Light emitting diode epitaxial wafer and preparation method thereof, and light emitting diode

Abstract

The application discloses a light emitting diode epitaxial wafer and a preparation method thereof and a light emitting diode. The light emitting diode epitaxial wafer comprises a substrate, a buffer layer, a non-doped GaN layer, an N-type GaN layer, a stress offset layer, a multi-quantum well layer, an electron blocking layer and a P-type GaN layer which are sequentially stacked on the substrate; the stress offset layer comprises a first sub-layer and a second sub-layer; the first sub-layer is a Cr-doped GaN layer; and the second sub-layer comprises a Cr-doped AlGaN layer and a BGaN layer which are sequentially stacked. The light emitting diode prepared by the application can release the tensile stress of a GaN epitaxial layer and the mismatch stress of an active region, thereby improving the light emitting efficiency of the light emitting diode epitaxial wafer.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a light-emitting diode epitaxial wafer and its fabrication method, and a light-emitting diode. Background Technology

[0002] GaN-based semiconductors, characterized by high power, high efficiency, and high operating temperature, have been widely used in power electronics, microwave communications, and other fields. However, the high In content in the InGaN quantum well in the active region leads to significant mismatch stress between the InGaN quantum well and the n-type GaN layer. This mismatch stress generates interlayer and intralayer defects, resulting in leakage channels, difficulties in In composition incorporation into the InGaN quantum well, numerous crystal defects, and a large polarization electric field. To address this issue, an InGaN / GaN superlattice layer is typically inserted after the n-type GaN layer to buffer the mismatch stress in the active region.

[0003] However, significant tensile stress exists between the substrate and the GaN epitaxial layer. Using AlN as a buffer layer, due to the difference in lattice constants between GaN and AlN, some defects exist at the GaN-AlN interface, resulting in dislocation defects that extend into the light-emitting layer. Common InGaN / GaN superlattice stress-relieving layers cannot release the large tensile stress between the substrate and the GaN epitaxial layer. The continuous accumulation of tensile stress can even lead to epitaxial layer fracture. Furthermore, the high lattice torsion energy of GaN results in insufficient stress relief. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a light-emitting diode epitaxial wafer that can release the tensile stress of the GaN epitaxial layer and the mismatch stress of the active region, thereby improving the luminous efficiency of the light-emitting diode epitaxial wafer.

[0005] The technical problem to be solved by the present invention is to provide a method for preparing an epitaxial wafer of a light-emitting diode, which is simple in process and produces an epitaxial wafer of a light-emitting diode with high luminous efficiency.

[0006] To achieve the above-mentioned technical effects, the present invention provides a light-emitting diode epitaxial wafer, comprising a substrate and a buffer layer, an undoped GaN layer, an N-type GaN layer, a stress relief layer, a multiple quantum well layer, an electron blocking layer and a P-type GaN layer sequentially stacked on the substrate;

[0007] The stress relief layer includes a first sub-layer and a second sub-layer. The first sub-layer is a Cr-doped GaN layer, and the second sub-layer is a periodic structure formed by alternating layers of Cr-doped AlGaN and BGaN layers, with a period number of 1-20.

[0008] As an improvement to the above technical solution, the thickness of the first sublayer is 1nm-100nm.

[0009] As an improvement to the above technical solution, the thickness of the Cr-doped AlGaN layer is 5nm-10nm, and the thickness of the BGaN layer is 0.5nm-10nm.

[0010] As an improvement to the above technical solution, the doping concentration of the Cr-doped GaN layer is 1×10⁻⁶. 18 cm -3 -1×10 20 cm -3 .

[0011] As an improvement to the above technical solution, the doping concentration in the Cr-doped AlGaN layer is 1.5 × 10⁻⁶. 18 cm -3 -5×10 19 cm -3 .

[0012] As an improvement to the above technical solution, the Al composition ratio in the Cr-doped AlGaN layer is 0.01-0.6.

[0013] Accordingly, the present invention also discloses a method for preparing a light-emitting diode epitaxial wafer, which includes the following steps:

[0014] A substrate is provided on which a buffer layer, an undoped GaN layer, an N-type GaN layer, a stress relief layer, a multiple quantum well layer, an electron blocking layer and a P-type GaN layer are sequentially grown.

[0015] The stress relief layer includes a first sub-layer and a second sub-layer. The first sub-layer is a Cr-doped GaN layer, and the second sub-layer is a periodic structure formed by alternating layers of Cr-doped AlGaN and BGaN layers, with a period number of 1-20.

[0016] As an improvement to the above technical solution, the growth temperature of the stress-relief layer is 400℃-1100℃, and the growth pressure is 50Torr-500Torr.

[0017] As an improvement to the above technical solution, the growth atmosphere of the stress-relief layer is N2 and NH3, and the flow rate ratio of N2 to NH3 is 1:(1-10).

[0018] Accordingly, the present invention also discloses a light-emitting diode, including the above-mentioned light-emitting diode epitaxial wafer.

[0019] Implementing the embodiments of the present invention has the following beneficial effects:

[0020] This invention grows a stress-relief layer between an N-type GaN layer and a multi-quantum-well layer. The stress-relief layer comprises a first sub-layer and a second sub-layer. The first sub-layer is a Cr-doped GaN layer, and the second sub-layer is a periodic structure formed by alternating layers of Cr-doped AlGaN and BGaN layers. The deposition of the Cr-doped GaN layer, with the introduction of Cr acting as an acceptor level, can alleviate electron migration rates, thereby reducing electron overflow. The lattice constant of the Cr-doped AlGaN layer is greater than that of the BGaN layer. The alternating stacking of these layers results in alternating tensile and compressive stresses, effectively releasing the stress accumulated in the epitaxial layer. This also improves the crystal quality of the interface and prevents dislocation lines from extending into the multi-quantum-well layer and causing piezoelectric polarization. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the light-emitting diode epitaxial wafer provided in an embodiment of the present invention;

[0022] Figure 2 This is a flowchart of the method for fabricating a light-emitting diode epitaxial wafer provided in an embodiment of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments.

[0024] like Figure 1 As shown, an embodiment of the present invention provides a light-emitting diode epitaxial wafer, including a substrate 1 and a buffer layer 2, an undoped GaN layer 3, an N-type GaN layer 4, a stress-relief layer 5, a multiple quantum well layer 6, an electron blocking layer 7, and a P-type GaN layer 8 sequentially stacked on the substrate 1.

[0025] The stress-relief layer includes a first sub-layer and a second sub-layer. The first sub-layer is a Cr-doped GaN layer, and the second sub-layer is a periodic structure formed by alternating layers of Cr-doped AlGaN and BGaN layers, with a period number of 1-20.

[0026] First, the first sublayer is deposited. Cr is mainly introduced into the GaN lattice as Ga substitution sites, increasing the lattice constant of the GaN layer along the C-axis. Because the lattice constant of the Cr-doped GaN layer is greater than that of GaN, it generates tensile stress in the GaN to counteract the compressive stress accumulated from the underlying layer. Simultaneously, the introduction of Cr acts as an acceptor level, which can alleviate electron migration rates and reduce electron overflow. Next, the second sublayer is deposited. Alternating layers of Cr-doped AlGaN and BGaN reduce defects, improve the crystal quality of the interface, and reduce the extension of dislocation lines into the multi-quantum-well layer, avoiding piezoelectric polarization. Furthermore, because B atoms are small, they can continuously fill defects, thereby improving luminescence efficiency.

[0027] In one embodiment, the thickness of the first sublayer is 1 nm to 100 nm. For example, the thickness of the first sublayer is 1 nm, 10 nm, 20 nm, 50 nm or 100 nm, but is not limited thereto.

[0028] In one embodiment, the thickness of the Cr-doped AlGaN layer is 5 nm-10 nm, and the thickness of the BGaN layer is 0.5 nm-10 nm. The alternating stacking of Cr-doped AlGaN and BGaN layers, due to their sufficiently thin thickness, can continuously distort the stress at the interface during the alternating growth process. Furthermore, because the lattice constant of the Cr-doped AlGaN layer is greater than that of the BGaN layer, the alternating stacking of the two layers causes alternating tensile and compressive stresses, further effectively releasing the stress accumulated in the epitaxial layer.

[0029] In one embodiment, the doping concentration of the Cr-doped GaN layer is 1 × 10⁻⁶. 18 cm -3 -1×10 20 cm -3 If the doping concentration of the Cr-doped GaN layer is < 1 × 10⁻⁶ 18 cm -3 It cannot provide sufficient tensile stress; if the doping concentration of the Cr-doped GaN layer is >1×10⁻⁶, it will not provide sufficient tensile stress. 20 cm -3 This will affect the lattice matching between the Cr-doped GaN layer and GaN. For example, the Cr-doped GaN layer has a doping concentration of 1 × 10⁻⁶. 18 cm -3 1.5×10 18 cm -3 7×10 18 cm -3 1×10 19 cm -3 5×10 18 cm -3 Or 1×10 20 cm -3 However, it is not limited to this.

[0030] In one embodiment, the doping concentration in the Cr-doped AlGaN layer is 1.5 × 10⁻⁶. 18 cm -3 -5×10 19 cm -3 If the doping concentration of the Cr-doped AlGaN layer is < 1.5 × 10⁻⁶ 18 cm -3 It cannot prevent dislocation propagation; if the doping concentration of the Cr-doped AlGaN layer is >5×10 19 cm-3 This will affect the lattice matching of the Cr-doped AlGaN and BGaN layers. For example, the Cr-doped AlGaN layer has a doping concentration of 1.5 × 10⁻⁶. 18 cm -3 5×10 18 cm -3 1×10 19 cm -3 Or 5×10 19 cm -3 However, it is not limited to this.

[0031] In one embodiment, the Al content in the Cr-doped AlGaN layer is 0.01-0.6%. For example, the Al content in the Cr-doped AlGaN layer is 0.01, 0.05, 0.2, 0.4, or 0.6, but is not limited thereto.

[0032] In addition to the stress-relief layer mentioned above, the other features of the layered structure of the present invention are as follows:

[0033] In one embodiment, the substrate 1 is one of a sapphire substrate, a SiO2 / sapphire composite substrate, a silicon substrate, a silicon carbide substrate, a gallium nitride substrate, and a zinc oxide substrate. Preferably, the substrate 1 is a sapphire substrate.

[0034] In one embodiment, the buffer layer 2 is an AlGaN buffer layer or an AlN buffer layer. Preferably, the nucleation layer 2 is an AlN buffer layer, and the thickness of the buffer layer 2 is 10 nm-50 nm.

[0035] In one embodiment, the thickness of the undoped GaN layer 3 is 1 μm-5 μm.

[0036] In one embodiment, the thickness of the N-type GaN layer 4 is 2μm-3μm, and the N-type doping can be Si doping with a Si doping concentration of 1×10⁻⁶. 19 cm -3 -5×10 19 cm -3 .

[0037] In one embodiment, the multi-quantum-well layer 6 comprises periodically stacked InGaN quantum well layers and AlGaN quantum barrier layers, with a stacking period of 6-12. The InGaN quantum well layer has a thickness of 2nm-5nm and an In composition of 0.1-0.3; the AlGaN quantum barrier layer has a thickness of 5nm-15nm and an Al composition of 0.01-0.1.

[0038] In one embodiment, the electron blocking layer 7 is an AlInGaN layer with a thickness of 10nm-40nm, wherein the Al component accounts for 0.005-0.1% and the In component accounts for 0.01-0.2%.

[0039] In one embodiment, the thickness of the p-type GaN layer 8 is 10nm-50nm, and the p-type doping can be Mg doping with a Mg doping concentration of 1×10⁻⁶. 19 cm -3 -1×10 21 cm -3 .

[0040] Correspondingly, such as Figure 2 As shown, the present invention also provides a method for fabricating a light-emitting diode epitaxial wafer, comprising the following steps:

[0041] S100 provides a substrate:

[0042] A sapphire substrate was selected and loaded into the MOCVD chamber. The reaction chamber temperature was controlled at 1000℃-1200℃ and the pressure at 200Torr-600Torr. The sapphire substrate was subjected to high-temperature annealing for 5-8 minutes in an H2 atmosphere to clean the particles and oxides on the surface of the sapphire substrate.

[0043] S200 growth buffer layer:

[0044] PVD growth is employed, with sputtering temperature controlled at 600℃-900℃, sputtering power at 1500W-3000W, target material being pure aluminum (99.999% purity), and sputtering reaction gas being a mixture of N2 and Ar.

[0045] In one implementation, it further includes:

[0046] S300 pre-treats the substrate with the deposited buffer layer:

[0047] The substrate with the buffer layer deposited is transferred into MOCVD and pretreated in H2 atmosphere for 1 min-10 min at a temperature of 1000℃-1200℃, and then nitrided.

[0048] S400 growth of undoped GaN layers:

[0049] MOCVD growth was employed, with the reaction chamber temperature controlled at 1050℃-1200℃ and the pressure at 100Torr-600Torr. NH3 was introduced as the N source, N2 and H2 were introduced as the carrier gas, and TMGa was introduced as the Ga source.

[0050] S500 growth of N-type GaN layers:

[0051] MOCVD growth was employed, with the reaction chamber temperature controlled at 1050℃-1200℃ and the pressure at 100Torr-600Torr. NH3 was introduced as the N source, N2 and H2 as the carrier gas, TMGa as the Ga source, and SiH4 as the doping source.

[0052] The S600 growth stress-relief layer, specifically, in one embodiment, includes the following steps:

[0053] S601 grows the first sublayer:

[0054] GaN thin films were prepared by MOCVD, with the reaction chamber temperature controlled at 800℃-1100℃ and the pressure at 50Torr-500Torr. NH3 was introduced as the N source and N2 as the carrier gas, with a flow ratio of N2 to NH3 of 1:(1-10). TEGa was introduced as the Ga source. After cooling, chromium ions were implanted at 350℃-450℃ using high-energy ion implantation at 100keV-300keV to grow a Cr-doped GaN layer.

[0055] S602 grows the second sublayer:

[0056] AlGaN thin films were prepared by MOCVD. The reaction chamber temperature was controlled at 800℃-1000℃ and the pressure at 50Torr-500Torr. NH3 was introduced as the N source and N2 as the carrier gas, with a flow ratio of N2 to NH3 of 1:(1-10). TMAl was introduced as the Al source and TEGa as the Ga source. After cooling, chromium ions were implanted at 350℃-450℃ using high-energy ion implantation at 100keV-300keV to grow a Cr-doped AlGaN layer. The reaction chamber temperature and pressure were kept constant, and NH3 was introduced as the N source, N2 as the carrier gas, TEGa as the Ga source, and TEB as the B source to grow a BGaN layer.

[0057] In one embodiment, Cr-doped AlGaN and BGaN layers are repeatedly stacked and periodically grown.

[0058] S700 growth of multiple quantum well layers:

[0059] MOCVD growth was employed, with the reaction chamber temperature controlled at 790℃-810℃ and the pressure at 50Torr-300Torr. NH3 was introduced as the N source, N2 as the carrier gas, TEGa as the Ga source, and TMIn as the In source to grow an InGaN quantum well layer. The reaction chamber temperature was controlled at 800℃-900℃, while maintaining constant pressure. NH3 was introduced as the N source, N2 and H2 as the carrier gases, TEGa as the Ga source, and TMAl as the Al source to grow an AlGaN quantum barrier layer. InGaN quantum well layers and AlGaN quantum barrier layers were then repeatedly stacked and periodically grown.

[0060] S800 electron blocking layer growth:

[0061] MOCVD growth was employed, with the reaction chamber temperature controlled at 900℃-1000℃ and the pressure at 100Torr-300Torr. NH3 was introduced as the N source, N2 and H2 as the carrier gas, TMGa as the Ga source, TMAl as the Al source, and TMIn as the In source.

[0062] S900 growth of P-type GaN layers:

[0063] MOCVD growth was employed, with the reaction chamber temperature controlled at 900℃-1050℃ and the pressure at 100Torr-600Torr. NH3 was introduced as the N source, N2 and H2 as the carrier gas, TMGa as the Ga source, and CP2Mg as the doping source.

[0064] The present invention will be further illustrated below with specific embodiments.

[0065] Example 1

[0066] This embodiment provides a light-emitting diode epitaxial wafer, including a substrate and a buffer layer, an undoped GaN layer, an N-type GaN layer, a stress-relief layer, a multiple quantum well layer, an electron blocking layer, and a P-type GaN layer sequentially stacked on the substrate.

[0067] The substrate is a sapphire substrate.

[0068] The buffer layer is an AlN buffer layer with a thickness of 15nm.

[0069] The thickness of the undoped GaN layer is 2 μm.

[0070] The thickness of the N-type GaN layer is 2 μm, and the Si doping concentration is 2.5 × 10⁻⁶. 19 cm -3 .

[0071] The stress-relief layer consists of a first sublayer and a second sublayer. The first sublayer is a Cr-doped GaN layer with a thickness of 60 nm and a Cr doping concentration of 1.5 × 10⁻⁶.19 cm -3 The second sublayer is a periodic structure formed by alternating layers of Cr-doped AlGaN and BGaN layers, with a period number of 10. The thickness of a single Cr-doped AlGaN layer is 6 nm, and the Cr doping concentration is 1.5 × 10⁻⁶. 19 cm -3 The Al component accounts for 0.1% of the total content; the thickness of a single BGaN layer is 3 nm.

[0072] The multiple quantum well layer consists of alternating layers of InGaN quantum wells and AlGaN quantum barriers, with a stacking period of 10. The InGaN quantum well layer is 3.5 nm thick with an In content of 0.2%; the AlGaN quantum barrier layer is 9.8 nm thick with an Al content of 0.05%.

[0073] The electron blocking layer is an AlInGaN layer with a thickness of 15 nm. The Al content gradually changes from 0.01 to 0.05 along the growth direction of the epitaxial layer, and the In content is 0.01.

[0074] The thickness of the p-type GaN layer is 15 nm, and the Mg doping concentration is 2 × 10⁻⁶. 20 cm -3 .

[0075] The above-mentioned method for fabricating an epitaxial wafer of a light-emitting diode includes the following steps:

[0076] S100 provides a substrate:

[0077] A sapphire substrate was selected and loaded into the MOCVD chamber. The reaction chamber temperature was controlled at 1100℃ and the pressure at 250 Torr. The sapphire substrate was subjected to high-temperature annealing for 6 minutes in an H2 atmosphere to clean the particles and oxides on the surface of the sapphire substrate.

[0078] S200 growth buffer layer:

[0079] PVD growth was employed, with the sputtering temperature controlled at 750℃, the sputtering power at 2000W, the target material being pure aluminum (99.999% purity), and the sputtering reaction gas being a mixture of N2 and Ar.

[0080] S300 pre-treats the substrate with the deposited buffer layer:

[0081] The substrate with the buffer layer deposited was transferred into MOCVD and pretreated in H2 atmosphere for 6 min at a temperature of 1100℃, and then nitrided.

[0082] S400 growth of undoped GaN layers:

[0083] MOCVD growth was employed, with the reaction chamber temperature controlled at 1100℃ and the pressure at 150 Torr. NH3 was introduced as the N source, N2 and H2 were introduced as the carrier gas, and TMGa was introduced as the Ga source.

[0084] S500 growth of N-type GaN layers:

[0085] MOCVD growth was employed, with the reaction chamber temperature controlled at 1120℃ and the pressure at 200 Torr. NH3 was introduced as the N source, N2 and H2 as the carrier gas, TMGa as the Ga source, and SiH4 as the doping source.

[0086] The S600 growth stress-compensating layer specifically includes the following steps:

[0087] S601 grows the first sublayer:

[0088] GaN thin films were prepared by MOCVD, with the reaction chamber temperature controlled at 900℃ and the pressure at 150 Torr. NH3 was introduced as the N source and N2 as the carrier gas, with a flow ratio of N2 to NH3 of 1:10. TEGa was introduced as the Ga source. After cooling, chromium ions were implanted at 250 keV using high-energy ion implantation at 450℃ to grow a Cr-doped GaN layer.

[0089] S602 grows the second sublayer:

[0090] AlGaN thin films were prepared by MOCVD. The reaction chamber temperature was controlled at 950℃ and the pressure at 150 Torr. NH3 was introduced as the N source and N2 as the carrier gas, with a flow rate ratio of N2 to NH3 of 1:10. TMAl was introduced as the Al source and TEGa as the Ga source. After cooling, chromium ions were implanted at 250 keV using high-energy ion implantation at 450℃ to grow a Cr-doped AlGaN layer. Keeping the reaction chamber temperature and pressure constant, NH3 was introduced as the N source and N2 as the carrier gas. TEGa was introduced as the Ga source and TEB as the B source to grow a BGaN layer. The Cr-doped AlGaN and BGaN layers were repeatedly stacked and periodically grown.

[0091] S700 growth of multiple quantum well layers:

[0092] MOCVD growth was employed, with the reaction chamber temperature controlled at 795℃ and the pressure at 200 Torr. NH3 was introduced as the N source, N2 as the carrier gas, TEGa as the Ga source, and TMIn as the In source to grow an InGaN quantum well layer. The reaction chamber temperature was then controlled at 855℃, while maintaining constant pressure. NH3 was introduced as the N source, N2 and H2 as the carrier gases, TEGa as the Ga source, and TMAl as the Al source to grow an AlGaN quantum barrier layer. InGaN quantum well layers and AlGaN quantum barrier layers were then repeatedly stacked and periodically grown.

[0093] S800 electron blocking layer growth:

[0094] MOCVD growth was employed, with the reaction chamber temperature controlled at 965℃ and the pressure at 200 Torr. NH3 was introduced as the N source, N2 and H2 as the carrier gas, TMGa as the Ga source, TMAl as the Al source, and TMIn as the In source.

[0095] S900 growth of P-type GaN layers:

[0096] MOCVD growth was employed, with the reaction chamber temperature controlled at 985℃ and the pressure at 200 Torr. NH3 was introduced as the N source, N2 and H2 as the carrier gas, TMGa as the Ga source, and CP2Mg as the doping source.

[0097] Example 2

[0098] This embodiment provides a light-emitting diode epitaxial wafer, wherein the stress-relief layer includes a first sub-layer and a second sub-layer. The first sub-layer is a Cr-doped GaN layer with a thickness of 60 nm and a Cr doping concentration of 5 × 10⁻⁶. 19 cm -3 The second sublayer is a periodic structure formed by alternating layers of Cr-doped AlGaN and BGaN, with a period number of 10. The thickness of a single Cr-doped AlGaN layer is 6 nm, and the Cr doping concentration is 1.5 × 10⁻⁶. 19 cm -3 The Al component accounts for 0.1% of the total composition; the thickness of a single BGaN layer is 3 nm. Everything else is the same as in Example 1.

[0099] Example 3

[0100] This embodiment provides a light-emitting diode epitaxial wafer, wherein the stress-relief layer includes a first sub-layer and a second sub-layer. The first sub-layer is a Cr-doped GaN layer with a thickness of 60 nm and a Cr doping concentration of 5 × 10⁻⁶. 18 cm -3 The second sublayer is a periodic structure formed by alternating layers of Cr-doped AlGaN and BGaN, with a period number of 10. The thickness of a single Cr-doped AlGaN layer is 6 nm, and the Cr doping concentration is 1.5 × 10⁻⁶. 19 cm -3 The Al component accounts for 0.1% of the total composition; the thickness of a single BGaN layer is 3 nm. Everything else is the same as in Example 1.

[0101] Comparative Example 1

[0102] This comparative example provides a light-emitting diode epitaxial wafer, which differs from Example 1 in that it does not include a stress-relief layer. Correspondingly, the fabrication method also excludes the step of preparing the stress-relief layer. Everything else is the same as in Example 1.

[0103] Comparative Example 2

[0104] This comparative example provides a light-emitting diode epitaxial wafer, which differs from Example 1 in that the stress-relief layer is a Cr-doped GaN layer with a thickness of 60 nm and a Cr doping concentration of 5 × 10⁻⁶. 18 cm -3 Accordingly, the preparation method does not include the step of preparing the second sublayer. Everything else is the same as in Example 1.

[0105] Comparative Example 3

[0106] This comparative example provides a light-emitting diode epitaxial wafer, which differs from Example 1 in that the stress-relief layer is a periodic structure formed by alternating layers of Cr-doped AlGaN and BGaN layers, with a period number of 10. The thickness of a single Cr-doped AlGaN layer is 6 nm, and the Cr doping concentration is 1.5 × 10⁻⁶. 19 cm -3 The Al component accounts for 0.1% of the total composition; the thickness of a single BGaN layer is 3 nm. Correspondingly, the preparation method does not include the preparation step of the first sublayer. Everything else is the same as in Example 2.

[0107] Performance testing:

[0108] The light-emitting diode epitaxial wafers obtained in Examples 1-3 and Comparative Examples 1-3 were fabricated into chips of 10mil×24mil and their photoelectric performance was tested at 120mA / 60mA current. The luminous efficacy improvement of Examples 1-3 and Comparative Examples 2 and 3 compared to Comparative Example 1 was calculated, and the results are shown in Table 1.

[0109] Table 1. Photoelectric performance test results of LED epitaxial wafers

[0110] Example 1 2.0％ Example 2 3.6％ Example 3 2.5％ Comparative Example 2 0.4％ Comparative Example 3 0.7％

[0111] As shown in Table 1, the luminous efficacy of the light-emitting diode using the stress-relief layer of the present invention can be improved by 2.0%-3.6% compared with the traditional epitaxial structure, indicating that the stress-relief layer in the present invention can effectively improve the luminous efficacy of the light-emitting diode.

[0112] 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 are also considered to be within the scope of protection of the present invention.

Claims

1. A light-emitting diode epitaxial wafer, characterized in that, It includes a substrate and a buffer layer, an undoped GaN layer, an N-type GaN layer, a stress relief layer, a multiple quantum well layer, an electron blocking layer and a P-type GaN layer sequentially stacked on the substrate; The stress relief layer includes a first sub-layer and a second sub-layer. The first sub-layer is a Cr-doped GaN layer, and the second sub-layer is a periodic structure formed by alternating layers of Cr-doped AlGaN and BGaN layers, with a period number of 1-20. The thickness of the first sublayer is 1nm-100nm; The thickness of the Cr-doped AlGaN layer is 5nm-10nm, and the thickness of the BGaN layer is 0.5nm-10nm.

2. The light-emitting diode epitaxial wafer as described in claim 1, characterized in that, The doping concentration of the Cr-doped GaN layer is 1×10⁻⁶. 18 cm -3 -1×10 20 cm -3 .

3. The light-emitting diode epitaxial wafer as described in claim 1, characterized in that, The doping concentration in the Cr-doped AlGaN layer is 1.5 × 10⁻⁶. 18 cm -3 -5×10 19 cm -3 .

4. The light-emitting diode epitaxial wafer as described in claim 1, characterized in that, The Al content in the Cr-doped AlGaN layer is 0.01-0.6%.

5. A method for fabricating a light-emitting diode epitaxial wafer, used to fabricate a light-emitting diode epitaxial wafer as described in any one of claims 1-4, characterized in that, Includes the following steps: A substrate is provided on which a buffer layer, an undoped GaN layer, an N-type GaN layer, a stress relief layer, a multiple quantum well layer, an electron blocking layer and a P-type GaN layer are sequentially grown. The stress relief layer includes a first sub-layer and a second sub-layer. The first sub-layer is a Cr-doped GaN layer, and the second sub-layer is a periodic structure formed by alternating layers of Cr-doped AlGaN and BGaN layers, with a period number of 1-20.

6. The method for fabricating a light-emitting diode epitaxial wafer as described in claim 5, characterized in that, The stress-relief layer is grown at a temperature of 400℃-1100℃ and a growth pressure of 50Torr-500Torr.

7. The method for fabricating a light-emitting diode epitaxial wafer as described in claim 5, characterized in that, The growth atmosphere of the stress-relief layer is N2 and NH3, and the flow rate ratio of N2 to NH3 is 1:(1-10).

8. A light-emitting diode, characterized in that, The light-emitting diode includes a light-emitting diode epitaxial wafer as described in any one of claims 1-4.

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