CN113013305A

CN113013305A - Ultraviolet LED high-counter electrode and preparation method and application thereof

Info

Publication number: CN113013305A
Application number: CN202110301894.8A
Authority: CN
Inventors: 徐厚强; 蒋洁安; 郭炜; 叶继春
Original assignee: Ningbo Institute of Material Technology and Engineering of CAS
Current assignee: Ningbo Institute of Material Technology and Engineering of CAS
Priority date: 2021-03-22
Filing date: 2021-03-22
Publication date: 2021-06-22
Anticipated expiration: 2041-03-22
Also published as: CN113013305B

Abstract

The invention relates to the field of photoelectric materials and devices, in particular to an ultraviolet LED high-counter electrode and a preparation method and application thereof. According to the invention, metal with the work function of more than or equal to 4.6eV is used as the ohmic contact layer, the metal ohmic contact layer is patterned, and the patterning rate is controlled within 5% -40%, so that the optical performance of the electrode is ensured, and the ohmic contact between the metal aluminum reflecting layer and the LED chip layer is not influenced. The scheme provided by the invention balances the requirements of the ultraviolet LED high-reflection electrode on the electrical property and the optical property, avoids the problems of low yield, poor controllability and rise of the device turn-on voltage caused by that a metal ohmic contact layer needs to be made as thin as possible to improve the optical property in the prior art, and obviously improves the optical property compared with the prior art. In addition, because the ohmic contact layer only partially covers the high work function metal, compared with the existing full-coverage scheme, the use amount of the high work function metal is reduced, and the production cost is reduced.

Description

Ultraviolet LED high-counter electrode and preparation method and application thereof

Technical Field

The invention relates to the field of photoelectric materials and devices, in particular to an ultraviolet LED high-counter electrode and a preparation method and application thereof.

Background

Due to the existence of the P-type GaN contact layer and the strong absorption effect of the metal electrode on ultraviolet light, the design of back light emission is generally adopted in the industry at present. It is estimated that about 1/3 of photons generated by the active layer (quantum well) between the P-type layer and the N-type layer will reach the N-type layer, and part of the photons will exit successfully and be extracted successfully, and in addition, 1/3 of photons reaching the P-type layer will be completely absorbed by the P-GaN contact layer and the P-type electrode. In order to form a good ohmic contact with the P-type layer and reduce the turn-on voltage of the device, a Ni/Au laminated structure is generally adopted as the P-type electrode. The Ni/Au electrode has low ultraviolet reflectivity, and is only 50nm thick, so that the Ni/Au electrode can completely absorb deep ultraviolet light below 300 nm. Therefore, by adopting the electrode with higher reflectivity to ultraviolet light, part of light reaching the P-type layer can be reflected to the N-type layer towards the substrate direction, and further can be smoothly extracted out of the device, and the electrode is of great importance for improving the external quantum efficiency of the device.

The metallic aluminum has high reflectivity (about 92%) in an ultraviolet light band, but the work function of the aluminum is only 4.3eV, the work function of the P-GaN is about 6.5eV, the metallic aluminum directly contacts with a P type to generate a high potential barrier, good ohmic contact is difficult to form, and the I-V characteristic and the stability of the device are influenced. In the prior art, it is reported that the reflectivity of the Ni/Al electrode with this structure is reduced (about 68%) due to the absorption of ultraviolet light by the metal nickel, which is used as the contact metal to improve the contact performance and then covered by the thicker metal aluminum to make the reflector. Although the reflective nickel can play a certain role, the nickel is thin, the controllability is poor, the yield is low, and the turn-on voltage of the device is high, so that the reflective nickel is not suitable for commercial use.

In addition, metal rhodium is reported to be used as a high counter electrode, although good ohmic contact can be formed between the metal rhodium and a P-type layer, the ultraviolet reflectivity of the metal rhodium is only about 68%, the melting point of the metal rhodium is as high as 2237K, and the deposition difficulty is large. It is expensive and not suitable for large-scale commercial chips.

It has also been reported that the use of a laminated structure of metal 1nm ultrathin nickel and 200nm metal magnesium as a high counter electrode of an ultraviolet LED has a reflectivity of 88%, but the working voltage is 3V-5V higher than that of an LED with a Ni/Au electrode. In addition, magnesium metal is also a reactive metal, and is easily reacted with oxygen in the air, thereby affecting the service life and performance of the device.

Disclosure of Invention

Therefore, it is necessary to provide an ultraviolet LED high-reflectivity electrode, which has high ultraviolet reflectivity, can form good ohmic contact with P-type nitride, has low working and turn-on voltages, and has superior electrical characteristics and stability, and a preparation method and applications thereof.

In one aspect of the invention, an ultraviolet LED high-reflection electrode is provided, which comprises an LED chip layer, a metal ohmic contact layer and an aluminum reflection layer which are arranged in sequence; the substrate layer is a top P-type doped layer of the ultraviolet LED epitaxial wafer, the metal ohmic contact layer is a graphical layer made of metal materials with work functions larger than or equal to 4.6eV, and the orthographic projection area of the metal ohmic contact layer is 5% -40% of that of the LED chip layer.

According to the invention, metal with the work function of more than or equal to 4.6eV is used as the metal ohmic contact layer, meanwhile, the metal ohmic contact layer is patterned, and the percentage of the orthographic projection area of the metal ohmic contact layer to the orthographic projection area of the LED chip layer is controlled within 5% -40%, so that the part which is not covered by the high work function metal can smoothly transmit light, the absorption of the high work function metal to ultraviolet light is reduced, the optical performance of the ultraviolet LED high-reflection electrode is improved, the ohmic contact between the metal aluminum reflection layer and the LED chip layer is not influenced, and the electrical performance and the stability of the ultraviolet LED high-reflection electrode are ensured. The scheme provided by the invention well balances the requirements of the ultraviolet LED high-counter electrode on the electrical property and the optical property, avoids the problems of low yield, poor controllability and rise of device turn-on voltage caused by the fact that a metal ohmic contact layer needs to be made as thin as possible to improve the optical property in the prior art, obviously improves the optical property compared with the prior art, and improves the maximum luminous intensity of a device prepared by utilizing the ultraviolet LED high-counter electrode of the invention for ultraviolet light with the wavelength of 310nm from 1.0 multiplied by 10 in the prior art⁶Remarkably rises to 1.25 multiplied by 10⁶The lifting proportion reaches 25 percent. Meanwhile, the metal ohmic contact layer only partially covers the high work function metal, so that the high work function metal is reduced compared with the existing full-coverage schemeThe dosage of the lead-free anode material greatly reduces the production cost of the electrode prepared from noble metals such as platinum, palladium, beryllium, gold and the like, so that the lead-free anode material has good commercial prospect.

In one embodiment, the metal with work function of 4.6eV or more is at least one of nickel, chromium, platinum, palladium, beryllium and gold.

In one embodiment, the thickness of the metal ohmic contact layer is 5nm to 50 nm.

In one embodiment, the thickness of the aluminum reflecting layer is 50nm to 1 μm.

In one embodiment, the patterned layer is an arrangement of solid dots, the diameter of each solid dot is 50nm to 1 μm, and the distance between centers of adjacent solid dots is 100nm to 12 μm.

In one embodiment, the patterned layer is a tightly arranged hollow-out net with dots having a diameter of 100nm to 10 μm.

In another aspect of the present invention, a preparation method of the ultraviolet LED high-counter electrode is further provided, which includes the following steps:

providing an ultraviolet LED epitaxial wafer with a top epitaxial layer as a P-type doping layer, covering a patterned photoresist on the P-type doping layer, then depositing metal with the work function more than or equal to 4.6eV on the part, which is not covered by the photoresist, on the P-type doping layer, removing the photoresist after the deposition is finished, and uniformly covering a layer of metal aluminum as a reflecting layer.

In another aspect of the present invention, another method for preparing the ultraviolet LED high-counter electrode is provided, which includes the following steps:

providing an ultraviolet LED epitaxial wafer with a P-type doping layer as a top epitaxial layer, arranging a single layer of nano microspheres on the P-type doping layer, then depositing metal with work function larger than or equal to 4.6eV in gaps among the adjacent nano microspheres and gaps between the nano microspheres and the P-type doping layer, removing the nano microspheres after deposition is finished, and uniformly covering a layer of metal aluminum as a reflecting layer.

In one embodiment, the material of the nano-microsphere is at least one of silicon dioxide, polystyrene or graphite.

The invention also provides a preparation method of the third ultraviolet LED high-counter electrode, which comprises the following steps:

providing an ultraviolet LED epitaxial wafer with a top epitaxial layer as a P-type doped layer, directly depositing metal with the work function of more than or equal to 4.6eV on the P-type doped layer, annealing in an inert atmosphere after deposition is finished to obtain island-shaped distributed metal clusters, and then uniformly covering a layer of metal aluminum as a reflecting layer.

In one embodiment, the inert atmosphere is provided by nitrogen or argon, the annealing temperature is 600-1000 ℃, and the annealing time is 5-60 min.

The invention also provides an ultraviolet LED which comprises the ultraviolet LED high-counter electrode.

Drawings

FIG. 1 is a graph showing a comparison of the luminous intensities of the high-counter electrode EL prepared in example 2;

FIG. 2 shows the nickel remaining on the epitaxial wafer during the preparation of example 2;

fig. 3 shows island-shaped metal clusters remaining on the epitaxial wafer after annealing in the preparation process of example 3.

Detailed Description

To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the invention, "a plurality" means at least two, e.g., two, three, etc., unless explicitly specified otherwise. In the description of the present invention, "a plurality" means at least one, e.g., one, two, etc., unless specifically limited otherwise.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

In one aspect of the invention, an ultraviolet LED high-reflection electrode is provided, which comprises an LED chip layer, a metal ohmic contact layer and an aluminum reflection layer which are arranged in sequence; the LED chip layer is a top P-type doped layer of the ultraviolet LED epitaxial wafer, the metal ohmic contact layer is a patterned layer made of metal materials with work functions larger than or equal to 4.6eV, the orthographic projection area of the metal ohmic contact layer is 5% -40% of the orthographic projection area of the LED chip layer, and preferably, the orthographic projection area of the metal ohmic contact layer is 10% -30% of the orthographic projection area of the LED chip layer. The percentage of the orthographic projection area of the metal ohmic contact layer in the orthographic projection area of the LED chip layer can be called the patterning rate, the patterning rate directly influences the electrical performance, the optical performance and the stability of the high-counter electrode, and the patterning rate is too low, so that the ohmic contact of the high-counter electrode is deteriorated, and the electrical performance and the stability of the electrode are influenced; the patterning rate is too high, and the high work function metal absorbs too much ultraviolet light, so that the reflection performance of the high counter electrode is influenced, and the light-emitting efficiency of the finally prepared device is too low.

According to the invention, metal with the work function of more than or equal to 4.6eV is used as the metal ohmic contact layer, the metal ohmic contact layer is patterned, and the patterning rate is controlled within 5% -40%, so that the part which is not covered by the high work function metal can be smoothly transmitted, the absorption of the high work function metal to ultraviolet light is reduced, the optical performance of the ultraviolet LED high-counter electrode is improved, the ohmic contact between the metal aluminum reflecting layer and the LED chip layer is not influenced, and the electrical performance and the stability of the ultraviolet LED high-counter electrode are ensured. The scheme provided by the invention well balances the requirements of the ultraviolet LED high-reflection electrode on the electrical property and the optical propertyThe method avoids the low yield, poor controllability and increase of the device starting voltage caused by the need of making a metal ohmic contact layer as thin as possible to improve the optical performance in the prior art, obviously improves the optical performance compared with the prior art, and improves the maximum luminous intensity of a device prepared by using the ultraviolet LED high-counter electrode of the invention for ultraviolet light with the wavelength of 310nm from 1.0 multiplied by 10 in the prior art⁶Remarkably rises to 1.25 multiplied by 10⁶The lifting proportion reaches 25 percent. Meanwhile, the metal ohmic contact layer only partially covers the high work function metal, so that the using amount of the high work function metal is reduced compared with the full-coverage existing scheme, and the production cost of the electrode prepared by the noble metals such as platinum, palladium, beryllium, gold and the like is greatly reduced, so that the invention has good commercial prospect.

In a specific example, the metal with the work function of 4.6eV or more is at least one of nickel, chromium, platinum, palladium, beryllium and gold. The nickel, chromium, platinum, palladium, beryllium and metal are higher than high work function metal, the contact potential barrier with the P-type layer is smaller, good ohmic contact can be formed, and the improvement of the electrical property and the stability of the ultraviolet LED high-counter electrode are facilitated.

In a specific example, the thickness of the metal ohmic contact layer is 5nm to 50nm, and optionally, the thickness of the metal ohmic contact layer may be, for example, 5nm to 45nm, and further, for example, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, and 40 nm. The thickness of the metal ohmic contact layer is also one of important factors influencing the electrical performance and the optical performance of the ultraviolet LED high-reflection electrode pair, and within a preset thickness range, the reflectivity of the electrode pair to ultraviolet light is not greatly reduced, and meanwhile, an overlarge contact potential barrier is not formed, so that ohmic contact is influenced, and the starting voltage of a device is overhigh.

In a specific example, the thickness of the aluminum reflective layer is 50nm to 1 μm, and optionally, the thickness of the aluminum reflective layer may be, for example, 100nm to 950nm, and further, for example, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, 800nm, 850nm, 900 nm. The thickness of the aluminum reflecting layer directly influences the reflectivity of the ultraviolet LED high-reflection electrode to ultraviolet light, and within a preset range, the high-reflection electrode can be guaranteed to have good optical performance, meanwhile, the metal deposition time is reasonable, and the process difficulty is low.

In a specific example, the patterned layer is an arrangement of solid dots, the diameter of the solid dots is 50nm to 1 μm, and the distance between the centers of adjacent solid dots is 100nm to 12 μm, alternatively, the diameter of the solid dots may be, for example, 100nm to 900nm, and further, may be, for example, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800 nm; alternatively, the distance between the centers of adjacent solid dots may be, for example, 300nm to 11 μm, or, for example, 600nm, 800nm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm. The patterning layer is arranged and processed according to the solid round points with preset diameters and circle center distances, the patterning rate of the patterning layer is within a preset range, the basic electrical and optical characteristics of the high-reflection electrode are guaranteed, the ohmic contact of the reflecting layer and the basal layer is more stable, the reflection of ultraviolet light is more uniform, and the ultraviolet light is easy to process.

In a specific example, the patterned layer is a dot-like hollow-out mesh, and the diameter of the hollow-out dots is 100nm to 10 μm, alternatively, the diameter of the hollow-out dots can be, for example, 300nm to 9.6 μm, or can be, for example, 600nm, 900nm, 1.2 μm, 1.5 μm, 1.8 μm, 2.1 μm, 2.4 μm, 2.7 μm, 3.0 μm, 3.3 μm, 3.6 μm, 3.9 μm, 4.2 μm, 4.5 μm, 4.8 μm, 5.1 μm, 5.4 μm, 5.7 μm, 6.0 μm, 6.3 μm, 6.6 μm, 6.9 μm, 7.2 μm, 7.5 μm, 7.8 μm, 8.1 μm, 8.4 μm, 8.7 μm, 9.0 μm, 9.2 μm, 9.4 μm. Arrange the processing according to the fretwork dot of predetermineeing the diameter within range with the patterning layer, make the metal ohmic contact layer of fretwork, not only can be so that the patterning rate on patterning layer is in predetermineeing the within range, guarantee the basic electricity and the optical characteristic of high counter electrode, still make the ohmic contact on reflector layer and stratum basale more stable, also more even to the reflection of ultraviolet ray, and easily processing.

providing an ultraviolet LED epitaxial wafer with a P-type doped layer as a top epitaxial layer, covering a patterned photoresist on the P-type doped layer, then depositing metal with the work function more than or equal to 4.6eV on the part, which is not covered by the photoresist, of the P-type doped layer, removing the photoresist after the deposition is finished, and uniformly covering a layer of metal aluminum as a reflecting layer.

providing an ultraviolet LED epitaxial wafer with a P-type doping layer as a top epitaxial layer, arranging a single layer of nano microspheres on the P-type doping layer, then depositing metal with work function more than or equal to 4.6eV in gaps among the adjacent nano microspheres and gaps between the nano microspheres and the P-type doping layer, removing the nano microspheres after deposition is finished, and uniformly covering a layer of metal aluminum as a reflecting layer.

In a specific example, the material of the nanoparticle is at least one of silicon dioxide, polystyrene or graphite.

In a specific example, the inert atmosphere is provided by nitrogen or argon, the annealing temperature is 600 ℃ to 1000 ℃, the annealing time is 5min to 60min, preferably, the annealing temperature is 700 ℃ to 900 ℃, and the annealing time is 10min to 50 min. Due to the proper annealing time and annealing temperature, the island-shaped distributed metal clusters formed after the annealing of the high work function metal can meet the requirement of the patterning rate, are distributed more uniformly, and are beneficial to improving the electrical property, the optical property and the stability of the electrode.

In the preparation method, the mode of depositing the high work function metal can select thermal evaporation, electron beam deposition or magnetron sputtering; the method for removing the photoresist or the nanospheres may be cleaning with an organic solvent such as acetone or ethanol and ultra-pure water.

The present invention will be described in further detail with reference to specific examples and comparative examples. It is understood that the following examples are more specific to the apparatus and materials used, and in other embodiments, are not limited thereto.

Example 1

Providing an ultraviolet LED epitaxial wafer with a P-type doping layer as a top epitaxial layer, covering a patterned photoresist on the P-type doping layer, depositing metal platinum with the thickness of 20nm on the part, which is not covered by the photoresist, of the P-type doping layer by using an electron beam, after the deposition is finished, cleaning a sample by using acetone, ethanol and ultrapure water in sequence to remove the photoresist, leaving the metal platinum distributed in a solid round point shape on the P-type doping layer, wherein the diameter of each round point is 500nm, the center distance between adjacent solid round points is 4 mu m (the patterning rate is about 10%), depositing metal aluminum with the thickness of 1 mu m by using the electron beam, uniformly covering the metal aluminum, using the metal aluminum as a reflecting layer, and finally cleaning the sample again by using the acetone, the ethanol and the ultrapure water in sequence to obtain the ultraviolet LED platinum/aluminum high-reflection electrode.

Example 2

Providing an ultraviolet LED epitaxial wafer with a P-type doping layer as a top epitaxial layer, arranging polystyrene nano microspheres with the diameter of 5 microns on the P-type doping layer in a self-assembly mode, depositing metal nickel with the thickness of 5nm by using an electron beam, cleaning a sample by using acetone, ethanol and ultrapure water in sequence after deposition to remove the nano microspheres, leaving the metal nickel in gaps between adjacent nano microspheres on the P-type doping layer (the patterning rate is about 20%), depositing metal aluminum with the thickness of 300nm by using the electron beam to uniformly cover the metal aluminum to serve as a reflecting layer, and finally cleaning the sample again by using the acetone, the ethanol and the ultrapure water in sequence to obtain the ultraviolet LED nickel/aluminum high-reflection electrode.

Example 3

Providing an ultraviolet LED epitaxial wafer with a P-type doping layer as a top epitaxial layer, depositing metal nickel with the thickness of 5nm on the P-type doping layer by utilizing magnetron sputtering, cleaning a sample by sequentially using acetone, ethanol and ultrapure water after deposition, annealing the sample in nitrogen at the annealing temperature of 1000 ℃ for 10min to form island-shaped distributed metal clusters (the patterning rate is about 20%) on the surface of the sample by using the metal nickel, then depositing metal aluminum with the thickness of 300nm by using an electron beam to uniformly cover the metal aluminum to serve as a reflecting layer, and finally cleaning the sample again by sequentially using the acetone, the ethanol and the ultrapure water to obtain the ultraviolet LED nickel/aluminum high-reflectivity electrode.

Example 4

Providing an ultraviolet LED epitaxial wafer with a P-type doping layer as a top epitaxial layer, covering a patterned photoresist on the P-type doping layer, depositing metal platinum with the thickness of 20nm on the part, which is not covered by the photoresist, of the P-type doping layer by using an electron beam, after the deposition is finished, cleaning a sample by using acetone, ethanol and ultrapure water in sequence to remove the photoresist, leaving the metal platinum distributed in a solid round point shape on the P-type doping layer, wherein the diameter of each round point is 1.2 mu m, the distance between the centers of adjacent round points is 7.4 mu m (the patterning rate is about 20%), depositing metal aluminum with the thickness of 1 mu m by using the electron beam, uniformly covering the metal aluminum to serve as a reflecting layer, and finally cleaning the sample by using the acetone, the ethanol and the ultrapure water in sequence to obtain the ultraviolet LED platinum/aluminum high-reflection electrode.

Example 5

Providing an ultraviolet LED epitaxial wafer with a P-type doping layer as a top epitaxial layer, dispersing and distributing polystyrene nano microspheres with the diameter of 3 mu m on the P-type doping layer, depositing metal nickel with the thickness of 10nm by using an electron beam, cleaning a sample by using acetone, ethanol and ultrapure water in sequence after deposition to remove the nano microspheres, leaving metal nickel (the patterning rate is about 30%) in gaps of adjacent nano microspheres on the P-type doping layer, depositing metal aluminum with the thickness of 300nm by using the electron beam, uniformly covering the metal aluminum to serve as a reflecting layer, and finally cleaning the sample again by using the acetone, the ethanol and the ultrapure water in sequence to obtain the ultraviolet LED nickel/aluminum high-reflectivity electrode.

Example 6

Providing an ultraviolet LED epitaxial wafer with a P-type doping layer as a top epitaxial layer, covering a patterned photoresist on the P-type doping layer, depositing metal platinum with the thickness of 20nm on the part, which is not covered by the photoresist, of the P-type doping layer by using an electron beam, after the deposition is finished, cleaning a sample by using acetone, ethanol and ultrapure water in sequence to remove the photoresist, leaving the metal platinum distributed in a solid round point shape on the P-type doping layer, wherein the diameter of each round point is 1.78 mu m, the center distance of each round point is 6.56 mu m (the patterning rate is about 40%), depositing metal aluminum with the thickness of 1 mu m by using the electron beam, uniformly covering the metal aluminum to serve as a reflecting layer, and finally cleaning the sample again by using the acetone, the ethanol and the ultrapure water in sequence to obtain the ultraviolet LED platinum/aluminum high-reflection electrode.

Example 7

Providing an ultraviolet LED epitaxial wafer with a P-type doping layer as a top epitaxial layer, depositing metal nickel with the thickness of 25nm on the P-type doping layer by utilizing magnetron sputtering, cleaning a sample by sequentially using acetone, ethanol and ultrapure water after deposition, annealing the sample in nitrogen at the annealing temperature of 1000 ℃ for 5min to form island-shaped distributed metal clusters (the patterning rate is about 40%) on the surface of the sample by using the metal nickel, then depositing metal aluminum with the thickness of 300nm by using an electron beam to uniformly cover the metal aluminum to serve as a reflecting layer, and finally cleaning the sample again by sequentially using the acetone, the ethanol and the ultrapure water to obtain the ultraviolet LED nickel/aluminum high-reflectivity electrode.

Example 8

Providing an ultraviolet LED epitaxial wafer with a P-type doping layer as a top epitaxial layer, dispersing and distributing polystyrene nano microspheres with the diameter of 5 microns on the P-type doping layer, depositing metal nickel with the thickness of 10nm by using an electron beam, cleaning a sample by using acetone, ethanol and ultrapure water in sequence after deposition to remove the nano microspheres, leaving metal nickel (the patterning rate is about 40%) in gaps of adjacent nano microspheres on the P-type doping layer, depositing metal aluminum with the thickness of 300nm by using the electron beam, uniformly covering the metal aluminum to serve as a reflecting layer, and finally cleaning the sample again by using the acetone, the ethanol and the ultrapure water in sequence to obtain the ultraviolet LED nickel/aluminum high-reflectivity electrode.

Comparative example 1

Providing an ultraviolet LED epitaxial wafer with a P-type doping layer as a top epitaxial layer, depositing metal nickel with the thickness of 5nm on the P-type doping layer by utilizing magnetron sputtering, cleaning a sample by sequentially using acetone, ethanol and ultrapure water after deposition, depositing metal aluminum with the thickness of 300nm by using an electron beam to uniformly cover the metal aluminum to be used as a reflecting layer, and finally cleaning the sample again by sequentially using the acetone, the ethanol and the ultrapure water to obtain the ultraviolet LED nickel/aluminum high-reflection electrode.

Comparative example 2

Providing an ultraviolet LED epitaxial wafer with a P-type doping layer as a top epitaxial layer, depositing metal nickel with the thickness of 5nm on the P-type doping layer by utilizing magnetron sputtering, cleaning a sample by sequentially using acetone, ethanol and ultrapure water after deposition, annealing the sample in nitrogen at 1500 ℃, wherein the annealing temperature is 1500 ℃, and the time is 10min, so that the metal nickel forms island-shaped distributed metal clusters (the patterning rate is about 4%) on the surface of the sample, depositing metal aluminum with the thickness of 300nm by using an electron beam, uniformly covering the metal aluminum to be used as a reflecting layer, and finally cleaning the sample again by sequentially using the acetone, the ethanol and the ultrapure water to obtain the ultraviolet LED nickel/aluminum high-reflectivity electrode.

Comparative example 3

Providing an ultraviolet LED epitaxial wafer with a P-type doping layer as a top epitaxial layer, depositing metal nickel with the thickness of 25nm on the P-type doping layer by utilizing magnetron sputtering, cleaning a sample by sequentially using acetone, ethanol and ultrapure water after deposition, annealing the sample in nitrogen at the annealing temperature of 500 ℃ for 5min to form island-shaped distributed metal clusters (the patterning rate is about 60%) on the surface of the sample by using the metal nickel, then depositing metal aluminum with the thickness of 300nm by using an electron beam to uniformly cover the metal aluminum to serve as a reflecting layer, and finally cleaning the sample again by sequentially using the acetone, the ethanol and the ultrapure water to obtain the ultraviolet LED nickel/aluminum high-reflectivity electrode.

Comparative example 4

Providing an ultraviolet LED epitaxial wafer with a P-type doping layer as a top epitaxial layer, arranging polystyrene nano microspheres with the diameter of 5 microns on the P-type doping layer in a self-assembly mode, depositing metal nickel with the thickness of 1nm by using an electron beam, cleaning a sample by using acetone, ethanol and ultrapure water in sequence after deposition to remove the nano microspheres, leaving the metal nickel in gaps between adjacent nano microspheres on the P-type doping layer (the patterning rate is about 20%), depositing metal aluminum with the thickness of 300nm by using the electron beam to uniformly cover the metal aluminum to serve as a reflecting layer, and finally cleaning the sample again by using the acetone, the ethanol and the ultrapure water in sequence to obtain the ultraviolet LED nickel/aluminum high-reflection electrode.

Comparative example 5

Providing an ultraviolet LED epitaxial wafer with a P-type doping layer as a top epitaxial layer, arranging polystyrene nano microspheres with the diameter of 5 microns on the P-type doping layer in a self-assembly mode, depositing metal nickel with the thickness of 100nm by using an electron beam, cleaning a sample by using acetone, ethanol and ultrapure water in sequence after deposition to remove the nano microspheres, leaving the metal nickel in gaps between adjacent nano microspheres on the P-type doping layer (the patterning rate is about 23%), depositing metal aluminum with the thickness of 300nm by using the electron beam to uniformly cover the metal aluminum to serve as a reflecting layer, and finally cleaning the sample again by using the acetone, the ethanol and the ultrapure water in sequence to obtain the ultraviolet LED nickel/aluminum high-reflection electrode.

And (3) performance testing:

the above samples were optically tested using a UV-visible spectrophotometer model Lambda 950, Perkin-Elmer, USA. The test conditions were that a light source was incident from the back of the sample and light was collected from the back through an integrating sphere, and the reflectance of each sample was obtained. The resulting reflectivities were all at a wavelength of 300 nm. The patterning rates and reflectivities for the different schemes are shown in the table.

Tests were conducted on lightly doped P-AlGaN using the methods provided in the examples and comparative examples shown above, respectively, to form a CTLM test pattern for ohmic contact with a Keithley-4200-SCS as a test instrument for the I-V characteristics of ohmic contact and at room temperature.

TABLE 1 optical and Electrical Properties of the examples and comparative examples

On the premise that the reflectivity of the high-counter electrode prepared by the embodiments of the invention is maintained at the lowest 63%, the highest contact resistance is not more than 7 omega/cm²Preferably, the reflectivity is maintained at the lowest levelThe optical property and the electrical property of the high-counter electrode are well balanced by about 70%, and a plurality of different modes are provided for preparation, so that the yield is higher than that of the traditional full-coverage scheme.

Compared with the comparative example 1 in the full-coverage traditional scheme, the embodiment 2 has the advantages that the metal nickel layer with the same thickness is deposited, the electrical performance is not reduced, the reflectivity is improved from 68% to 78%, the deposition mode is simple, the high yield is achieved, and the situation that the starting voltage of the device is too high due to the fact that the too thin metal layer in the full-coverage scheme is difficult to prepare uniformly is avoided; in comparative example 2, the patterning rate was low due to the excessively high annealing temperature, resulting in excessively high contact resistance; in comparative example 3, the annealing temperature was too low, resulting in a high patterning rate and a reflectivity of only 50%; in comparative example 4, the electrical properties were greatly reduced due to the excessively thin metal ohmic contact layer, and the contact resistance was as high as 15 Ω/cm²(ii) a In comparative example 5, the metal ohmic contact layer was too thick, which resulted in a limited improvement in electrical properties compared to example 2, but resulted in a large decrease in reflectivity.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. An ultraviolet LED high-reflection electrode is characterized by comprising an LED chip layer, a metal ohmic contact layer and an aluminum reflection layer which are sequentially arranged; the LED chip layer is a top P-type doped layer of the ultraviolet LED epitaxial wafer, the metal ohmic contact layer is a graphical layer made of metal materials with work functions larger than or equal to 4.6eV, and the orthographic projection area of the metal ohmic contact layer is 5% -40% of the orthographic projection area of the LED chip layer.

2. The ultraviolet LED high-counter electrode according to claim 1, wherein the metal with work function of 4.6eV or more is at least one of nickel, chromium, platinum, palladium, beryllium and gold.

3. The ultraviolet LED high-counter electrode according to claim 2, wherein the thickness of the metal ohmic contact layer is 5nm to 50 nm.

4. The ultraviolet LED high-counter electrode according to claim 1, wherein the aluminum reflective layer has a thickness of 50nm to 1 μm.

5. The ultraviolet LED high-counter electrode according to any one of claims 1 to 4, wherein the patterned layer is an arrangement of solid dots, the diameter of each solid dot is 50nm to 1 μm, and the distance between centers of adjacent solid dots is 100nm to 12 μm.

6. The ultraviolet LED high-reflection electrode as claimed in any one of claims 1 to 4, wherein the patterned layer is a closely arranged hollow-out net in the shape of dots, and the diameter of the hollow-out dots is 100nm to 10 μm.

7. The preparation method of the ultraviolet LED high-counter electrode according to any one of claims 1 to 6, characterized by comprising the following steps:

8. The method for preparing the ultraviolet LED high-counter electrode according to any one of claims 1 to 4 and claim 6, which is characterized by comprising the following steps:

9. The method according to claim 8, wherein the material of the nanospheres is at least one of silica, polystyrene or graphite.

10. The preparation method of the ultraviolet LED high-counter electrode according to any one of claims 1 to 4, characterized by comprising the following steps:

11. The method according to claim 10, wherein the inert atmosphere is provided by nitrogen or argon, the annealing temperature is 600 ℃ to 1000 ℃, and the annealing time is 5min to 60 min.

12. An ultraviolet LED comprising the ultraviolet LED high-counter electrode according to any one of claims 1 to 6.