A micro-led array device with improved light efficiency and a preparation method thereof

Abstract

The present application relates to a kind of piece under inverted trapezoidal micro-mirror Micro-LED array device and its preparation method of improving light efficiency, array device is composed of multiple piece under inverted trapezoidal micro-mirror Micro-LED device, each Micro-LED device includes p type doped layer, multiple quantum well layer, n type doped inverted trapezoidal structure, reflecting electrode, n type metal electrode substrate, transparent conductive layer, dielectric layer and top p electrode.The present application benefits from piece under inverted trapezoidal combination surface mirror structure, can effectively change optical path, realize the improvement of top Micro-LED light extraction efficiency.Compared with the method for improving light extraction efficiency of inclined side wall, the present application will not increase the exposed area of multiple quantum well layer, side wall defect can be inhibited, reduce the charge coupling effect at side wall, so as to weaken quantum confinement starker effect at side wall, reduce the convergence of hole to side wall, and then reduce non-radiative recombination, so that light emitting performance is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of visible light and ultraviolet light emitting devices, in particular to a sheet-down inverted trapezoidal micro-mirror Micro-LED array device and a preparation method thereof. BACKGROUND

[0002] In recent years, Micro-LED display technology has attracted widespread attention. Compared with traditional LEDs and liquid crystal displays, it has the advantages of high brightness, high light-emitting efficiency, long service life, wide color gamut, and the like. Moreover, Micro-LED displays have greater application potential due to their self-emission, good outdoor visibility, strong environmental tolerance, and compact optical structure. However, the refractive index of group III nitride used to prepare Micro-LEDs is about 2.5, which has a large refractive index difference with the surrounding air medium, thus causing serious total internal reflection and severely weakening the top light emission. Therefore, it is necessary to improve the light extraction efficiency of Micro-LEDs.

[0003] Moreover, as the size of the LED decreases, the proportion of the sidewall area will increase significantly. When the chip size is reduced to 15 μm, the sidewall emission ratio of red, green, and blue Micro-LEDs will increase by 184%, 24%, and 24%, respectively.

[0004] At present, the methods for improving the light extraction efficiency of Micro-LEDs include surface photonic crystal arrays, patterned substrates, high-reflection electrodes, surface plasmons, and the like. However, the above-mentioned solutions have problems such as high processing difficulty, high equipment requirements, and high preparation precision. In addition, there is also a scheme of inclined sidewall of the LED chip, but the inclined sidewall will increase the exposed area of the multi-quantum well layer, which will bring more defects, increase the charge coupling effect at the sidewall, intensify the quantum confinement Stark effect (QCSE) at the sidewall, and cause the holes to converge to the sidewall, thereby generating enhanced non-radiative recombination (SRH) and reducing the light-emitting performance. SUMMARY

[0005] The present application solves the technical problems in the prior art and provides a sheet-down inverted trapezoidal micro-mirror Micro-LED array device and a preparation method thereof. The sheet-down inverted trapezoidal micro-mirror structure of the present application can not only improve the front light extraction efficiency, but also reduce the charge coupling effect at the sidewall.

[0006] To solve the above technical problems, the technical solution of the present application is as follows:

[0007] A sheet-down inverted trapezoidal micro-mirror Micro-LED array device for improving light efficiency, which is an array device composed of a plurality of discrete sheet-down inverted trapezoidal micro-mirror Micro-LED devices;

[0008] Each of the micro-mirror Micro-LED devices comprises:

[0009] An n-type metal electrode substrate with an inverted-trapezoidal groove array pattern formed thereon;

[0010] A reflective electrode on the upper side of the n-type metal electrode substrate;

[0011] Further comprising, sequentially arranged on the reflective electrode and away from one side of the n-type metal electrode substrate:

[0012] An n-type doped inverted-trapezoidal structure, a multi-quantum well layer, a p-type doped layer, and a transparent conductive layer;

[0013] The n-type doped inverted-trapezoidal structure, the multi-quantum well layer, and the p-type doped layer form a single inverted-trapezoidal Micro-LED epitaxial mesa;

[0014] A dielectric layer between two adjacent single inverted-trapezoidal Micro-LED epitaxial mesas and in contact with the reflective electrode;

[0015] A top p-electrode on the transparent conductive layer and the dielectric layer;

[0016] The n-type doped inverted-trapezoidal structure and the reflective electrode form an inverted-trapezoidal micro-mirror structure, and the air / nitride interface of the n-type doped inverted-trapezoidal structure is smooth and flat.

[0017] In the above technical solution, preferably, the thickness of the n-type metal electrode substrate is between 100 nm and 5 mm, and the material is aluminum, copper, chromium, or silver.

[0018] In the above technical solution, preferably, the thickness of the reflective electrode and the top p-electrode is between 10 nm and 1 mm, and the material is gold, silver, chromium, aluminum, nickel, or Ti / Al / Ti / Au multilayer alloy, wherein the thickness of Al in the Ti / Al / Ti / Au multilayer alloy is 0.1-10 μm.

[0019] In the above technical solution, preferably, the material of the n-type doped inverted-trapezoidal structure and the p-type doped layer is GaN, AlGaN, InGaN, or AlN; and the bottom inclination angle of the n-type doped inverted-trapezoidal structure is between 90° and 175°.

[0020] In the above technical solution, preferably, the multi-quantum well layer is InGaN / GaN or Al x Ga 1-x N / Al y Ga 1-yN is a multi-quantum well layer, wherein 0 < x < 1, 0 < y < 1; or the multi-quantum well layer is at least two combinations of InN, InGaN, AlN, InAlN, InAlGaN;

[0021] The multi-quantum well layer has a well / barrier layer cycle number m, wherein 5 ≤ m ≤ 20, and m is an integer; the well layer thickness of the multi-quantum well layer is 0.5-5 nm, and the barrier layer thickness is 5-15 nm.

[0022] In the above technical solution, preferably, the transparent conductive layer is ITO, Ni / Au alloy or graphene, and the transmittance of the transparent conductive layer is in the range of 50%-100%.

[0023] In the above technical solution, preferably, the dielectric layer is silicon dioxide, titanium dioxide, titanium pentoxide, a Bragg reflector composed of multiple layers of dielectric materials, an omnidirectional reflector composed of multiple layers of dielectric materials, a photosensitive glue polyimide, a photosensitive glue SU-8 or a flexible material polydimethylsiloxane (PDMS).

[0024] In the above technical solution, preferably, the mesa size of the single piece-down inverted-trapezoidal Micro-LED epitaxial mesa is 1 μm-1 mm.

[0025] In the above technical solution, preferably, the discrete piece-down inverted-trapezoidal micro-mirror Micro-LED array device material system includes but is not limited to GaN-based blue Micro-LED, green Micro-LED and red Micro-LED, and AlGaInP-based red Micro-LED and AlGaN-based ultraviolet Micro-LED; the device structure includes a flip structure and a vertical structure; the light-emitting wavelength is 250-1000 nm.

[0026] A preparation method of a piece-down inverted-trapezoidal micro-mirror Micro-LED array device for improving light efficiency, comprising the following steps:

[0027] S1, first clean the epitaxial wafer; the epitaxial wafer includes a p-type doped layer, a multi-quantum well layer, an n-type doped layer and a growth substrate;

[0028] S2, then bond a temporary substrate on the p-type doped layer side and away from the growth substrate side;

[0029] S3, after bonding the temporary substrate, peel off the growth substrate;

[0030] S4, then etch the n-type doped layer to form an inverted-trapezoidal groove structure and an n-type doped inverted-trapezoidal structure;

[0031] S5, then evaporate the reflective electrode on the etched inverted trapezoidal groove structure and the n-type doped inverted trapezoidal structure;

[0032] S6, after the metal reflective electrode is evaporated, an n-type metal electrode substrate is prepared by using an electroplating process;

[0033] S7, then the temporary substrate is removed;

[0034] S8, after the temporary substrate is removed, a transparent conductive layer is evaporated above the p-type doped layer;

[0035] S9, the epitaxial wafer is etched to form an isolation channel and a wafer-down inverted trapezoidal Micro-LED epitaxial mesa;

[0036] S10, then a dielectric layer is deposited on the etched isolation channel and wafer-down inverted trapezoidal Micro-LED epitaxial mesa;

[0037] S11, after the dielectric layer is deposited, the dielectric layer is patterned by using etching or photolithography technology to form a dielectric region and a dielectric exposed region; wherein the dielectric region fills the isolation channel, and the dielectric exposed region is located at the wafer-down inverted trapezoidal Micro-LED epitaxial mesa;

[0038] S12, finally, a top p electrode is deposited on part of the transparent conductive layer and the dielectric region to form an array device composed of a plurality of wafer-down inverted trapezoidal micro-mirrors Micro-LED devices.

[0039] The beneficial effects of the present application are:

[0040] The Micro-LED array device with improved light efficiency of the present application is composed of a plurality of separated Micro-LED devices with inverted-trapezoidal micro-reflector, each of which comprises a p-type doped layer, a multi-quantum well layer, an n-type doped inverted-trapezoidal structure, a reflective electrode, an n-type metal electrode substrate, a transparent conductive layer, a dielectric layer and a top p-electrode, wherein the p-type doped layer, the multi-quantum well layer and the n-type doped inverted-trapezoidal structure form a single Micro-LED epitaxial mesa with inverted-trapezoidal micro-reflector. The n-type doped inverted-trapezoidal structure and the reflective electrode form an inverted-trapezoidal micro-reflector structure, and the air / nitride interface of the n-type doped inverted-trapezoidal structure is smooth and flat. The Micro-LED device with inverted-trapezoidal micro-reflector of the present application can effectively change the light path and improve the top Micro-LED light extraction efficiency due to the inverted-trapezoidal micro-reflector structure. The Micro-LED device with inverted-trapezoidal micro-reflector of the present application can effectively reduce the guided-mode light and increase the proportion of light in the radiation mode due to the homogeneity of the inverted-trapezoidal dielectric filling material and the epitaxial layer, which is conducive to the front light extraction. Compared with the method of improving light extraction efficiency by tilting the sidewall, the present method only etches the n-type doped layer without tilting the multi-quantum well layer, so the exposed area of the multi-quantum well layer does not increase, thus the sidewall defects can be suppressed, the charge coupling effect at the sidewall is reduced, the quantum confinement Stark effect (QCSE) at the sidewall is weakened, the hole convergence to the sidewall is reduced, the non-radiative recombination (SRH) is reduced, and the light-emitting performance is improved. In addition, the present device adopts a vertical structure, so it can bear a larger injection current compared with the flip-chip structure. BRIEF DESCRIPTION OF DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments of the present application or the prior art description. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0042] Figure 1 is a structure schematic diagram of the Micro-LED device with inverted-trapezoidal micro-reflector provided in Embodiment 1 of the present application.

[0043] Figure 2 is a step flow chart of the preparation method of the Micro-LED device with inverted-trapezoidal micro-reflector provided in Embodiment 2 of the present application.

[0044] Figure 3 is a preparation dynamic diagram of the Micro-LED array device with inverted-trapezoidal micro-reflector provided in Embodiment 2 of the present application.

[0045] Figure 4 is a schematic diagram of a Micro-LED device structure with a side wall mirror structure of an inverted trapezoidal micro-mirror provided by an embodiment 3 of the present application.

[0046] Figure 5 is a traditional structure LED light path diagram of a planar mirror provided by an embodiment 4 of the present application.

[0047] Figure 6 is a LED light path diagram with an inverted trapezoidal mirror structure under a wafer provided by an embodiment 4 of the present application.

[0048] The reference signs in the drawings are indicated as follows:

[0049] 1-epitaxial wafer, 11-p-type doped layer, 12-multiquantum well layer, 13-n-type doped layer, 14-growth substrate, 15-isolation trench, 16-inverted trapezoidal Micro-LED epitaxial mesa under a wafer;

[0050] 2-temporary substrate, 3-reflective electrode, 4-n-type metal electrode substrate, 5-transparent conductive layer, 6-dielectric layer, 7-top p-electrode, 8-inverted trapezoidal Micro-LED device under a wafer;

[0051] 131-inverted trapezoidal groove structure, 132-n-type doped inverted trapezoidal structure;

[0052] 32-side wall reflective electrode;

[0053] 61-dielectric region, 62-dielectric bare region. DETAILED DESCRIPTION

[0054] The present application provides a Micro-LED array device with an inverted trapezoidal micro-mirror under a wafer to improve light efficiency, as shown in the figure, which is composed of an array device of a plurality of discrete inverted trapezoidal micro-mirrors under a wafer 8; each of the inverted trapezoidal micro-mirrors under a wafer 8 comprises: Figure 1

[0055] n-type metal electrode substrate 4, an inverted trapezoidal groove array pattern is formed on the n-type metal electrode substrate 4;

[0056] reflective electrode 3, located on the upper side of the n-type metal electrode substrate 4;

[0057] n-type doped inverted trapezoidal structure 132, located on the upper side of the reflective electrode 3 at the bottom and away from one side of the n-type metal electrode substrate 4;

[0058] multiquantum well layer 12, located on the upper side of the n-type doped inverted trapezoidal structure 132 and away from one side of the n-type metal electrode substrate 4;

[0059] ​a p-type doped layer 11 on the upside of the multiple quantum well layer 12 and away from the n-type metal electrode substrate 4;

[0060] a transparent conductive layer 5 on the upside of the p-type doped layer 11 and away from the n-type metal electrode substrate 4;

[0061] a single piece of inverted-trapezoidal Micro-LED epitaxial mesa 16 composed of the n-type doped inverted-trapezoidal structure 132, the multiple quantum well layer 12 and the p-type doped layer 11;

[0062] a dielectric layer 6 between two adjacent single pieces of inverted-trapezoidal Micro-LED epitaxial mesa 16 and in contact with the reflective electrode 3;

[0063] a top p-electrode 7 on the transparent conductive layer 5 and the dielectric layer 6;

[0064] The n-type doped inverted-trapezoidal structure 132 and the reflective electrode 3 form an inverted-trapezoidal micro-reflector structure, and the air / nitride interface of the n-type doped inverted-trapezoidal structure 132 is smooth and flat.

[0065] In some embodiments, the n-type metal electrode substrate 4 can be prepared by an electroplating process, with a thickness of 100 nm-5 mm and a material including but not limited to aluminum, copper, chromium or silver; the n-type metal electrode substrate 4 can serve as an n-electrode to drive the current of the Micro-LED, and also as a substrate to provide support for the array device while helping to dissipate heat from the device.

[0066] In some embodiments, the preparation process of the reflective electrode 3 and the top p-electrode 7 includes but is not limited to electron beam evaporation, magnetron sputtering and thermal evaporation, with a thickness of 10 nm-1 mm and a material including but not limited to single metals such as gold, silver, chromium, aluminum or nickel, and multi-layer alloys such as Ti / Al / Ti / Au (the thickness of Al is 0.1-10 μm); the reflective electrode 3 can serve as an n-type ohmic contact layer and also as a bottom reflector.

[0067] In some embodiments, the materials of the n-type doped inverted-trapezoidal structure 132 and the p-type doped layer 11 include but are not limited to GaN or AlGaN or InGaN or AlN; the bottom angle of the n-type doped inverted-trapezoidal structure 132 is between 90°-175°.

[0068] In some embodiments, the multiple quantum well layer 12 is a multiple quantum well layer of InGaN / GaN or AlxGa1-xN / AlyGa1-yN, where 0

[0069] In some embodiments, the number of well / barrier layer cycles of the multi-quantum well layer 12 is m, wherein 5≤m≤20, and m is an integer; the thickness of the well layer of the multi-quantum well layer 12 is 0.5-5 nm, and the thickness of the barrier layer of the multi-quantum well layer 12 is 5-15 nm.

[0070] In some embodiments, the transparent conductive layer 5 includes but is not limited to ITO, Ni / Au alloy, graphene, etc., and the transmittance of the transparent conductive layer 5 is in the range of 50%-100%.

[0071] In some embodiments, the dielectric layer 6 includes but is not limited to silicon dioxide, titanium dioxide, titanium pentoxide, Bragg reflector composed of multiple dielectric layers, omnidirectional reflector, photosensitive glue such as polyimide and SU-8, and flexible material such as polydimethylsiloxane (PDMS). The preparation methods include but are not limited to electron beam evaporation, magnetron sputtering, atomic layer deposition, optical coating, and plasma enhanced chemical vapor deposition (PECVD), photolithography, nanoimprint, etc.

[0072] In some embodiments, the size of the single inverted-trapezoidal Micro-LED epitaxial mesa 16 is 1 μm-1 mm.

[0073] In some embodiments, the material system of the discrete inverted-trapezoidal Micro-LED device 8 includes but is not limited to GaN-based blue Micro-LED, green Micro-LED, and red Micro-LED, AlGaInP-based red Micro-LED, and AlGaN-based ultraviolet Micro-LED; or the structure of the inverted-trapezoidal Micro-LED device 8 includes flip-chip structure and vertical structure; or the light-emitting wavelength of the inverted-trapezoidal Micro-LED device 8 is 250-1000 nm.

[0074] The present application also provides a preparation method of an inverted-trapezoidal Micro-LED array device with improved light efficiency, and the step flow chart and preparation dynamic diagram of the preparation method are shown in Figure 2 and 3 , which comprises the following steps:

[0075] S1, first, the epitaxial wafer 1 is cleaned. The cleaning method used includes but is not limited to plasma cleaning, 511 solution, buffered oxide etchant (BOE), N-methyl pyrrolidone (NMP) and various acidic solutions; the epitaxial wafer 1 mainly includes a p-type doped layer 11, a multi-quantum well layer 12, an n-type doped layer 13 and a growth substrate 14, but is not limited to it should be understood that the specific embodiments described herein are only used to explain the present application, and do not limit the present application. The growth substrate 14 material includes but is not limited to sapphire, silicon wafer, SiC, AlN and GaN.

[0076] S2, then bond the temporary substrate 2 on the p-type doped layer 11 side and away from the growth substrate 14 side. The temporary substrate 2 material includes but is not limited to non-metallic substrates such as sapphire, silicon wafer, SiC, AlN, GaN, and metallic substrates such as copper sheet, aluminum sheet, silver sheet; the thickness of the temporary substrate 2 is 0.5 μm-1 mm; the bonding method includes but is not limited to adhesive bonding, metal eutectic bonding, metal hot-press bonding and direct bonding.

[0077] S3, after bonding the temporary substrate 2, the growth substrate 14 is peeled off. The growth substrate 14 peeling method includes but is not limited to chemical wet peeling, laser peeling, mechanical peeling and high-energy ion beam peeling.

[0078] S4, then etch the n-type doped layer 13 to form an inverted-trapezoidal groove structure 131 and an n-type doped inverted-trapezoidal structure 132. The etching method includes but is not limited to reactive coupled plasma etching (ICP), reactive ion etching (RIE), and laser scribing and nano-imprinting; the etching groove depth is 50 nm-5 μm, and the multi-quantum well layer 12 is not etched, the groove etching bottom width is 100 nm-500 μm, and the formed mesa top width is 500 nm-10 mm.

[0079] S5, then evaporate the reflective electrode 3 on the inverted-trapezoidal groove structure 131 and the n-type doped inverted-trapezoidal structure 132 formed by etching. The preparation process of the reflective electrode 3 includes but is not limited to electron beam evaporation, magnetron sputtering and thermal evaporation, the thickness is between 10 nm-1 mm, and the material includes but is not limited to single metal such as gold, silver, chromium, aluminum or nickel, and multi-layer alloy such as Ti / Al / Ti / Au (the thickness of Al is 0.1-10 μm); the reflective electrode 3 can be used as an n-type ohmic contact layer and a bottom mirror.

[0080] S6, after the metal reflective electrode 3 is evaporated, an n-type metal electrode substrate 4 is prepared by electroplating process, with a thickness of 100 nm-5 mm and materials including but not limited to aluminum, copper, chromium or silver; the n-type metal electrode substrate 4 can not only drive the Micro-LED current as an n-electrode, but also can be used as a substrate to support the array device and help the device dissipate heat.

[0081] S7, then the temporary substrate 2 is removed. The substrate removal method includes but is not limited to wet etching with acid or alkaline solution, and laser stripping technology, or chemical reagent etching for specific organic bonding layer.

[0082] S8, after the temporary substrate 2 is removed, a transparent conductive layer 5 is evaporated above the p-type doped layer 11. The transparent conductive layer 5 includes but is not limited to ITO, Ni / Au alloy or graphene, etc., and the transmittance of the transparent conductive layer 5 is in the range of 50%-100%, and the thickness is 10 nm-2 μm.

[0083] S9, the epitaxial wafer 1 is etched to form an isolation channel 15 and a sub-wafer inverted trapezoidal Micro-LED epitaxial mesa 16. The etching method includes but is not limited to reactive coupled plasma etching (ICP), reactive ion etching (RIE) and laser scribing, etc.; the depth of the isolation channel 15 is 100 nm-5 μm, and the width is 100 nm-500 μm; the width of the sub-wafer inverted trapezoidal Micro-LED epitaxial mesa 16 is 500 nm-10 mm.

[0084] S10, then a dielectric layer 6 is deposited on the isolation channel 15 and the sub-wafer inverted trapezoidal Micro-LED epitaxial mesa 16 formed by etching. The dielectric layer 6 includes but is not limited to silicon dioxide, titanium dioxide, titanium pentoxide, or Bragg reflector composed of multiple dielectric materials, omnidirectional reflector, and photosensitive glue such as polyimide or SU-8, and flexible materials such as polydimethylsiloxane (PDMS). The preparation method includes but is not limited to electron beam evaporation, magnetron sputtering, atomic layer deposition, optical coating and plasma enhanced chemical vapor deposition (PECVD), photolithography and nanoimprint, etc. The thickness of the dielectric layer 6 is 20 nm-10 μm.

[0085] S11, after the dielectric layer 6 is deposited, it is patterned by etching or photolithography technology to form dielectric area 61 and dielectric exposed area 62, which correspond to the area with dielectric layer and the area without dielectric layer respectively. The dielectric area 61 fills the isolation channel 15, and the dielectric exposed area 62 is located at the sub-wafer inverted trapezoidal Micro-LED epitaxial mesa 16.

[0086] S12, finally depositing a top p-electrode 7 on the transparent conductive layer 5 and part of the dielectric region 61, the contact width of the top p-electrode 7 with the transparent conductive layer 5 is 100 nm-100 μm, the preparation process of the top p-electrode 7 includes but is not limited to electron beam evaporation, magnetron sputtering and thermal evaporation, the thickness is between 10 nm-1 mm, and the material includes but is not limited to single metal such as gold, silver, chromium, aluminum or nickel, and multi-layer alloy such as Ti / Al / Ti / Au (the thickness of Al is 0.1-10 μm). An array device composed of a plurality of inverted trapezoidal micro-mirror Micro-LED devices 8 is formed, and has a vertical structure, and can realize light emission in the transparent conductive layer 5 region.

[0087] According to the micro-nano processing process, the inverted trapezoidal micro-mirror Micro-LED device is obtained.

[0088] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference signs represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0089] In the description of the present application, it should be understood that the terms "upper", "lower", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application.

[0090] In addition, the terms "first", "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0091] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and examples.

[0092] Example 1

[0093] Please refer to Figure 1A structure schematic diagram of a flip-trapezoidal Micro-LED array device is provided in an embodiment of the present application, which is an array device composed of a plurality of flip-trapezoidal Micro-LED devices 8; each of the flip-trapezoidal Micro-LED devices 8 comprises an n-type metal electrode substrate 4, a reflective electrode 3 located on the upper side of the n-type metal electrode substrate 4, an n-type doped trapezoidal structure 132 located on the upper side of the reflective electrode 3 and away from one side of the n-type metal electrode substrate 4, a multi-quantum well layer 12 located on the upper side of the n-type doped trapezoidal structure 132 and away from one side of the n-type metal electrode substrate 4, a p-type doped layer 11 located on the upper side of the multi-quantum well layer 12 and away from one side of the n-type metal electrode substrate 4, a transparent conductive layer 5 located on the upper side of the p-type doped layer 11 and away from one side of the n-type metal electrode substrate 4, a single flip-trapezoidal Micro-LED epitaxial mesa 16 composed of the n-type doped trapezoidal structure 132, the multi-quantum well layer 12 and the p-type doped layer 11, a dielectric layer 6 located between two adjacent single flip-trapezoidal Micro-LED epitaxial mesas 16 and in contact with the reflective electrode 3, and a top p-electrode 7 located on the transparent conductive layer 5 and the dielectric layer 6.

[0094] The n-type doped trapezoidal structure 132 and the reflective electrode 3 form a flip-trapezoidal Micro-LED structure, and the air / nitride interface of the n-type doped trapezoidal structure 132 is smooth and flat.

[0095] The implementation of each component is described below.

[0096] In the embodiment, the n-type metal electrode substrate 4 can be prepared by an electroplating process, with a thickness of 100 nm-5 mm and a material including but not limited to aluminum, copper, chromium or silver; the n-type metal electrode substrate 4 can serve as an n-electrode to drive the current of the Micro-LED, and also as a substrate to provide support for the array device and help the device dissipate heat.

[0097] In the embodiment, the preparation process of the reflective electrode 3 and the top p-electrode 7 includes but is not limited to electron beam evaporation, magnetron sputtering and thermal evaporation, with a thickness of 10 nm-1 mm and a material including but not limited to single metals such as gold, silver, chromium, aluminum or nickel, and multi-layer alloys such as Ti / Al / Ti / Au (the thickness of Al is 0.1-10 μm); the reflective electrode 3 can serve as an n-type ohmic contact layer and also as a bottom mirror.

[0098] In the embodiment, the n-doped inverted-trapezoidal structure 132 and the p-doped layer 11 material include, but are not limited to, GaN or AlGaN or InGaN or AlN; wherein the bottom angle of the n-doped inverted-trapezoidal structure 132 is between 90°-175°.

[0099] In the embodiment, the multi-quantum well layer 12 is a multi-quantum well layer of InGaN / GaN or AlxGa1-xN / AlyGa1-yN, wherein 0

[0100] In the embodiment, the multi-quantum well layer 12 has a well / barrier layer period number of m; wherein 5≤m≤20, m is an integer; the well layer thickness of the multi-quantum well layer 12 is 0.5-5 nm, and the barrier layer thickness of the multi-quantum well layer 12 is 5-15 nm.

[0101] In the embodiment, the transparent conductive layer 5 includes, but is not limited to, ITO, Ni / Au alloy, graphene, etc., and the transmittance of the transparent conductive layer 5 is in the range of 50%-100%.

[0102] In the embodiment, the dielectric layer 6 includes, but is not limited to, silicon dioxide, titanium dioxide, titanium pentoxide, or a Bragg reflector composed of multiple dielectric materials and an omnidirectional reflector, and a photosensitive glue such as polyimide or SU-8, and a flexible material such as polydimethylsiloxane (PDMS).

[0103] In the embodiment, the single piece-down inverted-trapezoidal Micro-LED epitaxial mesa 16 has a mesa size of 1 μm-1 mm.

[0104] In the embodiment, the discrete piece-down inverted-trapezoidal Micro-LED device 8 material system includes, but is not limited to, GaN-based blue Micro-LED, green Micro-LED, and red Micro-LED, and AlGaInP-based red Micro-LED and AlGaN-based ultraviolet Micro-LED; or the device 8 structure includes a flip structure and a vertical structure; or the device 8 has a light-emitting wavelength of 250-1000 nm.

[0105] The Micro-LED array device with the inverted trapezoidal micro-mirror provided by the above-mentioned embodiments of the present application can change the light path, so that the front light extraction efficiency is enhanced, thanks to the optimized angle of the n-type doped inverted trapezoidal structure 132; the light irradiated on the bottom of the epitaxial wafer 1 can be effectively reflected by the reflective electrode 3, so as to improve the light intensity received by the detector; the thickened n-type metal electrode substrate 4 can provide substrate support for the device, and also can serve as an n-type conductive electrode and a heat dissipation layer, which is conducive to the stable performance of the device; the dielectric layer 6 can electrically isolate the device to prevent the device from leaking, and also has the effect of sidewall passivation, which can further reduce the sidewall defects.

[0106] Embodiment 2

[0107] Please refer to Figure 2 , which shows the preparation flow chart of the Micro-LED array device with the inverted trapezoidal micro-mirror. The preparation method of the Micro-LED array device with the inverted trapezoidal micro-mirror according to the second embodiment of the present application comprises the following steps:

[0108] S1, first, the epitaxial wafer 1 is cleaned. The cleaning method used includes but is not limited to plasma cleaning, 511 solution, buffer oxide etching liquid (BOE), N-methyl pyrrolidone (NMP) and various acidic solutions. The epitaxial wafer 1 mainly includes a p-type doped layer 11, a multi-quantum well layer 12, an n-type doped layer 13 and a growth substrate 14, but is not limited to it should be understood that the specific embodiments described herein are only used to explain the present application, and do not limit the present application. The growth substrate 14 material includes but is not limited to sapphire, silicon wafer, SiC, AlN and GaN.

[0109] S2, then bond the temporary substrate 2 on the side of the p-type doped layer 11 and away from the growth substrate 14 side. The temporary substrate 2 material includes but is not limited to non-metallic substrates such as sapphire, silicon wafer, SiC, AlN, GaN, and metal substrates such as copper sheet, aluminum sheet, silver sheet; the thickness of the temporary substrate is 0.5-1 mm; the bonding method includes but is not limited to adhesive bonding, metal eutectic bonding, metal hot-press bonding and direct bonding.

[0110] S3, after bonding the temporary substrate 2, the growth substrate 14 is peeled off. The growth substrate 14 peeling method includes but is not limited to chemical wet peeling, laser peeling, mechanical peeling and high-energy ion beam peeling.

[0111] S4, then etching the n-type doped layer 13 to form an inverted-trapezoidal groove structure 131 and an n-type doped inverted-trapezoidal mesa structure 132. The etching method includes but is not limited to reactive coupled plasma etching (ICP), reactive ion etching (RIE), and laser scribing and nano-imprinting, etc.; the etching groove depth is 50 nm-5 μm, and the multi-quantum well layer 12 is not etched, the groove etching bottom width is 100 nm-500 μm, and the formed mesa top width is 500 nm-10 mm.

[0112] S5, then evaporating a reflective electrode 3 on the etched inverted-trapezoidal groove structure 131 and the n-type doped inverted-trapezoidal mesa structure 132, the preparation process of the reflective electrode 3 includes but is not limited to electron beam evaporation, magnetron sputtering and thermal evaporation, the thickness is between 10 nm-1 mm, and the material includes but is not limited to single metal such as gold, silver, chromium, aluminum or nickel, and multi-layer alloy such as Ti / Al / Ti / Au (the thickness of Al is 0.1-10 μm); the reflective electrode 3 can be used as an n-type ohmic contact layer and a bottom mirror.

[0113] S6, after the metal reflective electrode 3 is evaporated, an n-type metal electrode substrate 4 is prepared by electroplating process, the thickness is between 100 nm-5 mm, and the material includes but is not limited to aluminum, copper, chromium or silver; the n-type metal electrode substrate 4 can be used as an n-electrode to drive the Micro-LED current, and can also be used as a substrate to provide support for the array device, and help the device heat dissipation.

[0114] S7, then the temporary substrate 2 is removed. The substrate removal method includes but is not limited to wet etching by using acid and alkaline solution, and laser stripping technology, or chemical reagent etching for specific organic bonding layer.

[0115] S8, after the temporary substrate 2 is removed, a transparent conductive layer 5 is evaporated above the p-type doped layer 11. The transparent conductive layer 5 includes but is not limited to ITO, Ni / Au alloy or graphene, etc., the transmittance of the transparent conductive layer 5 is in the range of 50%-100%, and the thickness is 10 nm-2 μm.

[0116] S9, the epitaxial wafer 1 is etched to form an isolation channel 15 and a wafer-down inverted-trapezoidal Micro-LED epitaxial mesa 16. The etching method includes but is not limited to reactive coupled plasma etching (ICP), reactive ion etching (RIE), and laser scribing, etc.; the depth of the isolation channel 15 is 100 nm-5 μm, and the width is 100 nm-500 μm; the width of the wafer-down inverted-trapezoidal Micro-LED epitaxial mesa 16 is 500 nm-10 mm.

[0117] S10, then deposit a dielectric layer 6 on the isolation channel 15 and the inverted-trapezoidal Micro-LED epitaxial mesa 16 formed by etching. The dielectric layer 6 includes but is not limited to silicon dioxide, titanium dioxide, titanium pentoxide, or a Bragg reflector composed of multiple dielectric layers, and an omnidirectional reflector, and a photosensitive glue such as polyimide or SU-8, and a flexible material such as polydimethylsiloxane (PDMS). The preparation method includes but is not limited to electron beam evaporation, magnetron sputtering, atomic layer deposition, optical coating, and plasma enhanced chemical vapor deposition (PECVD), photolithography, and nanoimprint, etc. The thickness of the dielectric layer 6 is 20 nm-10 μm.

[0118] S11, after the deposition of the dielectric layer 6, it is patterned by etching or lithography technology to form dielectric regions 61 and dielectric exposed regions 62, which correspond to regions with and without dielectric layer respectively. The dielectric region 61 fills the isolation channel 15, and the dielectric exposed region 62 is located at the inverted-trapezoidal Micro-LED epitaxial mesa 16.

[0119] S12, finally, a top p-electrode 7 is deposited on part of the transparent conductive layer 5 and the dielectric region 61, the contact width of the top p-electrode 7 with the transparent conductive layer 5 is 100 nm-100 μm, and the preparation process of the top p-electrode 7 includes but is not limited to electron beam evaporation, magnetron sputtering and thermal evaporation, the thickness is 10 nm-1 mm, and the material includes but is not limited to single metal such as gold, silver, chromium, aluminum or nickel, and multilayer alloy such as Ti / Al / Ti / Au (the thickness of Al is 0.1-10 μm). An array device composed of multiple inverted-trapezoidal Micro-LED devices 8 is formed, and has a vertical structure, which can realize light emission in the transparent conductive layer region.

[0120] In particular, Figure 3 The preparation dynamic diagram of the inverted-trapezoidal Micro-LED array device is shown.

[0121] First, bond a temporary substrate 2 on the epitaxial wafer 1, and peel off the native substrate to expose the n-type doped layer. Then etch the n-type doped layer 13 to form a trapezoidal mesa array, and then evaporate a reflective electrode 3 on the surface of the entire n-type doped layer 13, which can also be used as an ohmic contact layer, followed by metal electrode thickening to form a support substrate and achieve good electrical and thermal conductivity. Then remove the temporary substrate 2, deposit a transparent conductive layer 5 on the surface of the p-type doped layer 11 to achieve good p-type ohmic contact and light transmission effect. Then etch the LED mesa to form a discrete inverted-trapezoidal Micro-LED epitaxial mesa 16 array. Finally, deposit a dielectric layer 6 for electrical isolation, and selectively open holes for depositing a top p-electrode 7 to complete the device preparation.

[0122] Embodiment 3

[0123] Please refer to Figure 4 , which shows a Micro-LED device with a side-wall mirror structure. Compared with the device shown in Figure 1 , the difference is that the device is etched at the dielectric region (61) and a side-wall reflective electrode 32 is deposited, the preparation process of which includes but is not limited to electron beam evaporation, magnetron sputtering and thermal evaporation, with a thickness of 10 nm-1 mm and a material including but not limited to single metal such as gold, silver, chromium, aluminum or nickel, and multi-layer alloy such as Ti / Al / Ti / Au (the thickness of Al is 0.1-10 μm). Compared with the device shown in Figure 1 , the device has the feature of reflecting side-wall light, which can reduce light crosstalk and further improve the front light efficiency.

[0124] Embodiment 4

[0125] Please refer to Figure 5 and Figure 6 , which are respectively the traditional LED light path diagram with a planar mirror and the LED light path diagram with a submount inverted-trapezoidal mirror structure. Preferably, the light considered in the present light path diagram is the light emitted downward to the reflector, and the same applies to the light emitted upward.

[0126] As shown in Figure 5 , for a point light source in a multi-quantum well, as shown by light ray ①, when the exit angle is less than the critical angle of the LED epitaxial wafer and air, the light ray can be effectively emitted from the front after being reflected by the bottom mirror. Such light rays are radiation mode light rays. When the light emission angle continues to increase to the critical angle, for light ray ②, the light ray cannot be effectively emitted from the front of the LED after being reflected by the mirror, but forms a waveguide structure, and the light ray is emitted from the side wall. Similarly, when the light emission angle exceeds the critical angle, as shown by light ray ③, the same waveguide structure as light ray ② is formed, so light rays ② and ③ are guided mode light rays. In addition, Figure 5 , the escape cone of the light emitted by a point light source is also marked. When the light emission angle is less than the critical angle, the light ray is within the escape cone (such as light ray ①), and the light ray can be effectively emitted from the front; but when the light emission angle exceeds or equals the escape cone angle, the light ray will be reflected multiple times and emitted from the side wall (as shown by light rays ② and ③). For GaN-based LEDs, the critical angle of the multi-quantum well layer and air is about 24°, and for AlGaN-based LEDs, the critical angle of the multi-quantum well layer and air is about 22.6°.

[0127] As shown in Figure 6As shown, when the inverted trapezoidal micro-mirror is adopted, good light extraction effect can be achieved by optimizing the inverted trapezoidal structure, as described in detail below: for a point light source, when the light extraction angle is less than the critical angle, as shown by light ray ①, the light ray can be emitted from the front after being reflected by the bottom mirror. When the light extraction angle increases to the critical angle, as shown by light ray ②, the light ray is emitted from the front after being reflected by the bottom mirror, total internal reflection on the upper surface of the epitaxial layer, and twice inverted trapezoidal mirror reflection. When the light extraction angle further increases, as shown by light ray ③, the light ray is emitted from the front after being reflected by the bottom mirror and the inverted trapezoidal mirror. When the light extraction angle continues to increase, as shown by light ray ④, the light ray is emitted from the front after being reflected by the inverted trapezoidal mirror once. Similarly, for the light ray emitted upward but greater than the critical angle, as shown by light ray ⑤, the light ray can still be emitted from the front after being reflected by the total internal reflection on the upper surface of the epitaxial wafer and the inverted trapezoidal mirror.

[0128] Therefore, without considering material absorption loss and metal reflection and absorption loss, the front emission of the light ray can be achieved regardless of the light extraction angle.

[0129] The technical features of the above-described embodiments can be combined in any manner. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described, but as long as the combinations of the technical features do not contradict, they should be considered within the scope of the present disclosure.

[0130] The above is only a preferred embodiment of the present application, and only the technical principles of the present application are specifically described. These descriptions are only for the purpose of explaining the principles of the present application and cannot be interpreted in any way as a limitation on the scope of protection of the present application. Based on the explanations herein, any modifications, equivalent replacements and improvements made within the spirit and principles of the present application, and other specific embodiments of the present application that can be conceived by those skilled in the art without creative labor, should be included within the scope of protection of the present application.

Claims

1. A light efficiency improved under-chip inverted-trapezoidal micro-mirror Micro-LED array device, characterized in that, It is an array device composed of a plurality of discrete inverted-trapezoidal micro-mirror Micro-LED devices (8); Each of the inverted-trapezoidal micro-mirror Micro-LED devices (8) comprises: An n-type metal electrode substrate (4) having an inverted-trapezoidal groove array pattern formed thereon; A reflective electrode (3) located on the upper side of the n-type metal electrode substrate (4); Further comprising, sequentially arranged on the reflective electrode (3) and away from one side of the n-type metal electrode substrate (4): An n-type doped inverted-trapezoidal structure (132), a multi-quantum well layer (12), a p-type doped layer (11), and a transparent conductive layer (5); The n-type doped inverted-trapezoidal structure (132), the multi-quantum well layer (12), and the p-type doped layer (11) form a single inverted-trapezoidal Micro-LED epitaxial mesa (16); A dielectric layer (6) located between two adjacent single inverted-trapezoidal Micro-LED epitaxial mesas (16) and in contact with the reflective electrode (3); A top p-electrode (7) located above the transparent conductive layer (5) and the dielectric layer (6); The n-type doped inverted-trapezoidal structure (132) and the reflective electrode (3) form an inverted-trapezoidal micro-mirror structure, and the air and nitride interface of the n-type doped inverted-trapezoidal structure (132) is smooth and flat.

2. The light efficiency improved under-shoot-inverted-trapezoidal micro-mirror Micro-LED array device according to claim 1, characterized in that, The thickness of the n-type metal electrode substrate (4) is between 100 nm and 5 mm, and the material is aluminum, copper, chromium, or silver.

3. The light efficiency improved under-shoot-inverted-trapezoidal micro-mirror Micro-LED array device according to claim 1, wherein, The thickness of the reflective electrode (3) and the top p-electrode (7) is between 10 nm and 1 mm, and the material is gold, silver, chromium, aluminum, nickel, or Ti / Al / Ti / Au multilayer alloy, wherein the thickness of Al in the Ti / Al / Ti / Au multilayer alloy is 0.1-10 μm.

4. The light efficiency improved under-shoot-inverted-trapezoidal micro-mirror Micro-LED array device according to claim 1, wherein, The materials of the n-type doped inverted-trapezoidal structure (132) and the p-type doped layer (11) are GaN, AlGaN, InGaN, or AlN; and the bottom inclination angle of the n-type doped inverted-trapezoidal structure (132) is between 90° and 175°.

5. The light efficiency improved under-shoot-inverted-trapezoidal micro-mirror Micro-LED array device according to claim 1, wherein, The multi-quantum well layer (12) is InGaN / GaN or Al x Ga 1-x N / Al y Ga 1-y N multi-quantum well layer, wherein 0 < x < 1, 0 < y < 1; or the multi-quantum well layer (12) is at least two combinations of InN, InGaN, AlN, InAlN, InAlGaN; The number of well / barrier layer periods of the multi-quantum well layer (12) is m; wherein 5≤m≤20, and m is an integer; the well layer thickness of the multi-quantum well layer (12) is 0.5-5 nm, and the barrier layer thickness is 5-15 nm.

6. The light efficiency improved under-shoot-inverted-trapezoidal micro-mirror Micro-LED array device according to claim 1, wherein, The transparent conductive layer (5) is ITO, Ni / Au alloy, or graphene, and the transmittance of the transparent conductive layer (5) is in the range of 50%-100%.

7. The light efficiency improved under-shoot-inverted-trapezoidal micro-mirror Micro-LED array device according to claim 1, wherein, The dielectric layer (6) is silicon dioxide, titanium dioxide, titanium pentoxide, a Bragg reflector composed of multiple dielectric layers, an omnidirectional reflector composed of multiple dielectric layers, a photosensitive glue polyimide, a photosensitive glue SU-8, or a flexible material polydimethylsiloxane.

8. The light efficiency improved under-shoot-inverted-trapezoidal micro-mirror Micro-LED array device according to claim 1, wherein, The mesa size of the single inverted-trapezoidal Micro-LED epitaxial mesa (16) is 1 μm-1 mm.

9. The light efficiency improved under-shoot-inverted-trapezoidal micro-mirror Micro-LED array device according to claim 1, wherein, The material system of the inverted-trapezoidal micro-mirror Micro-LED device (8) is GaN-based blue Micro-LED, green Micro-LED, red Micro-LED, AlGaInP-based red Micro-LED or AlGaN-based ultraviolet Micro-LED, and the device structure includes a flip structure and a vertical structure; the light-emitting wavelength is 250-1000 nm.

10. A method for preparing a high light efficiency inverted-trapezoidal micro-mirror Micro-LED array device according to any one of claims 1-9, characterized in that, The method comprises the following steps: S1, first cleaning the epitaxial wafer (1); the epitaxial wafer (1) comprises a p-type doped layer (11), a multi-quantum well layer (12), an n-type doped layer (13) and a growth substrate (14); S2, then bonding a temporary substrate (2) on the side of the p-type doped layer (11) and away from the side of the growth substrate (14); S3, after bonding the temporary substrate (2), peeling off the growth substrate (14); S4, then etching the n-type doped layer (13) to form an inverted-trapezoidal groove structure (131) and an n-type doped inverted-trapezoidal structure (132); S5, then evaporating a reflective electrode (3) on the inverted-trapezoidal groove structure (131) and the n-type doped inverted-trapezoidal structure (132) formed by etching; S6, after evaporating the metal reflective electrode (3), preparing an n-type metal electrode substrate (4) by using an electroplating process; S7, then removing the temporary substrate (2); S8, after removing the temporary substrate (2), evaporating a transparent conductive layer (5) above the p-type doped layer (11); S9, etching the epitaxial wafer (1) to form an isolation channel (15) and an inverted-trapezoidal Micro-LED epitaxial mesa (16) under the wafer; S10, then depositing a dielectric layer (6) on the isolation channel (15) and the inverted-trapezoidal Micro-LED epitaxial mesa (16) formed by etching; S11, after depositing the dielectric layer (6), patterning it by using etching or photolithography technology to form a dielectric region (61) and a dielectric exposed region (62); wherein the dielectric region (61) fills the isolation channel (15), and the dielectric exposed region (62) is located at the inverted-trapezoidal Micro-LED epitaxial mesa (16) under the wafer; S12, finally depositing a top p-electrode (7) on part of the transparent conductive layer (5) and the dielectric region (61) to form an array device composed of a plurality of inverted-trapezoidal micro-mirror Micro-LED devices (8).

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