Light emitting diode epitaxial structure, manufacturing method thereof and display panel

Abstract

The invention relates to a light emitting diode epitaxial structure, which comprises a substrate; an N-type layer; the active layer is located on the N type; the P-type layer is located on the active layer; wherein the P-type layer comprises a P-type window layer, the P-type window layer comprises a plurality of first laminated structures, each first laminated structure comprises a GaInP layer, a first GaP layer and a second GaP layer which are sequentially laminated, and the P-type doping concentration of the second GaP layer in each first laminated structure is greater than that of the first GaP layer. The GaInP layer has a relatively high forbidden bandwidth, plays a role of an optical window layer, and can reduce light absorption loss; the GaInP has a relatively low forbidden band width, and the first GaP layer and the second GaP layer play a role of a buffer layer / transition layer, so that the combination of the GaInP layer, the first GaP layer and the second GaP layer realizes the balance of energy band matching and carrier transmission efficiency, and is beneficial to the efficient expansion of current.

Description

TECHNICAL FIELD

[0001] The present application relates to a semiconductor device, in particular to a light emitting diode epitaxial structure, and to a manufacturing method of the light emitting diode epitaxial structure, and to a display panel. BACKGROUND

[0002] Currently, there are still many technical challenges in the field of red light LED (light emitting diode) technology. An exemplary red light LED realizes the injection and recombination of carriers through a multilayer heterostructure. However, in practical applications, carriers are prone to non-radiative recombination or scattering at the interface, resulting in a decrease in light emitting efficiency and a shortening of the service life of the device. Therefore, how to optimize the material structure, improve the carrier transport efficiency and the photon extraction capability is still one of the key directions of the current red light LED technology development. SUMMARY

[0003] Therefore, it is necessary to provide a light emitting diode epitaxial structure with high carrier transport efficiency, a manufacturing method thereof, and a display panel.

[0004] A light emitting diode epitaxial structure comprises a substrate, an N-type layer located on one side of the substrate, an active layer located on a side of the N-type layer away from the substrate, and a P-type layer located on a side of the active layer away from the N-type layer. The P-type layer comprises a P-type window layer, and the P-type window layer comprises a plurality of first stacked layer structures. Each first stacked layer structure comprises a GaInP layer, a first GaP layer and a second GaP layer stacked in sequence. The potential barrier height of the second GaP layer in each first stacked layer structure is greater than the potential barrier height of the first GaP layer, and / or the P-type doping concentration of the second GaP layer in each first stacked layer structure is greater than the P-type doping concentration of the first GaP layer.

[0005] The light emitting diode epitaxial structure has a plurality of first stack structures arranged repeatedly, the GaInP layer in the first stack structure has a higher band gap, and functions as an optical window layer to reduce light absorption loss; the GaP has a lower band gap, and the first GaP layer and the second GaP layer function as buffer layers / transition layers, so that the combination of the GaInP layer, the first GaP layer and the second GaP layer realizes the balance of band matching and carrier transport efficiency, and is beneficial to efficient current spreading. Since each first stack structure is composed of film layers with different band gaps and barrier heights / doping concentrations, band bending and barriers can be formed at the interfaces of the film layers, the change of the band can regulate the transport characteristics of the carriers, reduce lateral diffusion, realize directional transport of the carriers, enhance the spatial uniformity of current spreading, and improve the carrier conduction efficiency of the device under working voltage. In addition, the first stack structure of the P-type window layer helps to relieve thermal stress, reduce cracks or defects caused by the difference in thermal expansion coefficient, and can improve the reliability of the device in a high-temperature environment.

[0006] In one of the embodiments, the P-type window layer further comprises a GaP current spreading layer, and each of the first stack structures is located between the GaP current spreading layer and the active layer.

[0007] In one of the embodiments, the thickness of the GaP current spreading layer is greater than the thickness of each of the first stack structures.

[0008] In one of the embodiments, the P-type doping concentration of the GaP current spreading layer is greater than the P-type doping concentration of each of the second GaP layers.

[0009] In one of the embodiments, the barrier height of the GaP current spreading layer is greater than the barrier height of each of the second GaP layers.

[0010] In one of the embodiments, the thickness of the GaP current spreading layer is 3-5 microns.

[0011] In one of the embodiments, in each of the first stack structures, the thickness of the GaInP layer is 50-150 nanometers, the thickness of the first GaP layer is 50-150 nanometers, and the thickness of the second GaP layer is 50-150 nanometers.

[0012] In one of the embodiments, the number of the first stack structures in the P-type window layer is 15-50.

[0013] In one of the embodiments, the total thickness of all the first stack structures in the P-type window layer is 2.3-5 microns.

[0014] In one of the embodiments, the GaInP layer is Ga x3 In（1-x3） P layer, 0.5 < x3 < 1.

[0015] In one embodiment, the GaInP layer has a P-type doping concentration of 1.5E18 - 3E18 atoms / cm3, the first GaP layer has a P-type doping concentration of 7E17 - 1E18 atoms / cm3, and the second GaP layer has a P-type doping concentration of 1.2E18 - 2.5E18 atoms / cm3.

[0016] In one embodiment, the GaInP layer has a band gap of 1.82 - 2.23 eV, the first GaP layer has a band gap of 2.25 - 2.26 eV, and the second GaP layer has a band gap of 2.20 - 2.23 eV.

[0017] In one embodiment, the P-type window layer has a superlattice structure.

[0018] In one embodiment, the P-type doping concentration of the first stack structure away from the active layer is greater than the P-type doping concentration of the first stack structure close to the active layer.

[0019] In one embodiment, the barrier height of the first stack structure away from the active layer is greater than the barrier height of the first stack structure close to the active layer.

[0020] In one embodiment, the band gap of the first stack structure away from the active layer is greater than the band gap of the first stack structure close to the active layer.

[0021] In one embodiment, the P-type layer further comprises a transition layer between the P-type window layer and the active layer, the transition layer comprising a plurality of second stack structures, each second stack structure comprising an AlInP layer and an AlGaInP layer.

[0022] In one embodiment, in each of the second stack structures, the AlInP layer has a thickness of 20 to 50 nanometers, and the AlGaInP layer has a thickness of 30 to 50 nanometers.

[0023] In one embodiment, the transition layer has a thickness of 100 to 500 nanometers.

[0024] In one embodiment, the AlInP layer is Al x1 In y P layer, the AlGaInP layer is Al x2 Ga （1-x2） 0.5 In0.5P layer, x1 > x2, 0.5 < x1 < 1, 0.15 < x2 < 0.6, 0.3 < y < 0.5.

[0025] In one of the embodiments, in each of the second stack structures, the P-type doping concentration of the AlInP layer is 1E17-3E17 atoms / cm³, and the P-type doping concentration of the AlGaInP layer is 3E17-7E17 atoms / cm³.

[0026] In one of the embodiments, the Al content of the second stack structure far away from the active layer is less than the Al content of the second stack structure close to the active layer.

[0027] In one of the embodiments, the Al band of the second stack structure far away from the active layer is less than the Al band of the second stack structure close to the active layer.

[0028] In one of the embodiments, the number of the second stack structures in the transition layer is 3-15.

[0029] In one of the embodiments, the P-type layer further comprises a waveguide layer between the active layer and the transition layer, and a confinement layer between the waveguide layer and the transition layer, the waveguide layer is an AlGaInP layer, and the confinement layer is an AlInP layer.

[0030] In one of the embodiments, the light-emitting diode epitaxial structure is an epitaxial structure of a red LED.

[0031] A display panel comprising a plurality of red LEDs, each of the red LEDs having the light-emitting diode epitaxial structure according to any one of the preceding embodiments.

[0032] A manufacturing method of a light-emitting diode epitaxial structure, comprising: obtaining a substrate; forming an N-type layer on one side of the substrate; forming an active layer on the side of the N-type layer away from the substrate; alternately forming a GaInP layer, a first GaP layer and a second GaP layer on the side of the active layer away from the N-type layer, each GaInP layer, first GaP layer and second GaP layer serving as a first stack structure, until a target number of first stack structures are formed; the barrier height of the second GaP layer in each first stack structure is greater than the barrier height of the first GaP layer, and / or the P-type doping concentration of the second GaP layer in each first stack structure is greater than the P-type doping concentration of the first GaP layer.

[0033] The manufacturing method of the light emitting diode epitaxial structure alternately forms GaInP layer, first GaP layer and second GaP layer as P-type window layer on the active layer, the GaInP layer has higher band gap and plays the role of optical window layer, which can reduce the light absorption loss; the GaP has lower band gap, the first GaP layer and the second GaP layer play the role of buffer layer / transition layer, so that the combination of the GaInP layer, the first GaP layer and the second GaP layer realizes the balance of band matching and carrier transport efficiency, which is beneficial to the efficient expansion of current. Because the P-type window layer is composed of film layers with different band gaps and barrier heights / doping concentrations, the band bending and barrier can be formed at the interface of these film layers, the change of the band can regulate the transport characteristics of the carriers, reduce the lateral diffusion, realize the directional transport of the carriers, enhance the spatial uniformity of the current expansion, and improve the carrier conduction efficiency of the device under working voltage. In addition, the P-type window layer with the multi-layer alternating structure of different materials helps to relieve thermal stress, reduce cracks or defects caused by the difference in thermal expansion coefficient, and improve the reliability of the device under high temperature environment.

[0034] In one of the embodiments, it further comprises: forming a GaP current expansion layer on a side of a first stack structure farthest from the active layer and away from the active layer, the thickness of the GaP current expansion layer is greater than the thickness of each of the first stack structure, and the P-type doping concentration of the GaP current expansion layer is greater than the P-type doping concentration of each of the second GaP layer.

[0035] In one of the embodiments, before the step of alternately forming GaInP layer, first GaP layer and second GaP layer on a side of the active layer away from the N-type layer, it further comprises the step of alternately forming AlInP layer and AlGaInP layer on a side of the active layer away from the N-type layer. BRIEF DESCRIPTION OF DRAWINGS

[0036] For better describing and illustrating the embodiments and / or examples of the inventions disclosed herein, reference can be made to one or more drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed inventions, the presently described embodiments and / or examples, and the best mode presently understood of these inventions.

[0037] Figure 1 is a structural schematic diagram of a light emitting diode epitaxial structure in an embodiment of the present application.

[0038] Figure 2 is a structural schematic diagram of a P-type window layer 41 in an embodiment of the present application.

[0039] Figure 3 is a structural schematic diagram of a P-type window layer 41 in another embodiment of the present application.

[0040] Figure 4 FIG. 1 is a schematic diagram of a structure of a P-type layer 40 in an embodiment of the present application.

[0041] Figure 5 FIG. 2 is a schematic diagram of a structure of a transition layer TL 42 in an embodiment of the present application.

[0042] Figure 6 FIG. 3 is a schematic diagram of a structure of a P-type layer 40 in another embodiment of the present application.

[0043] Figure 7 FIG. 4 is a schematic diagram of a structure of a P-type layer 40 in yet another embodiment of the present application.

[0044] Figure 8 FIG. 5 is a schematic diagram of a structure of an N-type layer 20 in an embodiment of the present application.

[0045] Figure 9 FIG. 6 is a flow chart of a method for manufacturing a light emitting diode epitaxial structure in an embodiment of the present application.

[0046] Figure 10 FIG. 7 is a flow chart of a method for manufacturing a light emitting diode epitaxial structure in another embodiment of the present application.

[0047] Figure 11 FIG. 8 is a flow chart of a method for manufacturing a light emitting diode epitaxial structure in yet another embodiment of the present application. DETAILED DESCRIPTION

[0048] In order to facilitate the understanding of the present application, a more complete understanding of the present application can be had by reference to the following description in conjunction with the accompanying drawings. The preferred embodiments of the present application are illustrated in the attached drawings. However, the present application can be realized 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. It will be apparent, however, to one of ordinary skill in the art that the present application can be realized in other forms.

[0049] Unless otherwise defined, 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 application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0050] It will be understood that when an element or layer is referred to as being "on" or "connected to" another element or layer, it can be directly on or connected to the other element or layer or intervening elements or layers can be present. In contrast, when an element is referred to as being "directly on" or "directly connected to" another element or layer, there are no intervening elements or layers present. It will also be understood that, although the terms first, second, third, etc. can be used herein to describe various elements, components, regions, layers and / or sections, these terms are not intended to be limiting. These terms are used only to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present application.

[0051] Spatially relative terms, such as "beneath", "below", "lower", "under", "above", "upper" and the like, can be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" or "over" the other elements or features. Thus, the exemplary term "below" can encompass both an orientation of above and below. The device can be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0052] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising", when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. As used herein the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0053] Embodiments of the application are described herein with reference to the drawings, which show ideal embodiments (and intermediate structures) of the application. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and / or tolerances, are to be expected. Thus, embodiments of the application should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, an implanted region illustrated as a rectangle will, typically, have rounded or curved features and / or a gradient of implant concentration at its edges rather than a binary change from implanted to non-implanted region. Similarly, a buried region formed by implantation can result in some implantation in a region between the buried region and the surface through which the implant was performed. Thus, the regions illustrated in the figures are schematic only and their shapes are not intended to illustrate the precise shape of a region of a device and are not intended to limit the scope of the application.

[0054] As mentioned in the background, due to material interface defects and lattice mismatch problems, carriers are prone to non-radiative recombination or scattering at the interface, resulting in a decrease in light-emitting efficiency and shortening the service life of the device. In addition, as the main channel for photon propagation, the structural design and material properties of the window layer have a significant impact on light extraction efficiency. In current technology, the propagation path of photons in the window layer is limited, which is prone to problems of light loss or poor directionality, further restricting the optical performance of the device. At the same time, the quality of the epitaxial layer is subject to the control difficulty of the growth process, and it is difficult to achieve a highly uniform crystal structure, thereby affecting the stability and consistency of the device.

[0055] The present application proposes a novel structure of light-emitting diode epitaxial structure to optimize the performance of the LED. Referring to Figure 1 , the light-emitting diode epitaxial structure includes a substrate 10, an N-type layer 20, an active layer 30 and a P-type layer 40 which are sequentially stacked. Each film layer in the N-type layer 20 has N-type doping, and each film layer in the P-type layer 40 has P-type doping. The P-type layer 40 includes a P-type window layer 41, and the P-type window layer 41 includes a plurality of first stacked layer structures 410, referring to Figure 2 . Each first stacked layer structure 410 includes a GaInP layer 412, a first GaP layer 414 and a second GaP layer 416 which are sequentially stacked. The first GaP layer 414 is a low-doped GaP layer, and the second GaP layer 416 is a high-doped GaP layer. In each first stacked layer structure 410, the P-type doping concentration of the second GaP layer 416 is greater than the P-type doping concentration of the first GaP layer 414, and / or the barrier height of the second GaP layer 416 is greater than the barrier height of the first GaP layer 414. The P-type doping concentration of the second GaP layer 416 can be adjusted to be greater than the P-type doping concentration of the first GaP layer 414, so that the barrier height of the second GaP layer 416 is greater than the barrier height of the first GaP layer 414.

[0056] The conventional P-type GaP window layer usually adopts a single material, while the first stack structure 410 of the P-type window layer 41 in the present application adopts a multi-layer heterostructure of GaInP / GaP1 / GaP2. This structure design can realize more accurate carrier control and electrical performance optimization through energy band engineering, and has obvious material combination advantages over the single-material P-type GaP window layer. Among them, the GaInP layer 412 in the first stack structure 410 has a relatively high band gap (a typical value is about 1.85 eV), which plays the role of an optical window layer and can reduce optical absorption loss; the GaP has a relatively low band gap (a typical value is about 1.35 eV), and the first GaP layer 414 and the second GaP layer 416 play the role of buffer layer / transition layer, so the combination of the GaInP layer 412, the first GaP layer 414 and the second GaP layer 416 realizes the balance of energy band matching and carrier transmission efficiency, which is beneficial to the efficient expansion of current. Since each first stack structure 410 is composed of film layers with different band gaps and doping concentrations, the interface of these film layers can form a band bending and a potential barrier, and the change of the energy band can regulate the transmission characteristics of the carriers, reduce the lateral diffusion, realize the directional transport of the carriers, enhance the spatial uniformity of the current expansion, and improve the carrier conduction efficiency of the device under working voltage. In addition, the first stack structure 410 in the P-type window layer 41 helps to relieve thermal stress, reduce cracks or defects caused by the difference in thermal expansion coefficient, and can improve the reliability of the LED in a high-temperature environment.

[0057] In an embodiment of the present application, the P-type window layer 41 further comprises a GaP current expansion layer 417, and each first stack structure 410 is located between the GaP current expansion layer 417 and the active layer 30. In an embodiment of the present application, the P-type doping concentration of the GaP current expansion layer 417 is greater than the P-type doping concentration of each second GaP layer 416, so that the potential barrier height of the GaP current expansion layer 417 is greater than the potential barrier height of each second GaP layer 416. As part of the P-type window layer 41, the GaP current expansion layer 417 has good P-type conductivity and can further enhance the longitudinal expansion capability of the current. In an embodiment of the present application, the P-type doping concentration of the GaP current expansion layer 417 is 1E18-5E18 atoms / cm³, and the reduced doping helps to reduce the interface defect density and improve the stability of current expansion.

[0058] In an embodiment of the present application, the P-type window layer 41 has a superlattice structure.

[0059] In an embodiment of the present application, the number of first stack structures 410 in the P-type window layer 41 is 15-50, i.e. the loop (also referred to as growth cycle) is 15-50.

[0060] In one embodiment of the present application, the material of the GaInP layer 412 is Ga x3 In （1-x3） P, 0.5≤x3<1.

[0061] In one embodiment of the present application, the P-type doping concentration of each film layer in each first stack structure 410 is in the following order: GaInP layer 412 > second GaP layer 416 > first GaP layer 414. The high-doped GaInP layer 412 and the second GaP layer 416 improve the conductivity and form a good p-type conductive channel. The low-doped first GaP layer 414 acts as a buffer to reduce interface scattering, and the overall structure helps to reduce the contact resistance and series resistance. The doping gradient of GaInP layer 412 > second GaP layer 416 > first GaP layer 414 helps to efficiently inject carriers (holes) from the electrode to the active region, improving the carrier injection efficiency of the device.

[0062] In one embodiment of the present application, the P-type doping concentration of the GaInP layer 142 is 1.5E18-3E18 atoms / cm³, the P-type doping concentration of the first GaP layer 144 is 7E17-1E18 atoms / cm³, and the P-type doping concentration of the second GaP layer 146 is 1.2E18-2.5E18 atoms / cm³.

[0063] In one embodiment of the present application, the band gap of the GaInP layer 142 is 1.82-2.23eV, the band gap of the first GaP layer 144 is 2.25-2.26eV, and the band gap of the second GaP layer 146 is 2.20-2.23eV.

[0064] In one embodiment of the present application, the P-type doping concentration of the first stack structure 410 away from the active layer 30 is greater than the P-type doping concentration of the first stack structure 410 close to the active layer 30. That is, as the growth period increases, the P-type doping concentration of the first stack structure 410 gradually increases along the stacking direction. Also, the band gap of the first stack structure 410 away from the active layer 30 is greater than the band gap of the first stack structure 410 close to the active layer 30. That is, as the growth period increases, the band gap of the first stack structure 410 gradually increases along the stacking direction.

[0065] In one embodiment of the present application, in each first stack structure 410, the thickness of the GaInP layer 412 is 50 to 150 nanometers, the thickness of the first GaP layer 414 is 50 to 150 nanometers, and the thickness of the second GaP layer 416 is 50 to 150 nanometers. In one embodiment of the present application, the total thickness of all first stack structures 410 in the P-type window layer 41 is 2.3 to 5 micrometers.

[0066] In an embodiment of the present application, the thickness of the GaP current spreading layer 417 is greater than the thickness of each first stack structure 410.

[0067] In an embodiment of the present application, the thickness of the GaP current spreading layer 417 is 3 to 5 microns.

[0068] In an embodiment of the present application, the P-type layer 40 further comprises a transition layer TL 42 between the P-type window layer 41 and the active layer 30, see Figure 4 The transition layer TL 42 comprises a plurality of second stack structures 420, each second stack structure 420 comprising a P-type doped AlInP layer 422 and a P-type doped AlGaInP layer 424.

[0069] The second stack structures 420 of the transition layer TL 42 comprise AlInP layers 422 and AlGaInP layers 424, compared with the conventional transition layer TL which uses AlGaInP material, usually only adjusts the Al component in one direction, it is difficult to simultaneously consider the lattice matching with the film layer below the transition layer TL (usually AlInP) and the film layer above the transition layer TL (P-type window layer 41), and direct growth is prone to generate a large number of dislocations and defects, and the interface quality is poor. While the new transition layer TL 42 of the embodiment of the present application adopts superlattice design, the double-component structure of the AlInP layer 422 and the AlGaInP layer 424 is more flexible in component control, and by adjusting the Al component and the In / Ga ratio at the same time, the lattice gradual matching with the film layers above and below the transition layer TL 42 can be better realized, so as to effectively reduce the interface defect density and improve the crystal quality. On the other hand, by introducing AlInP, the thermal stability of the material can be enhanced, so that it is more suitable for devices used in high-temperature working environment.

[0070] In an embodiment of the present application, the material of the AlInP layer 422 is Al x1 In y P, and the material of the AlGaInP layer 424 is Al x2 Ga （1-x2） 0.5In0.5P, x1>x2, 0.5≤x1<1, 0.15≤x2≤0.6, 0.3≤y≤0.5. By adjusting the In / Ga ratio, the thermal expansion coefficients of the film layers above and below the transition layer TL 42 can be better matched, the cracks or peeling caused by thermal stress can be reduced, and the lattice quality of the epitaxial layer can be improved.

[0071] In an embodiment of the present application, the Al content of the second stack structure 420 far from the active layer 30 is less than the Al content of the second stack structure 420 close to the active layer 30. That is, with the increase of the growth period, the Al component in the second stack structure 420 gradually decreases in the stacking direction.

[0072] The band structure of the conventional transition layer TL is relatively fixed, while the new superlattice transition layer TL 42 of the embodiment of the application can bring a band gradient structure by adjusting the ratio of Al, In, Ga and the gradient change of the Al component, so as to more accurately control the carrier distribution. The high Al content region (AlInP layer 422) has a higher band gap, which helps to form a potential barrier and optimize the carrier confinement. Especially under the condition of p-type doping, it helps to improve the hole mobility and carrier transport efficiency, and improve the light emitting efficiency and electrical performance of the device.

[0073] In an embodiment of the application, the number of the second stack structures 420 in the transition layer TL 42 is 3-15, that is, the loop is 3-15.

[0074] In an embodiment of the application, the P-type doping concentration of the AlInP layer 422 is 1E17-3E17 atoms / cm³, and the P-type doping concentration of the AlGaInP layer 424 is 3E17-7E17 atoms / cm³.

[0075] In an embodiment of the application, the thickness of the transition layer TL 42 is 150-500 nanometers.

[0076] In an embodiment of the application, in each second stack structure 420, the thickness of the AlInP layer 422 is 20-50 nanometers, and the thickness of the AlGaInP layer 424 is 30-50 nanometers.

[0077] Further, the synergistic mechanism of the transition layer TL 42 and the P-type window layer 41 of the two superlattice designs is as follows: first, carrier injection and transport synergy: the P-type window layer 41 provides high carrier injection efficiency, and the transition layer TL 42 provides a low-resistance transport path, which together improves the carrier injection efficiency and electrical performance of the device. Second, lattice matching and material quality synergy: the P-type window layer 41 stabilizes the epitaxial structure, and the transition layer TL 42 buffers the lattice mismatch, which together improves the overall crystal quality and thermal stability of the epitaxial layer. Third, the P-type window layer 41 controls the photon propagation path, and the transition layer TL 42 optimizes the carrier distribution, which together improves the optical performance and light emitting efficiency of the device.

[0078] Referring to Figure 6 In an embodiment of the application, the P-type layer 40 further includes a waveguide layer 402 and a cladding layer 404 located between the active layer 30 and the transition layer TL 42. The cladding layer 404 is located between the waveguide layer 402 and the transition layer TL 42, the material of the waveguide layer 402 is P-type doped AlGaInP, and the material of the cladding layer 404 is P-type doped AlInP.

[0079] Referring to Figure 7In an embodiment of the present application, the P-type layer 40 further comprises a P-type ohmic contact layer on the P-type window layer 41, which is made of P-type doped GaP.

[0080] Referring to Figure 8 In an embodiment of the present application, the N-type layer 20 comprises a buffer layer 201 on the substrate 10, a cutoff layer 202 on the buffer layer 201, an N-type ohmic contact layer 203 on the cutoff layer 202, a window layer 204 on the N-type ohmic contact layer 203, a confinement layer 205 on the window layer 204, and a waveguide layer 206 on the confinement layer 205. The buffer layer 201 is made of N-type doped GaAs, the cutoff layer 202 (etching cutoff layer) is made of N-type doped GaInP, the N-type ohmic contact layer 203 is made of N-type doped GaAs, the window layer 204 is made of N-type doped AlGaInP, the confinement layer 205 is made of N-type doped AlInP, and the waveguide layer 206 is made of N-type doped AlGaInP.

[0081] In an embodiment of the present application, the aforementioned light-emitting diode epitaxial structure is an epitaxial structure of a red LED.

[0082] Based on all the above embodiments, by optimizing the P-type window layer 41 and the transition layer TL 42, and utilizing the synergistic effect of the two, the carrier injection efficiency is improved, the resistance path is reduced, the carrier transport efficiency is improved, and thus the overall electrical performance of the device is improved. In addition, the P-type window layer 41 also plays a role in regulating the photon propagation path, which helps to optimize the light output efficiency. The transition layer TL 42 buffers the lattice mismatch, improves the crystal quality and thermal stability of the epitaxial layer, and thus enhances the reliability of the device.

[0083] The present application correspondingly provides a display panel comprising a plurality of red LEDs, wherein the red LEDs have the light-emitting diode epitaxial structure of any one of the aforementioned embodiments.

[0084] The present application correspondingly provides a manufacturing method of a light-emitting diode epitaxial structure, Figure 9 is a flowchart of the manufacturing method of the light-emitting diode epitaxial structure in an embodiment of the present application, comprising the following steps:

[0085] S110, obtaining a substrate.

[0086] In an embodiment of the present application, the substrate 10 is a GaAs substrate.

[0087] S120, forming an N-type layer on the substrate.

[0088] The N-type layer 20 is formed on one side of the substrate 10.

[0089] S130, forming an active layer on the N-type layer.

[0090] The active layer 30 is formed on the side of the N-type layer 20 away from the substrate 10.

[0091] S140, alternately forming GaInP layers, first GaP layers and second GaP layers on the active layer.

[0092] The GaInP layers 412, the first GaP layers 414 and the second GaP layers 416 are alternately formed on the side of the active layer 30 away from the N-type layer 20, each GaInP layer 412, first GaP layer 414 and second GaP layer 416 being a first stack structure 410, until a target number of first stack structures 410 are formed. The P-type doping concentration of the second GaP layer 416 in each first stack structure 410 is greater than that of the first GaP layer 414. In an embodiment of the present application, the loop (also referred to as growth cycle) of the first stack structure 410 is 15-50.

[0093] The method for manufacturing the epitaxial structure of the light emitting diode alternately forms the GaInP layers 412, the first GaP layers 414 and the second GaP layers 416 as the P-type window layer 41 on the active layer 30. The GaInP layers 412 have a higher band gap, and function as an optical window layer, thereby reducing light absorption loss. The GaP has a lower band gap, and the first GaP layers 414 and the second GaP layers 416 function as buffer layers / transition layers. Therefore, the combination of the GaInP layers 412, the first GaP layers 414 and the second GaP layers 416 realizes a balance between band matching and carrier transport efficiency, and is conducive to efficient current spreading. Since the P-type window layer 41 is composed of film layers with different band gaps and doping concentrations, a band bending and a potential barrier can be formed at the interface of the film layers. The change in the band can regulate the transport characteristics of the carriers, reduce lateral diffusion, realize directional transport of the carriers, enhance the spatial uniformity of current spreading, and improve the carrier conduction efficiency of the device under working voltage. In addition, the P-type window layer 41 with the multi-layer alternating structure of different materials helps to relieve thermal stress, reduce cracks or defects caused by differences in thermal expansion coefficients, and improve the reliability of the device in a high-temperature environment.

[0094] Referring to Figure 10 In an embodiment of the present application, after step S140, step S150 of forming a GaP current spreading layer on the first stack structure farthest from the active layer is further included.

[0095] In an embodiment of the present application, the thickness of the GaP current spreading layer 417 is greater than the thickness of each first stack structure 410, and the P-type doping concentration of the GaP current spreading layer 417 is greater than the P-type doping concentration of each second GaP layer 416. The GaP current spreading layer 417, as a part of the P-type window layer 41, has good P-type conductivity and can further enhance the longitudinal current spreading capability. In an embodiment of the present application, the P-type doping concentration of the GaP current spreading layer 417 is 1E18-5E18 atoms / cm3, and the reduced doping helps to reduce the interface defect density and improve the stability of current spreading.

[0096] In an embodiment of the present application, the material of the GaInP layer 142 is Ga x3 In （1-x3） P, 0.5≤x3<1.

[0097] In an embodiment of the present application, the P-type doping concentration of each film layer in each first stack structure 410 is in the order of: GaInP layer 412>second GaP layer 416>first GaP layer 414. The high-doped GaInP layer 412 and the second GaP layer 416 improve the conductivity and form a good p-type conductive channel. The low-doped first GaP layer 414 acts as a buffer to reduce interface scattering, and the overall structure helps to reduce the contact resistance and series resistance. The doping gradient of GaInP layer 412>second GaP layer 416>first GaP layer 414 helps to efficiently inject carriers (holes) from the electrode to the active region, improving the carrier injection efficiency of the device.

[0098] The P-type doping concentration of the GaInP layer 142 is 1.5E18-3E18 atoms / cm3, the P-type doping concentration of the first GaP layer 144 is 7E17-1E18 atoms / cm3, and the P-type doping concentration of the second GaP layer 146 is 1.2E18-2.5E18 atoms / cm3.

[0099] In an embodiment of the present application, the P-type doping concentration of the first stack structure 410 away from the active layer 30 is greater than the P-type doping concentration of the first stack structure 410 close to the active layer 30. That is, as the growth period increases, the P-type doping concentration of the first stack structure 410 gradually increases along the stacking direction. And, the band gap of the first stack structure 410 away from the active layer 30 is greater than the band gap of the first stack structure 410 close to the active layer 30. That is, as the growth period increases, the band gap of the first stack structure 410 gradually increases along the stacking direction.

[0100] In one embodiment of the present application, in each first stack structure 410, the thickness of the GaInP layer 412 is 50-150 nm, the thickness of the first GaP layer 414 is 50-150 nm, and the thickness of the second GaP layer 416 is 50-150 nm.

[0101] Figure 11 is a flow chart of a method for manufacturing an epitaxial structure of a light emitting diode in another embodiment of the present application, comprising the following steps:

[0102] S210, obtaining a substrate.

[0103] The step S110 can be the same as that described above and will not be repeated here.

[0104] S220, forming an N-type layer on the substrate.

[0105] The step S120 can be the same as that described above and will not be repeated here.

[0106] S230, forming an active layer on the N-type layer.

[0107] The step S130 can be the same as that described above and will not be repeated here.

[0108] S240, alternately forming AlInP layers and AlGaInP layers as transition layers TL on the active layer.

[0109] The AlInP layers 422 and the AlGaInP layers 424 are alternately formed on the side of the active layer 30 away from the N-type layer 20 until the second stack structure 420 of the target number of layers is formed as the transition layer TL 42. In one embodiment of the present application, the loop of the second stack structure 420 is 3-15.

[0110] S250, alternately forming GaInP layers, first GaP layers and second GaP layers on the transition layer TL.

[0111] The GaInP layers 412, the first GaP layers 414 and the second GaP layers 416 are alternately formed on the side of the transition layer TL 42 away from the active layer 30, each GaInP layer 412, first GaP layer 414 and second GaP layer 416 being a first stack structure 410, until the first stack structure 410 of the target number of layers is formed. In each first stack structure 410, the P-type doping concentration of the second GaP layer 416 is greater than that of the first GaP layer 414, and / or the barrier height of the second GaP layer 416 is greater than that of the first GaP layer 414. In one embodiment of the present application, the loop of the first stack structure 410 is 15-50.

[0112] S260, forming a GaP current spreading layer on a first stack structure farthest from the active layer.

[0113] The step S150 can be the same as the step S150, which is not described herein.

[0114] In an embodiment of the present application, a step of forming a P-type ohmic contact layer on the GaP current spreading layer 417 is further included, and a material of the P-type ohmic contact layer is P-type doped GaP.

[0115] In an embodiment of the present application, a material of the AlInP layer 422 is Al x1 In y P, a material of the AlGaInP layer 424 is Al x2 Ga （1-x2） 0.5In0.5P, x1>x2, 0.5≤x1<1, 0.15≤x2≤0.6, 0.3≤y≤0.5. By adjusting the In / Ga ratio, the thermal expansion coefficients of the upper and lower film layers on the transition layer TL 42 can be better matched, the cracks or peeling caused by thermal stress can be reduced, and the lattice quality of the epitaxial layer can be improved.

[0116] In an embodiment of the present application, an Al content of the second stack structure 420 far from the active layer 30 is less than an Al content of the second stack structure 420 close to the active layer 30. That is, with the increase of the growth period, the Al component in the second stack structure 420 gradually decreases in the stacking direction. In an embodiment of the present application, an Al band of the second stack structure 420 far from the active layer 30 is less than an Al band of the second stack structure 420 close to the active layer 30. By setting the Al content of the second stack structure 420 far from the active layer 30 to be less than the Al content of the second stack structure 420 close to the active layer 30, the Al band of the second stack structure 420 far from the active layer 30 can be made to be less than the Al band of the second stack structure 420 close to the active layer 30. In an embodiment of the present application, a P-type doping concentration of the AlInP layer 422 is 1E17-3E17 atoms / cm³, and a P-type doping concentration of the AlGaInP layer 424 is 3E17-7E17 atoms / cm³.

[0117] In an embodiment of the present application, a thickness of the transition layer TL 42 is 100-500 nanometers.

[0118] In an embodiment of the present application, in each second stack structure 420, a thickness of the AlInP layer 422 is 20-50 nanometers, and a thickness of the AlGaInP layer 424 is 30-50 nanometers.

[0119] In an embodiment of the present application, between step S230 and step S240, a step of forming a waveguide layer 402 and a cladding layer 404 on the active layer is further included, and then step S240 is performed to form the transition layer TL 42 on the cladding layer 404. The material of the waveguide layer 402 is P-doped AlGaInP, and the material of the cladding layer 404 is P-doped AlInP.

[0120] In an embodiment of the present application, the N-type layer 20 includes a buffer layer 201 on the substrate 10, a cutoff layer 202 on the buffer layer 201, an N-type ohmic contact layer 203 on the cutoff layer 202, a window layer 204 on the N-type ohmic contact layer 203, a cladding layer 205 on the window layer 204, and a waveguide layer 206 on the cladding layer 205. The material of the buffer layer 201 is N-doped GaAs, the material of the cutoff layer 202 is N-doped GaInP, the material of the N-type ohmic contact layer 203 is N-doped GaAs, the material of the window layer 204 is N-doped AlGaInP, the material of the cladding layer 205 is N-doped AlInP, and the material of the waveguide layer 206 is N-doped AlGaInP.

[0121] In an embodiment of the present application, the method for manufacturing the light-emitting diode epitaxial structure is to use a metal organic chemical vapor deposition (MOCVD) process to epitaxially grow, on a GaAs substrate 10, an n-GaAs buffer layer 201, an n-GaInP cutoff layer 202, an n-GaAs N-type ohmic contact layer 203, an n-(Al X Ga 1-X )0.5In0.5P window layer 204, an n-AlInP cladding layer 205, an n-(Al X Ga 1-X )0.5In0.5P waveguide layer 206, an active layer 30, a p-(Al X Ga 1-X )0.5In0.5P waveguide layer 402, a p-AlInP cladding layer 404, a transition layer TL 42, a P-type window layer 41, and a P-type ohmic contact layer 406.

[0122] In an embodiment of the present application, the method for manufacturing the light-emitting diode epitaxial structure described above can be used to manufacture a red light LED.

[0123] The method for manufacturing the light-emitting diode epitaxial structure of the present application and the light-emitting diode epitaxial structure are based on the same inventive concept, and the contents not specifically described in the method for manufacturing the light-emitting diode epitaxial structure can be referred to the introduction of the light-emitting diode epitaxial structure above.

[0124] In the description of the specification, the description of the terms "some embodiments", "other embodiments", "ideal embodiments", etc. means that the specific features, structures, materials or characteristics described in connection with the embodiments or examples are contained in at least one embodiment or example of the present application. In the description, the illustrative description of the above terms does not necessarily refer to the same embodiment or example.

[0125] The technical features of the above-described embodiments can be combined arbitrarily. In order to make the description simple, all possible combinations of the technical features of the above-described embodiments are not described, but as long as the combinations of the technical features do not contradict each other, they should be considered as the scope of the present application.

[0126] The above-described embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the patent application scope. It should be noted that for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the patent protection scope of the present application should be subject to the appended claims.

Claims

1. A light emitting diode epitaxial structure, comprising: The application relates to a red light LED, comprising: a substrate; an N-type layer on one side of the substrate; an active layer on the side of the N-type layer away from the substrate; a P-type layer on the side of the active layer away from the N-type layer; wherein the P-type layer comprises a P-type window layer, the P-type window layer comprises a plurality of first stacked structures, each first stacked structure comprises a GaInP layer, a first GaP layer and a second GaP layer which are sequentially stacked, and the barrier height of the second GaP layer in each first stacked structure is greater than the barrier height of the first GaP layer.

2. The light emitting diode epitaxial structure of claim 1, wherein, The P-type window layer further comprises a GaP current spreading layer, each first stacked structure is located between the GaP current spreading layer and the active layer, the thickness of the GaP current spreading layer is greater than the thickness of each first stacked structure, and the barrier height of the GaP current spreading layer is greater than the barrier height of each second GaP layer.

3. The light emitting diode epitaxial structure of claim 1, wherein, The number of first stacked structures in the P-type window layer is 15-50; and / or the GaInP layer is Ga x3 In （1-x3） P layer, 0.5≤x3<1.

4. The light emitting diode epitaxial structure of claim 1, wherein, The band gap of the GaInP layer is 1.82-2.23 eV, the band gap of the first GaP layer is 2.25-2.26 eV, and the band gap of the second GaP layer is 2.20-2.23 eV.

5. The light emitting diode epitaxial structure of any of claims 1-4, wherein, The P-type window layer has a superlattice structure; The barrier height of the first stacked structure away from the active layer is greater than the barrier height of the first stacked structure close to the active layer, and / or the band gap of the first stacked structure away from the active layer is greater than the band gap of the first stacked structure close to the active layer.

6. The light emitting diode epitaxial structure of claim 1, wherein, The P-type layer further comprises a transition layer located between the P-type window layer and the active layer, and the transition layer comprises a plurality of second stacked structures, each second stacked structure comprises an AlInP layer and an AlGaInP layer.

7. The light emitting diode epitaxial structure of claim 6, wherein, the AlInP layer is Al x1 In y P layer, the AlGaInP layer is Al x2 Ga （1-x2） 0.5In0.5P layer, x1>x2, 0.5≤x1<1, 0.15≤x2≤0.6, 0.3≤y≤0.

5.

8. The light emitting diode epitaxial structure of claim 6 or 7, wherein, The Al energy band of the second stacked structure away from the active layer is less than the Al energy band of the second stacked structure close to the active layer; and / or the number of second stacked structures in the transition layer is 3-15.

9. The light emitting diode epitaxial structure of claim 6 or 7, wherein, The P-type layer further comprises a waveguide layer located between the active layer and the transition layer, and a confinement layer located between the waveguide layer and the transition layer, the waveguide layer is an AlGaInP waveguide layer, and the confinement layer is an AlInP confinement layer.

10. A display panel comprising a plurality of red LEDs, characterized in that, Each red light LED has the light-emitting diode epitaxial structure according to any one of claims 1-9.

11. A manufacturing method of a light-emitting diode epitaxial structure, comprising: obtaining a substrate; forming an N-type layer on one side of the substrate; forming an active layer on the side of the N-type layer away from the substrate; alternately forming a GaInP layer, a first GaP layer and a second GaP layer on the side of the active layer away from the N-type layer, each GaInP layer, first GaP layer and second GaP layer serving as a first stacked structure, until a target number of first stacked structures are formed; and the barrier height of the second GaP layer in each first stacked structure is greater than the barrier height of the first GaP layer.

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