Micro light emitting diode and preparation method thereof, and light emitting device

Abstract

This application discloses a micro-LED, a method for manufacturing the same, and a light-emitting device. The micro-LED comprises a semiconductor stack consisting of a first semiconductor layer, an active layer, and a second semiconductor layer. A window layer is provided on the surface of the second semiconductor layer facing away from the active layer. The window layer comprises an aluminum gallium arsenide layer and a passivation layer having a predetermined thickness formed by oxidizing the outer surface of the aluminum gallium arsenide layer's sidewalls inward. The present application oxidizes the sidewalls of the window layer to form a passivation layer. This passivation layer prevents injected current from flowing through the window layer and the sidewalls of the semiconductor stack, thereby preventing non-radiative recombination caused by defects in the sidewalls of the window layer and the semiconductor stack, and improving the luminous efficiency of the micro-LED.

Description

Technical Field

[0001] The present application relates to the field of semiconductor-related technologies, and in particular to a micro light-emitting diode, a preparation method thereof, and a light-emitting device. Background Art

[0002] Micro light emitting diodes (Micro LEDs) are a new generation of display technology with the advantages of small size, light weight, high brightness, long life, low power consumption, fast response time, and strong controllability. In the preparation process of micro light emitting diodes, dry etching is required to remove part of the semiconductor stacking layer and the window layer formed on part of the semiconductor stacking layer to form a mesa structure. During dry etching, defects will be formed on the sidewalls of the mesa structure. These sidewall defects will act as charge carrier traps and increase the possibility of leakage current and non-radiative recombination, thereby reducing the luminous efficiency of the micro light emitting diode. The light emitting area of ​​a micro light emitting diode is generally less than 50×50μm 2 , which has a high sidewall perimeter / luminous area ratio. The larger the sidewall perimeter / luminous area ratio, the more serious the non-radiative recombination phenomenon caused by sidewall defects, and seriously affects the luminous efficiency of the microdiode.

[0003] Therefore, how to provide a micro light emitting diode to reduce the non-radiative recombination phenomenon caused by sidewall defects and improve the luminous efficiency of the micro light emitting diode has become an urgent problem to be solved in this field. Summary of the Invention

[0004] The purpose of the present application is to provide a micro light-emitting diode, which oxidizes the side walls of the window layer into a passivation layer to ensure that the injected current does not flow through the side walls of the window layer and the semiconductor stack layer, thereby avoiding the non-radiative recombination phenomenon caused by side wall defects and improving the luminous efficiency of the micro light-emitting diode.

[0005] Another object is to provide a method for preparing a micro light emitting diode and a light emitting device.

[0006] In a first aspect, an embodiment of the present application provides a micro-light emitting diode, comprising a semiconductor stack layer, the semiconductor stack layer comprising a first semiconductor layer, a second semiconductor layer, and an active layer located therebetween, wherein a window layer is provided on a surface of the second semiconductor layer away from the active layer;

[0007] The window layer includes an aluminum gallium arsenide layer and a passivation layer with a preset thickness oxidized inwardly from the outer surface of the sidewall of the aluminum gallium arsenide layer.

[0008] In one possible embodiment, the surface of the window layer close to the second semiconductor layer is defined as surface A, and the thickness D of the passivation layer at surface A is A1 Between 1 and 4 μm.

[0009] In one possible embodiment, the window layer comprises Al x Ga 1-x As, in the height direction of the semiconductor stack layer, x is a constant value, and the value of x is between 0.45 and 1, and the thickness D1 of the passivation layer is a constant value.

[0010] In one possible embodiment, the window layer comprises Al y Ga 1-y As, in the height direction of the semiconductor stack layer, y is a gradient value, and the value of y is between 0.45 and 1, and the thickness D1 of the passivation layer is gradient.

[0011] In a possible embodiment, the surface of the window layer close to the second semiconductor layer is defined as surface A, and the surface of the window layer away from the second semiconductor layer is defined as surface B. The value of y decreases from surface A to surface B, and the thickness D1 of the passivation layer decreases from surface A to surface B.

[0012] In a possible embodiment, the surface of the window layer close to the second semiconductor layer is defined as surface A, and the surface of the window layer away from the second semiconductor layer is defined as surface B. The value of y increases from surface A to surface B, and the thickness D1 of the passivation layer increases from surface A to surface B.

[0013] In one possible embodiment, the window layer includes a periodic structure formed by alternating first and second stacks, and in each period the first stack is located on the side of the window layer close to the second semiconductor layer; in the height direction of the semiconductor stack layer, the aluminum content in the window layer gradually changes, and the thickness D1 of the passivation layer gradually changes.

[0014] In one possible embodiment, the thickness D1 of the passivation layer is between 0.1 μm and 4 μm.

[0015] In one possible embodiment, in each cycle, the aluminum content in the first stack is greater than the aluminum content in the second stack.

[0016] In one possible embodiment, the surface of the window layer close to the second semiconductor layer is defined as surface A, and the surface of the window layer away from the second semiconductor layer is defined as surface B. The aluminum content of the window layer at surface A is greater than the aluminum content of the window layer at surface B. The thickness D of the passivation layer at surface A is A1 Greater than the thickness D of the passivation layer on surface B B1 .

[0017] In one possible embodiment, the first stack includes Al m1 Ga 1-m1 As, the value of m1 ranges from 0.45 to 1. As the number of window layer periods increases, m1 in the first stack decreases, and the thickness D1 of the passivation layer at the sidewall of the first stack decreases.

[0018] In a possible embodiment, the value of m1 on the A surface is between 0.90 and 1, and the thickness D of the passivation layer on the A surface is A1 Between 1 and 4 μm.

[0019] In one possible embodiment, the second stack includes Al m2 Ga 1-m2 As, the value of m2 ranges from 0.45 to 0.6; as the number of window layer periods increases, m2 in the second stack remains unchanged or decreases, and the thickness D1 of the passivation layer at the sidewall of the second stack remains unchanged or decreases.

[0020] In a possible embodiment, the number of periods of the window layer is 3 to 20, and the total height of the first stacked layer and the second stacked layer in each period is between 0.1 and 0.2 μm.

[0021] In one possible embodiment, within each period, the refractive index of the first stack is different from that of the second stack; the refractive index of the first stack is between 3.18 and 3.22, and the refractive index of the second stack is between 3.37 and 3.42.

[0022] In one possible embodiment, the micro-LED further includes a reflective layer that covers the window layer, the area on the upper surface of the semiconductor stack layer except the window layer, and the sidewalls of the semiconductor stack layer; the reflective layer includes a metal reflector or a distributed Bragg reflector.

[0023] In a second aspect, an embodiment of the present application provides a method for preparing a micro light emitting diode, which includes:

[0024] forming a semiconductor stack layer, the semiconductor stack layer comprising a first semiconductor layer, a second semiconductor layer and an active layer located therebetween;

[0025] forming a window layer on a surface of the second semiconductor layer away from the active layer, wherein the window layer comprises an aluminum gallium arsenide layer;

[0026] etching the window layer and the semiconductor stack layer to form a mesa structure;

[0027] The sidewalls of the window layer are oxidized, and a passivation layer is formed on the sidewalls of the window layer and extends inward from an outer surface of the sidewalls to a preset thickness.

[0028] In a third aspect, an embodiment of the present application provides a light-emitting device, which includes a substrate and a plurality of micro-light-emitting diodes according to the above embodiment fixed on the substrate.

[0029] Compared with the prior art, this application has at least the following beneficial effects:

[0030] 1) The sidewalls of the window layer are oxidized into a passivation layer, which can ensure that the injected current does not flow through the sidewalls of the window layer. Under the limiting effect of the passivation layer, when the current flows from the window layer into the semiconductor stack layer, the current flows to the middle area of ​​the semiconductor stack layer, thereby preventing the current from flowing through the sidewalls of the semiconductor stack layer, thereby avoiding the non-radiative recombination phenomenon caused by defects in the sidewalls of the window layer and the semiconductor stack layer, and improving the luminous efficiency of the micro light-emitting diode.

[0031] 2) The thickness of the passivation layer is gradual, and the thickness D of the passivation layer at surface A is A1 Greater than the thickness D of the passivation layer at surface B B1 , further enhancing the ability of current to flow to the middle region of the semiconductor stack layer, so as to avoid non-radiative recombination caused by sidewall defects of the window layer and the semiconductor stack layer.

[0032] 3) The window layer is a periodic structure formed by alternating layers of two different refractive indices. The window layer has a good reflective effect. It can directly reflect the light emitted by the active layer and reduce the propagation distance of the above light before reflection, increase the normal light output, and reduce the light-emitting angle of the micro light-emitting diode. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0034] Figure 1 is a schematic cross-sectional view of a micro light emitting diode according to an embodiment of the present application;

[0035] Figure 2 is a schematic cross-sectional view of a window layer according to an embodiment of the present application;

[0036] Figure 3 is a schematic cross-sectional view of a window layer according to an embodiment of the present application;

[0037] Figure 4 is a schematic cross-sectional view of a window layer according to an embodiment of the present application;

[0038] Figure 5 is a schematic cross-sectional view of a micro light emitting diode according to an embodiment of the present application;

[0039] Figure 6 is a schematic cross-sectional view of a window layer according to an embodiment of the present application;

[0040] Figure 7 is a schematic cross-sectional view of a micro light emitting diode according to an embodiment of the present application;

[0041] Figure 8 is a schematic cross-sectional view of a micro light emitting diode according to an embodiment of the present application;

[0042] Figure 9 is a schematic cross-sectional view of a micro light emitting diode according to an embodiment of the present application;

[0043] Figure 10 is a schematic cross-sectional view of a micro light emitting diode according to an embodiment of the present application;

[0044] Figures 11 to 16 Schematic cross-sectional views of a micro light-emitting diode at different preparation stages according to an embodiment of the present application.

[0045] Illustration:

[0046] 100 substrate; 200 semiconductor stack layer; 210 first semiconductor layer; 220 active layer; 230 second semiconductor layer; 300 window layer; 310 first stack layer; 320 second stack layer; 400 groove; 500 passivation layer; 600 reflective layer; 700 first electrode; 710 second electrode; 800 first pad; 810 second pad; 900 substrate; 910 bonding layer. DETAILED DESCRIPTION

[0047] The following describes the implementation of the present application through specific embodiments. Those skilled in the art will readily understand the other advantages and benefits of the present application from the disclosure herein. The present application may also be implemented or operated through various other specific implementations, and the details of the present application may be modified or altered based on different viewpoints and applications without departing from the spirit of the present application.

[0048] In the description of this application, it should be noted that the terms "upper", "lower", "inner" and "outer" indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or the orientations or positional relationships in which the product of the application is usually placed when in use. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they should not be understood as limitations on this application.

[0049] According to one aspect of the present application, a micro light emitting diode is provided. Figure 1 and Figure 7 The flip-chip structure light emitting diode shown or Figure 8 The vertical structure light emitting diode shown.

[0050] See also Figure 1 、 Figure 7 and Figure 8 The micro-LED includes a semiconductor stack 200, which includes a first semiconductor layer 210, an active layer 220, and a second semiconductor layer 230 arranged in sequence. The surface of the first semiconductor layer 210 away from the active layer 220 is preferably provided with a recessed rough surface. In this embodiment, the first semiconductor layer 210 is an N-type semiconductor layer, the second semiconductor layer 230 is a P-type semiconductor layer, and the active layer 220 is a multi-layer quantum well layer capable of providing blue, green, red, or infrared light. The first semiconductor layer 210, the active layer 220, and the second semiconductor layer 230 are all AlInGaP.

[0051] A window layer 300 with excellent current spreading performance is provided on the surface of the second semiconductor layer 230 facing away from the active layer 220. The window layer 300 includes an aluminum gallium arsenide layer and a passivation layer 500 formed by oxidizing the outer surface of the aluminum gallium arsenide layer's sidewalls inward to a predetermined thickness. The projection of the unpassivated portion of the aluminum gallium arsenide layer falls within the projection of the second semiconductor layer 230 along a predetermined projection direction, which corresponds to the height of the semiconductor stack 200.

[0052] The sidewalls of the window layer 300 are oxidized to form a passivation layer 500. This passivation layer 500 ensures that the injected current flows only through the unpassivated regions of the window layer 300 and not through the sidewalls of the window layer 300, thereby preventing non-radiative recombination caused by sidewall defects in the window layer 300. Under the restrictive effect of the passivation layer 500, when current flows from the window layer 300 into the semiconductor stack layer 200, because the width of the unpassivated region of the window layer 300 is smaller than that of the semiconductor stack layer 200, the window layer 300 flows toward the central region of the semiconductor stack layer 200, preventing the current from flowing through the sidewalls of the semiconductor stack layer 200. This, in turn, avoids non-radiative recombination caused by sidewall defects in the semiconductor stack layer 200, thereby improving the luminous efficiency of the micro-LED.

[0053] In one embodiment, see Figure 2 In the height direction of the semiconductor stacked layer 200 , the aluminum content in the window layer 300 remains unchanged, and the thickness D1 of the passivation layer 500 remains unchanged.

[0054] Specifically, the window layer 300 includes Al x Ga 1-xAs, x is a constant value in the height direction of the semiconductor stack 200, and the value of x ranges from 0.45 to 1. The passivation layer 500 is formed by an in-situ water vapor oxidation process. The passivation layer 500 is an aluminum oxide layer. The thickness D1 of the passivation layer 500 is related to oxidation parameters such as oxidation temperature, oxidation time, and water vapor content. In the height direction of the semiconductor stack 200, since the aluminum content in the window layer 300 is a constant value, the thickness D1 of the passivation layer 500 is also a constant value. The thickness D1 of the passivation layer 500 is preferably between 1 and 4 μm.

[0055] In one embodiment, see Figure 3 In the height direction of the semiconductor stacked layer 200 , the aluminum content in the window layer 300 changes gradually, and the thickness D1 of the passivation layer 500 changes gradually.

[0056] Specifically, the window layer 300 includes Al y Ga 1-y As, y is a gradient value along the height direction of the semiconductor stack 200, and the value of y ranges from 0.45 to 1. The passivation layer 500 is formed by an in-situ water vapor oxidation process. The passivation layer 500 is an aluminum oxide layer. The thickness D1 of the passivation layer 500 is related to oxidation parameters such as oxidation temperature, oxidation time, and water vapor content. Along the height direction of the semiconductor stack 200, due to the gradual change in the aluminum content in the window layer 300, the thickness D1 of the passivation layer 500 gradually changes. The thickness D1 of the passivation layer 500 is preferably between 0.1 and 4 μm.

[0057] For example, see Figure 3 The surface of the window layer 300 close to the second semiconductor layer 230 is defined as surface A, and the surface of the window layer 300 away from the second semiconductor layer 230 is defined as surface B. The value of y decreases from surface A to surface B, and the thickness D1 of the passivation layer 500 decreases from surface A to surface B. The thickness D1 of the passivation layer 500 at surface A is A1 Greater than the thickness D of the passivation layer 500 at the B surface B1 , further enhancing the ability of current to flow to the middle region of the semiconductor stack layer 200, thereby avoiding the non-radiative recombination phenomenon caused by the sidewall defects of the window layer 300 and the semiconductor stack layer 200. In this embodiment, the thickness D of the passivation layer 500 at the A surface is A1 Between 1 and 4 μm.

[0058] As an example, the surface of the window layer 300 close to the second semiconductor layer 230 is defined as surface A, and the surface of the window layer 300 away from the second semiconductor layer 230 is defined as surface B. The value of y increases from surface A to surface B, and the thickness D1 of the passivation layer 500 increases from surface A to surface B. In this embodiment, the thickness D1 of the passivation layer 500 at surface A is A1 Between 1 and 4 μm.

[0059] In one embodiment, see Figure 4 The window layer 300 includes a periodic structure formed by alternating first stacks 310 and second stacks 320. Within each period, the first stack 310 is located on the side of the window layer 300 close to the second semiconductor layer 230. Along the height direction of the semiconductor stack 200, the aluminum content in the window layer 300 gradually changes, and the thickness D1 of the passivation layer 500 gradually changes, and the thickness D1 of the passivation layer 500 ranges from 0.1 to 4 μm.

[0060] In each cycle, the aluminum content in the first stack 310 is greater than the aluminum content in the second stack 320. The surface of the window layer 300 close to the second semiconductor layer 230 is defined as the A surface, and the surface of the window layer 300 away from the second semiconductor layer 230 is defined as the B surface. The aluminum content of the window layer 300 at the A surface is greater than the aluminum content of the window layer 300 at the B surface. The thickness D of the passivation layer 500 at the A surface is A1 Greater than the thickness D of the passivation layer 500 on the B surface B1 , further enhancing the ability of current to flow to the middle region of the semiconductor stack layer 200 , so as to avoid the non-radiative recombination phenomenon caused by sidewall defects of the window layer 300 and the semiconductor stack layer 200 .

[0061] Specifically, the first stack 310 includes Al m1 Ga 1-m1 As, the value of m1 ranges from 0.45 to 1. Within the same period of the window layer 300, m1 in the first stack 310 is a constant value; as the number of window layer 300 periods increases, m1 in the first stack 310 decreases. The passivation layer 500 at the sidewall of the first stack 310 is an aluminum oxide layer obtained by an in-situ oxidation water vapor process. Under the same oxidation parameters, the thickness D1 of the passivation layer 500 at the sidewall of the first stack 310 is related to the aluminum content in the first stack 310. In other words, within the same period of the window layer 300, the thickness D1 of the passivation layer 500 at the sidewall of the first stack 310 remains unchanged; as the number of window layer 300 periods increases, the thickness D1 of the passivation layer 500 at the sidewall of the first stack 310 decreases.

[0062] The value of m1 on the A surface is between 0.90 and 1, which can also be described as the value of m1 in the first stack 310 located on the A surface is between 0.90 and 1, and the thickness D of the passivation layer 500 on the A surface is A1 Between 1 and 4 μm.

[0063] The second stack 320 includes Al m2 Ga 1-m2As, the value of m2 is between 0.45 and 0.6. Within the same period of the window layer 300, m2 in the second stack 320 is a constant value; as the number of periods of the window layer 300 increases, m2 in the second stack 320 remains unchanged or decreases. The passivation layer 500 at the sidewall of the second stack 320 is an aluminum oxide layer obtained by an in-situ oxidation water vapor process. Under the same oxidation parameters, the thickness D1 of the passivation layer 500 at the sidewall of the second stack 320 is related to the aluminum content in the second stack 320. That is, within the same period of the window layer 300, the thickness D1 of the passivation layer 500 at the sidewall of the second stack 320 remains unchanged; as the number of periods of the window layer 300 increases, the thickness D1 of the passivation layer 500 at the sidewall of the second stack 320 remains unchanged or decreases.

[0064] In one embodiment, see Figure 4 The window layer 300 has a periodicity of 3 to 20, and within each period, the refractive index of the first stack 310 is different from the refractive index of the second stack 320. The window layer 300 is a periodic structure formed by alternating layers of two different refractive indices. This window layer 300 exhibits excellent reflective properties, directly reflecting light emitted from the active layer 220 and reducing the distance it travels before reflection, increasing normal light output and reducing the light emission angle of the micro-LED. In this embodiment, the window layer 300 has a periodicity of 10, achieving a reflectivity exceeding 95%, and the micro-LED has a light emission angle of 125°.

[0065] The total height of the first stack 310 and the second stack 320 in each cycle must meet the following requirements: Here, λ is the wavelength of the micro-LED, and n is the average refractive index of the first stack 310 and the second stack 320 within each period. For example, within each period, the refractive index of the first stack 310 is between 3.18 and 3.22, and the refractive index of the second stack 320 is between 3.37 and 3.42. The total height of the first stack 310 and the second stack 320 is preferably between 0.1 and 0.2 μm.

[0066] As an alternative embodiment, see Figure 5 , the micro light emitting diode does not include the passivation layer 500 , that is, the outer surface of the sidewall of the window layer 300 is not oxidized to form the passivation layer 500 .

[0067] See also Figure 6 In this embodiment, the structure of the window layer 300 is similar to Figure 4 The structure of the window layer 300 is the same as that of the active layer 220, and will not be described in detail here. The window layer 300 has a good reflective effect, which can directly reflect the light emitted by the active layer 220 and reduce the propagation distance of the light before reflection, thereby increasing the normal light output and reducing the light emission angle of the micro-LED.

[0068] Experiments have shown that compared to conventional micro-LEDs, when the window layer 300 of the micro-LED in this embodiment has a period number of 10, the reflectivity of the window layer 300 can reach over 95%, and the light-emitting angle of the micro-LED is 125°, which is reduced by at least 10°.

[0069] In one embodiment, see Figure 1 and Figure 5 The micro-LED is a flip-chip structure LED, and further comprises a reflective layer 600, which covers the window layer 300 and the upper surface of the semiconductor stack layer 200 except the window layer 300. The reflective layer 600 comprises a metal reflector or a distributed Bragg reflector. The material of the metal reflector includes but is not limited to gold, silver, aluminum, platinum, titanium, nickel or any combination of the above materials. The material of the distributed Bragg reflector includes but is not limited to silicon oxide and titanium oxide. Preferably, the reflective layer 600 has a horizontal bridge portion ( Figure 7 ), the horizontal bridge portion is used to connect the semiconductor stack layer 200 and the substrate 900.

[0070] A first electrode 700 is formed on the first semiconductor layer 210 , and a second electrode 710 is formed on the window layer 300 . Both the first electrode 700 and the second electrode 710 are located below the reflective layer 600 .

[0071] The reflective layer 600 is provided with through holes for forming the first pad 800 and the second pad 810 . The first pad 800 fills the corresponding through hole and is electrically connected to the first electrode 700 . The second pad 810 fills the corresponding through hole and is electrically connected to the second electrode 710 .

[0072] In one embodiment, see Figure 8 The micro-LED is a vertical structure LED. The semiconductor stack layer 200 is disposed on a substrate 100. The substrate 100 is preferably a conductive substrate, such as a silicon substrate or a silicon carbide substrate. The first electrode 700 is disposed on a surface of the substrate 100 away from the semiconductor stack layer 200. The second electrode 710 is disposed on the window layer 300.

[0073] In one embodiment, see Figure 9 The micro-LED also includes a substrate 900 for supporting the micro-LED. Substrate 900 includes, but is not limited to, a metal substrate, a sapphire substrate, a glass substrate, a silicon substrate, a silicon carbide substrate, or a support film. When substrate 900 is a metal substrate, a sapphire substrate, a glass substrate, a silicon substrate, or a silicon carbide substrate, a bonding layer 910 is provided on the surface of substrate 900 for supporting the micro-LED. Bonding layer 910 includes, but is not limited to, benzocyclobutene (BCB) or polyimide (PI).

[0074] The micro LED has a light emitting surface, which is specifically a surface of the first semiconductor layer 210 away from the active layer 220 , and faces the substrate 900 .

[0075] As an alternative embodiment, see Figure 10 The light emitting surface of the micro LED faces away from the substrate 900 , and the bonding layer 910 in the substrate 900 is connected to the horizontal bridge portion in the reflective layer 600 . The width of the bonding layer 910 is preferably smaller than the width of the semiconductor stack layer 200 .

[0076] Preferably, a sacrificial layer is further included between the micro-LEDs and substrate 900. The sacrificial layer can be removed more efficiently than the micro-LEDs, at least in certain circumstances, such as chemical or physical decomposition, such as ultraviolet light decomposition, etching removal, or impact removal. The sacrificial layer is preferably made of an oxide, a nitride, or a material that can be selectively removed relative to other layers.

[0077] According to one aspect of the present application, a method for preparing a micro light emitting diode is provided. Figure 1 The preparation method of the micro-light emitting diode shown is used as an example, and the preparation method includes the following steps:

[0078] S1 . Form a semiconductor stacked layer 200 . The semiconductor stacked layer 200 includes a first semiconductor layer 210 , a second semiconductor layer 230 , and an active layer 220 located therebetween.

[0079] In one embodiment, see Figure 11 A substrate 100 is provided, and the substrate 100 includes a gallium arsenide substrate; a semiconductor stack layer 200 is formed on the substrate 100 by a chemical vapor deposition method; the semiconductor stack layer 200 includes a first semiconductor layer 210, an active layer 220 and a second semiconductor layer 230 from bottom to top.

[0080] S2. Forming a window layer 300 on a surface of the second semiconductor layer 230 away from the active layer 220. The window layer 300 includes an aluminum gallium arsenide layer.

[0081] In one embodiment, see Figure 12 A window layer 300 is formed on the upper surface of the second semiconductor layer 230. The material of the window layer 300 includes aluminum gallium arsenide, which is deposited on the second semiconductor layer 230 by chemical vapor deposition. The lower surface of the window layer 300 is defined as the A surface, and the upper surface of the window layer 300 is defined as the B surface.

[0082] As an example, in the direction perpendicular to the A-plane, the aluminum content in the window layer 300 remains unchanged. Specifically, the window layer 300 includes Al x Ga1-x As, in the direction perpendicular to the A surface, x is a constant, and the value of x is between 0.45 and 1.

[0083] As an example, in a direction perpendicular to the A-plane, the aluminum content in the window layer 300 is gradually changed. Specifically, the window layer 300 includes Al y Ga 1-y As, in the direction perpendicular to surface A, y is a gradient value, and the value of y is between 0.45 and 1. The value of y decreases from surface A to surface B, or the value of y increases from surface A to surface B.

[0084] As an example, the window layer 300 includes a periodic structure formed by alternating first stacks 310 and second stacks 320, and within each period, the first stack 310 is located on a side of the window layer 300 close to the second semiconductor layer 230. In a direction perpendicular to the A-plane, the aluminum content in the window layer 300 changes gradually.

[0085] In each period, the aluminum content in the first stack 310 is greater than the aluminum content in the second stack 320. The aluminum content at the A surface of the window layer 300 is greater than the aluminum content at the B surface of the window layer 300.

[0086] Specifically, the first stack 310 includes Al m1 Ga 1-m1 As, m1 has a value between 0.45 and 1. Within the same period of the window layer 300, m1 in the first stack 310 is constant; as the number of periods of the window layer 300 increases, m1 in the first stack 310 decreases. The value of m1 on the A surface is preferably between 0.90 and 1.

[0087] The second stack 320 includes Al m2 Ga 1-m2 As, m2 has a value between 0.45 and 0.6. Within the same period of the window layer 300, m2 in the second stack 320 is a constant value; as the number of periods of the window layer 300 increases, m2 in the second stack 320 remains unchanged or decreases.

[0088] Preferably, the number of periods of the window layer 300 is 3 to 20, and the refractive index of the first stack 310 in each period is different from the refractive index of the second stack 320. The total height of the first stack 310 and the second stack 320 in each period must satisfy: Wherein, λ is the wavelength of the micro-LED, and n is the average refractive index of the first stack 310 and the second stack 320 in each period.

[0089] For example, in each period, the refractive index of the first stack 310 is between 3.18 and 3.22, and the refractive index of the second stack 320 is between 3.37 and 3.42. The total height of the first stack 310 and the second stack 320 is preferably between 0.1 and 0.2 μm.

[0090] S3 , etching the window layer 300 and the semiconductor stack layer 200 to form a mesa structure.

[0091] In one embodiment, see Figure 13 The semiconductor stack layer 200 includes a light-emitting region and a cutout region surrounding the light-emitting region. A dry etching process is used to remove the semiconductor stack layer 200 and the window layer 300 in the cutout region. The window layer 300 and the semiconductor stack layer 200 in the light-emitting region are further etched to form a mesa structure. A trench 400 extending from the window layer 300 to the interior of the first semiconductor layer 210 is formed on the semiconductor stack layer 200 in the light-emitting region. The trench 400 exposes the first semiconductor layer 210.

[0092] S4. Oxidize the sidewalls of the window layer 300 and form a passivation layer 500 on the sidewalls of the window layer 300 to extend inward from the outer surface of the sidewalls to a preset thickness.

[0093] In one embodiment, see Figure 14 , a protective layer is covered on the upper surface of the window layer 300, and the protective layer is used to protect the upper surface of the window layer 300 from being oxidized during the subsequent oxidation process. The window layer 300 is oxidized by an in-situ water vapor oxidation process, and a passivation layer 500 of a preset thickness extending inward from the outer surface of the side wall is formed on the side wall of the window layer 300. In the projection direction perpendicular to the height direction of the semiconductor stack layer 200, the projection of the unpassivated part of the window layer 300 falls inside the projection of the second semiconductor layer 230. The passivation layer 500 is an aluminum oxide layer, and its thickness is related to oxidation parameters such as oxidation temperature, oxidation time and water vapor content. When the above oxidation parameters are the same, the thickness D1 of the passivation layer 500 is related to the aluminum content in the window layer 300. After the oxidation is completed, the above protective layer is removed.

[0094] As an example, when the aluminum content in the window layer 300 is constant, the thickness D1 of the passivation layer 500 is constant, and the thickness D1 of the passivation layer 500 is preferably between 1 μm and 4 μm.

[0095] As an example, the window layer 300 includes Al y Ga 1-yAs, when y is a gradient value in the direction perpendicular to surface A, the thickness D1 of the passivation layer 500 is gradient, and the thickness D1 of the passivation layer 500 is preferably between 0.1 and 4 μm. When the value of y decreases from surface A to surface B, the thickness D1 of the passivation layer 500 decreases from surface A to surface B; when the value of y increases from surface A to surface B, the thickness D1 of the passivation layer 500 increases from surface A to surface B.

[0096] As an example, when the window layer 300 includes a first stack 310 and a second stack 320, within the same period of the window layer 300, the thickness D1 of the passivation layer 500 at the sidewall of the first stack 310 remains unchanged; as the number of periods of the window layer 300 increases, the thickness D1 of the passivation layer 500 at the sidewall of the first stack 310 decreases; the thickness D1 of the passivation layer 500 at the A surface decreases. A1 Between 1 and 4 μm.

[0097] Within the same period of the window layer 300 , the thickness D1 of the passivation layer 500 at the sidewall of the second stack 320 remains unchanged; as the number of periods of the window layer 300 increases, the thickness D1 of the passivation layer 500 at the sidewall of the second stack 320 remains unchanged or decreases.

[0098] After the above steps are completed, the following steps are also included:

[0099] S5, see Figure 15 , forming a first electrode 700, a second electrode 710, and a reflective layer 600. The first electrode 700 is located on the first semiconductor layer 210, and the second electrode 710 is located on the window layer 300. The reflective layer 600 covers the window layer 300, the area on the upper surface of the semiconductor stack layer 200 except the window layer 300, and the sidewalls of the semiconductor stack layer 200, and covers the first electrode 700 and the second electrode 710. Through holes are respectively opened in the reflective layer 600 at positions corresponding to the first electrode 700 and the second electrode 710. The reflective layer 600 includes a metal reflector or a distributed Bragg reflector.

[0100] S6, see Figure 16 , a first pad 800 electrically connected to the first electrode 700 and a second pad 810 electrically connected to the second electrode 710 are manufactured.

[0101] S7. Transfer the semiconductor stack 200 onto a substrate 900. The substrate 900 includes, but is not limited to, a metal substrate, a sapphire substrate, a glass substrate, a silicon substrate, a silicon carbide substrate, or a support film. When the substrate 900 is a metal substrate, a sapphire substrate, a glass substrate, a silicon substrate, or a silicon carbide substrate, a bonding layer 910 is provided on the surface of the substrate 900 that supports the micro-LEDs. The bonding layer 910 includes, but is not limited to, benzocyclobutene (BCB) or polyimide (PI).

[0102] Preferably, before transferring the semiconductor stacked layer 200 to the substrate 900 , the method further includes:

[0103] A sacrificial layer (not shown) is coated on the semiconductor stack 200. The thickness of the sacrificial layer is greater than 1 μm. The sacrificial layer can be removed more efficiently than the micro-LEDs, at least in certain circumstances. These circumstances include chemical or physical decomposition, such as ultraviolet light decomposition, etching removal, or impact removal. The sacrificial layer can be made of an oxide, a nitride, or a material that can be selectively removed relative to other layers.

[0104] S8 , peeling off the substrate 100 , and roughening the surface of the first semiconductor layer 210 away from the active layer 220 by wet etching or dry etching.

[0105] The micro-LEDs are separated from the substrate 900 by laser stripping or transfer printing, and the like. Figure 1 The micro-light emitting diodes shown.

[0106] According to one aspect of the present application, a light emitting device is provided, which includes a substrate and a plurality of micro-light emitting diodes according to the above embodiment fixed on the substrate.

[0107] It can be seen from the above technical solution that the present application oxidizes the sidewalls of the window layer 300 into a passivation layer 500. The passivation layer 500 can ensure that the injected current will not flow through the sidewalls of the window layer 300, and under the limiting effect of the passivation layer 500, when the current flows from the window layer 300 into the semiconductor stack layer 200, the current flows toward the middle area of ​​the semiconductor stack layer 200, avoiding the current from flowing through the sidewalls of the semiconductor stack layer 200, thereby avoiding the non-radiative recombination phenomenon caused by defects in the sidewalls of the window layer 300 and the semiconductor stack layer 200, and improving the luminous efficiency of the micro light-emitting diode.

[0108] Furthermore, the thickness D1 of the passivation layer 500 is gradual, and the thickness D A1 Greater than the thickness D of the passivation layer 500 at the B surface B1 , further enhancing the ability of current to flow to the middle region of the semiconductor stack layer 200 , so as to avoid the non-radiative recombination phenomenon caused by sidewall defects of the window layer 300 and the semiconductor stack layer 200 .

[0109] Furthermore, the window layer 300 is a periodic structure formed by alternating layers of two different refractive indices. The window layer 300 has a good reflective effect. It can directly reflect the light emitted by the active layer 220, reduce the propagation distance of the above light before reflection, increase the normal light output, and reduce the light-emitting angle of the micro light-emitting diode.

[0110] The above is only a preferred embodiment of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and replacements can be made without departing from the technical principles of the present application. These improvements and replacements should also be regarded as the scope of protection of the present application.

Claims

1. A micro-light emitting diode comprising a semiconductor stack, wherein the semiconductor stack comprises a first semiconductor layer, a second semiconductor layer, and an active layer located therebetween, wherein a window layer is provided on a surface of the second semiconductor layer away from the active layer; It is characterized by: The window layer includes an aluminum gallium arsenide layer and a passivation layer of a preset thickness oxidized inwardly from the outer surface of the sidewall of the aluminum gallium arsenide layer. The window layer includes a periodic structure formed by alternating first and second stacks, and in each period, the first stack is located on the side of the window layer close to the second semiconductor layer. In each period, the aluminum content in the first stack is greater than the aluminum content in the second stack. The surface of the window layer close to the second semiconductor layer is defined as surface A, and the surface of the window layer away from the second semiconductor layer is defined as surface B. The thickness D of the passivation layer on surface A is 0.01mm. A1 Greater than the thickness D of the passivation layer on surface B B1 ; As the number of window layer periods increases, the thickness of the passivation layer at the sidewall of the first stack decreases, and the thickness of the passivation layer at the sidewall of the second stack remains unchanged or decreases.

2. The micro light emitting diode according to claim 1, characterized in that: The thickness D1 of the passivation layer is between 0.1 μm and 4 μm.

3. The micro light emitting diode according to claim 1, characterized in that The aluminum content of the window layer at the A surface is greater than the aluminum content of the window layer at the B surface.

4. The micro light emitting diode according to claim 1, characterized in that The first stack includes Al m1 Ga 1- m1 As, m1 The value of is between 0.45 and 1; as the number of periods of the window layer increases, the m1 Decrease.

5. The micro light emitting diode according to claim 4, characterized in that: described m1 The value of the passivation layer at the A surface is between 0.90 and 1, and the thickness D of the passivation layer at the A surface is A1 Between 1~4μm.

6. The micro light emitting diode according to claim 1, characterized in that The second stack includes Al m2 Ga 1- m2 As, m2 The value of is between 0.45 and 0.6; as the number of periods of the window layer increases, the m2 Remain the same or decrease.

7. The micro light emitting diode according to claim 1, characterized in that: The number of periods of the window layer is 3-20, and the total height of the first stacked layer and the second stacked layer in each period is between 0.1-0.2 μm.

8. The micro light emitting diode according to claim 1, characterized in that: In each period, the refractive index of the first stack is different from the refractive index of the second stack; the refractive index of the first stack is between 3.18 and 3.22, and the refractive index of the second stack is between 3.37 and 3.

42.

9. The micro light emitting diode according to claim 1, characterized in that: It also includes a reflective layer, which covers the window layer, the area on the upper surface of the semiconductor stack layer except the window layer, and the sidewalls of the semiconductor stack layer; the reflective layer includes a metal reflector or a distributed Bragg reflector.

10. A method for preparing the micro light emitting diode according to any one of claims 1 to 9, characterized in that: include: forming a semiconductor stacked layer, the semiconductor stacked layer comprising a first semiconductor layer, a second semiconductor layer, and an active layer located therebetween; forming a window layer on a surface of the second semiconductor layer away from the active layer, wherein the window layer comprises an aluminum gallium arsenide layer; etching the window layer and the semiconductor stack layer to form a mesa structure; The sidewalls of the window layer are oxidized, and a passivation layer with a preset thickness extending inward from an outer surface of the sidewalls is formed on the sidewalls of the window layer.

11. A light emitting device, characterized in that: The invention comprises a substrate and a plurality of micro-light emitting diodes according to any one of claims 1 to 9 fixed on the substrate.

Images