Aluminum gallium nitride-based deep ultraviolet light emitting diode and method of fabricating the same

Abstract

The application provides an aluminum gallium nitride-based deep ultraviolet light emitting diode and a preparation method thereof, and can be applied to the technical field of semiconductor optoelectronic devices. The structure of the aluminum gallium nitride-based deep ultraviolet light emitting diode comprises a sapphire substrate, an aluminum nitride buffer layer, an n-type aluminum gallium nitride layer, a multi-quantum well layer, an electron blocking layer, a p-type aluminum gallium nitride layer, a p-type gallium nitride contact layer and a metal electrode which are arranged in sequence, wherein the p-type aluminum gallium nitride layer and the p-type gallium nitride contact layer are provided with a mesa micro-nano reflective structure, the mesa micro-nano reflective structure comprises a plurality of array-distributed mesa micro-nano reflective units, and the mesa micro-nano reflective structure is obtained by optimizing a chaotic-Jaya algorithm and is used for improving the light extraction efficiency of the deep ultraviolet light emitting diode.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of light-emitting diode packaging structure, and more particularly to an aluminum gallium nitride-based deep ultraviolet light-emitting diode and a preparation method thereof. BACKGROUND

[0002] Since the 21st century, several large-scale public health events have highlighted unprecedented public health and safety challenges, significantly increasing the demand for safe and environmentally friendly semiconductor ultraviolet (UV) light sources, especially aluminum gallium nitride-based deep ultraviolet light-emitting diodes (DUV-LEDs). In addition to the demand for public health and safety, DUV-LEDs have also been widely used in industrial manufacturing fields, such as rapid curing of printing ink, high-precision ultraviolet lithography, processing of liquid crystal display panels, and deep purification of drinking water, etc. In modern agriculture, DUV-LEDs are also used to promote plant growth and monitor the growth state. In addition, due to the unique "solar blind" characteristics of deep ultraviolet (UVC) band ultraviolet light, in recent years, DUV-LEDs have attracted more and more research interest and attention in the fields of wireless optical communication, missile early warning systems and other national defense technologies.

[0003] Currently, the main obstacle for large-scale application of AlGaN-based DUV-LEDs is how to achieve high power output efficiency, which is mainly due to the low intrinsic external quantum efficiency (EQE). The external quantum efficiency (EQE) of the LED is determined by the internal quantum efficiency (IQE) and the light extraction efficiency (LEE). Although the IQE has been improved to more than 80% by optimizing the epitaxial growth technology and active region structure design, the LEE of DUV-LEDs remains at a low level. For the traditional flip-chip structure of DUV-LEDs, the main reasons for the low light extraction efficiency include: the reduction of light escape angle caused by the significant refractive index difference between the light emitting interface and the air, the optical loss caused by the high absorption of ultraviolet light by p-type gallium nitride, and the increase of the proportion of transverse magnetic (TM) polarized light in high aluminum content aluminum gallium nitride quantum well (QWs). In view of the above problems, researchers have proposed a method of constructing a patterned structure on the surface of p-type gallium nitride. Existing research shows that the micron-scale pattern structure on the surface of p-type gallium nitride has a significant effect on improving LEE, but there is still a lack of systematic research on sub-wavelength nanoscale patterned p-type gallium nitride layer of DUV-LEDs. At the same time, existing research focuses on the overall improvement of LEE, and there are few reports on the enhancement strategy of different polarization mode light LEE, especially the improvement strategy of TM polarized light LEE in DUV-LEDs. SUMMARY

[0004] (I) Technical problems to be solved

[0005] To solve at least one of the above problems, the present application provides an AlGaN-based deep ultraviolet light-emitting diode and a preparation method thereof, which adopts an artificial intelligence (AI) assisted reverse design method to optimize the reflective structure, introduces a new type of p-type gallium nitride (p-GaN) surface wall micro-nano reflective structure, and further improves the light extraction efficiency by enhancing the scattering effect.

[0006] (II) Technical solutions

[0007] In view of the above technical problems, the embodiments of the present application provide an AlGaN-based deep ultraviolet light-emitting diode and a preparation method thereof.

[0008] According to a first aspect of the present application, there is provided an aluminum gallium nitride-based deep ultraviolet light emitting diode, comprising: a sapphire substrate; an aluminum nitride buffer layer located on a surface of the sapphire substrate; an n-type aluminum gallium nitride layer located on a side of the aluminum nitride buffer layer away from the sapphire substrate; a multi-quantum well layer located on a side of the n-type aluminum gallium nitride layer away from the sapphire substrate; an electron blocking layer located on a side of the multi-quantum well layer away from the sapphire substrate; a p-type aluminum gallium nitride layer located on a side of the electron blocking layer away from the sapphire substrate; a p-type gallium nitride contact layer located on a side of the p-type aluminum gallium nitride layer away from the sapphire substrate; a metal electrode located on a side of the p-type gallium nitride contact layer away from the sapphire substrate; and a mesa micro-nano reflective structure disposed in the p-type aluminum gallium nitride layer and the p-type gallium nitride contact layer, the mesa micro-nano reflective structure comprising a plurality of arrayed mesa micro-nano reflective units, the mesa micro-nano reflective structure being obtained by optimization using a chaotic-Jaya algorithm, and used to improve the light extraction efficiency of the deep ultraviolet light emitting diode.

[0009] In some exemplary embodiments, the mesa micro-nano reflective unit is a composite structure composed of a cylinder and a circular truncated cone, wherein the parameters of the mesa micro-nano reflective unit include a period p, a height h, a top diameter d1, and a bottom diameter d2; and a metal aluminum layer is deposited between adjacent mesa micro-nano reflective units as a reflective material.

[0010] In some exemplary embodiments, the period p is 650 nm ± 65 nm, the height h is 85.0 nm ± 8.5 nm, the top diameter d1 is 450 nm ± 45 nm, and the bottom diameter d2 is 300 nm ± 30 nm.

[0011] In some exemplary embodiments, the method for optimizing the parameters of the mesa micro-nano reflective structure using the chaotic-Jaya algorithm comprises: randomly generating initial particles as the first generation of individuals within a preset parameter range, the particles representing a plurality of combinations of the parameters of the mesa micro-nano reflective structure; simulating and calculating the fitness function value of each particle using the finite difference time domain method; sorting the fitness function values of all particles and selecting the particle with the highest fitness function value as the representative particle of the current generation; feeding back the fitness function value of the representative particle to the chaotic-Jaya algorithm and adjusting the current position and speed of the particle to generate a particle swarm for the next generation; and repeating the above iteration process until a preset convergence criterion is met or the maximum number of iterations is reached, wherein the preset parameters include the height h, the period p, the top diameter d1, and the bottom diameter d2.

[0012] In some exemplary embodiments, the doping element of the n-type aluminum gallium nitride layer is silicon, and the doping concentration of the silicon element is 1.3 × 10 19 cm -3 ~1.7 × 10 19 cm -3The thickness of the n-type aluminum gallium nitride layer is 2.0 μm±0.2 μm.

[0013] In some exemplary embodiments, the multiple quantum well layer is composed of alternating aluminum gallium nitride barrier layers and aluminum gallium nitride well layers, wherein the thickness of the multiple quantum well layer is 100 nm±10 nm; the molar fraction of aluminum component in the aluminum gallium nitride barrier layer is 56%±5%; and the molar fraction of aluminum component in the aluminum gallium nitride well layer is 40%±4%.

[0014] In some exemplary embodiments, the material of the electron blocking layer is p-type aluminum gallium nitride, the molar fraction of aluminum component in the electron blocking layer is 45%, and the doping element of the p-type aluminum gallium nitride is magnesium element; the thickness of the electron blocking layer is 30 nm±3 nm.

[0015] In some exemplary embodiments, the doping element of the p-type aluminum gallium nitride layer is magnesium element, and the doping concentration of the magnesium element is 0.8×10 16 cm -3 ~1.2×10 16 cm -3 The thickness of the p-type aluminum gallium nitride layer is 70 nm±7 nm.

[0016] In some exemplary embodiments, the doping element of the p-type gallium nitride contact layer is magnesium element, and the doping concentration of the magnesium element is 0.8×10 18 cm -3 ~1.2×10 18 cm -3 The thickness of the p-type gallium nitride contact layer is 100 nm±10 nm.

[0017] According to a second aspect of the present application, a preparation method of an aluminum gallium nitride-based deep ultraviolet light emitting diode is provided, comprising: obtaining a sapphire substrate; epitaxially growing, on the sapphire substrate, an aluminum nitride buffer layer, an n-type aluminum gallium nitride layer, a multiple quantum well layer, an electron blocking layer, a p-type aluminum gallium nitride layer, and a p-type gallium nitride contact layer in sequence, the p-type aluminum gallium nitride layer being located away from the sapphire substrate; using electron beam lithography and inductively coupled plasma etching technology to etch a mesa micro-nano reflective structure on the p-type aluminum gallium nitride layer and the p-type gallium nitride contact layer, the mesa micro-nano reflective structure comprising a plurality of array-distributed mesa micro-nano reflective units, the mesa micro-nano reflective structure being obtained by optimization through a chaotic-Jaya algorithm, and being used to improve the light extraction efficiency of the deep ultraviolet light emitting diode; depositing a metal aluminum layer as a reflective material between adjacent mesa micro-nano reflective units; and preparing a metal electrode on the metal aluminum.

[0018] (Three) beneficial effects

[0019] As can be seen from the above technical solutions, the aluminum gallium nitride-based deep ultraviolet light emitting diode and the preparation method thereof provided by the embodiments of the present application have at least the following beneficial effects:

[0020] (1) By designing the micro-nano mesa reflector structure and using the chaos-Jaya (C-Jaya) algorithm combined with the three-dimensional electromagnetic simulation software based on the finite-difference time-domain method for optimization, the optimal micro-nano mesa reflector structure parameters are obtained. The experimental preparation and light-emitting characterization results show that the LEE of the flip-chip AlGaN DUV-LED is increased by more than 200%. Compared with the traditional structure (LEE is 3.1%) and the structure with an aluminum reflector layer (LEE is 5.8%), the LED with the optimal micro-nano mesa reflector structure achieves a LEE of 16.54%, which is increased by 442% and 185%, respectively.

[0021] (2) Compared with the traditional metal reflector, the micro-nano mesa reflector structure provides a more flexible and fine-tunable structure design space. The structure is defined by height h, period p, and top / bottom width (d1 / d2). By adjusting these parameters, the propagation path of light in the device can be accurately controlled, significantly improving the probability of deep ultraviolet light escaping into the air, and thus better meeting the needs of different application scenarios for light output.

[0022] (3) Considering the process tolerance in the preparation process, such as decrease in bottom diameter, increase in bottom diameter, and decrease in structure depth due to insufficient etching, the three-dimensional electromagnetic simulation software based on the finite-difference time-domain method is used for analysis. When the disorder degree of the structure parameters is controlled below 10%, the LEE decreases by no more than 4.8%. This indicates that the structure has a certain fault tolerance in the actual preparation process, reducing the process difficulty and cost.

[0023] (4) The LED light-emitting angle analysis under different reflector structures shows that the LED with the micro-nano mesa reflector structure proposed in the invention has lower extraction of type I and type III radiation light than the LED with the metal reflector structure, but the extraction intensity of type II radiation light (22°-158°, which is difficult to directly emit without regulation) is significantly enhanced. This characteristic enables the structure to more effectively improve the light extraction efficiency of the LED and meet the requirements of different application scenarios for light distribution.

[0024] (5) The room-temperature photoluminescence (RTPL) is used to characterize and analyze the light-emitting performance of the AlGaN-based DUV-LED with the micro-nano mesa reflector structure. The spectral test results show that the peak wavelength of the measured sample is 278 nm, which is basically consistent with the target wavelength of 280 nm, indicating that the prepared LED epitaxial wafer meets the expected design specifications. At the same time, the radiation intensity of the LED with the micro-nano mesa reflector structure proposed in the invention at the peak wavelength is 2.11 times that of the LED with the Al reflector layer, further verifying the effectiveness of the structure. BRIEF DESCRIPTION OF DRAWINGS

[0025] The above content of the present application and other purposes, features and advantages will be more apparent through the following description of the embodiments of the present application with reference to the accompanying drawings, in which:

[0026] Figure 1 A schematic diagram of an aluminum gallium nitride-based deep ultraviolet light emitting diode structure according to an embodiment of the present application is shown;

[0027] Figure 2 A flowchart of a method for preparing an aluminum gallium nitride-based deep ultraviolet light emitting diode according to an embodiment of the present application is shown;

[0028] Figure 3 A comparison diagram of an aluminum gallium nitride-based deep ultraviolet light emitting diode structure according to an embodiment of the present application and a conventional structure is shown;

[0029] Figure 4 A schematic diagram of a single iteration result in a reverse design process according to an embodiment of the present application is shown;

[0030] Figure 5 A schematic diagram of an analysis result of light extraction efficiency of an aluminum gallium nitride-based deep ultraviolet light emitting diode under different tolerances according to an embodiment of the present application is shown;

[0031] Figure 6 A comparison diagram of light emitting angles of a mesa-wall micro-nano reflective structure and a conventional reflective structure LED is shown;

[0032] Figure 7 A schematic diagram of a preparation process of a mesa-wall micro-nano reflective structure according to an embodiment of the present application is shown;

[0033] Figure 8 A schematic diagram of a mesa-wall micro-nano reflective structure according to an embodiment of the present application is shown;

[0034] Figure 9 A schematic diagram of a spectrum result of an LED epitaxial wafer sample of an Al reflective layer and a mesa-wall micro-nano reflective structure obtained by using a room-temperature photoluminescence test system is shown.

[0035] Reference signs:

[0036] 1-sapphire substrate; 2-aluminum nitride buffer layer; 3-n-type aluminum gallium nitride layer; 4-multi-quantum well layer; 5-electron blocking layer; 6-p-type aluminum gallium nitride layer; 7-p-type gallium nitride contact layer; 8-metal electrode; 9-metal aluminum layer. DETAILED DESCRIPTION

[0037] Embodiments of the present application will be described below with reference to the accompanying drawings. It should be understood, however, that the description that follows is merely exemplary and is not intended to limit the scope of the application. In the following detailed description of embodiments of the present application, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that one or more embodiments of the present application can be practiced without these specific details. In other instances, well-known structures and functions have not been described in detail in order to avoid obscuring aspects of the present application.

[0038] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. As used herein, the term "includes" and tautological equivalents thereof, means the inclusion of a feature, step, operation, and / or component but not to the exclusion of other features, steps, operations, and / or components.

[0039] All terms used herein including technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art unless otherwise defined herein. It should be noted that the use of terms such as "comprises", "comprising", "includes", "including", or "has", "having" should be construed to be open-ended, allowing for the inclusion of unspecified items, and that the use of terms such as "comprises", "comprising", "includes", "including", or "has", "having" should not be construed as excluding the presence of unspecified items.

[0040] In the case where expressions such as "at least one of A, B, and C, etc." are used, it should be generally construed that the meaning is the same as "at least one of A or B or C" (e.g., "a system having at least one of A, B, and C" should include, but not be limited to, a system having A alone, a system having B alone, a system having C alone, a system having both A and B, a system having both A and C, a system having both B and C, and / or a system having A, B, and C, etc.).

[0041] Figure 1 An aluminum gallium nitride-based deep ultraviolet light emitting diode structure according to an embodiment of the present application is schematically shown.

[0042] As Figure 1As shown, the aluminum gallium nitride-based deep ultraviolet light emitting diode according to the embodiment of the application comprises a sapphire substrate 1; an aluminum nitride buffer layer 2 located on the surface of the sapphire substrate 1; an n-type aluminum gallium nitride layer 3 located on the side of the aluminum nitride buffer layer 2 away from the sapphire substrate 1; a multi-quantum well layer 4 located on the side of the n-type aluminum gallium nitride layer 3 away from the sapphire substrate 1; an electron blocking layer 5 located on the side of the multi-quantum well layer 4 away from the sapphire substrate 1; a p-type aluminum gallium nitride layer 6 located on the side of the electron blocking layer 5 away from the sapphire substrate 1; a p-type gallium nitride contact layer 7 located on the side of the p-type aluminum gallium nitride layer 6 away from the sapphire substrate 1; a metal electrode 8 located on the side of the p-type gallium nitride contact layer 7 away from the sapphire substrate 1; and a mesa micro-nano reflective structure arranged in the p-type aluminum gallium nitride layer 6 and the p-type gallium nitride contact layer 7, the mesa micro-nano reflective structure comprising a plurality of array-distributed mesa micro-nano reflective units, the mesa micro-nano reflective structure being obtained by optimization through a chaotic-Jaya (C-Jaya) algorithm, and used for improving the light extraction efficiency of the deep ultraviolet light emitting diode.

[0043] The Jaya optimization algorithm is a meta-heuristic algorithm based on the principle of "seeking benefits and avoiding harm", the core idea of which is to search for a global optimal solution by constantly approaching the current optimal solution and moving away from the worst solution in the iteration process, and the search direction is dynamically adjusted by using random numbers in the algorithm formula, so that the algorithm does not need to set complex algorithm parameters and does not need to rely on gradient information, and therefore has the characteristics of simple structure, strong adaptability and easy implementation, and is suitable for continuous optimization problems and exhibits high efficient solving capacity in the fields of engineering design, power system dispatching and mechanical optimization.

[0044] The C-Jaya algorithm is an efficient meta-heuristic algorithm improved based on the Jaya optimization algorithm, the global search capability and convergence speed of which are significantly enhanced by introducing a chaotic mapping to replace the traditional random number generation strategy and combining an adaptive parameter adjustment mechanism, and the algorithm balances exploration and development by using a hybrid strategy, so that it exhibits stronger robustness and solving precision in complex nonlinear optimization problems, and is especially suitable for high-dimensional, multi-peak functions or scenes sensitive to initial solutions.

[0045] In the embodiment of the application, the mesa micro-nano reflective unit is a composite structure composed of a cylinder and a circular truncated cone, wherein the parameters of the mesa micro-nano reflective unit affecting the aluminum gallium nitride-based deep ultraviolet light emitting diode include a period p, a height h, a structure top diameter d1 and a structure bottom diameter d2; and a metal aluminum layer 9 is deposited between adjacent mesa micro-nano reflective units as a reflective material.

[0046] In the embodiment of the application, the period p is 650nm±65nm; the height h is 85.0nm±8.5nm; the structure top diameter d1 is 450nm±45nm; and the structure bottom diameter d2 is 300nm±30nm. ​​

[0047] Optionally, the doping element of the n-type aluminum gallium nitride layer 3 is silicon element, and the doping concentration of the silicon element is 1.3×10 19 cm -3 -1.7×10 19 cm -3 ; the thickness of the n-type aluminum gallium nitride layer 3 is 2.0 μm±0.2 μm.

[0048] Optionally, the multi-quantum well layer 4 is composed of alternating aluminum gallium nitride barrier layers and aluminum gallium nitride well layers, wherein the thickness of the multi-quantum well layer 4 is 100 nm±10 nm; the molar fraction of aluminum component in the aluminum gallium nitride barrier layer is 56%±5%; and the molar fraction of aluminum component in the aluminum gallium nitride well layer is 40%±4%.

[0049] Optionally, the material of the electron blocking layer 5 is p-type aluminum gallium nitride, the molar fraction of aluminum component in the electron blocking layer 5 is 45%, and the doping element of the p-type aluminum gallium nitride is magnesium element; the thickness of the electron blocking layer 5 is 30 nm±3 nm.

[0050] Optionally, the doping element of the p-type aluminum gallium nitride layer 6 is magnesium element, and the doping concentration of the magnesium element is 0.8×10 16 cm -3 -1.2×10 16 cm -3 ; the thickness of the p-type aluminum gallium nitride layer 6 is 70 nm±7 nm.

[0051] Optionally, the doping element of the p-type gallium nitride contact layer 7 is magnesium element, and the doping concentration of the magnesium element is 0.8×10 18 cm -3 -1.2×10 18 cm -3 ; the thickness of the p-type gallium nitride contact layer 7 is 100 nm±10 nm.

[0052] In some exemplary embodiments, the method for optimizing the parameters of the mesa micro-nano reflective structure by using the chaos-Jaya algorithm comprises the following steps: randomly generating initial particles as the first generation individuals in a preset parameter range, the particles representing various combinations of the parameters of the mesa micro-nano reflective structure; simulating and calculating the fitness function value of each particle by using the finite difference time domain method; sorting the fitness function values of all particles and selecting the particle with the highest fitness function value as the representative particle of the current generation; feeding back the fitness function value of the representative particle to the chaos-Jaya algorithm and adjusting the current position and speed of the particle to generate a particle swarm for the next generation; repeating the above iteration process until a preset convergence criterion is met or the maximum number of iterations is reached, wherein the preset parameters include height h, period p, structure top diameter , and structure bottom diameter .

[0053] Specifically, a model of the emission characteristics of DUV-LEDs is first established. This model is built by first obtaining the polarization characteristics of the radiated light in the active region, then establishing a compact equivalent replacement model, and finally introducing a light source with an adjustable polarization ratio into the active region. The light source is modeled as a planar emitter that radiates light outwards with angle-dependent intensity variations, based on... Perturbation theory ( Perturbation theory is an important method in solid-state physics used to calculate the band structure and optical properties of crystals. Light propagating in a specific direction simultaneously contains a transverse electric polarization component (TE) and a transverse magnetic polarization component (TM). Polarization characteristics during propagation are described by introducing s-polarization and p-polarization components, whose directionality is accurately characterized by the azimuth angle φ and the spatial angle θ. The electric field of the s-polarization component (-sinφ, -cosφ, 0) is defined as perpendicular to the direction of light propagation and in a plane determined by the c-axis, while the p-polarization component (-cosθcosφ, -cosθsinφ, sinθ) is characterized by an electric field orientation perpendicular to s. Based on the theoretical framework of the hexagonal symmetry principle and the biaxial stress assumption, the polarization characteristics of light along the propagation direction can be derived from the polarization characteristics of spontaneous emission radiation.

[0054]

[0055] in, The reflection coefficient under s-polarization, The reflection coefficient under p-polarization, The reflection coefficient in TE mode. This is the reflection coefficient in TM mode.

[0056] In embodiments of the present invention, the light extraction behavior of radiated light with different polarization characteristics in AlGaN-based DUV-LEDs was further studied using three-dimensional electromagnetic simulation software based on the finite-difference time-domain method. By defining specific electromagnetic field distributions and propagation characteristics, a plane wave source was used to simulate an actual incident electromagnetic wave with transverse uniformity. When the plane wave radiates energy at a specific elevation angle θ, the light extraction factor α in that direction is defined. θ Energy P collected on the substrate side export With plane wave source input energy P source The ratio:

[0057]

[0058] The ratio of radiant energy to the total energy of the light source at each spatial angle is defined as the light emission factor at that angle. Weighting factors The normalized spatial volume corresponding to this angle with the normalized spatial volume containing all light source angles ratio determination, i.e.,

[0059]

[0060] After multiplying with its corresponding angular weight factor and integrating, the light extraction efficiency LEE is obtained:

[0061]

[0062] When the ratio of TE and TM polarization modes in the DUV-LED spontaneous emission light changes, the θ corresponding angular weight factor will be dynamically adjusted accordingly. Specifically, the p:cos 2 polarized source, s:1 polarized source, and p:sin 2 polarized source are included. The corresponding LEE calculation formulas are as follows:

[0063]

[0064]

[0065]

[0066] where, represents the LEE of the p:cos 2 polarized source, represents the LEE of the s:1 polarized source, represents the LEE of the p:sin 2 polarized source, and n represents the minimum refractive index value. is the angular transmission factor corresponding to the kth minimum refractive index. Under different polarization ratios, the weight factor distribution of the spontaneous emission light in the spatial angle also changes, and the 50% light power cutoff angles are 34°, 62°, and 70°, respectively. Therefore, the angular weight factor changes with the angle and depends on the polarization composition of the radiation light.

[0067] To improve the light extraction efficiency of AlGaN-based DUV-LEDs, the present application proposes a mesa-wall micro-nano reflective structure combining the C-Jaya algorithm and a three-dimensional electromagnetic simulation software based on the finite-difference time-domain method. The structure first randomly generates a large number of initial particles as the first generation individuals within a predetermined parameter range, which represent various combinations of structure parameters. Then, the fitness function value of each particle is simulated and calculated by the finite-difference time-domain method. Next, the fitness function values of all particles are sorted, and the optimal particle with the highest fitness function value is selected as the representative of the current generation. This fitness value is fed back to the C-Jaya algorithm to adjust the current position and speed of the particles, thereby generating a particle swarm for the next generation. This iteration process continues until the predetermined convergence criteria are met or the maximum number of iterations is reached.

[0068] Figure 2 A flowchart of a preparation method of an aluminum gallium nitride-based deep ultraviolet light-emitting diode according to an embodiment of the present application is schematically shown.

[0069] As shown in Figure 2 , the preparation method of an aluminum gallium nitride-based deep ultraviolet light-emitting diode according to an embodiment of the present application includes steps S110-S150.

[0070] In step S110, a sapphire substrate 1 is obtained.

[0071] In step S120, an aluminum nitride buffer layer 2, an n-type aluminum gallium nitride layer 3, a multi-quantum well layer 4, an electron blocking layer 5, a p-type aluminum gallium nitride layer 6, and a p-type gallium nitride contact layer 7 are sequentially epitaxially grown on the sapphire substrate 1, located away from the sapphire substrate 1 on the side of the p-type aluminum gallium nitride layer 6.

[0072] In step S130, a mesa-wall micro-nano reflective structure including a plurality of array-distributed mesa-wall micro-nano reflective units is etched on the p-type aluminum gallium nitride layer 6 and the p-type gallium nitride contact layer 7 using electron beam lithography and inductively coupled plasma etching technology. The mesa-wall micro-nano reflective structure is obtained by optimization using the chaotic-Jaya algorithm, and is used to improve the light extraction efficiency of the deep ultraviolet light-emitting diode.

[0073] In step S140, a metal aluminum layer 9 is deposited as a reflective material between adjacent mesa-wall micro-nano reflective units.

[0074] In step S150, a metal electrode 8 is prepared on the metal aluminum. Optionally, the material of the metal electrode 8 can include gold, copper, aluminum, etc. Preferably, the material of the metal electrode 8 is gold.

[0075] For example, the LEE of flip-chip AlGaN-based DUV-LEDs is simulated and analyzed by using the three-dimensional finite-difference time-domain method. First, the overall layout of the device is constructed. The traditional LED device is sequentially arranged from top to bottom as follows: a 2-μm sapphire substrate 1, a 1-μm AlN buffer layer, a 2-μm n-AlGaN layer, a 100-nm MQWs layer, a 30-nm electron blocking layer 5, a 70-nm p-AlGaN layer, and a 100-nm p-GaN contact layer, as shown in (a) of FIG. 1. Figure 3 In the LED epitaxial structure, a 30-nm GaN buffer layer and a 70-nm aluminum reflection layer can be introduced, as shown in (b) of FIG. 1, to enhance the reflection of light. Figure 3 The LED configuration with the micro-nano reflective structure according to an embodiment of the present application is shown in (c) of FIG. 1. Each unit of the reflective structure is defined by a height h, a period p, and a ratio (d1 / d2) of a diameter d1 of a top of the structure to a diameter d2 of a bottom of the structure, and aluminum is deposited between adjacent structure units as a reflective material. Figure 3

[0076] The device is set to have a single period of a unit structure in the lateral direction, Bloch boundary conditions are added to the lateral boundary, a 280-nm single wavelength is set as the light source and is placed in the center of the MQWs region in the epitaxial wafer, a non-uniform grid is set, the minimum grid size is 5 nm, perfect matched layers are set on the upper and lower surfaces of the simulation model, and a power monitor is set, which is located 50 nm above the sapphire substrate 1.

[0077] The C-Jaya intelligent optimization algorithm is used to perform reverse design on the micro-nano reflective structure of the AlGaN-based DUV-LEDs, Figure 4 and a schematic diagram of a single iteration result in the reverse design process according to an embodiment of the present application is shown schematically. The LEE value of the traditional device structure is represented by a solid rectangle, the LEE value of the device with the aluminum reflection layer is represented by a solid triangle, the LEE value of each particle in the current iteration is represented by a hollow circle, the optimal LEE value accumulated in the current iteration process is marked by a solid diamond, and the algorithm gradually approaches the optimal solution as the number of iterations increases.

[0078] After multiple rounds of iteration, the optimal LEE of the micro-nano reflective structure and the corresponding parameters are obtained. The structure period p is about 650 nm, which has a significant influence on the interference and diffraction effects of light. The structure height h is about 85 nm, which determines the propagation path of light in the nano structure and the number of reflections. The diameters of the top and bottom of the structure and are 450 nm and 300 nm, respectively, which define the shape and size of the nano structure. The LED with the optimal structure achieves a LEE of 16.54%, which is increased by 442% and 185% compared with the traditional structure (3.1%) and the structure with the aluminum reflection layer (5.8%), respectively. ​

[0079] Figure 5 The diagram illustrates the light extraction efficiency analysis results of an aluminum gallium nitride-based deep ultraviolet light-emitting diode under different tolerances according to an embodiment of the present invention.

[0080] like Figure 5 As shown in (a), considering process tolerances during fabrication, the main tolerances include: reduced bottom diameter, increased bottom diameter, and reduced structural depth due to insufficient etching, defined as deviation categories A, B, and C, respectively. Using three-dimensional electromagnetic simulation software based on the finite-difference time-domain method, the ratio of structural deviation amplitude to standard structural parameter values ​​was used as a measure of structural disorder. The impact of different types of deviations on the LEE was analyzed, and the analysis results are shown in [reference missing]. Figure 5 (b) in the middle, by Figure 5 As shown in (b), when the disorder of the structural parameters is controlled below 10%, the decrease in LEE does not exceed 4.8%. Furthermore, due to the coupling effect between the structural parameters and the optical cavity effect, the trend of LEE change is not a monotonically decreasing trend when the structural disorder increases.

[0081] Figure 6 The diagram illustrates a comparison of the LED emission angles between the micro / nano reflective structure on the platform wall and the traditional reflective structure.

[0082] like Figure 6 As shown, the following structures are configured: a traditional non-reflective structure, a structure with a 100 nmp-GaN / 75 nmp AlGaN reflective layer, a structure with a 30 nmp-GaN / 100 nmp-AlGaN / Al reflective layer, and the micro / nano reflective structure of the stage wall proposed in this invention. Type I radiation (0°~22°): more easily emitted directly from the top surface; Type II radiation (22°~158°): difficult to emit directly without control; Type III radiation (68°~180°): more likely to be redirected and emitted through reflection. Figure 6 It is evident that, in the mesa-wall micro / nano reflective structure LED according to embodiments of the present invention, although the extraction amounts of Type I and Type III radiation light are lower than those of the metal reflective layer structure LED, the extraction intensity of Type II radiation light is significantly enhanced, effectively improving the light extraction efficiency of the LED. In the mesa-wall nanoscale reflective structure LED, although the extraction amounts of Type I and Type III radiation light are lower than those of the metal reflective layer structure LED, the extraction intensity of Type II radiation light is significantly enhanced. This enhancement is mainly due to the proposed reflective structure modulating the light propagation path through scattering and cavity effects, allowing more radiation light to be redirected and emitted from the sapphire surface, thereby more effectively improving the light extraction efficiency of the LED.

[0083] The micro / nano reflective structure with a mesa wall proposed in this invention was fabricated using metal-organic chemical vapor deposition (MOCVD) on a sapphire substrate 1 via epitaxial growth, including a 2 μm Si-doped n-AlGaN layer with a doping concentration of 1.5 × 10⁻⁶. 19 cm -3 The active region of the MQWs consists of an Al barrier layer with 56% Al and a well layer with 40% Al, a 30nm Mg-doped electron barrier layer with 45% Al, and a 70nm Mg-doped p-AlGaN layer with a doping concentration of 1×10⁻⁶. 16 cm -3 And a 100nm Mg-doped p-GaN layer with a doping concentration of 1×10⁻⁶. 18 cm -3 .

[0084] Figure 7 The schematic diagram illustrates the fabrication process of the micro / nano reflective structure of the platform wall according to an embodiment of the present invention.

[0085] like Figure 7 As shown, a mesa-shaped micro / nano reflective structure on the p-type sidewall, composed of p-GaN and p-AlGaN layers, was fabricated using electron beam lithography (EBL) and inductively coupled plasma (ICP) etching. The main steps included: epitaxial wafer cleaning and drying, spin-coating a 0.4 μm thick negative resist AR-N7520.17, pre-baking at 85°C for 1 min, and etching at 400°C. Exposure metering, EBL, 85°C post-baking for 90 seconds, development, and ICP etching was performed on GaN and p-AlGaN layers, and 400 nm Al was deposited by electron beam evaporation to form a reflective layer. The preparation results are shown in [Figure number missing]. Figure 8 .

[0086] The luminescence performance of AlGaN-based DUV-LEDs with a stage-wall micro / nano reflective structure was characterized and analyzed using room-temperature photoluminescence (RTPL). The test procedure was as follows: A 266 nm laser was incident on the sample surface at a 45° angle, exciting the active region to generate electronic transitions and initiating spontaneous emission. The excited light propagated inside the LED and was collected by optical elements and focused at the entrance slit of the spectrometer. After dispersion by a grating, the light was received by a photomultiplier tube and converted into an electrical signal, ultimately obtaining the photoluminescence spectrum of the sample. By adjusting the position of the displacement platform, the optical response of the LED under different laser incident positions could be tested and acquired.

[0087] Figure 9The schematic diagram illustrates the spectral results of an LED epitaxial wafer sample with an Al reflective layer and a mesa-wall micro / nano reflective structure obtained using a room-temperature photoluminescence testing system.

[0088] Depend on Figure 9 The spectral test results show that the peak wavelength of the measured sample is 278 nm, which is basically consistent with the target wavelength of 280 nm, indicating that the prepared LED epitaxial wafer has achieved the expected design specifications. Furthermore, the mesa-wall micro-nano reflective structure LED according to the embodiment of the present invention exhibits a radiation intensity at its peak wavelength that is 2.11 times that of the LED with an Al reflective layer, demonstrating that the mesa-wall micro-nano reflective structure proposed in this invention effectively improves the light emission intensity of the LED.

[0089] Those skilled in the art will understand that the features described in the various embodiments of the present invention can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in the present invention. In particular, the features described in the various embodiments of the present invention can be combined and / or combined in various ways without departing from the spirit and teachings of the present invention. All such combinations and / or combinations fall within the scope of the present invention.

Claims

1. An aluminum gallium nitride-based deep ultraviolet light-emitting diode, characterized in that, include: Sapphire substrate; An aluminum nitride buffer layer is located on the surface of the sapphire substrate; An n-type aluminum gallium nitride layer is located on the side of the aluminum nitride buffer layer away from the sapphire substrate; A multi-quantum-well layer is located on the side of the n-type aluminum gallium nitride layer away from the sapphire substrate; An electron blocking layer is located on the side of the multiple quantum well layer away from the sapphire substrate; A p-type aluminum gallium nitride layer is located on the side of the electron blocking layer away from the sapphire substrate; The p-type gallium nitride contact layer is located on the side of the p-type aluminum gallium nitride layer away from the sapphire substrate; A metal electrode is located on the side of the p-type gallium nitride contact layer away from the sapphire substrate; as well as A mesa-shaped micro / nano-reflective structure is disposed within the p-type aluminum gallium nitride layer and the p-type gallium nitride contact layer. The mesa-shaped micro / nano-reflective structure includes multiple arrayed mesa-shaped micro / nano-reflective units, each of which is a composite structure composed of cylinders and frustums. A metallic aluminum layer is deposited between adjacent mesa-shaped micro / nano-reflective units as a reflective material. The parameters of the mesa-shaped micro / nano-reflective units are optimized using a chaotic-Jaya algorithm to improve the light extraction efficiency of the deep ultraviolet light-emitting diode. The parameters of the mesa-shaped micro / nano-reflective units include period p, height h, top diameter d1, and bottom diameter d2.

2. The aluminum gallium nitride-based deep ultraviolet light-emitting diode according to claim 1, characterized in that, The period p is 650nm ± 65nm; The height h is 85.0 nm ± 8.5 nm; The top diameter d1 of the structure is 450nm ± 45nm; The bottom diameter d2 of the structure is 300nm ± 30nm.

3. The aluminum gallium nitride-based deep ultraviolet light-emitting diode according to claim 1, characterized in that, The method for optimizing the parameters of the table wall micro / nano reflective unit using the chaotic-Jaya algorithm includes: Initial particles are randomly generated within a preset parameter range as first-generation individuals, and the particles represent multiple combinations of parameters of the micro-nano reflective unit of the platform wall. The fitness function value of each particle was calculated by simulation using the finite-difference time-domain method. The fitness function values ​​of all particles are sorted, and the particle with the highest fitness function value is selected as the representative particle of the current generation. The fitness function value of the representative particle is fed back into the chaos-Jaya algorithm, and the current position and velocity of the particle are adjusted to generate a particle swarm for the next generation. Repeat the above iterative process until the preset convergence criterion is met or the maximum number of iterations is reached. The preset parameters include height h, period p, and top diameter of the structure. And the bottom diameter d2 of the structure.

4. The aluminum gallium nitride-based deep ultraviolet light-emitting diode according to claim 1, characterized in that, The n-type aluminum gallium nitride layer is doped with silicon, and the silicon doping concentration is 1.3 × 10⁻⁶. 19 cm -3 ~1.7×10 19 cm -3 ; The thickness of the n-type aluminum gallium nitride layer is 2.0 μm ± 0.2 μm.

5. The aluminum gallium nitride-based deep ultraviolet light-emitting diode according to claim 1, characterized in that, The multiple quantum well layer consists of alternating aluminum gallium nitride barrier layers and aluminum gallium nitride well layers. The thickness of the multiple quantum well layer is 100nm ± 10nm; The molar fraction of aluminum in the aluminum gallium nitride barrier layer is 56% ± 5%; The molar fraction of aluminum in the aluminum gallium nitride potential well layer is 40% ± 4%.

6. The aluminum gallium nitride-based deep ultraviolet light-emitting diode according to claim 1, characterized in that, The electron blocking layer is made of p-type aluminum gallium nitride, with an aluminum molar fraction of 45% and magnesium as the doping element. The thickness of the electron blocking layer is 30nm ± 3nm.

7. The aluminum gallium nitride-based deep ultraviolet light-emitting diode according to claim 1, characterized in that, The p-type aluminum gallium nitride layer is doped with magnesium, and the magnesium doping concentration is 0.8 × 10⁻⁶. 16 cm -3 ~1.2×10 16 cm -3 ; The thickness of the p-type aluminum gallium nitride layer is 70 nm ± 7 nm.

8. The aluminum gallium nitride-based deep ultraviolet light-emitting diode according to claim 1, characterized in that, The p-type gallium nitride contact layer is doped with magnesium, and the magnesium doping concentration is 0.8 × 10⁻⁶. 18 cm -3 ~1.2×10 18 cm -3 ; The thickness of the p-type gallium nitride contact layer is 100nm ± 10nm.

9. A method for fabricating an aluminum gallium nitride-based deep ultraviolet light-emitting diode, characterized in that, include: Obtaining a sapphire substrate; An aluminum nitride buffer layer, an n-type aluminum gallium nitride layer, a multiple quantum well layer, an electron blocking layer, a p-type aluminum gallium nitride layer, and a p-type gallium nitride contact layer are epitaxially grown sequentially on the sapphire substrate, with the p-type aluminum gallium nitride layer located on the side away from the sapphire substrate. Electron beam lithography and inductively coupled plasma etching (ICP-C) techniques were used to etch a mesa-shaped micro / nano-reflective structure between the p-type aluminum gallium nitride (AlGaN) layer and the p-type gallium nitride (GaN) contact layer. The mesa-shaped micro / nano-reflective structure comprises multiple arrayed mesa-shaped micro / nano-reflective units, each a composite structure consisting of cylinders and frustums. The parameters of the mesa-shaped micro / nano-reflective structure are optimized using a chaotic-Jaya algorithm to improve the light extraction efficiency of the deep ultraviolet (DUV) light-emitting diode (LED). The parameters of the mesa-shaped micro / nano-reflective units include period p, height h, top diameter d1, and bottom diameter d2. A layer of metallic aluminum is deposited between adjacent micro / nano reflective units on the stage wall as a reflective material; A metal electrode is prepared on the aluminum metal.

Images