Epitaxial structure, preparation method thereof and semiconductor device

Abstract

The invention discloses an epitaxial structure, a preparation method thereof and a semiconductor device. An epitaxial structure according to an embodiment of the present invention comprises: a substrate; the multi-period h-BN / AlN layer is located above the substrate, and the multi-period h-BN / AlN layer comprises h-BN layers and AlN layers which are alternately stacked. According to the epitaxial structure, the preparation method thereof and the semiconductor device provided by the embodiment of the invention, the voltage withstanding performance can be effectively improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to an epitaxial structure, its fabrication method, and a semiconductor device. Background Technology

[0002] Currently, the high-resistivity layer in GaN (Gallium Nitride) based HEMT (High Electron Mobility Transistor) devices is typically a carbon-doped GaN layer. The carbon doping introduces deep-level traps into GaN, resulting in its high-resistivity characteristics. This method has been widely used in GaN-based HEMT epitaxial structures.

[0003] However, in existing GaN-based HEMT epitaxial structures, the introduction of C atoms introduces impurity-related defects. High precision in doping concentration control and a narrow growth window increase the complexity of the process. The breakdown voltage of C-doped GaN is limited, making it difficult to meet the application requirements of next-generation high-voltage power devices (>1.5kV) with thinner buffer layer structures. Furthermore, doping introduces impurity-related defects, affecting device performance. In addition, in existing technologies, thermal mismatch stress is mainly alleviated through thick buffer layer structures, which suffers from complex processes and limited effectiveness. Current GaN channel layer growth largely relies on thick buffer layer processes to improve crystal quality, leading to increased epitaxial layer thickness and process complexity, with limited improvement in crystal quality.

[0004] Therefore, it is desirable to have a new epitaxial structure, its fabrication method, and a semiconductor device that can overcome at least one of the above problems. Summary of the Invention

[0005] In view of the above problems, the purpose of this invention is to provide an epitaxial structure and its preparation method, a semiconductor device, and in particular a GaN-based HEMT epitaxial structure with an h-BN / AlN high resistivity layer and its preparation method, thereby improving the withstand voltage performance.

[0006] According to one aspect of the present invention, an epitaxial structure is provided, comprising: Substrate; A multi-period h-BN / AlN layer located above the substrate, wherein the multi-period h-BN / AlN layer comprises alternately stacked h-BN layers and AlN layers.

[0007] Optionally, the epitaxial structure further includes: An h-BN channel buffer layer disposed above the multi-period h-BN / AlN layer; and a channel layer disposed above the h-BN channel buffer layer.

[0008] Optionally, the epitaxial structure further includes: A first buffer layer is disposed above the substrate, and the multi-period h-BN / AlN layer is disposed above the first buffer layer; An insertion layer disposed above the channel layer; A barrier layer disposed above the insertion layer; and a cap layer disposed above the barrier layer.

[0009] Optionally, the first buffer layer is an AlN buffer layer; the thickness of the AlN buffer layer is between 50-300 nm. The thickness of the h-BN layer in the multi-period h-BN / AlN layer is between 1 and 10 nm; the thickness of the AlN layer in the multi-period h-BN / AlN layer is between 30 and 500 nm. The thickness of the h-BN channel buffer layer is between 1 and 10 nm; The channel layer is a GaN channel layer; the thickness of the GaN channel layer is between 50-300 nm. The insertion layer is an AlN insertion layer; the thickness of the AlN insertion layer is between 0.5-1.5 nm. The barrier layer is an AlGaN barrier layer; the thickness of the AlGaN barrier layer is between 20-30 nm; the Al content in the AlGaN barrier layer is between 20%-35%. The cap layer is a SiN cap layer; the thickness of the SiN cap layer is between 10-100 nm.

[0010] Optionally, the number of cycles of the alternately stacked h-BN layers and AlN layers is between 2 and 10; A first buffer layer is disposed above the substrate, and the multi-period h-BN / AlN layer is disposed above the first buffer layer; the first buffer layer is in direct contact with the h-BN layer of the multi-period h-BN / AlN layer.

[0011] According to another aspect of the present invention, a semiconductor device is provided, comprising: The epitaxial structure as described above.

[0012] According to another aspect of the present invention, a method for preparing an epitaxial structure is provided, comprising: Provide a substrate; Forming a multi-period h-BN / AlN layer on the substrate, wherein forming the multi-period h-BN / AlN layer on the substrate includes: h-BN layers and AlN layers are alternately stacked on the substrate.

[0013] Optionally, alternating stacking of h-BN layers and AlN layers on the substrate includes: Under the first reaction conditions, an h-BN layer with a thickness between 1 and 10 nm is grown using TEB as the B source and NH3 as the N source; the first reaction conditions include a growth temperature between 1000 and 1300 °C, a reaction pressure between 50 and 500 mbar, and a group V to group III ratio between 500 and 2000. Under the second reaction conditions, an AlN layer with a thickness between 30-500 nm is grown using TMAl as the Al source and NH3 as the N source. The second reaction conditions include a growth temperature between 1000-1300 °C, a reaction pressure between 30-100 mbar, and a group V-III ratio between 50-2000, wherein the number of cycles of the alternating stacked h-BN layer and AlN layer is between 2-10.

[0014] Optionally, the preparation method further includes: An h-BN channel buffer layer is formed on the multi-period h-BN / AlN layer; and a channel layer is formed on the h-BN channel buffer layer.

[0015] Optionally, the preparation method further includes: The substrate is baked under a third reaction condition, which includes a reaction temperature between 1000-1100°C and an H2 atmosphere; the baking time is between 5-10 minutes. Under the fourth reaction conditions, using TMAl as the Al source and NH3 as the N source, an AlN buffer layer with a thickness between 50-300 nm is grown on the substrate; the fourth reaction conditions include a growth temperature between 1000-1300 °C, a reaction pressure between 30-100 mbar, and a group V-III ratio between 50-2000. The multi-period h-BN / AlN layer is generated on the AlN buffer layer; Under the fifth reaction conditions, using TEB as the B source and NH3 as the N source, an h-BN channel buffer layer with a thickness between 1 and 10 nm is grown on the multi-period h-BN / AlN layer; the fifth reaction conditions include a growth temperature between 1000 and 1300 °C, a reaction pressure between 50 and 500 mbar, and a group V to group III ratio between 500 and 2000; Under the sixth reaction conditions, using TMGa as the Ga source and NH3 as the N source, a channel layer with a thickness between 50-300 nm is grown on the h-BN channel buffer layer; the channel layer is a GaN channel layer; the sixth reaction conditions include a growth temperature between 1000-1100 °C, a reaction pressure between 50-300 mbar, and a group V to group III ratio between 1000-20000; Under the seventh reaction conditions, using TMAl as the Al source and NH3 as the N source, an AlN insertion layer with a thickness between 0.5 and 1.5 nm is grown on the GaN channel layer; the seventh reaction conditions include a growth temperature between 1000 and 1300 °C, a reaction pressure between 30 and 100 mbar, and a group V to group III ratio between 50 and 2000. Under the eighth reaction conditions, using TMGa as the Ga source, TMAl as the Al source, and NH3 as the N source, an AlGaN barrier layer with a thickness between 20-30 nm is grown on the AlN insertion layer; the eighth reaction conditions include a reaction pressure between 50-200 mbar and a group V-III ratio between 500-10000; the Al composition in the AlGaN barrier layer is between 20%-35%. Under the ninth reaction conditions, using SiH4 as the Si source and NH3 as the N source, a SiN cap layer with a thickness between 10 and 100 nm is grown on the AlGaN barrier layer; the ninth reaction conditions include a growth temperature between 900 and 1100 °C, a reaction pressure between 50 and 200 mbar, and a reaction pressure between 2 × 10⁻⁶ mbar and 10⁻⁶ mbar. -7 - 5×10 -5 The molar ratio of SiH4 / NH3 between them.

[0016] The epitaxial structure, its fabrication method, and semiconductor device provided by this invention, having a multi-period h-BN / AlN layer with alternating stacked h-BN and AlN layers, can effectively improve the withstand voltage performance.

[0017] Furthermore, the multi-period h-BN / AlN (high resistance) layer structure utilizes the insulation properties of wide bandgap h-BN and AlN, effectively improving the overall withstand voltage performance (upper withstand voltage limit) of HEMT without introducing doping impurities.

[0018] Furthermore, using an h-BN channel buffer layer as a buffer layer for the GaN channel, which is connected to the GaN layer by weak van der Waals forces, can effectively alleviate lattice mismatch and thermal mismatch in the GaN channel layer (in epitaxy), reduce the formation of dislocations and cracks, and facilitate the realization of a high-quality GaN channel layer, thereby improving device performance. The process is simple and the effect is better.

[0019] Furthermore, an h-BN / AlN periodic structure is used as a high-resistivity layer. h-BN is a two-dimensional material, and it is connected to AlN by weak van der Waals forces. While serving as a high-resistivity layer, it also alleviates thermal mismatch stress. It can absorb and alleviate thermal mismatch stress between the epitaxial structure and the substrate. During epitaxial growth and cooling, it can release the stress caused by thermal mismatch through slip, reducing the formation of dislocations (defects) and cracks. There is no need to set an additional thick buffer layer, and the effect of alleviating thermal mismatch stress is better. Attached Figure Description

[0020] The above and other objects, features and advantages of the present invention will become more apparent from the following description of embodiments of the invention with reference to the accompanying drawings, in which: Figure 1 A schematic diagram of the epitaxial structure according to Embodiment 1 of the present invention is shown; Figure 2 A schematic diagram of the extensional structure according to Embodiment 2 of the present invention is shown; Figure 3 A schematic diagram of the structure of a multi-period h-BN / AlN layer according to an embodiment of the present invention is shown; Figure 4 A flowchart illustrating a method for preparing an epitaxial structure according to an embodiment of the present invention is shown. Detailed Implementation

[0021] Various embodiments of the invention will now be described in more detail with reference to the accompanying drawings. In the various drawings, the same elements are indicated by the same or similar reference numerals. For clarity, the various parts in the drawings are not drawn to scale. Furthermore, certain well-known parts may not be shown in the drawings.

[0022] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. Many specific details of the invention, such as the structure, materials, dimensions, processing techniques, and methods of the components, are described below to provide a clearer understanding of the invention. However, as those skilled in the art will understand, the invention may be implemented without following these specific details.

[0023] It should be understood that when describing the structure of a component, when referring to a layer or region as being "above" or "on top of" another layer or region, it can mean that it is directly above the other layer or region, or that other layers or regions are contained between it and the other layer or region. Furthermore, if the component is flipped, the layer or region will be located "below" or "under" the other layer or region. In the description of numerical ranges in this application, the expression "between" includes the stated number.

[0024] According to one aspect of the present invention, an epitaxial structure is provided. The epitaxial structure includes a substrate and a multi-period h-BN / AlN layer located above the substrate. The multi-period h-BN / AlN layer comprises alternately stacked h-BN layers and AlN layers.

[0025] Specifically, an epitaxial structure refers to a single-crystal thin film layer system that is directionally deposited on a single-crystal substrate using epitaxial growth technology. The epitaxial structure in this application is, for example, a HEMT epitaxial structure, which is a semiconductor material stacking system formed layer by layer on a substrate using epitaxial growth technology (such as MOCVD, MBE) for constructing a High Electron Mobility Transistor (HEMT).

[0026] The epitaxial structure includes a substrate and a multi-period h-BN / AlN layer above the substrate. The multi-period h-BN / AlN layer comprises alternating stacked h-BN and AlN layers. The multi-period h-BN / AlN layer is used, for example, as a high-resistivity layer to block current leakage paths, improve device isolation, and enhance breakdown voltage. The multi-period h-BN / AlN layer is a one- or multi-layer material structure with high resistivity formed in semiconductor devices (especially gallium nitride-based high-frequency, high-power devices) using a combination or heterostructure of hexagonal boron nitride (h-BN) and aluminum nitride (AlN). The h-BN (hexagonal boron nitride) layer structure is similar to graphite, consisting of alternating hexagonal honeycomb layers of boron and nitrogen atoms. The AlN (aluminum nitride) layer is, for example, a wurtzite crystal structure.

[0027] According to the epitaxial structure of the present invention, the wide bandgap h-BN and AlN of the multi-period h-BN / AlN layer can withstand higher electric fields, improve breakdown voltage, and effectively enhance the overall breakdown voltage performance of HEMT. Furthermore, it can prevent current leakage from the active region (such as the channel) to the substrate or other regions, improving device efficiency. In the multi-period h-BN / AlN layer, h-BN and AlN are bonded by weak van der Waals forces, which can absorb and alleviate thermal mismatch stress between the epitaxial structure and the substrate, reducing the formation of defects and cracks. This eliminates the need for an additional thick buffer layer and provides better thermal mismatch stress relief.

[0028] Figure 1 A schematic diagram of the epitaxial structure according to Embodiment 1 of the present invention is shown. Figure 1 As shown, the epitaxial structure according to Embodiment 1 of the present invention includes, from bottom to top, a substrate 10, a multi-period h-BN / AIN (high resistivity) layer 30, an (h-BN) channel buffer layer 40, and a (GaN) channel layer 50.

[0029] Specifically, a multi-period h-BN / AIN (high resistivity) layer 30 is disposed above the substrate 10.

[0030] The h-BN channel buffer layer 40 is disposed above the multi-cycle h-BN / AlN (high resistance) layer 30.

[0031] The channel layer 50 is disposed above the h-BN channel buffer layer 40, and the channel layer 50 is, for example, a GaN channel layer.

[0032] In the epitaxial structure described in the above embodiments, the h-BN channel buffer layer serves as a buffer layer for GaN channel growth, effectively alleviating lattice mismatch and thermal mismatch stress in the GaN channel layer, reducing dislocation density, achieving a high-quality thin GaN channel layer, and improving the crystal quality of the GaN channel layer.

[0033] Figure 2 A schematic diagram of the extensional structure according to Embodiment 2 of the present invention is shown. Figure 2 As shown, the epitaxial structure according to Embodiment 2 of the present invention includes, from bottom to top, a substrate 10, a buffer layer 20, a multi-period h-BN / AlN (high resistivity) layer 30, a channel buffer layer 40, a channel layer 50, an insertion layer 60, a barrier layer 70, and a cap layer 80.

[0034] Specifically, the substrate 10 includes at least one selected from Si substrates, sapphire substrates, and SiC substrates.

[0035] A buffer layer 20 is disposed above the substrate 10. The buffer layer 20 is, for example, an AlN buffer layer. The thickness of the AlN buffer layer is between 50-300 nm.

[0036] A multi-period h-BN / AlN (high resistivity) layer 30 is disposed above the buffer layer 20. The thickness of the h-BN layer in the multi-period h-BN / AlN (high resistivity) layer 30 is between 1 and 10 nm. The thickness of the AlN layer in the multi-period h-BN / AlN (high resistivity) layer 30 is between 30 and 500 nm.

[0037] The channel buffer layer 40 is disposed above the multi-period h-BN / AlN (high-resistivity) layer 30. The channel buffer layer 40 is, for example, an h-BN channel buffer layer, and the thickness of the h-BN channel buffer layer is between 1-10 nm.

[0038] The channel layer 50 is disposed above the channel buffer layer 40. The channel layer 50 is, for example, a GaN channel layer, and the thickness of the GaN channel layer is between 50-300 nm.

[0039] An insertion layer 60 is disposed above the channel layer 50. The insertion layer 60 is, for example, an AlN insertion layer, and the thickness of the AlN insertion layer is between 0.5 and 1.5 nm.

[0040] A barrier layer 70 is disposed above the insertion layer 60. The barrier layer 70 is, for example, an AlGaN barrier layer with a thickness between 20-30 nm and an Al content between 20% and 35%.

[0041] A cap layer 80 is disposed above the barrier layer 70. The cap layer 80 is, for example, a SiN cap layer, and the thickness of the SiN cap layer is between 10-100 nm.

[0042] Figure 3 A schematic diagram of a multi-period h-BN / AlN layer according to an embodiment of the present invention is shown. The multi-period h-BN / AlN layer according to an embodiment of the present invention comprises alternating stacks of h-BN layers and AlN layers, i.e., one layer of h-BN layer, one layer of AlN layer, one layer of h-BN layer, and one layer of AlN layer stacked together. Figure 3 As shown, a first AlN layer 32 is disposed on the first h-BN layer 31, a second h-BN layer 33 is disposed on the first AlN layer 32, a second AlN layer 34 is disposed on the second h-BN layer 33, ..., and an Nth AlN layer 38 is disposed on the Nth (layer) h-BN layer 37. Optionally, the number of cycles of the alternately stacked h-BN layers and AlN layers is between 2 and 10 (inclusive), that is, the number of h-BN layers in the multi-cycle h-BN / AlN layer is between 2 and 10, and the number of AlN layers in the multi-cycle h-BN / AlN layer is between 2 and 10.

[0043] Optionally, a first buffer layer is disposed above the substrate, and a multi-period h-BN / AlN layer is disposed above the first buffer layer. The first buffer layer is in direct contact with the h-BN layer of the multi-period h-BN / AlN layer.

[0044] According to another aspect of the present invention, a semiconductor device is provided. This semiconductor device includes the epitaxial structure described above. The semiconductor device described in this application is an electronic functional unit manufactured through processes such as doping, epitaxy, and photolithography, utilizing the unique electrical properties of semiconductor materials (such as silicon (Si), germanium (Ge), gallium arsenide (GaAs), gallium nitride (GaN), etc.). Its core lies in precisely controlling the conduction and blocking of current through external signals (voltage, current, illumination, etc.) to achieve core functions such as signal amplification, switching, and energy conversion.

[0045] According to another aspect of the present invention, a method for preparing an epitaxial structure is provided. Figure 4 A flowchart illustrating a method for fabricating an epitaxial structure according to an embodiment of the present invention is shown. Figure 4 As shown, the method for preparing an epitaxial structure according to an embodiment of the present invention includes the following steps: In step S101, a substrate is provided; A substrate is provided. The provided substrate includes at least one selected from Si substrates, sapphire substrates, and SiC substrates.

[0046] In step S102, a multi-period h-BN / AlN layer is formed on the substrate.

[0047] h-BN and AlN layers are alternately stacked on a substrate to form a multi-period h-BN / AlN layer.

[0048] Specifically, the scheme in this application employs a periodically alternating h-BN / AlN multilayer structure as the high-resistivity layer of the GaN-based HEMT. The overall HEMT epitaxial structure, from bottom to top, consists of: a substrate, an AlN buffer layer, a multi-period h-BN / AlN high-resistivity layer, an h-BN channel buffer layer, a GaN channel layer, an AlN insertion layer, an AlGaN barrier layer, and a SiN cap layer. The parameters and fabrication methods of each layer are as follows: Take a substrate and raise the temperature of the metal-organic chemical vapor deposition (MOCVD) reaction chamber to 1000-1100℃, and bake it at high temperature for 5-10 minutes in H2 atmosphere (baking the substrate under the third reaction condition).

[0049] Under the fourth reaction conditions, an AlN buffer layer with a thickness between 50 and 300 nm is grown on the substrate using TMAl as the Al source and NH3 as the N source. The fourth reaction conditions include a growth temperature between 1000 and 1300 °C, a reaction pressure (reaction chamber pressure) between 30 and 100 mbar, and a group V / III (V / III) ratio between 50 and 2000.

[0050] AlN buffer layers and h-BN layers are alternately stacked on an AlN buffer layer to generate a multi-period h-BN / AlN layer. Specifically, under the first reaction conditions, an h-BN layer with a thickness between 1 and 10 nm is grown using TEB as the B source and NH3 as the N source (on the AlN buffer layer). The first reaction conditions include a growth temperature between 1000 and 1300 °C, a reaction pressure between 50 and 500 mbar, and a group V-III ratio between 500 and 2000. Under the second reaction conditions, an AlN layer with a thickness between 30 and 500 nm is grown using TMAl as the Al source and NH3 as the N source (on the h-BN layer). The second reaction conditions include a growth temperature between 1000 and 1300 °C, a reaction pressure between 30 and 100 mbar, and a group V-III ratio between 50 and 2000. Optionally, the number of alternating stacked h-BN and AlN layers is between 2 and 10. The h-BN layer and the AlN layer are directly connected by weak van der Waals forces, which can release thermal mismatch stress through slip. The high resistance of the h-BN layer and the AlN layer can effectively improve the breakdown voltage of GaN-based HEMTs. Compared with traditional C doping technology, it does not introduce doping impurities and can increase the upper limit of breakdown voltage.

[0051] Under the fifth reaction conditions, using TEB as the boron source and NH3 as the nitrogen source, h-BN channel buffer layers with thicknesses ranging from 1 to 10 nm were grown on multi-period h-BN / AlN layers. The fifth reaction conditions included a growth temperature between 1000 and 1300 °C, a reaction pressure between 50 and 500 mbar, and a group V / group III ratio between 500 and 2000. The two-dimensional material h-BN, serving as a buffer layer for GaN channels, is connected to GaN by weak van der Waals forces. This effectively alleviates lattice and thermal mismatches during GaN channel epitaxy, reduces dislocation and crack formation, and facilitates the achievement of high-quality GaN channel layers, thereby improving device performance.

[0052] Under the sixth reaction conditions, using TMGa as the Ga source and NH3 as the N source, a channel layer with a thickness between 50 and 300 nm was grown on the h-BN channel buffer layer. The channel layer was a GaN channel layer. The sixth reaction conditions included a growth temperature between 1000 and 1100 °C, a reaction pressure between 50 and 300 mbar, and a group V to group III ratio between 1000 and 20000.

[0053] Under the seventh reaction conditions, using TMAl as the Al source and NH3 as the N source, an AlN insertion layer with a thickness between 0.5 and 1.5 nm was grown on the GaN channel layer. The seventh reaction conditions included a growth temperature between 1000 and 1300 °C, a reaction pressure between 30 and 100 mbar, and a group V to group III ratio between 50 and 2000.

[0054] Under the eighth reaction conditions, using TMGa as the Ga source, TMAl as the Al source, and NH3 as the N source, an AlGaN barrier layer with a thickness between 20 and 30 nm was grown on the AlN insertion layer. The eighth reaction conditions included a reaction pressure between 50 and 200 mbar and a group V-III ratio between 500 and 10000. The Al composition in the AlGaN barrier layer was between 20% and 35%.

[0055] Under the ninth reaction conditions, using SiH4 as the Si source and NH3 as the N source, a SiN cap layer with a thickness between 10 and 100 nm was grown on the AlGaN barrier layer. The ninth reaction conditions included a growth temperature between 900 and 1100 °C, a reaction pressure between 50 and 200 mbar, and a reaction pressure between 2 × 10⁻⁶ mbar and 2 × 10⁻⁶ mbar. -7 - 5×10 -5 The molar ratio of SiH4 / NH3 between them.

[0056] This completes the epitaxial growth of the GaN-based HEMT structure with h-BN / AlN high resistivity layer.

[0057] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0058] As described above, these embodiments of the present invention do not exhaustively cover all details, nor do they limit the invention to the specific embodiments described. Clearly, many modifications and variations can be made based on the above description. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to effectively utilize the invention and its modifications. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. An extensional structure, comprising: Substrate; A multi-period h-BN / AlN layer is located above the substrate. The multi-period h-BN / AlN layer comprises alternating stacked h-BN and AlN layers.

2. The epitaxial structure according to claim 1, wherein, The epitaxial structure further includes: An h-BN channel buffer layer disposed above the multi-period h-BN / AlN layer; and The channel layer is disposed above the h-BN channel buffer layer.

3. The epitaxial structure according to claim 2, wherein, The epitaxial structure further includes: A first buffer layer is disposed above the substrate, and the multi-period h-BN / AlN layer is disposed above the first buffer layer; An insertion layer disposed above the channel layer; A barrier layer disposed above the insertion layer; and A cap layer disposed above the barrier layer.

4. The epitaxial structure according to claim 3, wherein, The first buffer layer is an AlN buffer layer; the thickness of the AlN buffer layer is between 50-300 nm. The thickness of the h-BN layer in the multi-period h-BN / AlN layer is between 1 and 10 nm; the thickness of the AlN layer in the multi-period h-BN / AlN layer is between 30 and 500 nm. The thickness of the h-BN channel buffer layer is between 1 and 10 nm; The channel layer is a GaN channel layer; the thickness of the GaN channel layer is between 50-300 nm. The insertion layer is an AlN insertion layer; the thickness of the AlN insertion layer is between 0.5-1.5 nm. The barrier layer is an AlGaN barrier layer; the thickness of the AlGaN barrier layer is between 20-30 nm; the Al content in the AlGaN barrier layer is between 20%-35%. The cap layer is a SiN cap layer; the thickness of the SiN cap layer is between 10-100 nm.

5. The epitaxial structure according to claim 1, wherein, The number of cycles of the alternately stacked h-BN and AlN layers is between 2 and 10; A first buffer layer is disposed above the substrate, and the multi-period h-BN / AlN layer is disposed above the first buffer layer; the first buffer layer is in direct contact with the h-BN layer of the multi-period h-BN / AlN layer.

6. A semiconductor device, comprising: The epitaxial structure as described in any one of claims 1-5.

7. A method for preparing an epitaxial structure, comprising: Provide a substrate; A multi-period h-BN / AlN layer is formed on the substrate. The formation of a multi-period h-BN / AlN layer on the substrate includes: h-BN layers and AlN layers are alternately stacked on the substrate.

8. The preparation method according to claim 7, wherein, Alternating stacking of h-BN layers and AlN layers on the substrate includes: Under the first reaction conditions, an h-BN layer with a thickness between 1 and 10 nm is grown using TEB as the B source and NH3 as the N source; the first reaction conditions include a growth temperature between 1000 and 1300 °C, a reaction pressure between 50 and 500 mbar, and a group V to group III ratio between 500 and 2000. Under the second reaction conditions, an AlN layer with a thickness between 30 and 500 nm was grown using TMAl as the Al source and NH3 as the N source. The second reaction conditions included a growth temperature between 1000 and 1300 °C, a reaction pressure between 30 and 100 mbar, and a group V / III ratio between 50 and 2000. The number of cycles of the alternately stacked h-BN layers and AlN layers is between 2 and 10.

9. The preparation method according to claim 7, wherein, The preparation method further includes: An h-BN channel buffer layer is formed on the multi-period h-BN / AlN layer; and A channel layer is formed on the h-BN channel buffer layer.

10. The preparation method according to claim 9, wherein, The preparation method further includes: The substrate is baked under a third reaction condition, which includes a reaction temperature between 1000-1100°C and an H2 atmosphere; the baking time is between 5-10 minutes. Under the fourth reaction conditions, using TMAl as the Al source and NH3 as the N source, an AlN buffer layer with a thickness between 50-300 nm is grown on the substrate; the fourth reaction conditions include a growth temperature between 1000-1300 °C, a reaction pressure between 30-100 mbar, and a group V-III ratio between 50-2000. The multi-period h-BN / AlN layer is generated on the AlN buffer layer; Under the fifth reaction conditions, using TEB as the B source and NH3 as the N source, an h-BN channel buffer layer with a thickness between 1 and 10 nm is grown on the multi-period h-BN / AlN layer; the fifth reaction conditions include a growth temperature between 1000 and 1300 °C, a reaction pressure between 50 and 500 mbar, and a group V to group III ratio between 500 and 2000; Under the sixth reaction conditions, using TMGa as the Ga source and NH3 as the N source, a channel layer with a thickness between 50-300 nm is grown on the h-BN channel buffer layer; the channel layer is a GaN channel layer; the sixth reaction conditions include a growth temperature between 1000-1100 °C, a reaction pressure between 50-300 mbar, and a group V to group III ratio between 1000-20000; Under the seventh reaction conditions, using TMAl as the Al source and NH3 as the N source, an AlN insertion layer with a thickness between 0.5 and 1.5 nm is grown on the GaN channel layer; the seventh reaction conditions include a growth temperature between 1000 and 1300 °C, a reaction pressure between 30 and 100 mbar, and a group V to group III ratio between 50 and 2000. Under the eighth reaction conditions, using TMGa as the Ga source, TMAl as the Al source, and NH3 as the N source, an AlGaN barrier layer with a thickness between 20-30 nm is grown on the AlN insertion layer; the eighth reaction conditions include a reaction pressure between 50-200 mbar and a group V-III ratio between 500-10000; the Al composition in the AlGaN barrier layer is between 20%-35%. Under the ninth reaction conditions, using SiH4 as the Si source and NH3 as the N source, a SiN cap layer with a thickness between 10 and 100 nm is grown on the AlGaN barrier layer; the ninth reaction conditions include a growth temperature between 900 and 1100 °C, a reaction pressure between 50 and 200 mbar, and a reaction pressure between 2 × 10⁻⁶ mbar and 10⁻⁶ mbar. -7 - 5×10 -5 The molar ratio of SiH4 / NH3 between them.

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