Micro light-emitting element

Abstract

The present invention relates to a micro light-emitting element, which includes an epitaxial crystal grain grown by natural epitaxy without etching. Since the epitaxial crystal grain is grown by natural epitaxy, the roughness of at least a part of the sidewall surface is less than or equal to 10 nm, or the defect density is less than 10<supgt;8< / supgt> / cm<supgt;2< / supgt>, or the flatness error value is greater than 0.1 times the thickness of the epitaxial crystal grain. Therefore, the sidewall surface of the micro epitaxial crystal grain of the present invention is not damaged by etching, which can greatly reduce the generation of dangling bonds and reduce the sidewall damage effect, avoiding serious attenuation of the peak external quantum efficiency caused by the sidewall damage effect after the miniaturization of the light-emitting element.

Description

Technical Field

[0001] The present invention relates to a light-emitting element, and more particularly to a micro light-emitting element using natural epitaxial growth. Background Art

[0002] After the miniaturization of light-emitting elements, they can be used in different products or applications. However, as the size of light-emitting elements is reduced to the micron level, the peak external quantum efficiency of smaller micro light-emitting elements decays more significantly. Among them, red micro light-emitting elements are limited by the epitaxial materials, and their initial peak external quantum efficiency is relatively low, so they are more severely affected by the above attenuation problem.

[0003] The reason for the decay of the peak external quantum efficiency is that during the preparation process of micro light-emitting elements, the epitaxial layer must be cut into multiple microcrystals through a patterning etching process (such as reactive ion etching, RIE); during this process, the atomic bonds on the sidewall surface of the microcrystals will be broken to generate dangling bonds, resulting in the generation of a non-radiative recombination region for carriers, and this phenomenon is called side-wall damage. Taking wet etching as an example, the sidewall surface of the microcrystals presents uneven concave and convex patterns, and there are a large number of dangling bonds generated by etching on the surface of these patterns. When electrons approach the sidewall of the crystal grains, they are easily attracted by these unstable dangling bonds and recombine, resulting in a leakage problem.

[0004] In addition, as the size of the microcrystals decreases, the proportion of the sidewall area to the total area increases, and the side-wall damage effect becomes more obvious, so it is necessary to further improve it. Summary of the Invention

[0005] In view of the above technical defects of micro light-emitting elements, the main object of the present invention is to propose a new micro light-emitting element, so that the peak external quantum efficiency thereof is not severely attenuated by the side-wall damage effect.

[0006] To achieve the above object, the present invention proposes a micro light-emitting element, which includes: an epitaxial crystal grain, including a top surface, a bottom surface, and a plurality of sidewalls connecting the top surface and the bottom surface; wherein at least a part of the surface roughness of at least one of the sidewalls is less than or equal to 10 nm, or the defect density of at least a part of the surface is below 10 8 / cm 2 hereinafter, or the flatness error value of at least a part of the surface is greater than 0.1 times the thickness of the epitaxial crystal grain.

[0007] Since the micro epitaxial crystal grains of the present invention are grown by natural epitaxy, compared with the grain sidewalls defined by etching, the grain sidewalls of the present invention have the characteristics of smaller surface roughness and defect density and larger flatness error value; based on the above characteristics, the micro epitaxial crystal grains proposed by the present invention are not damaged by etching, which can greatly reduce the generation of dangling bonds and reduce the sidewall damage effect, avoiding the serious attenuation of the peak external quantum efficiency caused by the sidewall damage effect after the light-emitting element is miniaturized.

[0008] Another embodiment of the present invention provides a micro light-emitting element formed on a growth substrate having a patterned structure, and the patterned structure defines a growth region; the micro light-emitting element includes:

[0009] An epitaxial crystal grain including a top surface, a bottom surface, and a plurality of sidewalls connecting the top surface and the bottom surface; wherein the roughness of at least a part of the surface of at least one of the sidewalls is less than or equal to 10 nm, or the defect density of the at least a part of the surface is within 10 8 / cm 2 or less, or the flatness error value of the at least a part of the surface is greater than 0.1 times the thickness of the epitaxial crystal grain; the periphery of the bottom surface of the epitaxial crystal grain completely coincides with a bottom periphery of the growth region, and both the bottom surface and the growth region are in the same plane of the patterned structure on the growth substrate.

[0010] After the existing micro grains are formed by the patterned etching process, the surface of their sidewalls is damaged and uneven, and the peripheral contours of the top and bottom surfaces of the micro grains are not smooth due to the existence of a large number of etching marks; from the above description, it can be seen that the micro light-emitting element of the present invention cooperates with a growth substrate and the patterned structure thereon, and directly grows micro epitaxial crystal grains by natural epitaxy in the growth region of the patterned structure. Since the above epitaxial growth method is not etched, the periphery of the bottom surface of the micro epitaxial crystal grains of the present invention will completely coincide with the bottom periphery of the growth region compared with the existing micro grains.

[0011] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments, but it is not intended to limit the present invention. Description of the Drawings

[0012] Figures 1A to 1D : Schematic diagrams of the steps in a manufacturing process of the micro light-emitting element of the present invention.

[0013] Figure 2 : A side plan view of the first embodiment of the micro light-emitting element of the present invention.

[0014] Figure 3A : Figure 2 A top plan view of.

[0015] Figure 3B : Figure 2 Partial side perspective view of

[0016] Figure 3C : Figure 3A Schematic diagram of a partial longitudinal section of

[0017] Figures 4A to 4D : Schematic diagrams of the steps in the manufacturing process of the second embodiment of the micro light-emitting element of the present invention.

[0018] Figure 5 : The present invention Figure 4D Side plan view of an application example of a micro light-emitting element of the present invention.

[0019] Figure 6 : Side plan view of another application example of a micro light-emitting element of the present invention.

[0020] Figure 7A : Another patterning structure for manufacturing a micro light-emitting element of the present invention.

[0021] Figure 7B : Side plan view of the fifth embodiment of a micro light-emitting element of the present invention.

[0022] Figure 8A : Another patterning structure for manufacturing a micro light-emitting element of the present invention.

[0023] Figure 8B : Side plan view of the sixth embodiment of a micro light-emitting element of the present invention.

[0024] Figure 9A : Another patterning structure for manufacturing a micro light-emitting element of the present invention.

[0025] Figure 9B : Side plan view of the seventh embodiment of a micro light-emitting element of the present invention.

[0026] Figure 10A : Another patterning structure for manufacturing a micro light-emitting element of the present invention.

[0027] Figure 10B : Side plan view of the eighth embodiment of a micro light-emitting element of the present invention.

[0028] Figure 11A : Another patterning structure for manufacturing a micro light-emitting element of the present invention.

[0029] Figure 11B : Side plan view of the ninth embodiment of a micro light-emitting element of the present invention.

[0030] Among them, reference numerals:

[0031] 10: Growth substrate 11, 11a~11e: Patterning structure

[0032] 12, 12a~12e: Growth region 120: Bottom periphery

[0033] 121, 121a~121e: First space 122: Second space

[0034] 20, 20a, 20b, 20c: Epitaxial crystal grain 201: Bottom surface

[0035] 201a: Periphery 202: Top surface

[0036] 203: Side wall 203a: Surface

[0037] 204: Protrusion 205: Recess

[0038] 21, 21’: First - type epitaxial semiconductor layer 211: First platform surface

[0039] 211a: Top surface 211b: Side wall

[0040] 212: Second platform surface 213: Side - wall part

[0041] 22: Light - emitting layer 221: Top surface

[0042] 23: Second - type epitaxial semiconductor layer 231: Top surface

[0043] 30: First electrode 31: Second electrode

[0044] 32: Insulating layer 32a: Insulating - layer part

[0045] 32b: Insulating - layer part 33: Metal layer

[0046] 34: Transparent electrode Detailed implementation manners

[0047] The structural principle and working principle of the present invention will be specifically described below with reference to the accompanying drawings:

[0048] The micro - light - emitting element of the present invention mainly includes a light - emitting epitaxial crystal grain that is naturally epitaxially grown without etching. The epitaxial crystal grain can be a micro - light - emitting diode chip, but is not limited thereto. The natural epitaxial growth process of the epitaxial crystal grain will be further described below.

[0049] First, please refer to Figure 1AAs shown in the figure, a growth substrate 10 is prepared in advance. The growth substrate 10 has a patterned structure 11, and the patterned structure 11 defines a plurality of separate growth regions 12. The size of each growth region 12 matches the micro size of the epitaxial crystal grains mentioned above. In this embodiment, the growth regions 12 can be arranged in a matrix, and the bottom peripheral edge 120 of each growth region 12 is rectangular, but this is not limited thereto.

[0050] Again, Figure 1B As shown in the figure, the patterned structure 11 can be composed of a single material layer (such as a silicon oxide layer), or as shown in this embodiment, the patterned structure 11 is composed of a thin film layer 111 and a photoresist layer 112. The thin film layer 111 is formed on the growth substrate 10, and a first space 121 is formed corresponding to each growth region 12. The photoresist layer 112 is formed on the thin film layer 111, and a second space 122 is also formed corresponding to each growth region 12. The first space 121 and the second space 122 communicate with each other to form the growth region 12. In addition, the shapes of the first space 121 and the second space 122 can be the same or different. In this embodiment, the longitudinal cross-sectional shape of the first space 121 is trapezoidal, while the longitudinal cross-sectional shape of the second space 122 is rectangular.

[0051] Please continue to refer to Figure 1C As shown in the figure, an epitaxial crystal grain 20 is formed in each growth region 12 on the growth substrate 10 by epitaxial growth. The peripheral edge 201a of the bottom surface 201 of the epitaxial crystal grain 20 completely coincides with a bottom peripheral edge 120 of the growth region 12, that is, the bottom surface 201 and the growth region 12 are both on the same plane of the growth substrate 10 where the patterned structure 11 is located. Since each growth region 12 is of micro size, the epitaxial crystal grains 20 grown by natural epitaxy in each growth region 12 are also of micro size and do not need to go through an etching and cutting process.

[0052] As Figure 1D shown in the figure, after removing the patterned structure 11 on the growth substrate 10, multiple micro epitaxial crystal grains 20 can be obtained.

[0053] Please refer to Figure 2 shown in the figure, which is Figure 1D a longitudinal sectional view of one of the epitaxial crystal grains 20. The epitaxial crystal grain 20 includes a top surface 202, a bottom surface 201, and a plurality of side walls 203 connecting the top surface 202 and the bottom surface 201. Its body mainly includes a first-type epitaxial semiconductor layer 21, a light-emitting layer 22, and a second-type epitaxial semiconductor layer 23 from bottom to top. Again, Figure 2 and Figure 3AAs shown, the epitaxial crystal grain 20 of this embodiment is in the shape of a trapezoidal column. The periphery of the epitaxial crystal grain 20 includes a plurality of side walls 203. An angle θ exists between each side wall 203 and the bottom surface 201, and the angle θ is between 100 degrees and 130 degrees. The bottom surface area A1 of the epitaxial crystal grain 20 is larger than the area A2 of the top surface 202, that is, the cross-section of the epitaxial crystal grain 20 narrows from one side of the growth substrate 10 towards the top surface 202, but the shape of the epitaxial crystal grain 20 is not limited thereto. Since the epitaxial crystal grain 20 is grown by natural epitaxy, the surface roughness and defect density of each side wall 203 are smaller than those of the surface after etching. Please cooperate with Figure 2 Refer to Figure 3B , Figure 3B , the partial side view three-dimensional diagram of which shows one side wall 203 of the epitaxial crystal grain 20. There are non-periodic and uneven irregular dislocations on the surface of the side wall 203. However, since the surface of the side wall 203 is not etched, the surface roughness thereof is less than or equal to 10 nm, and its defect density is also within 10 8 / cm 2 Hereinafter, the so-called defect density (etch-pit density) refers to the number of etching holes in a unit area. In a preferred embodiment, the above-mentioned defect density can be within 10 7 / cm 2 Hereinafter.

[0054] As described above, due to the fact that the epitaxial crystal grain 20 is grown by natural epitaxy, the surfaces of its side walls 203 include curved surfaces; as Figure 3C shown, when a part of one side surface of the epitaxial crystal grain 20 is microscopically observed after longitudinal sectioning, since the epitaxial crystal grain 20 is not formed by isotropic or anisotropic etching, the tolerance of the surface flatness of its side wall 203 will be larger than that of the surface after etching. Here, regarding the calculation method of the flatness error value, the connecting line between the edges of the bottom surface 201 and the top surface 202 of the epitaxial crystal grain 20 is used as the reference plane. A plurality of convex portions 204 and concave portions 205 on the side wall 203 are taken, and the maximum distance of these convex portions 204 and concave portions 205 in the direction perpendicular to the reference plane (that is, Figure 3C the distance d' between the straight line L1 and the straight line L2 in Figure 3CAs shown, taking the thickness h of the epitaxial crystal grain 20 as 5 μm and the angle θ between its side wall 203 and the bottom surface 201 as 100 degrees to 130 degrees as an example, the range of the horizontal width w of the side wall 203 can be obtained to be approximately between 0.31 μm and 0.87 μm (the detailed calculation process is omitted here), and it can be further obtained that the distance d is about 0.17 μm to 0.64 μm. Then, according to the aforementioned condition that the angle θ is 100 degrees to 130 degrees, the vertical distance d' between these convex portions 204 and concave portions 205 can be obtained as 0.13 μm to 0.63 μm. However, considering the growth characteristics of the epitaxial material, the aforementioned angle θ is more commonly close to 130 degrees (for example Figure 3A as shown), so the intermediate value of the vertical distance d' can be obtained to be about 0.5 μm, which is 0.1 times the thickness h. For this example, the error value range of the surface flatness of the side wall 203 can be reasonably estimated to be 0.1 μm to 0.65 μm, or greater than 0.1 times the thickness h of the epitaxial crystal grain 20. Since the side wall boundaries of the grains formed by etching are mostly sharp straight lines, the error value of the surface flatness of its side wall will be significantly smaller than the above numerical range.

[0055] Please refer to Figure 4D , which is the second embodiment of the micro light-emitting element of the present invention. It is substantially the same as the epitaxial crystal grain 20 Figure 2 shown. That is, the body of the epitaxial crystal grain 20a of this embodiment also mainly includes a first-type epitaxial semiconductor layer 21', a light-emitting layer 22, and a second-type epitaxial semiconductor layer 23 from bottom to top; but the epitaxial crystal grain 20a is a trapezoidal column with a wider top and a narrower bottom, and the first-type epitaxial semiconductor layer 21' includes a first platform surface 211, a second platform surface 212, and at least one side wall portion 213. The light-emitting layer 22 is formed on the first platform surface 211, and the second-type epitaxial semiconductor layer 23 is formed on a top surface 221 of the light-emitting layer 22. In this embodiment, the epitaxial crystal grain 20a has a projected area A1 on the plane of its bottom surface 201, and the projected area A1 is larger than the area A3 of the bottom surface 201.

[0056] Refer to Figure 4A and Figure 4B again. After the first-type epitaxial semiconductor layer 21 is formed on the growth substrate 10 by epitaxial growth, a stepped portion is etched on its top surface 211a and its corresponding side wall 211b to form a first platform surface 211, a second platform surface 212, and at least one side wall portion 213; therefore, the second platform surface 212 and at least one side wall portion 213 are etched surfaces and are not formed by natural epitaxial growth; then, as Figure 4C shown, the light-emitting layer 22 is formed on the first platform surface 211 of the first-type epitaxial semiconductor layer 21' by natural epitaxial growth; then, as Figure 4DAs shown, a second-type epitaxial semiconductor layer 23 is formed on the top surface of the light-emitting layer 22 by epitaxial growth. Therefore, in this embodiment, except that at least one sidewall portion 213 of the first-type epitaxial semiconductor layer 21' is etched, the surfaces of the remaining sidewalls still have the characteristics of natural epitaxial growth. Therefore, the light-emitting layer 22, which has the greatest impact on the external quantum efficiency peak, is still ensured to be natural epitaxial growth. In a micro light-emitting element, especially a micro light-emitting diode, the thicknesses of the light-emitting layer 22 and the second-type epitaxial semiconductor layer 23 are about 20% of the thickness of the epitaxial crystal grains 20a. In an actual manufacturing process, even if the sidewalls of the entire epitaxial crystal grains 20a are etched due to cutting requirements, at least in Figure 4D the surface 203a of the light-emitting layer 22 (and the second-type epitaxial semiconductor layer 23 above it) located above the sidewall portion 213 is reserved for natural epitaxial growth. As described above, the surface 203a located above the etched sidewall portion 213 accounts for about 20% of one sidewall 203 of the epitaxial crystal grains 20a. Therefore, if the epitaxial crystal grains 20a are regarded as rectangles with equal side lengths, 5% of the surface area of all the sidewalls 203 of the epitaxial crystal grains 20a (i.e., the proportion of the aforementioned surface 203a) is reserved for the characteristics of natural epitaxial growth, that is, the roughness of at least 5% of the surface is less than or equal to 10 nm, or the defect density is within 10 8 / cm 2 or less, or the flatness error value is greater than 0.1 times the thickness of the epitaxial crystal grains 20a. However, the above ratio is only an example for the convenience of understanding in conjunction with the drawings; in fact, since the widths of the respective sidewalls 203 of the epitaxial crystal grains 20a and the positions selected for the second platform surface 212 may vary with the manufacturing process selection, the above ratio may vary with the size defined by the growth region 12, such as 3%, 7%, 10%, 14%, 18%... etc.

[0057] Please refer to Figure 5 again. Shown in the figure is an application example of the micro light-emitting element of the present invention, which is substantially the same as the Figure 4D epitaxial crystal grains 20a shown, but further includes a first electrode 30 and a second electrode 31; wherein the first electrode 30 is formed on the second platform surface 212 of the first-type epitaxial semiconductor layer 21' of the epitaxial crystal grains 20b, and the second electrode 31 is formed on the top surface 231 of the second-type epitaxial semiconductor layer 23. As shown in Figure 5 the epitaxial crystal grains 20b, only the surfaces 203a of the light-emitting layer 22 and the second-type epitaxial semiconductor layer 23 located above the sidewall portion 213 can be grown in a natural epitaxial growth manner. It can be seen from the figure that the electrons moving between the first and second electrodes 30 and 31 will just be close to the sidewall portion 213; therefore, if the surface 203a is grown in an epitaxial growth manner without free bonds, the electrons can be effectively prevented from being deflected due to the attraction of free bonds and the electrical effect from deteriorating.

[0058] Please refer to again Figure 6 As shown in the figure, another application example of the micro light-emitting element of the present invention is presented. The epitaxial crystal grain 20c is a trapezoidal columnar body with a wider top and a narrower bottom, and an insulating layer 32 is formed on the surfaces of its multiple side walls 203 and a partial surface of the bottom surface 201. A first electrode 30 and a second electrode 31 are formed on the insulating layer portion 32a located on the bottom surface 201. Among them, the first electrode 30 is connected to the bottom surface 201, and the second electrode 31 is connected to a transparent electrode layer 34 located on the top surface 202 of the epitaxial crystal grain 20c through a conductive layer 33. The conductive layer 33 can be formed on the insulating layer portion 32b corresponding to one of the side walls 203. Thus, such a micro light-emitting element can use an epitaxial crystal grain that is completely grown by natural epitaxy and has not been etched.

[0059] Please refer to again Figure 7A and Figure 7B As shown, another patterned structure 11a on the growth substrate 10 of Figure 1A has a longitudinal cross-sectional shape of the first space 121a in the growth region 12a of the patterned structure 11a being bowl-shaped, while the longitudinal cross-sectional shape of the second space 122 is rectangular. In such a growth region 12a, an epitaxial process is performed to form a bowl-shaped epitaxial crystal grain 20 that matches the first space 121a.

[0060] For another example Figure 8A and Figure 8B As shown, the longitudinal cross-sectional shape of the first space 121b in the growth region 12b of the patterned structure 11b is elliptical, and an elliptical epitaxial crystal grain 20 that matches the first space 121b can be formed.

[0061] For another example Figure 9A and Figure 9B As shown, the longitudinal cross-sectional shape of the first space 121c in the growth region 12c of the patterned structure 11c is trapezoidal at the bottom and rectangular at the top, and a trapezoidal-at-the-bottom-and-rectangular-at-the-top epitaxial crystal grain 20 that matches the first space 121c can be formed.

[0062] For another example Figure 10A and Figure 10B As shown, the longitudinal cross-sectional shape of the first space 121d in the growth region 12d of the patterned structure 11d is inverted trapezoidal, and an epitaxial crystal grain 20a as shown in Figure 4D can be formed.

[0063] For another example Figure 11A and Figure 11BAs shown, the patterned structure 11e further includes a first material layer 113 and a second material layer 114. The first material layer 113 is formed between the growth substrate 10e and the thin film layer 111, and the second material layer 114 is formed between the thin film layer 111 and the photoresist layer 112. Both the first material layer 111 and the second material layer 114 are wider than the thin film layer 111, so that the first space shape 121e of this embodiment is cross-shaped, and a cross-shaped epitaxial crystal grain matching the first space 121e can be formed. In this embodiment, the first and second material layers 113 and 114 can be selected to have different etching ratios from the thin film layer 111, and a cross-shaped first space 121e can be formed after the etching process.

[0064] In summary, the micro light-emitting element of the present invention mainly includes a micro epitaxial crystal grain grown by natural epitaxy, the roughness of at least a part of the sidewall surface thereof is less than or equal to 10 nm, or the defect density is 10 8 / cm 2 or less, or the flatness error value is greater than 0.1 times the thickness of the epitaxial crystal grain. Since the sidewall surface of the micro epitaxial crystal grain of the present invention is not damaged by etching, the generation of dangling bonds can be greatly reduced, and the sidewall damage effect can be reduced, avoiding serious attenuation of the peak external quantum efficiency due to the sidewall damage effect after the miniaturization of the light-emitting element.

[0065] Of course, the present invention can also have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and deformations according to the present invention, but these corresponding changes and deformations should all fall within the protection scope of the appended claims of the present invention.

Claims

1. A micro light-emitting element is formed on a growth substrate, the growth substrate having a patterned structure, and the patterned structure defining a plurality of separated growth regions, and the patterned structure forming a space around each of the growth regions; Characterized in that, The micro light-emitting element includes: A single crystal grain, comprising a top surface, a bottom surface, and a plurality of sidewalls connecting the top surface and the bottom surface; wherein the roughness of at least a part of the surface of at least one of the sidewalls is less than or equal to 10 nm, or the defect density of the at least a part of the surface is 10 8 / cm 2 or less, or the flatness error value of the at least a part of the surface is greater than 0.1 times the thickness of the single crystal grain; wherein the periphery of the bottom surface of the single crystal grain completely coincides with a bottom periphery of one of the growth regions, and the sidewalls of the single crystal grain also fit the patterned structure, so that the single crystal grain matches the shape of the space.

2. The micro light-emitting element according to claim 1, Characterized in that, The defect density of at least a part of the surface is 10 7 / cm 2 or less, or the absolute value of the flatness error value of at least a part of the surface is 0.1 μm to 0.65 μm.

3. The micro light-emitting element according to claim 1, Characterized in that, The area of this part of the surface accounts for more than 5% of the total surface area of these side walls.

4. The micro light-emitting element according to claim 3, Characterized in that, The epitaxial crystal grains include: A first-type epitaxial semiconductor layer; A light-emitting layer formed on the first-type epitaxial semiconductor layer; and A second-type epitaxial semiconductor layer formed on the light-emitting layer; Wherein at least a part of the surface is connected to the first-type epitaxial semiconductor layer and the top surface of the epitaxial crystal grains.

5. The micro light-emitting element according to claim 2, Characterized in that, Further comprising: A transparent electrode formed on the top surface; An insulating layer formed on the surfaces of these side walls and a part of the bottom surface; A conductive layer formed on the part of the insulating layer corresponding to one of the side walls; A first electrode formed on the insulating layer of the bottom surface and connected to the bottom surface; and A second electrode formed on the insulating layer of the bottom surface and connected to the conductive layer.

6. The micro light-emitting element according to claim 1, Characterized in that, There is an included angle between the at least one side wall and the bottom surface, and the angle of the included angle is 100 degrees to 130 degrees.

7. The micro light-emitting element according to claim 1, Characterized in that, The longitudinal cross-sectional shape of each of the epitaxial structures is selected from a bowl shape, an oval shape, a trapezoid shape, an inverted trapezoid shape, a cross shape, a rectangle shape or a combination thereof.

8. The micro light-emitting element according to claim 1, Characterized in that, The surfaces of these side walls include curved surfaces.

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