Method for preparing homogeneous / heterojunction and realizing metal-semiconductor edge contact through optical manipulation

Abstract

The invention relates to a method for preparing a heterojunction and realizing metal-semiconductor edge contact by optical manipulation. When the material is excited by pulse laser, lattice units expand and contract to generate elastic waves. The elastic waves can carry enough momentum to enable the nanosheets to move on the dry substrate under the condition that the nanosheets are not uniformly illuminated. By using Gaussian beam irradiation, the nanosheets can stably move towards the center of the beam. By continuously changing the relative position between the nanosheet and the substrate, the nanosheet can freely move on the substrate. On the basis, the nanosheets made of different materials on the dry substrate are controlled to be close to each other and make contact with each other through pulse laser, or one nanosheet moves to the position above the other nanosheet, and a transverse heterojunction (homojunction) or a vertical heterojunction (homojunction) can be prepared. In addition, on the substrate with the prepared metal electrode, metal-semiconductor edge contact can be achieved by driving the nanosheet to make contact with the edge of the metal electrode, and the electrical performance of the device is improved.

Description

Technical Field

[0001] The present invention relates to the fields of optical manipulation and heterojunction preparation technology, and in particular to a method for preparing a heterojunction and a metal-semiconductor edge contact by optical manipulation. Technical Background

[0002] With the rapid development of technology, hetero (homo) junctions have shown great application potential in optoelectronics, microelectronics, and new energy fields, promoting the development of devices towards high efficiency and low energy consumption. The preparation of hetero (homo) junctions mainly relies on the combination of materials to form superior electronic and optoelectronic properties. These structures usually have good carrier transport properties, which can effectively improve the efficiency and performance of devices. The main methods for preparing heterojunctions are mechanical stacking, chemical vapor deposition, and molecular beam epitaxy, etc. By precisely controlling growth conditions such as temperature, doping concentration, and growth rate, the preparation of heterojunctions can be achieved. However, these preparation methods have disadvantages such as complex processes or surface contamination, and the preparation of lateral heterojunctions is currently mainly achieved through chemical vapor deposition, which involves a complex growth process, and differences in various parameters will cause differences in device performance. These challenges make it difficult to achieve large-scale and high-quality heteroepitaxial integration. Therefore, there is an urgent need for a new method for preparing heterojunctions that can be easily implemented and prepared on a large scale.

[0003] In addition, the realization of heterointegration of metal-semiconductors can enable applications such as field-effect transistors, photodetectors, and neuromorphic devices. However, due to the ultra-thin structure of two-dimensional materials, the device is easily affected by the interface between the two-dimensional material and the metal contact. Due to its easy implementation, top contact has become the most commonly used contact method, but due to the existence of van der Waals air gaps, conventional metal-two-dimensional semiconductor contacts have problems such as poor stability, high contact resistance, and low on-state current density, which greatly limit the device performance. Compared with top contact, strong orbital overlap, no SB, and lower tunneling barriers are all advantages of the edge contact structure. Therefore, edge contact has higher electron injection ability, thereby reducing the contact resistance. The manufacturing complexity of edge contact has brought continuous challenges, which has prompted a large amount of research to improve its performance, such as the combination of reactive ion etching, in-situ Ar ion sputtering, and annealing, etc. However, etching may cause serious damage to the contact, such as defects and etching residues at the metal / TMD interface. In addition, the time delay between the trench etching and the metal deposition steps and exposure to an uncontrolled environment will greatly reduce the device performance, and the lattice structure of two-dimensional materials is extremely vulnerable to damage during the high-energy metal evaporation process. Therefore, developing a new method for realizing metal-semiconductor edge contact is of great significance for preparing optoelectronic devices with excellent performance. Summary of the Invention

[0004] In view of the problems of complex processes, long preparation time, and high costs in the preparation of traditional heterojunctions and the realization of metal-semiconductor edge contacts, a method for preparing heterojunctions and realizing metal-semiconductor edge contacts by optical manipulation is proposed. When a pulsed laser is perpendicularly irradiated on the surface of a two-dimensional material, the material absorbs light and rapidly heats up within a few nanoseconds, and the lattice units expand and contract to form elastic acoustic waves. When the temperature rise of the irradiated nanosheet is asymmetric, the thermal stress inside the nanosheet is also asymmetric, resulting in a non-zero net momentum carried by the acoustic waves, thereby driving the nanosheet to move freely on the substrate surface. By continuously changing the position of the substrate or the light beam, the continuous movement of the nanosheet on the substrate surface can be manipulated. By using a pulsed laser to drive different nanosheets pre-deposited on the substrate to approach and contact / stack with each other, heterojunctions can be effectively prepared or metal-semiconductor edge contacts can be realized.

[0005] To achieve the above objectives, the present invention is realized through the following technical solutions:

[0006] A method for preparing a hetero (homo) junction by optical manipulation, which uses a pulsed laser to manipulate different types of nanosheets on a substrate to approach and contact / stack, includes the following steps:

[0007] (1) Prepare samples of the first material into several small nanosheets by mechanical exfoliation or other means, and deposit them on the target substrate.

[0008] (2) Prepare samples of the second material into several small nanosheets by mechanical exfoliation or other means, and deposit them on the same substrate as above.

[0009] (3) Select a certain nanosheet that meets the preparation requirements from each of the two (same) materials as the target nanosheet, and select an appropriate laser wavelength according to the absorption characteristics of the two materials.

[0010] (4) Use the laser to drive the two nanosheets to approach each other or one to approach the other, until their edges come into contact or stack.

[0011] (5) Select an appropriate temperature and perform thermal annealing in a protective gas atmosphere to enhance material contact and realize the preparation of lateral hetero (homo) junctions or vertical hetero (homo) junctions.

[0012] A method for realizing metal-semiconductor edge contact by optical manipulation, which uses a pulsed laser to manipulate a nanosheet to approach and contact the edge of a pre-deposited metal structure, includes the following steps:

[0013] (1) Prepare the metal structure to be contacted on the target substrate.

[0014] (2) Prepare samples of the material into several small nanosheets by mechanical exfoliation or other means, and deposit them on the same substrate as above.

[0015] (3) Select one of the nanosheets as the target nanosheet and choose an appropriate laser wavelength according to the absorption characteristics of the nanosheet.

[0016] (4) Use the laser to drive the nanosheet close to the metal structure and make it contact with its edge.

[0017] (5) Select an appropriate temperature and perform thermal annealing in a protective gas atmosphere to enhance material contact and achieve edge contact between the metal and the semiconductor.

[0018] Optionally, the laser is a femtosecond laser, and the pulse repetition frequency is adjustable within the range of 1 Hz - 100 kHz, but not limited to this. Any laser that can generate pulsed laser meets the requirements.

[0019] Optionally, the laser wavelength is 1040 nm, but not limited to this. Any wavelength within the strong absorption range of the driven nanosheet meets the requirements.

[0020] Optionally, the shape of the nanosheet can be arbitrary. The size of the driven nanosheet is 2 - 20 μm, and the thickness is between a few nanometers and a hundred nanometers.

[0021] Optionally, the nanosheet needs to have a high light absorption coefficient and a high coefficient of thermal expansion.

[0022] Optionally, the method for preparing the nanosheet is mechanical exfoliation, but not limited to this. Any method that can prepare nanosheets, such as chemical vapor deposition and liquid-phase exfoliation, meets the requirements.

[0023] Optionally, the nanosheet can be cut using a focused laser beam to trim the shape and expand the area of edge contact.

[0024] Optionally, the substrate needs to be a dry and rigid substrate with a smooth surface.

[0025] Optionally, the annealing temperature is 100 - 400 °C, but not limited to this. Any annealing temperature that does not change the material properties meets the requirements.

[0026] Optionally, the protective gas can be argon or nitrogen, but not limited to this. Any gas that can protect the material from chemical transformation during annealing meets the requirements.

[0027] The beneficial effects of the present invention are as follows:

[0028] The present invention relates to a method for preparing heterojunctions and metal-semiconductor edge contacts using optical manipulation. The manipulation device and method are simple, easy to set up, time-consuming in preparation, capable of driving various materials on a substrate, and thus can be used for the synthesis of various heterostructures. It has high tunability, can arbitrarily adjust the contact area or length of two materials, has high manipulation precision, is not limited by the type of substrate, and does not cause damage to the materials, with a wide range of applications. It does not require the complex processes and long cycles of traditional heterojunction and metal-semiconductor edge contact preparation, and overcomes the drawback of non-adjustable contact areas in traditional structure preparation, can precisely control the movement of materials, and achieve the preparation of target structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a flow chart of the method for preparing heterojunctions and achieving metal-semiconductor edge contact by optical manipulation according to the present invention;

[0030] Figure 2 It is an optical sequence diagram for preparing vertical homojunctions by optical manipulation according to the present invention. (a) is a position diagram of two nanosheets at the initial time t0, and (b) is a position diagram after the laser drives nanosheet 1 to move above nanosheet 2 to form a vertical homojunction at time t1;

[0031] Figure 3 It is an optical sequence diagram for preparing lateral homojunctions by optical manipulation according to the present invention. (a) is a position diagram of two nanosheets at the initial time t0, and (b) is a position diagram after the laser drives the two nanosheets to approach each other and form a lateral homojunction at time t1;

[0032] Figure 4 It is an optical sequence diagram for preparing heterojunctions by optical manipulation according to the present invention. (a) is a position diagram of two nanosheets at the initial time t0, (b) is a position diagram after the laser drives the VSe2 nanosheet to move at time t1, and (c) is a position diagram after the laser drives the MoTe2 nanosheet to move and contact the VSe2 nanosheet at time t2;

[0033] Figure 5 It is an optical sequence diagram for preparing edge contact between two-dimensional materials and metal structures by optical manipulation according to the present invention. (a) is a position diagram of the nanosheet at the initial time t0, and (b) is a position diagram after the laser drives the VSe2 nanosheet to move and contact the edge of the Au structure at time t1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art shall fall within the protection scope of the present invention.

[0035] In the present invention, by utilizing the high light absorption and large thermal expansion coefficient of the material, when a pulsed laser irradiates the surface of the material, the material absorbs light to generate thermal expansion, and the thermal stress caused by the thermal expansion will generate surface acoustic waves, which will carry sufficient momentum to move the nanosheets on the substrate surface. Based on this, a pulsed laser is used to drive different materials pre-deposited on the substrate to approach, stack or contact each other, and then thermal annealing is carried out to enhance the contact between the materials, so that vertical or lateral hetero (homo) junctions can be successfully fabricated, and metal-semiconductor edge contact can also be achieved.

[0036] As Figure 1 shown in the flowchart of the method for fabricating hetero-junctions and realizing metal-semiconductor edge contact by optical manipulation, a method for fabricating hetero-junctions by optical manipulation and a method for realizing metal-semiconductor edge contact by optical manipulation are briefly introduced.

[0037] The method for fabricating hetero (homo) junctions by optical manipulation uses a pulsed laser to manipulate different types of nanosheets on the substrate to approach and contact / stack, and includes the following steps:

[0038] (1) Prepare samples of the first material into several small nanosheets by mechanical exfoliation or other means, and deposit them on the target substrate;

[0039] (2) Prepare samples of the second material into several small nanosheets by mechanical exfoliation or other means, and deposit them on the same substrate as above;

[0040] (3) Select a certain qualified nanosheet of each of the two (same) materials as the target nanosheet, and select an appropriate laser wavelength according to the absorption characteristics of the two materials;

[0041] (4) Use the laser to drive the two nanosheets to approach each other or one to approach the other, so that their edges are in contact or stacked;

[0042] (5) Select an appropriate temperature and perform thermal annealing in a protective gas atmosphere to enhance the material contact and realize the fabrication of lateral hetero (homo) junctions or vertical hetero (homo) junctions.

[0043] The method for realizing metal-semiconductor edge contact by optical manipulation uses a pulsed laser to manipulate the nanosheets to approach and contact the edge of the pre-deposited metal structure, and includes the following steps:

[0044] (1) Fabricate the metal structure to be contacted on the target substrate;

[0045] (2) Prepare samples into several small nanosheets by mechanical exfoliation or other means, and deposit them on the same substrate as above;

[0046] (2) Select one of the nanosheets as the target nanosheet and select an appropriate laser wavelength according to the absorption characteristics of the nanosheet;

[0047] (4) Use the laser to drive the nanosheet close to the metal structure and contact its edge;

[0048] (5) Select an appropriate temperature and perform thermal annealing in a protective gas atmosphere to enhance material contact and achieve edge contact between the metal and the semiconductor.

[0049] In some embodiments, the laser is a femtosecond laser, and the pulse repetition frequency is adjustable in the range of 1 Hz - 100 kHz, but not limited thereto. Any laser that can generate pulsed laser satisfies the conditions.

[0050] In some embodiments, the laser wavelength is 1040 nm, but not limited thereto. Any wavelength within the absorption range of the driven nanosheet satisfies the conditions.

[0051] In some embodiments, the shape of the nanosheet can be arbitrary. The size of the driven nanosheet is 2 - 20 μm, and the thickness is between a few nanometers and one hundred nanometers.

[0052] In some embodiments, the nanosheet needs to have a high light absorption coefficient and a high coefficient of thermal expansion.

[0053] In some embodiments, the method for preparing the nanosheet is mechanical exfoliation, but not limited thereto. Any method capable of preparing nanosheets, such as chemical vapor deposition and liquid-phase exfoliation, satisfies the conditions.

[0054] In some embodiments, the nanosheet can be cut using a focused laser beam to trim the shape and expand the area of the edge contact.

[0055] In some embodiments, the dry substrate is made of sapphire, silicon, or quartz, but not limited thereto. Any rigid substrate with a smooth surface satisfies the conditions.

[0056] In some embodiments, the annealing temperature is 100 - 400 °C, but not limited thereto. Any annealing temperature that does not change the material properties satisfies the conditions.

[0057] In some embodiments, the protective gas can be argon or nitrogen, but not limited thereto. Any gas that can protect the material from chemical transformation during annealing satisfies the conditions. Specific Example 1:

[0059] Optical operation for preparing a vertical homojunction:

[0060] Figure 2This is the optical sequence diagram for optically controlling the preparation of a vertical homojunction in the present invention. A number of VSe2 nanosheets are pre-deposited on a sapphire substrate by mechanical exfoliation. Select the nanosheet 1 to be driven and the nanosheet 2 for preparing the homojunction as the target nanosheets. Under laser irradiation with a wavelength of 1040 nm, a pulse width of 380 fs, a spot diameter of 10 μm, a pulse repetition frequency of 1 kHz, and a laser energy of 2 nJ, the nanosheet 1 can be continuously driven by the laser to near the nanosheet 2. When the nanosheet 2 is relatively thin, under the further driving of the laser, the nanosheet 1 can move above the nanosheet 2, generating a stacked area in the vertical direction, that is, forming a vertical homojunction. Specific Example 2:

[0062] Optically controlling the preparation of a lateral homojunction:

[0063] Figure 3 This is the optical sequence diagram for optically controlling the preparation of a lateral homojunction in the present invention. A number of VSe2 nanosheets are pre-deposited on a sapphire substrate by mechanical exfoliation. Select the nanosheet 1 and the nanosheet 2 to be driven and for preparing the homojunction as the target nanosheets. Under laser irradiation with a wavelength of 1040 nm, a pulse width of 380 fs, a spot diameter of 10 μm, a pulse repetition frequency of 1 kHz, and a laser energy of 2 nJ, drive the nanosheet 1 to approach the nanosheet 2, and then drive the nanosheet 2 to move towards the nanosheet 1. Adjust the angle between the two nanosheets with a light beam, and finally achieve the edge contact of the two nanosheets, forming a lateral hetero (homo) junction. Specific Example 3:

[0065] Optically controlling the preparation of a heterojunction:

[0066] Figure 4 This is the optical sequence diagram for optically controlling the preparation of a heterojunction in the present invention. Deposit VSe2 nanosheets on a sapphire substrate by mechanical exfoliation, and then deposit MoTe2 nanosheets in the same area of the substrate in the same way. Select a VSe2 nanosheet and a MoTe2 nanosheet with appropriate sizes and close distances as the target nanosheets respectively. Use a light beam with a wavelength of 1040 nm, a pulse width of 380 fs, a spot diameter of 10 μm, a pulse repetition frequency of 1 kHz, and a laser energy of 2 nJ to drive the VSe2 nanosheet to move a certain distance towards the MoTe2 nanosheet; then use a light beam with a pulse repetition frequency of 2 kHz and a laser energy of 3.75 nJ to drive the MoTe2 nanosheet to move towards the VSe2 nanosheet and finally make its edge contact, at this time, a lateral heterojunction is successfully prepared. Specific Example 4:

[0068] Controlling the nanosheet to approach and contact the edge of the metal structure:

[0069] Figure 5This is the optical sequence diagram of the edge contact between the nanosheets and the metal structure of the present invention. First, the metal structure is deposited on the substrate by using photolithography technology and magnetron sputtering technology. Then, several VSe2 nanosheets are deposited on the substrate by mechanical exfoliation. One VSe2 nanosheet to be driven is selected as the target nanosheet. Under the irradiation of a laser with a wavelength of 1040 nm, a pulse width of 380 fs, a spot diameter of 10 μm, a pulse repetition frequency of 1 kHz, and a laser energy of 2 nJ, the VSe2 nanosheet gradually approaches and contacts the metal edge, forming a metal-semiconductor edge contact.

[0070] The present invention is not limited to the above-mentioned optimal implementation mode. Any person can obtain other various forms of products under the inspiration of the present invention. However, no matter what changes are made in its shape or structure, as long as it has the same or similar technical solutions as the present application, it falls within the protection scope of the present invention.

Claims

1. A method for preparing a homo / heterojunction by optical manipulation, characterized in that Using pulsed laser to manipulate the approach, contact or stacking of the same or different types of nanosheets on a substrate, including the following steps: (1) Prepare a number of small pieces of nanosheets from a material sample by means of mechanical exfoliation or the like, and deposit them on a target substrate; (2) When preparing a heterojunction, repeat step (1) using a second different material; (3) Select one of the same or two different materials that meets the preparation requirements as the target nanosheet respectively, and select a suitable laser wavelength according to the absorption characteristics of the nanosheet; (4) Use the laser to drive the two target nanosheets to approach each other or one to approach the other, until their edges are in contact or stacked; (5) Select a suitable temperature and perform thermal annealing in an inert gas atmosphere to enhance material contact and achieve the preparation of lateral homo / heterojunctions or vertical homo / heterojunctions.

2. A method for achieving metal-semiconductor edge contact by optical manipulation, characterized in that, Using pulsed laser to manipulate the approach of a nanosheet to the edge of a pre-deposited metal structure and contact it, including the following steps: (1) Prepare the metal structure to be contacted on a target substrate; (2) Prepare a number of small pieces of nanosheets from a semiconductor sample by means of mechanical exfoliation or the like, and deposit them on the same target substrate as above; (3) Select one of the nanosheets that meets the preparation requirements as the target nanosheet, and select a suitable laser wavelength according to the absorption characteristics of the nanosheet; (4) Use the laser to drive the target nanosheet to approach the metal structure and contact its edge; (5) Select a suitable temperature and perform thermal annealing in an inert gas atmosphere to enhance material contact and achieve the edge contact of metal-semiconductor.

3. The method according to claim 1 or 2, characterized in that, The pulsed laser is a femtosecond laser, and the pulse repetition frequency is adjustable in the range of 1 Hz - 100 kHz, but not limited to this. Others that can generate the pulsed laser also meet the conditions.

4. The method according to claim 1 or 2, characterized in that, The wavelength of the pulsed laser is 1040 nm, but not limited to this. As long as the wavelength is within the strong absorption range of the driven target nanosheet, it meets the conditions.

5. The method according to claim 1 or 2, characterized in that, The shape of the nanosheet can be arbitrary. The size of the driven nanosheet is 2 - 20 μm, and the thickness is between a few nanometers and a hundred nanometers.

6. The method according to claim 1 or 2, characterized in that The nanosheet needs to have a high light absorption coefficient and a high coefficient of thermal expansion.

7. The method according to claim 1 or 2, characterized in that, The method for preparing the nanosheet is mechanical exfoliation, but not limited to this. Chemical vapor deposition, liquid exfoliation and other methods that can prepare nanosheets also meet the conditions.

8. The method according to claim 1 or 2 or 7, characterized in that The nanosheet can be cut using a focused laser beam to achieve shape trimming and expand the area of edge contact.

9. The method according to claim 1 or 2, characterized in that The substrate needs to be a dry, smooth and rigid substrate.

10. The method according to claim 1 or 2, characterized in that, The annealing temperature is 100 - 400 °C, but not limited to this. Annealing temperatures that do not change the material properties also meet the conditions.

11. The method according to claim 1 or 2, characterized in that, The inert gas can be argon or nitrogen, but not limited to this. Gases that can protect the material from chemical transformation during annealing also meet the conditions.

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