A method for preparing a superconducting heterojunction by a molecular beam epitaxy growth technique, a superconducting heterojunction and application

Abstract

The application discloses a method for preparing a superconducting heterojunction by using a molecular beam epitaxy growth technique, a superconducting heterojunction and application, and relates to the technical field of semiconductors.The application uses (001) crystal surface insulating SrTiO3 single crystal as a substrate, and precisely and layer by layer grows SnSe thin films and SnTe thin films with a thickness of 60 nm at a constant substrate temperature, so that the two-dimensional superconducting characteristics of the heterojunction are realized.The process of the application is controllable at the atomic level, has high crystallization quality, is highly repeatable, and has excellent air stability.The obtained superconducting heterojunction has both the surface state of the SnTe topological crystal insulator and the two-dimensional superconducting characteristics, has a broad application prospect in the field of superconducting electronic devices, and can be popularized and applied to frontier superconducting devices such as superconducting nanowire single-photon detectors and Majorana zero-energy mode devices.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, specifically to the field of low-dimensional quantum materials and superconducting device fabrication technology, and more specifically, to a method for fabricating superconducting heterojunctions using molecular beam epitaxy, the superconducting heterojunctions, and their applications. Background Technology

[0002] Topological superconducting materials are core candidate systems for fault-tolerant qubits and quantum computing devices due to their ability to stably support Majorana zero modes. SnTe, a topological crystalline insulator, is protected by its crystal point group symmetry and possesses gapless topological surface states, giving it an inherent advantage in constructing topological superconductivity. However, achieving low-temperature superconductivity in pure SnTe films typically requires high concentrations of tin vacancies, heavy metal doping, or superconducting nearest-neighbor coupling, making it difficult to obtain high-quality intrinsically superconducting SnTe films using conventional fabrication processes. Existing methods for achieving SnTe superconductivity have significant shortcomings: 1) Chemical doping easily introduces numerous lattice defects and impurity scattering, disrupting the integrity of the topological surface states; 2) Severe diffusion occurs at the interface of superconducting metal-nearest neighbor heterostructures, resulting in poor interface quality; 3) The SnTe / PbTe superlattice superconducting transition temperature is relatively low, and there is no ability to synergistically control topological superconductivity.

[0003] There are currently no reports on achieving two-dimensional superconductivity through homo-cation heterojunctions. Furthermore, there are no reports on the fabrication of superconducting SnSe / SnTe heterojunctions using molecular beam epitaxy (MBE). Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned defects in the prior art and to provide a method for preparing superconducting heterojunctions using molecular beam epitaxy, as well as the superconducting heterojunctions and their applications.

[0005] This invention proposes to construct a heterojunction using (1) SnSe-orthogonal narrow bandgap semiconductor and (2) SnTe-topological crystal insulator. Both cations are Sn, and their crystal structures are derived from rock salt structures, enabling epitaxial stacking without cation interdiffusion. This invention develops a stable, mass-producible molecular beam epitaxial growth process with atomically flat interfaces. Relying on precise atomic-level thickness, temperature, and beam current control, using (001) crystal plane insulating SrTiO3 single crystal as a substrate, at a substrate temperature of 300℃, SnSe and SnTe films with a thickness of 60nm are precisely grown in layers to obtain a stacked heterostructure with steep interfaces and no obvious interdiffusion. Two-dimensional superconductivity is achieved by relying on the synergistic induction of interfacial compressive strain and band bending charge accumulation. The results of heterojunction electrical transport tests show that when the heterojunction is a SnSe / SnTe / STO forward heterojunction, the superconducting onset transition temperature is... T c onset =3.46K, zero resistance temperatureT c zero =2.10K; when the heterojunction is a SnTe / SnSe / STO reverse heterojunction, the superconducting onset transition temperature is... T c onset =3.81K, zero resistance temperature T c zero =2.67K; Thermal transport tests show that the charge carrier type is p-type holes, and the charge carrier type can be tuned to n-type electrons by inserting a 0.4nm ultrathin Sn layer between the two thin films. This process is atomically controllable, has high crystal quality, strong repeatability, and excellent air stability. The resulting superconducting heterojunction combines the surface states of SnTe topological crystal insulators with two-dimensional superconducting properties, and has broad application prospects in the field of superconducting electronic devices. It can be extended to cutting-edge superconducting devices such as superconducting nanowire single-photon detectors and Majorana zero-mode devices.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: A method for preparing superconducting heterostructures using molecular beam epitaxy includes the following steps: S1. Select a (001) crystal plane insulating SrTiO3 single crystal as the substrate. After cleaning the substrate, place it in the ultra-vacuum cavity of the molecular beam epitaxy equipment, and control the vacuum degree of the ultra-vacuum cavity to be ≤2×10. -10 mbar, the substrate is heated to 300°C for annealing to remove surface adsorbates and obtain the pretreated substrate; S2. Using Sn, Se, and Te sources as evaporation sources, molecular beam epitaxy (MBE) is employed to epitaxially grow a first thin film on the pretreated substrate surface. The first thin film is either a SnTe or SnSe thin film. After growth, the substrate is allowed to stand for 5-10 minutes to stabilize the interface. Subsequently, a second thin film is epitaxially grown on the side of the first thin film away from the substrate. The second thin film is either a SnTe or SnSe thin film, and the material of the second thin film is different from that of the first thin film. During growth, the Sn source beam current rate is 2 nm / min, the Se source beam current rate is 20 nm / min, the Te source beam current rate is 20 nm / min, the Sn source growth temperature is 1000℃, the Se source growth temperature is 130℃, the Te source growth temperature is 350℃, and the temperature of the pretreated substrate is 300℃, resulting in a heterojunction. The thicknesses of the first and second thin films are both 60 nm. The heterojunction exhibits two-dimensional superconducting properties.

[0007] Optionally, the epitaxial orientation relationship of the heterojunction is

[002] SnTe /

[400] SnSe; SnTe is cubic rock salt. F 3m Phase, SnSe is orthogonally distorted rock salt Pnma Mutually.

[0008] Optional, Ginzburg-Landau zero-temperature coherence length ξ GL (0) = 61.86 nm, effective superconducting thickness d sc =44.09nm, which satisfies ξ GL (0)> d sc .

[0009] Optionally, the heterojunction carrier type is p-type holes.

[0010] Optionally, when the first thin film is SnTe and the second thin film is SnSe, a SnSe / SnTe / STO forward heterojunction is obtained.

[0011] Optionally, when the first thin film is SnSe and the second thin film is SnTe, a SnTe / SnSe / STO reverse heterojunction is obtained.

[0012] Optionally, when the heterojunction is a SnSe / SnTe / STO forward heterojunction, the superconducting onset transition temperature is... T c onset =3.46K, zero resistance temperature T c zero =2.10K.

[0013] Optionally, when the heterojunction is a SnTe / SnSe / STO reverse heterojunction, the superconducting onset transition temperature is... T c onset =3.81K, zero resistance temperature T c zero =2.67K.

[0014] Optionally, the out-of-plane compressive strain of SnTe in the heterojunction is -1.10% to -1.20%. This strain range can compress the SnTe lattice and improve the electroacoustic coupling strength, which is the core mechanical condition for inducing superconductivity; if the strain is too small, there is no superconductivity, and if it is too large, thin film cracks and lattice mismatch defects are likely to occur.

[0015] Optionally, the method further includes: after the first thin film has grown, allowing it to stand for 5-10 minutes, then separately turning on the Sn source baffle to deposit a Sn layer on the surface of the first thin film away from the substrate; after growth, allowing it to stand for 30 minutes, and then epitaxially growing a second thin film on the surface of the Sn layer away from the first thin film, so that the heterojunction carrier type is modulated from p-type holes to n-type electrons; the thickness of the Sn layer is 0.4 nm; and the superconducting onset transition temperature is... T c onset =4.32K.

[0016] Optionally, in step S1, the annealing process takes 2 hours.

[0017] Optionally, in step S1, the cleaning includes: ultrasonically cleaning the substrate sequentially with acetone and anhydrous ethanol, with each ultrasonic cleaning lasting 10-15 minutes.

[0018] Optionally, in step S2, the heating rate of the Sn source is 20°C / min; the heating rate of the Se source is 15°C / min; and the heating rate of the Te source is 20°C / min.

[0019] Optionally, in step S2, the Sn source is a Sn elemental source with a purity ≥ 99.999%; the Te source is a Te elemental source with a purity ≥ 99.999%; and the Se source is a Se elemental source with a purity ≥ 99.999%.

[0020] Optionally, the Sn source, the Te source, and the Se source are each filled using a Knudsen evaporator.

[0021] The present invention also discloses a method for preparing a superconducting heterojunction using the molecular beam epitaxy growth technique described above.

[0022] The present invention also discloses a superconducting heterojunction prepared by the method of preparing a superconducting heterojunction using the molecular beam epitaxy growth technique described above, or the application of the superconducting heterojunction in superconducting electronic devices as described above.

[0023] Optionally, the superconducting electronic device is a superconducting device such as a nanowire single-photon detector and a Majorana zero-mode device.

[0024] Implementing the embodiments of the present invention will have the following beneficial effects: The superconducting heterojunction prepared using the molecular beam epitaxy process of this invention has the following performance characteristics as verified by systematic characterization: 1. Crystal structure: SnTe is a cubic rock salt phase ( F 3mSnSe is an orthogonal GeS distorted rock salt facies ( Pnma ), extensional orientation relationship

[002] SnTe /

[400] SnSe.

[0025] 2. Superconducting properties: SnSe / SnTe / STO forward heterojunction, superconducting onset transition temperature T c onset =3.46K, zero resistance temperature T c zero =2.10K. SnTe / SnSe / STO reverse heterojunction, superconducting onset transition temperature. T c onset =3.81K, zero resistance temperature T c zero =2.67K.

[0026] 3. Superconductivity dimension: Ginzburg-Landau zero-temperature coherence length ξ GL (0) = 61.86 nm, effective superconducting thickness d sc =44.09nm, ξ GL (0)> d sc It exhibits a standard two-dimensional superconducting anisotropic magnetic field response; the magnetic field anisotropy is significant, and the vertical magnetic field has a much stronger inhibitory effect on superconductivity than the parallel magnetic field.

[0027] 4. Charge carriers: Thermal transport test results show that the charge carrier type is p-type hole conduction, and the charge carrier type can be tuned to n-type electron conduction by inserting a 0.4 nm ultrathin Sn layer between the two thin films.

[0028] 5. Interface quality: The interface is steep. XPS verification shows that the surface Te atom content is ≤3%, and there is no large-scale Se-Te alloying. UPS measurement shows that the work function of SnSe is 4.58 eV and the work function of SnTe is 4.36 eV, confirming the transfer of interface electrons from SnSe to SnTe and the metallization of the SnTe interface layer.

[0029] In summary, the obtained superconducting heterojunction possesses both the surface states of SnTe topological crystal insulators and two-dimensional superconducting properties, and has broad application prospects in the field of superconducting electronic devices. Attached Figure Description

[0030] Figure 1The X-ray diffraction data are for the SnSe(60nm) / SnTe(60nm) / STO forward superconducting heterojunction of Example 1 and the SnTe(60nm) / SnSe(60nm) / STO reverse superconducting heterojunction of Example 2 of this invention.

[0031] Figure 2 This is the X-ray electron spectrum of Embodiment 1 of the present invention. Among them, a is the XPS full spectrum of the SnSe(60nm) / SnTe(60nm) / STO heterojunction, where the nominal thickness of the SnSe layer and the SnTe layer is 60nm; b~d are the fine scan spectra of the binding energy of the characteristic peaks of the inner layers of Sn3d, Se3d, and Te3d, respectively.

[0032] Figure 3 This is a schematic diagram of the SnSe(60nm) / SnTe(60nm) / STO forward superconducting heterojunction of Embodiment 1 of the present invention. Wherein, a is a schematic diagram of the SnSe / SnTe / STO vertical heterojunction; b is a schematic diagram of the atomic structure.

[0033] Figure 4 This is a scanning electron microscope image of the SnSe(60nm) / SnTe(60nm) / STO forward superconducting heterojunction of Embodiment 1 of the present invention.

[0034] Figure 5 This is a scanning electron microscope image of the SnTe(60nm) / SnSe(60nm) / STO reverse superconducting heterojunction of Embodiment 2 of the present invention.

[0035] Figure 6 The low-temperature resistance-temperature curves and Seebeck coefficient-temperature curves of the SnSe(60nm) / SnTe(60nm) / STO forward superconducting heterojunction in Example 1 of this invention are shown.

[0036] Figure 7 The low-temperature resistance-temperature curves and Seebeck coefficient-temperature curves of the SnTe(60nm) / SnSe(60nm) / STO reverse superconducting heterojunction in Embodiment 2 of the present invention are shown.

[0037] Figure 8 The low-temperature resistance-temperature curves and Seebeck coefficient-temperature curves of the SnTe(60nm) / Sn(0.4nm) / SnSe(60nm) / STO heterojunction in Example 3 of the present invention are shown.

[0038] Figure 9 The ultraviolet photoelectron spectra of Comparative Examples 1-2 of this invention are shown.

[0039] Figure 10 The resistance-temperature data and Seebeck coefficient-temperature curves for SnTe(60nm) / STO in Comparative Example 2 of this invention are shown.

[0040] Figure 11 The resistance-temperature data and Seebeck coefficient-temperature curve of the SnTe(40nm) / SnSe(40nm) / STO heterojunction of Comparative Example 3 of this invention are shown.

[0041] Figure 12 The critical magnetic field-temperature fitting curves of the SnSe(60nm) / SnTe(60nm) / STO forward superconducting heterojunction in Example 1 of the present invention are shown, where a is the vertical magnetic field and b is the parallel magnetic field. Detailed Implementation

[0042] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0043] Example 1 The method for preparing superconducting heterojunctions using molecular beam epitaxy in this embodiment includes the following steps: S1. Select a (001) crystal plane insulating SrTiO3 single crystal as the substrate. After ultrasonically cleaning the substrate with acetone and anhydrous ethanol in sequence, place it in the ultra-vacuum cavity of the molecular beam epitaxy equipment, and control the vacuum degree of the ultra-vacuum cavity to be 1.8 × 10⁻⁶. -10 The substrate was heated to 300°C and annealed for 2 hours to obtain the pretreated substrate.

[0044] S2. Using Sn (≥99.999% purity), Se (≥99.999% purity), and Te (≥99.999% purity) as evaporation sources, molecular beam epitaxy (MBE) was employed to epitaxially grow a first SnTe film on a pretreated substrate. After growth, the substrate was allowed to stand for 8 minutes. Subsequently, a second SnSe film was epitaxially grown on the side of the first film away from the substrate. During growth, the Sn source beam current rate was 2 nm / min, and the Se source beam current rate was... The Te source beam rate was 20 nm / min, the Sn source was heated to 1000 °C at a rate of 20 °C / min, the Se source was heated to 130 °C at a rate of 15 °C / min, the Te source was heated to 350 °C at a rate of 20 °C / min, and the temperature of the pretreated substrate was 300 °C, resulting in a SnSe(60 nm) / SnTe(60 nm) / STO forward heterojunction; the thicknesses of the SnTe film and the SnSe film were 60 nm, respectively.

[0045] Test Example 1 X-ray diffraction (XRD) test In this embodiment 1, XRD tests were conducted at room temperature to detect the crystalline phase in the heterojunction. Figure 1 The data indicate that SnTe in the heterojunction is cubic rock salt.F 3m Phase, SnSe is orthogonally distorted rock salt Pnma The phases are

[002] SnTe /

[400] SnSe, and the epitaxial orientation relationship is

[002] SnTe /

[400] SnSe. XRD measured the out-of-plane compressive strain of SnTe to be -1.11%.

[0046] Test Example 2 X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy (XPS / UPS) testing In this example 1, in-situ X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy were performed at room temperature to characterize the chemical bonding state of the sample. Figure 2 X-ray photoelectron spectroscopy uses a magnesium target. K α X-rays were used as the excitation source, with a photon energy of 1253.6 eV. The test pass energy was set to 30 eV, and the detection incident angle was 53° to the sample plane. All test spectra were calibrated using a platinum foil standard sample. After subtracting the Shirley nonlinear baseline, the characteristic peak positions were determined by Gauss-Lorentz function fitting. Ultraviolet photoelectron spectroscopy (UVP) was performed using a helium-I source, with corresponding photon energies of 21.22 eV and 40.81 eV, and a detection incident angle of 61° to the sample plane. The platinum foil reference sample used in the experiment underwent multiple sputtering and annealing treatments in an ultra-high vacuum environment to thoroughly remove surface impurities and oxide layers. X-ray electron spectroscopy was used to characterize the elemental detection and semi-quantitative analysis within a 10 nm thickness of the surface. The chemical elements in Example 1 consisted of Sn, Se, and Te, and the semi-quantitative composition of the surface elements was SnSe. 0.97 Te 0.03 This indicates that there was not a large amount of Se and Te elements diffused on the surface.

[0047] Test Example 3 Scanning electron microscopy (SEM) testing In this embodiment 1, SEM testing was conducted at room temperature using a JSM-7800F Schottky field emission SEM. Figure 4 The test voltage was set to 5kV, and a backscattered electron detector was used to characterize the surface morphology. In this embodiment 1, the surface morphology shows regular undulations, and the surface film may be subject to stress modulation.

[0048] Test Example 4 Integrated Physical Property Measurement System (PPMS) Testing This embodiment 1 employs a comprehensive physical property measurement system. The electrical transport properties of the sample, i.e., resistance-temperature data acquisition, are tested using the standard four-probe method. The accompanying thermal transport testing module is used to complete Seebeck coefficient-temperature data acquisition in a high-vacuum environment within the temperature range of 2K to 300K. Figure 6The sample dimensions were 2mm × 10mm × 0.5mm. Conductive epoxy resin was used to fix the sample to a dedicated test base, ensuring good thermal contact. A stable temperature gradient was established using an integrated temperature control component, and temperature and voltage test signals were simultaneously acquired. The test system was calibrated using a nickel standard sample, and the Seebeck coefficient test error was controlled within ±0.5 μV / K. The test results show that Example 1 possesses two-dimensional superconducting properties, and the superconducting onset transition temperature is [not specified in the original text]. T c onset =3.46 K, zero resistance temperature T c zero =2.10 K, and the charge carriers are p-type holes.

[0049] Test Example 5 The test conditions were: temperature 0-3K, vertical magnetic field 0-0.03T, and in-plane magnetic field 0-0.15T, under which the resistance-temperature curve was measured. For example... Figure 12 As shown, the critical magnetic field-temperature fitting curve of the SnSe(60nm) / SnTe(60nm) / STO forward superconducting heterojunction in Example 1 yields the superconducting Ginzburg-Landau zero-temperature coherence length. ξ GL (0) = 61.86 nm, effective superconducting thickness d sc =44.09nm, which satisfies ξ GL (0)> d sc .

[0050] Example 2 The method for preparing superconducting heterojunctions using molecular beam epitaxy in this embodiment includes the following steps: S1. The pretreated substrate is obtained by processing according to step S1 of Example 1.

[0051] S2. Using Sn (≥99.999% purity), Se (≥99.999% purity), and Te (≥99.999% purity) as evaporation sources, molecular beam epitaxy (MBE) was employed to epitaxially grow a first SnSe film on a pretreated substrate. After growth, the substrate was allowed to stand for 8 minutes. Subsequently, a second SnTe film was epitaxially grown on the side of the first film away from the substrate. During the growth process, the Sn source beam current rate was 2 nm / min, and the Se source beam current rate was... The Te source beam rate was 20 nm / min, the Sn source was heated to 1000 °C at a rate of 20 °C / min, the Se source was heated to 130 °C at a rate of 15 °C / min, the Te source was heated to 350 °C at a rate of 20 °C / min, and the temperature of the pretreated substrate was 300 °C, resulting in a SnTe(60 nm) / SnSe(60 nm) / STO reverse heterojunction; the thicknesses of the SnSe film and the SnTe film were 60 nm, respectively.

[0052] X-ray diffraction (XRD) characterization was performed using the same test conditions as in Example 1, such as... Figure 1 As shown, the data indicates that SnTe in the heterojunction is cubic rock salt. F 3m Phase, SnSe is orthogonally distorted rock salt Pnma The phases are

[002] SnTe /

[400] SnSe, and their epitaxial orientation relationship is

[002] SnTe /

[400] SnSe. Analysis of XRD data showed that the out-of-plane compressive strain of SnTe was -1.19%.

[0053] Scanning electron microscopy (SEM) characterization was performed under the same test conditions as in Example 1, and the results are as follows: Figure 5 As shown, the surface morphology of this embodiment 2 presents a relatively smooth film.

[0054] The Power Property Measurement System (PPMS) was characterized using the same test conditions as in Example 1, and the results are as follows: Figure 7 As shown, Example 2 exhibits two-dimensional superconducting properties, with a superconducting onset transition temperature. T c onset =3.81K, zero resistance temperature T c zero =2.67K, and the charge carriers are p-type holes.

[0055] Example 3 The method for preparing superconducting heterojunctions using molecular beam epitaxy in this embodiment includes the following steps: S1. The pretreated substrate is obtained by processing according to step S1 of Example 1.

[0056] S2. Using Sn (≥99.999% purity), Se (≥99.999% purity), and Te (≥99.999% purity) single-element sources as evaporation sources, molecular beam epitaxy (MBE) was employed to epitaxially grow a first SnSe film on the pretreated substrate surface. After growth, the substrate was allowed to stand for 8 minutes. Subsequently, the Sn source baffle was turned on separately to deposit a Sn layer on the side of the SnSe film away from the substrate. After growth, the substrate was allowed to stand for 30 minutes. Then, a second SnTe film was epitaxially grown on the side of the Sn layer away from the SnSe film. During the growth process, the Sn source beam current rate was [missing information]. The beam rates were 20 nm / min for the Se source and 20 nm / min for the Te source. The Sn source was heated to 1000 °C at a rate of 20 °C / min, the Se source was heated to 130 °C at a rate of 15 °C / min, and the Te source was heated to 350 °C at a rate of 20 °C / min. The temperature of the pretreated substrate was 300 °C, resulting in a SnTe(60 nm) / Sn(0.4 nm) / SnSe(60 nm) / STO heterojunction. The thicknesses of the SnTe and SnSe films were 60 nm, and the Sn layer thickness was 0.4 nm.

[0057] The Power Property Measurement System (PPMS) was characterized using the same test conditions as in Example 1, and the results are as follows: Figure 8 As shown, the superconducting onset transition temperature T c onset =4.32K, still exhibiting superconducting transition, no zero-resistance state, and carrier type is n-type electron.

[0058] Comparative Example 1 The method for preparing heterojunctions using molecular beam epitaxy in this comparative example includes the following steps: S1. The pretreated substrate is obtained by processing according to step S1 of Example 1.

[0059] S2. Using Sn single-element source with purity ≥99.999% and Se single-element source with purity ≥99.999% as evaporation sources, a SnSe thin film was epitaxially grown on the surface of a pretreated substrate using molecular beam epitaxy. During the growth process, the Sn source beam current rate was 2 nm / min, the Se source beam current rate was 20 nm / min, the Sn source was heated to 1000℃ at a rate of 20°C / min, and the Se source was heated to 130℃ at a rate of 15°C / min. The temperature of the pretreated substrate was 300℃. The thickness of the SnSe thin film was 60 nm.

[0060] Comparative Example 2 The method for preparing heterojunctions using molecular beam epitaxy in this comparative example includes the following steps: S1. The pretreated substrate is obtained by processing according to step S1 of Example 1.

[0061] S2. Using Sn single-element source with a purity ≥99.999% and Te single-element source with a purity ≥99.999% as evaporation sources, a SnTe thin film was epitaxially grown on the surface of a pretreated substrate using molecular beam epitaxy. During the growth process, the Sn source beam current rate was 2 nm / min, the Te source beam current rate was 20 nm / min, the Sn source was heated to 1000℃ at a rate of 20°C / min, the Te source was heated to 350℃ at a rate of 20°C / min, and the temperature of the pretreated substrate was 300℃; the thickness of the SnTe thin film was 60 nm.

[0062] Figure 9 For the ultraviolet photoelectron spectra of Comparative Examples 1-2 (test conditions are the same as in Example 1), the UPS test work function is as follows: (SnSe) = 4.58 eV, (SnTe) = 4.36 eV; Figure 10 The resistance-temperature curve and Seebeck coefficient-temperature curve of Comparative Example 2 (test conditions are the same as in Example 1) show that the temperature range of 1.9-300K exhibits p-type carrier conductivity with no superconducting transition.

[0063] Comparative Example 3 The only difference between this comparative example and Example 2 is that the thicknesses of the SnSe and SnTe films are 40 nm, respectively.

[0064] Figure 11 The resistance-temperature data and Seebeck coefficient-temperature curve of the SnTe(40nm) / SnSe(40nm) / STO heterojunction of Comparative Example 3 of the present invention are shown (test conditions are the same as in Example 1). The results show that the temperature range of 1.9-300K exhibits p-type carrier conductivity and no superconducting transition.

[0065] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A method for preparing superconducting heterostructures using molecular beam epitaxy, characterized in that, Includes the following steps: S1. Select a (001) crystal plane insulating SrTiO3 single crystal as the substrate. After cleaning the substrate, place it in the ultra-vacuum cavity of the molecular beam epitaxy equipment, and control the vacuum degree of the ultra-vacuum cavity to be ≤2×10. -10 mbar, the substrate is heated to 300°C for annealing to obtain the pretreated substrate; S2. Using Sn, Se, and Te sources as evaporation sources, molecular beam epitaxy (MBE) is employed to epitaxially grow a first thin film on the pretreated substrate surface. The first thin film is either a SnTe or SnSe film. After growth, the substrate is allowed to stand for 5-10 minutes. Subsequently, a second thin film is epitaxially grown on the side of the first thin film away from the substrate. The second thin film is also either a SnTe or SnSe film, and its material differs from that of the first thin film. During growth, the Sn source beam current rate is 2 nm / min, the Se source beam current rate is 20 nm / min, the Te source beam current rate is 20 nm / min, the Sn source growth temperature is 1000℃, the Se source growth temperature is 130℃, the Te source growth temperature is 350℃, and the temperature of the pretreated substrate is 300℃, resulting in a heterojunction. The thicknesses of the first and second thin films are both 60 nm. The heterojunction exhibits two-dimensional superconducting properties.

2. The method for preparing superconducting heterojunctions using molecular beam epitaxy as described in claim 1, characterized in that, The epitaxial orientation relationship of the heterojunction is [002]SnTe / [400]SnSe; SnTe is cubic rock salt. F 3m Phase, SnSe is orthogonally distorted rock salt Pnma Phase; Ginzburg-Landau zero-temperature coherence length ξ GL (0) = 61.86 nm, effective superconducting thickness d sc =44.09nm, which meets the requirements. ξ GL (0)> d sc .

3. The method for preparing superconducting heterojunctions using molecular beam epitaxy as described in claim 1, characterized in that, The heterojunction carrier type is p-type holes.

4. The method for preparing superconducting heterojunctions using molecular beam epitaxy as described in claim 1, characterized in that, When the first thin film is SnTe and the second thin film is SnSe, a SnSe / SnTe / STO forward heterojunction is obtained; When the first thin film is SnSe and the second thin film is SnTe, a SnTe / SnSe / STO reverse heterojunction is obtained.

5. The method for preparing superconducting heterojunctions using molecular beam epitaxy as described in claim 4, characterized in that, When the heterojunction is a SnSe / SnTe / STO forward heterojunction, the superconducting onset transition temperature is... T c onset =3.46K, zero resistance temperature T c zero =2.10K; When the heterojunction is a SnTe / SnSe / STO reverse heterojunction, the superconducting onset transition temperature is... T c onset =3.81K, zero resistance temperature T c zero =2.67K.

6. The method for preparing superconducting heterojunctions using molecular beam epitaxy as described in claim 1, characterized in that, The out-of-plane compressive strain of SnTe in the heterojunction is -1.10% to -1.20%.

7. The method for preparing superconducting heterojunctions using molecular beam epitaxy as described in claim 1, characterized in that, In step S1, the annealing process takes 2 hours. In step S1, the cleaning includes: ultrasonically cleaning the substrate sequentially with acetone and anhydrous ethanol; In step S2, the heating rate of the Sn source is 20°C / min; the heating rate of the Se source is 15°C / min; and the heating rate of the Te source is 20°C / min. In step S2, the Sn source is a Sn elemental source with a purity ≥ 99.999%; the Te source is a Te elemental source with a purity ≥ 99.999%; and the Se source is a Se elemental source with a purity ≥ 99.999%.

8. A superconducting heterojunction prepared by a method for preparing a superconducting heterojunction using molecular beam epitaxy as described in any one of claims 1-7.

9. A superconducting heterojunction prepared by a method for preparing a superconducting heterojunction using molecular beam epitaxy as described in any one of claims 1-7, or the application of the superconducting heterojunction as described in claim 8 in superconducting electronic devices.

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