Light emitting diode and preparation method thereof

Abstract

The invention provides a light emitting diode and a preparation method thereof, and belongs to the technical field of semiconductors. The light emitting diode comprises an epitaxial structure, a reflection passivation layer, a first electrode and a second electrode. The epitaxial structure comprises a p-type semiconductor layer, a light-emitting layer and an n-type semiconductor layer which are stacked in sequence; the n-type semiconductor layer comprises an n-type ohmic contact layer, the n-type ohmic contact layer comprises a plurality of AlAs layers and a plurality of AlGaAs layers, and the AlAs layers and the AlGaAs layers are alternately stacked; the first electrode and the second electrode are positioned on the same side of the epitaxial structure; the reflection passivation layer covers the surface, away from the light-emitting layer, of the n-type semiconductor layer, the first electrode and the second electrode, and is provided with a window exposing the first electrode and the second electrode. The brightness of the light emitting diode can be improved.

Description

Technical Field

[0001] This disclosure belongs to the field of semiconductor technology, and specifically relates to a light-emitting diode and its fabrication method. Background Technology

[0002] As an energy-saving and environmentally friendly new type of light source, light-emitting diodes (LEDs) are widely used in full-color displays, lighting, automotive lights, and other fields.

[0003] In related technologies, a light-emitting diode (LED) includes an epitaxial structure, a first electrode, a second electrode, and a reflective passivation layer. The epitaxial structure comprises a p-type semiconductor layer, a light-emitting layer, and an n-type semiconductor layer stacked sequentially. The n-type semiconductor layer includes an n-type GaAs ohmic contact layer. The first electrode and the second electrode are located on the same side of the epitaxial structure. The reflective passivation layer covers the surface of the epitaxial structure and the first and second electrodes. The reflective passivation layer has openings that expose the first and second electrodes.

[0004] However, light emitted from the light-emitting layer is reflected by the reflective passivation layer before emanating from the substrate. Because the reflective passivation layer has openings for exposing the first and second electrodes, there are areas in the reflective passivation layer that fail to reflect light, resulting in low reflectivity and ultimately low brightness of the light-emitting diode. Summary of the Invention

[0005] This disclosure provides a light-emitting diode (LED) and its fabrication method, which can improve the brightness of the LED. The technical solution is as follows: This disclosure provides a light-emitting diode (LED) comprising an epitaxial structure, a reflective passivation layer, a first electrode, and a second electrode. The epitaxial structure comprises a p-type semiconductor layer, a light-emitting layer, and an n-type semiconductor layer stacked sequentially. The n-type semiconductor layer includes an n-type ohmic contact layer, which comprises multiple AlAs layers and multiple AlGaAs layers, with the AlAs layers and AlGaAs layers stacked alternately. The first electrode and the second electrode are located on the same side of the epitaxial structure. The reflective passivation layer covers the surface of the n-type semiconductor layer away from the light-emitting layer, the first electrode, and the second electrode, and has an opening that exposes the first electrode and the second electrode.

[0006] In another implementation of this disclosure, the total thickness of the n-type ohmic contact layer is 0.5 μm to 1.5 μm.

[0007] In another implementation of this disclosure, the thickness of the AlAs layer in each of the periodic structures is 400 Å to 650 Å.

[0008] In another implementation of this disclosure, the thickness of the AlGaAs layer in each of the periodic structures is 400 Å to 650 Å.

[0009] In another implementation of this disclosure, the thicknesses of both the AlAs layer and the AlGaAs layer satisfy the following formula: ; Where d represents the thickness of the AlAs layer and the AlGaAs layer, respectively; λ represents the wavelength of the light reflected by the n-type ohmic contact layer in vacuum; and n represents the refractive index of the AlAs layer and the AlGaAs layer, respectively.

[0010] In another implementation of this disclosure, the Al component content in the AlGaAs layer of each of the periodic structures is 0.4 to 0.6.

[0011] In another implementation of this disclosure, the n-type ohmic contact layer is doped with a carrier concentration of 5 × 10⁻⁶. 18 ~8×10 18 / cm 3 .

[0012] In another implementation of this disclosure, the number of AlAs layers is 5 to 15.

[0013] In another implementation of this disclosure, the n-type semiconductor layer further includes an n-type confinement layer located between the light-emitting layer and the n-type ohmic contact layer.

[0014] On the other hand, embodiments of this disclosure also provide a method for fabricating a light-emitting diode, the method comprising: fabricating an epitaxial structure, the epitaxial structure comprising a p-type semiconductor layer, a light-emitting layer and an n-type semiconductor layer stacked sequentially, the n-type semiconductor layer comprising an n-type ohmic contact layer, the n-type ohmic contact layer comprising multiple AlAs layers and multiple AGaAs layers, the AlAs layers and the AlGaAs layers being stacked alternately; fabricating a first electrode and a second electrode, the first electrode and the second electrode being located on the same side of the epitaxial structure; and fabricating a passivation layer, the reflective passivation layer covering the surface of the n-type semiconductor layer away from the light-emitting layer, the first electrode and the second electrode, and having an opening exposing the first electrode and the second electrode.

[0015] The beneficial effects of the technical solutions provided in this disclosure are: Because this light-emitting diode (LED) includes an epitaxial structure comprising a p-type semiconductor layer, a light-emitting layer, and an n-type semiconductor layer stacked sequentially, and the n-type semiconductor layer includes an n-type ohmic contact layer, which comprises multiple periodic structures formed by alternating AlAs and AlGaAs layers, this periodic structure allows the n-type ohmic contact layer to form an n-type AlAs / AlGaAs superlattice ohmic contact layer. When light emitted from the light-emitting layer strikes this superlattice ohmic contact layer, reflection occurs at the interface between the AlAs and AlGaAs layers. The reflected light from several repeating interfaces superimposes, ultimately forming a mirror effect with a very high total reflectivity. This allows the n-type ohmic contact layer to reflect the light emitted from the light-emitting layer, redirecting light that would otherwise be unable to be reflected by the passivation layer back to the light-emitting surface, thus increasing the brightness of the LED. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this disclosure, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the structure of a light-emitting diode provided in an embodiment of the present disclosure; Figure 2 for Figure 1 A schematic diagram of the structure of the n-type ohmic contact layer in the diagram; Figure 3 This is a schematic diagram of another light-emitting diode structure provided in an embodiment of the present disclosure; Figure 4 A flowchart illustrating a method for fabricating a light-emitting diode (LED) according to an embodiment of this disclosure; Figure 5 A flowchart illustrating another method for fabricating a light-emitting diode as provided in this disclosure embodiment; Figure 6 This is a comparison chart of the brightness of light-emitting diodes.

[0018] The symbols in the diagram represent the following meanings: 1. Substrate; 2. Epitaxial structure; 21. Light-emitting layer; 22. n-type semiconductor layer; 221. n-type ohmic contact layer; 2211. AlAs layer; 2212. AlGaAs layer; 222. n-type confinement layer; 223. n-type current spreading layer; 224. Electrode bonding layer; 23. p-type semiconductor layer; 231. p-type confinement layer; 232. p-type current spreading layer; 233. p-type stress transition layer; 3. Reflective passivation layer; 5. First electrode; 6. Second electrode; 101. First step; 102. Second step. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this disclosure clearer, the embodiments of this disclosure will be described in further detail below with reference to the accompanying drawings.

[0020] This disclosure provides a light-emitting diode, such as... Figure 1 As shown, the light-emitting diode includes an epitaxial structure 2, a reflective passivation layer 3, a first electrode 5, and a second electrode 6. The epitaxial structure 2 includes a p-type semiconductor layer 23, a light-emitting layer 21, and an n-type semiconductor layer 22 stacked sequentially. The first electrode 5 and the second electrode 6 are located on the same side of the epitaxial structure 2. The reflective passivation layer 3 covers the surface of the n-type semiconductor layer 22 away from the light-emitting layer 21, the first electrode 5, and the second electrode 6, and has openings that expose the first electrode 5 and the second electrode 6.

[0021] Figure 2 for Figure 1 A schematic diagram of the structure of the n-type ohmic contact layer, combined with Figure 2 The n-type semiconductor layer 22 includes an n-type ohmic contact layer 221, which includes multiple AlAs layers 2211 and multiple AlGaAs layers 2212, with AlAs layers 2211 and AlGaAs layers 2212 stacked alternately.

[0022] Since the light-emitting diode includes an epitaxial structure 2, and the epitaxial structure 2 includes a p-type semiconductor layer 23, a light-emitting layer 21, and an n-type semiconductor layer 22 stacked sequentially, the n-type semiconductor layer 22 includes an n-type ohmic contact layer 221, wherein the n-type ohmic contact layer 221 includes multiple periodic structures formed by alternating AlAs layers 2211 and AlGaAs layers 2212. This periodic structure formed by alternating AlAs layers 2211 and AlGaAs layers 2212 allows the n-type ohmic contact layer 221 to form an n-type AlAs / AlGaAs superlattice ohmic contact layer. When light emitted from the light-emitting layer 21 strikes this superlattice ohmic contact layer, reflection occurs at the interface between the AlAs and AlGaAs layers. The reflected light from several periodically repeating interfaces superimposes, ultimately forming a mirror effect with a very high total reflectivity. This allows the n-type ohmic contact layer 221 to reflect the light emitted from the light-emitting layer, redirecting light that the passivation layer 3 could not originally reflect back to the light-emitting surface, thus improving the brightness of the light-emitting diode. At the same time, the n-type ohmic contact layer 221 can form a low resistance, ensuring that the current can be injected efficiently and smoothly.

[0023] In this embodiment, the light-emitting diode (LED) is a red LED. An AlAs / AlGaAs superlattice structure is applied to the n-type ohmic contact layer of the red LED. The alternating AlAs / AlGaAs superlattice structure can reflect light emitted from the light-emitting layer, improving light emission; it can also effectively annihilate dislocations generated during the growth of the underlying layer. Furthermore, the AlAs / AlGaAs superlattice acts as a thermal stress buffer, preventing stress concentration. Moreover, the Al composition of the AlGaAs layer is adjustable, allowing for a balance between voltage and chip brightness.

[0024] It should be noted that the reflective passivation layer 3 has windows that expose the first electrode 5 and the second electrode 6. These windows are designed to expose the connection points of the first electrode 5 and the second electrode 6, so that external circuits or leads can directly contact the first electrode 5 and the second electrode 6 and achieve a reliable electrical connection. At the same time, the effect of the reflective passivation layer 4 on the non-passivation function of the surface of the epitaxial structure 2 should be minimized.

[0025] Optionally, the total thickness of the n-type ohmic contact layer 221 is 0.5 μm to 1.5 μm.

[0026] In the above implementation, the total thickness of the n-type ohmic contact layer 221 is 0.5 μm to 1.5 μm. This thickness ensures that the resistance of the n-type ohmic contact layer 221 is low, providing a sufficient and low-resistance path for charge carriers and ensuring the formation of excellent ohmic contacts. If the thickness is too thin (much less than 0.5 μm), it may lead to excessively high series resistance, affecting current injection efficiency. Moreover, since the n-type ohmic contact layer 221 is formed by alternating growth of two materials with slightly different lattice constants, if the total thickness is too large (e.g., exceeding 1.5 μm), the accumulated stress may cause defects in the crystal (such as dislocations), or even cause the n-type ohmic contact layer 221 to crack.

[0027] For example, the thickness of the n-type ohmic contact layer 221 is 0.8, 1.0, 1.2 μm, etc. This ensures low resistance and stable and reliable ohmic contact of the n-type ohmic contact layer 221. At the same time, it can also give it high reflectivity, so as to significantly improve the light extraction efficiency of the light-emitting diode.

[0028] Optionally, the thickness of each AlAs layer is 400 Å to 650 Å. The thickness of the AlGaAs layer is 400 Å to 650 Å.

[0029] In the above implementation, controlling the thickness of the AlAs or AlGaAs layer to below 65nm can effectively suppress the generation of defects such as dislocations, ensuring the high quality and reliability of the epitaxial material. Furthermore, a thinner monolayer means a shorter growth time, which improves production efficiency and reduces costs. Choosing a thinner layer within the allowable range, while meeting optical performance requirements, can maximize efficiency.

[0030] Furthermore, to accommodate the specific emission wavelength of the adapter (for example, in this embodiment, the light-emitting diode is suitable for wavelengths of 620-640nm, meaning the wavelength range of light reflected by the n-type ohmic contact layer 221 is 620 to 640nm), the thickness of the AlAs layer 2211 or AlGaAs layer 2212 in the n-type ohmic contact layer 221 is made to satisfy the following formula in order to achieve extremely high reflectivity: (1) Where d is the thickness of AlAs layer 2211 and AlGaAs layer 2212; λ is the wavelength of light reflected by n-type ohmic contact layer 221 in vacuum; and n is the refractive index of AlAs layer 2211 and AlGaAs layer 2212.

[0031] When light travels from a low-refractive-index layer to a high-refractive-index layer, the reflected light undergoes a 180° phase flip; however, when light travels from a high-refractive-index layer to a low-refractive-index layer, there is no phase flip. Light passes through a λ / 4 thick film layer and is reflected back, resulting in a total optical path difference of λ / 2. This λ / 2 optical path difference itself introduces a 180° phase difference. Therefore, by alternating between AlAs layer 2211 and AlGaAs layer 2212, it can be ensured that the light waves reflected from all interfaces are in phase. These in-phase reflected light waves superimpose their amplitudes rather than cancel each other out. As the logarithm of the period increases, the total reflectivity can easily reach over 99%. It is evident that by setting the thickness of AlAs layer 2211 and AlGaAs layer 2212 to λ / 4n, the n-type ohmic contact layer 221 achieves optimal reflection of light at a specific wavelength (620-640nm), thereby significantly improving luminous efficiency.

[0032] For example, the refractive index n of AlAs layer 2211 is 2.9-3.0. The refractive index n of AlGaAs layer 2212 is related to the Al content. The higher the aluminum content, the wider the band gap of the material, and the lower its refractive index n. The lower the aluminum content (i.e., the higher the gallium content), the narrower the band gap of the material, and the higher its refractive index n.

[0033] In this embodiment, the Al component content in the AlGaAs layer in each periodic structure is 0.4~0.6.

[0034] When the Al content is 0.4–0.6%, the refractive index of the corresponding AlGaAs layer is typically between 3.15 and 3.30. This configuration allows for a significant refractive index difference between the AlGaAs and AlAs layers, enabling the construction of a highly efficient mirror, while its wide bandgap characteristic maximizes photon utilization. Furthermore, this configuration also facilitates the formation of low-resistance ohmic contacts.

[0035] Optionally, the n-type ohmic contact layer 221 is silicon-doped with a carrier concentration of 5 × 10⁻⁶. 18 ~8×10 18 / cm 3 .

[0036] In the above implementation, the n-doped source used when forming the n-type ohmic contact layer 221 is a silicon source.

[0037] In III-V semiconductors such as GaAs and AlAs, silicon atoms (Si) occupy the positions of group III elements (such as Ga and Al). Since silicon is a group IV element with four valence electrons, while group III elements only have three, there is one extra free electron. This free electron becomes a charge carrier, thus achieving n-type doping.

[0038] Common silicon sources include SiH4 and Si2H6. Because SiH4 and Si2H6 can decompose at appropriate temperatures and provide silicon atoms, and the doping concentration can be precisely controlled by adjusting the gas flow rate, they are well-suited for large-scale production.

[0039] In addition, the carrier concentration in the n-type ohmic contact layer 221 is set to 5 × 10⁻⁶. 18 ~8×10 18 / cm 3 This indicates that within the n-type ohmic contact layer 221, there are 5 × 10⁻⁶ ohmic points per cubic centimeter of volume. 18 ~8×10 18 One free electron. This is represented by heavy doping. Through heavy doping, an extremely thin depletion region is formed on the surface of the n-type semiconductor layer, allowing electrons to easily pass through via quantum tunneling, thereby forming a linear, low-resistance ohmic contact that ensures efficient and low-loss current injection.

[0040] Optionally, the number of AlAs layers 2211 is 5 to 15; the number of AlGaAs layers 2212 is 5 to 15.

[0041] In the above implementation, the reflectivity of the superlattice structure increases with the number of periods, but the relationship is not linear. For the n-type ohmic contact layer 221 in this embodiment, its reflectivity increases sharply with the increase in the number of periodic structures, but then the change becomes relatively gradual.

[0042] In this embodiment, the refractive index difference (Δn) between the AlAs layer 2211 and the AlGaAs layer 2212 in the n-type ohmic contact layer 221 is approximately 0.3. When there are 5 AlAs layers 2211, a reflectivity of 85%-92% can be achieved. When the number of periodic structures is 10, a reflectivity of 97%-99% can be achieved. When the number of periodic structures is 15, a reflectivity of over 99.5% can be achieved. Therefore, setting the number of AlAs layers 2211 to 5-15 is precisely at the stage where the reflectivity curve transitions from a rapid rise to a saturation plateau, while also helping to maintain a low series resistance. However, when the number of periodic structures increases to more than 20 pairs, the reflectivity may only increase from 99.5% to 99.9%, but the growth time, cost, and potential risks increase exponentially. Moreover, by controlling the number of periodic structures, the thickness of the n-type ohmic contact layer 221 can also be controlled, effectively preventing stress accumulation due to excessive thickness, avoiding cracks or dislocations in the epitaxial structure, and ensuring the long-term reliability of the material.

[0043] In other words, limiting the AlAs layer 2211 to 5-15mm thickness allows the n-type ohmic contact layer 221 to achieve a sufficiently high reflectivity (>97%), significantly improving light extraction efficiency. Simultaneously, it maintains a low series resistance, ensuring efficient current injection. Furthermore, it allows for control of the total thickness, reducing growth time and cost, lowering stress and defect risks, and improving yield.

[0044] For example, the number of AlAs layers 2211 is 10. This can achieve a reflectivity of up to 99% within a limited cost, which is sufficient for the vast majority of applications.

[0045] Optionally, from the p-type semiconductor layer 23 to the light-emitting layer 21, both the upper and lower surfaces of the n-type ohmic contact layer 221 are AlGaAs layers 2212. This ensures that both the upper and lower surfaces of the superlattice are in contact with adjacent layers using AlGaAs layers, reducing lattice mismatch.

[0046] Figure 3 For another schematic diagram of the structure of a light-emitting diode provided in this disclosure embodiment, see [link to schematic diagram]. Figure 3 Optionally, the n-type semiconductor layer 22 further includes an n-type confinement layer 222, which is located between the light-emitting layer 21 and the n-type ohmic contact layer 221. The n-type confinement layer 222 is an n-type AlInP layer.

[0047] In the above implementation, setting an n-type confinement layer 222 can effectively confine the charge carriers, thereby improving the recombination efficiency.

[0048] Because the band gap of AlInP is wider than that of the emitting layer 21 (AlGaInP layer), this band gap difference is represented by a conduction band level on the band structure. Therefore, electrons injected from the n-type region encounter this energy barrier formed by the AlInP layer when they reach the emitting layer 21. Electrons find it difficult to overcome this barrier and continue diffusing forward. Electrons are effectively "confined" within the emitting layer 21, greatly increasing the probability of electrons recombinating with holes injected from the p-type region within the emitting layer 21 and emitting light. Without the n-type confinement layer 222, a large number of electrons would pass through the emitting layer 21 and continue diffusing into the p-type semiconductor layer 23. These electrons would eventually recombine in the non-emitting layer, causing carrier leakage. Carrier leakage significantly reduces the internal quantum efficiency of the light-emitting diode and causes the efficiency to decrease rapidly with increasing current.

[0049] For example, the thickness of the n-type confinement layer 222 is 250~350 nm, the dopant is SiH4 / Si2H6, and the carrier concentration is 1×10⁻⁶. 18 ~2×10 18 / cm 3 .

[0050] The n-type confinement layer 222 is used to confine electrons within the central light-emitting layer 21. A thickness of 250–350 nm ensures a sufficiently wide potential barrier, effectively confining electrons and improving carrier recombination efficiency (reducing non-radiative recombination). SiH4 (silane) and Si2H6 (disilane) are commonly used n-type doping sources in III-V semiconductors (such as AlGaInP). After decomposition, they stably provide Si atoms (replacing Ga / Al atoms and providing free electrons), exhibiting high doping efficiency and good uniformity. Setting the above carrier concentration ensures that the conductivity of the n-type confinement layer 222 is sufficiently high (reducing current transport losses) without increasing crystal defects due to excessive doping (defects reduce carrier mobility).

[0051] Optionally, the n-type semiconductor layer 22 further includes an n-type current spreading layer 223, which is located between the n-type confinement layer 222 and the n-type ohmic contact layer 221, and the n-type current spreading layer 223 is an n-type AlGaInP layer.

[0052] In the above implementation, the n-type current spreading layer 223 is used to rapidly and uniformly spread the injected point or line current in the lateral direction (parallel to the surface of the substrate), so that it can be uniformly injected into the entire light-emitting layer, thereby avoiding current congestion, achieving uniform light emission, and improving device performance and reliability. Without the n-type current spreading layer 223, the current will take the shortest path with the least resistance, resulting in a highly uneven current density distribution.

[0053] The reason for choosing an n-type AlGaInP layer as the n-type current spreading layer 223 is that the n-type AlGaInP layer has a low resistivity, acting as a conductive platform that allows the current to diffuse laterally before reaching the light-emitting layer 21. Moreover, the AlGaInP material can achieve good lattice matching with the underlying n-type confinement layer 222 and the light-emitting layer 21, enabling the growth of a high-quality, low-defect single-crystal layer, thereby obtaining low resistivity.

[0054] Optionally, the thickness of the n-type current spreading layer 223 is 2~3 μm. The dopant is SiH4 / Si2H6, and the carrier concentration is 7 × 10⁻⁶. 17 ~2×10 18 / cm 3 .

[0055] A 2-3 μm thick n-type current spreading layer 223 provides sufficient lateral transport paths, allowing current to diffuse uniformly from the electrode contact point to the entire active region, avoiding current concentration below the electrode (excessive local current density can lead to heat generation, decreased luminous efficiency, and even burnout of the active region). SiH4 and Si2H6 are preferred n-type doping sources for III-V semiconductors. They can rapidly decompose at high temperatures (MOCVD growth temperature 600-700℃), releasing Si atoms—Si atoms can stably replace Ga / Al atoms in the lattice, providing free electrons. Moreover, this carrier concentration ensures that the conductivity of the current spreading layer is sufficiently high, preventing a decrease in overall device efficiency due to heat generation.

[0056] Optionally, the n-type semiconductor layer 22 further includes an electrode bonding layer 224, which is located between the n-type ohmic contact layer 221 and the n-type current spreading layer 223.

[0057] The electrode bonding layer 224 is used to improve the adhesion and thermal stability of the metal electrode to the semiconductor material. By inserting the electrode bonding layer 224 between the n-type ohmic contact layer and the current spreading layer, the electrode can be prevented from peeling, over-alloying or electrical performance degradation during high-temperature processes or long-term operation, thereby improving the reliability and lifespan of the device.

[0058] For example, the electrode bonding layer 224 is an n-type GaInP layer. The thickness of the electrode bonding layer 224 is 10~20 nm, the dopant is SiH4 / Si2H6, and the carrier concentration is 5 × 10⁻⁶. 18 ~1×10 19 / cm 3 .

[0059] Because GaInP material has excellent chemical stability and good adhesion properties with metal electrodes, when the electrode bonding layer 224 is an n-type GaInP layer, the electrode bonding layer 224 can effectively suppress the diffusion of electrode metal to the light-emitting layer during high-temperature processes or long-term operation.

[0060] The thickness specified above results in extremely low additional series resistance due to the introduction of the electrode bonding layer 224, having minimal impact on current spreading efficiency. Meanwhile, the higher carrier concentration provides ample tunnelable carriers, significantly reducing the contact resistance between the electrode metal and the electrode bonding layer 224.

[0061] Optionally, the light-emitting diode further includes a substrate 1, which is located on the side of the epitaxial structure 2 away from the reflective passivation layer 3, and the substrate 1 is connected to the p-type semiconductor layer 23 in the epitaxial structure 2. The substrate 1 is a sapphire substrate. The substrate 1 is used to provide support for the epitaxial structure 2. Using sapphire as the substrate 1 not only provides high visible light transmittance but also excellent chemical stability and high temperature resistance, thus improving the reliability of the device.

[0062] The p-type semiconductor layer 23 includes a p-type confinement layer 231 and a p-type current spreading layer 232, with the p-type confinement layer 231 located between the light-emitting layer 21 and the p-type current spreading layer 232. The p-type current spreading layer 232 is connected to the substrate 1. The p-type confinement layer 231 is a p-type Al. 0.5 In 0.5 P-layer. The p-type current extension layer 232 is a p-type GaP layer.

[0063] In the above implementation, the p-type current extension layer 232 in the epitaxial structure 2 is bonded to a transparent sapphire substrate 1, which means that the light-emitting diode is a flip-chip structure, that is, light is emitted from the substrate 1 after passing through the p-type semiconductor layer 23.

[0064] The p-type confinement layer 231, made of a wide-bandgap AlInP material, creates a bandgap difference between the p-type confinement layer 231 and the light-emitting layer 21. This bandgap difference is represented by a high potential barrier on the band structure diagram. Holes reaching the light-emitting layer are blocked by this barrier and cannot diffuse further to the n-type semiconductor layer 22, thus being effectively confined within the light-emitting layer 21. This significantly increases the probability of holes recombinating with electrons injected from the n-type semiconductor layer 22 within the light-emitting layer 21. Moreover, the refractive index of the p-type confinement layer 231 is typically lower than that of the light-emitting layer. Together with the n-type confinement layer, the p-type confinement layer 231 can better confine photons generated by the light-emitting layer 21 in the vertical direction, guiding light propagation towards the light-emitting surface and reducing lateral light loss.

[0065] The p-type current spreading layer 232 is used to uniformly spread the injected current, whether in the form of dots or lines, laterally (parallel to the surface of the substrate 1), so that the current is uniformly injected into the entire light-emitting layer 21. The p-type current spreading layer 232 is made of p-type GaP material, which can give the device low resistivity and high conductivity. This makes the p-type current spreading layer 232 an excellent lateral conductive layer, allowing the current to spread rapidly laterally before reaching the light-emitting layer 21, avoiding local current congestion, and thus ensuring uniform and efficient light emission.

[0066] For example, the thickness of the p-type confinement layer 231 is 300 nm to 800 nm, the dopant is magnesia-diocene (molecular formula Mg(C5H5)2, Cp2Mg), and the carrier concentration is 3 × 10⁻⁶. 17 ~1×10 18 / cm 3 .

[0067] The p-type current extension layer 232 has a thickness of 5µm~10µm, uses Cp2Mg as the dopant, and has a carrier concentration of 4×10⁻⁶. 17 ~3×10 18 / cm 3 .

[0068] Optionally, the p-type semiconductor layer 23 further includes a p-type stress transition layer 233, which is located between the p-type confinement layer 231 and the p-type current spreading layer 232.

[0069] The p-type stress transition layer 233 is used to adjust the lattice constant and stress state between the p-type confinement layer 231 and the p-type current extension layer 232, thereby achieving a smooth stress transition between the two, avoiding crystal defects (such as dislocations and cracks) caused by stress abrupt changes, ensuring the crystal quality of the upper structure, and improving the reliability of the electrical and optical performance of the device.

[0070] For example, the p-type stress transition layer 233 is p-type AlGaInP. The p-type AlGaInP layer and the p-type confinement layer 231 are lattice-matched homogeneous materials, thus the p-type confinement layer 231 (AlGaInP) can be precisely adjusted to achieve the desired stress transition from Al to Ga. 0.5 In 0.5 The smooth gradient of the lattice constant and band structure from the P-layer to the p-type current-extended layer 232 (GaP layer) reduces defects while simultaneously releasing stress.

[0071] Optionally, the light-emitting layer 21 includes multiple quantum well layers and multiple quantum barrier layers, with the quantum well layers and quantum barrier layers stacked alternately. Both the quantum well layers and the quantum barrier layers are Al. x Ga 1-xInP layers, where x is greater than 0 and less than 1. The x value in the quantum well layer is less than that in the quantum barrier layer. The thickness of the quantum well layer is 2–6 nm, the thickness of the quantum barrier layer is 5–10 nm, and the number of alternating quantum well and quantum barrier layers is 10–25.

[0072] The above structure, by varying the Al composition of the quantum well layer and the quantum barrier layer, creates a bandgap gradient. Combined with a quantum well layer thickness of 2–6 nm, electrons and holes are efficiently confined within the quantum well through quantum confinement. The 5–10 nm thickness of the quantum barrier layer both prevents carrier escape and ensures successful carrier injection. An alternating stack of 10–25 quantum wells further expands the effective region for carrier radiative recombination.

[0073] See you again Figure 1 In the epitaxial structure 2, a first step 101 is formed between the p-type semiconductor layer 23 and the n-type semiconductor layer 22 to expose the p-type semiconductor layer 23. The second electrode 6 is located on the top surface of the first step 101 and is electrically connected to the p-type semiconductor layer 23. A second step 102 is formed between the n-type ohmic contact layer 221 and the n-type current spreading layer 223 in the n-type semiconductor layer 22 to expose the n-type current spreading layer 223. The first electrode 5 is located on the top surface of the second step 102 and is electrically connected to the n-type ohmic contact layer 221. A reflective passivation layer 3 covers the first electrode 5, the second electrode 6, the n-type ohmic contact layer 221, the exposed top surface and sidewalls of the first step 101, the exposed top surface and sidewalls of the second step 102, and the sidewalls of the epitaxial structure 2. This allows the reflective passivation layer 3 to protect the epitaxial structure 2.

[0074] This disclosure also provides a method for fabricating a light-emitting diode, such as... Figure 4 As shown, the preparation method includes: S401: Fabrication of epitaxial structures.

[0075] The epitaxial structure includes a p-type semiconductor layer, a light-emitting layer, and an n-type semiconductor layer stacked sequentially. The n-type semiconductor layer includes an n-type ohmic contact layer, which includes multiple AlAs layers and multiple AGaAs layers, with AlAs and AlGaAs layers stacked alternately.

[0076] S402: Prepare the first electrode and the second electrode.

[0077] The first electrode and the second electrode are located on the same side of the epitaxial structure.

[0078] S403: Prepare a reflective passivation layer.

[0079] A reflective passivation layer covers the surface of the n-type semiconductor layer away from the light-emitting layer and has openings that expose the first and second electrodes.

[0080] The above preparation methods have the same beneficial effects as the aforementioned light-emitting diodes, and will not be repeated here.

[0081] This disclosure also provides another method for fabricating a light-emitting diode, such as... Figure 5 As shown, the preparation method includes: S501: An n-type semiconductor layer is formed on a growth substrate.

[0082] Optionally, S501 includes: 5011: An n-type buffer layer and an n-type etching stop layer are sequentially stacked on a growth substrate.

[0083] For example, the growth substrate can be a GaAs substrate. The growth substrate serves as the base for epitaxial layer growth, providing physical support; at the same time, GaAs is a group III-V semiconductor, and its lattice constant can achieve good matching with the subsequent GaAs buffer layer, providing a high-quality growth substrate for the epitaxial layer.

[0084] The n-type buffer layer is an n-type GaAs layer. The surface of the GaAs growth substrate may contain oxide layers and micro-defects. The n-type GaAs layer, acting as an n-type buffer layer, can cover these defects, providing a smooth and clean growth interface for subsequent layers. Furthermore, the n-type GaAs layer has the same lattice constant as the GaAs growth substrate, avoiding lattice mismatch stress and further improving the crystal quality of subsequent epitaxial layers.

[0085] The n-type etching stop layer is an n-type GaInP layer. The GaInP layer exhibits extremely high etching selectivity with the n-type buffer layer and the subsequent n-type ohmic contact layer 221. For example, in H3PO4 / H2O2 etchants, the etching rate of GaInP is much lower than that of GaAs. When this layer is etched, etching stops rapidly, avoiding damage to the underlying GaAs substrate / buffer layer or over-etching of the upper functional layer. It is a critical etching endpoint layer for fabricating the electrode contact area of ​​the device.

[0086] For example, the thickness of the n-type buffer layer is 150~300 nm, the dopant is SiH4 / Si2H6, and the doping concentration is 1×10⁻⁶. 18 ~2×10 18 / cm 3 .

[0087] In this embodiment, an n-type buffer layer is formed using metal-organic chemical vapor deposition (MOCVD). The specific process is as follows: A GaAs growth substrate is placed in a reaction chamber and heated to 500-600°C. Hydrogen gas (H2) is introduced to purge the substrate, removing the oxide layer and contaminants on the substrate surface to obtain a clean growth interface. Then, the reaction chamber temperature is raised to 600-700°C, and a Ga source (such as trimethylgallium) and an As source (such as arsine AsH3) are introduced. The two gases react on the substrate surface, initiating the deposition of a GaAs thin film to form the n-type buffer layer. Simultaneously, dopant SiH4 or Si2H6 is introduced. These silicon-containing gases decompose at high temperatures, incorporating silicon atoms into the GaAs lattice, replacing Ga atoms and providing free electrons, thus making the GaAs layer an n-type semiconductor. By adjusting the source gas flow rate and growth time, the final thickness of the n-type buffer layer is 150 nm to 300 nm; simultaneously, by adjusting the SiH4 / Si2H6 flow rate, the doping concentration is achieved to 1 × 10⁻⁶. 18 ~2×10 18 / cm³.

[0088] The thickness of the n-type etch stop layer is 180 nm, the dopant is SiH4 / Si2H6, and the carrier concentration is 3 × 10⁻⁶. 18 ~6×10 18 / cm 3 .

[0089] The n-type etch stop layer is also formed using metal-organic chemical vapor deposition (MOCVD). The specific process is as follows: the temperature of the reaction chamber is controlled at 640-680℃. Trimethylgallium (TMGa) and trimethylindium (TMIn) are introduced into the reaction chamber as the sources of Ga and In, respectively, while phosphine (PH3) is introduced as the P source. By adjusting the flow rate of the source gases and the growth time, the thickness of the n-type etch stop layer 102 is achieved to be 180 nm. The composition of GaInP is controlled by precisely adjusting the flow rate ratio of TMGa to TMIn. Simultaneously, dopant SiH4 / Si2H6 is introduced. By adjusting the flow rate of the dopant gas, the doping concentration of the GaInP layer is achieved to be 3 × 10⁻⁶. 18 ~6×10 18 / cm 3 This ensures that charge carriers can be transported smoothly.

[0090] 5012: An n-type ohmic contact layer is formed in the n-type corrosion stop layer.

[0091] In this embodiment, the n-type ohmic contact layer 221 is still formed using a metal-organic chemical vapor deposition process. By alternately growing AlAs and AlGaAs layers and controlling Si doping, the carrier concentration is controlled to be 5 × 10⁻⁶. 18 ~8×10 18 / cm 3This allows the n-type ohmic contact layer 221 to achieve a low-resistance ohmic contact with the first electrode.

[0092] Optionally, in the n-type ohmic contact layer 221, the temperature of the reaction chamber is controlled at 700–740℃, and SiH4 or Si2H6 is introduced as an n-type dopant. During growth, trimethylaluminum (TMAl) and trimethylgallium (TMGa) are introduced as Al and Ga sources, and arsine (AsH3) is introduced as an As source; when growing the AlAs layer, the TMGa gas source is turned off, and only TMAl and AsH3 are introduced; Al… x Ga （1-x） During the As layer process, the Al component content is controlled by adjusting the flow rate ratio of TMAl to TMGa, ensuring that x is 0.4~0.6. The growth time of each layer is controlled to regulate the thickness of each layer.

[0093] 5013: An electrode bonding layer 224 is formed on the n-type ohmic contact layer 221.

[0094] For example, the electrode bonding layer 224 is an n-type GaInP layer. The thickness of the electrode bonding layer 224 is 10~20 nm, the dopant is SiH4 / Si2H6, and the carrier concentration is 5 × 10⁻⁶. 18 ~1×10 19 / cm 3 .

[0095] The growth process is the same as the aforementioned n-type corrosion stop layer 102, and will not be repeated here.

[0096] 5014: An n-type current extension layer and an n-type confinement layer are stacked on the electrode bonding layer.

[0097] Optionally, the n-type current spreading layer is an n-type AlGaInP layer with a thickness of 2~3 μm, the dopant is SiH4 / Si2H6, and the carrier concentration is 7×10⁻⁶. 17 ~2×10 18 / cm 3 .

[0098] In this embodiment, the n-type current extension layer is also formed using a metal-organic chemical vapor deposition process. The reaction chamber temperature is adjusted to approximately 700°C, and TMAl, TMGa, TMIn, and PH3 are simultaneously introduced, along with a SiH4 or Si2H6 doping source, with the doping concentration controlled at 7 × 10⁻⁶. 17 ~2×10 18 / cm 3 .

[0099] The n-type confinement layer is an AlInP layer with a thickness of 250~350 nm, and the dopant is SiH4 / Si2H6 with a carrier concentration of 1×10⁻⁶. 18 ~2×1018 / cm 3 .

[0100] In this embodiment, the growth process of the n-type confinement layer is similar to that of the n-type current extension layer, except that the Ga source is turned off, which will not be described in detail here.

[0101] S502: Prepare the light-emitting layer.

[0102] In this embodiment, the light-emitting layer is also formed using a metal-organic chemical vapor deposition process. The light-emitting layer can be formed by alternately growing quantum well layers and wide-bandgap quantum barrier layers.

[0103] Both the quantum well layer and the quantum barrier layer are Al x Ga （1-x） InP layers (0 < x < 1), where x in the quantum well layer is less than x in the quantum barrier layer. The thickness of the quantum well layer is 2–6 nm, the thickness of the quantum barrier layer is 5–10 nm, and the number of periodic structures formed by the quantum well layer and the quantum barrier layer is 10–25.

[0104] The growth process of the light-emitting layer can be referred to the above-mentioned n-type current extension layer, and will not be repeated here.

[0105] S503: A p-type semiconductor layer is formed on the light-emitting layer.

[0106] Optionally, S503 includes the following steps: which can be obtained in the following ways: 5031: A p-type confinement layer is formed on the luminescent layer.

[0107] Among them, the p-type confinement layer is a p-type Al with a thickness of 300-800 nm. 0.5 In 0.5 P-layer. The dopant is Cp₂Mg, and the carrier concentration is 3 × 10⁻⁶. 17 ~1×10 18 / cm 3 .

[0108] The p-type confinement layer is also formed using a metal-organic chemical vapor deposition process. The specific process can be found in the section on the n-type confinement layer mentioned earlier. It will not be repeated here.

[0109] 5032: A p-type stress transition layer is formed on the p-type confinement layer.

[0110] For example, the p-type stress transition layer is p-type AlGaInP. p-type AlGaInP is also formed using a metal-organic chemical vapor deposition process. The specific process can be found in the descriptions of other layers above, and will not be repeated here.

[0111] 5032: A p-type current spreading layer is formed on the p-type stress transition layer.

[0112] The p-type current spreading layer is a 5-10 µm p-type GaP layer. The dopant is Cp₂Mg, and the carrier concentration is 4 × 10⁻⁶. 17 ~3×10 18 / cm 3 .

[0113] The p-type current-spreading layer is formed using a metal-organic chemical vapor deposition process. The specific process can be found in the descriptions of other layers above, and will not be repeated here.

[0114] The above steps will yield the epitaxial structure.

[0115] S504: The above epitaxial structure is bonded to a sapphire substrate.

[0116] Optionally, S504 includes the following steps: 5041: Clean the epitaxial structure obtained from S503. This removes impurities from the growth substrate and the surface of the epitaxial structure.

[0117] 5042: In the epitaxial structure, a bonding layer is formed on the surface of the p-type current extension layer away from the light-emitting layer, and the epitaxial structure is bonded to the sapphire substrate through the bonding layer.

[0118] In this embodiment, a bonding layer is deposited on the p-type current spreading layer. The epitaxial structure can then be bonded to the sapphire substrate 1 via the bonding layer.

[0119] 5043: Remove the growth substrate to obtain an epitaxial structure with a sapphire substrate.

[0120] Next, the GaAs growth substrate can be removed through etching, thereby obtaining an epitaxial structure with a sapphire substrate. That is, the epitaxial structure is bonded to the sapphire substrate.

[0121] S505: Prepare the first electrode and the second electrode.

[0122] In this embodiment, the first and second electrodes can be formed by photolithography and electron beam evaporation, so that the first electrode makes ohmic contact with the n-type ohmic contact layer 221. The second electrode 6 makes ohmic contact with the p-type current spreading layer 232.

[0123] S506: Prepare a reflective passivation layer.

[0124] A reflective passivation layer is fabricated on the surface of an epitaxial structure with a first electrode and a second electrode using a plasma-enhanced chemical vapor deposition (PECVD) machine or an electron beam evaporation device. The corresponding pattern is then fabricated in the reflective passivation layer using photolithography and inductively coupled plasma (ICP) dry etching techniques.

[0125] Then, the LED can be packaged so that it can be used in different devices.

[0126] To further illustrate the superior performance of the LED provided in this embodiment, it is compared with other LEDs.

[0127] Among them, the multiple light-emitting diode chips in the first group are through Figure 5 The method shown illustrates the fabrication of a second group of multiple LED chips, which are prepared according to relevant techniques. The difference between the two groups lies in the materials used for the n-type ohmic contact layers. In the first group, the n-type ohmic contact layer is a structure formed by alternating AlAs layers 2211 and AlGaAs layers 2212. In the second group, the n-type ohmic contact layer is an n-type GaAs layer. Photoluminescence tests were performed on both groups of LED chips, and the emitted light wavelength ranged from 620 to 640 nm, with the corresponding brightness (radiant power) measured.

[0128] Figure 6 For a brightness comparison chart of LEDs, please refer to [link / reference]. Figure 6 , Figure 6 The vertical axis represents brightness values, and the horizontal axis represents multiple chip samples. From Figure 6 As can be seen, the overall brightness (radiated power) of the multiple LED chips in the second group remains stable at around 215mW, with very small fluctuations (only slight variations between 210-220mW), which is considered normal brightness under basic conditions. In contrast, the brightness of the multiple LED chips in the first group exhibits a high brightness characteristic with significant fluctuations, showing multiple obvious peaks (exceeding 235mW), far exceeding the brightness of the second group; even during periods of low brightness, it is basically on par with the brightness of the first group. This indicates that the brightness performance of the LEDs in the first group is significantly better than that of the LEDs in the second group. It not only achieves multiple significant brightness increases but also ensures that the minimum brightness is not lower than that of the second group. This demonstrates that the optimized scheme used in manufacturing the LED chips in the second group effectively improves brightness while maintaining the stability of basic performance.

[0129] This marks the first application of an AlAs / AlGaAs superlattice structure in the n-type ohmic contact layer of a red light-emitting diode. The alternating growth of the AlAs / AlGaAs superlattice structure effectively annihilates dislocations generated during the underlying growth process. Furthermore, the superlattice formed by AlAs / AlGaAs acts as a thermal stress buffer, preventing stress concentration. Secondly, the Al composition of the AlGaAs layer is adjustable, balancing voltage and chip brightness. Finally, this superlattice structure reflects light emitted from the light-emitting layer, improving light extraction efficiency.

[0130] In this embodiment, the traditional n-type GaAs ohmic contact layer is replaced with an n-type AlAs / AlGaAs superlattice ohmic contact layer. The alternating stacking design alleviates thermal stress and improves the epitaxial layer growth quality. AlAs and Al... x Ga (1-x) As (x = 0.4~0.6), with 5~15 repetitions. Photoluminescence testing was then performed on the superlattice structure, and the emitted light wavelength ranged from 620nm to 640nm. The superlattice interface disperses thermal stress and inhibits crack initiation. Furthermore, the superlattice growth temperature is compatible with existing confinement layer processes, making the process simple.

[0131] The above description is merely an optional embodiment of this disclosure and is not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. A light-emitting diode, characterized in that, The light-emitting diode includes an epitaxial structure (2), a reflective passivation layer (3), a first electrode (5), and a second electrode (6); The epitaxial structure (2) includes a p-type semiconductor layer (23), a light-emitting layer (21), and an n-type semiconductor layer (22) stacked sequentially. The n-type semiconductor layer (22) includes an n-type ohmic contact layer (221), which includes multiple AlAs layers (2211) and multiple AlGaAs layers (2212), wherein the AlAs layers (2211) and the AlGaAs layers (2212) are stacked alternately. The first electrode (5) and the second electrode (6) are located on the same side of the epitaxial structure (2); The reflective passivation layer (3) covers the surface of the n-type semiconductor layer (22) away from the light-emitting layer (21), the first electrode (5) and the second electrode (6), and has an opening that exposes the first electrode (5) and the second electrode (6).

2. The light-emitting diode according to claim 1, characterized in that, The total thickness of the n-type ohmic contact layer (221) is 0.5 μm to 1.5 μm.

3. The light-emitting diode according to claim 1, characterized in that, The thickness of the AlAs layer (2211) is 400 Å to 650 Å.

4. The light-emitting diode according to claim 1, characterized in that, The thickness of the AlGaAs layer (2212) is 400 Å to 650 Å.

5. The light-emitting diode according to claim 1, characterized in that, The thicknesses of both the AlAs layer (2211) and the AlGaAs layer (2212) satisfy the following formula: ； Where d represents the thickness of the AlAs layer (2211) and the AlGaAs layer (2212), respectively; λ represents the wavelength of the light reflected by the n-type ohmic contact layer (221) in vacuum; and n represents the refractive index of the AlAs layer (2211) and the AlGaAs layer (2212), respectively.

6. The light-emitting diode according to claim 1, characterized in that, The Al component content in the AlGaAs layer (2212) is 0.4~0.6%.

7. The light-emitting diode according to claim 1, characterized in that, The n-type ohmic contact layer (221) is silicon-doped with a carrier concentration of 5 × 10⁻⁶. 18 ~8×10 18 / cm 3 .

8. The light-emitting diode according to claim 1, characterized in that, The number of AlAs layers (2211) is 5 to 15.

9. The light-emitting diode according to any one of claims 1-8, characterized in that, The n-type semiconductor layer (22) further includes an n-type confinement layer (222), which is located between the light-emitting layer (21) and the n-type ohmic contact layer (221).

10. A method for fabricating a light-emitting diode, characterized in that, The preparation method includes: An epitaxial structure is fabricated, the epitaxial structure comprising a p-type semiconductor layer, a light-emitting layer and an n-type semiconductor layer stacked sequentially, the n-type semiconductor layer comprising an n-type ohmic contact layer, the n-type ohmic contact layer comprising multiple AlAs layers and multiple AGaAs layers, the AlAs layers and the AlGaAs layers being stacked alternately. A first electrode and a second electrode are fabricated, wherein the first electrode and the second electrode are located on the same side of the epitaxial structure; A passivation layer is prepared, the reflective passivation layer covering the surface of the n-type semiconductor layer away from the light-emitting layer, the first electrode, and the second electrode, and having an opening that exposes the first electrode and the second electrode.

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