Silicon carbide-based graphene lithium niobate composite material and preparation method thereof

Abstract

The invention relates to a silicon carbide-based graphene lithium niobate composite material and a preparation method thereof. The preparation method comprises the following steps: S1, pretreating a silicon carbide substrate; s2, growing a graphene buffer layer on the surface of the pretreated silicon carbide substrate through a high-temperature pyrolysis process; s3, hydrogen passivation is carried out, and the graphene buffer layer is converted into a near-free-state graphene layer; s4, preparing a lithium niobate film on the surface of the near-free-state graphene layer; and S5, annealing to obtain the silicon carbide-based graphene lithium niobate composite material. The graphene buffer layer is prepared through a high-temperature pyrolysis method, and covalent bond connection between the graphene buffer layer and the SiC substrate is broken through hydrogen passivation, so that the graphene buffer layer is converted into a near-free-state graphene layer, the requirement for direct growth of lithium niobate is met, high-quality and low-defect lithium niobate can be obtained through direct growth, and the preparation method is simple and low in cost.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor technology, and in particular relates to a silicon carbide-based graphene lithium niobate composite material and a preparation method thereof. Background Art

[0002] With the rise of the Internet of Things and the new era of 5G, people have put forward higher requirements for signal propagation, exploration and modulation. Photons have a faster response speed than electrons and have higher capacity and lower crosstalk in the field of information propagation, which makes optical integrated devices gradually become a hot topic of research.

[0003] Lithium niobate on insulator (LNOI) has a strong limiting effect on the light field due to its extremely thin lithium niobate film thickness, which can improve the efficiency of electro-optic modulation and has important applications in integrated electro-optic modulation devices and high-speed electro-optic switches. Silicon carbide (SiC) has good thermal conductivity. Choosing silicon carbide as the insulating substrate in LNOI can increase the heat dissipation during the application of the device. And as one of the representatives of the third generation of semiconductors, silicon carbide has a wide range of applications in the field of power electronics. It is relatively easy to integrate lithium niobate on silicon carbide into silicon carbide integrated devices, which helps to realize multifunctional silicon carbide integrated devices and has important research value.

[0004] The prior art transfers and bonds a lithium niobate film to a silicon carbide substrate through an ion slicing process. However, the ion slicing process is complex and costly, which greatly limits the application of lithium niobate on silicon carbide. Summary of the invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a silicon carbide-based graphene lithium niobate composite material and a preparation method thereof. The technical problem to be solved by the present invention is achieved by the following technical solutions:

[0006] A first aspect of the present invention provides a method for preparing a silicon carbide-based graphene lithium niobate composite material, comprising the following steps:

[0007] S1: pre-treating the silicon carbide substrate;

[0008] S2: growing a graphene buffer layer on the surface of the pretreated silicon carbide substrate through a high temperature pyrolysis process;

[0009] S3: performing hydrogen passivation to transform the graphene buffer layer into a nearly free-state graphene layer;

[0010] S4: preparing a lithium niobate film on the surface of the nearly free-state graphene layer;

[0011] S5: performing annealing to obtain a silicon carbide-based graphene lithium niobate composite material.

[0012] In one achievable manner, the pretreatment includes: chemical mechanical polishing, cleaning, and hydrogen etching performed in sequence.

[0013] In one achievable manner, the temperature of the hydrogen etching is 1400-1600°C.

[0014] In one achievable manner, the temperature of the high temperature pyrolysis process is 1400-1500° C. and the pressure is 300-500 mbar.

[0015] In one achievable manner, the temperature of the hydrogen passivation is 900-1000°C.

[0016] In an achievable manner, the high temperature pyrolysis process lasts for 50 to 60 minutes;

[0017] The thickness of the nearly free-state graphene layer is 2-4 nm.

[0018] In one achievable manner, the specific steps of S4 include:

[0019] A lithium niobate film is prepared on the surface of the nearly free-state graphene layer by a physical vapor deposition process or an ion slice process.

[0020] In one achievable manner, the specific steps of S4 include:

[0021] Growing a lithium niobate film on the surface of the nearly free-state graphene layer by a physical vapor deposition process;

[0022] The temperature of the physical vapor deposition process is 700-900° C., the sputtering atmosphere is argon or nitrogen, the sputtering power is 50-60W, and the sputtering time is 120-240 minutes.

[0023] In one achievable manner, the annealing temperature in S5 is 600-800° C., and the atmosphere is argon.

[0024] A second aspect of the present invention provides a silicon carbide-based graphene-lithium niobate composite material, comprising: a silicon carbide substrate, a nearly free-state graphene layer, and a lithium niobate film arranged in sequence from bottom to top.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The method for preparing a silicon carbide-based graphene lithium niobate composite material provided by the present invention comprises the following steps: preparing a graphene buffer layer by a high-temperature pyrolysis method, and disconnecting the covalent bond connection between the graphene buffer layer and the SiC substrate by hydrogen passivation, so that the graphene buffer layer is transformed into a nearly free-state graphene layer, thereby preventing the C-Si covalent bond formed between the graphene buffer layer and the SiC substrate from affecting the properties of the graphene, meeting the requirements for directly growing lithium niobate, being able to directly grow high-quality, low-defect lithium niobate, having a simple preparation method and low cost; and, graphene has a larger refractive index and can better constrain the light field propagating in the material. Compared with directly preparing lithium niobate on a SiC substrate, the silicon carbide-based graphene lithium niobate composite material can further improve the electro-optic modulation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a flow chart of the steps of a method for preparing a silicon carbide-based graphene lithium niobate composite material provided by an embodiment of the present invention;

[0028] Figure 2 It is a schematic structural diagram of a silicon carbide-based graphene lithium niobate composite material provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0030] Embodiment 1

[0031] See also Figure 1 , Figure 1 It is a flow chart of the steps of a method for preparing a silicon carbide-based graphene lithium niobate composite material provided by an embodiment of the present invention.

[0032] The present embodiment provides a method for preparing a silicon carbide-based graphene lithium niobate composite material, comprising the following steps:

[0033] S1: Pre-treating the silicon carbide substrate.

[0034] In this embodiment, the pretreatment includes: chemical mechanical polishing, cleaning and hydrogen etching performed in sequence. The temperature of hydrogen etching is 1400-1600°C.

[0035] Specifically, a SiC (0001) substrate was selected, chemical mechanical polishing was performed on the SiC substrate, and then concentrated sulfuric acid, aqua regia, hydrofluoric acid and deionized water were used to clean it in sequence. After cleaning, the SiC substrate was etched with hydrogen at a temperature of 1400-1600°C for 25 minutes to remove the damaged layer and scratches on the surface of the SiC substrate.

[0036] Exemplarily, the SiC substrate is etched with hydrogen at a temperature of 1600° C. for 25 minutes to remove the damaged layer and scratches on the surface of the SiC substrate.

[0037] S2: A graphene buffer layer is grown on the surface of the pretreated silicon carbide substrate through a high temperature pyrolysis process.

[0038] In this embodiment, the temperature of the high temperature pyrolysis process is 1400-1500° C., the pressure is 300-500 mbar, the time of the high temperature pyrolysis process is 50-60 min, and the thickness of the grown graphene buffer layer is 2-4 nm. The growth environment is an argon atmosphere.

[0039] Specifically, under high temperature and low pressure conditions, the crystal structure of the silicon carbide substrate changes, and the C atoms on the surface of the silicon carbide substrate gradually transform into a layered structure of graphite to generate graphene. A portion of the C atoms in the graphene buffer layer grown by the high temperature pyrolysis process provided in this embodiment combines with the Si atoms in the SiC substrate to form C-Si covalent bonds, that is, the graphene buffer layer and the SiC substrate are connected by C-Si covalent bonds.

[0040] Exemplarily, the growth environment is an argon atmosphere, the growth temperature is 1500°C, the growth pressure is 500 mbar (1 mbar = 100 Pa), the growth time is 50 min, and the silicon carbide substrate is subjected to high-temperature pyrolysis to form a graphene buffer layer. 30% of the C atoms in the graphene buffer layer obtained by the preparation method provided in this embodiment are combined with Si atoms in the SiC substrate to form C-Si covalent bonds.

[0041] S3: Perform hydrogen passivation to transform the graphene buffer layer into a nearly free-state graphene layer.

[0042] In this embodiment, the temperature of hydrogen passivation is 900-1000° C. The thickness of the nearly free-state graphene layer is 2-4 nm.

[0043] Specifically, the sample obtained in step S2 is exposed to a hydrogen environment at 900 to 1000°C for hydrogen passivation, so that the graphene buffer layer is transformed into a nearly free-state graphene layer. Furthermore, in a high-temperature hydrogen environment, H atoms are inserted between the graphene buffer layer and the SiC substrate, the C-Si covalent bond is broken, and the H atoms replace the C atoms to form H-Si bonds with the Si atoms in the SiC substrate, thereby realizing graphene passivation, disconnecting the covalent bond connection between the graphene buffer layer and the SiC substrate, so that the C atoms in the graphene are suspended on the surface of the SiC substrate to form a nearly free-state graphene layer, that is, the C atoms of the nearly free-state graphene layer are suspended on the surface of the silicon carbide substrate. It should be understood that during the hydrogen passivation process, the internal structure of the graphene does not change, only the C-Si covalent bond between the graphene and the SiC substrate is broken. Compared with the graphene buffer layer, the nearly free graphene layer breaks the C-Si covalent bond, thereby reducing interface scattering and long-range phonon scattering of the SiC substrate, greatly improving the electrical properties of graphene and increasing mobility.

[0044] Exemplarily, the sample obtained in step S2 is exposed to a hydrogen environment at 900° C. for hydrogen passivation to obtain a nearly free-state graphene layer.

[0045] S4: Preparing a lithium niobate film on the surface of a nearly free-state graphene layer.

[0046] In one achievable manner, the specific steps of S4 include:

[0047] A lithium niobate film is prepared on the surface of a nearly free-state graphene layer by a physical vapor deposition process or an ion slicing process.

[0048] Specifically, defects in lithium niobate optical devices will greatly reduce device performance. Therefore, reducing defects in lithium niobate materials is an important part of lithium niobate optical applications. Due to the large lattice constant mismatch between lithium niobate and SiC, it is difficult to directly grow high-quality, low-defect lithium niobate on SiC. Therefore, existing technologies transfer and bond lithium niobate films to the SiC surface through an ion slicing process. In addition, the thermal expansion coefficients of lithium niobate and SiC are quite different, which further increases the technical requirements for the ion slicing process.

[0049] Graphene has a larger refractive index than silicon carbide, and the higher high refractive index contrast can better constrain the light field propagating in the material, and graphene can play the role of a buffer layer, reducing the stress caused by lattice mismatch between silicon carbide and lithium niobate. In this embodiment, a graphene buffer layer is prepared by high-temperature pyrolysis, and the covalent bond connection between the graphene buffer layer and the SiC substrate is disconnected by hydrogen passivation, so that the graphene buffer layer is transformed into a nearly free-state graphene layer, avoiding the C-Si covalent bond formed between the graphene buffer layer and the SiC substrate from affecting the properties of graphene. Under the action of the nearly free-state graphene layer, the sample surface obtained in this embodiment S4 meets the requirements for direct growth of lithium niobate, and high-quality, low-defect lithium niobate can be directly grown. In addition, when lithium niobate is transferred and bonded to the sample surface obtained in this embodiment S4 by an ion slicing process, the bonding difficulty of lithium niobate and the sample obtained in this embodiment S4 is also much lower than directly transferring and bonding the lithium niobate film to the SiC surface.

[0050] In this embodiment, the specific steps of S4 include:

[0051] A lithium niobate film is grown on the surface of a nearly free-state graphene layer by a physical vapor deposition (PVD) process, wherein the temperature of the physical vapor deposition process is 700 to 900° C., the sputtering atmosphere is argon or nitrogen, the sputtering power is 50 to 60 W, and the sputtering time is 120 to 240 minutes.

[0052] Exemplarily, a lithium niobate film is grown on the surface of a nearly free-state graphene layer by a PVD process, wherein the sputtering atmosphere is an argon atmosphere, the growth temperature is 800° C., the sputtering power is 60 W, and the sputtering time is 240 min.

[0053] In this embodiment, only argon and hydrogen are needed in the high-temperature pyrolysis process and the hydrogen passivation process. The raw materials and processes are simple and the cost is low. The lithium niobate film can be directly prepared by the physical vapor deposition process. When preparing lithium niobate by physical vapor deposition, the stoichiometric ratio of the growing film can be controlled and a relatively low deposition temperature can be achieved. The overall process is simple and the cost is low. The prepared lithium niobate film is of high quality and good performance, and can better constrain the light field propagating in the material. Compared with directly preparing lithium niobate on a SiC substrate, the electro-optical modulation efficiency can be further improved.

[0054] S5: performing annealing to obtain a silicon carbide-based graphene lithium niobate composite material.

[0055] In this embodiment, the annealing temperature in S5 is 600-800°C, and the atmosphere is argon. Exemplarily, the annealing temperature is 800°C.

[0056] The second aspect of this embodiment provides a silicon carbide-based graphene lithium niobate composite material, see Figure 2 , Figure 2 Schematic diagram of the structure of a silicon carbide-based graphene lithium niobate composite material provided in an embodiment of the present invention. The silicon carbide-based graphene lithium niobate composite material provided in this embodiment includes: a silicon carbide substrate, a near-free graphene layer and a lithium niobate film arranged in sequence from bottom to top. Among them, the near-free graphene layer is obtained by hydrogen passivation of the graphene buffer layer, and the C atoms in the near-free graphene layer are suspended on the surface of the silicon carbide substrate.

[0057] The method for preparing the silicon carbide-based graphene lithium niobate composite material provided in this embodiment prepares the graphene buffer layer by high-temperature pyrolysis, and disconnects the covalent bond connection between the graphene buffer layer and the SiC substrate by hydrogen passivation, so that the graphene buffer layer is transformed into a nearly free-state graphene layer, avoiding the C-Si covalent bond formed between the graphene buffer layer and the SiC substrate from affecting the properties of the graphene, meeting the requirements for direct growth of lithium niobate, and being able to directly grow high-quality, low-defect lithium niobate, with a simple preparation method and low cost. In addition, graphene has a larger refractive index and can better constrain the light field propagating in the material. Compared with directly preparing lithium niobate on a SiC substrate, the silicon carbide-based graphene lithium niobate composite material can further improve the efficiency of electro-optical modulation.

[0058] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A method for preparing a silicon carbide-based graphene lithium niobate composite material, characterized in that: The following steps are involved: S1: pre-treating the silicon carbide substrate; S2: growing a graphene buffer layer on the surface of the pretreated silicon carbide substrate through a high temperature pyrolysis process; S3: performing hydrogen passivation to transform the graphene buffer layer into a nearly free-state graphene layer; S4: preparing a lithium niobate film on the surface of the nearly free-state graphene layer; S5: performing annealing to obtain a silicon carbide-based graphene lithium niobate composite material.

2. The method for preparing the silicon carbide-based graphene lithium niobate composite material according to claim 1, characterized in that: Preprocessing includes: Chemical mechanical polishing, cleaning and hydrogen etching are performed sequentially.

3. The method for preparing the silicon carbide-based graphene lithium niobate composite material according to claim 2, characterized in that: The temperature of the hydrogen etching is 1400-1600°C.

4. The method for preparing the silicon carbide-based graphene lithium niobate composite material according to claim 1, characterized in that: The temperature of the high temperature pyrolysis process is 1400-1500° C. and the pressure is 300-500 mbar.

5. The method for preparing the silicon carbide-based graphene lithium niobate composite material according to claim 1, characterized in that: The temperature of the hydrogen passivation is 900-1000°C.

6. The method for preparing the silicon carbide-based graphene lithium niobate composite material according to claim 1, characterized in that: The high temperature pyrolysis process takes 50 to 60 minutes; The thickness of the nearly free-state graphene layer is 2-4 nm.

7. The method for preparing the silicon carbide-based graphene lithium niobate composite material according to claim 1, characterized in that: The specific steps of S4 include: A lithium niobate film is prepared on the surface of the nearly free-state graphene layer by a physical vapor deposition process or an ion slice process.

8. The method for preparing the silicon carbide-based graphene lithium niobate composite material according to claim 1, characterized in that: The specific steps of S4 include: Growing a lithium niobate film on the surface of the nearly free-state graphene layer by a physical vapor deposition process; The temperature of the physical vapor deposition process is 700-900° C., the sputtering atmosphere is argon or nitrogen, the sputtering power is 50-60W, and the sputtering time is 120-240 minutes.

9. The method for preparing the silicon carbide-based graphene lithium niobate composite material according to claim 1, characterized in that: The annealing temperature in S5 is 600 to 800° C., and the atmosphere is argon.

10. A silicon carbide-based graphene lithium niobate composite material, characterized in that: include: The silicon carbide substrate, the nearly free-state graphene layer and the lithium niobate film are arranged in sequence from bottom to top.

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