Method for epitaxially preparing wafer-level room-temperature two-dimensional ferromagnetic material on GaAs substrate

Abstract

The invention belongs to the technical field of two-dimensional ferromagnetic materials, and particularly relates to a method for epitaxially preparing a wafer-level room-temperature two-dimensional ferromagnetic material on a GaAs substrate. Most existing two-dimensional ferromagnetic films are obtained through a mechanical stripping method, have the problems of uncontrollable thickness and size and the like, and are difficult to be used for spintronics devices. According to the method, an ultrahigh vacuum molecular beam epitaxial growth technology is adopted, GaAs (111) is subjected to high-temperature annealing in a tellurium atmosphere, a surface oxide layer is removed, a two-dimensional GaTe infiltration layer without dangling bonds grows, and a key foundation is laid for preparing a two-dimensional ferromagnetic Fe3GaTe2 film. In the preparation process of the Fe3GaTe2 material, the beam ratio of the three source materials of Fe, Ga and Te and the temperature of the substrate are accurately controlled, the high-quality two-dimensional room-temperature ferromagnetic Fe3GaTe2 film with the controllable number of unit cell layers is obtained, and a revolutionary material platform is provided for a room-temperature spin electronic device and a high-density storage technology.

Description

Technical Field

[0001] The present invention belongs to the technical field of two-dimensional ferromagnetic materials, and in particular relates to a method for epitaxially preparing wafer-level room-temperature two-dimensional ferromagnetic materials on a GaAs substrate. Background Art

[0002] Two-dimensional ferromagnetic materials have important application value in spin electronics and new memory devices due to their advantages such as no dangling bonds on the surface and no need to consider lattice matching issues when stacking materials. At the same time, since the layers of two-dimensional ferromagnetic materials interact with each other through van der Waals forces, intrinsic two-dimensional ferromagnetic films are currently mainly obtained by mechanically peeling off single crystal blocks. However, this technology has high requirements on the quality of raw materials, and the two-dimensional ferromagnetic materials obtained by cleavage have problems such as random distribution on the substrate and uncontrollable number of layers and size. It is not only difficult to prepare in large quantities, but also impossible to put into practical application and achieve industrialization. Therefore, exploring high-quality, wafer-level two-dimensional ferromagnetic film preparation methods that are compatible with existing semiconductor preparation technologies is of great research significance for promoting the practical application of two-dimensional ferromagnetic materials.

[0003] Fe3GaTe2, a new type of intrinsic two-dimensional ferromagnetic material, exhibits excellent room-temperature strong magnetic order. Studies have shown that the Curie temperature of bulk Fe3GaTe2 is approximately 356K, while that of epitaxially grown Fe3GaTe2 thin films can even reach over 400K. Furthermore, Fe3GaTe2 exhibits strong perpendicular magnetic anisotropy at room temperature, enabling it to maintain stable ferromagnetism even in the low-dimensional limit. Therefore, this two-dimensional ferromagnetic material is considered an ideal material for achieving ferromagnetic order at room temperature, offering greater possibilities for the design of novel spintronic devices. Currently, research on Fe3GaTe2 is limited to small-scale (micrometer-scale) samples obtained through mechanical exfoliation. The technical challenge of achieving wafer-scale epitaxial growth with a controllable number of layers on semiconductor-compatible substrates has yet to be overcome, hindering its practical application in large-scale integration processes. In the current semiconductor industry, gallium arsenide (GaAs) substrates, due to their mature fabrication process, have become an indispensable substrate material for high-performance electronic devices. Therefore, it is urgent to develop a molecular beam epitaxy method suitable for GaAs substrates to achieve the preparation of high-quality, large-area Fe3GaTe2 two-dimensional ferromagnetic materials. Summary of the Invention

[0004] To overcome the shortcomings of the aforementioned prior art, the present invention provides a method for epitaxially growing wafer-scale, room-temperature, two-dimensional ferromagnetic material Fe3GaTe2 on a GaAs substrate compatible with existing semiconductor fabrication techniques. This method utilizes a wafer-scale GaAs substrate, grows a GaTe wetting layer, precisely controls the evaporation rates of the Fe, Ga, and Te sources, and utilizes molecular beam epitaxy to successfully produce wafer-scale single-crystalline, two-dimensional ferromagnetic Fe3GaTe2 thin films. This growth process exhibits excellent stability and holds great promise for advancing the development of intrinsic two-dimensional ferromagnetic materials in high-density storage and spintronic devices, accelerating their practical application.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] The present invention provides a method for epitaxially growing a wafer-level two-dimensional ferromagnetic material Fe3GaTe2 on a GaAs substrate, the method comprising the following steps:

[0007] S1, heating and evaporating a Te source through a crucible evaporation source, performing a high-temperature annealing pretreatment on a GaAs(111) substrate in a Te atmosphere to remove the oxide layer on the substrate surface, and then cooling it to the growth temperature;

[0008] S2. Grow a GaTe wetting layer using molecular beam epitaxy: Evaporate Ga and Te using different crucible evaporation sources. Once the evaporation rate stabilizes, begin film growth until sharp GaTe stripes appear and a single layer of GaTe is formed, resulting in a GaTe wetting layer.

[0009] S3. Use molecular beam epitaxy technology to grow Fe3GaTe2: Heat and evaporate Fe source, Ga source and Te source through different crucible evaporation sources respectively. After the evaporation rate stabilizes, start film growth. By controlling the epitaxial growth time, wafer-level two-dimensional ferromagnetic material Fe3GaTe2 with controllable number of unit cell layers can be grown on the GaAs substrate.

[0010] Preferably, steps S1-S3 are all performed in a molecular beam epitaxy device, and all process steps are performed under ultra-high vacuum.

[0011] Preferably, in step S1, the temperature of the heated and evaporated Te source is 300-350°C, and the growth temperature is 330-350°C.

[0012] Preferably, in step S1, the high temperature annealing pretreatment is to raise the temperature to 510-550°C at a heating rate of 3-7°C / min until two sharp stripes representing different crystal phases can be seen by a reflection high energy electron diffractometer.

[0013] Preferably, in step S2, the Ga source temperature is set to 910-950°C, and the Te source temperature is set to 310-350°C.

[0014] Preferably, in step S2, the time required to grow a single layer of GaTe is 4-5 minutes.

[0015] Preferably, in step S3, the Fe source temperature is 1310-1350°C, the Ga source temperature is 910-950°C, and the Te source temperature is 310-350°C.

[0016] Preferably, the purity of the Fe source is above 99.99%, the purity of the Ga source is above 99.99%, and the purity of the Te source is above 99.99%.

[0017] Preferably, in step S3, the epitaxial growth time required to grow one unit cell layer of wafer-level two-dimensional ferromagnetic material Fe3GaTe2 is 4-5 minutes.

[0018] The present invention also provides a wafer-level two-dimensional ferromagnetic material Fe3GaTe2 obtained by epitaxial growth on a GaAs substrate using the above method.

[0019] The present invention also provides the use of the wafer-scale two-dimensional ferromagnetic material Fe3GaTe2 in room-temperature spintronic devices. Specifically, the wafer-scale two-dimensional ferromagnetic material Fe3GaTe2, grown epitaxially on a GaAs substrate, can be used in room-temperature spintronic devices compatible with current semiconductor manufacturing technology.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] Existing two-dimensional ferromagnetic films are basically obtained by traditional mechanical exfoliation methods. The thickness and size of the films are uncontrollable, making them difficult to be applied in magnetic and spintronic devices. To this end, the present invention adopts ultra-high vacuum molecular beam epitaxial growth technology. First, GaAs (111) is subjected to high-temperature annealing in a tellurium atmosphere to remove the surface oxide layer and grow a two-dimensional GaTe wetting layer without dangling bonds, laying a key foundation for the preparation of two-dimensional room-temperature ferromagnetic Fe3GaTe2 films. Then, in the preparation process of Fe3GaTe2 materials, by precisely controlling the beam ratio (evaporation rate) of the three source materials Fe, Ga, and Te and the temperature of the substrate, a high-quality two-dimensional room-temperature ferromagnetic Fe3GaTe2 film with controllable unit cell layer number is obtained, providing a revolutionary material platform for room-temperature spintronic devices, high-density storage and quantum technology.

[0022] Specifically, the present invention has the following advantages:

[0023] (1) The present invention has created a method for growing a large area of ​​continuous single-crystal Fe3GaTe2 two-dimensional ferromagnetic thin film material on a GaAs substrate. The method first pre-treats the wafer-level GaAs substrate by high-temperature annealing, then controls the evaporation rates of Ga and Te sources to grow a GaTe wetting layer, and then evaporates the Fe source, Ga source, and Te source separately, and precisely controls the evaporation rates of different sources, thereby stably growing the Fe3GaTe2 thin film.

[0024] (2) The substrate used in the present invention is GaAs. This type of substrate surface is usually ultra-smooth, free of surface / subsurface damage, and has low residual stress, which helps achieve high-quality epitaxial growth and ensures the crystal quality of the epitaxial layer. At the same time, this type of substrate can also be seamlessly integrated with existing semiconductor manufacturing processes. This compatibility not only reduces the subsequent R&D and production costs of epitaxially growing two-dimensional ferromagnetic materials on GaAs substrates, but also promotes the industrial production of Fe3GaTe2 two-dimensional thin films.

[0025] (3) The present invention introduces a GaTe wetting layer when epitaxially growing a Fe3GaTe2 thin film on a GaAs substrate, thereby significantly optimizing the material's growth quality and interface properties while ensuring the growth of the Fe3GaTe2 thin film. Furthermore, due to the good lattice compatibility and chemical compatibility between GaTe and the GaAs substrate, the interfacial lattice mismatch stress can be effectively reduced, thereby improving the surface wettability of the Fe3GaTe2 and promoting the two-dimensional layered epitaxial growth of the Fe3GaTe2 thin film, thereby reducing interface defects and dislocation density.

[0026] (4) The Fe3GaTe2 thin film prepared by the present invention has high uniformity, a Curie temperature higher than room temperature, and strong perpendicular magnetic anisotropy. In addition, this two-dimensional ferromagnetic material Fe3GaTe2 with controllable unit cell layer number has a significantly lower magnetization reversal energy barrier compared to traditional three-dimensional ferromagnetic materials due to its weak interlayer van der Waals interaction characteristics. These advantages will help promote the application of two-dimensional ferromagnetic materials in room-temperature spintronic devices;

[0027] (5) Compared with the chemical vapor deposition method, the growth technology of the present invention can obtain single-crystal two-dimensional ferromagnetic films with higher crystal quality, more uniform films, and more controllable growth process; compared with the mechanical stripping method, the growth technology of the present invention can obtain wafer-level two-dimensional ferromagnetic films with controllable number of layers and size, which is beneficial to the subsequent preparation of large-area Fe3GaTe2 magnetic storage devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The growth flow chart (a) and schematic diagram (b) of wafer-level two-dimensional ferromagnetic material Fe3GaTe2;

[0029] Figure 2This is an optical picture of a wafer-level GaAs substrate;

[0030] Figure 3 The reflection high energy electron diffraction (RHEED) results of GaAs substrate and Fe3GaTe2;

[0031] Figure 4 Schematic diagram of the crystal structure of Fe3GaTe2 (a) and scanning transmission electron microscopy results (b);

[0032] Figure 5 Schematic diagram of the magnetization intensity of three unit cell layers Fe3GaTe2 changing with temperature under an out-of-plane magnetic field of 2000Oe;

[0033] Figure 6 The hysteresis loop results of three unit cell layers Fe3GaTe2 under an external magnetic field perpendicular to the plane at different temperatures. DETAILED DESCRIPTION

[0034] The following is a further description of specific embodiments of the present invention. It should be noted that the description of these embodiments is intended to facilitate understanding of the present invention and does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0035] The experimental methods in the following examples are conventional methods unless otherwise specified, and the experimental materials used in the following examples are commercially available unless otherwise specified.

[0036] Example 1: Method for epitaxially growing wafer-level two-dimensional ferromagnetic material Fe3GaTe2 on a GaAs substrate

[0037] All steps are carried out in molecular beam epitaxy equipment (produced by OMICRON), and ultra-high vacuum is maintained during all processes. Figure 1 a is the growth flow chart of wafer-level two-dimensional ferromagnetic material Fe3GaTe2, the specific steps are as follows:

[0038] (1) Pretreatment of substrate

[0039] The GaAs substrate used in this embodiment has a specification of (111) and a circular substrate with a diameter of 1 inch. Figure 2 As shown in the figure, the GaAs substrate is placed on the support plate in the sample delivery chamber of the molecular beam epitaxy equipment, and the vacuum degree is drawn to 10 - 8Torr, then the substrate is transferred to the growth chamber, and the temperature of the Te crucible evaporation source is set to 300°C. The beam source baffle of the Te source is opened (the purity of the Te source used in this embodiment is above 99.99%), and the substrate is gradually heated in the Te atmosphere (the heating rate is about 5°C / min). After it reaches about 530°C, two sharp fringe patterns representing different crystal phases can be monitored in situ by RHEED, such as Figure 3 It is shown that there is no oxide layer on the surface of the annealed GaAs substrate, which is conducive to the epitaxial growth of high-quality two-dimensional ferromagnetic material Fe3GaTe2.

[0040] (2) Growth of GaTe Wetting Layer

[0041] The substrate temperature was set to 340°C, and the GaAs substrate after high-temperature annealing pretreatment was cooled from 530°C to 340°C. The beam source baffle of the Ga source was then opened (the purity of the Ga source used in this embodiment was above 99.99%), and the Ga crucible evaporation source temperature was set to 910°C, and the Te crucible evaporation source temperature was set to 310°C. After the evaporation temperature and evaporation rate stabilized, the baffle under the substrate tray was opened to start growing the GaTe infiltration layer. During this period, RHEED observation was performed until sharp GaTe stripes appeared and the growth stopped. At this time, a single layer of GaTe was grown, and the growth time was about 4 minutes 30 seconds. After the growth was completed, the baffle under the substrate tray was closed.

[0042] (3) Growth of wafer-level Fe3GaTe2 two-dimensional ferromagnetic materials with controllable layer numbers

[0043] ①Regulate substrate temperature and evaporation source temperature

[0044] The substrate temperature was maintained at 340°C. After multiple experiments, it was found that when the substrate temperature was lower than 330°C, polycrystalline phenomenon was prone to occur (the RHEED image was ring-shaped), and when it was higher than 350°C, molecular desorption was prone to occur (no new stripes could be seen in the RHEED image), resulting in poor crystallinity. Therefore, 340°C was finally selected as the optimal growth substrate temperature for Fe3GaTe2.

[0045] Before the two-dimensional material growth, the beam source baffle of the Fe source was kept open (the purity of the Fe source used in this embodiment was above 99.99%). The Fe crucible evaporation source temperature was set to 1310°C, while the Ga crucible and Te crucible evaporation source temperatures remained unchanged at 910°C and 310°C, respectively. Before the two-dimensional Fe3GaTe2 growth, the evaporation temperatures of the Fe, Ga, and Te sources were brought to the set values, and the evaporation rates were kept stable.

[0046] ②Control growth time

[0047] After each source reaches the set value and the evaporation rate stabilizes, open the baffle under the substrate tray to epitaxially grow two-dimensional Fe3GaTe2. During this period, the growth rate is observed by RHEED. After about 4 minutes and 30 seconds, a Fe3GaTe2 crystal cell layer is grown (the judgment standard is: through RHEED observation, new stripes are gradually generated next to the GaTe stripes, until the new stripes become clear and sharp, and the GaTe stripes disappear, then a Fe3GaTe2 crystal cell layer is grown). By setting different epitaxial growth times at this growth rate, the required wafer-level high-quality Fe3GaTe2 two-dimensional materials with different crystal cell layer thicknesses can be obtained. After the growth is completed, it is naturally cooled to room temperature. According to Figure 3 The lattice constant of Fe3GaTe2 in a single unit cell layer can be calculated from the RHEED diffraction fringe spacing of Fe3GaTe2. Experimental Example 1: Characterization and Performance Testing of Wafer-Scale Two-Dimensional Ferromagnetic Material Fe3GaTe2

[0048] The following is the characterization and performance test of Fe3GaTe2 with three unit cell layers:

[0049] 1. Scanning transmission electron microscopy test of Fe3GaTe2 two-dimensional ferromagnetic materials

[0050] The cross-sectional crystal structure of a 4.7 nm thick 3-unit cell layer Fe3GaTe2 sample was characterized using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Figure 4 As shown in a, the STEM image shows that there is an atomically smooth interface between Fe3GaTe2 and the GaAs substrate, indicating that high-quality Fe3GaTe2 has been successfully grown on the GaAs substrate by molecular beam epitaxy. During the growth of Fe3GaTe2, due to atomic diffusion, highly active Fe atoms enter the GaTe layer, converting GaTe into Fe3GaTe2, as shown in Figure 1 As shown in b, Figure 4 No GaTe wetting layer was observed in a.

[0051] STEM images reveal the layered features and atomic arrangement within the Fe3GaTe2 layers. Figure 4 Figure b shows the side view of the crystal structure of Fe3GaTe2 along the (210) crystallographic direction. Each unit cell layer consists of two layers of Fe3GaTe2 and a van der Waals gap, and each Fe3GaTe2 layer is composed of an Fe3Ga heterometallic layer sandwiched between two Te layers.

[0052] 2. Test of magnetization intensity of Fe3GaTe2 two-dimensional ferromagnetic material with temperature

[0053] The three-cell Fe3GaTe2 was fabricated into Hall effect devices by conventional photolithography. The magnetization intensity of the three-cell Fe3GaTe2 was measured with a comprehensive physical property measurement system (PPMS) under an out-of-plane magnetic field of 2000 Oe. Figure 5 ). The curve shows that the three-cell layer Fe3GaTe2 film grown on a GaAs substrate by molecular beam epitaxy has perpendicular magnetic anisotropy and a Curie temperature of up to 440K, which is about 80K higher than that of the Fe3GaTe2 bulk (the Curie temperature of the bulk Fe3GaTe2 is 356K, see "Hu G, Guo H, Lv S, et al. Room-Temperature Antisymmetric Magnetoresistance in van der Waals Ferromagnet Fe3GaTe2 Nanosheets[J]. Advanced Materials, 2024, 36(27): 2403154.").

[0054] 3. Hysteresis loop test of Fe3GaTe2 two-dimensional ferromagnetic material at different temperatures

[0055] The three-cell Fe3GaTe2 was made into a Hall device, and the hysteresis loop of the three-cell Fe3GaTe2 at different temperatures (300-400K) was tested by PPMS under an external magnetic field perpendicular to the plane. The results are as follows Figure 6 As shown. The nearly square ferromagnetic hysteresis loop confirms the existence of robust ferromagnetic order and the easy magnetic axis is perpendicular to the film plane. At the same time, although the coercive field (H C ) decreases with increasing temperature, but the ferromagnetism is still very strong above room temperature, indicating that Fe3GaTe2 films have great advantages in the application of room-temperature ferromagnetic devices.

[0056] In summary, the present invention uses molecular beam epitaxy technology to achieve the growth of wafer-level Fe3GaTe2 two-dimensional ferromagnetic materials on GaAs substrates. Compared with methods such as mechanical striping, the sample crystal film grown is more uniform (such as sharp stripes in the RHEED image, clear atoms and interfaces in the STEM image, etc.), and the number of layers and size are controllable, and Fe3GaTe2 two-dimensional ferromagnetic materials with different unit cell layer thicknesses can be obtained. The Fe3GaTe2 two-dimensional ferromagnetic material with controllable unit cell layer number has a lower magnetization reversal energy barrier due to weak interlayer van der Waals interaction. In addition, Fe3GaTe2 can still exhibit stable ferromagnetism at temperatures above room temperature, which is conducive to the application of two-dimensional ferromagnetic materials in room temperature spintronic devices. The GaAs substrate utilized by the present invention can be connected with existing semiconductor preparation processes, so that high-quality and large-area Fe3GaTe2 two-dimensional ferromagnetic materials can be epitaxially prepared on the GaAs substrate, which is conducive to the actual industrial application of subsequent large-area integrated magnetic storage devices.

[0057] The embodiments of the present invention are described in detail above, but the present invention is not limited to the described embodiments. It is apparent to those skilled in the art that various changes, modifications, substitutions, and variations of these embodiments may be made without departing from the principles and spirit of the present invention, and the changes still fall within the scope of protection of the present invention.

Claims

1. A method for epitaxially growing wafer-level two-dimensional ferromagnetic material Fe3GaTe2 on a GaAs substrate, characterized in that: The following steps are involved: S1, heating and evaporating a Te source through a crucible evaporation source, performing a high-temperature annealing pretreatment on a GaAs(111) substrate in a Te atmosphere to remove the oxide layer on the substrate surface, and then cooling it to the growth temperature; S2. Grow a GaTe wetting layer using molecular beam epitaxy: Evaporate Ga and Te using different crucible evaporation sources. Once the evaporation rate stabilizes, begin film growth until sharp GaTe stripes appear and a single layer of GaTe is formed, resulting in a GaTe wetting layer. S3. Use molecular beam epitaxy technology to grow Fe3GaTe2: Heat and evaporate Fe source, Ga source and Te source through different crucible evaporation sources respectively. After the evaporation rate stabilizes, start film growth. By controlling the epitaxial growth time, wafer-level two-dimensional ferromagnetic material Fe3GaTe2 with controllable number of unit cell layers can be grown on the GaAs substrate.

2. The method for epitaxially growing wafer-level two-dimensional ferromagnetic material Fe3GaTe2 on a GaAs substrate according to claim 1, characterized in that: Steps S1-S3 are all performed in a molecular beam epitaxy device, and all process steps are performed under ultra-high vacuum.

3. The method for epitaxially growing wafer-level two-dimensional ferromagnetic material Fe3GaTe2 on a GaAs substrate according to claim 1, characterized in that: In step S1, the temperature of the heated and evaporated Te source is 300-350°C, and the growth temperature is 330-350°C.

4. The method for epitaxially growing wafer-level two-dimensional ferromagnetic material Fe3GaTe2 on a GaAs substrate according to claim 1, characterized in that: In step S1, the high temperature annealing pretreatment is to raise the temperature to 510-550°C at a heating rate of 3-7°C / min until two sharp stripes representing different crystal phases can be seen by a reflection high energy electron diffractometer.

5. The method for epitaxially growing wafer-level two-dimensional ferromagnetic material Fe3GaTe2 on a GaAs substrate according to claim 1, characterized in that: In step S2, the Ga source temperature is set to 910-950°C, and the Te source temperature is set to 310-350°C.

6. The method for epitaxially growing wafer-level two-dimensional ferromagnetic material Fe3GaTe2 on a GaAs substrate according to claim 1, characterized in that: In step S3, the Fe source temperature is 1310-1350°C, the Ga source temperature is 910-950°C, and the Te source temperature is 310-350°C.

7. The method for epitaxially growing wafer-level two-dimensional ferromagnetic material Fe3GaTe2 on a GaAs substrate according to claim 1, characterized in that: The purity of the Fe source is above 99.99%, the purity of the Ga source is above 99.99%, and the purity of the Te source is above 99.99%.

8. The method for epitaxially growing wafer-level two-dimensional ferromagnetic material Fe3GaTe2 on a GaAs substrate according to claim 1, characterized in that: In step S3, the epitaxial growth time required to grow one unit cell layer of wafer-level two-dimensional ferromagnetic material Fe3GaTe2 is 4-5 minutes.

9. Wafer-scale two-dimensional ferromagnetic material Fe3GaTe2 obtained by epitaxial growth on a GaAs substrate using the method described in any one of claims 1 to 8.

10. Use of the wafer-level two-dimensional ferromagnetic material Fe3GaTe2 according to claim 9 in room-temperature spintronic devices.

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