A ternary layered selenide Ge 0.85 Bi 2.15+x Se4 semiconductor material and a method of preparing the same

Abstract

This invention relates to the field of crystal material preparation technology, specifically to a ternary layered selenide Ge 0.85 Bi 2.15+x Se4 semiconductor material and its preparation method. The preparation method includes the following steps: according to the chemical formula Ge... 0.85 Bi 2.15+x The molar ratio of germanium powder, bismuth powder, and selenium powder in Se4 is weighed, where 0 ≤ x ≤ 0.06. The weighed raw materials are mixed evenly and placed in a quartz tube. The quartz tube is then sealed under vacuum. The vacuum-sealed quartz tube is placed in a heating furnace and heated from room temperature to 900-950℃, held at this temperature for 12-24 hours. After the holding period, the quartz tube is removed from the heating furnace and quenched. The quenched and cooled quartz tube is then placed back in the heating furnace and heated from room temperature to 540-560℃, held at this temperature for 3-5 days for annealing, thus obtaining the ternary layered selenide Ge. 0.85 Bi 2.15+x Se4 semiconductor material. This invention successfully solves the technical problem of obtaining a single phase in the GeBi2Se4 system by precisely controlling the Ge / Bi ratio and employing high-temperature quenching and low-temperature long-time annealing processes.

Description

Technical Field

[0001] This invention relates to the field of semiconductor material preparation technology, specifically to a ternary layered selenide Ge 0.85 Bi 2.15+x Se4 semiconductor materials and their preparation methods. Background Technology

[0002] Layered chalcogenides are an important class of materials formed by stacking two-dimensional or quasi-two-dimensional layered building blocks along a direction perpendicular to the layer plane to create a three-dimensional periodic crystal structure. Due to the strong covalent or metallic bonds between atoms within the layers, and the weak van der Waals interactions between the building blocks, these materials exhibit significant anisotropy in physical and chemical properties and are easily exfoliated. These unique properties make them promising for applications in high-tech fields such as high-performance field-effect transistors, photodetectors, gas sensors, spintronics, thermoelectric devices, and solar cells.

[0003] Among numerous layered chalcogenides, the ternary selenide GeBi₂Se₄ is one of the first compounds discovered in the Ge-Bi-Se system. Studies have shown that GeBi₂Se₄ possesses a rhombohedral crystal structure (space group: R-3m), composed of layered structural units stacked perpendicular to the layer planes. As a narrow bandgap semiconductor material (approximately 0.27 eV), GeBi₂Se₄ has significant potential applications in high-tech fields such as infrared light detection, terahertz wave response, and thermal energy conversion.

[0004] However, existing methods for preparing GeBi₂Se₄ have significant technical limitations. Currently disclosed preparation processes primarily employ argon protection combined with ball milling and vacuum hot-pressing sintering to synthesize GeBi₂Se₄ materials. While this process yields bulk materials, the resulting products often contain germanium-rich impurities, preventing the production of pure-phase (single-phase) materials. The presence of these impurities severely interferes with the accurate characterization of the material's intrinsic physical properties and limits its practical application in high-precision functional devices. Therefore, exploring a simple and controllable method for growing pure-phase Ge-Bi-Se ternary layered selenide semiconductors is of great significance for advancing the study of the properties and application development of this type of material. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the object of the present invention is to provide a ternary layered selenide Ge 0.85 Bi 2.15+x The invention relates to Se4 semiconductor materials and their preparation methods, aiming to solve the technical challenges of complex processes and the presence of impurity phases in the preparation of GeBi2Se4 materials in the prior art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A ternary layered selenide Ge 0.85 Bi 2.15+x A method for preparing Se4 semiconductor material, comprising the following steps:

[0008] S100, using germanium powder, bismuth powder and selenium powder as raw materials, according to the chemical formula Ge 0.85 Bi 2.15+x Weigh the molar ratio of Se4, where 0≤x≤0.06. After the weighed raw materials are mixed evenly, place them in a quartz tube, evacuate the quartz tube, and then seal the quartz tube.

[0009] S200. Place the vacuum-sealed quartz tube from step S100 into a heating furnace, raise the temperature from room temperature to 900-950℃ and hold it at that temperature for 12-24 hours. After the holding period, remove the quartz tube from the heating furnace and quench it to cool it down to room temperature.

[0010] S300: Place the quartz tube, which has been quenched and cooled in step S200, back into the heating furnace. Heat the tube from room temperature to 540-560℃ and hold it at this temperature for 3-5 days for annealing. After the holding period, allow the quartz tube to cool naturally to room temperature with the furnace. Then, remove the obtained ternary layered selenide Ge from the quartz tube. 0.85 Bi 2.15+x Se4 semiconductor material.

[0011] The ternary layered selenide Ge 0.85 Bi 2.15+x A method for preparing Se4 semiconductor materials, wherein the purity of germanium powder, bismuth powder and selenium powder is all above 99.99%.

[0012] The ternary layered selenide Ge 0.85 Bi 2.15+x A method for preparing Se4 semiconductor material, wherein in step S100, the quartz tube is evacuated to a pressure ≤1 Pa before being sealed.

[0013] The ternary layered selenide Ge 0.85 Bi 2.15+x The method for preparing Se4 semiconductor material, wherein the quenching and cooling method in step S200 is to quickly remove the quartz tube from the furnace and place it in cold water for rapid cooling.

[0014] The ternary layered selenide Ge 0.85 Bi 2.15+x A method for preparing Se4 semiconductor material, wherein in step S200, the temperature is increased from room temperature to 900-950℃ at a heating rate of 2-5℃ / min.

[0015] The ternary layered selenide Ge 0.85 Bi 2.15+x The method for preparing Se4 semiconductor material includes step S300, in which the temperature is increased from room temperature to 540-560℃ at a heating rate of 2-5℃ / min.

[0016] A ternary layered selenide Ge 0.85 Bi 2.15+x Se4 semiconductor material, wherein the ternary layered selenide Ge described in this invention is used. 0.85 Bi 2.15+x Se4 semiconductor material was prepared by a specific method.

[0017] The ternary layered selenide Ge 0.85 Bi 2.15+x Se4 semiconductor material, wherein the ternary layered selenide Ge 0.85 Bi 2.15+x Se4 semiconductor material has a rhombohedral crystal structure with space group R-3m and exhibits a layered morphology.

[0018] Beneficial effects: This invention employs a two-step heat treatment process of high-temperature melting and quenching followed by low-temperature long-term annealing. First, high-temperature melting (900-950℃) allows all elements to fully react and homogenize. Then, quenching rapidly freezes the homogeneous state from the high temperature to room temperature, avoiding the precipitation of impurity phases during slow cooling. Next, low-temperature annealing at a precise temperature of 540-560℃ for 3-5 days provides sufficient energy and time for atomic rearrangement and crystal structure ordering, thereby promoting the precipitation of the target phase Ge. 0.85 Bi 2.15+x Se4 fully nucleates and grows, forming a high-quality single-phase material. Ge prepared by the method of this invention... 0.85 Bi 2.15+x Se4 is a pure phase with a complete crystal structure and obvious layered characteristics. It exhibits low thermal conductivity and low resistivity, making it a promising candidate for applications in photoelectric detection and thermoelectric conversion. The preparation method described in this invention is simple, highly controllable, and reproducible, providing a reliable technical reference for the controllable growth of Ge-Bi-Se compounds and offering high-quality material support for subsequent property studies, device development, and applications. Attached Figure Description

[0019] Figure 1 Ge in Example 1 0.85 Bi 2.15 Optical photograph of Se4 material.

[0020] Figure 2 Ge in Example 10.85 Bi 2.15 Powder X-ray diffraction pattern of Se4 material.

[0021] Figure 3 Ge in Example 1 0.85 Bi 2.15 Scanning electron microscope image of the microstructure of Se4 material.

[0022] Figure 4 Ge in Example 1 0.85 Bi 2.15 X-ray energy spectrum of Se4 material.

[0023] Figure 5 Ge in Example 1 0.85 Bi 2.15 Scanning electron microscope backscattered electron image of Se4 material.

[0024] Figure 6 Ge in Example 1 0.85 Bi 2.15 Atomic resolution structural diagram of Se4 material

[100] projected along the direction.

[0025] Figure 7 Ge in Example 2 0.85 Bi 2.21 Powder X-ray diffraction pattern of Se4 material.

[0026] Figure 8 Ge in Example 2 0.85 Bi 2.21 Scanning electron microscope backscattered electron image of Se4 material.

[0027] Figure 9 The image shows the X-ray powder diffraction pattern of the material prepared in Comparative Example 1.

[0028] Figure 10 The image shows the X-ray powder diffraction pattern of the material prepared in Comparative Example 2.

[0029] Figure 11 The image shows the X-ray powder diffraction pattern of the material prepared in Comparative Example 3.

[0030] Figure 12 The image shows the X-ray powder diffraction pattern of the material prepared in Comparative Example 4.

[0031] Figure 13 The image shows the X-ray powder diffraction pattern of the material prepared in Comparative Example 5.

[0032] Figure 14 This is a scanning electron microscope backscattered electron image of the material prepared in Comparative Example 6.

[0033] Figure 15This is a scanning electron microscope backscattered electron image of the material prepared in Comparative Example 7. Detailed Implementation

[0034] This invention provides a ternary layered selenide Ge 0.85 Bi 2.15+x Se4 semiconductor materials and their preparation methods: To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0035] This invention provides a ternary layered selenide Ge 0.85 Bi 2.15+x The preparation method of Se4 semiconductor material includes the following steps:

[0036] S100, using germanium powder, bismuth powder and selenium powder as raw materials, according to the chemical formula Ge 0.85 Bi 2.15+x Weigh the molar ratio of Se4, where 0≤x≤0.06. After the weighed raw materials are mixed evenly, place them in a quartz tube, evacuate the quartz tube, and then seal the quartz tube.

[0037] S200. Place the vacuum-sealed quartz tube from step S100 into a heating furnace, raise the temperature from room temperature to 900-950℃ and hold it at that temperature for 12-24 hours. After the holding period, remove the quartz tube from the heating furnace and quench it to cool it down to room temperature.

[0038] S300: Place the quartz tube, which has been quenched and cooled in step S200, back into the heating furnace. Heat the tube from room temperature to 540-560℃ and hold it at this temperature for 3-5 days for annealing. After the holding period, allow the quartz tube to cool naturally to room temperature with the furnace. Then, remove the obtained ternary layered selenide Ge from the quartz tube. 0.85 Bi 2.15+x Se4 semiconductor material.

[0039] Specifically, the ideal stoichiometric compound GeBi2Se4 (Ge:Bi:Se = 1:2:4) in the Ge-Bi-Se ternary system was reported for the first time. However, when performing solid-state reactions according to this stoichiometric ratio using existing techniques, the products always contain germanium-rich impurities (such as GeSe, GeSe2, etc.). This is because: germanium has multiple valence states (+2, +4) in selenides and forms various stable compounds with selenium (GeSe, GeSe2), resulting in a complex phase diagram; bismuth mainly exists in the +3 valence state and forms Bi2Se3 with selenium. In the GeBi2Se4 structure, Ge... 2+ and Bi 3+They jointly occupy cation sites, forming an ordered layered structure; when the proportion of Ge is 1, the excess Ge in the system... 2+ Unable to fully enter the cation sites, it tends to combine with Se to form germanium-rich binary phases (such as GeSe) and precipitate out.

[0040] This invention, through systematic compositional screening experiments, discovered that when the Ge ratio is precisely controlled at 0.85, the ratio of cation sites (Ge / Bi) reaches an optimal balance, capable of fully accommodating Ge. 2+ and Bi 3+ This forms an ordered layered structure. Specifically, for example, in Ge... 0.85 Bi 2.15 In Se4, the average cation charge is (0.85×2 + 2.15×3) / 3 = 2.47, which is similar to that of Se. 2- The charge-matching degree of GeBi₂Se₄ is better than that of GeBi₂Se₄ (2.33), which is conducive to the formation of a more stable crystal structure; Ge 2+ Ionic radius smaller than Bi 3+ At a ratio of 0.85:2.15, Ge 2+ Prioritizing the occupation of specific crystallographic positions avoids the effects of excessive Ge. 2+ However, it is forced to enter interstitial sites or form impurities; the Bi content of the present invention can be finely adjusted in the range of 2.15~2.21 (i.e. x from 0 to 0.06), indicating that the phase has a certain solid solubility, but if it exceeds this range (x<0 or x>0.06), component segregation will occur. Therefore, 0.85:(2.15~2.21):4 is the critical composition range for forming a stable pure phase.

[0041] Traditional solid-state sintering or melting methods typically employ a process of high-temperature melting followed by slow cooling. Under this process, the melt undergoes the following problems during slow cooling: phase separation: as the temperature decreases, the solubility of different components in the melt changes, leading to the sequential precipitation of different solid phases; impurity phase nucleation: germanium-rich phases (such as GeSe) may preferentially nucleate and grow during the cooling process, eventually being encapsulated within the main phase; compositional inhomogeneity: slow cooling cannot preserve the homogeneous state at high temperatures, resulting in compositional segregation in the final product.

[0042] This invention employs a two-step heat treatment process—high-temperature melting and quenching followed by low-temperature long-term annealing—to prepare single-phase ternary layered selenide semiconductor materials. The quenching process freezes the high-temperature homogeneous melt to room temperature, forming a metastable precursor. Specifically, at a high temperature of 900-950℃, Ge, Bi, and Se completely melt and diffuse, forming a homogeneous melt.

[0043] Quenching allows the homogeneous melt to pass through the crystallization temperature range at a relatively fast rate, effectively suppressing crystal growth. Subsequently, a precisely controlled low-temperature annealing treatment at 540-560℃ drives the metastable precursor towards the target single-phase Ge. 0.85 Bi 2.15+x The Se4 transformation is chosen at 540-560℃ because within this temperature range, it can provide sufficient atomic migration energy to promote the rearrangement of Ge, Bi, and Se atoms to form an ordered layered structure, while avoiding secondary phase separation that may occur at high temperatures.

[0044] Crystal growth is a diffusion-controlled process, Ge 0.85 Bi 2.15+x The formation of the Se4 layered structure requires sufficient time for atoms to arrange themselves in an orderly manner over a long range. A holding time of 3-5 days provides sufficient kinetic conditions for the formation, growth, and migration of crystal nuclei and grain boundaries, ensuring that the reaction proceeds completely. Too short a time (<3 days) may lead to incomplete reaction. Too long a time (>5 days) has no negative impact, but it increases energy consumption and reduces economic efficiency.

[0045] In this invention, high-temperature melting and quenching and low-temperature long-time annealing are not simply two independent steps superimposed, but rather exhibit a significant synergistic effect. The uniform metastable precursor obtained through quenching provides a single composition source for subsequent annealing, avoiding the precipitation of impurity phases due to compositional inhomogeneity during annealing. The temperature window of 540-560℃ is precisely the optimal temperature for the metastable precursor to transform into the target crystal structure. Excessive temperature fails to yield a pure phase, while excessively low temperature necessitates significantly extended holding time, increasing energy consumption. Only when the composition is precisely controlled within the Ge... 0.85 Bi 2.15+x When using Se4, this two-step process is necessary to obtain pure-phase ternary layered selenides.

[0046] In some embodiments, the germanium powder, bismuth powder, and selenium powder all have a purity of 99.99% or higher. High-purity raw materials are the foundation for obtaining high-quality single-phase materials. Impurities in the raw materials (especially transition metal impurities) may act as heterogeneous nucleation centers, inducing the formation of impurity phases, or entering the crystal lattice and disrupting the order of the layered structure.

[0047] In some embodiments, the quenching and cooling method described in step S200 is to quickly remove the quartz tube from the furnace and place it in cold water for rapid cooling, but it is not limited to this.

[0048] In this embodiment, the quenching cooling rate is fast (≥200℃ / min), freezing the microstructure of the material at high temperature and effectively avoiding grain growth and phase separation during slow cooling. Cold water quenching is preferred in this embodiment.

[0049] In some embodiments, in step S200, the temperature is increased from room temperature to 900-950°C at a heating rate of 2-5°C / min. In this embodiment, excessively slow heating would prolong the process cycle, increase energy consumption, and the prolonged residence time of the quartz tube in the high-temperature zone might increase the risk of reaction between the tube wall and the raw materials; excessively rapid heating might cause the raw materials to react violently and exothermically, leading to quartz tube breakage (especially since selenium powder is prone to sublimation at high temperatures, generating high pressure). This embodiment selects a heating rate of 2-5°C / min to achieve the best balance between safety and efficiency.

[0050] In some embodiments, in step S300, the temperature is increased from room temperature to 540-560°C at a heating rate of 2-5°C / min. Similarly, this embodiment selects a heating rate of 2-5°C / min to avoid thermal stress causing the quartz tube to crack, while ensuring the stability of temperature control.

[0051] In some embodiments, a ternary layered selenide Ge is also provided. 0.85 Bi 2.15+x Se4 semiconductor material, wherein the ternary layered selenide Ge described in this invention is used. 0.85 Bi 2.15+x Se4 semiconductor material was prepared using a method for preparing the ternary layered selenide Ge. 0.85 Bi 2.15+x Se4 semiconductor material has a rhombohedral crystal structure with space group R-3m and exhibits a layered morphology.

[0052] Example 1

[0053] A ternary layered selenide Ge 0.85 Bi 2.15 The preparation method of Se4 semiconductor material includes the following steps:

[0054] Step 1: Ingredient Preparation and Packaging

[0055] Using germanium powder, bismuth powder, and selenium powder with a purity of 99.99% as raw materials, for the chemical formula Ge 0.85 Bi 2.15 Se4 is prepared by weighing germanium powder, bismuth powder, and selenium powder in a molar ratio of 0.85:2.15:4. The weighed raw materials are placed in a mortar and thoroughly mixed. The mixture is then placed into a clean quartz tube. The quartz tube is connected to a vacuum system and evacuated until the internal pressure is ≤1 Pa to remove air and moisture, preventing oxidation of the raw materials at high temperatures. Subsequently, the quartz tube is sealed using an oxyhydrogen flame sealing device to ensure it remains under vacuum during subsequent heat treatment.

[0056] Step 2: High-temperature melting and firing

[0057] The vacuum-sealed quartz tube was placed vertically in a single-temperature zone pit furnace, with the tube near the thermocouple. The temperature was increased from room temperature to 950°C at a rate of 5°C / min and held at this temperature for 12 hours. After holding, the tube was quenched and cooled to room temperature. The purpose of this high-temperature melting step was to allow germanium, bismuth, and selenium to fully diffuse and react in the molten state, forming a homogeneous melt. After holding, the quartz tube was quickly removed from the furnace and placed in cold water for quenching. The key to the quenching operation was achieving rapid cooling, which froze the homogeneous melt at high temperature, preventing phase separation or precipitation of impurities during cooling, thus laying the foundation for the subsequent formation of a single target phase.

[0058] Step 3: Material Annealing

[0059] For the material quenched and cooled in step two, the temperature was increased to 560°C at a rate of 5°C / min and held at this temperature for 3 days. It was then cooled to room temperature in the furnace and subsequently removed from the quartz tube. This low-temperature, long-duration annealing step is crucial to the entire invention. At this precise temperature of 560°C, the diffusion and migration capabilities of atoms are moderate, allowing the previously frozen precursor to acquire sufficient energy for structural relaxation and atomic rearrangement, thereby driving the Ge... 0.85 Bi 2.15 The formation and growth of Se4 crystal nuclei are facilitated by a 3-day heat preservation period, which provides sufficient kinetic conditions for crystal growth, ensuring that the reaction can proceed completely and form a single-phase material with uniform composition and complete crystal structure. After the heat preservation is completed, the quartz tube is allowed to cool naturally to room temperature with the furnace to obtain a stable product.

[0060] Material microstructure and structural analysis

[0061] The morphology, chemical composition, and structure of the prepared materials were analyzed and characterized using optical microscopy, X-ray diffraction, scanning electron microscopy, X-ray energy dispersive spectroscopy, and transmission electron microscopy. Specific characterization results are as follows: Figures 1 to 6 As shown. Among them, Figure 1 The optical photographs of the obtained material show that it is a block with a metallic luster, a smooth surface, and no obvious impurities. Figure 2 The powder X-ray diffraction pattern was compared with a standard card (based on the known GeBi2Se4 structure). All diffraction peaks could be indexed to the rhombohedral crystal system (space group R-3m), and no diffraction peaks of any other impurities appeared, proving that the obtained material is a pure phase. Figure 3 The scanning electron microscope images show that the material has typical layered morphological characteristics. Figure 4 X-ray energy dispersive spectroscopy analysis confirmed that the chemical composition of the material is mainly composed of three elements: Ge, Bi, and Se, with an atomic percentage close to 0.85:2.15:4, which is consistent with the target chemical formula. Figure 5In the scanning electron microscope backscattered electron image, the contrast was uniform, and no contrast between light and dark caused by differences in atomic number was observed, further proving the material's compositional uniformity and phase purity. Figure 6 Atomic resolution transmission electron microscopy (TEM) images clearly show the layered crystal structure of the material, with the layer growth direction aligned with the c-axis of the crystal, perfectly consistent with the structural model of GeBi₂Se₄. Based on the above characterization results, it can be confirmed that this embodiment successfully prepared a single-phase ternary layered selenide, GeBi₂Se₄. 0.85 Bi 2.15 Se4 semiconductor material.

[0062] Example 2

[0063] A ternary layered selenide Ge 0.85 Bi 2.21 The preparation method of Se4 semiconductor material includes the following steps:

[0064] Step 1: Ingredient Preparation and Packaging

[0065] Using germanium powder, bismuth powder, and selenium powder with a purity of 99.99% as raw materials, for the chemical formula Ge 0.85 Bi 2.21 Se4 was prepared by weighing and mixing germanium powder, bismuth powder and selenium powder in a molar ratio of 0.85:2.21:4 in a quartz tube, evacuating the vacuum to ≤1Pa, and then sealing the quartz tube containing the sample using a flame sealing device.

[0066] Step 2: High-temperature melting and firing

[0067] A vacuum-sealed quartz tube is placed vertically in a single-temperature zone pit furnace, with the tube near the thermocouple. The temperature is increased from room temperature to 900°C at a rate of 2°C / min, and held at this temperature for 24 hours. After holding, the tube is quenched and cooled to room temperature.

[0068] Step 3: Material Annealing

[0069] For the material that has been quenched and cooled in step two, the temperature is increased to 540°C at a heating rate of 2°C / min and held at this temperature for 5 days; then it is cooled to room temperature in the furnace and then the material is taken out of the quartz tube.

[0070] Material microstructure and structural analysis

[0071] The material obtained in step three of this embodiment is characterized. Figure 7 The powder X-ray diffraction pattern shows that all diffraction peaks are well matched with the structure of GeBi2Se4, and there are no impurity phase peaks. Figure 8The image is a scanning electron microscope backscattered electron image. The uniform image contrast indicates that the material composition is homogeneous and that no second phase exists. These results demonstrate the successful synthesis of a single-phase material. Therefore, this embodiment verifies that when x=0.06, i.e., the Bi content increases to 2.21, the preparation method described in this invention can still obtain pure-phase Ge. 0.85 Bi 2.21 The presence of Se4 material demonstrates the universality of the technical solution of this invention within a certain compositional range.

[0072] Example 3

[0073] A ternary layered selenide Ge 0.85 Bi 2.18 The preparation method of Se4 semiconductor material includes the following steps:

[0074] Step 1: Ingredient Preparation and Packaging

[0075] Using germanium powder, bismuth powder, and selenium powder with a purity of 99.99% as raw materials, for the chemical formula Ge 0.85 Bi 2.18 Se4 was prepared by weighing and mixing germanium powder, bismuth powder and selenium powder in a molar ratio of 0.85:2.18:4 in a quartz tube, evacuating the vacuum to ≤1Pa, and then sealing the quartz tube containing the sample using a flame sealing device.

[0076] Step 2: High-temperature melting and firing

[0077] The vacuum-sealed quartz tube was placed vertically in a single-temperature zone pit furnace, with the tube close to the thermocouple. The temperature was increased from room temperature to 930°C at a rate of 2.5°C / min, and held at this temperature for 18 hours. After holding, the tube was quenched and cooled to room temperature.

[0078] Step 3: Material Annealing

[0079] For the material that has been quenched and cooled in step two, the temperature is increased to 550°C at a heating rate of 2.5°C / min and held at this temperature for 4 days; then it is cooled to room temperature in the furnace and then the material is taken out of the quartz tube.

[0080] Material microstructure and structural analysis

[0081] The morphology, chemical composition, and structure of the prepared material were analyzed and characterized using optical microscopy, X-ray diffraction, scanning electron microscopy, and X-ray energy dispersive spectroscopy, as well as transmission electron microscopy. The results confirmed that the material obtained under these conditions is a single-phase material with a chemical composition of Ge. 0.85 Bi 2.18 Se4.

[0082] Comparative Example 1

[0083] A method for preparing a ternary layered selenide semiconductor material includes the following steps:

[0084] Step 1: Ingredient Preparation and Packaging

[0085] Using germanium powder, bismuth powder, and selenium powder with a purity of 99.99%, 99.99%, and 99.99%, respectively, with the chemical formula GeBi2Se4, germanium powder, bismuth powder, and selenium powder in a molar ratio of 1:2:4 were weighed and mixed in a quartz tube. The tube was then evacuated to a vacuum of ≤1 Pa, and subsequently sealed with a flame sealing device.

[0086] Step 2: High-temperature melting and firing

[0087] The vacuum-sealed quartz tube was placed vertically in a single-temperature zone pit furnace, with the tube close to the thermocouple. The temperature was increased from room temperature to 950 °C at a rate of 5 °C / min, and held at this temperature for 12 h. After holding, the tube was quenched and cooled to room temperature.

[0088] Step 3: Material Annealing

[0089] For step two, the temperature is increased to 550 ℃ at a heating rate of 5 ℃ / min and held at this temperature for 3 days; then the furnace is cooled to room temperature, and the material is then removed from the quartz tube.

[0090] Organization and structural analysis

[0091] The prepared materials were characterized. Figure 9 The image shows the powder X-ray diffraction pattern of the obtained material. Besides the diffraction peaks corresponding to the GeBi₂Se₄ phase, several other distinct additional diffraction peaks are present (indicated by arrows in the image). These peaks, after analysis, are attributed to germanium-rich impurity phases (such as GeSe). This indicates that even with the quenching and annealing process of this invention, the formation of germanium-rich impurity phases cannot be avoided under the traditional 1:2:4 stoichiometric ratio. This directly proves the non-stoichiometric composition (GeBi₂Se₄) determined in this invention. 0.85 Bi 2.15+x Se4) is necessary for obtaining single-phase materials.

[0092] Comparative Example 2

[0093] A method for preparing a ternary layered selenide semiconductor material includes the following steps:

[0094] Step 1: Ingredient Preparation and Packaging

[0095] Using germanium powder, bismuth powder, and selenium powder with a purity of 99.99% as raw materials, for the chemical formula Ge 0.9 Bi 2.1Se4 was prepared by weighing and mixing germanium powder, bismuth powder and selenium powder in a molar ratio of 0.9:2.1:4 in a quartz tube, evacuating the tube to ≤1 Pa, and then sealing the quartz tube containing the sample using a flame sealing device.

[0096] Step 2: High-temperature melting and firing

[0097] The vacuum-sealed quartz tube was placed vertically in a single-temperature zone pit furnace, with the tube close to the thermocouple. The temperature was increased from room temperature to 950°C at a rate of 5°C / min, and held at that temperature for 12 hours. After holding, the tube was quenched and cooled to room temperature.

[0098] Step 3: Material Annealing

[0099] For step two, the temperature is increased to 550°C at a rate of 5°C / min and held at that temperature for 3 days; then the furnace is cooled to room temperature, and the material is then removed from the quartz tube.

[0100] Organization and structural analysis

[0101] The material prepared in step three of this embodiment was characterized. Figure 10 The image shows the powder X-ray diffraction pattern of the obtained material. The pattern reveals that, in addition to the diffraction peaks of the main phase GeBi₂Se₄, there are still weak impurity phase peaks (indicated by arrows), indicating that when the Ge ratio was increased from 0.85 to 0.9, the reaction was not complete, and a small amount of impurity phase remained. This demonstrates that the Ge ratio must be precisely controlled at 0.85 to effectively suppress the impurity phase.

[0102] Comparative Example 3

[0103] A method for preparing a ternary layered selenide semiconductor material includes the following steps:

[0104] Step 1: Ingredient Preparation and Packaging

[0105] Using germanium powder, bismuth powder, and selenium powder with a purity of 99.99% as raw materials, for the chemical formula Ge 0.8 Bi 2.2 Se4 was prepared by weighing and mixing germanium powder, bismuth powder and selenium powder in a molar ratio of 0.8:2.2:4 in a quartz tube, evacuating to a vacuum of ≤1 Pa, and then sealing the quartz tube containing the sample using a flame sealing device.

[0106] Step 2: High-temperature melting and firing

[0107] The vacuum-sealed quartz tube was placed vertically in a single-temperature zone pit furnace, with the tube close to the thermocouple. The temperature was increased from room temperature to 950 °C at a rate of 5 °C / min, and held at this temperature for 12 h. After holding, the tube was quenched and cooled to room temperature.

[0108] Step 3: Material Annealing

[0109] For step two, the temperature is increased to 550 ℃ at a heating rate of 5 ℃ / min and held at this temperature for 3 days; then the furnace is cooled to room temperature, and the material is then removed from the quartz tube.

[0110] Organization and structural analysis

[0111] The material prepared in step three of this embodiment was characterized. Figure 11 The image shows the powder X-ray diffraction pattern of the obtained material. The pattern also reveals impurity phase peaks (indicated by arrows) in addition to the main phase, indicating that even when the Ge ratio is reduced to 0.8, a pure phase cannot be obtained. This comparative example, together with Comparative Example 2, demonstrates that when the Ge ratio deviates from 0.85, it is difficult to obtain a single-phase material even using the same process, further verifying the uniqueness and criticality of the material composition of this invention.

[0112] Comparative Example 4

[0113] A method for preparing a ternary layered selenide semiconductor material includes the following steps:

[0114] Step 1: Ingredient Preparation and Packaging

[0115] Using germanium powder, bismuth powder, and selenium powder with a purity of 99.99%, bismuth powder, and selenium powder (chemical formula GeBi2Se4), the germanium powder, bismuth powder, and selenium powder in a molar ratio of 0.85:2.15:4 were weighed and mixed in a quartz tube. The tube was then evacuated to a vacuum of ≤1 Pa, and the quartz tube containing the sample was sealed using a flame sealing device.

[0116] Step 2: High-temperature melting and firing

[0117] The vacuum-sealed quartz tube was placed vertically in a single-temperature zone pit furnace, with the tube close to the thermocouple. The temperature was increased from room temperature to 950 °C at a rate of 5 °C / min, and held at that temperature for 12 h; then cooled to room temperature with the furnace.

[0118] Step 3: Material Annealing

[0119] For the material cooled in the furnace in step two, the temperature is increased to 560°C at a rate of 5°C / min and held at this temperature for 3 days; then it is cooled to room temperature in the furnace and then the material is removed from the quartz tube.

[0120] Organization and structural analysis

[0121] The material prepared in step three of this embodiment was characterized. Figure 12The image shows the powder X-ray diffraction pattern of the obtained material. The pattern reveals distinct impurity phase peaks (indicated by arrows) in addition to the GeBi₂Se₄ phase. This is because during the slow furnace cooling process, the high-temperature homogeneous melt undergoes a relatively long temperature range. During this process, different components precipitate sequentially due to changes in solubility, leading to phase separation and impurity phase formation. This comparative example demonstrates the crucial role of the quenching step in freezing the high-temperature homogeneous state and providing a single precursor for subsequent low-temperature annealing.

[0122] Comparative Example 5

[0123] A method for preparing a ternary layered selenide semiconductor material includes the following steps:

[0124] Step 1: Ingredient Preparation and Packaging

[0125] Using germanium powder, bismuth powder, and selenium powder with a purity of 99.99%, bismuth powder, and selenium powder (chemical formula GeBi2Se4), the germanium powder, bismuth powder, and selenium powder in a molar ratio of 0.85:2.15:4 were weighed and mixed in a quartz tube. The tube was then evacuated to a vacuum of ≤1 Pa, and the quartz tube containing the sample was sealed using a flame sealing device.

[0126] Step 2: High-temperature melting and firing

[0127] The vacuum-sealed quartz tube was placed vertically in a single-temperature zone pit furnace, with the tube close to the thermocouple. The temperature was increased from room temperature to 950°C at a rate of 5°C / min, and held at that temperature for 12 hours. After holding, the tube was quenched and cooled to room temperature.

[0128] Step 3: Material Annealing

[0129] For step two, the temperature is increased to 500°C at a rate of 5°C / min and held at that temperature for 3 days; then the furnace is cooled to room temperature, and the material is then removed from the quartz tube.

[0130] Organization and structural analysis

[0131] The material prepared in step three of this embodiment was characterized. Figure 13 The image shows the powder X-ray diffraction pattern of the obtained material. The pattern reveals that the overall intensity of the diffraction peaks is weak, and there are obvious impurity phase peaks (indicated by arrows). This indicates that when the annealing temperature is too low (500℃), the diffusion and migration capabilities of atoms are insufficient, failing to drive the precursor to fully transform into the target phase, resulting in incomplete reaction and the presence of impurity phases in the product. This comparative example demonstrates the necessity of precisely controlling the annealing temperature within the specific range of 540-560℃.

[0132] Comparative Example 6

[0133] A method for preparing a ternary layered selenide semiconductor material includes the following steps:

[0134] Step 1: Ingredient Preparation and Packaging

[0135] Using germanium powder, bismuth powder, and selenium powder with a purity of 99.99% as raw materials, for the chemical formula Ge 0.85 Bi 2.1 Se4 was prepared by weighing and mixing germanium powder, bismuth powder and selenium powder in a molar ratio of 0.85:2.1:4 in a quartz tube, evacuating to a vacuum of ≤1 Pa, and then sealing the quartz tube containing the sample using a flame sealing device.

[0136] Step 2: High-temperature melting and firing

[0137] The vacuum-sealed quartz tube was placed vertically in a single-temperature zone pit furnace, with the tube close to the thermocouple. The temperature was increased from room temperature to 950 °C at a rate of 5 °C / min, and held at this temperature for 12 h. After holding, the tube was quenched and cooled to room temperature.

[0138] Step 3: Material Annealing

[0139] For step two, the temperature is increased to 550 ℃ at a heating rate of 5 ℃ / min and held at this temperature for 3 days; then the furnace is cooled to room temperature, and the material is then removed from the quartz tube.

[0140] Organization and structural analysis

[0141] The material prepared in step three of this embodiment was characterized. Figure 14 The image shows a scanning electron microscope (SEM) backscattered electron image of the obtained material. Although no other obvious diffraction peaks were observed in the powder X-ray diffraction pattern, a significant difference in atomic number contrast (areas of varying brightness in the image) was observed in the backscattered electron image, indicating the presence of a second phase with different chemical composition (higher atomic number in the bright area and lower atomic number in the dark area). This demonstrates that when the Bi content is below the lower limit (2.15) required by this invention, even if the XRD shows a single phase, microscopic compositional segregation still exists, and it is not a true single-phase solid solution. This emphasizes the criticality of the compositional range (0 ≤ x ≤ 0.06) of this invention for obtaining a homogeneous pure-phase material.

[0142] Comparative Example 7

[0143] A method for preparing a ternary layered selenide semiconductor material includes the following steps:

[0144] Step 1: Ingredient Preparation and Packaging

[0145] Using germanium powder, bismuth powder, and selenium powder with a purity of 99.99% as raw materials, for the chemical formula Ge 0.8 Bi2.25 Se4 was prepared by weighing and mixing germanium powder, bismuth powder and selenium powder in a molar ratio of 0.85:2.25:4 in a quartz tube, evacuating to ≤1 Pa, and then sealing the quartz tube containing the sample using a flame sealing device.

[0146] Step 2: High-temperature melting and firing

[0147] The vacuum-sealed quartz tube was placed vertically in a single-temperature zone pit furnace, with the tube close to the thermocouple. The temperature was increased from room temperature to 950 °C at a rate of 5 °C / min, and held at this temperature for 12 h. After holding, the tube was quenched and cooled to room temperature.

[0148] Step 3: Material Annealing

[0149] For step two, the temperature is increased to 550 ℃ at a heating rate of 5 ℃ / min and held at this temperature for 3 days; then the furnace is cooled to room temperature, and the material is then removed from the quartz tube.

[0150] Organization and structural analysis

[0151] The material prepared in step three of this embodiment was characterized. Figure 15 The image shows a scanning electron microscope backscattered electron image of the obtained material. Similar to Comparative Example 6, the backscattered electron image also shows a significant difference in atomic number contrast, indicating the presence of compositional segregation and a microscopic second phase in the material. This demonstrates that even when the Bi content exceeds the upper limit (2.21) required by this invention, a homogeneous pure-phase material cannot be obtained.

[0152] In summary, through extensive experiments, the inventors discovered that when the Ge ratio is precisely adjusted to 0.85 and the Bi ratio is within the range of 2.15 to 2.21 (i.e., x ranges from 0 to 0.06), the formation of impurity phases can be successfully suppressed. Comparative Example 2 (Ge 0.9 Bi 2.1 Se4) and Comparative Example 3 (Ge 0.8 Bi 2.2 Se4 shows that even fine-tuning the Ge ratio to 0.9 or 0.8 does not yield a pure phase. Comparative Examples 6 (x = -0.05) and 7 (x = 0.1) show that when the Bi ratio deviates slightly from the range of this invention, compositional segregation (difference in backscattered image contrast) occurs within the material. This fully demonstrates that the chemical formula Ge defined in this invention... 0.85 Bi 2.15+x Se4 (0≤x≤0.06) is not a simple equivalent replacement for the existing GeBi2Se4, but a carefully selected and verified new composition range capable of forming stable pure phases.

[0153] This invention proposes a two-step process of high-temperature melting and quenching followed by low-temperature long-time annealing. Comparative Example 4 demonstrates the indispensability of the quenching step, which preserves the homogeneous state at high temperature through rapid cooling, providing a single precursor for subsequent annealing. Comparative Example 5 demonstrates the necessity of precisely controlling the annealing temperature at 540-560℃; temperatures too low (500℃) cannot provide sufficient atomic migration energy, resulting in incomplete reactions. The preferred 540-560℃ and 3-5 day holding time of this invention precisely provide the optimal conditions for the precursor to convert to Ge. 0.85 Bi 2.15+x The single-phase transformation of Se4 provides optimal kinetic conditions. This process design approach, especially the synergistic effect of the two steps, is crucial for obtaining the target pure phase.

[0154] This invention not only makes a groundbreaking choice in material composition (Ge 0.85 Bi 2.15+x Se4) overcomes the long-standing technical bias in the field of obtaining pure ternary phases of the Ge-Bi-Se system, and designs a set of key processes (high-temperature quenching and low-temperature long-term annealing) that can stably synthesize this pure phase material. The synergistic effect of the two processes successfully yields pure-phase ternary layered selenide semiconductor materials.

[0155] It is understood that those skilled in the art can make equivalent substitutions or modifications to the technical solution and inventive concept of the present invention, and all such substitutions or modifications should fall within the protection scope of the appended claims.

Claims

1. A ternary layered selenide Ge 0.85 Bi 2.15+x The method for preparing Se4 semiconductor material is characterized by... Including the following steps: S100, using germanium powder, bismuth powder and selenium powder as raw materials, according to the chemical formula Ge 0.85 Bi 2.15+x Weigh the molar ratio of Se4, where 0≤x≤0.

06. After the weighed raw materials are mixed evenly, place them in a quartz tube, evacuate the quartz tube, and then seal the quartz tube. S200. Place the vacuum-sealed quartz tube from step S100 into a heating furnace, raise the temperature from room temperature to 900-950℃ and hold it at that temperature for 12-24 hours. After the holding period, remove the quartz tube from the heating furnace and quench it to cool it down to room temperature. S300: Place the quartz tube, which has been quenched and cooled in step S200, back into the heating furnace. Heat the tube from room temperature to 540-560℃ and hold it at this temperature for 3-5 days for annealing. After the holding period, allow the quartz tube to cool naturally to room temperature with the furnace. Then, remove the obtained ternary layered selenide Ge from the quartz tube. 0.85 Bi 2.15+x Se4 semiconductor material.

2. The ternary layered selenide Ge according to claim 1 0.85 Bi 2.15+x The method for preparing Se4 semiconductor material is characterized by... The germanium powder, bismuth powder, and selenium powder all have a purity of 99.99% or higher.

3. The ternary layered selenide Ge according to claim 1 0.85 Bi 2.15+x The method for preparing Se4 semiconductor material is characterized by... In step S100, the quartz tube is evacuated until the internal pressure is ≤1 Pa before being sealed.

4. The ternary layered selenide Ge according to claim 1 0.85 Bi 2.15+x The method for preparing Se4 semiconductor material is characterized by... The quenching and cooling method described in step S200 is to quickly remove the quartz tube from the furnace and place it in cold water for rapid cooling.

5. The ternary layered selenide Ge according to claim 1 0.85 Bi 2.15+x The method for preparing Se4 semiconductor material is characterized by... In step S200, the temperature is increased from room temperature to 900-950℃ at a heating rate of 2-5℃ / min.

6. The ternary layered selenide Ge according to claim 1 0.85 Bi 2.15+x The method for preparing Se4 semiconductor material is characterized by... In step S300, the temperature is increased from room temperature to 540-560℃ at a heating rate of 2-5℃ / min.

7. A ternary layered selenide Ge 0.85 Bi 2.15+x Se4 semiconductor material, characterized in that... Using any one of the ternary layered selenide Ge as described in claims 1-6 0.85 Bi 2.15+x Se4 semiconductor material was prepared by a specific method.

8. The ternary layered selenide Ge according to claim 7 0.85 Bi 2.15+x Se4 semiconductor material, characterized in that... The ternary layered selenide Ge 0.85 Bi 2.15+x Se4 semiconductor material has a rhombohedral crystal structure with space group R-3m and exhibits a layered morphology.

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