A gallium nitride-based epitaxial structure for red LEDs and its fabrication method

Abstract

This invention provides a gallium nitride-based epitaxial structure for red LEDs and its fabrication method. A composite stress relief structure is provided between the N-type semiconductor layer and the active layer. The composite stress relief structure includes a stress accumulation layer and a stress relief layer sequentially disposed along a first direction. The stress accumulation layer and the adjacent N-type semiconductor layer exhibit lattice mismatch, resulting in stress accumulation. The stress relief layer releases the stress accumulated in the stress accumulation layer by forming internal holes. The first direction is perpendicular to the substrate and points from the substrate to the N-type semiconductor layer. Thus, the synergistic effect of the stress accumulation layer and the stress relief layer in forming holes to release the accumulated stress effectively solves the lattice mismatch problem of the active layer.

Description

Technical Field

[0001] This invention relates to the field of light-emitting diodes, and more particularly to an epitaxial structure for a red LED based on gallium nitride and its fabrication method. Background Technology

[0002] In recent years, Group III and V nitrides have attracted significant attention in the fields of electrical and optical engineering due to their excellent physical and chemical properties, such as large band gaps, high breakdown electric fields, and high electron saturation mobility. For example, Mini / Micro LEDs, VR, AR, wearable devices, and smartphones, which are currently gaining popularity due to their broad application prospects, are highly sought after. However, due to limitations in materials, structure, and processes, the large-scale application of Mini / Micro LEDs still faces many challenges in practical applications. Generally, Micro LEDs require a combination of three colors: blue, green, and red (RGB). Currently, the urgent task is to develop epitaxial structures for red Micro LEDs in small sizes.

[0003] Currently, red micro LEDs are implemented using AlInGaP-based and InGaN-based structures. AlInGaP, as the main commercially viable red LED structure, experiences a sharp decline in efficiency as chip size decreases. In contrast, InGaN-based red LEDs, due to InGaN's low carrier diffusion coefficient, exhibit low surface recombination efficiency and significant carrier localization, resulting in higher luminous efficiency and a less pronounced efficiency drop at smaller sizes compared to AlInGaP-based structures. However, the growth process of InGaN-based red micro LEDs is hampered by issues such as electron-hole injection imbalance, low hole injection efficiency, stress accumulation, and strong polarization electric fields, hindering their widespread adoption.

[0004] In view of this, the inventors have specifically designed an epitaxial structure for red LEDs based on gallium nitride applications and a method for its fabrication, which leads to this invention. Summary of the Invention

[0005] The purpose of this invention is to provide an epitaxial structure for red LEDs based on gallium nitride (GaN) systems and its fabrication method, in order to solve the problem of low luminous efficiency of red LEDs based on GaN systems.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] An epitaxial structure for red LEDs based on gallium nitride (GaN) systems, comprising:

[0008] A substrate and an N-type semiconductor layer, a composite stress relief structure, an active layer, and a P-type semiconductor layer sequentially stacked on the surface of the substrate;

[0009] The composite stress relief structure includes a stress accumulation layer and a stress relief layer sequentially arranged along the first direction; wherein the stress accumulation layer and the adjacent N-type semiconductor layer have a lattice mismatch to form stress accumulation, and the stress relief layer releases the stress accumulated in the stress accumulation layer by forming holes inside; the first direction is perpendicular to the substrate and points from the substrate to the N-type semiconductor layer.

[0010] Preferably, the stress accumulation layer comprises an InGaN / InN superlattice structure, and the growth temperature of the stress relief layer is greater than that of the stress accumulation layer.

[0011] Preferably, the stress relief layer comprises a GaN stress relief layer.

[0012] Preferably, the stress relief layer includes a first stress relief layer and a second stress relief layer along the first direction; wherein the growth temperature of the first stress relief layer is greater than the growth temperature of the stress accumulation layer, and the second stress relief layer is formed in an atmosphere of pulsed hydrogen gas introduction.

[0013] Preferably, the first stress relief layer includes a first GaN stress relief layer, and the second stress relief layer includes a second GaN stress relief layer; wherein the growth temperature of the first GaN stress relief layer is greater than the growth temperature of the stress accumulation layer, and the second GaN stress relief layer is formed in an atmosphere of pulsed hydrogen gas introduction.

[0014] Preferably, the growth temperature of the stress accumulation layer is T1, and the growth temperature of the first GaN stress relief layer is T2, then 50℃≤T2-T1≤100℃.

[0015] Preferably, a stress buffer layer is provided between the composite stress relief structure and the active layer; further, the stress buffer layer includes an InGaN buffer layer.

[0016] This invention also provides a method for fabricating a red LED epitaxial structure based on gallium nitride, comprising:

[0017] Provide a substrate;

[0018] An N-type semiconductor layer, a composite stress relief structure, an active layer, and a P-type semiconductor layer are sequentially grown on the substrate surface. The composite stress relief structure includes a stress accumulation layer and a stress relief layer sequentially arranged along the first direction. The stress accumulation layer and the adjacent N-type semiconductor layer have a lattice mismatch to form stress accumulation, and the stress relief layer releases the stress formed by the stress accumulation layer by forming internal holes.

[0019] Preferably, the stress accumulation layer comprises an InGaN / InN superlattice structure, wherein the growth temperature of the stress relief layer is greater than the growth temperature of the stress accumulation layer.

[0020] Preferably, the stress relief layer includes a first stress relief layer and a second stress relief layer along the first direction; wherein the growth temperature of the first stress relief layer is greater than the growth temperature of the stress accumulation layer, and the second stress relief layer is formed in an atmosphere of pulsed hydrogen gas introduction;

[0021] The first stress relief layer includes a first GaN stress relief layer, and the second stress relief layer includes a second GaN stress relief layer; wherein the growth temperature of the first GaN stress relief layer is greater than the growth temperature of the stress accumulation layer, and the second GaN stress relief layer is formed in an atmosphere of pulsed hydrogen gas introduction.

[0022] Preferably, a stress buffer layer is provided between the composite stress relief structure and the active layer; further, the stress buffer layer includes an InGaN buffer layer.

[0023] As can be seen from the above technical solution, the gallium nitride-based red LED epitaxial structure provided by the present invention includes a composite stress relief structure between the N-type semiconductor layer and the active layer. The composite stress relief structure comprises a stress accumulation layer and a stress relief layer sequentially disposed along a first direction. The stress accumulation layer and the adjacent N-type semiconductor layer exhibit lattice mismatch to form stress accumulation. The stress relief layer releases the stress accumulated by forming internal holes. The first direction is perpendicular to the substrate and points from the substrate to the N-type semiconductor layer. Therefore, the synergistic effect of the stress accumulation layer and the stress relief layer in forming holes to release the accumulated stress effectively solves the lattice mismatch problem of the active layer.

[0024] Secondly, by setting the stress accumulation layer to include an InGaN / InN superlattice structure, and the growth temperature of the stress relief layer being higher than that of the stress accumulation layer, the stress accumulation layer is configured as an InGaN / InN superlattice structure. This allows for pulsed growth (the Ga source is introduced in an on-off...on-off pulsed manner), enabling Ga atoms to migrate a longer distance to incorporate into the lattice, thereby achieving two-dimensional growth to accumulate stress. Simultaneously, the stress accumulation layer is grown at a relatively low temperature to ensure the In content of the layer, making it a high-In layer. This results in a severe lattice mismatch between the stress accumulation layer and the N-type semiconductor layer (N-type GaN), maximizing stress accumulation.

[0025] Then, through the setting that "the stress relief layer includes a first stress relief layer and a second stress relief layer along the first direction; wherein the growth temperature of the first stress relief layer is greater than the growth temperature of the stress accumulation layer, and the second stress relief layer is formed in an atmosphere of pulsed hydrogen gas introduction," specifically, the first stress relief layer includes a first GaN stress relief layer, and the second stress relief layer includes a second GaN stress relief layer; wherein, the growth temperature of the first GaN stress relief layer is greater than the growth temperature of the stress accumulation layer, and the second GaN stress relief layer is formed in an atmosphere of pulsed hydrogen gas introduction. This technical solution is mainly based on the fact that the low growth temperature of the stress accumulation layer damages the crystal quality and surface quality of the stress accumulation layer, thus reducing the performance of the LED; therefore, in this application, the first stress relief layer, through a higher growth temperature, can further optimize the surface quality and crystal quality of the stress accumulation layer, and decompose the In incorporated from the InGaN / InN superlattice structure to form pores inside, so that the first stress relief layer can generate stress relaxation to achieve the purpose of releasing the stress accumulated in the stress accumulation layer. Next, by setting the second stress-relieving layer to be formed in an atmosphere of pulsed hydrogen gas, the etching effect of H2 is used to further decompose the In incorporated from the InGaN / InN superlattice structure, generate more pores, and achieve further stress relaxation.

[0026] Finally, a stress buffer layer is provided between the composite stress relief structure and the active layer; this layer, as a buffer transition layer, can effectively connect the growth of the composite stress relief structure and the active layer, so as to further reduce the problem of lattice mismatch.

[0027] This invention also provides a method for fabricating a red LED epitaxial structure based on gallium nitride, which achieves the above-mentioned technical effects while being simple to operate and easy to implement. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the epitaxial structure of a red LED based on gallium nitride applications provided in an embodiment of the present invention.

[0030] Figure 2 This is a schematic diagram of a red LED epitaxial structure based on gallium nitride applications provided in another embodiment of the present invention.

[0031] Figure 3 This is a schematic diagram of the composite stress relief structure provided in an embodiment of the present invention;

[0032] Figure 4 This is a schematic diagram of the stress accumulation layer provided in an embodiment of the present invention;

[0033] Figure 5 This is a schematic diagram of the stress relief layer provided in an embodiment of the present invention;

[0034] Figure 6 This is a schematic diagram of the active layer structure provided in an embodiment of the present invention;

[0035] Figure 7 This is a schematic diagram of the growth control method for the composite stress relief structure provided in an embodiment of the present invention;

[0036] Explanation of symbols in the diagram:

[0037] 1. Substrate;

[0038] 2. Buffer layer;

[0039] 3. U-GaN layer;

[0040] 4. N-type semiconductor layer;

[0041] 5. Composite stress relief structure:

[0042] 5.1 Stress accumulation layer; 5.1.1 InGaN layer; 5.1.2 InN layer;

[0043] 5.2 Stress relief layer; 5.2.1 First stress relief layer; 5.2.2 Second stress relief layer;

[0044] 5.3 Stress buffer layer;

[0045] 6. Active layer; 6.1 GaN quantum barrier layer; 6.2 InGaN quantum well layer;

[0046] 7. P-type semiconductor layer. Detailed Implementation

[0047] To make the content of this invention clearer, the following description, in conjunction with the accompanying drawings, further illustrates the invention. This invention is not limited to this specific embodiment. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0048] like Figure 1 , Figure 3 As shown, a red LED epitaxial structure based on gallium nitride (GaN) systems includes:

[0049] Substrate 1 and N-type semiconductor layer 4, composite stress relief structure 5, active layer 6 and P-type semiconductor layer 7 sequentially stacked on the surface of substrate 1;

[0050] The composite stress relief structure 5 includes a stress accumulation layer 5.1 and a stress relief layer 5.2 arranged sequentially along the first direction; wherein the stress accumulation layer 5.1 and the adjacent N-type semiconductor layer 4 are lattice mismatched to form stress accumulation, and the stress relief layer 5.2 releases the stress accumulated by the stress accumulation layer 5.1 by forming holes inside; the first direction is perpendicular to the substrate 1 and points from the substrate 1 to the N-type semiconductor layer 4.

[0051] It is worth mentioning that the type of substrate 1 is not limited in this embodiment. For example, substrate 1 includes any one of sapphire, silicon carbide, silicon, gallium nitride, and aluminum nitride. In addition, the types of N-type semiconductor layer 4 and P-type semiconductor layer 7 are also not limited. For example, N-type semiconductor layer 4 can be, but is not limited to, gallium nitride layer, and correspondingly, P-type semiconductor layer 7 can be, but is not limited to, gallium nitride layer.

[0052] Furthermore, in another embodiment of the present invention, a stress buffer layer 5.3 is provided between the composite stress relief structure 5 and the active layer 6; further, the stress buffer layer 5.3 includes an InGaN buffer layer 2.

[0053] In another embodiment of the invention, such as Figure 2 As shown, a buffer layer 2 and a U-GaN layer 3 are also provided between the substrate 1 and the N-type semiconductor layer 4.

[0054] Furthermore, based on the above embodiments of the present invention, such as Figure 4As shown, the stress accumulation layer 5.1 comprises an InGaN / InN superlattice structure composed of alternating stacks of InGaN layers 5.1.1 and InN layers 5.1.2, and the growth temperature of the stress relief layer 5.2 is greater than that of the stress accumulation layer 5.1.

[0055] Furthermore, based on the above embodiments of the present invention, the stress relief layer 5.2 includes a GaN stress relief layer 5.2.

[0056] Furthermore, based on the above embodiments of the present invention, such as Figure 5 As shown, the stress relief layer 5.2 includes a first stress relief layer 5.2.1 and a second stress relief layer 5.2.2 along the first direction; wherein the growth temperature of the first stress relief layer 5.2.1 is greater than the growth temperature of the stress accumulation layer 5.1, and the second stress relief layer 5.2.2 is formed in an atmosphere of pulsed hydrogen gas introduction.

[0057] Furthermore, based on the above embodiments of the present invention, the first stress relief layer 5.2.1 includes a first GaN stress relief layer 5.2, and the second stress relief layer 5.2.2 includes a second GaN stress relief layer 5.2; wherein, the growth temperature of the first GaN stress relief layer 5.2 is greater than the growth temperature of the stress accumulation layer 5.1, and the second GaN stress relief layer 5.2 is formed in an atmosphere of pulsed hydrogen gas introduction.

[0058] Furthermore, based on the above embodiments of the present invention, the growth temperature of the stress accumulation layer 5.1 is T1, and the growth temperature of the first GaN stress relief layer 5.2 is T2, then 50℃≤T2-T1≤100℃.

[0059] Furthermore, based on the above embodiments of the present invention, such as Figure 6 As shown, the active layer 6 includes alternating stacked GaN quantum barrier layers 6.1 and InGaN quantum well layers 6.2.

[0060] This invention also provides a method for fabricating a red LED epitaxial structure based on gallium nitride (GaN) systems. The equipment used is MOCVD, and the entire reaction growth pressure is 100-300 torr. Trimethyl / ethylgallium (TMGa / TEGa), trimethylaluminum (TMAl), and ammonia (NH3) are used as the Ga, Al, and nitrogen sources, respectively, with N2 as the carrier gas. The N-type and P-type doping sources are silane (SiH4) and magnesium pyrocene (CP2Mg), respectively. The method includes:

[0061] S01, Provide a substrate 1;

[0062] Substrate 1 includes, but is not limited to, sapphire substrate 1.

[0063] S02, A buffer layer 2 and a U-GaN layer 3 are sequentially grown on the surface of the substrate 1;

[0064] Specifically, in this step, the substrate 1 is placed in the MOCVD reaction chamber, and high-purity hydrogen is introduced at a temperature of about 1100°C for about 5 minutes to hydrogenate it. Then, the temperature is lowered to about 950°C to 970°C, and Al source and nitrogen source are introduced to grow an undoped AlN buffer layer 2 with a thickness of about 10nm to 20nm to form the buffer layer 2.

[0065] Next, the temperature is raised to 1000℃~1150℃, the Al source is turned off, and the Ga source is introduced to grow an undoped GaN layer with a thickness of 2.5um~3.5um to form the U-GaN layer 3. The purpose is to reduce the lattice mismatch between the sapphire substrate 1 and the subsequent growth materials by growing a high-quality GaN layer.

[0066] S03, grow an N-type semiconductor layer 4; in one embodiment of the present invention, the N-type semiconductor layer 4 includes an N-type doped GaN layer, which is not limited in the present invention;

[0067] Specifically, in this step, silane is introduced to grow a GaN layer with a thickness of approximately 1.3 μm to 1.8 μm and containing Si doping (i.e., an N-type doped GaN layer), with a doping concentration of 1*10⁻⁶. 18 cm -3 -10*10 18 cm -3 To form the N-type semiconductor layer 4.

[0068] S04, growing a composite stress relief structure 5; wherein the composite stress relief structure 5 includes a stress accumulation layer 5.1 and a stress relief layer 5.2 arranged sequentially along the growth direction; wherein the stress accumulation layer 5.1 and the adjacent N-type semiconductor layer 4 have a lattice mismatch to form stress accumulation, and the stress relief layer 5.2 releases the stress accumulated by the stress accumulation layer 5.1 by forming holes inside;

[0069] Furthermore, based on the above embodiments of the present invention, the stress accumulation layer 5.1 includes an InGaN / InN superlattice structure, and the growth temperature of the stress relief layer 5.2 is greater than the growth temperature of the stress accumulation layer 5.1.

[0070] Furthermore, based on the above embodiments of the present invention, the stress relief layer 5.2 includes a GaN stress relief layer 5.2.

[0071] Furthermore, based on the above embodiments of the present invention, the stress relief layer 5.2 includes a first stress relief layer 5.2.1 and a second stress relief layer 5.2.2 along the first direction; wherein the growth temperature of the first stress relief layer 5.2.1 is greater than the growth temperature of the stress accumulation layer 5.1, and the second stress relief layer 5.2.2 is formed in an atmosphere of pulsed hydrogen gas introduction.

[0072] Furthermore, based on the above embodiments of the present invention, the first stress relief layer 5.2.1 includes a first GaN stress relief layer 5.2, and the second stress relief layer 5.2.2 includes a second GaN stress relief layer 5.2; wherein, the growth temperature of the first GaN stress relief layer 5.2 is greater than the growth temperature of the stress accumulation layer 5.1, and the second GaN stress relief layer 5.2 is formed in an atmosphere of pulsed hydrogen gas introduction.

[0073] Furthermore, based on the above embodiments of the present invention, the growth temperature of the stress accumulation layer 5.1 is T1, and the growth temperature of the first GaN stress relief layer 5.2 is T2, then 50℃≤T2-T1≤100℃.

[0074] Specifically, in this step, such as Figure 7 As shown, the temperature was lowered to 600℃ < T1 < 730℃, the silane was turned off, and the In source was introduced to grow In. X Ga 1-X N layers are grown, where 0.2 < X < 0.5, for a growth time of t0, to form an InGaN layer 5.1.1. Then, the Ga source is turned off, and an InN layer 5.1.2 is grown for a growth time of t1. This cycle is repeated for N growth cycles, where N is 5–10, to obtain an InGaN / InN superlattice structure with a thickness of approximately 1.5–4 nm, forming the stress accumulation layer 5.1. This allows for pulsed growth (Ga source entry is in an on-off…on-off pulse pattern), enabling Ga atoms to migrate a longer distance to incorporate into the lattice, thus achieving two-dimensional growth to accumulate stress. Simultaneously, the stress accumulation layer 5.1 is grown at a relatively low temperature (600℃ < T1 < 730℃) to ensure the In content of this layer, making the stress accumulation layer 5.1 a high-In layer. This layer suffers from severe lattice mismatch with the N-type semiconductor layer 4 (N-type GaN), resulting in maximum stress accumulation.

[0075] Then, the temperature is increased to 700℃ < T2 < 830℃, the In source is turned off, and the Ga source is introduced. The growth time is t2, and a GaN layer with a thickness of 100-150nm is grown to form the first GaN stress relief layer 5.2. The growth temperature T2 of the first GaN stress relief layer 5.2 satisfies the same condition as the growth temperature T1 of the stress accumulation layer 5.1: 50℃ ≤ T2 - T1 ≤ 100℃. This is mainly because the lower growth temperature of the stress accumulation layer 5.1 will damage the crystal quality and surface quality of the stress accumulation layer 5.1, thus reducing the performance of the LED. Therefore, in this step, the first stress relief layer 5.2.1 can further optimize the surface quality and crystal quality of the stress accumulation layer 5.1 by growing at a higher temperature. After decomposing the In incorporated from the InGaN / InN superlattice structure, it forms pores inside, so that the first stress relief layer 5.2.1 can generate stress relaxation to release the stress accumulated in the stress accumulation layer 5.1.

[0076] Next, the temperature is maintained at T2 (700℃ < T2 < 830℃), and a Ga source is introduced to grow a GaN layer for a growth time of t3. Then, the Ga source is turned off, and H2 is introduced for a time of t4. This cycle is repeated for a growth period of N1, where N1 is 5 to 10, ultimately obtaining a 10 nm thick GaN layer to form the second stress-relieving layer 5.2.2. In this step, the second stress-relieving layer 5.2.2 is formed under a pulsed hydrogen atmosphere to utilize the etching effect of H2 to further decompose the In incorporated from the InGaN / InN superlattice structure, generating more pores and achieving further stress relaxation.

[0077] S05, growth stress buffer layer 5.3, further, the stress buffer layer 5.3 includes InGaN buffer layer 2;

[0078] Specifically, in this step, the temperature is increased to approximately 900℃ (T3), the growth time is t5, and the In layer thickness is 100–200 nm. Y Ga 1-Y N, where 0.02 < Y < 0.06. This layer serves as a transition layer or buffer layer 2, connecting the stress-relieving stack and the multi-quantum-well layer. As a new InGaN substrate, growing the multi-quantum-well layer can reduce lattice mismatch. Since the In content of InGaN red LEDs must be at least 30%, stress accumulation must be minimized to ensure better In doping. Therefore, the relevant design of this step is proposed.

[0079] S06, grow an active layer 6; further, the active layer 6 includes alternating stacked GaN quantum barrier layers 6.1 and InGaN quantum well layers 6.2;

[0080] Specifically, in this step: the In source is turned off, and a GaN quantum barrier layer 6.1 with a thickness of 7nm to 16nm is grown; then, the In source is introduced, and an InGaN quantum well layer 6.2 with a thickness of 1nm to 5nm is grown, wherein the proportion of In is between 20% and 50%, including the endpoint value; finally, the above cycle is repeated, with a growth cycle of N, where N is 6 to 15, to form the active layer 6.

[0081] Furthermore, a GaN capping layer is provided on the surface of the InGaN quantum well layer 6.2 facing away from the GaN quantum barrier layer 6.1, but this application does not limit this.

[0082] S07. Fabricating a P-type semiconductor layer 7; In one embodiment of the present invention, the P-type semiconductor layer 7 includes a P-type doped GaN layer, which is not limited in the present invention;

[0083] In this step, the temperature is adjusted to 900-1000℃, and a TMGa source, a nitrogen source, and a magnesia-diocene source are introduced to grow a p-type GaN layer with a thickness of 10-20 nm and a doping concentration of 1*10⁻⁶. 19 cm -3 Up to 5*10 19 cm -3 The P-type semiconductor layer 7 is then annealed at 850-900°C for 20-30 minutes under an N2 atmosphere to finally form the P-type semiconductor layer 7.

[0084] As can be seen from the above technical solution, the gallium nitride-based red LED epitaxial structure provided by the present invention includes a composite stress relief structure 5 between the N-type semiconductor layer 4 and the active layer 6. The composite stress relief structure 5 includes a stress accumulation layer 5.1 and a stress relief layer 5.2 sequentially arranged along a first direction. The stress accumulation layer 5.1 and the adjacent N-type semiconductor layer 4 exhibit lattice mismatch, resulting in stress accumulation. The stress relief layer 5.2 forms internal holes to release the stress accumulated by the stress accumulation layer 5.1. The first direction is perpendicular to the substrate 1 and points from the substrate 1 to the N-type semiconductor layer 4. Therefore, the synergistic effect of the stress accumulation layer 5.1 and the stress relief layer 5.2 in forming holes to release the accumulated stress in the stress accumulation layer 5.1 effectively solves the lattice mismatch problem of the active layer 6.

[0085] Secondly, by setting the stress accumulation layer 5.1 to include an InGaN / InN superlattice structure, and the growth temperature of the stress relief layer 5.2 being higher than that of the stress accumulation layer 5.1, the stress accumulation layer 5.1, being an InGaN / InN superlattice structure, enables pulsed growth (the Ga source is introduced in an on-off...on-off pulse), allowing Ga atoms to have a longer migration distance to incorporate into the lattice, thereby achieving two-dimensional growth to accumulate stress. Simultaneously, the stress accumulation layer 5.1 is grown at a relatively low temperature to ensure the In composition content of this layer.

[0086] Then, by setting that "the stress relief layer 5.2 includes a first stress relief layer 5.2.1 and a second stress relief layer 5.2.2 along the first direction; wherein the growth temperature of the first stress relief layer 5.2.1 is greater than the growth temperature of the stress accumulation layer 5.1, and the second stress relief layer 5.2.2 is formed in an atmosphere of pulsed hydrogen introduction", specifically, the first stress relief layer 5.2.1 includes a first GaN stress relief layer 5.2, and the second stress relief layer 5.2.2 includes a second GaN stress relief layer 5.2; wherein the growth temperature of the first GaN stress relief layer 5.2 is greater than the growth temperature of the stress accumulation layer 5.1, and the second GaN stress relief layer 5.2 is formed in an atmosphere of pulsed hydrogen introduction. This technical solution is mainly based on the fact that the low growth temperature of the stress accumulation layer 5.1 damages the crystal quality and surface quality of the stress accumulation layer 5.1, thus reducing the performance of the LED. Therefore, in this application, the first stress relief layer 5.2.1, grown at a higher temperature, can further optimize the surface quality and crystal quality of the stress accumulation layer 5.1, and decompose the In incorporated from the InGaN / InN superlattice structure to form pores inside, thereby causing stress relaxation in the first stress relief layer 5.2.1 to release the stress accumulated in the stress accumulation layer 5.1. Next, the second stress relief layer 5.2.2 is formed in an atmosphere with pulsed hydrogen gas to utilize the etching effect of H2 to further decompose the In incorporated from the InGaN / InN superlattice structure, generating more pores and achieving further stress relaxation.

[0087] Finally, a stress buffer layer 5.3 is provided between the composite stress relief structure 5 and the active layer 6; this layer serves as a buffer transition layer, which can effectively connect the growth of the composite stress relief structure 5 and the active layer 6, thereby further reducing the problem of lattice mismatch.

[0088] This invention also provides a method for fabricating a red LED epitaxial structure based on gallium nitride, which achieves the above-mentioned technical effects while being simple to operate and easy to implement.

[0089] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0090] It should also be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or apparatus comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or apparatus that includes the aforementioned element.

[0091] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A red LED epitaxial structure based on gallium nitride systems, characterized in that, include: A substrate and an N-type semiconductor layer, a composite stress relief structure, an active layer, and a P-type semiconductor layer sequentially stacked on the surface of the substrate; The composite stress relief structure includes a stress accumulation layer and a stress relief layer sequentially arranged along a first direction; wherein the stress accumulation layer and the adjacent N-type semiconductor layer have a lattice mismatch to form stress accumulation, and the stress relief layer releases the stress accumulated in the stress accumulation layer by forming holes inside; the first direction is perpendicular to the substrate and points from the substrate to the N-type semiconductor layer; The stress accumulation layer comprises an InGaN / InN superlattice structure, and the growth temperature of the stress relief layer is greater than that of the stress accumulation layer.

2. The red LED epitaxial structure based on gallium nitride systems according to claim 1, characterized in that, The stress relief layer includes a GaN stress relief layer.

3. The gallium nitride-based red LED epitaxial structure according to claim 1 or 2, characterized in that, The stress relief layer includes a first stress relief layer and a second stress relief layer along the first direction; wherein the growth temperature of the first stress relief layer is greater than the growth temperature of the stress accumulation layer, and the second stress relief layer is formed in an atmosphere of pulsed hydrogen gas introduction.

4. The red LED epitaxial structure based on gallium nitride systems according to claim 3, characterized in that, The first stress relief layer includes a first GaN stress relief layer, and the second stress relief layer includes a second GaN stress relief layer; wherein the growth temperature of the first GaN stress relief layer is greater than the growth temperature of the stress accumulation layer, and the second GaN stress relief layer is formed in an atmosphere of pulsed hydrogen gas introduction.

5. The red LED epitaxial structure based on gallium nitride systems according to claim 4, characterized in that, The growth temperature of the stress accumulation layer is T1, and the growth temperature of the first GaN stress relief layer is T2. Then, 50℃≤T2-T1≤100℃.

6. The red LED epitaxial structure based on gallium nitride systems according to claim 1, characterized in that, A stress buffer layer is also provided between the composite stress relief structure and the active layer.

7. The red LED epitaxial structure based on gallium nitride systems according to claim 6, characterized in that, The stress buffer layer includes an InGaN buffer layer.

8. A method for fabricating a red LED epitaxial structure based on gallium nitride, characterized in that, include: Provide a substrate; An N-type semiconductor layer, a composite stress relief structure, an active layer, and a P-type semiconductor layer are sequentially grown on the substrate surface; wherein, the composite stress relief structure includes a stress accumulation layer and a stress relief layer sequentially disposed along a first direction; wherein, the stress accumulation layer and the adjacent N-type semiconductor layer have a lattice mismatch to form stress accumulation, and the stress relief layer releases the stress formed by the stress accumulation layer by forming a hole inside. The stress accumulation layer comprises an InGaN / InN superlattice structure, wherein the growth temperature of the stress relief layer is greater than that of the stress accumulation layer.

9. The method for fabricating a red LED epitaxial structure based on gallium nitride as described in claim 8, characterized in that, The stress relief layer includes a first stress relief layer and a second stress relief layer along the first direction; wherein the growth temperature of the first stress relief layer is greater than the growth temperature of the stress accumulation layer, and the second stress relief layer is formed in an atmosphere of pulsed hydrogen gas introduction. The first stress relief layer includes a first GaN stress relief layer, and the second stress relief layer includes a second GaN stress relief layer; wherein the growth temperature of the first GaN stress relief layer is greater than the growth temperature of the stress accumulation layer, and the second GaN stress relief layer is formed in an atmosphere of pulsed hydrogen gas introduction.

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