CN111146314B - Method for improving light extraction efficiency of nitride semiconductor ultraviolet light-emitting diode and application - Google Patents
Method for improving light extraction efficiency of nitride semiconductor ultraviolet light-emitting diode and application Download PDFInfo
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- CN111146314B CN111146314B CN201811314183.9A CN201811314183A CN111146314B CN 111146314 B CN111146314 B CN 111146314B CN 201811314183 A CN201811314183 A CN 201811314183A CN 111146314 B CN111146314 B CN 111146314B
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/005—Processes
- H01L33/0062—Processes for devices with an active region comprising only III-V compounds
- H01L33/0075—Processes for devices with an active region comprising only III-V compounds comprising nitride compounds
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/02—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
- H01L33/20—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a particular shape, e.g. curved or truncated substrate
- H01L33/22—Roughened surfaces, e.g. at the interface between epitaxial layers
Abstract
The invention discloses a method for improving nitride semiconductor ultraviolet luminescenceA method for extracting light efficiency of a polar tube and application thereof. The method comprises the following steps: growing a nitride semiconductor ultraviolet light emitting diode structure on a substrate to obtain an epitaxial wafer, wherein the nitride semiconductor ultraviolet light emitting diode structure comprises a first contact layer, an active region, an electron blocking layer and a second contact layer which are sequentially formed, and the method further comprises the following steps: by rotating dislocation method, any side of the photo-etched pattern can be kept away from the nitride semiconductor ultraviolet LED structure
A crystal orientation; repairing etching damage by wet etching technique to convert irregular rough side wall of nitride semiconductor ultraviolet LED structure into m surface
A zigzag side wall is formed. The invention combines the rotation dislocation and the side wall corrosion process to realize the side wall coarsening and the etching damage repair of the epitaxial wafer, can obviously improve the light extraction efficiency of the nitride semiconductor ultraviolet light-emitting diode and improve the performance of the ultraviolet light-emitting diode device.
Description
Technical Field
The invention relates to a nitride semiconductor ultraviolet light emitting diode, in particular to a method for improving the light extraction efficiency of the nitride semiconductor ultraviolet light emitting diode and application thereof, belonging to the technical field of semiconductor photoelectricity.
Background
The ultraviolet band can be generally divided into long-wave ultraviolet or UVA (320< lambda < 400nm), medium-wave ultraviolet or UVB (280< lambda < 320nm), short-wave ultraviolet or UVC (200< lambda < 280nm), and vacuum ultraviolet VUV (10< lambda < 200nm), depending on the wavelength. The ultraviolet light emitting diode device based on nitride (AlN, AlGaN, AlInGaN, AlInN and the like) materials has the advantages that the light emitting wavelength of the ultraviolet light emitting diode device can cover the ultraviolet band of 200-400 nm, the photoelectric conversion efficiency is high, and the ultraviolet light emitting diode device is an ideal material for preparing the ultraviolet light emitting diode device. Compared with the traditional ultraviolet mercury lamp, the nitride semiconductor ultraviolet light-emitting diode has the advantages of long service life, low voltage, adjustable wavelength, environmental protection, good directivity, shock resistance, moisture resistance, portability, flexibility and the like, and has important application prospect and market value in the fields of white light illumination, polymer curing, sterilization and disinfection, environment purification, medical diagnosis, biochemical detection, confidential communication and the like. With the development of the third generation semiconductor technology, the nitride semiconductor ultraviolet light emitting diode will gradually replace the traditional ultraviolet light source, and become the mainstream of new applications in the future.
However, the external quantum efficiency of the nitride semiconductor ultraviolet light emitting diode at present is less than 10%, and one of the main reasons is that the TM mode polarization effect causes the light extraction efficiency of the deep ultraviolet light emitting diode device to be reduced. For (In) GaN semiconductor materials, which emit light primarily In the TE polarization mode, light can exit the surface of the light emitting diode chip. For Al (in) GaN material, as the Al component increases and the wavelength decreases, the valence band structure of the material changes, and the ultraviolet luminescence is gradually converted from TE polarization mode dominance to TM polarization mode dominance. This effect will prevent photons from exiting the surface of the led device, only the sides of the led device. This problem is particularly acute with deep ultraviolet light emitting diode devices. The nitride deep ultraviolet light emitting diode device has a higher Al component, the proportion of TE polarized light in an active region is less, the proportion of TM polarized light is more, and most of light can be transmitted along a plane and cannot be emitted from the surface of a chip. Therefore, improving the sidewall extraction efficiency is particularly important for deep ultraviolet light emitting diode devices. In addition, when a traditional ultraviolet light emitting diode chip is manufactured, the side wall of the ultraviolet light emitting diode chip is irregularly etched and damaged by a dry etching process, so that the side wall is very rough. The irregular rough side wall can increase the diffuse reflection effect of the side wall on ultraviolet light and increase the extraction efficiency of TM mode ultraviolet light in an active region, but also comprises a large amount of etching damage and surface defect states, so that serious photon absorption and carrier nonradiative recombination are caused. This not only greatly reduces the light extraction efficiency of the uv led device, but also leads to poor device stability and heat dissipation.
In summary, it can be seen that the polarization effect of the TM mode and the sidewall etching damage are important reasons that the light extraction efficiency of the ultraviolet, especially deep ultraviolet light emitting diode device is extremely low. Therefore, how to overcome the polarization effect of the TM mode and remove the etching damage to improve the light extraction efficiency of the ultraviolet light emitting diode device becomes a problem to be solved urgently.
For the existing scheme for improving the light extraction efficiency of the ultraviolet light emitting diode device with the flip structure, patent CN102655194A adopts a mode of roughening the back surface of the substrate. Firstly, the sapphire substrate of the ultraviolet LED epitaxial wafer needs to be thinned and polished, and the process may damage the ultraviolet LED epitaxial layer. Secondly, depositing a layer of nitride on the back surface of the sapphire substrate, and then roughening the surface of the nitride layer by utilizing dry etching or wet etching. However, this surface roughening method can only improve the TE mode uv light emitted from the upper and lower surfaces of the chip, but does not help in TM mode uv light extraction. As the Al composition increases and the wavelength decreases, the proportion of TE mode polarized light decreases greatly. Secondly, the side wall of the ultraviolet light emitting diode device is damaged by an etching process adopted during chip isolation, a large number of surface non-radiative composite defects are introduced into the damage, the quantum efficiency of the ultraviolet light emitting diode device is reduced, and serious photon absorption is caused. Therefore, it is difficult to improve the light extraction efficiency of the deep ultraviolet light emitting diode device with this solution.
For another example, patent CN107623058A discloses a method for growing an ultraviolet LED film on the surface of a film having an etch defect structure by secondary epitaxy. And (3) processing the aluminum nitride film on the substrate by wet etching to form an inner hexagonal defect structure. And then, growing an ultraviolet LED on the defect structure in a secondary epitaxial manner, and utilizing the hexagonal defect structure to coarsen an interface and improve the light extraction efficiency of the deep ultraviolet LED device. However, this method suffers from unintended incorporation of impurities at the secondary epitaxial interface, which may have an effect on the electrical properties of the device. More importantly, the method is only effective for extracting the TE mode ultraviolet light and does not help TM mode polarized light propagating in an active area plane, so that the light extraction efficiency of the deep ultraviolet light-emitting diode device is difficult to improve.
For the existing scheme for improving the light extraction efficiency of the ultraviolet light emitting diode device with the vertical structure, the patent CN105720144A adopts a surface roughening method. After the substrate for growing the AlGaN epitaxial layer is stripped, the surface of the stripped epitaxial layer is roughened by wet etching to increase interface diffuse reflection. The surface roughening can improve the extraction of TE mode ultraviolet light in the epitaxial direction of the vertical chip to a certain extent, and does not help the extraction of TM mode ultraviolet light, so that the light extraction efficiency of the deep ultraviolet light emitting diode device is difficult to improve by the scheme.
For another example, patent CN 105957934a adopts a resonant cavity structure, and n-type nitride DBRs (distributed bragg reflectors) are grown on and under the active region as the resonant cavity to enhance the TE mode polarized light and improve the light extraction efficiency of the ultraviolet LED. And a p-n junction inverted structure is realized by introducing a nitride polarization induced tunneling junction, so that an ultraviolet LED device with a vertical structure is realized. However, the introduction of the DBR may increase the series resistance and the thermal resistance of the device, which may increase the operating voltage of the device and decrease the reliability. More importantly, the DBR structure is still only effective for improving the TE mode polarized light, and the light extraction efficiency of the TM mode polarized light deep ultraviolet light cannot be improved.
It can be found that the above-mentioned existing methods for improving the light extraction efficiency of nitride semiconductor ultraviolet light emitting diodes have some common disadvantages: 1) cannot improve the extraction efficiency of TM mode ultraviolet light from the side wall; 2) the etching damage of the side wall of the chip is not repaired, and the light absorption and non-radiation compounding of the surface of the side wall cannot be reduced; 3) the growth/process complexity is improved, the device stability is poor, and the practicability is poor.
Disclosure of Invention
The invention mainly aims to provide a method for improving the light extraction efficiency of a nitride semiconductor ultraviolet light-emitting diode and application thereof, so as to overcome the defects of the prior art.
In order to achieve the purpose, the technical scheme adopted by the invention comprises the following steps:
the embodiment of the invention provides a method for improving the light extraction efficiency of a nitride semiconductor ultraviolet light-emitting diode, which comprises the following steps: growing a nitride semiconductor ultraviolet light emitting diode structure on a substrate to obtain an epitaxial wafer, wherein the nitride semiconductor ultraviolet light emitting diode structure comprises a first contact layer, an active region, an electron blocking layer and a second contact layer which are sequentially formed, and the method further comprises the following steps:
by rotating dislocation method, any side of the photo-etched pattern can be kept away from the nitride semiconductor ultraviolet LED structure
A crystal orientation;
and repairing etching damage by wet etching technique to convert irregular rough side wall of nitride semiconductor ultraviolet LED structure into m surface
A zigzag side wall is formed.
Further, wherein the pattern is lithographically patterned
The effect of exposing the a-plane in the crystal direction is optimal.
In some preferred embodiments, the method specifically comprises:
growing a nitride semiconductor ultraviolet light-emitting diode structure on a substrate to obtain an epitaxial wafer, wherein the nitride semiconductor ultraviolet light-emitting diode structure comprises a first contact layer, an active region, an electron blocking layer and a second contact layer which are sequentially formed;
determining the crystal orientation of the epitaxial wafer using diffraction techniques and
a crystal orientation;
arranging a second electrode layer on the second contact layer, and enabling the second electrode layer and the second contact layer to form ohmic contact;
arranging photoresist on the second electrode layer, and adopting rotation dislocation method to make any side of the photoetching pattern avoid the structure of nitride semiconductor ultraviolet light-emitting diode
A crystal orientation;
etching the first contact layer by adopting an etching technology to expose at least a local area of the first contact layer and preliminarily form a random rough side wall;
arranging a first electrode layer on the first contact layer, and enabling the first electrode layer and the first contact layer to form ohmic contact;
and contacting the obtained epitaxial wafer with corrosive liquid, repairing etching damage and coarsening the side wall, so that the irregular rough side wall of the nitride semiconductor ultraviolet light-emitting diode structure is converted into a saw-tooth-shaped m-surface side wall.
In other preferred embodiments, the method may further include:
growing a nitride semiconductor ultraviolet light-emitting diode structure on a substrate to obtain an epitaxial wafer, wherein the nitride semiconductor ultraviolet light-emitting diode structure comprises a first contact layer, an active region, an electron blocking layer and a second contact layer which are sequentially formed;
determining the crystal orientation of the epitaxial wafer using diffraction techniques and
a crystal orientation;
arranging a second electrode layer on the second contact layer, and enabling the second electrode layer and the second contact layer to form ohmic contact;
bonding the second electrode layer to a first surface of a support substrate;
stripping the nitride semiconductor ultraviolet light-emitting diode structure from the substrate to expose the first contact layer;
manufacturing an optical micro-nano structure on a light-emitting surface of the nitride semiconductor ultraviolet light-emitting diode structure, wherein the optical micro-nano structure is used for enhancing light emission;
arranging a first electrode layer on the first contact layer, and enabling the first electrode layer and the first contact layer to form ohmic contact;
arranging photoresist on the first electrode layer, and adopting rotation dislocation method to make any edge of the photoetching pattern avoid the structure of nitride semiconductor ultraviolet light-emitting diode
A crystal orientation;
etching the second electrode layer by adopting an etching technology to preliminarily form a random rough side wall;
and contacting the obtained epitaxial wafer with corrosive liquid, repairing etching damage and coarsening the side wall, so that the irregular rough side wall of the nitride semiconductor ultraviolet light-emitting diode structure is converted into a saw-tooth-shaped m-surface side wall.
Further, the method may further include: and after photoetching, thinning the support substrate, and depositing a metal electrode on a second surface of the support substrate, wherein the second surface is opposite to the first surface.
The embodiment of the invention provides a nitride semiconductor ultraviolet light-emitting diode manufactured by any one of the methods.
Further, the nitride semiconductor ultraviolet light emitting diode comprises a nitride semiconductor ultraviolet light emitting diode structure formed by growing on a substrate, and the side wall of the nitride semiconductor ultraviolet light emitting diode structure is a sawtooth-shaped m-plane side wall.
Compared with the prior art, the method for improving the light extraction efficiency of the nitride semiconductor ultraviolet light-emitting diode provided by the invention combines the processes of rotary dislocation and side wall corrosion to realize the coarsening of the side wall of the epitaxial chip and the repair of etching damage, so that the side wall of the nitride semiconductor ultraviolet light-emitting diode chip is a sawtooth-shaped side wall, the light extraction efficiency of the active area ultraviolet light-emitting diode can be obviously improved, and the preparation process is compatible with the existing light-emitting diode preparation process and is completely suitable for large-scale production.
Drawings
Fig. 1 is a schematic view showing an epitaxial structure of a nitride semiconductor ultraviolet light emitting diode in embodiment 1 of the present invention.
Fig. 2 is a schematic view showing the crystal orientation of the nitride semiconductor ultraviolet light emitting diode epitaxial wafer determined by the diffraction technique in embodiment 1 of the present invention.
Fig. 3 is a schematic structural diagram of an ultraviolet light emitting diode epitaxial wafer after a p-type ohmic contact is formed and a photoresist is spin-coated in embodiment 1 of the present invention.
Fig. 4 is a schematic diagram illustrating photolithography performed on an ultraviolet light emitting diode epitaxial wafer by a clockwise rotation dislocation method in embodiment 1 of the present invention.
Fig. 5 is a schematic top view illustrating the etching of the n-type contact layer and the formation of the irregular rough sidewall in embodiment 1 of the present invention.
Fig. 6 is a schematic cross-sectional view of an ultraviolet light emitting diode epitaxial wafer structure after depositing n-type ohmic contact metal in embodiment 1 of the present invention. Fig. 7a to 7e are schematic diagrams showing the shapes of the ultraviolet light emitting diode chips for etching in example 1 and example 2 of the present invention, respectively.
Fig. 8 is a schematic view of a zigzag nitride semiconductor uv led die after chemical solution etching in embodiment 1 of the present invention.
Fig. 9 is a schematic view of an epitaxial structure of a nitride semiconductor ultraviolet light emitting diode in embodiment 2 of the present invention.
Fig. 10 is a schematic view showing the crystal orientation of the nitride semiconductor ultraviolet light emitting diode epitaxial wafer determined by the diffraction technique in embodiment 2 of the present invention.
Fig. 11 is a schematic structural diagram of an ultraviolet light emitting diode epitaxial wafer after a p-type ohmic contact metal is formed in embodiment 2 of the present invention.
Fig. 12 is a schematic structural view of a p-type ohmic contact metal deposited with a bonding metal in embodiment 2 of the present invention.
Fig. 13 is a schematic structural view after the substrate and the buffer layer are removed and bonded to the supporting substrate in embodiment 2 of the present invention.
FIG. 14 shows a schematic view of a view of the embodiment 2 of the present invention
And preparing a structural schematic diagram of the ultraviolet light-emitting diode with an optical micro-nano structure for enhancing light emission on the nitrogen surface n-type ohmic contact layer.
Fig. 15 is a schematic diagram illustrating photolithography performed on an ultraviolet light emitting diode epitaxial wafer by a counter-clockwise rotation dislocation method in embodiment 2 of the present invention.
Fig. 16 is a schematic structural diagram of an ultraviolet light emitting diode epitaxial wafer after etching a p-type ohmic contact electrode in embodiment 2 of the present invention.
Fig. 17 is a schematic structural diagram of an ultraviolet light emitting diode epitaxial wafer after a metal electrode is deposited on the back surface of a support wafer in embodiment 2 of the present invention.
Fig. 18a to 18b are schematic views showing flip-chip and vertical structure nitride semiconductor ultraviolet light emitting diodes having serrated sidewalls in example 3 and example 2 of the present invention, respectively.
Description of reference numerals: 101 is a substrate, 102 is a buffer layer, 103 is an n-type contact layer, 104 is an active region, 105 is an electron blocking layer, 106 is a p-type contact layer, 107 is a p-type ohmic contact electrode or a combination of a transparent conductive film and a high-reflective film, 108 is photoresist, 109 is an n-type ohmic contact electrode, 110 is a whole epitaxial layer, 201 is a substrate, 202 is a buffer layer, 203 is an n-type contact layer, 204 is an active region, 205 is an electron blocking layer, 206 is a p-type contact layer, 207 is a p-type ohmic contact electrode or a combination of a transparent conductive film and a high-reflective film, 208 is a wafer bonding metal, 209 is solder, 210 is a support substrate, 211 is a metal electrode, 212 is a whole epitaxial layer, 213 is a nitrogen-face n-type ohmic contact electrode, and 214 is a nitrogen-face p-type ohmic contact electrode.
Detailed Description
As mentioned above, the existing deep ultraviolet light emitting diode has the problem that the light extraction efficiency of the deep ultraviolet light emitting diode chip is low due to the TM mode polarized light effect. In view of the deficiencies in the prior art, the inventors of the present invention have made extensive studies and extensive practices to provide technical solutions of the present invention. The technical solution, its implementation and principles, etc. will be further explained as follows. It is to be understood, however, that within the scope of the present invention, the above-described features of the present invention and those specifically described below (e.g., in the examples) may be combined with one another to form new or preferred embodiments. Not to be reiterated herein, but to the extent of space.
One aspect of the embodiments of the present invention provides a method for improving light extraction efficiency of a nitride semiconductor ultraviolet light emitting diode, including: growing a nitride semiconductor ultraviolet light emitting diode structure on a substrate to obtain an epitaxial wafer, wherein the nitride semiconductor ultraviolet light emitting diode structure comprises a first contact layer, an active region, an electron blocking layer and a second contact layer which are sequentially formed, and the method further comprises the following steps:
by rotating dislocation method, any side of the photo-etched pattern can be kept away from the nitride semiconductor ultraviolet LED structure
Crystal orientation in which the lithographic pattern is oriented
Crystal orientation exposes a face
The effect of the surface is optimal;
and repairing etching damage by wet etching technique to convert irregular rough side wall of nitride semiconductor ultraviolet LED structure into m surface
A zigzag side wall is formed.
In some preferred embodiments, the nitride semiconductor ultraviolet light emitting diode structure
The crystal orientation being a family of crystal orientations, including symmetrical equivalents
And
and (4) crystal orientation.
Further, the nitride semiconductor ultraviolet light emitting diode structure
The crystal orientation being a family of crystal orientations, including symmetrical equivalents
And
and (4) crystal orientation.
Further, the a-plane of the nitride semiconductor ultraviolet light emitting diode structure
Is a family of crystal planes, including symmetrically equivalent
And
a crystal plane.
Further, the m-plane of the nitride semiconductor ultraviolet light emitting diode structure
Is a crystal faceFamily, including symmetrical equivalents
And
a crystal plane.
In some preferred embodiments, the method specifically comprises:
growing a nitride semiconductor ultraviolet light-emitting diode structure on a substrate to obtain an epitaxial wafer, wherein the nitride semiconductor ultraviolet light-emitting diode structure comprises a first contact layer, an active region, an electron blocking layer and a second contact layer which are sequentially formed;
determining the crystal orientation of the epitaxial wafer using diffraction techniques and
a crystal orientation;
arranging a second electrode layer on the second contact layer, and enabling the second electrode layer and the second contact layer to form ohmic contact;
arranging photoresist on the second electrode layer, and adopting rotation dislocation method to make any side of the photoetching pattern avoid the structure of nitride semiconductor ultraviolet light-emitting diode
A crystal orientation;
etching the first contact layer by adopting an etching technology to expose at least a local area of the first contact layer and preliminarily form a random rough side wall;
arranging a first electrode layer on the first contact layer, and enabling the first electrode layer and the first contact layer to form ohmic contact;
and contacting the obtained epitaxial wafer with corrosive liquid, repairing etching damage and coarsening the side wall, so that the irregular rough side wall of the nitride semiconductor ultraviolet light-emitting diode structure is converted into a saw-tooth-shaped m-surface side wall.
In other preferred embodiments, the method may further include:
growing a nitride semiconductor ultraviolet light-emitting diode structure on a substrate to obtain an epitaxial wafer, wherein the nitride semiconductor ultraviolet light-emitting diode structure comprises a first contact layer, an active region, an electron blocking layer and a second contact layer which are sequentially formed;
determining the crystal orientation of the epitaxial wafer using diffraction techniques and
a crystal orientation;
arranging a second electrode layer on the second contact layer, and enabling the second electrode layer and the second contact layer to form ohmic contact;
bonding the second electrode layer to a first surface of a support substrate;
stripping the nitride semiconductor ultraviolet light-emitting diode structure from the substrate to expose the first contact layer;
manufacturing an optical micro-nano structure on a light-emitting surface of the nitride semiconductor ultraviolet light-emitting diode structure, wherein the optical micro-nano structure is used for enhancing light emission;
arranging a first electrode layer on the first contact layer, and enabling the first electrode layer and the first contact layer to form ohmic contact;
arranging photoresist on the first electrode layer, and adopting rotation dislocation method to make any edge of the photoetching pattern avoid the structure of nitride semiconductor ultraviolet light-emitting diode
A crystal orientation;
etching the second electrode layer by adopting an etching technology to preliminarily form a random rough side wall;
and contacting the obtained epitaxial wafer with corrosive liquid, repairing etching damage and coarsening the side wall, so that the irregular rough side wall of the nitride semiconductor ultraviolet light-emitting diode structure is converted into a saw-tooth-shaped m-surface side wall.
Further, the method may further include: and after photoetching, thinning the support substrate, and depositing a metal electrode on a second surface of the support substrate, wherein the second surface is opposite to the first surface.
In some embodiments, the photolithographic patterning is relative to the epitaxial wafer in the rotational misalignment process
The angle alpha of the crystal direction rotation is the non-edge of the photoetching pattern
Any angle of the crystal direction is preferably 1-60 degrees.
Further, in the rotational misalignment method, the direction of rotation may be clockwise or counterclockwise.
In some embodiments, the etching damage of the sidewall of the uv led can be removed by wet etching, wherein the etching solution used in the wet etching is an alkaline solution such as KOH, NaOH, TMAH, or the like, or H3PO4、HF、HNO3And the like, but not limited thereto.
In some embodiments, the nitride semiconductor ultraviolet light emitting diode structure includes a buffer layer, a first contact layer, an active region, an electron blocking layer, and a second contact layer, which are sequentially formed.
Further, the epitaxial layer structure includes, but is not limited to, a buffer layer, a first contact layer, an active region, an electron blocking layer, and a second contact layer, and may further include a DBR, SiO2Any one or a combination of two or more of the optical reflection layer structures such as the dielectric layer, but not limited thereto.
Further, the material of the substrate may be any one or a combination of two or more of GaN, AlN, BN, sapphire, Si, SiC, ZnO, and the like, but is not limited thereto.
In some embodiments, the active region quantum well of the nitride semiconductor ultraviolet light emitting diode structure includes any one or a combination of two or more of AlN, AlGaN, AlInGaN, and AlInN, but is not limited thereto.
In some embodiments, the method further comprises: and removing the substrate from the epitaxial wafer by adopting a wet etching method or a laser stripping method.
In some embodiments, the light emitting surface of the nitride semiconductor ultraviolet light emitting diode structure is made of nitride material
Nitrogen face.
In some embodiments, the optical micro-nano structure includes any one or a combination of two or more of zigzag, triangle, nano-column, trapezoid, inverted trapezoid, Mongolian yurt, micro-nano porous structure, and the like, and is not limited thereto.
Further, the method further comprises: and manufacturing the optical micro-nano structure by adopting any one or combination of more than two of dry etching, wet etching, electrochemical etching and photo-assisted electrochemical etching technologies.
In some embodiments, the method further comprises: the shape of the epitaxial wafer for etching includes any one or a combination of two or more of a square, a rectangle, a triangle, a hexagon, an octagon, a dodecagon, an inverted trapezoid, a disc, a circular ring, a spiral, or other shapes.
Further, the shape of the etched epitaxial wafer includes any one or a combination of two or more of a square, a rectangle, a triangle, a hexagon and an inverted trapezoid, but is not limited thereto.
Further, the method further comprises the following steps: and performing die cutting to form a single ultraviolet light emitting diode die with a sawtooth-shaped side wall.
Further, the first contact layer is an n-type contact layer, the first electrode layer comprises n-type ohmic contact metal, the second contact layer is a p-type contact layer, and the second electrode layer comprises p-type ohmic contact metal or a combination of a transparent conductive film and a high-reflection film.
Further, the n-type ohmic contact metal or the p-type ohmic contact metal of the uv light emitting diode of the present invention may be any one or a combination of two or more of materials such as Ni, Ti, Pd, Pt, Au, Al, TiN, ITO, and IGZO, but is not limited thereto.
In a more specific embodiment of the present invention, a method for improving light extraction efficiency of a nitride semiconductor ultraviolet light emitting diode comprises: (for the structure of ultraviolet light emitting diode)
(1) A nitride semiconductor ultraviolet light emitting diode structure is grown on a substrate, and specifically comprises a buffer layer, an n-type contact layer, an active region, an electron blocking layer and a p-type contact layer, as shown in fig. 1.
(2) Determining the crystal orientation of an epitaxial layer of an ultraviolet light emitting diode using diffraction techniques and
the crystal orientation is shown in fig. 2.
(3) And after the epitaxial wafer is cleaned, a p-type ohmic contact electrode is deposited on the whole surface of the p-type contact layer and annealed to form better ohmic contact. A photoresist is then spin coated on the p-type ohmic contact electrode as shown in fig. 3.
(4) By using a rotary dislocation method, the pattern of the reticle is made to face the AlGaN epitaxial film
The direction rotates around the central axis by an angle alpha, so that any one edge of the photoetching pattern is avoided
The crystal orientation is shown in fig. 4.
(5) After photoetching, the n-type contact layer is etched by adopting a dry etching technology, and irregular rough side walls are formed preliminarily, as shown in fig. 5.
(6) Through photolithography, metal deposition and lift-off processes, an n-type ohmic contact electrode and a p-type thickened electrode of the nitride semiconductor ultraviolet light emitting diode structure are formed, as shown in fig. 6.
(7) And placing the epitaxial wafer in a chemical solution for corrosion, repairing etching damage and realizing coarsening of the side wall. For wurtzite structure nitrides, the m-plane is
The surface is a cleavage surface, which has stable chemical properties and is not easy to be corroded, so that the irregular rough sidewall formed by etching can be converted into a regular saw-tooth sidewall after being corroded by a chemical solution, and the sidewall of each saw tooth is a GaN m-surface, as shown in fig. 7 a-7 e. As can be seen from the relationship of crystal planes, the a-plane is
The surface can be decomposed into two m-planes intersecting each other, and thus the best sidewall roughening effect can be achieved if the sidewall is etched into the a-plane. The ultraviolet light-emitting diode chip used for corrosion can be in any one or the combination of more than two of structures such as a rectangle, a triangle, a hexagon, an inverted trapezoid, a disc, a circular ring, a spiral shape or other shapes. For example, referring to fig. 7a, 7b, 7c, 7d, and 7e, the etched chip may have a square, rectangular, triangular, hexagonal, or inverted trapezoidal shape.
(8) And finally, thinning, grinding and polishing the substrate, and then splitting to form the zigzag nitride semiconductor ultraviolet light-emitting diode core with the repaired side wall, as shown in fig. 8.
In another more specific embodiment of the present invention, a method for improving light extraction efficiency of a nitride semiconductor ultraviolet light emitting diode comprises the following steps: (for flip chip structure and vertical structure UV LED)
(1) A nitride semiconductor ultraviolet light emitting diode structure is grown on a substrate, specifically comprising a buffer layer, an n-type contact layer, an active region, an electron blocking layer and a p-type contact layer, as shown in fig. 9.
(2) Determining the crystal orientation of an epitaxial layer of an ultraviolet light emitting diode using diffraction techniques and
the crystal orientation is shown in fig. 10.
(3) Cleaning the epitaxial wafer, depositing p-type ohmic contact metal or a combination of a transparent conductive film and a high-reflection film on the whole surface of the p-type contact layer, and carrying out ohmic contact annealing to form better ohmic contact, as shown in fig. 11.
(4) A layer of metal for wafer bonding (bonding) is deposited over the entire surface of the p-type ohmic contact metal, as shown in fig. 12.
(5) The epitaxial layer and the other supporting substrate are bonded together by using a wafer bonding technology, and the p-side of the nitride semiconductor ultraviolet light emitting diode is bonded with the supporting substrate in a downward mode. Then, wet etching or laser lift-off is used to remove the substrate, and then the buffer layer is removed by thinning, grinding, dry etching or wet etching to expose the n-type contact layer, so as to realize substrate transfer, as shown in fig. 13.
(6) In that
And preparing a micro-nano structure (namely surface roughening) for enhancing light emission on the nitrogen surface n-type ohmic contact layer by adopting any one or combination of more than two of dry etching, wet etching, electrochemical etching or photo-assisted electrochemical etching technologies. The micro-nano structure for enhancing the light extraction may be any one or a combination of more than two of a sawtooth shape, a triangle shape, a nano-pillar structure, a trapezoid shape, an inverted trapezoid shape, a yurt structure, a micro-nano porous structure, and the like, as shown in fig. 14.
(7) And depositing n-type ohmic contact metal on the partial surface area of the epitaxial wafer to form n-type ohmic contact.
(8) Spin-coating photoresist on the n-type ohmic contact layer, and making the pattern of the photoetching plate opposite to that of the AlGaN epitaxial film by using a rotary dislocation method
The direction rotates around the central axis by an angle alpha, so that any one edge of the photoetching pattern is avoided
The crystal orientation is shown in FIG. 15.
(9) After photolithography, isolated chips are patterned. Then, wet etching or dry etching is used to etch or etch the p-type ohmic contact electrode to initially form a random rough sidewall, as shown in fig. 16. Alternatively, the support sheet is thinned, and the metal electrode is deposited on the back surface of the support sheet, as shown in fig. 17.
(10) The epitaxial wafer is placed in a chemical solution to be etched to repair the etching damage, and finally, the serrated side wall is formed, as shown in fig. 7 a-7 e. The ultraviolet light-emitting diode chip used for corrosion can be in any one or the combination of more than two of structures such as a rectangle, a triangle, a hexagon, an inverted trapezoid, a disc, a circular ring, a spiral shape, or other shapes. For example, referring to fig. 7a, 7b, 7c, 7d, and 7e, the etched chip may have a square, rectangular, triangular, hexagonal, or inverted trapezoidal shape.
(11) And performing die cutting to form a single ultraviolet light-emitting diode die with zigzag side walls, for example, as shown in fig. 18a and 18b, and finally preparing a rectangular ultraviolet light-emitting diode die with a flip-chip and vertical structure with zigzag side walls.
In the nitride semiconductor ultraviolet light emitting diode provided by the embodiment of the invention, the p-type ohmic contact can be divided into two types, namely p-type ohmic contact metal, or a combination of a transparent conductive film and a high-reflection film. The p-type ohmic contact metal comprises any one or combination of more than two of materials such as Ni, Al, Ag, Pd, Pt, Au, TiN, Rh and the like, the transparent conductive film comprises any one or combination of more than two of materials such as AZO, IGZO, ITO, ZnO, MgO and the like, and the high-reflection film comprises Ag, Al, ZnO, MgO and SiO2、SiNx、TiO2、ZrO2、AlN、Al2O3、Ta2O5、HfO2、HfSiO4Any one or a combination of two or more of materials such as AlON, etc., but not limited thereto.
In an embodiment of the present invention, the method for manufacturing the optical micro-nano structure includes any one or a combination of two or more of dry etching, wet etching, electrochemical etching, or photo-assisted electrochemical etching technologies, and is not limited thereto.
In the embodiments of the present invention, the method for improving the light extraction efficiency of the nitride semiconductor ultraviolet light emitting diode provided by the present invention can reduce the total reflection of the sidewall and significantly improve the light extraction efficiency. Through the rotation dislocation method, the ultraviolet light-emitting diode can be prevented from exposing m cleavage planes, so that the side wall total reflection probability of TM mode deep ultraviolet light propagating along the transverse direction is greatly reduced, and the side wall light taking efficiency of the TM mode deep ultraviolet light is effectively enhanced.
Furthermore, the technology for reducing the total reflection of the m-plane cleavage plane of the nitride by the rotary dislocation method selects a photoetching pattern (photoetching plate) relative to an epitaxial layer according to the crystal orientation of the AlGaN epitaxial film
The crystal orientation is rotated by the angle alpha, so that the side wall of the ultraviolet light-emitting diode chip avoids the m-plane cleavage plane, the m-plane cleavage plane cannot be exposed on the whole surface in the subsequent corrosion process, and the total surface reflection is reduced.
In the foregoing embodiments of the present invention, the method for improving the light extraction efficiency of the nitride semiconductor ultraviolet light emitting diode provided by the present invention can reduce the sidewall surface recombination and improve the performance of the ultraviolet light emitting diode. After the rotation dislocation photoetching, although the etching process can form a random rough side wall, etching damage can be introduced at the same time, so that the light absorption on the surface of the side wall and the non-radiative recombination of carriers are increased, and the light extraction efficiency of the ultraviolet light-emitting diode is reduced. By combining the side wall corrosion process, the irregular rough side wall of the nitride semiconductor ultraviolet light emitting diode chip can be converted into the sawtooth-shaped m-side wall, which is beneficial to extraction of TM-mode deep ultraviolet light, and can repair side wall etching damage and reduce surface light absorption and non-radiative recombination of carriers, thereby improving the performance of the ultraviolet light emitting diode. In addition, the zigzag m-side wall can improve the uniformity of light emission of the side wall.
Furthermore, the invention utilizes the technology of exposing the specific crystal face by wet etching to improve the light emitting efficiency of the side wall, and after the etching by chemical solution, the irregular rough side wall formed by etching can be converted into the side wall with the saw-tooth-shaped m surface. The sawtooth-shaped side wall ensures the roughness of the side wall of the ultraviolet light emitting diode chip and can greatly improve the light emitting efficiency of the side wall of TM mode ultraviolet light.
In the foregoing embodiments of the present invention, the method for improving the light extraction efficiency of the nitride semiconductor ultraviolet light emitting diode provided by the present invention can enhance the heat dissipation effect of the ultraviolet light emitting diode. After being corroded by chemical solution, the irregular rough side wall is converted into a sawtooth-shaped m-surface side wall. The zigzag side wall further increases the contact area of the side wall with air, so that the heat dissipation effect can be enhanced.
Furthermore, the invention utilizes the technology of heat dissipation of the ultraviolet light emitting diode chip by enlarging the sawtooth (fold) crystal face, and after the chip is corroded by chemical solution, the irregular rough side wall formed by etching can be converted into the sawtooth m-face side wall. The zigzag side wall further increases the contact area of the side wall and air, so that the heat dissipation effect of the chip can be enhanced.
Furthermore, the invention adopts an etching damage repairing technology, after the n mesa of the ultraviolet light emitting diode is etched, the side wall of the ultraviolet light emitting diode can be etched and damaged through wet etching, and a side wall crystal face is obtained, thereby greatly reducing the light absorption of the side wall and the non-radiative recombination of a current carrier.
In the embodiment of the invention, the method for improving the light extraction efficiency of the nitride semiconductor ultraviolet light-emitting diode is simple in process, is compatible with the existing light-emitting diode self-prepared process, and is completely suitable for large-scale production. The rotation dislocation method only needs to make the photoetching pattern (photoetching plate) in the common LED process opposite to the epitaxial layer
And rotating the crystal direction by an angle alpha to ensure that the side wall of the ultraviolet light-emitting diode chip avoids the m-plane cleavage plane. The chemical corrosion is also a common flow in the preparation process of the light emitting diode, the process yield of repairing the etching damage through the chemical corrosion is high, and the epitaxial layer cannot be damaged. Therefore, the method is simple and efficient in process and is completely suitable for large-scale production.
In summary, the method for improving the light extraction efficiency of the nitride semiconductor ultraviolet light emitting diode provided by the invention has the advantages of easy realization of side wall coarsening, less side wall light loss, small carrier non-radiative recombination, good heat dissipation effect, simple process, good light extraction consistency, high stability and reliability and the like, can greatly enhance the performance and service life of the nitride semiconductor ultraviolet light emitting diode, and improves the stability of the device.
Another aspect of an embodiment of the present invention provides a nitride semiconductor ultraviolet light emitting diode fabricated by any one of the methods described above.
In some embodiments, the nitride semiconductor ultraviolet light emitting diode comprises a nitride semiconductor ultraviolet light emitting diode structure grown on a substrate, wherein the side wall of the nitride semiconductor ultraviolet light emitting diode structure is an m-plane
A zigzag side wall is formed.
Further, the side wall has an island-like shape of a triangular shape.
Further, the nitride semiconductor ultraviolet light emitting diode structure comprises an n-type contact layer, an active region, an electron blocking layer and a p-type contact layer which are sequentially grown, wherein n-type ohmic contact metal is arranged on the n-type contact layer, and p-type ohmic contact metal is arranged on the p-type contact layer.
Further, the nitride semiconductor ultraviolet light emitting diode structure comprises an n-type contact layer, an active region, an electron blocking layer and a p-type contact layer which are sequentially grown, a p-type ohmic contact metal or a combination of a transparent conductive film and a high-reflection film is arranged on the p-type contact layer, a supporting substrate is bonded on the surface of one side of the p-type ohmic contact metal, and the n-type ohmic contact metal is arranged on the n-type contact layer.
Further, the nitride semiconductor ultraviolet light emitting diode further includes: a metal electrode is deposited on the second surface of the support substrate.
Furthermore, the light-emitting wavelength of the nitride semiconductor ultraviolet light-emitting diode is 200-400 nm.
The technical solution of the present invention will be described in more detail with reference to several embodiments.
Example 1: an AlGaN-based deep ultraviolet light emitting diode (forward-mounted structure) with the wavelength of 265nm is prepared on an AlN substrate, and the specific manufacturing method comprises the following steps:
s1: growing an AlGaN-based ultraviolet light-emitting diode structure on an AlN substrate by adopting Metal Organic Chemical Vapor Deposition (MOCVD) equipment, specifically growing 800nm Al0.9Ga0.1N thick layer, and growing ultraviolet LED structure comprising 1200nmn-Al0.9Ga0.1N contact layer, 8 pairs of Al0.53Ga0.47N/Al0.9Ga0.1N multiple quantum well, wherein each layer of Al0.53Ga0.47N quantum well 1.5nm, each layer of Al0.9Ga0.1P-Al with 7nm and 20nm N quantum barrier0.98Ga0.02N-Electron Barrier layer, 50nm p-Al0.89Ga0.11N contact layer as shown in fig. 1.
S2: determining the crystal orientation of an epitaxial layer of an ultraviolet light emitting diode using diffraction techniques and
the crystal orientation is shown in fig. 2.
S3: cleaning epitaxial wafer with acetone, alcohol, hydrochloric acid and deionized water, etc., depositing 2nm Ni and 150nm Ag metal on p-AlGaN contact layer, or depositing 240nm AZO and 10-pair SiO with optical thickness of 1/4 wavelength2/TaO2High-reflection film, annealing at 400 deg.C for 8 min in compressed air atmosphere by using a rapid annealing furnace to form better ohmic contact, and spin-coating photoresist on the prepared p-type ohmic contact electrode, as shown in FIG. 3.
S4: performing photoetching by adopting a rotary dislocation method to enable the pattern of the photoetching plate to be opposite to the AlGaN epitaxial film
The direction rotates clockwise for 15 degrees around the central axis to ensure that any one edge of the photoetching pattern is avoided
The crystal orientation is shown in fig. 4. The pattern may be any one of triangular, rectangular, hexagonal, inverted trapezoidal, disc-shaped, circular, spiral, or other structuresOne or a combination of two or more.
S5: depositing 230nm SiO on the surface of the epitaxial wafer2Insulating dielectric film, and dry etching to reach 1000nm to n-type Al0.9Ga0.1N contact layer, forming random rough sidewalls, as shown in fig. 5.
S6: 50nmTi/50nm Pt/100nm Au is deposited in sequence, and then stripped to form an n-type ohmic contact electrode and a p-type thickened electrode, as shown in FIG. 6.
S7: and (3) placing the epitaxial chip in TMAH solution with the concentration of 25% to corrode for 120 minutes at 85 ℃, removing the etching damage of the side wall of the ultraviolet light-emitting diode, and obtaining the sawtooth-shaped side wall, as shown in figures 7 a-7 e.
S8: die dicing is performed to form individual uv led dies, as shown in fig. 8. The chip has the light emitting wavelength of 265nm, high light extraction efficiency, external quantum efficiency of over 20 percent and service life of more than 2000 hours.
Example 2: an AlGaN-based deep ultraviolet light emitting diode (vertical structure) with the light emitting wavelength of 280nm is prepared on a Si substrate, and the specific manufacturing method comprises the following steps:
s1: an AlGaN-based ultraviolet light-emitting diode structure grows on a Si substrate by using MOCVD equipment, and the structure specifically comprises the following steps: firstly growing an AlN nucleating layer with the thickness of 25nm, then growing an AlN thick layer with the thickness of 700nm, a GaN inserting layer with the thickness of 20nm and an AlN layer with the thickness of 500nm, and finally growing an AlGaN-based ultraviolet light-emitting diode structure, particularly comprising 2000nm n-Al0.65Ga0.35N contact layer, 8 pairs of Al0.45Ga0.55N/Al0.65Ga0.35N multiple quantum well, wherein each layer of Al0.45Ga0.55N quantum well 2.5nm, each layer of Al0.65Ga0.35N quantum barrier 8nm, 20nm p-Al0.9Ga0.1N-Electron Barrier layer, 70nm p-Al0.45Ga0.55N contact layer as shown in fig. 9.
S2: determining the crystal orientation of an epitaxial layer of an ultraviolet light emitting diode using diffraction techniques and
the crystal orientation is shown in fig. 10.
S3: the epitaxial wafer is cleaned by acetone, alcohol, hydrochloric acid, deionized water and the like, 3nm of Ni and 200nm of Rh are sequentially deposited on the p-AlGaN contact layer, and annealing is carried out for 10 minutes at 550 ℃ in a compressed air atmosphere by using a rapid annealing furnace to form better ohmic contact, as shown in FIG. 11.
S4: an Au bonding metal is deposited over the entire surface of the p-type ohmic contact metal for wafer bonding, as shown in fig. 12.
S5: and the ultraviolet light emitting diode and the molybdenum-copper support are flip-chip bonded together by utilizing a wafer bonding technology. Then, the substrate is removed by wet etching or laser lift-off, and then the buffer layer is removed by thinning, grinding, dry etching or wet etching to expose the n-type contact layer, so as to realize substrate transfer, as shown in fig. 13.
S6: using a temperature of 70 ℃ (NH4)2Corrosion by S solution
A nitrogen surface n-type AlGaN contact layer, a micro-nano structure for enhancing light extraction is prepared, and the micro-nano structure can be a sawtooth shape, a triangle shape, a nano-pillar structure, a trapezoid shape, an inverted trapezoid shape, a Mongolian yurt structure and the like, as shown in FIG. 14; and an oxalic acid solution can also be adopted for electrochemical corrosion to prepare the micro-nano structure for enhancing the light extraction.
S7: and depositing 20nmTi/160nm Al/50nm Al/300nm Au on the surface of the epitaxial wafer to form n-type ohmic contact.
S8: and (6) photoetching. By using a rotary dislocation method, the pattern of the reticle is made to face the AlGaN epitaxial film
The direction is rotated clockwise by 20 degrees around the central axis to make any one edge of the photoetching pattern avoid
The crystal orientation is shown in FIG. 15. The photo-etching pattern is triangular, but is not limited thereto, and may be any one or two of rectangular, square, hexagonal, octagonal, dodecagonal, disc-shaped, circular, spiral, or other structuresCombinations of the above.
S9: thinning the support sheet, depositing a metal electrode 50nm Ti/100nmAu on the back of the support sheet, as shown in FIG. 18 b.
S10: and cutting the tube core to form a single ultraviolet light-emitting diode tube core with the light-emitting wavelength of 280 nm. The chip has high light extraction efficiency, the external quantum efficiency is up to 20 percent, and the service life is longer than 3000 hours.
Example 3: an AlGaN-based deep ultraviolet light emitting diode (flip-chip structure) with the light emitting wavelength of 310nm is prepared on a sapphire substrate, and the specific manufacturing method comprises the following steps:
s1: growing an ultraviolet light-emitting diode structure on a sapphire substrate by using MOCVD equipment, specifically comprising a 25nm GaN nucleating layer or a 20nm GaN and 5nm AlN composite nucleating layer, then growing a 1000nm AlN thick layer, and finally growing an AlGaN-based ultraviolet light-emitting diode structure, specifically comprising a 1000nm n-Al0.3Ga0.7N contact layer, 6 pairs of Al0.15Ga0.85N/Al0.25Ga0.75N multiple quantum well, wherein each layer of Al0.25Ga0.75N quantum well 2nm, each layer of Al0.3Ga0.7N quantum barrier 10nm, 20nm p-Al0.4Ga0.6N-Electron Barrier layer, 100nm p-Al0.3Ga0.7N contact layer as shown in fig. 9.
S2: determining the crystal orientation of an epitaxial layer of an ultraviolet light emitting diode using diffraction techniques and
the crystal orientation is shown in fig. 10.
S3: cleaning epitaxial wafer with acetone, alcohol, hydrochloric acid and deionized water, etc., depositing 5nm Ni and 100nm Ag metal on p-AlGaN contact layer, or depositing 200nm AZO and 8 SiO with optical thickness of 1/42/TiO2High-reflection film and annealed at 500 c for 3 minutes in a compressed air atmosphere using a rapid annealing furnace to form a better ohmic contact, as shown in fig. 11.
S4: an Au-Sn bonding metal is deposited over the entire surface of the p-type ohmic contact metal for wafer bonding, as shown in fig. 12.
S5: and (3) the p surface of the AlGaN-based ultraviolet light emitting diode faces downwards, and the ultraviolet light emitting diode and the molybdenum-copper support are bonded together in a flip-chip mode by utilizing a wafer bonding technology. Then, the substrate is removed by wet etching or laser lift-off, and then the buffer layer is removed by thinning, grinding, dry etching or wet etching to expose the n-type contact layer, so as to realize substrate transfer, as shown in fig. 13.
S6: in that
Hot phosphoric acid H is adopted on the N-type AlGaN contact layer on the nitrogen surface3PO4Preparing a micro-nano structure for enhancing light emission from the solution, wherein the micro-nano structure can be a sawtooth shape, a triangle shape, a nano-pillar structure, a trapezoid shape, an inverted trapezoid shape, a Mongolian yurt structure and the like, as shown in FIG. 14; and an oxalic acid solution can also be adopted for electrochemical corrosion to prepare the micro-nano structure for enhancing the light extraction.
S7: and depositing 50nm Cr/300nm Au on the surface of the epitaxial wafer to form n-type ohmic contact.
S8: and photoetching is carried out on the n-type AlGaN contact layer. By using a rotary dislocation method, the pattern of the reticle is made to face the AlGaN epitaxial film
The direction rotates around the central axis counterclockwise by 10 degrees, so that any edge of the photoetching pattern is avoided
The crystal orientation is shown in FIG. 15. The pattern to be etched is hexagonal, but is not limited to this, and may be any one or a combination of two or more of square, triangular, rectangular, octagonal, dodecagonal, disc-shaped, circular, spiral, or other structures.
S9: after photoetching, a single ultraviolet light emitting diode chip with irregular rough side walls is formed, then wet etching is carried out by using KOH solution with the temperature of 85 ℃ until a p-type ohmic contact electrode is corroded, and then the molybdenum-copper support sheet is thinned, as shown in figure 16.
S10: the epitaxial wafer was etched in a KOH solution at 80 c for 60 minutes to repair the etch damage and finally form a serrated sidewall as shown in fig. 18 a.
S11: and cutting the tube core to form a single ultraviolet light-emitting diode tube core with the light-emitting wavelength of 320 nm. The chip has high light extraction efficiency, the external quantum efficiency is as high as 50%, and the service life is more than 4000 hours.
Example 4: an AlGaN-based near ultraviolet light emitting diode (forward-mounted structure) with the light emitting wavelength of 365nm is prepared on a sapphire substrate, and the specific manufacturing method comprises the following steps:
s1: growing an AlGaN-based ultraviolet light-emitting diode structure on a sapphire substrate by using MOCVD equipment, specifically growing a 20nm GaN nucleating layer or a composite nucleating layer of 5nm GaN and 10nm AlN, and then growing 800nm Al0.1Ga0.9Growing a thick N layer, and finally growing an AlGaN-based ultraviolet light-emitting diode structure which specifically comprises 1200nm N-Al0.1Ga0.9N contact layer, 8 pairs of GaN/Al0.13Ga0.87N multiple quantum well with 4nm GaN quantum well layer and Al layer0.13Ga0.87N quantum barrier 8nm, 10nm p-Al0.3Ga0.7N-Electron Barrier layer, 130nm p-Al0.1Ga0.9N contact layer as shown in fig. 1.
S2: determining the crystal orientation of an epitaxial layer of an ultraviolet light emitting diode using diffraction techniques and
the crystal orientation is shown in fig. 2.
S3: cleaning epitaxial wafer with acetone, alcohol, hydrochloric acid and deionized water, etc., depositing 2nm Ni and 150nm Ag metal on p-AlGaN contact layer, or depositing 240nm AZO and 10-pair SiO with optical thickness of 1/4 wavelength2/TaO2High-reflection film, annealing at 400 deg.C for 8 min in compressed air atmosphere by using a rapid annealing furnace to form better ohmic contact, and spin-coating photoresist on the prepared p-type ohmic contact electrode, as shown in FIG. 3.
S4: performing photoetching by adopting a rotary dislocation method to enable the pattern of the photoetching plate to be opposite to the AlGaN epitaxial film
The direction rotates clockwise for 15 degrees around the central axis to ensure that any one edge of the photoetching pattern is avoided
The crystal orientation is shown in fig. 4. The pattern may be any one or a combination of two or more of square, triangular, hexagonal, rectangular, dodecagonal, disc-shaped, circular, spiral, and other shapes.
S5: depositing 230nm SiO on the surface of the epitaxial wafer2Insulating dielectric film, then etching 1700nm by dry etching technique to n-type AlGaN contact layer, and forming irregular rough side wall, as shown in FIG. 5.
S6: 50nmTi/50nm Pt/100nm Au is deposited in sequence, and then stripped to form an n-type ohmic contact electrode and a p-type thickened electrode, as shown in FIG. 6.
S7: using H at 80 deg.C3PO4And (5) carrying out wet etching on the solution to remove etching damage on the side wall of the ultraviolet light-emitting diode to obtain a serrated side wall, as shown in fig. 7 d.
S8: the sapphire substrate is thinned, ground and polished, and then is subjected to chipping to form an ultraviolet light emitting diode die, as shown in fig. 8. The chip has the light-emitting wavelength of 365nm, the light-taking efficiency is high, the external quantum efficiency exceeds 70 percent, and the service life is longer than 5000 hours.
The nitride semiconductor ultraviolet light-emitting diode structure provided by the embodiment of the invention has the advantages of high light extraction efficiency, weak side wall light absorption, small carrier non-radiative recombination, good heat dissipation effect, high stability and reliability and the like, and can greatly enhance the performance and the service life of the nitride semiconductor ultraviolet light-emitting diode.
It should be understood that the above-mentioned embodiments are merely illustrative of the technical concepts and features of the present invention, which are intended to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and therefore, the protection scope of the present invention is not limited thereby. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.
Claims (32)
1. A method for improving light extraction efficiency of nitride semiconductor ultraviolet light-emitting diodes comprises the following steps: growing a nitride semiconductor ultraviolet light emitting diode structure on a substrate to obtain an epitaxial wafer, wherein the nitride semiconductor ultraviolet light emitting diode structure comprises a first contact layer, an active region, an electron blocking layer and a second contact layer which are sequentially formed, and the method is characterized by further comprising the following steps of:
determining the crystal orientation of the epitaxial wafer using diffraction techniques and<
>a crystal orientation;
arranging a second electrode layer on the second contact layer, and enabling the second electrode layer and the second contact layer to form ohmic contact;
arranging photoresist on the second electrode layer, and adopting rotation dislocation method to make any side of the photoetching pattern avoid the structure of nitride semiconductor ultraviolet light-emitting diode<
>A crystal orientation;
etching the first contact layer by adopting an etching technology to expose at least a local area of the first contact layer and preliminarily form a random rough side wall;
arranging a first electrode layer on the first contact layer, and enabling the first electrode layer and the first contact layer to form ohmic contact;
and contacting the obtained epitaxial wafer with corrosive liquid, repairing etching damage and coarsening the side wall, so that the irregular rough side wall of the nitride semiconductor ultraviolet light-emitting diode structure is converted into a saw-tooth-shaped m-surface side wall.
2. The method of claim 1, comprising: making the photoetching pattern along<
>Crystal orientation exposed alpha face
}。
3. The method of claim 1, wherein: the nitride semiconductor ultraviolet light emitting diode structure<
>The crystal orientation is a family of crystal orientations comprising symmetrically equivalent [ alpha ], [ alpha ]
]、[
]、[
]、[
]、[
]And 2
]And (4) crystal orientation.
4. The method of claim 2, wherein: the nitride semiconductor ultraviolet light emitting diode structure<
>The crystal orientation is a family of crystal orientations comprising symmetrically equivalent [ alpha ], [ alpha ]
]、[
]、[
]、[
]、[
]And 2
]And (4) crystal orientation.
5. The method of claim 1, wherein: the a face of the nitride semiconductor ultraviolet light emitting diode structure
Is a family of crystal planes comprising symmetrically equivalent (
)、(
)、(
)、(
)、(
) And (a)
) A crystal plane.
6. The method of claim 1The method is characterized in that: the m face of the nitride semiconductor ultraviolet light emitting diode structure
Is a family of crystal planes comprising symmetrically equivalent (
)、(
)、(
)、(
)、(
) And (a)
) A crystal plane.
7. The method of claim 1, wherein: in the rotary dislocation method, the lithographic pattern is opposed to the epitaxial wafer<
>The angle alpha of the crystal direction rotation is the non-edge of the photoetching pattern<
>Any angle of crystal orientation.
8. The method of claim 7, wherein: the angle alpha is 1-60 degrees.
9. The method of claim 1, wherein: the corrosive liquid comprises an alkaline solution or an acidic solution.
10. The method of claim 9, wherein: the alkaline solution comprises any one or the combination of more than two of KOH solution, NaOH solution and TMAH solution.
11. The method of claim 9, wherein: the acidic solution comprises H3PO4Solution, HF solution and HNO3Any one or a combination of two or more of the solutions.
12. The method of claim 1, wherein: the nitride semiconductor ultraviolet light-emitting diode structure comprises a buffer layer, a first contact layer, an active region, an electron blocking layer and a second contact layer which are sequentially formed.
13. The method of claim 12, wherein: the nitride semiconductor ultraviolet light-emitting diode structure also comprises an optical reflection layer structure.
14. The method of claim 13, wherein: the optical reflection layer structure comprises DBR and/or SiO2A dielectric layer.
15. The method of claim 1, wherein: the substrate is made of any one or a combination of more than two of GaN, AlN, BN, sapphire, Si, SiC and ZnO.
16. The method of claim 1, wherein: the active region quantum well of the nitride semiconductor ultraviolet light-emitting diode structure comprises one or the combination of more than two of AlN, AlGaN, AlInGaN and AlInN.
17. The method of claim 7, further comprising: the shape of the epitaxial wafer for etching comprises any one or the combination of more than two of square, rectangle, triangle, hexagon, octagon, dodecagon, inverted trapezoid, disc, circular ring and spiral.
18. The method of claim 1, wherein: the first contact layer is an n-type contact layer, the first electrode layer comprises a combination of n-type ohmic contact metal or a transparent conductive film and a high-reflection film, the second contact layer is a p-type contact layer, and the second electrode layer comprises a combination of p-type ohmic contact metal or a transparent conductive film and a high-reflection film.
19. The method of claim 18, wherein: the n-type ohmic contact metal or the p-type ohmic contact metal comprises any one or a combination of more than two of Ni, Ti, Pd, Pt, Au, Al, TiN, ITO and IGZO.
20. A nitride semiconductor ultraviolet light emitting diode fabricated by the method of any one of claims 1-19.
21. The nitride semiconductor ultraviolet light emitting diode of claim 20, comprising a nitride semiconductor ultraviolet light emitting diode structure grown on a substrate, wherein the sidewalls of the nitride semiconductor ultraviolet light emitting diode structure are saw-tooth shaped m-plane sidewalls.
22. The nitride semiconductor ultraviolet light-emitting diode according to claim 21, characterized in that: the side wall has a triangular island-like shape.
23. The nitride semiconductor ultraviolet light-emitting diode according to claim 21, characterized in that: the nitride semiconductor ultraviolet light-emitting diode structure comprises an n-type contact layer, an active region, an electron blocking layer and a p-type contact layer which are sequentially grown, wherein n-type ohmic contact metal is arranged on the n-type contact layer, and p-type ohmic contact metal is arranged on the p-type contact layer.
24. The nitride semiconductor ultraviolet light-emitting diode according to claim 21, characterized in that: the light-emitting wavelength of the nitride semiconductor ultraviolet light-emitting diode is 200-400 nm.
25. A method for improving light extraction efficiency of nitride semiconductor ultraviolet light-emitting diodes comprises the following steps: growing a nitride semiconductor ultraviolet light emitting diode structure on a substrate to obtain an epitaxial wafer, wherein the nitride semiconductor ultraviolet light emitting diode structure comprises a first contact layer, an active region, an electron blocking layer and a second contact layer which are sequentially formed, and the method is characterized by further comprising the following steps of:
determining the crystal orientation of the epitaxial wafer using diffraction techniques and<
>a crystal orientation;
arranging a second electrode layer on the second contact layer, and enabling the second electrode layer and the second contact layer to form ohmic contact;
bonding the second electrode layer to a first surface of a support substrate;
stripping the nitride semiconductor ultraviolet light-emitting diode structure from the substrate to expose the first contact layer;
manufacturing an optical micro-nano structure on a light-emitting surface of the nitride semiconductor ultraviolet light-emitting diode structure, wherein the optical micro-nano structure is used for enhancing light emission;
arranging a first electrode layer on the first contact layer, and enabling the first electrode layer and the first contact layer to form ohmic contact;
arranging photoresist on the first electrode layer, and adopting rotation dislocation method to make any edge of the photoetching pattern avoid the structure of nitride semiconductor ultraviolet light-emitting diode<
>A crystal orientation;
etching the second electrode layer by adopting an etching technology to preliminarily form a random rough side wall;
and contacting the obtained epitaxial wafer with corrosive liquid, repairing etching damage and coarsening the side wall, so that the irregular rough side wall of the nitride semiconductor ultraviolet light-emitting diode structure is converted into a saw-tooth-shaped m-surface side wall.
26. The method of claim 25, further comprising:
and after photoetching, thinning the support substrate, and depositing a metal electrode on a second surface of the support substrate, wherein the second surface is opposite to the first surface.
27. The method of claim 25, further comprising: and removing the substrate from the epitaxial wafer by adopting a wet etching method or a laser stripping method.
28. The method of claim 25, wherein: the light-emitting surface of the nitride semiconductor ultraviolet light-emitting diode structure is made of nitride material (000)
) Nitrogen face.
29. The method of claim 25, wherein: the optical micro-nano structure comprises any one or combination of more than two of sawtooth-shaped, triangular, nano-column, trapezoid, inverted trapezoid, Mongolian yurt and micro-nano porous structure.
30. The method of claim 25, further comprising: and manufacturing the optical micro-nano structure by adopting any one or combination of more than two of dry etching, wet etching, electrochemical etching and photo-assisted electrochemical etching technologies.
31. A nitride semiconductor uv led fabricated by the method of any one of claims 25-30, comprising a nitride semiconductor uv led structure grown on a substrate, the sidewalls of the nitride semiconductor uv led structure being saw-tooth m-plane sidewalls,
the nitride semiconductor ultraviolet light-emitting diode structure comprises an n-type contact layer, an active region, an electron blocking layer and a p-type contact layer which are sequentially grown, wherein p-type ohmic contact metal or a combination of a transparent conductive film and a high-reflection film is arranged on the p-type contact layer, a supporting substrate is bonded on the surface of one side of the p-type ohmic contact metal, and n-type ohmic contact metal is arranged on the n-type contact layer.
32. The nitride semiconductor ultraviolet light-emitting diode according to claim 31, characterized in that: a metal electrode is deposited on the second surface of the support substrate.
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