N-polarity GaN / AlGaN-based rectifier and its manufacturing method

Abstract

The present invention discloses an N-polarity GaN / AlGaN-based rectifier and a preparation method thereof. The rectifier includes a rectifier epitaxial wafer and ohmic contact electrodes, a Si3N4 passivation layer, and Schottky contact electrodes disposed on the rectifier epitaxial wafer; the rectifier epitaxial wafer includes an AlN buffer layer, a dual SiN insertion layer structure, an undoped AlGaN barrier layer, and an undoped GaN channel layer sequentially grown on a silicon carbide substrate. The ohmic contact electrodes and the Si3N4 passivation layer are both disposed on the undoped GaN channel layer. Among them, the dual SiN insertion layer structure includes a lower SiN insertion layer, an AlGaN buffer layer, and an upper SiN insertion layer sequentially grown on the AlN buffer layer. By using an N-polarity GaN / AlGaN heterojunction epitaxial wafer to prepare the rectifier and designing a dual SiN insertion layer structure, the present invention can realize a high-performance rectifier with a low turn-on voltage and a high cut-off frequency.

Description

Technical Field

[0001] The present invention relates to the technical field of rectifiers, and particularly relates to an N-polarity GaN / AlGaN-based rectifier and a preparation method thereof. Background Art

[0002] Radio frequency rectifiers are core devices in space wireless energy transmission systems and have extensive applications in military and civilian fields such as satellite systems, aerospace vehicles, and household appliances. However, traditional Si-based devices face problems such as low breakdown field strength, large reverse leakage current, low thermal conductivity, and poor performance stability. Group III nitrides represented by GaN have characteristics such as a large bandgap width, high breakdown voltage, and high electron saturation velocity, and can generate a two-dimensional electron gas with high density and high mobility in the heterojunction under the action of the polarization effect, promising to achieve high-performance radio frequency rectifiers. However, problems such as insufficient threshold of the two-dimensional electron gas for traditional Ga-polarity GaN and difficulty in growing high-quality GaN heterojunctions have restricted the development of GaN-based high-frequency rectifiers. N-polarity GaN has better threshold of the two-dimensional electron gas and an opposite built-in electric field strength, having natural advantages in preparing rectifier devices. However, it is difficult to prepare N-polarity GaN thin films, and there is still a gap in crystal quality compared with Ga-polarity. On the one hand, surface defects of nitrides can trap electrons as traps, resulting in a decrease in the concentration of the two-dimensional electron gas at the heterojunction interface; on the other hand, aggregated dislocations can serve as leakage channels of the device, reducing the stability and reliability of the rectifier. Summary of the Invention

[0003] In order to solve the above deficiencies of the prior art, the present invention provides an N-polarity GaN / AlGaN-based rectifier and a preparation method thereof, which can achieve a high-performance rectifier with a low turn-on voltage and a high cut-off frequency.

[0004] The first object of the present invention is to provide an N-polarity GaN / AlGaN-based rectifier.

[0005] The second object of the present invention is to provide a preparation method of an N-polarity GaN / AlGaN-based rectifier.

[0006] The first object of the present invention can be achieved by adopting the following technical solutions:

[0007] An N-polarity GaN / AlGaN-based rectifier, comprising a rectifier epitaxial wafer and ohmic contact electrodes, a Si3N4 passivation layer, and Schottky contact electrodes disposed on the rectifier epitaxial wafer; the rectifier epitaxial wafer includes an AlN buffer layer, a dual SiN insertion layer structure, an undoped AlGaN barrier layer, and an undoped GaN channel layer sequentially grown on a silicon carbide substrate, and the ohmic contact electrodes and the Si3N4 passivation layer are both disposed on the undoped GaN channel layer, wherein the dual SiN insertion layer structure includes a lower SiN insertion layer, an AlGaN buffer layer, and an upper SiN insertion layer sequentially grown on the AlN buffer layer.

[0008] Further, the Al component of the AlGaN buffer layer is greater than the Al component in the undoped AlGaN barrier layer.

[0009] Further, the ohmic contact electrodes are prepared by sequentially evaporating ohmic contact electrode metals Ti / Al / Ni / Au, and the thickness is 200 - 300 nm.

[0010] Further, the Schottky contact electrodes are prepared by sequentially evaporating Schottky contact electrode metals Ni / Au;

[0011] The Schottky contact electrodes penetrate into the undoped GaN channel layer by etching and partially extend to the surface of the Si3N4 passivation layer, and the etching depth is 180 - 200 nm.

[0012] Further, the distance between the ohmic contact electrodes and the Schottky contact electrodes is 5 - 9 μm.

[0013] Further, the AlN buffer layer, the AlGaN buffer layer, the undoped AlGaN barrier layer, and the undoped GaN channel layer in the rectifier epitaxial wafer are all N-polarity and are all grown along the [000-1] direction.

[0014] The second object of the present invention can be achieved by adopting the following technical solutions:

[0015] A preparation method of an N-polarity GaN / AlGaN-based rectifier, the method comprising:

[0016] Growing an AlN buffer layer, a dual SiN insertion layer structure, an undoped AlGaN barrier layer, and an undoped GaN channel layer sequentially on a silicon carbide substrate to obtain a rectifier epitaxial wafer; wherein the dual SiN insertion layer structure includes a lower SiN insertion layer, an AlGaN buffer layer, and an upper SiN insertion layer sequentially grown on the AlN buffer layer; the deposition times of the lower SiN insertion layer and the upper SiN insertion layer are 30 - 50 s and 160 - 180 s respectively;

[0017] Pretreat the rectifier epitaxial wafer, perform photolithography on the pretreated rectifier epitaxial wafer, and obtain an ohmic electrode pattern on the undoped GaN channel layer;

[0018] Put the rectifier epitaxial wafer with the ohmic electrode pattern into an electron beam evaporation device, and sequentially evaporate the ohmic contact electrode metal to obtain an ohmic electrode;

[0019] Remove the photoresist on the surface of the rectifier epitaxial wafer with the ohmic electrode, and use the method of plasma enhanced chemical vapor deposition to deposit a Si3N4 passivation layer on the undoped GaN channel layer of the rectifier epitaxial wafer with the ohmic electrode;

[0020] Perform mask alignment, perform photolithography on the rectifier epitaxial wafer with the Si3N4 passivation layer, obtain a Schottky electrode pattern on the Si3N4 passivation layer, perform wet etching, etch off the excess passivation layer, and remove the photoresist on the surface of the rectifier epitaxial wafer;

[0021] Use the wet etching method to etch a Schottky electrode groove from the surface of the epitaxial wafer with the Schottky electrode pattern on the Si3N4 passivation layer, and the Schottky electrode groove penetrates to the surface of the undoped GaN channel layer and extends to the surface of the Si3N4 passivation layer;

[0022] Put the rectifier epitaxial wafer with the Schottky electrode groove into an electron beam evaporation device, and sequentially evaporate the Schottky contact electrode metal to obtain a Schottky electrode;

[0023] Remove the photoresist on the surface of the rectifier epitaxial wafer with the Schottky electrode, perform wire bonding and packaging to obtain an N-polarity GaN / AlGaN-based rectifier.

[0024] Furthermore, the Al component of the AlGaN buffer layer is greater than the Al component in the undoped AlGaN barrier layer.

[0025] Furthermore, the ohmic contact electrode is obtained by sequentially evaporating the ohmic contact electrode metals Ti / Al / Ni / Au;

[0026] The Schottky contact electrode is obtained by sequentially evaporating the Schottky contact electrode metals Ni / Au, and the distance between the electrode edge and the edge of the adjacent etching groove is 0.8 - 1 μm.

[0027] Furthermore, the AlN buffer layer, the AlGaN buffer layer, the undoped AlGaN barrier layer, and the undoped GaN channel layer in the rectifier epitaxial wafer are all N-polarity and all grow along the [000-1] direction.

[0028] The present invention has the following beneficial effects compared with the prior art:

[0029] 1. The present invention uses an N-polar GaN / AlGaN heterojunction epitaxial wafer to fabricate a rectifier, which has the following advantages compared with the traditional Ga-polar GaN / AlGaN heterojunction: (1) The N-polar AlGaN layer serves as a natural back barrier, which can enhance the confinement of the two-dimensional electron gas at the GaN / AlGaN heterojunction interface and improve the breakdown voltage of the device; (2) The undoped GaN channel layer is above the undoped AlGaN barrier layer, improving the forward conduction characteristics (reducing the forward turn-on voltage). Due to the above advantages, the rectifier has good rectification characteristics. At the same time, the ohmic contact electrode metal is directly connected to the top undoped GaN channel layer, enabling the formation of a good ohmic contact.

[0030] 2. The present invention designs a dual SiN insertion layer structure to improve the performance of the device. On the one hand, by adjusting the strain of the undoped AlGaN, the quality of the AlGaN / GaN heterojunction is improved, and the concentration of the two-dimensional electron gas is increased; on the other hand, the dual SiN insertion layer reduces the threading dislocations serving as leakage channels by changing the growth mode of AlGaN twice in succession, improving the stability of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0032] Figure 1 It is a schematic structural diagram of an N-polar GaN / AlGaN-based rectifier according to an embodiment of the present invention.

[0033] Figure 2 It is an optical microscope image of the electrodes of an N-polar GaN / AlGaN-based rectifier according to an embodiment of the present invention.

[0034] Figure 3 It is an I-V curve of an N-polar GaN / AlGaN-based rectifier prepared in Example 1 of the present invention.

[0035] Figure 4 It is an I-V curve of an N-polar GaN / AlGaN-based rectifier prepared in Example 4 of the present invention.

[0036] Figure 1 Wherein:

[0037] 1 - Silicon carbide substrate, 2 - N-polar AlN buffer layer, 3 - Dual SiN insertion layer structure, 4 - N-polar undoped AlGaN barrier layer, 5 - N-polar undoped GaN channel layer, 6 - Ohmic electrode, 7 - Si3N4 layer, 8 - Schottky electrode. Detailed implementation mode

[0038] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts fall within the scope of protection of the present invention. It should be understood that the specific embodiments described are only used to explain the present application and are not used to limit the present application.

[0039] Embodiment 1:

[0040] This embodiment provides a method for preparing an N-polar GaN / AlGaN-based rectifier, including the following steps:

[0041] (1) As shown in Figure 1 , grow an AlN buffer layer 2, a dual SiN insertion layer structure 3, an undoped AlGaN barrier layer 4, and an undoped GaN channel layer 5 on a silicon carbide substrate 1 in sequence to obtain a rectifier epitaxial wafer;

[0042] Among them, the preparation of the dual SiN insertion layer structure includes growing a lower SiN insertion layer, an AlGaN buffer layer, and an upper SiN insertion layer on the AlN buffer layer in sequence. The deposition times of the lower SiN insertion layer and the upper SiN insertion layer are 30 - 50 s and 160 - 180 s respectively;

[0043] In order to relieve lattice mismatch and release stress, the Al component of the AlGaN buffer layer is greater than the Al component in the undoped AlGaN barrier layer;

[0044] The AlN buffer layer, AlGaN buffer layer, undoped AlGaN barrier layer, and undoped GaN channel layer in the rectifier epitaxial wafer are all N-polar and grow along the [000-1] direction;

[0045] (2) Pretreat the obtained rectifier epitaxial wafer: Place the rectifier epitaxial wafer in acetone and ethanol respectively for ultrasonic cleaning, and then dry it with high-purity nitrogen;

[0046] (3) Perform photolithography on the pretreated rectifier epitaxial wafer to obtain an ohmic electrode pattern on the undoped GaN channel layer;

[0047] (4) Fabricate ohmic electrodes: Place the rectifier epitaxial wafer obtained in step (3) into an electron beam evaporation equipment, and sequentially deposit ohmic contact electrode metals Ti / Al / Ni / Au to obtain ohmic electrodes 6;

[0048] (5) Remove the photoresist on the surface of the rectifier epitaxial wafer obtained in step (4): Immerse the rectifier epitaxial wafer obtained in step (4) in a stripping solution for soaking, then place it successively in acetone and ethanol for ultrasonic treatment and dry it with high-purity nitrogen;

[0049] (6) Fabricate a passivation layer: Deposit a layer of Si3N4 passivation layer 7 on the undoped GaN channel layer of the rectifier epitaxial wafer obtained in step (5);

[0050] (6) Align through a mask and use a method similar to that in step (3) to obtain a Schottky electrode pattern, use a wet etching method to etch away the exposed passivation layer 7, and then remove the photoresist using the process in step (5);

[0051] (7) Use a wet etching method to etch a Schottky electrode groove on the surface of the epitaxial wafer obtained in step (5) from the Si3N4 passivation layer surface. The Schottky electrode groove penetrates to the surface of the undoped GaN channel layer and extends to the Si3N4 passivation layer surface; wherein, the etching depth of the Schottky contact electrode is 180 - 200 nm, and the distance between the Schottky contact electrode and the ohmic contact electrode is 5 - 9 μm;

[0052] (8) Place the rectifier epitaxial wafer etched with the Schottky electrode groove into an electron beam evaporation equipment, and sequentially deposit Schottky contact electrode metals Ni / Au to obtain Schottky electrodes 8. The radius of the Schottky contact electrode is 150 μm; The top view of the fabricated rectifier electrode structure is as Figure 2 shown;

[0053] (9) Remove the photoresist on the surface of the rectifier epitaxial wafer obtained in step (8), perform wire bonding and packaging to fabricate an N-polarity GaN / AlGaN-based rectifier.

[0054] As Figure 1 shown, the N-polarity GaN / AlGaN-based rectifier fabricated in this embodiment includes a rectifier epitaxial wafer and ohmic contact electrodes, a Si3N4 passivation layer, and Schottky contact electrodes provided on the rectifier epitaxial wafer; The rectifier epitaxial wafer includes an AlN buffer layer, a dual SiN insertion layer structure, an undoped AlGaN barrier layer, and an undoped GaN channel layer grown successively on a silicon carbide substrate. The ohmic contact electrodes and the Si3N4 passivation layer are both provided on the undoped GaN channel layer, where:

[0055] The dual SiN insertion layer structure includes a lower SiN insertion layer, an AlGaN buffer layer, and an upper SiN insertion layer that are sequentially grown on the AlN buffer layer. The Al component of the AlGaN buffer layer is greater than that of the undoped AlGaN barrier layer;

[0056] In the rectifier epitaxial wafer, the thicknesses of the AlN buffer layer, the dual SiN insertion layer structure, the undoped AlGaN barrier layer, and the undoped GaN channel layer are 160 - 180 nm, 500 - 600 nm, 300 - 320 nm, and 25 - 40 nm, respectively;

[0057] The thicknesses of the Si3N4 passivation layer and the ohmic contact electrode are 120 - 160 nm and 200 - 300 nm, respectively.

[0058] As Figure 3 shown, the GaN / AlGaN - based rectifier prepared in this embodiment has a lower turn - on voltage and a higher reverse breakdown voltage. It has good forward conduction characteristics and better rectification performance. Figure 3 The current trend curve is applicable to all embodiments of the present invention, including but not limited to the illustrated embodiments.

[0059] Example 2:

[0060] This embodiment provides a method for preparing an N - polar GaN / AlGaN - based rectifier, which specifically includes:

[0061] (1) As Figure 1 shown, a 160 - nm - thick N - polar AlN buffer layer 2, a 500 - nm - thick dual SiN insertion layer structure 3, a 300 - nm - thick undoped N - polar AlGaN barrier layer 4, and a 25 - nm - thick undoped N - polar GaN layer 5 are sequentially grown on the silicon carbide substrate 1 to obtain a rectifier epitaxial wafer;

[0062] Among them, the growth process of the dual SiN insertion layer structure 3 is as follows: the lower SiN insertion layer is grown on the N - polar AlN buffer layer for 50 s, the AlGaN buffer layer is grown on the lower SiN insertion layer, and then the upper SiN insertion layer is grown on the AlGaN buffer layer for 160 s; the Al component of the AlGaN buffer layer is greater than that of the undoped AlGaN barrier layer;

[0063] (2) Pretreat the obtained rectifier epitaxial wafer: place the rectifier epitaxial wafer obtained in step (1) in acetone and ultrasonically treat it for 3 min, then dry it with high - purity nitrogen, and then place it in ethanol and ultrasonically treat it for 3 min and dry it with high - purity nitrogen;

[0064] (3) Lithography is performed on the rectifier epitaxial wafer obtained in step (2): An appropriate amount of photoresist with the model RZJ304 is dropped on the surface of the rectifier epitaxial wafer and spin-coated in a spin coater for 40 s. The rectifier epitaxial wafer coated with photoresist is pre-baked at 95 °C for 45 s. Then, the rectifier epitaxial wafer is exposed for 2 s using a lithography machine to obtain an ohmic electrode pattern. Finally, the rectifier epitaxial wafer is immersed in a developer and cleaned after 60 s;

[0065] (4) The rectifier epitaxial wafer obtained in step (3) is placed in an electron beam evaporation equipment, evacuated to 1×10 -5 Pa, and successively evaporated with ohmic contact electrode metals Ti / Al / Ni / Au with a thickness of 200 nm. Then, it is annealed at 850 °C for 30 s to obtain ohmic electrode 6;

[0066] (5) Remove the photoresist on the surface of the rectifier epitaxial wafer obtained in step (4): Immerse the rectifier epitaxial wafer obtained in step (4) in a stripping solution, then successively place it in acetone and ethanol for ultrasonic treatment for 3 min and dry it with high-purity nitrogen;

[0067] (6) Prepare a passivation layer: Deposit a 120-nm-thick Si3N4 layer 7 on the surface of the epitaxial wafer obtained in step (5) by plasma-enhanced chemical vapor deposition (PECVD);

[0068] (7) Align through a mask and obtain a Schottky electrode pattern using a method similar to step (3). Use a wet etching method to etch away the exposed passivation layer 7, and then remove the photoresist using the process of step (5);

[0069] (8) Use a wet etching method to etch a Schottky electrode groove with a depth of 180 nm from the surface of the Si3N4 layer. The Schottky electrode groove penetrates to the surface of the undoped GaN channel layer; Then, the rectifier epitaxial wafer is placed in an electron beam evaporation equipment, evacuated to 1×10 -5 Pa, and successively evaporated with Schottky contact electrode metals Ni / Au. Then, it is annealed at 450 °C for 3 min to obtain Schottky electrode 8;

[0070] (9) Remove the photoresist using the process of step (5), perform wire bonding and packaging, and finally fabricate an N-polarity GaN / AlGaN-based rectifier.

[0071] Example 3:

[0072] This example provides a method for fabricating an N-polarity GaN / AlGaN-based rectifier, specifically including:

[0073] (1) As Figure 1As shown, an N-polar AlN buffer layer 2 with a thickness of 180 nm, a dual SiN insertion layer structure 3 with a thickness of 600 nm, an undoped N-polar AlGaN layer 4 with a thickness of 320 nm, and an undoped N-polar GaN layer 5 with a thickness of 40 nm are sequentially grown on a silicon carbide substrate 1 to obtain a rectifier epitaxial wafer;

[0074] Among them, the growth process of the dual SiN insertion layer structure 3 is as follows: the lower SiN insertion layer is grown on the N-polar AlN buffer layer 2 for 50 s, the AlGaN buffer layer is grown on the lower SiN insertion layer, and then the upper SiN insertion layer is grown on the AlGaN buffer layer for 180 s;

[0075] (2) Pretreat the obtained rectifier epitaxial wafer: place the rectifier epitaxial wafer obtained in step (1) in acetone and ultrasonically treat it for 5 min, then dry it with high-purity nitrogen, and then place it in ethanol and ultrasonically treat it for 5 min and dry it with high-purity nitrogen;

[0076] (3) Lithograph the rectifier epitaxial wafer obtained in step (2): drop an appropriate amount of photoresist, model RZJ304, on the surface of the rectifier epitaxial wafer, spin-coat it in a spin coater for 40 s, pre-bake the rectifier epitaxial wafer coated with photoresist at 95 °C for 45 s, then use a lithography machine to expose the rectifier epitaxial wafer for 2 s to obtain an ohmic electrode pattern, and finally immerse the rectifier epitaxial wafer in a developer for 60 s and then clean it;

[0077] (4) Place the rectifier epitaxial wafer obtained in step (3) into an electron beam evaporation device, evacuate to 3×10 -5 Pa and sequentially evaporate the ohmic contact electrode metals Ti / Al / Ni / Au with a thickness of 300 nm, and then anneal at 900 °C for 30 s to obtain an ohmic electrode 6;

[0078] (5) Remove the photoresist on the surface of the rectifier epitaxial wafer obtained in step (4): immerse the rectifier epitaxial wafer obtained in step (4) in a stripping solution, then ultrasonically treat it in acetone and ethanol for 5 min each and dry it with high-purity nitrogen;

[0079] (6) Prepare a passivation layer: deposit a 160-nm-thick Si3N4 layer 6 on the surface of the epitaxial wafer obtained in step (5) by plasma-enhanced chemical vapor deposition (PECVD);

[0080] (7) Align through a mask and obtain a Schottky electrode pattern by a method similar to step (3), use a wet etching method to etch away the exposed passivation layer 7, and then remove the photoresist by the process of step (5);

[0081] (8) Using a wet etching method, a Schottky electrode groove with a depth of 200 nm is etched on the rectifier epitaxial wafer, and the Schottky electrode groove penetrates to the surface of the undoped GaN channel layer; then the rectifier epitaxial wafer is placed in an electron beam evaporation equipment, evacuated to 3×10-5 Pa and sequentially evaporated with Schottky contact electrode metals Ni / Au, and then annealed at 500 °C for 3 min to obtain the Schottky electrode 8;

[0082] (9) Remove the photoresist using the process of step (5), perform wire bonding and packaging, and finally fabricate the N-polarity GaN / AlGaN-based rectifier.

[0083] Example 4:

[0084] This example provides a method for fabricating an N-polarity GaN / AlGaN-based rectifier, which specifically includes:

[0085] (1) As shown in Figure 1 , an N-polarity AlN buffer layer 2 with a thickness of 180 nm, a dual SiN insertion layer structure 3 with a thickness of 550 nm, an undoped N-polarity AlGaN layer 4 with a thickness of 320 nm, and an undoped N-polarity GaN layer 5 with a thickness of 30 nm are sequentially grown on the silicon carbide substrate 1 to obtain a rectifier epitaxial wafer;

[0086] Among them, the growth process of the dual SiN insertion layer structure 3 is: grow the lower SiN insertion layer on the N-polarity AlN buffer layer 2 for 30 s, grow an AlGaN buffer layer on the lower SiN insertion layer, and then grow the upper SiN insertion layer on the AlGaN buffer layer for 180 s;

[0087] (2) Pretreat the obtained rectifier epitaxial wafer: place the rectifier epitaxial wafer obtained in step (1) in acetone and ultrasonically treat it for 4 min, then dry it with high-purity nitrogen, and then place it in ethanol and ultrasonically treat it for 4 min and dry it with high-purity nitrogen;

[0088] (3) Perform photolithography on the rectifier epitaxial wafer obtained in step (2): drop an appropriate amount of photoresist, model RZJ304, on the surface of the rectifier epitaxial wafer, and spin-coat it in a spin coater for 40 s. Bake the rectifier epitaxial wafer with the photoresist at 95 °C for 45 s, then use a lithography machine to expose the rectifier epitaxial wafer for 4 s to obtain an ohmic electrode pattern, and finally immerse the rectifier epitaxial wafer in a developer for 60 s and then clean it;

[0089] (4) Place the rectifier epitaxial wafer obtained in step (3) in an electron beam evaporation equipment, evacuate to 1×10 -5 Pa and sequentially evaporate the ohmic contact electrode metals Ti / Al / Ni / Au with a thickness of 250 nm, and then anneal at 900 °C for 30 s to obtain the ohmic electrode 6;

[0090] (5) Remove the photoresist on the surface of the rectifier epitaxial wafer obtained in step (4): Immerse the rectifier epitaxial wafer obtained in step (4) in a photoresist-removing solution, then place it in acetone and ethanol successively for ultrasonic treatment for 4 min and dry it with high-purity nitrogen gas;

[0091] (6) Prepare a passivation layer: Deposit a 160-nm-thick Si3N4 passivation layer 7 on the surface of the epitaxial wafer obtained in step (5) by plasma-enhanced chemical vapor deposition (PECVD);

[0092] (7) Align through a mask and obtain a Schottky electrode pattern by a method similar to that in step (3). Use a wet etching method to etch away the exposed passivation layer 7, and then remove the photoresist by the process of step (5);

[0093] (8) Use a wet etching method to etch a Schottky electrode groove with a depth of 200 nm on the rectifier epitaxial wafer. The Schottky electrode groove penetrates to the surface of the undoped GaN channel layer; then place the rectifier epitaxial wafer in an electron beam evaporation device, evacuate to 1×10 -5 Pa and deposit the Schottky contact electrode metals Ni / Au successively, and then anneal at 500 °C for 3 min to obtain a Schottky electrode 8;

[0094] (9) Remove the photoresist by the process of step (5), perform wire bonding and packaging, and finally fabricate an N-polarity GaN / AlGaN-based rectifier.

[0095] The I-V curve of the N-polarity GaN / AlGaN-based rectifier prepared in this embodiment is as Figure 4 shown. When the bias voltage is greater than -4 V and less than 0, the current is almost 0; when the bias voltage is less than -4 V, the reverse current increases sharply; the forward turn-on voltage is about 1.5 V, and the forward conduction characteristic is good. It shows that the quality of the epitaxial wafer is good and the rectification performance of the device is excellent. This is mainly due to the growth time of the double SiN insertion layer structure 3, and the rectification performance of the device is the best among all embodiments.

[0096] In summary, the N-polarity GaN / AlGaN-based rectifier and its manufacturing method provided by the present invention. The N-polarity GaN / AlGaN-based rectifier includes a rectifier epitaxial wafer, an ohmic contact electrode, a Si3N4 passivation layer, and a Schottky contact electrode disposed on the rectifier epitaxial wafer. The rectifier epitaxial wafer includes an AlN buffer layer, a dual SiN insertion layer structure, an undoped AlGaN barrier layer, and an undoped GaN channel layer sequentially grown on a silicon carbide substrate. The ohmic contact electrode and the Si3N4 passivation layer are both disposed on the undoped GaN channel layer. The Schottky contact electrode penetrates into the undoped GaN channel layer by etching from the surface of the Si3N4 passivation layer and partially extends to the surface of the passivation layer. Among them, the dual SiN insertion layer structure includes a lower SiN insertion layer, an AlGaN buffer layer, and an upper SiN insertion layer sequentially grown on the AlN buffer layer. By using an N-polarity GaN / AlGaN heterojunction epitaxial wafer to prepare the rectifier and designing a dual SiN insertion layer structure, the present invention can realize a high-performance rectifier with a low turn-on voltage and a high cut-off frequency.

[0097] As described above, only the preferred embodiments of the present invention for patents are provided, but the protection scope of the present invention for patents is not limited thereto. Any person skilled in the art within the scope disclosed by the present invention for patents, according to the technical solutions and inventive concepts of the present invention for patents, makes equivalent substitutions or changes, and all belong to the protection scope of the present invention for patents.

Claims

1. An N-polarity GaN / AlGaN-based rectifier, characterized in that, It includes a rectifier epitaxial wafer and an ohmic contact electrode, a Si3N4 passivation layer, and a Schottky contact electrode disposed on the rectifier epitaxial wafer; the rectifier epitaxial wafer includes an AlN buffer layer, a dual SiN insertion layer structure, an undoped AlGaN barrier layer, and an undoped GaN channel layer grown sequentially on a silicon carbide substrate, and the ohmic contact electrode and the Si3N4 passivation layer are both disposed on the undoped GaN channel layer, wherein the dual SiN insertion layer structure includes a lower SiN insertion layer, an AlGaN buffer layer, and an upper SiN insertion layer grown sequentially on the AlN buffer layer.

2. The N-polarity GaN / AlGaN-based rectifier according to claim 1, characterized in that, The Al component of the AlGaN buffer layer is greater than that of the undoped AlGaN barrier layer.

3. The N-polarity GaN / AlGaN-based rectifier according to claim 1, characterized in that, The ohmic contact electrode is prepared by sequentially evaporating ohmic contact electrode metals Ti / Al / Ni / Au, and the thickness is 200 - 300 nm.

4. The N-polarity GaN / AlGaN-based rectifier according to claim 1, characterized in that, The Schottky contact electrode is prepared by sequentially evaporating Schottky contact electrode metals Ni / Au; The Schottky contact electrode penetrates into the undoped GaN channel layer by etching and partially extends to the surface of the Si3N4 passivation layer, and the etching depth is 180 - 200 nm.

5. The N-polarity GaN / AlGaN-based rectifier according to claim 1, characterized in that, The distance between the ohmic contact electrode and the Schottky contact electrode is 5 - 9 μm.

6. The N-polarity GaN / AlGaN-based rectifier according to any one of claims 1 to 5, characterized in that, The AlN buffer layer, the AlGaN buffer layer, the undoped AlGaN barrier layer, and the undoped GaN channel layer in the rectifier epitaxial wafer are all N-polar, that is, they are all grown along the [000-1] direction.

7. A method for preparing an N-polarity GaN / AlGaN-based rectifier, characterized in that, The method includes: Growing an AlN buffer layer, a dual SiN insertion layer structure, an undoped AlGaN barrier layer, and an undoped GaN channel layer sequentially on a silicon carbide substrate to obtain a rectifier epitaxial wafer; wherein the dual SiN insertion layer structure includes a lower SiN insertion layer, an AlGaN buffer layer, and an upper SiN insertion layer grown sequentially on the AlN buffer layer; the deposition times of the lower SiN insertion layer and the upper SiN insertion layer are 30 - 50 s and 160 - 180 s respectively; Preprocessing the rectifier epitaxial wafer, performing photolithography on the preprocessed rectifier epitaxial wafer, and obtaining an ohmic electrode pattern on the undoped GaN channel layer; Putting the rectifier epitaxial wafer with the ohmic electrode pattern into an electron beam evaporation device, and sequentially evaporating ohmic contact electrode metals to obtain an ohmic electrode; Removing the photoresist on the surface of the rectifier epitaxial wafer with the ohmic electrode, and using plasma enhanced chemical vapor deposition to deposit a Si3N4 passivation layer on the undoped GaN channel layer of the rectifier epitaxial wafer with the ohmic electrode; Performing mask alignment, performing photolithography on the rectifier epitaxial wafer with the Si3N4 passivation layer, obtaining a Schottky electrode pattern on the Si3N4 passivation layer, performing wet etching to etch away the redundant passivation layer, and removing the photoresist on the surface of the rectifier epitaxial wafer; Using a wet etching method, the epitaxial wafer with the Schottky electrode pattern is etched to form a Schottky electrode groove on the surface of the Si3N4 passivation layer. The Schottky electrode groove penetrates to the surface of the undoped GaN channel layer and extends to the surface of the Si3N4 passivation layer; The rectifier epitaxial wafer etched with the Schottky electrode groove is placed in an electron beam evaporation equipment, and the Schottky contact electrode metal is evaporated in sequence to obtain a Schottky electrode; The photoresist on the surface of the rectifier epitaxial wafer with the Schottky electrode is removed, and leads and packaging are carried out to fabricate an N-polarity GaN / AlGaN-based rectifier.

8. The preparation method according to claim 7, characterized in that, The Al component of the AlGaN buffer layer is greater than the Al component in the undoped AlGaN barrier layer.

9. The preparation method according to claim 7, characterized in that, The ohmic contact electrode is prepared by sequentially evaporating the ohmic contact electrode metals Ti / Al / Ni / Au; The Schottky contact electrode is prepared by sequentially evaporating the Schottky contact electrode metals Ni / Au, and the distance between the electrode edge and the edge of the adjacent etching groove is 0.8 - 1 μm.

10. The preparation method according to any one of claims 7 to 9, characterized in that, In the rectifier epitaxial wafer, the AlN buffer layer, the AlGaN buffer layer, the undoped AlGaN barrier layer, and the undoped GaN channel layer are all N-polarity and all grow along the [000-1] direction.

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