Preparation method of single crystal tin selenide thermoelectric thin film and single crystal tin selenide thermoelectric thin film

Abstract

The invention relates to the technical field of thin film thermoelectric materials, and particularly discloses a preparation method of a single crystal tin selenide thermoelectric thin film, and the preparation method specifically comprises the following steps: S1, cleaning a substrate; s2, placing a substrate; s3, vacuumizing is carried out; s4, degassing the substrate; s5, heating the evaporation source; s6, growing the thin film; s7, cooling the film; and S8, taking out the sample. The molecular beam epitaxy method is used for preparing the thin film, the selenium beam / tin beam ratio is strictly controlled, H2Se is adopted for selenium vacancy repairing in the thin film growth process, the high-quality a-axis orientation single crystal tin selenide thermoelectric thin film can be obtained, the thin film has good thermoelectric performance, and integrated packaging of chips is easy to achieve.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of thin film thermoelectric material, more particularly, it relates to a single crystal tin selenide thermoelectric thin film grown along a-axis. BACKGROUND

[0002] With the rapid development of electronic integrated packaging technology, the integration of chips is getting higher and higher, and the volume is getting smaller and smaller, and the unit energy consumption of the chip is getting higher and higher, and the local heat flux density of the chip is as high as 1300 W / cm 2 Therefore, efficient heat dissipation has become an important factor restricting the further improvement of chip performance.

[0003] Thermoelectric materials are a kind of functional materials that can directly realize the mutual conversion between heat and electricity based on the Seebeck effect and Peltier effect. The performance of thermoelectric materials is usually measured by the thermoelectric figure of merit (ZT), and the calculation formula of ZT is: ZT=(S S 2 σ / κ ) T . Among them, S S represents the Seebeck coefficient of the material, σ σ represents the electrical conductivity of the material, κ κ represents the thermal conductivity of the material, T T represents the absolute temperature, and the power factor PF= S 2 σ which can be used to measure the electrical transport properties of the material. The ideal thermoelectric material should have high power factor and low thermal conductivity.

[0004] Tin selenide (SnSe) is a lead-free semiconductor compound material, which is a typical p-type semiconductor material. SnSe material has a high Seebeck coefficient and extremely low thermal conductivity, and its thermoelectric figure of merit increases rapidly with temperature within a certain temperature range, and its ZT can be as high as 2.6. With appropriate control, even higher ZT can be achieved, so it has become a research hotspot in the field of thermoelectric materials. Such high performance makes tin selenide film expected to play a role in the field of chip refrigeration.

[0005] Compared with bulk thermoelectric materials, thin film thermoelectric materials are more suitable for highly integrated chips for heat dissipation due to their superior volume advantage. At present, the mainstream preparation methods of tin selenide film include Bridgman method, pulsed laser method, and magnetron sputtering method, but the tin selenide films obtained by these methods are mostly polycrystalline films, which seriously limits the thermoelectric performance of tin selenide film. SUMMARY

[0006] To solve the above technical problems, the application provides a preparation method of a single-crystal tin selenide thermoelectric thin film, solves the problem of heat dissipation at the grain boundary of a polycrystalline thin film, and provides a single-crystal tin selenide thermoelectric thin film with high orientation, high crystallinity and good lattice quality.

[0007] To achieve the above object, In a first aspect, the application provides a preparation method of a single-crystal tin selenide thermoelectric thin film, which adopts the following technical scheme: A preparation method of a single-crystal tin selenide thermoelectric thin film, comprising the following steps: S1, substrate cleaning: sequentially placing the substrate in different cleaning liquids for ultrasonic cleaning for 10 min each time, then washing with a flushing liquid and blowing dry with an air gun; S2, substrate placement: fixing the substrate on a molybdenum holder and transferring it to a sample inlet chamber of a molecular beam epitaxy device; S3, vacuum pumping: pumping the vacuum degree of the sample inlet chamber to 10 -8 mbar, and then transferring the substrate to an evaporation chamber; S4, substrate degassing: increasing the temperature of the substrate to 300 DEG C and maintaining for 3 h, and then increasing the temperature to 800 DEG C and maintaining for 0.5 h; S5, heating of the evaporation source: heating the tin evaporation source to 1000-1100 DEG C and heating the selenium evaporation source to 125-130 DEG C, with a control of the temperature rising rate < 10 DEG C / min; S6, thin film growth: adjusting the temperature of the substrate to 310-320 DEG C, opening the shutter of the evaporation source, and maintaining the vacuum degree below 10 - 8 mbar; S7, thin film cooling: after reaching the set time of thin film growth, closing the shutter, maintaining the temperature for a period of time, and reducing the temperature of the thin film to room temperature; S8, sample removal.

[0008] Further preferably, the substrate is made of r alumina.

[0009] r Alumina has high lattice matching degree with tin selenide, and the epitaxial growth of the thin film is relatively easy, in addition, r Alumina is relatively stable and is not prone to chemical reactions.

[0010] Further preferably, in step S1, the cleaning liquids used in sequence are acetone, isopropyl alcohol, anhydrous ethanol and deionized water, and the flushing liquid is anhydrous ethanol.

[0011] Cleaning the substrate with acetone, isopropyl alcohol, anhydrous ethanol and deionized water in sequence can effectively remove the organic matter and impurities adhered to the surface of the substrate, and finally washing with anhydrous ethanol can avoid the adhesion of a small amount of inorganic matter on the surface of the substrate in the deionized water.

[0012] Further preferably, in step S1, the gas gun can be selected from one of nitrogen gas gun and argon gas gun.

[0013] Further preferably, in step S2, the substrate is fixed on the molybdenum holder by the method of electrically welding the tantalum skin.

[0014] The tantalum skin can play the role of mask and facilitate the disassembly of the substrate.

[0015] Further preferably, in step S4, the heating rate of the substrate is controlled at 5-10℃ / min, and the evaporation chamber pressure is kept <10 -8 mbar.

[0016] In the present application, under the condition of evaporation chamber pressure <10 -8 mbar, the substrate is first slowly heated to 300℃ and kept for a period of time, which can ensure that most of the gas adsorbed by the substrate can be discharged, and sufficient time is given to reduce the vacuum degree, and then slowly heated to 800℃ and kept for a period of time, which can make the substrate surface oxide reorganize to obtain a more flat and smooth substrate surface, facilitating the subsequent epitaxial growth of thin film.

[0017] Further preferably, in step S5, the temperature of the tin evaporation source is 1000℃, and the temperature of the selenium evaporation source is 128℃.

[0018] The above heating temperature can generate a tin selenide thin film with an atomic molar ratio of 1:1, and can accelerate the thin film growth speed under the premise of ensuring high quality of the crystal lattice.

[0019] Further preferably, in step S5, the selenium beam current / tin beam current ratio is 1.5-1.8.

[0020] Further preferably, in step S6, the substrate temperature is adjusted to 314℃.

[0021] Lower temperature is easy to produce polycrystalline thin film, and higher temperature is easy to produce tin diselenide, and the above temperature is the most suitable growth temperature of the thin film, and under this temperature, it is more suitable for high-quality epitaxy of tin selenide crystal lattice.

[0022] Further preferably, in step S6, when the thin film growth thickness reaches 300nm, 5% H2Se gas is introduced for 5-30s.

[0023] Further preferably, in step S6, the 5% H2Se gas is a mixed gas composed of H2Se and Ar according to the volume ratio of 5%:95%.

[0024] Further preferably, in step S6, the flow rate of the 5% H2Se gas is 3-8sccm.

[0025] Further preferably, in step S7, the thin film growth time is controlled to be < 3h, and the thin film thickness is 100-600nm.

[0026] Further preferably, in step S7, the thin film holding time is 10-15min, preferably 10min.

[0027] The thin film is held for a period of time after growth, which allows it to fully relax and avoids the evaporation of selenium caused by too long a time.

[0028] In a second aspect, the application provides a single-crystal tin selenide thermoelectric thin film, and the following technical solutions are adopted: A single-crystal tin selenide thermoelectric thin film, which is prepared by the above preparation method, has a thickness of 100-600nm, and a power factor PF of 4.53μWcm -1 K -2 .

[0029] In summary, the application has the following beneficial effects: The application uses a molecular beam epitaxy method to prepare a tin selenide thermoelectric thin film, which has the problems of simple preparation method, easy operation, and short preparation period. At the same time, the selenium beam current / tin beam current ratio is strictly controlled, and H2Se is used for selenium vacancy repair during thin film growth, which can obtain a high-quality a-axis oriented single-crystal tin selenide thermoelectric thin film. The thin film has good thermoelectric performance and is easy to realize chip integration and packaging. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 X-ray diffraction pattern of the single-crystal tin selenide thermoelectric thin film prepared in Example 1 of the application; Figure 2 Scanning electron microscope surface image of the single-crystal tin selenide thermoelectric thin film prepared in Example 1 of the application; Figure 3 Graph of the relationship between the electrical conductivity and the temperature of the single-crystal tin selenide thermoelectric thin film prepared in Example 1 of the application; Figure 4 Graph of the relationship between the Seebeck coefficient and the temperature of the single-crystal tin selenide thermoelectric thin film prepared in Example 1 of the application; Figure 5 Graph of the relationship between the power factor and the temperature of the single-crystal tin selenide thermoelectric thin film prepared in Example 1 of the application. DETAILED DESCRIPTION

[0031] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. This application 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 this application.

[0032] Furthermore, it should be understood that the one or more method steps mentioned in this application do not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and is not intended to limit the order of the method steps or limit the scope of implementation of this application. Changes or adjustments to their relative relationships, without substantially altering the technical content, shall also be considered as within the scope of implementation of this application.

[0033] Unless otherwise specified, the experimental conditions used in the examples are generally in accordance with conventional conditions in the art or the conditions recommended by the reagent company. Unless otherwise specified, the materials and reagents used in the examples can be purchased commercially. Example

[0034] Example 1 A method for preparing a single-crystal tin selenide thermoelectric thin film includes the following steps: S1, Substrate cleaning: Take a 10×10mm substrate... r The alumina substrate was placed in acetone, isopropanol, anhydrous ethanol, and deionized water, respectively, and sonicated for 10 minutes each. After removal, it was rinsed with anhydrous ethanol and then dried with a nitrogen gun. S2, Substrate Placement: The substrate is fixed on the molybdenum support by welding tantalum foil using an electric welding machine. Nitrogen gas is continuously introduced into the sample inlet chamber to transfer the substrate to the sample inlet chamber of the molecular beam epitaxy equipment. S3, Vacuuming: Evacuate the sample injection chamber to a vacuum level of 10. -8 After mbar, the substrate is transferred to the evaporation chamber; S4, Substrate Degassing: Raise the substrate temperature to 300℃ and hold for 3 hours to fully degas, then raise the temperature to 800℃ and hold for 0.5 hours to restructure the substrate surface. Maintain the gas pressure in the evaporation chamber <10 during the heating process. -8 mbar; S5, Evaporation source heating: Heat the tin evaporation source to 1000℃ and the selenium evaporation source to 128℃, control the heating rate to <10℃ / min, and control the selenium beam current / tin beam current ratio to 1.65; S6, Thin Film Growth: Adjust the substrate temperature to 314℃, open the evaporation source baffle, and maintain a vacuum level of 10.-8 mbar, when the thickness of the thin film reaches 300 nm, 5% H2Se gas is introduced for 15 s, the flow rate is controlled to be 5 sccm, and the titanium sublimation pump is turned on at the same time to absorb H2; S7, film cooling: after the thin film is grown for 2 h, the shutter is closed, the temperature is kept for 10 min, and the temperature of the thin film is reduced to room temperature; S8, the sample is taken out, and the single-crystal tin selenide thermoelectric thin film is obtained.

[0035] The single-crystal tin selenide thermoelectric thin film prepared in this embodiment is subjected to X-ray diffraction test, the X-ray diffraction angle range is 5-90°, and the test result is shown in Figure 1 . Figure 1 It can be seen from the test result that the thermoelectric thin film has a uniform (h00) orientation, the characteristic peak is discrete, and the single-crystal characteristics of good a-axis orientation are exhibited.

[0036] The single-crystal tin selenide thermoelectric thin film prepared in this embodiment is subjected to scanning electron microscope characterization, and the test result is shown in Figure 2 . Figure 2 It can be seen from the characterization result that the surface of the thermoelectric thin film presents a smooth plane, and there is no interlaced and staggered structure.

[0037] The single-crystal tin selenide thermoelectric thin film prepared in this embodiment is subjected to thermoelectric performance test, the test temperature range is 300-600 K, and the test result is shown in Figure 3 , Figure 4 , Figure 5 . Figures 4-5 It can be seen from the test result that the Seebeck coefficient of the thermoelectric thin film decreases with the increase of temperature, and the electrical conductivity increases with the increase of temperature. At a temperature of 542 K, the power factor of the thermoelectric thin film reaches a maximum value of 4.53 μWcm -1 K -2 .

[0038] Example 2 Preparation method of single-crystal tin selenide thermoelectric thin film: take r alumina as the substrate, control the selenium beam current / tin beam current ratio to be 1.5, and other conditions are the same as in Example 1.

[0039] Example 3 Preparation method of single-crystal tin selenide thermoelectric thin film: take r alumina as the substrate, control the selenium beam current / tin beam current ratio to be 1.8, and other conditions are the same as in Example 1.

[0040] Example 4 Preparation method of single-crystal tin selenide thermoelectric thin film: when the thickness of the thin film reaches 300 nm, 5% H2Se gas is introduced for 5 s, the flow rate is 8 sccm, and other conditions are the same as in Example 1.

[0041] Example 5 The method for preparing the single-crystal SnSe thermoelectric thin film: when the thin film growth thickness reaches 300 nm, 5% H2Se gas is introduced for 30 s at a flow rate of 3 sccm, and other conditions are the same as in Example 1.

[0042] Comparative Example Comparative Example 1 The method for preparing the single-crystal SnSe thermoelectric thin film: with r The method for preparing the single-crystal SnSe thermoelectric thin film: with

[0043] Comparative Example 2 The method for preparing the single-crystal SnSe thermoelectric thin film: no H2Se gas is introduced during the thin film growth, and other conditions are the same as in Example 1.

[0044] Performance detection test 1. Effect of Se / Sn beam current ratio on the performance of SnSe thermoelectric thin film The Seebeck coefficients of Examples 1-3 and Comparative Example 1 at 542 K were tested, and the results are recorded in Table 1 below.

[0045] Table 1 Seebeck coefficient test results As can be seen from the results in Table 1, when the Se / Sn beam current ratio is > 1.8, although the atomic molar ratio is close to 1:1, the Seebeck coefficient of the thin film is significantly reduced, which may be due to the formation of [Se-Se] 2- dimers when the beam current ratio is greater than 1.8, which causes defects in SnSe, resulting in a decrease in the Seebeck coefficient. Therefore, when preparing the SnSe thermoelectric thin film using the method of the present application, it is necessary to strictly control the Se / Sn beam current ratio ≤ 1.8.

[0046] 2. Effect of introducing H2Se gas on the performance of SnSe thermoelectric thin film The Seebeck coefficients and electrical conductivities of Examples 1, 4, 5, and Comparative Example 2 at 542 K were tested, and the results are recorded in Table 2 below.

[0047] Table 2 Seebeck coefficient and electrical conductivity test results H2Se is decomposed into H2 and active selenium atoms at high temperature, which can fill selenium vacancies in the thin film preferentially without forming dimers, thereby reducing the defect density of the thin film. As can be seen from the results in Table 2, the Seebeck coefficient of the product is obviously improved compared with the un-repaired thin film, because the repair of selenium vacancies can significantly reduce the carrier concentration of the thin film and improve the Seebeck coefficient.

[0048] The above description is only the preferred embodiment of the present application, and is not any form and substantial limitation of the present application. It should be pointed out that for ordinary skilled in the art, without departing from the method of the present application, a number of improvements and supplements can also be made, which should be considered as the protection scope of the present application. For those skilled in the art, without departing from the spirit and scope of the present application, some changes, modifications and equivalent changes made by using the above disclosed technical content are equivalent embodiments of the present application; at the same time, any equivalent changes, modifications and evolution of the above-mentioned embodiments according to the essential technology of the present application are still within the scope of the technical solutions of the present application.

Claims

1. A method for producing a single-crystal tin selenide thermoelectric thin film, characterized by, The method comprises the following steps: S1, substrate cleaning: sequentially placing the substrate in different cleaning solutions for ultrasonic cleaning for 10 min, washing with a flushing solution, and then blowing dry with an air gun; S2, substrate placement: fixing the substrate on a molybdenum holder and transferring to a sample inlet chamber of a molecular beam epitaxy device; S3, vacuum: The vacuum in the sample chamber is drawn to 10 -8 mbar after which the substrate is transferred to the evaporation chamber; S4, substrate degassing: increasing the substrate temperature to 300°C and maintaining for 3 h, and then increasing to 800°C and maintaining for 0.5 h; S5, evaporation source heating: heating the tin evaporation source to 1000-1100°C and the selenium evaporation source to 125-130°C, and controlling the temperature increasing rate to be less than 10°C / min; S6, thin film growth: The substrate temperature is adjusted to 310-320 °C, the shutter of the evaporation source is opened, and the vacuum is maintained at below 10 -8 mbar; S7, thin film cooling: after reaching the set time of thin film growth, closing the shutter, maintaining for a period of time, and reducing the thin film temperature to room temperature; S8, taking out the sample.

2. The method of claim 1, wherein the single crystal tin selenide thermoelectric thin film is prepared by a process comprising: The substrate is made of r to aluminum oxide.

3. The method of claim 1, wherein the single crystal tin selenide thermoelectric thin film is prepared by a process comprising: In step S4, the substrate temperature ramp rate is controlled at 5-10°C / min, and the vaporization chamber pressure is maintained at <10 mbar. -8 mbar.

4. The method of claim 1, wherein the single crystal tin selenide thermoelectric thin film is prepared by a process comprising: In step S5, the temperature of the tin evaporation source is 1000°C, and the temperature of the selenium evaporation source is 128°C.

5. The method for preparing a single-crystal tin selenide thermoelectric thin film according to claim 1, characterized in that, In step S5, the selenium beam current / tin beam current ratio is 1.5-1.

8.

6. The method of claim 1, wherein the single crystal tin selenide thermoelectric thin film is prepared by a process comprising: In step S6, when the thin film growth thickness reaches 300 nm, 5% H2Se gas is introduced for 5-30 s.

7. The method of claim 6, wherein the single crystal tin selenide thermoelectric thin film is prepared by a process comprising: In step S6, the 5% H2Se gas is a mixed gas composed of H2Se and Ar according to a volume ratio of 5:95, and the introduction flow rate of the 5% H2Se gas is 3-8 seem.

8. The method for preparing a single-crystal tin selenide thermoelectric thin film according to claim 1, characterized in that, In step S7, the thin film growth time is controlled to be less than 3 h, and the thin film thickness is 100-600 nm.

9. The method for preparing a single-crystal tin selenide thermoelectric thin film according to claim 1, characterized in that, In step S7, the thin film maintaining time is 10-15 min.

10. A single crystal tin selenide thermoelectric thin film, characterized in that, The single-crystal tin selenide thermoelectric thin film is prepared by the method of any one of claims 1-9, the thickness of the single-crystal tin selenide thermoelectric thin film is 100-600 nm, and the power factor PF of the thin film at 542 K is 4.53 μWcm -1 K -2 .

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