A preparation method of a cadmium telluride film with high-strength high-plasticity multi-stage gradient structure

Abstract

The application discloses a preparation method of a cadmium telluride film with a high-strength high-plasticity multi-stage gradient structure. The cadmium telluride film with a multi-stage gradient distribution of grain size and twin lamella thickness along the thickness direction of the film is prepared by means of magnetron sputtering, through adjusting and controlling sputtering temperature and sputtering pressure, the limit compressive strength of the film is 1.1 GPa-1.2 GPa, and the limit compressive strain is 16%-20%. Compared with the cadmium telluride film containing only columnar crystal structure, the cadmium telluride film with the multi-stage gradient structure has an increase of 37.5%-50% in strength and an increase of 23%-55% in plasticity; compared with the cadmium telluride film containing only equiaxed crystal structure, the cadmium telluride film has an increase of 0-10% in strength and an increase of 10%-36% in plasticity. Therefore, the multi-stage gradient structure design realizes the synergistic improvement of the strength and plasticity of the cadmium telluride film.

Description

Technical Field

[0001] This invention belongs to the field of flexible semiconductor thin films, specifically relating to a method for preparing cadmium telluride thin films with high strength and high plasticity, and multi-level gradient distribution of grain size and twin layer thickness along the thickness direction. Background Technology

[0002] Cadmium telluride (CdT) is a high-performance group II-VI semiconductor material with broad application prospects in optoelectronic devices and other fields. As semiconductor devices continue to evolve towards miniaturization and flexibility, the mechanical properties of semiconductor materials at the micro- and nano-scale pose significant challenges to their application in flexible scenarios. Inorganic semiconductors typically exhibit high brittleness, and their lack of mechanical strength and plasticity limits their further commercial applications. In recent years, researchers have discovered that gradient structure materials often exhibit mechanical properties and deformation mechanisms that differ significantly from single-structure materials. A well-designed gradient structure can break the strength-plasticity constraint, synergistically improving the strength and plasticity of the material. Bulk materials can have their surface grains refined through surface mechanical treatments, achieving a grain morphology with a gradient distribution from surface nanocrystals to internal microcrystals. However, due to the micrometer-scale thickness of thin film materials, it is difficult to obtain gradient structures through traditional surface mechanical treatments. Furthermore, current research mainly focuses on single-microstructure gradient designs, making the fabrication of multi-level gradient structures in thin films challenging. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for preparing cadmium telluride thin films with high strength and high plasticity and multi-level gradient structure, which addresses the shortcomings of the prior art. By controlling the sputtering temperature and sputtering pressure of magnetron sputtering, a cadmium telluride thin film with multi-level gradient distribution of grain size and twin layer thickness along the thickness direction is prepared, thereby achieving a synergistic improvement in strength and plasticity.

[0004] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows:

[0005] This invention utilizes argon gas ionization in a vacuum environment, first cleaning the substrate surface with plasma, and then performing radio frequency magnetron sputtering by bombarding a cadmium telluride target with argon ions under an electric field. By controlling the sputtering temperature and sputtering pressure, a cadmium telluride thin film with a high-strength, high-plasticity, multi-level gradient structure is obtained. Specifically, it involves the following two preparation methods:

[0006] The first method for preparing a cadmium telluride thin film with a high-strength, high-plasticity, multi-level gradient structure involves ionizing argon gas in a vacuum environment. First, the substrate surface is cleaned using argon ions. Then, under the influence of an electric field, argon ions bombard a cadmium telluride target for radio frequency magnetron sputtering. By controlling the sputtering temperature and sputtering pressure, a cadmium telluride thin film with a high-strength, high-plasticity, multi-level gradient structure is obtained. The sputtering temperature ranges sequentially include 450℃-500℃, 300℃-350℃, 150℃-200℃, and 20℃-50℃, with an interval of 100℃-200℃ between adjacent temperature ranges. The sputtering pressure is 1.5Pa-3.0Pa. The cadmium telluride thin film obtained by this preparation method is a high-strength and high-plasticity cadmium telluride thin film with multi-level gradient distribution of grain size and twin layer thickness along the film thickness direction. The gradient change trend of grain size and twin layer thickness is the same as the gradient change trend of sputtering temperature. With the gradient change range of sputtering temperature from high to low, the gradient change range of grain size of cadmium telluride thin film from bottom to top is 51.2nm-73.3nm, 39.4nm-52.4nm, 24.1nm-32.3nm and 3.9nm-12.8nm, respectively, and the gradient change range of twin layer thickness is 7.1nm-12.4nm, 4.2nm-6.5nm, 1.4nm-3.6nm and 1.0nm-1.3nm, respectively.

[0007] This invention also provides a method for preparing a cadmium telluride thin film with a high-strength, high-plasticity, multi-level gradient structure. The method is characterized by ionizing argon gas in a vacuum environment, firstly cleaning the substrate surface with argon ions, and then bombarding the cadmium telluride target with argon ions under an electric field for radio frequency magnetron sputtering. By controlling the sputtering temperature and sputtering pressure, a cadmium telluride thin film with a high-strength, high-plasticity, multi-level gradient structure is obtained. The sputtering temperature is 20℃-50℃; the sputtering pressure ranges sequentially include 0.5Pa-0.9Pa, 1.0Pa-1.4Pa, and 1.5Pa-3.0Pa, or sequentially include 1.5Pa-3.0Pa, 1.0Pa-1.4Pa, and 0.5Pa-0.9Pa; and the interval between two adjacent sputtering pressure ranges is 0.5Pa-1.0Pa. The cadmium telluride thin film obtained by this preparation method is a high-strength and high-plasticity cadmium telluride thin film with a multi-level gradient distribution of grain size and twin layer thickness along the film thickness direction. The gradient variation trend of grain size and twin layer thickness is opposite to the gradient variation trend of sputtering pressure. When the sputtering pressure range includes 0.5Pa-0.9Pa, 1.0Pa-1.4Pa, and 1.5Pa-3.0Pa respectively, the gradient variation range of grain size of cadmium telluride thin film from bottom to top is 22.5nm-43.8nm, 14.8nm-32.8nm, and 3.9nm-12.8nm respectively, and the gradient of twin layer thickness is... The variation ranges are 2.1nm-5.3nm, 1.6nm-3.2nm, and 1.0nm-1.3nm, respectively. When the sputtering pressure ranges include 1.5Pa-3.0Pa, 1.0Pa-1.4Pa, and 0.5Pa-0.9Pa, the gradient variation ranges of the grain size of the cadmium telluride film from bottom to top are 3.9nm-12.8nm, 14.8nm-32.8nm, and 22.5nm-43.8nm, respectively, and the gradient variation ranges of the twin layer thickness are 1.0nm-1.3nm, 1.6nm-3.2nm, and 2.1nm-5.3nm, respectively.

[0008] In both of the above preparation methods, the sputtering time for each sputtering temperature range or each sputtering pressure range is 1.0h-1.5h.

[0009] The cadmium telluride films obtained by the two preparation methods described above have a thickness of 1.5 μm-2.0 μm, an ultimate compressive strength of 1.1 GPa-1.2 GPa, and an ultimate compressive strain of 16%-20%. Compared with cadmium telluride films containing only columnar crystal structures, the strength is increased by 37.5%-50%, and the plasticity is increased by 23%-55%. Compared with cadmium telluride films containing only equiaxed crystal structures, the strength is increased by 0-10%, and the plasticity is increased by 10%-36%, respectively.

[0010] According to the above scheme, the present invention also provides a more specific method for preparing cadmium telluride thin films with high strength, high plasticity, and multi-level gradient structures, comprising the following steps:

[0011] 1) Place a clean single-crystal silicon substrate into the sputtering chamber for later use, fix the cadmium telluride target on the RF power supply, adjust the target-substrate distance to 9.0cm-10cm, and the sputtering angle to 60°-62°.

[0012] 2) Close the sputtering chamber door, start the mechanical pump and molecular pump in sequence to evacuate the sputtering chamber to a high vacuum state, then introduce argon gas as the working gas, apply bias voltage to ionize the argon gas, and use argon ions to clean the single crystal silicon substrate for 10 min-20 min.

[0013] 3) After the substrate is cleaned, adjust the RF power supply to the required power and turn on the RF power supply. Pre-sputter the target for 20-30 minutes to remove impurities on the target surface.

[0014] 4) After pre-sputtering is completed, the substrate temperature and sputtering pressure are set according to the two preparation methods mentioned above. The heating switch is turned on, and the substrate temperature is kept at the set value for a period of time. Then the shut-off valve is opened to adjust the sputtering pressure, and the substrate baffle, substrate stage rotation switch and RF power switch are turned on in sequence to sputter the thin film, so as to obtain a cadmium telluride thin film with a high strength, high plasticity and multi-level gradient structure.

[0015] Preferably, the vacuum level required for the high vacuum environment during thin film sputtering is 5 × 10⁻⁶. -4 Pa is below; the argon gas is high-purity argon gas with a purity of ≥99.999%.

[0016] Preferably, in step 2), the bias voltage is 700V-800V, the pulse duty cycle is 50%-80%, the argon flow rate is 60sccm-80sccm, and the working pressure is 2.0Pa-3.0Pa.

[0017] Furthermore, in step 4), the RF power supply is 30W-50W, the argon flow rate is 15sccm-80sccm, and the sputtering pressure is 0.5Pa-3Pa.

[0018] Further, in step 4), ① if a multi-level gradient cadmium telluride thin film is prepared by controlling the substrate temperature, the required temperature ranges for film sputtering are 20℃-50℃, 150℃-200℃, 300℃-350℃, and 450℃-500℃, respectively; the substrate is first heated to 450℃-500℃ for film sputtering, then naturally cooled to 300℃-350℃ under high vacuum for film sputtering, then naturally cooled to 150℃-200℃ under high vacuum for film sputtering, and finally naturally cooled to 20℃-50℃ under high vacuum for film sputtering. The interval between adjacent temperature ranges is 100℃-200℃. ② To prepare multi-gradient cadmium telluride thin films by controlling the sputtering pressure, the required sputtering pressure ranges are 0.5 Pa-0.9 Pa, 1.0 Pa-1.4 Pa, and 1.5 Pa-3.0 Pa, respectively: First, 45 sccm-80 sccm of argon gas is introduced to achieve a sputtering pressure of 1.5 Pa-3.0 Pa for sputtering. Then, the argon gas flow rate is reduced to 30 sccm-43 sccm to lower the sputtering pressure to 1.0 Pa-1.4 Pa for sputtering. Finally, the argon gas flow rate is reduced to 15 sccm-28 sccm to achieve a sputtering pressure of 0.5 Pa-0.9 Pa for sputtering. The interval between adjacent pressure ranges is 0.5 Pa-1.0 Pa. The sputtering time for each temperature and pressure range is 1.0 h-1.5 h, and the substrate rotation speed is 10-15 r / min.

[0019] Compared with the prior art, the present invention has the following advantages: The present invention utilizes the method of changing the sputtering film temperature and sputtering gas pressure to achieve multi-level gradient changes in the grain size and twin layer thickness of the cadmium telluride film along the thickness direction, and achieves a synergistic improvement in strength and plasticity.

[0020] Existing technologies rely on surface mechanical treatments to refine the surface grains, achieving a grain morphology with a gradient distribution from surface nanocrystals to internal microcrystals. Grain refinement, based on Hall-Petch strengthening theory, is an effective strengthening method for traditional materials; within a certain range, the material's strength increases with decreasing grain size. Simultaneously, the gradient structure design promotes the initiation and storage of geometrically necessary dislocations, generating additional work hardening capacity and thus improving the material's plastic deformation.

[0021] The grain size range involved in this invention has reached the deep nanoscale range, and the further refinement of the grains has broken through the critical size of the traditional Hall-Petch relationship. The equiaxed crystals prepared by this invention, due to their small grain size and aspect ratio, exhibit grain boundary-coordinated plastic deformation behaviors such as torsion and merging under stress, thereby improving plasticity. The slender columnar crystals with a high proportion of parallel grain boundaries require greater energy for crack initiation and propagation at the grain boundaries under stress, thus providing a strengthening effect. Simultaneously, the presence of gradient-distributed twin lamellae within the grains, similar to the grain boundary effect, coordinates plasticity through a detwinization mechanism of twin boundary migration. Nanoscale twins can effectively hinder dislocation movement while storing dislocations, improving the material's strength and work hardening ability.

[0022] This invention employs a multi-level gradient structure where different regions deform in a coordinated manner, avoiding abrupt changes in the crystal's internal structure and grain boundaries that could lead to lattice mismatch and localized stress concentration at grain boundaries. Under stress, equiaxed crystals experience greater plastic strain, while columnar crystals exhibit smaller plastic strain but provide strengthening. To maintain strain continuity across regions, twins and grains with different characteristic sizes coordinate with each other and initiate different deformation mechanisms, thereby improving the material's strength and plasticity. Simultaneously, the multi-level microstructure interfaces generate geometrically necessary dislocations to coordinate deformation. This intrinsic coupling effect of the multi-level gradient structure synergistically enhances the strength and plasticity of cadmium telluride films. Attached Figure Description

[0023] Figure 1 The X-ray diffraction (XRD) pattern of the cadmium telluride thin film prepared in Example 1 is shown below.

[0024] Figure 2 This is a scanning electron microscope (SEM) image (magnification 12000x) of the cross-section of the cadmium telluride thin film prepared in Example 1;

[0025] Figure 3 The images shown are transmission electron microscope (TEM) images, average grain size and average twin thickness distribution diagrams, and high-resolution transmission electron microscope (HRTEM) images of the thin cross-section of the cadmium telluride thin film prepared in Example 1 (a is the transmission electron image of the cross-section, b is the average grain size and average twin thickness distribution diagram, and c is the high-resolution transmission electron microscope image).

[0026] Figure 4 Transmission electron microscopy (TEM) images, selected area electron diffraction (SEAD) and elemental energy dispersive spectroscopy (EDS) results of the thin section of the cadmium telluride thin film prepared in Example 2 (a is the transmission electron image of the cross section, b is the selected area electron diffraction and calibration results, c and d are the surface scans of the energy dispersive spectroscopy).

[0027] Figure 5Transmission electron microscopy (TEM) images of cadmium telluride thin films prepared for Comparative Examples 1 and 2 (a is the TEM image of columnar crystals in Comparative Example 1, and b is the TEM image of equiaxed crystals in Comparative Example 2).

[0028] Figure 6 These are the compressive stress-strain curves of cadmium telluride thin films prepared in Examples 1 (gradient structure 1), 2 (gradient structure 2), and Comparative Examples 1 and 2. Detailed Implementation

[0029] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the present invention is not limited to the following embodiments.

[0030] Example 1

[0031] A method for preparing cadmium telluride thin films with high strength, high plasticity, and a multi-level gradient structure by controlling the sputtering temperature, the specific steps of which are as follows:

[0032] 1) Coating preparation: Place the single-sided polished monocrystalline silicon substrate in alcohol and sonicate for 10 minutes. After drying, place it in the sputtering equipment with the polished side facing down. Place the cadmium telluride target on the RF power supply, adjust the target-substrate distance to 10 cm, the sputtering angle to 60°, close the sputtering chamber door, and start the mechanical pump and molecular pump in sequence to evacuate the sputtering chamber to a high vacuum state.

[0033] 2) Argon ion cleaning of substrates: The vacuum level of the sputtering chamber reaches 5×10⁻⁶. -4 After Pa, the substrate rotation speed was set to 15 r / min, the substrate baffle was opened, high-purity argon gas was introduced, the argon gas flow rate was 80 sccm, the working gas pressure was 3.0 Pa, the bias voltage was set to 800 V, the pulse duty cycle was 80%, and the argon gas was used to ionize argon ions to clean the surface of the substrate polishing surface for 20 min.

[0034] 3) Target pre-sputtering: Turn off the substrate baffle and bias voltage, set the RF power supply to 40W and the pulse duty cycle to 80%, turn on the RF power supply to perform target pre-sputtering, and the pre-sputtering time is 30min to remove impurities on the target surface.

[0035] 4) Sputtering thin film: After pre-sputtering, turn off the RF power supply, turn on the heating switch to heat to the required coating temperature, and hold at that temperature for 10-30 minutes. Set the substrate rotation speed to 10-15 r / min, turn on the RF power supply and substrate baffle, and perform coating. The specific steps for sputtering thin film are as follows, depending on the set temperature range:

[0036] a. Turn off the RF power supply, set the target temperature to 450℃, the heating rate to 15℃ / min, turn on the heating switch, and hold the substrate at the target temperature (i.e., sputtering temperature) for 30 minutes. Then, introduce high-purity argon gas at a flow rate of 45 sccm, a working pressure of 1.5 Pa (i.e., sputtering pressure), and an RF power of 40W. Turn on the RF power supply and sputter for 1 hour.

[0037] b. Turn off the RF power supply and heating switch, set the target temperature to 300℃, and after the substrate cools naturally to this temperature, turn on the heating switch to maintain this temperature. The working pressure is 1.5Pa, the RF power is 40W, the RF power supply is turned on, and the sputtering time is 1h.

[0038] c. Turn off the RF power supply and heating switch, set the target temperature to 150℃, and after the substrate cools naturally to this temperature, turn on the heating switch to maintain this temperature. The working pressure is 1.5Pa, the RF power is 40W, the RF power supply is turned on, and the sputtering time is 1h.

[0039] d. Turn off the RF power supply and heating switch, set the target temperature to 20℃, and after the substrate cools naturally to this temperature, turn on the heating switch to maintain this temperature. The working pressure is 1.5Pa, the RF power is 40W, the RF power supply is turned on, and the sputtering time is 1h.

[0040] 5) After sputtering is complete, turn off the RF power supply, substrate baffle, and stop the argon gas supply. The film can be taken out after it has been stabilized in a high vacuum environment for 1-2 hours, thus obtaining a cadmium telluride film with a high strength, high plasticity, and multi-level gradient structure.

[0041] Example 2

[0042] A method for preparing cadmium telluride thin films with high strength, high plasticity, and a multi-level gradient structure by controlling the sputtering gas pressure, the specific steps of which are as follows:

[0043] The difference between Example 2 and Example 1 is that in step 4), the target temperature (i.e., sputtering temperature) is set to 20°C, argon gas is introduced by opening the shut-off valve to achieve the required gas pressure for sputtering the thin film, the substrate rotation speed is set to 15 r / min, the RF power supply and substrate baffle are turned on, and film deposition is performed. The specific gas pressure depends on the set pressure range. The specific steps for sputtering the thin film are as follows:

[0044] a. Open the shut-off valve, introduce high-purity argon gas, with an argon gas flow rate of 45 sccm, a working gas pressure of 1.5 Pa, a radio frequency power of 40 W, and a sputtering time of 1 h;

[0045] b. Set the argon flow rate to 30 sccm, the working pressure to 1.0 Pa, the RF power to 40 W, and the RF time to 1 h;

[0046] c. Set the argon flow rate to 15 sccm, the working pressure to 0.5 Pa, the RF power to 40 W, and the RF time to 1 hour;

[0047] After the thin film sputtering is completed, the RF power supply and substrate baffle are turned off, and the argon gas supply is stopped. The thin film can be taken out after stabilizing in a high vacuum environment for 1-2 hours, thus obtaining a cadmium telluride thin film with a high strength, high plasticity, and multi-level gradient structure.

[0048] Comparative Example 1

[0049] The difference between Comparative Example 1 and Example 1 is as follows: In step 4), the target temperature is set to 500℃, the heating rate is 15℃ / min, the heating switch is turned on, and after reaching the target temperature, it is held for 30 minutes. High-purity argon gas is introduced at a flow rate of 45 sccm, the working pressure is 1.5 Pa, the RF power is 40 W, the RF power supply is turned on, and the sputtering time is 4 hours. After sputtering is completed, the heating switch, RF power supply, and argon gas valve are turned off. After the substrate cools naturally to room temperature in a high vacuum environment, the molecular pump and mechanical pump are turned off, and the film is removed.

[0050] Comparative Example 2

[0051] The difference between Comparative Example 2 and Example 1 is that in step 4), the target temperature is set to 20°C, high-purity argon gas is introduced, the argon gas flow rate is 45 sccm, the working pressure is 1.5 Pa, the radio frequency power is 40 W, the radio frequency power supply is turned on, and the sputtering time is 4 h.

[0052] Example 1 shows a cadmium telluride thin film with a gradient distribution of grain size and twin layer thickness along the thickness direction obtained by changing the sputtering temperature under a high vacuum environment. Its XRD pattern is shown below. Figure 1 As shown, it matches the PDF card, and the phase structure is a face-centered cubic (FCC) structure with preferred orientations of (111), (311) and (220). Figure 2 This is a SEM image of a cross-section of a cadmium telluride film with a multi-gradient structure, magnified 12000x, showing a film thickness of 1.8 μm. A TEM image of the thin section of the cadmium telluride film with a multi-gradient structure is shown below. Figure 3 As shown in (a), ① is the thin film surface, and ④ and below it is a single-crystal silicon substrate. Regions ①-④ correspond to the cross-sections of thin films sputtered at different temperatures (regions ①-④ correspond to 20℃, 150℃, 300℃, and 450℃, respectively). The transitions between regions are natural and without distortion. Figure 3(b) It can be seen that the grain size and twin layer thickness increase with increasing sputtering temperature. From region ① to region ④, the grain size ranges are 9.5nm-12.8nm, 24.1nm-32.3nm, 39.4nm-52.4nm, and 51.2nm-73.3nm, respectively, and the twin layer thickness ranges are 1.0nm-1.3nm, 1.4nm-3.6nm, 4.2nm-6.5nm, and 7.1nm-12.4nm, respectively, achieving a multi-level gradient distribution of grain size and twin layer thickness; Figure 3 (c) It can be seen that the grains contain a large number of twins perpendicular to the grain boundaries.

[0053] like Figure 4 As shown in (a), Example 2 obtained a cross-sectional thin-area TEM image of a multi-level gradient cadmium telluride thin film by changing the sputtering gas pressure. The grain size and twin layer thickness decreased with increasing sputtering gas pressure. The average grain size from region ① to region ③ (corresponding to sputtering gas pressures of 0.5 Pa, 1.0 Pa, and 1.5 Pa, respectively) ranged from 22.5 nm to 43.8 nm, 14.8 nm to 32.8 nm, and 9.5 nm to 12.8 nm, respectively, and the twin layer thickness ranged from 2.1 nm to 5.3 nm, 1.6 nm to 3.2 nm, and 1.0 nm to 1.3 nm, respectively. This achieved a gradient change in grain size and twin layer thickness along the film thickness direction. The selected area electron diffraction and calibration results for the thin area are shown below. Figure 4 As shown in (b), the calibration results of the cadmium telluride polycrystalline thin film are in good agreement with the XRD results. Figure 4 (c) and (d) are the energy dispersive spectroscopy (EDS) spectra of Cd and Te, respectively, showing that Cd and Te are uniformly distributed. Therefore, this invention can not only prepare cadmium telluride films with multi-level gradient structures by controlling the sputtering temperature, but also by controlling the sputtering pressure.

[0054] The thin-area TEM images of Comparative Example 1 and Comparative Example 2 are as follows: Figure 5 As shown, Figure 5 (a) shows a columnar crystal morphology; Figure 5 (b) shows a grain morphology of equiaxed crystals.

[0055] Figure 6The figures show the compressive stress-strain curves of the films obtained in Examples 1, 2, 1, and 2. Examples 1 and 2 are cadmium telluride films with multi-level gradient structures, 1 is a cadmium telluride film with only columnar crystal morphology, and 2 is a cadmium telluride film with only equiaxed crystal morphology. According to the stress-strain curves, the ultimate compressive strength of the cadmium telluride film with a single columnar crystal structure is 0.8 GPa, and the ultimate compressive strain is 12.9%; the ultimate compressive strength of the cadmium telluride film with a single equiaxed crystal structure is 1.1 GPa, and the ultimate compressive strain is 14.7%. All films with a single microstructure exhibit softening after reaching the maximum compressive strength. The films prepared by this invention, exhibiting a multi-level gradient distribution of nanocrystalline grain size and nanotwin layer thickness, demonstrate continuous work hardening under compressive stress. Example 1 shows an ultimate compressive strength of 1.2 GPa and an ultimate compressive strain of 20%, representing a 50% and 10% increase in strength, respectively, and a 55% and 36% increase in plasticity, respectively, compared to cadmium telluride films containing only columnar or equiaxed crystal structures. Example 2 shows an ultimate compressive strength of 1.1 GPa and an ultimate compressive strain of 16%, comparable to cadmium telluride films containing only equiaxed crystal structures in strength, with a 10% increase in plasticity. Compared to cadmium telluride films containing only columnar crystal structures, the strength is increased by 37.5%, and the plasticity by 23%. Therefore, the cadmium telluride films prepared by this invention, with a multi-level gradient distribution of grain size and twin layer thickness along the film thickness direction, exhibit synergistic enhancement in strength and plasticity compared to cadmium telluride films with a single uniform composition structure.

[0056] Obviously, the above embodiments are merely examples for clear illustration and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a cadmium telluride thin film having a high-strength high-plasticity multi-stage gradient structure, characterized by, The argon gas is ionized in a vacuum environment, argon ions are used to clean the surface of the substrate first, and then argon ions bombard the cadmium telluride target under the action of an electric field to perform radio frequency magnetron sputtering, and through the regulation and control of sputtering temperature and sputtering pressure, a cadmium telluride film with a high-strength high-plasticity multi-stage gradient structure is obtained, the cadmium telluride film is a high-strength high-plasticity cadmium telluride film with a multi-stage gradient distribution of grain size and twin lamella thickness along the thickness direction of the film, wherein the sputtering pressure is 1.5 Pa-3 Pa, the sputtering temperature interval includes 450 DEG C-500 DEG C, 300 DEG C-350 DEG C, 150 DEG C-200 DEG C and 20 DEG C-50 DEG C in sequence, the gradient change interval of the grain size is 51.2 nm-73.3 nm, 39.4 nm-52.4 nm, 24.1 nm-32.3 nm and 3.9 nm-12.8 nm in sequence, and the gradient change interval of the twin lamella thickness is 7.1 nm-12.4 nm, 4.2 nm-6.5 nm, 1.4 nm-3.6 nm and 1.0 nm-1.3 nm in sequence; the interval between adjacent two temperature intervals is 100 DEG C-200 DEG C.

2. A method for preparing a cadmium telluride thin film having a high-strength high-plasticity multi-stage gradient structure, characterized by, The argon gas is ionized in a vacuum environment, argon ions are used to clean the surface of the substrate first, and then argon ions bombard the cadmium telluride target under the action of an electric field to perform radio frequency magnetron sputtering, and through the regulation and control of sputtering temperature and sputtering pressure, a cadmium telluride film with a high-strength high-plasticity multi-stage gradient structure is obtained, the cadmium telluride film is a high-strength high-plasticity cadmium telluride film with a multi-stage gradient distribution of grain size and twin lamella thickness along the thickness direction of the film, wherein the sputtering temperature is 20 DEG C-50 DEG C; the sputtering pressure interval includes 0.5 Pa-0.9 Pa, 1.0 Pa-1.4 Pa and 1.5 Pa-3.0 Pa in sequence, the gradient change interval of the grain size is 22.5 nm-43.8 nm, 14.8 nm-32.8 nm and 3.9 nm-12.8 nm in sequence, and the gradient change interval of the twin lamella thickness is 2.1 nm-5.3 nm, 1.6 nm-3.2 nm and 1.0 nm-1.3 nm in sequence; or the sputtering pressure interval includes 1.5 Pa-3.0 Pa, 1.0 Pa-1.4 Pa and 0.5 Pa-0.9 Pa in sequence, the gradient change interval of the grain size is 3.9 nm-12.8 nm, 14.8 nm-32.8 nm and 22.5 nm-43.8 nm in sequence, and the gradient change interval of the twin lamella thickness is 1.0 nm-1.3 nm, 1.6 nm-3.2 nm and 2.1 nm-5.3 nm in sequence; the interval between adjacent two sputtering pressure intervals is 0.5 Pa-1.0 Pa.

3. The method for preparing a cadmium telluride film with a high-strength high-plasticity multi-stage gradient structure according to claim 1 or 2, characterized in that, The sputtering time of each sputtering temperature interval or each sputtering pressure interval during sputtering is 1.0 h-1.5 h.

4. The method for preparing a cadmium telluride film with a high-strength high-plasticity multi-stage gradient structure according to claim 1 or 2, characterized in that, The thickness of the cadmium telluride film is 1.5-2.0 μm; the ultimate compressive strength of the cadmium telluride film is 1.1-1.2 GPa, and the ultimate compressive strain is 16-20%, the strength is increased by 37.5-50% and the plasticity is increased by 23-55% compared with the cadmium telluride film containing only columnar crystal structure; the strength is increased by 0-10% and the plasticity is increased by 10-36% compared with the cadmium telluride film containing only equiaxed crystal structure.

5. The method for preparing a cadmium telluride film with a high-strength high-plasticity multi-stage gradient structure according to claim 1 or 2, characterized in that, The method comprises the following steps: 1) placing a clean single crystal silicon substrate in a sputtering cavity for use, fixing a cadmium telluride target on a radio frequency power source, adjusting the target-substrate distance to 9-10 cm and the sputtering angle to 60-62°; 2) closing the sputtering cavity door, starting a mechanical pump and a molecular pump in sequence to draw the sputtering cavity to a high vacuum state, then introducing argon as a working gas, applying a bias voltage to ionize the argon, and cleaning the single crystal silicon substrate with argon ions for 10-20 min; 3) after the substrate is cleaned, adjusting the radio frequency power source to the required power, then opening the radio frequency power source, and pre-sputtering the target for 20-30 min to remove impurities on the surface of the target; 4) after pre-sputtering, setting the sputtering temperature and sputtering pressure according to claim 1 or 2, opening the heating switch, waiting for the substrate temperature to reach the set value, then opening the shut-off valve to adjust the sputtering pressure, and successively opening the substrate baffle, substrate table rotation switch and radio frequency power source switch to sputter the film, thereby obtaining a cadmium telluride film with high strength, high plasticity and multi-stage gradient structure.

6. The method of claim 5, wherein the method further comprises the step of: The vacuum degree required for high vacuum environment in sputtering thin film is required to be 5 x 10 -4 Pa or below; argon is high purity argon with purity ≥ 99.999%. ​ 7. The method of claim 5, wherein the method further comprises the step of: In step 2), the bias voltage is 700-800 V, the pulse duty cycle is 50-80%, the argon flow rate is 60-80 sccm, and the working gas pressure is 2.0-3.0 Pa. ​

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