Two-dimensional semiconductor TMDCs single crystal and preparation method thereof

Abstract

The invention discloses a preparation method of a two-dimensional semiconductor TMDCs single crystal, which comprises the following steps of: 1, fully grinding and uniformly mixing halide salt powder and TMDCs powder, putting the mixture into a corundum boat or a quartz boat, and covering a target substrate; step 2, vacuumizing, introducing protective gas for protection, heating to 600-700 DEG C, and preserving heat; and step 3, after the growth process is finished, cooling to room temperature, vacuumizing in the whole process, introducing protective gas for protection, and obtaining a two-dimensional TMDCs single crystal or large-size film on the substrate. According to the two-dimensional semiconductor TMDCs single crystal, single-layer and Bercal stacking few-layer single crystal growth is achieved through the crystal domain of the TMDCs single crystal, and the single crystal size of the TMDCs single crystal is 20 micrometers or above. According to the invention, the two-dimensional TMDCs single crystal and thin film with large size, low defect and high quality can be prepared at a relatively low temperature, and the single crystal nanosheet is low in defect density and strong in photoluminescence effect.

Description

Technical Field

[0001] The present invention relates to a two-dimensional single crystal and a preparation method thereof, specifically a two-dimensional semiconductor TMDCs single crystal and a preparation method thereof. Background Art

[0002] Two-dimensional transition metal dichalcogenides (TMDCs), such as MoS2 and WSe2, have attracted widespread attention in recent years for applications in field-effect transistors, photodetectors, and flexible electronics due to their exceptional layered structures, tunable band gaps, and outstanding electronic and optical properties. In the post-Moore era, two-dimensional semiconductors demonstrate enormous potential for applications in a wide range of fields, including high-performance electronic device integration, novel information devices, and computing. However, realizing these applications based on the exceptional physical properties of two-dimensional TMDCs requires overcoming several technical barriers. The most significant challenge is the controllable preparation of high-quality, large-size, low-defect-density TMDC single crystals. Currently, high-quality two-dimensional TMDC single crystals have been prepared by chemical vapor deposition using highly reactive halide ions. However, due to insufficient precursor chemical reaction, the defect density remains significantly lower than that of Group III and V wide-gap semiconductors, compromising device performance and reproducibility. Therefore, the preparation of high-quality two-dimensional TMDC single crystals remains a pressing technical challenge for the industry. Summary of the Invention

[0003] Purpose of the invention: In order to overcome the deficiencies in the prior art, the purpose of the present invention is to provide a low-temperature, low-cost and efficient method for preparing two-dimensional semiconductor TMDCs single crystals. Another purpose of the present invention is to provide a large-size, low-defect, high-quality two-dimensional semiconductor TMDCs single crystal.

[0004] Technical solution: The method for preparing a two-dimensional semiconductor TMDCs single crystal described in the present invention comprises the following steps:

[0005] Step 1: Grind and mix the halide salt powder and TMDCs powder thoroughly, place them in a corundum boat or a quartz boat, and cover the target substrate;

[0006] Step 2: evacuate, pass protective gas, heat to 600-700℃, and keep warm;

[0007] Step three: After the growth process is completed, cool to room temperature, evacuate the entire process and pass protective gas protection to obtain a two-dimensional TMDCs single crystal or large-size thin film on the substrate.

[0008] Furthermore, in step 1, the target substrate is a silicon wafer, sapphire or mica wafer.

[0009] Furthermore, in step 1, the halide salt powder is any one of NaCl, KCl, NaI, and KI.

[0010] Furthermore, in step one, the TMDCs powder is any one of MoS2, WS2, MoSe2, and WSe2.

[0011] Furthermore, in step 1, the molar ratio of the halide salt powder to the TMDCs powder is 2 to 20:1, and the purity is 4N or above.

[0012] Furthermore, in step 1, grinding is performed using a mortar or a planetary ball mill.

[0013] Furthermore, in step 2, the insulation time is 10 to 15 minutes.

[0014] Furthermore, in step three, the cooling is first programmed to decrease the temperature to 500° C. at a rate of 8-10° C. / min, and then naturally cooled to room temperature.

[0015] Furthermore, the protective gas is one or more of nitrogen, argon, and hydrogen, with a flow rate of 20 to 400 sccm.

[0016] The two-dimensional semiconductor TMDCs single crystal described in the present invention has a crystal domain of the TMDCs single crystal that realizes single-layer and Bernal stacking few-layer single crystal growth, and the single crystal size of the TMDCs single crystal is greater than 20 μm.

[0017] Preparation Principle: Halide salts are fused with TMDC powders at high temperatures to form a molten state with a low melting point, enabling vapor-phase growth at relatively low temperatures. The growth mechanism is that TMDC clusters and molten salt anions form readily evaporable precursors, which adsorb, migrate, nucleate, and grow on the target substrate in the vapor phase. Furthermore, the molten salt cations bind to the TMDC clusters, lowering the reaction energy barrier and promoting the growth of high-quality two-dimensional TMDC domains. By delaying the growth time, TMDC nanosheets can form large, continuous films through a connecting process.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0019] 1. Ability to prepare large-sized, low-defect, high-quality two-dimensional TMDCs single crystals and thin films at relatively low temperatures;

[0020] 2. The two-dimensional TMDCs single crystal nanosheets obtained on the target substrate by vapor deposition have low defect density and strong photoluminescence effect;

[0021] 3. The method is simple, efficient, and low-cost, with wafer-level growth prospects for industrial applications;

[0022] 4. Choose widely used silicon wafers, sapphire single crystals, and fluorophlogopite as substrates, which have fewer growth steps and shorter cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a diagram of the growth principle of the present invention;

[0024] Figure 2 This is a thermal analysis result diagram of the precursor mixed powder of the present invention;

[0025] Figure 3 These are optical microscope, atomic force microscope, and X-ray photoelectron spectroscopy images of the two-dimensional TMDCs nanosheets obtained in Example 1 of the present invention, wherein a is an optical microscope image, b is an atomic force microscope image, and c is a core state XPS spectrum of Mo and S elements in MoS2;

[0026] Figure 4 1 is a high-resolution transmission electron microscopy characterization of the MoS2 nanosheets obtained in Example 1 of the present invention, wherein a is a high-resolution transmission electron microscopy image of the prepared MoS2 nanosheets, b is a selected area electron diffraction image of the prepared MoS2 nanosheets, and c is an intensity image extracted along the direction of the red arrow;

[0027] Figure 5 2 is a characterization of the photoluminescence and absorption spectra of the MoS2 nanosheets prepared in Example 1 of the present invention, wherein a is an optical microscope image of the prepared MoS2 nanosheets, b is a photoluminescence intensity distribution diagram of the prepared MoS2 nanosheets, c is a peak position distribution diagram of the prepared MoS2 nanosheets, d is a half-peak width distribution diagram of the characteristic peak A of the prepared MoS2 nanosheets, e is a photoluminescence spectrum diagram of the prepared MoS2 nanosheets, f is a statistical distribution diagram of the half-peak width of the characteristic peak A of the prepared MoS2 nanosheets, and g is a power-dependent photoluminescence intensity diagram;

[0028] Figure 6 The Raman spectra of the MoS2 nanosheets prepared in Example 1 of the present invention are characterized, wherein a is an optical microscope image of the prepared MoS2 nanosheets, bd is the Raman spectra of the corresponding MoS2 nanosheets. Characteristic peak intensity distribution diagram, peak position distribution diagram, half-peak width distribution diagram; Figure e is the Raman spectrum of the prepared MoS2 nanosheets; f, g are the characteristic peaks of the Raman spectrum of the prepared MoS2 nanosheets With A 1g Statistical distribution histogram of half-peak width;

[0029] Figure 7 1 is a characteristic diagram of the field effect transistor device of the MoS2 nanosheet prepared in Example 1 of the present invention, wherein a is the device output characteristic curve and b is the device transfer characteristic curve;

[0030] Figure 8 is an optical microscope image of Bernal-stacked multilayer MoS2 nanosheets obtained in Example 2 of the present invention;

[0031] Figure 9 is an optical microscope image of the MoS2 nanoribbons obtained in Example 3 of the present invention;

[0032] Figure 10 is an optical microscope image of MoS2 nanosheets obtained in Example 4 of the present invention;

[0033] Figure 11 This is an optical microscope image of the recrystallization of the molten salt obtained in Comparative Example 1. DETAILED DESCRIPTION

[0034] Unless otherwise specified, the materials and reagents used in the following examples were commercially available. Experimental methods not specified in the examples were generally performed under conventional conditions or those recommended by the manufacturer. The purity of the halide salt powder and TMDC powder was 4N or higher.

[0035] Example 1

[0036] A method for preparing a two-dimensional semiconductor TMDCs single crystal comprises the following steps:

[0037] (1) Weigh KCl powder and MoS2 powder in a molar ratio of 10:1, place them in an agate mortar, and grind them evenly for 30 minutes to fully blend them.

[0038] (2) Weigh an appropriate mass of the precursor mixed powder and place it in a corundum boat so that the distance between it and the silicon wafer target substrate can be adjusted between 1 and 10 mm, and cover the target substrate upside down.

[0039] (3) Place the corundum boat into the center of the tubular furnace's temperature zone, inside the quartz tube. Use a mechanical pump to evacuate the quartz tube to a base vacuum of approximately 1 Pa. Flush the tube with high-purity protective gas, argon, to atmospheric pressure, and then evacuate again. Repeat this process several times. Continue introducing 200 sccm of protective gas.

[0040] (4) The temperature zone begins to heat up using a PID program to 650°C, and the heating process lasts for 30 minutes. After reaching the set temperature, high-quality two-dimensional MoS2 single crystal nanosheets are grown. During the growth period, the argon gas flow rate is 100 sccm, and the growth (holding) time is 10 minutes.

[0041] (5) After the growth process is completed, the heating power is turned off, the protective gas is 100 sccm, and the temperature is programmed to 500°C at a rate of 10°C / min, and then naturally cooled to room temperature. The entire process is vacuumed and protected by protective gas to obtain high-quality, large-area two-dimensional semiconductor TMDCs single crystals on the substrate.

[0042] Steps (3) to (5) are all performed under a low pressure or differential pressure environment of 100 Pa. The two-dimensional semiconductor TMDCs single crystal of the present invention has a single-layer and Bernal stacking few-layer single crystal growth in its crystal domain, and the single crystal size of the TMDCs single crystal is 20-500 μm.

[0043] like Figures 1 and 2 The halide salt and TMDC powder were uniformly mixed and placed in the small holes of a corundum boat. A significant weight loss began at around 650°C, indicating that the mixed powder was evaporating from the gas phase. A significant endothermic phenomenon occurred around 780°C, indicating that the reaction was intense at this temperature.

[0044] like Figure 3 , Figure 3 The height profile in b shows a height of 0.7 nm, proving to be a single-layer MoS 2， XPS spectrum ( Figure 3 c) Demonstration of the synthesis of MoS2 nanosheets.

[0045] Figure 4 a shows the high-resolution transmission electron microscopy image of the synthesized MoS2 single crystal, showing a typical periodic honeycomb lattice structure with no lattice defects. Figure 4 b) shows clear scattering points, proving its single crystal nature. Figure 4 c, intensity characterization along the red arrow, it can be seen that its lattice constant is It is proved that the synthesized crystal is high-quality MoS2.

[0046] like Figure 5 As shown in Figure 3, the systematic characterization of its photoluminescence spectra and images demonstrates that the synthesized MoS2 nanosheets have high crystalline quality.

[0047] like Figure 6 As shown, the Raman spectrum of MoS2 nanosheets is characterized, and its small characteristic peak half-peak proves its high crystalline quality.

[0048] like Figure 7 As shown, field-effect transistors were prepared based on the synthesized MoS2 nanosheets, and their mobility can reach 40cm 2 V -1 s -1 .

[0049] Example 2

[0050] A method for preparing a two-dimensional semiconductor TMDCs single crystal comprises the following steps:

[0051] (1) Weigh KCl powder and MoS2 powder in a molar ratio of 10:1, place them in a mortar, and grind them evenly for 30 minutes to fully blend them.

[0052] (2) Weigh an appropriate mass of the precursor mixed powder and place it in a corundum boat so that the distance between it and the silicon wafer target substrate can be adjusted between 1 and 10 mm, and cover the target substrate upside down.

[0053] (3) Place the corundum boat into the center of the tubular furnace's temperature zone, inside the quartz tube. Use a mechanical pump to evacuate the quartz tube to a base vacuum of approximately 1 Pa. Flush the tube with high-purity protective gas, argon, to atmospheric pressure, and then evacuate again. Repeat this process several times. Continue introducing 200 sccm of protective gas.

[0054] (4) The temperature zone begins to heat up using a PID program to 700°C, and the heating process lasts for 30 minutes. After reaching the set temperature, high-quality two-dimensional MoS2 single-crystal nanosheets are grown. During the growth period, the argon gas flow rate is 100 sccm, and the growth (holding) time is 10 minutes.

[0055] (5) After the growth process is completed, the heating power is turned off, the protective gas is 100 sccm, and the temperature is programmed to 500°C at a rate of 10°C / min, and then naturally cooled to room temperature. The entire process is vacuumed and protected by protective gas to obtain high-quality, large-area two-dimensional semiconductor TMDCs single crystals on the substrate.

[0056] Steps (3) to (5) are all carried out under a low pressure or differential pressure environment of 100 Pa.

[0057] like Figure 8 As shown, it is proved that by optimizing conditions such as increasing the growth temperature, multilayer two-dimensional MoS2 single crystal nanosheets with Bernal stacking structure can be prepared.

[0058] Example 3

[0059] A method for preparing a two-dimensional semiconductor TMDCs single crystal comprises the following steps:

[0060] (1) Weigh KCl powder and MoS2 powder in a molar ratio of 20:1, place them in a mortar, and grind them evenly for 30 minutes to fully blend them.

[0061] (2) Weigh an appropriate mass of the precursor mixed powder and place it in a corundum boat so that the distance between it and the silicon wafer target substrate can be adjusted between 1 and 10 mm, and cover the target substrate upside down.

[0062] (3) Place the corundum boat into the center of the tubular furnace's temperature zone, inside the quartz tube. Use a mechanical pump to evacuate the quartz tube to a base vacuum of approximately 1 Pa. Flush the tube with high-purity protective gas, argon, to atmospheric pressure, and then evacuate again. Repeat this process several times. Continue introducing 200 sccm of protective gas.

[0063] (4) The temperature zone begins to heat up using a PID program to 650°C, and the heating process lasts for 30 minutes. After reaching the set temperature, high-quality two-dimensional MoS2 single crystal nanosheets are grown. During the growth period, the argon gas flow rate is 100 sccm, and the growth (holding) time is 10 minutes.

[0064] (5) After the growth process is completed, the heating power is turned off, the protective gas is 100 sccm, and the temperature is programmed to 500°C at a rate of 10°C / min, and then naturally cooled to room temperature. The entire process is vacuumed and protected by protective gas to obtain high-quality, large-area two-dimensional semiconductor TMDCs single crystals on the substrate.

[0065] Steps (3) to (5) are all carried out under a low pressure or differential pressure environment of 100 Pa.

[0066] Figure 9 Shown is an optical microscope image of MoS2 strips with a high aspect ratio. The triangular morphology features are still visible, indicating that it is still affected by the symmetry of the MoS2 lattice structure.

[0067] Example 4

[0068] A method for preparing a two-dimensional semiconductor TMDCs single crystal comprises the following steps:

[0069] (1) Weigh KCl powder and MoS2 powder in a molar ratio of 10:1, place them in a mortar, and grind them evenly for 30 minutes to fully blend them.

[0070] (2) Weigh an appropriate mass of the precursor mixed powder and place it in a corundum boat so that the distance between it and the mica target substrate is adjustable between 1 and 10 mm, and cover the target substrate upside down.

[0071] (3) Place the corundum boat into the center of the tubular furnace's temperature zone, inside the quartz tube. Use a mechanical pump to evacuate the quartz tube to a base vacuum of approximately 1 Pa. Flush the tube with high-purity protective gas, argon, to atmospheric pressure, and then evacuate again. Repeat this process several times. Continue introducing 200 sccm of protective gas.

[0072] (4) The temperature zone begins to heat up using a PID program to 650°C, and the heating process lasts for 30 minutes. After reaching the set temperature, high-quality two-dimensional MoS2 single crystal nanosheets are grown. During the growth period, the argon gas flow rate is 100 sccm, and the growth (holding) time is 10 minutes.

[0073] (5) After the growth process is completed, the heating power is turned off, the protective gas is 100 sccm, and the temperature is programmed to 500°C at a rate of 10°C / min, and then naturally cooled to room temperature. The entire process is vacuumed and protected by protective gas to obtain high-quality, large-area two-dimensional semiconductor TMDCs single crystals on the substrate.

[0074] Steps (3) to (5) are all carried out under a low pressure or differential pressure environment of 100 Pa.

[0075] like Figure 10 As shown, the optical microscopy images of MoS2 single crystals with typical triangular morphology show that this growth method can be used on a variety of substrates.

[0076] Example 5

[0077] A method for preparing a two-dimensional semiconductor TMDCs single crystal comprises the following steps:

[0078] (1) Weigh NaCl powder and WS2 powder with a molar ratio of 10:1, place them in a planetary ball mill, and grind them evenly for 30 min to fully blend them.

[0079] (2) Weigh an appropriate mass of the precursor mixed powder and place it in a corundum boat so that the distance between it and the sapphire target substrate can be adjusted between 1 and 10 mm, and cover the target substrate upside down.

[0080] (3) Place the corundum boat into the center of the tubular furnace's temperature zone, inside the quartz tube. Use a mechanical pump to evacuate the quartz tube to a base vacuum of approximately 1 Pa. Flush the tube with high-purity nitrogen to atmospheric pressure, then evacuate again. Repeat this process several times. Continue introducing 20 sccm of protective gas.

[0081] (4) The temperature zone begins to heat up using a PID program to 600°C, and the heating process lasts for 30 minutes. After reaching the set temperature, high-quality two-dimensional MoS2 single crystal nanosheets are grown. During the growth period, the argon gas flow rate is 20 sccm, and the growth (holding) time is 15 minutes.

[0082] (5) After the growth process is completed, the heating power is turned off, the protective gas is 400 sccm, and the temperature is programmed to 500°C at a rate of 8°C / min, and then naturally cooled to room temperature. The entire process is vacuumed and protected by protective gas to obtain high-quality, large-area two-dimensional semiconductor TMDCs single crystals on the substrate.

[0083] Example 6

[0084] A method for preparing a two-dimensional semiconductor TMDCs single crystal comprises the following steps:

[0085] (1) Weigh KI powder and MoSe2 powder with a molar ratio of 20:1, place them in a planetary ball mill, and grind them evenly for 30 minutes to fully blend them.

[0086] (2) Weigh an appropriate mass of the precursor mixed powder and place it in a quartz boat so that the distance between it and the sapphire target substrate can be adjusted between 1 and 10 mm, and cover the target substrate upside down.

[0087] (3) Place the quartz boat in the center of the tube furnace's temperature zone, inside the quartz tube. Use a mechanical pump to pump the quartz tube down to a base vacuum of approximately 1 Pa. Flush the tube with a high-purity protective gas mixture of argon and hydrogen to atmospheric pressure, then pump down again. Repeat this process several times. Continue introducing 400 sccm of protective gas.

[0088] (4) The temperature zone begins to heat up using a PID program to 620°C, and the heating process lasts for 30 minutes. After reaching the set temperature, high-quality two-dimensional MoS2 single crystal nanosheets are grown. During the growth period, the argon gas flow rate is 400 seem, and the growth (holding) time is 10 minutes.

[0089] (5) After the growth process is completed, the heating power is turned off, the protective gas is 20 sccm, and the temperature is programmed to 500°C at a rate of 10°C / min, and then naturally cooled to room temperature. The entire process is vacuumed and protected by the protective gas to obtain high-quality, large-area two-dimensional semiconductor TMDCs single crystals on the substrate.

[0090] Among the above embodiments, embodiment 1 is the best embodiment.

[0091] Comparative Example 1

[0092] The remaining steps of this comparative example are the same as those of Example 1, with the only difference being that in step (5), the target substrate is taken out for observation before it cools to room temperature, i.e., the cooling step is omitted.

[0093] The optical microscope micromorphology characterization was carried out and the results showed that the growth of halide salt flow and gradual crystallization process, such as Figure 11 Compared to Example 1, the halide salt was not evaporated in large quantities but was deposited on the target substrate, indicating that the halide salt was in excess and could be deposited and grown on the substrate. The large amount of halide salt on the substrate also resulted in less growth of two-dimensional semiconductor TMDCs.

Claims

1. A method for preparing a two-dimensional semiconductor TMDCs single crystal, characterized in that: The following steps are involved: Step 1: Grind and mix the halide salt powder and TMDCs powder thoroughly, place them in a corundum boat or a quartz boat, and cover the target substrate; Step 2: evacuate, pass protective gas, heat to 600-700℃, and keep warm; Step three: After the growth process is completed, cool to room temperature, evacuate the entire process and pass protective gas protection to obtain a two-dimensional TMDCs single crystal or large-size thin film on the substrate.

2. The method for preparing a two-dimensional semiconductor TMDCs single crystal according to claim 1, characterized in that: In the step 1, the target substrate is a silicon wafer, sapphire or mica wafer.

3. The method for preparing a two-dimensional semiconductor TMDCs single crystal according to claim 1, characterized in that: In the step 1, the halide salt powder is any one of NaCl, KCl, NaI, and KI.

4. The method for preparing a two-dimensional semiconductor TMDCs single crystal according to claim 1, characterized in that: In the step 1, the TMDCs powder is any one of MoS2, WS2, MoSe2, and WSe2.

5. The method for preparing a two-dimensional semiconductor TMDCs single crystal according to claim 1, characterized in that: In the step 1, the molar ratio of the halide salt powder to the TMDCs powder is 2 to 20:1, and the purity of the precursor powder is 4N or above.

6. The method for preparing a two-dimensional semiconductor TMDCs single crystal according to claim 1, characterized in that: In the step 1, grinding is performed using a mortar or a planetary ball mill.

7. The method for preparing a two-dimensional semiconductor TMDCs single crystal according to claim 1, characterized in that: In the step 2, the holding time is 10 to 15 minutes.

8. The method for preparing a two-dimensional semiconductor TMDCs single crystal according to claim 1, characterized in that: In the step 3, the cooling is first programmed to decrease the temperature to 500° C. at a rate of 8-10° C. / min, and then naturally cooled to room temperature.

9. The method for preparing a two-dimensional semiconductor TMDCs single crystal according to claim 1, characterized in that: The protective gas is one or more of nitrogen, argon, and hydrogen, and the flow rate is 20 to 400 sccm.

10. A two-dimensional semiconductor TMDCs single crystal obtained by the method for preparing a two-dimensional semiconductor TMDCs single crystal according to any one of claims 1 to 9, characterized in that: The crystal domains of the TMDCs single crystal achieve single-layer and Bernal stacking few-layer single crystal growth, and the single crystal size of the TMDCs single crystal is greater than 20 μm.

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