B and ΔH are the barrier width and barrier height; is the reduced Planck constant, which is 6.58×10 -16 eV·S; m0 is the electron's static inertial mass, which is 9.11×10 -31 kg. The method of reading the potential barrier height and potential barrier width is as follows Figure 10 The settlement results show that the metal-semiconductor interface tunneling probability of Pt / MoS2 and Pt / Re-MoS2 is 9.67% and 19.71%, respectively, which indicates that the introduction of Re atoms alleviates the pinning effect to a certain extent and at the same time improves the tunneling mode for carriers to cross the potential barrier.

[0065] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing a two-dimensional MoS2 / Re-MoS2 lateral heterojunction on a GaN substrate, characterized in that: The following steps are involved: (1) Growth of MoS2 layer on SiO2 substrate: Place the clean SiO2 substrate on the left side of the quartz boat, mix the raw material MoO3 and the flux NaCl and place them on the right side of the quartz boat, and push them into the downstream of the quartz tube; put the sulfur powder into the quartz crucible and push it into the upstream of the quartz tube; The air in the quartz tube is exhausted, and a MoS2 layer is grown on the SiO2 substrate to obtain a SiO2 substrate with a MoS2 layer grown thereon; (2) Growing a Re-MoS2 layer on the side of the MoS2 layer prepared in step (1): Place the SiO2 substrate with the MoS2 layer on the left side of a new quartz boat, and cover the clean substrate on top of the SiO2 substrate with the MoS2 layer. Mix the raw materials rhenium source ReO3, molybdenum source MoO3 and flux NaCl and place them on the right side of the quartz boat, and push them all into the downstream of the new quartz tube; put sulfur powder into a quartz crucible and push it into the upstream of the quartz tube; The air in the quartz tube was exhausted, and a Re-MoS2 layer was grown on the side of the MoS2 layer to obtain a SiO2 substrate with a two-dimensional MoS2 / Re-MoS2 heterojunction: (3) Transferring the two-dimensional MoS2 / Re-MoS2 heterojunction to the GaN substrate surface: PMMA is spin-coated on the surface of the SiO2 substrate on which the two-dimensional MoS2 / Re-MoS2 heterojunction is grown, obtained in step (2), and the SiO2 substrate is etched in a hydrofluoric acid etchant. After observing that the PMMA layer floats above the etchant liquid surface, the GaN substrate is controlled to sink below the PMMA layer liquid surface, and the GaN substrate is pulled up to realize substrate transfer, thereby obtaining a two-dimensional MoS2 / Re-MoS2 lateral heterojunction on the GaN substrate.

2. The method for preparing a two-dimensional MoS2 / Re-MoS2 lateral heterojunction on a GaN substrate according to claim 1, characterized in that: In step (1), the mass ratio of the molybdenum source MoO3 to the flux NaCl is 1: (0.9-1.1).

3. The method for preparing a two-dimensional MoS2 / Re-MoS2 lateral heterojunction on a GaN substrate according to claim 2, characterized in that: The mass ratio of the molybdenum source MoO3 to sulfur powder is 1: (70-80).

4. The method for preparing a two-dimensional MoS2 / Re-MoS2 lateral heterojunction on a GaN substrate according to claim 3, characterized in that: The step (1) of growing a MoS2 layer on a SiO2 substrate is specifically as follows: The growth temperature is 780-800° C., the heating rate is 35-40° C. / min, the growth time is 20-25 min, the ambient pressure is 145-150 Torr, and the carrier gas Ar flow rate is 65-70 sccm.

5. The method for preparing a two-dimensional MoS2 / Re-MoS2 lateral heterojunction on a GaN substrate according to claim 4, characterized in that: The distance between the SiO2 substrate and the raw material is 2.8 to 3.0 cm, and the distance between the upstream and downstream vessels is 15 to 20 cm.

6. The method for preparing a two-dimensional MoS2 / Re-MoS2 lateral heterojunction on a GaN substrate according to claim 1, characterized in that: The mass ratio of the rhenium source ReO3, the molybdenum source MoO3 and the flux NaCl in step (2) is: 1: (0.9-1.1): (0.9-1.1).

7. The method for preparing a two-dimensional MoS2 / Re-MoS2 lateral heterojunction on a GaN substrate according to claim 6, characterized in that: The mass ratio of the molybdenum source MoO3 to sulfur powder is 1:(240-260).

8. The method for preparing a two-dimensional MoS2 / Re-MoS2 lateral heterojunction on a GaN substrate according to claim 6, characterized in that: The step (2) of growing a Re-MoS2 layer on the side of the MoS2 layer is specifically as follows: The growth temperature is 550-560° C., the heating rate is 25-30° C. / min, the growth time is 8-10 min, the ambient pressure is 0.01-0.02 Torr, and the carrier gas Ar flow rate is 70-80 sccm.

9. The method for preparing a two-dimensional MoS2 / Re-MoS2 lateral heterojunction on a GaN substrate according to claim 8, characterized in that: In step (2), the distance between the SiO2 substrate on which the MoS2 layer is grown and the raw material is 2.5 to 3.0 cm, and the distance between the upstream and downstream vessels is 15 to 20 cm.

10. The method for preparing a two-dimensional MoS2 / Re-MoS2 lateral heterojunction on a GaN substrate according to claim 9, characterized in that: In step (3), the SiO2 substrate is placed in a hydrofluoric acid etching solution and etched for 45 to 60 minutes.

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