Red-light LED epitaxial structure and preparation method therefor

Abstract

Provided in the present invention are a red-light LED epitaxial structure and a preparation method therefor. The red-light LED epitaxial structure sequentially comprises from bottom to top: a substrate, a first-type semiconductor layer, an active layer and a second-type semiconductor layer, the active layer sequentially comprising a preposed quantum well structure and a main quantum well structure from bottom to top, wherein the preposed quantum well structure is a periodic structure formed by means of alternately growing a preposed well layer and a preposed barrier layer, the preposed well layer contains an Al component, and the Al component of the preposed well layer in a previous period is less than the Al component of the preposed well layer in the next period. In the present application, by means of providing a preposed quantum well structure, the luminous intensity and temperature characteristics of a red-light LED can be improved.

Description

Red LED epitaxial structure and preparation method thereof Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a red light LED epitaxial structure and a preparation method thereof. Background Art

[0002] A light-emitting diode (LED) is a semiconductor solid-state light-emitting device that uses a semiconductor PN junction as the luminescent material to directly convert electricity into light. In recent years, LEDs have gained widespread application due to their low power consumption, long life, compact size, energy conservation, and environmental friendliness. In particular, with the maturation of metal-organic chemical vapor deposition (MOCVD) epitaxial growth technology, red LEDs, such as aluminum gallium indium phosphide (AlGaInP), have rapidly developed and entered large-scale commercialization.

[0003] In light-emitting diodes (LEDs), the carrier concentration within the active layer affects the probability of radiative recombination. Low carrier concentrations also reduce the probability of radiative recombination between electrons and holes, resulting in a decrease in the LED's luminous intensity. Furthermore, the temperature characteristics of LEDs are a key parameter of their performance. At high temperatures, thermal motion within the LED intensifies, leading to increased carrier escape and affecting the probability of radiative recombination.

[0004] Summary of the Invention

[0005] The object of the present invention is to provide a red light LED epitaxial structure and a preparation method thereof, so as to increase the carrier concentration of the active layer and enhance the quantum confinement effect, thereby improving the luminous intensity and temperature characteristics of the red light LED.

[0006] In order to achieve the above-mentioned objectives and other related objectives, the present invention provides a red light LED epitaxial structure, which comprises, from bottom to top, a substrate, a first-type semiconductor layer, an active layer, and a second-type semiconductor layer. The active layer comprises, from bottom to top, a pre-quantum well structure and a main quantum well structure. The pre-quantum well structure is a periodic structure formed by alternating growth of a pre-well layer and a pre-barrier layer. The pre-well layer contains an Al component, and the Al component of the pre-well layer in the previous period is less than the Al component of the pre-well layer in the next period.

[0007] Optionally, in the red LED epitaxial structure, the number of periods of the pre-quantum well structure is 1 to 10.

[0008] Optionally, in the red LED epitaxial structure, the material of the front well layer includes (Al xi Ga 1-xi ) y In 1-yP, and 0≤xi≤0.3, 0.3≤y≤0.7; the material of the front barrier layer includes (Al m Ga 1-m ) n In 1-n P, and 0.3≤m≤0.8, 0.3≤n≤0.7.

[0009] Optionally, in the red LED epitaxial structure, in the pre-quantum well structure, the thickness of the pre-well layer in the previous period is greater than the thickness of the pre-well layer in the next period.

[0010] Optionally, in the red light LED epitaxial structure, the total thickness of the pre-quantum well structure is 3nm~120nm, the single-period thickness of the pre-quantum well structure is 3nm~12nm, and the single-period thickness of the pre-well layer and the pre-barrier layer are both 1.5nm~10.5nm.

[0011] Optionally, in the red light LED epitaxial structure, in each period of the front quantum well structure, the Al component of the front well layer is a fixed component or a gradient component, and when the Al component of the front well layer is a gradient component, the In component of the front well layer gradually increases along the direction from the first type semiconductor layer to the second type semiconductor layer.

[0012] Optionally, in the red LED epitaxial structure, in the pre-quantum well structure, the energy band of the pre-well layer closest to the main quantum well structure is lower than or equal to the energy band of the main quantum well structure.

[0013] Optionally, in the red LED epitaxial structure, the active layer further includes a post-quantum well structure located on the main quantum well structure, and the post-quantum well structure is a periodic structure formed by alternating growth of post-well layers and post-barrier layers.

[0014] Optionally, in the red LED epitaxial structure, the period number of the post-quantum well structure is 1 to 10.

[0015] Optionally, in the red LED epitaxial structure, the material of the rear well layer includes (Al z Ga 1-z ) w In 1-w P, and 0≤z≤0.30, 0.3≤w≤0.7; the material of the post-barrier layer includes (Al jk Ga 1-jk ) d In 1-d P, and 0.3≤jk≤1, 0.3≤d≤0.7.

[0016] Optionally, in the red LED epitaxial structure, in the rear quantum well structure, the Al composition of the rear barrier layer in the previous period is less than or equal to the Al composition of the rear barrier layer in the next period.

[0017] Optionally, in the red LED epitaxial structure, in the post-quantum well structure, the thickness of the post-barrier layer in the previous period is less than or equal to the thickness of the post-barrier layer in the next period.

[0018] Optionally, in the red light LED epitaxial structure, the total thickness of the post-quantum well structure is 3nm to 120nm, the single-period thickness of the post-quantum well structure is 3nm to 12nm, and the single-period thickness of the post-well layer and the post-barrier layer are both 1.5nm to 10.5nm.

[0019] Optionally, in the red light LED epitaxial structure, in each period of the post-quantum well structure, the Al component of the post-barrier layer is a fixed component or a gradient component, and when the Al component of the post-barrier layer is a gradient component, the Al component of the post-barrier layer gradually increases in the direction from the first-type semiconductor layer to the second-type semiconductor layer.

[0020] Optionally, in the red light LED epitaxial structure, the main quantum well structure is a periodic structure formed by alternating growth of a main well layer and a main barrier layer, and the material, thickness and composition of the front barrier layer are the same as those of the main barrier layer, and the material, thickness and composition of the rear well layer are the same as those of the main well layer.

[0021] Optionally, in the red light LED epitaxial structure, the total thickness of the main quantum well structure is 15nm to 420nm, the single-period thickness of the main quantum well structure is 3nm to 12nm, and the single-period thickness of the main well layer and the main barrier layer are both 1.5nm to 10.5nm.

[0022] Optionally, in the red LED epitaxial structure, the red LED epitaxial structure further includes a bottom buffer layer and an etching stop layer stacked in sequence, the bottom buffer layer is located on the substrate, and the etching stop layer is located between the bottom buffer layer and the first-type semiconductor layer.

[0023] Optionally, in the red light LED epitaxial structure, the first-type semiconductor layer includes, from bottom to top, a first-type ohmic contact layer, a first-type window layer, a first-type confinement layer, and a first barrier layer.

[0024] Optionally, in the red LED epitaxial structure, the second-type semiconductor layer includes, from bottom to top, a second blocking layer, a second-type confinement layer, a second-type current spreading layer, and a second-type ohmic contact layer.

[0025] In order to achieve the above-mentioned and other related objects, the present invention further provides a method for preparing a red LED epitaxial structure, comprising the following steps:

[0026] providing a substrate;

[0027] A first-type semiconductor layer and an active layer are sequentially grown on the substrate, wherein the active layer comprises a pre-quantum well structure and a main quantum well structure from bottom to top, wherein the pre-quantum well structure is a periodic structure formed by alternating growth of a pre-well layer and a pre-barrier layer, wherein the pre-well layer contains an Al component, and the Al component of the pre-well layer in a previous period is less than the Al component of the pre-well layer in a subsequent period;

[0028] A second-type semiconductor layer is grown on the active layer.

[0029] Optionally, in the method for preparing the red LED epitaxial structure, the number of periods of the pre-quantum well structure is 1 to 10.

[0030] Optionally, in the method for preparing the red LED epitaxial structure, the material of the front well layer includes (Al xi Ga 1-xi ) y In 1-y P, and 0≤xi≤0.3, 0.3≤y≤0.7; the material of the front barrier layer includes (Al m Ga 1-m ) n In 1-n P, and 0.3≤m≤0.8, 0.3≤n≤0.7.

[0031] Optionally, in the method for preparing the red LED epitaxial structure, in the pre-quantum well structure, the thickness of the pre-well layer in the previous period is greater than the thickness of the pre-well layer in the next period.

[0032] Optionally, in the preparation method of the red light LED epitaxial structure, the total thickness of the pre-quantum well structure is 3nm~120nm, the single-period thickness of the pre-quantum well structure is 3nm~12nm, and the single-period thickness of the pre-well layer and the pre-barrier layer are both 1.5nm~10.5nm.

[0033] Optionally, in the preparation method of the red light LED epitaxial structure, in each period of the pre-quantum well structure, the Al component of the pre-well layer is a fixed component or a gradient component, and when the Al component of the pre-well layer is a gradient component, the In component of the pre-well layer gradually increases along the direction from the first-type semiconductor layer to the second-type semiconductor layer.

[0034] Optionally, in the method for preparing the red LED epitaxial structure, in the pre-quantum well structure, the energy band of the pre-well layer closest to the main quantum well structure is lower than or equal to the energy band of the main quantum well structure.

[0035] Optionally, in the method for preparing the red light LED epitaxial structure, the active layer further includes a post-quantum well structure located on the main quantum well structure, and the post-quantum well structure is a periodic structure formed by alternating growth of post-well layers and post-barrier layers.

[0036] Optionally, in the method for preparing the red LED epitaxial structure, the period number of the post-quantum well structure is 1 to 10.

[0037] Optionally, in the method for preparing the red LED epitaxial structure, the material of the rear well layer includes (Al z Ga 1-z ) w In 1-w P, and 0≤z≤0.30, 0.3≤w≤0.7; the material of the post-barrier layer includes (Al jk Ga 1-jk ) d In 1-d P, and 0.3≤jk≤1, 0.3≤d≤0.7.

[0038] Optionally, in the method for preparing the red LED epitaxial structure, in the post-quantum well structure, the Al composition of the post-barrier layer in the previous period is less than or equal to the Al composition of the post-barrier layer in the next period.

[0039] Optionally, in the method for preparing the red LED epitaxial structure, in the post-quantum well structure, the thickness of the post-barrier layer in the previous period is less than or equal to the thickness of the post-barrier layer in the next period.

[0040] Optionally, in the preparation method of the red light LED epitaxial structure, the total thickness of the post-quantum well structure is 3nm~120nm, the single-period thickness of the post-quantum well structure is 3nm~12nm, and the single-period thickness of the post-well layer and the post-barrier layer are both 1.5nm~10.5nm.

[0041] Optionally, in the preparation method of the red light LED epitaxial structure, in each period of the post-quantum well structure, the Al component of the post-barrier layer is a fixed component or a gradient component, and when the Al component of the post-barrier layer is a gradient component, the Al component of the post-barrier layer gradually increases along the direction from the first-type semiconductor layer to the second-type semiconductor layer.

[0042] Optionally, in the preparation method of the red light LED epitaxial structure, the main quantum well structure is a periodic structure formed by alternating growth of a main well layer and a main barrier layer, and the material, thickness and composition of the front barrier layer are the same as those of the main barrier layer, and the material, thickness and composition of the rear well layer are the same as those of the main well layer.

[0043] Optionally, in the preparation method of the red light LED epitaxial structure, the total thickness of the main quantum well structure is 15nm~420nm, the single-period thickness of the main quantum well structure is 3nm~12nm, and the single-period thickness of the main well layer and the main barrier layer are both 1.5nm~10.5nm.

[0044] Optionally, in the preparation method of the red light LED epitaxial structure, the preparation method also includes: growing a bottom buffer layer and a corrosion stop layer between the substrate and the first type semiconductor layer, the bottom buffer layer is located on the substrate, and the corrosion stop layer is located between the bottom buffer layer and the first type semiconductor layer.

[0045] Optionally, in the method for preparing the red LED epitaxial structure, the first-type semiconductor layer includes, from bottom to top, a first-type ohmic contact layer, a first-type window layer, a first-type confinement layer, and a first barrier layer.

[0046] Optionally, in the method for preparing the red LED epitaxial structure, the second-type semiconductor layer includes, from bottom to top, a second blocking layer, a second-type confinement layer, a second-type current spreading layer, and a second-type ohmic contact layer.

[0047] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0048] In the red light LED epitaxial structure provided by the present invention, the active layer includes a pre-quantum well structure and a main quantum well structure. In the pre-quantum well structure, the Al component of the pre-well layer of the previous period is less than the Al component of the pre-well layer of the next period, so as to increase the carrier concentration, improve the radiative recombination probability of the carriers, and improve the luminous intensity. It can also limit the carrier escape, enhance the quantum confinement effect, and improve the temperature characteristics of the red light LED; at the same time, it ensures that the luminous wavelength of the pre-quantum well structure gradually approaches the luminous wavelength of the main quantum well structure, preventing the luminous wavelength from deviating from the designed range.

[0049] Secondly, in the pre-quantum well structure of the present invention, the thickness of the pre-well layer of the previous cycle is greater than the thickness of the pre-well layer of the next cycle, so that the pre-quantum well of the previous cycle can accommodate more electrons, increase the concentration of carriers in the pre-quantum well, and improve the probability of radiative recombination. At the same time, when the thickness of the pre-well layer decreases, the energy difference between the bound state energy levels increases, and the wavelength of the light emitted by the pre-quantum well will also become shorter, ensuring that the light-emitting wavelength of the pre-quantum well gradually approaches the light-emitting wavelength of the main quantum well structure, preventing the light-emitting wavelength from deviating from the design range.

[0050] Furthermore, the active layer of the present invention may further include a post-quantum well structure, and the post-quantum well structure is a high-potential-barrier quantum well structure, and in the post-quantum well structure, the Al composition of the post-barrier layer of the previous cycle is less than or equal to the Al composition of the post-barrier layer of the next cycle, and / or the thickness of the post-barrier layer of the previous cycle is less than or equal to the thickness of the post-barrier layer of the next cycle. The present invention can form a high potential barrier by having the Al composition of the post-barrier layer of the previous cycle be less than or equal to the Al composition of the post-barrier layer of the next cycle, and the thickness of the post-barrier layer of the previous cycle be less than or equal to the thickness of the post-barrier layer of the next cycle, thereby preventing electrons from migrating to the second-type semiconductor layer, thereby increasing the carrier concentration in the active layer, increasing the probability of radiative recombination, reducing carrier overflow, and improving the temperature characteristics of the red light LED. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] FIG1 is a schematic diagram of a red LED epitaxial structure according to an embodiment of the present invention;

[0052] FIG2 is a schematic diagram of an active layer according to an embodiment of the present invention;

[0053] FIG3 is a schematic diagram of energy bands of an active layer according to an embodiment of the present invention;

[0054] 4 is a flow chart of a method for preparing a red LED epitaxial structure according to an embodiment of the present invention;

[0055] In Figures 1 to 4,

[0056] 10-substrate, 11-bottom buffer layer, 12-etching stop layer, 13-first type ohmic contact layer, 14-first type window layer, 15-first type confinement layer, 16-first barrier layer, 17-active layer, 171-front quantum well structure, 172-main quantum well structure, 173-rear quantum well structure, 18-second barrier layer, 19-second type confinement layer, 20-second type current spreading layer, 21-second type ohmic contact layer. DETAILED DESCRIPTION

[0057] The following is a detailed description of the red LED epitaxial structure and its fabrication method proposed by the present invention, with reference to the accompanying drawings and specific embodiments. The advantages and features of the present invention will become more apparent from the following description. It should be noted that the drawings are highly simplified and not to exact scale, and are intended solely to facilitate and clarify the purpose of illustrating the embodiments of the present invention.

[0058] The inventors have discovered that increasing the carrier concentration within quantum wells significantly impacts the luminous intensity of LEDs. Improving the quantum confinement effect of LEDs can improve the temperature characteristics of LEDs, reducing the drop in luminous intensity at high temperatures and enhancing their performance. Based on this, the present invention provides a red LED epitaxial structure that can enhance both the luminous intensity and temperature characteristics of red LEDs.

[0059] 1 and 2 , the red LED epitaxial structure provided by the present invention may include, from bottom to top, a substrate 10 , a first-type semiconductor layer, an active layer 17 , and a second-type semiconductor layer.

[0060] In this embodiment, the red LED epitaxial structure may further include a bottom buffer layer 11 and a corrosion stop layer 12 stacked in sequence, wherein the bottom buffer layer 11 is located on the substrate 10, and the corrosion stop layer 12 is located between the bottom buffer layer 11 and the first-type semiconductor layer.

[0061] The first-type semiconductor layer is preferably an n-type semiconductor layer, and the first-type semiconductor layer may include, from bottom to top, a first-type ohmic contact layer 13 , a first-type window layer 14 , a first-type confinement layer 15 and a first barrier layer 16 .

[0062] The active layer 17 may include, from bottom to top, a pre-quantum well structure 171 and a main quantum well structure 172. In addition, the active layer 17 may further include a post-quantum well structure 173, and the post-quantum well structure 173 is located on the main quantum well structure 172.

[0063] In this embodiment, the pre-quantum well structure 171 can emit light. The pre-quantum well structure 171 is a periodic structure formed by alternating growth of pre-well layers and pre-barrier layers. One pre-well layer and one pre-barrier layer constitute a pre-quantum well. In this embodiment, the Al composition of the pre-well layer in the previous period is less than the Al composition of the pre-well layer in the next period. The previous period refers to the period closer to the first semiconductor layer in the adjacent period, and the next period refers to the period closer to the second semiconductor layer in the adjacent period. Since the Al component of the pre-well layer of the previous cycle is less than the Al component of the pre-well layer of the next cycle, the energy band of the pre-quantum well of the previous cycle can be made lower than the energy band of the pre-quantum well of the next cycle (see Figure 3), which can increase the carrier concentration, improve the probability of carrier radiation recombination, and improve the luminous intensity. It can also limit carrier escape, enhance the quantum confinement effect, and improve the temperature characteristics of the red light LED; at the same time, the energy band of the pre-well layer closest to the main quantum well structure 172 must be lower than or equal to the energy band of the main quantum well structure 172, ensuring that the emission wavelength of the pre-quantum well gradually approaches the emission wavelength of the main quantum well structure 172, and preventing the emission wavelength from deviating from the design range.

[0064] This embodiment can also enhance the quantum confinement effect and improve the temperature characteristics of the red light LED by adjusting the thickness of the pre-well layer. Specifically, the thickness of the pre-well layer in the previous cycle is greater than the thickness of the pre-well layer in the next cycle. This allows the pre-quantum well in the previous cycle to accommodate more electrons, increases the concentration of carriers in the pre-quantum well, and improves the probability of radiative recombination. At the same time, when the thickness of the pre-well layer decreases, the energy difference between the bound state energy levels increases, and the wavelength of the light emitted by the pre-quantum well also shortens, ensuring that the light emission wavelength of the pre-quantum well gradually approaches the light emission wavelength of the main quantum well structure, preventing the light emission wavelength from deviating from the design range.

[0065] The main quantum well structure 172 is a periodic structure formed by alternating growth of main well layers and main barrier layers. In this embodiment, the main quantum well structure 172 serves as the main light-emitting layer.

[0066] In this embodiment, the post-quantum well structure 173 can also emit light. The post-quantum well structure 173 is a periodic structure formed by the alternating growth of a post-well layer and a post-barrier layer, and one post-well layer and one post-barrier layer constitute a post-quantum well. In the post-quantum well structure 173, the Al composition of the post-barrier layer in the previous period is less than or equal to the Al composition of the post-barrier layer in the next period, and / or the thickness of the post-barrier layer in the previous period is less than or equal to the thickness of the post-barrier layer in the next period. The previous period refers to the period closer to the first semiconductor layer in the adjacent periods, and the next period refers to the period closer to the second semiconductor layer in the adjacent periods. Since the Al composition and thickness of the post-barrier layer in the previous period are less than or equal to the Al composition and thickness of the post-barrier layer in the next period, electrons can be blocked from migrating to the second-type semiconductor layer, thereby increasing the carrier concentration in the active layer 17, increasing the probability of radiative recombination, reducing carrier overflow, and improving the temperature characteristics of the red light LED.

[0067] The second-type semiconductor layer may include, from bottom to top, a second blocking layer 18, a second-type confinement layer 19, a second-type current spreading layer 20, and a second-type ohmic contact layer 21. In this embodiment, the first-type semiconductor layer and the second-type semiconductor layer have opposite polarities. For example, if the first-type semiconductor layer is an n-type semiconductor layer, the corresponding second-type semiconductor layer is a p-type semiconductor layer.

[0068] 4 , the above-mentioned method for preparing the red LED epitaxial structure may include the following steps:

[0069] Step S1: providing a substrate 10;

[0070] Step S2: sequentially growing a first-type semiconductor layer and an active layer 17 on the substrate 10, wherein the active layer 17 includes, from bottom to top, a pre-quantum well structure 171 and a main quantum well structure 172, wherein the pre-quantum well structure 171 is a periodic structure formed by alternating growth of a pre-well layer and a pre-barrier layer, wherein the pre-well layer contains an Al component, and the Al component of the pre-well layer in the previous period is less than the Al component of the pre-well layer in the next period;

[0071] Step S3 : growing a second-type semiconductor layer on the active layer 17 .

[0072] In this embodiment, the preparation process for the red LED epitaxial structure can be any one of, but not limited to, a metal organic chemical vapor deposition (MOCVD) process, a molecular beam epitaxy (MBE) process, a hydrogenated vapor phase epitaxy (HVPE) process, a plasma-assisted chemical vapor deposition (PECVD) process, a sputtering process, and an ultra-high vacuum chemical vapor deposition (UHVCVD) process. Furthermore, the preparation process for the red LED epitaxial structure is preferably an MOCVD process. The following specific embodiments use the MOCVD process as an example for illustration.

[0073] Step S1 is performed to provide a substrate 10. The substrate 10 is preferably a GaAs (gallium arsenide) substrate, but is not limited thereto. For example, the substrate 10 may also be a Si (silicon) substrate.

[0074] The red LED epitaxial structure of this embodiment may further include a bottom buffer layer 11 and an etching stop layer 12 stacked in sequence. The bottom buffer layer 11 is located on the substrate 10, and the first-type semiconductor layer is located on the etching stop layer 12. Therefore, before performing step S2, the method for preparing the red LED epitaxial structure further includes: sequentially growing the bottom buffer layer 11 and the etching stop layer 12 on the substrate 10.

[0075] The bottom buffer layer 11 can eliminate the influence of the surface defects of the substrate 10 on the red light LED epitaxial structure to the greatest extent, reduce the defects and dislocations in the red light LED epitaxial structure, and provide a smooth interface for the next growth. The material of the bottom buffer layer 11 is preferably GaAs, but not limited to this. The bottom buffer layer 11 can be doped with a first-type dopant, such as an n-type dopant, which can be at least one of silicon (Si) and tellurium (Te), but not limited to this. Furthermore, the first-type dopant is preferably Si. In this embodiment, the thickness of the bottom buffer layer 11 is preferably 100nm to 400nm, for example, 200nm.

[0076] After growing the bottom buffer layer 11, an etch-stop layer 12 is grown on the bottom buffer layer 11. The material of the etch-stop layer 12 is preferably, but not limited to, GaInP. The etch-stop layer 12 may be doped with a first-type dopant, such as an n-type dopant, which may be at least one of silicon and tellurium, but not limited to these. Furthermore, the first-type dopant is preferably Si. In this embodiment, the thickness of the etch-stop layer 12 is preferably 150 nm to 300 nm, for example, 200 nm.

[0077] Step S2 is performed to grow a first-type semiconductor layer on the substrate 10. When the red LED epitaxial structure further includes a bottom buffer layer 11 and an etching stop layer 12 stacked in sequence, the first-type semiconductor layer is grown on the etching stop layer 12. In this embodiment, the first-type semiconductor layer is preferably an n-type semiconductor layer, and the first-type semiconductor layer may include, from bottom to top, a first-type ohmic contact layer 13, a first-type window layer 14, a first-type confinement layer 15, and a first barrier layer 16. Therefore, after the step of growing the etching stop layer 12, the first-type ohmic contact layer 13, the first-type window layer 14, the first-type confinement layer 15, and the first barrier layer 16 are sequentially grown on the etching stop layer 12.

[0078] A first-type ohmic contact layer 13 is grown on the corrosion stop layer 12. In this embodiment, the first-type ohmic contact layer 13 is preferably an n-type ohmic contact layer. The material of the first-type ohmic contact layer 13 may be AlGaInP or GaAs, but is not limited thereto. Furthermore, the material of the first-type ohmic contact layer 13 is preferably GaAs. The first-type ohmic contact layer 13 may be doped with a first-type dopant, such as an n-type dopant, which may be one of silicon and tellurium, but is not limited thereto. Furthermore, the first-type dopant is preferably Si. In this embodiment, the thickness of the first-type ohmic contact layer 13 is preferably 40 nm to 150 nm, for example, 90 nm.

[0079] After the step of growing the first-type ohmic contact layer 13, the first-type window layer 14 is grown on the first-type ohmic contact layer 13. The main functions of the first-type window layer 14 are first-type current expansion, light extraction and surface roughening. The first-type window layer 14 is preferably an n-type window layer. The material of the first-type window layer 14 is preferably AlGaInP, but not limited to this. The first-type window layer 14 can be doped with a first-type dopant, such as an n-type dopant, which can be at least one of silicon and tellurium, but not limited to this. Furthermore, the first-type dopant is preferably Si. In this embodiment, the thickness of the first-type window layer 14 is preferably 1μm to 5μm, for example, 3μm.

[0080] After growing the first-type window layer 14, a first-type confinement layer 15 is grown on the first-type window layer 14. The first-type confinement layer 15 is preferably an n-type confinement layer. The material of the first-type confinement layer 15 is preferably, but not limited to, AlInP. The first-type confinement layer 15 may be doped with a first-type dopant, such as an n-type dopant, which may be at least one of silicon and tellurium, but not limited to these. Furthermore, the first-type dopant is preferably Si. In this embodiment, the thickness of the first-type confinement layer 15 is preferably 100 nm to 500 nm, for example, 300 nm.

[0081] After growing the first-type confinement layer 15, the first barrier layer 16 is grown on the first-type confinement layer 15. The material of the first barrier layer 16 is preferably, but not limited to, AlGaInP. The first barrier layer 16 is preferably undoped, that is, it is preferably a non-doped structural layer to prevent first-type dopants from entering the active layer 17. In this embodiment, the thickness of the first barrier layer 16 is preferably 5 nm to 30 nm, for example, 20 nm.

[0082] After the step of growing the first barrier layer 16, an active layer 17 is grown on the first barrier layer 16. The active layer 17 includes a pre-quantum well structure 171 and a main quantum well structure 172, and may further include a post-quantum well structure 173. Therefore, after the step of growing the first barrier layer 16, the pre-quantum well structure 171 is grown on the first barrier layer 16.

[0083] The pre-quantum well structure 171 is a periodic structure formed by alternating growth of pre-well layers and pre-barrier layers, and the number of periods is preferably 1 to 10, preferably 6. The specific number of periods needs to be set according to the specific application. The total thickness of all periods of the pre-quantum well structure 171 is preferably 3nm to 120nm; the thickness of a single period of the pre-quantum well structure 171 is preferably 3nm to 12nm. In this embodiment, one pre-well layer and one pre-barrier layer constitute a pre-quantum well.

[0084] The material of the pre-well layer is preferably (Al xi Ga 1-xi ) y In 1-yP, 0≤xi≤0.3, 0.3≤y≤0.7, where i represents the periodic order, and the range of i can be 1 to 10, preferably 6. In this embodiment, the Al composition of the pre-well layer of the previous period is preferably less than the Al composition of the pre-well layer of the next period, so that the energy band of the pre-quantum well of the previous period can be lower than the energy band of the pre-quantum well of the next period, which can increase the carrier concentration, improve the probability of carrier radiative recombination, limit carrier escape, enhance the quantum confinement effect, and improve the temperature characteristics of the red light LED; at the same time, the energy band of the pre-well layer closest to the main quantum well structure 172 must be lower than or equal to the energy band of the main quantum well structure 172, ensuring that the emission wavelength of the pre-quantum well gradually approaches the emission wavelength of the main quantum well structure 172, preventing the emission wavelength from deviating from the designed range. Wherein, the previous period refers to the period closer to the first semiconductor layer in the adjacent period, and the next period refers to the period closer to the second semiconductor layer in the adjacent period. The smaller the i, the closer the period is to the first semiconductor layer, and the larger the i, the closer the period is to the second semiconductor layer. In this embodiment, the Al composition of the pre-well layer in each period can be the same as or different from the Al composition of the pre-well layer in the previous period. For example, the number of periods of the pre-quantum well structure 171 is 6, the Al composition of the pre-well layer in the first period is 0.05, and the Al composition of the pre-well layer in subsequent periods increases by 0.05 until the Al composition of the pre-well layer in the sixth period is 0.30. For another example, the number of periods of the pre-quantum well structure 171 is 3, the Al composition of the pre-well layer in the first period is 0.05, the Al composition of the pre-well layer in the second period increases by 0.03 (i.e., the Al composition of the pre-well layer in the second period is 0.08), and the Al composition of the pre-well layer in the third period increases by 0.05 compared to the Al composition of the pre-well layer in the second period (i.e., the Al composition of the pre-well layer in the third period is 0.13). Furthermore, in each period of the pre-quantum well structure 171, the Al composition of the pre-well layer is a fixed composition or a gradient composition. When the Al composition of the pre-well layer is a gradient composition, the Al composition of the pre-well layer preferably increases gradually along the direction from the first-type semiconductor layer to the second-type semiconductor layer. When the Al composition of the pre-well layer in each period is a gradient composition, the gradient of the Al composition can make the transmission of electrons and holes in the pre-well layer smoother, reduce the recombination and loss of carriers, and improve the electron and hole recombination efficiency and luminous efficiency. Secondly, the gradient of the Al composition can expand the emission wavelength range of the red light LED, enabling it to emit a wider spectrum to meet the needs of different applications.When the Al component of the pre-well layer in each cycle is a fixed component, the growth process can be simplified by fixing the Al component, and the complexity and error in the material growth process can be reduced; secondly, the stability and repeatability of the pre-well layer can be improved by fixing the Al component, making the performance of the red light LED more consistent and reliable; finally, the structure of the red light LED can be simplified by fixing the Al component, the thickness and complexity of the material can be reduced, and the manufacturing cost can be reduced.

[0085] In this embodiment, the thickness of the pre-well layer in a single cycle is preferably 1.5nm to 10.5nm, and the thickness of the pre-well layer in the previous cycle is preferably greater than the thickness of the pre-well layer in the next cycle, so that the pre-quantum well in the previous cycle can accommodate more electrons, increase the carrier concentration of the entire active layer 17, increase the probability of radiative recombination, and improve the luminous intensity and temperature characteristics; at the same time, when the thickness of the pre-well layer gradually decreases, the energy difference between the bound state energy levels increases, and the wavelength of the light emitted by the pre-quantum well will also become shorter, ensuring that the light emission wavelength of the pre-quantum well structure 171 gradually approaches the light emission wavelength of the main quantum structure 172, preventing the light emission wavelength from deviating from the design range. For example, the number of cycles of the pre-quantum well structure 171 is 2, the thickness of the pre-well layer in the first cycle is 10nm, and the thickness of the pre-well layer in the second cycle is 8nm.

[0086] The pre-quantum well structure 171 of this embodiment also emits light, and the length of its emission wavelength will change the band gap width, thereby affecting the radiative recombination probability in the active layer 17. In this embodiment, the emission wavelength of the pre-quantum well structure 171 can be controlled by two methods. One method is to directly change the Al composition of the pre-well layer (i.e., the Al composition of the pre-well layer in the previous cycle is less than the Al composition of the pre-well layer in the next cycle) to adjust the emission wavelength. The other method is to change the emission wavelength by changing the thickness of the pre-well layer (i.e., the thickness of the pre-well layer in the previous cycle is greater than the thickness of the pre-well layer in the next cycle). The two methods can be used in combination, and it is preferred to use a single method to control the emission wavelength of the pre-quantum well structure 171. In this embodiment, since the Al composition and thickness of the pre-well layer are changed, the depth and width of the pre-well layer are changed, thereby affecting the radiative recombination probability of the pre-quantum well structure 171 and the quantum confinement effect.

[0087] In this embodiment, the material of the front barrier layer is preferably (Al m Ga 1-m ) n In 1-n P, and 0.3≤m≤0.8, 0.3≤n≤0.7, for example (Al 0.65 Ga 0.35 ) 0.5 In 0.5The thickness of a single period of the pre-barrier layer is preferably 1.5 nm to 10.5 nm.

[0088] After the step of growing the pre-quantum well structure 171, a main quantum well structure 172 is grown on the pre-quantum well structure 171. The main quantum well structure 172 is a periodic structure formed by alternating growth of main well layers and main barrier layers, and the number of periods is preferably 5 to 35, preferably 25. The total thickness of all periods of the main quantum well structure 172 is preferably 15 nm to 420 nm, and the thickness of a single period of the main quantum well structure 172 is preferably 3 nm to 12 nm. In this embodiment, one main well layer and one main barrier layer constitute one main quantum well.

[0089] The main quantum well structure 172 serves as the main light emitting layer, and the material of the main well layer is preferably (Al t Ga 1-t ) g In 1-g P, where 0≤t≤0.3, 0.3≤g≤0.7. The thickness of the main well layer per cycle is preferably 1.5nm to 10.5nm. In this embodiment, the thickness of the main well layer per cycle is preferably equal to the thickness of the pre-well layer in the last cycle.

[0090] The material of the main barrier layer is preferably (Al u Ga 1-u ) v In 1-v P, where 0.3≤u≤0.8, 0.3≤v≤0.7. The single-period thickness of the main barrier layer is preferably 1.5nm to 10.5nm. In this embodiment, the material, thickness and composition of the main barrier layer are preferably the same as those of the pre-barrier layer. The pre-barrier layer and the main barrier layer having the same material, thickness and composition can achieve better lattice matching, help reduce lattice mismatch and stress problems, and improve the crystallization quality and growth performance of the active layer 17; the pre-barrier layer and the main barrier layer having the same material, thickness and composition can make electrons and holes more smoothly transmitted between the pre-quantum well structure 171 and the main quantum well structure 172, help reduce carrier recombination and loss, and improve carrier diffusion and transmission efficiency; and the pre-barrier layer and the main barrier layer having the same material, thickness and composition can simplify the growth process of the red light LED, reduce the complexity and error in the material growth process, help improve the stability and repeatability of the preparation process, and reduce manufacturing costs.

[0091] After the step of growing the main quantum well structure 172, a post-quantum well structure 173 is grown on the main quantum well structure 172. The post-quantum well structure 173 is a periodic structure formed by alternating growth of a post-well layer and a post-barrier layer. The number of periods is preferably 1 to 10, preferably 6, and the specific number of periods needs to be set according to the specific application. The total thickness of the post-quantum well structure 173 of all periods is preferably 3nm to 120nm, and the thickness of a single period of the post-quantum well structure 173 is preferably 3nm to 12nm. In this embodiment, one post-well layer and one post-barrier layer constitute a post-quantum well.

[0092] The material of the back well layer is preferably (Al z Ga 1-z ) w In 1-w P, and 0≤z≤0.3, 0.3≤w≤0.7, for example, z=0.3, w=0.5. The single-period thickness of the post-well layer is preferably 1.5nm~10.5nm. In this embodiment, the material, thickness and composition of the post-well layer are preferably the same as the material, thickness and composition of the main well layer. The post-well layer and the main well layer having the same material, thickness and composition can achieve better lattice matching, help reduce lattice mismatch and stress problems, improve the crystallization quality and growth performance of the material, and also improve the carrier transport capacity; the post-well layer and the main well layer having the same material, thickness and composition can make electrons and holes more smoothly transmitted between the post-quantum well structure 173 and the main quantum well structure 172, help reduce carrier recombination and loss, and improve carrier diffusion and transport efficiency; the post-well layer and the main well layer having the same material, thickness and composition can simplify the growth process of the red light LED, reduce the complexity and error in the material growth process, help improve the stability and repeatability of the preparation process, and reduce manufacturing costs.

[0093] The material of the rear barrier layer is preferably (Al jk Ga 1-jk ) d In 1-dP, and 0.3≤.jk≤1, 0.3≤d≤0.7, where k represents the periodic order, and the range of k is 1 to 10, preferably 6. In this embodiment, the Al composition of the post-barrier layer in the previous period is preferably less than or equal to the Al composition of the post-barrier layer in the next period. The previous period refers to the period closer to the first semiconductor layer in the adjacent periods, and the next period refers to the period closer to the second semiconductor layer in the adjacent periods. The smaller the k, the closer the period is to the first semiconductor layer, and the larger the k, the closer the period is to the second semiconductor layer. For example, the number of periods of the post-quantum well structure 173 is 6, the Al composition of the post-barrier layer in the first period is 0.70, and the Al composition of the post-barrier layer in the subsequent periods increases by 0.05 successively until the Al composition of the post-barrier layer in the sixth period is 0.95. The Al component of the rear barrier layer in this embodiment represents the height of the potential barrier of the rear barrier layer. As the Al component gradually increases, the potential barrier of the rear barrier layer gradually becomes higher, and the high potential barrier can limit the energy level of the electrons or holes in the active layer 17. When the energy of the potential barrier is high, only electrons or holes with energy lower than the potential barrier can exist in the active layer 17. This energy level restriction allows the electrons or holes in the active layer 17 to form discrete energy levels, which is similar to a two-dimensional energy level structure, and can increase the probability of carrier radiation recombination in the active layer 17; the high potential barrier has a great influence on the electrons or holes in the active layer 17. The movement of electrons or holes has a restrictive effect. In the potential barrier, electrons or holes can only move within the potential barrier and cannot diffuse freely to other areas. This restriction limits the movement of electrons or holes to the size of the barrier, thereby forming a one-dimensional, two-dimensional or three-dimensional restrictive movement, thereby reducing carrier overflow; a high potential barrier can form a localized resonant state, that is, electrons or holes within a specific energy range bounce back and forth in the active layer 17 and form a state similar to a standing wave. These resonant states have a specific energy and wave function distribution in the active layer 17.

[0094] In this embodiment, in each period of the post-quantum well structure 173, the Al composition of the post-barrier layer is a fixed composition or a graded composition. When the Al composition of the post-barrier layer is a graded composition, the Al composition of the post-barrier layer preferably increases gradually along the direction from the first-type semiconductor layer to the second-type semiconductor layer. When the Al composition of the post-barrier layer in each period is a graded composition, the graded Al composition of the post-barrier layer can reduce lattice mismatch and stress problems, and improve the crystallization quality and growth performance of the active layer 17. The graded Al composition of the post-barrier layer can also promote the transmission of carriers (electrons and holes) in the post-barrier layer, reduce carrier recombination and loss, and improve the electron and hole recombination efficiency and luminescence efficiency. When the Al component of the rear barrier layer in each cycle is a fixed component, the fixation of the Al component can improve the structural stability of the rear barrier layer, making it more resistant to high temperature, pressure and corrosion, thereby improving the stability and reliability of the red light LED; the fixation of the Al component can simplify the growth process of the red light LED, reduce the complexity and errors in the material growth process, thereby reducing the preparation cost; the fixation of the Al component can improve the component consistency of the rear barrier layer, make the performance of the red light LED more consistent, and reduce the difference between batches.

[0095] In this embodiment, the thickness of the rear barrier layer per cycle is preferably 1.5 nm to 10.5 nm, and the thickness of the rear barrier layer in the previous cycle is preferably less than or equal to the thickness of the rear barrier layer in the next cycle, thereby forming a high potential barrier, thereby increasing the probability of carrier radiative recombination in the active layer 17, reducing carrier overflow, and improving the temperature characteristics of the red light LED. For example, the rear quantum well structure 173 has two cycles, the thickness of the rear barrier layer in the first cycle is 8 nm, and the thickness of the rear barrier layer in the second cycle is 10 nm.

[0096] In this embodiment, a high potential barrier can be formed by two methods. One method is to change the Al composition of the rear barrier layer (i.e., the Al composition of the rear barrier layer in the previous cycle is less than or equal to the Al composition of the rear barrier layer in the next cycle) to increase the potential barrier and allow more carriers to remain in the active layer 17. The other method is to control the thickness of the rear barrier layer (i.e., the thickness of the rear barrier layer in the previous cycle is less than or equal to the thickness of the rear barrier layer in the next cycle) to allow more carriers to remain in the active layer 17. The two methods can be used in combination, but it is preferred to use a single method to form a high potential barrier.

[0097] Step S3 is performed: growing a second-type semiconductor layer on the active layer 17. The second-type semiconductor layer may include, from bottom to top, a second barrier layer 18, a second-type confinement layer 19, a second-type current spreading layer 20, and a second-type ohmic contact layer 21. Therefore, after the step of growing the active layer 17, the second barrier layer 18 is grown on the active layer 17.

[0098] The material of the second barrier layer 18 is preferably, but not limited to, AlGaInP. The second barrier layer 18 is preferably undoped, that is, the second barrier layer 18 is preferably a non-doped structural layer to prevent the second-type dopant from entering the active layer 17. The thickness of the second barrier layer 18 is preferably 100 to 300 nm, for example, 200 nm.

[0099] After growing the second barrier layer 18, a second-type confinement layer 19 is grown on the second barrier layer 18. The second-type confinement layer 19 is preferably a p-type confinement layer, and is used to provide holes. In this embodiment, the first-type confinement layer 15 and the second-type confinement layer 19 serve two main functions as confinement layers: first, they prevent minority carriers from overflowing the active layer 17, thereby improving the recombination luminescence efficiency; second, they serve as an important window, allowing photons emitted by the active layer 17 to easily pass through the confinement layers, thereby improving the luminous efficiency of the red LED.

[0100] The material of the second-type confinement layer 19 is preferably, but not limited to, AlInP. The second-type confinement layer 19 is doped with a second-type dopant, such as a p-type dopant, which may be at least one of magnesium (Mg) and zinc (Zn), but is not limited thereto. Furthermore, the second-type dopant is preferably Mg. The thickness of the second-type confinement layer 19 is preferably 150 nm to 500 nm, for example, 300 nm.

[0101] After growing the second-type confinement layer 19, a second-type current spreading layer 20 is grown on the second-type confinement layer 19. The second-type current spreading layer 20 is preferably a p-type current spreading layer and functions to spread current, preventing uneven current distribution across the red LED. The material of the second-type current spreading layer 20 is preferably, but not limited to, GaP. The dopant source of the second-type current spreading layer 20 is preferably, but not limited to, Mg. The thickness of the second-type current spreading layer 20 is preferably between 300 nm and 3000 nm, for example, 1500 nm.

[0102] After growing the second-type current spreading layer 20, a second-type ohmic contact layer 21 is grown on the second-type current spreading layer 20. The second-type ohmic contact layer 21 is used to form an ohmic contact with the metal electrode. The material of the second-type ohmic contact layer 21 is preferably GaP, but is not limited to this. The second-type ohmic contact layer 21 may be doped with carbon. The thickness of the second-type ohmic contact layer 21 is preferably 100 nm to 250 nm, for example, 200 nm.

[0103] In summary, it can be seen that the active layer of the present invention adopts the front quantum well structure, the main quantum well structure and the rear quantum well structure to effectively increase the carrier concentration in the active layer and enhance the quantum confinement effect.

[0104] The pre-quantum well structure of the present invention can store electrons, increase carrier concentration, improve the radiative recombination probability of carriers, and thus improve the luminous intensity. At the same time, it can also limit carrier escape, enhance the quantum confinement effect, and improve the temperature characteristics of red light LEDs.

[0105] The post-quantum well structure of the present invention is a high-potential-barrier quantum well structure that can block electron migration to the second-type semiconductor layer, increase the carrier concentration in the active layer, increase the probability of radiative recombination, and thus improve the luminous intensity; at the same time, it can also reduce carrier escape and improve the temperature characteristics of the red light LED.

[0106] In addition, it is understood that although the present invention has been disclosed above with reference to preferred embodiments, the above embodiments are not intended to limit the present invention. For any person skilled in the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or to modify it into an equivalent embodiment with equivalent changes. Therefore, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of protection of the technical solution of the present invention.

[0107] It should also be understood that the present invention is not limited to the specific methods, compounds, materials, manufacturing techniques, uses, and applications described herein, which may vary. It should also be understood that the terms described herein are used only to describe specific embodiments and are not intended to limit the scope of the present invention. It should be noted that the singular forms "a," "an," and "the" used herein and in the appended claims include plural references unless the context clearly indicates otherwise. Thus, for example, a reference to "a step" means a reference to one or more steps, and may include secondary steps. All conjunctions used should be understood in their broadest sense. Thus, the word "or" should be understood to have the definition of a logical "or," not a logical "exclusive or," unless the context clearly indicates otherwise. Structures described herein will be understood to also refer to functional equivalents of that structure. Language that can be interpreted as approximating should be so interpreted unless the context clearly indicates otherwise.

Claims

1. A red light LED epitaxial structure, characterized in that: The invention comprises, from bottom to top, a substrate, a first-type semiconductor layer, an active layer and a second-type semiconductor layer. The active layer comprises, from bottom to top, a pre-quantum well structure and a main quantum well structure. The pre-quantum well structure is a periodic structure formed by alternating growth of a pre-well layer and a pre-barrier layer. The pre-well layer contains an Al component, and the Al component of the pre-well layer in the previous period is less than the Al component of the pre-well layer in the next period.

2. The red LED epitaxial structure according to claim 1, characterized in that: The number of periods of the front quantum well structure is 1-10.

3. The red LED epitaxial structure according to claim 1, characterized in that: The material of the front well layer includes (Al xi Ga 1-xi ) y In 1-y P, and 0≤xi≤0.3, 0.3≤y≤0.7; the material of the front barrier layer includes (Al m Ga 1-m ) n In 1-n P, and 0.3≤m≤0.8, 0.3≤n≤0.

7.

4. The red LED epitaxial structure according to claim 1, characterized in that: In the pre-quantum well structure, the thickness of the pre-well layer in a previous period is greater than the thickness of the pre-well layer in a subsequent period.

5. The red LED epitaxial structure according to claim 1, characterized in that: The total thickness of the pre-quantum well structure is 3nm-120nm, the single-period thickness of the pre-quantum well structure is 3nm-12nm, and the single-period thickness of the pre-well layer and the pre-barrier layer are both 1.5nm-10.5nm.

6. The red LED epitaxial structure according to claim 1, characterized in that: In each period of the pre-quantum well structure, the Al component of the pre-well layer is a fixed component or a gradient component, and when the Al component of the pre-well layer is a gradient component, the In component of the pre-well layer gradually increases along the direction from the first-type semiconductor layer to the second-type semiconductor layer.

7. The red LED epitaxial structure according to claim 1, characterized in that: In the pre-quantum well structure, an energy band of a pre-well layer closest to the main quantum well structure is lower than or equal to an energy band of the main quantum well structure.

8. The red LED epitaxial structure according to claim 1, characterized in that: The active layer further includes a post-quantum well structure located on the main quantum well structure, and the post-quantum well structure is a periodic structure formed by alternating growth of a post-well layer and a post-barrier layer.

9. The red LED epitaxial structure according to claim 8, characterized in that: The period number of the post-quantum well structure is 1-10.

10. The red LED epitaxial structure according to claim 8, characterized in that: The material of the post-well layer includes (Al z Ga 1-z ) w In 1-w P, and 0≤z≤0.30, 0.3≤w≤0.7; the material of the post-barrier layer includes (Al jk Ga 1-jk ) d In 1-d P, and 0.3≤jk≤1, 0.3≤d≤0.

7.

11. The red LED epitaxial structure according to claim 8, characterized in that: In the post quantum well structure, the Al composition of the post barrier layer in the previous period is less than or equal to the Al composition of the post barrier layer in the next period.

12. The red LED epitaxial structure according to claim 8, characterized in that: In the post quantum well structure, the thickness of the post barrier layer in the previous period is less than or equal to the thickness of the post barrier layer in the next period.

13. The red LED epitaxial structure according to claim 8, characterized in that: The total thickness of the post quantum well structure is 3nm-120nm, the single period thickness of the post quantum well structure is 3nm-12nm, and the single period thickness of the post well layer and the post barrier layer are both 1.5nm-10.5nm.

14. The red LED epitaxial structure according to claim 8, characterized in that: In each period of the post quantum well structure, the Al composition of the post barrier layer is a fixed composition or a gradient composition, and when the Al composition of the post barrier layer is a gradient composition, the Al composition of the post barrier layer gradually increases along the direction from the first type semiconductor layer to the second type semiconductor layer.

15. The red LED epitaxial structure according to claim 8, characterized in that: The main quantum well structure is a periodic structure formed by alternating growth of a main well layer and a main barrier layer, and the material, thickness and composition of the front barrier layer are the same as those of the main barrier layer, and the material, thickness and composition of the rear well layer are the same as those of the main well layer.

16. The red LED epitaxial structure according to claim 15, characterized in that: The period number of the main quantum well structure is 5 to 35, the total thickness of the main quantum well structure is 15nm to 420nm, the single period thickness of the main quantum well structure is 3nm to 12nm, and the single period thickness of the main well layer and the main barrier layer are both 1.5nm to 10.5nm.

17. The red LED epitaxial structure according to claim 1, characterized in that: The red light LED epitaxial structure further includes a bottom buffer layer and a corrosion stop layer stacked in sequence, wherein the bottom buffer layer is located on the substrate, and the corrosion stop layer is located between the bottom buffer layer and the first type semiconductor layer.

18. The red LED epitaxial structure according to claim 1, characterized in that: The first-type semiconductor layer includes, from bottom to top, a first-type ohmic contact layer, a first-type window layer, a first-type confinement layer and a first barrier layer.

19. The red LED epitaxial structure according to claim 1, characterized in that: The second-type semiconductor layer includes, from bottom to top, a second blocking layer, a second-type confinement layer, a second-type current spreading layer and a second-type ohmic contact layer.

20. A method for preparing a red light LED epitaxial structure, characterized in that: The following steps are involved: providing a substrate; A first-type semiconductor layer and an active layer are sequentially grown on the substrate, wherein the active layer sequentially comprises a pre-quantum well structure and a main quantum well structure from bottom to top, wherein the pre-quantum well structure is a periodic structure formed by alternating growth of a pre-well layer and a pre-barrier layer, wherein the pre-well layer contains an Al component, and the Al component of the pre-well layer in a previous period is less than the Al component of the pre-well layer in a subsequent period; A second type semiconductor layer is grown on the active layer.

21. The method for preparing a red LED epitaxial structure according to claim 20, characterized in that: The number of periods of the front quantum well structure is 1-10.

22. The method for preparing a red LED epitaxial structure according to claim 20, characterized in that: The material of the front well layer includes (Al xi Ga 1-xi ) y In 1-y P, and 0≤xi≤0.3, 0.3≤y≤0.7; the material of the front barrier layer includes (Al m Ga 1-m ) n In 1-n P, and 0.3≤m≤0.8, 0.3≤n≤0.

7.

23. The method for preparing a red LED epitaxial structure according to claim 20, characterized in that: In the pre-quantum well structure, the thickness of the pre-well layer in a previous period is greater than the thickness of the pre-well layer in a subsequent period.

24. The method for preparing a red LED epitaxial structure according to claim 20, characterized in that: The total thickness of the pre-quantum well structure is 3nm-120nm, the single-period thickness of the pre-quantum well structure is 3nm-12nm, and the single-period thickness of the pre-well layer and the pre-barrier layer are both 1.5nm-10.5nm.

25. The method for preparing a red LED epitaxial structure according to claim 20, characterized in that: In each period of the pre-quantum well structure, the Al component of the pre-well layer is a fixed component or a gradient component, and when the Al component of the pre-well layer is a gradient component, the In component of the pre-well layer gradually increases along the direction from the first-type semiconductor layer to the second-type semiconductor layer.

26. The method for preparing a red LED epitaxial structure according to claim 20, characterized in that: In the pre-quantum well structure, an energy band of a pre-well layer closest to the main quantum well structure is lower than or equal to an energy band of the main quantum well structure.

27. The method for preparing a red LED epitaxial structure according to claim 20, characterized in that: The active layer further includes a post-quantum well structure located on the main quantum well structure, and the post-quantum well structure is a periodic structure formed by alternating growth of a post-well layer and a post-barrier layer.

28. The method for preparing a red LED epitaxial structure according to claim 27, characterized in that: The period number of the post-quantum well structure is 1-10.

29. The method for preparing a red LED epitaxial structure according to claim 27, characterized in that: The material of the post-well layer includes (Al z Ga 1-z ) w In 1-w P, and 0≤z≤0.30, 0.3≤w≤0.7; the material of the post-barrier layer includes (Al jk Ga 1-jk ) d In 1-d P, and 0.3≤jk≤1, 0.3≤d≤0.

7.

30. The method for preparing a red LED epitaxial structure according to claim 27, characterized in that: In the post quantum well structure, the Al composition of the post barrier layer in the previous period is less than or equal to the Al composition of the post barrier layer in the next period.

31. The method for preparing a red LED epitaxial structure according to claim 27, characterized in that: In the post quantum well structure, the thickness of the post barrier layer in the previous period is less than or equal to the thickness of the post barrier layer in the next period.

32. The method for preparing a red LED epitaxial structure according to claim 27, characterized in that: The total thickness of the post quantum well structure is 3nm-120nm, the single period thickness of the post quantum well structure is 3nm-12nm, and the single period thickness of the post well layer and the post barrier layer are both 1.5nm-10.5nm.

33. The method for preparing a red LED epitaxial structure according to claim 27, characterized in that: In each period of the post quantum well structure, the Al composition of the post barrier layer is a fixed composition or a gradient composition, and when the Al composition of the post barrier layer is a gradient composition, the Al composition of the post barrier layer gradually increases along the direction from the first type semiconductor layer to the second type semiconductor layer.

34. The method for preparing a red LED epitaxial structure according to claim 27, characterized in that: The main quantum well structure is a periodic structure formed by alternating growth of a main well layer and a main barrier layer, and the material, thickness and composition of the front barrier layer are the same as those of the main barrier layer, and the material, thickness and composition of the rear well layer are the same as those of the main well layer.

35. The method for preparing a red LED epitaxial structure according to claim 34, characterized in that: The total thickness of the main quantum well structure is 15nm-420nm, the single-period thickness of the main quantum well structure is 3nm-12nm, and the single-period thickness of the main well layer and the main barrier layer are both 1.5nm-10.5nm.

36. The method for preparing a red LED epitaxial structure according to claim 20, characterized in that: The preparation method further includes: growing a bottom buffer layer and an etching stop layer between the substrate and the first type semiconductor layer, wherein the bottom buffer layer is located on the substrate, and the etching stop layer is located between the bottom buffer layer and the first type semiconductor layer.

37. The method for preparing a red LED epitaxial structure according to claim 20, characterized in that: The first-type semiconductor layer includes, from bottom to top, a first-type ohmic contact layer, a first-type window layer, a first-type confinement layer and a first barrier layer.

38. The method for preparing a red LED epitaxial structure according to claim 20, characterized in that: The second-type semiconductor layer includes, from bottom to top, a second blocking layer, a second-type confinement layer, a second-type current spreading layer and a second-type ohmic contact layer.

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