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

Abstract

The invention 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; the mask dimming layer is positioned on one side of the substrate; the mask dimming layer is provided with a plurality of mask openings for exposing the substrate; a plurality of micro display units, wherein each micro display unit is correspondingly located in one mask opening; the micro-display unit comprises at least two light-emitting units which are sequentially far away from the substrate and an isolating layer located between the two adjacent light-emitting units; wherein the mask dimming layer is used for limiting an epitaxial area of the micro display unit and adjusting the propagation direction of light emitted from the light emitting unit to the mask dimming layer so as to reduce the included angle between the propagation direction of the light emitted from the side wall of the light emitting unit and the direction perpendicular to the substrate. According to the technical scheme provided by the invention, selective area epitaxy of the full-color micro-display epitaxial structure and extraction of transverse light of the micro-display unit are realized, and the light extraction efficiency of the micro-display device is improved.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of display technology, and in particular to a micro-display epitaxial structure and a preparation method thereof, and a preparation method of a micro-display device. Background Art

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

[0003] At present, the mainstream solutions for achieving full-color Micro-LED devices include mass transfer and vertically stacked pixels. Among them, the three-color pixel tiling solution using mass transfer has a relatively simple process route, but the product yield is low, and it also consumes a lot of preparation time, and there are large color differences and viewing angle differences in the display effect. The vertically stacked pixel solution can solve the above problems, but it introduces complex processes such as bonding and alignment, and has high requirements for the size, surface, morphology and alignment accuracy of the bonded wafer. In addition, the pixel etching process will inevitably cause surface damage to the sidewalls of the Micro-LED, seriously damaging the luminous efficiency of the Micro-LED.

[0004] Related technologies, using pattern masks and the confinement effect of growth, can form each film layer in Micro-LED from bottom to top, thus avoiding damage caused by pixel etching and effectively improving the luminous efficiency of Micro-LED. However, the existing selective epitaxy is mainly used for monochrome epitaxy process, lacks the application of full-color multi-color epitaxy structure, and ignores the extraction of lateral light of Micro-LED, which affects the light extraction efficiency of micro display devices. Summary of the invention

[0005] The embodiments of the present invention provide a micro-display epitaxial structure and a preparation method thereof, and a preparation method of a micro-display device, so as to realize the selective epitaxy of a full-color micro-display epitaxial structure and the extraction of lateral light of a micro-display unit, thereby improving the light extraction efficiency of the micro-display device.

[0006] According to one aspect of the present invention, there is provided a micro display epitaxial structure, comprising:

[0007] substrate;

[0008] 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;

[0009] A plurality of micro-display units, each of which is located in a corresponding mask opening; the micro-display unit comprises at least two light-emitting units which are sequentially away from the substrate and an isolation layer located between two adjacent light-emitting units;

[0010] The mask dimming layer is used to define the epitaxial area of ​​the micro display unit and to adjust the propagation direction of the light emitted from the light emitting unit to the mask dimming layer, so as to reduce the angle between the propagation direction of the light emitted from the side wall of the light emitting unit and the direction perpendicular to the substrate.

[0011] Optionally, when the mask dimming layer is used to define the epitaxial region 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 the 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,

[0012] When the mask dimming layer is used to define the epitaxial region of the micro-display unit and when the mask dimming layer is used to adjust the propagation direction of the 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;

[0013] 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;

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

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

[0016] 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.

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

[0018] The isolation layer includes a tunnel junction, a third semiconductor layer and a fourth semiconductor layer which are sequentially away from the substrate;

[0019] 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.

[0020] Optionally, the isolation layer further includes an insulating layer located on a side of the fourth semiconductor layer away from the third semiconductor layer;

[0021] 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.

[0022] Optionally, 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;

[0023] 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 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 away from the substrate; and metal layers of the same material are arranged on the first step surface and the second step surface.

[0024] According to another aspect of the present invention, a method for preparing a micro-display epitaxial structure is provided, which is used to prepare the micro-display epitaxial structure according to any embodiment of the present invention, comprising:

[0025] providing a substrate;

[0026] 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;

[0027] Based on the limitation of the epitaxial region by the mask opening 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 comprises at least two light-emitting units which are sequentially away from the substrate and an isolation layer located between two adjacent light-emitting units;

[0028] 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 the light emitted from the light-emitting unit to the mask dimming layer, thereby reducing the angle between the light emitted from the side walls of the light-emitting unit and the direction perpendicular to the substrate.

[0029] Optionally, forming a light-emitting unit in the micro display unit includes:

[0030] 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;

[0031] An isolation layer is formed between two adjacent light-emitting units, comprising:

[0032] A tunnel junction, a third semiconductor layer and a fourth semiconductor layer are formed on one side of the substrate in sequence 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.

[0033] Optionally, an isolation layer is formed between two adjacent light-emitting units, further comprising:

[0034] 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.

[0035] According to another aspect of the present invention, there is provided a method for preparing a micro display module, comprising:

[0036] Providing a drive substrate;

[0037] The micro display epitaxial structure described in any embodiment of the present invention is bonded to the surface of the driving substrate, and the substrate is removed.

[0038] The embodiments of the present invention provide 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 includes: a substrate; a mask dimming layer 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 micro-display unit correspondingly located in a mask opening; the micro-display unit includes at least two light-emitting units that are sequentially away from the substrate and an isolation layer located between two adjacent light-emitting units; wherein the mask dimming layer is used to limit the epitaxial region 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 light emitted from the side wall of the light-emitting unit and the direction perpendicular to the substrate. The technical solution provided by the present invention realizes the selective preparation of micro-display units by setting a patterned mask dimming layer on one side of the substrate based on the restriction of the epitaxial growth area by the mask dimming layer; and sets an isolation layer between the light-emitting units of two adjacent layers of the micro-display unit, which can prevent current crosstalk between the two adjacent light-emitting units, and is conducive to independent control of the drive of each light-emitting unit, thereby realizing the selective epitaxy of two-color and above micro-display units; in addition, the mask dimming layer is also used to adjust the propagation direction of light emitted from the light-emitting unit to the mask dimming layer, reducing the angle between the light emitted from the side wall of the light-emitting unit and the direction perpendicular to the substrate, thereby realizing the extraction of lateral light of the micro-display unit and improving the light extraction efficiency of the micro-display epitaxial structure.

[0039] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

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

[0042] Figure 2 It is a top view of a mask dimming layer and a substrate in a micro display epitaxial structure provided by an embodiment of the present invention;

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

[0044] Figure 4It is a schematic cross-sectional structure diagram of a micro-display unit after epitaxial growth in a selective area on one side of a substrate in a method for preparing a micro-display epitaxial structure provided by an embodiment of the present invention;

[0045] Figure 5 This is a simulation diagram of the focusing effect of a mask dimming layer with a uniform refractive index on light emitted from the side wall of a light-emitting unit provided by an embodiment of the present invention;

[0046] Figure 6 This is a simulation diagram of the focusing effect of a mask dimming layer with a gradient refractive index provided by an embodiment of the present invention on light emitted from the side wall of a light-emitting unit;

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

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

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

[0050] Fig.10 is a schematic cross-sectional structure diagram of a micro display unit having a side wall with a stepped surface provided by an embodiment of the present invention;

[0051] Fig.11 It is a flow chart of a method for preparing a micro display epitaxial structure provided by an embodiment of the present invention;

[0052] Fig.12 is a schematic diagram of a cross-sectional structure of a substrate provided in a method for preparing a micro-display epitaxial structure provided in an embodiment of the present invention;

[0053] Fig.13 It is a schematic diagram of a cross-sectional structure after an unpatterned mask dimming layer is formed on one side of a substrate in a method for preparing a micro display epitaxial structure provided by an embodiment of the present invention;

[0054] Fig.14 It is a schematic diagram of the cross-sectional structure after the mask dimming layer is patterned in a method for preparing a micro-display epitaxial structure provided by an embodiment of the present invention;

[0055] Fig.15 It is a schematic cross-sectional structure diagram after a micro-display unit is formed in a method for preparing a micro-display epitaxial structure provided by an embodiment of the present invention;

[0056] Fig.16 It is a schematic diagram of the cross-sectional structure after the side wall of the mask dimming layer is curved in a method for preparing a micro display epitaxial structure provided by an embodiment of the present invention;

[0057] Fig.17 It is a schematic cross-sectional structure diagram after a micro-display epitaxial structure is bonded to a surface of a driving substrate in a method for preparing a micro-display device provided by an embodiment of the present invention;

[0058] Fig.18 It is a schematic diagram of the cross-sectional structure of a method for preparing a micro display device provided by an embodiment of the present invention after removing the substrate. DETAILED DESCRIPTION

[0059] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0060] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0061] The embodiment of the present invention provides a micro display epitaxial structure. Figure 1 is a schematic cross-sectional structure diagram of a micro display epitaxial structure provided by an embodiment of the present invention, Figure 2 is a top view of a mask dimming layer and a substrate in a micro display epitaxial structure provided by an embodiment of the present invention, with reference to Figure 1 and Figure 2 , the micro display epitaxial structure includes:

[0062] Substrate 10;

[0063] The mask dimming layer 20 is located on one side of the substrate 10 ; the mask dimming 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 is located in a corresponding mask opening 21; the micro display unit 30 includes at least two light emitting units 31 which are sequentially away from the substrate 10 and an isolation layer 32 located between two adjacent light emitting units 31;

[0065] Among them, the mask dimming layer 20 is used to limit the epitaxial area of ​​the micro display unit 30, and to adjust the propagation direction of light emitted from the light emitting unit 31 to the mask dimming layer 20, so as to reduce the angle between the propagation direction of light emitted from the side wall of the light emitting unit 31 and the direction perpendicular to the substrate 10.

[0066] Specifically, the substrate 10 may be a silicon substrate, a sapphire substrate, a silicon carbide substrate, or the like, which is suitable for epitaxially preparing the micro display unit 30. In the process of epitaxially preparing the micro display unit 30 on the substrate 10, the mask dimming layer 20 is used as a mask layer to define the epitaxial region of the micro display unit 30. The mask dimming layer 20 is located on one side of the substrate 10. The mask dimming layer 20 may be in contact with the substrate 10 or may not be in contact with the substrate 10, as long as it satisfies the function of defining the epitaxial region of the micro display unit 30 in the process of epitaxially preparing the micro display unit 30 on the substrate 10. The mask dimming layer 20 has a plurality of mask openings 21 that expose the substrate 10, and each mask opening 21 corresponds to defining the epitaxial region of a micro display unit 30, thereby realizing the selective epitaxy of the micro display unit 30 on the substrate 10. As the size of devices decreases, the sidewall damage caused by the pixel etching scheme in the related art will seriously reduce the luminous efficiency of the micro display unit 30. The embodiment of the present invention utilizes the conditions that the nucleation energy of the mask dimming layer 20 is much greater than the nucleation energy of the surface of the substrate 10, the material of the mask dimming layer 20 is amorphous material, and the epitaxial material has a preferential orientation, so that the epitaxial material of the micro display unit 30 grows epitaxially in the opening area of ​​the mask dimming layer 20. This bottom-up epitaxial process can avoid the introduction of pixel etching, thereby fundamentally improving the light extraction efficiency of the micro display unit 30.

[0067] Each micro display unit 30 includes at least two light-emitting units 31 that are sequentially away from the substrate 10 and an isolation layer 32 between two adjacent light-emitting units 31. The light-emitting unit 31 can be a Micro-LED, that is, in the process of selective epitaxial growth of the mask-based dimming layer 20, at least two stacked Micro-LEDs are formed from bottom to top. Figure 3 is a schematic cross-sectional structure diagram of a light emitting unit provided in an embodiment of the present invention, with reference to Figure 3, each light-emitting unit 31 may include a first semiconductor layer 31a, a quantum well layer 31q, and a second semiconductor layer 31c stacked in sequence 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 side of the first semiconductor layer 31a away from the quantum well layer 31q also includes a buffer layer, and the buffer layer is configured to reduce the lattice mismatch and thermal mismatch between the substrate 10 and the layer to be formed on the buffer layer (the first semiconductor layer 31a), thereby reducing defects caused by mismatch / difference. In the same micro-display unit 30, at least two light-emitting units 31 have different light-emitting colors, and an isolation layer 32 is arranged between two adjacent light-emitting units 31. The isolation layer 32 can prevent current crosstalk between two adjacent light-emitting units 31, which is conducive to independent control of the drive of each light-emitting unit 31, meets the conditions for stacking two-color or more light-emitting units 31, and enables two-color or more selected area extension to be realized.

[0068] The material of the mask dimming layer 20 is light-transmissive, so that the light emitted from the side wall of the light-emitting unit 31 to the mask dimming layer 20 can be adjusted by the mask dimming layer 20 to change the propagation direction of the light and then be emitted from the mask dimming layer 20. The material of the mask dimming layer 20 includes but is not limited to at least one of SiO2, SiN and Ta2O5. The mask dimming layer 20 located between adjacent micro-display units 30 is used as a light-gathering structure (a light-transmissive layer with a curved surface) to convert the lateral light of the micro-display unit 30 into vertical light, thereby realizing the extraction of the lateral light of the micro-display unit 30, effectively improving the light extraction efficiency of the micro-display unit 30, and then significantly improving the comprehensive luminous performance of the micro-display unit 30. The lateral light is the light emitted from the side wall of the micro-display unit 30.

[0069] The micro-display epitaxial structure provided by the embodiment of the present invention realizes the selective preparation of the micro-display unit 30 by setting a patterned mask dimming layer 20 on one side of the substrate 10 based on the restriction of the epitaxial growth area by the mask dimming layer 20; and an isolation layer 32 is set between the light-emitting units 31 of two adjacent layers of the micro-display unit 30, which can prevent current crosstalk between the two adjacent light-emitting units 31, and is conducive to realizing independent control of the drive of each light-emitting unit 31, thereby realizing the selective epitaxy of the micro-display unit 30 of two colors or more; in addition, the mask dimming layer 20 is also used to adjust the propagation direction of the light emitted from the light-emitting unit 31 to the mask dimming layer 20, and reduce the angle between the propagation direction of the light emitted from the side wall of the light-emitting unit 31 and the direction perpendicular to the substrate 10, thereby realizing the extraction of lateral light of the micro-display unit 30 and improving the light extraction efficiency of the micro-display unit 30.

[0070] Based on the above embodiments, optionally, refer to Figure 1 , when the mask dimming layer 20 is used to define the epitaxial region of the micro display unit 30 and when the mask dimming layer 20 is used to adjust the propagation direction of the light emitted from the light emitting unit 31 to the mask dimming layer 20, the side wall 211 of the mask opening is curved, and the curved surface is convex toward the adjacent micro display unit 30. It can be understood that before defining the epitaxial region of the micro display unit 30, the side wall 211 of the mask opening 21 of the mask dimming layer 20 is curved, so that the surface of the mask dimming layer 20 is curved. Or,

[0071] Figure 4 is a schematic diagram of a cross-sectional structure after epitaxial growth of a micro-display unit in a selective area on one side of a substrate in a method for preparing a micro-display epitaxial structure provided by an embodiment of the present invention, with reference to Figure 4 , when the mask dimming layer 20 is used to define the epitaxial region of the micro display unit 30, the sidewall 211 of the mask opening is planar; Figure 1 When the mask dimming layer 20 is used to adjust the propagation direction of light emitted from the light emitting unit 31 to the mask dimming layer 20 , the sidewall 211 of the mask opening is curved, and the curved surface is convex toward the adjacent micro display unit 30 .

[0072] Specifically, when the mask dimming layer 20 is used as a mask layer, the sidewall 211 of the mask opening 21 is planar, which facilitates the epitaxial growth of the micro display unit 30 in the mask opening 21, and is beneficial to improving the epitaxial growth quality of the micro display unit 30. After completing the function of defining the epitaxial region of the micro display unit 30, the sidewall 211 of the mask opening 21 of the mask dimming layer 20 is curved, so that the surface of the mask dimming layer 20 facing the micro display unit 30 is curved, and the curved surface is convex toward the direction of the adjacent micro display unit 30, so that the mask dimming layer 20 between two adjacent micro display units 30 is adjusted to a light-gathering structure (a light-transmitting layer with a curved surface), so that the lateral light output of the micro display unit 30 becomes vertical light output, and the lateral light extraction is realized. The step of curving the sidewall 211 of the mask opening 21 of the mask dimming layer 20 includes wet and / or dry etching the mask layer, wherein the etching solution used in the wet etching process may 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 may be a plasma etching process.

[0073] Based on the above embodiments, Figure 1Optionally, an absolute value of a height difference d between a surface of the mask dimming layer 20 away from the substrate 10 and a 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 dimming 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. Among them, the distance from the surface of the mask dimming 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 dimming 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 dimming 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] In the case where the distance between the surface of the mask dimming layer 20 away from the substrate 10 and the substrate 10 is greater than the distance between the surface of the micro display unit 30 away from the substrate 10 and the substrate 10 (refer to Figure 1 ), the mask dimming layer 20 can expand the adjustment range of the light emitted from the side wall of the micro display unit 30, which is conducive to adjusting the propagation direction of the light emitted from the entire side wall of the micro display unit 30, thereby further improving the light extraction efficiency of the lateral light of the micro display unit 30.

[0076] When the distance from the surface of the mask dimming layer 20 away from the substrate 10 to the substrate 10 is smaller 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 extend from the mask opening 21 of the mask dimming layer 20, thereby facilitating the electrical connection between the micro display unit 30 and the driving electrode on the driving substrate during the process of bonding the micro display epitaxial structure to the driving substrate, thereby reducing the difficulty of preparing the micro display device.

[0077] When the distance from the surface of the mask dimming 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 from the side wall of the micro display unit 30 can be expanded while reducing the difficulty of electrically connecting the micro display unit 30 to the driving electrode on the driving substrate.

[0078] In addition, the absolute value of the height difference d between the surface of the mask dimming layer 20 away from the substrate 10 and the surface of the micro display unit 30 away from the substrate 10 is set to be less than or equal to 10 μm, which can prevent the absolute value of the height difference d between the surface of the mask dimming 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, thereby affecting the adjustment range of the light emitted from the side wall 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 dimming 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, so as to ensure the adjustment range of the light emitted from the side wall of the micro display unit 30 and reduce the difficulty of electrical connection between the micro display unit 30 and the driving electrode on the driving substrate.

[0079] Based on the above embodiments, optionally, the refractive index of the mask dimming layer 20 between two adjacent micro display units 30 is uniformly set; or, the refractive index of the mask dimming layer 20 between two adjacent micro display units 30 is gradually set in a direction parallel to the substrate 10.

[0080] Specifically, the mask dimming layer 20 between two adjacent 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 dimming layer 20 between two adjacent micro display units 30 can be a light-transmitting layer with a single refractive index, or a light-transmitting layer with a gradient refractive index. Figure 5 This is a simulation diagram of the focusing effect of a mask dimming layer with a uniform refractive index on light emitted from the side wall of a light-emitting unit provided by an embodiment of the present invention. Figure 6 This is a simulation diagram of the focusing effect of a mask dimming layer with a gradient refractive index on the light emitted from the side wall of the light-emitting unit provided by an embodiment of the present invention, with reference to Figure 5 and Figure 6 The light-transmitting layer with a high refractive index can bend lateral light (light propagating in a direction parallel to the substrate 10 ), thereby achieving a focusing effect and emitting the light in a direction perpendicular to the substrate 10 or a direction close to perpendicular to the substrate 10 .

[0081] contrast Figure 5 and Figure 6 When the refractive index of the mask dimming layer 20 between the micro display units 30 is set to gradually change in the direction parallel to the substrate 10, the propagation direction 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 side wall of the micro display unit 30 to be emitted in the direction perpendicular to the substrate 10, so as to further improve the light extraction efficiency of the lateral light output of the micro display unit 30.

[0082] It should be noted that, in the case where the mask dimming layer 20 located between two adjacent micro-display units 30 is a light-transmitting layer with a gradient refractive index, the gradient change mode of the refractive index of the mask dimming layer 20 is different from that of the adjacent micro-display units 30 on both sides of the mask dimming layer 20. For example, among the two adjacent micro-display units 30, one micro-display unit 30 is a first micro-display unit and the other micro-display unit 30 is a second micro-display unit. If the gradient change mode of the refractive index of the mask dimming layer 20 located between the first micro-display unit and the second micro-display unit is that the refractive index of the mask dimming layer 20 gradually increases in the direction from the first micro-display unit to the second micro-display unit, then the refractive index of the mask dimming layer 20 gradually decreases in the direction from the second micro-display unit to the first micro-display unit, so that the light incident on the mask dimming layer from the first micro-display unit after adjusting the propagation direction is different from the light incident on the mask dimming layer 20 from the second micro-display unit after adjusting the propagation direction, or even opposite. That is, after the mask dimming layer 20 adjusts the light emitted from the side wall of the first micro display unit 30 and the propagation direction of the light emitted from the side wall of the first micro display unit 30, the light emitted from the side wall of one micro display unit 30 propagates in a direction away from the substrate 10, and the light emitted from the side wall of the other micro display unit 30 propagates in a direction close to the substrate 10. Therefore, a reflective layer can be provided on the side of the mask dimming layer 20 close to the substrate or the side away from the substrate, so as to reflect the light along the target light emitting direction away from the micro display unit 30 into the target light emitting direction. The reflective layer can be a reflective layer of a metal material, or a DBR reflective layer.

[0083] Furthermore, the reflective layer may also extend to one side of the micro display unit 30, that is, the vertical projection of the reflective layer on the substrate 10 at least partially overlaps with the vertical projection of the micro display unit 30 on the substrate 10, and at least partially overlaps with the vertical projection of the mask dimming layer 20 on the substrate 10. Thus, the light extraction efficiency of the micro display unit 30 can be improved in the longitudinal direction, and the light extraction efficiency of the micro display unit 30 is further improved.

[0084] Optionally, when the refractive index of the mask dimming layer 20 between two adjacent micro display units 30 is uniformly set, a reflective layer may also be provided on a side of the mask dimming layer 20 close to or far from the substrate and extended to one side of the micro display unit 30 .

[0085] Based on 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 invention, with reference to Figure 7 Combined with Figure 3 Optionally, the isolation layer 32 includes a tunnel junction 32a, a third semiconductor layer 32b and a fourth semiconductor layer 32c which are sequentially away from the substrate 10;

[0086] Among them, the tunnel junction 32a contacts 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 the current injection into the second semiconductor layer 31c and the 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 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 lightly 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. To achieve vertical growth of multiple light-emitting units 31 and to achieve individual drive control, it is required that each light-emitting unit 31 can achieve good insulation isolation, and at the same time, good ohmic contact of the second semiconductor layer 31c (for example, a P-GaN layer) in the light-emitting unit 31 must be achieved. Due to the high resistance characteristics of the p-GaN layer, it will result in poor conductivity and high light absorption. In some embodiments, indium tin oxide (ITO) or some other transparent conductive oxides (such as zinc oxide) can be used to disperse the current to the light-emitting unit 31. Based on the practical, simple and efficient epitaxial means, the embodiment of the present invention sets a tunnel junction 32a in contact with the second semiconductor layer 31c in the isolation layer 32, and the tunnel junction 32a includes a stacked P-type heavily doped semiconductor layer and an N-type heavily doped semiconductor layer. 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 lightly 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 holes to be injected 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 transparent contacts such as Ni / Au metal contacts or transparent indium tin oxide (ITO), the tunnel junction 32a can also reduce light absorption and reduce light loss.

[0088] The conductivity type of the third semiconductor layer 32b is the same as that of the first semiconductor layer 31a, the conductivity type of the fourth semiconductor layer 32c is the same as that of the second semiconductor layer 31c, and both the third semiconductor layer 32b and the fourth semiconductor layer 32c are lightly doped film layers. 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 form a reverse bias, thereby isolating the current and preventing electrical crosstalk between the light-emitting units 31 located on the upper and lower sides of the isolation layer 32. In addition, the electrode layer that inputs current to the second semiconductor layer 31c can contact the surface of the third semiconductor layer 32b, because the material (N-GaN) of the third semiconductor layer 32b has a lower resistivity than the material (P-GaN) of the second semiconductor layer 31c, and it is easier to form a good ohmic contact.

[0089] Furthermore, with respect to insulation control, the isolation layer 32 may also include an insulating layer located 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 GaN layer doped with the C element, so as to further improve the electrical insulation of the isolation layer 32.

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

[0091] Based on the above embodiments, Fig. 9 is a schematic cross-sectional view of another micro-display epitaxial structure provided by an embodiment of the present invention, with reference to Fig. 9Optionally, the micro display unit 30 includes three light emitting units 31 which are sequentially away from the substrate 10, namely, 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; a first isolation layer 321 is provided between the first light emitting unit 311 and the second light emitting unit 312, and a second isolation layer 322 is provided between the second light emitting unit 312 and the third light emitting unit 313. 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 wavelength of the light emitting unit 31 is set to gradually increase along the direction of epitaxial growth (the direction away from the substrate 10), 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 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 32c in the first isolation layer 321 away from the substrate 10; the second step surface is formed by a portion of the surface of the fourth semiconductor layer 32c in the second isolation layer 322 away from the substrate 10; metal layers of the same material are arranged on the first step surface and the second step surface, so that the metal layers on the first step surface and the second step surface can be prepared at the same time.

[0093] Furthermore, in each micro display unit 30, an isolation layer 32 is provided on the side of the light emitting unit 31 located farthest from the substrate 10 away from the substrate 10, and the side wall of the isolation layer 32 also has a step surface for supporting the metal layer. Fig.10 is a schematic cross-sectional structure diagram of a micro display unit having a side wall with a stepped surface provided by an embodiment of the present invention, with reference to Fig.10 , and combined with Figure 8Each micro display unit 30 includes three light emitting units 31, namely, a first light emitting unit 311, a second light emitting unit 312 and a third light emitting unit 313. A third isolation layer 323 may be provided on a side of the third light emitting unit 313 away from the substrate 10. The sidewall of each micro display unit 30 may have six step surfaces, namely, a first step surface t1 exposing the fourth semiconductor layer 32c in the first isolation layer 321, a second step surface t2 exposing the fourth semiconductor layer 32c in the second isolation layer 322, a third step surface t3 exposing the fourth semiconductor layer 32c in the third isolation layer 323, a fourth step surface t4 exposing the first semiconductor layer 31a of the first light emitting unit 311, a fifth step surface t5 exposing the first semiconductor layer 31a of the second light emitting unit 312, and a sixth step 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 drive substrate is disposed on the first step surface t1 to the sixth step surface t6, and the materials of the metal layers on the first step surface t1 to the sixth step surface t6 can be the same, so that the metal layers on the first step surface t1 to the sixth step surface t6 can be prepared simultaneously.

[0094] The embodiment of the present invention further provides a method for preparing a micro-display epitaxial structure, which is used to prepare the micro-display epitaxial structure described in any embodiment of the present invention. Fig.11 is a flow chart of a method for preparing a micro display epitaxial structure provided by an embodiment of the present invention, with reference to Fig.11 , the preparation method of the micro display epitaxial structure includes:

[0095] S10. Provide a substrate.

[0096] For details, refer to Fig.12 The substrate 10 may be a silicon substrate, a sapphire substrate, a silicon carbide substrate or the like, which is suitable for epitaxially preparing a micro display unit.

[0097] S20, 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.

[0098] Specifically, refer to Fig.13 A mask dimming layer 20 is formed on one side of the substrate 10. The material of the mask dimming layer 20 includes but is not limited to at least one of SiO2, SiN and Ta2O5. Fig.14 The mask light-adjusting layer 20 may be patterned through a photolithography process, thereby forming a plurality of mask openings 21 exposing the substrate 10 in the mask light-adjusting layer 20 .

[0099] S30, based on the limitation of the epitaxial area by the mask opening in the mask dimming layer, a plurality of micro display units are formed; wherein each micro display unit is correspondingly located in a mask opening, and the micro display unit includes at least two light emitting units which are sequentially away from the substrate and an isolation layer located between two adjacent light emitting units.

[0100] Specifically, refer to Fig.15 By utilizing the conditions that the nucleation energy of the mask dimming layer 20 is much greater than the nucleation energy of the substrate 10 surface, the material of the mask dimming layer 20 is amorphous material, and the epitaxial material has a preferential orientation, the epitaxial material of the micro display unit 30 is epitaxially grown in the opening area of ​​the mask dimming layer 20. This bottom-up epitaxial process can completely avoid the introduction of pixel etching, thereby fundamentally improving the light output efficiency of the micro display unit 30.

[0101] S40, performing curved surface processing on the sidewalls of the mask openings in the mask dimming layer so that the mask dimming layer can also be used to adjust the propagation direction of the light emitted from the light emitting unit to the mask dimming layer, and reduce the angle between the light emitted from the sidewalls of the light emitting unit and the direction perpendicular to the substrate.

[0102] Specifically, refer to Fig.16 The side walls of the mask opening 21 in the mask dimming layer 20 are curved, including wet etching and / or dry etching the mask dimming layer 20, so that the mask dimming layer 20 located between two adjacent micro display units 30 is deformed into a focusing structure with a curved surface, thereby converting the lateral light output of the micro display unit 30 into vertical light output, thereby realizing light extraction of the lateral light output.

[0103] The method for preparing a micro-display epitaxial structure provided in an embodiment of the present invention forms a patterned mask dimming layer 20 on one side of a substrate 10, and based on the restriction of the epitaxial growth area by the patterned mask dimming layer 20, the selective preparation of the micro-display unit 30 is achieved, and the preparation process is simple; and an isolation layer 32 is formed between the light-emitting units 31 of two adjacent layers of the micro-display unit 30, which can prevent current crosstalk between two adjacent light-emitting units 31, and is conducive to achieving independent control of the drive of each light-emitting unit 31, thereby achieving selective epitaxy of two-color and above micro-display units 30, replacing complex mass transfer and vertical stacking schemes, reducing the preparation cost of the micro-display device, and effectively avoiding sidewall damage caused by pixel etching, thereby improving the reliability of the micro-display device. In addition, after forming a plurality of micro-display units 30, the side walls of the mask openings 21 in the mask dimming layer 20 are curved to deform the mask dimming layer 20 into a light-focusing structure, which can adjust the propagation direction of light emitted from the light-emitting unit 31 to the mask dimming layer 20, and reduce the angle between the light emitted from the side wall of the light-emitting unit 31 and the direction perpendicular to the substrate 10, thereby realizing the extraction of the lateral light output 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 curving process on the sidewalls of the mask openings in the mask dimming 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 dimming layer.

[0105] Optional, reference Figure 3 , forming a light emitting unit 31 in the micro display unit 30, including: forming a first semiconductor layer 31a, a quantum well layer 31q and a second semiconductor layer 31c on one side of the substrate 10 and being 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 and 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 the current injection into the second semiconductor layer 31c and the 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 ranging from 0.2μm to 10μm; the spacing range of the mask openings 21 is 0.4μm to 20μm.

[0109] for Fig. 9In the structure shown in FIG. 1 , in step S30, based on the limitation of the epitaxial region by the mask opening in the mask dimming layer, forming the micro display unit specifically includes:

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

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

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

[0113] The second isolation layer 322 is epitaxially grown above the second light emitting unit 312 . The second isolation layer 322 is formed in the same manner as the first isolation layer 321 , which will not be described in detail herein.

[0114] The epitaxial growth of the third light-emitting unit 313 is performed on the second isolation layer 322 by using the MOCVD process. Specifically, the first semiconductor layer 31a, the quantum well layer 31q and the second semiconductor layer 31c in the third light-emitting unit 313 are formed in sequence. The thickness of the first semiconductor layer 31a (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, and the In doping concentration is 22% to 35%; the thickness of the second semiconductor layer 31c (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] The specific steps of curving the sidewalls of the mask opening in the mask dimming layer in step S40 include: wet etching the mask dimming layer 20, which can be performed by immersing the mask dimming layer 20 for 1h to 3h in a temperature range of 50°C to 85°C with SC1 solution; the SC1 solution can be obtained by mixing a mixture of ammonium hydroxide, hydrogen peroxide, and water in a volume ratio of 1:5:40. Alternatively, the wet etching can be performed by immersing the mask dimming layer 20 for 40min to 120min in a temperature range of 50°C to 85°C with HF / EG solution; the HF / EG solution is obtained by mixing 49% hydrofluoric acid and ethylene glycol in a ratio of about 4:96. After etching, the mask dimming layer 20 is deformed into a focusing structure, thereby realizing the light extraction of lateral light.

[0117] The present invention also provides a method for preparing a micro display device, comprising:

[0118] Providing a drive substrate;

[0119] The micro display epitaxial structure described in any embodiment of the present invention is bonded to the surface of the driving substrate 100, and the substrate 10 (refer to Fig.17 and Fig.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 used. 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 more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and 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, 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 comprises at least two light emitting units which are sequentially away from the substrate and an isolation layer located between two adjacent light emitting units; The mask dimming layer is used to define the epitaxial area of ​​the micro display unit and to adjust the propagation direction of the light emitted from the light emitting unit to the mask dimming layer, so as to reduce the angle between the propagation direction of the light emitted from the side wall of the light emitting unit and the direction perpendicular to the substrate.

2. The micro display epitaxial structure according to claim 1, characterized in that: When the mask dimming layer is used to define the epitaxial region 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 region of the micro-display unit and when the mask dimming layer is used to adjust the propagation direction of the 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 SiO2, SiN and Ta2O5.

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, characterized in that: Each of the light-emitting units comprises a first semiconductor layer, a quantum well layer, and a second semiconductor layer which are sequentially away from the substrate; The isolation layer includes a tunnel junction, a third semiconductor layer and a fourth semiconductor layer which are 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; the third semiconductor layer and the fourth semiconductor layer are used to form a reverse bias to electrically isolate two adjacent light-emitting units.

5. The micro display epitaxial structure according to claim 4, characterized in that: The isolation layer further comprises 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 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 away from the substrate; and metal layers of the same material are arranged 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 limitation of the epitaxial region by the mask opening 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 comprises at least two light-emitting units which are sequentially away from the substrate and an isolation layer located between 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 the light emitted from the light-emitting unit to the mask dimming layer, thereby reducing the angle between the light emitted from the side walls of the light-emitting unit and the direction perpendicular to the substrate.

8. The method for preparing a micro display epitaxial structure according to claim 7, characterized in that: 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 in sequence 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 micro display epitaxial structure according to claim 8, characterized in that: An isolation layer is formed between two adjacent light-emitting units, and 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: Providing 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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