Flip-chip ultraviolet light-emitting diode chip and preparation method thereof

Abstract

The present disclosure provides a flip-chip ultraviolet light-emitting diode chip and a preparation method thereof, which belongs to the technical field of light-emitting diodes. The n-AlGaN layer is configured to include a transition n-AlGaN layer, a graphene layer, and a contact n-AlGaN layer stacked in sequence. The graphene layer can protect the surface of the contact n-AlGaN layer. The graphene layer itself is involved in the etching process and is realized by laser stripping. The ohmic contact between the contact n-AlGaN layer and the electrode metal is easier to form, which can reduce the electrode of the final ultraviolet light-emitting diode chip and reduce the operating voltage required for the ultraviolet light-emitting diode, thereby extending the service life of the ultraviolet light-emitting diode. The graphene layer can also improve the quality of the epitaxial material, transmit electrons and expand the current, and can also improve the light uniformity of the ultraviolet light-emitting diode.

Description

Technical Field

[0001] The present disclosure relates to the technical field of light emitting diodes, and in particular to a flip-chip ultraviolet light emitting diode chip and a preparation method thereof. Background Art

[0002] With the development of LED applications, the market demand for UV LEDs is growing. UV LEDs with a wavelength of 210-400nm have advantages that traditional UV light sources cannot match. UV LEDs are often used in lighting, biomedicine, anti-counterfeiting identification, air and water purification, biochemical testing, high-density information storage, etc.

[0003] The flip-chip UV LED chip is a common structure of the flip-chip UV LED. The flip-chip UV LED chip usually includes a substrate, a p-electrode, an n-electrode and an epitaxial layer. The p-electrode and the n-electrode are spaced apart and distributed on the substrate, and the epitaxial layer is stacked on the p-electrode and the n-electrode. The epitaxial layer includes a p-GaN layer, a p-AlGaN layer, a multi-quantum well layer and an n-AlGaN layer stacked on the p-electrode and the n-electrode in sequence. The p-electrode is connected to the p-GaN layer, and the n-electrode is connected to the n-AlGaN layer.

[0004] When preparing a flip-chip UV LED chip, the n-AlGaN layer needs to be connected to the surface of the n-electrode, and a groove extending to the surface of the n-AlGaN layer needs to be etched from the p-GaN layer, and the surface of the n-AlGaN layer will be affected by the etching. Since the Al component in the n-AlGaN layer is usually very high, the N vacancies generated by the etching of the n-AlGaN layer act as deep energy level compensation centers rather than shallow donors. The high connection barrier makes it more difficult to form an ohmic connection in the n-AlGaN layer. The difficulty in forming an ohmic connection will result in a high connection resistance between the electrode and the epitaxial layer, making the operating voltage required for the final UV LED chip extremely high, and the heat generated by the UV LED chip is large, which affects the service life of the UV LED. Summary of the invention

[0005] The embodiment of the present disclosure provides a flip-chip ultraviolet light-emitting diode chip and a preparation method thereof, which can reduce the ohmic contact between the n-electrode and the n-AlGaN layer to reduce the operating voltage of the obtained ultraviolet light-emitting diode chip and increase the service life of the ultraviolet light-emitting diode. The technical solution is as follows:

[0006] The embodiment of the present disclosure provides a flip-chip ultraviolet light-emitting diode chip and a preparation method thereof. The flip-chip ultraviolet light-emitting diode chip includes a substrate, a p-electrode, an n-electrode and an epitaxial layer. The p-electrode and the n-electrode are spaced apart and distributed on the substrate. The epitaxial layer is stacked on the p-electrode and the n-electrode. The epitaxial layer includes a p-GaN layer, a p-AlGaN layer, a multi-quantum well layer, a transitional n-AlGaN layer, a graphene layer, a contact n-AlGaN layer and a light-emitting substrate stacked on the p-electrode and the n-electrode in sequence. The p-electrode is connected to the p-GaN layer, the n-electrode is connected to the contact n-AlGaN layer, the graphene layer is etched by laser processing, the Al component in the contact n-AlGaN layer is 40%-60%, and the doping concentration of Si in the contact n-AlGaN layer is 1*10 18 -1*10 20 cm -3 .

[0007] Optionally, the thickness of the graphene layer is 20-60 nm.

[0008] Optionally, the Al doping concentration and the Si doping concentration in the contact n-AlGaN layer are respectively equal to the Al doping concentration and the Si doping concentration in the transition n-AlGaN layer.

[0009] Optionally, the thickness of the transition n-AlGaN layer is in the range of 10-1000 nm, and the thickness of the contact n-AlGaN layer is in the range of 100-2000 nm.

[0010] Optionally, the thickness of the contact n-AlGaN layer is greater than the thickness of the contact n-AlGaN layer.

[0011] Optionally, the epitaxial layer further includes an n-type ohmic contact metal layer stacked between the n-electrode and the contact n-AlGaN layer, and the n-type ohmic contact metal layer includes one or a combination of titanium, aluminum, nickel, gold, vanadium, chromium or an alloy thereof.

[0012] The present disclosure provides a method for preparing a flip-chip ultraviolet light-emitting diode chip, and the method for preparing a flip-chip ultraviolet light-emitting diode chip comprises:

[0013] Providing a substrate and a light emitting substrate;

[0014] A contact n-AlGaN layer, a graphene layer, a transition n-AlGaN layer, a multi-quantum well layer, a p-AlGaN layer and a p-GaN layer are sequentially grown on the light-emitting substrate, wherein the Al component in the contact n-AlGaN layer is 40%-60%, and the doping concentration of Si in the contact n-AlGaN layer is 1*10 18 -1*1020 cm -3 ;

[0015] forming a groove on the p-GaN layer extending to the surface of the graphene layer;

[0016] Using a laser to remove the surface of the graphene layer exposed by the groove to expose the surface in contact with the n-AlGaN layer;

[0017] forming an n-electrode and a p-electrode on the contact n-AlGaN layer and the p-GaN layer, respectively;

[0018] The n-electrode and the p-electrode are bonded to the substrate.

[0019] Optionally, the graphene layer is grown using a physical vapor deposition device, and the growth temperature and growth pressure of the graphene layer are 1000-1200° C. and 0.1-1 atm, respectively.

[0020] Optionally, the method for preparing the flip-chip ultraviolet light-emitting diode chip further comprises:

[0021] After laser removal of the surface of the graphene layer exposed by the groove to expose the surface of the contact n-AlGaN layer, before forming an n-electrode and a p-electrode on the contact n-AlGaN layer and the p-GaN layer, respectively,

[0022] forming an n-type ohmic contact metal layer on the surface of the contact n-AlGaN layer;

[0023] The n-type ohmic contact metal layer is annealed at a temperature of 600-1000° C. for 10-100 seconds.

[0024] The beneficial effects brought by the technical solution provided by the embodiments of the present disclosure include:

[0025] In addition to the substrate and the p and n electrodes, the epitaxial layer of the flip-chip ultraviolet light-emitting diode chip includes a p-GaN layer, a p-AlGaN layer, a multi-quantum well layer, a transition n-AlGaN layer, a graphene layer, a contact n-AlGaN layer and a light-emitting substrate stacked sequentially on the p electrode and the n electrode, the p electrode is connected to the p-GaN layer, and the n electrode is connected to the contact n-AlGaN layer. The conventional n-AlGaN layer is set to include a transition n-AlGaN layer, a graphene layer, and a contact n-AlGaN layer stacked sequentially. The graphene layer can protect the surface of the contact n-AlGaN layer and reduce the impact of etching on the contact n-AlGaN layer. The graphene layer itself is involved in the etching process and is realized by laser stripping, which can further ensure the integrity of the surface of the contact n-AlGaN layer, and the ohmic contact between the contact n-AlGaN layer and the electrode metal is easier to form, which can reduce the electrode of the final ultraviolet light-emitting diode chip and reduce the required operating voltage of the ultraviolet light-emitting diode, thereby extending the service life of the ultraviolet light-emitting diode. The graphene layer can also isolate the defects between the two adjacent n-type layers to improve the quality of the epitaxial material grown on the graphene layer, and the crystal quality of the final ultraviolet light-emitting diode chip can also be improved. The graphene layer itself can play the role of transmitting electrons and expanding current, and can also improve the light uniformity of the ultraviolet light-emitting diode. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1 It is a structural schematic diagram of a flip-chip ultraviolet light-emitting diode epitaxial wafer provided by an embodiment of the present disclosure;

[0028] Figure 2 It is a structural schematic diagram of another flip-chip ultraviolet light-emitting diode epitaxial wafer provided by an embodiment of the present disclosure;

[0029] Figure 3 It is a flow chart of a flip-chip ultraviolet light-emitting diode chip and a preparation method thereof provided by an embodiment of the present disclosure;

[0030] Figure 4 , Figure 5 It is a schematic diagram of the preparation process of the ultraviolet light emitting diode chip provided in the embodiment of the present disclosure;

[0031] Figure 6It is another flip-chip ultraviolet light-emitting diode chip and a flow chart of a preparation method thereof provided by an embodiment of the present disclosure;

[0032] Figure 7 It is the IV characteristic curve corresponding to the flip-chip ultraviolet light emitting diode provided in the embodiment of the present disclosure. DETAILED DESCRIPTION

[0033] In order to make the objectives, technical solutions and advantages of the present disclosure more clear, the embodiments of the present disclosure will be further described in detail below with reference to the accompanying drawings.

[0034] Figure 1 is a schematic diagram of the structure of a flip-chip ultraviolet light-emitting diode epitaxial wafer provided by the embodiment of the present disclosure, with reference to Figure 1 It can be seen that the embodiment of the present disclosure provides a flip-chip ultraviolet light-emitting diode chip and a preparation method thereof. The flip-chip ultraviolet light-emitting diode chip includes a substrate 1, a p-electrode 2, an n-electrode 3 and an epitaxial layer 4. The p-electrode 2 and the n-electrode 3 are spaced apart and distributed on the substrate 1. The epitaxial layer 4 is stacked on the p-electrode 2 and the n-electrode 3. The epitaxial layer 4 includes a p-GaN layer 401, a p-AlGaN layer 402, a multi-quantum well layer 403, a transition n-AlGaN layer 404, a graphene layer 405, a contact n-AlGaN layer 406 and a light-emitting substrate 407 which are sequentially stacked on the p-electrode 2 and the n-electrode 3. The p-electrode 2 is connected to the p-GaN layer 401, the n-electrode 3 is connected to the contact n-AlGaN layer 406, and the etching of the graphene layer 405 is performed by laser processing.

[0035] In addition to the substrate 1 and the p and n electrodes 3, the epitaxial layer 4 of the flip-chip ultraviolet light-emitting diode chip includes a p-GaN layer 401, a p-AlGaN layer 402, a multi-quantum well layer 403, a transition n-AlGaN layer 404, a graphene layer 405, a contact n-AlGaN layer 406 and a light-emitting substrate 407 stacked sequentially on the p electrode 2 and the n electrode 3, the p electrode 2 is connected to the p-GaN layer 401, and the n electrode 3 is connected to the contact n-AlGaN layer 406. The conventional n-AlGaN layer is set to include a transition n-AlGaN layer 404, a graphene layer 405, and a contact n-AlGaN layer 406 stacked sequentially. The graphene layer 405 can protect the surface of the contact n-AlGaN layer 406 and reduce the influence of etching on the contact n-AlGaN layer 406. The graphene layer 405 itself is implemented by laser stripping during the etching process, which can further ensure the integrity of the surface of the contact n-AlGaN layer 406, and the ohmic contact between the contact n-AlGaN layer 406 and the electrode metal is easier to form, which can reduce the electrode of the final ultraviolet light-emitting diode chip and reduce the required operating voltage of the ultraviolet light-emitting diode, thereby extending the service life of the ultraviolet light-emitting diode. The graphene layer 405 can also isolate the defects between the two adjacent n-type layers to improve the quality of the epitaxial material grown on the graphene layer 405, and the crystal quality of the final ultraviolet light-emitting diode chip can also be improved. The graphene layer 405 itself can play the role of transmitting electrons and expanding current, and can also improve the light uniformity of the ultraviolet light-emitting diode.

[0036] It should be noted that when the epitaxial layer 4 of the flip-chip UV LED chip is grown, in order to achieve good contact between the two electrodes and the epitaxial layer 4, it is necessary to etch a groove S extending to the side of the n-type semiconductor on one side of the p-type semiconductor, and both chemical etching and physical etching will have a certain impact on the surface roughness of the n-type semiconductor. In the implementation provided by the present disclosure, the p-GaN layer 401 is a p-type semiconductor, and the graphene layer 405 and the two layers of material adjacent to the graphene layer 405 are n-type semiconductors.

[0037] Optionally, the thickness of the graphene layer 405 is 20-60 nm.

[0038] The thickness of the graphene layer 405 within the above range can ensure that the quality of the obtained graphene layer 405 is good, and can achieve good protection of the surface contacting the n-AlGaN layer 406, effectively reducing the impact of etching or corrosion on the surface contacting the n-AlGaN layer 406.

[0039] In other implementations provided by the present disclosure, the thickness of the graphene layer 405 may also be selected within the range of 1-100 nm, and the present disclosure does not impose any limitation on this.

[0040] Optionally, the Al content in the contact n-AlGaN layer 406 is 40%-60%, and the doping concentration of Si in the contact n-AlGaN layer 406 is 1*10 18 -1*10 20 cm -3 .

[0041] When the Al component and Si doping concentration in the contact n-AlGaN layer 406 are within the above range, the crystal quality of the contact n-AlGaN layer 406 itself is good, and the stable supply and transmission of electrons can be guaranteed. There are fewer defects in the contact n-AlGaN layer 406, and the ohmic contact resistance between the contact n-AlGaN layer 406 and the electrode can be lowered, which can effectively reduce the operating voltage of the final ultraviolet light-emitting diode chip and increase the service life of the ultraviolet light-emitting diode.

[0042] Exemplarily, the Al doping concentration and the Si doping concentration in the contact n-AlGaN layer 406 are respectively equal to the Al doping concentration and the Si doping concentration in the transition n-AlGaN layer 404 .

[0043] The Al doping concentration and Si doping concentration in the contact n-AlGaN layer 406 are respectively equal to the Al doping concentration and Si doping concentration in the transition n-AlGaN layer 404, which can ensure that the crystal quality of the obtained contact n-AlGaN layer 406 and the transition n-AlGaN layer 404 are good. When actually growing two n-AlGaN layers, since the parameters basically do not need to be adjusted, the preparation efficiency of the ultraviolet light emitting diode chip can also be improved.

[0044] Optionally, the thickness of the transition n-AlGaN layer 404 is in a range of 10-1000 nm, and the thickness of the contact n-AlGaN layer 406 is in a range of 100-2000 nm.

[0045] The thickness of the transition n-AlGaN layer 404 and the contact n-AlGaN layer 406 are respectively within the above ranges, which can ensure that the quality of the obtained transition n-AlGaN layer 404 and the contact n-AlGaN layer 406 are both good, and the crystal quality of the epitaxial material grown on the transition n-AlGaN layer 404 is also good. It can also ensure that the transition n-AlGaN layer 404 and the contact n-AlGaN layer 406 can both provide enough electrons, ensuring that the number of electrons that finally emit light in the multi-quantum well layer 403 is relatively sufficient, and the luminous efficiency of the ultraviolet light-emitting diode can also be guaranteed.

[0046] Optionally, the thickness of the contact n-AlGaN layer 406 is greater than the thickness of the contact n-AlGaN layer 406 .

[0047] The thickness of the contact n-AlGaN layer 406 is greater than the thickness of the contact n-AlGaN layer 406, which can ensure that the contact n-AlGaN layer 406 grown on the graphene layer 405 has good crystal quality and can also ensure the stable growth of other epitaxial materials on the contact n-AlGaN layer 406. The thicker contact n-AlGaN layer 406 can also provide more sufficient electrons for recombination and light emission in the multi-quantum well layer 403.

[0048] Figure 2 is a schematic diagram of the structure of another flip-chip ultraviolet light-emitting diode epitaxial wafer provided in the embodiment of the present disclosure, with reference to Figure 2 It can be seen that the flip-chip ultraviolet light-emitting diode chip may include a substrate 1, a p-electrode 2, an n-electrode 3 and an epitaxial layer 4, the p-electrode 2 and the n-electrode 3 are spaced apart and distributed on the substrate 1, the epitaxial layer 4 is stacked on the p-electrode 2 and the n-electrode 3, the epitaxial layer 4 includes a p-GaN layer 401, a p-AlGaN layer 402, a multi-quantum well layer 403, a transition n-AlGaN layer 404, a graphene layer 405, a contact n-AlGaN layer 406, a buffer layer 408 and a light-emitting substrate 407 stacked on the p-electrode 2 and the n-electrode 3, the p-electrode 2 is connected to the p-GaN layer 401, the n-electrode 3 is connected to the contact n-AlGaN layer 406, the surface of the p-GaN layer 401 has a groove S extending to the contact n-AlGaN layer 406, the n-electrode 3 is located on the surface of the contact n-AlGaN layer 406 exposed by the groove S, and the etching of the graphene layer 405 is laser processed.

[0049] The epitaxial layer 4 may further include a p-type ohmic contact metal layer 409 disposed between the p-electrode 2 and the p-GaN layer 401, an n-type ohmic contact metal layer 410 disposed between the n-electrode 3 and the contact n-AlGaN layer 406, and an insulating layer 411. The orthographic projection area of ​​the n-type ohmic contact metal layer 410 on the surface of the substrate 1 is larger than the orthographic projection area of ​​the n-electrode 3 on the substrate 1, and the orthographic projection area of ​​the p-type ohmic contact metal layer 409 on the surface of the substrate 1 is larger than the orthographic projection area of ​​the p-electrode 2 on the surface of the substrate 1. The insulating layer 411 covers the sidewall of the epitaxial layer 4, the surface of the p-type ohmic contact metal layer 409 close to the base, and the surface of the n-type ohmic contact metal layer 410 close to the substrate 1. The insulating layer 411 has two through holes corresponding to the n-electrode 3 and the p-electrode 2, respectively. The n-electrode 3 and the p-electrode 2 are respectively located in the two through holes, and the n-electrode 3 and the p-electrode 2 are respectively connected to the n-type ohmic contact metal layer 410 and the p-type ohmic contact metal layer 409.

[0050] For example, the substrate 1 may be a circuit substrate 1 or a gallium nitride material substrate, which can achieve good contact with the n-electrode 3 and the p-electrode 2 and is easy to prepare.

[0051] Optionally, the n-electrode 3 includes a chromium sublayer, a platinum sublayer and a titanium sublayer sequentially stacked on the substrate 1 .

[0052] Optionally, the p-electrode 2 includes a titanium sublayer, a gold sublayer and an aluminum sublayer sequentially stacked on the substrate 1. Thus, the n-electrode 3 and the p-electrode 2 of good quality can be obtained.

[0053] For example, the insulating layer 411 may be a silicon oxide layer with a thickness of 2-3 micrometers, which can achieve good protection for structures such as the ohmic contact metal layer.

[0054] Exemplarily, the n-type ohmic contact metal layer 410 includes one or a combination of titanium, aluminum, nickel, gold, vanadium, chromium, or an alloy thereof.

[0055] In the present disclosure, the addition of the n-type ohmic contact metal layer 410 and the p-type ohmic contact metal layer 409 can play a role in expanding the current to a certain extent, and promote the light uniformity of the flip-chip ultraviolet light-emitting diode chip. The n-type ohmic contact metal layer 410 includes one or a combination of titanium, aluminum, nickel, gold, vanadium, chromium or their alloys, which can also ensure good contact between the n-type ohmic contact metal layer 410 and the contact n-AlGaN layer 406.

[0056] For example, the n-type ohmic contact metal layer 410 may include a titanium sublayer, an aluminum sublayer, and a nickel sublayer sequentially stacked on the n-electrode 3. The obtained n-type ohmic contact metal layer 410 has good quality.

[0057] In an implementation provided by the present disclosure, the structure of the n-type ohmic contact metal layer 410 may be the same as that of the p-type ohmic contact metal layer 409 , which facilitates the preparation of the n-type ohmic contact metal layer 410 and the p-type ohmic contact metal layer 409 .

[0058] Optionally, the thickness of the p-GaN layer 401 may be 100-300 nm.

[0059] Optionally, the P-type dopant in the p-AlGaN layer 402 may be Mg, with a doping concentration of 10 17 cm -3 -10 18 cm -3 .

[0060] Exemplarily, the thickness of the p-AlGaN layer 402 is 1-1.5 micrometers, which can ensure the crystal quality of the obtained ultraviolet light emitting diode chip.

[0061] Optionally, the multiple quantum well layer 403 includes a plurality of alternately grown quantum barrier layers and quantum well layers. The quantum well layer may be a GaN layer, and the quantum barrier layer may be an AlxGa1-xN (0 < x < 0.3) layer.

[0062] It should be noted that Figure 2 the structures of the transition n-AlGaN layer 404, the graphene layer 405, and the contact n-AlGaN layer 406 in Figure 1 are the same as those of the transition n-AlGaN layer 404, the graphene layer 405, and the contact n-AlGaN layer 406 in

[0063] Exemplarily, the buffer layer 408 includes an undoped AlGaN sublayer, an AlN / AlGaN multi-period stress modulation sublayer, and an AlN sublayer that are sequentially stacked on the contact n-AlGaN layer 406.

[0064] By setting the buffer layer 408 to include an AlN sublayer, an AlN / AlGaN multi-period stress modulation sublayer, and an undoped AlGaN sublayer that are sequentially stacked, a good transition from the substrate to the contact n-AlGaN layer 406 can be achieved. The AlN / AlGaN multi-period stress modulation sublayer can also effectively release a certain amount of stress, improve the crystal quality of the epitaxial material above the contact n-AlGaN layer 406, and improve the light emission efficiency of the finally obtained ultraviolet light-emitting diode epitaxial wafer.

[0065] It should be noted that the AlN / AlGaN multi-period stress modulation sublayer is a superlattice structure.

[0066] Optionally, the light extraction substrate 407 may be a sapphire substrate. It has good light transmittance and can meet the requirements for stable light emission of the light-emitting diode.

[0067] Figure 2 The flip-chip ultraviolet light-emitting diode chip shown in Figure 1 compared with the flip-chip ultraviolet light-emitting diode chip shown in

[0068] Figure 3 provides a more detailed description of each epitaxial material in the epitaxial layer 4, adds a buffer layer 408 between the light extraction substrate 407 and the contact n-AlGaN layer 406, and adds an ohmic contact metal layer between the electrode and the epitaxial material to be contacted by the electrode. Overall, it can further improve the quality of the obtained flip-chip ultraviolet light-emitting diode chip and can improve the light emission uniformity of the flip-chip ultraviolet light-emitting diode. Figure 3 As can be seen from

[0069] S101: Provide a substrate and a light emitting substrate.

[0070] S102: sequentially growing a buffer layer, a contact n-AlGaN layer, a graphene layer, a transition n-AlGaN layer, a multi-quantum well layer, a p-AlGaN layer and a p-GaN layer on a light emitting substrate.

[0071] S103: forming a groove on the p-GaN layer extending to the surface of the graphene layer.

[0072] S104: removing the surface of the graphene layer exposed by the groove by laser to expose the surface contacting the n-AlGaN layer.

[0073] S105: forming an n-electrode and a p-electrode on the contact n-AlGaN layer and the p-GaN layer respectively.

[0074] S106: Bonding the n-electrode and the p-electrode to the substrate.

[0075] The structure of the flip-chip UV LED chip obtained after executing step S106 can be referred to Figure 1 , Figure 3 The technical effects corresponding to the preparation method shown in Figure 1 The technical effect corresponding to the flip-chip ultraviolet light-emitting diode chip described in.

[0076] Optionally, laser removal of the surface of the graphene layer exposed by the groove to expose the surface in contact with the n-AlGaN layer includes: laser separation of the portion of the graphene layer exposed by the groove and the contact with the n-AlGaN layer; laser splitting of the portion of the graphene layer exposed by the groove and the portion of the graphene layer covered by the transition n-AlGaN layer.

[0077] The surface quality of the obtained contact n-AlGaN layer can be ensured to be good, and the side wall quality of the graphene layer itself is relatively flat, which is convenient for the growth and coverage of the insulating layer. The graphene layer will not affect the contact n-AlGaN layer during the cutting process.

[0078] For ease of understanding, here is provided Figure 4 and Figure 5 , Figure 4 , Figure 5 is a schematic diagram of the preparation process of the ultraviolet light emitting diode chip provided in the embodiment of the present disclosure, Figure 4 The state of the epitaxial layer of the flip-chip ultraviolet light-emitting diode after executing step S103 and before executing step S104 is shown, and at this time, the graphene layer is not etched or corroded; Figure 5, the epitaxial layer state of the flip-chip UV LED after executing step S104 and before executing step S105 is shown. Here, the graphene layer has been laser processed, and the surface contacting the n-AlGaN layer is exposed, which can be used for the preparation of n-electrode or different epitaxial materials.

[0079] Figure 6 is another flip-chip ultraviolet light-emitting diode chip and a flow chart of its preparation method provided by the embodiment of the present disclosure, refer to Figure 6 It can be seen that the method for preparing a flip-chip ultraviolet light-emitting diode chip may include:

[0080] S201: Provide a substrate and a light emitting substrate.

[0081] The substrate may be a gallium nitride substrate, a circuit substrate, or a gallium arsenide substrate, which is not limited in the present disclosure.

[0082] Optionally, the light emitting substrate may be a sapphire substrate, and the thickness of the light emitting substrate may be 3-5 microns, so as to ensure the light emitting efficiency of the obtained flip-chip ultraviolet light emitting diode.

[0083] S202: sequentially growing a buffer layer, a contact n-AlGaN layer, a graphene layer, a transition n-AlGaN layer, a multi-quantum well layer, a p-AlGaN layer and a p-GaN layer on the light emitting substrate.

[0084] In step S202, the growth conditions of each epitaxial material may be as follows:

[0085] Optionally, an AlN sublayer is grown on the substrate at a growth temperature of 1000-1400°C and a pressure of 50-100 mbar. The thickness of the AlN sublayer is 15 to 40 nm. Before growing the undoped AlGaN layer, the buffer layer (with substrate) is subjected to in-situ annealing in an MOCVD (Metal Organic Chemical Vapor Deposition) device at a temperature of 1000°C-1200°C, a pressure range of 150 Torr-500 Torr, and a time of 5 to 10 minutes. After the annealing is completed, the temperature of the MOCVD device is adjusted to 1000°C-1200°C, and an undoped AlGaN layer with a thickness of 0.1 to 3.0 microns is grown at a growth pressure of 50 Torr to 200 Torr. This ensures that the crystal quality of the obtained buffer layer is good.

[0086] Exemplarily, the growth temperature of the contact n-AlGaN layer and the transition n-AlGaN layer is 1000 - 1100 °C, and the growth pressure of the contact n-AlGaN layer and the transition n-AlGaN layer is 75 - 100 Torr. The quality of the obtained contact n-AlGaN layer and transition n-AlGaN layer can be improved, and impurity doping into the aluminum gallium nitride material can be promoted in a low-pressure environment, increasing the electron concentration entering the light-emitting layer.

[0087] Optionally, the graphene layer is grown using a physical vapor deposition device. The deposition temperature of the graphene layer is 300 - 600 °C, and the deposition pressure of the graphene layer is 50 - 100 Torr.

[0088] When the deposition temperature and deposition pressure of the graphene layer are within the above ranges, the quality of the obtained graphene layer can be improved, thereby improving the crystal quality of the finally obtained electron transport layer. Growing the graphene layer using a physical vapor deposition device can also increase the density of the graphene layer to effectively block defects.

[0089] Optionally, the multiple quantum well layer includes a number of alternately grown quantum barrier layers and quantum well layers. The quantum well layer can be a GaN layer, and the quantum barrier layer can be an AlxGa1-xN (0 < x < 0.3) layer. For example, the multiple quantum well layer is composed of 4 to 12 periods of GaN and AlxGa1-xN (0 < x < 0.3). The thickness of the quantum well layer is about 3 nm, the growth temperature ranges from 850 °C to 950 °C, and the pressure range is between 100 Torr and 300 Torr; the thickness of the quantum barrier layer is between 8 nm and 20 nm, the growth temperature is 900 °C - 1000 °C, and the growth pressure is between 50 Torr and 200 Torr.

[0090] Optionally, the p-AlGaN layer is grown on the electron blocking layer at a growth temperature of 950 - 1050 °C and a growth pressure of 100 Torr - 600 Torr.

[0091] Optionally, the growth temperature of the p-GaN layer is 800 - 900 °C. The crystal quality of the obtained p-GaN layer can be improved.

[0092] S203: Form a groove on the p-GaN layer that extends to the surface of the graphene layer.

[0093] It should be noted that the groove formed on the p-GaN layer that extends to the surface of the graphene layer can be obtained through a photolithography process. The surface of the graphene layer is the surface of the graphene layer that is parallel to the substrate and farthest from the substrate.

[0094] S204: Laser-remove the surface of the graphene layer exposed by the groove to expose the surface of the contact n-AlGaN layer.

[0095] Step S204 can refer to Figure 3 Step S104 shown in FIG. 1 is not described in detail here.

[0096] S205: forming an n-type ohmic contact metal layer and a p-type ohmic contact metal layer on the contact n-AlGaN layer and the p-GaN layer, respectively.

[0097] The n-type ohmic contact metal layer and the p-type ohmic contact metal layer can be prepared by sputtering or deposition in combination with a photolithography process.

[0098] S206: annealing the n-type ohmic contact metal layer and the p-type ohmic contact metal layer at a temperature of 600-1000° C. for 10-100 seconds.

[0099] Annealing under the above conditions can obtain an ohmic contact metal layer and epitaxial material with low contact resistance.

[0100] S207: Covering the surface of the n-type ohmic contact metal layer, the surface of the p-type ohmic contact metal layer and the sidewall of the epitaxial layer with an insulating layer, wherein the insulating layer has two through holes connected to the surface of the n-type ohmic contact metal layer and the surface of the p-type ohmic contact metal layer respectively.

[0101] Optionally, the insulating layer is made of silicon oxide material, and the through hole can be prepared by a photolithography process, so that an insulating layer with stable quality can be obtained.

[0102] S208: forming an n-electrode and a p-electrode on the contact n-AlGaN layer and the p-GaN layer, respectively, wherein the n-electrode and the p-electrode are respectively located in two through holes provided in the insulating layer.

[0103] The n-electrode and the p-electrode can be prepared by sputtering or deposition in combination with a photolithography process. For example, a photoresist layer is coated on the surface of the insulating layer, and an electrode hole connected to two through holes on the insulating layer is formed on the photoresist layer through exposure, development and etching operations. The n-electrode and the p-electrode are prepared in the electrode hole.

[0104] S209: Bonding the n-electrode and the p-electrode to the substrate.

[0105] Optionally, the bonding between the n-electrode, the p-electrode and the substrate can be achieved by applying pressure through a press at a temperature of 100-300° C. The bonding quality can be guaranteed.

[0106] It should be noted that the structure of the flip-chip ultraviolet light-emitting diode epitaxial wafer obtained after executing step S209 can be referred to Figure 2 The structure of the flip-chip UV LED epitaxial wafer shown in .

[0107] It should be noted that in the disclosed embodiments, the epitaxial material can be mainly prepared by MOCVD equipment, wherein high-purity H2 (hydrogen) or high-purity N2 (nitrogen) or a mixture of high-purity H2 and high-purity N2 is used as a carrier gas, high-purity NH3 is used as an N source, trimethylgallium (TMGa) and triethylgallium (TEGa) are used as gallium sources, silane (SiH4) is used as an N-type dopant, trimethylaluminum (TMAl) is used as an aluminum source, and bis(cyclopentadienyl)magnesium (CP2Mg) is used as a P-type dopant.

[0108] Also available here Figure 7 , Figure 7 is the IV characteristic curve corresponding to the flip-chip ultraviolet light-emitting diode provided in the embodiment of the present disclosure, Figure 7 Zhongwei Figure 2 The IV characteristic curve corresponding to the flip-chip ultraviolet light-emitting diode shown in the figure, I is the current and V is the voltage. Figure 7 The operating voltage of this chip is only 7V at 20mA. Figure 2 The chip prepared by the prior art, in which only the structure of the n-type AlGaN layer is different, has an operating voltage corresponding to a current of 20 mA of 8 V. The operating voltage of the ultraviolet light emitting diode in the present disclosure is effectively reduced.

[0109] The above description does not limit the present disclosure in any form. Although the present disclosure has been disclosed as above through the embodiments, it is not used to limit the present disclosure. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present disclosure. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present disclosure without departing from the content of the technical solution of the present disclosure still falls within the scope of the technical solution of the present disclosure.

Claims

1. A flip-chip ultraviolet light-emitting diode chip, characterized in that: The flip-chip ultraviolet light-emitting diode chip includes a substrate, a p-electrode, an n-electrode and an epitaxial layer. The p-electrode and the n-electrode are spaced apart and distributed on the substrate. The epitaxial layer is stacked on the p-electrode and the n-electrode. The epitaxial layer includes a p-GaN layer, a p-AlGaN layer, a multi-quantum well layer, a transition n-AlGaN layer, a graphene layer, a contact n-AlGaN layer and a light-emitting substrate sequentially stacked on the p-electrode and the n-electrode. The p-electrode is connected to the p-GaN layer, the n-electrode is connected to the contact n-AlGaN layer, the graphene layer is etched by laser processing, the Al component in the contact n-AlGaN layer is 40%-60%, and the doping concentration of Si in the contact n-AlGaN layer is 1*10 18 -1*10 20 cm -3 .

2. The flip-chip ultraviolet light emitting diode chip according to claim 1, characterized in that: The thickness of the graphene layer is 20-60 nm.

3. The flip-chip ultraviolet light emitting diode chip according to claim 1 or 2, characterized in that: The Al doping concentration and the Si doping concentration in the contact n-AlGaN layer are respectively equal to the Al doping concentration and the Si doping concentration in the transition n-AlGaN layer.

4. The flip-chip ultraviolet light emitting diode chip according to claim 1 or 2, characterized in that: The thickness of the transition n-AlGaN layer is in the range of 10-1000 nm, and the thickness of the contact n-AlGaN layer is in the range of 100-2000 nm.

5. The flip-chip ultraviolet light emitting diode chip according to claim 1 or 2, characterized in that: The thickness of the contact n-AlGaN layer is greater than the thickness of the transition n-AlGaN layer.

6. The flip-chip ultraviolet light emitting diode chip according to claim 1 or 2, characterized in that: The epitaxial layer also includes an n-type ohmic contact metal layer stacked between the n-electrode and the contact n-AlGaN layer, and the n-type ohmic contact metal layer includes one or a combination of titanium, aluminum, nickel, gold, vanadium, chromium or an alloy thereof.

7. A method for preparing a flip-chip ultraviolet light-emitting diode chip, characterized in that: The method for preparing the flip-chip ultraviolet light-emitting diode chip comprises: Providing a substrate and a light emitting substrate; A contact n-AlGaN layer, a graphene layer, a transition n-AlGaN layer, a multi-quantum well layer, a p-AlGaN layer and a p-GaN layer are sequentially grown on the light-emitting substrate, wherein the Al component in the contact n-AlGaN layer is 40%-60%, and the doping concentration of Si in the contact n-AlGaN layer is 1*10 18 -1*10 20 cm -3 ; forming a groove on the p-GaN layer extending to the surface of the graphene layer; Using a laser to remove the surface of the graphene layer exposed by the groove to expose the surface in contact with the n-AlGaN layer; forming an n-electrode and a p-electrode on the contact n-AlGaN layer and the p-GaN layer, respectively; The n-electrode and the p-electrode are bonded to the substrate.

8. The method for preparing a flip-chip ultraviolet light-emitting diode chip according to claim 7, characterized in that: The graphene layer is grown by using a physical vapor deposition device, and the growth temperature and growth pressure of the graphene layer are 1000-1200° C. and 0.1-1 atm respectively.

9. The method for preparing a flip-chip ultraviolet light-emitting diode chip according to claim 7, characterized in that: The method for preparing the flip-chip ultraviolet light-emitting diode chip further includes: After laser removal of the surface of the graphene layer exposed by the groove to expose the surface of the contact n-AlGaN layer, before forming an n-electrode and a p-electrode on the contact n-AlGaN layer and the p-GaN layer, respectively, forming an n-type ohmic contact metal layer on the surface of the contact n-AlGaN layer; The n-type ohmic contact metal layer is annealed at a temperature of 600-1000° C. for 10-100 seconds.

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