CN114582962B - Variable channel AlGaN/GaN HEMT structure and preparation method thereof - Google Patents

Abstract

The invention discloses a variable channel AlGaN/GaN HEMT structure and a preparation method. A buffer layer is grown on a substrate layer, and a multi-channel layer is regrown on the buffer layer, that is, two or more layers of AlGaN/GaN heterolayers are formed. Then, the multi-channel layer is selectively etched to form a stepped multi-channel layer; then a dielectric passivation layer is deposited on the surface of the device, and chemical and physical polishing is performed to form a stepped passivation layer and top passivation Finally, the metal electrode of the device is prepared by a micro-nano fabrication process to obtain a variable multi-channel AlGaN/GaN HEMT structure.

Description

Variable channel AlGaN/GaN HEMT structure and preparation method

technical field

The invention relates to a high-voltage power semiconductor, in particular to a variable channel AlGaN/GaN HEMT structure and a preparation method.

Background technique

The third-generation semiconductor material GaN has become a new type of developed material due to its excellent material properties such as wide band gap (3.39 eV), high electron saturation drift rate (3×10 ⁷ cm/s) and high critical breakdown electric field (3 MV/cm). Popular material for RF power semiconductor devices. In addition, thanks to the polarization effect of AlGaN/GaN heterojunction materials, two-dimensional (2D) high concentration (>1×10 ¹³ cm ^-2 ) and high electron mobility (>1500 cm ² /Vs) can be obtained at the heterojunction interface. Electron gas (2DEG). AlGaN/GaN HEMTs have the advantages of large current gain, high cut-off frequency, strong driving capability, low phase noise, and high power density, and have important application prospects in commercial and military fields such as high frequency, high power, high temperature, optoelectronics, and radiation resistance.

However, since AlGaN/GaN HEMTs need to bear higher operating voltages, the electric field lines will be concentrated at the electrodes, resulting in higher electric field peaks. When the electric field peak exceeds the critical breakdown electric field of the device, it will lead to device breakdown. Therefore, it is urgent to develop a new device structure to modulate the electric field distribution of the device, alleviate the electric field peak at the electrodes, and make the electric field distribution uniform. At present, the common electric field modulation structure is the field plate structure, which can effectively alleviate the electric field peak at the electrode and introduce a new electric field peak at the edge of the field plate. However, the field plate can only achieve the transfer of the electric field peak value and cannot obtain a uniform electric field distribution.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a variable channel AlGaN/GaN HEMT structure and a preparation method in view of the above-mentioned deficiencies of the prior art. The variable channel AlGaN/GaN HEMT structure and preparation method A buffer layer and multiple groups of GaN/AlGaN heterojunction stacks are grown on the bottom in turn, and the GaN/AlGaN heterojunction is sequentially etched to obtain a multi-channel layer whose charge density gradually increases from the gate electrode to the drain electrode. The device is passivated and metal electrodes are prepared, so as to uniformize the electric field distribution of the device and obtain better withstand voltage performance. The invention can greatly improve the withstand voltage performance of the device on the basis of less loss of open-state performance.

In order to solve the above-mentioned technical problems, the technical scheme adopted in the present invention is:

A variable channel AlGaN/GaN HEMT structure, comprising a substrate layer, a buffer layer, n groups of GaN/AlGaN heterojunction stacks, a passivation layer, a gate electrode, a source electrode and a drain electrode; wherein, n ≥ 2.

A buffer layer is epitaxially grown on top of the substrate layer.

The n groups of GaN/AlGaN heterojunction stacks are epitaxially grown on top of the buffer layer from bottom to top, and from bottom to top are the first group of GaN/AlGaN heterojunction stacks and the second group of GaN/AlGaN heterojunction stacks , ..., the nth group of GaN/AlGaN heterojunction stacks.

Each set of GaN/AlGaN heterojunction stacks includes a GaN channel layer and an AlGaN barrier layer epitaxially grown on the GaN channel layer.

The passivation layer includes a top passivation layer and a step passivation layer.

A top passivation layer is provided on top of the nth group of GaN/AlGaN heterojunction stacks.

The source electrode and the drain electrode are respectively embedded at both ends of the top passivation layer.

The gate electrode is embedded in the middle of the top passivation layer adjacent to the source electrode.

The stepped passivation layer is embedded in the second group of GaN/AlGaN heterojunction stacks between the gate electrode and the drain electrode to the nth group of GaN/AlGaN heterojunction stacks; the stepped passivation layer is an inverted stepped type , and one end is aligned with the gate electrode.

By adjusting the step width of the step passivation layer, the charge density between the gate electrode and the drain electrode is adjusted.

The material of the substrate layer is silicon, sapphire, gallium nitride or silicon carbide.

The buffer layer is a GaN material with a thickness of 2-6 microns.

The GaN channel layer is a GaN material with a thickness of 0.1 to 3 microns.

In terms of molar composition, the AlGaN barrier layer contains 0.1-0.3 parts of Al; the thickness of the AlGaN barrier layer is 15-30 nanometers.

A preparation method of a variable channel AlGaN/GaN HEMT structure, comprising the following steps.

Step 1. Prepare a gallium nitride multi-channel epitaxial wafer. The specific preparation method includes the following steps.

Step 1A, epitaxial growth of buffer layer: cleaning the substrate layer and epitaxially growing a buffer layer containing GaN material on the substrate layer.

Step 1B, epitaxial growth of the first group of GaN/AlGaN heterojunction stacks: epitaxially grow a GaN channel layer and an AlGaN barrier layer on the buffer layer from bottom to top.

Step 1C, epitaxially growing the nth group of GaN/AlGaN heterojunction stacks: on the first group of GaN/AlGaN heterojunction stacks, epitaxially grow the second group of GaN/AlGaN heterojunction stacks sequentially from bottom to top to the nth group A GaN/AlGaN heterojunction stack is formed to form a gallium nitride multi-channel epitaxial wafer.

Step 2. Etching the stepped grooves: sequentially etching from top to bottom from the middle of the second group of GaN/AlGaN heterojunction stacks to the nth group of GaN/AlGaN heterojunction stacks to form inverted stepped grooves.

Step 3, plating a passivation layer: plating a dielectric film on the inside of the stepped groove, the top of the stepped groove, and the top surfaces of the n -th group of GaN/AlGaN heterojunction stacks on both sides of the stepped groove, respectively, to form a passivation layer with a flat top surface; Among them, the passivation layer located inside the stepped groove is called the stepped passivation layer, and the remaining passivation layers are called the top passivation layer.

Step 4. Etch the electrode groove: the electrode groove includes a source electrode groove, a drain electrode groove and a gate electrode groove; both ends of the top passivation layer on both sides of the stepped groove are etched from top to bottom respectively to the n -th group of GaN/AlGaN heterostructures. The source electrode groove and the drain electrode groove are formed on the top surface of the mass junction stack; wherein, the source electrode groove is adjacent to the maximum groove depth of the stepped groove; on the top passivation layer between the stepped groove and the source electrode groove from above The top surface of the n -th group of GaN/AlGaN heterojunction stacks is etched down to form a gate electrode trench, and one sidewall surface of the gate electrode trench and one sidewall surface of the stepped trench are located on the same vertical plane.

Step 5. Preparation of source electrode and drain electrode: Evaporating or sputtering the source electrode multi-element alloy in the source electrode groove, evaporating or sputtering the drain electrode multi-element alloy in the drain electrode groove, and annealing respectively, then the source electrode and the leakage current are formed. pole.

Step 6, preparing the gate electrode: the gate electrode is formed by evaporating or sputtering the gate multi-element alloy in the gate electrode groove.

In step 1, n =3; in step 2, the stepped groove is a two-stage stepped groove, which are a first-stage stepped groove and a second-stage stepped groove respectively; wherein, the first-stage stepped groove vertically penetrates the second group of GaN/AlGaN The heterojunction stack and the third group of GaN/AlGaN heterojunction stacks; the second-level stepped groove vertically penetrates the third group of GaN/AlGaN heterojunction stacks.

In step 3, by adjusting the step width of the step passivation layer, the charge density between the gate electrode and the drain electrode can be adjusted.

In step 5, the annealing method is as follows: annealing for 30 seconds at 850 degrees Celsius and a nitrogen atmosphere.

The invention has the following beneficial effects: by sequentially etching multiple groups of GaN/AlGaN heterojunctions in the multi-channel layer of the gallium nitride epitaxial wafer, the multi-channel layer with the charge density gradually increasing from the gate electrode to the drain electrode is obtained, It can effectively modulate the electric field distribution when the device is off, avoid the premature breakdown and failure of the device caused by the excessive electric field peak value at the gate electrode, and significantly improve the withstand voltage performance. The invention can be applied to power integrated chips such as new energy vehicle drive, power management, vehicle charging pile, and smart phone fast charging.

Description of drawings

FIG. 1 shows a schematic structural diagram of a variable channel AlGaN/GaN HEMT structure of the present invention.

2a-2e show schematic diagrams of the fabrication process of a variable channel AlGaN/GaN HEMT structure of the present invention. Among them; Fig. 2a shows the structure diagram of the prepared gallium nitride multi-channel epitaxial wafer; Fig. 2b shows the structure diagram of the etched stepped groove; Fig. 2c shows the structure diagram of the passivation layer after plating; Figure 2d shows a schematic diagram of the structure of the etched electrode groove; Figure 2e shows the structure of the device after the electrode preparation is completed.

FIG. 3 shows a comparison diagram of the breakdown current-voltage curve of the present invention and the breakdown current-voltage curve of the general structure.

Figure 4 shows a comparison of the lateral electric field distribution at the heterojunction for the inventive and general structures at the same drain voltage.

Figure 5 shows a graph comparing the lateral electric field distribution at the heterojunction for the present invention and the general structure upon device breakdown.

Including:

1. Substrate layer; 2. Buffer layer;

3. The first group of GaN channel layers; 4. The first group of AlGaN barrier layers;

5. The second group of GaN channel layers; 6. The second group of AlGaN barrier layers;

7. The third group of GaN channel layers; 8. The third group of AlGaN barrier layers;

9. Passivation layer;

91. Top passivation layer; 92. Step passivation layer; 93. Step groove; 931. First step groove; 932. Second step groove;

10. Source electrode; 101. Source electrode groove;

11. Gate electrode; 111. Gate electrode groove;

12. Drain electrode; 121. Drain electrode groove.

Detailed ways

The present invention will be described in further detail below with reference to the accompanying drawings and specific preferred embodiments.

As shown in FIG. 1, a variable channel AlGaN/GaN HEMT structure includes a substrate layer 1, a buffer layer 2, an n -group GaN/AlGaN heterojunction stack, a passivation layer 9, a source electrode 10, and a gate electrode 11 and drain electrode 12 .

The material of the above-mentioned substrate layer is preferably silicon, sapphire, gallium nitride or silicon carbide.

The above buffer layer is epitaxially grown on the top of the substrate layer, preferably a GaN material with a thickness of 2-6 microns.

The n groups of GaN/AlGaN heterojunction stacks are epitaxially grown on top of the buffer layer from bottom to top, and from bottom to top are the first group of GaN/AlGaN heterojunction stacks and the second group of GaN/AlGaN heterojunction stacks , ..., the nth group of GaN/AlGaN heterojunction stacks. Wherein, n≧ 2, in this embodiment, preferably n =3, that is, there are three groups of GaN/AlGaN heterojunction stacks.

Each set of GaN/AlGaN heterojunction stacks (also called heterojunctions) includes a GaN channel layer and an AlGaN barrier layer epitaxially grown on the GaN channel layer.

The above-mentioned GaN channel layer is preferably a GaN material with a thickness of 0.1 to 3 μm.

In addition, in terms of molar composition, the AlGaN barrier layer preferably contains 0.1-0.3 parts of Al; the thickness of the AlGaN barrier layer is preferably 15-30 nm.

The above-mentioned first group of GaN/AlGaN heterojunction stacks includes a first group of GaN channel layers 3 and a first group of AlGaN barrier layers 4 .

The above-mentioned second group of GaN/AlGaN heterojunction stacks includes a second group of GaN channel layers 5 and a second group of AlGaN barrier layers 6 .

The above-mentioned third group of GaN/AlGaN heterojunction stacks includes a third group of GaN channel layers 7 and a third group of AlGaN barrier layers 8 .

The passivation layer is a dielectric material including but not limited to silicon dioxide, silicon nitride, aluminum oxide, hafnium dioxide, etc. The passivation layer includes a top passivation layer and a step passivation layer.

A top passivation layer is provided on top of the nth group of GaN/AlGaN heterojunction stacks.

The source electrode 10 and the drain electrode 12 are respectively embedded at both ends of the top passivation layer in the x direction.

The gate electrode 11 is embedded in the middle of the top passivation layer adjacent to the source electrode.

The stepped passivation layer is embedded in the second group of GaN/AlGaN heterojunction stacks between the gate electrode and the drain electrode to the nth group of GaN/AlGaN heterojunction stacks; the stepped passivation layer is an inverted stepped type , and preferably the end with the deepest thickness is aligned with the gate electrode. The present invention can adjust the charge density between the gate electrode and the drain electrode by adjusting the step width of the step passivation layer.

The invention is based on Gaussian cell analysis, and the direction of the gate electrode pointing to the drain electrode is the x direction, the side of the gate electrode close to the drain electrode is used as the origin, the thickness of the buffer layer is t _B , and the equivalent concentration is P ; the semiconductor in the step passivation layer is The layer thickness is t _S ( x _{), the equivalent concentration is NC , the equivalent capacitance of the passivation layer is C P ,} the equivalent surface density of the polarized charge of the heterojunction is σ , the charge quantity constant is q , and the critical strike of the GaN material is The penetration field strength is E _C . Under ideal conditions, the electric field strength of GaN material reaches its critical breakdown field strength, and the breakdown voltage can reach the highest value, so the device structure needs to satisfy the following formula:

In the formula, x represents the scale or coordinate value in the x -direction.

In the present invention, the setting of the step passivation layer enables t _S ( x ) to increase linearly from the gate electrode to the drain electrode. It can be seen from the above formula that the charge distribution between the gate electrode and the drain electrode can be reshaped, so that the gate electrode can be reshaped. The fixed positive charge density in the depletion region between the drain electrode and the gate electrode increases in steps from the gate electrode to the drain electrode. The optimized charge distribution is used to effectively modulate the electric field to obtain a more uniform electric field distribution, thereby improving the withstand voltage performance of the device.

As shown in Figs. 2a-2e, a method for preparing a variable channel AlGaN/GaN HEMT structure includes the following steps.

Step 1. Prepare a gallium nitride multi-channel epitaxial wafer. The specific preparation method includes the following steps.

Step 1A, epitaxial growth of buffer layer: cleaning the substrate layer and epitaxially growing a buffer layer containing GaN material on the substrate layer by MOCVD.

Step 1B, epitaxial growth of the first group of GaN/AlGaN heterojunction stacks: epitaxially grow a GaN channel layer and an AlGaN barrier layer on the buffer layer from bottom to top.

Step 1C, epitaxially growing the nth group of GaN/AlGaN heterojunction stacks: on the first group of GaN/AlGaN heterojunction stacks, epitaxially grow the second group of GaN/AlGaN heterojunction stacks sequentially from bottom to top to the nth group A GaN/AlGaN heterojunction stack is formed to form a gallium nitride multi-channel epitaxial wafer as shown in Figure 2a.

Step 2. Etch the stepped groove: etch from top to bottom from the middle of the second group of GaN/AlGaN heterojunction stacks to the nth group of GaN/AlGaN heterojunction stacks to form an inversion as shown in Figure 2b The stepped groove 93. At this time, the gallium nitride multi-channel epitaxial wafer with stepped grooves is also referred to as a stepped multi-channel layer.

In this embodiment, the stepped grooves are preferably two-stage stepped grooves, namely the first-stage stepped grooves 931 and the second-stage stepped grooves 932; wherein the first-stage stepped grooves vertically penetrate the second group of GaN/AlGaN heterojunctions The stack and the third group of GaN/AlGaN heterojunction stacks, that is, the maximum groove depth; the second-level stepped groove vertically penetrates the third group of GaN/AlGaN heterojunction stacks.

Step 3. Plating the passivation layer: the inside of the stepped groove, the top of the stepped groove, and the top surface of the n -th group of GaN/AlGaN heterojunction stacks on both sides of the stepped groove are respectively coated with a dielectric film, and chemically and physically polished to form as shown in the figure. The passivation layer 9 with a flat top surface shown in 2c; wherein, the passivation layer located inside the stepped groove is called the stepped passivation layer 92 , and the rest of the passivation layers are called the top passivation layer 91 .

In the present invention, by adjusting the step width of the step passivation layer, that is, the present invention has a variable multi-channel layer with a non-uniform distribution, and the variable multi-channel layer includes multiple groups of AlGaN/GaN heterojunction stacks with different lengths. Therefore, a two-dimensional electron gas with a stepped distribution can be obtained, thereby modulating the electric field distribution of the device, reducing the electric field peak value at the gate electrode, making the electric field distribution uniform, avoiding premature breakdown of the device, and improving the withstand voltage performance of the device.

Step 4. Etch the electrode groove

As shown in FIG. 2d , the electrode trench includes a source electrode trench 101 , a drain electrode trench 121 and a gate electrode trench 111 .

The specific etching method of the electrode groove is as follows: the two ends of the top passivation layer on both sides of the stepped groove are respectively etched from top to bottom to the top surface of the n -th group of GaN/AlGaN heterojunction stacks to form the source electrode groove. and drain electrode groove; wherein, the source electrode groove is adjacent to the maximum groove depth of the stepped groove (that is, adjacent to the first step groove); the top passivation layer between the stepped groove and the source electrode groove is etched from top to bottom To the top surface of the n -th group of GaN/AlGaN heterojunction stacks, a gate electrode trench is formed, and one sidewall surface of the gate electrode trench and one sidewall surface of the stepped trench (preferably the sidewall surface of the first-level stepped trench) are located in the same vertical on flat surface.

Step 5. Preparation of source electrode and drain electrode: Evaporating or sputtering the source electrode multi-element alloy in the source electrode groove, evaporating or sputtering the drain electrode multi-element alloy in the drain electrode groove, and annealing respectively, then the source electrode and the leakage current are formed. pole.

The above-mentioned annealing method is preferably: annealing for 30 seconds at 850 degrees Celsius and a nitrogen atmosphere.

Step 6, preparing the gate electrode: the gate electrode multi-element alloy is evaporated or sputtered in the gate electrode groove, and after metal stripping, the gate electrode with Schottky contact is formed.

The above-mentioned source electrode, drain electrode and gate electrode are alloys of metals including but not limited to Ti, Al, Ni, Au and the like.

Comparing the device structure of the present invention with the general structure in the prior art, the device of the present invention can significantly improve the breakdown voltage of the device by about 245%, as shown in FIG. 3 .

In addition, the device of the present invention can effectively reduce the peak value of the electric field at the gate electrode, expand the width of the depletion region, and make the electric field distribution more uniform, as shown in FIG. 4 .

Further, the device of the present invention can effectively reduce the electric field peak value at the gate electrode, expand the width of the depletion region, make the electric field distribution more uniform, avoid premature breakdown of the device, and the average electric field between the gate electrode and the drain electrode is close to 2MV/cm, Specifically as shown in Figure 5.

The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above-mentioned embodiments. Within the scope of the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention. These equivalent transformations All belong to the protection scope of the present invention.

Claims (10)

1. A variable channel AlGaN/GaN HEMT structure is characterized in that: comprises a substrate layer, a buffer layer,nThe group GaN/AlGaN heterojunction lamination, a passivation layer, a gate electrode, a source electrode and a drain electrode; wherein,n≥2；

the buffer layer is epitaxially grown on the top of the substrate layer;

nthe group GaN/AlGaN heterojunction lamination is epitaxially grown on the top of the buffer layer from bottom to top in sequence, and is respectively a 1 st group GaN/AlGaN heterojunction lamination, a 2 nd group GaN/AlGaN heterojunction lamination, … … and a fourth group GaN/AlGaN heterojunction lamination from bottom to topnForming a GaN/AlGaN heterojunction stack;

each group of GaN/AlGaN heterojunction lamination layers comprise a GaN channel layer and an AlGaN barrier layer epitaxially grown on the GaN channel layer;

the passivation layer comprises a top passivation layer and a step passivation layer;

a top passivation layer is arranged onnForming a top portion of the GaN/AlGaN heterojunction stack;

the source electrode and the drain electrode are respectively embedded at two ends of the top passivation layer;

the gate electrode is embedded in the middle of the top passivation layer adjacent to the source electrode;

a stepped passivation layer embedded between the 2 nd GaN/AlGaN heterojunction stack and the second drain electrodenIn a GaN/AlGaN heterojunction stack; the step passivation layer is in an inverted step shape, and one end of the step passivation layer is aligned with the gate electrode;

two-dimensional electron gas in step distribution can be obtained by adjusting the step width of the step passivation layer, so that the electric field distribution of the device is modulated, the electric field peak value at the grid electrode is reduced, the electric field distribution is homogenized, premature breakdown of the device is avoided, the voltage resistance of the device is improved, the breakdown voltage of the device can be increased, and the amplitude is increased by 245%.

2. The variable channel AlGaN/GaN HEMT structure of claim 1, wherein: the charge density between the gate electrode and the drain electrode is adjusted by adjusting the step width of the step passivation layer.

3. The variable channel AlGaN/GaN HEMT structure of claim 1, wherein: the substrate layer is made of silicon, sapphire, gallium nitride or silicon carbide.

4. The variable channel AlGaN/GaN HEMT structure of claim 1, wherein: the buffer layer is made of GaN material with the thickness of 2-6 microns.

5. The variable channel AlGaN/GaN HEMT structure of claim 1, wherein: the GaN channel layer is made of GaN material with the thickness of 0.1-3 micrometers.

6. The variable channel AlGaN/GaN HEMT structure of claim 1, wherein: the AlGaN barrier layer comprises 0.1-0.3 parts of Al by molar composition; the AlGaN barrier layers are 15-30 nm thick.

7. A preparation method of a variable channel AlGaN/GaN HEMT structure is characterized by comprising the following steps: the method comprises the following steps:

step 1, preparing a gallium nitride multi-channel epitaxial wafer, wherein the specific preparation method comprises the following steps:

step 1A, epitaxially growing a buffer layer: cleaning the substrate layer and epitaxially growing a buffer layer containing a GaN material on the substrate layer;

step 1B, epitaxially growing a 1 st group of GaN/AlGaN heterojunction lamination: epitaxially growing a GaN channel layer and an AlGaN barrier layer on the buffer layer from bottom to top in sequence;

step 1C, epitaxial growthnGroup GaN/AlGaN heterojunction stacks: sequentially epitaxially growing a 2 nd group GaN/AlGaN heterojunction lamination to a 1 st group GaN/AlGaN heterojunction lamination from bottom to topnForming a GaN/AlGaN heterojunction lamination layer so as to form a gallium nitride multi-channel epitaxial wafer;

step 2, etching the stepped groove: in the 2 nd group GaN/AlGaN heterojunction stack to the 2 nd groupnEtching the middle parts of the GaN/AlGaN heterojunction lamination layers from top to bottom in sequence to form an inverted stepped groove;

step 3, plating a passivation layer: in the interior of the stepped groove, at the top of the stepped groove and at both sides of the stepped groovenRespectively plating dielectric films on the top surfaces of the GaN/AlGaN heterojunction lamination layers to form a passivation layer with a flat top surface; the passivation layer positioned in the step groove is called a step passivation layer, and the rest passivation layers are called top passivation layers;

step 4, etching the electrode groove: the electrode grooves comprise a source electrode groove, a drain electrode groove and a gate electrode groove; etching the two ends of the top passivation layer at the two sides of the stepped groove from top to bottom respectivelynForming a top surface of the GaN/AlGaN heterojunction lamination layer to form the source electrode groove and the drain electrode groove; the source electrode groove is adjacent to the maximum groove depth of the stepped groove; etching the top passivation layer between the stepped groove and the source electrode groove from top to bottomnForming a grid electrode groove by combining the top surface of the GaN/AlGaN heterojunction lamination, wherein one side wall surface of the grid electrode groove and one side wall surface of the stepped groove are positioned on the same vertical plane;

step 5, preparing a source electrode and a drain electrode: evaporating or sputtering source electrode multi-element alloy in a source electrode groove, evaporating or sputtering drain electrode multi-element alloy in a drain electrode groove, and respectively annealing to form a source electrode and a drain electrode;

step 6, preparing a gate electrode: a gate electrode is formed by depositing or sputtering a gate multicomponent alloy in the gate electrode groove.

8. The method of manufacturing a variable channel AlGaN/GaN HEMT structure according to claim 7, wherein: in the step 1, the method comprises the following steps of,n= 3; in the step 2, the stepped groove is a two-stage stepped groove which is a first-stage stepped groove and a second-stage stepped groove respectively; the first-stage stepped groove vertically penetrates through the 2 nd group of GaN/AlGaN heterojunction lamination and the 3 rd group of GaN/AlGaN heterojunction lamination; the second-stage step groove vertically penetrates through the 3 rd group of GaN/AlGaN heterojunction lamination layers.

9. The method of claim 7, wherein the variable channel AlGaN/GaN HEMT structure is prepared by: in step 3, the charge density between the gate electrode and the drain electrode in step 6 can be adjusted by adjusting the step width of the step passivation layer.

10. The method of claim 7, wherein the variable channel AlGaN/GaN HEMT structure is prepared by: in the step 5, the annealing mode is as follows: annealing was performed at 850 degrees celsius for 30 seconds in a nitrogen atmosphere.

Images