Ultraviolet led preparation method based on composite film, composite film and ultraviolet led

Abstract

The application discloses a preparation method of an ultraviolet LED based on a composite film, the composite film and the ultraviolet LED, and relates to the technical field of semiconductors. The method comprises the following steps: providing a semiconductor substrate; sequentially forming a two-dimensional material layer and a three-dimensional nano-pattern layer on the semiconductor substrate to obtain a composite structure; performing plasma interface modification treatment on the composite structure to obtain a composite film; epitaxially growing an ultraviolet LED epitaxial layer on the surface of the composite film, wherein the epitaxial layer at least comprises a first conductive type layer, an active layer and a second conductive type layer; forming a first electrode on the first side of the epitaxial layer; removing at least part of the semiconductor substrate to expose at least part of the second side of the epitaxial layer; and forming a second electrode on the second side of the epitaxial layer. While ensuring that the substrate is peeled off without damage, the crystal quality of the epitaxial layer and the photoelectric performance of the device are significantly improved.

Description

Technical Field

[0001] This application relates to the field of semiconductor technology, and more specifically to a method for preparing ultraviolet LEDs based on composite thin films, the composite thin films, and the ultraviolet LEDs. Background Technology

[0002] Ultraviolet LEDs (Ultraviolet Light Emitting Diodes), as a new type of solid-state ultraviolet light source, have outstanding advantages such as low energy consumption, long lifespan, miniaturization, no mercury pollution, fast response speed, and strong controllability. They are gradually replacing traditional high-pressure mercury lamps and other ultraviolet light sources, which is in line with the development trend of the green optoelectronic industry.

[0003] Vertical-structure ultraviolet LEDs have become the mainstream development direction for high-power devices. The vertical structure refers to placing the positive and negative electrodes on opposite sides of the epitaxial layer of the device, with the current flowing longitudinally (vertically) through the active layer. This offers significant advantages such as uniform current distribution, short heat dissipation paths, and high voltage resistance. However, the fabrication of vertical-structure ultraviolet LEDs faces a key technological challenge—the removal of the semiconductor growth substrate. There are currently two main substrate removal technologies:

[0004] One method is laser lift-off technology, which uses high-energy lasers to irradiate the substrate interface to achieve lift-off. However, laser equipment is expensive, the process cost is high, and high-energy lasers are very likely to damage the active layer of multi-quantum wells, resulting in large leakage current and low yield of the device.

[0005] The second method is material epitaxial exfoliation technology. This method avoids laser damage, but the epitaxial crystal quality of a single two-dimensional buffer layer is poor and the dislocation density is high, which leads to a significant decrease in the optoelectronic performance of the device. Summary of the Invention

[0006] In view of the above problems, this application provides a method for fabricating ultraviolet LEDs based on composite thin films, the composite thin film, and the ultraviolet LED.

[0007] The first aspect of this application provides a method for fabricating ultraviolet LEDs based on composite thin films, comprising:

[0008] Provide semiconductor substrates;

[0009] A two-dimensional material layer and a three-dimensional nanopattern layer are sequentially formed on the semiconductor substrate to obtain a composite structure.

[0010] The composite structure was subjected to plasma interface modification treatment to obtain a composite thin film;

[0011] An ultraviolet LED epitaxial layer is epitaxially grown on the surface of the composite film, the epitaxial layer comprising at least a first conductivity type layer, an active layer, and a second conductivity type layer;

[0012] A first electrode is formed on a first side of the epitaxial layer;

[0013] At least a portion of the semiconductor substrate is removed to expose at least a portion of the second side of the epitaxial layer;

[0014] A second electrode is formed on the second side of the epitaxial layer.

[0015] According to an embodiment of this application, the two-dimensional material layer is a layered material bonded by van der Waals forces between the layers; the three-dimensional nanopatterned layer is used as a patterning mask layer to guide the lateral epitaxial growth of the ultraviolet LED epitaxial layer.

[0016] According to an embodiment of this application, the plasma interface modification treatment of the composite structure includes:

[0017] After the two-dimensional material layer is grown, a first plasma treatment is performed.

[0018] After the three-dimensional nano-patterned layer is prepared, a second plasma treatment is performed.

[0019] The first and second plasma treatments are both performed in an oxygen or nitrogen atmosphere.

[0020] According to an embodiment of this application, removing at least a portion of the semiconductor substrate includes:

[0021] The semiconductor substrate is removed by chemically wetting the interface between the semiconductor substrate and the two-dimensional material layer using the interlayer van der Waals forces of the two-dimensional material layer.

[0022] According to embodiments of this application, the two-dimensional material layer is graphene or hexagonal boron nitride.

[0023] According to the embodiments of this application, the three-dimensional nanopatterned layer is a silicon oxide nanosphere array or a carbon nanotube array.

[0024] When the three-dimensional nanopattern layer is a silicon oxide nanosphere array, the silicon oxide nanospheres are arranged into a close-packed monolayer and transferred to the surface of the two-dimensional material layer by gas-liquid interface self-assembly method, and then obtained by inductively coupled plasma etching.

[0025] When the three-dimensional nanopattern layer is a carbon nanotube array, the carbon nanotube array is transferred to the surface of the two-dimensional material layer, and after being soaked and dried with ethanol, the adjacent carbon nanotubes shrink and aggregate to form carbon nanotube bundles, thus obtaining a carbon nanotube array.

[0026] According to an embodiment of this application, the ultraviolet LED is a 365 nm near-ultraviolet LED.

[0027] According to an embodiment of this application, the first conductivity type layer is an n-type layer, the second conductivity type layer is a p-type layer, and the epitaxial layer includes, from bottom to top, a u-GaN layer, an n-GaN layer, a multi-quantum-well active layer, an electron blocking layer, a p-AlGaN layer, and a p⁺-GaN layer.

[0028] A second aspect of this application provides a composite film, comprising:

[0029] Two-dimensional material layers; and

[0030] A three-dimensional nanopatterned layer located on the two-dimensional material layer;

[0031] A plasma-modified interface is formed between the two-dimensional material layer and the three-dimensional nano-patterned layer.

[0032] A third aspect of this application provides a vertically structured ultraviolet LED, comprising:

[0033] A composite thin film layer comprising a two-dimensional material layer and a three-dimensional nanopatterned layer located on the two-dimensional material layer, wherein the interface between the two-dimensional material layer and the three-dimensional nanopatterned layer is subjected to plasma interface modification treatment.

[0034] An ultraviolet LED epitaxial layer located on the composite thin film layer, the epitaxial layer comprising a first conductivity type layer, an active layer, and a second conductivity type layer;

[0035] The first electrode electrically connected to the first side of the epitaxial layer; and

[0036] A second electrode electrically connected to the second side of the epitaxial layer, wherein the second electrode and the first electrode are located on opposite sides of the epitaxial layer.

[0037] Compared with the prior art, this application has at least one of the following beneficial effects:

[0038] 1. This application's embodiments construct a composite thin film structure of a "two-dimensional material layer + a three-dimensional nano-patterned layer." The two-dimensional material layer utilizes weak interlayer van der Waals forces to provide a natural dissociation interface, allowing the semiconductor substrate to be non-destructively peeled off under mild conditions via chemical wetting or mechanical methods, eliminating the need for high-energy laser irradiation. This completely avoids the problems of active layer susceptibility to thermal damage, high equipment costs, and low yield associated with laser peeling processes. Simultaneously, the three-dimensional nano-patterned layer serves as a patterned mask template, guiding the epitaxial layer to undergo lateral epitaxial growth, effectively reducing dislocation density and residual stress caused by lattice and thermal mismatches, and significantly improving the crystal quality of the epitaxial layer. The synergistic effect of these two features resolves the technical contradiction in existing technologies where a single approach cannot simultaneously achieve non-destructive peeling and high-quality epitaxy.

[0039] 2. In this embodiment, after the formation of the two-dimensional material layer and the three-dimensional nano-patterned layer, a further plasma interface modification treatment is performed. Plasma bombards and activates the surface of the composite structure, removing interface impurities, introducing active functional groups, and passivating interface defects, significantly improving the interfacial bonding between the two layers. This avoids delamination or peeling failure during subsequent epitaxial growth and substrate stripping, and provides a buffer substrate with low interface state density and optimized surface energy state for high-quality epitaxial growth, ensuring the structural stability and process repeatability of the composite film.

[0040] 3. The embodiments of this application realize a vertical structure in which the first electrode and the second electrode are located on opposite sides of the epitaxial layer. The current passes through the active layer in the longitudinal direction. Compared with the existing transverse structure, it has the advantages of uniform current distribution, short heat dissipation path and low current crowding effect, which can effectively improve the luminous efficiency, luminous uniformity, photoelectric conversion efficiency and long-term working reliability of 365 nm ultraviolet LED. Attached Figure Description

[0041] The above-mentioned contents, other objects, features and advantages of this application will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0042] Figure 1 A flowchart illustrating a method for fabricating ultraviolet LEDs based on composite thin films according to an embodiment of this application is shown schematically.

[0043] Figure 2 A flowchart illustrating the fabrication process of ultraviolet LEDs based on composite thin films according to embodiments of this application is shown in the schematic diagram.

[0044] Figure 3 The schematic diagram illustrates the composite thin film structure and the structure of the vertical ultraviolet LED according to embodiments of this application;

[0045] Figure 4 The illustration shows a specific cross-sectional structure of an ultraviolet LED epitaxial layer according to an embodiment of this application. Detailed Implementation

[0046] The embodiments of this application will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of this application. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of this application for ease of explanation. However, it will be apparent that one or more embodiments may be implemented without these specific details. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of this application.

[0047] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0048] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0049] When using expressions such as "at least one of A, B and C", they should generally be interpreted in accordance with the meaning that is commonly understood by those skilled in the art (e.g., "a system having at least one of A, B and C" should include, but is not limited to, a system having A alone, a system having B alone, a system having C alone, a system having A and B, a system having A and C, a system having B and C, and / or a system having A, B and C, etc.).

[0050] Figure 1 A flowchart illustrating a method for fabricating ultraviolet LEDs based on composite thin films according to an embodiment of this application is shown. Figure 2 A flowchart illustrating a composite thin film-based ultraviolet LED fabrication process according to an embodiment of this application is shown.

[0051] like Figure 1 As shown, the method of this embodiment includes operations S110 to S160.

[0052] In operation S110, a semiconductor substrate is provided.

[0053] According to embodiments of this application, a semiconductor substrate is used to provide a support substrate for the subsequent epitaxial growth of two-dimensional material layers. This application does not strictly limit the specific material type of the semiconductor substrate, as long as it can withstand the temperature conditions of the subsequent epitaxial growth process and has sufficient surface flatness.

[0054] According to an embodiment of this application, after providing the semiconductor substrate, the process further includes a cleaning step to remove oil, particulate impurities, and oxide layers that may be present on the substrate surface. Cleaning can be performed using an organic solvent and deionized water in a sequential ultrasonic cleaning process, followed by drying with high-purity nitrogen gas for later use.

[0055] By operating S120, a two-dimensional material layer and a three-dimensional nanopattern layer are sequentially formed on a semiconductor substrate to obtain a composite structure.

[0056] According to embodiments of this application, a two-dimensional material layer refers to a material layer having a layered crystal structure, where atoms within the layers are bonded by covalent or ionic bonds, and atoms between the layers are bonded by relatively weak van der Waals forces. Since the interlayer van der Waals forces are much weaker than covalent bonds, the two-dimensional material layer can serve as a dissociation interface in subsequent substrate removal processes, enabling the epitaxial layer to be separated from the substrate without damage.

[0057] This application does not strictly limit the specific material type of the two-dimensional material layer, as long as it can be continuously deposited on the semiconductor substrate surface, has weak interlayer bonding characteristics, and can withstand the subsequent epitaxial growth temperature. The two-dimensional material layer can be formed by chemical vapor deposition or metal-organic chemical vapor deposition, and can be directly grown on the semiconductor substrate surface.

[0058] According to embodiments of this application, a three-dimensional nanopatterned layer refers to a nanoscale patterned structure layer with a three-dimensional morphology distributed on the surface of a two-dimensional material layer. The three-dimensional nanopatterned layer exhibits a regular or quasi-regular spatial arrangement, with at least one dimension having a feature size on the nanometer scale. The three-dimensional nanopatterned layer can provide a nanoscale patterned template for the subsequent epitaxial growth of the ultraviolet LED epitaxial layer, guiding the epitaxial layer to undergo lateral epitaxial growth, thereby effectively reducing the dislocation density and residual stress caused by lattice mismatch and thermal mismatch between the semiconductor substrate and the epitaxial layer.

[0059] This application does not impose any particular restrictions on the specific material type and morphological structure of the three-dimensional nanopatterned layer, as long as a three-dimensional structure with nanoscale patterned features can be formed on the surface of a two-dimensional material layer. The methods for forming the three-dimensional nanopatterned layer may include self-assembly transfer, spin coating, chemical vapor deposition, etc.

[0060] According to the embodiments of this application, such as Figure 2 As shown in part (a), a composite structure is obtained by sequentially forming a two-dimensional material layer and a three-dimensional nanopattern layer on a semiconductor substrate.

[0061] Operation S130 is used to perform plasma interface modification treatment on the composite structure to obtain a composite thin film.

[0062] According to embodiments of this application, plasma interface modification treatment refers to a process of bombarding and activating the surface of a composite structure using plasma. This treatment can physically bombard and chemically modify the interface between the two-dimensional material layer and the three-dimensional nanopatterned layer, removing adsorbed impurities and contaminants from the interface region and reducing the interface state density; simultaneously, it can introduce active functional groups onto the surface of the two-dimensional material layer and / or the three-dimensional nanopatterned layer, enhancing the interfacial bonding force between the two layers; furthermore, it can fine-tune the surface morphology of the three-dimensional nanopatterned layer, making its surface more uniform.

[0063] This application does not impose specific limitations on the specific process conditions for plasma interface modification treatment, as long as the above-mentioned interface activation and modification effects can be achieved.

[0064] According to the embodiments of this application, the composite film refers to a two-layer composite structure formed after plasma interface modification treatment, consisting of a two-dimensional material layer and a three-dimensional nano-pattern layer, which serves as a buffer substrate for the subsequent growth of ultraviolet LED epitaxial layers.

[0065] Operation S140 is used to epitaxially grow an ultraviolet LED epitaxial layer on the surface of the composite film.

[0066] According to the embodiments of this application, such as Figure 2 As shown in section (b), an ultraviolet LED epitaxial layer is epitaxially grown on the surface of a composite thin film (i.e., on a three-dimensional nanopatterned layer). The epitaxial layer includes at least a first conductivity type layer, an active layer, and a second conductivity type layer.

[0067] According to embodiments of this application, epitaxial growth refers to the process of depositing semiconductor material on the surface of a composite thin film in a crystallographic manner, so that the newly grown semiconductor material grows in an orderly manner along the lattice orientation of the composite thin film or a preferred orientation induced by the patterned structure of the composite thin film. Epitaxial growth can be performed using metal-organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE).

[0068] According to embodiments of this application, the ultraviolet LED epitaxial layer refers to the core semiconductor layer structure constituting the ultraviolet light-emitting diode, which includes at least a first conductivity type layer, an active layer, and a second conductivity type layer, stacked sequentially in a vertical direction. The first conductivity type layer and the second conductivity type layer have opposite conductivity types to form a pn junction structure capable of injecting electrons and holes.

[0069] According to an embodiment of this application, the first conductivity type layer refers to a semiconductor layer having a first conductivity type by doping.

[0070] According to the embodiments of this application, the active layer refers to a semiconductor layer structure sandwiched between a first conductivity type layer and a second conductivity type layer, used to realize the recombination of electrons and holes for luminescence.

[0071] According to an embodiment of this application, the second conductivity type layer refers to a semiconductor layer having a second conductivity type by doping, and its conductivity type is opposite to that of the first conductivity type layer.

[0072] In this application, the designation of the first conductivity type layer and the second conductivity type layer as "first" and "second" does not imply a specific fabrication order or polar orientation. Epitaxial growth can begin with either an n-type layer or a p-type layer; both are technical solutions covered by this application.

[0073] Operation S150 forms a first electrode on the first side of the epitaxial layer.

[0074] According to an embodiment of this application, the first electrode is a metal contact electrode for injecting current into the epitaxial layer of a UV LED, and it is formed on a first side surface of the epitaxial layer. An ohmic contact should be formed between the first electrode and the semiconductor layer it contacts to ensure efficient current injection into the epitaxial layer. Figure 2 As shown in section (c), the first electrode is, for example, the p electrode.

[0075] This application does not impose any particular limitation on the specific material of the first electrode, as long as it can form a low-resistance ohmic contact with the semiconductor layer it contacts. The first electrode can be formed using thin film deposition processes such as electron beam evaporation, thermal evaporation, or magnetron sputtering, combined with photolithography and lift-off processes to achieve the fabrication of a patterned electrode. Optionally, annealing can also be performed after the first electrode has been deposited.

[0076] Operation S160 removes at least a portion of the semiconductor substrate to expose at least a portion of the second side of the epitaxial layer.

[0077] According to embodiments of this application, removing at least a portion of the semiconductor substrate refers to separating and removing all or part of the semiconductor substrate from the composite film by physical or chemical means to expose the epitaxial layer on the other side of the surface opposite the first electrode.

[0078] According to embodiments of this application, removing at least a portion can be completely removing the semiconductor substrate, for example, as... Figure 2 As shown in section (d); or only the central region of the semiconductor substrate is removed while the edge portion is retained; or the entire substrate is thinned first and then locally removed.

[0079] According to the embodiments of this application, since the two-dimensional material layer has the characteristic of weak interlayer van der Waals force bonding, the bonding force between the semiconductor substrate and the two-dimensional material layer is much lower than the bonding force formed by covalent bonds between the traditional epitaxial layer and the substrate. Therefore, the removal of the semiconductor substrate can be completed under relatively mild conditions, without the need for violent means such as high-energy laser irradiation that may damage the active layer. After substrate removal, the exposed surface of the second side of the epitaxial layer can optionally be surface treated, for example, by using inductively coupled plasma etching to remove surface residues or thin part of the epitaxial layer to expose the surface of the semiconductor layer with good conductivity.

[0080] Operation S170 forms a second electrode on the second side of the epitaxial layer.

[0081] According to an embodiment of this application, the second electrode is another metal contact electrode for injecting current into the epitaxial layer of the ultraviolet LED, and it is formed on the second exposed surface of the epitaxial layer. For example... Figure 2As shown in section (d), the second electrode is, for example, the n-electrode. The second electrode and the first electrode are located on opposite sides of the epitaxial layer, and a vertical current transport path is formed between them through the conductivity type layer and the active layer inside the epitaxial layer. This electrode configuration is called a "vertical structure"—current flows vertically from one electrode of the device through the active layer to the other electrode, which has advantages such as uniform current distribution, short heat dissipation path, and low current congestion effect. This application does not impose any particular limitation on the specific material of the second electrode, as long as it can form a low-resistance ohmic contact with the semiconductor layer it contacts.

[0082] After the above operations S110 to S170, a vertical structure ultraviolet LED device is obtained. In this device, the first electrode and the second electrode are located on opposite sides of the epitaxial layer, forming a vertical current injection path, which enables uniform light emission and efficient heat dissipation under high current density.

[0083] In some embodiments of this application, the two-dimensional material layer is a layered material bonded by van der Waals forces. As an example, the two-dimensional material layer can be graphene or hexagonal boron nitride. Graphene consists of carbon atoms arranged in a honeycomb-like single-atom layer structure with sp² hybridization, bonded by van der Waals forces, exhibiting excellent thermal and electrical conductivity and chemical stability. Hexagonal boron nitride has a similar layered hexagonal honeycomb structure to graphene, with a wide band gap, good insulation, and relatively small lattice mismatch with group III nitride semiconductor materials. The two-dimensional material layer can be formed using chemical vapor deposition (CVD) or metal-organic chemical vapor deposition (MOCVD).

[0084] In some embodiments of this application, a three-dimensional nanopatterned layer is used as a patterning mask layer to guide the lateral epitaxial growth of the ultraviolet LED epitaxial layer. As an example, the three-dimensional nanopatterned layer can be an array of silicon oxide nanospheres or an array of carbon nanotubes.

[0085] When the three-dimensional nanopattern layer is a silicon oxide nanosphere array, its preparation method may include: using a gas-liquid interface self-assembly method to complete the close-packed self-assembly of silicon oxide nanospheres on the surface of deionized water, and transferring the whole assembly to the surface of a rigid substrate covered with a two-dimensional material layer to achieve large-area uniform spreading of nanospheres; subsequently, using an ICP etching process to morphologically modify and etch the silicon oxide nanospheres, and by precisely controlling the etching gas flow rate, etching power and etching time, nanoarray patterns with different pore sizes and different arrangement densities can be obtained.

[0086] When the three-dimensional nanostructured layer is a carbon nanotube array, its preparation method may include: using iron powder as a catalyst and acetylene as a carbon source, growing a primitive carbon nanotube array on a silicon substrate through a low-pressure chemical vapor deposition process; after the prepared carbon nanotube array is pretreated by dry spinning, it is uniformly covered on the surface of a rigid substrate with a two-dimensional material layer; preparing a circular carbon nanotube film by a focused ion beam cutting process, immersing the cut film in electronic-grade ethanol and placing it in a room temperature air environment for natural drying; after ethanol wetting and drying treatment, adjacent carbon nanotubes spontaneously shrink and aggregate to form carbon nanotube bundles; the two layers of carbon nanotube arrays are arranged vertically and alternately to form a square nanoscale patterned structure, constituting a three-dimensional nanoarray mask layer.

[0087] In some embodiments of this application, plasma interface modification of the composite structure includes: performing a first plasma treatment after the growth of the two-dimensional material layer; and performing a second plasma treatment after the preparation of the three-dimensional nanopatterned layer; wherein both the first and second plasma treatments are performed in an oxygen-containing atmosphere.

[0088] The first plasma treatment is used to activate the surface of the two-dimensional material layer, introducing active functional groups on its surface and enhancing the interfacial bonding force between it and the subsequent three-dimensional nano-patterned layer.

[0089] The second plasma treatment is used to perform final activation and passivation of the interface between the two-dimensional material layer and the three-dimensional nano-patterned layer, remove adsorbed impurities and contaminants in the interface region, reduce the interface state density, and ensure the structural stability and interface performance of the composite film.

[0090] In some embodiments of this application, removing at least a portion of the semiconductor substrate includes: using the interlayer van der Waals forces of the two-dimensional material layer, chemically wetting the interface between the semiconductor substrate and the two-dimensional material layer to remove the semiconductor substrate.

[0091] Specifically, due to the weak van der Waals forces between two-dimensional material layers, the bonding force between the semiconductor substrate and the two-dimensional material layer is much lower than the bonding force formed by covalent bonds between a traditional epitaxial layer and the substrate. By immersing the sample in a chemical solution, the solution's wetting and penetration effects allow it to penetrate along the interfaces between the two-dimensional material layers or between the two-dimensional material layer and the semiconductor substrate. This chemical action weakens the interfacial bonding force, achieving non-destructive separation between the semiconductor substrate and the epitaxial layer. This method eliminates the need for high-energy laser irradiation, avoiding damage to the active layer. The chemical solution can be a weakly acidic solution or other solutions known in the art that can be used for selective etching or wetting stripping.

[0092] Figure 3 The illustration shows a composite thin film structure and a vertical structure ultraviolet LED according to an embodiment of this application.

[0093] like Figure 3 Part (a) shows a schematic diagram of the structure of the composite film according to an embodiment of this application. This application also provides a composite film comprising: a two-dimensional material layer; and a three-dimensional nanopatterned layer located on the two-dimensional material layer; a plasma-modified interface is formed between the two-dimensional material layer and the three-dimensional nanopatterned layer. This composite film can be used as a standalone intermediate product for the epitaxial growth of ultraviolet LEDs.

[0094] After plasma interface modification treatment, the interfacial bonding performance between the two-dimensional material layer and the three-dimensional nano-patterned layer is significantly improved, the interface defects are passivated, the interface state density is reduced, and a composite film with stable structure and excellent interface performance is formed.

[0095] Figure 3 Part (b) schematically illustrates a structural diagram of a vertically structured ultraviolet LED according to an embodiment of this application. This application also provides a vertically structured ultraviolet LED, comprising: a composite thin film layer including a two-dimensional material layer and a three-dimensional nanopatterned layer located on the two-dimensional material layer; an ultraviolet LED epitaxial layer located on the composite thin film layer, the epitaxial layer including a first conductivity type layer, an active layer, and a second conductivity type layer; a first electrode electrically connected to a first side of the epitaxial layer; and a second electrode electrically connected to a second side of the epitaxial layer, the second electrode and the first electrode being located on opposite sides of the epitaxial layer.

[0096] In this vertical structure UV LED, the first electrode (p electrode) and the second electrode (n electrode) are located on opposite sides of the epitaxial layer (UV LED epitaxial layer), forming a vertical current injection path. Current flows vertically from one electrode through the active layer to the other electrode, offering advantages such as uniform current distribution, short heat dissipation path, and low current congestion effect.

[0097] In some embodiments of the present invention, forming a two-dimensional material layer on the semiconductor substrate includes: growing the two-dimensional material layer on the surface of the semiconductor substrate using a metal-organic chemical vapor deposition (MOCVD) process or a chemical vapor deposition (CVD) process. Specifically, when the two-dimensional material layer is graphene, a CVD process is preferably used, with methane as the carbon source and hydrogen and argon as carrier gases, and grown at approximately 1000°C; when the two-dimensional material layer is hexagonal boron nitride, a metal-organic chemical vapor deposition process is preferably used, with triethylboron as the boron source and ammonia as the nitrogen source, and grown by alternating induction at 1000°C to 1500°C.

[0098] In some embodiments of the present invention, forming a three-dimensional nanopatterned layer on the two-dimensional material layer includes: arranging silica nanospheres into a close-packed monolayer using a gas-liquid interface self-assembly method and transferring them to the surface of the two-dimensional material layer, and obtaining a silica nanosphere array by inductively coupled plasma etching; or, transferring a carbon nanotube array to the surface of the two-dimensional material layer, and obtaining a carbon nanotube array by wetting and drying with ethanol to cause adjacent carbon nanotubes to shrink and aggregate to form carbon nanotube bundles.

[0099] Figure 4 The illustration shows a specific cross-sectional structure of an ultraviolet LED epitaxial layer according to an embodiment of this application.

[0100] like Figure 4 As shown, the epitaxial layer can include, from bottom to top, a u-GaN layer, an n-GaN layer, a multi-quantum-well active layer, a p-AlGaN layer, and a p-GaN layer.

[0101] The u-GaN layer, an unintentionally doped GaN layer located on the surface of the composite film, serves to improve the interface quality between the composite film surface and the epitaxial layer, releasing residual stress caused by lattice and thermal mismatches. The n-GaN layer, a silicon-doped n-type GaN layer, serves as the first conductivity type layer of the device. The multi-quantum-well active layer, composed of alternating well and barrier layers, is the core region for electron-hole recombination luminescence. The electron blocking layer, a p-type AlGaN layer, suppresses electron overflow from the active layer to the p-type layer. The p-AlGaN and p⁺-GaN layers together serve as the second conductivity type layer, with the p⁺-GaN layer forming a low-resistance ohmic contact with the first electrode.

[0102] In some embodiments of this application, the first electrode is a p-electrode, which adopts a Ni / Au metal system. After the electrode is deposited by vapor deposition, it undergoes high-temperature annealing in an air atmosphere. By adjusting the electrode film thickness and annealing process parameters, the sheet resistance and contact resistance of the p-electrode are reduced, thereby improving the p-type ohmic contact performance and conductivity stability.

[0103] In some embodiments of this application, the second electrode is an n-electrode, which adopts a Ti / Al / Ti / Au metal system. After the electrode is deposited by vapor deposition, it is annealed under a nitrogen protective atmosphere. By precisely controlling the electrode film thickness, annealing temperature, heating rate, and holding time, a low resistivity and high adhesion n-type ohmic contact electrode is prepared.

[0104] Example 1

[0105] This embodiment provides a specific method for fabricating a vertical structure ultraviolet LED based on a composite thin film.

[0106] In this embodiment, a sapphire substrate is selected as the semiconductor substrate. The sapphire substrate is placed in acetone, anhydrous ethanol, and deionized water in sequence, and ultrasonically cleaned for 10 minutes in each case, and then dried with high-purity nitrogen gas.

[0107] In this embodiment, the two-dimensional material layer is graphene. Graphene is grown on the surface of a sapphire substrate using chemical vapor deposition (CVD) at a growth temperature of approximately 1000°C. The carbon source is methane, and the carrier gas is a mixture of hydrogen and argon. One to two monolayer or few-layer graphene layers are obtained, with a graphene film coverage of not less than 98%.

[0108] After the two-dimensional material layer is grown, a first plasma treatment is performed. Specifically, the sapphire substrate with graphene is placed in a plasma treatment chamber and plasma treatment is performed under a nitrogen atmosphere with a radio frequency power of 100 W and a treatment time of 3 min.

[0109] In this embodiment, the three-dimensional nanopatterned layer employs a silica nanosphere array. First, silica nanospheres with an average diameter of 200 nm–500 nm are densely packed and self-assembled on a deionized water surface using a gas-liquid interface self-assembly method. Then, the densely packed nanospheres are transferred as a whole to the surface of a sapphire substrate covered with a graphene film. After the transfer, inductively coupled plasma (ICP) etching is used to modify the morphology of the silica nanospheres. The etching gas is a mixture of CHF3 and Ar, the etching power is 100 W–300 W, and the etching time is 30 s–300 s, resulting in nanopatterned arrays with different pore sizes and densities.

[0110] After the three-dimensional nanopatterned layer was fabricated, a second plasma treatment was performed. The conditions for the second plasma treatment were the same as the first: under a nitrogen atmosphere, with a radio frequency power of 100 W and a treatment time of 3 min. After two plasma treatments, a graphene / silica nanosphere composite film was obtained.

[0111] In this embodiment, the ultraviolet LED epitaxial layer is grown using MOCVD technology. The epitaxial layer, from bottom to top, comprises: a u-GaN layer (thickness 1 μm–2 μm), and an n-GaN layer (thickness 1 μm–3 μm, silicon doping concentration approximately 5 × 10¹). 8 cm⁻³), InGaN / GaN multiple quantum well active layers (5–10 cycles, well layer thickness 2 nm–4 nm, barrier layer thickness 8 nm–15 nm), p-AlGaN electron blocking layers (thickness 10 nm–30 nm, Al composition 10%–25%), p-AlGaN layers and p⁺-GaN layers (thickness 0.01 μm–0.02 μm, magnesium doping concentration not less than 1 × 10¹ 9P+-GaN can reduce the width of the metal / semiconductor barrier, and holes can be transported through tunneling, achieving low-resistance ohmic contacts, reducing forward voltage drop and Joule heating, and improving photoelectric conversion efficiency.

[0112] In this embodiment, the first electrode is a p electrode, which adopts a Ni / Au metal system (Ni layer 20 nm to 50 nm, Au layer 50 nm to 200 nm). After electron beam evaporation on the surface of the p⁺-GaN layer, the p electrode pattern is formed by photolithography patterning and lift-off process, and then annealed in air at 450°C to 550°C for 5 min to 10 min.

[0113] In this embodiment, the weak van der Waals forces between graphene layers are utilized, and a weakly acidic dilute HF solution is used to wet the substrate interface to achieve non-destructive removal of the sapphire substrate. After substrate removal, the u-GaN layer is removed using an ICP etching process to expose the n-GaN layer surface. The ICP etching gas is a mixture of Cl2 and BCl3, and the etching depth is 1 μm to 2 μm.

[0114] In this embodiment, the second electrode is an n-electrode, which adopts a Ti / Al / Ti / Au metal system (the thickness of each layer is 20nm / 100nm~200nm / 20nm / 50nm~100nm respectively). After being vapor-deposited on the exposed n-GaN layer surface, the n-electrode pattern is formed by photolithography patterning and lift-off process, and then rapidly annealed at 700℃~900℃ for 30s~120s in a nitrogen protective atmosphere.

[0115] Through the above steps, a vertical structure ultraviolet LED device is obtained.

[0116] Example 2

[0117] This embodiment provides another specific method for fabricating a vertical structure ultraviolet LED based on a composite thin film.

[0118] In this embodiment, a silicon carbide substrate is selected as the semiconductor substrate. The silicon carbide substrate is placed in acetone, anhydrous ethanol, and deionized water in sequence, and ultrasonically cleaned for 12 minutes in each case, and then dried with high-purity nitrogen gas.

[0119] In this embodiment, the two-dimensional material layer is hexagonal boron nitride (h-BN). h-BN is grown on a silicon carbide substrate using MOCVD, with triethylboron as the boron source and ammonia as the nitrogen source. The growth temperature is 1200℃~1300℃, and a growth mode of periodically alternating TEB and NH3 introduction is employed. The thickness of h-BN is controlled by adjusting the number of growth cycles, ultimately obtaining a uniform h-BN film with a thickness of no more than 1 nm.

[0120] After the two-dimensional material layer is grown, the first plasma treatment is performed. Specifically, the sapphire substrate with graphene is placed in the plasma treatment chamber and plasma treatment is performed in an oxygen atmosphere. The radio frequency power is 100 W and the treatment time is 3 min.

[0121] In this embodiment, the three-dimensional nanopatterned layer employs a carbon nanotube array. First, a raw carbon nanotube array is grown using iron powder as a catalyst and acetylene as a carbon source via low-pressure CVD. After dry spinning pretreatment, the prepared carbon nanotube array is uniformly coated onto the surface of a silicon carbide substrate with an h-BN layer. A 2-inch circular carbon nanotube film is then prepared by focused ion beam cutting, followed by immersion in electronic-grade ethanol and natural drying in air at room temperature. Following ethanol wetting and drying, adjacent carbon nanotubes spontaneously shrink and aggregate, forming carbon nanotube bundles with widths of 2 μm to 4 μm and a bundle spacing of 200 nm to 500 nm. The two carbon nanotube arrays are arranged in a vertically staggered manner, forming a square nanoscale patterned structure, constituting a three-dimensional nanoarray mask layer.

[0122] After the three-dimensional nanopatterned layer was prepared, a second plasma treatment was performed under the same conditions as the first. Following both plasma treatments, an h-BN / carbon nanotube composite film was obtained.

[0123] In this embodiment, the structure of the ultraviolet LED epitaxial layer and the fabrication processes of the first and second electrodes are the same as in Example 1, and will not be described again here.

[0124] Through the above steps, a vertical structure ultraviolet LED device based on an h-BN / carbon nanotube array composite film is obtained.

[0125] The specific process parameters given in the above embodiments are exemplary and not intended to limit this application. In actual implementation, those skilled in the art can optimize and adjust the above parameters through conventional experiments based on the specific material system, equipment conditions, and target device performance.

[0126] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for fabricating ultraviolet LEDs based on composite thin films, characterized in that, include: Provide semiconductor substrates; A two-dimensional material layer and a three-dimensional nanopattern layer are sequentially formed on the semiconductor substrate to obtain a composite structure. The composite structure was subjected to plasma interface modification treatment to obtain a composite thin film; An ultraviolet LED epitaxial layer is epitaxially grown on the surface of the composite film, the epitaxial layer comprising at least a first conductivity type layer, an active layer, and a second conductivity type layer; A first electrode is formed on a first side of the epitaxial layer; At least a portion of the semiconductor substrate is removed to expose at least a portion of the second side of the epitaxial layer; A second electrode is formed on the second side of the epitaxial layer.

2. The preparation method according to claim 1, characterized in that, The two-dimensional material layer is a layered material bonded by van der Waals forces between its layers; the three-dimensional nano-patterned layer is used as a patterning mask layer to guide the lateral epitaxial growth of the ultraviolet LED epitaxial layer.

3. The preparation method according to claim 1, characterized in that, The plasma interface modification treatment of the composite structure includes: After the two-dimensional material layer is grown, a first plasma treatment is performed. After the three-dimensional nano-patterned layer is prepared, a second plasma treatment is performed. The first and second plasma treatments are both performed in an oxygen or nitrogen atmosphere.

4. The preparation method according to claim 1 or 2, characterized in that, The removal of at least a portion of the semiconductor substrate includes: The semiconductor substrate is removed by chemically wetting the interface between the semiconductor substrate and the two-dimensional material layer using the interlayer van der Waals forces of the two-dimensional material layer.

5. The preparation method according to claim 1, characterized in that, The two-dimensional material layer is graphene or hexagonal boron nitride.

6. The preparation method according to claim 1, characterized in that, The three-dimensional nanopatterned layer is an array of silicon oxide nanospheres or a carbon nanotube array. When the three-dimensional nanopattern layer is a silicon oxide nanosphere array, the silicon oxide nanospheres are arranged into a close-packed monolayer and transferred to the surface of the two-dimensional material layer by gas-liquid interface self-assembly method, and then obtained by inductively coupled plasma etching. When the three-dimensional nanopattern layer is a carbon nanotube array, the carbon nanotube array is transferred to the surface of the two-dimensional material layer, and after being soaked and dried with ethanol, the adjacent carbon nanotubes shrink and aggregate to form carbon nanotube bundles, thus obtaining a carbon nanotube array.

7. The preparation method according to claim 1, characterized in that, The ultraviolet LED is a 365 nm near-ultraviolet LED.

8. The preparation method according to claim 2, characterized in that, The first conductivity type layer is an n-type layer, the second conductivity type layer is a p-type layer, and the epitaxial layers, from bottom to top, include a u-GaN layer, an n-GaN layer, a multi-quantum-well active layer, an electron blocking layer, a p-AlGaN layer, and a p⁺-GaN layer.

9. A composite film, characterized in that, include: Two-dimensional material layer; as well as A three-dimensional nanopatterned layer located on the two-dimensional material layer; A plasma-modified interface is formed between the two-dimensional material layer and the three-dimensional nano-patterned layer.

10. A vertically structured ultraviolet LED, characterized in that, include: A composite thin film layer comprising a two-dimensional material layer and a three-dimensional nanopatterned layer located on the two-dimensional material layer, wherein the interface between the two-dimensional material layer and the three-dimensional nanopatterned layer is subjected to plasma interface modification treatment. An ultraviolet LED epitaxial layer located on the composite thin film layer, the epitaxial layer comprising a first conductivity type layer, an active layer, and a second conductivity type layer; The first electrode is electrically connected to the first side of the epitaxial layer; as well as A second electrode electrically connected to the second side of the epitaxial layer, wherein the second electrode and the first electrode are located on opposite sides of the epitaxial layer.

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