Epitaxial structure of radio frequency device with improved stress mismatch and preparation method thereof

Abstract

The present disclosure provides an epitaxial structure of a radio frequency device with improved stress mismatch and a method for preparing the same, belonging to the field of semiconductor technology. The epitaxial structure of the radio frequency device with improved stress mismatch comprises a substrate, a hybrid nucleation layer, and a heterojunction layer stacked in sequence; the hybrid nucleation layer comprises a first AlN layer and a first GaN layer stacked in sequence on the substrate, and the heterojunction layer comprises an AlGaN layer and a second GaN layer stacked in sequence on the hybrid nucleation layer. The present disclosure can improve the stress mismatch between the substrate and the gallium nitride material, and enhance the growth quality of the AlGaN / GaN heterojunction.

Description

Technical Field

[0001] The present disclosure relates to the field of semiconductor technology, and in particular to an epitaxial structure of a radio frequency device for improving stress mismatch and a preparation method thereof. Background Art

[0002] Gallium nitride (GaN) is widely used in power electronics, radio frequency (RF) devices, and optoelectronic devices due to its wide bandgap and high mobility. RF devices are common semiconductor photoelectric conversion devices. Among them, the most widely used is the High Electron Mobility Transistor (HEMT).

[0003] In the related art, the epitaxial structure of a radio frequency device includes a silicon substrate and an AlGaN / GaN heterojunction stacked in sequence.

[0004] However, due to the lattice mismatch and thermal stress mismatch between GaN and the silicon substrate, there will be huge stress in the epitaxial structure, which will affect the growth quality of the AlGaN / GaN heterojunction. Summary of the Invention

[0005] The present disclosure provides an epitaxial structure of a radio frequency device with improved stress mismatch and a method for fabricating the same, which can improve the stress mismatch between the substrate and the gallium nitride material and enhance the growth quality of the AlGaN / GaN heterojunction. The technical solution is as follows:

[0006] An embodiment of the present disclosure provides an epitaxial structure of a radio frequency device for improving stress mismatch, wherein the epitaxial structure includes a substrate, a hybrid nucleation layer, and a heterojunction layer stacked in sequence; the hybrid nucleation layer includes a first AlN layer and a first GaN layer stacked in sequence on the substrate, and the heterojunction layer includes an AlGaN layer and a second GaN layer sequentially located on the hybrid nucleation layer.

[0007] In one implementation of the embodiment of the present disclosure, the first AlN layer includes AlN particles distributed on the surface of the substrate, and the first GaN layer includes GaN particles distributed on the surface of the first AlN layer; the particle distribution density of the first AlN layer is not greater than the particle distribution density of the first GaN layer.

[0008] In another implementation of the embodiment of the present disclosure, the particle distribution density of the first AlN layer is 10 8 cm -2 to 10 9 cm -2 The particle distribution density of the first GaN layer is 10 9 cm -2 to 10 10 cm-2 .

[0009] In another implementation of the embodiment of the present disclosure, the particle size of the AlN particles is 20 nm to 80 nm, and the particle size of the GaN particles is 50 nm to 100 nm.

[0010] In another implementation of the embodiment of the present disclosure, the epitaxial structure further includes a second AlN layer located between the hybrid nucleation layer and the heterojunction layer, and the thickness of the second AlN layer is 300 nm to 500 nm.

[0011] In another implementation of the embodiment of the present disclosure, the epitaxial structure further includes a third GaN layer located between the second AlN layer and the heterojunction layer, and the defect density of the third GaN layer is 5×10 8 cm -2 to 5×10 9 cm -2 .

[0012] In another implementation of the embodiment of the present disclosure, the epitaxial structure further includes a third AlN layer located between the second AlN layer and the heterojunction layer, and the thickness of the third AlN layer is 150 nm to 300 nm.

[0013] In another implementation of the embodiment of the present disclosure, the thickness of the AlGaN layer is 15 nm to 30 nm, the molar content of Al in the AlGaN layer is 0.2 to 0.35, and the thickness of the second GaN layer is 3 nm to 15 nm.

[0014] An embodiment of the present disclosure provides a method for preparing an epitaxial structure of a radio frequency device with improved stress mismatch, the method comprising: providing a substrate; sequentially forming a hybrid nucleation layer and a heterojunction layer on the substrate, the hybrid nucleation layer comprising a first AlN layer and a first GaN layer sequentially stacked on the substrate, and the heterojunction layer comprising an AlGaN layer and a second GaN layer sequentially located on the hybrid nucleation layer.

[0015] In another implementation of the embodiment of the present disclosure, forming the mixed nucleation layer on the substrate includes: controlling the temperature to 400°C to 800°C, the molar ratio of ammonia and metal Mo source to 3000 to 10000, depositing AlN particles on the substrate to form the first AlN layer; and depositing GaN particles to form the first GaN layer.

[0016] The beneficial effects of the technical solutions provided by the embodiments of the present disclosure include at least:

[0017] The epitaxial structure of a radio frequency device for improving stress mismatch provided by an embodiment of the present disclosure includes a substrate, a hybrid nucleation layer, and a heterojunction layer stacked in sequence, wherein the hybrid nucleation layer includes a first AlN layer and a first GaN layer stacked in sequence on the substrate, and the heterojunction layer includes an AlGaN layer and a second GaN layer sequentially located on the hybrid nucleation layer. By configuring the hybrid nucleation layer as a structure formed by stacking two film layers, wherein the two film layers are respectively the first AlN layer and the first GaN layer, different grain boundaries are formed in the hybrid nucleation layer, and different grain boundaries introduce different types of stress, thereby effectively balancing the stress accumulation of the subsequent epitaxial structure, improving the stress mismatch problem between the substrate and the gallium nitride material, and improving the growth quality of the AlGaN / GaN heterojunction. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0019] Figure 1 1 is a schematic structural diagram of an epitaxial structure of a radio frequency device for improving stress mismatch provided by an embodiment of the present disclosure;

[0020] Figure 2 This is a flow chart of a method for preparing an epitaxial structure of a radio frequency device for improving stress mismatch provided by an embodiment of the present disclosure;

[0021] Figure 3 This is a diagram showing the preparation state of an epitaxial structure of a radio frequency device for improving stress mismatch provided by an embodiment of the present disclosure;

[0022] Figure 4 This is a diagram of the preparation state of an epitaxial structure of a radio frequency device for improving stress mismatch provided by an embodiment of the present disclosure.

[0023] The descriptions of the marks in the figure are as follows:

[0024] 10. Substrate;

[0025] 20. Hybrid nucleation layer; 21. First AlN layer; 22. First GaN layer;

[0026] 30. Heterojunction layer; 31. AlGaN layer; 32. Second GaN layer;

[0027] 41. Second AlN layer; 42. Third GaN layer; 43. Third AlN layer. DETAILED DESCRIPTION

[0028] In order to make the objectives, technical solutions and advantages of the present disclosure more clear, the embodiments of the present disclosure will be further described in detail below with reference to the accompanying drawings.

[0029] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning understood by a person of ordinary skill in the art to which this disclosure pertains. The terms "first," "second," "third," and similar words used in the patent specification and claims of this disclosure do not indicate any order, quantity, or importance, but are merely used to distinguish between different components. Similarly, terms such as "a" or "an" do not indicate a quantitative limitation, but rather indicate the presence of at least one. Terms such as "include" or "comprise" mean that the elements or objects preceding "include" or "comprises" encompass the elements or objects listed after "include" or "comprises," and their equivalents, and do not exclude other elements or objects. Terms such as "connected" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," "right," "top," and "bottom" are used only to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0030] Figure 1 FIG. 1 is a schematic structural diagram of an epitaxial structure of a radio frequency device for improving stress mismatch provided by an embodiment of the present disclosure. Figure 1 As shown, the epitaxial structure of the radio frequency device for improving stress mismatch includes: the epitaxial structure includes a substrate 10, a hybrid nucleation layer 20 and a heterojunction layer 30 stacked in sequence.

[0031] like Figure 1 As shown, the hybrid nucleation layer 20 includes a first AlN layer 21 and a first GaN layer 22 sequentially stacked on the substrate 10 , and the heterojunction layer 30 includes an AlGaN layer 31 and a second GaN layer 32 sequentially located on the hybrid nucleation layer 20 .

[0032] The epitaxial structure of a radio frequency device for improving stress mismatch provided by an embodiment of the present disclosure includes a substrate 10, a hybrid nucleation layer 20, and a heterojunction layer 30 stacked in sequence, wherein the hybrid nucleation layer 20 includes a first AlN layer 21 and a first GaN layer 22 stacked in sequence on the substrate 10, and the heterojunction layer 30 includes an AlGaN layer 31 and a second GaN layer 32 sequentially located on the hybrid nucleation layer 20. By configuring the hybrid nucleation layer 20 as a structure formed by stacking two film layers, wherein the two film layers are the first AlN layer 21 and the first GaN layer 22, different grain boundaries are formed in the hybrid nucleation layer 20, and different grain boundaries introduce different stress types, thereby effectively balancing the stress accumulation of the subsequent epitaxial structure, improving the stress mismatch problem between the substrate 10 and the gallium nitride material, and improving the growth quality of the AlGaN / GaN heterojunction.

[0033] In the embodiment of the present disclosure, the substrate 10 may include one of a silicon substrate 10 , a sapphire substrate 10 , a silicon carbide substrate 10 , a glass substrate 10 , a gallium arsenide substrate 10 and a self-supporting substrate 10 .

[0034] Exemplarily, the substrate 10 may be a silicon substrate 10 , which is large in size and low in cost, is compatible with Si process lines, and has significant cost advantages and large-scale production capabilities.

[0035] Optionally, the first AlN layer 21 includes AlN particles distributed on the surface of the substrate 10, and the first AlN layer 21 is a film layer formed by depositing AlN particles. The first GaN layer 22 includes GaN particles distributed on the surface of the first AlN layer 21, and the first GaN layer 22 is a film layer formed by depositing GaN particles. The particle distribution density of the first AlN layer 21 is no greater than the particle distribution density of the first GaN layer 22.

[0036] The particle distribution density of the first AlN layer 21 refers to the number of AlN particles distributed per unit area in the first AlN layer 21. A greater particle distribution density indicates a greater number of AlN particles distributed per unit area, i.e., a denser distribution of AlN particles; a smaller particle distribution density indicates a smaller number of AlN particles distributed per unit area, i.e., a sparser distribution of AlN particles.

[0037] The particle distribution density of the first GaN layer 22 refers to the number of GaN particles distributed per unit area in the first GaN layer 22. A greater particle distribution density indicates a greater number of GaN particles distributed per unit area, i.e., a denser distribution of GaN particles; a smaller particle distribution density indicates a smaller number of GaN particles distributed per unit area, i.e., a sparser distribution of GaN particles.

[0038] In the above implementation, AlN particles are deposited to form the first AlN layer 21, and GaN particles are deposited to form the first GaN layer 22. Because particles can effectively relieve stress, the hybrid nucleation layer 20 formed using particles is more likely to alleviate stress accumulation. Furthermore, the particle distribution density of the first AlN layer 21 is controlled to be no greater than that of the first GaN layer 22, making it easier to form different grain boundaries within the hybrid nucleation layer 20. Because different grain boundaries introduce different types of stress, they can effectively balance the stress accumulation of the subsequent epitaxial structure, improve the stress mismatch between the substrate 10 and the gallium nitride material, and enhance the growth quality of the AlGaN / GaN heterojunction.

[0039] Optionally, the particle distribution density of the first AlN layer 21 is 10 8 cm -2 to 10 9 cm -2 The particle distribution density of the first GaN layer 22 is 10 9 cm -2 to 10 10 cm -2 .

[0040] In the above implementation, the particle distribution density of the first AlN layer 21 is set within the above range, and the particle distribution density of the first GaN layer 22 is set within the above range, so that the particle distribution density of the first AlN layer 21 can be higher than the particle distribution density of the first GaN layer 22, which makes it easier to form different grain boundaries in the mixed nucleation layer 20 and balance the stress accumulation of the subsequent epitaxial structure.

[0041] For example, the particle distribution density of the first AlN layer 21 is 10 8 cm -2 The particle distribution density of the first GaN layer 22 is 10 9 cm -2 .

[0042] Optionally, the particle size of the AlN particles is 20 nm to 80 nm, and the particle size of the GaN particles is 50 nm to 100 nm.

[0043] By setting the particle size of the AlN particles within the above range, and setting the particle size of the GaN particles within the above range, the size of the AlN particles in the first AlN layer 21 and the size of the GaN particles in the first GaN layer 22 can be reasonably controlled to avoid the particle size being too large or too small, which affects the effect of the particles in relieving stress.

[0044] For example, the AlN particles in the first AlN layer 21 may be spherical, and the particle size of the AlN particles may be 50 nm.

[0045] For example, the GaN particles in the first GaN layer 22 may be spherical, and the particle size of the GaN particles may be 80 nm.

[0046] Alternatively, as Figure 1 As shown, the epitaxial structure further includes a second AlN layer 41 located between the hybrid nucleation layer 20 and the heterojunction layer 30 .

[0047] The second AlN layer 41 has a thickness of 300 nm to 500 nm, and a thickness direction of the second AlN layer 41 is perpendicular to the substrate 10 .

[0048] In the above implementation, by growing the second AlN layer 41 with a relatively thick thickness, lattice relaxation can be achieved, which facilitates the subsequent epitaxial growth of a high-quality GaN crystal film.

[0049] Exemplarily, the thickness of the second AlN layer 41 is 350 nm.

[0050] Alternatively, as Figure 1 As shown, the epitaxial structure further includes a third GaN layer 42 located between the second AlN layer 41 and the heterojunction layer 30 .

[0051] The defect density of the third GaN layer 42 is 5×10 8 cm -2 to 5×10 9 cm -2 .

[0052] As an example, in the embodiment of the present disclosure, the defect density of the third GaN layer 42 is 5×10 8 cm -2 .

[0053] In the above implementation, the defect density of the third GaN layer 42 is controlled within the above range to form a high-quality third GaN layer 42 , thereby completing the lattice transformation and enabling subsequent film structures to grow with high quality.

[0054] Alternatively, as Figure 1 As shown, the epitaxial structure further includes a third AlN layer 43 located between the second AlN layer 41 and the heterojunction layer 30 .

[0055] By providing the third AlN layer 43 as a high resistance layer, the leakage current of the RF device can be effectively reduced, the additional capacitance can be reduced, and the efficient growth of the heterojunction layer 30 can be achieved, thereby improving the growth quality of the AlGaN / GaN heterojunction.

[0056] The thickness of the third AlN layer 43 is 150 nm to 300 nm.

[0057] By setting the thickness of the third AlN layer 43 within the above range, it is possible to prevent the third AlN layer 43 from being too thin, thereby affecting the performance of the third AlN layer 43 in improving the leakage current of the RF device, and it is also possible to prevent the third AlN layer 43 from being too thick, thereby increasing the manufacturing cost.

[0058] As an example, in the embodiment of the present disclosure, the thickness of the third AlN layer 43 is 200 nm.

[0059] Optionally, in the heterojunction layer 30, the AlGaN layer 31 has a thickness of 15 nm to 30 nm, and a molar content of Al in the AlGaN layer 31 is 0.2 to 0.35. The second GaN layer 32 has a thickness of 3 nm to 15 nm, and is undoped.

[0060] By setting the thickness of AlGaN layer 31 within the aforementioned range and the thickness of second GaN layer 32 within the aforementioned range, it is possible to prevent the AlGaN layer 31 and second GaN layer 32 from being too thin, thereby affecting the function of heterojunction layer 30. It is also possible to prevent the AlGaN layer 31 and second GaN layer 32 from being too thick, thereby increasing production costs. Furthermore, setting the molar content of Al in AlGaN layer 31 within the aforementioned range ensures the function of heterojunction layer 30.

[0061] As an example, in the embodiment of the present disclosure, the thickness of the AlGaN layer 31 is 20 nm, the molar content of Al in the AlGaN layer 31 is 0.3, and the thickness of the second GaN layer 32 is 10 nm.

[0062] Figure 2 This is a flow chart of a method for preparing an epitaxial structure of a radio frequency device for improving stress mismatch provided by an embodiment of the present disclosure. Figure 2 As shown, this preparation method is suitable for preparing Figure 1 The epitaxial structure of the radio frequency device shown includes:

[0063] Step S11: providing a substrate 10;

[0064] Step S12 : forming a hybrid nucleation layer 20 and a heterojunction layer 30 in sequence on the substrate 10 .

[0065] The hybrid nucleation layer 20 includes a first AlN layer 21 and a first GaN layer 22 sequentially stacked on the substrate 10 , and the heterojunction layer 30 includes an AlGaN layer 31 and a second GaN layer 32 sequentially located on the hybrid nucleation layer 20 .

[0066] In the epitaxial structure of the RF device for improving stress mismatch prepared in the embodiment of the present disclosure, the epitaxial structure includes a substrate 10, a hybrid nucleation layer 20, and a heterojunction layer 30 stacked in sequence, wherein the hybrid nucleation layer 20 includes a first AlN layer 21 and a first GaN layer 22 stacked in sequence on the substrate 10, and the heterojunction layer 30 includes an AlGaN layer 31 and a second GaN layer 32 sequentially located on the hybrid nucleation layer 20. By configuring the hybrid nucleation layer 20 as a structure composed of two film layers stacked together, wherein the two film layers are the first AlN layer 21 and the first GaN layer 22, different grain boundaries are formed in the hybrid nucleation layer 20, and different grain boundaries introduce different stress types, thereby effectively balancing the stress accumulation of the subsequent epitaxial structure, improving the stress mismatch problem between the substrate 10 and the gallium nitride material, and improving the growth quality of the AlGaN / GaN heterojunction.

[0067] In step S11 , the substrate 10 includes one of a silicon substrate 10 , a sapphire substrate 10 , a silicon carbide substrate 10 , a glass substrate 10 , a gallium arsenide substrate 10 and a free-standing substrate 10 .

[0068] The substrate 10 may be a silicon substrate 10 , which is large in size and low in cost, and is compatible with Si process lines, thus having significant cost advantages and large-scale production capabilities.

[0069] As an example, in the embodiment of the present disclosure, after cleaning the surface of the substrate 10 , the substrate 10 needs to be nitrided.

[0070] In step S12, as Figure 3 As shown, growing the hybrid nucleation layer 20 may include: controlling the temperature to 400°C to 800°C, maintaining a molar ratio of ammonia to a metallic Mo source of 3,000 to 10,000, depositing AlN particles on a substrate to form a first AlN layer, and depositing GaN particles to form a first GaN layer. The substrate is a heterogeneous substrate. A heterogeneous substrate is a substrate made of a material with a different lattice from the epitaxial material. For example, a heterogeneous substrate may include silicon wafers, sapphire, diamond, GaAs, and InP.

[0071] The specific process of growing the mixed nucleation layer 20 may include:

[0072] In the first step, the temperature is adjusted to 600° C., the molar ratio of the introduced ammonia gas to the metal Mo source is controlled to be 5000, and AlN particles are deposited to form a first AlN layer 21 on the substrate 10 .

[0073] In the second step, the temperature is adjusted to 600° C., the molar ratio of the introduced ammonia gas and the metal Mo source is controlled to be 5000, and GaN particles are deposited to form the first GaN layer 22 on the first AlN layer 21 .

[0074] The particle distribution density of the first AlN layer 21 is 10 8 cm -2 to 10 9 cm -2 The particle distribution density of the first GaN layer 22 is 10 9 cm -2 to 10 10 cm -2 .

[0075] By setting the particle distribution density of the first AlN layer 21 within the above range and setting the particle distribution density of the first GaN layer 22 within the above range, the particle distribution density of the first AlN layer 21 can be higher than the particle distribution density of the first GaN layer 22, which makes it easier to form different grain boundaries in the mixed nucleation layer 20 and balance the stress accumulation of the subsequent epitaxial structure.

[0076] For example, the particle distribution density of the first AlN layer 21 is 10 8 cm -2 The particle distribution density of the first GaN layer 22 is 10 9 cm -2 .

[0077] Optionally, the particle size of the first AlN layer 21 is 20 nm to 80 nm, and the particle size of the first GaN layer 22 is 50 nm to 100 nm.

[0078] By setting the particle size of the first AlN layer 21 within the above range and the particle size of the first GaN layer 22 within the above range, the size of the AlN particles in the first AlN layer 21 and the size of the GaN particles in the first GaN layer 22 can be reasonably controlled to avoid the particle size being too large or too small, which affects the effect of the particles in relieving stress.

[0079] For example, the AlN particles in the first AlN layer 21 may be spherical, and the particle size is the diameter of the particles. The particle size of the first AlN layer 21 may be 50 nm.

[0080] For example, the GaN particles in the first GaN layer 22 may be spherical, and the particle size is the diameter of the particles. The particle size of the first GaN layer 22 may be 80 nm.

[0081] In the embodiment of the present disclosure, after forming the hybrid nucleation layer 20 , the method further includes: performing in-situ annealing on the hybrid nucleation layer 20 .

[0082] The annealing temperature is between 1000° C. and 1200° C., and the annealing time is between 5 minutes and 10 minutes.

[0083] In step S12, Figure 4As shown, before forming the heterojunction layer 30 , the process includes growing a second AlN layer 41 on the mixed nucleation layer 20 .

[0084] The second AlN layer 41 has a thickness of 300 nm to 500 nm, and a thickness direction of the second AlN layer 41 is perpendicular to the substrate 10 .

[0085] For example, the thickness of the second AlN layer 41 is 350 nm. By growing the second AlN layer 41 with a relatively thick thickness, lattice relaxation can be achieved, facilitating the subsequent epitaxial growth of a high-quality GaN crystal film.

[0086] The growth temperature of the second AlN layer 41 may be 1000° C. to 1200° C.

[0087] In step S12, Figure 4 As shown, after forming the second AlN layer 41 , the process includes growing a third GaN layer 42 on the second AlN layer 41 .

[0088] The defect density of the third GaN layer 42 is 5×10 8 cm -2 to 5×10 9 cm -2 .

[0089] As an example, in the embodiment of the present disclosure, the defect density of the third GaN layer 42 is 5×10 8 cm -2 .

[0090] In the above implementation, the defect density of the third GaN layer 42 is controlled within the above range to form a high-quality third GaN layer 42 , thereby completing the lattice transformation and enabling subsequent film structures to grow with high quality.

[0091] The thickness of the third GaN layer 42 is 200 nm to 500 nm, and the thickness direction of the third GaN layer 42 is perpendicular to the substrate 10. For example, the thickness of the second GaN layer 32 is 500 nm.

[0092] The growth temperature of the third GaN layer 42 may be 1000° C. to 1200° C.

[0093] In step S12, Figure 4 As shown, after forming the third GaN layer 42 , the process includes growing a third AlN layer 43 on the third GaN layer 42 .

[0094] By providing the third AlN layer 43 as a high resistance layer, the leakage current of the RF device can be effectively reduced, the additional capacitance can be reduced, and the efficient growth of the heterojunction layer 30 can be achieved, thereby improving the growth quality of the AlGaN / GaN heterojunction.

[0095] The thickness of the third AlN layer 43 is 150 nm to 300 nm.

[0096] By setting the thickness of the third AlN layer 43 within the above range, it is possible to prevent the third AlN layer 43 from being too thin, thereby affecting the performance of the third AlN layer 43 in improving the leakage current of the RF device, and it is also possible to prevent the third AlN layer 43 from being too thick, thereby increasing the manufacturing cost.

[0097] As an example, in the embodiment of the present disclosure, the thickness of the third AlN layer 43 is 200 nm.

[0098] The growth temperature of the third AlN layer 43 may be 1000° C. to 1200° C.

[0099] In step S12, Figure 1 As shown, forming the heterojunction layer 30 includes the following two steps:

[0100] In the first step, the temperature is adjusted to 1000° C. to 1200° C., and the AlGaN layer 31 is grown on the third AlN layer 43 .

[0101] In the second step, the temperature is adjusted to 1000° C. to 1200° C., and a second GaN layer 32 is grown on the AlGaN layer 31 .

[0102] In the heterojunction layer 30, the AlGaN layer 31 has a thickness of 15 nm to 30 nm, and a molar content of Al in the AlGaN layer 31 is 0.2 to 0.35. The second GaN layer 32 has a thickness of 3 nm to 15 nm, and is undoped.

[0103] By setting the thickness of AlGaN layer 31 within the aforementioned range and the thickness of second GaN layer 32 within the aforementioned range, it is possible to prevent the AlGaN layer 31 and second GaN layer 32 from being too thin, thereby affecting the function of heterojunction layer 30. It is also possible to prevent the AlGaN layer 31 and second GaN layer 32 from being too thick, thereby increasing production costs. Furthermore, setting the molar content of Al in AlGaN layer 31 within the aforementioned range ensures the function of heterojunction layer 30.

[0104] As an example, in the embodiment of the present disclosure, the thickness of the AlGaN layer 31 is 20 nm, the molar content of Al in the AlGaN layer 31 is 0.3, and the thickness of the second GaN layer 32 is 10 nm.

[0105] Finally, after the epitaxial growth is completed, the temperature is lowered to room temperature and the epitaxial structure is taken out for future use.

[0106] The above does not limit the present disclosure in any form. Although the present disclosure has been disclosed as above through the embodiments, it is not intended to limit the present disclosure. Any technician familiar with the profession can make slight changes or modifications to equivalent embodiments with equivalent changes using the technical content disclosed above without departing from the scope of the technical solution of the present disclosure. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present disclosure without departing from the content of the technical solution of the present disclosure are still within the scope of the technical solution of the present disclosure.

Claims

1. An epitaxial structure of a radio frequency device for improving stress mismatch, characterized in that: The epitaxial structure comprises a substrate (10), a mixed nucleation layer (20) and a heterojunction layer (30) stacked in sequence; The hybrid nucleation layer (20) comprises a first AlN layer (21) and a first GaN layer (22) sequentially stacked on the substrate (10); the heterojunction layer (30) comprises an AlGaN layer (31) and a second GaN layer (32) sequentially located on the hybrid nucleation layer (20); the first AlN layer (21) comprises AlN particles distributed on the surface of the substrate (10); the first GaN layer (22) comprises GaN particles distributed on the surface of the first AlN layer (21); the particle distribution density of the first AlN layer (21) is not greater than the particle distribution density of the first GaN layer (22); the particle distribution density of the first AlN layer (21) refers to the number of AlN particles distributed per unit area in the first AlN layer (21); and the particle distribution density of the first GaN layer (22) refers to the number of GaN particles distributed per unit area in the first GaN layer (22).

2. The epitaxial structure according to claim 1, wherein: The particle distribution density of the first AlN layer (21) is 10 8 cm -2 to 10 9 cm -2 The particle distribution density of the first GaN layer (22) is 10 9 cm -2 to 10 10 cm -2 .

3. The epitaxial structure according to claim 1, wherein: The particle size of the AlN particles is 20 nm to 80 nm, and the particle size of the GaN particles is 50 nm to 100 nm.

4. The epitaxial structure according to any one of claims 1 to 3, characterized in that: The epitaxial structure further comprises a second AlN layer (41) located between the mixed nucleation layer (20) and the heterojunction layer (30), and the thickness of the second AlN layer (41) is 300 nm to 500 nm.

5. The epitaxial structure according to claim 4, characterized in that The epitaxial structure further includes a third GaN layer (42) located between the second AlN layer (41) and the heterojunction layer (30), wherein the defect density of the third GaN layer (42) is 5×10 8 cm -2 to 5×10 9 cm -2 .

6. The epitaxial structure according to claim 4, wherein: The epitaxial structure further comprises a third AlN layer (43) located between the second AlN layer (41) and the heterojunction layer (30), and the thickness of the third AlN layer (43) is 150 nm to 300 nm.

7. The epitaxial structure according to any one of claims 1 to 3, characterized in that: The thickness of the AlGaN layer (31) is 15 nm to 30 nm, the molar content of Al in the AlGaN layer (31) is 0.2 to 0.35, and the thickness of the second GaN layer (32) is 3 nm to 15 nm.

8. A method for preparing an epitaxial structure of a radio frequency device with improved stress mismatch, characterized in that: The preparation method comprises: providing a substrate; A mixed nucleation layer and a heterojunction layer are sequentially formed on the substrate, the mixed nucleation layer comprising a first AlN layer and a first GaN layer sequentially stacked on the substrate, the heterojunction layer comprising an AlGaN layer and a second GaN layer sequentially located on the mixed nucleation layer, the first AlN layer (21) comprising AlN particles distributed on the surface of the substrate (10), and the first GaN layer (22) comprising GaN particles distributed on the surface of the first AlN layer (21); the particle distribution density of the first AlN layer (21) is not greater than the particle distribution density of the first GaN layer (22), the particle distribution density of the first AlN layer (21) refers to: the distribution number of AlN particles per unit area in the first AlN layer (21), and the particle distribution density of the first GaN layer (22) refers to: the distribution number of GaN particles per unit area in the first GaN layer (22).

9. The preparation method according to claim 8, characterized in that Forming the hybrid nucleation layer on the substrate includes: Controlling the temperature to be 400° C. to 800° C., the molar ratio of ammonia gas to the metal Mo source to be 3000 to 10000, and depositing AlN particles on the substrate to form the first AlN layer; GaN particles are deposited to form the first GaN layer.

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