CN109841714B - Vertical structure near ultraviolet light-emitting diode and preparation method thereof - Google Patents
Vertical structure near ultraviolet light-emitting diode and preparation method thereof Download PDFInfo
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Abstract
The invention relates to the field of illumination, display and optical communication, in particular to a vertical-structure near ultraviolet light-emitting diode and a preparation method thereof. The vertical structure near ultraviolet light emitting diode comprises: a conductive substrate having a first surface and a second surface opposite the first surface; the metal reflecting layer is positioned on the first surface; the nitride epitaxial layer is positioned on the surface of the metal reflecting layer and comprises a P-type GaN layer, a quantum well layer, a preparation layer and an N-type AlGaN layer which are sequentially overlapped along the direction vertical to the conductive substrate, and the thickness of the nitride epitaxial layer is smaller than the wavelength of near ultraviolet light; the N-type electrode is positioned on the surface of the N-type AlGaN layer; and the P-type electrode is positioned on the second surface. The invention reduces the absorption loss in the LED and greatly improves the light extraction efficiency.
Description
Technical Field
The invention relates to the field of illumination, display and optical communication, in particular to a vertical-structure near ultraviolet light-emitting diode and a preparation method thereof.
Background
Light Emitting Diodes (LEDs) have the advantages of small size, high efficiency, long lifetime, and the like, and have a wide application prospect in the fields of illumination, display, and optical communication. Conventional light emitting diodes use sapphire as a growth substrate. However, since the sapphire substrate is not conductive, the conventional light emitting diode generally employs a lateral structure in which electrodes are on the same side. This lateral structure has at least two disadvantages: on one hand, the current flows in the N-type layer in a transverse direction at unequal intervals, so that the current congestion phenomenon exists, the local heat productivity of the light-emitting diode device is high, and the performance of the device is influenced; on the other hand, the sapphire substrate has poor thermal conductivity, so that the heat dissipation of the light-emitting diode device is limited, and the service life of the light-emitting diode device is influenced. In order to overcome the drawbacks of lateral light emitting diode devices, vertical structure light emitting diodes have appeared in the prior art.
However, in the conventional vertical structure light emitting diode, there are many optically Confined modes (defined modes) due to the limitation of the thick film. When the light emitting diode with the electron injection and the vertical structure emits light, most of the emergent light is limited in the thick film of the epitaxial layer of the light emitting diode, so that transmission and absorption in the film are caused, and the light emitting efficiency of the light emitting diode is greatly reduced.
Therefore, how to avoid the restriction of the thickness of the light emitting diode device on the emergent light to improve the light emitting efficiency of the light emitting diode is a technical problem to be solved urgently at present.
Disclosure of Invention
The invention relates to a near ultraviolet light emitting diode with a vertical structure and a preparation method thereof, which are used for solving the problem of low light emitting efficiency of the existing near ultraviolet light emitting diode.
In order to solve the above problems, the present invention provides a vertical structure near ultraviolet light emitting diode, comprising:
a conductive substrate having a first surface and a second surface opposite the first surface;
the metal reflecting layer is positioned on the first surface;
the nitride epitaxial layer is positioned on the surface of the metal reflecting layer and comprises a P-type GaN layer, a quantum well layer, a preparation layer and an N-type AlGaN layer which are sequentially overlapped along the direction vertical to the conductive substrate, and the thickness of the nitride epitaxial layer is smaller than the wavelength of near ultraviolet light;
the N-type electrode is positioned on the surface of the N-type AlGaN layer;
and the P-type electrode is positioned on the second surface.
Preferably, the thickness of the nitride epitaxial layer is 300nm or less.
Preferably, the metal reflection layer is formed on the conductive substrate and comprises a NiSn bonding layer between the conductive substrate and the metal reflection layer.
Preferably, the vertical-structure near ultraviolet light emitting diode is of a step-shaped structure; the step-shaped structure comprises a lower step and an upper step formed by the nitride epitaxial layer; the lower step comprises the P-type electrode, the conductive substrate and the metal reflecting layer, and the lower step protrudes out of the upper step along a direction parallel to the conductive substrate.
Preferably, the P-type GaN layer has a thickness of 80nm to 100nm, the quantum well layer has a thickness of 98nm to 118nm, and the preparation layer has a thickness of 95nm to 115 nm.
In order to solve the above problems, the present invention further provides a method for manufacturing a vertical structure near ultraviolet light emitting diode, comprising the following steps:
bonding a growth substrate and a conductive substrate, wherein the surface of the growth substrate is provided with a nitride epitaxial layer and a metal reflecting layer, the nitride epitaxial layer comprises a buffer layer, an undoped GaN layer, an N-type AlGaN layer, a preparation layer, a quantum well layer and a P-type GaN layer which are sequentially superposed along the direction vertical to the growth substrate, and the metal reflecting layer is positioned on the surface of the P-type GaN layer; the conductive substrate comprises a first surface and a second surface opposite to the first surface, and the second surface is provided with a P-type electrode;
stripping the growth substrate;
etching the nitride epitaxial layer, removing the buffer layer and the undoped GaN layer, and thinning the N-type AlGaN layer to ensure that the thickness of the residual nitride epitaxial layer is smaller than the wavelength of near ultraviolet light;
and forming an N-type electrode on the surface of the residual N-type AlGaN layer.
Preferably, the thickness of the remaining nitride epitaxial layer is 300nm or less.
Preferably, the specific step of bonding a growth substrate and a conductive substrate comprises:
forming a first NiSn bonding layer on the surface of the metal reflecting layer;
forming a second NiSn bonding layer on the first surface of the conductive substrate;
and bonding the first NiSn bonding layer and the second NiSn bonding layer.
Preferably, the specific step of etching the nitride epitaxial layer includes:
etching the nitride epitaxial layer to the N-type AlGaN layer, removing the buffer layer and the undoped GaN layer, and thinning the N-type AlGaN layer to enable the thickness of the residual nitride epitaxial layer to be smaller than the wavelength of near ultraviolet light;
defining a device region in the residual nitride epitaxial layer;
etching the residual nitride epitaxial layer around the device region to the metal reflecting layer to form a step-shaped structure; the step-shaped structure comprises a lower step and an upper step formed by the residual nitride epitaxial layer in the device region; the lower step comprises the P-type electrode, the conductive substrate and the metal reflecting layer, and the lower step protrudes out of the upper step along a direction parallel to the conductive substrate.
Preferably, the P-type GaN layer has a thickness of 80nm to 100nm, the quantum well layer has a thickness of 98nm to 118nm, and the preparation layer has a thickness of 95nm to 115 nm.
According to the near ultraviolet light-emitting diode with the vertical structure and the preparation method thereof, the device adopts the vertical structure, so that the electric injection efficiency is improved; meanwhile, the thickness of the nitride epitaxial layer is set to be smaller than the wavelength of near ultraviolet light, so that the vertical-structure near ultraviolet light-emitting diode is not limited by a constrained mode, the transmission of emergent light of the light-emitting diode in the nitride epitaxial layer is reduced or even eliminated, the internal absorption loss is reduced, and the light-emitting efficiency of the light-emitting diode is greatly improved; meanwhile, the arrangement of the metal reflecting layer further enhances the light emitting efficiency of the light emitting diode.
Drawings
FIG. 1 is a schematic diagram of a vertical structure of a near-UV LED according to an embodiment of the present invention;
FIG. 2 is a flow chart of a method for manufacturing a vertical structure near ultraviolet light emitting diode according to an embodiment of the present invention;
fig. 3A-3G are schematic cross-sectional views of the main processes for fabricating vertical structure near-uv led in accordance with the embodiments of the present invention.
Detailed Description
The following describes in detail specific embodiments of the vertical structure near-ultraviolet light emitting diode and the method for manufacturing the same according to the present invention with reference to the accompanying drawings.
The present embodiment provides a vertical structure near-ultraviolet light emitting diode, and fig. 1 is a schematic structural diagram of a vertical structure near-ultraviolet light emitting diode according to the present embodiment. As shown in fig. 1, the near ultraviolet light emitting diode with a vertical structure provided in this embodiment includes:
a conductive substrate 10, the conductive substrate 10 having a first surface and a second surface opposite to the first surface;
a metal reflective layer 11 on the first surface;
the nitride epitaxial layer is positioned on the surface of the metal reflecting layer 11 and comprises a P-type GaN layer 12, a quantum well layer 13, a preparation layer 18 and an N-type AlGaN layer 14 which are sequentially stacked along the direction vertical to the conductive substrate 10, and the thickness of the nitride epitaxial layer is smaller than the wavelength of near ultraviolet light;
an N-type electrode 15 on the surface of the N-type AlGaN layer 14;
and the P-type electrode 16 is positioned on the second surface.
Specifically, the wavelength range of the near ultraviolet light emitted by the vertical structure near ultraviolet light-emitting diode is 380 nm-400 nm. The quantum well layer 13 may be an InGaN/GaN quantum well layer. The conductive substrate 10 may be a metal substrate or a Si substrate, and those skilled in the art can select the substrate according to actual needs. In this embodiment, the conductive substrate 10 is preferably a Si substrate having a crystal orientation 100. The material of the metal reflective layer 11 may be one of nickel and silver, or an alloy of both. The metal reflective layer 11 and the P-type GaN layer 12 form ohmic contact (electrical connection), the conductive substrate 10 and the metal reflective layer 11 are electrically contacted, and the P-type electrode 16 and the conductive substrate 10 are in ohmic contact (electrical connection). The material of the preparation layer 18 may be GaN or AlGaN. The material of the N-type electrode 15 and the P-type electrode 16 may be chromium, platinum or gold.
In this embodiment, the N-type electrode 15 and the P-type electrode 16 are located on two opposite sides of the conductive substrate 10, and almost all current flows through the nitride epitaxial layer in a direction perpendicular to the conductive substrate 10, so that almost no current flows in a lateral direction, and the electrical injection efficiency is improved. Meanwhile, the thickness of the nitride epitaxial layer is set to be smaller than the wavelength of near ultraviolet light emitted by the vertical-structure near ultraviolet light-emitting diode, so that the vertical-structure near ultraviolet light-emitting diode is not limited by a constrained mode, the transmission of near ultraviolet light emitted by the light-emitting diode in the nitride epitaxial layer is reduced or even eliminated, the internal absorption loss is reduced, and the light-emitting efficiency of the light-emitting diode is greatly improved. In addition, the metal reflecting layer 11 reduces light loss, thereby further enhancing the light emitting efficiency of the light emitting diode.
In order to further improve the light extraction efficiency of the vertical structure near ultraviolet light emitting diode, the thickness of the nitride epitaxial layer is preferably less than 300 nm. At this moment, the thickness of the nitride epitaxial layer is far smaller than the wavelength of near ultraviolet light emitted by the light emitting diode, so that the limitation of the light emitting efficiency of the light emitting diode by a constraint mode is more effectively avoided.
Preferably, the vertical structure near ultraviolet light emitting diode further comprises a NiSn bonding layer 17 located between the conductive substrate 10 and the metal reflective layer 11.
The vertical structure near ultraviolet light emitting diode is obtained by bonding a conductive substrate 10 and a growth substrate, and the bonding layer 17 is formed by bonding a first NiSn bonding layer on the first surface of the conductive substrate 10 and a second NiSn bonding layer on the bonding surface of the growth substrate.
Preferably, the vertical-structure near ultraviolet light emitting diode is of a step-shaped structure; the step-shaped structure comprises a lower step and an upper step formed by the nitride epitaxial layer; the lower step includes the P-type electrode 16, the conductive substrate 10 and the metal reflective layer 11, and the lower step protrudes from the upper step along a direction parallel to the conductive substrate 10.
Specifically, as shown in fig. 1, the P-type GaN layer 12, the quantum well layer 13, the preparation layer 18, and the N-type AlGaN layer 14 sequentially stacked on the surface of the metal reflective layer 11 in the Y-axis direction form the upper step, the P-type electrode 16, the conductive substrate 10, and the metal reflective layer 11 sequentially stacked in the Y-axis direction form the lower step, and the lower step protrudes from the upper step in the X-axis direction, that is, the upper step protrudes from a partial region of the surface of the lower step, and the surface of the lower step not covered by the upper step exposes the metal reflective layer 11. By forming the step-shaped structure, a passivation layer is formed on the surface of the nitride epitaxial layer conveniently in the follow-up process so as to protect the nitride epitaxial layer.
Preferably, the thickness of the P-type GaN layer 12 is 80nm to 110nm, the thickness of the quantum well layer 13 is 98nm to 118nm, and the thickness of the preparation layer 18 is 95nm to 115 nm. The thicknesses of the P-type GaN layer 12, the quantum well layer 13, and the preparation layer 18 are not changed before and after the conductive substrate 10 is bonded to the growth substrate.
For example, the thickness of the P-type GaN layer 12 is 90nm, the thickness of the quantum well layer 13 is 108nm, and the thickness of the preparation layer 18 made of GaN or AlGaN is 105 nm.
Furthermore, the present embodiment further provides a method for manufacturing a vertical structure near-ultraviolet light emitting diode, fig. 2 is a flow chart of a method for manufacturing a vertical structure near-ultraviolet light emitting diode according to the present embodiment, fig. 3A to 3G are schematic process cross-sectional views of a process for manufacturing a vertical structure near-ultraviolet light emitting diode according to the present embodiment, and a specific structure of a vertical structure near-ultraviolet light emitting diode manufactured according to the present embodiment may be referred to fig. 1. As shown in fig. 1 to fig. 2 and fig. 3A to fig. 3G, the method for manufacturing a vertical structure near ultraviolet light emitting diode according to the present embodiment includes the following steps:
step S21, bonding a growth substrate 20 and a conductive substrate 10 to obtain the structure shown in fig. 3C; the surface of the growth substrate 20 is provided with a nitride epitaxial layer and a metal reflecting layer 11, the nitride epitaxial layer comprises a buffer layer 22, an undoped GaN layer 21, an N-type AlGaN layer 14, a preparation layer 18, a quantum well layer 13 and a P-type GaN layer 12 which are sequentially stacked along a direction perpendicular to the growth substrate 20, and the metal reflecting layer 11 is positioned on the surface of the P-type GaN layer 12, as shown in FIG. 3A; the conductive substrate 10 includes a first surface and a second surface opposite to the first surface, the second surface having a P-type electrode 16, as shown in fig. 3B.
The growth substrate 20 may be a group iii-v material substrate, a sapphire substrate, or a silicon substrate, and in the present embodiment, the growth substrate 20 is preferably a Si substrate with a crystal orientation 111. The specific steps of forming the growth substrate 20 include:
sequentially depositing a buffer layer 22, an undoped GaN (u-GaN) layer 21, an N-type AlGaN layer 14, a preparation layer 18, a quantum well layer 13 and a P-type GaN layer 12 on the surface of the growth substrate 20 to form an initial nitride epitaxial layer;
and forming a metal reflecting layer 11 on the surface of the P-type GaN layer 12.
The specific method for forming the metal reflective layer 11 on the surface of the P-type GaN layer 12 may be selected by those skilled in the art according to actual needs, and for example, an electron beam evaporation process, a magnetron sputtering process, a chemical vapor deposition, a physical vapor deposition, an atomic layer deposition, and the like may be adopted.
Specifically, the quantum well layer 13 may be an InGaN/GaN quantum well layer. The conductive substrate 10 may be a metal substrate or a Si substrate, and those skilled in the art can select the substrate according to actual needs. In this embodiment, the conductive substrate 10 is preferably a Si substrate having a crystal orientation 100. The material of the metal reflective layer 11 may be one of nickel and silver, or an alloy of both. The metal reflective layer 11 forms ohmic contact (electrical connection) with the P-type GaN layer 12. The material of the preparation layer 18 may be GaN or AlGaN. The material of the P-type electrode 16 may be chromium, platinum or gold. The buffer layer 22 is used to adjust the stress between the growth substrate 20 and the nitride epitaxial layer grown thereon.
In the growth substrate 20, the thicknesses of the layers in the nitride epitaxial layer that is initially grown are as follows: the buffer layer 22 is 1.2 to 1.4 μm, the undoped GaN (u-GaN) layer 21 is 0.6 to 0.8 μm, the N-type AlGaN layer 14 is 2.5 to 2.7 μm, the preparation layer 18 is 95 to 115nm, the quantum well layer 13 is 98 to 118nm, and the P-type GaN layer 12 is 80 to 100 nm. For example, the buffer layer 22 of AlN/AlGaN material has a thickness of 1.3 μm, the undoped GaN (u-GaN) layer 21 has a thickness of 0.7 μm, the N-type AlGaN layer 14 has a thickness of 2.63 μm, the preparation layer 18 of GaN material has a thickness of 105nm, the InGaN/GaN quantum well layer has a thickness of 108nm, and the P-type GaN layer 12 has a thickness of 90 nm.
The N-type AlGaN layer 14 initially grown in the growth substrate 20 may include a first N-type AlGaN layer and a second N-type AlGaN layer stacked on each other, wherein the second N-type AlGaN layer is located between the first N-type AlGaN layer and the preparation layer 18. The first N-type AlGaN layer may have a thickness of 2.5 μm, and the second N-type AlGaN layer may have a thickness of 130 nm. The contents of Al and Ga in the first N-type AlGaN layer and the second N-type AlGaN layer are distributed in a gradual change mode, and the doping concentration in the first N-type AlGaN layer is lower than that of the second N-type AlGaN layer.
In the bonding process, the conductive substrate 10 and the growth substrate 20 are bonded in the Y-axis direction in such a manner that the metal reflective layer 11 faces the first surface of the conductive substrate 10.
Specifically, the specific steps of bonding a growth substrate 20 and a conductive substrate 10 include:
forming a first NiSn bonding layer 171 on the surface of the metal reflective layer 11;
forming a second NiSn bonding layer 172 on the first surface of the conductive substrate 10;
bonding the first NiSn bonding layer 171 and the second NiSn bonding layer 172.
The specific method for forming the first NiSn bonding layer 171 on the surface of the metal reflective layer 11 and the specific method for forming the second NiSn bonding layer 172 on the first surface of the conductive substrate 10 may be any one of an electron beam evaporation process, a magnetron sputtering process, a chemical vapor deposition, a physical vapor deposition, and an atomic layer deposition. The first NiSn bonding layer 171 is in ohmic contact with the metal reflective layer 11, and the second NiSn bonding layer 172 is in ohmic contact with the conductive substrate 10.
Step S22, the growth substrate 20 is peeled off, as shown in fig. 3D.
Step S23, etching the nitride epitaxial layer, removing the buffer layer 22 and the undoped GaN layer 21, and thinning the N-type AlGaN layer 14, so that the thickness of the remaining nitride epitaxial layer is smaller than the wavelength of near ultraviolet light.
Preferably, the specific step of etching the nitride epitaxial layer includes:
etching the nitride epitaxial layer to the N-type AlGaN layer 14, removing the buffer layer 22 and the undoped GaN layer 21, and thinning the N-type AlGaN layer 14, so that the thickness of the remaining nitride epitaxial layer is smaller than the wavelength of near ultraviolet light, as shown in fig. 3E;
defining a device region in the residual nitride epitaxial layer;
etching the residual nitride epitaxial layer around the device region to the metal reflection layer 11 to form a step-shaped structure; the step-shaped structure comprises a lower step and an upper step formed by the residual nitride epitaxial layer in the device region; the lower step includes the P-type electrode 16, the conductive substrate 10 and the metal reflective layer 11, and the lower step protrudes from the upper step along a direction parallel to the conductive substrate 10, as shown in fig. 3F.
Specifically, the embodiment adopts a two-step etching process: in the first step of etching process, removing the buffer layer 22 and the undoped GaN layer 21, and thinning the N-type AlGaN layer 14, so as to control the thickness of the remaining nitride epitaxial layer; in the second etching process, the step-like structure is formed, wherein the remaining nitride epitaxial layer in the device region forms the upper step, the P-type electrode 16, the conductive substrate 10 and the metal reflective layer 11, which are sequentially stacked along the Y-axis direction, form the lower step, and the lower step protrudes from the upper step along the X-axis direction, that is, the upper step is protruded in a partial region of the surface of the lower step, and the surface of the lower step, which is not covered by the remaining nitride epitaxial layer, exposes the metal reflective layer 11. By forming the step-shaped structure, a passivation layer is formed on the surface of the nitride epitaxial layer conveniently in the follow-up process so as to protect the nitride epitaxial layer.
In order to further improve the light extraction efficiency of the vertical structure near ultraviolet light emitting diode, the thickness of the residual nitride epitaxial layer is preferably less than 300 nm. At the moment, the total thickness of the nitride epitaxial layer in the finally formed vertical-structure near ultraviolet light-emitting diode is far smaller than the wavelength of near ultraviolet light emitted by the light-emitting diode, so that the limitation of the light-emitting efficiency of the light-emitting diode by a constraint mode is more effectively avoided.
In step S24, an N-type electrode 15 is formed on the surface of the remaining N-type AlGaN layer 14, as shown in fig. 3G.
The materials of the N-type electrode 15 and the P-type electrode 16 may be chromium, platinum or gold. Specifically, the N-type electrode 15 may be formed on the surface of the thinned N-type AlGaN layer 14 by depositing a metal electrode.
According to the near ultraviolet light-emitting diode with the vertical structure and the preparation method thereof, as the device adopts the vertical structure, the electric injection efficiency is improved; meanwhile, the thickness of the nitride epitaxial layer is set to be smaller than the wavelength of near ultraviolet light, so that the vertical-structure near ultraviolet light-emitting diode is not limited by a constrained mode, the transmission of emergent light of the light-emitting diode in the nitride epitaxial layer is reduced or even eliminated, the internal absorption loss is reduced, and the light-emitting efficiency of the light-emitting diode is greatly improved; meanwhile, the arrangement of the metal reflecting layer further enhances the light emitting efficiency of the light emitting diode.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (6)
1. A vertical geometry near ultraviolet light emitting diode comprising:
a conductive substrate having a first surface and a second surface opposite the first surface;
the metal reflecting layer is positioned on the first surface;
the nitride epitaxial layer is positioned on the surface of the metal reflecting layer and comprises a P-type GaN layer, a quantum well layer, a preparation layer and a thinned N-type AlGaN layer which are sequentially overlapped in the direction vertical to the conductive substrate, and the thickness of the nitride epitaxial layer is smaller than the wavelength of near ultraviolet light emitted by the vertical structure near ultraviolet light-emitting diode, so that the vertical structure near ultraviolet light-emitting diode is not limited by a constrained mode; the wavelength range of near ultraviolet light emitted by the vertical structure near ultraviolet light-emitting diode is 380 nm-400 nm, and the thickness of the nitride epitaxial layer is below 300 nm;
the N-type AlGaN layer initially grown in the growth substrate comprises a first N-type AlGaN layer and a second N-type AlGaN layer which are mutually overlapped, wherein the second N-type AlGaN layer is positioned between the first N-type AlGaN layer and the preparation layer, and the contents of Al and Ga in the first N-type AlGaN layer and the second N-type AlGaN layer are distributed in a gradual change mode;
the N-type electrode is positioned on the surface of the N-type AlGaN layer;
the P-type electrode is positioned on the second surface, and the N-type electrode and the P-type electrode are positioned on two opposite sides of the conductive substrate, so that current flows through the nitride epitaxial layer along a direction perpendicular to the conductive substrate, and the electrical injection efficiency is improved;
the vertical structure near ultraviolet light-emitting diode is of a step-shaped structure; the step-shaped structure comprises a lower step and an upper step formed by the nitride epitaxial layer; the lower step comprises the P-type electrode, the conductive substrate and the metal reflecting layer, and the lower step protrudes out of the upper step along a direction parallel to the conductive substrate, so that a passivation layer is formed on the surface of the nitride epitaxial layer in a follow-up manner, and the nitride epitaxial layer is protected.
2. The vertical structure near ultraviolet light emitting diode of claim 1, further comprising a NiSn bonding layer between the conductive substrate and the metal reflective layer.
3. The vertical structure near ultraviolet light emitting diode of claim 1, wherein the thickness of the P-type GaN layer is 80nm to 100nm, the thickness of the quantum well layer is 98nm to 118nm, and the thickness of the preparation layer is 95nm to 115 nm.
4. A method for preparing a vertical structure near ultraviolet light emitting diode is characterized by comprising the following steps:
bonding a growth substrate and a conductive substrate, wherein the surface of the growth substrate is provided with a nitride epitaxial layer and a metal reflecting layer, the nitride epitaxial layer comprises a buffer layer, an undoped GaN layer, an N-type AlGaN layer, a preparation layer, a quantum well layer and a P-type GaN layer which are sequentially superposed along the direction vertical to the growth substrate, and the metal reflecting layer is positioned on the surface of the P-type GaN layer; the conductive substrate comprises a first surface and a second surface opposite to the first surface, and the second surface is provided with a P-type electrode;
stripping the growth substrate;
the N-type AlGaN layer initially grown in the growth substrate comprises a first N-type AlGaN layer and a second N-type AlGaN layer which are mutually overlapped, wherein the second N-type AlGaN layer is positioned between the first N-type AlGaN layer and the preparation layer, and the contents of Al and Ga in the first N-type AlGaN layer and the second N-type AlGaN layer are distributed in a gradual change mode;
etching the nitride epitaxial layer to the N-type AlGaN layer, removing the buffer layer and the undoped GaN layer, and thinning the N-type AlGaN layer to ensure that the thickness of the residual nitride epitaxial layer is smaller than the wavelength of near ultraviolet light emitted by the vertical structure near ultraviolet light-emitting diode, so that the vertical structure near ultraviolet light-emitting diode is not limited by a constrained mode;
defining a device region in the residual nitride epitaxial layer;
etching the residual nitride epitaxial layer around the device region to the metal reflecting layer to form a step-shaped structure; the step-shaped structure comprises a lower step and an upper step formed by the residual nitride epitaxial layer in the device region; the lower step comprises the P-type electrode, the conductive substrate and the metal reflecting layer, and the lower step protrudes out of the upper step along a direction parallel to the conductive substrate, so that a passivation layer is formed on the surface of the nitride epitaxial layer in the follow-up process to protect the nitride epitaxial layer;
forming N-type electrodes on the surface of the residual N-type AlGaN layer, wherein the N-type electrodes and the P-type electrodes are positioned on two opposite sides of the conductive substrate, so that current flows through the nitride epitaxial layer along the direction vertical to the conductive substrate, and the electrical injection efficiency is improved; the wavelength range of near ultraviolet light emitted by the vertical structure near ultraviolet light emitting diode is 380 nm-400 nm, and the thickness of the nitride epitaxial layer is below 300 nm.
5. The method of claim 4, wherein the step of bonding a growth substrate and a conductive substrate comprises:
forming a first NiSn bonding layer on the surface of the metal reflecting layer;
forming a second NiSn bonding layer on the first surface of the conductive substrate;
and bonding the first NiSn bonding layer and the second NiSn bonding layer.
6. The method for preparing a vertical-structure near ultraviolet light-emitting diode according to claim 4, wherein the thickness of the P-type GaN layer is 80nm to 100nm, the thickness of the quantum well layer is 98nm to 118nm, and the thickness of the preparation layer is 95nm to 115 nm.
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