阅读说明：本技术 一种单一材料pn异质结及其设计方法 (Single-material PN heterojunction and design method thereof ) 是由 李兴冀 李伟奇 杨剑群 应涛 魏亚东 于 2020-07-28 设计创作，主要内容包括：本发明提供了一种单一材料PN异质结及其设计方法,涉及PN异质结材料设计技术领域,包括：将一种二维过渡金属硫化物中的部分原子替换成替代原子,二维过渡金属硫化物具有单一N型半导体性质或单一P型半导体性质；通过原子替换形成缺陷型二维过渡金属硫化物,所述缺陷型二维过渡金属硫化物的半导体性质发生转变,适于与未进行原子替换的二维过渡金属硫化物形成PN异质结。本发明通过替代原子的引入使得本征半导体二维材料出现晶格缺陷,引入了缺陷能级,将同一种材料通过原子替换形成具备P型半导体性质与N型半导体性质两种同晶格材料,并从能带分布中判断体系的多数载流子,为实现单一材料PN异质结提供了理论依据。(The invention provides a single material PN heterojunction and a design method thereof, which relate to the technical field of PN heterojunction material design and comprise the following steps: replacing a portion of atoms in a two-dimensional transition metal sulfide with substitute atoms, the two-dimensional transition metal sulfide having a single N-type semiconductor property or a single P-type semiconductor property; the defect type two-dimensional transition metal sulfide is formed through atom replacement, the semiconductor property of the defect type two-dimensional transition metal sulfide is changed, and the defect type two-dimensional transition metal sulfide is suitable for forming a PN heterojunction with the two-dimensional transition metal sulfide which is not subjected to atom replacement. According to the invention, lattice defects of the intrinsic semiconductor two-dimensional material are caused by introducing substitutional atoms, defect energy levels are introduced, the same material is subjected to atom substitution to form two kinds of materials with the same lattice, namely a P-type semiconductor property and an N-type semiconductor property, and majority carriers of a system are judged from energy band distribution, so that a theoretical basis is provided for realizing a single material PN heterojunction.)

1. A design method of a single material PN heterojunction is characterized by comprising the following steps:

replacing a portion of atoms in a two-dimensional transition metal sulfide with substitute atoms, the two-dimensional transition metal sulfide having a single N-type semiconductor property or a single P-type semiconductor property;

forming a defective two-dimensional transition metal sulfide by atomic substitution, the defective two-dimensional transition metal sulfide having a defect structure that converts a P-type semiconductor property of the two-dimensional transition metal sulfide to an N-type semiconductor property; or converting the N-type semiconductor property of the two-dimensional transition metal sulfide into a P-type semiconductor property;

the defective two-dimensional transition metal sulfide has different semiconductor properties from the two-dimensional transition metal sulfide not subjected to the atomic substitution, and is suitable for forming a PN heterojunction.

2. The method of designing a single material PN heterojunction as claimed in claim 1, further comprising:

searching lattice parameters of the hexagonal crystal cells of the two-dimensional transition metal sulfide, selecting certain lattice unit cell edge length a and lattice unit cell edge length c, expanding an original crystal cell to a certain number of supercells, determining energy band structure information and state density of the two-dimensional transition metal sulfide, and determining that the two-dimensional transition metal sulfide is of a single N-type semiconductor property or a single P-type semiconductor property according to the energy band structure information and the state density;

replacing part of atoms in the two-dimensional transition metal sulfide with substitute atoms, optimizing the lattice parameter of the two-dimensional transition metal sulfide after the atom replacement, taking the lattice parameter of the lowest point of energy, adjusting truncation energy, determining the energy band structure information, state density and Fermi energy level of the two-dimensional transition metal sulfide after the atom replacement, and determining whether the two-dimensional transition metal sulfide after the atom replacement has semiconductor property change or not through the Fermi energy level, defect energy level, conduction band bottom and valence band top, wherein the semiconductor property change comprises the following steps: the two-dimensional transition metal sulfide after the atom replacement converts the property of the P-type semiconductor into the property of the N-type semiconductor; alternatively, the two-dimensional transition metal sulfide after the atom replacement converts the N-type semiconductor property into the P-type semiconductor property.

3. The method of designing a single material PN heterojunction as claimed in claim 1 or 2, wherein said two-dimensional transition metal sulfide is WSe₂What is, what isThe substitute atom is Ta atom for substituting WSe₂Se atom in (1).

4. The method of claim 3, wherein the searching for lattice parameters of hexagonal lattice cells of two-dimensional transition metal sulfides comprises selecting a certain lattice unit edge length a and a lattice unit edge length c, expanding an original lattice cell to a supercell with a certain repetition number, and determining energy band structure information and state density of the two-dimensional transition metal sulfides comprises:

searching the lattice parameter of the hexagonal unit cell of the two-dimensional transition metal sulfide by using FINDIT software, and selecting the lattice parameter of the two-dimensional transition metal sulfide as

5. The method of claim 4, wherein the lattice parameter of the two-dimensional transition metal sulfide is selected as

6. The method of claim 5, wherein the optimizing lattice parameters of the atom-substituted two-dimensional transition metal sulfide, selecting lattice parameters of energy lowest points, adjusting truncation energy to ensure convergence of self-consistent wave function results, and determining the band structure information, state density and fermi level of the atom-substituted two-dimensional transition metal sulfide comprises:

lattice parameters of the two-dimensional transition metal sulfide after the atomic replacement are optimized through VASP software, the truncation capacity is 400eV, the K point is 1 multiplied by 1, the electron convergence precision is 1E-5, the ion convergence precision is 1E-2, and the lattice parameter of the lowest energy point is

wherein a, b and c are the edge lengths of the unit cell in three mutually perpendicular directions.

7. The design method of single material PN heterojunction as claimed in claim 6, wherein any one of said 32 Se atoms is replaced by a Ta atom.

8. The method of designing a single material PN heterojunction as claimed in claim 1 or 2, further comprising: and regulating the performance of the PN heterojunction by controlling the number of atom substitutions in the atom-substituted two-dimensional transition metal sulfide.

9. The method for designing a single material PN heterojunction as claimed in claim 8, wherein said adjusting the performance of a PN heterojunction by controlling the number of atomic substitutions in said atom-substituted two-dimensional transition metal sulfide comprises:

by Ar, N₂And O₂The number and the concentration of the defect structures are controlled by plasma bombardment;

and/or controlling the number and concentration of defect structures by adjusting the irradiation duration and the irradiation dose of laser irradiation;

and/or controlling the number and concentration of defect structures by adjusting the irradiation duration and irradiation dose of electron ion beam irradiation;

and/or, controlling the concentration of the defect structure by adjusting one or two combinations of the annealing temperature and the annealing atmosphere concentration;

and/or, the replacement doping is achieved by irradiating the two-dimensional material with a transition metal ion beam.

10. A single material PN heterojunction as designed by the method of designing a single material PN heterojunction as claimed in any of the preceding claims 1 to 9, wherein said single material PN heterojunction comprises a two-dimensional transition metal sulfide adapted to form a defective two-dimensional transition metal sulfide by atomic substitution, said defective two-dimensional transition metal sulfide having different semiconductor properties from said two-dimensional transition metal sulfide without said atomic substitution.

Technical Field

The invention relates to the technical field of PN heterojunction material design, in particular to a single material PN heterojunction and a design method thereof.

Background

The existing two-dimensional materials such as transition metal sulfides have the advantages of direct band gap of optical band, excellent chemical stability, simple preparation process, environmental friendliness and the like, so that the two-dimensional materials have wide application in various aspects such as photocatalysts, infrared photodetectors, nonlinear optical information processing devices, light emitting diodes and the like.

Since the transition metal sulfide is a two-dimensional material, the integration of structure and function can be carried out in a mode of constructing Van der Waals heterojunction in the aspect of integration, and thus the optically-related multifunctional device is prepared. However, the lattice matching requirements for constructing a heterojunction are high, and the difficulty of the coplanar heterojunction in the preparation process is large. At present, more than two layers of different semiconductor material films are deposited on the same base in sequence to form a PN heterojunction, and internal stress is easily introduced into materials when different semiconductor materials have certain difference in lattice matching, so that the stability of the heterojunction is poor, and the electronic property and the optical property of the heterojunction are reduced.

Disclosure of Invention

The invention solves the problems that the requirements on lattice matching are high when different semiconductor materials construct heterojunction, and the lattice matching has certain difference and is easy to introduce internal stress into the materials, thereby influencing the stability, electronic characteristics, optical characteristics and the like of devices.

In order to solve the above problems, the present invention provides a method for designing a single material PN heterojunction, comprising:

replacing a portion of atoms in a two-dimensional transition metal sulfide with substitute atoms, the two-dimensional transition metal sulfide having a single N-type semiconductor property or a single P-type semiconductor property;

forming a defective two-dimensional transition metal sulfide by atomic substitution, the defective two-dimensional transition metal sulfide having a defect structure that converts a P-type semiconductor property of the two-dimensional transition metal sulfide to an N-type semiconductor property; or converting the N-type semiconductor property of the two-dimensional transition metal sulfide into a P-type semiconductor property;

the defective two-dimensional transition metal sulfide has different semiconductor properties from the two-dimensional transition metal sulfide not subjected to the atomic substitution, and is suitable for forming a PN heterojunction.

Optionally, the method further comprises: searching lattice parameters of the hexagonal crystal cells of the two-dimensional transition metal sulfide, selecting certain lattice unit cell edge length a and lattice unit cell edge length c, expanding an original crystal cell to a certain number of supercells, determining energy band structure information and state density of the two-dimensional transition metal sulfide, and determining that the two-dimensional transition metal sulfide is of a single N-type semiconductor property or a single P-type semiconductor property according to the energy band structure information and the state density;

replacing part of atoms in the two-dimensional transition metal sulfide with substitute atoms, optimizing the lattice parameter of the two-dimensional transition metal sulfide after the atom replacement, taking the lattice parameter of the lowest point of energy, adjusting truncation energy, determining the energy band structure information, state density and Fermi energy level of the two-dimensional transition metal sulfide after the atom replacement, and determining whether the two-dimensional transition metal sulfide after the atom replacement has semiconductor property change or not through the Fermi energy level, defect energy level, conduction band bottom and valence band top, wherein the semiconductor property change comprises the following steps: the two-dimensional transition metal sulfide after the atom replacement converts the property of the P-type semiconductor into the property of the N-type semiconductor; alternatively, the two-dimensional transition metal sulfide after the atom replacement converts the N-type semiconductor property into the P-type semiconductor property.

Optionally, the two-dimensional transition metal sulfide is WSe₂The substitute atom is a Ta atom for substituting WSe₂Se atom in (1).

Optionally, the searching for the lattice parameter of the hexagonal lattice cell of the two-dimensional transition metal sulfide, selecting a certain lattice unit edge length a and a certain lattice unit edge length c, expanding the original lattice cell to a supercell with a certain repetition number, and determining the energy band structure information and the state density of the two-dimensional transition metal sulfide includes:

searching the lattice parameter of the hexagonal unit cell of the two-dimensional transition metal sulfide by using FINDIT software, and selecting the lattice parameter of the two-dimensional transition metal sulfide asExpanding the original unit cell to a super cell with a repetition number of 4 × 4 × 1, which comprises 16W atoms and 32 Se atoms, determines the band structure information and the state density of the two-dimensional transition metal sulfide.

Optionally, the lattice parameter of the two-dimensional transition metal sulfide is selected to be

And then, certain unit cell angle parameters are selected, wherein the unit cell angle parameters are alpha-90 degrees, beta-90 degrees and gamma-120 degrees, and alpha, beta and gamma are three angle parameters of the lattice unit cell.

Optionally, the optimizing the lattice parameter of the two-dimensional transition metal sulfide after the atomic replacement, taking the lattice parameter of the lowest point of energy, adjusting truncation energy to ensure convergence of a self-consistent wave function result, and determining the energy band structure information, the state density, and the fermi level of the two-dimensional transition metal sulfide after the atomic replacement includes:

lattice parameters of the two-dimensional transition metal sulfide after the atomic replacement are optimized through VASP software, the truncation capacity is 400eV, the K point is 1 multiplied by 1, the electron convergence precision is 1E-5, the ion convergence precision is 1E-2, and the lattice parameter of the lowest energy point isThe unit cell adopts a supercell of 4 multiplied by 1, contains 48 atoms, and determines the energy band structure information and the state density of the two-dimensional transition metal sulfide after atom replacement;

wherein a, b and c are the edge lengths of the unit cell in three mutually perpendicular directions.

Optionally, any one Se atom of the 32 Se atoms is replaced with a Ta atom.

Optionally, the method further comprises: and regulating the performance of the PN heterojunction by controlling the number of atom substitutions in the atom-substituted two-dimensional transition metal sulfide.

Optionally, the adjusting the performance of the PN heterojunction by controlling the number of atom substitutions in the atom-substituted two-dimensional transition metal sulfide includes:

by Ar, N₂And O₂The number and the concentration of the defect structures are controlled by plasma bombardment;

and/or controlling the number and concentration of defect structures by adjusting the irradiation duration and the irradiation dose of laser irradiation;

and/or controlling the number and concentration of defect structures by adjusting the irradiation duration and irradiation dose of electron ion beam irradiation;

and/or controlling the concentration of the defect structure by adjusting one or two combinations of the annealing temperature and the annealing atmosphere concentration.

Another object of the present invention is to provide a single material PN heterojunction designed by the method for designing a single material PN heterojunction as described in any of the above, wherein the single material PN heterojunction comprises a two-dimensional transition metal sulfide adapted to form a defective two-dimensional transition metal sulfide by atomic substitution, the defective two-dimensional transition metal sulfide having a different semiconductor property from the two-dimensional transition metal sulfide not subjected to the atomic substitution.

Compared with the prior art, the single-material PN heterojunction and the design method thereof have the following advantages that:

(1) according to the invention, lattice defects of the intrinsic semiconductor two-dimensional material are caused by introducing the substitute atoms, the defect energy level is introduced, and a single material is replaced by atoms to form two isomorphous materials with P-type semiconductor properties and N-type semiconductor properties, so that the problems that the stability, electronic properties, optical properties and the like of a device are influenced because internal stress is easily introduced into the materials when different semiconductor materials construct heterojunction are avoided.

(2) According to the method, lattice atom replacement is carried out on the two-dimensional transition metal sulfide to form a two-dimensional material with certain defects, majority carriers of a system are judged from energy band distribution through a simulation calculation method, and after defect system information of the two-dimensional transition metal sulfide is replaced through Fermi level, defect level, conduction band bottom and valence band top information atoms, a single two-dimensional material with the defects suitable for preparing the PN heterojunction can be determined according to the defect system information, so that a theoretical basis is provided for the single preparation material for preparing the PN heterojunction.

(3) The single material combining the P-type semiconductor and the N-level semiconductor is prepared, namely the PN heterojunction can be constructed by the single intrinsic semiconductor preparation material, the working link of searching for lattice matching and considering the influence of the physical characteristics of a lattice mismatch system is omitted, the prepared PN heterojunction does not have lattice matching difference, and therefore a two-dimensional material structure device is prepared and applied more efficiently, and the prepared structure has better stability, electronic characteristics and optical characteristics during the period.

(4) The method for designing the single-material PN heterojunction has the advantages of simple steps, easiness in operation, low time consumption and low cost, can be used for designing a composite structure of a semiconductor material, can provide necessary basis for controlling and utilizing the defects of a semiconductor to design a device, and has obvious advantages and wide application prospect in defect research of the semiconductor.

Drawings

FIG. 1 is a structural diagram of a defect system after Ta atoms replace Se atoms and are optimized;

FIG. 2 is a perfect single crystal WSe₂Energy band diagram of (1);

FIG. 3 is a perfect single crystal WSe₂A density of states map of;

FIG. 4 is WSe with Se atoms replaced with Ta atoms₂The band diagram of the supercell;

FIG. 5 is WSe with Se atoms replaced with Ta atoms₂Density of states of the supercell.

Detailed Description

The PN heterojunction is a common semiconductor material, and is formed by sequentially depositing more than two layers of different semiconductor material films on the same base, and the two materials forming the PN heterojunction have different energy band gaps. An ideal PN heterojunction requires that the lattice constants of the two materials of fabrication be the same, and that the lattice atoms be as identical as possible, in order to fabricate the intrinsic semiconductor. If the lattice mismatch of the two materials is easy to form dangling bonds, mismatch errors are caused, so that the stability of the heterojunction is poor, and the electronic characteristics and the optical characteristics of the heterojunction are reduced.

The invention introduces different defects into two-dimensional materials such as transition metal sulfide and the like, and dopes other atoms into the same intrinsic semiconductor system preparation material to form an N-type semiconductor and a P-type semiconductor, and is suitable for being combined to form a PN heterojunction.

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.

The invention provides a design method of a single material PN heterojunction, which specifically comprises the following steps:

replacing a portion of atoms in a two-dimensional transition metal sulfide with substitute atoms, the two-dimensional transition metal sulfide having a single N-type semiconductor property or a single P-type semiconductor property;

forming a defective two-dimensional transition metal sulfide by atomic substitution, the defective two-dimensional transition metal sulfide having a defect structure that converts a P-type semiconductor property of the two-dimensional transition metal sulfide to an N-type semiconductor property; or converting the N-type semiconductor property of the two-dimensional transition metal sulfide into a P-type semiconductor property;

the defective two-dimensional transition metal sulfide has different semiconductor properties from the two-dimensional transition metal sulfide not subjected to the atomic substitution, and is suitable for forming a PN heterojunction.

According to the invention, lattice defects of the intrinsic semiconductor two-dimensional material are caused by introducing the substitute atoms, the defect energy level is introduced, and a single material is replaced by atoms to form two isomorphous materials with P-type semiconductor properties and N-type semiconductor properties, so that the problems that the stability, electronic properties, optical properties and the like of a device are influenced because internal stress is easily introduced into the materials when different semiconductor materials construct heterojunction are avoided.

Specifically, the design method further includes: searching lattice parameters of the hexagonal crystal cells of the two-dimensional transition metal sulfide, selecting certain lattice unit cell edge length a and lattice unit cell edge length c, expanding an original crystal cell to a certain number of supercells, determining energy band structure information and state density of the two-dimensional transition metal sulfide, and determining that the two-dimensional transition metal sulfide is of a single N-type semiconductor property or a single P-type semiconductor property according to the energy band structure information and the state density;

replacing part of atoms in the two-dimensional transition metal sulfide with substitute atoms, optimizing the lattice parameter of the two-dimensional transition metal sulfide after the atom replacement, taking the lattice parameter of the lowest point of energy, adjusting truncation energy, determining the energy band structure information, state density and Fermi energy level of the two-dimensional transition metal sulfide after the atom replacement, and determining whether the two-dimensional transition metal sulfide after the atom replacement has semiconductor property change or not through the Fermi energy level, defect energy level, conduction band bottom and valence band top, wherein the semiconductor property change comprises the following steps: the two-dimensional transition metal sulfide after the atom replacement converts the property of the P-type semiconductor into the property of the N-type semiconductor; alternatively, the two-dimensional transition metal sulfide after the atom replacement converts the N-type semiconductor property into the P-type semiconductor property.

The method comprises the steps of carrying out lattice atom replacement on a two-dimensional transition metal sulfide to form a two-dimensional material with certain defects, determining a single two-dimensional material with the defects suitable for preparing the PN heterojunction according to defect system information after the defect system information of the two-dimensional transition metal sulfide is replaced by Fermi level, defect level, conduction band bottom and valence band top information atoms, and providing raw materials for preparing the PN heterojunction.

The invention judges the majority carrier of the system from the energy band distribution and provides a basis for judging the electronic property of the defect structure. The introduction of substitutional atoms causes lattice defects to exist in the semiconductor two-dimensional material, the introduction of the defects causes the energy band property of the semiconductor two-dimensional material to be changed, defect energy levels are introduced, and the introduced defect energy levels belong to donor energy levels through the judgment of an energy band diagram, so that the system is easy to conduct electrons to form a typical N-type semiconductor. On the other hand, intrinsic semiconductor two-dimensional materials are weak P-type semiconductors because the fermi level is near the top of the valence band. The semiconductor properties of the two-dimensional transition metal sulfide are converted through atomic replacement to form defective two-dimensional transition metal sulfide, the defective two-dimensional transition metal sulfide and the two-dimensional transition metal sulfide which is not subjected to the atomic replacement have different semiconductor properties, the PN heterojunction can be constructed by the single intrinsic semiconductor preparation material, a working link of searching lattice matching and considering the influence of physical properties of a lattice mismatch system is omitted, the prepared PN heterojunction does not have lattice matching difference, and therefore two-dimensional material structure devices are prepared and applied more efficiently, and the prepared structure has better stability, electronic properties and optical properties during the period.

Specifically, the design method of the single-material PN heterojunction described in this embodiment is applicable to all transition metal sulfides with band gap layered structures, and the atoms of the composition are different for each intrinsic material, so that the convergence of the self-consistent wave function result can be ensured by adjusting the truncation in each calculation step.

Preferably, the two-dimensional transition metal sulfide is WSe in this embodiment₂For example, substituting atoms with Ta for WSe₂Replacement of the Se atom, the Ta atom in (a) results in a change in the doped component semiconductor properties, from a p-type semiconductor to an n-type semiconductor.

Preferably, WSe is being applied₂In the case where one Se atom is replaced with a Ta atom, any one Se atom of 32 Se atoms may be replaced with a Ta atom.

The method for designing the single-material PN heterojunction has the advantages of simple steps, easiness in operation, low time consumption and low cost, can be used for designing a composite structure of a semiconductor material, can provide necessary basis for controlling and utilizing the defects of a semiconductor to design a device, and has obvious advantages and wide application prospect in defect research of the semiconductor.

Preferably, on the basis of the above embodiment, the method for designing a single material PN heterojunction further includes: the PN heterojunction performance is regulated and controlled by controlling the number and concentration of defect structures formed by replacing atoms in the two-dimensional transition metal sulfide with substitute atoms.

According to the current manufacturing process, such as Metal Organic Chemical Vapor Deposition (MOCVD), Hydride Vapor Phase Epitaxy (HVPE), Molecular Beam Epitaxy (MBE), etc., it is possible to introduce defects into the material, causing changes in the physical properties of the material, such as optical and electronic properties.

Specifically, by Ar, N₂And O₂Controlling the number and concentration of defect structures by one or more of plasma bombardment, laser irradiation and electron ion beam irradiation;

and/or controlling the concentration of the defect structure by adjusting the annealing temperature, the annealing atmosphere and by adjusting one or more of the doping component elements, the amount and the concentration.

In particular, for controlling the type and concentration of lattice defects in two-dimensional materials, more than one physical method is adopted, mainly by Ar and N₂Or O₂The laser irradiation and the electron ion beam irradiation, and the like, and the defect type and the concentration system control are realized by changing the laser irradiation and the electron ion beam irradiation time and the irradiation dose.

It should be noted that, for the general crystal growth situation, the defect concentration is usually controlled by (1) adjusting the annealing temperature; (2) adjusting the concentration of annealing atmosphere so that the higher the content of a specific element during annealing, the lower the concentration of vacancy defects corresponding to the introduction of the specific element, and specifically, the specific element may be a type of defect in which constituent atoms form vacancies or dislocations, such as WSe₂Se element in (1); (3) by regulating the number of defects by the concentration of doping elements, and thus regulating the doping concentration, e.g. regulating the concentration of Ta to adjust defects formed by substitutional atomsAnd (4) concentration. Even if only one billion defects are introduced into the material in the above process, the factors such as conductivity, free carrier mobility and carrier lifetime may be greatly changed, for example, as the defect concentration increases, the lower the conductivity of the PN junction minority carriers, the lower the majority carrier mobility and the reduced carrier lifetime. The defect concentration is controlled in a better range by the method so as to control the PN heterojunction to achieve the best property. It should be noted that the general crystal growth means that the above regulation mode is suitable for controlling the defect concentration in the crystal material growth link. The crystal atom substitution in the invention can occur in a plurality of scenes, including intentionally exposing the crystal to irradiation conditions for modification or spontaneously generating property change in application scenes.

On the basis of the above embodiment, there is also provided a specific design method for realizing a two-dimensional material single-component PN heterojunction based on doping, including:

finding two-dimensional transition metal sulfide WSe through FINDIT software₂Selecting WSe as lattice parameter of hexagonal crystal cell₂The lattice parameter of the hexagonal unit cell isWherein a and c are the edge lengths of the unit cells in two mutually perpendicular directions;

expanding an original unit cell to a supercell with the repetition number of 4 multiplied by 1, and containing 16W atoms and 32 Se atoms, and calculating the energy band structure information and the state density of the two-dimensional transition metal sulfide through a DFT energy band. FIG. 1 shows, in combination with FIG. 3, a diagram of a defect system in which Se atoms are replaced by Ta atoms and optimized, in which one Se atom in the lattice system is replaced by a Ta atom, and FIG. 2 shows a perfect single crystal WSe₂FIG. 3 is a diagram of a perfect single crystal WSe₂The state density diagram of (1), WSe of which atomic replacement does not occur is known from the band diagram simulation result₂The band gap of the perfect single crystal is 1.6eV, the obtained simulation result is basically consistent with the experimental result, and the simulation result of the method is WSe₂The energy band and state density of a perfect structure, and the energy band result reflects that the system is a direct band gap semiconductor with a band gap of 16 eV. According to the 2015 publication "Yeh P C, Jin W, Zaki N, et al layer-dependent electronic structure of an atomic heav two-dimensional dichalcogenide [ J]Physical Review B,2015,91(4):041407 ", the results of the angle-resolved photoelectron spectroscopy measurements reflect a band gap between 1.4 and 2.3eV, which shows that the simulation calculation results described in this example are reasonable and can be used in the design method of single-material PN heterojunction described in this invention.

Replacing one Se atom in the two-dimensional transition metal sulfide with a Ta atom, optimizing the lattice parameter of the two-dimensional transition metal sulfide after atom replacement through VASP software, wherein the truncation capacity is 400eV, the K point is 1 multiplied by 1, the electron convergence precision is 1E-5, the ion convergence precision is 1E-2, and the lattice parameter of the lowest point of energy is taken as

Wherein a, b and c are the edge lengths of the unit cell in three mutually perpendicular directions; obtaining an energy band diagram and state density through DFT energy band calculation, determining a Fermi energy level, determining defect system information of the two-dimensional transition metal sulfide after atom replacement according to the Fermi energy level, the defect energy level, a conduction band bottom and a valence band top, providing theoretical support for a single defective two-dimensional material suitable for preparing a PN heterojunction, and providing basis for obtaining raw materials for preparing the PN heterojunction, wherein shown in a combined manner of figure 4 and figure 5, figure 4 is WSe with Se atoms replaced by Ta atoms₂FIG. 5 is a diagram of energy bands of a superlattice, and WSe in which Se atoms are replaced with Ta atoms₂The state density diagrams of the supercell, as shown in fig. 4 and 5, show that after atoms are replaced, the system has the electrical properties of a p-type semiconductor due to the participation of defect energy levels shown in fig. 4 and the fact that the fermi level marked by a vertical line in the state density diagram of fig. 5 is closer to the conduction band bottom. This is contrary to the result of fig. 3 where the fermi level of the perfect system is close to the valence band top, and the perfect system without atomic substitution has the electrical properties of an n-type semiconductor, so that a PN heterojunction structure can be formed by combining the two, and a PN heterojunction of a single material which is easy to prepare is realized.

Specifically, the energy band structure and the state density are read through P4VASP, the Fermi level is read in an energy band diagram or an OUTCAR output file, and the position of a state density peak belonging to a defect state in a forbidden band relative to the Fermi level is observed.

The defect structure type of the two-dimensional material after atomic replacement is predicted and detected by utilizing a first principle, possible majority carriers of the defect structure type are investigated, the Fermi level is obtained from energy band calculation, the defect system information of the two-dimensional transition metal sulfide after atomic replacement is determined according to the Fermi level, the defect level, the conduction band bottom and the valence band top, and WSe after atomic replacement is different when the majority carriers and the perfect unit cells which are not replaced by atoms exist in a defect system formed by replacing Se atoms by Ta atoms₂Can be used as a single preparation material for synthesizing PN heterojunction.

Preferably, in this embodiment, when a certain lattice unit edge length a and a certain lattice unit edge length c are selected, a certain unit cell angle parameter is also selected, where α, β, and γ are three angle parameters of the lattice unit, where α, β, and γ are 90 °, β, and γ are 120 °.

On the basis of the above embodiment, this embodiment further provides a single-material PN heterojunction designed by the single-material PN heterojunction design method according to any of the above embodiments, wherein the single-material PN heterojunction includes a two-dimensional transition metal sulfide adapted to form a defective two-dimensional transition metal sulfide by atomic substitution, and the defective two-dimensional transition metal sulfide has a different semiconductor property from the two-dimensional transition metal sulfide without the atomic substitution.

The single material combining the P-type semiconductor and the N-level semiconductor is prepared, namely the PN heterojunction can be constructed by the single intrinsic semiconductor preparation material, the working link of searching for lattice matching and considering the influence of the physical characteristics of a lattice mismatch system is omitted, the prepared PN heterojunction does not have lattice matching difference, and therefore a two-dimensional material structure device is prepared and applied more efficiently, and the prepared structure has better stability, electronic characteristics and optical characteristics during the period.

On the basis of the foregoing embodiments, this embodiment further provides a regulation and control system for a single-material PN heterojunction, including:

the lattice selection module is used for searching lattice parameters of the hexagonal lattice of the two-dimensional transition metal sulfide, selecting certain lattice unit edge length a and lattice unit edge length c, expanding an original lattice to a supercell with certain repetition number, and determining energy band structure information and state density of the two-dimensional transition metal sulfide;

an atom replacement module for replacing one atom in the two-dimensional transition metal sulfide with a replacement atom;

the lattice optimization module is used for optimizing lattice parameters of the two-dimensional transition metal sulfide after the atom replacement, taking the lattice parameter with the lowest energy point and determining energy band structure information and state density of the two-dimensional transition metal sulfide after the atom replacement;

and the determining module is used for determining the defect system information of the two-dimensional transition metal sulfide after the atomic replacement according to the Fermi level, the defect level, the conduction band bottom and the valence band top.

On the basis of the foregoing embodiments, the present embodiment further provides a computer-readable storage medium, where a computer program is stored, and when the computer program is read and executed by a processor, the computer program implements the method for designing a single-material PN heterojunction as described in any one of the foregoing embodiments.

Although the present invention has been disclosed above, the scope of the invention is not limited thereto. Various changes and modifications may be made by those skilled in the art without departing from the spirit and scope of the invention, and these changes and modifications are intended to be within the scope of the invention.