TWI544116B - Sapphire substrate - Google Patents

Description

Sapphire substrate

This invention relates to a substrate, and more particularly to a sapphire substrate.

A light-emitting diode (LED) is a light-emitting element made of a compound semiconductor. By combining electrons and holes, electric energy can be converted into light energy and released. Since the light-emitting diode has the advantages of power saving, small volume, short reaction time, long life, and the like, it has been widely used in the fields of display and illumination. In recent years, in order to reduce the cost of the light-emitting diode and make the application level of the light-emitting diode wider, how to improve the luminous efficiency of the light-emitting diode is one of the current research priorities. Among them, the internal quantum efficiency (IQE) of the light-emitting diode electroluminescence is an important factor affecting the overall luminous efficiency of the light-emitting diode.

In general, the better the semiconductor epitaxial quality of the light-emitting diode, for example, the lower the defect density, the higher the internal quantum efficiency of the light-emitting diode. In order to improve the luminous efficiency of the light-emitting diode, it has been known in the prior art to use a patterned substrate to combine different light-emitting diode semiconductor materials for epitaxy. Taking gallium nitride (GaN) light-emitting diodes as an example, a plurality of microstructured sapphire substrates have been grown to grow gallium nitride epitaxial films to suppress the lateral growth of gallium nitride and avoid side A defect is generated between the grown gallium nitride and the forward grown gallium nitride. However, these patterned substrates have limited effectiveness in inhibiting the lateral growth of gallium nitride on these microstructures, such that the sides of these microstructures still grow gallium nitride. Therefore, the defect density of the gallium nitride epitaxial film is hard to be lowered, and the luminous efficiency of the light-emitting diode is not easily improved.

The present invention provides a sapphire substrate. The epitaxial structure of the light-emitting diode grown on the sapphire substrate has a low defect density and a high luminous efficiency of the light-emitting diode.

The sapphire substrate of the present invention includes a plurality of pyramidal structures. These pyramid structures protrude from the upper surface of the sapphire substrate. The crystal orientation of the upper surface is (0001). Each pyramidal structure has three crystal faces of the first group, three crystal faces of the second group, and an axis perpendicular to the upper surface and passing through the apex of the pyramid structure. The crystal faces of the first group are alternately arranged with the crystal faces of the second group to surround the axis. The crystal faces of the first group are rotationally symmetric with respect to the axis at 120 degrees, and the crystal faces of the second group are rotationally symmetric with respect to the axis at 120 degrees. The crystallographic direction of one of the crystal faces of the first group is ( ). One of the crystal faces of the second group is located in the center of the crystal direction ( ).

In an embodiment of the invention, the crystal faces of the first group are flat, and the crystal faces of the second group are curved.

In an embodiment of the invention, each of the crystal faces of the second group is disposed between adjacent two crystal faces of the first group. The crystal faces of the first group and the crystal faces of the second group are adjacent to each other.

In an embodiment of the invention, the ratio of the total area of the crystal faces of the first group to the sum of the areas of the crystal faces of the second group falls within a range of 0.5 to 9.5.

In an embodiment of the invention, the ratio of the projected area of the pyramid structure to the area of the upper surface of the cone structure falls within a range of 0.5 to 0.95.

In an embodiment of the invention, the height values of the respective pyramid structures described above fall within the range of 1.0 micrometers to 3.5 micrometers.

In an embodiment of the invention, the cone structures are arranged in a plurality of rows, and the even rows of the pyramid structures are respectively offset from the odd rows of the pyramid structures.

In an embodiment of the invention, the pitch of the adjacent diconical structures described above falls within the range of 0.5 microns to 5.0 microns.

Based on the above, the sapphire substrate of the embodiment of the present invention protrudes from the upper surface of the sapphire substrate because these pyramid structures. The crystal orientation of the upper surface is (0001). Each pyramidal structure has three crystal faces of the first group, three crystal faces of the second group, and an axis perpendicular to the upper surface and passing through the apex of the pyramid structure. The crystal faces of the first group are alternately arranged with the crystal faces of the second group to surround the axis. The crystal faces of the first group are rotationally symmetric with respect to the axis at 120 degrees, and the crystal faces of the second group are rotationally symmetric with respect to the axis at 120 degrees. The crystallographic direction of one of the crystal faces of the first group is ( ). One of the crystal faces of the second group is located in the center of the crystal direction ( ). Therefore, the epitaxial structure of the light-emitting diode grown on the sapphire substrate has a low defect density and a high luminous efficiency of the light-emitting diode.

The above described features and advantages of the invention will be apparent from the following description.

FIG. 1A is a schematic perspective view of a sapphire substrate according to an embodiment of the invention. Specifically, in order to clearly express the various components of the sapphire substrate, the sapphire substrate 100 illustrated in FIG. 1A is only a portion of the complete sapphire substrate. In the present embodiment, the related description of the sapphire substrate 100 is representative of the sapphire substrate.

FIG. 1B is a top view of the sapphire substrate region A of the embodiment of FIG. 1A. Please refer to FIG. 1A and FIG. 1B. In the present embodiment, the sapphire substrate 100 has opposing upper and lower surfaces 102, 104, and the crystallographic direction of the upper surface 102 is (0001). In particular, the sapphire substrate 100 includes a plurality of pyramid structures 110 that protrude from the upper surface 102 of the sapphire substrate 100. The sapphire substrate 100 may be, for example, a C-plane sapphire substrate 100.

In the present embodiment, each of the pyramid structures 110 of the sapphire substrate 100 has three crystal faces of the first group, that is, a crystal face 112a, a crystal face 112b, and a crystal face 112c. In addition, each of the pyramid structures 110 further has three crystal faces of the second group, that is, a crystal face 114a, a crystal face 114b, and a crystal face 114c. In addition, each pyramid structure 110 has a vertical upper surface 102 and passes through an axis Ax of the apex of the pyramid structure 110. Specifically, the lattice arrangement of the sapphire substrate 100 is hexagonal close-packed (HCP). In each of the pyramid structures 110 of the sapphire substrate 100, the crystal faces of the first group are alternately arranged with the crystal faces of the second group to surround the axis Ax. Specifically, the crystal face 112a, the crystal face 112b, and the crystal face 112c of the first group are alternately arranged with the crystal face 114a, the crystal face 114b, and the crystal face 114c of the second group to surround the axis Ax. The crystal face 112a, the crystal face 112b, and the crystal face 112c of the first group are rotationally symmetric with respect to the axis Ax at 120 degrees, and the crystal face 114a, the crystal face 114b, and the crystal face 114c of the second group are rotationally symmetric with respect to the axis Ax by 120 degrees. .

In this embodiment, each crystal plane of the second group is disposed between adjacent two crystal faces of the first group, and the crystal faces of the first group and the crystal faces of the second group are adjacent to each other Pick up. Specifically, the crystal faces 114a of the second group are disposed between the adjacent crystal faces 112a and the crystal faces 112b of the first group, and the crystal faces 114b of the second group are disposed adjacent to the first group. The crystal face 112b and the crystal face 112c are disposed between the adjacent crystal faces 112a and the crystal faces 112c of the first group. Further, the crystal face 112a, the crystal face 112b, and the crystal face 112c of the first group are adjacent to the crystal face 114a, the crystal face 114b, and the crystal face 114c of the first group.

In the present embodiment, the pyramid structures 110 are arranged in a plurality of rows, and the even rows of the pyramid structures 110 are respectively offset from the odd rows of the pyramid structures 110. Specifically, the pyramid structures 110 are arranged in a staggered manner, and the pyramid structures 110 are evenly arranged on the upper surface 102 of the sapphire substrate 100. Additionally, the ratio of the projected area of the pyramidal structure 110 to the upper surface 102 to the area of the upper surface 102 falls within the range of 0.5 to 0.95, preferably falls within the range of 0.73 to 0.88. In some embodiments, the pyramid structures 110 may also be arranged in a lattice shape on the upper surface 102, radially arranged, or arbitrarily arranged to form a pattern, and the invention is not limited thereto. In addition, in other embodiments, the pyramid structures 110 may be disposed on the lower surface 104 of the sapphire substrate 100, or the pyramid structures 110 may be disposed on the upper surface 102 and the lower surface 104 of the sapphire substrate 100 at the same time. The invention is not limited thereto.

In this embodiment, the crystal faces of the first group are planes, and the crystal faces of the second group are curved surfaces. Specifically, the crystal face 112a, the crystal face 112b, and the crystal face 112c of the first group are substantially flat planes, and the crystal face 114a, the crystal face 114b, and the crystal face 114c of the second group are curved surfaces, for example, a cone Part of the surface. However, in some embodiments, the crystal faces 112a, the crystal faces 112b, and the crystal faces 112c of the first group may also be non-planar, for example, curved surfaces, and the second group of the crystal faces 114a, the crystal faces 114b, and the crystal faces 114c may also be a plane, and the invention is not limited thereto.

In this embodiment, the crystal faces of the first group have a specific crystallographic direction, and the positions of the crystal faces of the second group at the center of each crystal face also have a specific crystallographic direction. The center of each crystal face of the second group refers, for example, to the position of the geometric center of each crystal face of the second group. In this embodiment, the crystallographic direction of one of the crystal faces of the first group is ( ), and one of the crystal faces of the second group is located in the center of the crystal direction ( ). Specifically, the crystal direction of one of the crystal face 112a, the crystal face 112b, and the crystal face 112c of the first group is ( ), wherein the crystallographic direction of the crystal face 112a is, for example, ). The crystal direction of one of the crystal face 114a, the crystal face 114b, and the crystal face 114c of the second group is located at the center ( ), wherein the crystallographic direction of the crystal face 114a is, for example, ). In some embodiments, the crystal faces of the pyramid structures 110 may be designed to have other crystal orientations according to actual needs, and the invention is not limited thereto.

Referring to FIG. 1B, in the present embodiment, the total area of the crystal face 112a, the crystal face 112b, and the crystal face 112c of the first group and the crystal face 114a, the crystal face 114b, and the crystal face 114c of the second group. The sum of the areas, the ratio of the two falls within the range of 0.5 to 9.5, preferably falls within the range of 3 to 8. In other embodiments, the crystal faces of the first group may be designed to have other proportional relationships with the crystal faces of the second group according to actual needs, and the invention is not limited thereto.

1C is a side cross-sectional view of the sapphire substrate of the embodiment of FIG. 1B taken along line I-I', with reference to FIG. 1B and FIG. 1C. In the present embodiment, the line segment I-I' is taken as a line to assist in explaining the component topography of the sapphire substrate 100. The line segment I-I' of this embodiment is not intended to limit the invention. In the present embodiment, the height value of each of the pyramid structures 110 of the sapphire substrate 100 falls within the range of 1.0 micrometer to 3.5 micrometers, preferably falls within the range of 1.65 micrometers to 1.95 micrometers. Furthermore, the pitch of adjacent di-cone structures 110 falls within the range of 0.5 microns to 5.0 microns. In other embodiments, according to actual needs, each of the pyramid structures 110 of the sapphire substrate 100 may have other height values and other pitch values between the adjacent two pyramid structures 110, and the present invention does not Limited.

In the present embodiment, when the sapphire substrate 100 is applied to fabricate a light-emitting diode, for example, when a gallium nitride (GaN) light-emitting diode is fabricated, the sapphire substrate 100 is used as a light-emitting diode epitaxial body. The substrate is plated with gallium nitride on the upper surface 102 of the sapphire substrate 100. Specifically, these pyramid structures 110 protrude from the upper surface 102 of the sapphire substrate 100, and the crystal orientation of the upper surface 102 is (0001). Each of the pyramid structures 110 has a first group of crystal faces 112a, crystal faces 112b, and crystal faces 112c, and each of the pyramid structures 110 further has a second group of crystal faces 114a, crystal faces 114b, and crystal faces 114c. The crystallographic direction of one of the crystal faces of the first group is ( ), and one of the crystal faces of the second group is located in the center of the crystal direction ( ). In general, gallium nitride has a faster growth rate in the (0001) direction during epitaxy. During the epitaxy of gallium nitride, the crystal faces of the pyramid structures 110 of the sapphire substrate 100 can inhibit the lateral growth of gallium nitride, and the growth of gallium nitride in the (0001) direction is dominated by nitridation. The gallium is grown entirely on the sapphire substrate 100 to form a flat gallium nitride epitaxial layer. Since these crystal faces suppress the lateral growth of gallium nitride, it is possible to reduce the occurrence of defects between the laterally grown gallium nitride and the gallium nitride grown in the forward direction (ie, the growth of gallium nitride on (0001)). That is to say, when the sapphire substrate 100 is applied to fabricate a light-emitting diode, for example, when applied to a gallium nitride light-emitting diode, the defect density of the light-emitting diode epitaxial structure is low, so that the interior of the light-emitting diode is made. The quantum efficiency is high, and the luminous efficiency of the light-emitting diode is high.

2A-2C are schematic diagrams showing a method of fabricating a sapphire substrate according to another embodiment of the present invention. Please refer to FIG. 2A first. In the present embodiment, first, a sapphire substrate 200 is prepared. The sapphire substrate 200 has opposing upper and lower surfaces 202, 204, and the crystallographic direction of the upper surface 202 is (0001). Next, referring to FIG. 2B, etching is performed on the upper surface 202 of the sapphire substrate 200. In the present embodiment, the method of etching on the upper surface 202 of the sapphire substrate 200 includes performing a photoresist process on the sapphire substrate 200 to define the locations of the pyramid structures 210. Next, the upper surface 202 of the sapphire substrate 200 is subjected to dry etching, and the reaction gas includes boron trichloride and chlorine gas, and the etching time is, for example, falling within a range of 5 minutes to 60 minutes. Specifically, after the upper surface 202 of the sapphire substrate 200 is etched, the etched upper surface 202' is formed, and the plurality of pyramid structures 210 protrude from the upper surface 202' of the etched sapphire substrate 200'. Each pyramid structure 210 has side surfaces 212, and these side surfaces 212 are, for example, conical surfaces.

Next, referring to Fig. 2C, the sapphire substrate 200' is wet etched. In the present embodiment, the method of wet etching the sapphire substrate 200' includes etching the side surfaces 212 of the pyramid structures 210 with an etchant to form a plurality of pyramid structures 210' on the etched sapphire substrate 200''. On the upper surface 202''. Specifically, these pyramid structures 210' are similar to the pyramid structure 110 of FIGS. 1A-1C. The structure of the pyramid structure 210' and related descriptions may refer to the pyramid structure 110 of the embodiment of FIGS. 1A-1C. I won't go into details. Similarly, the pyramid structure 210' has a first group of three crystal faces, such as a crystal face 212', and the pyramid structure 210' also has a second group of three crystal faces, such as a crystal face 214' . In the present embodiment, the crystal face 212' may be, for example, the crystal face 112a of the embodiment of Fig. 1B, and the crystal face 214' may be, for example, the crystal face 114b of the embodiment of Fig. 1B. Alternatively, the crystal face 212' may be, for example, the crystal face 112b of the embodiment of Fig. 1B, and the crystal face 214' may be, for example, the crystal face 114c of the embodiment of Fig. 1B. Further, the crystal face 212' may be, for example, the crystal face 112c of the embodiment of Fig. 1B, and the crystal face 214' may be, for example, the crystal face 114a of the embodiment of Fig. 1B.

In the present embodiment, the etching liquid is a mixed liquid of sulfuric acid and phosphoric acid. In this mixed solution, the ratio of sulfuric acid to phosphoric acid falls within the range of 1.0 to 1.0 to 4.0 to 1.0, and preferably, the ratio of sulfuric acid to phosphoric acid is 1.55 to 1. Further, the etching time is, for example, 10 seconds to 1800 seconds, and preferably, the etching time for etching the side surface 212 of the pyramid structure 210 with an etching solution is 180 seconds. Further, the etching temperature falls, for example, in the range of 30 ° C to 310 ° C. Preferably, the side surface 212 of the pyramid structure 210 is etched with an etching solution in an etching temperature of 235 ° C. Specifically, during the etching process, the etching solution etches out the three crystal faces of the first group of the pyramid structures 210', and the unetched portions between the adjacent two crystal faces form a cone. A crystal face of the second group of structures 210'. Specifically, the method of fabricating the sapphire substrate of the present embodiment can be applied to at least the sapphire substrate 100 of the embodiment of FIGS. 1A to 1C.

3A is a side cross-sectional view of the sapphire substrate 200' of the embodiment of FIG. 2B as viewed by an electron microscope, and FIG. 3B is a top view of the sapphire substrate 200' of the embodiment of FIG. 2B as viewed from an electron microscope, with reference to FIGS. 3A and 3B. In the present embodiment, the pyramid structures 210 on the sapphire substrate 200' have side surfaces 212, and the side surfaces 212 are, for example, conical curved surfaces.

4 is a top plan view of epitaxial gallium nitride on a sapphire substrate and viewed by an electron microscope according to still another embodiment of the present invention. Please refer to FIG. 4. In the present embodiment, the sapphire substrate 400 is similar to the sapphire substrate 100 of the embodiment of FIGS. 1A-1C. The structure of the sapphire substrate 400 and related description can be referred to the sapphire substrate 100 of the embodiment of FIGS. 1A to 1C, and details are not described herein again. In the present embodiment, the sapphire substrate 400 includes a plurality of pyramid structures that protrude from the upper surface 402 of the sapphire substrate 400. Each pyramidal structure has a first group of three crystal faces, such as a crystal face 412, and each pyramid structure has a second group of three crystal faces, such as a crystal face 414. In the present embodiment, the crystal faces of the first group of each pyramid structure are similar to the crystal faces of the first group of each pyramid structure 110 of the embodiment of Figures 1A-1C. Additionally, in the present embodiment, the crystal faces of the second group of each pyramid structure are similar to the crystal faces of the second group of the pyramid structures 110 of the embodiment of Figures 1A-1C. Specifically, gallium nitride is epitaxially grown on the upper surface 402 of the sapphire substrate 400, and the gallium nitride has not yet formed a flat gallium nitride surface.

The following (Table 1) will show the result of elemental analysis on the upper surface 402 of the sapphire substrate 400 after the gallium nitride epitaxial layer of the embodiment of FIG. 4 is epitaxially deposited on the upper surface 402 of the sapphire substrate 400. The position of this elemental analysis is as shown in FIG. Position PO1 in the middle, and position PO1 is located between adjacent two pyramid structures. In addition, (Table 2) will also show the result of elemental analysis on the upper surface 402 of the sapphire substrate 400 after the gallium nitride epitaxial of the embodiment of FIG. 4 is epitaxially deposited on the upper surface 402 of the sapphire substrate 400. Position PO2 in Figure 4, and position PO2 is located on the surface of the pyramid structure and is located at the location of the crystal face 412 of the first group. It should be noted that the data listed in Table 1 and Table 2 below are only data of an embodiment of the present invention, and are not intended to limit the present invention. Any person having ordinary skill in the art, after referring to the present invention, may appropriately adapt its parameters or settings when applying the principles of the present invention, but it should still fall within the scope of the present invention. (Table I)         <TABLE border="1" borderColor="#000000" width="_0008"><TBODY><tr><td> Element </td><td> Carbon (C) </td><td> Nitrogen (N </td><td> Oxygen (O) </td><td> Gallium (Ga) </td><td> Aluminum (Al) </td></tr><tr><td> Weight percent (wt%) </td><td> 5.69 </td><td> 9.12 </td><td> 0.63 </td><td> 80.84 </td><td> 1.02 </td></ Tr><tr><td> atomic percentage (at%) </td><td> 26.73 </td><td> 29.54 </td><td> 2.24 </td><td> 65.48 </td> <td> 2.13 </td></tr></TBODY></TABLE> (Table 2)         <TABLE border="1" borderColor="#000000" width="85%"><TBODY><tr><td> Element</td><td> Carbon (C) </td><td> Nitrogen N) </td><td> Oxygen (O) </td><td> Gallium (Ga) </td><td> Aluminum (Al) </td></tr><tr><td> Weight Percentage (wt%) </td><td> 3.83 </td><td> 9.14 </td><td> 28.74 </td><td> 9.25 </td><td> 49.04 </td>< /tr><tr><td> Atomic percentage (at%) </td><td> 7.76 </td><td> 1.14 </td><td> 43.68 </td><td> 3.23 </td ><td> 44.19 </td></tr></TBODY></TABLE>

It can be seen from (Table 1) and (Table 2) that in the present embodiment, the sapphire substrate 400 is located at a position between adjacent two pyramid structures (ie, position PO1), and the nitrogen content and the gallium content thereof are clearly The nitrogen content and the gallium content are higher than the position of the sapphire substrate 400 at the position of the crystal face 412 of the first group (ie, the position PO2). In addition, the oxygen content and the aluminum content of the position PO2 are significantly higher than the oxygen content and the aluminum content of the position PO1, respectively. Specifically, since the nitrogen element and the gallium element are main components of gallium arsenide, and the oxygen element and the aluminum element are main components of the sapphire substrate, gallium gallium can be found in different positions on the sapphire substrate 400 by the above elemental analysis. The epitaxial situation. In the present embodiment, the gallium arsenide growth rate of the sapphire substrate 400 at a position between adjacent two pyramid structures is significantly higher than the position of the sapphire substrate 400 at the crystal face 412 of the first group. That is, these pyramidal structures of the sapphire substrate 400 can suppress the lateral growth of gallium nitride, and the growth of gallium nitride in the (0001) direction dominates the growth of gallium nitride on the sapphire substrate 400 as a whole. Specifically, as the gallium nitride epitaxial progresses, gallium nitride is grown in a direction of (0001) from a position between two adjacent pyramid structures on the sapphire substrate 400, and gradually covers the pyramid structures, Further, a flat gallium nitride epitaxial layer is formed. In the present embodiment, the sapphire substrate 400 has an effect similar to the sapphire substrate 100 of the embodiment of FIGS. 1A to 1C. When the sapphire substrate 400 is applied to fabricate a gallium nitride light-emitting diode, the defect density of the epitaxial structure of the light-emitting diode is low, and the light-emitting efficiency of the light-emitting diode is high.

In summary, the sapphire substrate of the embodiment of the present invention has a plurality of pyramid structures protruding from the upper surface of the sapphire substrate. The crystal orientation of the upper surface is (0001). Each pyramidal structure has three crystal faces of the first group, three crystal faces of the second group, and an axis perpendicular to the upper surface and passing through the apex of the pyramid structure. The crystal faces of the first group are alternately arranged with the crystal faces of the second group to surround the axis. The crystal faces of the first group are rotationally symmetric with respect to the axis at 120 degrees, and the crystal faces of the second group are rotationally symmetric with respect to the axis at 120 degrees. The crystallographic direction of one of the crystal faces of the first group is ( ), and one of the crystal faces of the second group is located in the center of the crystal direction ( ). Therefore, the epitaxial structure of the light-emitting diode grown on the sapphire substrate has a low defect density and a high luminous efficiency of the light-emitting diode.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention, and any one of ordinary skill in the art can make some changes and refinements without departing from the spirit and scope of the present invention. The scope of the invention is defined by the scope of the appended claims.

100, 200, 200', 200'', 400‧‧‧ sapphire substrates
102, 202, 202', 202'', 402‧‧‧ upper surface
104, 204‧‧‧ lower surface
110, 210, 210'‧‧‧ cone structure
112a, 112b, 112c, 114a, 114b, 114c, 212', 214', 412, 414‧‧ ‧ crystal face
212‧‧‧ side surface
A‧‧‧ area
Ax‧‧‧ axis
H‧‧‧ Height
I-I'‧‧‧ segment
P‧‧‧ pitch
PO1, PO2‧‧‧ position

FIG. 1A is a schematic perspective view of a sapphire substrate according to an embodiment of the invention. FIG. 1B is a top view of the sapphire substrate region A of the embodiment of FIG. 1A. 1C is a side cross-sectional view of the sapphire substrate of the embodiment of FIG. 1B taken along line segment I-I'. 2A to 2C are schematic views showing a method of fabricating a sapphire substrate according to another embodiment of the present invention. Figure 3A is a side cross-sectional view of the sapphire substrate 200' of the embodiment of Figure 2B as viewed by an electron microscope. Figure 3B is a top plan view of the sapphire substrate 200' of the embodiment of Figure 2B as viewed by an electron microscope. 4 is a top plan view of epitaxial gallium nitride on a sapphire substrate and viewed by an electron microscope according to still another embodiment of the present invention.

100‧‧‧Sapphire substrate

102‧‧‧ upper surface

110‧‧‧ cone structure

112a, 112b, 112c, 114a, 114b, 114c‧‧‧ crystal face

A‧‧‧ area

Ax‧‧‧ axis

I-I’‧‧‧ segment

Claims (8)

A sapphire substrate comprising a plurality of pyramid structures protruding from an upper surface of the sapphire substrate, the upper surface having a crystal orientation of (0001), each of the pyramid structures having a first group Three crystal faces, three crystal faces of a second group, and an axis perpendicular to the upper surface and passing through the apex of the pyramid structure, the crystal faces of the first group and the crystals of the second group The faces are alternately arranged to surround the axis, wherein the crystal faces of the first group are rotationally symmetric with respect to the axis at 120 degrees, and the crystal faces of the second group are rotationally symmetric with respect to the axis at 120 degrees. The crystallographic direction of one of the crystal faces of the first group is ( And the crystallographic direction of one of the crystal faces of the second group is located in the center ( ). The sapphire substrate of claim 1, wherein the crystal faces of the first group are planar, and the crystal faces of the second group are curved. The sapphire substrate according to claim 1, wherein each of the crystal faces of the second group is disposed between two adjacent crystal faces of the first group, and the first group of the first group The crystal faces and the crystal faces of the second group are adjacent to each other. The sapphire substrate according to claim 1, wherein a ratio of a total area of the crystal faces of the first group to a total area of the crystal faces of the second group falls within a range of 0.5 to 9.5. Inside. The sapphire substrate according to claim 1, wherein a ratio of a projected area of the pyramid structure to the upper surface and an area of the upper surface falls within a range of 0.5 to 0.95. The sapphire substrate according to claim 1, wherein the height value of each of the pyramid structures falls within a range of 1.0 micrometer to 3.5 micrometers. The sapphire substrate of claim 1, wherein the pyramid structures are arranged in a plurality of rows, and the even rows of the pyramid structures are respectively offset from the odd rows of the pyramid structures. The sapphire substrate of claim 1, wherein the pitch of adjacent two of the pyramid structures falls within a range of 0.5 micrometers to 5.0 micrometers.