Inverted UVC semiconductor light-emitting element and sterilization device

Abstract

The invention belongs to the field of sterilization devices, and relates to an inverted UVC semiconductor light-emitting element for a sterilization device and the sterilization device. The UVC semiconductor light-emitting element comprises a transparent substrate and a plurality of light-emitting units which are distributed on the substrate in an m * n matrix mode. The light-emitting units are square and are provided with inclined side walls in four directions and four table tops, and the table tops between every two adjacent light-emitting units are connected to form a shared table top; a plurality of first electrodes, each first electrode being located on each mesa and forming electrical contact, and a common first electrode being formed on a common mesa between adjacent light emitting units; a plurality of second electrodes are respectively formed on the second semiconductor layer of each light-emitting unit and form electric contact; the reflecting layer at least covers the four side wall sides of each light-emitting unit. Through the micro light-emitting unit array structure and the four-way distributed electrode design, the proportion of the light extraction area of the side wall is increased, and the overall light extraction efficiency is remarkably improved by combining the inclination of the side wall and the reflecting layer.

Description

Technical Field

[0001] The present invention belongs to the field of sterilization devices, and particularly relates to an inverted UVC semiconductor light-emitting element for a sterilization device and a sterilization device. Background Art

[0002] The UVC semiconductor light-emitting element (UVC light-emitting diode, UVC LED) is a light-emitting technology that uses deep ultraviolet light with a wavelength of 200-280 nanometers for sterilization, and has developed rapidly in the disinfection field in recent years.

[0003] The AlGaN-based UVC LED has a short emission wavelength and is easily absorbed inside the device, resulting in low light extraction efficiency, which leads to low photoelectric conversion efficiency and limits its application. To solve the problem of ultraviolet light self-absorption in UVC LED devices, an inverted structure is mainly adopted at present. Therefore, the p-type electrode pad and the n-type electrode pad of the chip can only be prepared on the same side of the surface of the epitaxial wafer. The AlGaN epitaxial material with a high Al component has a high resistance effect, resulting in low current spreading efficiency. Therefore, a serious current crowding effect is likely to occur inside the device. The current crowding effect will not only affect the electrical injection efficiency, but also cause the junction temperature of the device to rise, affecting the service life of the device.

[0004] Therefore, it is crucial to achieve uniform current spreading in the device and improve the light extraction efficiency. Existing research shows that reasonable design of the electrode layout can optimize the current transport path and make the current distribution more uniform.

[0005] The present application provides an arrayed quasi-micro-LED level structure for enhancing the light output power, which can achieve uniform current spreading in the device and improve the light extraction efficiency of deep ultraviolet light. Summary of the Invention

[0006] The purpose of the present invention is to solve two key technical problems existing in high-Al-component AlGaN-based UVC LED devices: (1) the current crowding effect caused by the high resistance characteristics of the AlGaN epitaxial material with a high Al component; (2) the problem of low light extraction efficiency caused by self-absorption of short-wavelength ultraviolet light inside the device. For this reason, the present invention proposes a novel arrayed inverted UVC semiconductor light-emitting element, which comprehensively improves the device performance by synergistically optimizing the current spreading path and the light field distribution.

[0007] To achieve the above purpose, the first aspect of the present invention provides an inverted UVC semiconductor light-emitting element, including:

[0008] A transparent substrate;

[0009] Multiple light-emitting units are arranged in an m*n matrix on a substrate (m≥2, n≥2). Each light-emitting unit includes a first semiconductor layer, an active layer, and a second semiconductor layer stacked in sequence. Each light-emitting unit has a square bottom, with four inclined sidewalls and corresponding four mesa surfaces. The mesa surfaces are formed by the surfaces of the first semiconductor layer exposed from the inclined sidewall sides. Each inclined sidewall is divided into two parts: the first part extends from the second semiconductor layer to the mesa surface, and the second part extends to the surface of the transparent substrate. The mesa surfaces between every two adjacent light-emitting units are connected to form a common mesa surface.

[0010] Multiple first electrodes are respectively disposed on each mesa surface of each light-emitting unit and are in electrical contact with the mesa surface. A common first electrode is disposed on the common mesa surface of adjacent light-emitting units.

[0011] Multiple second electrodes are respectively disposed on the second semiconductor layers of each light-emitting unit and are in electrical contact therewith.

[0012] A reflective layer covers at least the sidewalls of each light-emitting unit to reflect the laterally emitted light.

[0013] Preferably, the inclination angle of each sidewall of each light-emitting unit is 30 to 50°; the width of each inclined sidewall is greater than the width of each mesa surface.

[0014] Preferably, the aspect ratio of the length to the width of the bottom of each light-emitting unit is (1 to 5):1, the length is 5 to 150 μm, and the width is 5 to 150 μm.

[0015] Preferably, the reflective layer is a metal reflective layer or an insulating reflective layer.

[0016] Preferably, the metal reflective layer includes materials such as Al, Ag, Rh, or Au.

[0017] Preferably, the second electrode includes a reflective layer.

[0018] Preferably, it further includes a first pad and a second pad. The first pad is connected to the first electrode, and the second pad is connected to the second electrode.

[0019] Preferably, it further includes a first intermediate electrode and a second intermediate electrode. The first intermediate electrode is located above the first electrode and connects multiple first electrodes in parallel; the second intermediate electrode is located above the second electrode and connects multiple second electrodes in parallel; the first pad is located above the first intermediate electrode and is connected to the first intermediate electrode; the second pad is located above the second intermediate electrode and is connected to the second intermediate electrode; at least one of the first intermediate electrode and the second intermediate electrode includes a reflective layer.

[0020] Preferably, the insulating reflective layer is a DBR reflective layer; the metal reflective layer is located between two insulating layers and is wrapped by the two insulating layers.

[0021] The second aspect of the present invention lies in a sterilization device, including the flip-chip UVC semiconductor light-emitting element described in the first aspect of the present invention.

[0022] The technical solution of the present invention has at least the following beneficial effects:

[0023] 1. Aiming at the current crowding effect of deep ultraviolet LED devices (especially large-size and high-power chips), the present invention innovatively proposes a quasi-micro-LED level light-emitting unit array structure arranged in an m*n (m, n≥2) matrix. By decomposing the traditional large-size single chip into multiple sub-micron level light-emitting units, the lateral transport distance of carriers is significantly shortened, which is beneficial to the current transmission uniformity and light emission uniformity. At the same time, the ratio of the sidewall area is increased, which is conducive to light extraction from the sidewall, thereby improving the light emission efficiency.

[0024] 2. For each micro light-emitting unit, the present invention innovatively proposes a four-way distributed electrode design: four corresponding mesa surfaces are symmetrically arranged around the four sidewalls of each square light-emitting unit, and a first electrode (n-type contact) is arranged in each mesa area. Adjacent units share the mesa to form a common electrode network. This three-dimensional electrode layout changes the current expansion path from the traditional planar unidirectional current expansion to the multi-directional uniform expansion from the surrounding to the middle area, effectively reducing the contact resistance (Rc) and the spreading resistance (Rs).

[0025] 3. The quasi-micro-LED level light-emitting unit array structure arranged in a matrix, combined with the four mesa surfaces symmetrically arranged around the sidewalls, realizes a significant improvement in the current expansion efficiency and the uniformity of the current density, thereby significantly improving the light distribution uniformity.

[0026] 4. Based on the arrangement of multiple light-emitting units arranged in a matrix, combined with the inclined sidewalls of the chips of each light-emitting unit (except for the mesa positions where the first electrodes are designed) extending to the substrate. Thus, the ratio of the sidewall area of the entire light-emitting unit is further improved, which is conducive to light extraction from the sidewall.

[0027] 5. Further, due to the high proportion of a large amount of TM polarized light emitted by the AlGaN active region, the TM polarized light propagates parallel to the growth plane. The structure of the high-reflection sidewall combined with the high ratio of the sidewall area can correct the propagation mode of the TM polarized light, so that more photons escape from the inside of the device, significantly improving the light extraction efficiency of the light-emitting unit. In addition, the inclined sidewalls change the propagation direction of the photons originally parallel to the growth plane after multiple reflections, combined with the refractive index matching layer of the transparent substrate, the overall light extraction efficiency is significantly improved. Description of the Drawings

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0029] Figure 1 It is a schematic plan view of the planar structure of an inverted UVC semiconductor light-emitting element according to a specific embodiment of the present invention.

[0030] Figure 2 a and 2b are respectively cross-sectional structure diagrams obtained from the positions of the dotted lines a and b on the schematic plan view based on Figure 1 the planar structure diagram.

[0031] Figure 3 It is Figure 1 a schematic diagram of the optical path distribution of a single light-emitting unit of

[0032] Figure 4 a schematic cross-sectional view of the planar structure of an inverted UVC semiconductor light-emitting element.

[0033] Figure 5 It is a schematic diagram of the stacked structure of the first intermediate electrode.

[0034] Figure 6 It is a schematic diagram of the stacked structure of the second intermediate electrode.

[0035] Figure 7 It is a schematic diagram of the stacked structure of the second electrode.

[0036] Figure 8 It is a schematic diagram of the stacked structure of the insulating layer.

[0037] Figure 9 a, b, c, and d are respectively schematic plan views of structures A, B, C, and D.

[0038] Figure 10 It is the simulation test result of the current density distribution when structures A, B, C, and D are energized at 100 mA.

[0039] Figure 11 It is the simulation test result of the standard deviation of the current density and the light extraction rate gain (relative to structure A) when structures A, B, C, and D are energized at 100 mA.

[0040] Figure 12 It is the simulation test result of the current-voltage characteristic curves of structures A, B, C, and D.

[0041] Figure 13The simulation test results of the external quantum efficiency and the optical power-current curves of structures A, B, C, and D.

[0042] Reference numerals: 1 - transparent substrate; 2 - light-emitting unit; 21 - first semiconductor layer; 22 - active layer; 23 - second semiconductor layer; 201 - first part of the sidewall; 202 - second part of the sidewall; 211 - mesa; 31 - first electrode; 32 - second electrode; 33 - first intermediate electrode; 34 - second intermediate electrode; 321 - ohmic contact layer; 322 - reflective layer; 323 - protective layer; 34, 512, 522 - reflective layers; 51, 52, 511, 513, 521, 523 - insulating layers. Detailed implementation manners

[0043] The present invention will be described in detail below through embodiments.

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention; the technical features designed in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other; all other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0045] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "transverse", "upper", "lower", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention.

[0046] In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more. In addition, the term "comprising" and any of its variations means "including at least". The meaning of "corresponding" is adjacent. The comparison of the "widths" of different parts refers to the widths measured at the same height and in the same direction respectively.

[0047] To achieve at least one of the above-mentioned purposes or other purposes, an embodiment of the present invention provides a UVC semiconductor light-emitting element, which is a flip-chip structure. The UVC semiconductor light-emitting element includes:

[0048] A transparent substrate;

[0049] Multiple light-emitting units are arranged in an m*n matrix on a substrate (m≥2, n≥2). Each light-emitting unit includes a first semiconductor layer, an active layer, and a second semiconductor layer stacked in sequence. Each light-emitting unit has a square bottom with four inclined sidewalls and corresponding four mesa surfaces, and the mesa surfaces are formed by the surfaces of the first semiconductor layer exposed from the inclined sidewall sides. Each inclined sidewall is divided into two parts: the first part extends from the second semiconductor layer to the mesa surface, and the second part extends to the surface of the transparent substrate. The mesa surfaces between every two adjacent light-emitting units are connected to form a common mesa surface.

[0050] Multiple first electrodes are respectively disposed on each mesa surface of each light-emitting unit and are in electrical contact with the mesa surface. A common first electrode is disposed on the common mesa surface of adjacent light-emitting units.

[0051] Multiple second electrodes are respectively disposed on the second semiconductor layers of each light-emitting unit and are in electrical contact with them.

[0052] A reflective layer covers at least the sidewalls of each light-emitting unit to reflect the laterally emitted light.

[0053] Thus, by adopting a micro light-emitting unit array structure arranged in an m*n (m,n≥2) matrix, that is, decomposing a traditional large-size single chip into multiple sub-micron light-emitting units, the lateral transport distance of carriers can be significantly shortened, which is beneficial to the current transmission uniformity and light emission uniformity. At the same time, the proportion of the sidewall area is increased, which is conducive to light extraction from the sidewalls.

[0054] In addition, based on the four-way distributed electrode design proposed in the present invention: a first electrode (n-type contact) is arranged in the mesa area exposed on the four sidewalls of each square light-emitting unit, and adjacent units share the mesa to form a common electrode network. This three-dimensional electrode layout changes the current expansion path from the traditional planar one-way expansion to the spatial multi-way expansion, effectively reducing the contact resistance (Rc) and the spreading resistance (Rs), and can effectively solve the problems of high component resistance of the high Al component in a traditional single UVC semiconductor light-emitting element and low current diffusion efficiency, and improve the light emission efficiency of each light-emitting unit.

[0055] The structure with high-reflection sidewalls combined with a high proportion of the sidewall area can correct the propagation mode of TM polarized light, so that more photons escape from the device interior, significantly improving the light extraction efficiency of the light-emitting unit. In addition, the inclined sidewalls change the propagation direction of the photons originally parallel to the growth surface after multiple reflections on the inclined sidewalls. Combined with the refractive index matching layer of the transparent substrate, the overall light extraction efficiency is significantly improved.

[0056] For details, please refer to Figure 1 and Figure 2 a-2b, Figure 1 which is a schematic plan view of a flip-chip UVC semiconductor light-emitting element provided in this embodiment. Figure 2a and 2b are cross-sectional structure diagrams obtained from the positions of the dashed lines a and b on the planar structure diagram based on Figure 1 respectively.

[0057] Among them, the transparent substrate 1 can be made of a transparent material or a translucent material. Preferably, the transparent substrate 1 is an insulating substrate. In the illustrated embodiment, the transparent substrate 1 is a sapphire substrate. In a more preferred embodiment, the transparent substrate 1 can be a patterned sapphire substrate. The lower surface and sidewalls of the transparent substrate are used for light output, and the upper surface of the transparent substrate 1 is used to support the light-emitting unit.

[0058] A plurality of light-emitting units 2, each of the light-emitting units 2 including a first semiconductor layer 21, an active layer 22, and a second semiconductor layer 23 stacked in sequence on the substrate.

[0059] Among them, the first semiconductor layer 21 has an upper surface and a lower surface that are opposite to each other. The first semiconductor layer 21 can be an N-type semiconductor layer, and can supply electrons to the active layer under the action of a power source. In some embodiments, the first semiconductor layer 21 includes an N-type doped nitride layer. The N-type doped nitride layer may include N-type impurities of one or more Group IV elements. The N-type impurities may include one or a combination of Si, Ge, and Sn. In some embodiments, a buffer layer may also be provided between the first semiconductor layer 21 and the transparent substrate 1 to reduce the lattice mismatch between the transparent substrate 1 and the first semiconductor layer 21. The buffer layer may include an unintentionally doped GaN layer (un-doped GaN, abbreviated as: u-GaN) or an unintentionally doped AlGaN layer (un-doped AlGaN, abbreviated as: u-AlGaN). The first semiconductor layer can also be connected to the transparent substrate through an adhesive layer.

[0060] The active layer 22 is disposed on a partial upper surface of the first semiconductor layer 21. The active layer 22 can be a quantum well structure (Quantum Well, abbreviated as QW). In some embodiments, the active layer 22 can also be a multiple quantum well structure (Multiple Quantum Well, abbreviated as MQW), where the multiple quantum well structure includes a plurality of quantum well layers (Well) and a plurality of quantum barrier layers (Barrier) alternately arranged in a repeating manner. For example, it can be an AlGaN / AlGaN multiple quantum well structure. In addition, the composition and thickness of the well layers in the active layer 22 determine the wavelength of the generated light. In order to improve the light-emitting efficiency of the active layer 22, it can be achieved by changing the depth of the quantum well, the number of pairs of quantum wells and quantum barriers, the thickness, and / or other characteristics in the active layer 22.

[0061] The second semiconductor layer 23 is disposed above the active layer 22. The second semiconductor layer 23 can be a P-type semiconductor layer, which can provide holes to the active layer under the action of a power supply. In some embodiments, the second semiconductor layer 23 includes a P-type doped nitride layer. The P-type doped nitride layer may include one or more P-type impurities. The P-type impurities may include one or a combination of Mg, Zn, and Be. The second semiconductor layer 23 can be a single-layer structure or a multi-layer structure, and the multi-layer structure has different compositions. In addition, the setting of the epitaxial structure is not limited to this, and other types of epitaxial structures can be selected according to actual needs.

[0062] In the present invention, the central emission wavelength range of the UVC semiconductor light-emitting element is 220-280 nm. For this reason, the material of the first semiconductor layer 21 is preferably an N-type AlGaN layer, the material of the active layer 22 is preferably an undoped AlGaN / AlGaN multi-quantum well structure, and the material of the second semiconductor layer 23 is preferably a stacked structure of P-type AlGaN / GaN.

[0063] A plurality of light-emitting units 2 are arranged in an m*n matrix distribution on the substrate, where m is greater than or equal to 2 and n is greater than or equal to 2. Where m*n can be 3*3, or 3*4, or 4*5, or 5*5 or 7*7 or 10*10, etc. Through the reasonable design of the n and m values, the array of light-emitting units is realized, a higher sidewall area ratio is formed, the sidewall light extraction efficiency is improved, and the light-emitting efficiency of the entire light-emitting element is improved. Figure 1 Shown in the figure is 49 light-emitting units arranged in a 7*7 matrix distribution.

[0064] Wherein, the bottom of each light-emitting unit 2 is square, and each light-emitting unit 2 has sidewalls in four directions and corresponding four mesa surfaces 211. The sidewalls in the four directions here correspond to the four sides of the square bottom of each light-emitting unit.

[0065] The four mesa surfaces 211 corresponding to each light-emitting unit 2 are symmetrically distributed on the four sidewalls of the light-emitting unit. Each mesa surface 211 is respectively formed by the surface of a part of the first semiconductor layer 21 exposed on each side, that is, a mesa surface 211 is formed on each of the four sidewalls of the light-emitting unit 2. Each mesa surface 211 is the upper surface of a part of the first semiconductor layer 21, and this part of the upper surface is not covered by the active layer 22 but is exposed. Thus, the four mesa surfaces realize the uniform injection of current into the light-emitting unit, and the brightness of the light-emitting unit is made uniform. The symmetry here means that every two mesa surfaces are axisymmetric with respect to the central axis of the four sides of the light-emitting unit.

[0066] As Figure 2As shown in FIGS. 2a and 2b, the sidewalls in four directions all have the following characteristics: each sidewall includes a first portion 201 extending from the second semiconductor layer to the mesa 22 and a second portion 202 extending from the second semiconductor layer 23 to the surface of the transparent substrate 1, and the second portion 202 is disposed adjacent to the first portion 201. That is, the width of each sidewall is greater than the width of the corresponding mesa 22, and the two width values are measured in the same direction and at the same height. Therefore, as Figure 1 shown, there is a gap region between the sidewalls of adjacent light-emitting elements in addition to the region of the mesa 211, and the bottom of the gap region is the upper surface of the transparent substrate 1. Thus, in addition to four first electrode mesas 22 are provided in four directions for injecting current simultaneously, the remaining sidewall positions can extend to the upper surface of the transparent substrate 1, maximizing the proportion of the sidewall area of each light-emitting unit and facilitating the improvement of the light extraction efficiency.

[0067] Among them, as Figure 2 shown in FIG. 2a, the mesas 211 between every two adjacent light-emitting units 2 are connected to form a common mesa 211. Thus, the adjacent light-emitting units 2 are not formed completely independently of each other on the transparent substrate 1, but are partially electrically connected through the common mesa 211.

[0068] Preferably, the light-emitting unit 2 is square, and the specific square can be a square or a rectangle, and the side length of each square in terms of length or width is between 5 and 150 μm, and each square light-emitting unit has a suitable aspect ratio, preferably (1-5):1. Optionally, the aspect ratio is 1:1, 2:1, 3:1, 4:1 or 5:1.

[0069] More preferably, a plurality of light-emitting units 2 are distributed on the upper surface of the transparent substrate 1 with the same size, and the same size means the same length, width and geometric projection area. And the adjacent light-emitting units 2 maintain a constant horizontal spacing, that is, the gap widths between any two adjacent light-emitting units are equal. Thus, a plurality of independent and size-standardized light-emitting regions can be formed, ensuring the uniformity of the brightness distribution of the light-emitting surface, especially suitable for a parallel circuit architecture, each light-emitting unit can obtain an independent current path, and under the condition of the same driving current, each unit can achieve a highly consistent light-emitting brightness, effectively eliminating the brightness difference.

[0070] Among them, a plurality of first electrodes 31 are respectively formed on each mesa 211 of each light-emitting unit 2, and each first electrode 31 is in electrical contact with each mesa 211 of each light-emitting unit 2. A plurality of second electrodes 32 are respectively formed on the second semiconductor layer 23 of each light-emitting unit 2, and each second electrode 32 is in electrical contact with the second semiconductor layer 23. Thus, when the flip-chip light-emitting element is mounted on an external circuit board and the circuit board is powered on, current is uniformly injected into the first semiconductor layer 21 through the first electrodes 31 distributed in four directions of the light-emitting unit 2, thereby realizing the lateral current diffusion of each light-emitting unit and uniformly flowing to the second semiconductor layer 23, improving the light-emitting efficiency and uniformity.

[0071] In order to achieve the electrical contact effect, the first electrode 31 at least includes a metal layer capable of forming an ohmic contact with the first semiconductor layer 21, such as a metal layer of Ti, Cr, etc., and its thickness is 0.1 - 10 nm; the first electrode 31 can also be a laminated structure, at least including other conductive metal layers located on the ohmic contact metal layer, such as at least one layer of Al, Au, Ni, Pt, Ru, Ti, etc., or further can include some metal protection layers to prevent the diffusion or oxidation of the lower metal layer such as the Al layer, such as at least one layer of Pt or Ti, etc., and the thickness of each layer is 10 - 200 nm. Among them, the first electrode 31 can be conventionally selected according to actual needs to achieve the electrical contact effect, and will not be elaborated here.

[0072] Among them, a common first electrode 31 is formed on the common mesa 211 between adjacent light-emitting units 2. Thus, independent current supply to adjacent light-emitting units is achieved through the common first electrode 31, ensuring uniform current and light emission in each light-emitting area. At the same time, the electrode area required for setting the first electrode 31 can be reduced, and the effective area ratio of the light-emitting area can be increased.

[0073] The second electrode 32 is formed on the second semiconductor layer 23, and at least includes an ohmic contact layer such as ITO capable of forming an ohmic contact with the second semiconductor layer 23, and its thickness is 0.1 - 10 nm. The ITO layer can cover almost the entire surface of the second semiconductor layer 23 of each light-emitting unit to form electrical contact; the second electrode 32 can also be a laminated structure, at least including other conductive metal layers located on the ohmic contact layer, such as at least one layer of Al, Au, Ni, Pt, Ru, Ti, etc., or further can include some metal protection layers to prevent the diffusion or oxidation of the lower metal layer such as the Al layer, such as at least one layer of Pt or Ti, etc. Among them, the second electrode 32 can be conventionally selected according to actual needs to achieve the electrical contact effect, and will not be elaborated here.

[0074] The side walls of each light-emitting unit 2 are designed to be inclined, thereby increasing the proportion of the side wall area, which is beneficial for light extraction from the side walls. At the same time, the reflective layer covers at least the four inclined side walls of each light-emitting unit, for at least reflecting the light emitted from the side walls of each light-emitting unit. Thus, as Figure 3 shown, the structure of the high-reflectivity side walls combined with the high proportion of the side wall area can at least correct the propagation mode of the TM-polarized light, so that more photons escape from the device interior, significantly improving the light extraction efficiency of the light-emitting unit. In addition, the inclined side walls change the propagation direction of the photons originally parallel to the growth surface after multiple reflections, and combined with the refractive index matching layer of the transparent substrate, the overall light extraction efficiency is significantly improved.

[0075] Preferably, the inclination of each side wall of each light-emitting unit 2 is 30 to 50°, and the inclination is relative to the lower surface of the transparent substrate.

[0076] Among them, the reflective layer 4 covers at least the side walls of each light-emitting unit in four directions. The reflective layer can be an insulating reflective layer or a metal reflective layer; the insulating reflective layer can be, for example, a DBR reflective layer, and the DBR layer can be a repeating pair stack formed by combining two layers of insulating layers of materials such as silicon oxide, titanium oxide, magnesium oxide, and silicon nitride. The specific materials can be conventionally selected according to the emission wavelength range of the UVC light-emitting element. The metal reflective layer includes one of reflective metal materials such as Al, Ag, Rh, or Au, and this material has a high reflectivity in the emission wavelength range of the UVC light-emitting element, usually having a reflectivity of more than 50%. The thickness of the metal reflective layer can be 1 to 200 nm, and can be conventionally selected and designed according to actual requirements.

[0077] Preferably, the reflective layer 4 also covers the upper surface of the transparent substrate between adjacent light-emitting units, for reflecting the light reaching this area, so as to realize the output of light from the lower surface side of the substrate in a larger proportion.

[0078] In order to mount the flip-chip UVC light-emitting element to an external circuit board, as Figure 4 shown, which schematically shows two light-emitting units (actually, there can be more light-emitting units), the flip-chip UVC light-emitting element further includes a first pad 35 and a second pad 36, wherein the first pad 35 is connected to the first electrode 31, and the second pad 36 is connected to the second electrode 32. The first pad 35 and the second pad 36 are respectively arranged on the uppermost surface of the flip-chip UVC light-emitting element, and are arranged at a certain distance, and usually the two pads respectively have a square shape.

[0079] The two pads at least have a metal soldering layer on the outermost layer, such as a gold layer or a tin layer. Through the processes of applying solder paste and reflow soldering, the two pads can be connected to an external circuit board. Optionally, the two pads can further respectively include some lower conductive metal layers, such as at least one layer of Al, Au, Ni, Pt, Ru, Ti, etc., or further can include some intermediate layers, such as a metal protection layer, to prevent the diffusion or oxidation of the lower metal layer, such as an Al layer, like at least one layer of Pt or Ti, etc., and the thickness of each layer is 10 - 200 nm.

[0080] Further, the flip-chip UVC light-emitting element, such as Figure 4 shown, further includes a first intermediate electrode 33 and a second intermediate electrode 34. The first intermediate electrode 33 is located above the plurality of first electrodes 31 and electrically connects the plurality of first electrodes 31 of the plurality of light-emitting units in parallel; the second intermediate electrode 33 is located above the plurality of second electrodes 32 and electrically connects the plurality of second electrodes 32 of the plurality of light-emitting units in parallel.

[0081] The first intermediate electrode 33 and the second intermediate electrode 34 can optionally include some conductive metal layers, such as at least one layer of Al, Au, Ni, Pt, Ru, Ti, etc., or further can be a laminated structure, at least including some metal protection layers to prevent the diffusion or oxidation of the lower metal layer, such as an Al layer, like at least one layer of Pt or Ti, etc., and the thickness of each layer is 10 - 200 nm; or at least including some conductive layers.

[0082] The first pad 35 is located above the first intermediate electrode 33 and connected to the first intermediate electrode 33, and the second pad 35 is located above the second intermediate electrode 34 and connected to the second intermediate electrode 34.

[0083] To achieve electrical insulation between contact electrodes, intermediate electrodes, and pads with different electrical properties, the light-emitting element further includes an insulating layer. As Figure 4 shown, the light-emitting element further includes a first insulating layer 51 covering the first electrodes 31 and the second electrodes 32 and located under the first intermediate electrode 33 and the second intermediate electrode 34, and further includes a second insulating layer 52 covering the first intermediate electrode 33 and the second intermediate electrode 34 and located under the first pad 35 and the second pad 36, and some conductive vias are respectively arranged on the first insulating layer 51 and the second insulating layer 52 for the contact between electrodes, intermediate electrodes, and pads with the same electrical property to achieve electrical connection. The insulating layer can optionally be a transparent insulating layer such as silicon oxide, magnesium oxide, titanium oxide, etc., and the thickness of the insulating layer can be optionally selected and designed conventionally within the range of 10 - 400 nm.

[0084] To set up the reflective layer, as a preferred embodiment, Figure 4 the first insulating layer 51 shown is the reflective layer, such as a DBR reflective layer (a multi-layer structure not shown in the figure). The first insulating layer 51 as the reflective layer not only covers the inclined sidewalls of the light-emitting units but also covers the upper surface of the transparent substrate 1 between the light-emitting units. Thus, light can be reflected as much as possible to the lower surface of the transparent substrate 1 for light output. Optionally, the second insulating layer 52 can also be the reflective layer, such as a DBR reflective layer (a multi-layer structure not shown in the figure).

[0085] To set up the metal reflective layer, as an alternative embodiment, as Figure 5 、 6 shown, at least one of the first intermediate electrode 33 and the second intermediate electrode 34 can include a metal reflective layer as the lower layer, where the metal reflective layer serves both as a conductor and a reflector. Specifically, the first intermediate electrode 33 can include a reflective layer 332 and a protective layer 333, and the second intermediate electrode 34 can include a reflective layer 342 and a protective layer 343. The reflective layers 332 and 342 can be one layer of Al, Ag, Rh, or Au, and the protective layer can be at least one layer such as Pt or Ti. Further, to increase adhesion, a thin adhesion layer of metals such as Cr or Ti, for example, a layer with a thickness between 0.1 and 2 nm that can transmit light, can be added under the reflective layer 342 to facilitate the adhesion of the intermediate electrode to the surface of the insulating layer. Thus, the reflective layer serves both as a conductive metal layer and a sidewall reflector. The reflective layer is located in the stacked structure of the first intermediate electrode 33 and the second intermediate electrode 34, and the first intermediate electrode 33 and the second intermediate electrode 34 simultaneously cover the four sidewalls of multiple light-emitting units (not shown in the figure), playing the role of reflecting light while electrically connecting in parallel multiple first electrodes (including the common first electrode) 31 and second electrodes 32 of each light-emitting unit to achieve uniform electrical transmission.

[0086] As an alternative embodiment, the second electrode includes a metal reflective layer. Specifically, as Figure 7 shown, the second electrode 32 includes an ohmic contact layer 321, such as an ITO transparent conductive ohmic contact layer 321, to form a good ohmic contact with the second semiconductor layer 23; the second electrode 32 further includes a reflective layer 322 and a protective layer 323 formed on the ohmic contact layer, where the reflective layer can be one layer of Al, Ag, Rh, or Au, and the protective layer can be at least one layer such as Pt or Ti. Thus, the second electrode 32 can be formed almost entirely on the second semiconductor layer 3, serving as an ohmic contact while also playing a role in light reflection.

[0087] As an alternative embodiment, the metal reflective layer covers both the second semiconductor layer and the sidewall positions, and may cover the upper surface of the transparent substrate between adjacent light-emitting units, but is electrically insulated from between the first electrode and the second electrode. Thus, the metal reflective layer serves only as a reflective layer. To achieve electrical insulation, the metal reflective layer is formed between two adjacent insulating layers and is encapsulated by the two insulating layers. Specifically, Figure 4 the first insulating layer 51 shown is replaced with Figure 8 an insulating stack structure shown, which includes two insulating layers 511, 513 and a metal reflective layer 512 between the insulating layers 511, 513. The metal reflective layer 512 is completely encapsulated by the two insulating layers 511, 513.

[0088] The following is a software simulation of optical and electrical tests on four light-emitting structures to illustrate the beneficial technical effects of the present invention:

[0089] As Figure 9 shown in a-d, is a schematic structural diagram of a deep ultraviolet LED for simulation testing, which are four chip structures A, B, C, and D respectively. Among them, the three structures A, B, and D are comparative example structures, and the C structure is an example structure; the central emission wavelength of the four chips is 275 nm, the sizes of the four chips are all 1220 um * 1220 um, each chip includes a transparent substrate 1 and a light-emitting unit 2 on the transparent substrate 1, and each light-emitting unit 2 includes an N-type layer, an active layer, a P-type layer, a first electrode 3 (N electrode) and a second electrode 4 (P electrode). Among them, the material of the N electrode is a Ti / Al alloy metal layer (the Al metal layer contains a part of Ti metal to improve the electrical contact effect), and the P electrode includes a combination of a bottom ITO layer and an Al reflective metal layer on the ITO layer. There is also a Ni metal cluster arranged between the ITO and the Al metal layer to improve adhesion and reduce the ohmic contact resistance. The sidewalls of the light-emitting units of structures A, B, C, and D are all inclined, and the inclination angle is 45°. In addition, a reflective layer Al layer is provided on the sidewalls, and the Al layer is electrically insulated from the light-emitting unit, the N and P electrodes.

[0090] The four structures are different in the following aspects: Structure A includes a single light-emitting unit formed on a transparent substrate 1 and a mesa surrounding the light-emitting unit. An N electrode surrounding the light-emitting unit is formed on the mesa, and a P electrode 32 covering the entire P-type layer is formed on the P-type layer. Structures B and D are chips in which Structure A is divided into 4 (2×2 matrix) and 49 (7×7 matrix) light-emitting units respectively. Each light-emitting unit has a mesa surrounding the light-emitting unit and a surrounding N electrode formed on the mesa, and a P electrode is on the top surface of the light-emitting unit. Structure C is cut from Structure A into 49 (7×7 matrix) light-emitting units. Four mesas are symmetrically arranged around each light-emitting unit, and an N electrode and a P electrode are on each mesa. The N electrodes between two adjacent light-emitting units are formed on a common mesa as a common N electrode; the width of the sidewall of each light-emitting unit is greater than the width of the corresponding mesa, that is, the width of the mesa area of Structure C is less than the width of each light-emitting unit. Therefore, except for the common mesa area, the rest of the area between adjacent light-emitting units is a gap. The bottom of the gap is the upper surface of the transparent substrate. The inclined sidewalls of each light-emitting unit are covered with a metal reflective layer, and both the sidewalls and the reflective layer extend to the mesa and the upper surface of the transparent substrate at the bottom of the gap between the light-emitting units.

[0091] As Figure 10 shown, by simulating the simulation results of the active region current density distribution of the four structures through simulation software, it can be seen that the current spreading of Structure C is better than that of Structures A and B, and the current distribution in the active region is more uniform; as Figure 11 shown, by calculating the standard deviation of the active region current density of the four structures under a working current of 100 mA, from the obtained results, the current distribution of the array structure of Structure C is more uniform. By comparing the light extraction efficiencies of the four structures, since Structure C has a larger ratio of the sidewall reflection area, the light extraction of Structure C is improved by 15.5%, 15.2% and 9.3% compared with Structures A, B and D respectively. As Figure 12 shown, the current-voltage characteristic curves of the four structures are respectively. It can be seen that under the same voltage conditions, Structure C has a higher current injection than Structures A and B, and has the same good current injection effect as Structure D. In addition, as Figure 13 shown, the external quantum efficiency and light power-current curves of the four structures are respectively. It can be seen that Structure C uses a smaller size design to achieve more current transmission paths, and can have good current spreading; in addition, by designing mesas around the light-emitting units, the N electrode area is further reduced, the ratio of the inclined sidewalls is increased to achieve stronger light reflection, and a higher light extraction efficiency, external quantum efficiency and light output power are obtained, which are more excellent than Structures A, B and D.

[0092] This is because, although the B structure adopts a design of four matrix light-emitting units, the size of its light-emitting area is still relatively large. If a design of four mesa structures and four first electrodes (N electrodes) of the C structure is adopted, the current spreading effect is poor, so a ring-shaped first electrode is used instead. However, since the B structure only contains four light-emitting units, its current spreading effect and current density uniformity are still inferior to those of the C structure. In addition, due to the relatively small proportion of the sidewall area, the light-emitting efficiency is also lower than that of the C structure. Although the D structure is also a matrix design like the C structure and has a similar current spreading effect and current density uniformity, its first electrode (N electrode) is a ring-shaped design, and the light-emitting units are connected by a ring-shaped mesa. The sidewall only extends to the ring-shaped mesa, resulting in a relatively small proportion of the sidewall area. Therefore, the light extraction efficiency of the sidewall is limited, and the light-emitting efficiency is relatively low.

[0093] In summary, the above UVC light-emitting element provided by the present invention is a flip-chip structure, which is combined with the matrix-arranged micro light-emitting unit array structure, four-way distributed electrode design and high sidewall area ratio of the present invention, and is covered with a reflective layer, so that more effective light output can be realized through the top and sidewalls of the sapphire substrate of the light-emitting element, and the light-emitting surface has no electrode obstruction, the light output is uniform, and the light-emitting efficiency is higher. The flip-chip UVC light-emitting element of the present invention can be widely applied to sterilization devices, specifically for surface sterilization, air purification, water treatment and other application fields. Moreover, the design and installation of the flip-chip structure can achieve efficient heat dissipation, reduce the junction temperature, and extend the service life; and it also has a high power density, can support a larger current drive (such as above 350 mA), has a stronger light output per unit area, and is suitable for compact sterilization design; in addition, it also has the advantage of strong stability, no gold wire corrosion problem, resistance to current impact, and is suitable for high-frequency switching pulse sterilization mode. In addition, the UVC radiation efficiency can be further improved by matching with a lens or a reflector cup.

[0094] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and purposes of the present invention.

Claims

1. An inverted UVC semiconductor light-emitting element, characterized in that, The UVC semiconductor light-emitting element includes: A transparent substrate; A plurality of light-emitting units arranged in an m*n matrix on the substrate, where m≥2 and n≥2. Each light-emitting unit includes a first semiconductor layer, an active layer, and a second semiconductor layer stacked in sequence. Each light-emitting unit has a square bottom with four inclined sidewalls and corresponding four mesa surfaces, and the mesa surfaces are formed by the surfaces of the first semiconductor layer exposed from the inclined sidewall sides. Each inclined sidewall is divided into two parts: the first part extends from the second semiconductor layer to the mesa surface, and the second part extends to the surface of the transparent substrate. The mesa surfaces between every two adjacent light-emitting units are connected to form a common mesa surface; A plurality of first electrodes are respectively disposed on each mesa surface of each light-emitting unit and are in electrical contact with the mesa surface, and a common first electrode is disposed on the common mesa surface of adjacent light-emitting units; A plurality of second electrodes are respectively disposed on and in electrical contact with the second semiconductor layers of the respective light-emitting units; A reflective layer that at least covers the sidewalls of each light-emitting unit and reflects the laterally emitted light.

2. The flip-chip UVC semiconductor light-emitting element according to claim 1, wherein: The inclination angle of each sidewall of each light-emitting unit is 30 to 50°; the width of each inclined sidewall is greater than the width of the corresponding mesa surface.

3. The flip-chip UVC semiconductor light-emitting element according to claim 2, characterized in that: The aspect ratio of the bottom of each light-emitting unit is (1 to 5):1, and the length is 5 to 150 μm ， The width is 5 to 150 μm.

4. The flip-chip UVC semiconductor light-emitting element according to claim 1, wherein: The reflective layer is a metal reflective layer or an insulating reflective layer.

5. The flip-chip UVC semiconductor light-emitting element according to claim 4, characterized in that: The metal reflective layer includes materials such as Al, Ag, Rh, or Au.

6. The flip - chip UVC semiconductor light - emitting element according to claim 1, characterized in that: The second electrode includes a reflective layer.

7. The light-emitting element according to claim 1, characterized in that: It further includes a first pad and a second pad. The first pad is connected to the first electrode, and the second pad is connected to the second electrode.

8. The flip-chip UVC semiconductor light-emitting element according to claim 7, characterized in that: It further includes a first intermediate electrode and a second intermediate electrode. The first intermediate electrode is located above the first electrode and connects the plurality of first electrodes in parallel; the second intermediate electrode is located above the second electrode and connects the plurality of second electrodes in parallel; the first pad is located above the first intermediate electrode and is connected to the first intermediate electrode, and the second pad is located above the second intermediate electrode and is connected to the second intermediate electrode; at least one of the first intermediate electrode and the second intermediate electrode includes a reflective layer.

9. The flip-chip UVC semiconductor light-emitting element according to claim 4, characterized in that: The insulating reflective layer is a DBR reflective layer; the metal reflective layer is located between two insulating layers and is wrapped by the two insulating layers.

10. A sterilization device, characterized in that, Including the flip-chip UVC semiconductor light-emitting element according to any one of claims 1-9.

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