An AlGaN / GaN Schottky diode with a composite passivation layer and p-NiO embedded islands and a preparation method thereof

Abstract

This invention discloses an AlGaN / GaN Schottky diode with a composite passivation layer and p-NiO islands, and its fabrication method. It relates to semiconductor power devices, including a substrate layer, an epitaxial layer, a cathode, and an anode structure, arranged from bottom to top. The epitaxial layer includes a GaN buffer layer, a GaN channel layer, and an AlGaN barrier layer above the substrate layer. A two-dimensional electron gas is formed at the interface between the GaN channel layer and the AlGaN barrier layer. This invention aims to solve the problems of high reverse leakage current and low breakdown voltage in existing GaN-based SBDs. Its GaN-based heterojunction power diode has a novel structure, is easy to fabricate, and possesses high blocking voltage and extremely low leakage current.

Description

Technical Field

[0001] This invention relates to the field of semiconductor power device technology, specifically to an AlGaN / GaN Schottky diode with a composite passivation layer and p-NiO islands, and its fabrication method. Background Technology

[0002] Gallium nitride (GaN)-based Schottky diodes (SBDs) have great potential in high-efficiency power electronics conversion due to their wide bandgap, modified critical breakdown electric field, and high electron mobility. However, traditional GaN SBDs face the following technical bottlenecks:

[0003] 1. The contradiction between leakage current and turn-on voltage: In order to reduce the turn-on voltage, a low work function Schottky metal is required, but this will cause the interface electric field to concentrate under reverse bias, resulting in a severe image force barrier reduction effect and increasing the reverse leakage current.

[0004] 2. Limited breakdown voltage: The electric field spikes at the anode edge can easily cause the device to break down prematurely. Traditional field plate structures introduce huge parasitic capacitances while increasing voltage, which limits high-frequency performance.

[0005] Therefore, it does not meet the existing requirements. In response, we propose an AlGaN / GaN Schottky diode with a composite passivation layer and p-NiO islands and its fabrication method. Summary of the Invention

[0006] The purpose of this invention is to provide an AlGaN / GaN Schottky diode with a composite passivation layer and p-NiO islands and a method for fabricating the same, in order to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: an AlGaN / GaN Schottky diode having a composite passivation layer and p-NiO intercalation, comprising a substrate layer, an epitaxial layer, a cathode and an anode region structure, wherein the substrate layer, the epitaxial layer, the cathode and the anode region structure are arranged from bottom to top;

[0008] The epitaxial layer includes a GaN buffer layer, a GaN channel layer, and an AlGaN barrier layer located above the substrate layer. A two-dimensional electron gas is formed at the interface between the GaN channel layer and the AlGaN barrier layer.

[0009] The cathode is located on one side above the AlGaN barrier layer, forming a low-resistance ohmic contact with the two-dimensional electron gas.

[0010] The anode structure is located on the other side above the AlGaN barrier layer, and the anode structure includes an island array trench structure, p-NiO, a Schottky contact region, a first passivation dielectric layer HfO, a second passivation dielectric layer SiNx, and an anode. There are multiple island array trench structures, which are arranged at equal intervals in the AlGaN barrier layer below the anode. The multiple island array trench structures have the same width and depth, and all penetrate downward through the AlGaN barrier layer, exposing the bottom GaN channel layer.

[0011] Preferably, the p-NiO is an embedded p-type metal oxide layer that fills the island array trench structure. Its bottom is in direct contact with the GaN channel layer, and its sidewalls are in contact with the AlGaN barrier layer. The p-NiO and the bottom GaN channel layer form a heterojunction.

[0012] Preferably, an AlGaN barrier layer mesa is maintained between adjacent island array trench structures. The top of this mesa is in direct contact with the anode disposed above, forming a Schottky contact region. The width of the AlGaN barrier layer mesa is 0.5 μm to 2 μm, and the width of the island array trench structure is 1 μm to 3 μm.

[0013] Preferably, the first passivation dielectric layer HfO is located on the upper surface of the AlGaN barrier layer between the anode and the cathode, and has a thickness of 20nm~100nm. Specifically, the first passivation dielectric layer HfO extends from the cathode side boundary of the direct contact interface between the anode and the AlGaN barrier layer to the cathode sidewall, and has a first sidewall at the end near the anode side.

[0014] Preferably, the second passivation dielectric layer SiNx is located on the upper surface of the first passivation dielectric layer HfO, and has a thickness of 200nm~350nm. The end face of the second passivation dielectric layer SiNx near the cathode is also in direct contact with the sidewall of the cathode.

[0015] Preferably, the length of the second passivation dielectric layer SiNx extending from the cathode to the anode is less than that of the first passivation dielectric layer HfO, and the retraction distance is 0.5μm~2μm, thereby exposing part of the top surface and the first sidewall of the first passivation dielectric layer HfO on the side near the anode; the second passivation dielectric layer SiNx is provided with a second sidewall at the end near the anode side.

[0016] Preferably, the anode includes a bottom contact portion and a stepped field plate portion. The bottom contact portion completely covers and contacts the top surface of the p-NiO layer within the island array trench structure and the top surface of the adjacent AlGaN barrier layer mesa, and extends towards the cathode direction to abut against the first sidewall of the first passivation dielectric layer HfO.

[0017] Preferably, the stepped field plate portion is continuously attached to and covers the first exposed sidewall and part of the top surface of the first passivation dielectric layer HfO, as well as the second sidewall and part of the top surface near the anode side of the second passivation dielectric layer SiNx, starting from the first sidewall, thereby forming a composite stepped field plate structure extending towards the cathode direction.

[0018] A method for fabricating an AlGaN / GaN Schottky diode with a composite passivation layer and p-NiO islands includes the following steps:

[0019] Step 1: On the substrate, GaN buffer layer, GaN channel layer and AlGaN barrier layer are grown sequentially by MOCVD. The thickness of AlGaN barrier layer is nm. Two-dimensional electron gas (DEG) is spontaneously formed at the AlGaN-GaN interface. The substrate consists of GaN buffer layer, GaN channel layer, AlGaN barrier layer, cathode p-NiO first passivation dielectric layer, HfO second passivation dielectric layer, and SiNx anode.

[0020] Step 2: Define the active region of the device using inductively coupled plasma etching or ion implantation to achieve electrical isolation between devices;

[0021] Step 3: Define the cathode region using photolithography, then deposit metal using electron beam evaporation as the cathode, and then perform high-temperature rapid thermal annealing at 800℃~850℃ in a nitrogen atmosphere for 30s~60s to form a good ohmic contact.

[0022] Step 4: Define the array pattern of the anode region using photolithography, and etch the AlGaN barrier layer using ICP dry etching process to form an island-shaped array trench structure. The etching depth is controlled at 30±3nm to ensure penetration through the AlGaN barrier layer. The trench width is 2μm, and the mesa width between adjacent trenches is 1.5μm.

[0023] Step 5: After completing the trench etching, p-NiO is deposited on the whole wafer using magnetron sputtering. The specific conditions are: NiO target material is used, sputtering deposition is carried out at 300℃, and then excess NiO is removed by photolithography and dry etching to form p-NiO islands.

[0024] Step 6: A high-k dielectric layer HfO with a thickness of 50nm is deposited at 250℃~300℃ using ALD technology as the first passivation dielectric layer. A window is opened directly above the anode region using photolithography and dry etching to expose the p-NiO top and the unetched AlGaN mesa below. The window forms the first sidewall on the anode side.

[0025] Step 7: Deposit a SiNx passivation layer at 350℃ using PECVD as the second passivation dielectric layer with a thickness of 200nm. Then, perform photolithography to open a window again. This time, the window size is larger than the window size in the previous step. Its boundary near the anode side is recessed by 1μm towards the cathode to form a second sidewall, thereby exposing part of the top surface of the first passivation dielectric layer HfO and the first sidewall, forming a stepped structure.

[0026] Step 8: Photolithography defines the anode metal pattern. Electron beam evaporation is used to deposit metal as the anode. The anode metal fills the window, covers the p-NiO and AlGaN mesa, and climbs up to cover the first sidewall, the top surface of the first passivation dielectric layer exposed in the step, the second sidewall, and the top surface of the second passivation dielectric layer, forming a composite stepped field plate.

[0027] Preferably, the deposited metal in step 3 is Ti / Al / Ni / Au, and the thicknesses of Ti / Al / Ni / Au are 20nm / 150nm / 50nm / 50nm respectively;

[0028] The deposited metal in step 2 is Ni / Au, with Ni / Au thicknesses of 50 nm and 150 nm, respectively.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] 1. This invention adopts an island array trench p-NiO structure. When forward biased, the current is conducted through the unetched mesa region (metal / AlGaN interface), maintaining the advantage of low turn-on voltage of Schottky diode. When reverse biased, the embedded p-NiO forms a heterojunction with the bottom GaN and the sidewall AlGaN. As the reverse bias increases, the depletion region expands laterally from both sides of the trench to the middle mesa region, quickly "pinching off" the two-dimensional electron gas channel, thereby completely blocking the leakage path.

[0031] 2. This invention extends the trench-shaped p-NiO / GaN heterojunction to below the two-dimensional electron gas 2DEG, which can effectively bear most of the reverse voltage drop. It physically isolates the fragile Schottky contact interface in the mesa region from the high electric field of the bottom layer. Combined with the HfO2 / SiNx composite stepped field plate on the top, it realizes the combination of internal trench body electric field modulation and external surface electric field modulation, which greatly improves the voltage withstand capability of the device.

[0032] 3. This invention uses magnetron sputtering to deposit p-NiO to fill trenches, avoiding the high-temperature process of p-GaN secondary epitaxy. This effectively avoids the problem of stress relaxation at the AlGaN-GaN interface caused by high temperature, which in turn leads to severe thermal degradation of 2DEG. In addition, the sputtered p-NiO has good physical compatibility with the trench mesa, which can form a dense heterojunction interface, significantly reducing manufacturing difficulty and cost while improving the electrical performance of the device. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the AlGaN / GaN epitaxial structure of the present invention;

[0034] Figure 2 This is a schematic diagram of the cathode fabricated on the surface of the AlGaN layer according to the present invention;

[0035] Figure 3 This is a schematic diagram of the island-shaped trench array etched according to the present invention;

[0036] Figure 4 This is a schematic diagram showing the p-NiO trench filling process after the present invention is completed;

[0037] Figure 5 This is a schematic diagram of the first dielectric passivation layer after deposition according to the present invention;

[0038] Figure 6 This is a schematic diagram of the second dielectric passivation layer after deposition according to the present invention;

[0039] Figure 7 This is a schematic diagram of the Schottky electrode fabricated in the anode region according to the present invention.

[0040] In the figure: 1. Substrate layer; 2. GaN buffer layer; 3. GaN channel layer; 4. AlGaN barrier layer; 5. Cathode; 6. p-NiO; 7. First passivation dielectric layer HfO2; 8. Second passivation dielectric layer SiNx; 9. Anode. Detailed Implementation

[0041] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0042] Please see Figures 1 to 7 One embodiment provided by the present invention:

[0043] An AlGaN / GaN Schottky diode with a composite passivation layer and p-NiO islands includes a substrate layer 1, an epitaxial layer, a cathode 5, and an anode region structure, wherein the substrate layer 1, the epitaxial layer, the cathode 5, and the anode region structure are arranged from bottom to top.

[0044] The epitaxial layer includes a GaN buffer layer 2, a GaN channel layer 3, and an AlGaN barrier layer 4 located above the substrate layer 1. A two-dimensional electron gas (2DEG) is formed at the interface between the GaN channel layer 3 and the AlGaN barrier layer 4.

[0045] The cathode 5 is located on one side above the AlGaN barrier layer 4, forming a low-resistance ohmic contact with the two-dimensional electron gas.

[0046] The anode structure is located on the other side above the AlGaN barrier layer 4, and the anode structure includes an island array trench structure, p-NiO6, a Schottky contact region, a first passivation dielectric layer HfO27, a second passivation dielectric layer SiNx8, and an anode 9. There are multiple island array trench structures, which are arranged at equal intervals in the AlGaN barrier layer 4 below the anode 9. The multiple island array trench structures have the same width and depth, and all penetrate downward through the AlGaN barrier layer 4, exposing the bottom GaN channel layer 3.

[0047] p-NiO6 is an embedded p-type metal oxide layer that fills the island array trench structure. Its bottom is in direct contact with the GaN channel layer 3, and its sidewalls are in contact with the AlGaN barrier layer 4. p-NiO6 and the bottom GaN channel layer 3 form a heterojunction.

[0048] Employing an island-array trench p-NiO structure, during forward conduction, current is conducted through the unetched mesa region (metal / AlGaN interface), maintaining the advantage of low turn-on voltage of Schottky diodes. During reverse blocking, the embedded p-NiO forms a heterojunction with the bottom GaN and the sidewall AlGaN. As the reverse bias increases, the depletion region expands laterally from both sides of the trench towards the middle mesa region, rapidly "pinching off" the two-dimensional electron gas channel, thereby completely blocking the leakage path.

[0049] The trench-shaped p-NiO / GaN heterojunction extends below the two-dimensional electron gas 2DEG, which can effectively bear most of the reverse voltage drop and physically isolate the fragile Schottky contact interface in the mesa region from the high electric field of the bottom layer. Combined with the HfO2 / SiNx composite stepped field plate on the top, it realizes the combination of internal trench body electric field modulation and external surface electric field modulation, which greatly improves the breakdown voltage of the device.

[0050] AlGaN barrier layer 4 mesa is retained between adjacent island array trench structures. The top of the mesa is in direct contact with the anode 9 set above, forming a Schottky contact region. The width of the AlGaN barrier layer 4 mesa is 0.5μm~2μm, and the width of the island array trench structure is 1μm~3μm.

[0051] The first passivation dielectric layer HfO27 is located on the upper surface of the AlGaN barrier layer between the anode and the cathode, with a thickness of 20nm~100nm. Specifically, the first passivation dielectric layer HfO27 extends from the side boundary of the direct contact interface between the anode 9 and the AlGaN barrier layer 4 near the cathode 5, all the way to the sidewall of the cathode 5, and the end near the anode 9 is provided with a first sidewall.

[0052] The second passivation dielectric layer SiNx8 is located on the upper surface of the first passivation dielectric layer HfO27, with a thickness of 200nm~350nm. The end face of the second passivation dielectric layer SiNx8 near the cathode 5 is also in direct contact with the sidewall of the cathode 5.

[0053] Furthermore, the length of the second passivation dielectric layer SiNx8 extending from the cathode 5 to the anode 9 is less than that of the first passivation dielectric layer HfO27, with a retraction distance of 0.5μm~2μm, thereby exposing part of the top surface and the first sidewall of the first passivation dielectric layer HfO27 on the side near the anode 9; the second passivation dielectric layer SiNx8 is provided with a second sidewall at the end near the anode 9.

[0054] The anode 9 includes a bottom contact portion and a stepped field plate portion. The bottom contact portion completely covers and contacts the top surface of p-NiO6 in the island array trench structure and the top surface of the adjacent AlGaN barrier layer 4 mesa, and extends towards the cathode 5 to abut against the first sidewall of the first passivation dielectric layer HfO27.

[0055] The stepped field plate portion is continuously attached to and covers the first sidewall and part of the top surface of the first passivation dielectric layer HfO27 exposed from the first sidewall, as well as the second sidewall and part of the top surface of the second passivation dielectric layer SiNx8 near the anode 9, thereby forming a composite stepped field plate structure extending toward the cathode 5.

[0056] The above-mentioned method for fabricating AlGaN / GaN Schottky diodes with composite passivation layers and p-NiO islands includes the following steps:

[0057] Step 1: On substrate 1, GaN buffer layer 2, GaN channel layer 3 and AlGaN barrier layer 4 are grown sequentially by MOCVD, wherein the thickness of AlGaN barrier layer 4 is 25nm, and a two-dimensional electron gas 2DEG is spontaneously formed at the AlGaN-GaN interface; Substrate 1 GaN buffer layer 2 GaN channel layer 3 AlGaN barrier layer 4 Cathode 5p-NiO 6 First passivation dielectric layer HfO2 7 Second passivation dielectric layer SiNx 8 Anode 9;

[0058] Step 2: Define the active region of the device using inductively coupled plasma (ICP) etching or ion implantation to achieve electrical isolation between devices;

[0059] Step 3: Define the cathode region using photolithography, and then deposit metal Ti / Al / Ni / Au (20nm / 150nm / 50nm / 50nm) using electron beam evaporation as cathode 5. Subsequently, perform high-temperature rapid thermal annealing at 800℃~850℃ in a nitrogen atmosphere for 30s~60s to form good ohmic contact.

[0060] Step 4: Define the array pattern of the anode region using photolithography, and etch the AlGaN barrier layer 4 using ICP dry etching process to form an island-shaped array trench structure. The etching depth is controlled at 30nm±3nm to ensure penetration through the AlGaN barrier layer 4. The trench width is 2μm, and the mesa width between adjacent trenches is 1.5μm.

[0061] Step 5: After completing the trench etching, p-NiO6 is deposited on the whole wafer using magnetron sputtering. The specific conditions are: NiO target material is used, sputtering deposition is carried out at 300℃, and then excess NiO is removed by photolithography and dry etching to form p-NiO islands.

[0062] The magnetron sputtering process is used to deposit p-NiO filling trenches, which avoids the high-temperature process of p-GaN secondary epitaxy. This effectively avoids the problem of stress relaxation at the AlGaN-GaN interface caused by high temperature, which in turn causes severe thermal degradation of 2DEG.

[0063] In addition, sputtered p-NiO has good physical compatibility with trench mesa, which can form a dense heterojunction interface, significantly reducing manufacturing difficulty and cost while improving the electrical performance of the device.

[0064] Step 6: A high-k dielectric layer HfO2 with a thickness of 50nm is deposited at 250℃~300℃ using ALD technology as the first passivation dielectric layer. A window is opened directly above the anode region using photolithography and dry etching to expose the p-NiO top and the unetched AlGaN mesa below. The window forms the first sidewall on the anode side.

[0065] Step 7: Deposit a SiNx passivation layer at 350℃ using PECVD as the second passivation dielectric layer 8 with a thickness of 200nm. Then, perform photolithography to open a window again. This time, the window size is larger than the window size in Step 6. Its boundary near the anode side is recessed by 1μm towards the cathode to form a second sidewall, thereby exposing part of the top surface and the first sidewall of the first passivation dielectric layer HfO27, forming a stepped structure.

[0066] Step 8: Photolithography defines the anode metal pattern. Electron beam evaporation is used to deposit Ni / Au (50nm / 150nm) metal as the anode 9. The anode metal fills the window, covering the p-NiO6 and AlGaN mesa, and climbs up to cover the first sidewall, the top surface of the first passivation dielectric layer exposed in step 7, the second sidewall, and the top surface of the second passivation dielectric layer to form a composite stepped field plate.

[0067] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. An AlGaN / GaN Schottky diode with a composite passivation layer and p-NiO islands and its fabrication method, comprising a substrate layer (1), a GaN buffer layer (2), a GaN channel layer (3), an AlGaN barrier layer (4), a cathode (5), p-NiO (6), a first passivation dielectric layer HfO2 (7), a second passivation dielectric layer SiNx (8), an anode (9), an epitaxial layer, a cathode (5), and an anode region structure, characterized in that: The substrate layer (1), epitaxial layer, cathode (5) and anode region structure are arranged from bottom to top; The epitaxial layer includes a GaN buffer layer (2) above the substrate layer (1), a GaN channel layer (3) and an AlGaN barrier layer (4) above the GaN channel layer (3), and a two-dimensional electron gas is formed at the interface between the GaN channel layer (3) and the AlGaN barrier layer (4). The cathode (5) is located on one side above the AlGaN barrier layer (4) and forms a low-resistance ohmic contact with the two-dimensional electron gas; The anode structure is located on the other side above the AlGaN barrier layer (4), and the anode structure includes an island array trench structure, p-NiO (6), a Schottky contact region, a first passivation dielectric layer HfO2 (7), a second passivation dielectric layer SiNx (8) and an anode (9). There are multiple island array trench structures, which are arranged at equal intervals in the AlGaN barrier layer (4) below the anode (9). The multiple island array trench structures have the same width and depth, and all penetrate downward through the AlGaN barrier layer (4), exposing the bottom GaN channel layer (3).

2. The AlGaN / GaN Schottky diode with a composite passivation layer and p-NiO islands as described in claim 1, and its fabrication method thereof, characterized in that: The p-NiO (6) is an embedded p-type metal oxide layer that fills the island array trench structure. Its bottom is in direct contact with the GaN channel layer (3), and its sidewall is in contact with the AlGaN barrier layer (4). The p-NiO (6) and the bottom GaN channel layer (3) form a heterojunction.

3. The AlGaN / GaN Schottky diode with a composite passivation layer and p-NiO islands as described in claim 2, and its fabrication method thereof, characterized in that: An AlGaN barrier layer (4) mesa is retained between adjacent island array trench structures. The top of the mesa is in direct contact with the anode (9) above it to form a Schottky contact region. The width of the AlGaN barrier layer (4) mesa is 0.5μm~2μm, and the width of the island array trench structure is 1μm~3μm.

4. The AlGaN / GaN Schottky diode with a composite passivation layer and p-NiO islands as described in claim 3, and its fabrication method thereof, characterized in that: The first passivation dielectric layer HfO2 (7) is located on the upper surface of the AlGaN barrier layer between the anode and the cathode, with a thickness of 20nm~100nm. Specifically, the first passivation dielectric layer HfO2 (7) extends from the side boundary of the direct contact interface between the anode (9) and the AlGaN barrier layer (4) near the cathode (5) to the side wall of the cathode (5), and its end near the anode (9) is provided with a first side wall.

5. The AlGaN / GaN Schottky diode with a composite passivation layer and p-NiO islands as described in claim 4, and its fabrication method thereof, characterized in that: The second passivation dielectric layer SiNx (8) is located on the upper surface of the first passivation dielectric layer HfO2 (7) and has a thickness of 200nm~350nm. The end face of the second passivation dielectric layer SiNx (8) near the cathode (5) is also in direct contact with the sidewall of the cathode (5).

6. The AlGaN / GaN Schottky diode with a composite passivation layer and p-NiO islands as described in claim 5, and its fabrication method thereof, characterized in that: The second passivation dielectric layer SiNx (8) extends from the cathode (5) to the anode (9) in a length shorter than the first passivation dielectric layer HfO2 (7), with a retraction distance of 0.5μm~2μm, thereby exposing part of the top surface and the first sidewall of the first passivation dielectric layer HfO2 (7) on the side near the anode (9); the second passivation dielectric layer SiNx (8) has a second sidewall at one end near the anode (9).

7. An AlGaN / GaN Schottky diode with a composite passivation layer and p-NiO islands as described in claim 6, and its fabrication method thereof, characterized in that: The anode (9) includes a bottom contact portion and a stepped field plate portion. The bottom contact portion completely covers and contacts the top surface of the p-NiO (6) in the island array trench structure and the top surface of the adjacent AlGaN barrier layer (4) platform, and extends towards the cathode (5) to abut against the first sidewall of the first passivation dielectric layer HfO2 (7).

8. An AlGaN / GaN Schottky diode with a composite passivation layer and p-NiO islands as described in claim 7, characterized in that: The stepped field plate portion is continuously attached to and covers the first exposed sidewall and part of the top surface of the first passivation dielectric layer HfO2 (7), as well as the second sidewall and part of the top surface near the anode (9) of the second passivation dielectric layer SiNx (8), thereby forming a composite stepped field plate structure extending toward the cathode (5).

9. A method for fabricating an AlGaN / GaN Schottky diode with a composite passivation layer and p-NiO islands according to claim 8, characterized in that, Includes the following steps: Step 1: GaN buffer layer (2), GaN channel layer (3) and AlGaN barrier layer (4) are grown sequentially on substrate layer (1) by MOCVD, wherein the thickness of AlGaN barrier layer (4) is 25nm, and a two-dimensional electron gas is spontaneously formed at the interface between AlGaN and GaN. Step 2: Define the active region of the device using inductively coupled plasma (ICP) etching or ion implantation to achieve electrical isolation between devices; Step 3: Define the cathode region using photolithography, and then deposit metal using electron beam evaporation as the cathode (5). Then, perform high-temperature rapid thermal annealing at 800℃~850℃ in a nitrogen atmosphere for 30s~60s to form a good ohmic contact. Step 4: Define the array pattern of the anode region using photolithography, and etch the AlGaN barrier layer (4) using ICP dry etching process to form an island array trench structure. The etching depth is controlled at 30±3nm to ensure penetration through the AlGaN barrier layer (4). The trench width is 2μm, and the mesa width between adjacent trenches is 1.5μm. Step 5: After completing the trench etching, p-NiO is deposited on the whole wafer using magnetron sputtering (6). The specific conditions are: NiO target material is used, sputtering deposition is performed at 300℃, and then excess NiO is removed by photolithography and dry etching to form p-NiO islands. Step 6: A high-k dielectric layer HfO2 with a thickness of 50nm is deposited at 250℃~300℃ using ALD technology as the first passivation dielectric layer. A window is opened directly above the anode region using photolithography and dry etching to expose the p-NiO top and the unetched AlGaN mesa below. The window forms the first sidewall on the anode side. Step 7: Deposit a SiNx passivation layer at 350℃ using PECVD as the second passivation dielectric layer 8 with a thickness of 200nm. Then, perform photolithography to open a window again. This time, the window size is larger than the window size in Step 6. Its boundary near the anode side is recessed by 1μm towards the cathode to form a second sidewall, thereby exposing part of the top surface of the first passivation dielectric layer HfO2 (7) and the first sidewall, forming a stepped structure. Step 8: Photolithography defines the anode metal pattern. Electron beam evaporation is used to deposit metal as the anode 9. The anode metal fills the window, covers the p-NiO (6) and AlGaN mesa, and climbs up to cover the first sidewall, the top surface of the first passivation dielectric layer exposed in step 7, the second sidewall and the top surface of the second passivation dielectric layer, forming a composite stepped field plate.

10. The method for fabricating an AlGaN / GaN Schottky diode with a composite passivation layer and p-NiO islands according to claim 9, characterized in that: The deposited metal in step 3 is Ti / Al / Ni / Au, and the thicknesses of Ti / Al / Ni / Au are 20nm / 150nm / 50nm / 50nm respectively; The deposited metal in step 2 is Ni / Au, with Ni / Au thicknesses of 50 nm and 150 nm, respectively.

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