Method for manufacturing epitaxial structure and epitaxial structure

Abstract

To provide a method for manufacturing an epitaxial structure, capable of providing an epitaxial structure that has a good withstand voltage performance and that is suppressed in formation of defects.SOLUTION: A method for manufacturing an epitaxial structure includes: providing a substrate; forming a first buffer layer above the substrate; forming a roughened layer above the first buffer layer, a process of forming the roughened layer including performing a first low-temperature growth step and a high-temperature growth step, the first low-temperature growth step including forming a first intrinsically doped structure at a first low-temperature, the high-temperature growth step including forming an extrinsically doped structure at a high-temperature, the process of forming the roughened layer including performing the first low-temperature growth step and the high-temperature growth step in sequence at least one time to form the roughened layer, the high-temperature being greater than the first low-temperature; forming a second buffer layer above the roughened layer; and forming a channel layer above the second buffer layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to epitaxial structures, and in particular to epitaxial structures having doping. [Background technology]

[0002] A known high electron mobility transistor (HEMT) is a transistor containing a two-dimensional electron gas (2-DEG) adjacent to a heterojunction between two materials with different bandgaps. Because a high electron mobility transistor uses a high electron mobility 2-DEG as the carrier channel rather than a doped region, the high electron mobility transistor has properties such as a high breakdown voltage, a high electron transition rate, a low conduction resistance, and a low input capacitance, making it suitable for a wide range of high-power semiconductor devices.

[0003] High electron mobility transistors generally use doping structures to enhance their voltage endurance capability. However, commonly used doping structures have problems, such as the tendency to form defects. Therefore, how to provide an epitaxial structure that enhances voltage endurance capability and is not prone to defect formation is an issue that needs to be addressed as soon as possible. Summary of the Invention [Problem to be solved by the invention]

[0004] In view of this, the present invention aims to provide a method for fabricating an epitaxial structure, which can provide an epitaxial structure that has excellent voltage resistance capability and is not prone to forming defects. [Means for solving the problem]

[0005] To achieve the above object, the present invention provides a method for fabricating an epitaxial structure, comprising the steps of: providing a substrate; forming a first buffer layer above the substrate; and forming a roughened layer above the first buffer layer, wherein the process of forming the roughened layer comprises performing a first low-temperature growth step and a high-temperature growth step, wherein the first low-temperature growth step comprises forming a first intrinsic doping structure at a first low-temperature temperature; and the high-temperature growth step comprises forming an extrinsic impurity doping structure at a high-temperature temperature. The process of forming the roughened layer comprises performing the first low-temperature growth step and the high-temperature growth step in sequence at least once to form the roughened layer, wherein the high-temperature temperature is higher than the first low-temperature temperature; forming a second buffer layer above the roughened layer; and forming a channel layer above the second buffer layer.

[0006] In one embodiment, the difference between the high temperature and the first low temperature is 50 degrees Celsius or more.

[0007] In one embodiment, the high temperature is 1000 degrees Celsius or higher and the first low temperature is 980 degrees Celsius or lower.

[0008] In one embodiment, the first low temperature growth step includes forming the first intrinsic doping configuration at a first low temperature process pressure, and the high temperature growth step includes forming the extrinsic impurity doping configuration at a high temperature process pressure, the high temperature process pressure being greater than the first low temperature process pressure.

[0009] In one embodiment, the high temperature step pressure is at least twice the first low temperature step pressure.

[0010] In one embodiment, the high temperature step pressure is 150 torr or more and the first low temperature step pressure is 75 torr or less.

[0011] In one embodiment, the thickness of the first intrinsic doping arrangement is greater than the thickness of the extrinsic impurity doping arrangement.

[0012] In one embodiment, the thickness of the first intrinsic doping structure is 2 to 6 times the thickness of the extrinsic impurity doping structure.

[0013] In one embodiment, the total thickness of the first essential doping composition in the roughened layer is 60% or more of the thickness in the roughened layer, and the thickness of the roughened layer is greater than or equal to 600 nm and less than or equal to 1000 nm.

[0014] In one embodiment, the aluminum content in the first buffer layer at a portion in contact with the roughened layer is controlled to be 20% or less, and the roughened layer does not contain aluminum.

[0015] In one embodiment, the carbon doping concentration in the first intrinsic doping configuration and the extrinsic impurity doping configuration is 1E19 cm -3 That's all.

[0016] In one embodiment, the step of forming the roughened layer includes a second low-temperature growth step, and the step of forming the roughened layer includes performing the first low-temperature growth step, the high-temperature growth step, and the second low-temperature growth step in sequence at least once to form the roughened layer, and the second low-temperature growth step includes forming a second intrinsic doping configuration at a second low-temperature temperature, and the high-temperature temperature is greater than the second low-temperature temperature.

[0017] In one embodiment, the second low temperature growth step includes forming the second intrinsic doping configuration at a second low temperature process pressure, the high temperature process pressure being greater than the second low temperature process pressure.

[0018] In one embodiment, the first cryo-temperature is equal to the second cryo-temperature and the first cryo-step pressure is equal to the second cryo-step pressure.

[0019] In one embodiment, the sum of the thicknesses of the first intrinsic doping structure and the second intrinsic doping structure in the roughened layer is 80% or more of the thickness of the roughened layer, and the thickness of the roughened layer is greater than or equal to 600 nm and less than or equal to 1000 nm.

[0020] In one embodiment, the thickness of the second intrinsic doping arrangement is greater than or equal to the thickness of the extrinsic impurity doping arrangement, and the thickness of the first intrinsic doping arrangement is greater than or equal to the thickness of the second intrinsic doping arrangement.

[0021] In one embodiment, the carbon doping concentration in the second intrinsic doping configuration is 1E19 cm -3 That's all.

[0022] The present invention further provides an epitaxial structure comprising a substrate, a first buffer layer, a roughened layer, a second buffer layer and a channel layer, wherein the first buffer layer is located above the substrate, the roughened layer is located above the first buffer layer, the roughened layer comprises at least one doping structure, the at least one doping structure comprising a first intrinsic doping structure and an external impurity doping structure superimposed on each other, the second buffer layer is located above the roughened layer, and the channel layer is located above the second buffer layer, wherein the aluminum content in the portion of the first buffer layer in contact with the roughened layer is 20% or less, the roughened layer does not contain aluminum, and the doping concentration of the first intrinsic doping structure is equal to or greater than that of the external impurity doping structure.

[0023] In one embodiment, the carbon doping concentration in the first intrinsic doping configuration and the extrinsic impurity doping configuration is 1E19 cm -3 That's all.

[0024] In one embodiment, the thickness of the first intrinsic doping arrangement is greater than the thickness of the extrinsic impurity doping arrangement.

[0025] In one embodiment, the thickness of the first intrinsic doping structure is 2 to 6 times the thickness of the extrinsic impurity doping structure.

[0026] In one embodiment, the total thickness of the first essential doping composition in the roughened layer is 60% or more of the thickness in the roughened layer, and the thickness of the roughened layer is greater than or equal to 600 nm and less than or equal to 1000 nm.

[0027] In one embodiment, at least one of the doping configurations includes a second intrinsic doping configuration, wherein the first intrinsic doping configuration, the extrinsic impurity doping configuration, and the second intrinsic doping configuration are sequentially stacked, and the carbon doping concentration in the second intrinsic doping configuration is equal to or greater than that of the extrinsic impurity doping configuration, and the carbon doping concentration in the second intrinsic doping configuration is 1E19 cm -3 That's all.

[0028] In one embodiment, the sum of the thicknesses of the first intrinsic doping structure and the second intrinsic doping structure in the roughened layer is 80% or more of the thickness of the roughened layer, and the thickness of the roughened layer is greater than or equal to 600 nm and less than or equal to 1000 nm.

[0029] In one embodiment, the thickness of the second intrinsic doping arrangement is greater than or equal to the thickness of the extrinsic impurity doping arrangement, and the thickness of the first intrinsic doping arrangement is greater than or equal to the thickness of the second intrinsic doping arrangement. [Effects of the Invention]

[0030] The advantage of the present invention is that by performing the first low-temperature growth step and the high-temperature growth step in sequence at least once to form the roughened layer, an epitaxial structure with excellent epitaxial quality can be provided, which not only effectively improves the voltage resistance of the epitaxial structure, but also makes it less likely for defects to form on the surface of the epitaxial structure. [Brief explanation of the drawings]

[0031] [Figure 1] 2 is a flow chart illustrating a method for fabricating an epitaxial structure according to a preferred embodiment of the present invention. [Figure 2] 1 shows an epitaxial structure according to a first preferred embodiment of the present invention. [Figure 3] 1 shows an epitaxial structure according to another preferred embodiment of the present invention. [Figure 4] 1 shows an epitaxial structure according to a second preferred embodiment of the present invention. [Figure 5] 1 shows an epitaxial structure according to another preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0032] In order to more clearly explain the present invention, preferred embodiments will be described in detail below with reference to the drawings. As shown in Figure 1, a flow chart of a method for fabricating an epitaxial structure 1 according to a first preferred embodiment of the present invention is shown, and the method for fabricating the epitaxial structure 1 includes the following steps:

[0033] Step S02 provides a substrate 10, which may be, for example, a silicon substrate or a silicon carbide substrate.

[0034] Step S04 forms a first buffer layer 20 above the substrate 10. The first buffer layer 20 may be an aluminum-containing nitride layer, such as aluminum gallium nitride (AlGaN). Step S04 further includes controlling the surface aluminum content of the first buffer layer 20 to be 20 at% or less.

[0035] In this embodiment, the aluminum content of the surface of the first buffer layer 20 is set to 10 at %, and the thickness T1 of the first buffer layer 20 is preferably 3 μm or more, thereby improving the withstand voltage capability. The aluminum content of the first buffer layer 20 may decrease stepwise or linearly from the surface in contact with the substrate 10 toward the surface of the first buffer layer 20. The first buffer layer 20 may be composed of a single layer, multiple layers, or a superlattice layer.

[0036] Step S06 forms a roughened layer 30 on the first buffer layer 20. The process of forming the roughened layer 30 includes performing a first low-temperature growth step and a high-temperature growth step, where the first low-temperature growth step includes forming a first intrinsic doping structure 32 at a first low-temperature temperature and the high-temperature growth step includes forming an extrinsic impurity doping structure 34 at a high-temperature temperature. The process of forming the roughened layer 30 includes performing the first low-temperature growth step and the high-temperature growth step sequentially at least once to form the roughened layer 30, where the high-temperature temperature is greater than the first low-temperature temperature. The roughened layer 30 does not contain aluminum. In this embodiment, the roughened layer 30 is a gallium nitride (GaN) layer.

[0037] Wherein, the difference between the high temperature and the first low temperature is 50 degrees Celsius or more. The high temperature is 1000 degrees Celsius or more. The first low temperature is 980 degrees Celsius or less. It is preferable that the first low temperature is 925 degrees Celsius or more and 975 degrees Celsius or less.

[0038] The first low-temperature growth step includes forming the first intrinsic doping structure 32 at a first low-temperature process pressure, and the high-temperature growth step includes forming the extrinsic impurity doping structure 34 at a high-temperature process pressure, the high-temperature process pressure being greater than the first low-temperature process pressure, the high-temperature process pressure being at least twice the first low-temperature process pressure, the high-temperature process pressure being greater than 150 torr, and the first low-temperature process pressure being less than 75 torr.

[0039] Wherein, the thickness T2 of the first intrinsic doping structure 32 is greater than the thickness T3 of the external impurity doping structure 34. The thickness T2 of the first intrinsic doping structure 32 is two to six times the thickness T3 of the external impurity doping structure 34. In this embodiment, the thickness T2 is five times as large as the external impurity doping structure 34. The total thickness of the first intrinsic doping structure 32 in the roughened layer 30 is 60% or more of the thickness T of the roughened layer 30, and the thickness T of the roughened layer 30 is greater than or equal to 600 nm and less than or equal to 1000 nm.

[0040] In this embodiment, the doped element in the first intrinsic doping structure 32 and the extrinsic impurity doping structure 34 is carbon. No special carbon source is provided when forming the first intrinsic doping structure 32, while the carbon source when forming the extrinsic impurity doping structure 34 is a carbon source such as trimethylgallium (TMGa) or triethylgallium (TEGa). The carbon doping concentration in the first intrinsic doping structure 32 and the extrinsic impurity doping structure 34 is 1E19 cm -3 In this embodiment, the carbon doping concentration in the first essential doping structure 32 is 3E19 cm -3 and the carbon doping concentration in the external impurity doping structure 34 is equal to 1E19 cm -3 is equal to.

[0041] Step S08 forms a second buffer layer 40 on the roughened layer 30. In this embodiment, the second buffer layer 40 is a gallium nitride (GaN) layer that does not contain aluminum, and the thickness T4 of the second buffer layer 40 is 1.5 μm or more. The second buffer layer 40 is formed in a high temperature environment of more than 1000° C. and a high pressure environment of more than 150 torr and less than 200 torr. The external impurity doping carbon concentration in the second buffer layer 40 is 1E19 cm -3 Above 3E19cm -3 The following is the result.

[0042] Step S10 forms a channel layer 50 above the second buffer layer 40, and the channel layer 50 may be a nitride channel layer, for example, gallium nitride (GaN).

[0043] In this embodiment, the first low-temperature growth step and the high-temperature growth step are sequentially performed at least once to form the roughened layer 30, which is formed by overlapping the first intrinsic doping structure 32 and the external impurity doping structure 34 (see FIG. 2). In another embodiment, the epitaxial structure 1' shown in FIG. 3 may be used. The first low-temperature growth step and the high-temperature growth step are sequentially performed multiple times to form the roughened layer 30, which is formed by overlapping the first intrinsic doping structure 32 and the external impurity doping structure 34. In the roughened layer 30, the total thickness of the first intrinsic doping structure 32 is 60% or more of the thickness T of the roughened layer 30. Preferably, the first low-temperature growth step and the high-temperature growth step are sequentially performed two to four times.

[0044] In the second preferred embodiment, the method for fabricating an epitaxial structure is substantially the same as that of the first preferred embodiment, except for the following differences: the step of forming the roughened layer 30 further includes a second low-temperature growth step; the step of forming the roughened layer 30 includes sequentially performing the first low-temperature growth step, the high-temperature growth step, and the second low-temperature growth step once to form the roughened layer 30; the second low-temperature growth step includes forming a second intrinsically doped structure 32′ at a second low-temperature temperature, the high-temperature temperature being greater than the second low-temperature temperature; the second low-temperature growth step includes forming the second intrinsically doped structure 32′ at a second low-temperature process pressure, the high-temperature process pressure being greater than the second low-temperature process pressure; the first low-temperature temperature is equal to the second low-temperature temperature, and the first low-temperature process pressure is equal to the second low-temperature process pressure.

[0045] The total thickness of the first intrinsically doped structure 32 and the second intrinsically doped structure 32' of the roughened layer 30 is 80% or more of the thickness of the roughened layer T, the thickness T of the roughened layer 30 is greater than or equal to 600 nm and less than or equal to 1000 nm, the thickness T1' of the second intrinsically doped structure 32' is greater than or equal to the thickness T2 of the external impurity doped structure 34, the thickness T2 of the first intrinsically doped structure 32 is greater than or equal to the thickness T2' of the second intrinsically doped structure 32', and the carbon doping concentration of the second intrinsically doped structure 32' is 1E19 cm -3 That's all.

[0046] In the second preferred embodiment described above, the roughened layer 30 is formed by stacking the first intrinsic doping configuration 32, the extrinsic impurity doping configuration 34, and the second intrinsic doping configuration 32' by sequentially performing the first low-temperature growth step, the high-temperature growth step, and the second low-temperature growth step only once (see FIG. 4). In another embodiment, the epitaxial structure 2' shown in FIG. 5 may be formed. The roughened layer 30 is formed by stacking the first intrinsic doping configuration 32, the extrinsic impurity doping configuration 34, and the second intrinsic doping configuration 32' by sequentially performing the first low-temperature growth step, the high-temperature growth step, and the second low-temperature growth step multiple times. The total thickness of the first intrinsic doping configuration 32 and the second intrinsic doping configuration 32' is 80% or more of the thickness of the roughened layer T. Among these, the number of times that the first low-temperature growth step, the high-temperature growth step, and the second low-temperature growth step are carried out in sequence is preferably once to twice.

[0047] As shown in FIG. 2, the epitaxial structure 1 is fabricated by the method for fabricating an epitaxial structure according to the first preferred embodiment. The epitaxial structure 1 includes the substrate 10, the first buffer layer 20, the roughened layer 30, the second buffer layer 40, and the channel layer 50, wherein the first buffer layer 20 is located above the substrate 10, the roughened layer 30 is located above the first buffer layer 20, and the roughened layer 30 includes a doping structure, which includes the first intrinsic doping structure 32 and the extrinsic impurity doping structure 34 stacked on top of each other, the second buffer layer 40 is located above the roughened layer 30, and the channel layer 50 is located above the second buffer layer 40, wherein the aluminum content of the portion of the first buffer layer 20 in contact with the roughened layer 30 is 20% or less, the roughened layer 30 does not contain aluminum, and the doping concentration of the first intrinsic doping structure 32 is equal to or greater than that of the extrinsic impurity doping structure 34.

[0048] As shown in FIG. 3, in another embodiment, the roughened layer 30 may include multiple doping structures, i.e., the first intrinsic doping structure 32 and the external impurity doping structure 34 stacked in multiple layers, preferably a doped structure with 2 to 4 layers.

[0049] 4 shows an epitaxial structure 2 fabricated by the method for fabricating an epitaxial structure according to the second preferred embodiment. The epitaxial structure 2 includes the substrate 10, the first buffer layer 20, the roughened layer 30, the second buffer layer 40, and the channel layer 50. The first buffer layer 20 is located above the substrate 10, and the roughened layer 30 is located above the first buffer layer 20, with the roughened layer 30 including the doping structure. The doping structure includes the first intrinsic doping structure 32 and the extrinsic impurity doping structure 34, which are stacked on top of each other, and further includes the second intrinsic doping structure 32' stacked on top of the extrinsic impurity doping structure 34. The second buffer layer 40 is located above the roughened layer 30. The channel layer 50 is located above the second buffer layer 40. Wherein, the aluminum content in the portion of the first buffer layer 20 in contact with the roughened layer 30 is 20% or less, the roughened layer 30 does not contain aluminum, the doping concentration in the first intrinsic doping structure 32 is equal to or greater than that in the external impurity doping structure 34, and the carbon doping concentration in the second intrinsic doping structure 32' is equal to or greater than that in the external impurity doping structure 34.

[0050] As shown in FIG. 5, in another embodiment, the roughening layer may include multiple doping structures, i.e., the first intrinsic doping structure 32, the external impurity doping structure 34, and the second intrinsic doping structure 32', which are stacked in multiple layers, and a doping structure with one to two layers is preferred.

[0051] In the epitaxial structures 1, 1', 2, and 2' fabricated by the epitaxial structure fabrication method, the average number of defects per square centimeter on the surface of the channel layer 50 that are 0.3 μm or less in diameter is 2 or less, the average number of defects per square centimeter that are 0.2 μm or less in diameter is 1 or less, and the average number of defects per square centimeter that are 0.1 μm or less in diameter is 0.5 or less. The defects include, for example, hexagonal defects, stacked defects, and hole-shaped defects that are commonly found in epitaxial processes, but do not include defects formed by external forces such as dust or scratches. Furthermore, when a forward voltage of 650 V is applied to the epitaxial structures 1, 1', 2, and 2', the leakage current of the epitaxial structures 1, 1', 2, and 2' is 3E-7 A / cm. -2 is smaller than.

[0052] In summary, the advantages of the present invention are as follows: By performing the first low-temperature growth step and the high-temperature growth step in sequence at least once to form the roughened layer 30, an epitaxial structure with excellent epitaxial quality can be provided, which not only effectively improves the voltage resistance of the epitaxial structure, but also makes it less likely for defects to form on the surface of the epitaxial structure.

[0053] The above description is merely a preferred embodiment of the present invention, and any equivalent replacements made by applying the claims together with the specification of the present invention should be included in the scope of the claims of the present invention. [Explanation of symbols]

[0054] 1. Epitaxial structure 1' Epitaxial structure 2. Epitaxial structure 2' epitaxial structure 10 Substrate 20 First buffer layer 30 Roughening layer 32 First essential doping configuration 34 External impurity doping configuration 32' Second essential doping structure T Thickness T1 Thickness T2 Thickness T2' thickness T3 Thickness T4 thickness 40 Second buffer layer 50 Channel Layer S02 Step S04 Step S06 Step S08 Step S10 Step

Claims

1. providing a substrate; forming a first buffer layer over the substrate; forming a roughened layer above the first buffer layer, the step of forming the roughened layer comprising performing a first low-temperature growth step and a high-temperature growth step, the first low-temperature growth step comprising forming a first intrinsic doping configuration at a first low-temperature temperature, the high-temperature growth step comprising forming an extrinsic impurity doping configuration at a high-temperature temperature, the step of forming the roughened layer comprising performing the first low-temperature growth step and the high-temperature growth step in sequence at least once to form the roughened layer, the high-temperature temperature being higher than the first low-temperature temperature; forming a second buffer layer above the roughened layer; and forming a channel layer above the second buffer layer.

2. 2. The method of claim 1, wherein the difference between said high temperature and said first low temperature is greater than or equal to 50 degrees Celsius.

3. The high temperature is 1000 degrees Celsius or higher, 2. The method of claim 1, wherein the first cryogenic temperature is less than or equal to 980 degrees Celsius.

4. the first low temperature growing step includes forming the first intrinsic doping structure at a first low temperature process pressure, and the high temperature growing step includes forming the extrinsic impurity doping structure at a high temperature process pressure; 2. The method of claim 1, wherein said high temperature process pressure is greater than said first low temperature process pressure.

5. 5. The method of claim 4, wherein the high temperature step pressure is at least twice the first low temperature step pressure.

6. forming the roughened layer includes a second low-temperature growth step; the step of forming the roughened layer includes performing the first low-temperature growth step, the high-temperature growth step, and the second low-temperature growth step in sequence at least once to form the roughened layer; the second low temperature growing step includes forming a second intrinsic doping configuration at a second low temperature; 5. The method of claim 4, wherein said high temperature is greater than said second low temperature.

7. 7. The method of claim 6, wherein the second low temperature growth step includes forming the second intrinsic doping structure at a second low temperature process pressure, the high temperature process pressure being greater than the second low temperature process pressure.

8. the first cryogenic temperature is equal to the second cryogenic temperature; 8. The method of claim 7, wherein the first cold step pressure is equal to the second cold step pressure.

9. A substrate; a first buffer layer positioned above the substrate; a roughening layer located above the first buffer layer, the roughening layer including at least one doping structure, the at least one doping structure including a first intrinsic doping structure and an extrinsic impurity doping structure superimposed on each other; a second buffer layer located above the roughened layer; a channel layer located above the second buffer layer; an epitaxial structure comprising: an aluminum content of 20% or less at a portion of the first buffer layer in contact with the roughened layer; no aluminum in the roughened layer; and a doping concentration of the first intrinsic doping structure that is equal to or greater than that of the extrinsic impurity doping structure.

10. The first intrinsic doping structure and the external impurity doping structure have a carbon doping concentration of 1E19 cm -3 10. The epitaxial structure of claim 9, wherein:

11. 10. The epitaxial structure of claim 9, wherein a thickness of the first intrinsic doping structure is greater than a thickness of the extrinsic impurity doping structure.

12. 10. The epitaxial structure of claim 9, wherein the thickness of the first intrinsic doping structure is between two and six times the thickness of the extrinsic impurity doping structure.

13. 10. The epitaxial structure of claim 9, wherein the total thickness of the first instrinsic doping composition in the roughened layer is equal to or greater than 60% of the thickness of the roughened layer, and the thickness of the roughened layer is greater than or equal to 600 nm and less than or equal to 1000 nm.

14. At least one of the doping configurations includes a second intrinsic doping configuration, and the first intrinsic doping configuration, the extrinsic impurity doping configuration, and the second intrinsic doping configuration are sequentially superimposed; The carbon doping concentration in the second intrinsic doping structure is equal to or greater than that in the extrinsic impurity doping structure, and the carbon doping concentration in the second intrinsic doping structure is 1E19 cm -3 10. The epitaxial structure of claim 9, wherein:

15. 15. The epitaxial structure of claim 14, wherein the sum of the thicknesses of the first intrinsic doping composition and the second intrinsic doping composition in the roughened layer is 80% or more of the thickness of the roughened layer, and the thickness of the roughened layer is greater than or equal to 600 nm and less than or equal to 1000 nm.

16. the thickness of the second intrinsic doping structure is equal to or greater than the thickness of the extrinsic impurity doping structure; 15. The epitaxial structure of claim 14, wherein a thickness of the first intrinsic doping structure is equal to or greater than a thickness of the second intrinsic doping structure.

17. When a forward voltage of 650 V is applied to the epitaxial structure, the leakage current of the epitaxial structure is 3E-7 A / cm -2 10. The epitaxial structure of claim 9, wherein the epitaxial structure is smaller than

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