Epitaxial structure and method of manufacturing the same, semiconductor device

Abstract

The application discloses an epitaxial structure and a preparation method thereof and a semiconductor device. The epitaxial structure according to the embodiment of the application comprises a substrate; and a multi-period h-BN / AlN layer located above the substrate, wherein the multi-period h-BN / AlN layer comprises h-BN layers and AlN layers which are alternately stacked. The epitaxial structure and the preparation method thereof and the semiconductor device according to the embodiment of the application can effectively improve the withstand voltage performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor technology, and in particular to an epitaxial structure, a preparation method thereof, and a semiconductor device. BACKGROUND

[0002] In current GaN (Gallium Nitride) -based HEMT (High Electron Mobility Transistor) devices, the high resistance layer is usually a C (carbon)-doped GaN layer (C-doped GaN). The doping of carbon atoms introduces deep level traps in GaN, which makes it exhibit high resistance characteristics. This method has been widely used in GaN-based HEMT epitaxial structures.

[0003] However, in the existing GaN-based HEMT epitaxial structure, the introduction of C atoms forms impurity-related defects. The doping concentration control accuracy is high, the growth window is narrow, and the process difficulty is increased. The voltage resistance performance of C-doped GaN is limited, and it is also difficult to meet the application requirements of the new generation of high-voltage power devices (>1.5kV) under a thinner buffer layer structure, and the doping introduces impurity-related defects, which affects the device performance. In addition, in the prior art, thermal mismatch stress is mainly relieved through a thick buffer layer structure, which has the problems of complex process and limited effect; the growth of the existing GaN channel layer mainly depends on the thick buffer layer process to improve the crystal quality, which increases the epitaxial layer thickness and process complexity, and the improvement of the crystal quality is limited.

[0004] Therefore, it is desirable to have a new epitaxial structure, a preparation method thereof, and a semiconductor device, which can overcome at least one of the above problems. SUMMARY

[0005] In view of the above problems, the purpose of the present application is to provide an epitaxial structure, a preparation method thereof, and a semiconductor device, in particular a GaN-based HEMT epitaxial structure with a h-BN / AlN high resistance layer and a preparation method thereof, so as to improve the voltage resistance performance.

[0006] According to an aspect of the present application, an epitaxial structure is provided, comprising:

[0007] a substrate;

[0008] a multi-period h-BN / AlN layer located above the substrate, wherein the multi-period h-BN / AlN layer comprises h-BN layers and AlN layers which are alternately stacked.

[0009] Optionally, the epitaxial structure further comprises:

[0010] a 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.

[0011] Optionally, the epitaxial structure further comprises:

[0012] a first buffer layer disposed above the substrate, the first buffer layer having the multi-period h-BN / AlN layer disposed thereon;

[0013] an interlayer disposed above the channel layer;

[0014] a barrier layer disposed above the interlayer; and a cap layer disposed above the barrier layer.

[0015] Optionally, the first buffer layer is an AlN buffer layer; the AlN buffer layer has a thickness between 50-300 nm;

[0016] the h-BN layer in the multi-period h-BN / AlN layer has a thickness between 1-10 nm; the AlN layer in the multi-period h-BN / AlN layer has a thickness between 30-500 nm;

[0017] the h-BN channel buffer layer has a thickness between 1-10 nm;

[0018] the channel layer is a GaN channel layer; the GaN channel layer has a thickness between 50-300 nm;

[0019] the interlayer is an AlN interlayer; the AlN interlayer has a thickness between 0.5-1.5 nm;

[0020] the barrier layer is an AlGaN barrier layer; the AlGaN barrier layer has a thickness between 20-30 nm; the Al component in the AlGaN barrier layer is between 20%-35%;

[0021] the cap layer is a SiN cap layer; the SiN cap layer has a thickness between 10-100 nm.

[0022] Optionally, the number of periods of the alternating stack of h-BN layers and AlN layers is between 2-10;

[0023] the substrate has a first buffer layer disposed thereon, the first buffer layer having the multi-period h-BN / AlN layer disposed thereon; the first buffer layer is in direct contact with the h-BN layer of the multi-period h-BN / AlN layer.

[0024] According to another aspect of the present application, there is provided a semiconductor device comprising:

[0025] An epitaxial structure as described above.

[0026] According to yet another aspect of the present application, there is provided a method for preparing an epitaxial structure, comprising:

[0027] providing a substrate;

[0028] forming a multi-period h-BN / AlN layer on the substrate, wherein forming the multi-period h-BN / AlN layer on the substrate comprises:

[0029] alternately stacking h-BN layers and AlN layers on the substrate.

[0030] Optionally, alternately stacking the h-BN layers and the AlN layers on the substrate comprises:

[0031] growing the h-BN layers with a thickness between 1-10 nm under a first reaction condition with TEB as a B source and NH3 as an N source; the first reaction condition comprises a growth temperature between 1000-1300 °C, a reaction pressure between 50-500 mbar, and a quintuple-to-triple ratio between 500-2000;

[0032] growing the AlN layers with a thickness between 30-500 nm under a second reaction condition with TMAl as an Al source and NH3 as an N source; the second reaction condition comprises a growth temperature between 1000-1300 °C, a reaction pressure between 30-100 mbar, and a quintuple-to-triple ratio between 50-2000, wherein the number of periods of alternately stacking the h-BN layers and the AlN layers is between 2-10.

[0033] Optionally, the method for preparing further comprises:

[0034] forming a h-BN channel buffer layer on the multi-period h-BN / AlN layer; and forming a channel layer on the h-BN channel buffer layer.

[0035] Optionally, the method for preparing further comprises:

[0036] performing baking on the substrate under a third reaction condition; the third reaction condition comprises a reaction temperature between 1000-1100 °C and a H2 atmosphere; the baking is performed for a time between 5-10 min;

[0037] growing an AlN buffer layer with a thickness between 50-300 nm on the substrate under a fourth reaction condition with TMAl as an Al source and NH3 as an N source; the fourth reaction condition comprises a growth temperature between 1000-1300 °C, a reaction pressure between 30-100 mbar, and a quintuple-to-triple ratio between 50-2000;

[0038] generating the multi-period h-BN / AlN layer on the AlN buffer layer;

[0039] under the fifth reaction condition, growing the h-BN channel buffer layer with a thickness between 1-10nm on the multi-period h-BN / AlN layer by taking TEB as the B source and NH3 as the N source; the fifth reaction condition includes a growth temperature between 1000-1300℃, a reaction pressure between 50-500mbar and a quintet-to-trit group ratio between 500-2000;

[0040] under the sixth reaction condition, growing the channel layer with a thickness between 50-300nm on the h-BN channel buffer layer by taking TMGa as the Ga source and NH3 as the N source; the channel layer is a GaN channel layer; the sixth reaction condition includes a growth temperature between 1000-1100℃, a reaction pressure between 50-300mbar and a quintet-to-trit group ratio between 1000-20000;

[0041] under the seventh reaction condition, growing the AlN insertion layer with a thickness between 0.5-1.5nm on the GaN channel layer by taking TMAl as the Al source and NH3 as the N source; the seventh reaction condition includes a growth temperature between 1000-1300℃, a reaction pressure between 30-100mbar and a quintet-to-trit group ratio between 50-2000;

[0042] under the eighth reaction condition, growing the AlGaN barrier layer with a thickness between 20-30nm on the AlN insertion layer by taking TMGa as the Ga source, TMAl as the Al source and NH3 as the N source; the eighth reaction condition includes a reaction pressure between 50-200mbar and a quintet-to-trit group ratio between 500-10000; the Al component in the AlGaN barrier layer is between 20%-35%;

[0043] under the ninth reaction condition, growing the SiN cap layer with a thickness between 10-100nm on the AlGaN barrier layer by taking SiH4 as the Si source and NH3 as the N source; the ninth reaction condition includes a growth temperature between 900-1100℃, a reaction pressure between 50-200mbar and a SiH4 / NH3 molar ratio between 2×10 -7 - 5×10 -5 .

[0044] The epitaxial structure provided by the application and the preparation method thereof and the semiconductor device are provided with the multi-period h-BN / AlN layer of the alternately stacked h-BN layer and AlN layer, and the withstand voltage performance can be effectively improved.

[0045] Further, the multi-period h-BN / AlN (high resistance) layer structure utilizes the insulating properties of wide band gap h-BN and AlN, which can effectively improve the overall withstand voltage performance (upper limit of withstand voltage) of the HEMT without introducing doped impurities.

[0046] Further, the h-BN channel buffer layer is used as the buffer layer of the GaN channel, which is connected to the GaN layer by weak van der Waals force, which can effectively alleviate the lattice mismatch and thermal mismatch of the GaN channel layer (when epitaxial), reduce the formation of dislocations and cracks, and is conducive to realizing a high-crystal-quality GaN channel layer, thereby improving the device performance. The process is simple and the effect is better.

[0047] Further, the h-BN / AlN periodic structure is used as a high resistance layer, and the h-BN is a two-dimensional material connected to the AlN by weak van der Waals force, which can alleviate the thermal mismatch stress while serving as a high resistance layer, can absorb and alleviate the thermal mismatch stress between the epitaxial structure and the substrate, and can release the stress caused by thermal mismatch through slip during epitaxial growth and cooling process, reducing the formation of dislocations (defects) and cracks; no additional thick buffer layer is needed, and the effect of relieving thermal mismatch stress is better. BRIEF DESCRIPTION OF DRAWINGS

[0048] The above and other objects, features and advantages of the present application will become more apparent from the following description of embodiments of the present application taken in conjunction with the accompanying drawings, in which:

[0049] Figure 1 A structure diagram of an epitaxial structure according to Embodiment One of the present application is shown;

[0050] Figure 2 A structure diagram of an epitaxial structure according to Embodiment Two of the present application is shown;

[0051] Figure 3 A structure diagram of a multi-period h-BN / AlN layer according to the present application is shown;

[0052] Figure 4 A method flowchart of a preparation method of an epitaxial structure according to the present application is shown. DETAILED DESCRIPTION

[0053] Various embodiments of the present application will be described in detail with reference to the accompanying drawings. In the various drawings, the same elements are denoted by the same or similar reference numerals. For the sake of clarity, each part in the drawings is not drawn to scale. In addition, some parts that are well known can not be shown in the drawings.

[0054] The specific embodiments of the present application will be further described in conjunction with the drawings and examples. Many specific details of the application are described below in order to provide a thorough understanding of the present application. However, as will be apparent to those skilled in the art, the present application can be practiced without incorporating these specific details.

[0055] It should be understood that when a layer, one region is referred to as being "on" or "above" another layer, one region, it can be directly on or above the other layer, one region or intervening layers or regions can also be present. In addition, if it is stated that a layer, one region is "under" or "below" another layer, one region, it can be directly under or below the other layer, one region or intervening layers or regions can also be present. In the description of numerical ranges of values, the expression "between" includes the numbers.

[0056] According to an aspect of the present application, an epitaxial structure is provided. The epitaxial structure includes a substrate and a multi-period h-BN / AlN layer above the substrate. The multi-period h-BN / AlN layer includes h-BN layers and AlN layers alternately stacked.

[0057] Specifically, an epitaxial structure refers to a monocrystalline thin film layer system deposited directionally on a monocrystalline substrate by epitaxial growth technology. The epitaxial structure in the present application is, for example, a HEMT epitaxial structure, i.e., a semiconductor material stacking system for building a high electron mobility transistor (HEMT) formed by layer-by-layer deposition on a substrate by epitaxial growth technology (such as MOCVD, MBE).

[0058] The epitaxial structure includes a substrate and a multi-period h-BN / AlN layer above the substrate. The multi-period h-BN / AlN layer includes h-BN layers and AlN layers alternately stacked. The multi-period h-BN / AlN layer is used as a high-resistivity layer, for example, to block current leakage paths, improve device isolation, and enhance breakdown voltage. The multi-period h-BN / AlN layer is a one or more layer material structure with high resistivity characteristics formed using a combination of hexagonal boron nitride (h-BN) and aluminum nitride (AlN) or a heterostructure in semiconductor devices, particularly gallium nitride-based high-frequency, high-power devices, etc. The h-BN (hexagonal boron nitride) layer structure is similar to graphite, with boron atoms and nitrogen atoms alternately arranged in a hexagonal honeycomb layer. The AlN (aluminum nitride) layer is, for example, a wurtzite structure crystal.

[0059] The epitaxial structure according to the embodiment of the present application can withstand a higher electric field, improve the breakdown voltage, effectively improve the overall withstand voltage performance of the HEMT, and prevent current from leaking from the active region (such as the channel) to the substrate or other regions, thereby improving the efficiency of the device. In the multi-period h-BN / AlN layer, the h-BN and the AlN are combined by weak van der Waals force, can absorb and relieve the thermal mismatch stress between the epitaxial structure and the substrate, reduce the formation of defects and cracks, and do not need to make an additional thick buffer layer, and the effect of relieving the thermal mismatch stress is better.

[0060] Figure 1 A structural schematic diagram of an epitaxial structure according to an embodiment of the present application is shown. As shown in the figure, the epitaxial structure according to the embodiment of the present application comprises, from bottom to top, a substrate 10, a multi-period h-BN / AlN (high resistance) layer 30, a (h-BN) channel buffer layer 40, and a (GaN) channel layer 50. Figure 1

[0061] Specifically, the multi-period h-BN / AlN (high resistance) layer 30 is arranged above the substrate 10.

[0062] The h-BN channel buffer layer 40 is arranged above the multi-period h-BN / AlN (high resistance) layer 30.

[0063] The channel layer 50 is arranged above the h-BN channel buffer layer 40, and the channel layer 50 is, for example, a GaN channel layer.

[0064] The epitaxial structure described in the above embodiment can effectively relieve the lattice mismatch and thermal mismatch stress of the GaN channel layer, reduce the dislocation density, realize a high-quality thin GaN channel layer, and improve the crystal quality of the GaN channel layer.

[0065] Figure 2 A structural schematic diagram of an epitaxial structure according to an embodiment of the present application is shown. As shown in the figure, the epitaxial structure according to the embodiment of the present application comprises, from bottom to top, a substrate 10, a buffer layer 20, a multi-period h-BN / AlN (high resistance) layer 30, a channel buffer layer 40, a channel layer 50, an insertion layer 60, a barrier layer 70, and a cap layer 80. Figure 2

[0066] Specifically, the substrate 10 comprises at least one selected from a Si substrate, a sapphire substrate, and a SiC substrate.

[0067] The buffer layer 20 is arranged 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.

[0068] ​​A multi-period h-BN / AlN (high resistance) layer 30 is disposed above the buffer layer 20. The thickness of the h-BN layer in the multi-period h-BN / AlN (high resistance) layer 30 is between 1-10 nm. The thickness of the AlN layer in the multi-period h-BN / AlN (high resistance) layer 30 is between 30-500 nm.

[0069] A channel buffer layer 40 is disposed above the multi-period h-BN / AlN (high resistance) 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.

[0070] A 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.

[0071] 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 0.5-1.5 nm.

[0072] A barrier layer 70 is disposed above the insertion layer 60. The barrier layer 70 is, for example, an AlGaN barrier layer, and the thickness of the AlGaN barrier layer is between 20-30 nm, and the Al component in the AlGaN barrier layer is between 20%-35%.

[0073] 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.

[0074] Figure 3 A structure diagram of a multi-period h-BN / AlN layer according to an embodiment of the present application is shown. The multi-period h-BN / AlN layer according to the embodiment of the present application comprises h-BN layers and AlN layers alternately stacked (in sequence), i.e. a stack of one h-BN layer, one AlN layer, one h-BN layer, one AlN layer, and so on. As shown, Figure 3 a first AlN layer 32 is disposed above the first h-BN layer 31, a second h-BN layer 33 is disposed above the first AlN layer 32, a second AlN layer 34 is disposed above the second h-BN layer 33, and so on, and an N(th) AlN layer 38 is disposed above an N(th) h-BN layer 37. Optionally, the number of periods of the alternately stacked h-BN layers and AlN layers is between 2-10 (inclusive), i.e. the number of h-BN layers in the multi-period h-BN / AlN layer is between 2-10, and the number of AlN layers in the multi-period h-BN / AlN layer is between 2-10.

[0075] Optionally, a first buffer layer is arranged above the substrate, and the multi-period h-BN / AlN layer is arranged 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.

[0076] According to another aspect of the present application, a semiconductor device is provided. The semiconductor device comprises the epitaxial structure as described above. The semiconductor device described in the present application is an electronic functional unit manufactured by doping, epitaxy, photolithography and other processes using the unique electrical properties of semiconductor materials such as silicon (Si), germanium (Ge), gallium arsenide (GaAs), gallium nitride (GaN), etc. The core is to accurately control the conduction and blocking of current by external signals (voltage, current, light, etc.), to realize core functions such as signal amplification, switching, energy conversion, etc.

[0077] According to still another aspect of the present application, a preparation method of an epitaxial structure is provided. Figure 4 A method flowchart of the preparation method of the epitaxial structure according to an embodiment of the present application is shown. As shown in the figure, the preparation method of the epitaxial structure according to an embodiment of the present application comprises the following steps: Figure 4

[0078] In step S101, a substrate is provided.

[0079] A substrate is provided. The provided substrate comprises at least one selected from Si substrate, sapphire substrate, SiC substrate, etc.

[0080] In step S102, a multi-period h-BN / AlN layer is formed on the substrate.

[0081] The h-BN layer and the AlN layer are alternately stacked on the substrate to form the multi-period h-BN / AlN layer.

[0082] Specifically, the scheme of the present application adopts a periodically alternating h-BN / AlN multilayer structure as the high resistance layer of the GaN-based HEMT, and the overall HEMT epitaxial structure is sequentially from bottom to top: substrate, AlN buffer layer, multi-period h-BN / AlN high resistance layer, h-BN channel buffer layer, GaN channel layer, AlN insertion layer, AlGaN barrier layer and SiN cap layer. The parameters and preparation methods of each layer are as follows:

[0083] A substrate is taken, the temperature of the metal-organic chemical vapor deposition (MOCVD) reaction chamber is raised to 1000-1100℃, and high-temperature bake treatment is performed under H2 atmosphere for 5-10min (the substrate is baked under the third reaction condition).

[0084] ​Under the fourth reaction condition, an AlN buffer layer with a thickness between 50-300 nm is grown on the substrate using TMAl as the Al source and NH3 as the N source. The fourth reaction condition includes a growth temperature between 1000-1300 °C, a reaction pressure (chamber pressure) between 30-100 mbar, and a ratio of group V to group III (V / III) between 50-2000.

[0085] A multi-period h-BN / AlN layer is generated by alternately stacking h-BN layers and AlN layers on the AlN buffer layer. Specifically, an h-BN layer with a thickness between 1-10 nm is grown under the first reaction condition using TEB as the B source and NH3 as the N source (on the AlN buffer layer). The first reaction condition includes a growth temperature between 1000-1300 °C, a reaction pressure between 50-500 mbar, and a ratio of group V to group III between 500-2000. An AlN layer with a thickness between 30-500 nm is grown under the second reaction condition using TMAl as the Al source and NH3 as the N source (on the h-BN layer). The second reaction condition includes a growth temperature between 1000-1300 °C, a reaction pressure between 30-100 mbar, and a ratio of group V to group III between 50-2000. Optionally, the number of periods of alternately stacking h-BN layers and AlN layers is between 2-10. The h-BN layers and the AlN layers are directly connected by weak van der Waals forces, and the thermal mismatch stress can be released by slip; the high resistance characteristics of the h-BN layers and the AlN layers can effectively improve the voltage resistance of the GaN-based HEMT, and compared with the traditional C-doping technology, no doping impurities are introduced, and the upper limit of the voltage resistance can be improved.

[0086] Under the fifth reaction condition, an h-BN channel buffer layer with a thickness between 1-10 nm is grown on the multi-period h-BN / AlN layer using TEB as the B source and NH3 as the N source. The fifth reaction condition includes a growth temperature between 1000-1300 °C, a reaction pressure between 50-500 mbar, and a ratio of group V to group III between 500-2000. The two-dimensional material h-BN as the buffer layer of the GaN channel layer is connected to the GaN by weak van der Waals forces, which can effectively relieve the lattice mismatch and thermal mismatch during the epitaxy of the GaN channel layer, reduce the formation of dislocations and cracks, and be conducive to realizing a GaN channel layer with high crystal quality, thereby improving the performance of the device.

[0087] Under the sixth reaction condition, a channel layer with a thickness between 50-300 nm is grown on the h-BN channel buffer layer using TMGa as the Ga source and NH3 as the N source. The channel layer is a GaN channel layer. The sixth reaction condition includes a growth temperature between 1000-1100 °C, a reaction pressure between 50-300 mbar, and a ratio of group V to group III between 1000-20000.

[0088] Under the seventh reaction condition, an AlN interlayer with a thickness between 0.5-1.5 nm is grown on the GaN channel layer using TMAl as the Al source and NH3 as the N source. The seventh reaction condition includes a growth temperature between 1000-1300 °C, a reaction pressure between 30-100 mbar, and a group V / group III ratio between 50-2000.

[0089] Under the eighth reaction condition, an AlGaN barrier layer with a thickness between 20-30 nm is grown on the AlN interlayer using TMGa as the Ga source, TMAl as the Al source, and NH3 as the N source. The eighth reaction condition includes a reaction pressure between 50-200 mbar and a group V / group III ratio between 500-10000. The Al composition in the AlGaN barrier layer is between 20%-35%.

[0090] Under the ninth reaction condition, a SiN cap layer with a thickness between 10-100 nm is grown on the AlGaN barrier layer using SiH4 as the Si source and NH3 as the N source. The ninth reaction condition includes a growth temperature between 900-1100 °C, a reaction pressure between 50-200 mbar, and a SiH4 / NH3 molar ratio between 2x10 -7 - 5x10 -5 .

[0091] Up to this point, the GaN-based HEMT epitaxial full structure growth of the h-BN / AlN high-resistance layer is completed.

[0092] It should be noted that the relational terms herein such as first and second and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any such actual relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without more limitations, an element preceded by "comprises... a" does not, without more constraints, foreclose the existence of additional identical elements in the process, method, article, or apparatus that comprises the recited element.

[0093] In accordance with the practices of the present invention, these embodiments have been described in relation to the above-described embodiments, which are intended to be illustrative only and not restrictive of the invention. Obviously, many modifications and variations of this invention can be effected without departing from the scope of the novel concept of the disclosure. No limitation with respect to the specific implementation techniques and applications presented thereby should be inferred into the scope of the invention, as understood by those skilled in the art. The specification and drawings should be regarded as illustrative only and in no way limiting of the scope of the invention as defined by the appended claims and equivalents thereof.

Claims

1. An extensional structure, comprising: Substrate; An AlN buffer layer is disposed above the substrate; A multi-period h-BN / AlN layer is located above the AlN buffer layer, the multi-period h-BN / AlN layer being used to improve the breakdown voltage; and An h-BN channel buffer layer is disposed above the multi-period h-BN / AlN layer; The epitaxial structure is a gallium nitride epitaxial structure. The multi-period h-BN / AlN layer comprises alternating stacked h-BN layers and AlN layers; 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.

2. The epitaxial structure according to claim 1, wherein, The epitaxial structure further includes: 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: 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 thickness of the AlN buffer layer is between 50-300 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; An AlN buffer layer is formed on the substrate; A multi-period h-BN / AlN layer is formed on the AlN buffer layer, and the multi-period h-BN / AlN layer is used to improve the breakdown voltage. An h-BN channel buffer layer is formed above the multi-period h-BN / AlN layer. The epitaxial structure is a gallium nitride epitaxial structure. Forming a multi-period h-BN / AlN layer on the substrate includes: h-BN layers and AlN layers are alternately stacked on the substrate, wherein the thickness of the h-BN layer in the multi-period h-BN / AlN layer is between 1 and 10 nm; and the thickness of the AlN layer in the multi-period h-BN / AlN layer is between 30 and 500 nm.

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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