Double-layer metal reflective electrode of UVLED, UVLED and method for improving light extraction efficiency of UVLED

Abstract

The present invention discloses a double-layer metal reflective electrode of a UVLED, a UVLED and a method for improving the light extraction efficiency of the UVLED, wherein the double-layer metal reflective electrode of the UVLED comprises a first metal reflective layer, a dielectric layer, a contact layer and a second metal reflective layer; wherein the second metal reflective layer, the dielectric layer and the first metal reflective layer are arranged along the epitaxial direction, and the dielectric layer separates the first metal reflective layer from the second metal reflective layer; an accommodation space for accommodating the contact layer is provided on the first metal reflective layer and the dielectric layer, and one end of the contact layer facing the second metal reflective layer contacts the second metal reflective layer, and one end of the contact layer facing away from the second metal reflective layer forms a plane together with the first metal reflective layer. Thus, local enhancement of light can be formed, local reflected light can be enhanced, the strong absorption of deep ultraviolet light by GaN in the contact layer can be reduced, and phase modulation of local reflected light can be performed, leakage can be avoided, and electrical connection can be achieved when the double-layer metal reflective electrode is connected to other structures.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor lighting, and in particular to a double-layer metal reflective electrode of a UVLED, a UVLED and a method for improving the light extraction efficiency of the UVLED. Background Art

[0002] Since AlGaN-based ultraviolet light emitting diodes (UVLEDs) have the advantages of continuously adjustable bandgap, mature preparation process and low production cost, AlGaN-based UVLEDs have important applications and broad market prospects in the fields of fluorescence detection, sterilization and disinfection, water purification, biomedicine, etc.

[0003] However, the light extraction efficiency (LEE) of AlGaN-based UVLEDs is still very low, mainly due to the unique optical polarization characteristics of AlGaN-based UVLEDs and the total reflection at the interface caused by the large refractive index difference. The total reflection at the interface will limit the emission of light, resulting in reduced light extraction efficiency and more light being absorbed by the device material and converted into heat energy.

[0004] Studies have shown that etching patterns on the device's output surface, such as triangular prisms, quadrangular pyramids, hemispheres and other structures, can effectively improve its light extraction efficiency. In addition, for flip-chip LED structures, constructing micro-nano structures on the metal reflective layer, such as nanoparticles, inclined reflective sidewalls, etc., can improve scattering or reflection, thereby improving light extraction efficiency. However, these structures are usually non-planar structures, which can easily cause leakage in the device. Summary of the invention

[0005] In order to solve at least one of the above problems, according to one aspect of the present invention, a double-layer metal reflective electrode for a UVLED is provided.

[0006] The double-layer metal reflective electrode of the UVLED includes a first metal reflective layer, a dielectric layer, a contact layer and a second metal reflective layer; wherein the first metal reflective layer, the dielectric layer and the second metal reflective layer are arranged along the epitaxial direction, and the dielectric layer separates the first metal reflective layer from the second metal reflective layer; an accommodating space for accommodating the contact layer is provided on the first metal reflective layer and the dielectric layer, an end of the contact layer facing the second metal reflective layer contacts the second metal reflective layer, and an end of the contact layer facing away from the second metal reflective layer forms a plane together with the first metal reflective layer.

[0007] Since the double-layer metal reflective electrode is a planar structure, leakage can be avoided during use; and since the dielectric layer is located between the first metal reflective layer and the second metal reflective layer, a gap can be formed between the first metal reflective layer and the second metal reflective layer, and the gap can enable the localized plasma excitation of the first metal reflective layer to couple with the second metal reflective layer of the lower layer, thereby forming a local enhancement of light. When the light reflected by the first metal reflective layer and the light reflected by the second metal reflective layer are coherently enhanced, the localized reflected light can be enhanced, and the localized reflected light can be effectively phase modulated; when the magnetic dipole resonance excited by the light passing through the first metal reflective layer, the dielectric layer, and the second metal reflective layer can be localized between the first metal reflective layer and the second metal reflective layer, and the contact layer contains GaN material, the strong absorption of deep ultraviolet light by GaN in the contact layer can be reduced; at the same time, the dielectric layer can also play a role of physical support for the first metal reflective layer; in addition, the setting of the contact layer can realize electrical connection when the double-layer metal reflective electrode is connected to other structures, thereby ensuring that the current can flow smoothly into and out of the UVLED chip, thereby stimulating the chip to emit light.

[0008] In some embodiments, the first metal reflective layer is composed of a metal nanoarray; the metal nanoarray is composed of metal nanocolumns; and the space between the metal nanocolumns is a space for accommodating the contact layer. Thus, light can excite local magnetic dipole resonance through the first metal reflective layer, the dielectric layer, and the second metal reflective layer, so that the light can be localized in the dielectric layer between the first metal reflective layer and the second metal reflective layer. When the contact layer contains GaN material, the strong absorption of deep ultraviolet light by GaN can be reduced. The phase of the local reflected light can also be regulated by using the magnetic dipole resonance locally excited by metal nanocolumns of different sizes according to the different phases of the local reflected light of metal nanocolumns of different sizes, and the wavefront of part of the reflected light can be controlled so that more reflected light is located in the escape light cone of the UVLED, thereby further improving the light extraction efficiency of the UV-LED.

[0009] In some embodiments, the thickness t1 of the second metal reflective layer is greater than 100 nm to ensure that the UVLED has a high reflection efficiency; and / or the thickness h of the contact layer is in the range of 60 nm to 150 nm to ensure that the UVLED has a high reflection efficiency. Since the thickness of the double-layer metal reflective electrode is much smaller than the wavelength of the light emitted by the UVLED, the light scattering of the double-layer metal reflective electrode can be improved, thereby improving the light extraction efficiency of the UV-LED.

[0010] In some embodiments, the thickness t2 of the first metal reflective layer ranges from 20 nm to 50 nm. Within this thickness range, the efficiency of the excited localized plasma resonance is high and it is also easier to achieve using existing processes.

[0011] In some embodiments, the spacing d between the metal nanopillars is greater than the diameter r of the metal nanopillars to avoid overlapping areas between the two metal nanopillars; d<λ0, λ0 is the central wavelength of the UVLED in a vacuum, to avoid diffraction and discontinuity of light, and ensure the electric field modulation effect and the light emitting effect of the UVLED. The values ​​of d and r can be optimized by FDTD simulation.

[0012] In some embodiments, the thickness of the dielectric layer is g=h-t2, and g=λ0 / 2n g , where n g is the effective refractive index of the material selected for the dielectric layer. Thus, by adjusting the values ​​of t2 and g, the reflected light of the first metal reflective layer and the second metal reflective layer can be coherently enhanced to improve the reflectivity; and the dielectric layer is selected to have this thickness so that the light reflected by the first metal reflective layer and the light reflected by the second metal reflective layer can be coherently enhanced, thereby enhancing the local reflected light and performing phase modulation on the local reflected light. Preferably, t2 and g can be optimized by FDTD simulation.

[0013] In some embodiments, at least one of the first metal reflective layer and the second metal reflective layer is selected to have a reflectivity greater than 0.4 and / or an absorption coefficient less than 1.8×10 6 / cm. Therefore, by adjusting the first metal reflective layer and the second metal reflective layer, the coherence enhancement of the reflected light can be achieved, thereby improving the reflectivity of the double-layer metal reflective electrode to light.

[0014] In some embodiments, the first metal reflective layer includes at least one of Au, Ag and Al; and / or the second metal reflective layer includes at least one of Au, Ag and Al, so as to ensure that the first metal reflective layer and the second metal reflective layer have high reflectivity.

[0015] In some embodiments, the contact layer is made of a material with a small ohmic contact and small growth defects, for example, the contact layer is p-GaN or p-AlGaN; and / or the dielectric layer includes a dielectric material that can be deposited on the first metal reflective layer and the second metal reflective layer, and the dielectric material is a material with a lower deep ultraviolet absorption capacity than p-GaN, or an absorption coefficient of deep ultraviolet less than 1.7×10 5 / cm material, for example, at least one of SiO2, TiO2, Al2O3 and MgF2 is selected.

[0016] In some embodiments, the double-layer metal reflective electrode is a p-type electrode, and the contact layer is p-GaN or p-AlGaN. For the p-GaN contact layer, although p-GaN has extremely strong absorption of deep ultraviolet light, the second metal reflective layer can block part of the light from contacting the p-GaN contact layer, thereby reducing the absorption of light by p-GaN; for the p-AlGaN contact layer, p-AlGaN has weak absorption of deep ultraviolet light. Selecting p-GaN or p-AlGaN as the material for the contact layer can maintain a simpler process and lower cost.

[0017] In some embodiments, the diameters r of the metal nanocolumns are not exactly the same. For the p-GaN contact layer and the p-AlGaN contact layer, the magnetic dipoles excited by the metal nanocolumns of different sizes have different electromagnetic field control capabilities. The antenna array is formed by using metal nanoarrays of different sizes to modulate the wavefront of the reflected light, which is more effective in improving the light extraction efficiency of the reflected light.

[0018] In some embodiments, the phase distribution of the metal nanoarray is:

[0019]

[0020] Where f is the focal length of the metal nanoarray, floor{…} is the rounding operation, λ0 is the central wavelength of the UVLED in vacuum, is the maximum value of the phase change with the diameter r of the metal nanocolumn. Therefore, the reflected light can be more concentrated into the photon escape light cone of the UVLED through the phase modulation of the lens, thereby improving the light extraction efficiency of the UVLED.

[0021] According to another aspect of the present invention, a UVLED is provided, the UVLED comprising the aforementioned double-layer metal reflective electrode; the UVLED is a flip-chip UVLED; and / or the double-layer metal reflective electrode is a p-type double-layer metal reflective electrode, thereby avoiding leakage during use.

[0022] According to yet another aspect of the present invention, a method for improving light extraction efficiency of a UVLED is provided.

[0023] In the method for improving the light extraction efficiency of UVLED, the UVLED includes the aforementioned double-layer metal reflective electrode; or the UVLED is the aforementioned UVLED; the thickness h of the contact layer ranges from 60nm to 150nm, the thickness g of the dielectric layer is h-t2, and the optimal values ​​of t2 and g are obtained by FDTD simulation to obtain the double-layer metal reflective electrode, thereby, by adjusting the values ​​of t2 and g, the reflected light of the first metal reflective layer and the second metal reflective layer can be coherently enhanced to improve the reflectivity; and / or the metal nanoarray is composed of metal nanocolumns, the contact layer is filled between adjacent metal nanocolumns and in the accommodating space of the dielectric layer that accommodates the contact layer, and the optimal value of at least one of the spacing d of the metal nanocolumns and the diameter r of the metal nanocolumns is obtained by FDTD simulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic structural diagram of a double-layer metal reflective electrode of a UVLED according to an embodiment of the present invention;

[0025] Figure 2 for Figure 1 A schematic diagram of the cross-sectional structure of the double-layer metal reflective electrode of the UVLED shown along the AA direction;

[0026] Figure 3 for Figure 1 A schematic structural diagram of the double-layer metal reflective electrode of the UVLED shown in FIG. 1 from another perspective;

[0027] Figure 4 for Figure 3 A schematic diagram of the cross-sectional structure of the double-layer metal reflective electrode of the UVLED shown along the BB direction;

[0028] Figure 5 A schematic diagram of the structure of a metal nanoarray according to one embodiment of the present invention;

[0029] Figure 6 A schematic structural diagram of a metal nanoarray according to another embodiment of the present invention;

[0030] Figure 7 A schematic structural diagram of a metal nanoarray according to another embodiment of the present invention;

[0031] Figure 8 A schematic diagram of the structure of a periodically arranged metal nanoarray according to one embodiment of the present invention;

[0032] Fig. 9 It is a schematic structural diagram of a UVLED according to one embodiment of the present invention;

[0033] Figure numerals: 10, base; 20, double-layer metal reflective electrode; 21, first metal reflective layer; 211, metal nanoarray; 2111, metal nanocolumn; 22, dielectric layer; 23, second metal reflective layer; 24, contact layer; 30, p-AlGaN layer; 40, multi-quantum well layer; 50, n-AlGaN layer; 60, AlN layer; 70, substrate; 80, n-type metal electrode. DETAILED DESCRIPTION

[0034] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application may be combined with each other.

[0035] It should also be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the terms "include" and "comprise" include not only those elements, but also other elements that are not explicitly listed, or also include elements inherent to such processes, methods, articles or equipment. In the absence of further restrictions, the elements defined by the statement "include..." do not exclude the existence of other identical elements in the process, method, article or equipment that includes the elements. The terms used in this article are generally commonly used terms by those skilled in the art. If they are inconsistent with commonly used terms, the terms in this article shall prevail.

[0036] Furthermore, for ease of description, spatially relative terms such as "below," "beneath," "lower," "above," "upper," etc. may be used herein to describe the relationship of one element or component to another (or additional) elements or components as shown in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations), and the spatially relative descriptors used herein should be interpreted accordingly.

[0037] As used herein, the term "central wavelength" refers to the wavelength of the component with the highest energy within a wavelength range.

[0038] In this article, the term "effective refractive index" is the amount of phase delay when light propagates per unit length in a medium. It is a complex number, the real part represents the mode refractive index, and the imaginary part represents the gain or loss of the waveguide structure. The effective refractive index (neff) is a physical quantity used to describe the propagation of light in a waveguide structure. It represents the phase change of light propagating per unit length in the waveguide, which is equivalent to a certain proportion of the phase change when the same length is propagated in a vacuum. In a homogeneous transparent medium, the ordinary refractive index describes the degree to which the medium increases the wave number of light (that is, the phase change per unit length), while the effective refractive index extends this concept to make it applicable to waveguide structures. The value of the effective refractive index depends not only on the refractive index of the waveguide material itself, but also on the geometric structure of the waveguide, the operating wavelength, and the propagation mode. This means that even in the same material, the effective refractive index of different modes may be different. The effective refractive index can be a real number or a complex number. When it is a complex number, its real part reflects the phase change of the wave, while the imaginary part represents the gain or loss of the waveguide structure.

[0039] In this article, the term "reflectance coefficient" refers to the reflectivity of light, which is the ratio of the amount of light that an object's surface can reflect to the amount of light it receives, and is usually expressed as a percentage or decimal.

[0040] As used herein, the term "absorption coefficient" refers to the absorbance of light per unit distance in a medium.

[0041] In this article, the term "phase" refers to the position of a wave at a particular moment in its cycle: a measure of whether it is at a crest, trough, or somewhere in between. "Phase compensation" is achieved through phase modulation. "Phase modulation" refers to the phase of a light wave changing in a certain pattern in its spatial distribution.

[0042] In this article, the basic idea of ​​the term "Finite-Difference Time-Domain (FDTD)" is to replace the first-order partial derivatives of the field quantity in time and space with the central difference quotient, and to obtain the field distribution by recursively simulating the wave propagation process in the time domain. It directly discretizes the time domain wave equation and does not require any form of derived equation, so its application scope will not be limited by the mathematical model.

[0043] In this article, the term "magnetic dipole" is a physical model established by analogy with the electric dipole. A system consisting of two point magnetic charges of equal value and opposite sign is called a magnetic dipole.

[0044] In this article, the term "wavefront" refers to the surface formed by the particles that have just started to displace at a certain moment when the wave propagates in the medium. It represents the spatial position where the wave energy reaches at a certain moment, and it is moving. The wavefront is orthogonal to the ray (but in anisotropic media such as birefringent crystals, the light is generally not perpendicular to the wavefront). Therefore, it is equivalent to use rays or wavefronts to study waves. According to the shape of the wavefront, waves can generally be divided into spherical waves, plane waves, cylindrical waves, etc.

[0045] In this article, the term "multi-quantum well" refers to a system of multiple quantum wells combined together. In terms of material structure and growth process, there is no substantial difference between multi-quantum wells and superlattices, except that the superlattice barrier layer is relatively thin, the coupling between the potential wells is strong, and a microstrip is formed; while the barrier layer between multi-quantum wells is thick, there is basically no tunneling coupling, and no microstrip is formed.

[0046] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] Figures 1 to 8 A double-layer metal reflective electrode of a UVLED according to an embodiment of the present invention is schematically shown.

[0048] like Figure 2 and Figure 3 As shown, the double-layer metal reflective electrode of the UVLED includes a first metal reflective layer, a dielectric layer and a second metal reflective layer arranged in sequence along the epitaxial direction; wherein the dielectric layer separates the first metal reflective layer from the second metal reflective layer; the double-layer metal reflective electrode of the UVLED also includes a contact layer; an accommodating space for accommodating the contact layer is provided on the first metal reflective layer and the dielectric layer, an end of the contact layer facing the second metal reflective layer contacts the second metal reflective layer, and an end of the contact layer facing away from the second metal reflective layer forms a plane together with the first metal reflective layer.

[0049] Since the dielectric layer is spaced between the first metal reflective layer and the second metal reflective layer, and the spacing can make the localized plasmon excited by the first metal reflective layer coupled with the second metal reflective layer to form local enhancement of light, when the light reflected by the first metal reflective layer and the light reflected by the second metal reflective layer are coherently enhanced, the localized reflected light can be enhanced, and the localized reflected light can be effectively phase modulated; moreover, when the magnetic dipole resonance excited by the light passing through the first metal reflective layer, the dielectric layer, and the second metal reflective layer can be localized between the first metal reflective layer and the second metal reflective layer, and the contact layer contains GaN material, the strong absorption of deep ultraviolet light by GaN in the contact layer can be reduced; at the same time, the dielectric layer can also play a role of physical support for the first metal reflective layer; in addition, the setting of the contact layer can realize electrical connection when the double-layer metal reflective electrode is connected to other structures, ensuring that the current can smoothly flow into and out of the UVLED chip, thereby stimulating the chip to emit light, and at the same time, the contact layer and the first metal reflective layer together form a plane, which can also avoid leakage during use.

[0050] In some specific embodiments, the first metal reflective layer has a reflectivity greater than 0.4 and / or an absorption coefficient less than 1.8×10 6 / cm. For example, the first metal reflective layer includes at least one of gold (Au), silver (Ag) and aluminum (Al). Thus, by adjusting the first metal reflective layer and the second metal reflective layer, the coherence enhancement of the reflected light can be achieved, thereby improving the reflectivity of the double-layer metal reflective electrode to light.

[0051] In some specific embodiments, the second metal reflective layer has a reflectivity greater than 0.4 and / or an absorption coefficient less than 1.8×10 6 / cm. For example, the second metal reflective layer contains at least one of gold (Au), silver (Ag) and aluminum (Al). The material of the second metal reflective layer can be the same as that of the first metal reflective layer, or it can be different from the material of the first metal reflective layer; as long as the second metal reflective layer has a reflection coefficient greater than 0.4 and / or an absorption coefficient less than 1.8×10 6 / cm material, the coherence enhancement of the reflected light can be achieved by adjusting the first metal reflective layer and the second metal reflective layer, thereby improving the reflectivity of the double-layer metal reflective electrode to light.

[0052] In some specific embodiments, the dielectric layer includes a dielectric material that can be deposited on the first metal reflective layer and the second metal reflective layer, and the dielectric material is a material with a lower absorption capacity for deep ultraviolet light than p-GaN, or has an absorption coefficient for deep ultraviolet light less than 1.7×10 5 / cm material; wherein the dielectric layer can be deposited on the first metal reflective layer and the second metal reflective layer means that after the dielectric layer is deposited on the first metal reflective layer and the second metal reflective layer by MOCVD (chemical vapor deposition) process, it will not peel off from the first metal reflective layer and the second metal reflective layer. For example, the dielectric layer includes at least one of SiO2, TiO2, Al2O3 and MgF2.

[0053] In some specific embodiments, the contact layer is p-GaN or p-AlGaN. The preparation process of the p-GaN contact layer is relatively mature; the p-AlGaN contact layer has weak absorption of deep ultraviolet light.

[0054] In some specific embodiments, Figure 2 and Figure 3 As shown, the thickness t2 of the first metal reflective layer ranges from 20 nm to 50 nm. Through FDTD simulation calculation, it can be known that controlling the thickness of the first metal reflective layer within the range of 20 nm to 50 nm can make the excited localized plasma resonance have a higher efficiency.

[0055] In some specific embodiments, Figure 2 and Figure 3 As shown, the thickness t1 of the second metal reflective layer is greater than 100 nm. Through FDTD simulation calculation, it can be known that controlling the thickness of the second metal reflective layer to be greater than 100 nm can ensure that the double-layer metal reflective electrode has a higher reflection efficiency.

[0056] In some specific embodiments, Figure 2 As shown, the thickness of the contact layer is h, and the thickness of the dielectric layer is g=h-t2. Preferably, the thickness h of the contact layer is in the range of (60nm-150nm), for example, h is 61nm, 65nm, 70nm, 90nm, 149nm, etc.

[0057] In some specific embodiments, Figure 2 and Figure 3 As shown, the thickness of the dielectric layer g = (60nm-150nm)-t2. In some preferred embodiments, g = λ0 / 2n g , where λ0 is the central wavelength of UVLED in vacuum, n gis the effective refractive index of the material selected for the dielectric layer. The dielectric layer is selected to have this thickness so that the light reflected by the first metal reflective layer and the light reflected by the second metal reflective layer can be coherently enhanced, thereby enhancing the local reflected light and performing phase modulation on the local reflected light. In some preferred embodiments, when the thickness t1 of the second metal reflective layer is greater than 100nm; the thickness t2 of the first metal reflective layer ranges from 20nm to 50nm; the thickness g of the dielectric layer is equal to (60nm to 150nm)-t2. The thickness of the obtained reflective electrode is much smaller than the wavelength of the light emitted by the UVLED, thereby improving the light scattering of the double-layer metal reflective electrode, thereby improving the light extraction efficiency of the UVLED. t2 and g can be optimized by FDTD simulation. At this time, the double-layer metal reflective electrode can have a higher reflectivity by coherently enhancing the reflected light of the second metal reflective layer and the first metal reflective layer.

[0058] In some preferred embodiments, Figures 1 to 3 As shown, the first metal reflective layer is composed of a metal nanoarray. The number of metal nanoarrays can be one, two, or more. When there are more than two metal nanoarrays constituting the first metal reflective layer, the period p of the metal nanoarray and the value range of the period p are relatively flexible and need to be adjusted for different UVLED parameters. Considering the process and actual effects, p>500nm can be selected. The metal nanoarray is composed of an array of metal nanocolumns. The diameters of all metal nanocolumns can be the same or different. The same or different diameters r of the metal nanocolumns are effective in improving the light extraction efficiency of the UVLED; the space between the metal nanocolumns is the accommodation space for the contact layer. Each metal nanocolumn, the dielectric layer, and the second metal reflective layer is equivalent to a local phase modulator, which excites the local magnetic dipole resonance. When the diameter r of the metal nanocolumn changes, the local field phase can be achieved. Any modulation within the range, where is the maximum value of the phase change with r; the local phase of the reflected light of metal nanorods with different diameters can be obtained through FDTD simulation. For example, when r changes from 40nm to 98nm, Therefore, metal nanopillars of different diameters can be arranged to achieve phase modulation of part of the reflected light in a double-layer metal reflective electrode with a planar structure. For the p-GaN contact layer and the p-AlGaN contact layer, the magnetic dipoles excited by metal nanopillars of different sizes have different electromagnetic field control capabilities. Using metal nanoarrays of different sizes to form an antenna array can modulate the wavefront of the reflected light, which is more effective in improving the light extraction efficiency of the reflected light.

[0059] In some specific embodiments, Figure 5As shown in FIG. 1 , when the metal nanorods are distributed in a triangular distribution, the cross-section of the metal nanorods is circular. In other specific embodiments, as shown in FIG. Figure 6 As shown, when the metal nanocolumns are distributed in a square distribution, the cross-section of the metal nanocolumns is in a square shape. In some specific embodiments, the metal nanoarray can be reconstructed by an array lens phase or a grating phase. Taking the metal nanoarray constructed by the array lens phase as an example, the phase distribution of the reconstructed single plane lens is:

[0060]

[0061] Where, f is the focal length of the metal nanoarray, floor{…} is the rounding down operation, is the maximum value of phase change with the diameter r of the metal nanorod, and λ0 is the central wavelength of the UVLED in vacuum. Figure 7 As shown, a lens array composed of multiple lens units with a period of p is as follows Figure 8 The double-layer metal reflective electrode constructed by the lens array phase has a certain phase modulation effect on part of the reflected light, which is more conducive to the reflected light being emitted from the UVLED light-emitting surface.

[0062] Preferably, the spacing d between the metal nanocolumns is greater than the diameter r of the metal nanocolumns to avoid overlapping areas between the two metal nanocolumns. Preferably, the spacing d between the metal nanocolumns is less than λ0, where λ0 is the central wavelength of the UVLED in a vacuum to avoid diffraction and discontinuity of light and ensure the electric field modulation effect and the light emitting effect of the UVLED. The values ​​of d and r can be optimized by FDTD simulation.

[0063] In some specific embodiments, the dielectric layer may also be composed of a dielectric nanoarray, which may be one, two, or more. The dielectric nanoarray is composed of a dielectric nanocolumn array, and the dielectric nanocolumns are arranged in a space for accommodating the contact layer; the diameters of all dielectric nanocolumns may be the same or different. The dielectric nanocolumns may correspond one-to-one with the metal nanocolumns in the first metal reflective layer to improve processing efficiency (e.g., Figure 4 as shown); they may not completely correspond, as long as some of the metal nanocolumns are connected to the first metal reflective layer through the dielectric nanocolumns.

[0064] Fig. 9 A UVLED according to one embodiment of the invention is schematically shown.

[0065] like Fig. 9 As shown, the UVLED includes the aforementioned double-layer metal reflective electrode.

[0066] In some specific embodiments, Fig. 9As shown, the UVLED is a flip-chip structure; and / or the double-layer metal reflective electrode is a p-double-layer metal reflective electrode. In some further specific embodiments, the second metal reflective layer and the n-type metal electrode of the double-layer metal reflective electrode are arranged on the base; the p-AlGaN layer is arranged on the side of the double-layer metal reflective electrode away from the base; the p-AlGaN layer, the multi-quantum well layer, the n-AlGaN layer and the AlN layer are arranged away from the base in sequence on the side of the double-layer metal reflective electrode away from the base; the substrate is arranged on the side of the AlN layer and the n-type metal electrode away from the base. In some embodiments of preparing UVLED, first, an AlN layer and an n-type metal electrode are prepared on a substrate; then, an n-AlGaN layer, a multi-quantum well layer, a p-AlGaN layer, and a contact layer are sequentially prepared on the AlN layer; then, the contact layer is etched to form holes in the contact layer; then, a first metal reflective layer and a dielectric layer are sequentially prepared in the holes in the contact layer; then, a second metal reflective layer is prepared on the contact layer and the dielectric layer; and then a base is arranged on the second metal reflective layer and the n-type metal electrode.

[0067] In some specific embodiments, the substrate is a sapphire substrate. The flip-chip structure has become the mainstream structure of deep ultraviolet LEDs due to its advantages such as high heat dissipation efficiency and simple process. Moreover, the metal electrodes of the upright structure UVLED are all on the light-emitting surface, which needs to be light-transmissive. The metal electrodes are usually made relatively small. If the metal electrodes are set as double-layer metal reflective electrodes, it is not conducive to light extraction. The present invention sets a double-layer metal electrode on the basis of the flip-chip structure, and the light-emitting surface is located on the side where the substrate is located, which will not affect the growth of the quantum well and can also improve the light extraction efficiency of the UVLED. Fig. 9 Preferably, the substrate is a patterned substrate to improve the light extraction efficiency of the UVLED.

[0068] In some specific embodiments, since the p-type electrode of the flip-chip UVLED has a reflective function and the n-type electrode has no reflective function, a double-layer metal reflective electrode is disposed on the p-type electrode.

[0069] In some preferred embodiments, the UVLED is an AlGaN-based UVLED. Although the double-layer metal reflective electrode also has a certain effect on improving the light extraction efficiency of UVLEDs in other bands, due to the different light emission modes of LEDs in other bands (no TM mode, or extremely low TM mode, or a large photon escape angle, etc.), even if a double-layer metal reflective electrode with a double-layer metal structure is used, the effect of improving the light extraction efficiency of the UVLED may not be obvious. Generally, other processing procedures need to be added to achieve a better effect of improving the light extraction efficiency, and the operation process is cumbersome; when the UVLED is an AlGaN-based flip-chip UVLED, no other processing procedures need to be added to make the UVLED have a higher light extraction efficiency, and the operation is convenient.

[0070] According to an embodiment of the present invention, a method for improving the light extraction efficiency of a UVLED is provided, wherein the UVLED comprises the aforementioned double-layer metal reflective electrode or the aforementioned UVLED; the double-layer metal reflective electrode comprises a first metal reflective layer, a dielectric layer, a contact layer and a second metal reflective layer; the first metal reflective layer is composed of a metal nanoarray; the metal nanoarray is composed of metal nanocolumns, and the contact layer is filled between adjacent metal nanocolumns and in the accommodating space of the dielectric layer accommodating the contact layer; the thickness h of the contact layer ranges from 60nm to 150nm; the thickness g of the dielectric layer is equal to h-t2; the optimal values ​​of t2 and g are obtained through FDTD simulation.

[0071] According to another embodiment of the present invention, a method for improving the light extraction efficiency of a UVLED is provided, wherein the UVLED includes the aforementioned double-layer metal reflective electrode or the aforementioned UVLED; the first metal reflective layer is composed of a metal nanoarray; the metal nanoarray is composed of metal nanocolumns; and the optimal value of at least one of the spacing d of the metal nanocolumns and the diameter r of the metal nanocolumns is obtained by FDTD simulation.

[0072] Through simulation, when f=3, the light extraction efficiency of TE and TM modes of the double-layer metal reflective electrode is improved by 63% and 335% respectively compared with the traditional double-layer metal reflective electrode, and the LED designed with the double-layer metal reflective electrode is improved by 63% and 335% compared with the LED designed with the conventional metal double-layer metal reflective electrode.

[0073] The above are only some embodiments of the present invention. For those skilled in the art, several modifications and improvements can be made without departing from the creative concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. The double-layer metal reflective electrode of UVLED is characterized by: It includes a first metal reflection layer, a dielectric layer, a contact layer and a second metal reflection layer; wherein, The first metal reflective layer, the dielectric layer and the second metal reflective layer are arranged along the epitaxial direction, and the dielectric layer separates the first metal reflective layer from the second metal reflective layer; An accommodating space for accommodating the contact layer is provided on the first metal reflective layer and the dielectric layer, an end of the contact layer facing the second metal reflective layer contacts the second metal reflective layer, and an end of the contact layer facing away from the second metal reflective layer forms a plane together with the first metal reflective layer; The thickness of the dielectric layer is selected to be a thickness that can enhance the coherence of the light reflected by the first metal reflective layer and the light reflected by the second metal reflective layer; The first metal reflective layer is composed of a metal nanoarray; The metal nanoarray is composed of metal nanopillars; The space between the metal nano-pillars is the accommodation space of the contact layer.

2. The double-layer metal reflective electrode of UVLED according to claim 1, characterized in that: The thickness of the second metal reflective layer t1>100nm; and / or The thickness h of the contact layer ranges from 60 nm to 150 nm.

3. The double-layer metal reflective electrode of UVLED according to claim 2, characterized in that: The thickness t2 of the first metal reflective layer ranges from 20 nm to 50 nm; and / or The spacing d between the metal nanocolumns is greater than the diameter r of the metal nanocolumns; d<λ0, λ0 is the central wavelength of the UVLED in vacuum.

4. The double-layer metal reflective electrode of UVLED according to claim 3, characterized in that: The thickness of the dielectric layer g = h-t2, and g = λ0 / 2n g , where n g is the effective refractive index of the material selected for the dielectric layer.

5. The double-layer metal reflective electrode of UVLED according to any one of claims 1 to 4, characterized in that: At least one of the first metal reflective layer and the second metal reflective layer is selected to have a reflection coefficient greater than 0.4 and / or an absorption coefficient less than 1.8×10 6 / cm material.

6. The double-layer metal reflective electrode of UVLED according to any one of claims 1 to 4, characterized in that: The dielectric layer comprises a dielectric material that can be deposited on the first metal reflective layer and the second metal reflective layer, and the dielectric material is a material with a lower absorption capacity for deep ultraviolet radiation than p-GaN, or an absorption coefficient for deep ultraviolet radiation of less than 1.7×10 5 / cm material.

7. The double-layer metal reflective electrode of UVLED according to any one of claims 1 to 4, characterized in that: The double-layer metal reflective electrode is a p-type electrode, and the contact layer is p-GaN or p-AlGaN; and / or The diameters r of the metal nanorods are not completely the same.

8. UVLED, characterized in that A double-layer metal reflective electrode comprising any one of claims 1 to 7; The UVLED is a flip-chip UVLED; and / or The double-layer metal reflective electrode is a p-type double-layer metal reflective electrode.

9. A method for improving the light extraction efficiency of UVLED, characterized in that: The UVLED comprises the double-layer metal reflective electrode according to any one of claims 1 to 7; or the UVLED is the UVLED according to claim 8; The thickness h of the contact layer ranges from 60 nm to 150 nm, the thickness g of the dielectric layer is h-t2, and the optimal values ​​of t2 and g are obtained through FDTD simulation; and / or The first metal reflective layer is composed of a metal nanoarray, and the metal nanoarray is composed of metal nanocolumns. The contact layer is filled between adjacent metal nanocolumns and in the accommodating space of the dielectric layer that accommodates the contact layer. The optimal value of at least one of the spacing d between the metal nanocolumns and the diameter r of the metal nanocolumns is obtained through FDTD simulation.

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