An epitaxial structure and method of epitaxy of a high linearity AlGaN / GaN heterojunction

Abstract

The application discloses an epitaxial structure and method of a high-linearity AlGaN / GaN heterojunction, which sequentially comprises a single-crystal substrate, an AlN nucleation layer, a GaN buffer layer, a GaN channel layer, an AlGaN channel layer, a first AlGaN barrier layer and a second AlGaN barrier layer. The technical scheme uses epitaxial technologies such as metal organic chemical vapor deposition (MOCVD), adopts a high-temperature and low-rate process for the GaN channel layer, improves the crystallization quality and surface morphology of the GaN channel layer, and is favorable for reducing the defect density of the subsequent AlGaN channel layer and barrier layer. The AlGaN channel layer structure is introduced, the small conduction band step of the AlGaN channel layer / GaN channel layer is used, three-dimensional distribution of an electron gas in the GaN / AlGaN composite channel layer is realized, the first AlGaN barrier layer structure of polarization modulation doping is introduced, the electron gas penetrates into the barrier layer, and the three-dimensional depth of the electron gas is further widened, the second AlGaN barrier layer with strong polarization is used, the electron gas surface density and the transconductance peak value are improved, and the application is suitable for the development of a high-linearity GaN radio frequency device.

Description

Technical Field

[0001] This invention relates to an epitaxial structure and method for a high linearity AlGaN / GaN heterojunction, particularly a material structure and epitaxial method for a high linearity AlGaN / GaN heterojunction that utilizes a high-temperature and low-rate GaN channel layer growth process to reduce the defect density of the heterojunction and utilizes a GaN / AlGaN composite channel layer and a polarization-modulated AlGaN barrier layer structure to broaden the three-dimensional depth of the electron gas. This invention belongs to the field of semiconductor epitaxial material technology. Background Technology

[0002] GaN high electron mobility field-effect transistors (HEPFETs) offer significant advantages in the radio frequency (RF) field. They provide high output power while operating stably in various harsh environments, strongly driving system upgrades and replacements, particularly in base station applications. Unlike base stations that prioritize high saturation power, satellite communication requires shielding against electromagnetic interference from other frequency bands. This means GaN RF devices must simultaneously achieve high gain and high linearity to enable wideband data transmission and ensure a high signal-to-noise ratio (SNR). However, conventional GaN HEPFETs exhibit a typical peak-characteristic transconductance curve, with significant degradation after reaching the peak at the rising edge. This low transconductance flatness causes rapid gain compression and deterioration of intermodulation characteristics at high frequencies and input power, leading to severe signal amplification distortion and poor linearity, failing to meet the requirements of satellite communication.

[0003] Conventional AlGaN / GaN heterojunction materials grown using existing technologies have structures such as Figure 2 As shown, from bottom to top, the layers are: 1. Silicon carbide single crystal substrate; 2. 50 nm thick AlN nucleation layer; 3. 1.5 μm thick GaN buffer layer; 4. 0.15 μm thick GaN channel layer; 5. 20 nm thick Al... 0.3 Ga 0.7 The epitaxial method for the N-barrier layer 5c includes the following steps:

[0004] Step 1: Select a 4-inch silicon carbide single crystal substrate and place it on the base inside the MOCVD equipment;

[0005] Step 2: Heat the reaction chamber to 1070℃, set the pressure to 100 torr, and bake the substrate in a hydrogen atmosphere for 10 minutes to remove contaminants from the substrate surface;

[0006] Step 3: Heat the reaction chamber to 1150℃, set the pressure to 80 torr, introduce 10 slm ammonia and 300 sccm trimethylaluminum, grow a 50 nm thick AlN nucleation layer, and then turn off the trimethylaluminum.

[0007] Step 4: In an ammonia atmosphere, lower the temperature to 1030℃, increase the pressure to 200 torr, introduce trimethylgallium, and adjust the flow rate of trimethylgallium to achieve a GaN growth rate of 2.0 μm / h, growing a 1.5 μm thick GaN buffer layer.

[0008] Step 5: Keep the reaction chamber temperature, pressure, and GaN growth rate constant, grow a 0.15 μm thick GaN channel layer, and turn off trimethylgallium;

[0009] Step 6: Set the temperature to 1000℃ and the pressure to 100 torr in an ammonia atmosphere, introduce trimethylgallium and trimethylaluminum, and grow a 20nm thick Al0.3Ga0.7N barrier layer by adjusting the flow rate of trimethylgallium and trimethylaluminum, and then turn off trimethylgallium and trimethylaluminum.

[0010] The low transconductance flatness of conventional GaN high electron mobility field-effect transistors is due to the small two-dimensional electron gas depth (~2nm) at the AlGaN / GaN heterojunction interface. This results in the transconductance only maintaining a high level within a small gate voltage range before channel pinch-off. Therefore, the key to improving transconductance flatness is to broaden the three-dimensional depth of the electron gas, thereby achieving a high and flat transconductance curve over a larger gate voltage range. Currently, the mainstream solutions for improving transconductance flatness include multi-channel and barrier layer polarization modulation doped structures. Multi-channel structures achieve multiple transconductance peaks based on the principle of top-down, layer-by-layer depletion of channels, thus improving transconductance flatness. However, multi-channel structures and epitaxial processes are complex, and the pinch-off voltage is too high, making implementation difficult. Barrier layer polarization modulation doped structures, on the other hand, utilize the downward bending of the barrier layer band to extend the electron gas towards the barrier layer, effectively widening the three-dimensional depth of the electron gas and thus improving transconductance flatness. However, the low net polarization charge density at the heterojunction interface of barrier layer polarization modulation doped structures leads to poor electron gas surface density, transconductance peaks, and other output characteristics. Beyond GaN RF device and circuit design, designing the AlGaN / GaN heterojunction epitaxial material process and structure to achieve a significant improvement in transconductance flatness without causing other performance degradation has important scientific significance and practical value for the application of GaN RF devices in high-frequency satellites and 5G communications.

[0011] Furthermore, reducing the defect density within the AlGaN / GaN heterojunction helps improve the reliability of GaN RF devices and ensure the stability of communication systems. Summary of the Invention

[0012] The purpose of this invention is to provide an epitaxial structure and method for a high linearity AlGaN / GaN heterojunction. While maintaining a high electron gas surface density, output current density, and transconductance peak value, it reduces the defect density of the AlGaN / GaN heterojunction material and significantly broadens the three-dimensional depth of the electron gas, which is beneficial to improving transconductance flatness and is suitable for the development of high linearity GaN RF devices.

[0013] To achieve the above objectives, the solution of the present invention is:

[0014] An epitaxial method for a highly linear AlGaN / GaN heterojunction includes the following steps:

[0015] Step 1: Select a single crystal substrate and place it on the base inside the equipment for vapor phase epitaxial growth such as MOCVD;

[0016] Step 2: Heat the reaction chamber to 1000-1100℃, set the pressure to 50-150 torr, and bake the substrate in a hydrogen atmosphere for 5-15 minutes to remove contaminants from the substrate surface.

[0017] Step 3: The reaction chamber is heated to 1100-1250℃, the pressure is set to 30-150 torr, ammonia and aluminum source are introduced, and an AlN nucleation layer of 30-200 nm thickness is grown. The aluminum source is then turned off.

[0018] Step 4: In an ammonia atmosphere, lower the temperature to 930–1080℃, increase the pressure to 150–500 torr, introduce a gallium source, and adjust the gallium source flow rate to achieve a GaN growth rate of 1.3–3.0 μm / h, grow a GaN buffer layer with a thickness of 0.2–3.0 μm, and then turn off the gallium source.

[0019] Step 5: In an ammonia atmosphere, raise the temperature to T, set the pressure to 150-500 torr, introduce the gallium source, and adjust the gallium source flow rate to achieve the GaN growth rate V, grow a GaN channel layer with a thickness of 0.05-0.5 μm, and then turn off the gallium source.

[0020] Step 6: In an ammonia atmosphere, set the temperature to 950–1100℃ and the pressure to 30–150 torr, introduce gallium and aluminum sources, and grow Al with an aluminum composition of x1 and a thickness of t1 by adjusting the flow rates of the gallium and aluminum sources. x1 Ga 1-x1 N-channel layer;

[0021] Step 7: Maintain constant temperature and pressure in an ammonia atmosphere, and grow a first Al with an aluminum composition of x2 and a thickness of t2 by either fixing the gallium source flow rate and linearly increasing the aluminum source flow rate, or fixing the aluminum source flow rate and linearly decreasing the gallium source flow rate. x2 Ga 1-x2 N-barrier layer, shutting off gallium and aluminum sources;

[0022] Step 8: Maintain constant temperature and pressure in an ammonia atmosphere, introduce gallium and aluminum sources, and grow a second Al with an Al composition of x3 and a thickness of t3 by adjusting the flow rates of the gallium and aluminum sources. x3 Ga 1-x3 The N-barrier layer shuts off the gallium and aluminum sources.

[0023] Step 9: Under ammonia protection, allow the temperature to drop to room temperature, then remove the epitaxial wafer.

[0024] After the GaN channel layer is grown in step five above, the Al layer grown in step six continues. x1 Ga 1-x1 The N-channel layer constitutes the GaN / Al x1 Ga 1-x1 N-composite channel layer structure;

[0025] In this invention, the growth temperature T of the GaN channel layer in step five is higher than that of the GaN buffer layer, ranging from 1080 to 1130°C, and its growth rate V is lower than that of the GaN buffer layer, ranging from 0.2 to 1.2 μm / h. The high-temperature growth process of 1080–1130°C for the GaN channel layer can improve the lateral migration rate of gallium atoms, promote a two-dimensional layered growth mode, improve the surface smoothness of the material, and simultaneously increase the decomposition efficiency of ammonia gas to generate an ammonia-rich atmosphere, which is beneficial for reducing point defect density and improving the crystal quality of the material. The low-rate epitaxial growth process of 0.2–1.2 μm / h can promote the migration of gallium atoms at the growth interface to ideal lattice sites before combining with N atoms, which is beneficial for suppressing the formation of lattice defects and providing an ideal substrate for the subsequent high-quality growth of the AlGaN channel layer and barrier layer.

[0026] In this invention, Al in step six x1 Ga 1-x1 The N-channel layer has an aluminum composition (x1) ranging from 3% to 10% and a thickness (t1) ranging from 3 to 15 nm. This is to achieve electron gas in GaN / Al... x1 Ga 1-x1 Three-dimensional distribution of N-composite channel layer, Al x1 Ga 1-x1 The conduction band step at the N-channel / GaN-channel interface should not be too small, and Alx1Ga 1-x1 The thickness t1 of the N-channel layer should not be too small; therefore, the aluminum composition x1 should not be less than 3%, and the thickness t1 should not be less than 3 nm. This is to achieve a relatively uniform distribution of electron gas in the GaN / Al layer. x1 Ga 1-x1 Within the N-composite channel layer, the conduction band step at the AlGaN channel layer / GaN channel layer interface should not be too large, and the AlGaN channel layer thickness t1 should not be too large. Therefore, the aluminum composition x1 should not be greater than 10%, and the thickness t1 should not be greater than 15nm.

[0027] In this invention, the first Al in step seven x2 Ga 1-x2 The N-barrier layer, whose aluminum composition x2 is derived from the first Al along the epitaxial direction. x2 Ga 1-x2 The N-barrier layer gradually increases in size from the back to the top, forming a polarization-modulated doped barrier layer structure. The minimum value of x2 is not lower than Al in step six. x1 Ga 1-x1 The aluminum composition (x1) of the N-channel layer is no higher than 15%, with a maximum range of 20%–45%; its thickness (t2) ranges from 15 to 40 nm. This is to ensure the first Al... x2 Ga 1-x2 The N-barrier layer energy band bends significantly downwards, allowing electron gas to effectively penetrate into the first Al. x2 Ga 1-x2 N-barrier layer, whose aluminum composition x2 is derived from the first Al x2 Ga 1-x2 The gradient from the back to the top of the N-barrier layer should be relatively large; therefore, the minimum value of x2 should not exceed 15%, the maximum value should not be less than 20%, and t2 should not exceed 40 nm. This is to ensure the first Al... x2 Ga 1-x2 The N-barrier layer has a low tensile stress, with x2 not exceeding 45%; to ensure electron gas in the first Al x2 Ga 1-x2 If the three-dimensional depth of the N-barrier layer is relatively wide, then t2 is not less than 15nm; in order to maintain the first Al x2 Ga 1-x2 N-barrier layer / Al x1 Ga 1-x1 The N-channel layer interface exhibits good electron connectivity, and the minimum value of x2 is not lower than Al in step six. x1 Ga 1-x1 The aluminum composition of the N-channel layer is x1.

[0028] In this invention, the second Al in step eight x3 Ga 1-x3 The N-barrier layer, whose aluminum composition x3 is not less than the first Al in step seven. x2 Ga 1-x2 The maximum value of aluminum composition x2 in the N-barrier layer is not higher than 100%, and its thickness t3 ranges from 3 to 10 nm. To significantly improve the electron gas surface density and current density of the heterojunction, the aluminum composition x3 is not lower than the first Al in step seven. x2 Ga 1-x2 The maximum value of aluminum composition x2 in the N-barrier layer, and the thickness t3 is not less than 3nm; in order to keep the transconductance peak at a high level and control the overall stress of the heterojunction at a low level, t3 is not higher than 10nm.

[0029] An epitaxial structure of a highly linear AlGaN / GaN heterojunction is fabricated based on the above-mentioned epitaxial method. The epitaxial structure consists of, from bottom to top, a single crystal substrate, an AlN nucleation layer, a GaN buffer layer, a GaN channel layer, an AlGaN channel layer, a first AlGaN barrier layer, and a second AlGaN barrier layer.

[0030] Compared with existing technologies, the present invention, by adopting the above scheme, has the following advantages: By designing a new epitaxial structure and epitaxial process, the present invention improves the crystal quality and surface morphology of the GaN channel layer and reduces the defect density of subsequent AlGaN channel layers and barrier layers without reducing performance such as transconductance peak value and current density. The introduction of a GaN / AlGaN composite channel layer and a polarization-modulated doped first AlGaN barrier layer significantly broadens the three-dimensional depth of the electron gas. A strongly polarized second AlGaN barrier layer further enhances the electron gas surface density and transconductance peak value. While reducing the defect density of the AlGaN / GaN heterojunction material, the present invention significantly broadens the three-dimensional depth of the electron gas, improves transconductance flatness, and enhances the functionality of GaN RF devices in high-frequency satellite communication. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the high linearity AlGaN / GaN heterojunction material of the present invention;

[0032] Figure 2 This is a schematic diagram of a conventional AlGaN / GaN heterojunction material in the prior art;

[0033] Figure 3 This is a comparison of the photoluminescence intensity curves of the high linear AlGaN / GaN heterojunction material provided by this invention and conventional AlGaN / GaN heterojunction materials grown by existing technology at room temperature with yellow bands.

[0034] Figure 4 This is a comparison of the longitudinal distribution curves of electron gas between the high linearity AlGaN / GaN heterojunction material provided by this invention and conventional AlGaN / GaN heterojunction materials grown by existing technologies.

[0035] Figure 5 This is a comparison of the transconductance characteristic curves of the high linearity AlGaN / GaN heterojunction material provided by this invention and conventional AlGaN / GaN heterojunction materials grown by existing technologies.

[0036] Figure 6 This is a comparison chart of the IV characteristic curves of the high linearity AlGaN / GaN heterojunction material provided by this invention and conventional AlGaN / GaN heterojunction materials grown by existing technologies. Detailed Implementation

[0037] The technical solution of the present invention will be described in detail below, but the scope of protection of the present invention is not limited to the embodiments described.

[0038] like Figure 1 As shown, the present invention is based on the epitaxial structure and epitaxial method of a high linear AlGaN / GaN heterojunction. The proposed high linear AlGaN / GaN heterojunction epitaxial structure consists of, from bottom to top, a silicon carbide single crystal substrate 1, an AlN nucleation layer 2, a GaN buffer layer 3, a GaN channel layer 4a, an AlGaN channel layer 4b, a first AlGaN barrier layer 5a, and a second AlGaN barrier layer 5b.

[0039] The epitaxial method for high linearity AlGaN / GaN heterojunctions proposed in this invention includes the following steps:

[0040] Step 1: Select a 4-inch silicon carbide single crystal substrate and place it on the base inside the MOCVD equipment;

[0041] Step 2: Heat the reaction chamber to 1070℃, set the pressure to 100 torr, and bake the substrate in a hydrogen atmosphere for 10 minutes to remove contaminants from the substrate surface;

[0042] Step 3: Heat the reaction chamber to 1150℃, set the pressure to 80 torr, introduce 10 slm ammonia and 300 sccm trimethylaluminum, grow a 50 nm thick AlN nucleation layer, and then turn off the trimethylaluminum.

[0043] Step 4: In an ammonia atmosphere, lower the temperature to 1030℃, increase the pressure to 200 torr, introduce trimethylgallium, and adjust the flow rate of trimethylgallium to achieve a GaN growth rate of 2.0 μm / h, grow a 1.5 μm thick GaN buffer layer, and then turn off trimethylgallium.

[0044] Step 5: In an ammonia atmosphere, raise the temperature to 1100℃, set the pressure to 300 torr, introduce trimethylgallium, and adjust the flow rate of trimethylgallium to achieve a GaN growth rate of 0.6μm / h, grow a 0.15μm thick GaN channel layer, and then turn off trimethylgallium.

[0045] Step Six: In an ammonia atmosphere, set the temperature to 1000℃ and the pressure to 100 torr, introduce trimethylgallium and trimethylaluminum, and grow an 8nm thick Al layer by adjusting the flow rates of trimethylgallium and trimethylaluminum. 0.05 Ga 0.95 N-channel layer;

[0046] Step 7: Maintaining constant temperature and pressure in an ammonia atmosphere, grow a 30nm thick first Al layer by keeping the trimethylgallium flow rate constant and linearly increasing the trimethylaluminum flow rate. x2 Ga 1-x2N-barrier layer, wherein aluminum component x2 is derived from the first Al x2 Ga 1-x2 The N-barrier layer gradually increases from 0.05 on the back side to 0.35 on the top side, shutting off the gallium and aluminum sources;

[0047] Step 8: Maintain constant temperature and pressure in an ammonia atmosphere, introduce trimethylgallium and trimethylaluminum, and grow a 7nm thick second Al by adjusting the flow rates of trimethylgallium and trimethylaluminum. 0.50 Ga 0.50 N-barrier layer, shutting off trimethylgallium and trimethylaluminum;

[0048] Step 9: Under ammonia protection, allow the temperature to drop to room temperature, then remove the epitaxial wafer.

[0049] The embodiments provided by this invention employ a high-temperature, low-rate GaN channel layer growth process, introduce a GaN / AlGaN composite channel layer and a first AlGaN barrier layer structure with polarization modulation doping, and introduce a highly polarized second AlGaN barrier layer structure to create a high-linearity AlGaN / GaN heterojunction material. Compared with conventional AlGaN / GaN heterojunction materials grown using existing technologies, the signal intensity of yellow-band photoluminescence at room temperature decreases by 60%, as shown in the attached figure. Figure 3 As shown, the high-quality GaN channel layer grown using a high-temperature, low-rate process can effectively reduce the defect density of subsequent AlGaN channel layers and barrier layers, thereby suppressing the trapping effect of defect energy levels in the barrier layer.

[0050] The electron gas surface density of the high linearity AlGaN / GaN heterojunction material provided in this embodiment of the invention is 1.35*10⁻⁶. 13 cm -2 The electron gas surface density of conventional AlGaN / GaN heterojunction materials grown using existing technologies is 1.06*10⁻⁶. 13 cm -2 This indicates that the strongly polarized second AlGaN barrier layer effectively increases the electron gas surface density; the longitudinal distribution of electron gas in the two heterojunction materials is as follows: Figure 4 As shown, the longitudinal distribution of the electron gas in the high-linearity AlGaN / GaN heterojunction material is significantly wider than that in conventional AlGaN / GaN heterojunction materials grown using existing techniques. This indicates that the introduction of a GaN / AlGaN composite channel layer and a polarization-modulated doped first AlGaN barrier layer structure can significantly broaden the three-dimensional depth of the electron gas. The transconductance curves of the two heterojunction materials are shown in the figure. Figure 5As shown, the transconductance curve of the high-linearity AlGaN / GaN heterojunction material is high and flat within the gate-source voltage range of -7V to +2V, exhibiting better transconductance flatness than conventional AlGaN / GaN heterojunction materials grown using existing technologies. This indicates that the broadening of the three-dimensional depth of the electron gas improves the transconductance flatness. Furthermore, the peak transconductance of the high-linearity AlGaN / GaN heterojunction material is ~0.47 S / mm, slightly higher than the ~0.41 S / mm of conventional AlGaN / GaN heterojunction materials grown using existing technologies. The IV characteristic curves of the two heterojunction materials are shown below. Figure 6 As shown, there is no significant difference in current density between the two, and both reach ~1A / mm, indicating that the high linearity AlGaN / GaN heterojunction material provided by the present invention maintains a high current density.

[0051] Compared with conventional AlGaN / GaN heterojunction materials grown using existing technologies, the high linearity AlGaN / GaN heterojunction material provided in the embodiments of the present invention effectively reduces the defect density of AlGaN / GaN heterojunction materials while maintaining high output current density, electron gas surface density, and transconductance peak value, ensuring high reliability of GaN RF devices. At the same time, it significantly broadens the three-dimensional depth of the electron gas, improves transconductance flatness, and enhances the linearity of GaN RF devices.

[0052] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. There are many manufacturing methods that can actually be adopted. All equivalent changes and modifications made in accordance with the claims of the present invention are within the scope of the present invention.

Claims

1. An epitaxial method of high linear AlGaN / GaN heterojunction, characterized in that The method comprises the following steps: Step one, selecting a single crystal substrate and placing it on a base in a MOCVD vapor phase epitaxial growth device; Step two, baking the substrate in a hydrogen atmosphere for 5-15 minutes to remove surface contamination by heating the reaction chamber to 1000-1100℃ and setting the pressure to 50-150 torr; Step three, growing a 30-200 nm thick AlN nucleation layer by introducing ammonia and an aluminum source into the reaction chamber heated to 1100-1250℃ and set to a pressure of 30-150 torr, and then closing the aluminum source; Step four, growing a 0.2-3.0 μm thick GaN buffer layer by introducing a gallium source into the reaction chamber in an ammonia atmosphere, reducing the temperature to 930-1080℃, and increasing the pressure to 150-500 torr, and then adjusting the gallium source flow to achieve a GaN growth rate of 1.3-3.0 μm / h, and then closing the gallium source; Step five, growing a 0.05-0.5 μm thick GaN channel layer by introducing a gallium source into the reaction chamber in an ammonia atmosphere, increasing the temperature to T, and setting the pressure to 150-500 torr, and then adjusting the gallium source flow to achieve a GaN growth rate of V, and then closing the gallium source; Step six, in the ammonia atmosphere, set the temperature to 950-1100℃, set the pressure to 30-150 torr, and pass in the gallium source and the aluminum source, and grow the aluminum component with the aluminum component x1 and the thickness t1 by adjusting the flow of the gallium source and the aluminum source x1 Ga 1-x1 N channel layer Step seven, keeping the temperature and pressure constant in an ammonia atmosphere, growing a first Alx2Ga1-x2layer with a thickness of t2by fixing the gallium source flow and linearly increasing the aluminum source flow, or fixing the aluminum source flow and linearly decreasing the gallium source flow x2 Ga 1-x2 N barrier layer, turning off the gallium source and the aluminum source Step eight, keeping the temperature and pressure unchanged, gallium source and aluminum source are introduced into the atmosphere of ammonia, and the second Al component with x3 and thickness t3 is grown by adjusting the flow of gallium source and aluminum source x3 Ga 1-x3 N barrier layer, the gallium source and the aluminum source are turned off; Step nine, removing the epitaxial wafer after reducing the temperature to room temperature under an ammonia atmosphere.

2. The epitaxial method of claim 1, wherein: In step five, the growth temperature T of the GaN channel layer is higher than that of the GaN buffer layer, ranging from 1080-1130℃, and the growth rate V is lower than that of the GaN buffer layer, ranging from 0.2-1.2 μm / h.

3. The epitaxial method of claim 1, wherein: In step six, Al x1 Ga 1-x1 The aluminum component x1 of the GaN channel layer ranges from 3% to 10%, and the thickness t1 ranges from 3 to 15 nm.

4. The epitaxial method of claim 1, wherein: In step seven, the first Al x2 Ga 1-x2 The aluminum composition x2 of the N-barrier layer is derived from the first Al along the epitaxial direction. x2 Ga 1-x2 The N-barrier layer gradually increases in size from the back to the top, forming a polarization-modulated doped barrier layer structure. The minimum value of x2 is not less than that of Al in step six. x1 Ga 1-x1 The aluminum composition of the N-channel layer, x1, is no higher than 15%, with a maximum value ranging from 20% to 45%, and the thickness t2 ranges from 15 to 40 nm.

5. The epitaxial method of claim 1, wherein: The second Al x3 Ga 1-x3 The aluminum component x3 of the GaN barrier layer is not lower than the first Al x2 Ga 1-x2 The maximum value of the aluminum component x2 of the GaN barrier layer is not higher than 100%, and the thickness t3 ranges from 3 to 10 nm.

6. An epitaxial structure of high-linearity AlGaN / GaN heterojunction, which is made based on the epitaxial method of high-linearity AlGaN / GaN heterojunction as claimed in claim 1, characterized in that: From bottom to top, the single crystal substrate, AlN nucleation layer, GaN buffer layer, GaN channel layer, AlGaN channel layer, first AlGaN barrier layer, and second AlGaN barrier layer are sequentially arranged.

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