Micro-LED array and preparation method thereof

Abstract

The invention belongs to the technical field of Micro-LED micro-nano optical light field regulation and control and Micro-LED preparation, and relates to a Micro-LED array and a preparation method thereof. Comprising a Micro-LED mesa structure array, a second N-type GaN layer and a one-dimensional photonic crystal layer. The second N-type GaN layer is continuously arranged on the plane where the upper surface of the Micro-LED mesa structure array is located. The one-dimensional photonic crystal layer is arranged on the upper surface of the second N-type GaN layer and comprises a first dielectric layer and a second dielectric layer which are arranged in a stacked mode and are different in refractive index. The second N-type GaN layer is used for providing a flat surface and growing the high-quality one-dimensional photonic crystal layer, the one-dimensional photonic crystal layer is used for efficiently transmitting small-angle incident light rays and strongly reflecting large-angle incident light rays, light crosstalk between array structures is effectively reduced, and the light emitting collimation of the Micro-LED is greatly improved.

Description

Technical Field

[0001] The present invention relates to the field of Micro-LED micro-nano optical light field regulation and Micro-LED preparation technology, and in particular to a Micro-LED array and a preparation method thereof. Background Art

[0002] As an active light-emitting device, light-emitting diodes (LEDs) have a wide range of applications in display, lighting and other fields, such as direct use in ultra-large screen displays, LCD panel backlighting, etc. As people's requirements for super-resolution, integration, brightness and other aspects of display technology increase, emerging micro-light-emitting diodes (Micro-LEDs) have been proposed and developed. Compared with liquid crystals and organic light-emitting diodes, Micro-LEDs have the advantages of long light-emitting unit life, fast response speed, high color saturation and high brightness. Therefore, they have a broad market in high-end displays, mobile devices, augmented / virtual reality and wearable devices.

[0003] Due to the extremely small physical size of each Micro-LED light-emitting unit, the light waves are strongly scattered and diffracted at the top and side walls of the light-emitting unit. Therefore, the light-emitting characteristics of Micro-LED conform to the Lambertian distribution, and the light output angle covers -90°~90°. The large divergence angle light output characteristics of Micro-LED not only make it difficult for optical devices to regulate the light field distribution of Micro-LED, thereby giving it optical functions, but also the sidewall light emission of Micro-LED also causes serious crosstalk between pixel arrays, which also greatly limits the application scope of Micro-LED arrays. The relevant research on low-crosstalk and high-collimation light-emitting Micro-LED array devices is currently in its infancy. It is difficult for existing technologies to completely solve the problems of Micro-LED sidewall light leakage crosstalk and large divergence angle light emission, resulting in the inability of Micro-LED to achieve good low-crosstalk and high-collimation light output.

[0004] In summary, existing Micro-LEDs cannot achieve good low crosstalk and highly collimated light output. Summary of the invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the problem that Micro-LED in the prior art cannot achieve good low crosstalk and highly collimated light output.

[0006] In order to solve the above technical problems, the present invention provides a Micro-LED array, comprising: A micro-LED mesa structure array, comprising a plurality of micro-LED mesa structures arranged in an array, each micro-LED mesa structure comprising a first N-type GaN layer, a quantum well light-emitting layer, a P-type GaN layer and an ITO layer stacked in sequence from top to bottom; A second N-type GaN layer is continuously disposed on a plane where the upper surface of the Micro-LED mesa structure array is located, so that a plurality of Micro-LED mesa structures share the second N-type GaN layer; The one-dimensional photonic crystal layer is continuously arranged on the surface of the second N-type GaN layer on the side away from the Micro-LED mesa structure array, and includes at least one photonic crystal structure, and the photonic crystal structure includes a first medium layer and a second medium layer with different refractive indices arranged in a stacked manner.

[0007] In the present application, an inverted Micro-LED mesa structure array is designed, and a continuous second N-type GaN layer is set on the upper surface of the Micro-LED mesa structure array to obtain a common N-type Micro-LED mesa structure array, and a complete growth plane is provided for the one-dimensional photonic crystal layer; a one-dimensional photonic crystal layer is designed on the surface of the second N-type GaN layer, so that light with a smaller incident angle is transmitted from the top of the one-dimensional photonic crystal layer to the outside of the mesa structure, while light with a larger incident angle is reflected and refracted at the interface between the first medium layer and the second medium layer with different refractive indices, thereby returning to the inside of the Micro-LED mesa structure and entering the one-dimensional photonic crystal layer again until entering the one-dimensional photonic crystal layer at a small incident angle and transmitting to the outside of the mesa structure, thereby reducing the light beam divergence angle; a continuous and flat second N-type GaN layer and a continuous one-dimensional photonic crystal layer integrally integrated on the surface of the second N-type GaN layer are used to achieve highly collimated light emission of Micro-LED and avoid edge light leakage caused by truncation of the photonic crystal layer (that is, discretely integrated on the surface of each Micro-LED light-emitting unit).

[0008] Preferably, the thickness of the second N-type GaN layer is 0.1 μm-1.5 μm.

[0009] In the present application, the second N-type GaN layer serves as an intermediate transition layer, and its thickness directly affects the mutual optical coupling between the top one-dimensional photonic crystal layer and the Micro-LED; an inappropriate thickness of the second N-type GaN layer will cause light to interfere and destructively interact in the second N-type GaN layer, thereby affecting the light output energy of the Micro-LED, and when the second N-type GaN layer is too thick, it will increase the absorption and loss of light in the second N-type GaN layer, thereby reducing the light output energy of the Micro-LED. Therefore, the present application limits the thickness of the second N-type GaN layer, thereby enhancing the interference of light in the second N-type GaN layer, thereby improving the light output energy of the Micro-LED.

[0010] Preferably, the number of the photonic crystal structures is 1 to 20; The material of the first dielectric layer includes SiO2, Al2O3, and HfO2; the thickness of the first dielectric layer is 60nm-200nm; The material of the second dielectric layer includes TiO2, SiN, and Ta2O5; the thickness of the second dielectric layer is 30nm-100nm.

[0011] In the present application, by controlling the number of photonic crystal structures, both the collimation effect of the one-dimensional photonic crystal layer on the light beam and the volume of the Micro-LED are taken into account; by controlling the material and thickness of the first dielectric layer and the second dielectric layer, the collimation effect of the one-dimensional photonic crystal layer on the light beam can be changed, thereby reducing the divergence angle of the light beam.

[0012] Preferably, it also includes: The micro-distributed Bragg reflector is arranged on the side wall and bottom of each Micro-LED mesa structure, and on the surface of the second N-type GaN layer between adjacent Micro-LED mesa structures away from the one-dimensional photonic crystal layer, including at least one periodically stacked high-reflection film system structure, wherein the periodically stacked high-reflection film system structure includes a third medium layer and a fourth medium layer with different refractive indices stacked in layers.

[0013] In the present application, due to the setting of the second N-type GaN layer, when the light beam enters the one-dimensional photonic crystal layer and is reflected, part of the light beam will enter the second N-type GaN layer between adjacent mesa structures and be emitted from the bottom of the second N-type GaN layer, causing energy loss, resulting in reduced luminous efficiency of the Micro-LED. At the same time, each Micro-LED mesa structure has the problem of sidewall light leakage, resulting in beam crosstalk between adjacent light-emitting units, thereby affecting the quality of the Micro-LED display image. Therefore, the present application sets a micro-distributed Bragg reflector on the sidewall and bottom of each Micro-LED mesa structure, as well as on the bottom of the second N-type GaN layer between adjacent mesa structures, so that the light beam reflected back from the one-dimensional photonic crystal layer, the sidewall light beam emitted by the quantum well light-emitting layer, and the light beam emitted from the bottom of the mesa structure enter the micro-distributed Bragg reflector, and then strongly reflect on the alternating interface of the third medium layer and the fourth medium layer with different refractive indices, thereby reflecting back to the inside of the Micro-LED mesa structure and emitting from the top of the mesa structure, which not only solves the problem of beam crosstalk between adjacent light-emitting units, but also improves the top light output rate of the Micro-LED.

[0014] Preferably, the number of the periodically stacked high-reflection film system structures is 5 to 15; The material of the third dielectric layer includes SiO2, Al2O3, and HfO2; the thickness of the third dielectric layer is 60nm-100nm; The material of the fourth dielectric layer includes TiO2, SiN, and Ta2O5; the thickness of the fourth dielectric layer is 30nm-100nm.

[0015] In the present application, by controlling the number of periodically stacked high-reflection film structures, a good reflection effect can be achieved on the light beams at the side walls and bottom of the mesa structure, and the light emitted from the bottom of the second N-type GaN layer has a high reflectivity, while taking into account the absorption loss of the distributed Bragg reflector; by controlling the material and thickness of the third dielectric layer and the fourth dielectric layer, the emissivity of the micro-distributed Bragg reflector to the light beam can be changed, thereby avoiding the sidewall light leakage phenomenon and the light beam crosstalk problem between adjacent light-emitting units.

[0016] The present invention also provides a method for preparing a Micro-LED array, which is used to prepare the above-mentioned Micro-LED array, comprising: Prepare an epitaxial wafer, wherein the epitaxial wafer includes a first N-type GaN layer, a quantum well light-emitting layer, and a P-type GaN layer stacked in sequence from top to bottom; Etching the P-type GaN layer, the quantum well light-emitting layer and a portion of the first N-type GaN layer to form a plurality of first pillars and a second N-type GaN layer continuously arranged on a plane where upper surfaces of the plurality of first pillars are located; An ITO layer is prepared on the lower surface of the first column to form a plurality of Micro-LED mesa structures; wherein each of the Micro-LED mesa structures comprises a first N-type GaN layer, a quantum well light-emitting layer, a P-type GaN layer and an ITO layer which are stacked; The second N-type GaN layer is thinned and polished, and a one-dimensional photonic crystal layer is formed on the upper surface of the second N-type GaN layer; wherein the one-dimensional photonic crystal layer includes at least one photonic crystal structure, and the photonic crystal structure includes a first medium layer and a second medium layer with different refractive indices that are stacked.

[0017] Preferably, it also includes: A micro-distributed Bragg reflector is formed on the side wall of the Micro-LED mesa structure, the lower surface of the Micro-LED mesa structure, and the lower surface of the second N-type GaN layer between adjacent Micro-LED mesa structures; wherein the micro-distributed Bragg reflector includes at least one periodically stacked high-reflection film system structure, and the periodically stacked high-reflection film system structure includes a third medium layer and a fourth medium layer with different refractive indices stacked.

[0018] The Micro-LED array provided in the present application arranges a one-dimensional photonic crystal layer on the top of the Micro-LED table structure, and uses the dielectric layers with different refractive indices in the one-dimensional photonic crystal layer to collimate the light beam emitted by the Micro-LED, thereby reducing the light beam divergence angle of the Micro-LED; however, since the Micro-LED table structure is discretely arranged, if a discrete one-dimensional photonic crystal layer is directly arranged on the surface of each Micro-LED table structure, the light beam will refract and reflect between the dielectric layers after entering the one-dimensional photonic crystal layer, and will eventually be emitted not only from the surface of the one-dimensional photonic crystal layer, but also from the side wall, and there is still the problem of excessive divergence angle of the Micro-LED light beam. Therefore, the present application designs an inverted A Micro-LED mesa structure is installed, and a continuous second N-type GaN layer is set on the upper surface of the Micro-LED mesa structure array to obtain a Micro-LED mesa structure array with a common N pole. The second N-type GaN layer is used to provide a growth plane for the one-dimensional photonic crystal layer, so that a complete one-dimensional photonic crystal layer can be grown on the entire Micro-LED mesa structure array, and the light beam emitted by the entire Micro-LED mesa structure array can be directly collimated, which can not only have the effect of light beam collimation for the Micro-LED, but also avoid the problem of large light beam divergence angle caused by light leakage from the side wall of the truncated one-dimensional photonic crystal layer, thereby reducing the light beam divergence angle of the Micro-LED to the greatest extent and increasing the top light output. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to make the content of the present application easier to understand, the present application is further described in detail below based on the specific embodiments of the present application and in conjunction with the accompanying drawings, wherein: Figure 1 Schematic diagram of the Micro-LED array provided for this application; Figure 2 The main view of the Micro-LED array provided for this application; Figure 3 A schematic diagram of the transmittance curve of the one-dimensional photonic crystal layer provided in the present application to light rays at different incident angles; Figure 4 Schematic diagram of the Micro-LED light beam divergence angle and top light energy provided in this application; Figure 5 A schematic diagram showing the relationship between the thickness of the second N-type GaN layer provided in the present application and the energy of the top light output; Figure 6 A schematic diagram showing the relationship between the reflectivity of light incident on a micro-distributed Bragg reflector and the incident waveband provided in this application; Figure 7A schematic diagram of the reflectivity of the micro-distributed Bragg reflector corresponding to different numbers of periodically stacked high-reflection film system structures provided in this application to the normal incident light; Figure 8 A schematic diagram of the reflectivity of a micro-distributed Bragg reflector corresponding to different numbers of periodically stacked high-reflection film system structures provided in this application to a 20° oblique incident light; Fig. 9 The preparation process flow chart of the Micro-LED array provided in this application; wherein, Fig. 9 (a) is a schematic diagram of the epitaxial wafer structure. Fig. 9 (b) in Fig. 9 Schematic diagram of the structure of the first column and the second N-type GaN layer prepared on (a), Fig. 9 (c) in Fig. 9 Schematic diagram of the structure of the ITO layer prepared on (b). Fig. 9 (d) in Fig. 9 Schematic diagram of the structure of the micro-distributed Bragg reflector prepared in (c). Fig. 9 The (e) in Fig. 9 Schematic diagram of the preparation of N / P electrode in (d). Fig. 9 (f) in Fig. 9 Schematic diagram of preparing a one-dimensional photonic crystal layer in (e); Fig.10 A schematic diagram of the light beam divergence angle of the common N-type GaN-based Micro-LED array provided in Example 3; Fig.11 A schematic diagram of the beam divergence angle of a non-common N-type GaN-based Micro-LED array provided as a comparative example; Fig.12 A schematic diagram comparing the beam divergence angles of a common N-type GaN-based Micro-LED array and a non-common N-type GaN-based Micro-LED array provided in an embodiment of the present application; Explanation of the reference numerals in the specification: 1. Micro-LED table structure; 10. First N-type GaN layer; 11. Quantum well light-emitting layer; 12. P-type GaN layer; 13. ITO layer; 2. Second N-type GaN layer; 3. One-dimensional photonic crystal layer; U1. Photonic crystal structure; 31. First dielectric layer; 32. Second dielectric layer; 4. Micro-distributed Bragg reflector; U2. Periodically stacked high-reflection film system structure; 41. Third dielectric layer; 42. Fourth dielectric layer; 5. P electrode; 6. N electrode. DETAILED DESCRIPTION

[0020] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0021] See also Figure 1 and Figure 2 , Figure 1 A schematic diagram of a Micro-LED array provided in an embodiment of the present application, Figure 2 Shown is a front view of a Micro-LED array provided in an embodiment of the present application, wherein the Micro-LED array includes: a Micro-LED mesa structure array composed of a Micro-LED mesa structure 1 , a second N-type GaN layer 2 , and a one-dimensional photonic crystal layer 3 .

[0022] Each Micro-LED mesa structure 1 includes a first N-type GaN layer 10 , a quantum well light-emitting layer 11 , a P-type GaN layer 12 , and an ITO layer 13 which are stacked in sequence from top to bottom.

[0023] Specifically, the main function of the first N-type GaN layer 10 is to transport electrons; the quantum well light-emitting layer 11 is the light-emitting area, and its main function is to provide a place for electron-hole recombination; the main function of the P-type GaN layer 12 is to transport holes; and the ITO layer 13 is a transparent electrode, and its main function is to promote current expansion.

[0024] The second N-type GaN layer 2 is continuously disposed on the plane where the upper surface of the Micro-LED mesa structure array is located, so that a plurality of Micro-LED mesa structures 1 share the second N-type GaN layer 2 .

[0025] The one-dimensional photonic crystal layer 3 is arranged on the surface of the second N-type GaN layer 2 away from the Micro-LED mesa structure array, and includes at least one photonic crystal structure U1; wherein the photonic crystal structure U1 includes a first medium layer 31 and a second medium layer 32 with different refractive indices stacked.

[0026] Specifically, Figure 3 The figure shows a schematic diagram of the transmittance curve of the one-dimensional photonic crystal layer for light with different incident angles. When the light beam enters the one-dimensional photonic crystal layer, the photonic crystal bandgap effect causes the light beam with a smaller incident angle to be transmitted from the top of the one-dimensional photonic crystal layer to the outside of the table structure, while the light beam with a larger incident angle is reflected and refracted at the interface between the first medium layer and the second medium layer with different refractive indices, thereby returning to the inside of the Micro-LED table structure and entering the one-dimensional photonic crystal layer again, until it enters the one-dimensional photonic crystal layer with a small incident angle and is transmitted to the outside of the table structure. Therefore, the one-dimensional photonic crystal layer can collimate the light beam, thereby reducing the divergence angle of the light beam.

[0027] However, since most Micro-LEDs are obtained by etching away continuous functional epitaxial layers to obtain multiple completely isolated light-emitting units, namely, multiple Micro-LED mesa structures, if a one-dimensional photonic crystal layer is directly set on the top of each Micro-LED mesa structure, each one-dimensional photonic crystal layer will be truncated, and the light beam will be refracted or reflected in the one-dimensional photonic crystal layer and will not only be emitted from the top, but also from its side wall. Therefore, even if a one-dimensional photonic crystal layer is set on the surface of each Micro-LED mesa structure, there will still be problems such as large light beam divergence angle and low light energy from the top, and it will also cause light beam crosstalk between adjacent Micro-LED mesa structures. Therefore, the present application considers setting a common N-type structure on the surface of the Micro-LED mesa structure array to provide a growth plane for the one-dimensional photonic crystal layer.

[0028] The present application designs an inverted Micro-LED table structure and arranges a continuous second N-type GaN layer on the upper surface of the Micro-LED table structure array, so that each Micro-LED table structure shares an N pole. Since the second N-type GaN layer directly covers the entire Micro-LED array, a complete one-dimensional photonic crystal layer can be formed on the second N-type GaN layer, avoiding the side wall light leakage problem of the discrete one-dimensional photonic crystal layer, and directly collimating the light beam emitted by the entire Micro-LED table structure array, which not only effectively reduces the light beam divergence angle, but also maximizes the top light output of the Micro-LED.

[0029] In addition, the general driving method of Micro-LED array chips requires the preparation of N electrode points and P electrode points on each chip, and then the Micro-LED array chip and the driving circuit board are bonded and connected, and the driving circuit board is powered. However, the Micro-LED array provided in this application adopts a common N-pole design, so that all Micro-LED table structures share one N electrode point, and at the same time, each table structure has a separate P electrode point, which simplifies the electrode preparation process and ensures that each Micro-LED table structure can emit light independently.

[0030] In summary, the present application designs an inverted Micro-LED table structure, arranges a continuous second N-type GaN layer on the upper surface of the Micro-LED table structure array, and obtains a Micro-LED table structure array with a common N electrode. The second N-type GaN layer is used to provide a growth plane for the one-dimensional photonic crystal layer, so that a complete one-dimensional photonic crystal layer can be grown on the entire Micro-LED table structure array, and the light beam emitted by the entire Micro-LED table structure array can be directly collimated, which can not only achieve the effect of light beam collimation for the Micro-LED, but also avoid the problem of large light beam divergence angle caused by light leakage from the side wall of the truncated one-dimensional photonic crystal layer, thereby minimizing the light beam divergence angle of the Micro-LED and increasing the light output from the top.

[0031] In some embodiments of the present application, the thickness of the second N-type GaN layer 2 is 0.1 μm-1.5 μm.

[0032] Since the second N-type GaN layer serves as an intermediate transition layer, its thickness directly affects the mutual optical coupling between the top one-dimensional photonic crystal layer and the Micro-LED; specifically, if the thickness of the second N-type GaN layer is not set properly, it will cause light to interfere and destructively interfere in the GaN layer, thereby affecting the light output energy of the Micro-LED. If the second N-type GaN layer is too thick, it will increase the absorption and loss of light in the second N-type GaN layer, reducing the light output energy of the Micro-LED.

[0033] like Figure 4 The figure shows the schematic diagram of the divergence angle of the Micro-LED beam with a central wavelength of 436nm and the top light energy. The horizontal axis in the figure is the beam divergence angle, and the vertical axis is the top light energy. The multiple curves in the figure correspond to the Micro-LEDs with the thickness of the second N-type GaN layer of 0.1μm, 0.3μm, 0.5μm, 0.7μm and 1μm respectively; Figure 5 The figure shows the relationship between the thickness of the second N-type GaN layer and the top light energy. Figure 4 and Figure 5 It can also be seen that different thicknesses of the second N-type GaN layer will not affect the beam divergence angle of the Micro-LED, but will affect the top emission energy of the Micro-LED. Therefore, the present application limits the thickness of the second N-type GaN layer to near an even multiple of the Micro-LED emission wavelength, thereby maximizing the top light energy emitted through the one-dimensional photonic crystal layer.

[0034] Preferably, as a specific example of the present application, the thickness of the second N-type GaN layer 2 is 1 μm. When the thickness of the second N-type GaN layer 2 is 1 μm, the top light output energy of the Micro-LED reaches a maximum.

[0035] Further, in some embodiments of the present application, the number of the photonic crystal structures U1 is 1 to 20; The material of the first dielectric layer 31 includes SiO2, Al2O3, and HfO2; the thickness of the first dielectric layer 31 is 60nm-200nm; The material of the second dielectric layer 32 includes TiO 2 , SiN, and Ta 2 O 5 ; the thickness of the second dielectric layer 32 is 30 nm to 100 nm.

[0036] As the number of photonic crystal structures U1 increases, the one-dimensional photonic crystal layer 3 has a better effect on constraining the light beam angle, but the size of the corresponding Micro-LED will also increase accordingly. The embodiment of the present application limits the number of photonic crystal structures U1 to 1 to 20, which can not only constrain the light beam angle but also take into account the volume of the Micro-LED.

[0037] Preferably, when the number of the photonic crystal structures U1 is 15, that is, the total number of the first dielectric layer 31 and the second dielectric layer 32 is 30, the one-dimensional photonic crystal layer 3 can already achieve a collimated light output effect of ±15°.

[0038] By adjusting the material and thickness of the first dielectric layer 31 and the second dielectric layer 32, the light beam with a smaller incident angle when entering the one-dimensional photonic crystal layer 3 can be transmitted from the top to the outside, while the light beam with a larger incident angle is reflected back into the Micro-LED, thereby collimating the light beam and reducing the beam divergence angle of the Micro-LED.

[0039] Preferably, when the thickness of the first dielectric layer is 100 nm and the thickness of the second dielectric layer is 43 nm, the normal-incident transmittance of the photonic crystal structure reaches a maximum.

[0040] In some embodiments of the present application, the preparation method of the one-dimensional photonic crystal layer 3 includes chemical vapor deposition, electron beam evaporation, and atomic layer deposition.

[0041] Since most Micro-LEDs are obtained by etching away continuous functional epitaxial layers to obtain multiple completely isolated light-emitting units, each light-emitting unit has the problem of sidewall light leakage, which leads to the problem of light beam crosstalk between adjacent light-emitting units. As the size of Micro-LEDs is further reduced, the light beam crosstalk problem becomes more serious, thereby affecting the quality of the Micro-LED display image; in addition, since a second N-type GaN layer is set on the entire array structure in the present application, when the light beam enters the one-dimensional photonic crystal layer and is reflected, part of the light beam will enter the second N-type GaN layer between adjacent Micro-LED table structures and be emitted from the bottom, causing energy loss and reducing the luminous efficiency of the Micro-LED.

[0042] Based on this, Figure 2 As shown, in some embodiments of the present application, the Micro-LED array further includes: a micro-distributed Bragg reflector 4.

[0043] The micro-distributed Bragg reflector 4 is arranged on the side wall and bottom of each Micro-LED mesa structure 1, and on the surface of the second N-type GaN layer 2 between adjacent Micro-LED mesa structures away from the one-dimensional photonic crystal layer 3, including at least one periodically stacked high-reflection film system structure U2; wherein the periodically stacked high-reflection film system structure U2 includes a third medium layer 41 and a fourth medium layer 42 with different refractive indices that are stacked.

[0044] By setting micro-distributed Bragg reflectors on the sidewalls and bottom of each Micro-LED mesa structure, the sidewall light beam emitted by the quantum well light-emitting layer and the light beam emitted from the bottom of the mesa structure enter the micro-distributed Bragg reflector, and then reflect strongly on the alternating interfaces of the third medium layer and the fourth medium layer with different refractive indices, and then reflect back into the inside of the Micro-LED mesa structure and emit from the top of the mesa structure, thus avoiding the sidewall light leakage phenomenon, solving the problem of light beam crosstalk between adjacent light-emitting units, and increasing the light output from the top of the Micro-LED. At the same time, the light beam reflected from the one-dimensional photonic crystal layer to the second N-type GaN layer enters the micro-distributed Bragg reflector set at its bottom, and is reflected again to the top of the Micro-LED and emits from the top, thus avoiding the energy loss caused by the second N-type GaN layer.

[0045] In some embodiments of the present application, the preparation method of the micro-distributed Bragg reflector 4 includes chemical vapor deposition, electron beam evaporation, and atomic layer deposition.

[0046] Specifically, the thickness of the third dielectric layer and the fourth dielectric layer is given by the formula Determine, among which, represents the refractive index of the dielectric layer, represents the dielectric layer thickness, represents the incident angle of the light beam, Indicates the central wavelength of the light beam.

[0047] In some embodiments of the present application, the number of periodically stacked high-reflection film system structures U2 is 5 to 15; The material of the third dielectric layer 41 includes SiO2, Al2O3, and HfO2; the thickness of the third dielectric layer 41 is 60nm-100nm; The material of the fourth dielectric layer 42 includes TiO 2 , SiN, and Ta 2 O 5 ; the thickness of the fourth dielectric layer 42 is 30 nm to 100 nm.

[0048] As the number of periodically stacked high-reflection film structures U2 increases, the reflectivity of the micro-distributed Bragg reflector 4 for the light beam becomes higher and higher, and its absorption loss becomes larger and larger. The embodiment of the present application controls the number of periodically stacked high-reflection film structures U2 to 5 to 15, which not only has a good reflection effect on the light beam on the side wall and bottom of the mesa structure, but also matches the electronic structure and application requirements of the second N-type GaN layer 2, has a higher reflectivity for the light emitted from the bottom of the second N-type GaN layer 2, while taking into account the absorption loss of the micro-distributed Bragg reflector 4.

[0049] like Figure 6 The figure shows the relationship between the reflectivity of light incident on the micro-distributed Bragg reflector and the incident waveband; Figure 7 The figure shows the reflectivity of the micro-distributed Bragg reflector to the normal incident light when the number of periodically superimposed high-reflection film system structures is different; Figure 8 The figure shows the reflectivity of the micro-distributed Bragg reflector for 20° oblique incident light when the number of periodically superimposed high-reflection film structures is different. It can be seen from the figure that when the number of periodically superimposed high-reflection film structures is between 5 and 10, that is, the number of dielectric layers is between 10 and 20, the micro-distributed Bragg reflector has a higher reflectivity for both normally incident light and oblique incident light.

[0050] Preferably, when the number of periodically stacked high-reflection film system structures U2 is 10, that is, the total number of the third dielectric layer and the fourth dielectric layer is 20, the reflectivity within the normally incident blue light Micro-LED emission spectrum achieves nearly 100% total reflection.

[0051] By controlling the material and thickness of the third dielectric layer 41 and the fourth dielectric layer 42, the sidewall light beam emitted by the quantum well light-emitting layer 11 in the Micro-LED mesa structure 1 is reflected back to the Micro-LED mesa structure 1, thereby reducing sidewall light leakage, improving the top light output rate and preventing light beam crosstalk between adjacent light-emitting units.

[0052] Preferably, when the thickness of the third dielectric layer 41 is 76 nm and the thickness of the fourth dielectric layer 42 is 45 nm, the reflectivity of the periodically stacked high-reflection film structure includes the emission wavelength of the blue light Micro-LED, and the reflection effect is optimal.

[0053] Optionally, in some embodiments of the present application, the Micro-LED table structure is a chamfered cone structure or an inverted truncated cone structure. By adopting a chamfered cone structure or an inverted truncated cone structure to introduce an inclination angle, the Micro-LED opening is facing upward, so that the light beam emitted by the quantum well light-emitting layer can be reflected from the side wall and converged on the top, further improving the top luminescence efficiency.

[0054] For example, in some embodiments, the Micro-LED mesa structure is an inverted frustum, and the diameter of the surface of the side close to the second N-type GaN layer is smaller than the lateral distance and the longitudinal distance between adjacent Micro-LED mesa structures; in other embodiments, the Micro-LED mesa structure is an inverted quadrangular pyramid, and the length of the surface of the side close to the second N-type GaN layer is smaller than the lateral distance between adjacent Micro-LED mesa structures, and the width of the surface of the side close to the second N-type GaN layer is smaller than the longitudinal distance between adjacent Micro-LED mesa structures; Among them, the lateral distance between adjacent Micro-LED mesa structures is: the distance between adjacent Micro-LED mesa structures along the length direction of the surface of the Micro-LED mesa structure close to the second N-type GaN layer; the longitudinal distance between adjacent Micro-LED mesa structures is: the distance between adjacent Micro-LED mesa structures along the width direction of the surface of the Micro-LED mesa structure close to the second N-type GaN layer.

[0055] As a specific example of the present application, the lateral spacing between adjacent LED chips is greater than the length of the LED chip, and the longitudinal spacing is greater than the width of the LED chip; the bottom length of the inverted tetrahedral pyramid structure is less than or equal to the length of the LED chip, and the bottom width of the inverted tetrahedral pyramid structure is less than or equal to the width of the LED chip; the top length of the inverted tetrahedral pyramid structure is equal to the length of the LED chip, and is less than the lateral spacing between adjacent LED chips; the top width of the inverted tetrahedral pyramid structure is equal to the width of the LED chip, and is less than the longitudinal spacing between adjacent LED chips.

[0056] Specifically, Figure 2 As shown, the P electrode 5 of the Micro-LED array contacts the ITO layer 13 in each Micro-LED mesa structure 1; the N electrode 6 contacts the second N-type GaN layer 2; The material of the P electrode 5 is one of Au, Al and Ag, and its preparation method includes chemical vapor deposition, electron beam evaporation, thermal evaporation and magnetron sputtering.

[0057] Based on the Micro-LED array provided in the above embodiment, the embodiment of the present application further provides a method for preparing a Micro-LED array, including: S10: preparing an epitaxial wafer, wherein the epitaxial wafer comprises a first N-type GaN layer 10, a quantum well light-emitting layer 11 and a P-type GaN layer 12 which are stacked in sequence from top to bottom, such as Fig. 9 As shown in (a); As a specific example of the present application, the thickness of the first N-type GaN layer 10 is 4 μm; the thickness of the quantum well light-emitting layer 11 is 60 nm; and the thickness of the P-type GaN layer 12 is 100 nm.

[0058] S20: Etching the P-type GaN layer 12, the quantum well light-emitting layer 11 and a portion of the first N-type GaN layer 10 to form a plurality of first pillars and a second N-type GaN layer 2 continuously arranged on the plane where the upper surfaces of the plurality of first pillars are located, such as Fig. 9 As shown in (b); Specifically, in some embodiments of the present application, etching the P-type GaN layer, the quantum well light-emitting layer and a portion of the first N-type GaN layer includes: growing SiO2 at the bottom of the P-type GaN layer by chemical vapor deposition, performing organic cleaning, defining an etching area by spin coating photoresist on the SiO2 surface, pre-baking, alignment exposure, development, microscopic inspection, and hardening, etching the SiO2 layer by an AOE process, and removing the photoresist by organic cleaning, and finally etching the P-type GaN layer, the quantum well light-emitting layer and a portion of the first N-type GaN layer by an ICP process to form a plurality of first columns, and finally etching SiO2 by a BOE process.

[0059] As a specific example of the present application, the thickness of the SiO2 layer is 250 nm.

[0060] S30: preparing an ITO layer 13 on the lower surface of the first column to form a plurality of Micro-LED mesa structures; wherein each Micro-LED mesa structure includes a first N-type GaN layer 10, a quantum well light-emitting layer 11, a P-type GaN layer 12 and an ITO layer 13 stacked, such as Fig. 9 As shown in (c); The steps of preparing an ITO layer at the bottom of the first column include: growing SiO2 on the lower surface of the first column and the surface of the groove between two adjacent first columns by chemical vapor deposition, performing organic cleaning, defining the photolithography area after spin coating photoresist on the SiO2 surface, pre-baking, alignment exposure, development, microscopic inspection, and hardening, etching the SiO2 layer by AOE, and removing the photoresist by organic cleaning, making an ITO layer on the lower surface of the first column and the surface of the groove between two adjacent first columns by EBE process, spin coating photoresist on the surface of the ITO layer, pre-baking, alignment exposure, development, microscopic inspection, and hardening, defining other areas except the ITO area after double exposure, etching the ITO layer by IBE, and finally etching SiO2 by BOE.

[0061] As a specific example of the present application, the thickness of the SiO2 layer is 250 nm.

[0062] S40: forming a micro-distributed Bragg reflector 4 on the side wall of the Micro-LED mesa structure, the lower surface of the Micro-LED mesa structure, and the lower surface of the second N-type GaN layer 2 between adjacent Micro-LED mesa structures, such as Fig. 9As shown in (d) in the figure, the micro-distributed Bragg reflector 4 includes at least one periodically stacked high-reflection film system structure, and the periodically stacked high-reflection film system structure includes a third medium layer and a fourth medium layer with different refractive indices stacked.

[0063] Specifically, Fig. 9 As shown in (e), after the micro-distributed Bragg reflector is prepared, the N / P electrode area of ​​the Micro-LED array is defined by photolithography, and the metal N / P electrodes 5 / 6 are made.

[0064] S50: thinning and polishing the second N-type GaN layer 2, and forming a one-dimensional photonic crystal layer 3 on the upper surface of the second N-type GaN layer 2; wherein the one-dimensional photonic crystal layer 3 includes at least one photonic crystal structure U1, and the photonic crystal structure U1 includes a first medium layer 31 and a second medium layer 32 with different refractive indices arranged in a stacked manner, such as Fig. 9 As shown in (f) in .

[0065] The technical solution of the present application will be described in detail below in combination with a plurality of embodiments and comparative examples, but it should be understood that the following embodiments are only for explaining and illustrating the technical solution but do not limit the scope of the present application. Example 1

[0066] The present embodiment provides a common N-type GaN-based Micro-LED array, which includes a Micro-LED mesa structure array composed of Micro-LED mesa structures, a second N-type GaN layer, a one-dimensional photonic crystal layer, a micro-distributed Bragg reflector, a P electrode and an N electrode.

[0067] The Micro-LED mesa structure includes a first N-type GaN layer, a quantum well light-emitting layer, a P-type GaN layer and an ITO layer stacked in sequence from top to bottom.

[0068] The Micro-LED table structure is an inverted quadrangular pyramid structure, with the length and width of the top quadrilateral both being 10μm, the depth being 1.2μm, and the side wall inclination being 85°; the thickness of the quantum well light-emitting layer is 100nm.

[0069] The thickness of the second N-type GaN layer is 0.1 μm.

[0070] The one-dimensional photonic crystal layers were prepared using atomic layer deposition; The number of the photonic crystal structure is 1, the material of the first dielectric layer is SiO2, and its thickness is 60 nm, and the material of the second dielectric layer is TiO2, and its thickness is 30 nm.

[0071] The micro-distributed Bragg reflectors were fabricated using atomic layer deposition; The number of periodically stacked high-reflection film system structures is 5, the material of the third dielectric layer is SiO2, and its thickness is 60nm, and the material of the fourth dielectric layer is TiO2, and its thickness is 30nm.

[0072] The material of the P electrode is Au, and its thickness is 100 nm. Example 2

[0073] The present embodiment provides a common N-type GaN-based Micro-LED array, which includes a Micro-LED mesa structure array composed of Micro-LED mesa structures, a second N-type GaN layer, a one-dimensional photonic crystal layer, a micro-distributed Bragg reflector, a P electrode and an N electrode.

[0074] The Micro-LED mesa structure includes a first N-type GaN layer, a quantum well light-emitting layer, a P-type GaN layer and an ITO layer stacked in sequence from top to bottom.

[0075] The Micro-LED table structure is an inverted quadrangular pyramid structure, with the length and width of the top quadrilateral both being 10μm, the depth being 1.2μm, and the side wall inclination being 85°; the thickness of the quantum well light-emitting layer is 100nm.

[0076] The thickness of the second N-type GaN layer is 0.7 μm.

[0077] The one-dimensional photonic crystal layers were prepared using atomic layer deposition; The number of photonic crystal structures is 10, the material of the first dielectric layer is SiO2, and its thickness is 130 nm, and the material of the second dielectric layer is TiO2, and its thickness is 65 nm.

[0078] The micro-distributed Bragg reflectors were fabricated using atomic layer deposition; The number of periodically stacked high-reflection film system structures is 10, the material of the third dielectric layer is SiO2, and its thickness is 80nm, and the material of the fourth dielectric layer is TiO2, and its thickness is 65nm.

[0079] The material of the P electrode is Au, and its thickness is 100 nm. Example 3

[0080] The present embodiment provides a common N-type GaN-based Micro-LED array, which includes a Micro-LED mesa structure array composed of Micro-LED mesa structures, a second N-type GaN layer, a one-dimensional photonic crystal layer, a micro-distributed Bragg reflector, a P electrode and an N electrode.

[0081] The Micro-LED mesa structure includes a first N-type GaN layer, a quantum well light-emitting layer, a P-type GaN layer and an ITO layer stacked in sequence from top to bottom.

[0082] The Micro-LED table structure is an inverted quadrangular pyramid structure, with the length and width of the top quadrilateral both being 10μm, the depth being 1.2μm, and the side wall inclination being 85°; the thickness of the quantum well light-emitting layer is 100nm.

[0083] The thickness of the second N-type GaN layer is 1.5 μm.

[0084] The one-dimensional photonic crystal layers were prepared using atomic layer deposition; The number of the photonic crystal structures is 20, the material of the first dielectric layer is SiO2, and the thickness thereof is 200 nm, and the material of the second dielectric layer is TiO2, and the thickness thereof is 100 nm.

[0085] The micro-distributed Bragg reflectors were fabricated using atomic layer deposition; The number of periodically stacked high-reflection film system structures is 15, the material of the third dielectric layer is SiO2, and its thickness is 100 nm, and the material of the fourth dielectric layer is TiO2, and its thickness is 100 nm.

[0086] The material of the P electrode is Au, and its thickness is 100 nm.

[0087] Comparative Example The present embodiment provides a non-common N-type GaN-based Micro-LED array, which includes a Micro-LED mesa structure array composed of Micro-LED mesa structures, a one-dimensional photonic crystal layer, a P electrode and an N electrode arranged on the upper surface of each Micro-LED mesa structure.

[0088] The Micro-LED mesa structure includes an N-type GaN layer, a quantum well light-emitting layer, a P-type GaN layer and an ITO layer stacked in sequence from top to bottom.

[0089] The Micro-LED table structure is an inverted quadrangular pyramid structure, with the length and width of the top quadrilateral both being 10μm, the depth being 1.2μm, and the side wall inclination being 85°; the thickness of the quantum well light-emitting layer is 100nm.

[0090] The one-dimensional photonic crystal layers were prepared using atomic layer deposition; The number of the photonic crystal structures is 20, the material of the first dielectric layer is SiO2, and the thickness thereof is 200 nm, and the material of the second dielectric layer is TiO2, and the thickness thereof is 100 nm.

[0091] The material of the P electrode is Au, and its thickness is 100 nm.

[0092] like Fig.10 FIG. 1 is a schematic diagram of the beam divergence angle of the common N-type GaN-based Micro-LED array provided in Example 3. Fig.11 FIG. 1 is a schematic diagram of the beam divergence angle of the non-common N-type GaN-based Micro-LED array provided in the comparative example. Fig.12 Shown is a schematic diagram comparing the beam divergence angles of a common N-type GaN-based Micro-LED array and a non-common N-type GaN-based Micro-LED array provided in this application.

[0093] As can be seen from the figure, the beam divergence angle of the common N-type GaN-based Micro-LED array provided in the present application is within the range of ±15°, while the beam divergence angle of the non-common N-type GaN-based Micro-LED array provided in the comparative example is within the range of ±80°, which fully proves that the present application uses the second N-type GaN layer to provide a growth plane for the one-dimensional photonic crystal layer, thereby using the complete one-dimensional photonic crystal layer to directly collimate the light emitted by the entire Micro-LED mesa structure array, which has a better beam collimation effect and greatly reduces the beam divergence angle; at the same time, by forming a micro-distributed Bragg reflector on the side wall, bottom of each Micro-LED mesa structure and the bottom of the second N-type GaN layer between adjacent mesa structures, the light loss of the device is reduced.

[0094] In addition, through simulation of the common N-type GaN-based Micro-LED arrays provided in Examples 1 to 3, it was found that by changing the structural parameters of the second N-type GaN layer, the one-dimensional photonic crystal layer and the micro-distributed Bragg reflector within the parameter range given in the embodiments of the present application, the beam divergence angle of the device still fluctuates around ±15°, which fully proves that the Micro-LED array provided in the present application has a good beam collimation effect.

[0095] Obviously, the above embodiments are merely examples for the purpose of clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A Micro-LED array, characterized in that: include: A micro-LED mesa structure array, comprising a plurality of micro-LED mesa structures arranged in an array, each micro-LED mesa structure comprising a first N-type GaN layer, a quantum well light-emitting layer, a P-type GaN layer and an ITO layer stacked in sequence from top to bottom; A second N-type GaN layer is continuously disposed on a plane where the upper surface of the Micro-LED mesa structure array is located, so that a plurality of Micro-LED mesa structures share the second N-type GaN layer; The one-dimensional photonic crystal layer is continuously arranged on the surface of the second N-type GaN layer on the side away from the Micro-LED mesa structure array, and includes at least one photonic crystal structure, and the photonic crystal structure includes a first medium layer and a second medium layer with different refractive indices arranged in a stacked manner.

2. The Micro-LED array according to claim 1, characterized in that: The thickness of the second N-type GaN layer is 0.1 μm-1.5 μm.

3. The Micro-LED array according to claim 1, characterized in that: The number of the photonic crystal structures is 1 to 20; The material of the first dielectric layer includes SiO2, Al2O3, and HfO2; the thickness of the first dielectric layer is 60nm-200nm; The material of the second dielectric layer includes TiO2, SiN, and Ta2O5; the thickness of the second dielectric layer is 30nm-100nm.

4. The Micro-LED array according to claim 1, characterized in that: Also includes: The micro-distributed Bragg reflector is arranged on the side wall and bottom of each Micro-LED mesa structure, and on the surface of the second N-type GaN layer between adjacent Micro-LED mesa structures away from the one-dimensional photonic crystal layer, including at least one periodically stacked high-reflection film system structure, wherein the periodically stacked high-reflection film system structure includes a third medium layer and a fourth medium layer with different refractive indices stacked in layers.

5. The Micro-LED array according to claim 4, characterized in that: The number of the periodically stacked high-reflection film system structures is 5 to 15; The material of the third dielectric layer includes SiO2, Al2O3, and HfO2; the thickness of the third dielectric layer is 60nm-100nm; The material of the fourth dielectric layer includes TiO2, SiN, and Ta2O5; the thickness of the fourth dielectric layer is 30nm-100nm.

6. A method for preparing a Micro-LED array, characterized in that: For preparing the Micro-LED array according to any one of claims 1 to 5, comprising: Prepare an epitaxial wafer, wherein the epitaxial wafer includes a first N-type GaN layer, a quantum well light-emitting layer, and a P-type GaN layer stacked in sequence from top to bottom; Etching the P-type GaN layer, the quantum well light-emitting layer and a portion of the first N-type GaN layer to form a plurality of first pillars and a second N-type GaN layer continuously arranged on a plane where upper surfaces of the plurality of first pillars are located; An ITO layer is prepared on the lower surface of the first column to form a plurality of Micro-LED mesa structures; wherein each of the Micro-LED mesa structures comprises a first N-type GaN layer, a quantum well light-emitting layer, a P-type GaN layer and an ITO layer which are stacked; The second N-type GaN layer is thinned and polished, and a one-dimensional photonic crystal layer is formed on the upper surface of the second N-type GaN layer; wherein the one-dimensional photonic crystal layer includes at least one photonic crystal structure, and the photonic crystal structure includes a first medium layer and a second medium layer with different refractive indices that are stacked.

7. The method for preparing a Micro-LED array according to claim 6, characterized in that: Also includes: A micro-distributed Bragg reflector is formed on the side wall of the Micro-LED mesa structure, the lower surface of the Micro-LED mesa structure, and the lower surface of the second N-type GaN layer between adjacent Micro-LED mesa structures; wherein the micro-distributed Bragg reflector includes at least one periodically stacked high-reflection film system structure, and the periodically stacked high-reflection film system structure includes a third medium layer and a fourth medium layer with different refractive indices stacked.

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