A vertical epitaxial structure LED chip and a preparation method thereof

Abstract

The application provides a vertical epitaxial structure LED chip and a preparation method thereof, and comprises a substrate, an insertion layer, a conductive layer, a low-doped conductive layer and an LED structure layer arranged in sequence. The insertion layer is a hexagonal boron nitride layer. The conductive layer comprises a plurality of gallium aluminum nitride / gallium nitride heterojunction layers. The interaction force between the hexagonal boron nitride layer structure is small, and the peeling damage to the upper epitaxial structure is small. By using the characteristics of the hexagonal boron nitride layer structure, the laser peeling technology will not damage the structure on the hexagonal boron nitride layer, thereby improving the yield of the LED chip. The structure of the gallium aluminum nitride / gallium nitride heterojunction can play a similar chip DBR role due to the different materials. Moreover, by gradually reducing the silicon doping concentration of the gallium aluminum nitride / gallium nitride heterojunction layer, the electrode can be well matched, and the conductive and ohmic contact effects are good.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of LED chip, in particular to a vertical epitaxial structure LED chip and a preparation method thereof. BACKGROUND

[0002] With the gradual application of LED in the field of lighting, the market has higher and higher requirements for the light efficiency of white LED (light emitting diode); GaN (gallium nitride) based vertical structure LED has the advantages of single-sided light emission, excellent heat dissipation efficiency, uniform current distribution, improved current congestion, ability to carry large current injection, and full utilization of light emitting layer materials.

[0003] The industry mainly uses MOCVD (Metal-Organic Chemical Vapour Deposition, metal organic chemical vapor deposition) method to prepare the epitaxial wafer of LED, and generally uses PSS substrate (Patterned Sapphire Substrate, patterned sapphire substrate). A mask for dry etching is grown on the PSS substrate material, and the mask is patterned by a standard photolithography process, and then the ICP etching technology is used to etch the sapphire and remove the mask, and GaN material is grown thereon, so that the longitudinal epitaxy of GaN material is changed to lateral epitaxy. On the one hand, it can effectively reduce the dislocation density of GaN epitaxial material, thereby reducing the non-radiative recombination of the active region, reducing the reverse leakage current, and improving the life of the LED; on the other hand, the light emitted by the active region is scattered multiple times through the interface between GaN and the sapphire substrate, changing the exit angle of the totally reflected light and increasing the probability of light emitted from the sapphire substrate, thereby improving the light extraction efficiency.

[0004] However, sapphire is an insulating material, so the growth substrate needs to be peeled off, and the peeling technology is not mature, the substrate peeling is poor, the upper epitaxial structure is easily damaged, the leakage rate increases, the performance of the LED chip deteriorates, and the peeling yield is low, increasing the production cost. SUMMARY

[0005] The present application provides a vertical epitaxial structure LED chip and a preparation method thereof to solve the problem of poor substrate peeling, easy damage to the upper epitaxial structure, increased leakage rate, poor performance of the LED chip, low peeling yield, and increased production cost.

[0006] In a first aspect, the application provides a vertical epitaxial structure LED chip, comprising: a substrate, an interlayer, a conductive layer, a low-doped conductive layer and an LED structure layer arranged in sequence, the interlayer being a hexagonal boron nitride (h-BN) layer; the conductive layer comprising a plurality of gallium aluminum nitride (AlGaN) / gallium nitride (GaN) heterojunction layers, the AlGaN / GaN heterojunction layer being composed of an AlGaN layer and a GaN layer; the AlGaN / GaN heterojunction layer being doped with silicon (Si), the concentration of the doped Si decreasing from the interlayer to the low-doped conductive layer; and the low-doped conductive layer being a Si-doped GaN layer.

[0007] The interlayer serves as a buffer for the substrate and the upper layer structure, and will not damage the upper layer epitaxial structure when being peeled off. The conductive layer provides good ohmic contact for the electrode. The low-doped conductive layer is used for conduction and has a certain thickness, which makes the lattice quality of the epitaxial structure grown thereon better. The LED structure layer is the main working structure of the LED chip, and the existing technology can be used.

[0008] Hexagonal boron nitride (h-BN) is the most common crystal form, which has a similar layered structure to graphite. The interaction between the layered structures is small, and the damage to the upper layer epitaxial structure during peeling is small. By using the layered structure characteristics of the h-BN layer, the laser peeling technology will not damage the structure on the h-BN layer, and will not affect the electrical performance of the LED chip. This enhances the success rate and yield of the vertical structure laser peeling, reduces the leakage rate, and thus improves the yield of the LED chip. Secondly, by using the small interaction between the h-BN layers, the thermal expansion and lattice constant mismatch between the sapphire substrate and GaN are relieved, which can enhance the quality of the epitaxial structure crystal grown thereon.

[0009] The AlGaN / GaN heterojunction structure has different reflectivity due to different materials, which has a good reflection effect on light, similar to the DBR (Distribution Blagg Reflector) function of the chip. The DBR structure is composed of alternating multiple layers of high and low refractive index materials. By using different refractive indexes of different materials, the light extraction efficiency is improved. Moreover, by doping Si in the AlGaN / GaN heterojunction layer, a good ohmic contact and current expansion can be formed, which is beneficial to the performance improvement of the LED chip. The gradually reduced Si concentration in the AlGaN / GaN heterojunction layer can reduce the resistance of the AlGaN / GaN heterojunction layer by doping Si, improve the conductivity, and can be well matched with the electrode, having a good conductive and ohmic contact effect.

[0010] Optionally, the LED structure layer comprises: an N-type gallium nitride (N-GaN) layer, a stress release layer, an electron enrichment layer, a multiple quantum well layer and a P layer arranged in sequence.

[0011] N-GaN layer, used for forming N-type region of LED, the electrons provided by the N-type region recombine with holes in the quantum well to emit light, which is one of the main structures of LED.

[0012] Stress release layer, used for releasing stress between lattices.

[0013] Electron enrichment layer, used for generating enrichment effect for the electrons of the N-type region.

[0014] Multiple quantum well layer (MQW), refers to a system in which multiple quantum wells are combined together. In terms of material structure and growth process, there is no substantial difference between multiple quantum well and superlattice, only that the superlattice barrier layer is relatively thin, and the coupling between potential wells is relatively strong, forming a microstrip; while the barrier layer between multiple quantum wells is thick, and there is basically no tunneling coupling, nor does it form a microstrip. Multiple quantum well structure is mainly applied to its optical properties, and is one of the basic structure layers of LED epitaxial structure.

[0015] P layer, used for forming P-type region of LED, which is one of the main structures of LED.

[0016] Optionally, the thickness of the hexagonal boron nitride layer is 1.8-2 μm.

[0017] The thickness of the h-BN layer is higher than the height of the substrate pattern, so as not to affect the quality of the upper layer structure during peeling.

[0018] Optionally, the number of the gallium aluminum nitride / gallium nitride heterojunction layers is 2-8.

[0019] Optionally, in the gallium aluminum nitride / gallium nitride heterojunction layer, the thickness of the gallium aluminum nitride layer is 50-200 A, and the thickness of the gallium nitride layer is 100-400 A.

[0020] The AlGaN / GaN heterojunction layer plays a role similar to that of a chip DBR, and the DBR structure is composed of alternating multiple layers of high and low refractive index materials, and the light extraction efficiency is improved by the difference in refractive index of different materials. The number and thickness of the AlGaN / GaN heterojunction layer are set according to the actual experimental results and are continuously adjusted and optimized.

[0021] Optionally, in the gallium aluminum nitride / gallium nitride heterojunction layer, the concentration of the doped silicon is a first concentration close to the insertion layer, and the concentration of the doped silicon is a second concentration close to the LED structure layer, the first concentration is 1E19-2E19, and the second concentration is 1E18-5E18.

[0022] The Si is doped to reduce the resistance, and the higher the concentration of the doped Si, the better the conductivity. After the stripping, the AlGaN / GaN heterojunction layer close to the insertion layer is connected with the electrode, the first concentration is high-doped Si, which can improve the conductivity and well match the electrode, and has good conductivity and ohmic contact effect; the AlGaN / GaN heterojunction layer close to the LED structure layer is connected with the low-doped conductive layer, and the second concentration is equivalent to the concentration of the doped Si in the low-doped conductive layer.

[0023] Optionally, the thickness of the low-doped conductive layer is 1.5-2 μm.

[0024] In this way, the lattice quality of the epitaxial growth on the low-doped conductive layer is better.

[0025] Optionally, the concentration of the doped Si in the low-doped conductive layer is 1E18-3E18.

[0026] In this way, the low-doped conductive layer has a certain conductivity.

[0027] In the second aspect, the application provides a preparation method of a vertical epitaxial structure LED chip, comprising the following steps: epitaxially growing the hexagonal boron nitride layer on a substrate in a metal organic chemical vapor deposition (MOCVD) reaction furnace; epitaxially growing the gallium aluminum nitride layer on the hexagonal boron nitride layer, and doping Si during the epitaxial growth of the gallium aluminum nitride layer, and the concentration of the doped Si is a first concentration; epitaxially growing the gallium nitride layer on the gallium aluminum nitride layer, and doping Si during the epitaxial growth of the gallium nitride layer, and the concentration of the doped Si is the first concentration; the gallium aluminum nitride layer and the gallium nitride layer are cyclically grown for multiple times to obtain the conductive layer, and the concentration of the doped Si decreases in turn during the cyclic growth, and the concentration of the doped Si in the last growth is a second concentration, and the first concentration is higher than the second concentration; epitaxially growing the gallium nitride layer on the conductive layer to obtain the low-doped conductive layer, and doping Si during the epitaxial growth of the gallium nitride layer; and epitaxially growing the LED structure layer on the low-doped conductive layer.

[0028] Epitaxial growth refers to growing a single crystal layer with certain requirements on a single crystal substrate (substrate), which is like extending the original crystal outward. There are various methods for growing epitaxial layers, such as: liquid phase epitaxy (PE), metal organic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy (HVPE), molecular beam epitaxy (MBE), etc., and the most commonly used method for industrial production is MOCVD epitaxial process.

[0029] MOCVD (Metal-organic Chemical Vapor Deposition) is a new type of vapor phase epitaxial growth technology developed on the basis of VPE (Vapor Phase Epitaxy). MOCVD is a vapor phase epitaxy on a substrate with thermal decomposition reaction mode, using organic compounds of group III, group II elements and hydride of group V, group VI elements as crystal growth source materials, to grow thin layer single crystal materials of various group III-V main group, group II-VI secondary group compound semiconductors and their multi-element solid solution. MOCVD has the advantages of accurate control of crystal growth, good repeatability, large output, and suitability for industrial mass production.

[0030] Doping Si means that when the corresponding structure is epitaxially grown, Si / Mg and other dopants are introduced to form different doped semiconductors, for example: by replacing Ga atoms with Si atoms, the outermost 4 electrons of Si atoms are replaced by Ga, and one extra electron is formed to form a N layer semiconductor.

[0031] The insertion layer is used as a buffer between the substrate and the upper layer structure, and will not damage the upper layer epitaxial structure when peeled off. The conductive layer is used to make electrodes to provide good ohmic contact. The low-doped conductive layer is used for conduction and has a certain thickness, which can make the lattice quality of the crystal grown thereon better. The LED structure layer is the main working structure of the LED chip, and the existing technology can be used.

[0032] Hexagonal boron nitride (h-BN) is the most common crystal form, which has a similar layered structure to graphite. The interaction between the layered structures is small, and the damage to the upper epitaxial structure during peeling is small. By using the layered structure characteristics of h-BN, the laser peeling technology will not damage the structure on the h-BN layer, and will not affect the electrical performance of the LED chip. It enhances the success rate and yield of vertical structure laser peeling, reduces the leakage rate, and thus improves the yield of the LED chip. Secondly, by using the small interaction between h-BN layers, the mismatch between the thermal expansion and lattice constant of the sapphire substrate and GaN is relieved, which can enhance the quality of the epitaxial structure crystal grown thereon.

[0033] The structure of the AlGaN / GaN heterojunction has different reflectivity due to different materials, which has a good reflection effect on light, similar to the effect of a chip DBR (Distribution Blagg Reflector). The DBR structure is composed of alternating multiple layers of high and low refractive index materials. By using different materials with different refractive indexes, the light extraction efficiency is improved. Moreover, by doping Si in the AlGaN / GaN heterojunction layer, a good ohmic contact and current expansion can be formed, which is beneficial to the performance improvement of the LED chip. The design of gradually reducing the concentration of Si-doped AlGaN / GaN heterojunction layer can reduce the resistance of the AlGaN / GaN heterojunction layer by doping Si, improve the conductivity, and well match the electrode, having a good conductive and ohmic contact effect.

[0034] Optionally, the step of epitaxially growing the LED structure layer on the conductive layer comprises: epitaxially growing the N-type gallium nitride layer on the low-doped conductive layer; epitaxially growing the stress release layer on the N-type gallium nitride layer; epitaxially growing the electron-rich layer on the stress release layer; epitaxially growing the multiple quantum well layer on the electron-rich layer; and epitaxially growing the P layer on the multiple quantum well layer.

[0035] The N-GaN layer is used to form an N-type region of an LED. The electrons provided by the N-type region recombine with holes in the quantum well to emit light, which is one of the main structures of the LED.

[0036] The stress release layer is used to release the stress between the lattices.

[0037] The electron-rich layer is used to produce a rich effect for the electrons of the N-type region.

[0038] The multiple quantum well layer (MQW) refers to a system in which multiple quantum wells are combined together. In terms of material structure and growth process, there is no substantial difference between the multiple quantum well and the superlattice, except that the superlattice has a relatively thin potential barrier layer and a strong coupling between the potential wells, forming a microstrip. The potential barrier layer between the multiple quantum wells is thick, and there is basically no tunneling coupling, nor does it form a microstrip. The multiple quantum well structure is mainly applied to its optical properties, and is one of the basic structure layers of the LED epitaxial structure.

[0039] The P layer is used to form a P-type region of an LED, which is one of the main structures of the LED.

[0040] Optionally, the thickness of the hexagonal boron nitride layer epitaxially grown on the substrate is 1.8-2 μm.

[0041] The thickness of the h-BN layer is higher than the height of the substrate pattern, so that the quality of the upper structure is not affected during peeling.

[0042] Optionally, the number of cycles of growing the gallium aluminum nitride layer and the gallium nitride layer is 2-8.

[0043] Optionally, the thickness of the gallium aluminum nitride layer is 50-200A, and the thickness of the gallium nitride layer is 100-400A.

[0044] The AlGaN / GaN heterojunction layer plays a role similar to a chip DBR, and the DBR structure is composed of alternating multilayer high and low refractive index materials, and the light extraction efficiency is improved by the difference in refractive index of different materials. The number and thickness of the AlGaN / GaN heterojunction layer are set according to the actual experimental results and are continuously adjusted and optimized.

[0045] Optionally, the first concentration is 1E19-2E19, and the second concentration is 1E18-5E18.

[0046] Doping Si is to reduce the resistance, and the higher the concentration of doped Si, the better the conductivity. After stripping, the AlGaN / GaN heterojunction layer close to the insertion layer will be connected with the electrode, the first concentration is high-doped Si, which can improve the conductivity and can be well matched with the electrode, and has good conductivity and ohmic contact effect; the AlGaN / GaN heterojunction layer close to the LED structure layer will be connected with the low-doped conductive layer, and the second concentration should be equivalent to the concentration of doped Si in the low-doped conductive layer.

[0047] Optionally, the thickness of the low-doped conductive layer is 1.5-2μm.

[0048] This setting can make the lattice quality of the epitaxially grown low-doped conductive layer better.

[0049] Optionally, the concentration of doped silicon in the low-doped conductive layer is 1E18-3E18.

[0050] This setting can make the low-doped conductive layer have certain conductivity.

[0051] The application provides a vertical epitaxial structure LED chip and a preparation method thereof, which comprises a substrate, an insertion layer, a conductive layer, a low-doped conductive layer and an LED structure layer arranged in sequence in a laminated manner, wherein the insertion layer is an h-BN layer; and the conductive layer comprises a plurality of AlGaN / GaN heterojunction layers. h-BN is the most common crystal form, which has a similar layered structure as graphite structure, and the interaction force between the layered structures is small, and the damage to the upper epitaxial structure caused by peeling is small. By using the layered structure characteristics of the h-BN layer, the laser peeling technology will not damage the structure on the h-BN layer, and will not affect the electrical performance of the LED chip, thereby enhancing the success rate and yield of the vertical structure laser peeling, reducing the leakage rate, and improving the yield of the LED chip. Secondly, by using the small interaction force between the h-BN layers, the mismatch between the thermal expansion and the lattice constant of the sapphire substrate and GaN is relieved, and the quality of the epitaxial structure crystal grown thereon is enhanced. Due to the different materials and different reflectivities of the AlGaN / GaN heterojunction structure, the light has a good reflection effect, similar to the DBR effect of the chip. Moreover, by doping Si in the AlGaN / GaN heterojunction layer, a good ohmic contact and current expansion can be formed, which is beneficial to the performance improvement of the LED chip. The concentration of the Si-doped AlGaN / GaN heterojunction layer is gradually reduced, the resistance of the AlGaN / GaN heterojunction layer is reduced by doping Si, the conductivity is improved, and the electrode can be well matched, thereby having a good conductive and ohmic contact effect. BRIEF DESCRIPTION OF DRAWINGS

[0052] In order to more clearly illustrate the technical solutions of the application, the drawings needed in the embodiments will be briefly introduced below. Obviously, other drawings can also be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0053] Figure 1 The structure schematic diagram of the LED chip described in the application;

[0054] Figure 2 The first structure schematic diagram of the AlGaN / GaN heterojunction layer described in the application;

[0055] Figure 3 The second structure schematic diagram of the AlGaN / GaN heterojunction layer described in the application;

[0056] Figure 4 The crystal structure schematic diagram of the h-BN layer described in the application;

[0057] Figure 5 The flowchart schematic diagram of the preparation method of the LED chip described in the application;

[0058] Figure 6 The flowchart schematic diagram of the epitaxial growth of the LED structure layer described in the application. DETAILED DESCRIPTION

[0059] The embodiments will be described in detail below with reference to examples thereof as illustrated in the accompanying drawings. In the following description, unless otherwise indicated, like numbers in the different figures represent the same or similar elements. The embodiments described in the following detailed description are not meant to be exhaustive or to be limited to the precise form disclosed. They are chosen and described to provide the fullest explanation of the systems and methods consistent with some aspects of the present application as detailed in the claims.

[0060] LED is a light-emitting diode, a commonly used light-emitting device, which releases energy by electron and hole recombination to emit light. It is widely used in the field of lighting. The core part of the light-emitting diode is a wafer composed of P-type semiconductor and N-type semiconductor. There is a transition layer between the P-type semiconductor and the N-type semiconductor, which is called PN junction. The light-emitting diode, like the ordinary diode, is composed of a PN junction and has unidirectional conductivity. When a forward voltage is applied to the light-emitting diode, the holes injected from the P region to the N region and the electrons injected from the N region to the P region recombine with the N region and the P region, respectively, within a few microns near the PN junction, and produce spontaneous fluorescence. The energy states of electrons and holes in different semiconductor materials are different. In the PN junction of some semiconductor materials, the recombination of the injected minority carriers and the majority carriers releases excess energy in the form of light, thereby directly converting electrical energy into light energy. When the energy released by the recombination of electrons and holes is different, the more energy released, the shorter the wavelength of the light emitted.

[0061] Referring to Figure 1 , it is a structural schematic diagram of a vertical epitaxial structure LED chip.

[0062] The vertical epitaxial structure LED chip provided by the present application comprises: a substrate, an insertion layer, a conductive layer, a low-doped conductive layer and an LED structure layer arranged in sequence. The insertion layer is a hexagonal boron nitride (h-BN) layer. The conductive layer comprises a plurality of gallium aluminum nitride (AlGaN) / gallium nitride (GaN) heterojunction layers, and the gallium aluminum nitride / gallium nitride heterojunction layer is composed of a gallium aluminum nitride layer and a gallium nitride layer. The gallium aluminum nitride / gallium nitride heterojunction layer is doped with silicon (Si), and the concentration of the doped silicon is distributed from high to low from the insertion layer to the low-doped conductive layer. The low-doped conductive layer is a silicon-doped gallium nitride layer.

[0063] The insertion layer is used as a buffer for the substrate and the upper layer structure, and will not damage the upper layer epitaxial structure when it is peeled off. The conductive layer is used to make electrodes to provide good ohmic contact. The low-doped conductive layer is used for conduction and has a certain thickness, which can make the lattice quality of the crystal grown thereon better. The LED structure layer is the main working structure of the LED chip, and the existing technology can be used.

[0064] As Figure 4As shown, hexagonal boron nitride (h-BN) is the most common crystal form, with a similar layered structure to graphite, and the interaction between layers is small, and the damage to the upper layer epitaxial structure is small. Using the layered structure of h-BN, the laser lift-off technology will not damage the structure on the h-BN layer, and will not affect the electrical performance of the LED chip, and will enhance the success rate and yield of the vertical structure laser lift-off, and will reduce the leakage rate, thereby improving the yield of the LED chip. Secondly, using the small interaction between h-BN layers, the thermal expansion and lattice constant mismatch between the sapphire substrate and GaN can be relieved, and the quality of the epitaxial structure crystal grown thereon can be enhanced.

[0065] The structure of the AlGaN / GaN heterojunction is different due to the different materials and reflectivity, which has a good reflection effect on light, similar to the DBR (Distribution Blagg Reflector) function of the chip. The DBR structure is composed of alternating multiple layers of high and low refractive index materials. By changing the refractive index of different materials, the light efficiency is improved. Moreover, by doping Si in the AlGaN / GaN heterojunction layer, a good ohmic contact and current expansion can be formed, which is beneficial to the performance improvement of the LED chip. The design of gradually reducing the Si concentration in the AlGaN / GaN heterojunction layer can reduce the resistance of the AlGaN / GaN heterojunction layer by doping Si, improve the conductivity, and can be well matched with the electrode, having good conductivity and ohmic contact effect.

[0066] In an illustrative embodiment, the LED structure layer includes: an N-type gallium nitride (N-GaN) layer, a stress release layer, an electron enrichment layer, a multiple quantum well layer, and a P layer arranged in sequence.

[0067] The N-GaN layer is used to form an N-type region of the LED, and the electrons provided by the N-type region recombine with holes in the quantum well to emit light, which is one of the main structures of the LED.

[0068] The stress release layer is used to release the stress between the lattices.

[0069] The electron enrichment layer is used to produce an enrichment effect for the electrons of the N-type region.

[0070] The multiple quantum well layer (MQW) refers to a system in which multiple quantum wells are combined together. In terms of material structure and growth process, there is no substantial difference between multiple quantum wells and superlattices, except that the superlattice has a relatively thin potential barrier layer and a strong coupling between potential wells, forming a microstrip; while the potential barrier layer between multiple quantum wells is thick, and there is basically no tunneling coupling, and no microstrip is formed. Multiple quantum well structure is mainly applied to its optical properties, and is one of the basic structure layers of LED epitaxial structure.

[0071] The P layer is used to form a P-type region of the LED, and is one of the main structures of the LED.

[0072] In an illustrative embodiment, the thickness of the hexagonal boron nitride layer is 1.8-2 μm.

[0073] The thickness of the h-BN layer is higher than the height of the substrate pattern, so that the quality of the upper layer structure is not affected during peeling.

[0074] In an illustrative embodiment, the number of the gallium aluminum nitride / gallium nitride heterojunction layers is 2-8.

[0075] As shown in FIG. 1, it is a schematic diagram of a structure with the number of AlGaN / GaN heterojunction layers being 2, the concentration of Si doping in the lower AlGaN layer and GaN layer is a first concentration; the concentration of Si doping in the upper AlGaN layer and GaN layer is a second concentration. Figure 2 As shown in FIG. 2, it is a schematic diagram of a structure with the number of AlGaN / GaN heterojunction layers being 8, the concentration of Si doping in the lowermost AlGaN layer and GaN layer is a first concentration; the concentration of Si doping in the uppermost AlGaN layer and GaN layer is a second concentration. The concentration of Si doping in the middle AlGaN layer and GaN layer decreases from the first concentration to the second concentration.

[0076] Figure 3 As shown in FIG. 2, it is a schematic diagram of a structure with the number of AlGaN / GaN heterojunction layers being 8, the concentration of Si doping in the lowermost AlGaN layer and GaN layer is a first concentration; the concentration of Si doping in the uppermost AlGaN layer and GaN layer is a second concentration. The concentration of Si doping in the middle AlGaN layer and GaN layer decreases from the first concentration to the second concentration.

[0077] In an illustrative embodiment, in the gallium aluminum nitride / gallium nitride heterojunction layer, the thickness of the gallium aluminum nitride layer is 50-200 A, and the thickness of the gallium nitride layer is 100-400 A.

[0078] The AlGaN / GaN heterojunction layer plays a role similar to that of a chip DBR, and the DBR structure is composed of alternating multiple layers of high and low refractive index materials. The number and thickness of the AlGaN / GaN heterojunction layers are set according to actual experimental results and are continuously adjusted and optimized.

[0079] In an illustrative embodiment, in the gallium aluminum nitride / gallium nitride heterojunction layer, the concentration of Si doping near the insertion layer is a first concentration, and the concentration of Si doping near the LED structure layer is a second concentration, the first concentration is 1E19-2E19, and the second concentration is 1E18-5E18.

[0080] Si doping is to reduce the resistance, and the higher the concentration of Si doping, the better the conductivity. After peeling, the AlGaN / GaN heterojunction layer near the insertion layer will be connected with the electrode, the first concentration is high Si doping, which can improve the conductivity and match the electrode well, and has a good conductive and ohmic contact effect; the AlGaN / GaN heterojunction layer near the LED structure layer will be connected with the low-doped conductive layer, and the second concentration should be comparable to the concentration of Si doping in the low-doped conductive layer.​

[0081] In one illustrative embodiment, the thickness of the low-doped conductive layer is 1.5-2 μm.

[0082] This configuration can result in better lattice quality when epitaxially grown on a lightly doped conductive layer.

[0083] In one illustrative embodiment, the silicon doping concentration in the low-doped conductive layer is 1E18-3E18.

[0084] This configuration allows the low-doped conductive layer to have a certain degree of conductivity.

[0085] This application provides a method for fabricating a vertical epitaxial LED chip, such as... Figure 5 As shown, the process includes the following steps: In a metal-organic chemical vapor deposition (MOCVD) furnace, a hexagonal boron nitride layer is epitaxially grown on a substrate; a gallium aluminum nitride layer is epitaxially grown on the hexagonal boron nitride layer, with silicon doping occurring simultaneously during the growth of the gallium aluminum nitride, at a first silicon doping concentration; a gallium nitride layer is epitaxially grown on the gallium aluminum nitride layer, with silicon doping occurring simultaneously during the growth of the gallium nitride, at a first silicon doping concentration; the gallium aluminum nitride layer and the gallium nitride layer are cyclically grown multiple times to obtain the conductive layer, with the silicon doping concentration decreasing sequentially during the cyclic growth, and the silicon doping concentration in the final growth being a second concentration, where the first concentration is higher than the second concentration; a gallium nitride layer is epitaxially grown on the conductive layer to obtain the low-doped conductive layer, with silicon doping occurring simultaneously during the growth of the gallium nitride; and the LED structure layer is epitaxially grown on the low-doped conductive layer.

[0086] Epitaxial growth refers to the growth of a single-crystal layer with specific requirements and the same crystal orientation as the substrate on a single-crystal substrate, as if the original crystal has been extended outward. There are various methods for growing epitaxial layers, such as liquid phase epitaxy (PE), metal-organic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy (HVPE), and molecular beam epitaxy (MBE). MOCVD epitaxy is the most commonly used process in industrial production.

[0087] MOCVD (Metal-organic Chemical Vapor Deposition) is a new type of vapor phase epitaxy technology developed on the basis of VPE (Vapor Phase Epitaxy). MOCVD is a vapor phase epitaxy technology that uses organic compounds of group III and group II elements and hydrides of group V and group VI elements as crystal growth source materials, and performs vapor phase epitaxy on a substrate by thermal decomposition reaction to grow thin layer single crystal materials of various group III-V main group, group II-VI secondary group compounds and their multi-element solid solution. MOCVD has the advantages of precise control of crystal growth, good repeatability, high yield, and suitability for industrial mass production.

[0088] Doping Si means that, when epitaxially growing a corresponding structure, Si / Mg or the like is introduced to form different doped semiconductors, for example, by replacing Ga atoms with Si atoms, the outermost 4 electrons of the Si atom are replaced with Ga, and one extra electron is formed to form a N layer semiconductor.

[0089] As shown in the detailed steps in Figure 5 , the detailed steps are as follows:

[0090] S100: Place the PSS substrate in the MOCVD reaction chamber, evacuate the MOCVD reaction chamber to reduce the pressure to 200 Torr, and raise the temperature of the MOCVD reaction chamber to 1050-1090°C at a rotation speed of 900 RPM; the pressure in the MOCVD reaction chamber is maintained at 200 Torr; use nitrogen (N2) as a carrier gas, and sequentially introduce active substances such as borane (B2H6) or boron trifluoride (BF3), ammonia (NH3), hydrogen (H2), nitrogen (N2), and the like to grow a mixed gas for 10-30 min, thereby generating a h-BN layer with a thickness of 1.8-2 μm on the PSS patterned substrate as an interlayer.

[0091] Maintain the temperature at 1100-1200°C, and only introduce a protective gas such as a mixture of ammonia (NH3), hydrogen (H2), nitrogen (N2), and the like to grow for 30-60 s, thereby further improving the lattice quality of the h-BN structure.

[0092] S200: Increase the rotation speed of the MOCVD reaction chamber to 1000 RPM, reduce the temperature of the MOCVD reaction chamber to 800-850°C, and reduce the pressure in the MOCVD reaction chamber to 100 Torr, and epitaxially grow an AlGaN layer with a thickness of 50-200 A under the condition of N2:H2:NH3=3:0:1. Dope Si during the epitaxial growth of the AlGaN layer, and the concentration of the doped Si is 1E19-2E19.

[0093] S300: Continue to epitaxially grow GaN layer on AlGaN layer, thickness is 100-400A. Dope Si during epitaxial growth of GaN, concentration of doped Si is 1E19-2E19.

[0094] S400: Repeat S200-S300 steps for one cycle, epitaxially grow 2-8 cycles. Concentration of doped Si uniformly decreases from 1E19-2E19 to 1E18-5E18. Growth of conductive layer with thickness of about 300-4800A.

[0095] S500: Continue to epitaxially grow GaN layer on conductive layer, thickness is 1.5-2μm. Dope Si during epitaxial growth of GaN, concentration of doped Si is 1E18-3E18.

[0096] S600: Continue to epitaxially grow LED structure layer on low-doped conductive layer.

[0097] The insertion layer is used as a buffer for the substrate and the upper layer structure, and will not damage the upper layer epitaxial structure when peeled off. The conductive layer is used to make electrodes to provide good ohmic contact. The low-doped conductive layer is used for conduction and has a certain thickness to make the lattice quality of the structure grown thereon better. The LED structure layer is the main working structure of the LED chip, and existing technologies can be used.

[0098] Hexagonal boron nitride (h-BN) is the most common crystal form, which has a similar layered structure to graphite. The interaction between the layered structures is small, and the damage to the upper layer epitaxial structure during peeling is small. By using the layered structure characteristics of h-BN, the laser peeling technology will not damage the structure on the h-BN layer, and will not affect the electrical performance of the LED chip, thereby enhancing the success rate and yield of vertical structure laser peeling, reducing the leakage rate, and thus improving the yield of the LED chip. Secondly, by using the small interaction between h-BN layers, the mismatch between the thermal expansion and lattice constant of the sapphire substrate and GaN can be relieved, which can enhance the quality of the epitaxial structure grown thereon.

[0099] The structure of AlGaN / GaN heterojunction has different reflectivity due to different materials, which has a good reflection effect on light, similar to the DBR (Distribution Blagg Reflector) function of the chip. The DBR structure is composed of alternating multiple layers of high and low refractive index materials. By using different refractive indexes of different materials, the light extraction efficiency is improved. Moreover, by doping Si in the AlGaN / GaN heterojunction layer, good ohmic contact and current expansion can be formed, which is beneficial to the performance improvement of the LED chip. The design of gradually reducing the concentration of Si doped in the AlGaN / GaN heterojunction layer can reduce the resistance of the AlGaN / GaN heterojunction layer by doping Si, thereby improving the conductivity and matching with the electrode well, and having good conductivity and ohmic contact effect.

[0100] In an exemplary embodiment, as shown in Figure 6 the step of epitaxially growing the LED structure layer on the conductive layer includes: epitaxially growing the N-type gallium nitride layer on the low-doped conductive layer; epitaxially growing the stress release layer on the N-type gallium nitride layer; epitaxially growing the electron-rich layer on the stress release layer; epitaxially growing the multiple quantum well layer on the electron-rich layer; and epitaxially growing the P layer on the multiple quantum well layer.

[0101] The epitaxial growth of the LED structure layer can use existing technology.

[0102] The N-GaN layer is used to form the N-type region of the LED, and the electrons provided by the N-type region recombine with holes in the quantum well to emit light, which is one of the main structures of the LED.

[0103] The stress release layer is used to release the stress between lattices.

[0104] The electron-rich layer is used to produce a rich effect for the electrons of the N-type region.

[0105] The multiple quantum well layer (MQW) refers to a system in which multiple quantum wells are combined together. In terms of material structure and growth process, there is no substantial difference between the multiple quantum well and the superlattice, except that the superlattice has a relatively thin potential barrier layer and a strong coupling between potential wells, forming a microstrip; while the multiple quantum well has a thick potential barrier layer between the wells, and there is basically no tunneling coupling, nor does it form a microstrip. The multiple quantum well structure is mainly applied to its optical properties, and is one of the basic structure layers of the LED epitaxial structure.

[0106] The P layer is used to form the P-type region of the LED, and is one of the main structures of the LED.

[0107] The application provides a vertical epitaxial structure LED chip and a preparation method thereof, which comprises a substrate, an insertion layer, a conductive layer, a low-doped conductive layer and an LED structure layer arranged in sequence in a laminated manner, wherein the insertion layer is an h-BN layer; and the conductive layer comprises a plurality of AlGaN / GaN heterojunction layers. h-BN is the most common crystal form, has a similar layered structure as graphite structure, and the interaction force between the layered structures is small, so that the damage to the upper epitaxial structure caused by peeling is small. By using the layered structure characteristics of the h-BN layer, the laser peeling technology will not damage the structure on the h-BN layer, will not affect the electrical performance of the LED chip, will enhance the success rate and yield of the vertical structure laser peeling, will reduce the leakage rate, and thus will improve the yield of the LED chip. Secondly, by using the small interaction force between the h-BN layers, the mismatch between the thermal expansion and the lattice constant of the sapphire substrate and GaN is relieved, and the quality of the epitaxial structure crystal grown thereon is enhanced. The AlGaN / GaN heterojunction structure has different reflectivity due to different materials, has a good reflection effect on light, and is similar to the DBR effect of the chip. Moreover, by doping Si in the AlGaN / GaN heterojunction layer, a good ohmic contact and current expansion can be formed, which is beneficial to the performance improvement of the LED chip. The concentration of the Si-doped AlGaN / GaN heterojunction layer is gradually reduced, the resistance of the AlGaN / GaN heterojunction layer is reduced by doping Si, the conductivity is improved, the electrode can be well matched, and good conductivity and ohmic contact effects are achieved.

[0108] The similar parts among the embodiments provided in the application can be referred to each other, the specific embodiments provided above are only several examples under the general concept of the application, and do not limit the protection scope of the application. Any other embodiments extended on the basis of the application scheme without creative labor belong to the protection scope of the application.

Claims

1. A vertical epitaxial structure LED chip, characterized in that, Comprise: Substrate, intercalation layer, conductive layer, low-doped conductive layer and LED structure layer arranged in sequence; The intercalation layer is a hexagonal boron nitride layer; The conductive layer comprises a plurality of gallium aluminum nitride / gallium nitride heterojunction layers, which are composed of a gallium aluminum nitride layer and a gallium nitride layer; The gallium aluminum nitride / gallium nitride heterojunction layer is doped with silicon, and the concentration of the doped silicon decreases from the intercalation layer to the low-doped conductive layer; The low-doped conductive layer is a silicon-doped gallium nitride layer; The thickness of the hexagonal boron nitride layer is 1.8-2μm; In the gallium aluminum nitride / gallium nitride heterojunction layer, the concentration of the doped silicon near the intercalation layer is a first concentration, and the concentration of the doped silicon near the LED structure layer is a second concentration, the first concentration is 1E19-2E19, and the second concentration is 1E18-5E18.

2. The vertical epitaxial structure LED chip according to claim 1, wherein, The LED structure layer comprises: N-type gallium nitride layer, stress release layer, electron enrichment layer, multiple quantum well layer and P layer arranged in sequence.

3. The vertical epitaxial structure LED chip according to claim 1, wherein, The number of gallium aluminum nitride / gallium nitride heterojunction layers is 2-8.

4. The vertical epitaxial structure LED chip according to claim 1, wherein, In the gallium aluminum nitride / gallium nitride heterojunction layer, the thickness of the gallium aluminum nitride layer is 50-200A, and the thickness of the gallium nitride layer is 100-400A.

5. The vertical epitaxial structure LED chip according to claim 1, wherein, The thickness of the low-doped conductive layer is 1.5-2μm.

6. The vertical epitaxial structure LED chip according to claim 1, wherein, The concentration of silicon-doped in the low-doped conductive layer is 1E18-3E18.

7. A method for fabricating a vertical epitaxial structure LED chip, characterized in that, Comprise the following steps: Epitaxially grow a hexagonal boron nitride layer on a substrate in a metal organic compound chemical vapor deposition reaction furnace; Epitaxially grow a gallium aluminum nitride layer on the hexagonal boron nitride layer, and dope silicon during the epitaxial growth of the gallium aluminum nitride, the concentration of the doped silicon is a first concentration; Epitaxially grow the gallium nitride layer on the gallium aluminum nitride layer, and dope silicon during the epitaxial growth of the gallium nitride, the concentration of the doped silicon is a first concentration; The gallium aluminum nitride layer and the gallium nitride layer are grown in cycles to obtain a conductive layer, and the concentration of the doped silicon decreases in sequence during the cycle growth, the concentration of the doped silicon in the last growth is a second concentration, and the first concentration is higher than the second concentration; Epitaxially grow a gallium nitride layer on the conductive layer to obtain a low-doped conductive layer, and dope silicon during the epitaxial growth of the gallium nitride; Epitaxially grow the LED structure layer on the low-doped conductive layer; The thickness of the hexagonal boron nitride layer epitaxially grown on the substrate is 1.8-2μm; The first concentration is 1E19-2E19, and the second concentration is 1E18-5E18.

8. The method of claim 7, wherein the method further comprises: The step of epitaxially growing the LED structure layer on the conductive layer comprises: Epitaxially grow an N-type gallium nitride layer on the low-doped conductive layer; Epitaxially grow a stress release layer on the N-type gallium nitride layer; Epitaxially grow an electron enrichment layer on the stress release layer; Epitaxially grow a multiple quantum well layer on the electron enrichment layer; Epitaxially grow a P layer on the multiple quantum well layer.

9. The method of claim 7, wherein the method further comprises: The number of cycles of the gallium aluminum nitride layer and the gallium nitride layer is 2-8Loop.

10. The method of claim 7, wherein the method further comprises: The thickness of the epitaxially grown gallium aluminum nitride layer is 50-200A, and the thickness of the epitaxially grown gallium nitride layer is 100-400A.

11. The method of claim 7, wherein the method further comprises: The thickness of the low doped conductive layer is 1.5-2 μm.

12. The method of claim 7, wherein the method further comprises: The concentration of the silicon doping in the low doped conductive layer is 1E18-3E18.

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