A reverse polarity LED with a composition of a gradual step-like roughening layer and a preparation method thereof

Abstract

The application relates to a reverse polarity LED with a gradually changed stepped roughening layer component and a preparation method thereof, and belongs to the technical field of LED epitaxial structures. The LED comprises, from bottom to top, a substrate, a buffer layer, an etching stop layer, an N-type ohmic contact layer, a roughening layer, an N-type limiting layer, an active layer, a P-type limiting layer, a transition layer and a P-type ohmic contact layer, wherein the roughening layer is a gradually changed stepped AlGaInP layer. The application can improve the light extraction efficiency of the LED chip without the aid of a complex chip process, and can guarantee the stability and repeatability of the epitaxial wafer structure and performance.

Description

Technical Field

[0001] This invention relates to a reverse polarity LED with a gradually changing stepped roughened layer composition and its preparation method, belonging to the field of LED epitaxial structure technology. Background Technology

[0002] Quaternary AlGaInP-based light-emitting diodes (LEDs) are widely used in indoor lighting, full-color displays, traffic lights, and garden lights due to their long lifespan, energy efficiency, and low power consumption. While the development of AlGaInP-based LED chips has a mature structural framework, low light extraction efficiency remains a major obstacle to their application. Light extraction efficiency is primarily limited by two factors: first, uneven current density distribution, leading to low effective radiative recombination efficiency in the active region; and second, the mismatch between the refractive index of the epitaxial material and its surface and the surrounding air, resulting in multiple total internal reflections at various interfaces.

[0003] Optimizing the two factors mentioned above is an effective way to improve LED brightness. In existing technologies, based on chip manufacturing processes, several effective solutions have been proposed to improve light extraction efficiency, such as surface roughening structures, changing chip shape, transparent substrate structures, and bonding techniques. However, to date, measures to improve light extraction efficiency from the perspective of optimizing the epitaxial wafer structure itself are rarely reported. In particular, the Al composition in the AlGaInP system affects its resistivity and refractive index, thus significantly impacting light extraction efficiency and current diffusion. Considering the unnecessary risks brought about by fluctuations in chip manufacturing processes, optimizing the roughening layer structure of the epitaxial wafer for inverse polarity LEDs to increase light emission efficiency is imperative. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a reverse polarity LED with a gradient step-like roughening layer composition, which can improve the light extraction efficiency of LED chips without relying on complex chip manufacturing processes, and can also ensure the stability and repeatability of epitaxial wafer structure and performance.

[0005] The present invention also provides a method for preparing the above-mentioned reverse polarity LED having a gradient step-like roughening layer composition.

[0006] The technical solution of the present invention is as follows:

[0007] A reverse polarity LED with a gradient stepped roughening layer composition includes, from bottom to top, a substrate, a buffer layer, an etching stop layer, an N-type ohmic contact layer, a roughening layer, an N-type confinement layer, an active layer, a P-type confinement layer, a transition layer, and a P-type ohmic contact layer, wherein the roughening layer is a gradient stepped AlGaInP layer.

[0008] Preferably, the substrate is an N-type GaAs substrate, the buffer layer is an N-type GaAs buffer layer, the etch stop layer is an N-type GaInP etch stop layer, the N-type ohmic contact layer is an N-type GaAs ohmic contact layer, the N-type confinement layer is an N-type AlInP confinement layer, the active layer is an MQW quantum well active layer, the P-type confinement layer is a P-type AlInP confinement layer, and the transition layer is Al x Ga y In z P transition layer, and the P-type ohmic contact layer is a P-GaP ohmic contact layer, wherein in Al x Ga y In z P transition layer, x+y+z=1.

[0009] Preferably, the roughening layer is a graded stepped {Al x Ga 0.5-x In 0.5 P / Al x→z Ga 0.5-(x→z) In 0.5 P / Al z Ga 0.5-z In 0.5 P} / {Al x-y Ga 0.5-(x-y) In 0.5 P / Al (x-y)→(z-y) Ga 0.5-[(x-y)→(z-y)] In 0.5 P / Al z-y Ga 0.5-(z-y) In 0.5 P} / … / {Al x-Ky Ga 0.5-(x-Ky) In 0.5 P / Al (x-Ky)→(z-Ky) Ga 0.5-[(x-Ky)→(z-Ky)] In 0.5 P / Al z-Ky Ga 0.5-(z-Ky) In 0.5 P} roughening layer, wherein 0<x<z<0.5, 0<y<0.5, K is an integer of 1, 2, 3, 4..., x, y and z are all definite values, x→z represents that the component is gradually changed from x to z, the structure in each {} forms a graded step, and each graded step comprises 3 sequentially stacked AlGaInP layers.

[0010] On the premise of not introducing lattice mismatch, the lateral expansion of current is increased by utilizing the energy band difference of the graded stepped structure, so as to improve the uniformity of current density distribution in the active region; meanwhile, the total reflection probability between each epitaxial layer is reduced by utilizing the refractive index change of the graded stepped structure, so as to increase the light extraction rate of the LED.

[0011] More preferably, the roughening layer includes K+1 gradient steps, each gradient step having a thickness of hnm, and a total thickness of h*(K+1)nm.

[0012] The preparation method of the above-mentioned reverse polarity LED with a gradually changing stepped roughened layer composition includes the following steps:

[0013] (1) Place the substrate in the MOCVD reaction chamber, heat it to about 840℃, introduce an AsH3 source, and perform a pretreatment for about 5 minutes. Then cool it down to about 700℃, introduce TMGa and Si2H6 sources, using the Si2H6 source as the doping source, and grow an N-type GaAs buffer layer with a doping concentration of 0.5*10. 18 cm -3 -1*10 18 cm -3 ;

[0014] (2) Turn off the AsH3 source and introduce TMI and PH3 sources. Maintain an ambient temperature of 700–730℃ to grow an N-type GaInP layer, obtaining an N-type GaInP etching stop layer with a doping concentration of 0.5 × 10⁻⁶. 18 cm -3 -1*10 18 cm -3 ;

[0015] (3) Turn off the TMI and PH3 sources, introduce the AsH3 source, and grow the GaAs layer at an ambient temperature of 700–730℃ to obtain an N-type GaAs ohmic contact layer with a doping concentration of 0.5 × 10⁻⁶. 18 cm -3 -1*10 18 cm -3 ;

[0016] (4) Turn off the AsH3 source and introduce TMAl, TMIn, and PH3 sources. Maintain an ambient temperature of 700–730℃. The growth composition will exhibit a gradual, stepwise pattern of {Al}. x Ga 0.5-x In 0.5 P / Al x→z Ga 0.5-(x→z) In 0.5 P / Al z Ga 0.5-z In 0.5 P} / {Al x-y Ga 0.5-(x-y) In 0.5 P / Al (x-y)→(z-y) Ga 0.5-[(x-y)→(z-y)] In 0.5 P / Al z-y Ga 0.5-(z-y) In 0.5 P} / … / {Alx-Ky Ga 0.5-(x-Ky) In 0.5 P / Al (x-Ky)→(z-Ky) Ga 0.5-[(x-Ky)→(z-Ky)] In 0.5 P / Al z-Ky Ga 0.5-(z-Ky) In 0.5 P} roughening layer, wherein 0<x<z<0.5, 0<y<0.5, K is an integer 1, 2, 3, 4..., the doping concentration ranges from 0.5*10 18 cm -3 gradually to 2*10 18 cm -3 ;

[0017] (5) turning off the TMGa source, adjusting the ambient temperature to 730~730℃, growing an AlInP layer to obtain an N-type AlInP confinement layer with a doping concentration of 2*10 18 cm -3 -3*10 18 cm -3 ;

[0018] (6) turning off the doping source, continuously introducing TMAl, TMGa and TMIn sources, setting the ambient temperature to 720~750℃, growing AlGaInP quantum barriers, then turning off the Al source, growing GaInP quantum wells, repeating the growth for 8 to 15 periods to form an MQW quantum well active layer;

[0019] (7) adjusting the temperature to 730~760℃, turning off the Ga source, introducing a Cp2Mg source, using the Cp2Mg source as a doping source, growing an AlInP layer with a doping concentration of 2*10 18 cm -3 -3*10 18 cm -3 to obtain a P-type AlInP confinement layer;

[0020] (8) introducing a TMGa source, setting the ambient temperature to 740~770℃, growing Al x Ga y In z P layer, and simultaneously adjusting the components of each source to allow the energy band and lattice to gradually change from AlInP to GaP slowly, forming an Al x Ga y In z P transition layer with a doping concentration of 1*10 18 cm -3 -2*10 18 cm -3 ;

[0021] (9) TMGa and PH3 sources are continuously introduced at an ambient temperature of 680–710℃ to grow a GaP layer, resulting in a P-GaP ohmic contact layer with a doping concentration of 0.5 × 10⁻⁶. 20 cm -3 -1*10 20 cm -3 .

[0022] Preferably, in step (1), the thickness of the N-type GaAs buffer layer is 50 nm;

[0023] In step (2), the thickness of the N-type GaInP layer is 100 nm.

[0024] Preferably, the thickness of the N-type GaAs ohmic contact in step (3) is 50 nm.

[0025] Preferably, in step (4), the method for growing the roughened layer is as follows: at the end of the growth of the N-type GaAs ohmic contact layer, the flow rates of TMAl and TMGa are adjusted, and Al is grown sequentially. x Ga 0.5-x In 0.5 P / Al x→z Ga 0.5-(x→z) In 0.5 P / Al z Ga 0.5-z In 0.5 P, Al x-y Ga 0.5-(x-y) In 0.5 P / Al (x-y)→(z-y) Ga 0.5-[(x-y)→(z-y)] In 0.5 P / Al z-y Ga 0.5-(z-y) In 0.5 P…Al x- Ky Ga 0.5-(x-Ky) In 0.5 P / Al (x-Ky)→(z-Ky) Ga 0.5-[(x-Ky)→(z-Ky)] In 0.5 P / Al z-Ky Ga 0.5-(z-Ky) In 0.5 P.

[0026] Preferably, the growth thickness of the N-type AlInP confinement layer in step (5) is 400 nm;

[0027] In step (6), the AlGaInP quantum barrier has a growth thickness of 10 nm, and the GaInP quantum well has a growth thickness of 9 nm.

[0028] Preferably, the thickness of the P-type AlInP confinement layer in step (7) is 550 nm;

[0029] In step (8), P-type Al x Ga y In z The thickness of the P transition layer is 200 nm.

[0030] In step (9), the growth thickness of the P-GaP ohmic contact layer is 1600 nm.

[0031] This invention utilizes metal-organic chemical vapor deposition (MOCVD) to grow epitaxial structures on N-type GaAs substrates. The epitaxial source materials used include trimethylaluminum (TMAl), trimethylgallium (TMGa), trimethylindium (TMIn), phosphine (PH3), arsine (AsH3), silane (Si2H6), and magnesium dicthene (cp2Mg), among others. Si2H6 and cp2Mg are used for N-type and P-type doping, respectively. Furthermore, nitrogen (N2) and hydrogen (H2) are used as carrier gases during the epitaxial growth process.

[0032] For any details not covered in this invention, please refer to the prior art.

[0033] The beneficial effects of this invention are as follows:

[0034] The different composition and doping concentration of the roughening layer used in this invention result in different conduction band levels and electrical conductivity. The conduction band energy decreases gradually in a step-like manner from the N-type electrode to the quantum well region, and the electrical conductivity also gradually decreases. This allows the electrons driven by the current to be effectively extended laterally in the roughening layer. The dispersed current after the extension is more uniform than before, which increases the effective radiative recombination area of ​​the quantum well region and thus increases the photon output efficiency.

[0035] Furthermore, the refractive index decreases gradually in a step-like manner from the quantum well to the surface of the roughened layer. This gradual decrease in refractive index reduces the probability of total internal reflection, allowing more photons to be emitted. The stepped structure provides a accommodating area for this increased photon emission. Compared to the original structure, setting the roughened layer to a step-like structure with a gradually decreasing composition and a linearly increasing doping concentration allows for more uniform electron injection into the active region, increasing the effective activation area and generating more photons, thus improving the internal quantum efficiency. Simultaneously, setting the roughened layer to a step-like structure increases the probability of photons that would otherwise be unable to escape due to total internal reflection being emitted, thereby increasing the external quantum efficiency. Moreover, this invention also ensures the stability of the epitaxial wafer performance and the reproducibility of production. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of the present invention;

[0037] Figure 2 This is a schematic diagram of the roughening layer structure of the present invention;

[0038] Figure 3 This is a schematic diagram of the gradient step structure of the present invention;

[0039] Among them: 1. Substrate, 2. Buffer layer, 3. Etching stop layer, 4. N-type ohmic contact layer, 5. Roughening layer, 6. N-type confinement layer, 7. Active layer, 8. P-type confinement layer, 9. Transition layer, 10. P-type ohmic contact layer.

[0040] 51. Al x Ga 0.5-x In 0.5 P / Al x→z Ga 0.5-(x→z) In 0.5 P / Al z Ga 0.5-z In 0.5 P layer, 52, Al x-y Ga 0.5-(x-y) In 0.5 P / Al (x-y)→(z-y) Ga 0.5-[(x-y)→(z-y)] In 0.5 P / Al z-y Ga 0.5-(z-y) In 0.5 P layer, 51+K, Al x-Ky Ga 0.5-(x-Ky) In 0.5 P / Al (x-Ky)→(z-Ky) Ga 0.5-[(x-Ky)→(z-Ky)] In 0.5 P / Al z-Ky Ga 0.5-(z-Ky) In 0.5 P layer;

[0041] 511, Al x Ga 0.5-x In 0.5 P layer, 512, Al x→z Ga 0.5-(x→z) In 0.5 P layer, 513, Al z Ga 0.5-z In 0.5 P layer. Detailed Implementation

[0042] The present invention will be further described below with reference to the embodiments and accompanying drawings, but is not limited thereto.

[0043] Example 1:

[0044] like Figure 1-3As shown, this embodiment provides an inverted polarity LED with a graded stepped roughened layer composition, comprising a substrate 1, a buffer layer 2, an etch stop layer 3, an N-type ohmic contact layer 4, a roughened layer 5, an N-type confinement layer 6, an active layer 7, a P-type confinement layer 8, a transition layer 9 and a P-type ohmic contact layer 10 arranged sequentially from bottom to top, wherein the roughened layer is a graded stepped AlGaInP layer.

[0045] The substrate is an N-type GaAs substrate, the buffer layer is an N-type GaAs buffer layer, the etch stop layer is an N-type GaInP etch stop layer, the N-type ohmic contact layer is an N-type GaAs ohmic contact layer, the N-type confinement layer is an N-type AlInP confinement layer, the active layer is an MQW quantum well active layer, the P-type confinement layer is a P-type AlInP confinement layer, and the transition layer is Al x Ga y In z P transition layer, the P-type ohmic contact layer is a P-GaP ohmic contact layer, wherein in Al x Ga y In z P transition layer, x+y+z=1.

[0046] The roughened layer is a graded stepped {Al x Ga 0.5-x In 0.5 P / Al x→z Ga 0.5-(x→z) In 0.5 P / Al z Ga 0.5- z In 0.5 P} / {Al x-y Ga 0.5-(x-y) In 0.5 P / Al (x-y)→(z-y) Ga 0.5-[(x-y)→(z-y)] In 0.5 P / Al z-y Ga 0.5-(z-y) In 0.5 P} / … / {Al x-Ky Ga 0.5-(x-Ky) In 0.5 P / Al (x-Ky)→(z-Ky) Ga 0.5-[(x-Ky)→(z-Ky)] In 0.5 P / Al z-Ky Ga 0.5-(z-Ky) In 0.5 P} roughened layer, wherein 0<x<z<0.5, 0<y<0.5, K is an integer of 1, 2, 3, 4..., x, y and z are all definite values, x→z represents that the component is graded from x to z, the structure in each {} forms a graded step, and each graded step comprises three sequentially stacked AlGaInP layers.

[0047] Without introducing lattice mismatch, the gradual step-like band difference is used to increase the lateral spread of the current and improve the uniformity of the current density distribution in the active region. At the same time, the gradual step-like refractive index change is used to reduce the probability of total internal reflection between epitaxial layers and increase the light output efficiency of the LED.

[0048] The roughening layer consists of K+1 gradient steps, each with a thickness of hnm, and a total thickness of h*(K+1)nm.

[0049] The preparation method of the above-mentioned reverse polarity LED with a gradually changing stepped roughened layer composition includes the following steps:

[0050] (1) Place the substrate in the MOCVD reaction chamber, heat it to about 840℃, introduce an AsH3 source, and perform a pretreatment for about 5 minutes. Then cool it down to about 700℃, introduce TMGa and Si2H6 sources, using the Si2H6 source as the doping source, and grow an N-type GaAs buffer layer with a doping concentration of 0.5*10. 18 cm -3 -1*10 18 cm -3 ;

[0051] (2) Turn off the AsH3 source and introduce TMI and PH3 sources. Maintain an ambient temperature of 700–730℃ to grow an N-type GaInP layer, obtaining an N-type GaInP etching stop layer with a doping concentration of 0.5 × 10⁻⁶. 18 cm -3 -1*10 18 cm -3 ;

[0052] (3) Turn off the TMI and PH3 sources, introduce the AsH3 source, and grow the GaAs layer at an ambient temperature of 700–730℃ to obtain an N-type GaAs ohmic contact layer with a doping concentration of 0.5 × 10⁻⁶. 18 cm -3 -1*10 18 cm -3 ;

[0053] (4) Turn off the AsH3 source and introduce TMAl, TMIn, and PH3 sources. Maintain an ambient temperature of 700–730℃. The growth composition will exhibit a gradual, stepwise pattern of {Al}. x Ga 0.5-x In 0.5 P / Al x→z Ga 0.5-(x→z) In 0.5 P / Al z Ga 0.5-z In 0.5 P} / {Al x-y Ga0.5-(x-y) Indium 0.5 Phosphorus / Aluminum (x-y)→(z-y) Gallium 0.5-[(x-y)→(z-y)] Indium 0.5 Phosphorus / Aluminum z-y Gallium 0.5-(z-y) Indium 0.5 Phosphorus} / … / {Aluminum x-Ky Gallium 0.5-(x-Ky) Indium 0.5 Phosphorus / Aluminum (x-Ky)→(z-Ky) Gallium 0.5-[(x-Ky)→(z-Ky)] Indium 0.5 Phosphorus / Aluminum z-Ky Gallium 0.5-(z-Ky) Indium 0.5 Phosphorus} roughened layer, wherein 0<x<z<0.5, 0<y<0.5, K is an integer 1, 2, 3, 4..., the doping concentration ranges from 0.5*10 18 cm -3 gradually changes to 2*10 18 cm -3 ;

[0054] (5) turning off the TMGa source, setting the ambient temperature to 730~730°C, growing an AlInP layer to obtain an N-type AlInP confinement layer, with a doping concentration of 2*10 18 cm -3 -3*10 18 cm -3 ;

[0055] (6) turning off the doping source, continuously feeding TMAl, TMGa and TMIn sources, setting the ambient temperature to 720~750°C, growing AlGaInP quantum barriers, then turning off the Al source, growing GaInP quantum wells, repeating the growth for 8 to 15 cycles to form an MQW quantum well active layer;

[0056] (7) adjusting the temperature to 730~760°C, turning off the Ga source, feeding a Cp2Mg source, using the Cp2Mg source as the doping source, growing an AlInP layer, with a doping concentration of 2*10 18 cm -3 -3*10 18 cm -3 to obtain a P-type AlInP confinement layer;

[0057] (8) feeding a TMGa source, setting the ambient temperature to 740~770°C, growing Al x Ga y In z P layer, and adjusting the components of each source simultaneously to make the energy band and lattice gradually change from AlInP to GaP slowly, forming Al x Ga y In zP-transition layer, with a doping concentration of 1*10⁻⁶. 18 cm -3 -2*10 18 cm -3 ;

[0058] (9) TMGa and PH3 sources are continuously introduced at an ambient temperature of 680–710℃ to grow a GaP layer, resulting in a P-GaP ohmic contact layer with a doping concentration of 0.5 × 10⁻⁶. 20 cm -3 -1*10 20 cm -3 .

[0059] In step (1), the thickness of the N-type GaAs buffer layer is 50 nm; in step (2), the thickness of the N-type GaInP layer is 100 nm; in step (3), the thickness of the N-type GaAs ohmic contact is 50 nm; in step (4), the growth method of the roughened layer is as follows: at the end of the growth of the N-type GaAs ohmic contact layer, the flow rates of TMAl and TMGa are adjusted, and Al is grown sequentially. x Ga 0.5-x In 0.5 P / Al x→ z Ga 0.5-(x→z) In 0.5 P / Al z Ga 0.5-z In 0.5 P, Al x-y Ga 0.5-(x-y) In 0.5 P / Al (x-y)→(z-y) Ga 0.5-[(x-y)→(z-y)] In 0.5 P / Al z-y Ga 0.5-(z-y) In 0.5 P…Al x-Ky Ga 0.5-(x-Ky) In 0.5 P / Al (x-Ky)→(z-Ky) Ga 0.5-[(x-Ky)→(z-Ky)] In 0.5 P / Al z- Ky Ga 0.5-(z-Ky) In 0.5 P, the roughening layer consists of 6 gradient steps, each with 3 layers of structure with thicknesses of 50nm, 150nm and 50nm respectively, for a total thickness of 1500nm.

[0060] In step (5), the growth thickness of the N-type AlInP confinement layer is 400 nm; in step (6), the growth thickness of the AlGaInP quantum barrier is 10 nm, the growth thickness of the GaInP quantum well is 9 nm, and in step (7), the thickness of the P-type AlInP confinement layer is 550 nm.

[0061] In step (8), P-type Al x Ga y In z The thickness of the P transition layer is 200 nm; the thickness of the P-GaP ohmic contact layer in step (9) is 1600 nm.

[0062] Example 2:

[0063] A method for preparing an anti-polarity LED with a gradient step-like roughening layer composition, the steps of which are as described in Example 1, except that the roughening layer includes 6 gradient steps, and the thicknesses of the three-layer structure in each gradient step are 100nm, 150nm and 100nm respectively, with a total thickness of 2100nm.

[0064] Example 3:

[0065] A method for preparing an anti-polarity LED with a gradient step-like roughening layer composition, the steps of which are as described in Example 1, except that the roughening layer includes 6 gradient steps, and the thicknesses of the three-layer structure in each gradient step are 50 nm, 300 nm and 50 nm, respectively, with a total thickness of 2400 nm.

[0066] Example 4:

[0067] A method for preparing an anti-polarity LED with a gradient step-like roughening layer composition, the steps of which are as described in Example 1, except that the roughening layer includes three gradient steps, and the thicknesses of the three layers in each gradient step are 100 nm, 600 nm and 100 nm, respectively, with a total thickness of 2400 nm.

[0068] Example 5:

[0069] A method for fabricating an anti-polarity LED with a gradient step-like roughening layer composition, the steps of which are as described in Example 1, except that the roughening layer includes 12 gradient steps, and the thicknesses of the three-layer structure in each gradient step are 25nm, 150nm and 25nm, respectively, with a total thickness of 2400nm.

[0070] Using the same chip manufacturing process and testing conditions, the epitaxial wafers prepared in Examples 1-5 were processed and tested at 5.7 mil. All chips were tested at a working current of 20 mA. The traditional epitaxial wafer structure, i.e., the roughening layer has a fixed composition and doping concentration, has a brightness of approximately 585 mcd. After the roughening layer was changed to a gradually changing step-like composition and linear doping, and then fabricated using die-cutting technology, the corresponding brightness and aging degradation data are shown in Table 1.

[0071] Table 1: Brightness and Aging Decay Data Table

[0072] Example 1 50nm, 150nm and 50nm 6 1500nm 575mcd Example 2 100nm, 150nm and 100nm 6 2100nm 587mcd Example 3 50nm, 300nm and 50nm 6 2400nm 609mcd Example 4 100nm, 600nm and 100nm 3 2400nm 594mcd Example 5 25nm, 150nm and 25nm 12 2400nm 627mcd

[0073] Examples 1, 2, and 3 compared the effects of different thicknesses on chip brightness under the same composition and number of steps in a gradient-stepped structure. Examples 3, 4, and 5 compared the effects of different compositions and numbers on chip brightness under the same total thickness in a gradient-stepped structure. Based on the above results, compared with chips with traditional epitaxial structures, the brightness is significantly improved after the introduction of a superlattice structure in the roughening layer. Preferably, Example 5 has a more prominent effect on improving chip brightness.

[0074] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A reverse polarity LED having a gradually changing stepped roughening layer composition, characterized in that, It includes, from bottom to top, a substrate, a buffer layer, an etching stop layer, an N-type ohmic contact layer, a roughening layer, an N-type confinement layer, an active layer, a P-type confinement layer, a transition layer, and a P-type ohmic contact layer, wherein the roughening layer is a graded stepped AlGaInP layer. The roughening layer is a gradual stepped {Al x Ga 0.5-x In 0.5 P / Al x→z Ga 0.5-(x→z) In 0.5 P / Al z Ga 0.5-z In 0.5 P} / {Al x-y Ga 0.5-(x-y) In 0.5 P / Al (x-y)→(z-y) Ga 0.5-[(x-y)→(z-y)] In 0.5 P / Al z-y Ga 0.5-(z-y) In 0.5 P} / … / {Al x-Ky Ga 0.5-(x-Ky) In 0.5 P / Al (x-Ky)→(z-Ky) Ga 0.5-[(x-Ky)→(z-Ky)] In 0.5 P / Al z-Ky Ga 0.5-(z-Ky) In 0.5 P}roughening layer, wherein 0<x<z<0.5, 0<y<0.5, K is an integer of 1, 2, 3, 4..., x, y and z are all definite values, x→z represents that the component gradually changes from x to z, the structure in each {} forms one gradual step, and each gradual step comprises three sequentially superimposed AlGaInP layers; The roughening layer consists of K+1 gradient steps, each with a thickness of hnm, and a total thickness of h*(K+1)nm.

2. The reverse polarity LED with a gradually changing stepped roughened layer composition as described in claim 1, characterized in that, The substrate is an N-type GaAs substrate, the buffer layer is an N-type GaAs buffer layer, the etch stop layer is an N-type GaInP etch stop layer, the N-type ohmic contact layer is an N-type GaAs ohmic contact layer, the N-type confinement layer is an N-type AlInP confinement layer, the active layer is an MQW quantum well active layer, the P-type confinement layer is a P-type AlInP confinement layer, and the transition layer is Al x Ga y In z The P-transition layer and the P-type ohmic contact layer are P-GaP ohmic contact layers, wherein Al x Ga y In z In the P transition layer, x+y+z=1.

3. The method for preparing a reverse polarity LED with a gradually changing stepped roughened layer composition as described in claim 2, characterized in that, The steps are as follows: (1) Place the substrate in the MOCVD reaction chamber, heat it to about 840℃, introduce an AsH3 source, perform a pretreatment for about 5 minutes, then cool it down to about 700℃, introduce TMGa and Si2H6 sources, using the Si2H6 source as the doping source, and grow an N-type GaAs buffer layer with a doping concentration of 0.5*10. 18 cm -3 -1*10 18 cm -3 ; (2) Turn off the AsH3 source and introduce the TMI and PH3 sources. The ambient temperature is 700~730℃ to grow an N-type GaInP layer, obtaining an N-type GaInP etching stop layer with a doping concentration of 0.5*10. 18 cm -3 -1*10 18 cm -3 ; (3) Turn off the TMI and PH3 sources, introduce the AsH3 source, and grow the GaAs layer at an ambient temperature of 700~730℃ to obtain an N-type GaAs ohmic contact layer with a doping concentration of 0.5*10. 18 cm -3 -1*10 18 cm -3 ; (4) Turn off the AsH₃ source, feed in TMAl, TMIn and PH₃ sources, set the ambient temperature to 700~730°C, grow the {Al x Ga 0.5-x In 0.5 P / Al x→z Ga 0.5-(x→z) In 0.5 P / Al z Ga 0.5-z In 0.5 P} / {Al x-y Ga 0.5-(x-y) In 0.5 P / Al (x-y)→(z-y) Ga 0.5-[(x-y)→(z-y)] In 0.5 P / Al z-y Ga 0.5-(z-y) In 0.5 P} / … / {Al x-Ky Ga 0.5-(x-Ky) In 0.5 P / Al (x-Ky)→(z-Ky) Ga 0.5-[(x-Ky)→(z-Ky)] In 0.5 P / Al z-Ky Ga 0.5-(z-Ky) In 0.5 P} graded stepped roughened layer, where 0<x<z<0.5, 0<y<0.5, K is an integer of 1, 2, 3, 4..., the doping concentration varies from 0.5*10 18 cm -3 gradually changes to 2*10 18 cm -3 ; (5) Turn off the TMGa source, maintain the ambient temperature at 730℃, and grow an AlInP layer to obtain an N-type AlInP confinement layer with a doping concentration of 2*10. 18 cm -3 -3*10 18 cm -3 ; (6) Turn off the doping source and continuously introduce TMAl, TMGa and TMIn sources at an ambient temperature of 720~750℃ to grow AlGaInP quantum barrier. Then turn off the Al source and grow GaInP quantum well. Repeat the growth for 8~15 cycles to form MQW quantum well active layer. (7) Adjust the temperature to 730~760℃, turn off the Ga source, and introduce the Cp2Mg source. Use the Cp2Mg source as the doping source to grow the AlInP layer with a doping concentration of 2*10. 18 cm -3 -3*10 18 cm -3 A P-type AlInP confinement layer is obtained; (8) Introduce the TMGa source at an ambient temperature of 740~770℃ to grow Al. x Ga y In z The P-layer is constructed by simultaneously adjusting the composition of each source, causing the energy band and lattice to gradually transition from AlInP to GaP, thus forming Al. x Ga y In z P-transition layer, with a doping concentration of 1*10⁻⁶ 18 cm -3 -2*10 18 cm -3 ; (9) TMGa and PH3 sources are continuously introduced at an ambient temperature of 680~710℃ to grow a GaP layer, resulting in a P-GaP ohmic contact layer with a doping concentration of 0.5*10. 20 cm -3 -1*10 20 cm -3 .

4. The method for preparing a reverse polarity LED with a gradually changing stepped roughened layer composition as described in claim 3, characterized in that, In step (1), the thickness of the N-type GaAs buffer layer is 50 nm; In step (2), the thickness of the N-type GaInP layer is 100 nm.

5. The method for preparing a reverse polarity LED with a gradually changing stepped roughened layer composition as described in claim 3, characterized in that, In step (3), the thickness of the N-type GaAs ohmic contact is 50 nm.

6. The method for preparing a reverse polarity LED with a gradually changing stepped roughened layer composition as described in claim 3, characterized in that, In step (4), the method for growing the roughened layer is as follows: at the end of the growth of the N-type GaAs ohmic contact layer, the flow rates of TMAl and TMGa are adjusted, and Al is grown sequentially. x Ga 0.5-x In 0.5 P / Al x→z Ga 0.5-(x→z) In 0.5 P / Al z Ga 0.5-z In 0.5 P, Al x-y Ga 0.5-(x-y) In 0.5 P / Al (x-y)→(z-y) Ga 0.5-[(x-y)→(z-y)] In 0.5 P / Al z-y Ga 0.5-(z-y) In 0.5 P… Al x-Ky Ga 0.5-(x-Ky) In 0.5 P / Al (x-Ky)→(z-Ky) Ga 0.5-[(x-Ky)→(z-Ky)] In 0.5 P / Al z-Ky Ga 0.5-(z-Ky) In 0.5 P.

7. The method for preparing a reverse polarity LED with a gradually changing stepped roughened layer composition as described in claim 3, characterized in that, In step (5), the growth thickness of the N-type AlInP confinement layer is 400 nm; In step (6), the AlGaInP quantum barrier has a growth thickness of 10 nm, and the GaInP quantum well has a growth thickness of 9 nm.

8. The method for preparing a reverse polarity LED with a gradually changing stepped roughened layer composition as described in claim 3, characterized in that, In step (7), the thickness of the P-type AlInP confinement layer is 550 nm; in step (8), the thickness of the P-type Al... x Ga y In z The thickness of the P transition layer is 200 nm; the thickness of the P-GaP ohmic contact layer in step (9) is 1600 nm.

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