Methods for improving LED light extraction efficiency based on metasurfaces, and corresponding LED devices and applications.

Abstract

This invention discloses a method for improving LED light extraction efficiency based on metasurfaces, as well as corresponding LED devices and applications. The method includes step S10: fabricating at least one metaunit on the light-emitting surface of an LED chip. All metaunits form a metasurface on the light-emitting surface to form an LED device. The thickness of each metaunit is uniform throughout, and the metaunits are configured to provide -φ(x,y) phase compensation to the light-emitting surface, where λ0 is the center wavelength of the LED chip, and f is the optical path length from the multiple quantum wells in the LED chip to the light-emitting surface. Even with uniform thickness in each metaunit, arbitrary modulation of the local field phase within the range of 0–2π can be achieved, enabling phase modulation of the emitted light from the light-emitting surface. This allows the wavefront of the emitted light to approximate as planar light, thereby simplifying the shape of the metaunits while improving the light extraction efficiency of the fabricated LED device.

Description

Technical Field

[0001] This invention relates to the field of LED device technology, specifically to a method for improving LED light extraction efficiency based on metasurfaces, and corresponding LED devices and applications. Background Technology

[0002] When an LED chip emits light, the light emitted from inside the chip travels through a denser medium to a less dense medium. When the angle of incidence exceeds a critical angle, the light no longer refracts but returns entirely to the LED chip. This is known as total internal reflection (TIR). Because of TIR, the light emitted by the LED chip cannot escape completely, resulting in a lower light extraction efficiency (LEE).

[0003] Although pattern etching on the surface of LED chips can improve total internal reflection and increase light extraction efficiency, most of the etched patterns are currently triangular prisms, square pyramids, hemispherical structures, etc. These structures use the thickness difference of the etched pattern to achieve wavefront control. Because the etched pattern has thickness differences, the etching depth is large, the number of etching times is large, and the etching efficiency is low. Summary of the Invention

[0004] To address the issue of improving total internal reflection in LED chips through pattern etching, which requires etching patterns with varying thicknesses, leading to at least one of the following problems: complex pattern shapes, large etching depths, numerous etching passes, and low etching efficiency, the inventors conducted extensive research and experiments on the light emission modes of LED chips. They discovered that, without considering reflection from the p-type reflective electrode, the phase of each dipole in the multiple quantum wells (MQWs) layer of the LED chip at the light-emitting surface can be approximated as dipole radiation, and the phase distribution of this dipole at the light-emitting surface can be approximated as... Wherein, λ0 is the center wavelength of the LED chip, and f is the optical path from the multiple quantum wells of the LED chip to its emitting surface. The emitting modes of the multiple quantum well layer, which serves as the emitting layer of the LED chip, include TE mode and TM mode. This emitting mode can be equivalently represented as the superposition of multiple electric dipoles (corresponding to TE mode) and multiple magnetic dipoles (corresponding to TM mode) in the multiple quantum well layer. Electric dipoles and magnetic dipoles are collectively referred to as dipoles. Based on the above findings, the inventors conceived of fabricating a metamaterial on the emitting surface of the LED chip capable of performing -φ(x,y) phase compensation on the emitting surface to solve at least one of the above problems. Therefore, according to one aspect of the present invention, a method for improving LED light extraction efficiency based on a metamaterial surface is provided.

[0005] The method for improving LED light extraction efficiency based on metasurfaces includes step S10: fabricating at least one metaunit on the light-emitting surface of the LED chip, wherein all metaunits form a metasurface on the light-emitting surface to form an LED device, the thickness of the metaunits is uniform everywhere, and the metaunits are configured to provide -φ(x,y) phase compensation to the light-emitting surface, wherein... λ0 is the center wavelength of the LED chip, and f is the optical path length from the multiple quantum wells in the LED chip to the light-emitting surface.

[0006] Therefore, even if the thickness of each metaunit is equal everywhere, arbitrary modulation of the local field phase in the range of 0 to 2π can be achieved at this position to achieve phase modulation of the emitted light from the light-emitting surface, so that the wavefront of the emitted light can be approximated as planar light, thereby improving the light extraction efficiency of the fabricated LED device while simplifying the shape of the metaunit.

[0007] In some embodiments, the metaunit includes at least two cylinders of equal height distributed on the light-emitting surface. The cylinders are made of a dielectric material, and at least two of the cylinders constituting the metaunit have unequal diameters. Using cylinders of equal height to form the metaunit simplifies the shape of the constituent units, allowing the metaunit to be obtained with only one etching operation when fabricated by etching, thus greatly improving etching efficiency. Furthermore, since dielectric cylinders of different diameters modulate the local optical field differently, the local optical field can be arbitrarily modulated within the range of 0–2π, thereby controlling the wavefront of the transmitted light. By using appropriate cylinder diameters and distribution, the emitted light can be phase-modulated, making the wavefront of the emitted light approximately planar.

[0008] In some embodiments, all the cylinders constituting a metaunit are arranged in a hexagonal grid structure on the light-emitting surface; the diameter of the cylinders ranges from 0.1λ0 to 0.5λ0; the center distance between two adjacent cylinders in the hexagonal grid structure ranges from d. max<a<λ0, where d max Let d be the maximum value of d, where d is the diameter of the cylinder. Thus, by adjusting the size and layout of the cylinder, the resulting hexagonal mesh structure of the meta-units can achieve phase modulation of 0 to 2π at their local locations, making the wavefront of the emitted light approximately planar.

[0009] In some implementations, in step S10, Corrections were made using FDTD simulation; specifically, the thickness of the metacell and the diameter of the cylinder were obtained through FDTD simulation combined with the center wavelength λ0 of the LED chip. By adjusting the specifications and layout of the cylinder, the resulting metacell can perform phase compensation of -φ(x,y) on the light-emitting surface, so that the wavefront of the emitted light from the resulting LED chip can be approximated as planar light.

[0010] In some embodiments, the LED chip is a UV LED chip, an AlGaN-based LED chip, and / or the metacells fabricated on the light-emitting surface of the LED chip have a refractive index greater than 2 and an absorption coefficient < 10 in the UV band. -2 The material is made of μm. Due to the unique optical polarization characteristics and large refractive index difference of AlGaN-based ultraviolet light-emitting diodes (UVLEDs), the proportion of total internal reflection is higher and the light extraction efficiency is lower. This invention prepares a metasurface on the light-emitting surface of the LED chip that can perform phase compensation of -φ(x,y) on the light-emitting surface, so that the wavefront of the emitted light of the LED chip can be approximately planar.

[0011] In some embodiments, in step S10, multiple meta-units are fabricated on the light-emitting surface of the LED chip; preferably, the multiple meta-units are arrayed on the light-emitting surface with a period of P, where the period P ranges from 0.5f < P < 2f. Since the focal length f of the meta-surface (each unit is equivalent to a plane lens with a focal length f, which is equal to the optical path f from the multiple quantum wells to the light-emitting surface) is much smaller than the size of the light-emitting surface of the LED chip, and the light source is the entire multiple quantum well layer, arraying the meta-units on the light-emitting surface of the LED chip with a period of P forms a meta-surface on the light-emitting surface of the LED chip, thereby further improving the phase modulation efficiency of the light-emitting surface of the LED chip and further improving the light extraction efficiency of the LED chip.

[0012] In some implementations, step S10 includes:

[0013] Step S11: Prepare a dielectric layer on the light-emitting surface of the prepared LED chip;

[0014] Step S20: Etch the dielectric layer to obtain at least one metaunit. The metaunit is capable of providing -φ(x,y) phase compensation to the light-emitting surface. λ0 is the center wavelength of the LED chip, and f is the optical path length from the multiple quantum wells in the LED chip to the light-emitting surface.

[0015] Since the metacells are composed of cylinders of uniform height, only a single etching of the dielectric layer on the light-emitting surface of the LED chip is required to obtain a wavefront that approximates a planar light, greatly improving etching efficiency.

[0016] According to one aspect of the present invention, an LED device with high light extraction efficiency is provided, which is fabricated using the aforementioned method for improving LED light extraction efficiency based on metasurfaces. The metasurface in the fabricated LED device with high light extraction efficiency can perform -φ(x,y) phase compensation on the light-emitting surface of the LED chip, making the wavefront of the emitted light from the LED chip approximately planar, significantly reducing the proportion of total internal reflection in the LED chip, thereby greatly improving the light extraction efficiency of the fabricated LED device.

[0017] According to another aspect of the present invention, an LED device with high light extraction efficiency is provided, the LED device comprising: an LED chip; and at least one meta-unit disposed on the light-emitting surface of the LED chip, capable of performing phase compensation of -φ(x,y) on the light-emitting surface; wherein, λ0 is the center wavelength of the LED chip, and f is the optical path length from the multiple quantum wells of the LED chip to the light-emitting surface.

[0018] because To determine the phase distribution of dipole radiation generated by each dipole on the light-emitting surface of multiple dipoles equivalent to the light-emitting mode of the LED chip, a metacell capable of performing phase compensation of -φ(x,y) on the light-emitting surface of the LED chip is set up, so that the wavefront of the emitted light can be approximated as planar light, thereby improving the light extraction efficiency of the LED device.

[0019] In some embodiments, the meta-unit includes multiple cylinders of equal height distributed on the light-emitting surface. The cylinders are made of a dielectric material, and at least two of the cylinders constituting the meta-unit have unequal diameters. All the cylinders constituting a meta-unit are arranged in a hexagonal grid structure on the light-emitting surface. The diameter of the cylinders ranges from 0.1λ0 to 0.5λ0, and the center-to-center distance between two adjacent cylinders in the hexagonal grid structure ranges from d. max <a<λ0; the height of the cylinder ranges from 300nm to 500nm.

[0020] Since at least two of all the cylinders constituting the meta - unit are set as cylinders with different diameters, the cylinders constituting the meta - unit are arranged in a hexagonal grid structure. At the same time, the value range of the diameter of the cylinders is set to be 0.1 - 0.5λ0, and the value range of the center - to - center distance between two adjacent cylinders in the hexagonal grid structure is d max <a < λ0, where d max is the maximum value of d, so that when the height of the cylinder is within the range of 300 nm - 500 nm, the wavefront of the light emitted by the LED device can be approximated as plane light. The height of the meta - unit obtained thereby is much smaller than the height of the general etched pattern, which can simplify the preparation method of the meta - unit and improve the preparation efficiency of the meta - unit.

[0021] According to another aspect of the present invention, there is provided an ultraviolet light - emitting device, which includes the aforementioned LED device. Since the bandgap width of the ternary AlGaN alloy is continuously adjustable and its emission wavelength can cover near - ultraviolet to deep - ultraviolet, when the aforementioned LED device with high light extraction efficiency is used in the ultraviolet light - emitting device, due to its high light extraction efficiency, it has good use effects whether it is used in fields such as ultraviolet curing, biomedicine, fluorescence detection, skin disease prevention and treatment, or water purification. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic flow chart of a method for improving the light extraction efficiency of an LED based on a metasurface according to an embodiment of the present invention;

[0023] Figure 2 is Figure 1 a specific schematic flow chart of step S10 of the method for improving the light extraction efficiency of an LED based on a metasurface shown;

[0024] Figure 3 is a schematic structural diagram of an LED device with high light extraction efficiency according to an embodiment of the present invention;

[0025] Figure 4 is Figure 3 a schematic structural diagram of another perspective of the LED device with high light extraction efficiency shown;

[0026] Figure 5 is Figure 4 a schematic cross - sectional structural diagram of the LED device with high light extraction efficiency shown;

[0027] Figure 6 y is Figure 4 a schematic enlarged partial structural diagram of the LED device with high light extraction efficiency shown;

[0028] Figure 7This is a schematic diagram of the structure of an LED device with high light extraction efficiency according to another embodiment of the present invention;

[0029] Figure 8 The light field distributions of an LED with a metasurface and an LED without a metasurface, prepared using the method of Example 2 of this invention, are shown in TE mode: Figure 8 Figure A in the figure shows the light field distribution of an LED without a metasurface in TE mode; Figure 8 Figure B in the figure shows the light field distribution of an LED with a metasurface in TE mode;

[0030] Figure 9 The light field distributions of an LED with a metasurface and an LED without a metasurface, prepared using the method of Example 2 of this invention, in TM mode are as follows: Figure 9 Figure A in the figure shows the light field distribution of an LED without a metasurface in TM mode; Figure 9 Figure B in the figure shows the light field distribution of an LED with a metasurface in TM mode;

[0031] Reference numerals: 20, LED chip; 21, base; 22, p-type reflective electrode; 23, n-type AlGaN contact electrode; 24, p-GaN layer; 25, p-AlGaN layer; 26, multiple quantum well layer; 261, quantum well; 27, n-AlGaN layer; 300, dielectric layer; 30, metasurface; 31, metaunit; 311, cylinder; 40, air. Detailed Implementation

[0032] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0033] It should also be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising" or "including" include not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. The terminology used herein is generally that commonly used by those skilled in the art; in case of any discrepancy with commonly used terminology, the terminology used herein shall prevail.

[0034] In this paper, the term "metasurface" refers to an artificial two-dimensional material that utilizes the interaction between its subwavelength-scale unit structure and incident electromagnetic waves to achieve efficient control over the amplitude, phase, and polarization of electromagnetic waves.

[0035] In this paper, the term "LED chip" refers to the LED chip commonly used in the field of LED device technology, such as an LED chip formed by epitaxially growing a p-type reflective electrode, a p-GaN layer, a p-AlGaN layer and a multi-quantum well layer sequentially on a substrate, and epitaxially growing an n-type AlGaN contact electrode on the substrate, while epitaxially growing an n-AlGaN layer on the multi-quantum well layer and the n-type AlGaN contact electrode.

[0036] In this article, the term "Light Extraction Efficiency (LEE)" refers to the ratio of the emitted light energy to the generated light energy within an LED. Only a portion of the photons generated by electrical energy are emitted; some are refracted and leave the device, while others are continuously reflected internally and eventually absorbed. Essentially, it's the ratio of emitted to generated light energy. This concept doesn't simply refer to the efficiency of converting electrical energy into light energy. Within an LED light source device, there are two efficiencies in the conversion of electrical energy into light energy: internal quantum efficiency and external quantum efficiency. Light extraction efficiency refers to the ratio of external quantum efficiency to internal quantum efficiency.

[0037] In this paper, "Internal Quantum Efficiency (IQE)" refers to the ratio of the number of electrons generated to the number of absorbed photons when photons are incident on the surface of a photosensitive device (such as a CCD). The absorbed photons will excite the photosensitive material to generate electron-hole pairs and form an electric current.

[0038] In this paper, "External Quantum Efficiency (EQE)" refers to the ratio of the number of electrons generated to the total number of incident photons when photons are incident on the surface of a photosensitive device, and some photons excite the photosensitive material to generate electron-hole pairs and form an electric current.

[0039] In this article, the term "light-emitting surface of an LED chip" refers to the surface of an LED chip that faces away from its base.

[0040] In this paper, the term "phase" refers to the position of a wave at a specific moment within its cycle: a scale indicating whether it is at a crest, trough, or somewhere in between. "Phase compensation" is achieved through phase modulation. "Phase modulation" refers to the change in the phase of a light wave according to a certain pattern in its spatial distribution.

[0041] In this paper, the term "center wavelength" refers to the wavelength of the component with the highest energy within the wavelength range.

[0042] In this paper, the term "multiple quantum wells" refers to a system in which multiple quantum wells are combined together. In terms of material structure and growth process, there is no substantial difference between multiple quantum wells and superlattices. The only difference is that the barrier layer of a superlattice is relatively thin, and the coupling between the potential wells is stronger, forming a microstrip; while the barrier layer between multiple quantum wells is thick, there is basically no tunneling coupling, and no microstrip is formed.

[0043] In this paper, the term "optical path difference" refers to the difference in optical path length between two beams of light; where "optical path length" refers to the product of the geometric path length of light propagation and the refractive index of the medium.

[0044] In this paper, the term "transverse electric (TE)" refers to the transverse electric mode, which means that the direction of the electric field is perpendicular to the direction of propagation.

[0045] In this paper, the term "transverse magnetic (TM)" refers to a transverse magnetic mode, which means that the direction of the magnetic field is perpendicular to the direction of propagation.

[0046] In this paper, the term "electric dipole" refers to a system consisting of two point charges of equal magnitude but opposite sign.

[0047] In this paper, the term "magnetic dipole" is a physical model established by analogy to an electric dipole. A system consisting of two point magnetic charges of equal value but opposite sign is called a magnetic dipole.

[0048] In this paper, the term "dipole radiation" refers to the radiation emitted by a dipole of equal energy but opposite signs in motion, including electric dipole radiation and magnetic dipole radiation. For example, electric dipole radiation is the radiation emitted by an electric dipole composed of two electric charges of equal magnitude but opposite signs in resonant motion.

[0049] In this paper, the term "dielectric" refers to an insulator that can be polarized.

[0050] In this paper, the term "wavefront" refers to the surface formed by particles that have just begun to displace at a given moment as a wave propagates through a medium. It represents the spatial position where the wave energy arrives at a given moment, and it is in motion. The wavefront is orthogonal to a ray (however, in anisotropic media such as birefringent crystals, rays are generally not perpendicular to the wavefront). Therefore, using rays or wavefronts to study waves is equivalent. Based on the shape of the wavefront, waves can generally be classified into spherical waves, plane waves, cylindrical waves, etc.

[0051] In this paper, the basic idea of ​​the term "Finite-Difference Time-Domain (FDTD)" is to replace the first-order partial derivative of the field quantity with respect to time and space with the central difference quotient. By recursively simulating the wave propagation process in the time domain, the field distribution is obtained. It directly discretizes the wave equation in the time domain and does not require any form of derived equation. Therefore, its application scope is not limited by the mathematical model.

[0052] In this paper, the term "absorption coefficient" refers to the absorbance of light per unit distance traveled in a medium.

[0053] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] Figure 1 The diagram schematically illustrates a method for improving LED light extraction efficiency based on a metasurface according to an embodiment of the present invention.

[0055] like Figure 1 As shown, the method for improving LED light extraction efficiency based on metasurfaces includes step S10: fabricating at least one metaunit on the light-emitting surface of an LED chip, all metaunits forming a metasurface on the light-emitting surface, thereby forming an LED device with a metasurface on the light-emitting surface of the LED chip. The thickness of the metaunits is set to be uniform everywhere, and the metaunits are configured to provide phase compensation of -φ(x,y) for the light-emitting surface. λ0 is the center wavelength of the LED chip, and f is the optical path length from the multiple quantum wells in the LED chip to the light-emitting surface.

[0056] For example, such as Figure 3 , Figure 5 and Figure 6 As shown, the meta-unit includes at least two cylinders of equal height h distributed on the light-emitting surface. The cylinders are made of a dielectric material, and among the cylinders constituting the meta-unit, at least two cylinders have unequal diameters. Since the aforementioned cylinders are grown on the light-emitting surface of the LED chip, the height of the cylinder is the distance from the end of the cylinder in contact with the light-emitting surface of the LED chip to the end away from the base of the LED chip. This simplifies the shape of the constituent units of the meta-unit, allowing it to be obtained with only one etching operation when fabricated by etching, greatly improving etching efficiency. Preferably, referring to... Figure 3 , Figure 5 and Figure 6 As shown, multiple cylinders constituting a meta-unit are arranged on the light-emitting surface according to certain rules, such as a hexagonal grid structure. Furthermore, with... Figure 6 For example, when all the cylinders constituting the metaunit are arranged in a hexagonal grid structure on the light-emitting surface of the LED chip, the center distance between two adjacent cylinders in the hexagonal grid structure is denoted by 'a'. The diameter of the cylinders is set to 0.1λ0~0.5λ0, and the center distance 'a' between two adjacent cylinders in the hexagonal grid structure is set to 'd'. max <a<λ0. Thus, by adjusting the size and layout of the cylinder, the resulting hexagonal mesh structure metacells can achieve phase modulation of 0 to 2π at their local locations, making the wavefront of the emitted light approximately planar.

[0057] Therefore, even if the thickness of each metaunit is uniform everywhere, arbitrary modulation of the local field phase within the range of 0 to 2π can be achieved at that location, enabling phase modulation of the emitted light from the light-emitting surface, so that the wavefront of the emitted light can be approximated as planar light, such as... Figure 5 As shown, this method aims to improve the light extraction efficiency of the fabricated LED device while simplifying the shape of the metaunit.

[0058] In a preferred embodiment, during step S10, Corrections can be made through FDTD simulation. In particular, when the center wavelength λ0 of the LED chip can be determined, the thickness of the meta-unit and the diameter of the cylinder can be obtained by combining FDTD simulation. By adjusting the specifications and layout of the cylinder, the resulting meta-unit can perform phase compensation of -φ(x,y) on the light-emitting surface, so that the wavefront of the emitted light from the LED chip can be approximated as planar light.

[0059] In a preferred embodiment, considering that the focal length f of the metasurface is much smaller than the size of the light-emitting surface of the LED chip, and the light source is the entire multi-quantum-well layer, during step S10, the metasurface units are arrayed on the light-emitting surface of the LED chip in a manner with a period of P, such as... Figure 4 As shown, this is to further improve the phase modulation efficiency of the light-emitting surface of the LED chip and further improve the light extraction efficiency of the LED chip.

[0060] As one specific implementation of step S10, such as Figure 2 As shown, step S10 is implemented by including:

[0061] Step S11: Prepare a dielectric layer on the light-emitting surface of the prepared LED chip;

[0062] Step S20: Etch the dielectric layer to obtain at least one metaunit. The metaunit is capable of providing -φ(x,y) phase compensation to the light-emitting surface. λ0 is the center wavelength of the LED chip, and f is the optical path length from the multiple quantum wells in the LED chip to the light-emitting surface.

[0063] In this invention, when performing step S11, a dielectric layer can be prepared on the light-emitting surface of the LED chip using conventional preparation methods, such as MOCVD, molecular beam epitaxy (MBE), or ultra-high vacuum chemical vapor deposition (UHV / CVD).

[0064] In this invention, during step S12, conventional methods can be used to etch the dielectric layer. For example, a mask is first deposited on the dielectric layer, and then the mask is removed by photolithography and etching. Exemplarily, the mask can be deposited on the dielectric layer using methods such as electron beam evaporation, plasma-enhanced chemical vapor deposition (PECVD), low-pressure chemical vapor deposition (LPCVD), metal-organic chemical vapor deposition (MOCVD), or magnetron sputtering. The mask material can be selected based on the dielectric layer material, for example, at least one of silicon, silicon oxide, silicon nitride, silicon oxynitride, zinc oxide, and gallium oxide. Exemplarily, etching is performed using any one of wet chemical etching, inductively coupled plasma (ICP) etching, and reactive ion etching (RIE).

[0065] Since the metacells are composed of cylinders of uniform height, only a single etching of the dielectric layer on the light-emitting surface of the LED chip is required to obtain a wavefront that approximates a planar light, greatly improving etching efficiency.

[0066] As one embodiment of the LED chip, the LED chip is an AlGaN-based LED chip. In this embodiment, the metacells fabricated on the light-emitting surface of the LED chip are made of a material with a refractive index greater than 2. As another embodiment of the LED chip, the LED chip is an ultraviolet LED chip. Of course, ultraviolet LED chips also include AlGaN-based ultraviolet LED chips, for example, such as... Figure 3 As shown, the AlGaN-based ultraviolet LED chip includes a base on which a p-type reflective electrode, a p-GaN layer, a p-AlGaN layer, and a multi-quantum well layer are epitaxially grown sequentially. An n-type AlGaN contact electrode is epitaxially grown on the base, and an n-AlGaN layer is epitaxially grown on the multi-quantum well layer and the n-type AlGaN contact electrode. The light-emitting surface of the AlGaN-based ultraviolet LED chip is the surface of the n-AlGaN layer facing away from the base. Metacells are fabricated on the surface of the n-AlGaN layer facing away from the base. In this embodiment, the metacells fabricated on the light-emitting surface of the LED chip have a refractive index greater than 2 and an absorption coefficient < 10 in the UV band. -2 Materials with a diameter of 0.5 μm, such as AlN, AlGaN, or sapphire, are used. Due to the unique optical polarization characteristics and large refractive index difference of AlGaN-based UV LEDs, the proportion of total internal reflection is higher and the light extraction efficiency is lower. This invention addresses this by fabricating a metasurface on the light-emitting surface of the LED chip that can provide -φ(x,y) phase compensation, allowing the wavefront of the emitted light from the resulting LED chip to approximate a planar beam, thus significantly improving the light extraction efficiency.

[0067] The following describes one embodiment of a method for improving LED light extraction efficiency based on metasurfaces, with reference to specific examples.

[0068] Example 1

[0069] The first step is to deposit a dielectric layer, which is an AlN layer, on the light-emitting surface of the LED chip using the MBE method.

[0070] The second step is to deposit a mask on the light-emitting surface using the PECVD method, wherein the mask material is silicon nitride;

[0071] The third step involves etching away the mask using ICP etching to form a metasurface on the light-emitting surface of the LED chip. This metasurface is composed of at least one metasurface unit and is capable of providing phase compensation of -φ(x,y) to the light-emitting surface, ultimately producing the LED device.

[0072] Example 2

[0073] The main differences between this embodiment and Embodiment 1 lie in the first and third steps:

[0074] In the first step, the LED chip is an AlGaN-based ultraviolet LED chip. The AlGaN-based ultraviolet LED chip includes a base. On the base, a p-type reflective electrode, a p-GaN layer, a p-AlGaN layer, and a multi-quantum well layer are epitaxially grown in sequence. An n-type AlGaN contact electrode is epitaxially grown on the base. An n-AlGaN layer is epitaxially grown on the multi-quantum well layer and the n-type AlGaN contact electrode. A dielectric layer is deposited on the surface of the n-AlGaN layer facing away from the base. The dielectric layer is made of AlN and has a thickness of 400 nm.

[0075] In the third step, the mask is removed by ICP etching to form a metasurface on the light-emitting surface of the LED chip, which is capable of phase compensation of -φ(x,y) on the light-emitting surface, and is composed of at least one metasurface unit, thus finally obtaining the LED device. Among all the cylinders constituting the metasurface unit, at least two cylinders have different diameters, and the diameter of all cylinders ranges from 0.1λ0 to 0.5λ0. All the cylinders constituting the metasurface unit are arranged in a hexagonal grid structure, and the center distance between two adjacent cylinders in the hexagonal grid structure is a = λ0 / 2. Multiple metasurface units are prepared on the light-emitting surface of the LED chip, and the metasurface units are arrayed on the light-emitting surface of the LED chip in a periodic manner, with the period P being 0.55f.

[0076] The light extraction efficiency of the LEDs prepared by the method in Example 2 was simulated and analyzed using FDTD. The light field distribution of the LED without a metasurface and the LED with a metasurface prepared by the method in Example 2 were compared in TE mode. Figure 8 As shown, it can be seen that the metasurface in the LED with metasurface prepared by the method of Example 2 can modulate the TE mode light field, making it easier for light to radiate from the AlGaN in the LED into the air, thereby improving the light extraction efficiency of the LED; the light field distribution in TM mode is also compared between the LED without metasurface and the LED with metasurface prepared by the method of Example 2. Figure 9 As shown, it can be seen that the metasurface in the LED with metasurface prepared by the method of Example 2 can modulate the TM mode light field, making it easier for light to radiate from AlGaN in the LED into the air, thereby improving the light extraction efficiency of the LED.

[0077] Example 3

[0078] The main difference between this embodiment and Embodiment 1 lies in the first step:

[0079] In the first step, a dielectric layer is deposited on the light-emitting surface of the LED chip using the MBE method. The dielectric layer is made of AlGaN.

[0080] Example 4

[0081] The main difference between this embodiment and Embodiment 1 lies in the first step:

[0082] In the first step, a dielectric layer is deposited on the light-emitting surface of the LED chip using the MBE method. The dielectric layer is made of sapphire.

[0083] The light extraction efficiency of the LED device prepared by the method in Example 2 was increased by 5.53 times and 2.3 times in TE mode and TM mode, respectively, compared with the LED device without metasurface.

[0084] Figures 3 to 6 The illustration schematically shows an LED device with high light extraction efficiency prepared according to an embodiment of the present invention, using the aforementioned method for improving LED light extraction efficiency based on metasurfaces. The LED device with high light extraction efficiency prepared using the aforementioned method for improving LED light extraction efficiency based on metasurfaces is as described above and will not be repeated here.

[0085] Since the metasurface in the LED device with high light extraction efficiency can perform phase compensation of -φ(x,y) on the light-emitting surface of the LED chip, the wavefront of the emitted light from the LED chip can be approximately planar, greatly reducing the proportion of total internal reflection in the LED chip, thereby significantly improving the light extraction efficiency of the LED device.

[0086] Figures 3 to 6 An LED device with high light extraction efficiency according to one embodiment of the present invention is schematically shown.

[0087] like Figures 3 to 6 As shown, the LED device with high light extraction efficiency includes: an LED chip; and at least one meta-unit disposed on the light-emitting surface of the LED chip, capable of performing phase compensation of -φ(x,y) on the light-emitting surface; wherein, λ0 is the center wavelength of the LED chip, and f is the optical path length from the multiple quantum wells of the LED chip to the light-emitting surface.

[0088] The selection of LED chips can refer to the selection method of improving LED light extraction efficiency based on metasurfaces, which will not be elaborated here.

[0089] because To determine the phase distribution of dipole radiation generated at the light-emitting surface by each dipole in a plurality of dipoles equivalent to the light-emitting mode of an LED chip, a meta-unit capable of providing -φ(x,y) phase compensation is placed on the light-emitting surface of the LED chip, so that the wavefront of the emitted light can be approximated as planar light, such as... Figure 5As shown, this improves the light extraction efficiency of LED devices.

[0090] The specific implementation of the meta-unit can also refer to the selection method of the method for improving LED light extraction efficiency based on meta-surface. For example, the meta-unit includes multiple cylinders of equal height distributed on the light-emitting surface. The cylinders are made of dielectric material, and at least two of the cylinders constituting the meta-unit have different diameters. The multiple cylinders constituting a meta-unit are arranged in a hexagonal grid structure on the light-emitting surface. The diameter of the cylinders ranges from 0.1λ0 to 0.5λ0, and the center distance between two adjacent cylinders in the hexagonal grid structure ranges from d. max <a<λ0; the height of the cylinder ranges from 300nm to 500nm. Preferably, such as... Figure 6 As shown, the multiple cylinders arranged in a hexagonal grid structure include a cylinder located at the center of the hexagonal grid structure and at least one hexagonal unit centered at the center of the hexagonal grid structure. Each hexagonal unit has sides formed by at least two cylinders. The diameters of the cylinders forming the sides of the hexagonal unit can be equal or unequal. When there are two or more cylinders forming the sides of the hexagonal unit, the distance between two adjacent cylinders can be equal or unequal. When there are two or more hexagonal units constituting the hexagonal grid structure, each hexagonal unit has a different size, and the edges of every two hexagonal units are parallel to each other. All the cylinders constituting the hexagonal grid structure neither overlap nor intersect on the light-emitting surface of the LED chip, and the height direction of the cylinders is parallel to the epitaxial growth direction of the LED chip, so as to simplify the fabrication method of the meta-unit while ensuring the phase modulation effect of the meta-unit. This allows the wavefront of the emitted light from the LED device to be approximately planar, and the height of the resulting metacell is much smaller than that of a typical etched pattern, which simplifies the fabrication method of the metacell and improves the fabrication efficiency of the metacell.

[0091] In a preferred embodiment, such as Figure 7 As shown, the metasurface comprises multiple metaunits, which are arrayed on the light-emitting surface in a period of P. Preferably, the edges of adjacent metaunits in the metasurface are arranged in parallel. More preferably, when there are six metaunits adjacent to a single metaunit, each edge of the central metaunit is parallel to and adjacent to the edges of its neighboring metaunits, forming a honeycomb-like structure. This achieves a compact arrangement of the metaunits, thereby further enhancing their phase modulation effect.

[0092] According to another aspect of the present invention, an ultraviolet light-emitting device is provided, which includes the aforementioned LED device. Since the bandgap of the ternary AlGaN alloy is continuously adjustable, its emission wavelength can cover the near-ultraviolet to deep ultraviolet range. Using the aforementioned LED device with high light extraction efficiency in an ultraviolet light-emitting device yields good results due to its high light extraction efficiency, whether for ultraviolet curing, biomedicine, fluorescence detection, skin disease prevention and treatment, or water purification.

[0093] In this invention, x and y represent the coordinates of the plane where the light-emitting surface of the LED chip is located, and z represents the coordinates of the epitaxial growth direction of the LED chip.

[0094] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A method for improving LED light extraction efficiency based on metasurfaces, characterized in that, include Step S10: At least one meta-unit is fabricated on the light-emitting surface of the LED chip. All meta-units form a metasurface on the light-emitting surface to form an LED device. The thickness of the meta-unit is uniform everywhere, and the meta-unit is configured to be able to affect the light-emitting surface. Phase compensation, where, , Here, f is the center wavelength of the LED chip, and f is the optical path from the multiple quantum wells in the LED chip to the light-emitting surface, so as to achieve phase modulation of the emitted light from the light-emitting surface, reduce the proportion of total internal reflection of the LED chip, and make the wavefront of the emitted light approximately planar. The LED chip is an ultraviolet LED chip, and the metacellular units fabricated on the light-emitting surface of the LED chip have a refractive index greater than 2 and an absorption coefficient of <10 in the UV band. -2 Made of materials with a density of / μm; The meta-unit includes at least two cylinders of equal height and unequal diameter, distributed on the light-emitting surface, with a height range of 300nm to 500nm. All the cylinders that make up a superunit are arranged in a hexagonal grid structure on the light-emitting surface; The range of the center distance between two adjacent cylinders in the hexagonal grid structure is d. max <a< dmax is the maximum value of d, where d is the diameter of the cylinder; Multiple meta-units are arrayed on the light-emitting surface with a period of P, where the period P ranges from 0.5f < P < 2f. The supercells of the hexagonal grid structure are arranged in an axisymmetric structure, and the axis of symmetry is the line connecting the longest diagonal of the hexagonal grid structure and the midpoints of two opposite edges. The edges of each pair of hexagonal grid structures are parallel.

2. The method for improving LED light extraction efficiency based on metasurfaces according to claim 1, characterized in that, The cylinder is made of a dielectric material.

3. The method for improving LED light extraction efficiency based on metasurfaces according to claim 1, characterized in that, The diameter of the cylinder ranges from 0.

1. ~0.5 .

4. The method for improving LED light extraction efficiency based on metasurfaces according to claim 2, characterized in that, In step S10, the Corrections were made using FDTD simulation.

5. The method for improving LED light extraction efficiency based on metasurfaces according to claim 3, characterized in that, In step S10, the Corrections were made using FDTD simulation.

6. The method for improving LED light extraction efficiency based on metasurfaces according to claim 4, characterized in that, The thickness of the meta-unit and the diameter of the cylinder are combined with the center wavelength of the LED chip via FDTD. Obtained through simulation.

7. The method for improving LED light extraction efficiency based on metasurfaces according to claim 5, characterized in that, The thickness of the meta-unit and the diameter of the cylinder are combined with the center wavelength of the LED chip via FDTD. Obtained through simulation.

8. The method for improving LED light extraction efficiency based on metasurfaces according to any one of claims 1 to 7, characterized in that, The LED chip is an AlGaN-based LED chip.

9. The method for improving LED light extraction efficiency based on metasurfaces according to any one of claims 1 to 7, characterized in that, In step S10, multiple meta-units are fabricated on the light-emitting surface of the LED chip.

10. The method for improving LED light extraction efficiency based on metasurfaces according to claim 8, characterized in that, In step S10, multiple meta-units are fabricated on the light-emitting surface of the LED chip.

11. The method for improving LED light extraction efficiency based on metasurfaces according to any one of claims 1 to 7, characterized in that, Step S10 is implemented by including: Step S11: Prepare a dielectric layer on the light-emitting surface of the prepared LED chip; Step S20: Etch the dielectric layer to obtain at least one meta-unit, wherein the meta-unit is capable of processing the light-emitting surface. Phase compensation, where, , λ is the center wavelength of the LED chip, and f is the optical path length from the multiple quantum wells in the LED chip to the light-emitting surface.

12. The method for improving LED light extraction efficiency based on metasurfaces according to claim 8, characterized in that, Step S10 is implemented by including: Step S11: Prepare a dielectric layer on the light-emitting surface of the prepared LED chip; Step S20: Etch the dielectric layer to obtain at least one meta-unit, wherein the meta-unit is capable of processing the light-emitting surface. Phase compensation, where, , λ is the center wavelength of the LED chip, and f is the optical path length from the multiple quantum wells in the LED chip to the light-emitting surface.

13. The method for improving LED light extraction efficiency based on metasurfaces according to claim 9, characterized in that, Step S10 is implemented by including: Step S11: Prepare a dielectric layer on the light-emitting surface of the prepared LED chip; Step S20: Etch the dielectric layer to obtain at least one meta-unit, wherein the meta-unit is capable of processing the light-emitting surface. Phase compensation, where, , λ is the center wavelength of the LED chip, and f is the optical path length from the multiple quantum wells in the LED chip to the light-emitting surface.

14. The method for improving LED light extraction efficiency based on metasurfaces according to claim 10, characterized in that, Step S10 is implemented by including: Step S11: Prepare a dielectric layer on the light-emitting surface of the prepared LED chip; Step S20: Etch the dielectric layer to obtain at least one meta-unit, wherein the meta-unit is capable of processing the light-emitting surface. Phase compensation, where, , λ is the center wavelength of the LED chip, and f is the optical path length from the multiple quantum wells in the LED chip to the light-emitting surface.

15. An LED device with high light extraction efficiency, characterized in that, It is prepared by the method of improving LED light extraction efficiency based on metasurface as described in any one of claims 1 to 14.

16. An LED device with high light extraction efficiency, characterized in that, include: LED chips; and at least one of the light-emitting surfaces disposed on the light-emitting surface of the LED chip is capable of performing [operations on] the light-emitting surface. Phase-compensated meta-units, all of which form a metasurface on the light-emitting surface; wherein... , Here, f is the center wavelength of the LED chip, and f is the optical path from the multiple quantum wells of the LED chip to the light-emitting surface, so as to achieve phase modulation of the emitted light from the light-emitting surface, reduce the proportion of total internal reflection of the LED chip, and make the wavefront of the emitted light approximately planar. The LED chip is an ultraviolet LED chip, and the metacellular units fabricated on the light-emitting surface of the LED chip have a refractive index greater than 2 and an absorption coefficient of <10 in the UV band. -2 Made of materials with a density of / μm; The meta-unit includes at least two cylinders of equal height and unequal diameter, distributed on the light-emitting surface, with a height range of 300nm to 500nm. All the cylinders that make up a superunit are arranged in a hexagonal grid structure on the light-emitting surface; The range of the center distance between two adjacent cylinders in the hexagonal grid structure is d. max <a< dmax is the maximum value of d, where d is the diameter of the cylinder; Multiple meta-units are arrayed on the light-emitting surface with a period of P, wherein the period P ranges from 0.5f < P < 2f. The supercell of the hexagonal mesh structure is an axisymmetric structure, and the axis of symmetry is the line connecting the longest diagonal of the hexagonal mesh structure and the midpoints of two opposite edges.

17. The LED device with high light extraction efficiency according to claim 16, characterized in that, The cylinder is made of a dielectric material; The diameter of the cylinder ranges from 0.

1. ~0.5 .

18. An ultraviolet light-emitting device, characterized in that, Includes the LED chip according to any one of claims 1 to 14; or the LED device according to any one of claims 15 to 17.

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