Light emitting diode and light emitting device

Abstract

The invention discloses a light-emitting diode and a light-emitting device. The light-emitting diode at least comprises an epitaxial structure, wherein the epitaxial structure at least comprises a first semiconductor layer, an active layer and a second semiconductor layer which are stacked in sequence; wherein the active layer comprises M well layers and barrier layers which are repeatedly stacked periodically, and the well layers are nitride material layers containing In; the M well layers at least comprise N first well layers, M and N are positive integers, M > = N > = 1, and each first well layer comprises a first sub-well layer and a second sub-well layer which are adjacent to each other; the first sub-well layer is close to the first semiconductor layer; in the thickness direction of the active layer, the indium content of the first sub-well layer is increased from the first content to the second content, and the indium content of the second sub-well layer is the second content. Therefore, by optimizing the structure of the active layer, lattice mismatch between the barrier layer and the well layer with high indium component can be relieved, the phenomenon of uneven carrier distribution can be improved, the radiation recombination probability of the active layer can be improved, and the internal quantum efficiency can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor devices, in particular to a light emitting diode and a light emitting device. BACKGROUND

[0002] In the rapid development of the LED (Light Emitting Diode) industry, gallium nitride-based LEDs have been quickly commercialized and widely used in many fields. From a technical point of view, further improving the light emitting efficiency of LED chips is still the focus of current industry development, and the core lies in improving the radiative recombination efficiency of the active region, thereby improving the internal quantum efficiency (IQE).

[0003] However, in practical applications, gallium nitride-based LEDs generally have problems such as low hole injection efficiency in multi-quantum wells, uneven carrier distribution, and the like, which further affect the radiative recombination efficiency, especially in gallium nitride-based green micro light emitting diodes operating at high current density. Therefore, how to effectively improve the radiative recombination efficiency of the active region has become a technical problem to be solved. SUMMARY

[0004] In view of the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a light emitting diode and a light emitting device to improve the radiative recombination efficiency of the active layer.

[0005] In order to achieve the above-mentioned purpose and other related purposes, the present application provides a light emitting diode, which at least comprises an epitaxial structure: the epitaxial structure at least comprises a first semiconductor layer, an active layer and a second semiconductor layer which are stacked in sequence; wherein:

[0006] The active layer comprises M periodically stacked well layers and barrier layers, the well layer is a nitride material layer containing In; at least N first well layers are included in the well layer, M and N are positive integers and M≥N≥1, each first well layer comprises adjacent first sub-well layer and second sub-well layer; the first sub-well layer is close to the first semiconductor layer; along the thickness direction of the active layer, the molar content of indium of the first sub-well layer increases from the first content to the second content, and the molar content of indium of the second sub-well layer is the second content.

[0007] According to one aspect of the present application, a light emitting diode is also provided, which at least comprises an epitaxial structure: the epitaxial structure at least comprises a first semiconductor layer, an active layer and a second semiconductor layer which are stacked in sequence; wherein:

[0008] The active layer comprises a plurality of periodically stacked well layers and barrier layers, and the active layer comprises a first sequence and a second sequence formed above the first sequence in a direction from the first semiconductor layer to the second semiconductor layer, the first sequence comprises periodically stacked first well layers and first barrier layers, and the second sequence comprises periodically stacked second well layers and second barrier layers; the first well layers and the second well layers are layers of In-containing nitride materials;

[0009] The first well layer comprises adjacent first and second sub-well layers; the first sub-well layer is close to the first semiconductor layer; in a thickness direction of the active layer, the molar content of indium of the first sub-well layer increases from a first content to a second content, and the molar content of indium of the second sub-well layer is the second content.

[0010] The second well layer comprises a third sub-well layer; the molar content of indium of the third sub-well layer is the second content.

[0011] According to one aspect of the present application, there is also provided a light-emitting device comprising a light-emitting source, which is the light-emitting diode described above.

[0012] Compared with the prior art, the light-emitting diode and the light-emitting device of the present application have at least the following beneficial effects through optimization of the active layer structure:

[0013] The arrangement of the light-emitting diode of the present application is advantageous in relieving the large lattice mismatch between the barrier layers and the high-indium-content well layers, relieving the structural stress and reducing the internal polarization electric field, so as to achieve: 1. improving the quantum confinement Stark effect (QCSE), thereby increasing the overlap of the electron and hole wave functions and improving the radiation recombination efficiency; 2. inhibiting the generation and proliferation of defects, thereby improving the quality of the crystal; 3. improving the interface quality between the well layers and the barrier layers, reducing the occurrence of indium clusters and indium precipitation, thereby improving the light-emitting uniformity and improving the efficiency Droop effect.

[0014] On the other hand, the overall phenomenon of uneven carrier distribution is improved, specifically: on the one hand, the potential barrier height for hole injection from the second semiconductor layer to the first semiconductor layer is reduced, promoting hole injection into the multi-quantum well close to the first semiconductor layer; on the other hand, the energy potential barrier for electron injection from the first semiconductor layer to the active layer is reduced, avoiding the accumulation of electrons in the multi-quantum well close to the first semiconductor layer, thereby further enhancing the wave function overlap of electrons and holes and effectively improving the radiation recombination efficiency of the active layer.

[0015] The light-emitting device of the present application comprises the light-emitting diode described above, and likewise has the technical effects described above. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 FIG. 1 is a structural schematic diagram of an epitaxial structure of a light-emitting diode in an example of the present application.

[0017] Figure 2 A schematic diagram of the structure of an epitaxial structure of a light emitting diode in another example of the present application.

[0018] Figure 3 A schematic diagram of the structure of an active layer in an example of the present application.

[0019] Figure 4 A schematic diagram of the structure of an active layer in another example of the present application.

[0020] Figure 5 A schematic diagram of the structure of an active layer in another example of the present application.

[0021] Figure 6 A schematic diagram of the structure of an active layer in another example of the present application.

[0022] Figure 7 A schematic diagram of the In content of an active layer of a light emitting diode in an example of the present application.

[0023] Figure 8 A schematic diagram of the In content of an active layer of a light emitting diode in another example of the present application.

[0024] Figure 9 A comparison diagram of the hole concentration of a light emitting diode with a first well layer having a gradually changing In content in an example of the present application and a light emitting diode without a gradually changing In content in a comparative example.

[0025] Figure 10 A comparison diagram of the radiative recombination efficiency of a light emitting diode with a first well layer having a gradually changing In content in an example of the present application and a light emitting diode without a gradually changing In content in a comparative example.

[0026] Figure 11 A schematic diagram of the polarization electric field intensity of a light emitting diode with a first well layer having a gradually changing In content in an example of the present application and a light emitting diode without a gradually changing In content in a comparative example.

[0027] Figure 12 A transmission electron microscope (TEM) image of an epitaxial structure in an example of the present application.

[0028] List of reference numerals:

[0029] 100 substrate

[0030] 200 buffer layer

[0031] 300 undoped layer

[0032] 400 first semiconductor layer

[0033] 500 superlattice layer

[0034] 501 first superlattice layer

[0035] 502 second superlattice layer

[0036] 600 active layer

[0037] 601 first sequence

[0038] 6011 first well layer

[0039] 6111 first sub-well layer

[0040] 6112 second sub-well layer

[0041] 6012 first barrier layer

[0042] 602 second sequence

[0043] 6021 second well layer

[0044] 6113 third sub-well layer

[0045] 6022 second barrier layer

[0046] 700 electron blocking layer

[0047] 800 low-temperature gallium nitride layer

[0048] 900 second semiconductor layer DETAILED DESCRIPTION

[0049] Embodiments of the present application will be described in detail by specific embodiments, and those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in the specification. The present application can also be implemented or applied by different specific embodiments, and each detail in the specification can be modified or changed based on different views and applications without departing from the spirit of the present application. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0050] It is to be understood that the illustrations provided in the embodiments of the present application are merely schematic and that, for example, the proportions in the drawings, the relative dimensions of the elements, or the shown dispositions of the elements do not necessarily correspond to the description provided herein and are merely intended to convey the basic idea of the application. The actual implementation of the described application can therefore differ from the schematic illustrations and depend, for example, on the chosen technology or the technical specifications. The illustrated structures, proportions, sizes, etc. in the drawings are merely intended to facilitate the understanding of the content disclosed herein for the person skilled in the art and are not intended to limit the application in any way. Any modification of the structures, change of the proportions or adjustment of the sizes, which do not affect the effect and the purpose of the application, should still fall within the scope of the technology disclosed herein.

[0051] In order to solve the problem of low radiation recombination efficiency in the prior art, the present embodiment provides a light emitting diode, which at least comprises an epitaxial structure: the epitaxial structure at least includes a first semiconductor layer, an active layer and a second semiconductor layer stacked in sequence; wherein:

[0052] The active layer comprises M periodically stacked well layers and barrier layers, the well layers are layers of In-containing nitride material; at least N first well layers are included in the well layers, M and N are positive integers and M≥N≥1, each of the first well layers comprises adjacent first sub-well layers and second sub-well layers; the first sub-well layers are close to the first semiconductor layer; along the thickness direction of the active layer, the molar content of indium of the first sub-well layers increases from a first content to a second content, and the molar content of indium of the second sub-well layers is the second content. By setting the first sub-well layers with gradually changing indium content, the large lattice mismatch between the barrier layers and the well layers with high indium component is alleviated, the structural stress is alleviated and the internal polarization electric field is reduced, so as to achieve: 1. improve the quantum confinement Stark effect (QCSE), thereby increase the overlap of electron and hole wave functions, and improve the radiation recombination efficiency; 2. suppress the generation and proliferation of defects, thereby improve the quality of the crystal; 3. improve the interface quality between the well layers and the barrier layers, reduce the indium cluster and indium precipitation, thereby improve the light emission uniformity and improve the efficiency Droop effect. Secondly, since the electron mobility is much higher than the hole, the hole is difficult to approach the multi-quantum well of the first semiconductor layer, the first sub-well layer with gradually changing indium content is closer to the first semiconductor layer than the second sub-well layer, on the one hand, it can reduce the potential barrier height of the hole injection from the second semiconductor layer to the first semiconductor layer, which is conducive to the uniform injection of holes into the multi-quantum well, on the other hand, it can reduce the energy barrier of the electron injection from the first semiconductor layer to the active layer, and avoid the accumulation of electrons in the multi-quantum well close to the first semiconductor layer. Therefore, the uneven distribution of carriers is improved as a whole, the electron-hole wave function overlap is further enhanced, and the radiation recombination efficiency of the active region is effectively improved, and the internal quantum efficiency of the light-emitting diode is optimized. In addition, by setting the second sub-well layer with constant indium content, the second sub-well layer serves as the main electron-hole recombination region, while ensuring the light emission intensity of the light-emitting diode, and finally improving the overall light emission efficiency of the light-emitting diode.

[0053] Optionally, at least the first well layer close to the first semiconductor layer is the first well layer. By setting the first well layer to contain the indium content gradient layer, the uniform injection of holes and the improvement of electron accumulation can be more effectively improved, and the overall uniformity of carriers is improved.

[0054] Optionally, the first content is 0% to 10%, and the second content is 25% to 28%. By designing the indium component of each pair of first sub-well layers to gradually increase from the first content with a lower concentration to the second content with a higher concentration, on the one hand, the radiation recombination efficiency can be improved, and on the other hand, the active layer can radiate light of the required wavelength.

[0055] Optionally, the thickness of the first sub-well layer is less than or equal to the thickness of the second sub-well layer. Since the second sub-well layer is a constant-indium-content layer, which is the main electron-hole recombination region, the thickness of the second sub-well layer is controlled to reserve enough space for electron-hole pairs to recombine to ensure the light emission intensity. On the other hand, the quantum well layer with high indium component can effectively confine carriers to avoid overflow and cause a surge in Auger recombination.

[0056] Optionally, when N≥2, the thickness ratio of the first sub-well layer to the second sub-well layer is the same. Controlling the same thickness ratio can reduce the process difficulty, while also improving the wavelength uniformity of the active layer radiation, achieving more consistent light emission characteristics, thereby improving the reliability and yield of the device.

[0057] Optionally, when N≥2, the thickness ratio of the first sub-well layer to the second sub-well layer gradually decreases along the direction from the first semiconductor layer to the second semiconductor layer. Thus, the gradual change in indium content near the first semiconductor layer can alleviate the lattice mismatch, and the gradually increasing thickness of the second sub-well layer near the main light-emitting region can ensure enough space for electron-hole recombination, thereby improving the overall light-emitting efficiency of the light-emitting diode.

[0058] Optionally, when N≥2, the thickness ratio of the first sub-well layer to the second sub-well layer in at least one well layer is 1:2. Under this thickness ratio, the lattice mismatch can be more effectively alleviated, and enough space for electron-hole recombination can be ensured.

[0059] Optionally, more than half of the well layers contain the first sub-well layer and the second sub-well layer to buffer the lattice mismatch of the barrier layer and the well layer with high indium component as much as possible.

[0060] Optionally, the active layer further includes a second well layer, and the molar content of indium in the second well layer is a second content. Through the second well layer with a constant indium component of the second content, enough space is ensured for electron-hole pairs to recombine to ensure the light emission intensity, and the active layer can emit light of the required wavelength. Preferably, the second well layer is closer to the second semiconductor layer, so that the constant-indium-content layer is located in the main light-emitting region, improving the light-emitting efficiency of the light-emitting diode.

[0061] Optionally, the thickness ratio of the well layer to the barrier layer is between 1:4 and 1:5. Since the thickness of the barrier layer is relatively small, the ratio of the barrier layer to the well layer is beneficial to expanding the area and density of the V-pit structure during epitaxial formation. The V-pit structure can induce more carrier injection into the deep multi-quantum well region, reduce the probability of carrier capture by dislocation and other non-radiative recombination centers, and thus improve the radiative recombination efficiency.

[0062] Optionally, the thickness of the barrier layer is not more than 1.5 nm. By reducing the thickness of the barrier layer, not only the thickness ratio of the barrier layer and the well layer can be better regulated, but also the rate and probability of carrier tunneling can be increased, further enhancing the wave function overlap of electron-hole pairs, effectively improving the radiation recombination efficiency. At the same time, this design also helps to reduce the proportion of Auger recombination which is not conducive to the application of high current density, and ultimately realizes the overall optimization of the internal quantum efficiency of the light-emitting diode.

[0063] Optionally, the well layer is Al x1 In y1 Ga z1 N layer, wherein 0 < x1 < 0.05, y1 < 0.28, 0 < z1 < 1.

[0064] Optionally, the barrier layer is Al x2 In y2 Ga z2 N layer, wherein 0 < x2 < 1, 0 < y2 < 1, 0 < z2 < 1.

[0065] By limiting the materials and In content of the well layer and the barrier layer, it is ensured that the active layer can radiate light of the required wavelength.

[0066] Optionally, a V-shaped pit is formed in the epitaxial structure, and the V-shaped pit extends from the side of the first semiconductor layer close to the active layer to the active layer. The arrangement of the V-shaped pit is conducive to inducing more carrier injection into the deep multi-quantum well, reducing the probability of carrier capture by dislocation and other non-radiative recombination centers, and improving the radiation recombination efficiency.

[0067] The embodiment also provides a light-emitting diode, which at least includes an epitaxial structure: the epitaxial structure at least includes a first semiconductor layer, an active layer and a second semiconductor layer which are stacked in sequence; wherein:

[0068] The active layer includes a plurality of periodically and repeatedly stacked well layers and barrier layers, and in the direction from the first semiconductor layer to the second semiconductor layer, the active layer includes a first sequence and a second sequence formed above the first sequence, the first sequence includes periodically and repeatedly stacked first well layers and first barrier layers, and the second sequence includes periodically and repeatedly stacked second well layers and second barrier layers; the first well layers and the second well layers are In-containing nitride material layers;

[0069] The first well layer includes adjacent first sub-well layers and second sub-well layers; the first sub-well layers are close to the first semiconductor layer; in the thickness direction of the active layer, the molar content of indium of the first sub-well layers increases from a first content to a second content, and the molar content of indium of the second sub-well layers is the second content.

[0070] The second well layer includes a third sub-well layer; the molar content of indium of the third sub-well layer is the second content,

[0071] By setting the gradual change of the indium content in the first sequence close to the first semiconductor layer, the large lattice mismatch between the barrier layer and the high-indium-composition well layer is alleviated, the structure stress is alleviated and the internal polarization electric field is reduced, thereby improving the radiation recombination efficiency and the quality of the crystal, reducing the indium cluster and indium precipitation, improving the light emission uniformity and improving the efficiency Droop effect. Secondly, the height of the potential barrier for the injection of holes from the second semiconductor layer to the first semiconductor layer and the energy barrier for the injection of electrons from the first semiconductor layer to the active layer are reduced, and the uneven distribution of carriers is improved as a whole, thereby further improving the radiation recombination efficiency of the active region and optimizing the internal quantum efficiency of the light-emitting diode, thereby improving the light-emitting efficiency of the light-emitting diode. At the same time, since the light-emitting region of the light-emitting diode is mainly close to the active region on the side of the second semiconductor layer, by designing the second sequence including the indium content constant layer to be closer to the second semiconductor layer, the indium content constant layer is located in the main light-emitting region, thereby further improving the light-emitting efficiency of the light-emitting diode.

[0072] Optionally, the first content is 0% to 10%, and the second content is 25% to 28%. By designing the indium composition of each pair of first sub-well layers to uniformly increase from the first content with a lower concentration to the second content with a higher concentration, on the one hand, the radiation recombination efficiency of the light-emitting diode is improved, and on the other hand, the active layer can radiate light of the required wavelength.

[0073] Optionally, the thickness of the first sub-well layer is less than or equal to the thickness of the second sub-well layer. Since the second sub-well layer is an indium content constant layer and is a main electron-hole recombination region, the thickness of the second sub-well layer is controlled to be larger to reserve enough space for electron-hole pairs to recombine to ensure the light-emitting intensity. At the same time, it is ensured that the high-indium-composition quantum well layer can effectively confine carriers to avoid overflow and cause a surge in Auger recombination.

[0074] Optionally, the thickness ratio of the first sub-well layer to the second sub-well layer is 1:2. Under this thickness ratio, the lattice mismatch can be effectively alleviated, and enough electron and hole recombination space is ensured.

[0075] Optionally, the repeating period of the well layer and the barrier layer is 2 to 20, the repeating period of the first well layer and the first barrier layer is 1 to 20, and the repeating period of the second well layer and the second barrier layer is 1 to 5. The lattice mismatch between the barrier layer and the high-indium-composition well layer is buffered as much as possible, and enough electron and hole recombination space is ensured.

[0076] Optionally, the first sub-well layer is Al a1 In b1 Ga c1 N layer, wherein 0 a2 In b2 Gac2 N layer, wherein 0 < a2 < 0.05, 0.25 ≤ b2 ≤ 0.28, 0 ≤ c2 ≤ 1; the third sub-well layer is Al a3 In b3 Ga c3 N layer, wherein 0 < a3 < 0.05, 0.25 ≤ b3 ≤ 0.28, 0 ≤ c3 ≤ 1. By limiting the material and In content of the well layer, it is ensured that the active layer can radiate light of the required wavelength.

[0077] Optionally, a V-shaped pit is formed in the epitaxial structure, and the V-shaped pit extends from the side of the first semiconductor layer close to the active layer to the active layer. The arrangement of the V-shaped pit is conducive to inducing more carriers to be injected into the deep multi-quantum well, reducing the probability of carriers being captured by non-radiative recombination centers such as dislocations, and improving the recombination efficiency.

[0078] Optionally, the side length of the light-emitting diode is less than or equal to 100 μm.

[0079] Optionally, the light-emitting wavelength of the active layer is between 500 nm and 550 nm.

[0080] Optionally, the current density of the light-emitting diode is greater than or equal to 20 A / cm 2 .

[0081] In the light-emitting diode of the above size and radiating the above wavelength range under a large current density, the demand for recombination efficiency is further increased.

[0082] The embodiment also provides a light-emitting device, which comprises a light-emitting source, and the light-emitting source is the light-emitting diode described above. Since the light-emitting device of the embodiment comprises the light-emitting diode described above, the recombination probability of the electrons and holes of the light-emitting source in the light-emitting device of the embodiment is higher, the light-emitting uniformity is better, and the light-emitting device has better quantum efficiency.

[0083] The chemical composition and dopant of each layer of the epitaxial structure of the light-emitting diode provided in the embodiment can be analyzed by any suitable method, for example, by a secondary ion mass spectrometer (SIMS), an energy dispersive X-ray spectrometer (EDX), or a high-resolution X-ray diffraction (HR-XRD). The thickness of each layer of the light-emitting diode provided in the embodiment can be analyzed by any suitable method, for example, a transmission electron microscope (TEM) or a scanning electron microscope (SEM), for the depth position of each layer in cooperation with, for example, the SIMS spectrum.

[0084] The application will be described in detail below with reference to specific embodiments.

[0085] Embodiment 1

[0086] The present embodiment provides a light emitting diode, referring to Figure 1 or Figure 2 The light emitting diode comprises a substrate 100 and an epitaxial structure. The substrate 100 can be made of conductive material or insulating material, and the material can be one of sapphire, aluminum nitride, gallium nitride or silicon nitride. The most commonly used substrate of LED epitaxial structure is sapphire substrate, which can be a patterned substrate, i.e. the surface of the sapphire substrate is formed with convex patterns of uniform size and uniform spacing by etching process, or the partial height of the convex patterns is replaced by a material with lower refractive index relative to the sapphire substrate.

[0087] Referring to Figure 1 , the epitaxial structure comprises at least a first semiconductor layer 400, an active layer 600 and a second semiconductor layer 900 stacked in sequence from the surface of the substrate 100. In the present embodiment, the first semiconductor layer 400 is an N-type semiconductor layer, and the second semiconductor layer 900 is a P-type semiconductor layer.

[0088] The first semiconductor layer 400 provides electrons by intentionally doping N-type impurities, which can be Si, Ge, Sn, Se and Te. In the present embodiment, the N-type impurities are Si, and the material of the first semiconductor layer 400 is an N-GaN layer. Optionally, referring to Figure 2 In order to buffer the lattice mismatch between the substrate 100 and the N-type semiconductor layer, a buffer layer 200 is further provided between the substrate 100 and the N-type semiconductor layer. In the present embodiment, the material of the buffer layer 200 can be an AlN layer, a GaN layer or AlGaN, etc. In the present embodiment, the material of the buffer layer 200 is an AlN layer. Optionally, referring to Figure 2 A non-doped layer 300 can be further provided between the buffer layer 200 and the N-type semiconductor layer to further alleviate the lattice mismatch, and the material of the non-doped layer 300 can be a GaN layer.

[0089] The active layer 600 is provided above the first semiconductor layer 400, and the active layer 600 is a region where electrons and holes are combined to generate light. The active layer 600 comprises M periods of repeatedly stacked well layers and barrier layers. Optionally, the repeating period of the well layer and the barrier layer is between 1-20, preferably the repeating period is 2-15, more preferably the repeating period is 6-12. In the present embodiment, the repeating period of the well layer and the barrier layer is 9. The well layer is an In-containing nitride material layer. The well layer is an Al x1 In y1 Ga z1N layer, wherein, 0 < x1 < 0.05, y1 < 0.28, 0 < z1 < 1. In the embodiment, the well layer is InGaN. The barrier layer is Al x2 In y2 Ga z2 N layer, wherein, 0 < x2 < 1, 0 < y2 < 1, 0 < z2 < 1. In the embodiment, the barrier layer is GaN. The embodiment adopts the barrier layer 602 without aluminum, which can reduce the large lattice mismatch between the barrier layer 602 and the well layer 601 with high indium component (25%) or more, relieve stress and reduce internal polarization electric field, improve quantum confinement Stark effect, thereby increasing the overlap of electron and hole wave functions and improving radiation recombination efficiency; on the other hand, it is conducive to constructing a larger area and density of V-pit structure in the epitaxial formation process, which can induce more carriers to inject into the deep multi-quantum well region, reduce the probability of carrier capture by dislocation and other non-radiative recombination centers, thereby improving the radiation recombination efficiency and reducing the operating voltage of the light-emitting diode; on the other hand, it is conducive to improving the rate and probability of carrier tunneling, further enhancing the wave function overlap of electron-hole pairs, and effectively improving the radiation recombination efficiency; on the other hand, it is conducive to reducing the proportion of Auger recombination which is not conducive to large current density application, and ultimately realizing the overall optimization of the internal quantum efficiency of the light-emitting diode.

[0090] In the embodiment, the thickness of each barrier layer 602 is greater than the thickness of each adjacent well layer 601. Optionally, the ratio of the thickness of the well layer to the thickness of the barrier layer is not greater than 1:4.5. Optionally, the ratio of the thickness of the well layer to the thickness of the barrier layer is between 1:4 and 1:5. A suitable ratio of the barrier layer to the well layer is conducive to expanding the area and density of the V-pit structure in the epitaxial formation process, which can induce more carriers to inject into the deep multi-quantum well region, reduce the probability of carrier capture by dislocation and other non-radiative recombination centers, thereby improving the radiation recombination efficiency. In the embodiment, the thickness of the well layer is between 2.5 nm and 3.5 nm, and the thickness of the barrier layer is between 8 nm and 12 nm. The thickness of the barrier layer is not more than 10 nm. For example, the thickness of the barrier layer is 9 nm. By reducing the thickness of the barrier layer, it not only helps to better regulate the thickness ratio of the barrier layer to the well layer, but also can increase the rate and probability of carrier tunneling, further enhance the wave function overlap of electron-hole pairs, effectively improve the radiation recombination efficiency, and at the same time, this design also helps to reduce the proportion of Auger recombination which is not conducive to large current density application, and ultimately realize the overall optimization of the internal quantum efficiency of the light-emitting diode.

[0091] A V-pit (not shown in the figure) is formed in the active layer 600, which extends from the side of the first semiconductor layer 400 close to the active layer 600 to the active layer 600. Due to the high molar content of indium in the well layer 601 of the embodiment, the thickness of the barrier layer 602 is relatively small, and the size and density of the V-pit 603 formed are larger, which is more conducive to inducing more carriers to be injected into the deep multi-quantum well, reducing the probability of carriers being captured by dislocation and other non-radiative recombination centers, and increasing the probability of radiative recombination. Optionally, the width of the top opening of the V-pit is W, and the depth of the V-pit is H, and the ratio of W to H in the embodiment is in the range of 0.3-4, preferably, the ratio of W to H is in the range of 0.5-2, more preferably, the ratio of W to H is in the range of 1-2. Optionally, W is in the range of 40-800 nm, and H is in the range of 70-600 nm, preferably, W is in the range of 50-800 nm, and H is in the range of 100-600 nm, more preferably, W is in the range of 60-800 nm, and H is in the range of 120-600 nm. Optionally, the longitudinal interface of the V-pit is triangular or triangular-like. Considering the actual process conditions and other factors in actual application, for example, the inclined side wall is not a complete smooth interface, the longitudinal interface of the V-pit of the present application is not limited to a triangle, but can be a triangular-like triangle. Optionally, the bottom of the V-pit has an included angle α, and the range of the included angle α is 40°-90°, for example, α is 40°, 45°, 50°, 55°, 60°, 65°, 70°, preferably, the range of α is 50°-70°.

[0092] Referring to Figures 3-8 , the well layer of the active layer 600 includes N first well layers 6011, N is a positive integer and M≥N≥1, each first well layer 6011 includes adjacent first and second sub-well layers 6111 and 6112; the first sub-well layer 6111 is closer to the first semiconductor layer 400 than the second sub-well layer 6112, and along the thickness direction of the active layer 600, referring to Figure 7 , the indium content of the first sub-well layer 6111 increases from the first content to the second content, and the indium content of the second sub-well layer 6112 is a constant second content. Optionally, referring to Figure 5 or Figure 6 or Figure 8 , in addition to at least the first well layer 6011 close to the first semiconductor layer 400, a second well layer 6021 is also included, and the content of the second well layer 6021 is a constant second content.

[0093] By setting the first sub-well layer 6111 with a gradual change in indium content in the first well layer 6011, on the one hand, the large lattice mismatch between the barrier layer and the well layer with a high indium component can be alleviated, the structural stress can be alleviated, and the internal polarization electric field can be reduced, thereby achieving: 1. improving the quantum confinement Stark effect (QCSE), thereby increasing the overlap of electron and hole wave functions and improving the radiation recombination efficiency; 2. inhibiting the generation and proliferation of defects, thereby improving the quality of the crystal; 3. improving the interface quality between the well layer and the barrier layer, reducing indium clusters and indium precipitation, thereby improving the light emission uniformity and improving the efficiency Droop effect. On the other hand, since the electron mobility is much higher than the hole, the hole is difficult to approach the multi-quantum well of the first semiconductor layer 400. By setting the first sub-well layer 6111 with a gradual change in indium content near the first semiconductor layer 400, on the one hand, the potential barrier height for hole injection from the second semiconductor layer 900 to the first semiconductor layer 400 can be reduced, which is beneficial to the uniform injection of holes into the multi-quantum well, and on the other hand, the energy barrier for electron injection from the first semiconductor layer 400 to the active layer 600 can be reduced, thereby avoiding the accumulation of electrons in the multi-quantum well near the first semiconductor layer 400. Thus, the uneven distribution of carriers is improved overall, the electron-hole wave function overlap is further enhanced, the radiation recombination efficiency of the active region is effectively improved, and finally the overall optimization of the internal quantum efficiency of the light-emitting diode is realized, thereby improving the light-emitting efficiency of the light-emitting diode. In addition, by setting the second sub-well layer 6112 with a constant indium content in the first well layer 6011, the second sub-well layer 6112 serves as the main electron-hole recombination region while ensuring the light emission intensity, thereby ultimately improving the overall light-emitting efficiency of the light-emitting diode.

[0094] In the present embodiment, the first content is 0% to 10%, and the second content is 25% to 28%. Preferably, the first content is 2% to 8%, and more preferably, the first content is 6% to 7%. The first sub-well layer 6111 is Al x1 In y1 Ga z1 N layer, where 0 < x1 < 0.05, 0 ≤ y1 ≤ 0.28, and 0 ≤ z1 ≤ 1. The second sub-well layer 6112 is an Al x1 In y1 Ga z1 N layer, where 0 < x1 < 0.05, 0.25 ≤ y1 ≤ 0.28, and 0 ≤ z1 ≤ 1. In the present embodiment, all well layers 601 are InGaN. By limiting the material and In content of the well layer, specifically by designing the indium component of each pair of first sub-well layers 6111 to gradually increase from the first content with a lower concentration to the second content with a higher concentration, on the one hand, the radiation recombination efficiency can be improved, and on the other hand, the active layer can be ensured to emit light of the required wavelength.

[0095] Optionally, the repeating period of the first well layer 6011 and the first barrier layer 6012 is between 1 and 20, preferably, the repeating period is between 2 and 15, more preferably, the repeating period is between 6 and 12. The repeating period of the second well layer 6021 and the second barrier layer 6022 is between 1 and 5.

[0096] Optionally, in the well layers of the active layer 600, at least the first well layer close to the first semiconductor layer 400 comprises a first sub-well layer 6111 and a second sub-well layer 6112. By setting the first well layer to comprise a gradient layer of indium content, the uniform injection of holes and the improvement of electron accumulation can be more effectively improved, and the overall uniformity of carriers can be improved.

[0097] Optionally, referring to Figures 3-6 , at least two well layers comprise a first sub-well layer 6111 and a second sub-well layer 6112, that is, N is at least greater than or equal to 2, and at least the first well layer close to the first semiconductor layer comprises a first sub-well layer 6111 and a second sub-well layer 6112. In this way, the technical effects of the present application can be more effectively achieved.

[0098] In an embodiment, referring to Figure 5 , at least half of the well layers comprise a first sub-well layer 6111 and a second sub-well layer 6112, that is, N is greater than or equal to M / 2, and the at least half of the well layers comprise the first well layer close to the first semiconductor layer 400, and are arranged in order from the first well layer to at least the M / 2th well layer along the direction from the first semiconductor layer 400 to the second semiconductor layer 900, so as to buffer the lattice mismatch of the barrier layer and the well layer with high indium content as much as possible, and better reduce the potential barrier height of the injection of holes from the second semiconductor layer to the first semiconductor layer, and further reduce the energy potential barrier of the injection of electrons from the first semiconductor layer to the active layer, thereby avoiding the accumulation of electrons in the multiple quantum wells close to the first semiconductor layer.

[0099] In an embodiment, all well layers (first well layer 6011) comprising a first sub-well layer 6111 and a second sub-well layer 6112 can be closely arranged, as shown in Figure 5 In an embodiment, a second well layer 6021 can also be inserted among a plurality of first well layers 6011 comprising a first sub-well layer 6111 and a second sub-well layer 6112, as shown in Figure 6As shown. The second well layer 6021 can be a single layer or multiple layers. Preferably, the first well layer 6011 is closer to the first semiconductor layer 400 than the second well layer 6021, and the second well layer 6021 is closer to the second semiconductor layer 900 than the first well layer 6011. Therefore, designing the first well layer 6011, which includes a gradient indium content layer, closer to the first semiconductor layer helps alleviate the large lattice mismatch between the barrier layer and the high indium content well layer, thereby improving the radiative recombination efficiency. Simultaneously, designing the second well layer 6021, which includes a constant indium content layer, closer to the main light-emitting region of the second semiconductor layer improves the luminous efficiency of the light-emitting diode.

[0100] In one embodiment, such as Figure 3 As shown in Figure 4, all well layers include an adjacent first sub-well layer 6111 and a second sub-well layer 6112.

[0101] Optionally, the thickness of the first sub-well layer 6111 is less than or equal to the thickness of the second sub-well layer 6112. Since the second sub-well layer 6112 is a layer with a constant indium content and is the main electron-hole recombination region, controlling the thickness of the second sub-well layer 6112 to be greater allows sufficient space for electron-hole recombination to ensure luminescence intensity, while ensuring that the high-indium quantum well layer can effectively confine charge carriers, preventing overflow and Auger recombination surges. Preferably, the thickness ratio of the first sub-well layer 6111 to the second sub-well layer 6112 is 1:2.

[0102] Optionally, the thickness ratio of the first sub-well layer 6111 to the thickness of the second sub-well layer 6112 in at least one well layer is 1:2. Optionally, the thickness ratio of the first sub-well layer 6111 closest to the first semiconductor layer 400 to the thickness of the second sub-well layer 6112 is 1:2. With this thickness ratio, lattice mismatch can be more effectively mitigated, and sufficient recombination space for electrons and holes can be ensured.

[0103] In one embodiment, reference is made to Figure 3 In all well layers, the thickness ratio of the first sub-well layer 6111 to the second sub-well layer 6112 is 1:2. Controlling the same thickness ratio can reduce the difficulty of the process and also help improve the wavelength uniformity of the active layer radiation, achieving more consistent light emission characteristics, thereby improving the reliability and yield of the device.

[0104] In one embodiment, reference is made to Figure 4In all the well layers, the ratio of the thickness of the first sub-well layer 6111 to the second sub-well layer 6112 gradually decreases in the direction from the first semiconductor layer 400 to the second semiconductor layer 900. That is, in the direction from the first semiconductor layer 400 to the second semiconductor layer 900, the thickness of the first sub-well layer 6111 gradually decreases, and the thickness of the second sub-well layer 6112 gradually increases. The ratio of the thickness of the first sub-well layer 6111 to the second sub-well layer 6112 in the well layer adjacent to the first semiconductor layer 400 is 1:1, and gradually changes to 1:1.5, 1:2, 1:2.5, 1:3, 1:4, and the like in the subsequent well layers. In this way, the gradual change in the indium content near the first semiconductor layer can alleviate the lattice mismatch, and since the electron mobility is usually much higher than the hole mobility, the light-emitting region of the light-emitting diode is mainly near the active region on the side of the second semiconductor layer, so by designing the second sub-well layer 6112 with a constant indium content to gradually increase in thickness as it gradually approaches the main light-emitting region, sufficient electron-hole recombination space can be ensured, thereby ensuring the light-emitting intensity and being conducive to improving the light-emitting efficiency of the light-emitting diode.

[0105] In an embodiment, referring to Figure 5 In the well layers arranged closely near the first semiconductor layer 400, the first sub-well layer 6111 and the second sub-well layer 6112 adjacent to each other are included. In this embodiment, the active layer 600 includes a first sequence 601 and a second sequence 602 formed above the first sequence 601, the first sequence 601 includes periodically and repeatedly stacked first well layers 6011 and first barrier layers 6012, and the second sequence 602 includes periodically and repeatedly stacked second well layers 6021 and second barrier layers 6022; the first well layers 6011 and the second well layers 6021 are layers of In-containing nitride material; the first well layers 6011 include the first sub-well layer 6111 and the second sub-well layer 6112 adjacent to each other; the first sub-well layer 6111 is close to the first semiconductor layer 400; in the thickness direction of the active layer 600, the indium content of the first sub-well layer 6111 increases from a first content to a second content, and the indium content of the second sub-well layer 6112 is a constant second content. The second well layer 6021 includes a third sub-well layer 6113, and the indium content of the third sub-well layer is a constant second content. In this embodiment, the third sub-well layer 6113 is the second well layer 6021. The third sub-well layer 6113 is an Al a3 In b3 Ga c3N layer, wherein, 0 < a3 < 0.05, 0.25 ≤ b3 ≤ 0.28, 0 ≤ c3 ≤ 1. By designing the active layer to include a first sequence of graded-indium-content layer and constant-indium-content layer and a second sequence of only constant-indium-content layer, and the first sequence is closer to the first semiconductor layer than the second sequence. Thus, by setting the graded-indium-content in the first sequence close to the first semiconductor layer, it is beneficial to alleviate the large lattice mismatch between the barrier layer and the high-indium-component well layer, to relieve the structure stress and reduce the internal polarization electric field, to improve the radiation recombination efficiency and the quality of the crystal, while reducing the indium cluster and indium precipitation, to improve the light-emitting uniformity and to improve the efficiency Droop effect. Secondly, it is able to reduce the potential barrier height of the hole injection from the second semiconductor layer to the first semiconductor layer and to reduce the energy barrier of the electron injection from the first semiconductor layer to the active layer, to improve the uneven distribution of the carriers as a whole, to further improve the radiation recombination efficiency of the active region, to optimize the internal quantum efficiency of the light-emitting diode, and to improve the light-emitting efficiency. At the same time, since the light-emitting region of the light-emitting diode is mainly close to the active region on the side of the second semiconductor layer, by designing the second sequence including the constant-indium-content layer to be closer to the second semiconductor layer, the constant-indium-content layer is located in the main light-emitting region, so as to further improve the light-emitting efficiency of the light-emitting diode.

[0106] Optionally, with reference to Figure 2 , in order to release the stress between the N-type semiconductor layer and the active layer 600, a superlattice layer 500 is further arranged between the first semiconductor layer 400 and the active layer 600, and the superlattice layer 500 is formed by repeatedly stacking barrier layers and well layers. In the embodiment, the superlattice layer 500 includes a repeated stack of InGaN / GaN, and the stack period is 3-8. Optionally, a V-shaped pit 603 extends from the superlattice layer 500 to the active layer 600, and the V-shaped pit 603 originates from the superlattice layer 500 and extends upward to the active layer 600 or to the side of the second semiconductor layer 900 close to the active layer 600. Optionally, the superlattice layer 500 in the embodiment can further include a first superlattice layer 501 and a second superlattice layer 502. The repetition period of the barrier layer and the well layer in the first superlattice layer 501 is 3-6, the repetition period of the barrier layer and the well layer in the second superlattice layer 502 is 3-6, and the repetition period of the first superlattice layer 501 is smaller than that of the second superlattice layer 502. The first superlattice layer 501 and the second superlattice layer 502 are both a repeated stack of InGaN / GaN.

[0107] With reference to Figure 1 or Figure 2, the second semiconductor layer 900 is arranged above the active layer 600, the second semiconductor layer 900 is a P-type semiconductor layer, the P-type semiconductor layer can provide holes by P-type impurities, the P-type impurities can be Mg, Zn, Ca, Sr and Ba. In the embodiment, the P-type impurities of the P-type semiconductor layer are Mg, and the material of the P-type semiconductor layer is P-GaN.

[0108] Optionally, referring to Figure 2 , in order to prevent electron overflow, an electron blocking layer 700 is further arranged between the second semiconductor layer 900 and the active layer 600, the electron blocking layer 700 can be AlGaN, repeated stacking of AlGaN / InGaN or repeated stacking of AlGaN / GaN or an AlN layer, and can be partially doped with Mg or fully doped with Mg or undoped. In the embodiment, the electron blocking layer 700 is P-type AlGaN, which can effectively block the leakage of electrons from the active layer 600, reduce electron overflow, and improve the recombination rate of electrons and holes. Optionally, the V-shaped pits 603 extend into the electron blocking layer 700.

[0109] Optionally, referring to Figure 2 , a low-temperature gallium nitride layer 800 can be further arranged between the electron blocking layer 700 and the second semiconductor layer 900. Since high-temperature growth of the GaN layer can cause the wafer warpage to become larger, resulting in uneven wavelength distribution of the grown GaN, the low-temperature growth of GaN in the embodiment can reduce the wafer warpage and improve the luminous brightness of the LED.

[0110] Optionally, the light-emitting diode further comprises a first electrode and a second electrode, the first electrode is in electrical connection with the first semiconductor layer 400, and the second electrode is formed on the second semiconductor layer 900 and is in electrical connection with the second semiconductor layer 900. The epitaxial structure, the first electrode and the second electrode are only basic constituent units of the light-emitting diode, and on this basis, the light-emitting diode can further comprise other functional structure layers which have an optimization effect on the performance of the light-emitting diode, which will not be described here in detail.

[0111] Optionally, the active layer 600 of the light-emitting diode of the embodiment has an emission wavelength between 500 nm and 550 nm, and the active layer can radiate green light. Optionally, the side length of the light-emitting diode is less than or equal to 100 μm. Optionally, the current density of the light-emitting diode is greater than or equal to 20 A / cm 2 . Under the working condition of high current density, especially in the light-emitting diode with a size less than or equal to 100 μm and an emission wavelength in the range of 500 nm to 550 nm, the technical problem involved in the present application is particularly prominent, and the optimization demand for the radiation recombination efficiency of the epitaxial structure of the light-emitting diode will be further improved.

[0112] The light emitting diode with the first well layer containing the gradual change of indium in the embodiment 1 of the present application is tested and compared with the light emitting diode without the gradual change of indium in the control example. The test results of the hole concentration, the radiative recombination efficiency and the polarization electric field intensity of the above two light emitting diodes are shown in the following tables. Figures 9-11 In the Figure 9 , the hole concentration of the light emitting diode in the embodiment of the present application is increased. In the Figure 10 , the radiative recombination rate of the light emitting diode in the embodiment of the present application is increased. In the Figure 11 , the polarization electric field intensity of the light emitting diode in the embodiment of the present application is decreased.

[0113] Referring to Figure 12 , Figure 12 is the transmission electron microscope (TEM) imaging diagram of the active layer in the embodiment of the present application, which is shown in the following figure. Figure 12 It can be seen that the well layer of the active layer contains the color uniform part (the color is pure black) and the color transition part (the color is transitioned from black to gray), wherein the color uniform part is the second sub-well layer 6112, and the color transition part is the first sub-well layer 6111.

[0114] Embodiment 2

[0115] The embodiment provides a light emitting device, which comprises a light emitting source. The light emitting source is the light emitting diode in the above embodiment 1. The light emitting device further comprises a circuit substrate, and at least one light emitting diode is fixed to the circuit substrate.

[0116] Since the light emitting device in the embodiment comprises the above light emitting diode, the recombination probability of the electron and the hole of the light emitting source in the light emitting device in the embodiment is higher, and the light emitting device has better quantum efficiency.

[0117] The above embodiments only exemplarily illustrate the principles and effects of the present application, and are not used to limit the present application. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes completed by those skilled in the art without departing from the spirit and technical thought of the present application should be covered by the claims of the present application.

Claims

1. A light emitting diode, characterized by, The light emitting diode comprises at least an epitaxial structure, the epitaxial structure comprises at least a first semiconductor layer, an active layer and a second semiconductor layer stacked in sequence, wherein: The active layer comprises M periodically stacked well layers and barrier layers, the well layers are In-containing nitride material layers; At least N first well layers are included in the M well layers, M and N are positive integers and M≥N≥1, each of the first well layers comprises adjacent first sub-well layers and second sub-well layers, the first sub-well layers are close to the first semiconductor layer, the molar content of indium in the first sub-well layers increases from a first content to a second content along the thickness direction of the active layer, and the molar content of indium in the second sub-well layers is the second content.

2. The light emitting diode of claim 1, wherein, The first well layer close to the first semiconductor layer is the first well layer.

3. The light emitting diode of claim 1, wherein, The first content is 0% to 10%, and the second content is 25% to 28%.

4. The light emitting diode of claim 1, wherein, The thickness of the first sub-well layer is less than or equal to the thickness of the second sub-well layer.

5. The light emitting diode of claim 1, wherein, When N≥2, the thickness ratio of the first sub-well layer to the second sub-well layer is the same.

6. The light emitting diode of claim 1, wherein, When N≥2, the thickness ratio of the first sub-well layer to the second sub-well layer gradually decreases along the direction from the first semiconductor layer to the second semiconductor layer.

7. The light emitting diode of claim 1, wherein, When N≥2, the thickness ratio of the first sub-well layer to the second sub-well layer in at least one of the well layers is 1:

2.

8. The light emitting diode of claim 1, wherein, More than half of the well layers comprise the first sub-well layers and the second sub-well layers.

9. The light emitting diode of claim 1, wherein, The active layer further comprises second well layers, and the molar content of indium in the second well layers is the second content.

10. The light emitting diode of claim 1, wherein, The thickness ratio of the well layers to the barrier layers is between 1:4 and 1:

5.

11. The light emitting diode of claim 1, wherein, The thickness of the barrier layer is not more than 12. The light emitting diode of claim 1, wherein, the well layer is Al x1 In y1 Ga z1 N layer, wherein 0 < x1 < 0.05, y1 < 0.28, 0 < z1 < 1, the barrier layer is Al x2 In y2 Ga z2 N layer, wherein 0 < x2 < 1, 0 < y2 < 1, 0 < z2 < 1.

13. The light emitting diode of claim 1, wherein, A V-shaped pit is formed in the epitaxial structure, and the V-shaped pit extends from the side of the first semiconductor layer close to the active layer to the active layer.

14. A light emitting diode, comprising: The light emitting diode comprises at least an epitaxial structure, the epitaxial structure comprises at least a first semiconductor layer, an active layer and a second semiconductor layer stacked in sequence, wherein: The active layer comprises a plurality of periodically stacked well layers and barrier layers, and along the direction from the first semiconductor layer to the second semiconductor layer, the active layer comprises a first sequence and a second sequence formed above the first sequence, the first sequence comprises periodically stacked first well layers and first barrier layers, and the second sequence comprises periodically stacked second well layers and second barrier layers; the first well layers and the second well layers are In-containing nitride material layers; The first well layers comprise adjacent first sub-well layers and second sub-well layers, the first sub-well layers are close to the first semiconductor layer, the molar content of indium in the first sub-well layers increases from a first content to a second content along the thickness direction of the active layer, and the molar content of indium in the second sub-well layers is the second content. The second well layers comprise third sub-well layers, and the molar content of indium in the third sub-well layers is the second content.

15. The light emitting diode of claim 14, wherein, The first content is 0% to 10%, and the second content is 25% to 28%.

16. The light emitting diode of claim 14, wherein, The thickness of the first sub-well layer is less than or equal to the thickness of the second sub-well layer.

17. The light emitting diode of claim 14, wherein, The thickness ratio of the first sub-well layer to the second sub-well layer is 1:

2.

18. The light emitting diode of claim 14, wherein, The repeating period of the well layer and the barrier layer is between 2 and 20, the repeating period of the first well layer and the first barrier layer is between 1 and 20, and the repeating period of the second well layer and the second barrier layer is between 1 and 5.

19. The light emitting diode of claim 14, wherein, the first sub-well layer is Al a1 In b1 Ga c1 N layer, wherein 0 a2 In b2 Ga c2 N layer, wherein 0 a3 In b3 Ga c3 N layer, wherein 0 20. The light emitting diode of claim 14, wherein, A V-shaped pit is formed in the epitaxial structure, and the V-shaped pit extends from the side of the first semiconductor layer close to the active layer to the active layer.

21. A light emitting device comprising: A light emitting source is included, and the light emitting source is a light emitting diode as claimed in claims 1-20.

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