Superflat twin-free bi x sb 2-x Molecular beam epitaxy method for te3 thin films

Abstract

This invention discloses for the first time an ultra-flat, twin-free Bi x Sb 2‑x A molecular beam epitaxy method for preparing Te3 thin films is described, which uses Bi, Sb, and Te as evaporation sources to perform epitaxy on a stepped Al2O3(0001) substrate, resulting in ultra-flat, twin-free Bi films. x Sb 2‑ x Te3 thin film. Bi prepared in this invention. x Sb 2‑x Te3 thin films have larger grain sizes and simpler processing, eliminating the problems of poor flatness and high twinning caused by lattice mismatch during epitaxy, thus effectively improving the power factor and providing a basis for Bi x Sb 2‑x This has laid a solid foundation for the high-quality preparation and large-scale application of Te3 thin films.

Description

Technical Field

[0001] This invention belongs to the field of materials preparation technology, specifically relating to an ultra-flat, twin-free Bi0.05 x Sb 2-x A molecular beam epitaxy method for preparing Te3 thin films. Background Technology

[0002] In recent years, with the rapid development of semiconductor and information technologies, the large-scale commercial application of 5G communication technology, and the gradual emergence of flexible wearable smart devices, the market demand for micro-power generation and refrigeration devices is quite urgent. Thermoelectric technology based on thermoelectric materials and the direct conversion of heat and electricity is expected to become an effective method to alleviate the energy crisis and improve energy efficiency.

[0003] As a narrow bandgap semiconductor, Bi x Sb 2-x Te3 materials are thermoelectric materials with excellent performance near room temperature, and have important applications in efficient solid-state refrigeration and thermoelectric power generation. Meanwhile, Bi... x Sb 2-x Te3 materials are also the most important three-dimensional topological insulator materials, and are a material system of great interest in the fields of thermoelectricity and condensed matter physics. Furthermore, Bi... x Sb 2-x Te3 thin film materials are more likely to enable the miniaturization and flexibility of thermoelectric devices, and have great application prospects. x Sb 2-x Twin structures are prevalent in Te3 films, and their interfaces adversely affect electrical transport properties. However, twins are difficult to eliminate by modifying film growth process parameters, which greatly hinders the development of Bi3 films. x Sb 2-x Te3 thin film materials have wide applications in device and transport research. Therefore, there is a need to find a twin-free Bi material with high crystallinity and high flatness. x Sb 2-x A method for epitaxial preparation of Te3 thin films is urgently needed. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an ultra-flat, twin-free Bi alloy that addresses the shortcomings of the prior art. x Sb 2-x The molecular beam epitaxy method for preparing Te3 thin films is simple in process and eliminates the problem of poor flatness caused by lattice mismatch during epitaxy, thus effectively suppressing twinning.

[0005] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows:

[0006] An ultra-flat, twin-free Bi xSb 2-x A molecular beam epitaxy method for preparing Te3 thin films is described, using elemental Bi, Sb, and Te as raw materials and a stepped Al2O3(0001) substrate to epitaxially obtain ultra-flat, twin-free Bi films. x Sb 2-x Te3 thin film. The specific steps are as follows:

[0007] (1) Pretreatment of Al2O3(0001) substrate outside the cavity: The Al2O3(0001) substrate was annealed at high temperature, then washed and dried to obtain an Al2O3(0001) substrate with a stepped morphology.

[0008] (2) Growth of low-temperature Bi2Te3 buffer layer: The Al2O3 (0001) substrate with the stepped morphology obtained in step (1) is placed in the pretreatment chamber (loadlock chamber) of molecular beam epitaxy. After baking to remove gas, the sample is transferred into the growth chamber and then heated to remove gas. The substrate temperature is controlled to 230℃~240℃ using Bi and Te as evaporation sources to grow a low-temperature Bi2Te3 buffer layer.

[0009] (3)Bi x Sb 1-x Growth of Te3 thin films: In the growth chamber, Bi, Sb, and Te were used as evaporation sources, and the substrate temperature was controlled at 240℃~340℃. Ultra-smooth, twin-free Bi2Te3 thin films were obtained by growing a low-temperature Bi2Te3 buffer layer. x Sb 2-x Te3 thin film.

[0010] According to the above plan, Bi x Sb 2-x In Te3 thin films, x is greater than or equal to 0 and less than or equal to 2.

[0011] According to the above scheme, in step (1), the Al2O3(0001) substrate is an alumina substrate with (0001) orientation; the high-temperature annealing temperature is 1000℃~1500℃, and the time is more than 4 hours; the washing is carried out in an organic solvent, an alkaline solution, an acidic solution, and deionized water in sequence, and the washing temperature is 45℃~100℃; the drying is carried out by blowing with an inert gas. Among them, the organic solvent is high-purity ethanol and high-purity acetone; the alkaline solution is an ammonia solution (3%~10%), and the acidic solution is a hydrochloric acid solution (5%~30%) or a nitric acid solution (5%~30%).

[0012] According to the above scheme, the Al2O3(0001) substrate with step morphology obtained in step (1) has a step height of 0.4nm to 3.0nm and a width of 20nm to 150nm.

[0013] According to the above scheme, in step (2), the vacuum of the pretreatment chamber is 5×10⁻⁶.-7 mbar~1×10 -8 The baking and degassing temperature is 100℃~160℃ for more than 3 hours; the heating and degassing temperature in the growth chamber is 650℃~850℃ for 0.5 hours~2 hours; when growing the low-temperature Bi2Te3 buffer layer, the Bi beam current is... Te beam is Growth time: 0.5 to 2 minutes; growth vacuum: 5 × 10⁻⁶ -9 mbar~1×10 -10 mbar.

[0014] According to the above scheme, in step (3), ultra-flat, twin-free Bi is grown. x Sb 2-x When using Te3 thin films, the total beam current of Bi and Sb is Bi beam is Sb beam current is Te beam is Growth time of more than 2 hours; Bi x Sb 1-x The growth vacuum for Te3 thin films is 5 × 10⁻⁶. -9 mbar~1×10 -10 mbar, with a thickness of 50nm or more.

[0015] The ultra-flat, twin-free Bi prepared by the above method x Sb 2-x Te3 thin films were grown on a low-temperature Bi2Te3 buffer layer, and the prepared Bi x Sb 2-x The Te3 thin films exhibit a twinning degree less than 0.1, a thickness greater than 50 nm, and good crystallinity. The n-type Bi₂Te₃ films show a power factor of 2.5 mW / m². -1 K -2 The above describes the optimal p-type component, Bi. 0.5 Sb 1.5 The power factor of Te3 is 3.0 mW / m². -1 K -2 above.

[0016] Based on the above content, without departing from the basic technical concept of the present invention, various modifications, substitutions or changes can be made to the content in various forms according to common technical knowledge and means in the field.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] First, this invention uses Bi, Sb, and Te as evaporation sources to perform epitaxy on a stepped Al2O3(0001) substrate, thereby obtaining an ultra-flat, twin-free Bi substrate. x Sb 2-x Te3 thin films have a simple process and eliminate the problems of poor flatness and high twinning caused by lattice mismatch during epitaxy.

[0019] Secondly, by combining the optimization of substrate pretreatment and growth conditions, this invention successfully prepared ultra-flat, twin-free Bi substrates using molecular beam epitaxy. x Sb 2-x Te3 thin films significantly reduced the twinning degree, resulting in the preparation of Bi... x Sb 2-x The Te3 thin film achieves micron-level grain size, simplifies the process, and eliminates the problems of poor flatness and high twinning caused by lattice mismatch during epitaxy. This effectively improves the power factor, providing a foundation for Bi... x Sb 2-x This has laid a solid foundation for the high-quality preparation and large-scale application of Te3 thin films.

[0020] Third, the Al2O3(0001) substrate selected in this invention has good thermal conductivity, high strength, good insulation, and low price. Furthermore, through high-temperature pretreatment of the Al2O3(0001) substrate, an orderly and flat step is formed on the substrate surface, which serves as a template to achieve high-quality Bi x Sb 2-x The efficient and controllable epitaxial growth of Te3 thin films provides a basis for ultra-flat Bi x Sb 2-x This has laid a solid foundation for the large-scale preparation and application of Te3 thin film materials. Attached Figure Description

[0021] Figure 1 The images (a) and (b) are atomic force microscopy surface images (h) of the substrates after annealing in step 1) of Examples 1, 2, and 3.

[0022] Figure 2 The images are reflection high-energy electron diffraction images of the low-temperature Bi2Te3 buffer layer in steps 2 of Examples 1, 2, and 3.

[0023] Figure 3 The image shows a reflection high-energy electron diffraction image of the Bi2Te3 thin film sample during the growth process in step 2) of Example 1.

[0024] Figure 4 The image shows the surface of the Bi2Te3 film grown in step 2) of Example 1 using a scanning tunneling microscope.

[0025] Figure 5 The phase characterization results are obtained from high-resolution X-ray diffraction coupled scanning of the Bi2Te3 thin film grown in step 2) of Example 1.

[0026] Figure 6 The results are obtained by high-resolution X-ray diffraction in-plane rotation of the Bi2Te3 thin film grown in step 2) of Example 1.

[0027] Figure 7 Characterization of the electrical transport properties of the Bi2Te3 thin film grown in step 2) of Example 1.

[0028] Figure 8 This is a reflection high-energy electron diffraction image of the Sb2Te3 thin film sample during the growth process in step 2) of Example 2.

[0029] Figure 9 The image shows the surface of the Sb2Te3 film grown in step 2) of Example 2 using a scanning tunneling microscope.

[0030] Figure 10 The phase characterization results are obtained from high-resolution X-ray diffraction coupled scanning of the Sb2Te3 thin film grown in step 2) of Example 2.

[0031] Figure 11 The results are obtained by high-resolution X-ray diffraction of the Sb2Te3 thin film grown in step 2) of Example 2, which shows the in-plane rotation.

[0032] Figure 12 Characterization of the electrical transport properties of the Sb2Te3 thin film grown in step 2) of Example 2.

[0033] Figure 13 For example, in step 2) of the growth process of Bi 0.5 Sb 1.5 Reflection high-energy electron diffraction image of a Te3 thin film sample.

[0034] Figure 14 Bi grown in step 2) of Example 3 0.5 Sb 1.5 Scanning tunneling microscopy surface image of Te3 thin film.

[0035] Figure 15 Bi grown in step 2) of Example 3 0.5 Sb 1.5 Phase characterization results of Te3 thin films using high-resolution X-ray diffraction coupled scanning.

[0036] Figure 16 Bi grown in step 2) of Example 3 0.5 Sb 1.5 The results of in-plane rotational X-ray diffraction of Te3 thin films.

[0037] Figure 17 Bi grown in step 2) of Example 3 0.5 Sb 1.5 Characterization of the electrical transport properties of Te3 thin films.

[0038] Figure 18 The results are obtained by high-resolution X-ray diffraction in-plane rotation scanning of the Bi2Te3 thin film grown in step 2) of Comparative Example 1.

[0039] Figure 19 This describes the electrical transport properties of the Bi2Te3 thin film grown in step 2) of Comparative Example 1.

[0040] Figure 20 The results are obtained by high-resolution X-ray diffraction in-plane rotation scanning of the Bi2Te3 thin film grown in step 2) of Comparative Example 2. Detailed Implementation

[0041] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0042] Example 1

[0043] The specific steps of the molecular beam epitaxy method for preparing ultra-flat, twin-free Bi2Te3 thin films are as follows:

[0044] 1) An Al2O3(0001) single crystal substrate provided by Hefei Kejing Company was selected and placed in an Al2O3 crucible boat. It was then annealed in a muffle furnace at 1300℃ for 6 hours. The annealed Al2O3(0001) substrate was placed in a beaker and cleaned on a heating stage at 70℃ with acetone, ammonia solution (5%), dilute hydrochloric acid (20%), and deionized water. It was then dried with argon gas. At this point, an Al2O3(0001) substrate with a step morphology was obtained.

[0045] 2) The Al2O3(0001) substrate obtained in step 1) is transferred into the pretreatment chamber of molecular beam epitaxy and baked at 130°C for 4 hours (for degassing); then the baked Al2O3(0001) substrate is transferred to the growth chamber of molecular beam epitaxy and heated at 750°C for 1 hour (for degassing), and then the substrate temperature is controlled to about 230°C to 240°C to grow a low-temperature Bi2Te3 buffer layer, with the Bi beam current being [missing value]. Te beam is The growth vacuum is 3×10 -10 mbar, growth time 1-2 minutes, then controlling the substrate temperature to 260℃, Bi beam current is... Te beam is The growth vacuum is 3×10 -10A Bi2Te3 film with a thickness of approximately 100 nm was grown for 4 hours at mbar.

[0046] Example 2

[0047] The specific steps of the molecular beam epitaxy method for preparing ultraflat, twin-free Sb₂Te₃ thin films are as follows:

[0048] 1) An Al2O3(0001) single crystal substrate provided by Hefei Kejing Company was selected and placed in an Al2O3 crucible boat. It was then annealed in a muffle furnace at 1300℃ for 6 hours. The annealed Al2O3(0001) substrate was placed in a beaker and cleaned on a heating stage at 70℃ with acetone, ammonia solution (5%), dilute hydrochloric acid (20%), and deionized water. It was then dried with argon gas. At this point, an Al2O3(0001) substrate with a step morphology was obtained.

[0049] 2) The Al2O3(0001) substrate obtained in step 1) is transferred into the pretreatment chamber of molecular beam epitaxy and baked at 130°C for 4 hours. Then, the baked Al2O3(0001) substrate is transferred to the growth chamber of molecular beam epitaxy and heated at 750°C for degassing for 1 hour. The substrate temperature is then controlled to approximately 230°C–240°C to grow a low-temperature Bi2Te3 buffer layer. The Bi beam current is [missing value]. Te beam is The growth vacuum is 3×10 -10 mbar, growth time 1-2 minutes, then controlling the substrate temperature to 280℃, Sb beam current is... Te beam is The growth vacuum is 3×10 -10 mbar, Sb2Te3 film grown for 4 hours, with a thickness in the range of 80nm to 120nm.

[0050] Example 3

[0051] Ultra-flat, twin-free Bi 0.5 Sb 1.5 The specific steps for preparing Te3 thin films by molecular beam epitaxy are as follows:

[0052] 1) An Al2O3(0001) single crystal substrate provided by Hefei Kejing Company was selected and placed in an Al2O3 crucible boat. It was then annealed in a muffle furnace at 1300℃ for 6 hours. The annealed Al2O3(0001) substrate was placed in a beaker and cleaned on a heating stage at 70℃ with acetone, ammonia solution (5%), dilute hydrochloric acid (20%), and deionized water. It was then dried with argon gas. At this point, an Al2O3(0001) substrate with a step morphology was obtained.

[0053] 2) The Al2O3(0001) substrate obtained in step 1) is transferred into the pretreatment chamber of molecular beam epitaxy and baked at 130°C for 4 hours. Then, the baked Al2O3(0001) substrate is transferred to the growth chamber of molecular beam epitaxy and heated at 750°C for degassing for 1 hour. The substrate temperature is then controlled to approximately 230°C–240°C to grow a low-temperature Bi2Te3 buffer layer. The Bi beam current is [missing value]. Te beam is The growth vacuum is 3×10 -10 mbar, growth time 1-2 minutes, then controlling the substrate temperature to 300℃, Bi beam current is... Sb beam current is Te beam is The growth vacuum is 3×10 - 10 mbar, Bi grown for 4 hours 0.5 Sb 1.5 Te3 thin films with thicknesses ranging from 80 nm to 120 nm.

[0054] like Figure 1 As shown, in Examples 1, 2, and 3, the surface morphology of the substrate after step 1) was analyzed. Al2O3(0001) formed ordered flat steps at high temperature, with a step height of 0.8nm to 2nm and a step width of 70nm to 110nm.

[0055] Figure 2 The images shown are reflection high-energy electron diffraction images of the Bi2Te3 buffer layer grown in step 2 of Examples 1, 2, and 3. The fringe features in the images demonstrate that the grown low-temperature Bi2Te3 buffer layer is of good quality.

[0056] Figure 3 The image shows a reflection high-energy electron diffraction pattern of the Bi2Te3 film grown in step 2 of Example 1. The sharp stripes in the image demonstrate the high crystallinity and high flatness of the Bi2Te3 film during the two-step process.

[0057] Figure 4 The image shown is a scanning tunneling microscope image of the Bi2Te3 film grown in step 2) of Example 1. The Bi2Te3 film is very smooth and has a large grain size, approximately 700nm to 1200nm.

[0058] Figure 5 The high-resolution X-ray diffraction scanning results of the Bi2Te3 thin film grown in step 2 of Example 1 prove that the thin film is a single crystal Bi2Te3 (00l).

[0059] Figure 6In step 2) of Example 1, the high-resolution X-ray diffraction in-plane rotational scanning results of the grown Bi2Te3 film showed that the six-fold symmetric peak changed to a state close to a triplet peak, and the twinning degree was 0.062, proving that the twinning inside the Bi2Te3 film was significantly suppressed.

[0060] Figure 7 This refers to the electrical transport properties of the Bi2Te3 thin film grown in step 2) of Example 1. The twin-free Bi2Te3 thin film sample achieved a maximum power factor of 4.36 mW / m² near room temperature. -1 K -2 It is at a relatively high level in terms of Bi2Te3 film performance.

[0061] Figure 8 This is a reflection high-energy electron diffraction image of the Sb2Te3 thin film grown in step 2) of Example 2. The sharp stripes in the image demonstrate the high crystallinity and high flatness of the Sb2Te3 thin film during the two-step process.

[0062] Figure 9 The image shown is a scanning tunneling microscope image of the Sb2Te3 film grown in step 2 of Example 2. The Sb2Te3 film is very smooth.

[0063] Figure 10 The high-resolution X-ray diffraction scanning results of the Sb2Te3 thin film grown in step 2 of Example 2 prove that the thin film is a single crystal Sb2Te3(00l).

[0064] Figure 11 In step 2 of Example 2, the high-resolution X-ray diffraction in-plane rotational scanning results of the grown Sb2Te3 film showed that the six-fold symmetric peak changed to a state close to a triplet peak, and the twinning degree was 0.094, proving that the twinning inside the Sb2Te3 film was significantly suppressed.

[0065] Figure 12 This refers to the electrical transport properties of the Sb₂Te₃ thin film grown in step 2) of Example 2. The twin-free Sb₂Te₃ thin film sample achieved a maximum PF = 3.73 mW / m² near room temperature. -1 K -2 It is at a relatively high level in terms of Sb2Te3 film performance.

[0066] Figure 13 In step 2) of Example 3, the Bi grown 0.5 Sb 1.5 Reflective high-energy electron diffraction pattern of Te3 thin film; the sharp fringes in the image demonstrate the two-step process of Bi. 0.5 Sb 1.5 Te3 films exhibit high crystallinity and high flatness.

[0067] Figure 14 In step 2) of Example 3, the Bi grown 0.5 Sb 1.5 Scanning tunneling microscopy images of Te3 thin films, Bi 0.5 Sb 1.5 The Te3 film is very smooth.

[0068] Figure 15 In step 2) of Example 3, the Bi grown 0.5 Sb 1.5 High-resolution X-ray diffraction combined with scanning results of the Te3 thin film confirms that the film is a single-crystal Bi. 0.5 Sb 1.5 Te3(00l).

[0069] Figure 16 In step 2) of Example 3, the Bi grown 0.5 Sb 1.5 The high-resolution X-ray diffraction in-plane rotational scanning results of the Te3 thin film showed a change from a six-fold symmetric peak to a near-triple peak, with a twinning degree of 0.013, proving that Bi... 0.5 Sb 1.5 Twin formation within the Te3 film was significantly suppressed.

[0070] Figure 17 In step 2) of Example 3, the Bi grown 0.5 Sb 1.5 The electrical transport properties of Te3 thin films, and the twin-free Bi 0.5 Sb 1.5 The Te3 thin film sample achieved a maximum PF of 5.01 mWm near room temperature. -1 K -2 , in Bi 0.5 Sb 1.5 The performance of Te3 thin films is at a relatively high level.

[0071] Comparative Example 1

[0072] A molecular beam epitaxy method for preparing twin-free Bi2Te3 thin films under high growth temperature and low Te beam current conditions, the specific steps of which are as follows:

[0073] 1) An Al2O3(0001) single crystal substrate provided by Hefei Kejing Company was selected and placed in an Al2O3 crucible boat. It was then annealed in a muffle furnace at 1300℃ for 6 hours. The annealed Al2O3(0001) substrate was placed in a beaker and cleaned on a heating stage at 70℃ with acetone, ammonia solution (5%), dilute hydrochloric acid (20%), and deionized water. It was then dried with argon gas. At this point, an Al2O3(0001) substrate with a step morphology was obtained.

[0074] 2) The Al2O3(0001) substrate obtained in step 1) is transferred into the pretreatment chamber of molecular beam epitaxy and baked at 130°C for 4 hours (for degassing); then the baked Al2O3(0001) substrate is transferred to the growth chamber of molecular beam epitaxy and heated at 750°C for 1 hour (for degassing), and then the substrate temperature is controlled to about 230°C to 240°C to grow a low-temperature Bi2Te3 buffer layer, with the Bi beam current being [missing value]. Te beam is The growth vacuum is 3×10 -10 mbar, growth time 1-2 minutes, then controlling the substrate temperature to 350℃, Bi beam current is... Te beam is The growth vacuum is 3×10 -10 mbar, Bi2Te3 film grown for 4 hours, with a thickness of approximately 80nm to 120nm.

[0075] Figure 18 The high-resolution X-ray diffraction in-plane rotational scanning results of the grown Bi2Te3 film in step 2) of Comparative Example 1 show that the six-fold symmetric peak changes to a state close to a triplet peak, and the twinning degree is 0.011, proving that the twinning inside the Bi2Te3 film is significantly suppressed.

[0076] Figure 19 The electrical transport properties of the Bi2Te3 thin film grown in step 4) of Comparative Example 1, at a growth temperature of 350℃ and a Bi beam current of Te beam is Under the specified growth conditions, the twin-free Bi₂Te₃ thin film sample achieved a maximum power factor of 0.93 mW / m² near room temperature. -1 K -2 The poor performance may be due to the relatively high growth temperature and the relatively small Te beam current.

[0077] Comparative Example 2

[0078] Comparative example of molecular beam epitaxy preparation of Bi2Te3 thin films, the specific steps of which are as follows:

[0079] 1) Select Al2O3(0001) single crystal substrate provided by Hefei Kejing Company, without annealing treatment, place it in a beaker, and clean it on a heating stage at 70℃ with acetone, ammonia solution (5%), dilute hydrochloric acid (20%), and deionized water, and blow it dry with argon gas. At this time, an Al2O3(0001) substrate with a step morphology is obtained.

[0080] 2) The Al2O3(0001) substrate obtained in step 1) is transferred into the pretreatment chamber of molecular beam epitaxy and baked at 130°C for 4 hours (for degassing); then the baked Al2O3(0001) substrate is transferred to the growth chamber of molecular beam epitaxy and heated at 750°C for 1 hour (for degassing), and then the substrate temperature is controlled to about 230°C to 240°C to grow a low-temperature Bi2Te3 buffer layer, with the Bi beam current being [missing value]. Te beam is The growth vacuum is 3×10 -10 mbar, growth time 1-2 minutes, then controlling the substrate temperature to 300℃, Bi beam current is... Te beam is The growth vacuum is 3×10 -10 mbar, Bi2Te3 film grown for 4 hours, with a thickness of approximately 80nm to 120nm.

[0081] Figure 20 The results of high-resolution X-ray diffraction in-plane rotation scanning of the Bi2Te3 thin film grown in step 2) of Comparative Example 2 show obvious sixfold symmetry peaks, a twinning degree of 0.67, and a high twinning content.

[0082] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A type of ultra-flat, twin-free Bi x Sb 2-x The method for preparing Te3 thin films by molecular beam epitaxy is characterized by, Includes the following steps: (1) Pretreatment of Al2O3(0001) substrate outside the cavity: The Al2O3(0001) substrate was subjected to high-temperature annealing at a temperature of 1300 ℃ ~ 1500 ℃ for more than 4 hours. Then it was washed and dried to obtain an Al2O3(0001) substrate with a step morphology, the step height being 0.8 nm ~ 2 nm and the step width being 70 nm ~ 110 nm. (2) Growth of low-temperature Bi2Te3 buffer layer: The Al2O3(0001) substrate with the stepped morphology obtained in step (1) is placed in the pretreatment chamber of molecular beam epitaxy. After baking to remove gas, the sample is transferred into the growth chamber and then heated to remove gas. The substrate temperature is controlled to 230 ℃~240 ℃ using Bi and Te as evaporation sources to grow a low-temperature Bi2Te3 buffer layer. The Bi beam current was 0.04 Å / s ~ 0.12 Å / s, the Te beam current was 0.2 Å / s ~ 0.8 Å / s, and the growth time was 0.5 min ~ 2 min. (3) Bi x Sb 2-x Growth of Te3 thin films: In the growth chamber, Bi, Sb, and Te were used as evaporation sources, and the substrate temperature was controlled at 240 ℃ ~ 340 ℃. Ultra-flat, twin-free Bi3 thin films were obtained by growing a low-temperature Bi2Te3 buffer layer. x Sb 2-x Te3 thin film; wherein the total beam current of Bi and Sb is 0.02 Å / s ~ 0.06 Å / s, the Bi beam current is 0 ~ 0.06 Å / s, the Sb beam current is 0 ~ 0.06 Å / s, the Te beam current is 0.1 Å / s ~ 0.8 Å / s, and the growth time is more than 2 hours; The ultra-flat, twin-free Bi x Sb 2-x The twinning degree of the Te3 thin film is less than 0.1, and the thickness is greater than 50 nm.

2. The ultra-flat, twin-free Bi alloy according to claim 1 x Sb 2-x The method for preparing Te3 thin films by molecular beam epitaxy is characterized by, Bi x Sb 2-x In Te3 thin films, x is greater than or equal to 0 and less than or equal to 2.

3. The ultra-flat, twin-free Bi alloy according to claim 1 x Sb 2-x The method for preparing Te3 thin films by molecular beam epitaxy is characterized by, In step (2), the vacuum in the pretreatment chamber is 5 × 10⁻⁶. -7 mbar ~ 1×10 -8 The baking degassing temperature is 100 ~ 160 ℃ for more than 3 hours; the heating degassing temperature in the growth chamber is 650 ℃ ~ 850 ℃ for 0.5 hours ~ 2 hours.

4. The ultra-flat, twin-free Bi alloy according to claim 1 x Sb 2-x The method for preparing Te3 thin films by molecular beam epitaxy is characterized by, In step (2), the growth vacuum of the low-temperature Bi2Te3 buffer layer is 5×10⁻⁶. -9 mbar ~ 1×10 -10 mbar; in step (3), Bi x Sb 1-x The growth vacuum for Te3 thin films is 5 × 10⁻⁶. -9 mbar ~ 1×10 -10 mbar, with a thickness of 50 nm or more.

5. The ultra-flat, twin-free Bi alloy according to claim 1 x Sb 2-x The method for preparing Te3 thin films by molecular beam epitaxy is characterized by, In step (1), the washing process involves sequentially cleaning in organic solvent, alkaline solvent, acidic solvent, and deionized water at a temperature of 45 ℃ ~ 100 ℃; drying is performed using inert gas.

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