A method for preparing an easily transferable PbX single crystal thin film

Abstract

The present invention discloses a method for preparing an easily transferable PbX single crystal thin film, which comprises the following steps: placing a water-soluble single crystal wafer substrate in a reaction vessel, filling it with an inert gas, heating it to 500 - 680 °C, and mixing and reacting the gases sublimated from PbCl2 powder and X powder respectively. After the reaction is completed, it is naturally cooled to room temperature, and a PbX single crystal thin film is heteroepitaxially grown on the surface of the single crystal wafer substrate; the single crystal wafer substrate is dissolved to obtain the PbX single crystal thin film; wherein, X is S, Te, or Se. The present invention adopts the chemical vapor deposition method, and the obtained single crystal thin film has high crystallinity, single crystal orientation, and few internal defects. The peeling process from the substrate does not damage the single crystal thin film, and the single crystal thin film can maintain the original crystal orientation and complete morphology. At the same time, this preparation method is simple, time-consuming short, highly controllable, and low in cost, and has good application prospects in the field of optoelectronics.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor materials, and more specifically to a method for preparing an easily transferable PbX single crystal thin film. Background Art

[0002] In recent years, with the continuous improvement of electronic device performance and the continuous expansion of the application scope of semiconductor nanomaterials, the research on the preparation of semiconductor thin film materials has made rapid progress, especially single crystal thin film materials, which have become one of the most active research topics in the field of microelectronics and materials science. Lead sulfide (PbS), as one of the typical representatives of functional semiconductor materials, has attracted widespread attention due to its excellent physical properties such as narrow band gap (0.42eV) and large Bohr exciton radius (18nm). PbS nanomaterials have been widely used in infrared detection, bioluminescent probes, solar cells and other fields. Unlike layered materials, non-layered materials such as PbS are strongly chemically bonded in the three-dimensional direction of space. When the longitudinal dimension is reduced, the unsaturated dangling bonds are exposed to the surface, and electron redistribution is required to achieve the lowest system energy and maintain stability. In addition, non-layered materials usually have completely different crystal structures from the substrate. These challenges undoubtedly increase the difficulty of preparing PbS thin films.

[0003] With the continuous advancement of nanomaterial preparation technology in the past few decades, a variety of methods for synthesizing PbS two-dimensional nanomaterials have been developed, such as vapor deposition, magnetron sputtering, wet chemistry and atomic layer deposition. The PbS two-dimensional structures such as nanosheets and thin films prepared by these methods are disorderly distributed, have different growth orientations, or cannot form complete and continuous films, or have poor crystallinity and many defects, which seriously restricts the performance and development prospects of PbS optoelectronic devices. In fact, the controllable preparation of large-scale PbS single crystal films is still a challenge. Summary of the invention

[0004] An object of the present invention is to provide a method for preparing an easily transferable PbS single crystal film, a PbTe single crystal film, and a PbSe single crystal film. The method uses a water-soluble single crystal wafer as a substrate, heteroepitaxially grows a PbX (X is S, Te, Se) single crystal film on the substrate, and then dissolves the single crystal wafer substrate to obtain a PbX (X is S, Te, Se) single crystal film. The single crystal film is easy to transfer and can be transferred to different substrates according to requirements.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for preparing an easily transferable PbX single crystal thin film comprises the following steps:

[0007] Place a water-soluble single-wafer substrate in a reaction vessel, fill it with inert gas, heat it to 500-680°C, and PbCl 2 The powder and the gas after the X powder is sublimated are mixed and reacted. After the reaction is completed, the mixture is naturally cooled to room temperature, and a PbX single crystal thin film is heteroepitaxially grown on the surface of the single crystal substrate; the single crystal substrate is dissolved to obtain a PbX single crystal thin film; wherein X is S, Te, and Se.

[0008] Preferably, the single wafer substrate is a NaCl single wafer or a KCl single wafer.

[0009] The present invention uses a NaCl single crystal or a KCl single crystal as a substrate, and extends and grows thereon to form an epitaxial layer, that is, a PbX single crystal thin film. The NaCl single crystal or the KCl single crystal is selected as the substrate. On the one hand, it is mainly considered that the NaCl single crystal or the KCl single crystal has the same crystal structure and similar unit cell parameters as the PbX single crystal. When the PbX single crystal thin film is formed by epitaxial growth thereon, the lattice matching degree between the substrate and the epitaxial layer is high, and the formed PbX single crystal thin film has high crystallinity, single crystal orientation, few internal defects, and stable structure; on the other hand, it is mainly because the NaCl single crystal or the KCl single crystal is soluble in water, while the PbX single crystal thin film is difficult to dissolve in water, so the substrate and the epitaxial layer can be separated by water dissolution, the peeling of the PbX single crystal thin film is completed, and the integrity of the PbX single crystal thin film structure can be ensured, and it can be transferred to various substrates as needed, and has good application potential; at the same time, the NaCl single crystal or the KCl single crystal is resistant to high temperature, and the structure will not change during the high-temperature generation of PbX.

[0010] Preferably, the pressure in the reaction vessel is 1 atmosphere.

[0011] In the present invention, PbCl 2 The mixed reaction of the powder and the gas after the X powder is sublimated is carried out in an inert gas atmosphere. In the specific implementation process, the reaction container must first be evacuated to a vacuum, and then the inert gas is introduced to keep the pressure in the container at 1 atmosphere.

[0012] Preferably, the heating rate in the reaction vessel is 15-30° C. / min.

[0013] Preferably, the gas after the X powder is sublimated uses an inert gas as a carrier to react with PbCl 2 Gas mixture reaction after powder sublimation.

[0014] The present invention uses PbCl 2 PbX is generated by mixing the gas after heating and sublimation. 2The sublimation point temperature of the powder is relatively high, and the sublimation point temperature of the X element powder is relatively low. When the X element powder sublimates, it is reacted with PbCl 2 The sublimated gases are mixed and react to form PbX. At the same time, PbCl 2 The powder is cheap and can save certain production costs.

[0015] Preferably, when the reactor is in the process of heating up, the flow rate of the inert gas is 300-500 sccm. During the heating process, a small amount of source powder will evaporate and grow nuclei on the substrate in advance. When the temperature is low, the quality of crystal nucleation is poor. Therefore, a larger flow rate should be selected to blow away the early reactants to ensure that no reactants are attached to the substrate during the heating process, so that all crystals grow at a specific temperature.

[0016] Preferably, when the reactor temperature is maintained at 500-680°C, the flow rate of the inert gas is 30-100 sccm. At this time, the inert gas is a carrier gas, which transports the sublimated gaseous X to the central temperature zone and PbCl 2 For gas reaction, a smaller flow rate is selected to ensure that the material can have a slow and stable growth rate, which helps to obtain high-quality crystals.

[0017] Preferably, dissolving a single crystal substrate to obtain a PbX single crystal thin film comprises the following steps: covering a single crystal substrate with a PbX single crystal thin film heteroepitaxially grown on the surface with a layer of PDMS, and then placing it in deionized water, after the single crystal substrate is completely dissolved, the PbX single crystal thin film and PDMS float to the water surface, and then taking them out, drying them, and removing the PDMS to obtain the PbX single crystal thin film.

[0018] The single crystal wafer substrate in the present invention is soluble in water. The epitaxial layer can be released from the substrate by dissolving the substrate in water, ensuring that the single crystal film is not damaged during the process of peeling off the substrate. After the single crystal film is transferred to the target substrate, the complete morphology and perfect single crystality can still be maintained. At the same time, the NaCl single crystal wafer or the KCl single crystal wafer has low cost and its single crystal wafer production process is mature.

[0019] The beneficial effects of the present invention are as follows:

[0020] The present invention adopts chemical vapor deposition method to epitaxially grow PbX (X is S, Te, Se) single crystal thin film on a soluble single crystal wafer substrate over a large area. The obtained single crystal thin film has high crystallinity, single crystal orientation, and few internal defects. The peeling process from the substrate does not damage the single crystal thin film. The single crystal thin film can maintain the original crystal orientation and complete morphology and be transferred to the required substrate. At the same time, the preparation method is simple, short in time, highly controllable, and low in cost, and has good application prospects in the field of optoelectronics. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0022] Figure 1 A reaction schematic diagram of the preparation method of Example 1 of the present invention is shown.

[0023] Figure 2 The scanning electron microscope (SEM) image and electron backscatter diffraction (EBSD) crystal orientation distribution diagram of the PbS single crystal film prepared in Example 1 of the present invention are shown, (a) is a side view of the SEM, (b) is a top view of the SEM, and (c) is an EBSD crystal orientation distribution diagram.

[0024] Figure 3 The X-ray diffraction (XRD) patterns of the PbS single crystal thin films prepared in Examples 1 and 2 of the present invention are shown.

[0025] Figure 4 Transmission electron microscope (TEM) images of the PbS single crystal film prepared in Example 1 of the present invention are shown, including (a) low-magnification bright field image; (b) selected area electron diffraction (SAED) image; (c) high-resolution TEM (HRTEM) image; and (d) atomic image under high-angle annular dark field (HAADF-STEM).

[0026] Figure 5 The X-ray photoelectron spectrum (XPS) of the PbS single crystal film prepared in Example 1 of the present invention is shown, wherein (a) is the full spectrum, (b) is the high-resolution Pb 4f spectrum, and (c) is the high-resolution S 2p spectrum.

[0027] Figure 6 The Raman spectrum of the PbS single crystal thin film prepared in Example 1 of the present invention is shown.

[0028] Figure 7 The XRD patterns and optical images of the PbS single crystal thin film obtained in Example 1 of the present invention after being transferred to different substrates are shown, where (a), (b) and (c) represent the XRD patterns of the PbS single crystal thin film transferred to SiO 2 / Si substrate, mica substrate and sapphire substrate. (d) is the optical image of PbS single crystal film transferred on mica. DETAILED DESCRIPTION

[0029] In order to more clearly illustrate the present invention, the present invention is further described below in conjunction with preferred embodiments and accompanying drawings. Similar components in the accompanying drawings are represented by the same reference numerals. It should be understood by those skilled in the art that the content specifically described below is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

[0030] Example 1

[0031] (1) A 10×5×2 mm NaCl (100) single crystal wafer is selected as the substrate, and the polished surface is usually selected as the epitaxial growth surface.

[0032] (2) Weigh 30 mg of PbCl 2 The powder is placed in a ceramic boat which is then placed in the heated center area of ​​a tube furnace. 2 Weigh 0.5 g of S powder and place it in another ceramic boat, which is placed about 20 cm upstream of the tube furnace.

[0033] (3) Turn on the mechanical pump to evacuate the chamber. When the pressure in the furnace drops to 0.1 Pa, quickly inject high-purity argon gas to return the pressure in the chamber to atmospheric pressure.

[0034] (4) Raise the temperature to 580°C at a rate of 30°C / min. During the heating process, the flow rate of argon is controlled at 300 sccm. When the heating center reaches the preset temperature, the temperature of the S powder is about 200°C. Change the flow rate to 40 sccm and keep it at the set temperature for 15 minutes.

[0035] (5) After the reaction is completed, when the center temperature drops below 400° C., the upper cover of the tube furnace is opened to quickly lower the temperature of the tube furnace to room temperature, and the NaCl single crystal substrate is taken out.

[0036] (6) Place the PbS single crystal film on top and the single crystal substrate on the bottom, and fix them on a glass slide. Use scissors to cut a piece of PDMS that is slightly larger than the sample size, then use tweezers to pick it up and cover it on the surface of the PbS film, and press gently to completely combine the PDMS and PbS film. Place the entire sample in deionized water. After a few minutes, the PbS single crystal film covered with PDMS floats on the water surface, and the single crystal substrate completely dissolves and disappears. Use tweezers to gently clamp the edge of the PDMS and place it on the mica sheet, absorb the excess moisture on the sample so that the PbS film fits tightly to the mica sheet. After the moisture attached to the substrate and the sample has completely evaporated, use tweezers to gently lift up the PDMS, and the transfer is complete. Figure 1 (a) and (b) show scanning electron microscope images of the PbS single crystal film prepared in Example 1; (c) shows the electron backscatter diffraction (EBSD) crystal orientation distribution diagram of the PbS single crystal film. The results show that the crystal orientation of the film is single, all in the (100) direction.

[0037] The transmission electron microscope (TEM) image of the PbS single crystal film prepared in Example 1 is as follows: Figure 4As shown, (a) is a low-magnification bright field image; (b) is a selected area electron diffraction (SAED) image, and it can be seen that the diffraction spots show regular four-fold symmetry characteristics; (c) is a high-resolution TEM (HRTEM) image, and the crystal plane spacing marked in the figure is 0.29nm, which is consistent with the lattice spacing of the PbS{100} crystal plane family; (d) is an atomic image under high-angle annular dark field (HAADF-STEM), and it can be seen that the atomic points are clear and sharp without defects, indicating that the PbS film also has excellent single crystallinity in the micro area.

[0038] The X-ray photoelectron spectrum (XPS) of the PbS single crystal film prepared in Example 1 is as follows: Figure 5 As shown, (a) is the full spectrum, (b) is the high-resolution Pb 4f spectrum, and (c) is the high-resolution S 2p spectrum; the Raman spectrum of the PbS single crystal film is shown in Figure 6 shown.

[0039] The PbS single crystal film prepared in Example 1 was transferred onto different substrates. Its XRD patterns and optical images are shown in Figure 2. Figure 7 As shown, (a), (b) and (c) represent the transfer to SiO 2 / Si substrate, mica substrate and sapphire substrate. (d) is the optical image of PbS single crystal film transferred on mica.

[0040] Example 2

[0041] (1) A 10×5×2 mm KCl (100) single crystal wafer is selected as the substrate, and the polished surface is usually selected as the epitaxial growth surface.

[0042] (2) Weigh 30 mg of PbCl 2 The powder is placed in a ceramic boat which is then placed in the heated center area of ​​a tube furnace. 2 Weigh 0.5 g of S powder and place it in another ceramic boat, which is placed about 21 cm upstream of the tube furnace.

[0043] (3) Turn on the mechanical pump to evacuate the chamber. When the pressure in the furnace drops to 0.1 Pa, quickly inject high-purity argon gas to return the pressure in the chamber to atmospheric pressure.

[0044] (4) Raise the temperature to 620°C at a rate of 30°C / min. During the heating process, the flow rate of argon is controlled at 300 sccm. When the heating center reaches the preset temperature, the temperature of the S powder is about 200°C. Change the flow rate to 40 sccm and keep it at the set temperature for 15 minutes.

[0045] (5) After the reaction is completed, when the center temperature drops below 400° C., the upper cover of the tube furnace is opened to quickly lower the temperature of the tube furnace to room temperature, and the KCl single crystal substrate is taken out.

[0046] (6) Place the PbS single crystal film on top and the single crystal substrate on the bottom, and fix them on a glass slide. Use scissors to cut a piece of PDMS that is slightly larger than the sample size, then use tweezers to pick it up and cover it on the surface of the PbS film, and press gently to completely combine the PDMS and PbS film. Place the entire sample in deionized water. After a few minutes, the PbS single crystal film covered with PDMS floats on the water surface, and the single crystal substrate completely dissolves and disappears. Use tweezers to gently clamp the edge of the PDMS and place it on the mica sheet, absorb the excess moisture on the sample so that the PbS film fits tightly to the mica sheet. After the moisture attached to the substrate and the sample has completely evaporated, use tweezers to gently lift up the PDMS, and the transfer is complete.

[0047] The X-ray diffraction (XRD) patterns of the PbS single crystal films prepared in Example 1 and Example 2 are as follows: Figure 3 As shown, it can be seen that the PbS single crystal film has high crystallinity and a cubic structure, which is consistent with the orientation of the NaCl single crystal and the KCl single crystal, and the epitaxial relationship is obvious.

[0048] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing an easily transferable PbX single crystal thin film, It is characterized in that The following steps are involved: Place a water-soluble single-wafer substrate in a reaction vessel, fill it with inert gas, heat it to 500-680°C, and PbCl 2 The gas mixture of the powder and the X powder after sublimation reacts, and after the reaction is completed, the mixture is naturally cooled to room temperature, and a PbX single crystal thin film is heteroepitaxially grown on the surface of the single crystal substrate; the single crystal substrate is dissolved to obtain a PbX single crystal thin film; wherein X is S; The single crystal substrate is selected from a NaCl single crystal or a KCl single crystal; the single crystal substrate is placed in a PbCl 2 On top of the powder; The gas after the X powder sublimates uses inert gas as a carrier and then reacts with PbCl 2 Gas mixture reaction after powder sublimation; When the reactor is in the process of heating up, the flow rate of the inert gas is 300-500 sccm; when the reactor temperature is maintained at 500-680° C., the flow rate of the inert gas is 30-100 sccm.

2. The preparation method according to claim 1, It is characterized in that The pressure in the reaction vessel was 1 atmosphere.

3. The preparation method according to claim 1, It is characterized in that The heating rate in the reaction vessel was 15-30°C / min.

4. The preparation method according to claim 1, It is characterized in that The process of dissolving a single crystal substrate to obtain a PbX single crystal thin film comprises the following steps: covering a single crystal substrate with a PbX single crystal thin film heteroepitaxially grown on the surface with a layer of PDMS, and then placing the single crystal substrate in deionized water; after the single crystal substrate is completely dissolved, the PbX single crystal thin film and the PDMS float to the water surface, and then the single crystal substrate is taken out, dried, and the PDMS is removed to obtain the PbX single crystal thin film.

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