CN111863625B - Single-material PN heterojunction and design method thereof - Google Patents
Single-material PN heterojunction and design method thereof Download PDFInfo
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Abstract
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; defective two-dimensional transition metal sulfides are formed by atomic substitution, and the semiconductor properties of the defective two-dimensional transition metal sulfides are transformed, so that the defective two-dimensional transition metal sulfides are suitable for forming PN heterojunction with two-dimensional transition metal sulfides which are not subjected to atomic substitution. 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.
Description
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 to form a PN heterojunction in sequence, 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 characteristic and the optical characteristic 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 internal stress is easily introduced into the materials due to certain difference of the lattice matching, so that the stability, the electronic property, the optical property and the like of a device are influenced.
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 a different semiconductor property from the two-dimensional transition metal sulfide which is 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 WSe 2 The substitute atom is Ta atom for substituting WSe 2 Se 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 FINDIT software, and selecting the lattice parameter of the two-dimensional transition metal sulfide as
Expanding 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
When the lattice unit cell angle is larger than the preset angle, a certain unit cell angle parameter is selected, wherein the unit cell angle parameter is alpha =90 degrees, beta =90 degrees, and gamma =120 degrees, and the alpha, the beta and the 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 atom 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 energy lowest point is
The 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, N 2 And O 2 The 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 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:
(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 WSe 2 Energy band diagram of (a);
FIG. 3 is a perfect single crystal WSe 2 A density of states map of;
FIG. 4 is WSe with Se atoms replaced with Ta atoms 2 The energy band diagram of a supercell;
FIG. 5 is WSe in which Se atom is replaced with Ta atom 2 Density 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 two materials to be fabricated have the same lattice constant and lattice atoms as identical as possible 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, and determining a single two-dimensional material with defects suitable for preparing a PN heterojunction according to defect system information after the defect system information of the two-dimensional transition metal sulfide is replaced by Fermi energy level, defect energy level, conduction band bottom and valence band top information atoms, so as to provide 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 can easily 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 the 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, the working link of searching lattice matching and considering the influence of the physical properties of a lattice mismatch system is omitted, the lattice matching difference of the prepared PN heterojunction cannot exist, and therefore the two-dimensional material structure device can be prepared and applied more efficiently, and the prepared structure has better stability, electronic properties and optical properties.
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 embodiment 2 For example, substituting atoms with Ta for WSe 2 Replacement 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 applied 2 In 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 according to the present invention further comprises: 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, N 2 And O 2 Controlling the number and concentration of defect structures by one or more of plasma bombardment, laser irradiation and electron ion beam irradiation;
and/or, the concentration of the defect structure is controlled by adjusting one or more of annealing temperature, annealing atmosphere and doping component elements, quantity and concentration.
In particular, for the control of the type and concentration of lattice defects in two-dimensional materials, more than one is to use physical methods, mainly Ar and N 2 Or O 2 The 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 WSe 2 Se element in (1); (3) The number of defects is regulated and controlled through the concentration of doping elements, and then the doping concentration is regulated and controlled, for example, the concentration of Ta element is regulated and the concentration of defects formed by replacing atoms is regulated and controlled. Even if only billions of defects are introduced into the material in the above process, 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 shorter the 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 present invention may occur in a variety of ways, including intentionally exposing the crystal to radiation for modification, orProperty changes occur spontaneously in the application scenario.
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 software 2 Selecting WSe as lattice parameter of hexagonal crystal cell 2 The lattice parameter of the hexagonal unit cell is
Wherein a and c are the edge lengths of the unit cells in two mutually perpendicular directions;
expanding the original unit cell to a supercell with the repetition number of 4 multiplied by 1 and containing 16W atoms and 32 Se atoms, and obtaining the energy band structure information and the state density of the two-dimensional transition metal sulfide through DFT energy band calculation. 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 WSe 2 FIG. 3 is a diagram of a perfect single crystal WSe 2 The result of band diagram simulation shows that no atomic substitution occurs in WSe 2 The 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 WSe 2 The energy band and the state density of a perfect structure reflect that the system is a direct band gap semiconductor and has a band gap of 1.6eV. 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 experimental measurement of angle-resolved photoelectron spectroscopy reflect that the band gap is 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 atom-replaced two-dimensional transition metal sulfide by VASP software, wherein the truncation capability is 400eV, the K point is 1 multiplied by 1, and the electron convergence essence isDegree of 1E-5, ion convergence accuracy of 1E-2, and lattice parameter of lowest point of energy
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 atoms 2 FIG. 5 is a schematic diagram of an energy band of a superlattice, and WSe in which Se atoms are replaced with Ta atoms 2 The 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 the defect energy level shown in fig. 4 and the fermi level marked by the vertical line in the state density diagram of fig. 5, which 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 atoms 2 Capable of acting as a synthetic PN heterojunctionA single preparation material.
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 further selected, where the unit cell angle parameter is α =90 °, β =90 °, γ =120 °, and α, β, and γ are three angle parameters of the lattice unit.
In addition to the above embodiments, this embodiment further provides a single-material PN heterojunction, which is designed by the single-material PN heterojunction design method according to any of the above embodiments, and the single-material PN heterojunction includes a two-dimensional transition metal sulfide, and the two-dimensional transition metal sulfide is suitable for forming a defective two-dimensional transition metal sulfide through atomic replacement, and the defective two-dimensional transition metal sulfide has different semiconductor properties from the two-dimensional transition metal sulfide without atomic replacement.
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 atomic replacement, taking the lattice parameter of the lowest point of energy and determining energy band structure information and state density of the two-dimensional transition metal sulfide after the atomic 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 disclosure has been described above, the scope of the present disclosure 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.
Claims (9)
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;
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 supercell with a certain repetition number, 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 partial atoms in the two-dimensional transition metal sulfide with substitute atoms, optimizing the lattice parameter of the two-dimensional transition metal sulfide after atom replacement, taking the lattice parameter of the lowest point of energy, adjusting truncation energy, determining energy band structure information, state density and Fermi energy level of the two-dimensional transition metal sulfide after atom replacement, and determining whether the two-dimensional transition metal sulfide after 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.
2. The method of claim 1, wherein the two-dimensional transition metal sulfide is WSe 2 The substitute atom is Ta atom for substituting WSe 2 Se atom in (1).
3. The method for designing a single-material PN heterojunction as claimed in claim 2, wherein said searching for lattice parameters of hexagonal lattice of two-dimensional transition metal sulfide, selecting a certain lattice unit cell edge length a and lattice unit cell edge length c, expanding an original lattice to a certain number of supercells, and determining the band structure information and state density of said two-dimensional transition metal sulfide 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
Expanding 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.
4. The method for designing a single-material PN heterojunction as claimed in claim 3, wherein the lattice parameter of said two-dimensional transition metal sulfide is selected as
When the lattice unit cell angle is larger than the preset angle, a certain unit cell angle parameter is selected, wherein the unit cell angle parameter is alpha =90 degrees, beta =90 degrees, and gamma =120 degrees, and the alpha, the beta and the gamma are three angle parameters of the lattice unit cell.
5. The method of claim 4, 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
The 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.
6. The design method of single-material PN heterojunction as claimed in claim 5, wherein any one Se atom in said 32 Se atoms is replaced by Ta atom.
7. The method of designing a single material PN heterojunction as claimed in claim 1, 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.
8. The method for designing a single material PN heterojunction as claimed in claim 7, 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, N 2 And O 2 The 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 the concentration of defect structures by adjusting the irradiation duration and the irradiation dose of the 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.
9. 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 8, 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.
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