Method for preparing bismuth selenide thin film

Abstract

The application discloses a preparation method of a Bi2Se3 thin film, and the method comprises the following steps: under vacuum, high temperature and hydrogen input, high-purity bismuth source and high-purity selenium source are plasma chemical vapor deposition onto a clean substrate to obtain a Bi2Se3 thin film crude product. The preparation of the Bi2Se3 thin film adopts the experimental method of plasma-assisted chemical vapor deposition, so that the deposition process can be carried out at a lower temperature, compared with the traditional method, the Se evaporation phenomenon caused by excessively high temperature can be effectively avoided, the vacancy defect density of Se in the thin film is reduced, and the crystallization quality of the Bi2Se3 thin film is improved. The Bi2Se3 thin film crude product is annealed to remove H impurities in the Bi2Se3 thin film crude product, and the internal stress of the thin film is reduced through the treatment of natural cooling to room temperature, so that the high-quality Bi2Se3 single crystal thin film can be obtained. In addition, the preparation method of the Bi2Se3 thin film can grow Bi2Se3 thin films with different shapes, sizes and thicknesses, which is beneficial to industrial production and application.

Description

Technical Field

[0001] This invention belongs to the field of transparent conductive film preparation technology, specifically relating to a method for preparing Bi2Se3 thin films. Background Technology

[0002] Infrared transparent conductive films are widely used in military and civilian infrared detectors due to their excellent infrared transmittance and strong electromagnetic shielding capabilities, such as anti-jamming infrared missile heads and high-sensitivity infrared gas / CO detectors.

[0003] Bi₂Se₃ (bismuth selenide) is a three-dimensional topological insulator material possessing both a gapped bulk state and a gapless surface state. Furthermore, the surface state is stably maintained due to time-reversal symmetry. Therefore, it exhibits surface conductivity while remaining internally insulating. Due to its unique surface states and transport properties, it has applications in numerous fields, including spintronic devices, high-frequency devices, and quantum computing. However, its infrared transparent conductivity has not yet been investigated.

[0004] Existing transparent conductive films all suffer from the inherent contradiction of high transmittance and low conductivity. The fundamental characteristic of Bi₂Se₃ three-dimensional topological insulators is the presence of four time-reversal symmetry points in the Brillouin zone of its surface states. At these points, Kramers degeneracy occurs, forming Dirac cones. The apex of the Dirac cone is called the Dirac point, and the dispersion relation between energy and momentum near this vertex is linear (not quadratic). Due to the spin-coupling effect, the spin direction of this surface state is always perpendicular to the momentum direction, allowing electrons to propagate across the surface at a speed similar to that of photons with low loss (or no loss) (surface mobility μ). s ≈6000cm 2 The structure has a density of / V·s, and its interior is insulatory. Therefore, the Bi2Se3 three-dimensional topological insulator meets the requirement of high mobility for mid- and far-infrared transparent conductive films.

[0005] Researchers have employed various methods to prepare Bi₂Se₃ thin films, such as pulsed laser deposition, magnetron sputtering, and chemical vapor deposition. However, these methods suffer from drawbacks, including high preparation temperatures and high saturated vapor pressures of Se, leading to the easy formation of Se vacancies. While Bi₂Se₃ containing Se defects exhibits excellent N-type semiconductor properties, this non-insulating "topological insulator" generates a strong bulk conductivity background during electrical transport measurements, thereby masking the surface state conductivity characteristics and significantly impacting the transparent conductivity of the topological insulator. Therefore, it is necessary to provide a method for preparing Bi₂Se₃ thin films that can improve their crystallinity. Summary of the Invention

[0006] This invention addresses the technical problem that the high Se vacancy defect density in Bi2Se3 films prepared by existing technologies severely affects the transparent conductivity of Bi2Se3 films. The aim is to provide a method for preparing Bi2Se3 films that can reduce the Se vacancy defect density and improve the crystallinity of the films.

[0007] The method for preparing Bi2Se3 thin films of the present invention includes: plasma chemical vapor deposition of high-purity bismuth source and high-purity selenium source onto a clean substrate under vacuum, high temperature and hydrogen gas to obtain crude Bi2Se3 thin film.

[0008] Preferably, the temperature of the plasma chemical vapor deposition is 150–300°C.

[0009] Preferably, the radio frequency power of the plasma chemical vapor deposition is 150-300W, the pulse frequency is 15-25KHz, the pressure is 30-70Pa, and the deposition time is 20-60min.

[0010] Preferably, the method further includes: after plasma chemical vapor deposition, annealing the crude Bi2Se3 film under an inert gas and then naturally cooling it to obtain the Bi2Se3 film.

[0011] Preferably, the substrate is one of sapphire (0001), ZnS, and single-crystal silicon;

[0012] Before plasma chemical vapor deposition, the substrate is ultrasonically cleaned in acetone solution, anhydrous ethanol solution, and deionized water, respectively, for 10 to 15 minutes each time.

[0013] Preferably, the high-purity bismuth source is 98% trimethylbismuth and the high-purity selenium source is 98% diethyl selenide.

[0014] Preferably, the hydrogen flow rate of the high-purity bismuth source is 15-50 sccm, and the partial pressure ratio of the hydrogen to the high-purity bismuth source is 95:1-108:1; the hydrogen flow rate of the high-purity selenium source is 25-120 sccm, and the partial pressure ratio of the hydrogen to the high-purity selenium source is 36:1-101:1; the partial pressure ratio of the high-purity bismuth source to the high-purity selenium source is 1:2-1:5.

[0015] Preferably, the annealing process refers to placing the crude Bi2Se3 film in a molybdenum boat and annealing it in an annealing furnace at a temperature of 200–350°C for 20–40 minutes.

[0016] Preferably, the plasma chemical vapor deposition chamber is first evacuated to 1×10⁻⁶ using a mechanical pump. -4 ~4×10 -4 Pa, then use a molecular pump to evacuate the plasma chemical vapor deposition chamber to 3 × 10⁻⁶ Pa. -6 ~6×10 -6 Pa.

[0017] The positive and progressive effects of this invention are as follows:

[0018] The present invention prepares Bi2Se3 thin films using plasma-assisted chemical vapor deposition. The plasma generated during the plasma chemical vapor deposition process can significantly promote the chemical reaction, allowing the deposition process to be carried out at a lower temperature. Compared with existing preparation methods, this method can effectively avoid Se evaporation caused by excessively high temperatures, reduce the Se vacancy defect density in the film, and thus improve the crystallinity of the Bi2Se3 thin film.

[0019] This invention involves annealing crude Bi₂Se₃ films to remove hydrogen impurities, followed by natural cooling to room temperature to reduce internal stress, thereby obtaining high-quality Bi₂Se₃ single-crystal films. Furthermore, the method for preparing Bi₂Se₃ films of this invention can grow Bi₂Se₃ films of different shapes, sizes, and thicknesses, which is beneficial for industrial production and application. Attached Figure Description

[0020] Figure 1A The X-ray diffraction pattern of the Bi2Se3 thin film obtained in Example 1 of the present invention;

[0021] Figure 1B The surface morphology of the Bi2Se3 thin film obtained in Example 1 of the present invention;

[0022] Figure 1C The infrared transmission spectrum of the Bi2Se3 thin film obtained in Example 1 of the present invention;

[0023] Figure 1D This is a surface resistivity-temperature diagram of the Bi2Se3 thin film obtained in Example 1 of the present invention;

[0024] Figure 2A The X-ray diffraction pattern of the Bi2Se3 thin film obtained in Example 2 of the present invention;

[0025] Figure 2B The surface morphology of the Bi2Se3 thin film obtained in Example 2 of the present invention;

[0026] Figure 2C The infrared transmission spectrum of the Bi2Se3 thin film obtained in Example 2 of the present invention;

[0027] Figure 2DThe surface resistivity-temperature diagram of the Bi2Se3 thin film obtained in Example 2 of the present invention;

[0028] Figure 3A The X-ray diffraction pattern of the Bi2Se3 thin film obtained in Example 3 of the present invention;

[0029] Figure 3B The surface morphology of the Bi2Se3 thin film obtained in Example 3 of the present invention;

[0030] Figure 3C The infrared transmission spectrum of the Bi2Se3 thin film obtained in Example 3 of the present invention;

[0031] Figure 3D The surface resistivity-temperature diagram of the Bi2Se3 thin film obtained in Example 3 of the present invention;

[0032] Figure 4A The X-ray diffraction pattern of the Bi2Se3 thin film obtained in Example 4 of the present invention;

[0033] Figure 4B The surface morphology of the Bi2Se3 thin film obtained in Example 4 of the present invention;

[0034] Figure 4C The infrared transmission spectrum of the Bi2Se3 thin film obtained in Example 4 of the present invention;

[0035] Figure 4D The resistivity-temperature diagram of the Bi2Se3 thin film obtained in Example 4 of the present invention;

[0036] Figure 5 This is a schematic diagram of the PN junction and its current-voltage characteristic curves prepared based on the Bi2Se3 thin film of the present invention. Detailed Implementation

[0037] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0038] The method for preparing the Bi2Se3 thin film of the present invention includes: plasma chemical vapor deposition of a high-purity bismuth source and a high-purity selenium source onto a clean substrate under vacuum, high temperature, and hydrogen gas purging to obtain a crude Bi2Se3 thin film. The specific steps of the Bi2Se3 thin film preparation method of the present invention are as follows:

[0039] Preparation of Bi2Se3 thin films in Examples 1-4

[0040] Step S1: Place substrate S 衬底 Ultrasonic cleaning was performed in 90% acetone solution, anhydrous ethanol solution, and deionized water, respectively, with each cleaning session lasting t. 清洗 After cleaning, the substrate S was purged with a nitrogen gun. 衬底 After drying, the sample is placed inside the cavity of a plasma chemical vapor deposition (PCVDC) apparatus and heated to the preset deposition temperature T. 沉积 The temperature was set to ℃ and maintained stably. Trimethylbismuth (TMBi, 98%) and diethyl selenide (DESe, 98%) were placed separately into diffusers within the cavity of the plasma chemical vapor deposition apparatus.

[0041] Step S2: First, use the mechanical pump of the plasma-enhanced chemical vapor deposition (PECVD) system (Orion III, manufactured by Trion Corporation, USA) to evacuate the PCVD chamber to P1 Pa. Then, use the molecular pump on the PCVD system to evacuate the chamber to P2 Pa. Turn on the power of the RF pulse generator on the PCVD system and adjust the RF power to P. 射频 W, pulse frequency is f 脉冲 KHz enables the generation of stable plasma within the plasma chemical vapor deposition chamber.

[0042] Step S3: Open the high-purity hydrogen valve to introduce high-purity hydrogen (99.999%). Adjust the hydrogen flow rate through the diffuser for trimethylbismuth (TMBi, 98%) to V1 sccm, and adjust the hydrogen flow rate through the diffuser for diethyl selenide (DESe, 98%) to V2 sccm, so that the hydrogen flow rates for trimethylbismuth (TMBi, 98%) and diethyl selenide (DESe, 98%) are respectively V1 sccm. TMBi sccm, V DESe The flow rate of sccm enters the substrate S 衬底 Within the cavity of the plasma chemical vapor deposition apparatus, it should be noted that the partial pressure ratio of hydrogen to trimethylbismuth (TMBi, 98%) is R1; the partial pressure ratio of hydrogen to diethyl selenide (DESe, 98%) is R2; and the partial pressure ratio of trimethylbismuth (TMBi, 98%) to diethyl selenide (DESe, 98%) is R3.

[0043] Step S4: Adjust the pressure in the cavity of the plasma chemical vapor deposition equipment to P3 Pa, and the deposition time to t. 沉积 min, to obtain a crude Bi2Se3 film of suitable thickness.

[0044] Step S5: Place the crude Bi2Se3 film obtained in step S4 into a molybdenum boat and put it into an annealing furnace (Hefei Kejing tube furnace OTF-1200X). Anneal in high-purity nitrogen (99.999%) to remove H impurities from the film. The temperature of the annealing furnace is set at V. 升温 Heating rate increased to T at ℃ / min 退火 ℃ and maintain this temperature t 退火 After annealing, the film was allowed to cool naturally to room temperature in the annealing furnace to obtain the Bi2Se3 film. The parameters are shown in Table 1.

[0045] Table 1. Experimental parameters for the preparation of Bi₂Se₃ thin films in Examples 1-4.

[0046]

[0047]

[0048] Performance Test Examples

[0049] The performance of the Bi2Se3 thin films prepared in Examples 1-4 was evaluated, and the evaluation results are shown in Table 2. It should be noted that the specific method for evaluating the performance of the Bi2Se3 thin films of the present invention was as follows: the obtained Bi2Se3 thin films were placed in an X-ray diffractometer (Bruker D8 X-ray diffractometer, Germany) to test the crystal structure and crystal orientation of the films; an infrared Fourier transform spectrometer (Shimadzu IRTracer-100 Fourier transform infrared spectrometer, Japan) to test the infrared transmittance of the films; and a Hall effect tester (NanometricsACCENT HL55OOPC) to test the surface resistivity of the films.

[0050] Table 2 Performance evaluation results of Bi2Se3 thin films prepared in Examples 1-4

[0051]

[0052]

[0053] Table 3 Performance evaluation results of other existing infrared transparent conductive films

[0054] <![CDATA[CuScO₂ thin film]]> 3~5μm 85% 1.047Ω·cm 96％ <![CDATA[CuSc 0.94 Sn 0.06 O2 thin film 3~5μm 90% <![CDATA[5.6×10 -2 Ohm cm]]> 90％ <![CDATA[In₂O₃:HfO₂ thin film]]> 3~5μm 68% <![CDATA[3.3×10 -2 Ohm cm]]> none <![CDATA[In₂O₃:W thin film]]> 0.78~2μm 75% <![CDATA[3.23×10 -4 Ohm cm]]> polycrystalline <![CDATA[Y₂O₃:Ru thin film]]> 3.5~12μm 65% <![CDATA[3.36×10 -3 Ohm cm]]> amorphous

[0055] The performance test graph of Example 1 is shown below. Figures 1A-1D As shown, Figure 1B Figure (a) shows an atomic force microscope image of the Bi₂Se₃ thin film in Example 1, and Figure (b) shows a high-resolution transmission electron microscope image and a selected area electron diffraction image of the Bi₂Se₃ thin film. According to... Figure 1AAs can be seen from the X-ray diffraction pattern, the Bi2Se3 thin film obtained in Example 1 of this invention is a single-crystal thin film with a highly preferred c-axis orientation.

[0056] The performance test graph of Example 2 is shown below. Figures 2A-2D As shown, Figure 2B Figure (a) in the image is an atomic force microscope image of the Bi₂Se₃ thin film of Example 2, and Figure (b) is a high-resolution transmission electron microscope image and a selected area electron diffraction image of the Bi₂Se₃ thin film of Example 2. According to... Figure 2A (X-ray diffraction pattern) and Figure 2C (Infrared transmission spectrum) shows that the Bi2Se3 thin film obtained in Example 2 of the present invention has high crystallinity and good mid- and far-infrared transmittance.

[0057] Performance test graph of Example 3 is shown below Figures 3A-3D As shown, Figure 3B Figure (a) shows an atomic force microscope image of the Bi₂Se₃ thin film in Example 3, and Figure (b) shows a high-resolution transmission electron microscope image and a selected area electron diffraction image of the Bi₂Se₃ thin film in Example 3. Figures 3A-3D It can be seen that the Bi2Se3 thin film obtained in Example 3 of the present invention has good crystallinity and conductivity.

[0058] The performance test graph of Example 4 is shown below. Figures 4A-4D As shown, Figure 4B Figure (a) shows the 2×2μm sample from Example 4. 2 (a) An atomic force microscope image of the Bi2Se3 thin film of Example 4, (b) a high-resolution transmission electron microscope image of the cross-section of the (001) oriented Bi2Se3 thin film of Example 4, and (c) a selected area electron diffraction image of the surface of the Bi2Se3 thin film of Example 4. Figure 4D As shown in the resistivity-temperature diagram, the lowest surface resistivity of the Bi₂Se₃ thin film obtained in Example 4 of this invention at room temperature is 2.6 × 10⁻⁶. -5 Ω·cm, indicating that the Bi2Se3 thin film obtained in Example 4 of this invention has good electrical conductivity at room temperature.

[0059] Table 2 shows the test results of the Bi2Se3 films obtained in Examples 1-4. The Bi2Se3 films obtained in this invention are highly c-axis-preferred oriented single-crystal films. They exhibit good transmittance in the mid- and far-infrared bands and good conductivity at room temperature. In other words, applying the Bi2Se3 film of this invention as a broadband infrared transparent conductive film balances conductivity and broadband transparency, successfully overcoming the inherent contradiction between high transmittance and low conductivity in existing broadband transparent conductive films. Comparing the data in Tables 2 and 3 shows that the Bi2Se3 infrared transparent conductive film prepared in this invention has higher crystallinity, higher infrared transmittance, and a wider infrared spectral transmission range compared to existing infrared transparent conductive films, while also exhibiting lower resistivity. This demonstrates that the Bi2Se3 infrared transparent conductive film prepared in this invention is a broadband, high-transmittance infrared transparent conductive film with good conductivity. Due to the excellent optical transmittance and strong electromagnetic shielding properties of the Bi2Se3 film of this invention, it is expected to be applied in various civilian and military infrared detectors. Furthermore, the Bi₂Se₃ thin film prepared by this invention can also be used in diode devices. The performance evaluation method involves placing the N-Bi₂Se₃ / P-Si diode device into an SDHG-186A frequency converter transformer current-voltage characteristic tester to test the diode's current-voltage characteristic curve. The evaluation results are as follows: Figure 5 As shown. It should be noted that the detectors and diodes described in the above applications are manufactured according to conventional methods in the prior art, and will not be described in detail here.

[0060] The present invention has been described in detail above with reference to the accompanying drawings and embodiments. Those skilled in the art can make various modifications to the present invention based on the above description. Therefore, certain details in the embodiments should not be construed as limiting the present invention, and the scope of protection of the present invention shall be defined by the appended claims.

Claims

1. A method for preparing a Bi₂Se₃ thin film, characterized in that... The method includes: depositing high-purity bismuth source and high-purity selenium source onto a clean substrate under vacuum, high temperature and hydrogen gas to obtain a crude Bi2Se3 thin film; The high-purity bismuth source is 98% trimethylbismuth, and the high-purity selenium source is 98% diethyl selenide. The hydrogen flow rate of the high-purity bismuth source is 15~50 sccm, and the partial pressure ratio of hydrogen to high-purity bismuth source is 95:1~108:

1. The hydrogen flow rate of the high-purity selenium source is 25~120 sccm, and the partial pressure ratio of hydrogen to high-purity selenium source is 36:1~101:

1. The partial pressure ratio of the high-purity bismuth source to the high-purity selenium source is 1:2 to 1:5; The temperature of the plasma chemical vapor deposition is 150~300℃; The method further includes: after plasma chemical vapor deposition, annealing the crude Bi2Se3 film under an inert gas and then naturally cooling it to obtain a Bi2Se3 film. The annealing process refers to placing the crude Bi2Se3 film in a molybdenum boat and annealing it in an annealing furnace at a temperature of 200~350℃ for 20~40min.

2. The method as described in claim 1, characterized in that... The radio frequency power of the plasma chemical vapor deposition is 150~300W, the pulse frequency is 10KHz, 15~25KHz, the pressure is 30~70Pa, and the deposition time is 20~60min.

3. The method as described in claim 1, characterized in that... The substrate is one of sapphire (0001), ZnS and single crystal silicon; Before plasma chemical vapor deposition, the substrate is ultrasonically cleaned in acetone solution, anhydrous ethanol solution, and deionized water, respectively, for 10-15 minutes each time.

4. The method as described in claim 1, characterized in that, First, use a mechanical pump to evacuate the plasma chemical vapor deposition chamber to 1×10⁻⁶. -4 ~4×10 -4 Pa, then use a molecular pump to evacuate the plasma chemical vapor deposition chamber to 3 × 10⁻⁶ Pa. -6 ~ 6×10 -6 Pa.

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