Light emitting diode

Abstract

The invention provides a light-emitting diode which comprises a substrate, a buffer layer and at least two light-emitting units. The buffer layer is stacked on the substrate. The at least two light-emitting units are sequentially stacked on the buffer layer in a stacking manner, each light-emitting unit comprises a semiconductor light-emitting structure and a two-dimensional material layer, the two-dimensional material layer is stacked on the semiconductor light-emitting structure, and each light-emitting unit emits light with a specific wavelength through the semiconductor light-emitting structure. Wherein the specific wavelength corresponding to any light-emitting unit closer to the substrate in the at least two light-emitting units is not less than the specific wavelength corresponding to the other light-emitting unit farther from the substrate.

Description

Technical Field

[0001] The present invention relates to a light-emitting diode, and more particularly to a light-emitting diode having a plurality of light-emitting units. Background Art

[0002] In recent years, light-emitting diodes have been widely used in various fields or products with lighting requirements. Currently, common light-emitting diodes mainly generate electroluminescence effects by passing current through the junction surface of two different semiconductor materials to convert electrical energy into light energy, enabling the light-emitting diodes to not only emit high-brightness light but also have energy-saving and power-saving effects.

[0003] Although traditional light-emitting diodes can change the emission wavelength by using different semiconductor materials, most traditional light-emitting diodes can only emit light of a single emission wavelength using a single set of light-emitting structures, which has many limitations in applications. In addition, although there are currently light-emitting diodes similar to those combining two sets of light-emitting structures, the two sets of light-emitting structures must be made of materials with similar lattice constants (or emission wavelengths) to facilitate the combination of the two sets of light-emitting structures, which also imposes limitations on the structural design and applications of traditional light-emitting diodes.

[0004] Therefore, how to design a light-emitting diode that can improve the aforementioned problems is indeed a research topic worthy of study. Summary of the Invention

[0005] The object of the present invention is to provide a light-emitting diode having a plurality of light-emitting units.

[0006] Another object of the present invention is to provide a light-emitting diode that can simultaneously emit light of more than one wavelength.

[0007] To achieve the above object, the light-emitting diode of the present invention includes a substrate, a buffer layer, and at least two light-emitting units. The buffer layer is laminated on the substrate. At least two light-emitting units are sequentially laminated on the buffer layer in a laminated manner. Each light-emitting unit includes a semiconductor light-emitting structure and a two-dimensional material layer, and the two-dimensional material layer is laminated on the semiconductor light-emitting structure, wherein each light-emitting unit emits light of a specific wavelength through the semiconductor light-emitting structure. Among them, the specific wavelength corresponding to any one of the at least two light-emitting units closer to the substrate is not less than the specific wavelength corresponding to the other light-emitting unit farther from the substrate.

[0008] In an embodiment of the present invention, the at least two light-emitting units include a first light-emitting unit and a second light-emitting unit. The first light-emitting unit is laminated on the buffer layer, and the second light-emitting unit is laminated on the two-dimensional material layer of the first light-emitting unit, and the semiconductor light-emitting structure of the first light-emitting unit is different from that of the second light-emitting unit.

[0009] In an embodiment of the present invention, the semiconductor light-emitting structure includes a first-type semiconductor epitaxial layer, a light-emitting layer, and a second-type semiconductor epitaxial layer, and the epitaxial layer stacking order of the first-type semiconductor epitaxial layer, the light-emitting layer, and the second-type semiconductor epitaxial layer of the first light-emitting unit is opposite to the epitaxial layer stacking order of the first-type semiconductor epitaxial layer, the light-emitting layer, and the second-type semiconductor epitaxial layer of the second light-emitting unit.

[0010] In an embodiment of the present invention, the cross-sectional area of the first light-emitting unit in the horizontal direction is smaller than the cross-sectional area of the buffer layer in the horizontal direction, and the cross-sectional area of the second light-emitting unit in the horizontal direction is smaller than the cross-sectional area of the first light-emitting unit in the horizontal direction.

[0011] In an embodiment of the present invention, the buffer layer is made of a two-dimensional material.

[0012] In an embodiment of the present invention, the light-emitting diode further includes a base electrode, the base electrode is stacked on the buffer layer, and the base electrode maintains a horizontal distance from at least two light-emitting units.

[0013] In an embodiment of the present invention, each light-emitting unit further includes an additional electrode, the additional electrode is stacked on the two-dimensional material layer, and the additional electrode of each light-emitting unit maintains a horizontal distance from another adjacent light-emitting unit.

[0014] In an embodiment of the present invention, the material of the two-dimensional material layer is selected from the group consisting of molybdenum disulfide, tungsten disulfide, molybdenum diselenide, and tungsten diselenide.

[0015] In an embodiment of the present invention, the substrate is made of gallium nitride, sapphire, silicon, or gallium arsenide.

[0016] With this design, the light-emitting diode of the present invention can stack multiple light-emitting units into the same structural member, and drive the corresponding single or multiple light-emitting units to emit light simultaneously by controlling whether each light-emitting unit is electrically conductive, so as to provide the light-emitting transformation effect of light with different wavelengths. And through the design of the conductive layer between different light-emitting units made of two-dimensional materials, the electron conductivity can be effectively improved, the resistance and driving voltage between the light-emitting units can be reduced, and different light-emitting units with relatively large lattice constant differences can be combined with each other. Description of the Drawings

[0017] Figure 1 It is a schematic diagram of the light-emitting diode of the present invention.

[0018] Figure 2 It is a schematic diagram of the first embodiment of the light-emitting diode of the present invention.

[0019] Figure 3 It is a schematic diagram of the second embodiment of the light-emitting diode of the present invention.

[0020] Description of the Reference Numerals

[0021] 1, 1a, 1b... light-emitting diodes

[0022] 10... substrate

[0023] 20... buffer layer

[0024] 30... light-emitting unit

[0025] 30a... first light-emitting unit

[0026] 30b... second light-emitting unit

[0027] 30n... nth light-emitting unit

[0028] 31... semiconductor light-emitting structure

[0029] 311... first-type semiconductor epitaxial layer

[0030] 312... light-emitting layer

[0031] 313... second-type semiconductor epitaxial layer

[0032] 32... two-dimensional material layer

[0033] 33... additional electrode

[0034] 40... base electrode

[0035] S1, S2, S3, Sn + 1... switches Detailed implementation manners

[0036] Since various solutions and embodiments are illustrative and non-limiting, after reading this specification, those with ordinary technical knowledge may also have other solutions and embodiments without departing from the scope of the present invention. According to the following detailed description and claims, the features and advantages of these embodiments will be more prominent

[0037] In this article, the terms "a" or "an" are used to describe the elements and components described herein. This is only for convenience of description and provides a general meaning to the scope of the present invention. Therefore, unless clearly indicated otherwise, such description should be understood to include one or at least one, and the singular also includes the plural

[0038] In this article, ordinal numbers such as "first" or "second" are mainly used to distinguish or refer to the same or similar elements or structures, and do not necessarily imply the order of these elements or structures in space or time. It should be understood that in certain situations or configurations, the ordinal numbers can be used interchangeably without affecting the implementation of the present invention

[0039] As used herein, the term "comprising", "having" or any other similar term is intended to cover non-exclusive inclusions. For example, an element or structure containing plural elements is not limited to only those elements listed herein, but may include other elements that are not explicitly listed but are generally inherent to the element or structure.

[0040] Please refer to Figure 1 a schematic diagram of the light-emitting diode of the present invention. As Figure 1 shown, the light-emitting diode 1 of the present invention mainly includes a substrate 10, a buffer layer 20, and at least two light-emitting units 30. The substrate 10 is a basic structural member of the light-emitting diode 1 of the present invention, and is used to carry the buffer layer 20, at least two light-emitting units 30, and other elements. In the present invention, the substrate 10 is made of gallium nitride (GaN), sapphire, silicon (Si), or gallium arsenide (GaAs), but the substrate 10 may also be made of other common substrate materials.

[0041] The buffer layer 20 is stacked on the substrate 10. In the present invention, the buffer layer 20 is made of a two-dimensional material selected from the group consisting of molybdenum disulfide (MoS2), tungsten disulfide (WS2), molybdenum diselenide (MoSe2), and tungsten diselenide (WSe2), so as to form a layered structure stacked by a single atomic layer or multiple atomic layers. However, the present invention is not limited thereto, and the buffer layer 20 may also use other two-dimensional materials with similar properties. The buffer layer 20 is used to handle the stress on the surface of the substrate 10, provide a better interface bonding effect between the substrate 10 and the light-emitting unit 30 adjacent to the substrate 10, and utilize the characteristic of high electron conductivity of the two-dimensional material to provide a good conductive effect.

[0042] At least two light-emitting units 30 are sequentially stacked on the buffer layer 20 in a stacked manner. That is to say, except for the light-emitting unit 30 adjacent to the buffer layer 20, any other light-emitting unit 30 is stacked on another light-emitting unit 30 to form a plurality of stacked light-emitting units 30. In the present invention, the number of light-emitting units 30 is at least 2, and can be increased to more than 2 according to different design requirements. Each light-emitting unit 30 includes a semiconductor light-emitting structure 31 and a two-dimensional material layer 32. The semiconductor light-emitting structure 31 is a basic structural member of the light-emitting unit 30, and is used to emit light with a specific wavelength after being conductive. That is to say, each light-emitting unit 30 independently corresponds to a specific wavelength through its semiconductor light-emitting structure 31. The aforementioned specific wavelength can be changed according to the materials used in the semiconductor light-emitting structure 31.

[0043] The two-dimensional material layer 32 of each light-emitting unit 30 is stacked on the semiconductor light-emitting structure 31. The two-dimensional material layer 32 is a layered structure formed by stacking a single atomic layer or multiple atomic layers. The two-dimensional material layer 32 mainly serves as a conductive layer, using the characteristic of high electron conductivity of the two-dimensional material to provide good conductivity, and can also provide a reduction in the resistance and driving voltage between adjacent light-emitting units. In addition, the two-dimensional material layer 32 can further solve the problem of possible lattice constant mismatch between different materials, enabling different light-emitting units with relatively large lattice constant differences (or relatively large light-emitting wavelength differences) to be successfully combined with each other. In the present invention, the material of the two-dimensional material layer 32 is also selected from the group consisting of molybdenum disulfide (MoS2), tungsten disulfide (WS2), molybdenum diselenide (MoSe2), and tungsten diselenide (WSe2). For example, the same two-dimensional material as the aforementioned buffer layer 20 can be used, but the present invention is not limited thereto.

[0044] In terms of design, the specific wavelength corresponding to any one of at least two light-emitting units 30 that is closer to the substrate 10 is not less than the specific wavelength corresponding to the other light-emitting unit 30 that is farther from the substrate 10. That is to say, for a plurality of stacked light-emitting units 30, the specific wavelength corresponding to the relatively lower light-emitting unit 30 will be greater than or equal to the specific wavelength corresponding to the light-emitting unit 30 stacked relatively above. When the two-dimensional material layer 32 of any selected light-emitting unit 30 is electrically connected to the two-dimensional material layer 32 of another adjacent light-emitting unit 30 below, or is electrically connected to the buffer layer 20 adjacent below, the selected target light-emitting unit 30 can emit light of a specific wavelength through its semiconductor light-emitting structure 31. Accordingly, the light-emitting diode 1 of the present invention can drive a single or multiple light-emitting units 30 that want to emit light by controlling whether each light-emitting unit 30 is electrically connected, thereby achieving different light-emitting transformation effects.

[0045] The following will illustrate the light-emitting diode of the present invention in terms of the actual structural design. Please refer to Figure 2 is a schematic diagram of the first embodiment of the light-emitting diode of the present invention. As Figure 2 shown, in this embodiment, the number of at least two light-emitting units of the light-emitting diode 1a of the present invention is 2, that is, it includes a first light-emitting unit 30a and a second light-emitting unit 30b. The first light-emitting unit 30a is stacked on the buffer layer 20, and the second light-emitting unit 30b is stacked on the first light-emitting unit 30a. In terms of structural design, the cross-sectional area of the first light-emitting unit 30a in the horizontal direction is smaller than the cross-sectional areas of the substrate 10 and the buffer layer 20 in the horizontal direction, so that the first light-emitting unit 30a can be completely stacked on the buffer layer 20; the cross-sectional area of the second light-emitting unit 30b in the horizontal direction is smaller than the cross-sectional area of the first light-emitting unit 30a in the horizontal direction, so that the second light-emitting unit 30b can be completely stacked on the first light-emitting unit 30a, but the present invention is not limited thereto.

[0046] In this embodiment, the semiconductor light-emitting structure 31 of the first light-emitting unit 30a includes a first-type semiconductor epitaxial layer 311, a light-emitting layer 312, and a second-type semiconductor epitaxial layer 313, and the semiconductor light-emitting structure 31 is formed according to the epitaxial layer stacking order of the first-type semiconductor epitaxial layer 311, the light-emitting layer 312, and the second-type semiconductor epitaxial layer 313. The semiconductor light-emitting structure 31 of the second light-emitting unit 30b also includes a first-type semiconductor epitaxial layer 311, a light-emitting layer 312, and a second-type semiconductor epitaxial layer 313. However, the semiconductor light-emitting structure 31 is formed according to the epitaxial layer stacking order of the second-type semiconductor epitaxial layer 313, the light-emitting layer 312, and the first-type semiconductor epitaxial layer 311. That is to say, the epitaxial layer stacking order of each structural layer of the semiconductor light-emitting structure 31 of the first light-emitting unit 30a is exactly opposite to that of each structural layer of the semiconductor light-emitting structure 31 of the second light-emitting unit 30b. For example, assuming that the first-type semiconductor epitaxial layer 311 is an N-type semiconductor epitaxial layer, the light-emitting layer 312 is a multiple-quantum well (MQW) layer, and the second-type semiconductor epitaxial layer 313 is a P-type semiconductor epitaxial layer, then the semiconductor light-emitting structure 31 of the first light-emitting unit 30a presents an N-MQW-P epitaxial layer stacking structure, and the semiconductor light-emitting structure 31 of the second light-emitting unit 30b presents a P-MQW-N epitaxial layer stacking structure. However, the present invention is not limited thereto, and the epitaxial layer stacking orders of the semiconductor light-emitting structure 31 of the foregoing first light-emitting unit 30a and the semiconductor light-emitting structure 31 of the second light-emitting unit 30b may also be interchanged with each other.

[0047] In this embodiment, the light-emitting diode 1a of the present invention further includes a base electrode 40. The base electrode 40 is electrically connected to the buffer layer 20, and the base electrode 40 is connected to an external power supply through a wire to conduct electricity to the buffer layer 20. In terms of structural design, the base electrode 40 is also stacked on the buffer layer 20, and a horizontal distance is maintained between the base electrode 40 and the first light-emitting unit 30a. The base electrode 40 is mainly made of a metal material, but the present invention is not limited thereto.

[0048] In addition, the first light-emitting unit 30a and the second light-emitting unit 30b of the light-emitting diode 1a of the present invention further respectively include additional electrodes 33. The additional electrode 33 of each light-emitting unit is electrically connected to the two-dimensional material layer 32 of the light-emitting unit, and the additional electrode 33 is connected to an external power supply through a wire to conduct electricity to the two-dimensional material layer 32. In terms of structural design, the additional electrode 33 of each light-emitting unit is stacked on the two-dimensional material layer 32 of the light-emitting unit, and a horizontal distance is maintained between the additional electrode 33 of the first light-emitting unit 30a and the adjacent second light-emitting unit 30b. The additional electrode 33 is mainly made of a metal material, but the present invention is not limited thereto.

[0049] In this embodiment, it is assumed that the specific wavelength corresponding to the first light-emitting unit 30a is λ1, and the specific wavelength corresponding to the second light-emitting unit 30b is λ2, then λ1≧λ2. In terms of circuit design, the basic electrode 40 of the light-emitting diode 1a of the present invention can be connected to the switch S1 through a wire, the additional electrode 33 of the first light-emitting unit 30a is connected to the switch S2 through a wire, and the additional electrode 33 of the second light-emitting unit 30b is connected to the switch S3 through a wire. When only the switch S1 and the switch S2 are turned on (ON), the light-emitting diode 1a of the present invention emits light of a specific wavelength λ1 through the first light-emitting unit 30a; when only the switch S2 and the switch S3 are turned on, the light-emitting diode 1a of the present invention emits light of a specific wavelength λ2 through the second light-emitting unit 30b; and when the switch S1, the switch S2, and the switch S3 are all turned on, the light-emitting diode 1a of the present invention emits light of a specific wavelength λ1+λ2 through the first light-emitting unit 30a and the second light-emitting unit 30b simultaneously. The above-mentioned various switch controls and corresponding light-emitting effects can be referred to Table 1 below. Accordingly, the light-emitting diode 1a of the present invention can selectively drive the single light emission of any light-emitting unit or the simultaneous light emission of multiple light-emitting units to provide the light-emitting conversion effect of light of different wavelengths.

[0050] Table 1

[0051] Specific wavelength Switch S1 Switch S2 Switch S3 λ1 ON ON OFF λ2 OFF ON ON λ1 + λ2 ON ON ON

[0052] Please refer to Figure 3 is a schematic diagram of the second embodiment of the light-emitting diode of the present invention. As Figure 3 shown, in this embodiment, the number of at least two light-emitting units of the light-emitting diode 1b of the present invention is n, that is, it includes the first light-emitting unit 30a, the second light-emitting unit 30b,..., and the nth light-emitting unit 30n, where n≧3. The first light-emitting unit 30a is stacked on the buffer layer 20, the second light-emitting unit 30b is stacked on the first light-emitting unit 30a,..., and the nth light-emitting unit 30n is stacked on the n-1th light-emitting unit (when n = 3, the n-1th light-emitting unit is the second light-emitting unit 30b). In terms of structural design, the cross-sectional area of the first light-emitting unit 30a in the horizontal direction is smaller than the cross-sectional areas of the substrate 10 and the buffer layer 20 in the horizontal direction, so that the first light-emitting unit 30a can be completely stacked on the buffer layer 20; the cross-sectional area of the second light-emitting unit 30b in the horizontal direction is smaller than the cross-sectional area of the first light-emitting unit 30a in the horizontal direction, so that the second light-emitting unit 30b can be completely stacked on the first light-emitting unit 30a;... the cross-sectional area of the nth light-emitting unit 30n in the horizontal direction is smaller than the cross-sectional area of the n-1th light-emitting unit in the horizontal direction, so that the nth light-emitting unit 30n can be completely stacked on the n-1th light-emitting unit.

[0053] When the number of at least two light-emitting units is not less than 3, the semiconductor light-emitting structure of any one of the at least two light-emitting units is different from that of another adjacent light-emitting unit. In this embodiment, the semiconductor light-emitting structure 31 of the first light-emitting unit 30a is formed according to the epitaxial layer stacking order of the first-type semiconductor epitaxial layer 311, the light-emitting layer 312, and the second-type semiconductor epitaxial layer 313. The semiconductor light-emitting structure 31 of the second light-emitting unit 30b is formed according to the epitaxial layer stacking order of the second-type semiconductor epitaxial layer 313, the light-emitting layer 312, and the first-type semiconductor epitaxial layer 311. After the second light-emitting unit 30b, when the subsequent stacked light-emitting units are odd-numbered (such as the third light-emitting unit, the fifth light-emitting unit, and so on), their semiconductor light-emitting structures are the same as that of the first light-emitting unit 30a, and are formed according to the epitaxial layer stacking order of the first-type semiconductor epitaxial layer 311, the light-emitting layer 312, and the second-type semiconductor epitaxial layer 313; when the subsequent stacked light-emitting units are even-numbered (such as the fourth light-emitting unit, the sixth light-emitting unit, and so on), their semiconductor light-emitting structures are the same as that of the second light-emitting unit 30b, and are formed according to the epitaxial layer stacking order of the second-type semiconductor epitaxial layer 313, the light-emitting layer 312, and the first-type semiconductor epitaxial layer 311. That is to say, when the number of light-emitting units is not less than 3, the epitaxial layer stacking order of the first-type semiconductor epitaxial layer, the light-emitting layer, and the second-type semiconductor epitaxial layer of any one of these light-emitting units is opposite to that of another adjacent light-emitting unit. For example, it is assumed that the semiconductor light-emitting structures of all odd-numbered light-emitting units all exhibit an N-MQW-P epitaxial layer stacking structure, while the semiconductor light-emitting structures of all even-numbered light-emitting units all exhibit a P-MQW-N epitaxial layer stacking structure, but the present invention is not limited thereto.

[0054] In this embodiment, the light-emitting diode 1b of the present invention also includes a base electrode 40, and the setting of the base electrode 40 is the same as that of the foregoing first embodiment, and will not be elaborated here. In addition, the first light-emitting unit 30a, the second light-emitting unit 30b,... and the nth light-emitting unit 30n of the light-emitting diode 1b of the present invention further include additional electrodes 33 respectively. The additional electrode 33 of each light-emitting unit is electrically connected to the two-dimensional material layer 32 of the light-emitting unit, and each additional electrode 33 is connected to an external power supply through a wire to conduct electricity to each two-dimensional material layer 32. In terms of structural design, the additional electrode 33 of each light-emitting unit is stacked on the two-dimensional material layer 32 of the light-emitting unit, and a spacing is maintained between the additional electrode 33 of the first light-emitting unit 30a and that of the second light-emitting unit 30b,... and a spacing is maintained between the additional electrode of the (n - 1)th light-emitting unit and that of the nth light-emitting unit 30n.

[0055] In this embodiment, it is assumed that the specific wavelength corresponding to the first light-emitting unit 30a is λ1, the specific wavelength corresponding to the second light-emitting unit 30b is λ2, ……, and the specific wavelength corresponding to the nth light-emitting unit 30n is λn, then λ1≧λ2≧……≧λn. In terms of circuit design, the light-emitting diode 1b of the present invention can connect the basic electrode 40 to the switch S1 through a wire, connect the additional electrode 33 of the first light-emitting unit 30a to the switch S2 through a wire, connect the additional electrode 33 of the second light-emitting unit 30b to the switch S3 through a wire, ……, and connect the additional electrode 33 of the nth light-emitting unit 30n to the switch Sn+1 through a wire. When only the switch S1 and the switch S2 are turned on, the light-emitting diode 1b of the present invention emits light with a specific wavelength λ1 through the first light-emitting unit 30a; when only the switch S2 and the switch S3 are turned on, the light-emitting diode 1b of the present invention emits light with a specific wavelength λ2 through the second light-emitting unit 30b; ……; when only the switch Sn (when n = 3, the switch Sn is the switch S3) and the switch Sn+1 are turned on, the light-emitting diode 1b of the present invention emits light with a specific wavelength λn through the nth light-emitting unit 30n. When only the switch S1, the switch S2, and the switch S3 are turned on, the light-emitting diode 1b of the present invention emits light with a specific wavelength λ1+λ2 through the first light-emitting unit 30a and the second light-emitting unit 30b simultaneously; when only the switch S1, the switch S2, the switch Sn, and the switch Sn+1 are turned on, the light-emitting diode 1b of the present invention emits light with a specific wavelength λ1+λn through the first light-emitting unit 30a and the nth light-emitting unit 30n simultaneously; ……; and when all the switches S1 to Sn+1 are turned on, the light-emitting diode 1b of the present invention emits light with a specific wavelength λ1+λ2+……+λn through the first light-emitting unit 30a to the nth light-emitting unit 30n simultaneously. The above-mentioned switch controls and corresponding light-emitting effects can be referred to Table 2 below. Accordingly, the light-emitting diode 1b of the present invention can also selectively drive the single light emission of any light-emitting unit or the simultaneous light emission of multiple light-emitting units to provide the light-emitting transformation effect of light with different wavelengths.

[0056] Table 2

[0057]

[0058] The above embodiments are essentially for illustrative purposes only and are not intended to limit the embodiments of the claims or the application or use of such embodiments. In addition, although at least one exemplary embodiment has been presented in the foregoing embodiments, it should be understood that the present invention may still have a large number of variations. It should also be understood that the embodiments described herein are not intended to limit the scope, use, or configuration of the claimed rights in any way. On the contrary, the foregoing embodiments will provide those of ordinary skill in the art with a simple guide to implement one or more of the embodiments. Furthermore, various changes can be made to the functions and arrangements of the elements without departing from the scope defined by the claims, and the claims include known equivalents and all foreseeable equivalents at the time of filing of the present patent application.

Claims

1. A light-emitting diode, characterized in that, Comprising: A substrate; A buffer layer stacked on the substrate; And At least two light-emitting units stacked on the buffer layer in a stacked manner in sequence. Each light-emitting unit includes a semiconductor light-emitting structure and a two-dimensional material layer, and the two-dimensional material layer is stacked on the semiconductor light-emitting structure, wherein each light-emitting unit emits light with a specific wavelength through the semiconductor light-emitting structure; Wherein the specific wavelength corresponding to any one of the at least two light-emitting units closer to the substrate is not less than the specific wavelength corresponding to the other light-emitting unit farther from the substrate.

2. The light-emitting diode according to claim 1, wherein the at least two light-emitting units include a first light-emitting unit and a second light-emitting unit. The first light-emitting unit is stacked on the buffer layer, the second light-emitting unit is stacked on the two-dimensional material layer of the first light-emitting unit, and the semiconductor light-emitting structure of the first light-emitting unit is different from the semiconductor light-emitting structure of the second light-emitting unit.

3. The light-emitting diode according to claim 2, wherein the semiconductor light-emitting structure includes a first-type semiconductor epitaxial layer, a light-emitting layer, and a second-type semiconductor epitaxial layer, and the epitaxial layer stacking order of the first-type semiconductor epitaxial layer, the light-emitting layer, and the second-type semiconductor epitaxial layer of the first light-emitting unit is opposite to the epitaxial layer stacking order of the first-type semiconductor epitaxial layer, the light-emitting layer, and the second-type semiconductor epitaxial layer of the second light-emitting unit.

4. The light-emitting diode according to claim 2, wherein the cross-sectional area of the first light-emitting unit in the horizontal direction is smaller than the cross-sectional area of the buffer layer in the horizontal direction, and the cross-sectional area of the second light-emitting unit in the horizontal direction is smaller than the cross-sectional area of the first light-emitting unit in the horizontal direction.

5. The light-emitting diode according to claim 1, wherein when the number of the at least two light-emitting units is not less than 3, the semiconductor light-emitting structure of any one of the at least two light-emitting units is different from the semiconductor light-emitting structure of the adjacent other light-emitting unit.

6. The light-emitting diode according to claim 5, wherein the semiconductor light-emitting structure includes a first-type semiconductor epitaxial layer, a light-emitting layer, and a second-type semiconductor epitaxial layer, and the epitaxial layer stacking order of the first-type semiconductor epitaxial layer, the light-emitting layer, and the second-type semiconductor epitaxial layer of any one of the light-emitting units is opposite to the epitaxial layer stacking order of the first-type semiconductor epitaxial layer, the light-emitting layer, and the second-type semiconductor epitaxial layer of the adjacent other light-emitting unit.

7. The light-emitting diode according to claim 1, wherein the buffer layer is made of a two-dimensional material.

8. The light-emitting diode according to claim 1, further comprising a base electrode stacked on the buffer layer, and the base electrode is spaced from the at least two light-emitting units in the horizontal direction.

9. The light-emitting diode according to claim 1, wherein each light-emitting unit further includes an additional electrode stacked on the two-dimensional material layer, and the additional electrode of each light-emitting unit is spaced from the adjacent other light-emitting unit in the horizontal direction.

10. The light-emitting diode according to claim 1, wherein the material of the two-dimensional material layer is selected from the group consisting of molybdenum disulfide, tungsten disulfide, molybdenum diselenide, and tungsten diselenide.

11. The light-emitting diode according to claim 1, wherein the substrate is made of gallium nitride, sapphire, silicon, or gallium arsenide.

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