Micro-display epitaxial structure and preparation method thereof, and preparation method of micro-display device

Abstract

The application discloses a micro display epitaxial structure and a preparation method thereof, and a preparation method of a micro display device. The micro display epitaxial structure comprises a substrate, a mask light adjusting layer located on one side of the substrate, and a plurality of micro display units corresponding to a plurality of mask openings of the mask light adjusting layer. Each micro display unit comprises at least two light emitting units and a separation layer between the two light emitting units. The mask light adjusting layer is used to define the epitaxial area of the micro display unit and adjust the propagation direction of the light emitted from the light emitting unit to the mask light adjusting layer, so as to reduce the included angle between the propagation direction of the light emitted from the sidewall of the light emitting unit and the direction perpendicular to the substrate. The technical scheme provided by the application realizes selective epitaxy of the full-color micro display epitaxial structure and extraction of the lateral light of the micro display unit, and improves the light extraction efficiency of the micro display device.

Description

TECHNICAL FIELD

[0001] Embodiments of the present application relate to the technical field of display, in particular to a micro display epitaxial structure, a preparation method thereof, and a preparation method of a micro display device. BACKGROUND

[0002] Micro-LED has great application value in high-resolution display, augmented reality, virtual reality, wearable electronics and other fields due to its small size, high resolution, low energy consumption, high reliability and other advantages.

[0003] At present, mainstream schemes for realizing full-color Micro-LED devices include massive transfer and vertical stacked pixels; among them, although the three-color pixel tiling scheme using massive transfer has a relatively simple process route, the yield of the prepared product is low, a large amount of preparation time is consumed, and there are problems such as large color difference and visual angle difference in display effect; the vertical stacked pixel scheme can solve the above problems, but introduces complex processes such as bonding and alignment, which has high requirements for the size, surface, and topography of the bonded wafer, and the alignment accuracy; in addition, the pixelization etching process inevitably causes surface damage to the sidewall of the Micro-LED, which seriously damages the light-emitting efficiency of the Micro-LED.

[0004] The related technology can form each film layer in the Micro-LED from bottom to top by using a pattern mask and a growth confinement effect, thereby avoiding the damage caused by pixelization etching and effectively improving the light-emitting efficiency of the Micro-LED. However, the existing selective epitaxy is mainly used for single-color epitaxy process, lacks the application of full-color multi-color epitaxial structure, and ignores the extraction of lateral light of the Micro-LED, which affects the light extraction efficiency of the micro display device. SUMMARY

[0005] Embodiments of the present application provide a micro display epitaxial structure, a preparation method thereof, and a preparation method of a micro display device, to realize selective epitaxy of a full-color micro display epitaxial structure and extraction of lateral light of a micro display unit, and improve the light extraction efficiency of the micro display device.

[0006] According to an aspect of the present application, a micro display epitaxial structure is provided, comprising:

[0007] a substrate;

[0008] a mask light adjustment layer located on one side of the substrate; the mask light adjustment layer has a plurality of mask openings exposing the substrate;

[0009] a plurality of micro display units, each of the micro display units corresponding to a mask opening; the micro display unit comprising at least two light emitting units and an isolation layer between two adjacent light emitting units, the light emitting units being away from the substrate in sequence;

[0010] The mask light adjusting layer is used to define the extension area of the micro display unit, and adjust the propagation direction of the light emitted by the light emitting unit to the mask light adjusting layer, so as to reduce the included angle between the propagation direction of the light emitted from the sidewall of the light emitting unit and the direction perpendicular to the substrate.

[0011] Optionally, in the process of defining the extension area of the micro display unit, the sidewall of the mask opening is planar; in the process of adjusting the propagation direction of the light emitted by the light emitting unit to the mask light adjusting layer, the sidewall of the mask opening is curved, and the curved surface is convex towards the adjacent micro display unit; or,

[0012] In the process of defining the extension area of the micro display unit and in the process of adjusting the propagation direction of the light emitted by the light emitting unit to the mask light adjusting layer, the sidewall of the mask opening is curved, and the curved surface is convex towards the adjacent micro display unit;

[0013] And / or, the absolute value of the height difference between the surface of the mask light adjusting layer away from the substrate and the surface of the micro display unit away from the substrate is less than or equal to 10 μm;

[0014] And / or, the material of the mask light adjusting layer comprises at least one of SiO2, SiN and Ta2O5.

[0015] Optionally, the refractive index of the mask light adjusting layer between two adjacent micro display units is uniformly set;

[0016] Or, the refractive index of the mask light adjusting layer between two adjacent micro display units is gradually changed in the direction parallel to the substrate.

[0017] Optionally, each of the light emitting units comprises a first semiconductor layer, a quantum well layer and a second semiconductor layer away from the substrate in sequence;

[0018] The isolation layer comprises a tunnel junction, a third semiconductor layer and a fourth semiconductor layer away from the substrate in sequence;

[0019] The tunnel junction is in contact with the second semiconductor layer of the light emitting unit on the side of the tunnel junction close to the substrate, and the tunnel junction is used to enhance the current injection to the second semiconductor layer and the current diffusion on the surface of the second semiconductor layer; the third semiconductor layer has the same conductive type as the first semiconductor layer, and the fourth semiconductor layer has the same conductive type as the second semiconductor layer; the conductive type of the first semiconductor layer is different from that of the second semiconductor layer; the third semiconductor layer and the fourth semiconductor layer are used to form a reverse bias and electrically isolate two adjacent light emitting units.

[0020] Optionally, the isolation layer further comprises an insulating layer on the side of the fourth semiconductor layer away from the third semiconductor layer.

[0021] The insulating layer comprises at least one of an undoped GaN layer, an AlN layer, an AlGaN layer, and a GaN layer doped with C elements.

[0022] Optionally, the micro display unit comprises three light emitting units sequentially away from the substrate, namely a first light emitting unit, a second light emitting unit, and a third light emitting unit; the light emitting wavelength of the first light emitting unit is less than that of the second light emitting unit, and the light emitting wavelength of the second light emitting unit is less than that of the third light emitting unit; a first isolation layer is arranged between the first light emitting unit and the second light emitting unit, and a second isolation layer is arranged between the second light emitting unit and the third light emitting unit.

[0023] The side wall of at least one side of the micro display unit is in a stepped shape, and the stepped side wall comprises a first step surface and a second step surface; the first step surface is formed by a part of the surface of the fourth semiconductor layer on the side of the fourth semiconductor layer away from the substrate in the first isolation layer; the second step surface is formed by a part of the surface of the fourth semiconductor layer on the side of the fourth semiconductor layer away from the substrate in the second isolation layer; a metal layer of the same material is arranged on the first step surface and the second step surface.

[0024] According to another aspect of the present application, a preparation method of a micro display epitaxial structure is provided, which is used to prepare the micro display epitaxial structure of any embodiment of the present application, and comprises the following steps:

[0025] A substrate is provided;

[0026] A mask light modulation layer is formed on one side of the substrate, and the mask light modulation layer is patterned to form a plurality of mask openings exposing the substrate in the mask light modulation layer;

[0027] forming a plurality of micro display units based on the limitation of the epitaxial region by the mask opening in the mask light modulation layer; wherein each of the micro display units is located in a mask opening, and each of the micro display units comprises at least two light emitting units away from the substrate in sequence and an isolation layer between the two adjacent light emitting units;

[0028] curving the sidewall of the mask opening in the mask light modulation layer to make the mask light modulation layer also used for adjusting the propagation direction of the light emitted by the light emitting unit to the mask light modulation layer, and reducing the included angle between the light emitted from the sidewall of the light emitting unit and the direction perpendicular to the substrate.

[0029] Optionally, the light emitting unit in the micro display unit is formed by:

[0030] forming a first semiconductor layer, a quantum well layer and a second semiconductor layer away from the substrate in sequence on one side of the substrate;

[0031] forming an isolation layer between the two adjacent light emitting units, comprising:

[0032] forming a tunnel junction, a third semiconductor layer and a fourth semiconductor layer away from the substrate in sequence on one side of the substrate; wherein the tunnel junction is in contact with the second semiconductor layer of the light emitting unit close to the substrate side of the tunnel junction, and the tunnel junction is used to enhance the current injection to the second semiconductor layer and the current diffusion on the surface of the second semiconductor layer; the third semiconductor layer has the same conductivity type as the first semiconductor layer, and the fourth semiconductor layer has the same conductivity type as the second semiconductor layer; the conductivity type of the first semiconductor layer is different from that of the second semiconductor layer; the third semiconductor layer and the fourth semiconductor layer are used to form a reverse bias to electrically isolate the two adjacent light emitting units.

[0033] Optionally, forming an isolation layer between the two adjacent light emitting units further comprises:

[0034] forming an insulating layer on the side of the fourth semiconductor layer away from the third semiconductor layer; wherein the insulating layer comprises at least one of undoped GaN layer, AlN layer, AlGaN layer and C-doped GaN layer.

[0035] According to another aspect of the present application, a preparation method of a micro display module is provided, comprising:

[0036] providing a driving substrate;

[0037] bonding the micro display epitaxial structure according to any of the embodiments of the present application on the surface of the driving substrate, and removing the substrate.

[0038] The embodiment of the present application provides a micro display epitaxial structure and a preparation method thereof, and a preparation method of a micro display module, wherein the micro display epitaxial structure comprises: a substrate; a mask light adjusting layer located on one side of the substrate; the mask light adjusting layer has a plurality of mask openings exposing the substrate; a plurality of micro display units, each of which is located in a mask opening; the micro display unit comprises at least two light emitting units away from the substrate in sequence and an isolation layer located between the two adjacent light emitting units; wherein the mask light adjusting layer is used for limiting the epitaxial area of the micro display unit, and adjusting the propagation direction of the light emitted by the light emitting unit to the mask light adjusting layer, so as to reduce the included angle between the light emitted from the sidewall of the light emitting unit and the direction perpendicular to the substrate. The technical scheme provided by the present application realizes the selected area preparation of the micro display unit by arranging the patterned mask light adjusting layer on one side of the substrate and limiting the epitaxial growth area based on the mask light adjusting layer; and the isolation layer arranged between the two adjacent light emitting units of the micro display unit can prevent the current crosstalk between the two adjacent light emitting units, which is beneficial to realize the independent control of the driving of each light emitting unit, so as to realize the selected area epitaxy of the micro display unit with double colors and more than double colors. In addition, the mask light adjusting layer is also used for adjusting the propagation direction of the light emitted by the light emitting unit to the mask light adjusting layer, reducing the included angle between the light emitted from the sidewall of the light emitting unit and the direction perpendicular to the substrate, so as to realize the extraction of the lateral light of the micro display unit and improve the light extraction efficiency of the micro display epitaxial structure.

[0039] It should be understood that the content described in this part is not intended to identify the key or important features of the embodiments of the present application, nor is it used to limit the scope of the present application. Other features of the present application will become apparent from the following description. BRIEF DESCRIPTION OF DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0041] Figure 1 is a cross-sectional structure schematic diagram of a micro display epitaxial structure provided by the embodiment of the present application;

[0042] Figure 2 is a top view of a mask light adjusting layer and a substrate in a micro display epitaxial structure provided by the embodiment of the present application;

[0043] Figure 3 is a cross-sectional structure schematic diagram of a light emitting unit provided by the embodiment of the present application;

[0044] Figure 4is a cross-sectional structure schematic diagram of a micro display epitaxial structure provided by an embodiment of the present application after a micro display unit is grown on one side of a substrate by selective epitaxy in a preparation method of the micro display epitaxial structure;

[0045] Figure 5 is a light condensing effect simulation diagram of a mask light adjusting layer with a uniform refractive index on light emitted by a sidewall of a light emitting unit provided by an embodiment of the present application;

[0046] Figure 6 is a light condensing effect simulation diagram of a mask light adjusting layer with a gradient refractive index on light emitted by a sidewall of a light emitting unit provided by an embodiment of the present application;

[0047] Figure 7 is a cross-sectional structure schematic diagram of an isolation layer provided by an embodiment of the present application;

[0048] Figure 8 is a cross-sectional structure schematic diagram of another isolation layer provided by an embodiment of the present application;

[0049] Figure 9 is a cross-sectional structure schematic diagram of another micro display epitaxial structure provided by an embodiment of the present application;

[0050] Figure 10 is a cross-sectional structure schematic diagram of a micro display unit with a sidewall having a stepped surface provided by an embodiment of the present application;

[0051] Figure 11 is a flowchart of a preparation method of a micro display epitaxial structure provided by an embodiment of the present application;

[0052] Figure 12 is a cross-sectional structure schematic diagram of a substrate provided by a preparation method of a micro display epitaxial structure provided by an embodiment of the present application;

[0053] Figure 13 is a cross-sectional structure schematic diagram after an unpatterned mask light adjusting layer is formed on one side of a substrate in a preparation method of a micro display epitaxial structure provided by an embodiment of the present application;

[0054] Figure 14 is a cross-sectional structure schematic diagram after the mask light adjusting layer is patterned in a preparation method of a micro display epitaxial structure provided by an embodiment of the present application;

[0055] Figure 15 is a cross-sectional structure schematic diagram after a micro display unit is formed in a preparation method of a micro display epitaxial structure provided by an embodiment of the present application;

[0056] Figure 16 is a cross-sectional structure schematic diagram after a sidewall of a mask light adjusting layer is curved in a preparation method of a micro display epitaxial structure provided by an embodiment of the present application;

[0057] Figure 17 is a cross-sectional structure schematic diagram of a micro display device after a micro display epitaxial structure is bonded on the surface of a driving substrate in a preparation method of the micro display device provided by an embodiment of the present application;

[0058] Figure 18 is a cross-sectional structure schematic diagram of a micro display device after a substrate is removed in a preparation method of the micro display device provided by an embodiment of the present application. DETAILED DESCRIPTION

[0059] In order to make the personnel in the technical field better understand the present application scheme, the technical scheme in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by the person skilled in the art without making creative efforts should belong to the scope of protection of the present application.

[0060] It should be noted that the terms "first", "second" and the like in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily indicate a specific order or a chronological sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units does not have to be limited to only those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0061] The present application provides a micro display epitaxial structure, Figure 1 is a cross-sectional structure schematic diagram of a micro display epitaxial structure provided by an embodiment of the present application, Figure 2 is a top view of a mask light modulation layer and a substrate in a micro display epitaxial structure provided by an embodiment of the present application, referring to Figure 1 and Figure 2 The micro display epitaxial structure comprises:

[0062] a substrate 10;

[0063] a mask light modulation layer 20 located on one side of the substrate 10; the mask light modulation layer 20 has a plurality of mask openings 21 exposing the substrate 10;

[0064] a plurality of micro display units 30, each micro display unit 30 corresponding to a mask opening 21; the micro display unit 30 comprises at least two light emitting units 31 sequentially away from the substrate 10 and an isolation layer 32 located between the adjacent two light emitting units 31;

[0065] The mask light modulation layer 20 is used to define the epitaxial area of the micro display unit 30, and to adjust the propagation direction of the light emitted by the light emitting unit 31 to the mask light modulation layer 20, so as to reduce the included angle between the propagation direction of the light emitted from the sidewall of the light emitting unit 31 and the direction perpendicular to the substrate 10.

[0066] Specifically, the substrate 10 can be a silicon substrate, a sapphire substrate, a silicon carbide substrate, etc. suitable for epitaxial preparation of the micro display unit 30. In the process of epitaxially preparing the micro display unit 30 on the substrate 10, the mask light modulation layer 20 is used as a mask layer to define the epitaxial area of the micro display unit 30. The mask light modulation layer 20 is located on one side of the substrate 10, and can be in contact with the substrate 10 or not in contact with the substrate 10, as long as it can define the epitaxial area of the micro display unit 30 in the process of epitaxially preparing the micro display unit 30 on the substrate 10. The mask light modulation layer 20 has a plurality of mask openings 21 exposing the substrate 10, and each mask opening 21 corresponds to an epitaxial area of a micro display unit 30, so as to realize selective epitaxy of the micro display unit 30 on the substrate 10. With the reduction of device size, the sidewall damage caused by the pixel etching scheme in the related art can seriously reduce the light emitting efficiency of the micro display unit 30. The epitaxial material of the micro display unit 30 is epitaxially grown in the opening area of the mask light modulation layer 20 by using the conditions that the nucleation energy of the mask light modulation layer 20 is much larger than the nucleation energy of the surface of the substrate 10, the material of the mask light modulation layer 20 is amorphous material, and the epitaxial material has a preferred orientation, which is a bottom-up epitaxial process that can avoid the introduction of pixel etching, and thus can fundamentally improve the light emitting efficiency of the micro display unit 30.

[0067] Each micro display unit 30 includes at least two light emitting units 31 sequentially away from the substrate 10 and a separation layer 32 located between the two adjacent light emitting units 31. Figure 3 is a cross-sectional structure schematic diagram of a light emitting unit provided by an embodiment of the present application, referring to Figure 3Each light emitting unit 31 can include a first semiconductor layer 31a, a quantum well layer 31q and a second semiconductor layer 31c which are sequentially stacked in a direction perpendicular to the substrate 10. The first semiconductor layer 31a, the quantum well layer 31q and the second semiconductor layer 31c are respectively an N-type semiconductor layer, a quantum well layer 31q and a P-type semiconductor layer, or a P-type semiconductor layer, a quantum well layer 31q and an N-type semiconductor layer. Further, in each light emitting unit 31, the first semiconductor layer 31a further includes a buffer layer on a side away from the quantum well layer 31q, and the buffer layer is configured to reduce lattice mismatch and thermal mismatch between the substrate 10 and a layer (the first semiconductor layer 31a) to be formed on the buffer layer, thereby reducing defects caused by the mismatch / difference. In the same micro display unit 30, the light emitting colors of at least two light emitting units 31 are different, and an isolation layer 32 is arranged between the two adjacent light emitting units 31, and the current cross talk between the two adjacent light emitting units 31 can be prevented through the isolation layer 32, which is conducive to achieving independent control of driving of each light emitting unit 31, meets the condition of stacking of the light emitting units 31 of double colors and above, and enables selective epitaxy of the micro display unit 30 of double colors and above.

[0068] The material of the mask light modulation layer 20 is light-transmissive, so that the light emitted from the sidewall of the light emitting unit 31 to the mask light modulation layer 20 can be adjusted by the mask light modulation layer 20 to change the propagation direction of the light and then be emitted from the mask light modulation layer 20. The material of the mask light modulation layer 20 includes but is not limited to at least one of SiO2, SiN and Ta2O5. The mask light modulation layer 20 located between the adjacent micro display units 30 is used as a light collecting structure (a light-transmissive layer with an arc surface) to change the lateral light emission of the micro display unit 30 into vertical light emission, thereby achieving extraction of the lateral light of the micro display unit 30 and effectively improving the light extraction efficiency of the micro display unit 30, and further significantly improving the overall light emitting performance of the micro display unit 30. The lateral light is the light emitted from the sidewall of the micro display unit 30.

[0069] The micro display epitaxial structure provided by the embodiment of the present application sets the patterned mask light modulation layer 20 on one side of the substrate 10, and realizes selective preparation of the micro display unit 30 based on the limitation of the epitaxial growth area by the mask light modulation layer 20. The isolation layer 32 is arranged between the light emitting units 31 of the adjacent two layers of the micro display unit 30, which can prevent current cross talk between the two adjacent light emitting units 31 and is conducive to achieving independent control of driving of each light emitting unit 31, thereby realizing selective epitaxy of the micro display unit 30 of double colors and above. In addition, the mask light modulation layer 20 is also used to adjust the propagation direction of the light emitted from the light emitting unit 31 to the mask light modulation layer 20, to reduce the included angle between the propagation direction of the light emitted from the sidewall of the light emitting unit 31 and the direction perpendicular to the substrate 10, thereby achieving extraction of the lateral light of the micro display unit 30 and improving the light extraction efficiency of the micro display unit 30.

[0070] On the basis of the above-mentioned embodiments, optionally, referring to Figure 1 , in the process of limiting the epitaxial area of the micro display unit 30 and in the process of adjusting the propagation direction of the light emitted by the light emitting unit 31 to the mask light adjusting layer 20, the sidewall 211 of the mask opening is curved, and the curved surface protrudes towards the adjacent micro display unit 30. It can be understood that, before the extension area of the micro display unit 30 is limited, the sidewall 211 of the mask opening 21 of the mask light adjusting layer 20 is curved, so that the surface of the mask light adjusting layer 20 is curved. Alternatively,

[0071] Figure 4 is a cross-sectional structure schematic diagram of the micro display epitaxial structure after the micro display unit is selectively epitaxially grown on one side of the substrate in the preparation method of the micro display epitaxial structure provided by the embodiment of the present application, referring to Figure 4 , in the process of limiting the epitaxial area of the micro display unit 30, the sidewall 211 of the mask opening is planar; referring to Figure 1 , in the process of adjusting the propagation direction of the light emitted by the light emitting unit 31 to the mask light adjusting layer 20, the sidewall 211 of the mask opening is curved, and the curved surface protrudes towards the adjacent micro display unit 30.

[0072] Specifically, when the mask light adjusting layer 20 is used as a mask layer, the sidewall 211 of the mask opening 21 is planar, which is beneficial to the epitaxial growth of the micro display unit 30 in the mask opening 21 and improves the epitaxial growth quality of the micro display unit 30. After the function of limiting the epitaxial area of the micro display unit 30 is completed, the sidewall 211 of the mask opening 21 of the mask light adjusting layer 20 is curved, so that the surface of the mask light adjusting layer 20 towards the micro display unit 30 is curved, and the curved surface protrudes towards the adjacent micro display unit 30, thereby adjusting the mask light adjusting layer 20 between the two adjacent micro display units 30 to a light collecting structure (a light-transmitting layer with an arc surface), changing the horizontal light emission of the micro display unit 30 to vertical light emission, and realizing the extraction of horizontal light. The step of curving the sidewall 211 of the mask opening 21 of the mask light adjusting layer 20 includes wet etching and / or dry etching of the mask layer, wherein the etching solution used in the wet etching process can include at least one of HF solution, BOE (Buffered Oxide Etch) solution, SC1 solution (SC1 solution is a mixture of ammonium hydroxide, hydrogen peroxide and water) and phosphoric acid solution. The dry etching process can be a plasma etching process.

[0073] On the basis of the above-mentioned embodiments, referring to Figure 1Optionally, the absolute value of the height difference d between the surface of the mask light-adjusting layer 20 away from the substrate 10 and the surface of the micro display unit 30 away from the substrate 10 is less than or equal to 10 μm.

[0074] It can be understood that the absolute value of the difference between the distance from the surface of the mask light-adjusting layer 20 away from the substrate 10 to the substrate 10 and the distance from the surface of the micro display unit 30 away from the substrate 10 to the substrate 10 is less than or equal to 10 μm. The distance from the surface of the mask light-adjusting layer 20 away from the substrate 10 to the substrate 10 can be greater than the distance from the surface of the micro display unit 30 away from the substrate 10 to the substrate 10. The distance from the surface of the mask light-adjusting layer 20 away from the substrate 10 to the substrate 10 can be equal to the distance from the surface of the micro display unit 30 away from the substrate 10 to the substrate 10. The distance from the surface of the mask light-adjusting layer 20 away from the substrate 10 to the substrate 10 can be less than the distance from the surface of the micro display unit 30 away from the substrate 10 to the substrate 10.

[0075] When the distance from the surface of the mask light-adjusting layer 20 away from the substrate 10 to the substrate 10 is greater than the distance from the surface of the micro display unit 30 away from the substrate 10 to the substrate 10 (see FIG. 2), the adjustment range of the light emitted by the sidewall of the micro display unit 30 can be expanded, which is conducive to adjusting the propagation direction of the light emitted by the entire sidewall of the micro display unit 30, thereby further improving the light extraction efficiency of the lateral light emission of the micro display unit 30. Figure 1

[0076] When the distance from the surface of the mask light-adjusting layer 20 away from the substrate 10 to the substrate 10 is less than the distance from the surface of the micro display unit 30 away from the substrate 10 to the substrate 10 (not shown), the top of the micro display unit 30 can protrude from the mask opening 21 of the mask light-adjusting layer 20, thereby facilitating the electrical connection between the micro display unit 30 and the driving electrode on the driving substrate during the bonding of the micro display epitaxial structure on the driving substrate, and reducing the preparation difficulty of the micro display device.

[0077] When the distance from the surface of the mask light-adjusting layer 20 away from the substrate 10 to the substrate 10 is equal to the distance from the surface of the micro display unit 30 away from the substrate 10 to the substrate 10 (not shown), the adjustment range of the light emitted by the sidewall of the micro display unit 30 can be expanded, and the difficulty of the electrical connection between the micro display unit 30 and the driving electrode on the driving substrate can be reduced.

[0078] ​In addition, the absolute value of the height difference d between the surface of the mask light-adjusting layer 20 away from the substrate 10 and the surface of the micro display unit 30 away from the substrate 10 is less than or equal to 10 μm, which can prevent the absolute value of the height difference d between the surface of the mask light-adjusting layer 20 away from the substrate 10 and the surface of the micro display unit 30 away from the substrate 10 from being too large, and thus affecting the adjustment range of the light emitted from the sidewall of the micro display unit 30 or affecting the electrical connection between the micro display unit 30 and the driving electrode on the driving substrate. Further, the absolute value of the height difference d between the surface of the mask light-adjusting layer 20 away from the substrate 10 and the surface of the micro display unit 30 away from the substrate 10 is less than or equal to 1 μm, which can ensure the adjustment range of the light emitted from the sidewall of the micro display unit 30 while reducing the difficulty of the electrical connection between the micro display unit 30 and the driving electrode on the driving substrate.

[0079] On the basis of the above-mentioned embodiments, the refractive index of the mask light-adjusting layer 20 between the adjacent two micro display units 30 is uniformly set; or the refractive index of the mask light-adjusting layer 20 between the adjacent two micro display units 30 is gradually changed in the direction parallel to the substrate 10.

[0080] Specifically, the mask light-adjusting layer 20 between the adjacent two micro display units 30 is a spherical light-transmitting layer with a high refractive index or an ellipsoidal light-transmitting layer with a high refractive index. The mask light-adjusting layer 20 between the adjacent two micro display units 30 can be a light-transmitting layer with a single refractive index or a light-transmitting layer with a gradually changed refractive index. Figure 5 is a simulation diagram of the light collecting effect of a mask light-adjusting layer with a uniform refractive index on the light emitted from the sidewall of a light-emitting unit, Figure 6 is a simulation diagram of the light collecting effect of a mask light-adjusting layer with a gradually changed refractive index on the light emitted from the sidewall of a light-emitting unit, for reference Figure 5 and Figure 6 The light-transmitting layer with a high refractive index can make the lateral light (the light propagating in the direction parallel to the substrate 10) bend, so as to achieve the light collecting effect and make the light emit along the direction perpendicular to the substrate 10 or the direction close to the direction perpendicular to the substrate 10.

[0081] By comparison Figure 5 and Figure 6 In the case where the refractive index of the mask light-adjusting layer 20 between the micro display units 30 is gradually changed in the direction parallel to the substrate 10, the direction of propagation of the light can be adjusted multiple times in the direction parallel to the substrate 10, which is more conducive to the light emitted from the sidewall of the micro display unit 30 emitting along the direction perpendicular to the substrate 10, so as to further improve the light extraction efficiency of the lateral light of the micro display unit 30.

[0082] It should be noted that in the case that the mask light-adjusting layer 20 between the two adjacent micro display units 30 is a light-transmitting layer with a gradient refractive index, the gradient mode of the refractive index of the mask light-adjusting layer 20 is different with respect to the two adjacent micro display units 30 on both sides of the mask light-adjusting layer 20. For example, in the two adjacent micro display units 30, one is a first micro display unit and the other is a second micro display unit, and the mask light-adjusting layer 20 between the first micro display unit and the second micro display unit has a gradient mode of gradually increasing the refractive index of the mask light-adjusting layer 20 in the direction from the first micro display unit to the second micro display unit, and gradually decreasing the refractive index of the mask light-adjusting layer 20 in the direction from the second micro display unit to the first micro display unit, so that the light emitted by the first micro display unit into the mask light-adjusting layer has a different or even opposite propagation direction after the adjustment of the propagation direction of the light emitted by the first micro display unit into the mask light-adjusting layer 20. That is, after the adjustment of the propagation direction of the light emitted by the first micro display unit into the mask light-adjusting layer 20, the light emitted by one of the micro display units 30 propagates in a direction away from the substrate 10, and the light emitted by the other micro display unit 30 propagates in a direction close to the substrate 10. Therefore, a light-reflecting layer can be arranged on the side of the mask light-adjusting layer 20 close to the substrate 10 or on the side of the mask light-adjusting layer 20 away from the substrate 10, so as to reflect the light in the target light-emitting direction away from the micro display unit 30 into the target light-emitting direction. The light-reflecting layer can be a light-reflecting layer made of a metal material or a DBR reflecting layer.

[0083] Further, the light-reflecting layer can also extend to one side of the micro display unit 30, that is, the vertical projection of the light-reflecting layer on the substrate 10 at least partially overlaps the vertical projection of the micro display unit 30 on the substrate 10 and at least partially overlaps the vertical projection of the mask light-adjusting layer 20 on the substrate 10. Therefore, the light extraction efficiency of the micro display unit 30 in the longitudinal direction can be improved, and the light extraction efficiency of the micro display unit 30 is further improved.

[0084] Optionally, in the case that the refractive index of the mask light-adjusting layer 20 between the two adjacent micro display units 30 is uniformly arranged, the light-reflecting layer can also be arranged on the side of the mask light-adjusting layer 20 close to or away from the substrate 10 and extend to one side of the micro display unit 30.

[0085] On the basis of the above embodiments, Figure 7 is a schematic diagram of a cross-sectional structure of an isolation layer provided by an embodiment of the present application, with reference to Figure 7 and in combination with Figure 3 Optionally, the isolation layer 32 includes a tunnel junction 32a, a third semiconductor layer 32b and a fourth semiconductor layer 32c in sequence away from the substrate 10.

[0086] The tunnel junction 32a is in contact with the second semiconductor layer 31c of the light emitting unit 31 on the side of the substrate 10, and is used to enhance the current injection to the second semiconductor layer 31c and the current diffusion on the surface of the second semiconductor layer 31c; the conductive type of the third semiconductor layer 32b is the same as that of the first semiconductor layer 31a, and the conductive type of the fourth semiconductor layer 32c is the same as that of the second semiconductor layer 31c; the conductive type of the first semiconductor layer 31a is different from that of the second semiconductor layer 31c; the third semiconductor layer 32b and the fourth semiconductor layer 32c are used to form a reverse bias and electrically isolate two adjacent light emitting units 31.

[0087] Specifically, in the light emitting unit 31, the first semiconductor layer 31a is an N-type semiconductor layer, and the second semiconductor layer 31c is a P-type semiconductor layer, and both are light-doped film layers. For example, the first semiconductor layer 31a is an N-GaN layer, and the second semiconductor layer 31c is a P-GaN layer. The vertical growth of multiple light emitting units 31 and the ability to achieve individual driving control require good insulation and isolation between each light emitting unit 31, and also require good ohmic contact of the second semiconductor layer 31c (for example, a P-GaN layer) in the light emitting unit 31. Due to the high resistance characteristics of the p-GaN layer, it will cause poor conductivity and high light absorption. In some embodiments, indium tin oxide (ITO) or some other transparent conductive oxide (such as zinc oxide) can be used to disperse current to the light emitting unit 31. From the actual simple and efficient epitaxial means, the embodiment of the present application provides a tunnel junction 32a in contact with the second semiconductor layer 31c in the isolation layer 32. The tunnel junction 32a includes a P-type heavily doped semiconductor layer and an N-type heavily doped semiconductor layer stacked. For example, the P-type heavily doped semiconductor layer in the tunnel junction 32a can be a P+GaN layer, and the N-type heavily doped semiconductor layer can be an N+GaN layer. The P-type heavily doped semiconductor layer in the tunnel junction 32a is in contact with the second semiconductor layer 31c (P-type light-doped semiconductor layer) in the light emitting unit 31. Due to the quantum tunneling effect, the electrons in the valence band of the P-type heavily doped semiconductor layer in the tunnel junction 32a can tunnel into the conduction band of the N-type heavily doped semiconductor layer, thereby causing hole injection into the second semiconductor layer 31c in the light emitting unit 31. Therefore, the tunnel junction 32a can enhance current injection and current diffusion. Compared with the use of Ni / Au metal contact or transparent indium tin oxide (ITO) and other transparent contacts, the tunnel junction 32a can also reduce light absorption and reduce light loss.

[0088] The conductive type of the third semiconductor layer 32b is the same as that of the first semiconductor layer 31a, the conductive type of the fourth semiconductor layer 32c is the same as that of the second semiconductor layer 31c, and the third semiconductor layer 32b and the fourth semiconductor layer 32c are both lightly doped films. For example, the third semiconductor layer 32b is an N-GaN layer, and the fourth semiconductor layer 32c is a P-GaN layer. The third semiconductor layer 32b and the fourth semiconductor layer 32c in the isolation layer 32 constitute a reverse bias, thereby isolating the current and preventing the electrical cross-talk between the light emitting units 31 on the upper and lower sides of the isolation layer 32. In addition, the electrode layer for inputting the current to the second semiconductor layer 31c can be in contact with the surface of the third semiconductor layer 32b, because the resistivity of the material (N-GaN) of the third semiconductor layer 32b is lower than that of the material (P-GaN) of the second semiconductor layer 31c, and a good ohmic contact is more easily formed.

[0089] Further, for the insulation control, the isolation layer 32 can further include an insulating layer on the side of the fourth semiconductor layer 32c away from the third semiconductor layer 32b; wherein the insulating layer includes at least one of an undoped GaN layer, an AlN layer, an AlGaN layer, and a C-doped GaN layer, to further improve the electrical insulation of the isolation layer 32.

[0090] For example, Figure 8 is another cross-sectional structure diagram of the isolation layer provided by the embodiment of the present application, referring to Figure 8 The isolation layer 32 further includes an insulating layer composed of a superlattice layer 32e composed of an undoped GaN layer 32d (U-GaN layer), an AlN layer, and an AlGaN layer arranged in sequence on the side of the fourth semiconductor layer 32c away from the third semiconductor layer 32b, and a C-doped GaN layer 32f (C-GaN layer). The C-doped GaN layer 32f has a high resistance characteristic, and is used as the last layer of the isolation layer 32 to completely cut off the current.

[0091] On the basis of the above embodiments, Figure 9 is another cross-sectional structure diagram of the micro-display epitaxial structure provided by the embodiment of the present application, referring to Figure 9Optionally, the micro display unit 30 comprises three light emitting units 31 arranged in sequence away from the substrate 10, which are respectively a first light emitting unit 311, a second light emitting unit 312 and a third light emitting unit 313; wherein the light emitting wavelength of the first light emitting unit 311 is smaller than the light emitting wavelength of the second light emitting unit 312, and the light emitting wavelength of the second light emitting unit 312 is smaller than the light emitting wavelength of the third light emitting unit 313; the first light emitting unit 311 and the second light emitting unit 312 are provided with a first isolation layer 321, and the second light emitting unit 312 and the third light emitting unit 313 are provided with a second isolation layer 322. Exemplarily, the first light emitting unit 311 is a blue light emitting unit for emitting blue light, the second light emitting unit 312 is a green light emitting unit for emitting green light, and the third light emitting unit 313 is a red light emitting unit for emitting red light. The light emitting units 31 are arranged in sequence along the direction of epitaxial growth (the direction away from the substrate 10), and the light emitting wavelength gradually increases, which is beneficial to the epitaxial growth of the micro display unit 30.

[0092] Optionally, the side wall of at least one side of the micro display unit 30 is in a stepped shape, and the stepped side wall comprises a first step surface and a second step surface; the first step surface is formed by a part of the surface of the fourth semiconductor layer 32c away from the substrate 10 in the first isolation layer 321; the second step surface is formed by a part of the surface of the fourth semiconductor layer 32c away from the substrate 10 in the second isolation layer 322; the first step surface and the second step surface are provided with a metal layer of the same material, so that the metal layer on the first step surface and the second step surface can be prepared at the same time.

[0093] Further, in each micro display unit 30, the side away from the substrate 10 of the light emitting unit 31 farthest from the substrate 10 is provided with an isolation layer 32, and the side wall of the isolation layer 32 also has a step surface for carrying a metal layer. Exemplarily, Figure 10 is a cross-sectional structure schematic diagram of a micro display unit with a stepped side wall provided by an embodiment of the present application, referring to Figure 10 , and combining Figure 8Each micro display unit 30 includes three light emitting units 31, i.e., a first light emitting unit 311, a second light emitting unit 312 and a third light emitting unit 313. A third isolation layer 323 can be arranged on the side of the third light emitting unit 313 away from the substrate 10. The sidewall of each micro display unit 30 can have six stepped surfaces, i.e., a first stepped surface t1 exposing the fourth semiconductor layer 32c in the first isolation layer 321, a second stepped surface t2 exposing the fourth semiconductor layer 32c in the second isolation layer 322, a third stepped surface t3 exposing the fourth semiconductor layer 32c in the third isolation layer 323, a fourth stepped surface t4 exposing the first semiconductor layer 31a of the first light emitting unit 311, a fifth stepped surface t5 exposing the first semiconductor layer 31a of the second light emitting unit 312 and a sixth stepped surface t6 exposing the first semiconductor layer 31a of the third light emitting unit 313. A metal layer (not shown) for electrical connection with the driving substrate is arranged on each of the first to sixth stepped surfaces t1-t6, and the metal layers on the first to sixth stepped surfaces t1-t6 can be made of the same material, so that the metal layers on the first to sixth stepped surfaces t1-t6 can be prepared at the same time.

[0094] The embodiment of the present application also provides a preparation method of the micro display epitaxial structure. Figure 11 The embodiment of the present application also provides a preparation method of the micro display epitaxial structure. Figure 11 The preparation method of the micro display epitaxial structure includes the following steps.

[0095] S10, providing a substrate.

[0096] Specifically, referring to Figure 12 The substrate 10 can be a silicon substrate, a sapphire substrate, a silicon carbide substrate or other suitable substrate for epitaxial preparation of micro display units.

[0097] S20, forming a mask light modulation layer on one side of the substrate and patterning the mask light modulation layer to form a plurality of mask openings exposing the substrate in the mask light modulation layer.

[0098] Specifically, referring to Figure 13 The mask light modulation layer 20 is formed on one side of the substrate 10, and the material of the mask light modulation layer 20 includes but is not limited to at least one of SiO2, SiN and Ta2O5. Figure 14 The mask light modulation layer 20 can be patterned by a photolithography process to form a plurality of mask openings 21 exposing the substrate 10 in the mask light modulation layer 20.

[0099] S30, forming a plurality of micro display units based on the limitation of the mask openings in the mask light modulation layer on the epitaxial region; wherein each micro display unit is located in a mask opening, and the micro display unit includes at least two light emitting units away from the substrate in sequence and an isolation layer between the two adjacent light emitting units.

[0100] Specifically, referring to Figure 15 , the nucleation energy of the mask light modulation layer 20 is much larger than that of the surface of the substrate 10, the material of the mask light modulation layer 20 is amorphous material, and the epitaxial material has the condition of preferred orientation, so that the epitaxial material of the micro display unit 30 grows epitaxially in the opening area of the mask light modulation layer 20. This bottom-up epitaxial process can completely avoid the introduction of pixel etching, so the light extraction efficiency of the micro display unit 30 can be fundamentally improved.

[0101] S40, performing curved surface processing on the sidewall of the mask opening in the mask light modulation layer, so that the mask light modulation layer is also used to adjust the propagation direction of the light emitted by the light emitting unit to the mask light modulation layer, and reduce the included angle between the light emitted from the sidewall of the light emitting unit and the direction perpendicular to the substrate.

[0102] Specifically, referring to Figure 16 , the curved surface processing on the sidewall of the mask opening 21 in the mask light modulation layer 20 includes wet etching processing and / or dry etching processing on the mask light modulation layer 20, so that the mask light modulation layer 20 between the two adjacent micro display units 30 is deformed into a light collecting structure with curved surface, so that the lateral light extraction of the micro display unit 30 can be changed into vertical light extraction, and the light extraction of the lateral light extraction is realized.

[0103] The preparation method of the micro display epitaxial structure provided by the embodiment of the application forms a patterned mask light modulation layer 20 on one side of the substrate 10, and realizes selective preparation of the micro display unit 30 based on the limitation of the patterned mask light modulation layer 20 on the epitaxial growth area. The preparation process is simple; and the isolation layer 32 is formed between the two adjacent layers of the light emitting unit 31 of the micro display unit 30, which can prevent current crosstalk between the two adjacent light emitting units 31, is conducive to realizing independent control of the driving of each light emitting unit 31, thereby realizing selective epitaxy of the micro display unit 30 with double colors and more than double colors, replacing the complex mass transfer and vertical stacking scheme, reducing the preparation cost of the micro display device, effectively avoiding the sidewall damage caused by pixel etching, and improving the reliability of the micro display device. In addition, after forming a plurality of micro display units 30, curved surface processing is performed on the sidewall of the mask opening 21 in the mask light modulation layer 20, so that the mask light modulation layer 20 is deformed into a light collecting structure, which can adjust the propagation direction of the light emitted by the light emitting unit 31 to the mask light modulation layer 20, and reduce the included angle between the light emitted from the sidewall of the light emitting unit 31 and the direction perpendicular to the substrate 10, thereby realizing the extraction of the lateral light extraction of the micro display unit 30, and improving the light extraction efficiency of the micro display unit 30.

[0104] Optionally, the step of performing a curved surface processing on the sidewalls of the mask openings in the mask light-adjusting layer may also be performed before the step of forming a plurality of micro-display units based on the definition of the epitaxial region by the mask openings in the mask light-adjusting layer.

[0105] Optional, reference Figure 3 , forming a light emitting unit 31 in the micro display unit 30, including: a first semiconductor layer 31a, a quantum well layer 31q and a second semiconductor layer 31c formed on one side of the substrate 10 and sequentially away from the substrate 10.

[0106] refer to Figure 7 , an isolation layer 32 is formed between two adjacent light-emitting units 31, including: a tunnel junction 32a, a third semiconductor layer 32b and a fourth semiconductor layer 32c are formed on one side of the substrate 10, which are sequentially away from the substrate 10; wherein the tunnel junction 32a is in contact with the second semiconductor layer 31c of the light-emitting unit 31 on the side of the tunnel junction 32a close to the substrate 10, and the tunnel junction 32a is used to enhance current injection into the second semiconductor layer 31c and current diffusion on the surface of the second semiconductor layer 31c; the conductivity type of the third semiconductor layer 32b is the same as the conductivity type of the first semiconductor layer 31a, and the conductivity type of the fourth semiconductor layer 32c is the same as the conductivity type of the second semiconductor layer 31c; the conductivity type of the first semiconductor layer 31a is different from the conductivity type of the second semiconductor layer 31c; the third semiconductor layer 32b and the fourth semiconductor layer 32c are used to form a reverse bias to electrically isolate the two adjacent light-emitting units 31.

[0107] For further reference, Figure 8 , forming an isolation layer 32 between two adjacent light-emitting units 31, and also including: forming an insulating layer on the side of the fourth semiconductor layer 32c away from the third semiconductor layer 32b; wherein the insulating layer includes at least one of an undoped GaN layer 32d, an AlN layer, an AlGaN layer, and a GaN layer 32f doped with C element.

[0108] On the basis of the above embodiments, optionally, in step S20, a mask dimming layer is formed on one side of the substrate, and the mask dimming layer is patterned to form a plurality of mask openings exposing the substrate in the mask dimming layer, specifically comprising: forming a mask dimming layer 20 on the cleaned substrate 10 by magnetron sputtering, electron beam evaporation or PECVD; and then forming a plurality of periodically arranged mask openings 21 by dry etching, wherein the mask openings 21 can be regular polygonal openings with a side length ranging from 0.2μm to 10μm, or can be circular openings with an aperture range of 0.2μm to 10μm; the spacing range of the mask openings 21 is 0.4μm to 20μm.

[0109] for Figure 9The structure shown, in step S30, based on the mask light layer in the mask opening to the extension area, forming a micro display unit specifically includes:

[0110] The first light emitting unit 311 is epitaxially grown in the mask opening 21 region by using the MOCVD process. Specifically, it includes: forming an AlN / AlGaN superlattice composite buffer layer on one side of the substrate 10, the thickness of the buffer layer ranges from 500 nm to 2000 nm; forming a first semiconductor layer 31a (lightly doped N-type semiconductor layer) on the side of the buffer layer away from the substrate 10, the thickness of the first semiconductor layer 31a ranges from 1 μm to 5 μm; forming a quantum well layer 31q on the side of the first semiconductor layer 31a away from the substrate 10, the thickness of the quantum well layer 31q ranges from 200 nm to 600 nm, and the In doping concentration is 5% to 13%; forming a second semiconductor layer 31c (lightly doped P-type semiconductor layer) on the side of the quantum well layer 31q away from the substrate 10, the thickness of the second semiconductor layer 31c ranges from 100 nm to 400 nm.

[0111] The first isolation layer 321 is epitaxially grown above the first light emitting unit 311. Specifically, it includes: sequentially forming a tunnel junction 32a, a third semiconductor layer 32b (lightly doped N-type semiconductor layer), a fourth semiconductor layer 32c (lightly doped P-type semiconductor layer), an undoped GaN layer 32d, an AlN layer and an AlGaN layer composed of a superlattice layer 32e, and a GaN layer doped with C element 32f on the side of the second semiconductor layer 31c of the first light emitting unit 311 away from the substrate 10. The tunnel junction 32a and the third semiconductor layer 32b in the first isolation layer 321 constitute the current spreading layer of the second semiconductor layer 31c in the first light emitting unit 311. Among them, the tunnel junction 32a is grown by using delta doping mode, and the specific structure can be a three-film layer structure of P+GaN layer / InGaN layer / N+GaN layer; in the tunnel junction 32a, the thickness of the P+GaN layer ranges from 10 nm to 30 nm, the P+GaN layer is doped with Mg, and the doping concentration of Mg ranges from 1E20 / cm 2 ~6E20 / cm 2 ; the thickness of the InGaN layer ranges from 0.3 nm to 2 nm; then the temperature is raised to 1020℃~1060℃, and the N+GaN layer is formed by using delta growth mode, the thickness of the N+GaN layer ranges from 5 nm to 25 nm, the N+GaN layer is doped with Si, and the doping concentration of Si ranges from 1E20 / cm 2 ~5E20 / cm 2Then, a third semiconductor layer 32b (lightly doped N-type semiconductor layer) is formed on the side of the tunnel junction 32a away from the substrate 10, the thickness of the third semiconductor layer 32b ranges from 400 nm to 1000 nm, the growth temperature ranges from 1040 °C to 1100 °C, and the Si doping concentration ranges from 1E19 / cm 2 to 8E19 / cm 2 A fourth semiconductor layer 32c (lightly doped P-type semiconductor layer) is formed on the side of the third semiconductor layer 32b away from the substrate 10, the thickness of the fourth semiconductor layer 32c ranges from 100 nm to 250 nm, the growth temperature ranges from 930 °C to 980 °C, and the Mg doping concentration ranges from 5E18 / cm 2 to 2E19 / cm 2 Further, a superlattice layer 32e composed of an undoped GaN layer 32d, an AlN layer and an AlGaN layer, and a GaN layer 32f doped with C element are sequentially formed, wherein the thickness of the undoped GaN layer 32d ranges from 400 nm to 1000 nm, the thickness of the superlattice layer 32e composed of the AlN layer and the AlGaN layer ranges from 100 nm to 200 nm, and the thickness of the GaN layer 32f doped with C element ranges from 100 nm to 400 nm.

[0112] The second light-emitting unit 312 is epitaxially grown on the first isolation layer 321 by MOCVD process. Specifically, the first semiconductor layer 31a, the quantum well layer 31q and the second semiconductor layer 31c in the second light-emitting unit 312 are sequentially formed. The thickness of the first semiconductor layer 31a (lightly doped N-type semiconductor layer) ranges from 300 nm to 5000 nm; the thickness of the quantum well layer 31q ranges from 200 nm to 600 nm, and the In doping concentration ranges from 15% to 22%; and the thickness of the second semiconductor layer 31c (lightly doped P-type semiconductor layer) ranges from 100 nm to 300 nm.

[0113] The second isolation layer 322 is epitaxially grown on the second light-emitting unit 312, and is formed in the same way as the first isolation layer 321, which will not be described here.

[0114] Epitaxial growth of the third light-emitting unit 313 is performed on the second isolation layer 322 using an MOCVD process. Specifically, the first semiconductor layer 31a, quantum well layer 31q, and second semiconductor layer 31c of the third light-emitting unit 313 are sequentially formed. The thickness of the first semiconductor layer 31a (a lightly doped N-type semiconductor layer) is in the range of 300 nm to 5000 nm; the thickness of the quantum well layer 31q is in the range of 200 nm to 600 nm, with an In doping concentration of 22% to 35%; and the thickness of the second semiconductor layer 31c (a lightly doped P-type semiconductor layer) is in the range of 100 nm to 300 nm.

[0115] The total epitaxial thickness does not exceed 10 micrometers of the thickness of the mask dimming layer 20 .

[0116] In step S40, the specific steps of curving the sidewalls of the mask openings in the mask dimming layer include: wet etching the mask dimming layer 20. The wet etching process can be performed by soaking the mask dimming layer 20 in an SC1 solution at a temperature range of 50°C to 85°C for 1 to 3 hours. The SC1 solution can be prepared by mixing ammonium hydroxide, hydrogen peroxide, and water in a volume ratio of 1:5:40. Alternatively, the wet etching process can be performed by soaking the mask dimming layer 20 in an HF / EG solution at a temperature range of 50°C to 85°C for 40 to 120 minutes. The HF / EG solution can be prepared by mixing 49% hydrofluoric acid and ethylene glycol in a ratio of approximately 4:96. After the etching process, the mask dimming layer 20 is deformed into a concentrating structure, thereby achieving lateral light extraction.

[0117] An embodiment of the present invention further provides a method for preparing a micro display device, comprising:

[0118] Provide a drive substrate;

[0119] The micro display epitaxial structure according to any embodiment of the present invention is bonded to the surface of the driving substrate 100, and the substrate 10 (refer to Figure 17 and Figure 18 ). It has the same technical effect and will not be described here.

[0120] Note that the above are only preferred embodiments of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments, and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments and may include many other equivalent embodiments without departing from the concept of the present invention. The scope of the present invention is determined by the scope of the appended claims.

Claims

1. A micro-display epitaxial structure, characterized in that: include: substrate; A mask dimming layer is located on one side of the substrate; The mask dimming layer has a plurality of mask openings exposing the substrate; A plurality of micro-display units, each of the micro-display units being located in a corresponding mask opening; The micro display unit includes at least two light emitting units sequentially away from the substrate and an isolation layer located between the two adjacent light emitting units; The mask dimming layer located between two adjacent micro-display units is a spherical or ellipsoidal light-transmitting layer; The mask dimming layer is used to define the epitaxial area of ​​the micro-display unit and to adjust the propagation direction of light emitted from the light-emitting unit toward the mask dimming layer, so as to reduce the angle between the propagation direction of light emitted from the side wall of the light-emitting unit and the direction perpendicular to the substrate, thereby improving the light extraction efficiency of the lateral light emitted from the micro-display unit; The isolation layer includes a tunnel junction, a third semiconductor layer and a fourth semiconductor layer that are sequentially away from the substrate; the tunnel junction includes a stacked P-type heavily doped semiconductor layer and an N-type heavily doped semiconductor layer; the tunnel junction is used to enhance current injection and current diffusion; the third semiconductor layer and the fourth semiconductor layer are used to form a reverse bias to electrically isolate two adjacent light-emitting units.

2. The micro-display epitaxial structure according to claim 1, characterized in that: When the mask dimming layer is used to define the epitaxial area of ​​the micro display unit, the sidewall of the mask opening is planar; When the mask dimming layer is used to adjust the propagation direction of light emitted from the light-emitting unit to the mask dimming layer, the sidewall of the mask opening is curved, and the curved surface is convex toward the adjacent micro-display unit; or, When the mask dimming layer is used to define the epitaxial area of ​​the micro-display unit and when the mask dimming layer is used to adjust the propagation direction of light emitted from the light-emitting unit to the mask dimming layer, the sidewall of the mask opening is curved, and the curved surface is convex toward the adjacent micro-display unit; And / or, an absolute value of a height difference between a surface of the mask dimming layer away from the substrate and a surface of the micro display unit away from the substrate is less than or equal to 10 μm; And / or, the material of the mask dimming layer includes at least one of SiO 2 , SiN and Ta 2 O 5 .

3. The micro-display epitaxial structure according to claim 2, characterized in that: The refractive index of the mask dimming layer located between two adjacent micro-display units is uniformly set; Alternatively, the refractive index of the mask dimming layer located between two adjacent micro display units is gradually changed in a direction parallel to the substrate.

4. The micro-display epitaxial structure according to claim 1, wherein: Each of the light-emitting units comprises a first semiconductor layer, a quantum well layer, and a second semiconductor layer sequentially away from the substrate; The tunnel junction contacts the second semiconductor layer of the light-emitting unit on the side of the tunnel junction close to the substrate, and the tunnel junction is used to enhance current injection into the second semiconductor layer and current diffusion on the surface of the second semiconductor layer; the conductivity type of the third semiconductor layer is the same as the conductivity type of the first semiconductor layer, and the conductivity type of the fourth semiconductor layer is the same as the conductivity type of the second semiconductor layer; the conductivity type of the first semiconductor layer is different from the conductivity type of the second semiconductor layer.

5. The micro-display epitaxial structure according to claim 4, characterized in that: The isolation layer further includes an insulating layer located on a side of the fourth semiconductor layer away from the third semiconductor layer; The insulating layer includes at least one of an undoped GaN layer, an AlN layer, an AlGaN layer, and a GaN layer doped with C element.

6. The micro-display epitaxial structure according to claim 4, characterized in that: The micro display unit includes three light-emitting units that are sequentially away from the substrate, namely a first light-emitting unit, a second light-emitting unit, and a third light-emitting unit; wherein the light-emitting wavelength of the first light-emitting unit is smaller than the light-emitting wavelength of the second light-emitting unit, and the light-emitting wavelength of the second light-emitting unit is smaller than the light-emitting wavelength of the third light-emitting unit; a first isolation layer is provided between the first light-emitting unit and the second light-emitting unit, and a second isolation layer is provided between the second light-emitting unit and the third light-emitting unit; The side wall of at least one side of the micro display unit is stepped, and the stepped side wall includes a first step surface and a second step surface; the first step surface is formed by a portion of the surface of the fourth semiconductor layer in the first isolation layer on a side away from the substrate; the second step surface is formed by a portion of the surface of the fourth semiconductor layer in the second isolation layer on a side away from the substrate; and metal layers of the same material are provided on the first step surface and the second step surface.

7. A method for preparing a micro-display epitaxial structure, characterized in that: Used to prepare the micro-display epitaxial structure according to any one of claims 1 to 6, comprising: providing a substrate; forming a mask dimming layer on one side of the substrate, and patterning the mask dimming layer to form a plurality of mask openings in the mask dimming layer that expose the substrate; Based on the definition of the epitaxial region by the mask openings in the mask dimming layer, a plurality of micro-display units are formed; wherein each of the micro-display units is correspondingly located in one of the mask openings, and the micro-display unit includes at least two light-emitting units that are sequentially away from the substrate and an isolation layer located between the two adjacent light-emitting units; The side walls of the mask openings in the mask dimming layer are curved so that the mask dimming layer is also used to adjust the propagation direction of light emitted from the light-emitting unit toward the mask dimming layer, reduce the angle between the light emitted from the side walls of the light-emitting unit and the direction perpendicular to the substrate, and improve the light extraction efficiency of the lateral light output of the micro display unit.

8. The method for preparing a microdisplay epitaxial structure according to claim 7, wherein: The light-emitting unit in the micro display unit is formed, comprising: forming a first semiconductor layer, a quantum well layer, and a second semiconductor layer on one side of the substrate, which are sequentially away from the substrate; An isolation layer is formed between two adjacent light-emitting units, comprising: A tunnel junction, a third semiconductor layer, and a fourth semiconductor layer are formed on one side of the substrate, which are sequentially away from the substrate; wherein the tunnel junction contacts the second semiconductor layer of the light-emitting unit on the side of the tunnel junction close to the substrate, and the tunnel junction is used to enhance current injection into the second semiconductor layer and current diffusion on the surface of the second semiconductor layer; the conductivity type of the third semiconductor layer is the same as the conductivity type of the first semiconductor layer, and the conductivity type of the fourth semiconductor layer is the same as the conductivity type of the second semiconductor layer; the conductivity type of the first semiconductor layer is different from the conductivity type of the second semiconductor layer; the third semiconductor layer and the fourth semiconductor layer are used to form a reverse bias to electrically isolate two adjacent light-emitting units.

9. The method for preparing a microdisplay epitaxial structure according to claim 8, wherein: An isolation layer is formed between two adjacent light-emitting units, further comprising: An insulating layer is formed on a side of the fourth semiconductor layer away from the third semiconductor layer; wherein the insulating layer includes at least one of an undoped GaN layer, an AlN layer, an AlGaN layer, and a GaN layer doped with C element.

10. A method for preparing a micro display device, characterized in that: include: Provide a drive substrate; The micro display epitaxial structure according to any one of claims 1 to 6 is bonded to the surface of the driving substrate, and the substrate is removed.

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