Epitaxial structure, method of fabrication and light emitting diode

Abstract

The application provides an epitaxial structure, a preparation method and a light emitting diode, relates to the technical field of light emitting diodes, and the three-dimensional nucleation layer of the epitaxial structure comprises a three-dimensional island structure layer which is formed by combining a plurality of three-dimensional island structures, the three-dimensional island structure layer comprises an AlN cap layer and a Si-doped GaN island layer, the Si-doped GaN island layer comprises a plurality of GaN island structures, and the AlN cap layer covers the Si-doped GaN island layer. The doped Si in the Si-doped GaN island layer replaces Ga sites in GaN, so that the Si-doped GaN island layer can reach a critical nucleation density at a second temperature which is less than a first temperature, and then high-density uniform nucleation can be realized at a lower temperature. In addition, the lattice constant of the AlN cap layer is less than the lattice constant of the Si-doped GaN island layer, the AlN cap layer and the Si-doped GaN island layer can be used to cooperatively control the geometric size of the GaN island structure, and the formation of giant V-pits can be avoided.

Description

Technical Field

[0001] This application relates to the field of light-emitting diode technology, and more particularly to an epitaxial structure, a fabrication method, and a light-emitting diode. Background Technology

[0002] The epitaxial structure of GaN-based light-emitting diodes (LEDs) is typically grown on heterogeneous substrates such as sapphire, SiC, or Si. Constrained by the dual mismatch of lattice constant and thermal expansion coefficient between GaN and the substrate, the epitaxial structure generates a high density of threading dislocations (TDs) during cooling and relaxation. These TDs not only act as stress relief channels but also induce V-pits above the active region of the quantum well. Traditionally, V-pits are classified as detrimental defects, emphasizing their negative effects as non-radiative recombination centers and leakage paths, significantly reducing internal quantum efficiency and weakening the device's electrostatic discharge (ESD) immunity. However, recent research has gradually revealed that V-pits, under appropriate geometry, can provide synergistic gains through dislocation shielding and enhanced hole injection. Furthermore, band bending can improve lateral hole transport, thereby mitigating the sharp efficiency drop at high current densities.

[0003] To reduce dislocation density, existing nucleation layers leave behind large V-pits, which become non-radiative recombination centers. Even with composition-gradient multilayer three-dimensional nucleation techniques to suppress dislocations, rapid coarsening of V-pits still occurs during the merging stage, hindering the large-scale fabrication of high-brightness, high-reliability LEDs. Therefore, effectively controlling the geometry of V-pits remains a key research challenge for engineers. Summary of the Invention

[0004] In view of this, this application provides an epitaxial structure, a method for fabricating the epitaxial structure, and a light-emitting diode, as follows:

[0005] An epitaxial structure, the epitaxial structure comprising:

[0006] Substrate;

[0007] A three-dimensional nucleation layer located on one side of the substrate, the three-dimensional nucleation layer including a three-dimensional island structure layer, the three-dimensional island structure layer being composed of multiple three-dimensional island structures;

[0008] The three-dimensional island structure layer includes an AlN cap layer and a Si-doped GaN island layer. The Si-doped GaN island layer is located on one side of the substrate, and the AlN cap layer is located on the side of the Si-doped GaN island layer away from the substrate and covers the Si-doped GaN island layer. The Si-doped GaN island layer includes multiple GaN island structures, and the AlN cap layer covers the multiple GaN island structures in the Si-doped GaN island layer to form the multiple three-dimensional island structures.

[0009] The doped Si in the Si-doped GaN island layer replaces the Ga sites in GaN, and the Si-doped GaN island layer reaches the critical nucleation density at a second temperature lower than the first temperature, wherein the undoped GaN island layer reaches the critical nucleation density at the first temperature.

[0010] The lattice constant of the AlN cap layer is smaller than that of the Si-doped GaN island layer, which suppresses the growth rate of the GaN island structure in the Si-doped GaN island layer in the lateral growth direction, which is parallel to the plane of the substrate.

[0011] Optionally, the Si doping concentration in the Si-doped GaN island layer ranges from 1 × 10⁻⁶. 16 atoms / cm 3 ~1×10 17 atoms / cm 3 This includes endpoint values.

[0012] Optionally, the three-dimensional nucleation layer further includes a merging layer located on the side of the AlN cap layer away from the substrate;

[0013] The merging layer is formed by introducing SiH4 into the three-dimensional island structure layer.

[0014] Optionally, along a direction perpendicular to the plane of the substrate, the AlN cap layer includes N sub-cap layers stacked together, where N is an integer greater than or equal to 1.

[0015] Optionally, the epitaxial structure further includes a buffer layer, an N-type layer, a superlattice stress relief layer, an active layer, a barrier layer, a P-type layer, and an ohmic contact layer;

[0016] The buffer layer is located between the substrate and the three-dimensional nucleation layer;

[0017] The N-type layer is located on the side of the three-dimensional nucleation layer away from the substrate, and the N-type layer, the superlattice stress relief layer, the active layer, the barrier layer, the P-type layer and the ohmic contact layer are arranged sequentially in the direction away from the substrate.

[0018] A method for preparing an epitaxial structure, comprising:

[0019] Provide a substrate;

[0020] A three-dimensional nucleation layer is formed on one side of the substrate. The three-dimensional nucleation layer includes a three-dimensional island structure layer, which is composed of multiple three-dimensional island structures.

[0021] The formation of the three-dimensional island structure layer includes: forming a Si-doped GaN island layer on one side of the substrate, followed by forming an AlN cap layer, wherein the AlN cap layer covers the side of the Si-doped GaN island layer away from the substrate; the Si-doped GaN island layer includes multiple GaN island structures, and the AlN cap layer covers the multiple GaN island structures in the Si-doped GaN island layer, thereby forming the multiple three-dimensional island structures.

[0022] In the Si-doped GaN island layer, the doped Si replaces the Ga sites in GaN, and the Si-doped GaN island layer reaches the critical nucleation density at a second temperature lower than the first temperature, while the undoped GaN island layer reaches the critical nucleation density at the first temperature.

[0023] The lattice constant of the AlN cap layer is smaller than that of the Si-doped GaN island layer, which suppresses the growth rate of the GaN island structure in the Si-doped GaN island layer in the lateral growth direction, which is parallel to the plane of the substrate.

[0024] Optionally, the formation of the Si-doped GaN island layer includes:

[0025] Under the second temperature and first pressure, a first source gas is introduced to form the initial layer of the Si-doped GaN island layer; wherein the first source gas includes Ga source gas, N source gas and Si source gas, and the molar flow ratio of N source gas and Ga source gas in the first source gas satisfies a preset ratio, and based on the Si source gas, the Si doping concentration in the initial layer of the Si-doped GaN island layer ranges from 1×10⁻⁶. 16 atoms / cm 3 ~1×10 17 atoms / cm 3 This includes endpoint values;

[0026] The initial layer is annealed at a third temperature and a second pressure, under a protective atmosphere of NH3, to form the Si-doped GaN island layer.

[0027] The third temperature is greater than the second temperature, and the second pressure is less than the first pressure.

[0028] Optionally, forming the AlN cap layer includes:

[0029] Under a fourth temperature and a third pressure, a second source gas is periodically introduced to form the AlN cap layer;

[0030] Wherein, the second source gas includes Al source gas, the fourth temperature is greater than the third temperature, and the third pressure is less than the first pressure; the number of cycles in which the second source gas is periodically introduced is M, where M is an integer greater than or equal to 1.

[0031] Optionally, the nucleation density of the GaN island structures in the initial layer ranges from 10. 8 cm -2 ~10 9 cm -2 The initial layer has a longitudinal dimension ranging from 60 nm to 100 nm, including the endpoint value, and a lateral dimension ranging from 100 nm to 200 nm, including the endpoint value. The longitudinal dimension is the dimension perpendicular to the plane of the substrate, and the lateral dimension is the dimension parallel to the plane of the substrate.

[0032] After annealing and before forming the AlN cap layer, the longitudinal dimension of the GaN island structure in the Si-doped GaN island layer ranges from 80nm to 120nm, including the endpoints, and the lateral dimension ranges from 130nm to 240nm, including the endpoints. The ratio of the longitudinal dimension to the lateral dimension of the GaN island structure in the Si-doped GaN island layer is 0.5 to 0.6.

[0033] After the AlN cap layer is formed, the longitudinal dimension of the GaN island structure in the Si-doped GaN island layer ranges from 80nm to 120nm, including the endpoint value, and the lateral dimension ranges from 180nm to 220nm, including the endpoint value.

[0034] Along the direction perpendicular to the plane of the substrate, the thickness of the AlN cap layer ranges from 2nm to 3nm, including the endpoint values.

[0035] Optionally, forming a three-dimensional nucleation layer on one side of the substrate further includes:

[0036] A merging layer is formed on the side of the AlN cap layer away from the substrate;

[0037] The formation of a merging layer on the side of the AlN cap layer away from the substrate includes:

[0038] After the three-dimensional island structure layer is formed, SiH4 is introduced into the three-dimensional island structure layer under the fifth temperature and fourth pressure to form the structure.

[0039] A light-emitting diode comprising the epitaxial structure described in any of the preceding claims.

[0040] Compared with existing technologies, the beneficial effects of the technical solution of this application are as follows:

[0041] The epitaxial structure includes a substrate and a three-dimensional nucleation layer located on one side of the substrate. This three-dimensional nucleation layer includes a three-dimensional island structure layer, which is formed by the merging of multiple three-dimensional island structures. The three-dimensional island structure layer includes an AlN cap layer and Si-doped GaN island layers. The Si-doped GaN island layers are located on one side of the substrate, and the AlN cap layer is located on the side of the Si-doped GaN island layers away from the substrate, covering the side of the Si-doped GaN island layers away from the substrate. Specifically, the Si-doped GaN island layers include multiple GaN island structures, and the AlN cap layer covers the Si-doped GaN island layers, forming multiple three-dimensional island structures, which can then be merged to form the three-dimensional island structure layer. The Si doping in the Si-doped GaN island layers replaces the Ga sites in GaN, allowing the Si-doped GaN island layers to reach a critical nucleation density at a second temperature lower than the first temperature, while simultaneously reducing the effective surface energy of the (0001) facet of the Si-doped GaN island layers. This enables control over the geometry of the GaN island structures and effectively avoids the formation of giant V-pits. Furthermore, the lattice constant of the AlN cap layer is lower than that of the Si-doped GaN island layer, suppressing the lateral growth rate of the GaN island structure in the Si-doped GaN island layer. Therefore, the three-dimensional nucleation layer of this epitaxial structure, comprising Si-doped GaN islands and an AlN cap layer, can lower the nucleation temperature threshold based on the Si-doped GaN islands, achieving high-density uniform nucleation at lower temperatures. Simultaneously, based on the dual synergistic control mechanism of the Si-doped GaN islands and the AlN cap layer, effective control of the GaN island structure geometry is achieved during the formation of the three-dimensional nucleation layer, providing a feasible solution to avoid the formation of giant V-pits. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0043] The structures, proportions, sizes, etc., shown in the accompanying drawings are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed in the specification, and are not intended to limit the implementation conditions of this application. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size should still fall within the scope of the technical content disclosed in this application, provided that they do not affect the effects and purposes that this application can produce.

[0044] Figure 1 A schematic diagram of an extensional structure provided in this application;

[0045] Figure 2 for Figure 1 Enlarged view of the area within the dashed box;

[0046] Figure 3 A schematic diagram of a three-dimensional nucleation layer in an epitaxial structure provided in this application;

[0047] Figure 4 and Figure 5 A schematic diagram of a GaN island structure in an epitaxial structure provided in this application;

[0048] Figure 6 A flowchart illustrating a method for preparing an epitaxial structure provided in this application.

[0049] The annotations in the attached figures are explained as follows:

[0050] Substrate 100, three-dimensional nucleation layer 200, three-dimensional island structure layer 210, three-dimensional island structure 212, AlN cap layer 216, Si-doped GaN island layer 214, GaN island structure 218, merging layer 220, buffer layer 300, N-type layer 302, superlattice stress relief layer 304, active layer 306, barrier layer 308, P-type layer 310, ohmic contact layer 312. Detailed Implementation

[0051] The embodiments of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0052] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0053] As described in the background section, effectively controlling the geometry of V-pits is a current challenge for researchers.

[0054] Based on the above, this application provides an extensional structure, such as Figure 1 and Figure 2 As shown, Figure 1 This is a schematic diagram of an extensional structure provided in this application. Figure 2 for Figure 1 The enlarged view of the area within the dashed box shows that the epitaxial structure includes a substrate 100 and a three-dimensional nucleation layer 200 located on one side of the substrate 100. The three-dimensional nucleation layer 200 includes a three-dimensional island structure layer 210, which is formed by merging multiple three-dimensional island structures 212.

[0055] like Figure 3 As shown, the three-dimensional island structure layer 210 includes an AlN cap layer 216 and a Si-doped GaN island layer 214. The Si-doped GaN island layer 214 is located on one side of the substrate 100, and the AlN cap layer 216 is located on the side of the Si-doped GaN island layer 214 away from the substrate and covers the Si-doped GaN island layer 214. The Si-doped GaN island layer 214 includes multiple GaN island structures 218, and before merging, there are gaps between adjacent GaN island structures 218. That is, the GaN island structures 218 in the Si-doped GaN island layer 214 are the initial island structures of the aforementioned three-dimensional island structure 212. The AlN cap layer 216 covers the multiple GaN island structures in the Si-doped GaN island layer 214, forming multiple three-dimensional island structures 212 composed of the GaN island structures 218 and the AlN cap layer 216 covering them, thereby forming the three-dimensional island structure layer 210.

[0056] It should be noted that the Si-doped GaN island layer 214 described above forms multiple GaN island structures 218, which can be understood as the formation of multiple three-dimensional protrusion structures within the Si-doped GaN island layer 214. These three-dimensional protrusion structures can be regularly formed, such as spheres, cubes, or cylinders, or they can be irregular shapes. Furthermore, the aforementioned gaps between adjacent GaN island structures refer to the fact that there are gaps between any parts of adjacent island structures (e.g., ...). Figure 4 As shown), it can also be that the bottoms of adjacent island-like structures are connected, while the remaining parts have gaps between them (such as...). Figure 5 (As shown). It should also be noted that, in order to clearly illustrate this extensional structure, Figures 2-5 The diagram shown is a schematic of the island-like structure before it is merged.

[0057] Specifically, in the Si-doped GaN island layer 214, Si replaces the Ga sites in GaN, thereby enabling the Si-doped GaN island layer 214 to reach the critical nucleation density at a second temperature lower than the first temperature. In contrast, the undoped GaN island layer reaches the critical nucleation density at the first temperature, and the second temperature is lower than the first temperature. This means that the doped Si in the Si-doped GaN island layer 214 replaces the Ga sites in GaN, which lowers the nucleation temperature threshold of the GaN island structure 218 in the Si-doped GaN island layer 214, allowing the Si-doped GaN island layer 214 to reach the critical nucleation density at the second temperature.

[0058] Specifically, by replacing Ga sites with doped Si atoms, the effective surface energy of the (0001) facet of the Si-doped GaN island layer 214 is reduced, thereby lowering the nucleation temperature threshold of the GaN island structure by approximately 80°C to 100°C. For example, high-density nucleation can be achieved at 550°C, avoiding uneven island size distribution and the formation of giant V-pits caused by high-temperature nucleation. It should be noted that undoped Si GaN island layers typically require higher temperatures (e.g., a first temperature of 630°C to 650°C) to achieve the same nucleation density as described above. High-temperature nucleation easily leads to coarsening of the island structure and uneven size distribution, resulting in the formation of giant V-pits during the merging stage. Therefore, this epitaxial structure lowers the nucleation temperature threshold of the GaN island structure through Si doping, enabling high-density uniform nucleation at a lower temperature, laying the foundation for subsequent morphology control.

[0059] Meanwhile, the Si-doped GaN island 214 uses doped Si to replace the Ga sites in GaN, reducing the effective surface energy of the (0001) plane of the Si-doped GaN island 214, thereby controlling the geometric dimensions of the GaN island structure 218 and effectively avoiding the formation of giant V-pits.

[0060] In addition to the above, the lattice constant of the AlN cap layer 216 is smaller than that of the Si-doped GaN island layer 214, which can suppress the growth rate of the GaN island structure 218 in the lateral growth direction of the Si-doped GaN island layer 214, also known as the lateral growth rate of the GaN island structure 218. The lateral growth direction is parallel to the plane of the substrate 100. Specifically, the lattice constant of the AlN cap layer 216 is smaller than that of the Si-doped GaN island layer 214. There is a lattice mismatch between the AlN cap layer 216 and the Si-doped GaN island layer 214, which introduces compressive stress on the surface of the GaN island structure 218. This results in a high-tension layer with a larger surface tension covering the Si-doped GaN island layer 214, forming a high-tension cap layer on the surface of the Si-doped GaN island layer 214. This reduces the adsorption capacity of Ga on the surface of the GaN island structure 218, suppresses the lateral growth rate of the GaN island structure 218 in the Si-doped GaN island layer 214, and can further control the geometric size of the GaN island structure 218, avoiding the formation of giant V-pits due to the rapid merging of the GaN island structure 218.

[0061] As described above, the three-dimensional nucleation layer of this epitaxial structure includes Si-doped GaN islands 214 and an AlN cap layer 216. The nucleation temperature threshold can be lowered based on the Si-doped GaN islands 214, enabling high-density, uniform nucleation at lower temperatures. This lays the foundation for subsequent morphology control and avoids the formation of giant V-pits. Furthermore, this epitaxial structure utilizes a dual control mechanism of the Si-doped GaN islands 214 and the AlN cap layer 216 for the geometry of the GaN island structure 218. During the formation of the three-dimensional nucleation layer 200, effective control of the geometry of the GaN island structure 218 is achieved, providing a feasible solution to avoid the formation of giant V-pits.

[0062] Meanwhile, the three-dimensional nucleation layer 200 of this epitaxial structure can effectively control the geometry of the GaN island structures 218, and thus the geometry of the V-pits. It is known that V-pits can play a beneficial role under appropriate geometry; therefore, this epitaxial structure can improve the luminous performance of GaN-based light-emitting diodes (LEDs) by controlling the geometry of the V-pits. Furthermore, different operating environments and device sizes may have different requirements for the geometry of the GaN island structures and V-pits. Since the geometry of the GaN island structures and V-pits in this epitaxial structure is controllable, it can be applied to a wider range of applications and has strong practicality.

[0063] In one embodiment of this application, the Si doping concentration in the Si-doped GaN island layer 214 ranges from 1 × 10⁻⁶.16 atoms / cm 3 ~1×10 17 atoms / cm 3 This includes endpoint values. However, this application does not impose any limitations on this; it depends on the specific circumstances.

[0064] In one embodiment of this application, such as Figure 3 As shown, the three-dimensional nucleation layer 200 of the epitaxial structure also includes a merging layer 220, which is located on the side of the AlN cap layer 216 away from the substrate 100. That is, the three-dimensional nucleation layer 200 sequentially includes a stacked three-dimensional island structure layer 210 and a merging layer 220. The merging layer 220 is formed by introducing SiH4 into the three-dimensional island structure layer 210; that is, after forming the three-dimensional island structure layer 210, SiH4 is introduced into the three-dimensional island structure layer 210 to form the merging layer 220. The Si doping concentration in the merging layer 220 can be 5 × 10⁻⁶. 16 atoms / cm 3 However, this application does not impose any restrictions on this, and it depends on the specific circumstances.

[0065] Specifically, after forming Si-doped GaN island layers 214 and AlN cap layers 216, a trace amount of SiH4 is introduced into the overall structure formed by the Si-doped GaN island layers 214 and AlN cap layers 216 to form a merging layer 220. In other words, during the preparation of the three-dimensional nucleation layer 200, after forming a three-dimensional island structure layer 210 including AlN cap layers 216 and Si-doped GaN island layers 214, a trace amount of SiH4 is introduced into the three-dimensional island structure layer 210 to form the merging layer 220. It should be noted that the introduction of trace amounts of SiH4 allows Si atoms to adsorb onto the surface of the GaN island structure 218, acting as a surfactant to reduce the surface energy of the formed GaN island structure 218, promoting atomic migration and lateral merging between islands, thereby accelerating the lateral merging of the GaN island structure 218 and enabling island-to-island merging at low temperatures.

[0066] It is known that the aforementioned merging layer 220 is formed after the formation of a three-dimensional island structure layer 210, including Si-doped GaN island layers 214 and AlN cap layers 216. That is, after controlling the geometry of the GaN island structure 218 through the Si-doped GaN island layers 214 and AlN cap layers 216, a merging layer 220 is grown to cover it, which helps to achieve low-temperature merging between islands. Based on this, the epitaxial structure can not only control the geometry of the GaN island structure 218, but also suppress the excessive lateral growth rate caused by high temperature and the expansion of V-pits opening, thereby achieving rapid, flat, and low-defect seamless splicing of islands, taking into account the dual goals of low dislocation density and low V-pits, thus achieving simultaneous optimization of low dislocation density and controllable V-pits.

[0067] In one embodiment of this application, along a direction perpendicular to the plane of the substrate 100, the AlN cap layer 216 includes N sub-cap layers (not shown in the figure) stacked together, where N is an integer greater than or equal to 1. Specifically, the AlN cap layer 216 can be formed by periodically introducing trimethylaluminum gas (also known as TMAl) during its formation process, and the number of sub-cap layers in the AlN cap layer 216 depends on the number of cycles of introducing trimethylaluminum gas.

[0068] In one embodiment of this application, the thickness of the AlN cap layer 216 ranges from 2nm to 3nm, including the endpoint value, and the thickness of the merging layer 220 can be approximately 2μm. However, this application does not limit the specific values ​​of the thickness of the AlN cap layer 216 and the merging layer 220, and it depends on the specific circumstances.

[0069] In one embodiment of this application, such as Figure 1 As shown, the epitaxial structure also includes a buffer layer 300, an N-type layer 302, a superlattice stress relief layer 304, an active layer 306, a barrier layer 308, a P-type layer 310, and an ohmic contact layer 312. The buffer layer 300 is located between the substrate 100 and the three-dimensional nucleation layer 200. This buffer layer 300 can be an AlN buffer layer, and its thickness can range from 20 nm to 80 nm, including the endpoint values.

[0070] The N-type layer 302 is located on the side of the three-dimensional nucleation layer 200 away from the substrate 100, and the N-type layer 302, the superlattice stress relief layer 304, the active layer 306, the barrier layer 308, the P-type layer 310, and the ohmic contact layer 312 are arranged sequentially in the direction away from the substrate 100. The N-type layer 302 is an N-type GaN layer, with Si as the N-type dopant and a doping concentration of approximately 4.5 × 10⁻⁶. 18 atoms / cm 3 Up to 9.5×10 18 atoms / cm 3The thickness, including endpoint values, can range from 1 μm to 3 μm, including endpoint values. After forming the N-type layer 302, a superlattice stress relief layer 304 is formed on the side of the N-type layer 302 away from the substrate 100 to alleviate the pressure adaptation between the N-type layer 302 and the subsequent active layer 306. After forming the superlattice stress relief layer 304, the active layer 306 is formed, which includes an InGaN quantum well layer grown at a growth temperature of 700℃-800℃, a GaN cap layer grown at a growth temperature of 720℃-820℃, and a quantum barrier layer grown at a growth temperature of 850℃-900℃. Subsequently, a barrier layer 308 (also called an electron barrier layer), a P-type layer 310, and an ohmic contact layer 312 are grown sequentially.

[0071] Accordingly, this application also provides a method for preparing an epitaxial structure, which is used to prepare the epitaxial structure described in any of the above embodiments. For example... Figure 6 As shown, Figure 6 A flowchart of a method for preparing an epitaxial structure provided in this application is included, the method comprising:

[0072] S1: A substrate 100 is provided, which may be sapphire, SiC or Si, etc. This application does not limit it, but depends on the specific circumstances.

[0073] S2: A three-dimensional nucleation layer 200 is formed on one side of the substrate 100. The three-dimensional nucleation layer 200 includes a three-dimensional island structure layer 210, which is formed by merging multiple three-dimensional island structures 212.

[0074] Specifically, forming the three-dimensional island structure layer 210 includes: forming a Si-doped GaN island layer 214 on one side of the substrate 100, followed by forming an AlN cap layer 216. The Si-doped GaN island layer 214 is located on one side of the substrate 100, and the AlN cap layer 216 is located on the side of the Si-doped GaN island layer 214 away from the substrate 100, and covers the side of the Si-doped GaN island layer 214 away from the substrate 100. The Si-doped GaN island layer 214 forms multiple GaN island structures 218, and before merging, there are gaps between adjacent GaN island structures 218. The AlN cap layer 216 covers the Si-doped GaN island layer 214, forming multiple three-dimensional island structures 212, which can then be merged to form the aforementioned three-dimensional island structure layer 210.

[0075] In the Si-doped GaN island layer 214, the doped Si replaces the Ga sites in GaN, allowing the Si-doped GaN island layer 214 to reach the critical nucleation density at a second temperature lower than the first temperature. In contrast, the undoped GaN island layer reaches the critical nucleation density at the first temperature. Since the second temperature is lower than the first temperature, the doped Si in the Si-doped GaN island layer 214 replaces the Ga sites in GaN, lowering the nucleation temperature threshold of the GaN island structure 218 in the Si-doped GaN island layer 214, enabling the Si-doped GaN island layer 214 to reach the critical nucleation density at the second temperature.

[0076] The lattice constant of the AlN cap layer 216 is smaller than that of the Si-doped GaN island layer 214, which suppresses the growth rate of the GaN island structure 218 in the lateral growth direction of the Si-doped GaN island layer 214. The lateral growth direction is parallel to the plane of the substrate 100.

[0077] As can be seen from the above, the three-dimensional nucleation layer of the epitaxial structure prepared by this method includes Si-doped GaN island layer 214 and AlN cap layer 216. The nucleation temperature threshold can be reduced based on the Si-doped GaN island layer 214, and high-density uniform nucleation can be achieved at a lower temperature, laying the foundation for subsequent morphology control and avoiding the formation of giant V-pits.

[0078] This preparation method also utilizes Si-doped GaN islands 214 to replace Ga sites in GaN, reducing the effective surface energy of the (0001) plane of the Si-doped GaN islands 214 and controlling the geometric dimensions of the GaN island structures 218, effectively avoiding the formation of giant V-pits. Simultaneously, the lattice constant of the AlN cap layer 216 is smaller than that of the Si-doped GaN islands 214, effectively covering the Si-doped GaN islands 214 with a high-tension layer with greater surface tension. This reduces the Ga adsorption capacity on the surface of the GaN island structures 218, suppressing the lateral growth rate of the GaN island structures 218 in the Si-doped GaN islands 214. This further controls the geometric dimensions of the GaN island structures 218, preventing the rapid merging of the GaN island structures 218 and thus avoiding the formation of giant V-pits.

[0079] Based on the above, this preparation method forms a three-dimensional nucleation layer comprising Si-doped GaN islands 214 and an AlN cap layer 216. The nucleation temperature threshold can be lowered based on the Si-doped GaN islands 214, enabling high-density, uniform nucleation at lower temperatures. This lays the foundation for subsequent morphology control and avoids the formation of giant V-pits. Furthermore, based on the dual control mechanism of the Si-doped GaN islands 214 and the AlN cap layer 216, effective control of the geometric dimensions of the GaN island structures 218 is achieved during the formation of the three-dimensional nucleation layer 200, providing a feasible solution to avoid the formation of giant V-pits.

[0080] Meanwhile, this fabrication method can effectively control the geometry of the GaN island structure 218, and thus the geometry of the V-pits. It is known that V-pits can play a beneficial role under appropriate geometry; therefore, this fabrication method can improve the luminous performance of GaN-based light-emitting diodes (LEDs) by controlling the geometry of the V-pits. Furthermore, different operating environments and device sizes may lead to different requirements for the geometry of the GaN island structure and V-pits. This fabrication method makes the geometry of the GaN island structure and V-pits controllable, thus making it applicable to more application scenarios and possessing strong practicality.

[0081] In one embodiment of this application, forming the Si-doped GaN island layer 214 includes:

[0082] Under a second temperature and a first pressure, a first source gas is introduced to form the initial layer of the Si-doped GaN island layer 214. The first source gas includes Ga source gas, N source gas, and Si source gas, and the molar flow rate ratio of the N source gas to the Ga source gas satisfies a preset ratio of 3000:10000. For example, the molar flow rate ratio of the N source gas to the Ga source gas can be 800:1200. Based on the Si source gas, the Si doping concentration in the initial layer of the Si-doped GaN island layer 214 ranges from 1×10⁻⁶. 16 atoms / cm 3 ~1×10 17 atoms / cm 3 This includes the endpoint values, meaning the Si doping concentration in the Si-doped GaN island layer 214 ranges from 1 × 10⁻⁶. 16 atoms / cm 3 ~1×10 17 atoms / cm 3 This includes endpoint values.

[0083] Subsequently, the initial layer was annealed at a third temperature and a second pressure, under a protective atmosphere of NH3, to form a Si-doped GaN island layer 214. The third temperature is higher than the second temperature, and the second pressure is lower than the first pressure.

[0084] Specifically, in the first stage, the temperature can be 550°C and the pressure can be 300 Torr, meaning the second temperature can be 550°C and the first pressure can be 300 Torr. The molar flow rate ratio of N source gas to Ga source gas can be 800:1200. The Si source gas can be SiH4, and based on SiH4, the Si doping concentration in the Si-doped GaN island layer 214 can be 1×10⁻⁶. 16 atoms / cm 3 ~1×10 17 atoms / cm 3 With a growth time of 180s to 300s, GaN island structures 218 with a height range (i.e., longitudinal dimension) of 60nm to 100nm and a diameter range (i.e., lateral dimension) of 100nm to 200nm can be obtained. It should be noted that after Si atoms replace Ga sites, the effective surface energy of the (0001) facet of the Si-doped GaN island layer 214 is reduced, which in turn lowers the formation temperature threshold of the island structure by about 80°C to 100°C. That is, the formation temperature of the island structure is lowered, making it easier to form the island structure and suppressing the formation of giant V-pits caused by high temperature.

[0085] The second stage, also known as the annealing stage, is carried out after the first stage and the GaN island structure has been grown. In-situ annealing is performed under an NH3 protective atmosphere. The annealing temperature can be 850°C~900°C (i.e., the third temperature), the annealing time can be 60s~120s, and the pressure is reduced to 50Torr~100Torr (i.e., the second pressure). The second-stage annealing process achieves the following effects: 1. Atom rearrangement on the surface of GaN island structure 218, thereby reducing the surface roughness of GaN island structure 218, making the surface of GaN island structure 218 more flat, and reducing interface defects of subsequent AlN cap layer 216; 2. Stress redistribution, promoting the relaxation of internal compressive stress of GaN island structure 218 towards the edge, making the shape of GaN island structure 218 more regular, such as forming a more regular hexagonal symmetric morphology, thereby ensuring uniform coverage of subsequent AlN cap layer 216; Si atom redistribution, allowing doped Si to segregate to the surface of island structure, further stabilizing the surface energy reduction effect and suppressing island merging and coarsening during the high-temperature merging stage.

[0086] Furthermore, the aforementioned annealing stage controls the lateral size shrinkage of the GaN island structure 218 to within 5%~8%, while maintaining its longitudinal size essentially unchanged. This results in an optimal ratio of longitudinal to lateral dimensions for the obtained island structure. For example, the ratio of longitudinal to lateral dimensions of the GaN island structure 218 in the Si-doped GaN island layer 214 is 0.5~0.6, providing an ideal geometric template for the "edge-locking effect" of the subsequent TMA1 pulse cap layer. It should be noted that the aforementioned annealing stage, based on the low-temperature, high-density nucleation achieved in the Si-doped GaN island layer, regularizes the morphology of the island structure through surface atomic rearrangement and stress redistribution. This, in conjunction with the Si-doped GaN island layer to lower the nucleation temperature threshold, effectively controls the geometric dimensions of the GaN island structure.

[0087] In one embodiment of this application, forming the AlN cap layer 216 includes:

[0088] At a fourth temperature and a third pressure, a second source gas is periodically introduced to form an AlN cap layer. After the AlN cap layer is formed, the lateral dimensions of the GaN island structures 218 in the Si-doped GaN island layer 214 range from 180 nm to 220 nm, including the endpoint values.

[0089] The second source gas includes an Al source gas; for example, the second source gas can be trimethylaluminum gas. The fourth temperature is higher than the third temperature, and the third pressure is lower than the first pressure. The number of cycles in which the second source gas is periodically introduced is N, where N is an integer greater than or equal to 1, for example, N=10. It should be noted that since the second source gas can be trimethylaluminum gas, the above-mentioned AlN cap layer can also be called a TMAl pulse cap layer.

[0090] Specifically, when forming the AlN cap layer 216, the temperature is raised to 950°C (i.e., the fourth temperature), and the pressure is 100 Torr (i.e., the third pressure). TMAl gas is periodically pulsed in, for example, for 0.5s, then stopped for 2s, then for 0.5s again, and so on, for a total of 10 cycles, to obtain an AlN high-tension cap layer with a thickness of 2nm~3nm.

[0091] It should be noted that, after the formation of the AlN cap layer 216, the lateral dimension (diameter) of the GaN island structure 218 in the Si-doped GaN island layer 214 ranges from 180 nm to 220 nm. Specifically, the lower limit of this range, 180 nm, ensures that a gap of 30 nm to 50 nm is maintained between the island structures, providing sufficient atomic migration channels for the subsequent formation of the merging layer 220 based on SiH4 to assist in the merging of islands. The upper limit of this range, 220 nm, prevents the island structure from becoming excessively coarsened, resulting in a larger V-pit opening diameter after merging, such as greater than 150 nm, thus reducing the formation of non-radiative recombination centers. The middle value of this range, 200 nm, can be matched with the thickness of the merging layer 220 (approximately 2 μm thick N-type GaN layer), so that the ratio of the V-pit opening diameter to the thickness of the epitaxial structure is <0.1, thereby ensuring that the V-pits are completely closed during the longitudinal growth of the epitaxial structure. Based on this, the lateral dimensions of the GaN island structure in the Si-doped GaN island layer can be set according to different needs to match different application scenarios.

[0092] In one embodiment of this application, in the first stage, the nucleation density of the GaN island structure in the initial layer of the Si-doped GaN island layer 214 ranges from 10. 8 cm -2 ~10 9 cm -2 The longitudinal dimension of the GaN island structure 218 in the initial layer of the Si-doped GaN island layer 214 ranges from 60nm to 100nm, including the endpoint value, and the lateral dimension of the GaN island structure 218 in the initial layer ranges from 100nm to 200nm, including the endpoint value.

[0093] After annealing and before forming the AlN cap layer 216, the longitudinal dimension of the GaN island structure 218 in the Si-doped GaN island layer 214 ranges from 80nm to 120nm, including the endpoints, and the lateral dimension of the GaN island structure 218 in the Si-doped GaN island layer 214 ranges from 130nm to 240nm, including the endpoints. The ratio of the longitudinal dimension to the lateral dimension of the GaN island structure 218 in the Si-doped GaN island layer 214 is 0.5 to 0.6.

[0094] After forming the AlN cap layer 216, the longitudinal dimension of the GaN island structure 218 in the Si-doped GaN island layer 214 ranges from 80nm to 120nm, including the endpoint value, and the lateral dimension of the GaN island structure 218 ranges from 180nm to 220nm, including the endpoint value.

[0095] Along the direction perpendicular to the plane of the substrate 100, the thickness of the AlN cap layer 216 ranges from 2nm to 3nm, including the endpoint values.

[0096] It should be noted that the longitudinal dimension of the GaN island structure 218 is the thickness of the GaN island structure 218 along the direction perpendicular to the plane of the substrate 100, and the lateral dimension of the GaN island structure 218 is the diameter of the GaN island structure 218 along the direction parallel to the plane of the substrate 100.

[0097] In one embodiment of this application, forming a three-dimensional nucleation layer 200 on one side of the substrate further includes forming a merging layer 220 on the side of the AlN cap layer 216 away from the substrate 100. The formation of the merging layer 220 on the side of the AlN cap layer 216 away from the substrate 100 includes: after forming a three-dimensional island structure layer, introducing SiH4 through the three-dimensional island structure layer at a fifth temperature and a fourth pressure to form the merging layer 220.

[0098] Specifically, after forming the AlN cap layer 216, the temperature is raised to 1050°C (i.e., the fifth temperature), the pressure is 200 Torr (i.e., the fourth pressure), and SiH4 is introduced. The Si doping concentration in the merged layer 220 formed by introducing SiH4 can be 5 × 10⁻⁶. 16 atoms / cm 3 The merging time can be 120 seconds to form a merged layer 220.

[0099] In addition, the preparation method also includes forming a buffer layer 300 between the substrate 100 and the three-dimensional nucleation layer 200, and sequentially forming an N-type layer 302, a superlattice stress relief layer 304, an active layer 306, a barrier layer 308, a P-type layer 310 and an ohmic contact layer 312 on the side of the three-dimensional nucleation layer 200 away from the substrate 100, which will not be described in detail here.

[0100] In summary, this application provides an epitaxial structure, a fabrication method, and a light-emitting diode. The epitaxial structure includes a substrate and a three-dimensional nucleation layer located on one side of the substrate. The three-dimensional nucleation layer includes a three-dimensional island structure layer, which is formed by merging multiple three-dimensional island structures. The three-dimensional island structure layer includes an AlN cap layer and Si-doped GaN island layers. The Si-doped GaN island layers are located on one side of the substrate, and the AlN cap layer is located on the side of the Si-doped GaN island layers away from the substrate and covers the side of the Si-doped GaN island layers away from the substrate. The Si-doped GaN island layers include multiple GaN island structures, and the AlN cap layer covers the Si-doped GaN island layers, forming multiple three-dimensional island structures. The Si doped in the Si-doped GaN island layers replaces the Ga sites in GaN, allowing the Si-doped GaN island layers to reach the critical nucleation density at a second temperature lower than a first temperature. Simultaneously, it reduces the effective surface energy of the (0001) facet of the Si-doped GaN island layers, achieving control over the geometric dimensions of the GaN island structures and effectively avoiding the formation of giant V-pits. Furthermore, the lattice constant of the AlN cap layer is lower than that of the Si-doped GaN island layer, suppressing the lateral growth rate of the GaN island structure in the Si-doped GaN island layer. Therefore, the three-dimensional nucleation layer of this epitaxial structure, comprising Si-doped GaN islands and an AlN cap layer, can lower the nucleation temperature threshold based on the Si-doped GaN islands, achieving high-density uniform nucleation at lower temperatures and laying the foundation for subsequent morphology control. Simultaneously, based on the dual synergistic control mechanism of the Si-doped GaN islands and the AlN cap layer on the geometric dimensions of the GaN island structure, effective control of the GaN island structure's geometric dimensions is achieved during the formation of the three-dimensional nucleation layer. This provides a feasible solution to avoid the formation of giant V-pits, or to form V-pits of suitable size, thereby improving the luminous performance of the LED chip.

[0101] The various embodiments in this specification are described in a progressive, parallel, or combined manner. Each embodiment focuses on its differences from other embodiments, and similar or identical parts between embodiments can be referred to interchangeably. For the apparatuses disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple, and relevant parts can be referred to the method section.

[0102] It should be noted that, in the description of this application, the terms "upper," "lower," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. When a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be a component centrally located at the same time.

[0103] 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.

[0104] 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. An epitaxial structure, characterized in that, The epitaxial structure includes: Substrate; A three-dimensional nucleation layer located on one side of the substrate, the three-dimensional nucleation layer including a three-dimensional island structure layer, the three-dimensional island structure layer being composed of multiple three-dimensional island structures; The three-dimensional island structure layer includes an AlN cap layer and a Si-doped GaN island layer. The Si-doped GaN island layer is located on one side of the substrate, and the AlN cap layer is located on the side of the Si-doped GaN island layer away from the substrate and covers the Si-doped GaN island layer. The Si-doped GaN island layer includes multiple GaN island structures, and the AlN cap layer covers the multiple GaN island structures in the Si-doped GaN island layer to form the multiple three-dimensional island structures. The doped Si in the Si-doped GaN island layer replaces the Ga sites in GaN, and the Si-doped GaN island layer reaches the critical nucleation density at a second temperature lower than the first temperature, wherein the undoped GaN island layer reaches the critical nucleation density at the first temperature. The lattice constant of the AlN cap layer is smaller than that of the Si-doped GaN island layer, which suppresses the growth rate of the GaN island structure in the Si-doped GaN island layer in the lateral growth direction, which is parallel to the plane of the substrate.

2. The epitaxial structure according to claim 1, characterized in that, The Si doping concentration in the Si-doped GaN island layer ranges from 1 × 10⁻⁶. 16 atoms / cm 3 ~1×10 17 atoms / cm 3 This includes endpoint values.

3. The epitaxial structure according to claim 1, characterized in that, The three-dimensional nucleation layer further includes a merging layer, which is located on the side of the AlN cap layer away from the substrate; The merging layer is formed by introducing SiH4 into the three-dimensional island structure layer.

4. The epitaxial structure according to claim 1, characterized in that, Along a direction perpendicular to the plane of the substrate, the AlN cap layer comprises N sub-cap layers stacked together, where N is an integer greater than or equal to 1.

5. The epitaxial structure according to claim 1, characterized in that, The epitaxial structure further includes a buffer layer, an N-type layer, a superlattice stress relief layer, an active layer, a barrier layer, a P-type layer, and an ohmic contact layer; The buffer layer is located between the substrate and the three-dimensional nucleation layer; The N-type layer is located on the side of the three-dimensional nucleation layer away from the substrate, and the N-type layer, the superlattice stress relief layer, the active layer, the barrier layer, the P-type layer and the ohmic contact layer are arranged sequentially in the direction away from the substrate.

6. A method for preparing an epitaxial structure, characterized in that, For preparing the epitaxial structure according to any one of claims 1-5, comprising: Provide a substrate; A three-dimensional nucleation layer is formed on one side of the substrate. The three-dimensional nucleation layer includes a three-dimensional island structure layer, which is composed of multiple three-dimensional island structures. The formation of the three-dimensional island structure layer includes: forming a Si-doped GaN island layer on one side of the substrate, followed by forming an AlN cap layer, wherein the AlN cap layer covers the side of the Si-doped GaN island layer away from the substrate; the Si-doped GaN island layer includes multiple GaN island structures, and the AlN cap layer covers the multiple GaN island structures in the Si-doped GaN island layer, thereby forming the multiple three-dimensional island structures. In the Si-doped GaN island layer, the doped Si replaces the Ga sites in GaN, and the Si-doped GaN island layer reaches the critical nucleation density at a second temperature lower than the first temperature, while the undoped GaN island layer reaches the critical nucleation density at the first temperature. The lattice constant of the AlN cap layer is smaller than that of the Si-doped GaN island layer, which suppresses the growth rate of the GaN island structure in the Si-doped GaN island layer in the lateral growth direction, which is parallel to the plane of the substrate.

7. The method for preparing the epitaxial structure according to claim 6, characterized in that, The Si-doped GaN island layer comprises: Under the second temperature and first pressure, a first source gas is introduced to form the initial layer of the Si-doped GaN island layer; wherein the first source gas includes Ga source gas, N source gas and Si source gas, and the molar flow ratio of N source gas and Ga source gas in the first source gas satisfies a preset ratio, and based on the Si source gas, the Si doping concentration in the initial layer of the Si-doped GaN island layer ranges from 1×10⁻⁶. 16 atoms / cm 3 ~1×10 17 atoms / cm 3 This includes endpoint values; The initial layer is annealed at a third temperature and a second pressure, under a protective atmosphere of NH3, to form the Si-doped GaN island layer. The third temperature is greater than the second temperature, and the second pressure is less than the first pressure.

8. The method for preparing the epitaxial structure according to claim 7, characterized in that, Forming the AlN cap layer includes: Under a fourth temperature and a third pressure, a second source gas is periodically introduced to form the AlN cap layer; Wherein, the second source gas includes Al source gas, the fourth temperature is greater than the third temperature, and the third pressure is less than the first pressure; the number of cycles in which the second source gas is periodically introduced is M, where M is an integer greater than or equal to 1.

9. The method for preparing the epitaxial structure according to claim 7, characterized in that, The nucleation density of the GaN island structures in the initial layer ranges from 10. 8 cm -2 ~10 9 cm -2 The initial layer has a longitudinal dimension ranging from 60 nm to 100 nm, including the endpoint value, and a lateral dimension ranging from 100 nm to 200 nm, including the endpoint value. The longitudinal dimension is the dimension perpendicular to the plane of the substrate, and the lateral dimension is the dimension parallel to the plane of the substrate. After annealing and before forming the AlN cap layer, the longitudinal dimension of the GaN island structure in the Si-doped GaN island layer ranges from 80nm to 120nm, including the endpoints, and the lateral dimension ranges from 130nm to 240nm, including the endpoints. The ratio of the longitudinal dimension to the lateral dimension of the GaN island structure in the Si-doped GaN island layer is 0.5 to 0.

6. After the AlN cap layer is formed, the longitudinal dimension of the GaN island structure in the Si-doped GaN island layer ranges from 80nm to 120nm, including the endpoint value, and the lateral dimension ranges from 180nm to 220nm, including the endpoint value. Along the direction perpendicular to the plane of the substrate, the thickness of the AlN cap layer ranges from 2nm to 3nm, including the endpoint values.

10. The method for preparing the epitaxial structure according to claim 6, characterized in that, Forming a three-dimensional nucleation layer on one side of the substrate further includes: A merging layer is formed on the side of the AlN cap layer away from the substrate; The formation of a merging layer on the side of the AlN cap layer away from the substrate includes: After the three-dimensional island structure layer is formed, SiH4 is introduced into the three-dimensional island structure layer under the fifth temperature and fourth pressure to form the structure.

11. A light-emitting diode, characterized in that, Includes the epitaxial structure as described in any one of claims 1-5.

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