Intrinsic p-type two-dimensional hexagonal beta-GaS single crystal prepared by spatial confinement CVD (chemical vapor deposition) method
High-quality intrinsic p-type two-dimensional hexagonal β-GaS single crystals were prepared by controlling reaction conditions using a spatially confined CVD method, which solved the size and crystal quality problems in the prior art and realized the excellent performance of two-dimensional β-GaS in photodetectors and field-effect transistors.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NORTHEAST NORMAL UNIVERSITY
- Filing Date
- 2026-02-13
- Publication Date
- 2026-05-12
AI Technical Summary
Two-dimensional β-GaS prepared by existing chemical vapor deposition methods suffers from small size, irregular shape, uneven number of layers, low crystal quality, and mainly n-type conductivity, which limits its application in fields such as photodetectors.
High-quality intrinsic p-type two-dimensional hexagonal β-GaS single crystals were prepared by using a spatial confinement CVD method, which involves setting up upper and lower substrates in a reactor to form a space, and controlling the ratio and temperature of the mixed gas of Ar and H2 in the atmosphere.
The prepared two-dimensional β-GaS single crystals exhibit good stability and p-type conductivity in photodetectors and field-effect transistors, improving photoresponsivity and conductivity.
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Figure CN122013308A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of two-dimensional material preparation technology, specifically relating to a spatially confined chemical vapor deposition method for obtaining high-quality intrinsic p-type two-dimensional hexagonal β-phase GaS single crystals. Background Technology
[0002] In recent years, III-VI semiconductor materials, with their unique band structure, rich phase structures, and excellent photoelectric properties, have shown broad application prospects in optoelectronics and become a research hotspot in the field of materials science. Gallium sulfide (GaS) is a typical III-VI semiconductor compound. As a layered material, two-dimensional GaS layers are connected by covalent bonds within the layers, with van der Waals interactions between the layers. Depending on the stacking order, GaS can form four different crystal phases, among which β-GaS has been studied more extensively due to its best chemical and thermal stability. Two-dimensional β-GaS is an indirect bandgap semiconductor with a single-layer bandgap of approximately 3.28 eV, which decreases with increasing layer number. Its wide bandgap, high stability, flexibility, and transparency make it widely applicable in flexible electronics, photodetectors, hydrogen evolution catalysis, and nonlinear optics.
[0003] Controllable preparation of two-dimensional β-GaS is a crucial prerequisite for its property research and widespread application. Currently, methods for preparing β-GaS mainly include top-down mechanical exfoliation and liquid-phase exfoliation, and bottom-up physical vapor deposition and chemical vapor deposition. Among these, chemical vapor deposition (CVD) offers advantages such as high controllability and industrial-scale production due to its ability to independently and precisely control various growth conditions. However, CVD-prepared β-GaS still suffers from problems such as small size, irregular shape, uneven layer count, and low crystallinity. Transistors based on β-GaS primarily exhibit n-type conductivity. Similar to traditional n-type and bipolar layered semiconductor materials, researchers often require specific chemical doping, electrode contacts, and gate voltage modulation to achieve p-type conductivity, which limits the application of β-GaS. To address the challenges in the growth and preparation of β-GaS and broaden its applications in photodetectors, existing technologies require further improvement and innovation. Summary of the Invention
[0004] To address the shortcomings of the prior art, the purpose of this invention is to provide a method for fabricating high-quality intrinsic p-type two-dimensional β-GaS, and to construct high-performance photodetectors and field-effect transistors based on this method.
[0005] An intrinsic p-type two-dimensional hexagonal β-GaS single crystal prepared by spatial confinement CVD is prepared by the following method:
[0006] 1) Preparation of precursor: Ga2S3 powder was placed in the high-temperature zone in the center of a horizontal reactor; Ar gas was introduced to raise the temperature to 810-830℃, and then a mixture of Ar and H2 gas was introduced, and the combustion reaction lasted for 20-40 min.
[0007] 2) Preparation of mixed precursor: Ga2S3 powder and precursor are mixed at a weight ratio of 4.5 to 5.5:1;
[0008] 3) Preparation of intrinsic p-type two-dimensional hexagonal β-GaS single crystals:
[0009] a. Place the mixed precursor, upper substrate, and lower substrate on a quartz boat, forming a space between the two substrates. Place the mixed precursor in the high-temperature zone in the center of the horizontal reactor, and place the upper substrate 12-14 cm downstream of the precursor at the left edge of the upper substrate.
[0010] b. In an Ar atmosphere, the reactor is heated to 860-900°C, and a mixture of Ar and H2 gas is introduced. The combustion reaction lasts for 30-50 minutes. After the temperature drops to room temperature, the upper and lower substrates are removed. The intrinsic p-type two-dimensional hexagonal β-GaS single crystals of the upper substrate and the intrinsic p-type two-dimensional hexagonal β-GaS single crystals of the lower substrate are obtained.
[0011] The mixed gas of Ar and H2 introduced has an H2 content of approximately 35-45%.
[0012] Step 3), b. The reactor is heated to 890°C.
[0013] The H2 content is approximately 40%;
[0014] The lower substrate is 1 cm × 1 cm in size and is placed below, while the upper substrate is 1.5 cm × 1.5 cm; the mixed precursor is 30–70 mg.
[0015] The mixed precursor is 70 mg;
[0016] The intrinsic p-type two-dimensional hexagonal β-GaS single crystal is an intrinsic p-type two-dimensional hexagonal β-GaS single crystal on the surface of the upper substrate.
[0017] This invention provides an intrinsic p-type two-dimensional hexagonal β-GaS single crystal prepared by a spatially confined CVD method, comprising the following steps: Precursor preparation: Ga₂S₃ powder is placed in the central high-temperature region of a horizontal reactor; a mixture of Ar and H₂ gas is introduced at 810–830°C, and the mixture reacts to form the precursor; the Ga₂S₃ powder and the precursor are mixed at a weight ratio of 5:1; the mixed precursor is placed in the central high-temperature region of the horizontal reactor, with the upper and lower substrates placed downstream of a quartz boat, forming a space between the two substrates; the reactor is heated to 860–900°C in an Ar atmosphere, and a mixture of Ar and H₂ gas is introduced, with the combustion reaction lasting 30–50 min; thus, intrinsic p-type two-dimensional hexagonal β-GaS single crystals on the upper and lower substrates are obtained. The prepared two-dimensional β-GaS photodetectors exhibit good stability in both cyclic operation and long-term storage. The back-gate field-effect transistor fabricated in this work demonstrates, through transfer and output characteristic curves, that the CVD-grown two-dimensional β-GaS exhibits p-type conductivity. After adding light, the responsivity can be increased to 25 mA / W due to gate voltage modulation. Attached Figure Description
[0018] Figure 1 Schematic diagram of high-quality two-dimensional β-GaS prepared by spatially confined CVD method;
[0019] Figure 2 OM images of samples with upper and lower substrates obtained by spatially confined CVD method;
[0020] Figure 3 (a) OM image; (b) SEM image of a two-dimensional GaS single crystal grown on a SiO2 / Si surface;
[0021] Figure 4 (a) XPS full spectrum of two-dimensional GaS grown on SiO2 / Si substrate; (b) XPS spectrum of Ga 2p orbital; (c) XPS spectrum of S 2p orbital; (d) EDS of S element and (e) Ga element; mapping image; (f) SEM image and (g) EDS energy spectrum corresponding to the white box, scale bar is 5 μm;
[0022] Figure 5 (a) Macroscopic photograph of the substrate of two-dimensional GaS prepared by conventional open CVD method; (b) OM image;
[0023] Figure 6 Structural characterization of two-dimensional hexagonal GaS. (a) Schematic diagram of the crystal structure of β-GaS; (b) High-resolution HADDF-STEM image of a cross-section of a two-dimensional GaS single crystal; (c) Elemental intensity map extracted from the blue dashed line position in (b);
[0024] Figure 7 (a) Absorption spectrum of two-dimensional β-GaS; (b) Tauc curve; (c) UPS spectrum; (d) Schematic diagram of band structure;
[0025] Figure 8 (a) Electrode drawings and enlarged views of individual electrodes created using CAD software; (b) Actual image of Au electrodes on a SiO2 / Si substrate;
[0026] Figure 9 (a) Schematic diagram of a two-dimensional β-GaS photodetector structure; (b) OM image;
[0027] Figure 10 Performance characterization of two-dimensional β-GaS photodetectors: (a) Output characteristic curves; (b) Dependence of photocurrent on incident light power; (c)-(d) Switching characteristics of photocurrent;
[0028] Figure 11 Stability testing of two-dimensional β-GaS photodetectors: (a) Optical switch stability; (b) Environmental stability.
[0029] Figure 12 (a) Transfer characteristic curve of a two-dimensional β-GaS field-effect transistor in the dark state; (b) Output characteristic curve in the dark state; (c) Change in band structure before and after contact between GaS and Au electrodes; (d) Transfer characteristic curve under illumination.
[0030] Figure 13 OM images of 2D GaS at different growth temperatures;
[0031] Figure 14 OM images of two-dimensional GaS with different H2 contents;
[0032] Figure 15 OM images of 2D GaS with different precursor dosages. Detailed Implementation
[0033] Example 1: Growth of two-dimensional hexagonal β-GaS single crystals using spatially confined CVD method
[0034] The gas path connections of the reaction system are as follows: Centered on a tubular muffle furnace, the inlet is connected to a high-purity argon and hydrogen generator via a mass flow meter; the outlet is connected to a tail gas treatment device, which consists of four conical flasks connected in series, containing, in sequence: color-changing silica gel → empty bottle → deionized water → color-changing silica gel. The muffle furnace contains a 1.2 m long, 25 mm diameter quartz tube. Before use, the muffle furnace must be temperature-measured using a thermocouple to determine the location with the highest actual temperature as the central temperature zone.
[0035] 1. Preparation of precursor: 50 mg of Ga2S3 powder was placed in the high-temperature zone in the center of a horizontal reactor. Ar gas was first introduced for 10 min to purge the air from the furnace tubes. Then, the reactor was heated to 820 °C in an Ar atmosphere (argon flow rate of 80 sccm, heating rate of 34 °C / min to 700 °C, then 10 °C / min to 820 °C). When the furnace temperature reached 820 °C, a mixture of Ar and H2 gas was introduced (gas flow rates of Ar: 55 sccm, H2: 35 sccm, respectively). After the combustion reaction lasted for 30 min, the powder was removed from the high-temperature zone to allow the sample to cool rapidly at room temperature, resulting in a yellow powder (precursor).
[0036] 2. Preparation of the mixed precursor: Unburned Ga2S3 powder and the above-mentioned burned powder (precursor) were mixed at a weight ratio of 5:1 to obtain a mixed powder used as a growth source. In this embodiment, 50 mg of unburned Ga2S3 powder and 10 mg of burned powder were mixed together and used as a mixed precursor for the preparation of two-dimensional β-GaS by CVD.
[0037] 3. Substrate Pretreatment: Remove the silicon wafers (SiO2 / Si) stored in the vacuum drying oven and cut them into 1 cm * 1 cm and 1.5 cm * 1.5 cm sizes using a precision cutting tool. After cutting, place the silicon wafers in deionized water and proceed to the subsequent cleaning steps as soon as possible to minimize exposure time. Clean polyethylene (PE) gloves must be worn throughout the process. Perform ultrasonic cleaning sequentially using acetone, isopropanol, anhydrous ethanol, and deionized water at a power of 40 W, for 15 minutes per step. After cleaning, dry the wafers with high-purity nitrogen gas and store them.
[0038] 4. Intrinsic p-type two-dimensional hexagonal β-GaS single crystal prepared by spatially confined CVD method:
[0039] The spatially confined CVD preparation process is as follows: Figure 1 As shown, the mixed precursor powder is placed in the middle of a clean quartz boat I with a length of 10 cm. Another clean quartz boat II with a length of 15 cm is taken, and two clean SiO2 / Si substrates are placed face-to-face at a position 8 cm from the bottom of quartz boat II, with a 1 cm × 1 cm lower substrate at the bottom and a 1.5 cm × 1.5 cm upper substrate at the top. The quartz boat is arc-shaped, and the two SiO2 / Si substrates form an inverted trapezoid, creating a space (spatial confinement) between the two substrates.
[0040] Two quartz boats, I and II, are placed in a tube furnace, with the mixed precursor positioned in the central temperature zone of the furnace and the left edge of the substrate located 13 cm downstream of the precursor.
[0041] After sealing the tubular muffle furnace, Ar was continuously introduced at a rate of 85 cubic centimeters per minute (sccm) for gas scrubbing to remove air from the quartz tube. The heating program for the tubular muffle furnace was set, starting from room temperature (25 °C) and increasing at 34 °C per minute. -1 The temperature was increased to 700 °C at a rate of 10 °C / min, and then further increased to 700 °C / min. -1 The Ar flow rate was increased to 890 °C. When the temperature of the tubular muffle furnace reached 840 °C, the Ar flow rate was adjusted to 55 sccm, and the furnace was simultaneously moved along a slide rail to position the precursor precisely in the central temperature zone. After 5 minutes, when the furnace temperature reached 890 °C, the Ar flow rate was kept constant, and H2 was introduced at a flow rate of 35 sccm as a reducing gas, initiating the material growth stage. The heating program was stopped after maintaining the temperature at 890 °C for 40 minutes, and the H2 introduction was halted, stopping the growth process. The muffle furnace was moved along a slide rail to remove the precursor and substrate from the heating area, and the Ar flow rate was adjusted to 85 sccm. After the temperature dropped to room temperature, the substrate was removed. Under an optical microscope, hexagonal samples were observed on both the upper and lower substrates, such as... Figure 2 As shown, the sample size and the number of samples per unit area on the upper substrate are both larger than those on the lower substrate. Overall, the growth on the upper substrate is better than that on the lower substrate. Therefore, samples from the upper substrate will be used for further characterization and testing.
[0042] The results were observed using an optical microscope (OM) and a scanning electron microscope (SEM) as follows: Figure 3 As shown in (ab), the substrate surface exhibits a regular hexagonal sheet structure with a lateral dimension exceeding 10 μm and clear, sharp edges. Further characterization of the hexagonal sample was performed using X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDS), with results as follows... Figure 4 As shown in (ag), the sample can be identified as a two-dimensional GaS material with uniform composition and conforming to stoichiometry.
[0043] As a control, under otherwise identical conditions, two-dimensional GaS was prepared using the traditional open-type CVD method, i.e., with only one substrate. The results are as follows: Figure 5 As shown, the growth sites of the two-dimensional GaS samples obtained by the open CVD method are concentrated at the gas inlet end of the substrate, with poor distribution uniformity and small grain size.
[0044] High-resolution HADDF-STEM analysis of the cross-section of regular hexagonal samples was performed using focused ion beam to determine the phase composition. The results are as follows: Figure 6As shown in (ac), the monolayers of S-Ga-Ga-S crystals are stacked in a specific manner. The stacking order shows that adjacent monolayers rotate 180° around the c-axis perpendicular to the layer plane. The atomic intensity distribution map also visually shows the stacking period of Ga and S atomic layers, confirming at the atomic scale that the prepared sample is β-GaS with high crystallinity.
[0045] The band structure of the two-dimensional β-GaS sample was characterized using ultraviolet-visible absorption spectroscopy (UV-vis) and ultraviolet electronic spectroscopy (UPS). The results are as follows: Figure 7 As shown. Calculations yielded an indirect bandgap of approximately 2.7 eV and a work function of 3.97 eV for the β-GaS sample. The valence band top relative to the Fermi level E... F With a voltage of 0.98 eV, the two-dimensional β-GaS grown by CVD in this experiment exhibits p-type semiconductor characteristics.
[0046] Example 2: Method for fabricating a two-dimensional β-GaS photodetector with good photoelectric properties
[0047] Electrode fabrication: Photoresist was uniformly coated onto a clean silicon wafer using spin coating technology, rotating at 4000 r / min for 30 s to control the photoresist layer thickness. The sample was then placed on a hot plate and heated at 120℃ for 1.5 min to cure the photoresist. After starting the lithography machine, key exposure parameters were set, and the focusing distance was fine-tuned to ensure the sample had the sharpest edges. The electrode drawing file designed in CAD software was then imported, such as... Figure 8 As shown in (a). During exposure, the system controls the beam to selectively irradiate the photoresist according to a preset pattern, precisely generating the pattern on the mask on the photoresist layer. The selectively irradiated silicon wafer is immersed in the developer to form the desired pattern on the silicon wafer surface. The developed sample is placed in a vacuum evaporation device, with a high-purity Au wire placed on a tungsten boat. Au is rapidly heated to the evaporation temperature by applying a current of 120 A or higher, and after 3 minutes to allow the evaporation material to fully evaporate, the thickness is observed to remain stable in the film thickness gauge before the current is slowly reduced to 0. In a high vacuum environment, Au is deposited to the silicon wafer surface at a depth of approximately 15-20 nm, forming an Au electrode structure in the area defined by the photoresist pattern. Then, the silicon wafer with the Au electrode evaporation completed is immersed in an acetone solution to dissolve and remove residual photoresist. Finally, the silicon wafer is immersed in an isopropanol solution to remove the acetone and then dried. A clean and complete metal electrode is finally obtained on the silicon wafer surface, as shown in (a). Figure 8 As shown in (b).
[0048] Next, the electrodes were peeled from the substrate using an 8% PVA solution for subsequent optoelectronic device fabrication. The preparation method was as follows: 4 g of PVA powder was accurately weighed using an electronic balance and placed in a sample vial equipped with a magnetic stir bar, followed by the addition of 46 mL of deionized water. The mixture was sealed and heated on a hot plate at 100 °C and 800 r / min for 5 h with stirring. It was then transferred to an oven and heated at 100 °C for another 1 h to ensure complete dissolution of the PVA. Finally, the solution was returned to the hot plate and heated for 1 h to ensure homogeneous mixing and form a clear, transparent homogeneous solution. A layer of PVA solution was spin-coated onto the substrate surface with the Au electrode deposited. After the PVA solution was allowed to air dry naturally at room temperature for 20 min to form a uniform solid film, PDMS was used as a flexible support layer to adhere it to the PVA / Au surface, and uniform, gentle pressure was applied to achieve good adhesion. Subsequently, taking advantage of the flexibility and viscoelasticity of the PDMS layer, it is slowly lifted with tweezers. At this time, the metal electrode (Au) is separated from the substrate along with the upper and lower polymer layers (PVA and PDMS), and finally a "PDMS / PVA / Au" sandwich-style independent composite structure is formed.
[0049] Finally, in order to complete the fabrication of the GaS optoelectronic device, it is necessary to use a transfer stage to precisely transfer the Au electrode to a specific location on the GaS material. The specific steps are as follows:
[0050] (1) Sample fixation: Place the silicon wafer with the low-dimensional GaS sample face up on the small perforated support of the transfer stage, and turn on the vacuum pump to adsorb and fix the silicon wafer. Adjust the focal plane to the surface of the silicon wafer using the microscopic imaging system, locate the target GaS sample and move it to the center of the field of view, and accurately mark the outline and position of the sample on the screen.
[0051] (2) Electrode structure clamping: Attach the “PDMS / PVA / Au” structure with the PDMS side down to the center of a clean glass slide, invert the entire structure and suspend it on the adjustable transfer platform so that the Au electrode surface and the GaS sample surface below are facing each other. Adjust the microscope focus until the Au electrode layer is clearly imaged, and fine-tune the horizontal position of the transfer platform so that the electrode channel is aligned with the target sample position marked on the screen.
[0052] (3) Thermal Assisted Bonding: The transfer platform is slowly lowered so that the Au electrode layer gradually approaches the GaS sample surface. During the descent, the focal length is adjusted in real time to ensure alignment. When the electrode is about to contact the sample, the descent speed is reduced until the "PDMS / PVA / Au" composite structure is gently bonded to the target position on the silicon wafer surface. Then, the heating stage program is started to heat the material, increasing the temperature from room temperature to 100°C in a stepwise manner at 10°C intervals, and continuing to heat at 100°C for 10 minutes. After heating is completed, the transfer platform is slowly raised. Due to the weak bonding force between PDMS and PVA, they separate, thereby accurately transferring PVA / Au to the GaS surface.
[0053] (4) PVA removal: Immerse the substrate containing the sample in deionized water for at least 30 minutes. Once the PVA is completely dissolved, dry the substrate surface with N2 to obtain a structurally complete low-dimensional GaS optoelectronic device, such as... Figure 9 As shown in (ab).
[0054] The test was conducted using a 405 nm wavelength laser as the excitation source. Figure 10 As shown in (a), the current-voltage (IV) characteristic curves of the device under different incident light powers and dark conditions were obtained. The tests showed that the two-dimensional β-GaS exhibits a high intrinsic resistance in the dark state, with a resistance value of 10 Ω. 12 The conductivity of the device is on the order of Ω; the conductivity under illumination can be increased by 10⁻⁶ compared to the dark state. 4 This demonstrates a good optical response gain, achieved by multiples of [value missing]. A power function I [value missing] was used. ph =I0+AP in α Fit the experimental results. For example... Figure 10 As shown in (b), the fitted α value is 0.92, close to 1, reflecting that the CVD-grown two-dimensional β-GaS single crystal has a low intrinsic defect density and excellent photoelectric properties. Further analysis using the formula R=I... Ph / P in The responsivity R of the two-dimensional β-GaS photodetector was calculated to be 0.3 mA / W. Under a fixed bias voltage of 4 V and an incident light power of 30 μW, the device was subjected to periodic square wave modulation for 20 s, resulting in the following... Figure 10 (c) Photocurrent switching characteristic curve. Figure 10 (d) Further magnified details of a single cycle are shown, with the rise time of the two-dimensional β-GaS-based photodetector measured to be 44 ms and the fall time to be 39 ms.
[0055] Next, the stability of the two-dimensional β-GaS photodetector was tested. For example... Figure 11As shown in (a), after irradiation with a laser at a switching frequency of 1 Hz for 60 min, the optical switching behavior of the device remains stable, and its responsivity can reach approximately 76% of the initial value. The newly fabricated device was placed in a centrifuge tube under normal air conditions. Figure 11 (b) This paper presents the results of photoelectric testing of the device after 10 days and 3 months of storage, comparing them with the initial state. The data shows that after 10 days of storage, the device's photoresponse remained above 95% of its initial value; after 3 months, the device's performance decreased slightly, but the responsivity still remained at approximately 75% of the initial value. These results demonstrate that the CVD-grown two-dimensional β-GaS in this paper exhibits good long-term environmental stability under non-special storage conditions, and the device built based on this exhibits good stability in both cyclic operation and long-term storage.
[0056] Example 3: Fabrication method of a two-dimensional β-GaS back-gate field-effect transistor with p-type conductivity.
[0057] Based on the existing structure of a two-dimensional β-GaS photodetector, a back-gate field-effect transistor was constructed using a convenient method. First, a highly conductive silver paste was uniformly coated onto the back side of a SiO2 / Si substrate with deposited Au electrodes. Then, the silver-coated substrate was firmly adhered to the surface of a copper adhesive tape fixed to a glass slide. Figure 12 The illustration in (b) shows a schematic diagram of the device structure. In this device, Cu acts as the back gate electrode, while the original Au electrodes remain as the source and drain, respectively. This allows for a rapid transition from a two-terminal to a three-terminal device on the same material without requiring additional complex processes, thus quickly completing the construction of a back-gate field-effect transistor. The electrical performance of the device was tested in darkness, and the results are as follows: Figure 12 As shown in (ab), the transfer and output characteristic curves confirm that the CVD-grown two-dimensional β-GaS exhibits p-type conductivity in this work. With the addition of light, the responsivity can be increased to 25 mA / W due to gate voltage modulation. Figure 11 As shown in (d), it exhibits good photoelectric properties.
[0058] Example 4: Preparation of two-dimensional GaS at different growth temperatures
[0059] The processing of other growth conditions, such as the precursor and substrate, was the same as in Example 1, except that the temperature of the central temperature zone of the tube muffle furnace was changed. The tube muffle furnace heating program was set, starting from room temperature (25 °C) and increasing at 34 °C per minute. -1 The temperature was increased to 700°C at a rate of 10°C / min, and then increased to 700°C / min. -1The Ar flow rate was increased to the target temperature (800 ℃, 830 ℃, 860 ℃, 890 ℃, 920 ℃, 950 ℃). When the temperature of the tubular muffle furnace was observed to rise to 50 ℃ below the target temperature, the Ar flow rate was adjusted to 55 sccm, and the tubular muffle furnace was moved by a slide rail to position the precursor precisely in the central temperature zone. After 5 min, when the temperature of the tubular muffle furnace reached the target temperature, the Ar flow rate was kept constant, and H2 was introduced at a flow rate of 35 sccm as a reducing gas, entering the material growth stage. After maintaining the target growth temperature for 40 min, the heating program was stopped, the H2 introduction was stopped, and the growth process stopped. The muffle furnace was moved by a slide rail to move the precursor and substrate away from the heating area, the Ar flow rate was adjusted to 85 sccm, and the substrate was removed after the temperature dropped to room temperature. During the process of increasing the growth temperature from 800 ℃ to 950 ℃, its significant impact on the preparation of two-dimensional GaS could be observed, such as... Figure 13 As shown, when the growth temperature is 800 °C, the formation of large-sized monolayer GaS triangular domains can be observed. As the growth temperature gradually increases, smaller, irregularly shaped nucleation sites appear at 830 °C and 860 °C. With further increases in growth temperature, the lateral size of the sample gradually expands, and the thickness also increases, while the morphology gradually becomes more regular. At 890 °C, relatively regular hexagonal sheets can be obtained, with an average lateral size of approximately 8 μm. However, further heating does not increase the sample size further but may cause secondary nucleation of the reaction source above the sample. At 920 °C, small triangular structures can be observed above the hexagonal sample. When the growth temperature reaches 950 °C, the sample thickness is uneven and the morphology is irregular. This example illustrates that the growth temperature can control the shape, size, and thickness of two-dimensional GaS.
[0060] Example 5: Preparation of two-dimensional GaS with different hydrogen contents
[0061] Other growth conditions were the same as in Example 1. Under a fixed total gas flow rate of 90 sccm, two-dimensional GaS was grown by changing the ratio of Ar and H2 gases, i.e., changing the H2 content in the carrier gas (25%–50%). The results are as follows. Figure 14As shown in the diagram. Specifically, when the temperature of the tubular muffle furnace reached 840 °C, the Ar flow rate was adjusted to 67.5 sccm, 63 sccm, 58.5 sccm, 55 sccm, 49.5 sccm, and 45 sccm, respectively. Simultaneously, the tubular muffle furnace was moved along a slide rail to position the precursor precisely in the central temperature zone. After 5 minutes, when the temperature of the tubular muffle furnace reached 890 °C, the Ar flow rate was kept constant, and H2 was introduced as a reducing gas at flow rates of 22.5 sccm, 27 sccm, 31.5 sccm, 35 sccm, 40.5 sccm, and 45 sccm, respectively, to initiate the material growth stage. After maintaining the temperature at 890 °C for 40 minutes, the heating program was stopped, H2 introduction was stopped, and the growth process ceased. The muffle furnace was moved along a slide rail to move the precursor and substrate away from the heating area, the Ar flow rate was adjusted to 85 sccm, and the substrate was removed after the temperature dropped to room temperature. As the H2 content increases, we can clearly observe that the lateral dimensions of 2D GaS first increase and then remain constant. When the H2 content is approximately 40%, the lateral dimensions of the 2D GaS sheets reach their maximum value, with the size of regular hexagonal domains reaching a maximum of 10 μm. This phenomenon indicates that an appropriate H2 content is beneficial for reducing the nucleation density and promoting the lateral expansion of existing nuclei. However, if the H2 ratio continues to increase, the sample size no longer increases, and the edge morphology changes significantly, gradually transforming from clear, sharp hexagons into irregularly contoured "flower-like" structures, indicating etching. This example demonstrates that hydrogen, as a reactive gas, participates in the activation and transport of the precursor; on the other hand, it also directly affects the reaction process of 2D GaS nucleation and lateral growth on the substrate surface.
[0062] Example 6: Preparation of two-dimensional GaS with different mixed precursor contents
[0063] Other growth conditions were the same as in Example 1, only the mass of the mixed precursor was changed, and the results were as follows: Figure 15 As shown, as the amount of the mixed precursor increased from 30 mg to 50 mg, the sample size gradually increased while the nucleation density gradually decreased. When the precursor amount was further increased to 60 mg, the sample size reached a maximum of approximately 10 μm, with a moderate nucleation density. When the mixed precursor mass reached 70 mg, the sample size no longer increased, but the nucleation density continued to increase, and the phenomenon of connection and stacking of the sample could be observed. However, when the mixed precursor mass was 80 mg, the sample exhibited large-area clustering, and the hexagonal regular morphology of single-crystal GaS no longer appeared. This example illustrates that the mixed precursor mass changes the nucleation density, crystal size, and morphology of two-dimensional GaS.
Claims
1. An intrinsic p-type two-dimensional hexagonal β-GaS single crystal prepared by a spatially confined CVD method is prepared by the following method: 1) Preparation of precursor: Ga2S3 powder was placed in the high-temperature zone in the center of a horizontal reactor; Ar gas was introduced to raise the temperature to 810-830℃, and then a mixture of Ar and H2 gas was introduced, and the combustion reaction lasted for 20-40 min. 2) Preparation of mixed precursor: Ga2S3 powder and precursor are mixed at a weight ratio of 4.5 to 5.5:1; 3) Preparation of intrinsic p-type two-dimensional hexagonal β-GaS single crystals: a. Place the mixed precursor, upper substrate, and lower substrate on a quartz boat, forming a space between the two substrates. Place the mixed precursor in the high-temperature zone in the center of the horizontal reactor, and place the upper substrate 12-14 cm downstream of the precursor at the left edge of the upper substrate. b. In an Ar atmosphere, the reactor is heated to 860-900°C, and a mixture of Ar and H2 gas is introduced. The combustion reaction lasts for 30-50 minutes. After the temperature drops to room temperature, the upper and lower substrates are removed. The intrinsic p-type two-dimensional hexagonal β-GaS single crystals of the upper substrate and the intrinsic p-type two-dimensional hexagonal β-GaS single crystals of the lower substrate are obtained. The mixed gas of Ar and H2 introduced has an H2 content of approximately 35-45%.
2. The intrinsic p-type two-dimensional hexagonal β-GaS single crystal prepared by spatial confinement CVD method according to claim 1, characterized in that: Step 3), b. The reactor is heated to 890°C.
3. The intrinsic p-type two-dimensional hexagonal β-GaS single crystal prepared by spatial confinement CVD method according to claim 2, characterized in that: The H2 content is approximately 40%.
4. An intrinsic p-type two-dimensional hexagonal β-GaS single crystal prepared by spatial confinement CVD method according to claim 1, 2 or 3, characterized in that: The lower substrate is 1 cm × 1 cm in size and is placed below, while the upper substrate is 1.5 cm × 1.5 cm; the mixed precursor is 30–70 mg.
5. An intrinsic p-type two-dimensional hexagonal β-GaS single crystal prepared by spatial confinement CVD method according to claim 4, characterized in that: The mixed precursor is 70 mg.
6. An intrinsic p-type two-dimensional hexagonal β-GaS single crystal prepared by spatial confinement CVD method according to claim 5, characterized in that: The ratio of Ga2S3 powder to precursor is 5:
1.
7. An intrinsic p-type two-dimensional hexagonal β-GaS single crystal prepared by spatial confinement CVD method according to claim 6, characterized in that: The intrinsic p-type two-dimensional hexagonal β-GaS single crystal is an intrinsic p-type two-dimensional hexagonal β-GaS single crystal with an upper substrate.