AlGaN-based ultraviolet LED epitaxial structure and its preparation method

Abstract

The present application discloses an AlGaN-based ultraviolet LED epitaxial structure and a preparation method thereof. The AlGaN-based ultraviolet LED epitaxial structure includes an N-type Al<subgt;b< / subgt;Ga<subgt;1-b< / subgt;N layer, a multi-quantum well active region, a P-type Al<subgt;c< / subgt>Ga<subgt;1-c< / subgt>N electron blocking layer, and a P-type GaN contact layer, which are sequentially arranged along a specified direction; the multi-quantum well active region includes a plurality of alternately grown Al<subgt;x< / subgt>Ga<subgt;1-x< / subgt>N quantum well layers and a plurality of Al<subgt;y< / subgt>Ga<subgt;1-y< / subgt>N quantum barrier layers, wherein the last Al<subgt;x< / subgt>Ga<subgt;1-x< / subgt>N quantum well layer in the specified direction is doped with Si, where 0 < (x, y) ≤ 1. Compared with the prior art, the light output power of the AlGaN-based ultraviolet LED epitaxial structure of the present application is significantly improved.

Description

Technical Field

[0001] The present application relates to an ultraviolet LED, and particularly to an AlGaN-based ultraviolet LED epitaxial structure and a preparation method thereof, belonging to the field of semiconductor technology. Background Art

[0002] Ultraviolet LEDs can be divided into UVA-LEDs (320 - 400 nm), UVB-LEDs (280 - 320 nm), and UVC-LEDs (200 - 280 nm) according to the emission wavelength. Among them, UVA is mainly applied in fields such as curing, anti-counterfeiting detection, and photocatalysis, UVB is mainly used for phototherapy, and UVC is mainly applied in disinfection and sterilization.

[0003] The material systems of UVC-LEDs and UVB-LEDs are AlGaN-based compound semiconductors. Limited by the low mobility of Al atoms, the lateral growth rate of AlN and AlGaN materials is slow, and the dislocation density of the grown AlGaN materials is high. Dislocations form non-radiative recombination channels for carriers, resulting in a decrease in the internal quantum efficiency (IQE) and external quantum efficiency (EQE) of ultraviolet LEDs. Due to the high Mg activation energy of high-Al-component p-AlGaN, the hole concentration is low and the series resistance is high. Usually, p-GaN is used as the contact layer, but the absorption of ultraviolet light by p-GaN leads to low light extraction efficiency.

[0004] CN 113782652 A discloses a quantum barrier doped ultraviolet LED epitaxial structure: at least one group of quantum barrier layers near the N-type AlGaN layer is a first quantum barrier layer doped with Si element, and the remaining quantum barrier layers are second quantum barrier layers doped with Mg element, which can improve the radiative recombination luminescence efficiency of the quantum well and at the same time make the ultraviolet LED epitaxial wafer have a higher internal quantum efficiency. However, in this device, Mg atoms are likely to diffuse into the quantum well, which will reduce the growth quality of the quantum well, so it is difficult to play a role in improving the ultraviolet light emission efficiency.

[0005] CN 111261758 A discloses an ultraviolet LED epitaxial structure: the Al x Ga 1-x N / Al y Ga 1-y N multiple quantum well active layer includes a first light-emitting structure and a second light-emitting structure. Since each first Al y Ga 1-y N quantum barrier layer of the first light-emitting structure is doped with Si, and at least one first Al x Ga 1-x N quantum well layer is doped with Si, which is beneficial to reducing the series resistance of the multiple quantum well active region, but the light output power of this device has not been improved. Summary of the Invention

[0006] The main object of the present application is to provide an AlGaN-based ultraviolet LED epitaxial structure and a preparation method thereof to overcome the deficiencies of the prior art.

[0007] To achieve the foregoing invention object, the technical solutions adopted in the present application include:

[0008] An AlGaN-based ultraviolet LED epitaxial structure provided in one aspect of the present application includes an N-type Al b Ga 1-b N layer, a multi-quantum well active region, a P-type Al c Ga 1-c N electron blocking layer, and a P-type GaN contact layer, where 0 < b ≤ 1 and 0 < c ≤ 1;

[0009] The multi-quantum well active region includes a plurality of Al x Ga 1-x N quantum well layers and a plurality of Al y Ga 1-y N quantum barrier layers, where 0 < x ≤ 1 and 0 < y ≤ 1, and the last Al x Ga 1-x N quantum well layer in the specified direction is doped with Si.

[0010] A preparation method of an AlGaN-based ultraviolet LED epitaxial structure provided in another aspect of the present application includes growing an N-type Al b Ga 1-b N layer, a multi-quantum well active region, a P-type Al c Ga 1-c N electron blocking layer, and a P-type GaN contact layer in sequence along a specified direction, where 0 < b ≤ 1 and 0 < c ≤ 1;

[0011] Among them, the step of growing the multi-quantum well active region specifically includes: alternately growing a plurality of Al x Ga 1-x N quantum well layers and a plurality of Al y Ga 1-y N quantum barrier layers, where 0 < x ≤ 1 and 0 < y ≤, and doping Si in the last Al x Ga 1- x N quantum well layer in the specified direction.

[0012] Compared with the prior art, in the AlGaN-based ultraviolet LED epitaxial structure of the present application, by doping Si in the last Al x Ga 1-x N quantum well layer in the multi-quantum well active region, the compressive strain of the AlGaN layer can be effectively reduced, thereby significantly improving the growth quality of the quantum well, reducing the non-radiative recombination center, and thus greatly improving the light output power. Description of the Drawings

[0013] Figure 1 Schematic diagram of an AlGaN-based ultraviolet LED epitaxial structure in a typical embodiment of the present application.

[0014] Figure 2 Schematic diagram of the preparation process flow of an AlGaN-based ultraviolet LED epitaxial structure in a typical embodiment of the present application. Detailed Description of the Invention

[0015] The inventors of the present application have found through long-term research and practice that for AlGaN-based deep ultraviolet LEDs, electrons and holes mainly generate radiative recombination in the last quantum well to emit ultraviolet light. Therefore, the last quantum well is the main light-emitting well. However, due to the compressive strain state of the AlGaN quantum well layer, the growth process will cause partial relaxation of the quantum well layer, resulting in poor growth quality of the quantum well, thus seriously affecting the light output power of the deep ultraviolet LED.

[0016] In view of this, the applicant of the present application has proposed the technical solution of the present application, which mainly reduces the compressive strain of the AlGaN layer by doping a certain concentration of Si in the main light-emitting well of the AlGaN-based deep ultraviolet LED, thereby improving the growth quality of the quantum well, reducing non-radiative recombination centers, and further increasing the light output power. The technical solution of the present application will be described in more detail below.

[0017] Some embodiments of the present application provide an AlGaN-based ultraviolet LED epitaxial structure, which includes an N-type Al b Ga 1-b N layer, a multi-quantum well active region, a P-type Al c Ga 1-c N electron blocking layer, and a P-type GaN contact layer, where 0 < b ≤ 1, 0 < c ≤ 1;

[0018] The multi-quantum well active region includes a plurality of alternately grown Al x Ga 1-x N quantum well layers and a plurality of Al y Ga 1-y N quantum barrier layers, where 0 < x ≤ 1, 0 < y ≤ 1, and the last Al x Ga 1-x N quantum well layer in the specified direction is doped with Si.

[0019] In one embodiment, the Si concentration doped in the last Al x Ga 1-x N quantum well layer in the specified direction is 1E+17 cm -3 ~1E+20 cm-3 .

[0020] In one embodiment, the last Al in the specified direction x Ga 1-x N quantum well layer is doped with Si in part or all of its regions. For example, the entire well of the last Al x Ga 1-x N quantum well layer in the specified direction is doped with Si, or the first part of the thickness of the well is doped with Si, or the middle part is doped with Si, or the last part of the thickness is doped with Si.

[0021] In one embodiment, the doping method of Si in the last Al x Ga 1-x N quantum well layer includes graded doping, gradient doping, pulse doping or uniform doping, and is not limited thereto.

[0022] In one embodiment, the multiple quantum well active region includes a first quantum well structure and a second quantum well structure arranged in sequence along the specified direction. The first quantum well structure includes the first Al grown alternately for m periods x1 Ga 1-x1 N quantum well layer and the first Al y1 Ga 1-y1 N quantum barrier layer, 0 < x1 ≤ 1, 0 < y1 ≤ 1, 1 ≤ m ≤ 10. The second quantum well structure includes a second Al x2 Ga 1-x2 N quantum well layer and a second Al y2 Ga 1-y2 N quantum barrier layer, 0 < x2 ≤ 1, 0 < y2 ≤ 1. The second Al x2 Ga 1-x2 N quantum well layer is the last Al x Ga 1-x N quantum well layer in the specified direction.

[0023] In one embodiment, the first Al y1 Ga 1-y1 N quantum barrier layer is doped with Si. The doping concentration of Si in the second Al x2 Ga 1-x2 N quantum well layer is higher or lower than the Si doping concentration in the first Al y1 Ga 1-y1 N quantum barrier layer. The first Al x1 Ga 1-x1 N quantum well layer is doped or not doped with Si.

[0024] In one embodiment, one Al that cooperates with each other x Ga 1-xAn N quantum well layer and an Al y Ga 1-y N quantum barrier layer, and the thickness of one period is 3 - 20 nm.

[0025] In one embodiment, 0 < x < y < 1, that is, the Al component in the x Ga 1-x N quantum well layer is lower than the Al component in the y Ga 1- y N quantum barrier layer.

[0026] In one embodiment, the AlGaN - based ultraviolet LED epitaxial structure includes an AlN layer, an Al a Ga 1-a N transition layer, an N - type Al b Ga 1-b N layer, a multi - quantum well active region, a P - type Al c Ga 1-c N electron blocking layer, and a P - type GaN contact layer, where 0 < a ≤ 1 and 0 < b ≤ 1.

[0027] In one embodiment, the Al a Ga 1-a N transition layer, the N - type Al b Ga 1-b N layer, and the P - type Al c Ga 1-c N electron blocking layer all have an Al component higher than the Al component in the multi - quantum well active region's x Ga 1-x N quantum well layer.

[0028] In one embodiment, the substrate includes sapphire, aluminum nitride, or silicon substrate, etc., and is not limited thereto.

[0029] Please refer to Figure 1 As shown, in a relatively typical embodiment of the present application, an AlGaN - based ultraviolet LED epitaxial structure includes:

[0030] An AlN layer located on the surface of the substrate;

[0031] An Al a Ga 1-a N transition layer located on the side of the AlN layer away from the substrate;

[0032] An N - type Al a Ga 1-a N layer located on the side of the b Ga 1-b N transition layer away from the substrate;

[0033] Located in the N-type Al b Ga 1-b The multiple quantum well active region on the side of the N layer away from the substrate, the multiple quantum well active region includes a first quantum well structure and a second quantum well structure located on the side of the first quantum well structure away from the substrate, the first quantum well structure includes 1 to 10 alternating growth cycles of the first Al x1 Ga 1-x1 N quantum well layer and the first Al y1 Ga 1-y1 N quantum barrier layer, the second quantum well structure includes a second Al x2 Ga 1-x2 N quantum well layer and a second Al y2 Ga 1-y2 N quantum barrier layer;

[0034] Located in the Al x Ga 1-x N / Al y Ga 1-y The P-type Al on the side of the multiple quantum well active region of N away from the substrate c Ga 1-c N electron blocking layer;

[0035] Located in the P-type Al c Ga 1-c The P-type GaN contact layer on the side of the N electron blocking layer away from the substrate.

[0036] In this exemplary embodiment, by doping Si in the last AlGaN quantum well, the compressive strain of the last well can be reduced, thereby improving the growth quality of the last well, which is beneficial to improving the radiative recombination efficiency of electrons and holes, and thus improving the light output power of the AlGaN-based ultraviolet LED.

[0037] Some embodiments of the present application provide a method for preparing an AlGaN-based ultraviolet LED epitaxial structure, including sequentially growing an N-type Al b Ga 1-b N layer, a multiple quantum well active region, a P-type Al c Ga 1-c N electron blocking layer and a P-type GaN contact layer, 0 < b ≤ 1, 0 < c ≤ 1; wherein, the step of growing the multiple quantum well active region specifically includes: alternately growing a plurality of Al x Ga 1-x N quantum well layers and a plurality of Al y Ga 1-y N quantum barrier layers, 0 < x ≤ 1, 0 < y ≤ 1, and doping Si in the last Al x Ga 1-x N quantum well layer in the specified direction.

[0038] In one embodiment, the preparation method specifically includes:

[0039] Growing an AlN layer on a substrate;

[0040] Growing Al a Ga 1-a N transition layer, where 0 < a ≤ 1;

[0041] Al a Ga 1-a Growing an N-type Al b Ga 1-b N layer on the N transition layer, where 0 < b ≤ 1;

[0042] Overlapping and growing m cycles of a first Al b Ga 1-b N quantum well layer and a first Al x1 Ga 1-x1 N quantum barrier layer on the N-type Al y1 Ga 1- y1 to form a first quantum well structure, where 1 ≤ m ≤ 10, 0 < x1 ≤ 1, 0 < y1 ≤ 1;

[0043] Growing a second Al x2 Ga 1-x2 N quantum well layer and a second Al y2 Ga 1-y2 N quantum barrier layer on the first quantum well structure, where 0 < x2 ≤ 1, 0 < y2 ≤ 1, to form a second quantum well structure, and the first quantum well structure and the second quantum well structure cooperate to form a multi-quantum well active region;

[0044] Growing a P-type Al c Ga 1-c N electron blocking layer on the multi-quantum well active region;

[0045] Growing a P-type GaN contact layer on the P-type Al c Ga 1-c N electron blocking layer.

[0046] Please refer to Figure 2 As shown, in a typical embodiment of the present application, a method for preparing the ultraviolet LED epitaxial structure includes:

[0047] (1) Providing a substrate;

[0048] (2) Placing the substrate into the reaction chamber of an MOCVD machine, and after heating to a first preset temperature, introducing an Al source and NH3 into the reaction chamber to form an AlN layer on the surface of the substrate;

[0049] (3) At the second preset temperature, introduce an Al source, a Ga source, and NH3 to form Al a Ga 1-a N transition layer on the side of the AlN layer away from the substrate;

[0050] (4) At the third preset temperature, form an N-type Al a Ga 1-a N layer on the side of the Al b Ga 1-b N transition layer away from the substrate;

[0051] (5) On the side of the N-type Al b Ga 1-b N layer away from the substrate, alternately grow m cycles of a first Al x1 Ga 1-x1 N quantum well layer and a first Al y1 Ga 1-y1 N quantum barrier layer to form a first quantum well structure; where 1 ≤ m ≤ 10, and the first Al y1 Ga 1-y1 N quantum barrier layer is doped with Si;

[0052] (6) Grow a last Si-doped Al x2 Ga 1-x2 N quantum well on the side of the first quantum well structure away from the substrate, and grow a last Al x2 Ga 1-x2 N quantum barrier on the side of the last quantum well Al y2 Ga 1-y2 N away from the substrate to form a second quantum well structure; the first quantum well structure and the second quantum well structure form an Al x Ga 1-x N / Al y Ga 1-y N multiple quantum well active region;

[0053] (7) Form a P-type Al x Ga 1-x N / Al y Ga 1-y N electron blocking layer on the side of the Al c Ga 1-c N multiple quantum well active region away from the substrate;

[0054] (8) Form a P-type GaN contact layer on the side of the P-type Al c Ga 1-c N electron blocking layer away from the substrate to obtain the fabricated AlGaN-based ultraviolet LED epitaxial structure.

[0055] Among them, the AlN layer may include a low-temperature AlN layer, a medium-temperature AlN layer, and a high-temperature AlN layer that are sequentially grown.

[0056] Among them, the first preset temperature may be higher than or lower than the second preset temperature, and the third preset temperature is lower than the second preset temperature.

[0057] The purpose, technical solution, and advantages of the present application will be further elaborated below in conjunction with specific embodiments.

[0058] Embodiment 1

[0059] Please refer to an AlGaN-based ultraviolet LED epitaxial structure provided in this embodiment Figure 1 .

[0060] A method for fabricating the AlGaN-based ultraviolet LED epitaxial structure includes the following steps:

[0061] S1: Place the sapphire substrate in the reaction chamber of the MOCVD machine. At 900 °C and a reaction chamber pressure of 60 mbar, introduce TMAl, NH3, and H2 to form a low-temperature AlN layer with a thickness of 20 nm on the substrate surface;

[0062] S2: At a temperature of 1100 °C, introduce TMAl, NH3, and H2 to form a medium-temperature AlN layer with a thickness of approximately 0.4 μm;

[0063] S3: At a temperature of 1250 °C, introduce TMAl, NH3, and H2 to form a high-temperature AlN layer with a thickness of approximately 2.5 μm;

[0064] S4: At a temperature of 1150 °C, introduce TMAl, TMGa, NH3, and H2 into the reaction chamber to form an Al a Ga 1-a N transition layer with 0.6 ≤ a ≤ 1;

[0065] S5: Lower the temperature to 1100 °C, introduce TMAl, TMGa, SiH4, NH3, and H2 to form an N-type Al 0.55 Ga 0.45 N layer with a thickness of approximately 1.8 μm. The doping concentration of Si is 1.0E+19 cm -3 ;

[0066] S6: At a temperature of 1100 °C, introduce TMAl, TMGa, NH3, and H2 to form a first Al 0.3 Ga 0.7 N quantum well layer with a thickness of 2 nm;

[0067] S7: Introduce TMAl, TMGa, SiH4, NH3 and H2 to form a Si-doped first Al 0.5 Ga 0.5 N quantum barrier layer with a thickness of 12 nm and a Si doping concentration of 9E+18 cm -3 ;

[0068] S8: After repeating steps S6 and S7 four times each, a first quantum well structure is obtained;

[0069] S9: Introduce TMAl, TMGa, SiH4, NH3 and H2 to form the last Si-doped Al x2 Ga 1-x2 N quantum well layer with a Si doping concentration of 3E+18 cm -3 , a thickness of 2 nm, and an Al component of 30%;

[0070] S10: Introduce TMAl, TMGa, NH3 and H2 to form the last non-Si-doped Al y2 Ga 1-y2 N quantum barrier layer with a thickness of 6 nm and an Al component of 50%;

[0071] S11: At a temperature of 1060 °C, introduce Cp2Mg, TMAl, TMGa, NH3 and H2 to form a P-type Al 0.7 Ga 0.3 N electron blocking layer with a Mg doping concentration of 8E+18 cm -3 ;

[0072] S12: Cool down to 930 °C, introduce Cp2Mg, TMGa, NH3 and H2 to form a P-type GaN contact layer with a Mg concentration of about 1E+20 cm -3 and a thickness of about 80 nm, obtaining the prepared ultraviolet LED epitaxial wafer.

[0073] The ultraviolet LED epitaxial wafer finally obtained in this embodiment is denoted as epitaxial wafer 1.

[0074] Example 2

[0075] An AlGaN-based ultraviolet LED epitaxial structure provided in this embodiment can also be referred to Figure 1 .

[0076] A method for fabricating the AlGaN-based ultraviolet LED epitaxial structure is similar to that in Example 1, except for steps S6 - S10. That is, the preparation method of the multi-quantum well active region in this embodiment is as follows:

[0077] S6: At a temperature of 1100 °C, introduce TMAl, TMGa, NH3 and H2 to form the first Al 0.3 Ga0.7 N quantum well layer with a thickness of 2 nm;

[0078] S7: Introduce TMAl, TMGa, SiH4, NH3 and H2 to form a first Si-doped Al 0.5 Ga 0.5 N quantum barrier layer with a thickness of 12 nm and a Si doping concentration of 9E+18 cm -3 ;

[0079] S8: After repeating steps S6 and S7 four times each, a first quantum well structure is obtained;

[0080] S9: Introduce TMAl, TMGa, SiH4, NH3 and H2 to form the last Si-doped Al 0.3 Ga 0.7 N quantum well with a Si doping concentration of 6E+18 cm -3 and a thickness of 2 nm;

[0081] S10: Introduce TMAl, TMGa, NH3 and H2 to form the last Si-undoped Al 0.5 Ga 0.5 N quantum barrier with a thickness of 6 nm.

[0082] The ultraviolet LED epitaxial wafer finally obtained in this embodiment is denoted as epitaxial wafer 2.

[0083] Example 3

[0084] An AlGaN-based ultraviolet LED epitaxial structure provided in this embodiment can also be referred to Figure 1 .

[0085] A method for fabricating the AlGaN-based ultraviolet LED epitaxial structure is similar to that in Example 1, except for steps S6 - S10. That is, the preparation method of the multi-quantum well active region in this embodiment is as follows:

[0086] S6: At a temperature of 1100 °C, introduce TMAl, TMGa, NH3 and H2 to form a first Al 0.3 Ga 0.7 N quantum well layer with a thickness of 2 nm;

[0087] S7: Introduce TMAl, TMGa, SiH4, NH3 and H2 to form a first Si-doped Al 0.5 Ga 0.5 N quantum barrier layer with a thickness of 12 nm and a Si doping concentration of 9E+18 cm -3 ;

[0088] S8: After repeating steps S6 and S7 four times each, a first quantum well structure is obtained;

[0089] S9: Introduce TMAl, TMGa, SiH4, NH3 and H2 to form the last Si-doped Al 0.3 Ga 0.7 N quantum well with a Si doping concentration of 9E+18 cm -3 , with a thickness of 2 nm;

[0090] S10: Introduce TMAl, TMGa, NH3 and H2 to form the last quantum barrier AlGaN without Si doping 0.5 Ga 0.5 N with a thickness of 6 nm.

[0091] The finally obtained ultraviolet LED epitaxial wafer in this embodiment is denoted as epitaxial wafer 3.

[0092] Example 4

[0093] The AlGaN-based ultraviolet LED epitaxial structure provided in this embodiment can also refer to Figure 1 .

[0094] A method for fabricating the AlGaN-based ultraviolet LED epitaxial structure is similar to that in Example 1, except for steps S6 - S10. That is, the preparation method of the multi-quantum well active region in this embodiment is as follows:

[0095] S6: At a temperature of 1100 °C, introduce TMAl, TMGa, NH3 and H2 to form the first Al x1 Ga 1-x1 N quantum well layer with a thickness of 2 nm and an Al composition of 30%;

[0096] S7: Introduce TMAl, TMGa, SiH4, NH3 and H2 to form the first Si-doped Al y Ga 1-y N quantum barrier layer with a thickness of 12 nm, an Al composition of 50%, and a Si doping concentration of 9E+18 cm -3 ;

[0097] S8: After repeating steps S6 and S7 four times each, obtain the first quantum well structure;

[0098] S9: Introduce TMAl, TMGa, SiH4, NH3 and H2 for 5 seconds to form a 0.4 nm AlGaN:Si layer, close SiH4 growth for 5 seconds to form a 0.4 nm AlGaN layer, alternately switch SiH4, and pulse-introduce SiH4 to form the last Al of the AlGaN:Si / AlGaN / AlGaN:Si / AlGaN / AlGaN:Si composite structure 0.3 Ga 0.7 N quantum well with a Si doping concentration of 6E+18 cm -3, with a thickness of 2 nm;

[0099] S10: Introduce TMAl, TMGa, NH3, and H2 to form the last Si-free quantum barrier Al 0.5 Ga 0.5 N, with a thickness of 6 nm.

[0100] In this embodiment, steps S1 - S5 and steps S11 - S12 in the preparation of the ultraviolet LED epitaxial structure are the same as those in the above-mentioned Embodiment 1, and will not be elaborated here.

[0101] The finally obtained ultraviolet LED epitaxial wafer in this embodiment is denoted as epitaxial wafer 4.

[0102] Comparative example:

[0103] A method for fabricating an AlGaN-based ultraviolet LED epitaxial structure is similar to that in Embodiment 1, except that in step S9, SiH4 is turned off during the growth of the last quantum well to form the last Si-free quantum well.

[0104] The finally obtained ultraviolet LED epitaxial wafer in this comparative example is denoted as epitaxial wafer 5.

[0105] The above-mentioned epitaxial wafers 1, 2, 3, 4, and 5 are respectively subjected to EL quick inspection measurements at currents of 100 mA, 40 mA, and 20 mA, and the results are shown in Table 1.

[0106] Table 1 EL quick inspection measurement results of epitaxial wafers 1 - 5

[0107]

[0108] Compared with epitaxial wafer 5, the brightness of epitaxial wafers 1 - 4 has been improved, especially the brightness improvement is more obvious at a small current of 20 mA. Among them, when the Si doping concentration is 6E+18 cm -3 , the brightness is the highest at currents of 100 mA, 40 mA, and 20 mA. The last AlGaN quantum well of the ultraviolet LED is the main light-emitting well, and electrons and holes mainly generate radiative recombination in the last well, emitting ultraviolet light. By doping Si in the last well, the stress state of the quantum well layer is adjusted to change from compressive strain to tensile strain, thereby reducing the compressive strain, improving the growth quality of the last quantum well, reducing the non-radiative recombination center, and playing a role in improving the light output power.

[0109] The above-described embodiments only represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several deformations and improvements can still be made, and these all belong to the protection scope of the present application.

Claims

1. An AlGaN-based ultraviolet LED epitaxial structure, comprising an N-type Al sequentially arranged in a specified direction b Ga 1-b N layer, a multi-quantum well active region, a P-type Al c Ga 1-c N electron blocking layer and a P-type GaN contact layer, where 0 < b ≤ 1, 0 < c ≤ 1; It is characterized in that: The multi-quantum well active region includes a first quantum well structure and a second quantum well structure arranged in sequence along the specified direction. The first quantum well structure includes m periods of alternately grown first Al x1 Ga 1-x1 N quantum well layers and first Al y1 Ga 1-y1 N quantum barrier layers, where 0 < x1 ≤ 1, 0 < y1 ≤ 1, and 1 ≤ m ≤ 10. The second quantum well structure includes a second Al x2 Ga 1-x2 N quantum well layer and a second Al y2 Ga 1-y2 N quantum barrier layer, where 0 < x2 ≤ 1, 0 < y2 ≤ 1. The second Al x2 Ga 1-x2 N quantum well layer is the last Al x Ga 1-x N quantum well layer in the specified direction. And the first Al x1 Ga 1-x1 N quantum well layer is not doped with Si, the first Al y1 Ga 1-y1 N quantum barrier layer is doped with Si, the second Al x2 Ga 1-x2 N quantum well layer is doped with Si, and the second Al y2 Ga 1-y2 N quantum barrier layer is not doped with Si.

2. The AlGaN-based ultraviolet LED epitaxial structure according to claim 1, wherein: The second Al x2 Ga 1-x2 The Si concentration doped in the N quantum well layer is 1E+17 cm -3 ~1E+20 cm -3 .

3. The AlGaN-based ultraviolet LED epitaxial structure according to claim 1, wherein: The second Al x2 Ga 1-x2 The local or all regions of the N quantum well layer are doped with Si.

4. The AlGaN-based ultraviolet LED epitaxial structure according to claim 1, wherein: The second Al x2 Ga 1-x2 The doping method of Si in the N quantum well layer includes graded doping, gradient doping, pulse doping or uniform doping.

5. The AlGaN-based ultraviolet LED epitaxial structure according to claim 1, characterized in that: The second Al x2 Ga 1-x2 The doping concentration of Si in the N quantum well layer is higher or lower than that of Si in the first Al y1 Ga 1-y1 N quantum barrier layer.

6. The AlGaN-based ultraviolet LED epitaxial structure according to claim 1, characterized in that: One period composed of a mutually cooperating Al x Ga 1-x N quantum well layer and an Al y Ga 1-y N quantum barrier layer has a thickness of 3 - 20 nm.

7. The AlGaN-based ultraviolet LED epitaxial structure according to claim 1, wherein: The Al component content of the quantum well layer in the multi-quantum well active region is lower than that of the quantum barrier layer.

8. The AlGaN-based ultraviolet LED epitaxial structure according to claim 1, characterized in that: The epitaxial structure includes an AlN layer, an Al a Ga 1-a N transition layer, an N-type Al b Ga 1-b N layer, a multi-quantum well active region, a P-type Al c Ga 1-c N electron blocking layer, and a P-type GaN contact layer, where 0 < a ≤ 1 and 0 < b ≤ 1.

9. The AlGaN-based ultraviolet LED epitaxial structure according to claim 8, characterized in that: The Al a Ga 1-a N transition layer, N-type Al b Ga 1-b N layer, and the Al composition content of the P-type Al c Ga 1-c N electron blocking layer is higher than the Al composition content of the quantum well layer in the multi-quantum well active region.

10. The AlGaN-based ultraviolet LED epitaxial structure according to claim 8, wherein, The substrate includes a sapphire, aluminum nitride or silicon substrate.

11. The preparation method of the AlGaN-based ultraviolet LED epitaxial structure according to any one of claims 1-10, characterized in that, Specifically, it includes: Growing an AlN layer on the substrate; Growing Al on the AlN layer a Ga 1-a N transition layer, where 0 < a ≤ 1; On the Al a Ga 1-a N buffer layer, an N-type Al b Ga 1-b N layer is grown, where 0 < b ≤ 1; On the N-type Al b Ga 1-b N layer, m periods of the first Al x1 Ga 1-x1 N quantum well layers and the first Al y1 Ga 1-y1 N quantum barrier layers are grown overlappingly to form a first quantum well structure, 1 ≤ m ≤ 10, 0 < x1 ≤ 1, 0 < y1 ≤ 1; A second Al is sequentially grown on the first quantum well structure x2 Ga 1-x2 N quantum well layer and a second Al y2 Ga 1-y2 N quantum barrier layer, where 0 < x2 ≤ 1 and 0 < y2 ≤ 1, to form a second quantum well structure, and the first quantum well structure and the second quantum well structure cooperate to form a multi-quantum well active region; Grow a P-type Al c Ga 1-c N electron blocking layer on the multi-quantum well active region; On the P-type Al c Ga 1-c A P-type GaN contact layer is grown on the N electron blocking layer.

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