A deep ultraviolet LED epitaxial wafer and its preparation method

Abstract

This invention relates to a deep ultraviolet LED epitaxial wafer and its fabrication method. The deep ultraviolet LED epitaxial wafer comprises, in sequence, the following: a patterned substrate; a nucleation layer; a buffer layer having a first layer of voids formed within it, the surface of which is a patterned structure; a transition layer having a second layer of voids formed within it; a Si3N4 layer; and an n-type layer, an MQW layer, an electron blocking layer, and a p-type layer.

Description

Technical Field

[0001] This invention relates to the field of semiconductor optoelectronic technology, and in particular to a deep ultraviolet LED epitaxial wafer and its preparation method. Background Technology

[0002] In recent years, AlGaN-based deep ultraviolet (DUV) LEDs have demonstrated application potential in fields such as sterilization, disinfection, biomedicine, and water purification due to their advantages of low energy consumption, high portability, long lifespan, and wavelength tunability, becoming one of the research hotspots in the semiconductor optoelectronics field. However, compared with traditional blue LEDs, the external quantum efficiency of DUV LEDs is still relatively low, which restricts the large-scale commercialization of DUV LEDs.

[0003] Internal quantum efficiency and light extraction efficiency are the main factors affecting external quantum efficiency. The low internal quantum efficiency is mainly due to the high dislocation density in currently heteroepitaxially grown AlN films and AlGaN-based epitaxial layers. These dislocations act as non-radiative recombination centers, significantly reducing the radiative recombination efficiency of charge carriers. The low light extraction efficiency is due to the high refractive index of AlGaN and AlN materials themselves, the total internal reflection caused by light emitted from the TM mode (transverse magnetic mode) with high Al content, which confines most of the light inside the device, and the absorption of ultraviolet light by the P-type layer.

[0004] Nanopatterned sapphire substrates have been shown to reduce dislocation density through lateral epitaxial growth. During epitaxial growth on patterned substrates / templates, air gap structures are formed during the lateral merging process of the epitaxial layers. Simultaneously, these air gap structures modulate the photon propagation path; the porous structure and the resulting air gaps significantly scatter photons, especially TM mode photons, encouraging more photons to propagate along the direction perpendicular to the substrate, thus significantly enhancing light extraction capability.

[0005] However, the existing technology has the following drawbacks: (1) A single patterned substrate has limited blocking and annihilation effects on dislocations, especially when the AlGaN layer is grown subsequently, the dislocations will continue to extend upwards, making it difficult to obtain high-quality materials that meet the performance requirements of the device; although the single-layer air gap structure formed can modulate the photon propagation path to a certain extent, its ability to suppress total internal reflection is limited due to the singleness of the structure, and the overall effect on improving the light extraction efficiency is not significant, which cannot meet the light extraction efficiency requirements of high-performance deep ultraviolet LEDs. (2) Since the pattern has a certain groove spacing, a thicker merging thickness is usually required to obtain a surface where the grooves are completely merged, which greatly increases the epitaxial time and cost. (3) The pattern provides different crystal planes and orientations, which leads to problems such as reduced material matching and uneven stress. This causes some positions of atoms to accumulate faster during the epitaxial process, and even if the trenches are merged, it is difficult to form a very smooth surface. In particular, AlGaN materials with high Al content often face problems such as poor crystal quality, uneven surface, and cracks during the epitaxial process due to their high surface energy and lattice mismatch.

[0006] How to achieve secondary innovation based on nanopatterned substrates to optimize the quality of AlGaN-based deep ultraviolet LED epitaxial crystals and improve external quantum efficiency has become a key technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0007] In view of the above analysis, the present invention aims to provide a deep ultraviolet LED epitaxial wafer and its preparation method to at least solve one of the above problems.

[0008] On one hand, the present invention provides a deep ultraviolet LED epitaxial wafer, comprising layers stacked sequentially: Patterned substrate; Nucleation layer; A buffer layer, in which a first layer of voids is formed, and the surface of the buffer layer has a patterned structure; A transition layer, within which a second layer of voids is formed; Si3N4 layer, and n-type layer, MQW layer, electron blocking layer, p-type layer.

[0009] Furthermore, the surface of the substrate is provided with a three-dimensional nanopattern structure, and the thickness of the substrate is 400~1000μm; The nucleation layer is an AlN layer with a thickness of 1~50nm; The buffer layer is an AlN buffer layer with a total thickness of 1~6μm; The transition layer is an AlGaN transition layer with a total thickness of 1~3μm and an Al content of 50~90%. The Si3N4 layer has a thickness of 1~10nm; The n-type layer is an n-AlGaN layer with a thickness of 500~2000 nm and an Al content percentage of 40~80%. The thickness of one cycle of the quantum wells and quantum barriers in the MQW layer is 5~30nm, and 1~5 cycles are grown. The Al composition percentage of the quantum wells is 20%~70%, and the Al composition percentage of the quantum barriers is 50%~90%. The electron blocking layer has a thickness of 5-200 nm and an Al content percentage of 50%-90%. The p-type layer is a p-AlGaN layer, comprising a first p-AlGaN layer and a second p-AlGaN layer. The first p-AlGaN layer is grown on top of an electron blocking layer, with a thickness of 5–200 nm and an Al content percentage of 20–80%. Mg is selected as the p-type dopant, with a Mg doping concentration of 1 × 10⁻⁶. 17 cm -3 ~1×10 21 cm -3 Subsequently, a second p-AlGaN layer was grown, with a thickness of 0–10 nm and an Al content of 0–50%. Mg was selected as the p-type dopant, with a Mg doping concentration of 1 × 10⁻⁶. 17 cm -3 ~1×10 21 cm -3 .

[0010] Furthermore, the AlN buffer layer with In incorporated AlN layer has a thickness of 10~100 nm, and the In doping amount is 10 6 ~10 8 cm -3 between.

[0011] Furthermore, the thickness of the In-doped AlGaN transition layer is 10~50 nm, and the In doping amount is 10 nm. 6 ~10 9 cm -3 between.

[0012] Furthermore, the AlGaN transition layer comprises three layers, namely an In-doped AlGaN layer, an undoped AlGaN layer, and a Si-doped AlGaN layer stacked sequentially from bottom to top. The second layer void extends upward from the In-doped AlGaN layer into the undoped AlGaN layer, but does not exceed the surface of the undoped AlGaN layer.

[0013] On the other hand, the present invention provides a method for preparing a deep ultraviolet LED epitaxial wafer, characterized in that it can at least be used to prepare the above-mentioned deep ultraviolet LED epitaxial wafer, and the preparation method includes the following steps: S100: A substrate with a three-dimensional nano-patterned structure on its surface is provided, and a nucleation layer is formed on the substrate; S200: In, as a surfactant, grows a buffer layer on the nucleation layer, and a first air gap is formed inside the buffer layer; S300: The surface of the buffer layer is patterned; S400: In, as a surfactant, grows a transition layer on the patterned buffer layer, and a second air gap is formed in the transition layer. S500: A Si3N4 layer is deposited on the surface of the transition layer; S600: An n-type layer, an MQW layer, an electron blocking layer, and a p-type layer are sequentially deposited on a Si3N4 layer to obtain a deep ultraviolet LED epitaxial wafer.

[0014] Furthermore, the preparation method includes the following steps: S100: A substrate with a three-dimensional nano-patterned structure on its surface is provided, and an AlN nucleation layer is formed on the substrate; S200: In is used as a surfactant to grow an AlN buffer layer on the AlN nucleation layer, and a first air gap is formed inside the AlN buffer layer. S300: The surface of the AlN buffer layer is patterned; S400: In is used as a surfactant to grow an AlGaN transition layer on the patterned AlN buffer layer, and a second air gap is formed in the AlGaN transition layer. S500: A Si3N4 layer is deposited on the surface of the AlGaN transition layer; S600: An n-AlGaN layer, an MQW layer, an electron blocking layer, and a p-AlGaN layer are sequentially deposited on a Si3N4 layer to obtain a deep ultraviolet LED epitaxial wafer.

[0015] Further, in step S100, an AlN nucleation layer is deposited on the substrate surface using a magnetron sputtering process, with a sputtering power of 200~4000W, an Ar gas flow rate of 20~50sccm, an N2 flow rate of 100~300sccm, an O2 flow rate of 0~5sccm, and a temperature of 500~700℃.

[0016] Further, in step S200, the substrate sputtered in S100 is placed in the MOCVD reaction chamber, the flow rate of carrier gas H2 is 10~50 L / min, the flow rate of TMAl is 10~100 μmol / min, the flow rate of NH3 is 1000~9000 sccm and the flow rate of TMIn is 0.3~10 μmol / min, and an AlN buffer layer is grown at a temperature of 900~1400℃ and a pressure of 5~200 mbar. The TMIn, acting as a surfactant, is introduced over a period of 0.5 to 10 minutes.

[0017] Furthermore, in step S300, the surface of the AlN buffer layer is provided with nano-patterns; In step S400, an AlGaN transition layer is grown on a nanopatterned AlN buffer layer. The wafer is placed in an MOCVD reaction chamber with an H2 flow rate of 10-50 L / min, a total flow rate of TMAl and TMGa of 200-600 μmol / min, an NH3 flow rate of 4000-6000 sccm, and a TMIn flow rate of 0.3-10 μmol / min. The AlGaN transition layer is grown at a temperature of 1100-1200℃ and a pressure of 50-200 mbar. Si is selected as the n-type dopant, and the SiH4 flow rate is... μmol / min, TMIn infusion time controlled between 0.5 and 10 min; In step S500, the wafer obtained in step S400 is placed in a PECVD reaction chamber and a Si3N4 layer is grown at a temperature of 200~400℃ and a pressure of 1~10 torr. Radio frequency or microwave excitation is used, and the Si source is SiH4 or SiF4, and the N source is NH3 or N2.

[0018] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0019] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0020] Figure 1 This is a schematic diagram of the deep ultraviolet LED epitaxial wafer in a specific implementation embodiment; Figure 2 This is a schematic diagram of the transition layer in a specific implementation method; Figure 3 This is a comparison image of the epitaxial wafers formed in the [Example] and [Comparative Example] embodiments under 50x optical magnification.

[0021] Figure label: 1-Patterned substrate; 2-Nucleation layer; 3-Buffer layer; 31-First layer void; 4-Transition layer; 41-Second layer void; 42-In-doped AlGaN layer; 43-Undoped AlGaN layer; 44-Si-doped AlGaN layer; 5-Si3N4 layer; 6-n-type layer; 7-MQW layer; 8-Electron blocking layer; 9-p-type layer. Detailed Implementation

[0022] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0023] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the term "connected" should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral connection; it can refer to a mechanical connection or an electrical connection; it can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0024] Throughout the text, the terms “top,” “bottom,” “above,” “below,” and “on top” refer to the relative positions of components of the device, such as the relative positions of the top and bottom substrates within the device. It is understood that the device is multifunctional and independent of its spatial orientation.

[0025] The working surface of this invention can typically be a plane or a curved surface, and can be inclined or horizontal. For ease of explanation, the embodiments of this invention are placed on a horizontal surface and used on a horizontal surface, thereby defining "height" and "vertical".

[0026] A specific embodiment of the present invention discloses a deep ultraviolet LED epitaxial wafer, such as... Figure 1 ,include: Patterned substrate 1; Nucleation layer 2; Buffer layer 3, with a first layer of voids 31 formed within the layer, and the surface of the buffer layer has a patterned structure; Transition layer 4, within which a second layer of voids 41 is formed; Si3N4 layer 5, and n-type layer 6, MQW layer 7, electron blocking layer 8, p-type layer 9.

[0027] The patterned substrate 1 has a three-dimensional nanopattern structure on its surface, with a substrate thickness of 400-1000 μm. The pattern on the substrate (i.e., the first layer of nanopatterns) is located on the epitaxial growth surface and is formed by etching into an array of recessed periods. The structure can be one of the following shapes: periodic cone, cylinder, frustum, cuboid, cube, prism, pyramid, frustum, or polyhedron. For example, the pattern is a periodic cone shape with a pattern spacing of 50-1000 nm, a depth of 50-1000 nm, and a top surface diameter of 100-1000 nm.

[0028] The nucleation layer 2 is an AlN layer, specifically an amorphous / microcrystalline AlN layer deposited on the substrate surface using magnetron sputtering as the nucleation layer for subsequent epitaxial growth. The thickness of the nucleation layer is 1~50nm.

[0029] The buffer layer 3 is an AlN buffer layer with a total thickness of 1~6 μm. An air gap layer is grown inside the buffer layer, and its surface has a patterned structure. Specifically, the sputtered sapphire substrate is placed in an MOCVD reaction chamber to grow the AlN buffer layer. TMI is introduced as a surfactant. Due to the high desorption rate of In, the actual amount of In incorporated is very small at the high growth temperature of AlN. The thickness of the In-incorporated AlN layer is 10~100 nm, and the In incorporation amount is 10... 6 ~10 8 cm -3 between.

[0030] The transition layer 4 is an AlGaN transition layer with a total thickness of 1-3 μm and an Al composition percentage of 50-90%. A second air gap layer is grown inside the AlGaN transition layer. TMI is introduced as a surfactant, and the In-doped AlGaN layer has a thickness of 10-50 nm and an In doping amount of 10 nm. 6 ~10 9 cm -3 Between these two layers, an undoped AlGaN transition layer is then grown, with a thickness ranging from 50 to 2000 nm. Si is chosen as the n-type dopant, with a Si doping concentration of 1 × 10⁻⁶. 18 cm -3 ~1×10 20 cm -3 The thickness of the Si-doped AlGaN layer is 500~1000nm.

[0031] like Figure 2 As shown, the AlGaN transition layer comprises three layers: an In-doped AlGaN layer 42, an undoped AlGaN layer 43, and a Si-doped AlGaN layer 44, stacked sequentially from bottom to top. The second layer void 41 extends upward from the In-doped AlGaN layer 42 into the undoped AlGaN layer 43, but does not exceed the surface of the undoped AlGaN layer 43. The undoped AlGaN layer 43 serves as a transition between the In-doped AlGaN layer 42 and the Si-doped AlGaN layer 44.

[0032] Since patterned substrates are difficult to fuse, In can be used as a surfactant, which significantly alters surface morphology by changing surface kinetics. In high-Al composition epitaxy, using In as a surfactant promotes subsequent AlN fusion, effectively reducing the AlN fusion thickness and obtaining AlN templates with low dislocation density and smooth surfaces. Furthermore, setting an undoped AlGaN layer 43 as a transition between the In-doped AlGaN layer 42 and the Si-doped AlGaN layer 44 prevents Si from diffusing from the Si-doped AlGaN layer 44 into the In-doped AlGaN layer 42, thus preventing poor fusion during surface growth.

[0033] The Si3N4 layer 5 has a thickness of 1~10nm. Specifically, the Si3N4 layer is grown by placing the wafer in a PECVD reaction chamber. The Si3N4 layer can change the extension direction of most of the defects from the bottom layer, causing them to converge and annihilate, thus reducing the number of dislocations.

[0034] The n-type layer 6 is an n-AlGaN layer with a thickness of 500~2000 nm and an Al composition percentage of 40~80%. Specifically, the wafer is placed in an MOCVD reaction chamber to grow the n-AlGaN layer, and Si is selected as the n-type dopant with a Si doping concentration of 1×10⁻⁶. 18 cm -3 ~1×10 20 cm -3 .

[0035] The thickness of one cycle of the quantum wells and quantum barriers in the MQW layer 7 is 5~30nm, and 1~5 cycles are grown. The Al composition percentage of the quantum wells is 20%~70%, and the Al composition percentage of the quantum barriers is 50%~90%.

[0036] The thickness of the electron blocking layer 8 is 5~200nm, and the percentage of Al composition is 50%~90%.

[0037] The p-type layer is a p-AlGaN layer, comprising a first p-AlGaN layer and a second p-AlGaN layer. The first p-AlGaN layer is grown on top of an electron blocking layer, with a thickness of 5–200 nm and an Al content percentage of 20–80%. Mg is selected as the p-type dopant, with a Mg doping concentration of 1 × 10⁻⁶. 17 cm -3 ~1×10 21 cm -3 Subsequently, a second p-AlGaN layer was grown, with a thickness of 0–10 nm and an Al content of 0–50%. Mg was selected as the p-type dopant, with a Mg doping concentration of 1 × 10⁻⁶. 17 cm -3 ~1×1021 cm -3 .

[0038] This invention also provides a method for preparing a deep ultraviolet LED epitaxial wafer, which can at least be used to prepare the aforementioned deep ultraviolet LED epitaxial wafer. The preparation method includes the following steps: S100: A substrate with a three-dimensional nano-patterned structure on its surface is provided, and a nucleation layer is formed on the substrate; S200: In, as a surfactant, grows a buffer layer on the nucleation layer, and a first air gap is formed inside the buffer layer; S300: The surface of the buffer layer is patterned; S400: In, as a surfactant, grows a transition layer on the patterned buffer layer, and a second air gap is formed in the transition layer. S500: A Si3N4 layer is deposited on the surface of the transition layer; S600: An n-type layer, an MQW layer, an electron blocking layer, and a p-type layer are sequentially deposited on a Si3N4 layer to obtain a deep ultraviolet LED epitaxial wafer.

[0039] Specifically, the preparation method includes the following steps: S100: A substrate with a three-dimensional nano-patterned structure on its surface is provided, and an AlN nucleation layer is formed on the substrate; S200: In is used as a surfactant to grow an AlN buffer layer on the AlN nucleation layer, and a first air gap is formed inside the AlN buffer layer. S300: The surface of the AlN buffer layer is patterned; S400: In is used as a surfactant to grow an AlGaN transition layer on the patterned AlN buffer layer, and a second air gap is formed in the AlGaN transition layer. S500: A Si3N4 layer is deposited on the surface of the AlGaN transition layer; S600: An n-AlGaN layer, an MQW layer, an electron blocking layer, and a p-AlGaN layer are sequentially deposited on a Si3N4 layer to obtain a deep ultraviolet LED epitaxial wafer.

[0040] In step S100, The substrate has a three-dimensional nanopattern structure on its surface and a thickness of 400~1000μm.

[0041] The pattern on the substrate (i.e., the first layer of nanopatterns) is located on the epitaxial growth surface and is formed by etching into a periodic array of recesses. The structure can be one of the following: a periodic cone, cylinder, frustum, cuboid, cube, prism, pyramid, frustum, or polyhedron. For example, the pattern is a periodic cone with a pattern spacing of 50-1000 nm, a depth of 50-1000 nm, and a top surface diameter of 100-1000 nm.

[0042] An amorphous / microcrystalline AlN layer (i.e., an AlN nucleation layer) is deposited on the substrate surface using magnetron sputtering as the nucleation layer for subsequent epitaxial growth. Specifically, the sputtering power is 200~4000W, the Ar gas flow rate is 20~50sccm, the N2 flow rate is 100~300sccm, the O2 flow rate is 0~5sccm, and the temperature is 500~700℃.

[0043] In step S200 Surfactants are substances that influence growth kinetics. In MOCVD (Metal-Organic Chemical Vapor Deposition) and other growth techniques, surfactants significantly alter surface morphology by changing surface kinetics. In high-Al composition epitaxy, using In as a surfactant can promote AlN coalescence, effectively reduce the coalescence thickness of AlN, and obtain AlN templates with low dislocation density and smooth surfaces.

[0044] The S100 sputtered substrate was placed in an MOCVD reaction chamber. The flow rate of carrier gas H2 was 10–50 L / min, the flow rate of TMAl (trimethylaluminum) was 10–100 μmol / min, the flow rate of NH3 was 1000–9000 sccm, and the flow rate of TMIn (trimethylindium) was 0.3–10 μmol / min. An AlN buffer layer was grown at a temperature of 900–1400 °C and a pressure of 5–200 mbar. The TMIn, as a surfactant, was introduced for 0.5–10 min.

[0045] The AlN buffer layer grows an initial air gap, reducing stress in the epitaxial layer, further decreasing the density of penetrating dislocations, improving the quality of the epitaxial material, and simultaneously modulating the photon propagation path to enhance light extraction efficiency. The height of the air gap varies depending on the specific pattern size and manufacturing process, and can be adjusted by controlling these factors. Air gap heights range from 50 to 4000 nm. Air gaps can be circular, candle-shaped, or elongated. The density is between 1.293 kg / m³. 3 and 3.26 g / cm 3 between.

[0046] In step S300 The surface of the AlN buffer layer is provided with nanopatterns (i.e., the second layer of nanopatterns). Specifically, these are formed by dry etching, creating an array of recessed periods. These patterns can be aligned with or offset from the first layer of nanopatterns, and the period and size can be designed independently. The structure can be one of the following shapes: periodic cone, cylinder, frustum, cuboid, cube, prism, pyramid, frustum, or polyhedron. For example, the second layer of nanopatterns is conical, with a pattern spacing of 50-1000 nm, a depth of 50-800 nm, and a top surface diameter of 50-800 nm.

[0047] The purpose of patterning the surface of the AlN buffer layer is to disrupt and block the dislocation directions extending from the AlN buffer layer, reduce the dislocation defect density, and at the same time reduce the light reflection problem at the AlN-AlGaN interface.

[0048] In step S400 An AlGaN transition layer was grown on a nanopatterned AlN buffer layer. Specifically, the wafer was placed in an MOCVD reaction chamber with an H2 flow rate of 10–50 L / min, a total flow rate of TMAl and TMGa (trimethylgallium) of 200–600 μmol / min, an Al composition percentage of 50–90%, an NH3 flow rate of 4000–6000 sccm, and a TMIn flow rate of 0.3–10 μmol / min. The AlGaN transition layer was grown at a temperature of 1100–1200 °C and a pressure of 50–200 mbar. Then, without introducing TMIn, and while maintaining the same conditions, an undoped AlGaN transition layer was grown. Si was selected as the n-type dopant, and the SiH4 flow rate was… μmol / min. TMIn infusion time was controlled between 0.5 and 10 min.

[0049] Using In as a surfactant promotes the merging of AlGaN on a patterned substrate, resulting in AlGaN materials with low dislocation density and smooth surface, thus reducing crack occurrence.

[0050] A second air gap is formed within the AlGaN transition layer, reducing stress in the epitaxial layer, further decreasing the density of penetrating dislocations, improving the quality of the epitaxial material, and simultaneously modulating the photon propagation path to improve light extraction efficiency. The height of the air gap varies depending on the specific pattern size and manufacturing process, and can be adjusted by controlling the process and pattern size. Air gap heights range from 50 to 2500 nm. Air gaps can be circular, candle-shaped, or elongated. The density is between 1.293 kg / m³. 3 and 3.26 g / cm 3 between.

[0051] In step S500 The wafer obtained in step S400 is placed in a PECVD (Plasma-Enhanced Chemical Vapor Deposition) reaction chamber, and a Si3N4 layer is grown at a temperature of 200~400℃ and a pressure of 1~10 torr. Radio frequency or microwave excitation is used, and the Si source is SiH4 or SiF4, and the N source is NH3 or N2.

[0052] The Si3N4 layer reduces the number of dislocations by altering the extension direction of most defects originating from the underlying line, causing them to converge and annihilate.

[0053] In step S600 In the MOCVD reaction chamber, an n-AlGaN layer, an MQW layer (multiple quantum well layer), an electron blocking layer, and a p-AlGaN layer are deposited sequentially.

[0054] n-AlGaN layer: The wafer is placed in an MOCVD reaction chamber and H2 is introduced. An n-AlGaN layer is grown at a temperature of 1000–1100℃ and a pressure of 50–100 mbar. The total flow rate of TMAl and TMGa is 300–600 μmol / min, the Al content percentage is 40–80%, and the NH3 flow rate is 3000–6000 sccm. Si is selected as the n-type dopant, and the SiH4 flow rate is… μmol / min.

[0055] MQW layer: The MQW layer is grown on the basis of the n-AlGaN layer at a temperature of 900~1100℃ and a pressure of 50~100mbar. The total flow rate of TMAl and TMGa is 250~350μmol / min. The Al composition percentage of the quantum well is 20%~70%, the Al composition percentage of the quantum barrier is 50%~90%, and the NH3 flow rate is 3000~6000sccm.

[0056] Electron blocking layer: An electron blocking layer is grown on the basis of the MQW layer at a temperature of 1000~1150℃, a pressure of 50~100mbar, a total flow rate of TMAl and TMGa of 150~200μmol / min, an Al component percentage of 50%~90%, and an NH3 flow rate of 3000~6000sccm.

[0057] p-AlGaN layer: The first p-AlGaN layer is grown on top of the electron blocking layer at a temperature of 1050–1150 °C and a pressure of 50–100 mbar. The total flow rate of TMAl and TMGa is 100–150 μmol / min, the Al composition percentage is 20–80%, the NH3 flow rate is 3000–6000 sccm, and Mg is selected as the p-type dopant with a doping concentration of 1 × 10⁻⁶. 17 cm -3 ~1×10 21 cm -3 Subsequently, a second p-AlGaN layer was grown at a temperature reduced to 700–950 °C, with the pressure maintained at 50–100 mbar. The total flow rate of TMAl and TMGa was 50–100 μmol / min, the Al content percentage was 0–50%, and the NH3 flow rate was 3000–6000 sccm. Mg was selected as the p-type dopant, with a Mg doping concentration of 1 × 10⁻⁶. 17 cm -3 ~1×10 21 cm -3 .

[0058] The present invention aims to provide a deep ultraviolet LED epitaxial wafer and its preparation method, which improves the existing technology by addressing the problems of insufficient dislocation suppression due to single patterns, limited improvement in light extraction efficiency, the need for thicker merging thickness, increased cost and time, uneven stress caused by patterns, uneven surface, and cracking, especially in high-Al materials.

[0059] [Example] A method for preparing a deep ultraviolet LED epitaxial wafer is provided, comprising the following steps: S100: A substrate with a three-dimensional nano-patterned structure on its surface is provided, and an AlN nucleation layer is formed on the substrate; The substrate has a thickness of 430 μm and a three-dimensional nanopatterned structure on its surface. The pattern is located on the epitaxial growth surface and is formed by etching into an array of periodic recesses. The structure is a periodic cone with a pattern spacing of 1000 nm, a depth of 500 nm, and a top surface diameter of 500 nm. An amorphous / microcrystalline AlN layer with a thickness of 20 nm is deposited on the substrate surface using magnetron sputtering. The sputtering power is 2500 W, the Ar gas flow rate is 30 sccm, the N2 flow rate is 100 sccm, the O2 flow rate is 4 sccm, and the temperature is 700 °C.

[0060] S200: In is used as a surfactant to grow an AlN buffer layer on the AlN nucleation layer, and a first air gap is formed inside the AlN buffer layer. The sputtered substrate was placed in the MOCVD reaction chamber to grow an AlN buffer layer. The H2 flow rate was 50 L / min, the TMAl flow rate was 90 μmol / min, and the NH3 flow rate was 9000 sccm. Nucleation stage: TMIn flow rate was 6 μmol / min, TMIn infusion time was 5 min, temperature was 980℃, pressure was 120 mbar, and growth time was 10 min. Three-dimensional growth stage: temperature was 1030℃, pressure was 120 mbar, and growth time was 80 min. Two-dimensional growth stage: temperature was 1100℃, pressure was 100 mbar, and growth time was 110 min. These settings were used to better integrate the surface pattern structure, resulting in a smoother surface.

[0061] The total thickness of the AlN buffer layer is 2.3 μm, and the thickness of the AlN layer with In incorporation is 30 nm. The first air gap layer is grown inside the AlN buffer layer, with a height of about 1.1 μm.

[0062] S300: The surface of the AlN buffer layer is patterned; The pattern is located on the surface of the AlN buffer layer and is formed by dry etching to form an array of recessed periods. The pattern structure is a periodic cone with a pattern spacing of 800 nm, a depth of 300 nm, and a top diameter of 300 nm.

[0063] S400: In is used as a surfactant to grow an AlGaN transition layer on the patterned AlN buffer layer, and a second air gap is formed in the AlGaN transition layer. An AlGaN transition layer was grown on a nanopatterned AlN buffer layer. The wafer was placed in an MOCVD reaction chamber with an H2 flow rate of 40 L / min. The total flow rate of TMAl and TMGa was 400 μmol / min, with an Al composition percentage of 71%. The NH3 flow rate was 5000 sccm, the TMIn flow rate was 3 μmol / min, and the TMIn infusion time was controlled at 3 min. The temperature was 1100 °C, and the pressure was 100 mbar. Si was selected as the n-type dopant, and it was introduced after 80 min of growth.

[0064] The total thickness of the AlGaN transition layer is 1 μm. Specifically, the In-doped AlGaN layer is 20 nm thick, and the Si-doped AlGaN layer is 500 nm thick, with a Si doping concentration of 5 × 10⁻⁶. 19 cm -3 A second air gap layer, approximately 800 nm high, is grown inside the AlGaN transition layer.

[0065] S500: A Si3N4 layer is deposited on the surface of the AlGaN transition layer; The wafer was placed in a PECVD reaction chamber at a temperature of 360°C and a pressure of 7 torr, using radio frequency excitation. The Si source was SiH4, and the N source was NH3. The Si3N4 layer thickness was 3 nm.

[0066] S600: An n-AlGaN layer, an MQW layer, an electron blocking layer, and a p-AlGaN layer are sequentially deposited on a Si3N4 layer to obtain a deep ultraviolet LED epitaxial wafer.

[0067] In the MOCVD reaction chamber, an n-AlGaN layer, an MQW layer, an electron blocking layer, and a p-AlGaN layer are deposited sequentially.

[0068] n-AlGaN layer: H2 is introduced at 1100℃ and 100 mbar. The total flow rate of TMAl and TMGa is 400 μmol / min, the flow rate of NH3 is 5000 sccm, and the flow rate of SiH4 is 0.01 μmol / min. The n-AlGaN layer thickness is 1.5 μm, the Al composition percentage is 68%, and the Si doping concentration is 5 × 10⁻⁶. 19 cm -3 .

[0069] MQW layer: Quantum barrier layer temperature 1050℃, quantum well layer temperature 1000℃, grown alternately in each cycle. The thickness of one cycle consisting of quantum wells and quantum barriers in the MQW layer is 20nm, and 4 cycles are grown. The Al composition percentage of the quantum wells is 55%, and the Al composition percentage of the quantum barriers is 69%.

[0070] Electron blocking layer: temperature 1100℃, pressure 70 mbar, total flow rate of TMAl and TMGa 150 μmol / min. Electron blocking layer thickness is 80 nm, Al content percentage is 76%.

[0071] The p-AlGaN layer was grown at a temperature of 1050℃ and a pressure of 70 mbar, with a total flow rate of 150 μmol / min for TMAl and TMGa and a Cp2Mg flow rate of 500 sccm. The temperature was then lowered to 950℃ to grow the second p-AlGaN layer, with a total flow rate of 60 μmol / min for TMAl and TMGa and a Cp2Mg flow rate of 500 sccm. The first p-AlGaN layer had a thickness of 150 nm, an Al content of 60%, and a Mg doping concentration of 5 × 10⁻⁶. 19 cm -3 The second p-AlGaN layer has a thickness of 6 nm, an Al content of 36%, and a Mg doping concentration of 5 × 10⁻⁶. 19 cm -3 .

[0072] [Comparative Example] No In was introduced as a surfactant during the growth of the AlN buffer layer; only one nanopattern was formed on the sapphire substrate (with parameters consistent with the first nanopattern in the example); the growth time for the AlN buffer layer nucleation stage was 10 min, the growth time for the three-dimensional growth stage was 140 min, and the growth time for the two-dimensional growth stage was 160 min; no nanopatterning was performed after the growth of the AlN buffer layer; no In was introduced as a surfactant during the growth of the AlGaN transition layer; no Si3N4 layer was formed; everything else was the same as in the example.

[0073] Table 1 compares the AlN layer thickness, AlN layer air gap height, EL wavelength of the resulting epitaxial wafer, number of protrusions, and crack condition between the [Example] and [Comparative Example]. A relatively smooth surface can be obtained by controlling the air gap height to approximately 0.5 times the AlN layer thickness, while the comparative example requires a longer time to grow a smooth AlN layer. The results show that a smooth surface can be obtained with an AlN layer thickness of 2.324 μm in the Example, while the comparative example requires 3.71 μm. The lower air gap height of the AlN layer in the Example indicates that using In as a surfactant during high-Al composition epitaxy promotes surface coalescence and effectively reduces the coalescence thickness. The EL wavelengths after epitaxial growth are comparable. The Example has significantly fewer protrusions than the comparative example and no cracks, further demonstrating that In, as a surfactant, significantly alters the surface morphology by changing surface kinetics.

[0074] Figure 3 The images show a comparison of the epitaxial wafers formed in the [Example] and [Comparative Example] under optical microscopy at 50x magnification. It can be seen from the images that the surface of the comparative example has unevenly distributed protrusions, while the surface of the example is smoother.

[0075] Table 1

[0076] Table 2 shows the results of fabricating 20 mil × 20 mil LED chips from the epitaxial wafers formed in the [Example] and [Comparative Example] using the same chip fabrication process. 200 LED chips were randomly selected from each example and tested at a current of 200 mA. The average wavelength of the Example was 273.5 nm, while the wavelength of the Comparative Example was slightly longer, averaging 273.9 nm. The average brightness of the Example was 93.5 mW, higher than the 78.2 mW of the Comparative Example. The photoelectric conversion efficiency of the Example was 8.97%, while that of the Comparative Example was 7.37%, representing a 1.6% improvement. This indicates that the double-layer air gap formed during the secondary patterned epitaxial growth process of the Example can more effectively change the photon propagation path and suppress total internal reflection, thereby achieving a higher light extraction efficiency than a single-layer air gap structure and improving the photoelectric conversion efficiency.

[0077] Table 2

[0078] Compared with the prior art, this invention achieves the following beneficial effects by introducing secondary patterning, the synergistic effect of indium surfactant and Si3N4 mask: (1) The secondary patterned structure constructs a second dislocation blocking interface on the basis of the first patterned substrate, forming a multiple dislocation suppression mechanism with the upper Si3N4 mask. It can effectively break, bend and promote the aggregation and annihilation of dislocations, effectively reduce the density of penetrating dislocations extending to the active region, thereby improving the internal quantum efficiency. (2) Introducing In as a surfactant during the growth of the AlN buffer layer and the AlGaN transition layer effectively enhances the surface mobility of Al atoms and promotes material merging. This reduces the epitaxial layer thickness required for complete trench merging on the nanopatterned substrate and yields a smoother, crack-free, high-quality crystal. (3) The double-layer air gap formed during the secondary patterned epitaxial growth process constitutes multiple internal light scattering interfaces, which can more effectively change the photon propagation path and suppress total internal reflection, thereby achieving a higher light extraction efficiency than the single-layer air gap structure, and improving the photoelectric conversion efficiency by 1.6%.

[0079] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A deep ultraviolet LED epitaxial wafer, characterized in that, The material comprises, in sequence, the following: a patterned substrate; a nucleation layer; a buffer layer having a first layer of voids formed within it, the surface of which is a patterned structure; a transition layer having a second layer of voids formed within it; a Si3N4 layer; and an n-type layer, an MQW layer, an electron blocking layer, and a p-type layer.

2. The deep ultraviolet LED epitaxial wafer according to claim 1, characterized in that, The surface of the substrate is provided with a three-dimensional nano-pattern structure, and the thickness of the substrate is 400~1000μm; The nucleation layer is an AlN layer with a thickness of 1~50nm; The buffer layer is an AlN buffer layer with a total thickness of 1~6μm; The transition layer is an AlGaN transition layer with a total thickness of 1~3μm and an Al content of 50~90%. The Si3N4 layer has a thickness of 1~10nm; The n-type layer is an n-AlGaN layer with a thickness of 500~2000 nm and an Al content percentage of 40~80%. The thickness of one cycle of the quantum wells and quantum barriers in the MQW layer is 5~30nm, and 1~5 cycles are grown. The Al composition percentage of the quantum wells is 20%~70%, and the Al composition percentage of the quantum barriers is 50%~90%. The electron blocking layer has a thickness of 5-200 nm and an Al content percentage of 50%-90%. The p-type layer is a p-AlGaN layer, comprising a first p-AlGaN layer and a second p-AlGaN layer. The first p-AlGaN layer is grown on top of an electron blocking layer, with a thickness of 5–200 nm and an Al content percentage of 20–80%. Mg is selected as the p-type dopant, with a Mg doping concentration of 1 × 10⁻⁶. 17 cm -3 ~1×10 21 cm -3 Subsequently, a second p-AlGaN layer was grown, with a thickness of 0–10 nm and an Al content of 0–50%. Mg was selected as the p-type dopant, with a Mg doping concentration of 1 × 10⁻⁶. 17 cm -3 ~1×10 21 cm -3 .

3. The deep ultraviolet LED epitaxial wafer according to claim 2, characterized in that, The AlN buffer layer, with In incorporated AlN layers, has a thickness of 10-100 nm and an In doping amount of 10. 6 ~10 8 cm -3 between.

4. The deep ultraviolet LED epitaxial wafer according to claim 2, characterized in that, The AlGaN transition layer, with In doped AlGaN layer thickness ranging from 10 to 50 nm, has an In doping content of approximately 10%. 6 ~10 9 cm -3 between.

5. The deep ultraviolet LED epitaxial wafer according to claim 4, characterized in that, The AlGaN transition layer comprises three layers: an In-doped AlGaN layer, an undoped AlGaN layer, and a Si-doped AlGaN layer stacked sequentially from bottom to top. The second layer void extends upward from the In-doped AlGaN layer into the undoped AlGaN layer, but does not exceed the surface of the undoped AlGaN layer.

6. A method for preparing a deep ultraviolet LED epitaxial wafer, characterized in that, It can be used at least to prepare the deep ultraviolet LED epitaxial wafer according to any one of claims 1 to 5, and the preparation method includes the following steps: S100: A substrate with a three-dimensional nano-patterned structure on its surface is provided, and a nucleation layer is formed on the substrate; S200: In, as a surfactant, grows a buffer layer on the nucleation layer, and a first air gap is formed inside the buffer layer; S300: The surface of the buffer layer is patterned; S400: In, as a surfactant, grows a transition layer on the patterned buffer layer, and a second air gap is formed in the transition layer. S500: A Si3N4 layer is deposited on the surface of the transition layer; S600: An n-type layer, an MQW layer, an electron blocking layer, and a p-type layer are sequentially deposited on a Si3N4 layer to obtain a deep ultraviolet LED epitaxial wafer.

7. The preparation method according to claim 6, characterized in that, Includes the following steps: S100: A substrate with a three-dimensional nano-patterned structure on its surface is provided, and an AlN nucleation layer is formed on the substrate; S200: In is used as a surfactant to grow an AlN buffer layer on the AlN nucleation layer, and a first air gap is formed inside the AlN buffer layer. S300: The surface of the AlN buffer layer is patterned; S400: In is used as a surfactant to grow an AlGaN transition layer on the patterned AlN buffer layer, and a second air gap is formed in the AlGaN transition layer. S5 00: A Si3N4 layer is deposited on the surface of the AlGaN transition layer; S600: An n-AlGaN layer, an MQW layer, an electron blocking layer, and a p-AlGaN layer are sequentially deposited on a Si3N4 layer to obtain a deep ultraviolet LED epitaxial wafer.

8. The preparation method according to claim 7, characterized in that, In step S100, an AlN nucleation layer is deposited on the substrate surface using a magnetron sputtering process. The sputtering power is 200~4000W, the Ar gas flow rate is 20~50sccm, the N2 flow rate is 100~300sccm, the O2 flow rate is 0~5sccm, and the temperature is 500~700℃.

9. The preparation method according to claim 8, characterized in that, In step S200, the substrate sputtered in S100 is placed in the MOCVD reaction chamber. The flow rate of carrier gas H2 is 10~50 L / min, the flow rate of TMAl is 10~100 μmol / min, the flow rate of NH3 is 1000~9000 sccm, and the flow rate of TMIn is 0.3~10 μmol / min. An AlN buffer layer is grown at a temperature of 900~1400℃ and a pressure of 5~200 mbar. The TMIn, acting as a surfactant, is introduced over a time period of 0.5 to 10 minutes.

10. The preparation method according to claim 9, characterized in that, In step S300, the surface of the AlN buffer layer is provided with nano-patterns; In step S400, an AlGaN transition layer is grown on a nanopatterned AlN buffer layer. The wafer is placed in an MOCVD reaction chamber with an H2 flow rate of 10-50 L / min, a total flow rate of TMAl and TMGa of 200-600 μmol / min, an NH3 flow rate of 4000-6000 sccm, and a TMIn flow rate of 0.3-10 μmol / min. The AlGaN transition layer is grown at a temperature of 1100-1200℃ and a pressure of 50-200 mbar. Si is selected as the n-type dopant, and the SiH4 flow rate is... μmol / min, TMIn infusion time controlled between 0.5 and 10 min; In step S500, the wafer obtained in step S400 is placed in a PECVD reaction chamber and a Si3N4 layer is grown at a temperature of 200~400℃ and a pressure of 1~10 torr. Radio frequency or microwave excitation is used, and the Si source is SiH4 or SiF4, and the N source is NH3 or N2.

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