A design method for Weyl semimetal material devices based on bias voltage regulation

Abstract

The present invention discloses a design method for a Weyl semimetal material device based on bias voltage regulation. The present invention reveals the correlation between the optoelectronic properties of the Weyl semimetal material and the bias voltage. By using first-principles calculations to obtain the energy band diagram, density of states diagram, and photocurrent magnitude of the Weyl semimetal material, it indirectly illustrates the relationship between the optoelectronic properties of the Weyl semimetal material device and electron energy band transitions, visually shows the magnitude of the photocurrent of the device under different bias voltages, and lays a theoretical foundation for the means of bias voltage regulation in related fields of device applications.

Description

Technical Field

[0001] The present invention relates to the field of two-dimensional material analysis and characterization, and particularly to a design method for Weyl semimetal material devices based on bias voltage regulation. Background Art

[0002] In recent years, following the rise of layered graphene, researchers have been dedicated to the exploration of two-dimensional layered materials. Weyl semimetal is another research hotspot after graphene and topological insulators. Compared with the latter, the unique three-dimensional gapless linear dispersion energy band structure of Weyl semimetal endows it with many peculiar properties, such as chiral anomaly, chiral magnetic effect, weak anti-localization, chiral Landau levels, and negative magnetoresistance effect, etc. Weyl semimetal has broadband photon absorption ability, high absorption coefficient, and high carrier mobility (comparable to graphene at room temperature), which makes Weyl semimetal widely used in optoelectronics, electronic communication, aerospace medicine and other fields.

[0003] In optoelectronic devices of low-dimensional materials, optoelectronic devices can directly convert photon energy into electrical signals and play an important bridging role in electronics and photonics. However, due to the small photocurrent generated by Weyl semimetal material devices under light illumination, it cannot meet the requirements of industrial production. Therefore, increasing the photocurrent of Weyl semimetal material devices through appropriate regulation means to achieve better optoelectronic performance has become a key problem to be solved urgently at present. Summary of the Invention

[0004] Aiming at the problems existing in the above technologies, the present invention provides a design method for Weyl semimetal material devices based on bias voltage regulation, revealing the correlation between the optoelectronic properties of Weyl semimetal materials and bias voltage. By calculating the energy band diagram, density of states diagram, and photocurrent magnitude of Weyl semimetal materials through first-principles, it indirectly illustrates the relationship between the optoelectronic properties of Weyl semimetal material devices and electronic energy band transitions, intuitively shows the photocurrent magnitude of the device under different bias voltages, and lays a theoretical foundation for the application of bias voltage regulation means in related fields of device applications.

[0005] In order to achieve the above object, the present invention provides a design method for Weyl semimetal material devices based on bias voltage regulation, which specifically comprises the following steps:

[0006] S1. Construct a Weyl semimetal material device model;

[0007] S2. Calculate the optoelectronic properties of the established Weyl semimetal material device model;

[0008] S3. Analyze and process the calculation results.

[0009] The specific content of step S1 is as follows:

[0010] S11. First, consult literature materials, construct a model of the primitive cell of the Weyl semimetal material, and optimize its structure. Second, reproduce its band structure to prove the accuracy of the primitive cell structure of the Weyl semimetal material. After that, perform a cell expansion operation on the optimized primitive cell model of the Weyl semimetal material to obtain the central region of the device model of the Weyl semimetal material. Select a certain material as the electrode material of the device model of the Weyl semimetal material, and construct the device model of the Weyl semimetal material.

[0011] The specific steps of step S11 are as follows:

[0012] Based on the first-principles study of density functional theory, use crystal structure visualization software to model the Weyl semimetal material, that is, the device model of the Weyl semimetal material;

[0013] The crystal structure visualization software used is Device Studio software to build the primitive cell and device model of the Weyl semimetal material.

[0014] The specific steps of step S2 are as follows:

[0015] S21. According to the characteristics of the Weyl semimetal material, the direction and magnitude of the applied bias voltage, set the input self-consistent file, and perform self-consistent calculations on the device model of the Weyl semimetal material;

[0016] S22. After the self-consistent calculation is completed, set the relevant parameters for the photocurrent calculation according to the type of polarized light selected, the photon energy range, the photon interval, the incident angle, and the number of illuminated atoms to obtain the input file of the photocurrent.

[0017] The specific steps of step S22 are as follows:

[0018] Based on the first-principles calculation method of non-equilibrium Green's function - density functional theory, use quantum transport calculation software to perform self-consistent, transmission spectrum, photocurrent, etc. calculations on the built device model of the Weyl semimetal material;

[0019] S23. Calculate the photocurrent file to obtain the photocurrent magnitude at different photon energies;

[0020] S24. By changing the magnitude of the bias voltage, obtain the photocurrent magnitude of the device model of the Weyl semimetal material under different bias voltages.

[0021] The specific steps of step S3 are as follows:

[0022] S31. Obtain the relevant information of the bond length, bond angle, and lattice constant of the established primitive cell model of the Weyl semimetal material through the crystal structure visualization software;

[0023] S32. Plot the energy band structure diagram, charge density diagram, density of states diagram of the primitive cell model of the Weyl semimetal material, and the transmission spectrum diagram and the diagram of photocurrent varying with photon energy of the Weyl semimetal material device model;

[0024] S33. Analyze the relationship between the change in photocurrent of the Weyl semimetal material device model and the applied bias voltage under the condition of applying a bias voltage.

[0025] The beneficial effects of the present invention are as follows:

[0026] Based on the first-principles calculation of density functional theory, the present invention uses the non-equilibrium Green's function method. Only by knowing the types of elements and the basic crystal structure of the Weyl semimetal material, the energy band, density of states of the primitive cell of the Weyl semimetal material, and properties such as the transmission spectrum and optoelectronic properties of the Weyl semimetal material device can be calculated without other information;

[0027] The present invention reveals the variation law of the optoelectronic properties of the Weyl semimetal material device under the condition of applying a bias voltage, provides a theoretical reference for the bias voltage regulation of the outer semimetal material device, and also provides a necessary supplement for the development of experiments;

[0028] The present invention adopts the calculation method of first principles. This method has accurate calculations, only requires high-performance computer equipment, does not require other expensive experimental materials, greatly reduces the research cost, has high efficiency, and is safe and risk-free during the implementation process. Description of the Drawings

[0029] Figure 1 It is a flow chart of the specific implementation method of the present invention;

[0030] Figure 2 It is the primitive cell diagram of the Weyl semimetal material of the present invention;

[0031] Figure 3(a) is a front view of the Weyl semimetal material device model;

[0032] Figure 3(b) is a top view of the Weyl semimetal material device model;

[0033] Figure 3(c) is a front view of the Weyl semimetal material device with vertically polarized light applied.

[0034] Figure 4 It is a data diagram of photocurrent varying with photon energy under the action of different bias voltages.

[0035] Embodiment

[0036] To make the objectives, implementation methods, technical steps, and advantages of the embodiments of the present invention clearer and more explicit, the present invention will be further described in detail below in combination with the accompanying drawings and specific implementation methods of the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention, not all of them.

[0037] The present invention will be further described clearly and completely below in combination with the accompanying drawings and specific implementation methods of the embodiments of the present invention.

[0038] Referring to the attached Figure 1 As shown, the present invention proposes a design method for a Weyl semimetal material device based on bias voltage regulation, and the specific implementation steps are as follows:

[0039] S1. Construct a Weyl semimetal device model

[0040] The present invention is a first-principles research based on density functional theory. With the help of crystal structure visualization software, the Weyl semimetal material and device are modeled. First, consult the literature, model the primitive cell of the Weyl semimetal material, perform relaxation calculations, optimize the structure of the primitive cell, calculate the band diagram of the optimized primitive cell structure, and perform parameter debugging to reproduce the previous research band diagram to ensure the accuracy of the established primitive cell model. Secondly, calculate the electronic properties of the accurate primitive cell model. After that, expand the primitive cell model of the Weyl semimetal to obtain the device central region, select a suitable material as the electrode material, and construct the optoelectronic device model of the Weyl semimetal. The primitive cell model of the Weyl semimetal material refers to the attached Figure 2 As shown, the Weyl semimetal material device model refers to Figures 3(a), 3(b), and 3(c). Among them, Figure 3(a) is the front view of the Weyl semimetal material device model; Figure 3(b) is the top view of the Weyl semimetal material device model; Figure 3(c) is the front view of the Weyl semimetal material device with vertically polarized linear light applied.

[0041] In the present invention, copper is selected as the electrode material because metallic copper has good electrical conductivity, heat transfer performance, stable performance, cold resistance, heat resistance, corrosion resistance, can be used in different environments for a long time, and its price is much lower than that of gold and silver materials, and it has a good matching degree with the central region material.

[0042] Among them, the crystal structure visualization software used is Device Studio software to build the primitive cell and device model of the Weyl semimetal material.

[0043] The calculation process of the electronic properties of the primitive cell of the Weyl semimetal material is as follows:

[0044] First, perform band structure calculations on the primitive cell to obtain the band structure of the primitive cell and ensure the accuracy of the structure. Then, perform calculations of the density of states and phonon spectrum to obtain the band structure diagram, density of states diagram, and phonon spectrum diagram of the primitive cell, and more clearly and intuitively obtain the electronic properties of the Weyl semimetal primitive cell.

[0045] S2. Calculate the optoelectronic properties of the established Weyl semimetal material device model;

[0046] The present invention is a first-principles calculation method based on the non-equilibrium Green's function - density functional theory. With the help of quantum transport calculation software, self-consistent and photocurrent calculations are performed on the established Weyl semimetal material device model. First, perform self-consistent calculations on the Weyl semimetal material device model. First, perform self-consistent calculations on the two electrodes, and then perform self-consistent calculations on the central region to obtain a file containing the self-consistent results and the total calculated energy. Second, after the self-consistent calculations are completed, set the relevant parameters for photocurrent calculations according to the type of polarized light selected, the photon energy range, the photon interval, the incident angle, and the number of illuminated atoms to obtain the input file for photocurrent calculations. After the photocurrent calculations are completed, obtain the magnitudes of the photocurrent at different photon energies. Finally, by changing the magnitude of the bias voltage, obtain the magnitudes of the photocurrent of the Weyl semimetal material device model under different bias voltages.

[0047] The quantum transport calculation software used is Nanodcal software to calculate the optoelectronic properties of the Weyl semimetal material device. Nanodcal software is a first-principles calculation software based on the non-equilibrium Green's function combined with density functional theory (NEGF-DFT), which can predict many transport properties such as the current-voltage characteristics and electron transmission probability of materials, and is a general software for calculating transport properties and optoelectronic properties.

[0048] Among them, the calculation of the photocurrent magnitude takes the magnitude of the applied bias voltage as a variable to investigate the influence of this variable on the photocurrent magnitude of the Weyl semimetal material device.

[0049] S3. Analyze and process the calculation results.

[0050] Optimize the structure of the Weyl semimetal material primitive cell model through crystal structure visualization software to obtain relevant information such as the lattice constant of the primitive cell; draw the band structure diagram, charge density diagram, density of states diagram of the established Weyl semimetal material primitive cell, and the transmission spectrum diagram and photocurrent vs. photon energy diagram of the Weyl semimetal material device model; analyze the relationship between the change in the photocurrent of the Weyl semimetal material device and the applied bias voltage under the condition of applying a bias voltage; provide a theoretical reference for bias voltage regulation of the outer semimetal optoelectronic device.

[0051] In this embodiment, taking the applied bias voltage range of 0 - 1.0 V as an example, by calculating the photocurrent magnitude of the Weyl semimetal material device, with the magnitude of the applied bias voltage as a variable, the influence of this variable on the photocurrent magnitude of the Weyl semimetal material device is investigated.

[0052] Step 1: Read the relevant data of the Weyl semimetal material from the literature, and based on the data, use crystal structure visualization software to model the primitive cell of the Weyl semimetal material. Among them, the structural data of the primitive cell of the Weyl semimetal material is shown in Table 1:

[0053] Table 1

[0054]

[0055]

[0056] After that, based on the above data, use crystal structure visualization software to model the primitive cell of the Weyl semimetal material. After the modeling is completed, perform relaxation calculations to further optimize the model structure. Adopt the generalized-gradient approximation (GGA - PBE). In the reciprocal lattice vector space, the cutoff energy is taken as 100 Hartree, and the reciprocal space grid size is taken as 15×7×7, where the convergence accuracy of each atom is 0.03 eV to ensure the rationality of its structure.

[0057] Step 2: Calculate the electronic properties of the primitive cell of the Weyl semimetal material. After the primitive cell is optimized, perform band structure calculations and draw the band structure diagram. The high-symmetry points in the reciprocal space of the band structure diagram are set as Γ - X - S - Γ - Y - S - R - U - Z - R - T - Z - Γ in sequence; based on the completed band structure calculations, perform analysis and calculations. The calculated band diagram can be perfectly reproduced to ensure the accuracy of the structure.

[0058] Step 3: Establish a model of the Weyl semimetal material device. Expand the primitive cell of the Weyl semimetal material by 2×2×1 times to obtain a monolayer Weyl semimetal material supercell model, and use the monolayer Weyl semimetal material supercell as the central scattering region of the device. Select copper as the electrode material, slice the copper primitive cell, and expand it by 2×2×1 times to make it match the central scattering region, and set the vacuum layer of the device as Select the upper - middle - lower structure to establish the device model, and the mismatch degree of the device is 2.15%. It can be seen that the matching degree between the central scattering region of the established Weyl semimetal optoelectronic device and the two poles is good, and the device structure is stable.

[0059] The Weyl semimetal material device is composed of three parts: a central scattering region, an upper electrode, and a lower electrode. Among them, the upper and lower electrodes are semi - infinite in length, and the whole system is periodic in the x - y plane.

[0060] Step 4: Calculate the optoelectronic properties of the established Weyl semimetal material device model. First, perform a self-consistent calculation on the device. The grid size in the reciprocal space is taken as 10×11×1, the cutoff energy is taken as 100 Hartree, and the generalized gradient approximation is also adopted.

[0061] Secondly, perform a photocurrent calculation on the established Weyl semimetal device model. In the embodiment, linearly polarized light is selected to vertically irradiate the central scattering region of the device. The photon energy range is set to 0.1 - 2.0 eV, the photon energy interval is set to 0.1 eV, and the frequency range of the light is in the red light range and the infrared band. According to the requirements of the embodiment, set the photocurrent calculation file and perform the photocurrent calculation of the Weyl semimetal device model. The variation trend of the photocurrent at different photon energies can be obtained.

[0062] After that, under the conditions of applying bias voltages of 0.2 V, 0.4 V, 0.6 V, 0.8 V, and 1.0 V to the Weyl semimetal material device respectively, perform photocurrent calculations, and the relationship between the change of the photocurrent of the Weyl semimetal device and the applied bias voltage can be analyzed and obtained.

[0063] The photocurrent described in the present invention is the normalized photocurrent, not the actual photocurrent, and its photocurrent expression is

[0064]

[0065] where e represents the charge of an electron, represents the defined photocurrent function.

[0066] The relationship between the photocurrent magnitude of the Weyl semimetal material device and the bias voltage is as shown in the appendix Figure 4 As shown. Calculate the photocurrent magnitude under different bias voltage conditions respectively. For different bias voltages, when the photon energy is 0.1 eV, the calculated photocurrent data is shown in Table 2

[0067] Table 2

[0068]

[0069] As shown in Table 2, under the influence of the bias voltage, the photocurrent magnitude of the Weyl semimetal material device increases exponentially, and reaches the maximum value when the photon energy is near 0.1 eV. When the bias voltage is 1.0 V, the photocurrent can reach 78.8994. Compared with the case without applying bias voltage, the photocurrent magnitude increases by about 5 times. From the appendix Figure 4As shown, when a bias voltage is applied, the magnitude of the photocurrent will increase overall. It can be seen that applying a bias voltage has a regulating effect on the magnitude of the photocurrent of the Weyl semimetal device. The research found that according to Fermi's golden rule, when linearly polarized light irradiates the Weyl semimetal optoelectronic device, by absorbing the corresponding photon energy, this energy will excite the transition of electrons from the valence band to the conduction band. Electrons and holes will be generated in the optoelectronic device. These photo-generated carriers will be separated to both sides under the action of an external electric field, generating a photocurrent. When a bias voltage is applied, it will accelerate the separation of electron-hole pairs, increase the transition probability of electrons from the valence band to the conduction band, enable the device to produce a continuous and stable photocurrent effect, and increase the photocurrent.

[0070] In summary, the present invention first obtains the fine parameters of the structure of the Weyl semimetal material by consulting literature, constructs the stable structure of the primitive cell of the Weyl semimetal material, and constructs the device model of the Weyl semimetal material after optimizing the primitive cell of the Weyl semimetal material. Secondly, based on the first-principles calculation of the non-equilibrium Green's function combined with density functional theory (NEGF-DFT), the accuracy and stability of the model are further verified and determined. Thirdly, by changing the magnitude of the applied bias voltage, the magnitude of the photocurrent of the Weyl semimetal material device model under different bias voltages is obtained, and the influence of the bias voltage on the magnitude of the photocurrent of the Weyl semimetal material device is analyzed. Finally, the reasons for generating the photocurrent and the bias voltage regulating the photocurrent are analyzed from a microscopic perspective. The present invention clarifies the relationship between the applied bias voltage and the photocurrent of the Weyl semimetal material device, reveals that the bias voltage has a regulating effect on the photocurrent of the Weyl semimetal material, and the bias voltage has a positive impact on the optoelectronic properties of the Weyl semimetal material. At the same time, it also lays a theoretical foundation for the application of the bias voltage regulation method in related fields of Weyl semimetal material devices.

[0071] The specific implementation manners of the present invention have been described in detail above with reference to the accompanying drawings. The described implementation cases are only the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those skilled in the art to the technical solution of the present invention should be included within the protection scope of the present invention.

Claims

1. A design method for a Weyl semimetal material device based on bias voltage regulation, characterized in that, the method specifically includes the following steps: S1. Construct a Weyl semimetal material device model, specifically: First, consult literature materials, construct a model of the primitive cell of the Weyl semimetal material, and optimize its structure; secondly, reproduce its energy band structure to prove the accuracy of the primitive cell structure of the Weyl semimetal material; After that, perform a cell expansion operation on the optimized primitive cell model of the Weyl semimetal material to obtain the central region of the Weyl semimetal material device model, select copper as the electrode material of the Weyl semimetal material device model, and construct the Weyl semimetal material device model; S2. Calculate the optoelectronic properties of the established Weyl semimetal material device model, specifically: S21. According to the characteristics of the Weyl semimetal material, the direction and magnitude of the applied bias voltage, set the input self-consistent file, and perform self-consistent calculations on the Weyl semimetal material device model; Specifically: first perform self-consistent calculations on the two electrodes, and then perform self-consistent calculations on the central region to obtain a file containing the self-consistent results and the total calculated energy; S22. After the self-consistent calculation is completed, set the parameters for photocurrent calculation according to the type of polarized light selected, the photon energy range, the photon interval, the incident angle, and the number of illuminated atoms to obtain the input file for photocurrent; S23. Calculate the input file for photocurrent to obtain the magnitude of the photocurrent at different photon energies; S24. By changing the magnitude of the bias voltage, obtain the magnitude of the photocurrent of the Weyl semimetal material device model under different bias voltages; S3. Analyze and process the calculation results, specifically: S31. Obtain information on bond lengths, bond angles, and lattice constants of the established primitive cell model of the Weyl semimetal material through crystal structure visualization software; S32. Plot the energy band structure diagram, charge density diagram, density of states diagram of the established primitive cell model of the Weyl semimetal material, as well as the transmission spectrum diagram and the photocurrent vs. photon energy diagram of the Weyl semimetal material device model; S33. Analyze the relationship between the change in photocurrent of the Weyl semimetal material device model and the applied bias voltage under the condition of applying a bias voltage.

2. A design method for a Weyl semimetal material device based on bias voltage regulation according to claim 1, characterized in that, step S1 is to model the Weyl semimetal material with the aid of crystal structure visualization software to obtain the primitive cell model and device model of the Weyl semimetal material.

3. A design method for a Weyl semimetal material device based on bias voltage regulation according to claim 2, characterized in that, the crystal structure visualization software used is Device Studio software.

4. A design method for a Weyl semimetal material device based on bias voltage regulation according to claim 1, characterized in that, step S22 is a first-principles calculation method based on the non-equilibrium Green's function-density functional theory, and the established Weyl semimetal material device model is subjected to self-consistent and photocurrent calculations with the aid of quantum transport calculation software.

5. A design method for a Weyl semimetal material device based on bias voltage regulation according to claim 4, characterized in that, the quantum transport calculation software used is Nanodcal software.

6. A design method for a Weyl semimetal material device based on bias voltage regulation according to claim 4 or 5, characterized in that, the non-equilibrium Green's function method is used to calculate the photocurrent. Specifically: first, the total Hamiltonian of the system is given, the self-energy correction of the system is calculated to obtain the Green's function of the system, and the Green's function is substituted into the photocurrent calculation formula to calculate the photocurrent.

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