Light emitting diode and method of manufacturing the same

Abstract

The present disclosure provides a light emitting diode and a preparation method thereof, and belongs to the technical field of semiconductors. The preparation method comprises: growing a buffer layer on a substrate; growing an AlN transition layer on the buffer layer; growing an undoped AlGaN layer, a first semiconductor layer, a light emitting layer and a second semiconductor layer on the AlN transition layer, the second semiconductor layer comprising a first AlN sublayer, a P-doped first AlGaN sublayer, a P-doped first GaN sublayer and a P-doped second AlGaN sublayer stacked in sequence on the light emitting layer, and the Al component in the second AlGaN sublayer being lower than the Al component in the first AlGaN sublayer.

Description

Technical Field

[0001] This disclosure relates to the field of semiconductor technology, and in particular to a light-emitting diode and a method for fabricating the same. Background Technology

[0002] Short-wavelength ultraviolet light-emitting diodes based on AlGaN materials have a wide range of applications and are an important research topic in the field of nitride semiconductor research.

[0003] The ultraviolet light-emitting diode includes a substrate, a buffer layer, an undoped AlGaN layer, a first semiconductor layer, an active layer, and a second semiconductor layer stacked on the substrate. The substrate is a sapphire substrate.

[0004] The second semiconductor layer is usually made of GaN material. However, GaN has a strong absorption effect on short-wavelength ultraviolet light, which causes a large part of the ultraviolet light emitted by the quantum well to be absorbed by the P-type GaN layer and cannot be effectively radiated, resulting in low luminous efficiency. Summary of the Invention

[0005] This disclosure provides a light-emitting diode (LED) and its fabrication method, which can improve the luminous efficiency of the LED. The technical solution is as follows: On the one hand, a method for fabricating a light-emitting diode is provided, the method comprising: A buffer layer is grown on the substrate; An AlN transition layer is grown on the buffer layer; An undoped AlGaN layer, a first semiconductor layer, a light-emitting layer, and a second semiconductor layer are grown on the AlN transition layer. The second semiconductor layer includes a first AlN sublayer, a P-type doped first AlGaN sublayer, a P-type doped first GaN sublayer, and a P-type doped second AlGaN sublayer, which are sequentially stacked on the light-emitting layer. The Al content in the second AlGaN sublayer is higher than that in the first AlGaN sublayer.

[0006] Optionally, the first AlN sublayer is an undoped AlN sublayer, or the first AlN sublayer is a Mg-doped AlN sublayer with a Mg doping concentration of 1*10⁻⁶. 18 -2*10 19 cm -3 ; The first AlGaN sublayer is a Mg-doped AlGaN sublayer with a Mg doping concentration of 1*10⁻⁶. 19 -2*10 20 cm -3 ; The first GaN sublayer is a Mg-doped GaN sublayer with a Mg doping concentration of 1*10⁻⁶. 19 -5*1021 cm -3 ; The second AlGaN sublayer is a Mg-doped AlGaN sublayer with a Mg doping concentration of 1*10⁻⁶. 19 -9*10 20 cm -3 .

[0007] Optionally, the first AlGaN sublayer is Al x Ga 1-x N layers, 0 <x<0.2; The second AlGaN sublayer is Al y Ga 1-y N layers, x <y,0.2<y<1。

[0008] Optionally, the Al composition of the first AlGaN sublayer and the second AlGaN sublayer changes with growth time during the growth process.

[0009] Optionally, the Al component is first decreased in gradient and then increased in gradient.

[0010] Optionally, the thickness of the first AlN sublayer is in the range of 2-200 nm, the thickness of the first AlGaN sublayer is in the range of 2-200 nm, the thickness of the first GaN sublayer is in the range of 2-200 nm, and the thickness of the second AlGaN sublayer is in the range of 2-200 nm.

[0011] Optionally, the first AlN sublayer, the first AlGaN sublayer, the first GaN sublayer, and the second AlGaN sublayer are all In-doped layers.

[0012] Optionally, the carrier gas used during the growth of the first GaN sublayer is pure nitrogen.

[0013] Optionally, the second semiconductor layer further includes a superlattice structure sequentially stacked on the second AlGaN sublayer, the superlattice structure including a second AlN sublayer, a P-type doped third AlGaN sublayer, a P-type doped second GaN sublayer, and a P-type doped fourth AlGaN sublayer.

[0014] On the other hand, a light-emitting diode is provided, which is prepared using the method described in the previous one.

[0015] In the light-emitting diode provided in this embodiment, the second semiconductor layer is implemented using a composite layer. The first AlN sublayer is grown close to the light-emitting layer, which reduces electron overflow and enhances electron confinement. A p-type doped first AlGaN sublayer, a p-type doped first GaN sublayer, and a p-type doped second AlGaN sublayer are grown in a stacked manner. The second AlGaN sublayer has a higher Al content, while the first AlGaN sublayer has a lower Al content. The high-Al-content AlGaN has a greater polarization intensity than the low-Al-content AlGaN, resulting in a net negative polarization charge at their interface. This net non-equilibrium negative charge induces the p-type dopant elements to ionize and release holes to neutralize their electric field, further confining electron overflow. Additionally, the Al in the AlGaN sublayer reduces light absorption by the GaN sublayer. Through this implementation, both quantum recombination in the light-emitting layer and light absorption by the semiconductor layer are increased, thereby improving luminous efficiency. 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 flowchart of a method for fabricating a light-emitting diode provided in an embodiment of this disclosure; Figure 2 This is a flowchart of another method for fabricating a light-emitting diode provided in this embodiment; Figures 3 to 7 This is a schematic diagram of a change curve provided in an embodiment of this disclosure; Figure 8 This is a schematic diagram of the structure of a light-emitting diode provided in an embodiment of this disclosure. Detailed Implementation

[0018] 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.

[0019] Figure 1 This is a flowchart of a method for fabricating a light-emitting diode provided in an embodiment of this disclosure, as shown below. Figure 1 As shown, the preparation method includes: Step 101: Grow a buffer layer on the substrate.

[0020] For example, the substrate is a sapphire substrate and the buffer layer is an AlN layer.

[0021] Step 102: Grow an AlN transition layer on the buffer layer.

[0022] The AlN transition layer includes multiple transition sublayers, the growth temperature of which changes during the growth process, and at least one of the transition sublayers pauses the introduction of the Al source and pre-introduces the N source at a first time before growth.

[0023] Step 103: Grow an undoped AlGaN layer, a first semiconductor layer, a light-emitting layer, and a second semiconductor layer on the AlN transition layer.

[0024] The first semiconductor layer is an N-type semiconductor layer, the light-emitting layer is an active layer, and the second semiconductor layer is a P-type semiconductor layer.

[0025] For example, the first semiconductor layer is an N-type contact layer, such as a Si-doped AlGaN layer. The active layer includes multiple alternating quantum well layers and quantum barrier layers, wherein the quantum well layers are Al... x Ga 1-x N layers, 0 < x < 1, quantum barrier layer is Al y Ga 1-y N-layer, 0 < y < 1. The second semiconductor layer may be a composite P-type layer, which includes a first AlN sublayer, a P-type doped first AlGaN sublayer, a P-type doped first GaN sublayer, and a P-type doped second AlGaN sublayer, wherein the Al content in the second AlGaN sublayer is higher than the Al content in the first AlGaN sublayer.

[0026] In the light-emitting diode provided in this embodiment, the second semiconductor layer is implemented using a composite layer. The first AlN sublayer is grown close to the light-emitting layer, which reduces electron overflow and enhances electron confinement. A p-type doped first AlGaN sublayer, a p-type doped first GaN sublayer, and a p-type doped second AlGaN sublayer are grown in a stacked manner. The second AlGaN sublayer has a higher Al content, while the first AlGaN sublayer has a lower Al content. The high-Al-content AlGaN has a greater polarization intensity than the low-Al-content AlGaN, resulting in a net negative polarization charge at their interface. This net non-equilibrium negative charge induces the p-type dopant elements to ionize and release holes to neutralize their electric field, further confining electron overflow. Additionally, the Al in the AlGaN sublayer reduces light absorption by the GaN sublayer. Through this implementation, both quantum recombination in the light-emitting layer and light absorption by the semiconductor layer are increased, thereby improving luminous efficiency.

[0027] Figure 2 This is a flowchart of another method for fabricating a light-emitting diode provided in this disclosure, as shown in the embodiment. Figure 2 As shown, the preparation method includes: Step 201: Provide a substrate.

[0028] The substrate can be a sapphire substrate or other substrates.

[0029] Optionally, the method may further include: stabilizing in a pure hydrogen atmosphere at 1030°C for 5 minutes to clean the substrate surface, wherein the heating and stabilization times can be set as needed.

[0030] In this embodiment, the preparation method is implemented using a Veeco K465i, C4, or RB MOCVD (Metal Organic Chemical Vapor Deposition) apparatus. High-purity H2 (hydrogen), high-purity N2 (nitrogen), or a mixture of high-purity H2 and high-purity N2 are used as the carrier gas; high-purity NH3 is used as the N source; trimethylgallium (TMGa) and triethylgallium (TEGa) are used as gallium sources; silane (SiH4) is used as the N-type dopant; trimethylaluminum (TMAl) is used as the aluminum source; and magnesium pyrocene (CP2Mg) is used as the P-type dopant.

[0031] Step 202: Grow a buffer layer on the substrate.

[0032] The buffer layer is an AlN layer.

[0033] In this embodiment, the substrate can be placed in the MOCVD reaction chamber, and TMAl and NH3 can be introduced into the reaction chamber to prepare an AlN thin film by chemical vapor deposition.

[0034] For example, the temperature inside the reaction chamber is controlled at 1010°C to deposit an AlN film with a thickness of 30 nm on a sapphire substrate.

[0035] Alternatively, the buffer layer can be prepared in other ways, such as in a PVD (Physical Vapor Deposition) reaction chamber.

[0036] Step 203: Grow an AlN transition layer on the buffer layer.

[0037] After depositing the buffer layer, the temperature is raised to 1200~1300℃ (e.g. 1235℃), and NH3 and TMAl are introduced under a pressure of 40~110mbar (e.g. 100mbar) to grow an AlN transition layer with a thickness of 1~2μm (e.g. 1.5μm).

[0038] Step 204: Grow a high-temperature AlN layer on the AlN transition layer.

[0039] For example, after the AlN transition layer is grown, the pressure and the flow rates of NH3 and TMAl remain unchanged, and the temperature is increased to 1350~1450℃ (e.g. 1355℃) to deposit a 1~2μm (e.g. 1.5μm) thick undoped high-temperature AlN layer.

[0040] Step 205: Grow an undoped AlGaN layer on the high-temperature AlN layer.

[0041] Cracks can occur when AlGaN layers are fabricated using conventional growth methods. Therefore, in this embodiment, an undoped AlGaN layer is prepared using a pulsed NH3 injection method under low pressure and high temperature conditions. Specifically, a MO source (TMAl and TMGa sources) is continuously introduced, while NH3 is intermittently injected into the reaction chamber in a pulsed manner. This method yields an AlGaN layer with superior crystal quality.

[0042] NH3 is intermittently introduced into the reaction chamber in a manner that is turned on for 30 seconds and off for 10 seconds.

[0043] For example, the temperature inside the reaction chamber is controlled to be reduced to 1300~1350°C (e.g. 1330°C), and an undoped AlGaN layer with a thickness of 0.5~1μm (e.g. 1μm) is grown on the high-temperature AlN layer at a growth pressure of 65~75mbar (e.g. 70mbar).

[0044] Step 206: Grow an N-type contact layer on the undoped AlGaN layer.

[0045] The N-type contact layer is a Si-doped AlGaN layer with a Si doping concentration of 5*10⁻⁶. 18 ~1*10 20 cm -3 .

[0046] For example, the temperature inside the reaction chamber is controlled at 1200~1300℃ and the pressure is 50~100mbar, and an N-type contact layer with a thickness of 1~2μm (e.g. 2μm) is grown on the undoped AlGaN layer at a growth pressure of 65~75mbar (e.g. 70mbar).

[0047] Step 207: Grow an active layer on the N-type contact layer.

[0048] The active layer comprises multiple periodically alternating quantum well layers and quantum barrier layers. The quantum well layers are made of Al. x Ga 1- x N layers, 0 < x < 1, quantum barrier layer is Al y Ga 1-y N layers, 0 < y < 1.

[0049] Optionally, the active layer includes 4 to 12 alternating quantum well layers and quantum barrier layers, such as 4-period Al... x Ga 1-x N / Al y Ga 1-y N layers.

[0050] Optionally, the thickness of the quantum well layer is 2-4 nm (e.g., 2 nm), and the thickness of the quantum barrier layer is 8-12 nm (e.g., 12 nm).

[0051] For example, the growth temperature of the quantum well layer is 1200°C, the growth temperature of the quantum barrier layer is 1215°C, and the growth pressure is 90~110 mbar (e.g., 100 mbar).

[0052] Step 208: Grow a P-type electron blocking layer on the active layer.

[0053] For example, the p-type electron blocking layer is Mg-doped Al. z Ga 1-z N-layer, 0.1 < z < 0.5, Mg doping concentration is 1*10 18 ~1*10 20 cm -3 .

[0054] For example, the growth temperature of the P-type electron blocking layer is 1235°C, the thickness is 50 nm, and the growth pressure is 90~110 mbar (e.g., 100 mbar).

[0055] Step 208 is an optional step, meaning that the light-emitting diode may not include a P-type electron blocking layer.

[0056] Step 209: Grow a composite P-type layer on the P-type electron blocking layer.

[0057] In one possible implementation of this disclosure, the composite P-type layer includes a first AlN sublayer, a P-type doped first AlGaN sublayer, a P-type doped first GaN sublayer, and a P-type doped second AlGaN sublayer stacked sequentially on a P-type electron blocking layer, wherein the Al content in the second AlGaN sublayer is higher than the Al content in the first AlGaN sublayer.

[0058] For example, the first AlN sublayer is an undoped AlN sublayer, or the first AlN sublayer is a Mg-doped AlN sublayer with a Mg doping concentration of 1*10⁻⁶. 18 -2*10 19 cm -3 ; The first AlGaN sublayer is a Mg-doped AlGaN sublayer with a Mg doping concentration of 1*10⁻⁶.19 -2*10 20 cm -3 ; The first GaN sublayer is a Mg-doped GaN sublayer with a Mg doping concentration of 1*10⁻⁶. 19 -5*10 21 cm -3 ; The second AlGaN sublayer is a Mg-doped AlGaN sublayer with a Mg doping concentration of 1*10⁻⁶. 19 -9*10 20 cm -3 .

[0059] In the implementation of undoped AlN sublayers, the AlN layer is undoped, the first AlGaN sublayer is a low-doped Mg layer, and the first GaN sublayer and the second AlGaN sublayer are high-doped Mg layers. This can enhance current diffusion and improve the electrical performance of the device.

[0060] For example, the first AlGaN sublayer is Al x Ga 1-x N layers, 0 <x<0.2; The second AlGaN sublayer is Al y Ga 1-y N layers, x <y,0.2<y<1。

[0061] For example, the first AlGaN sublayer is Al 0.14 Ga 0.86 N, the second AlGaN sublayer is Al 0.4 Ga 0.6 N. The second AlGaN sublayer has a higher Al content, while the first AlGaN sublayer has a lower Al content. The high-Al-content AlGaN has a greater polarization intensity than the low-Al-content AlGaN. A net negative polarization charge will be generated at the interface between the two. These net non-equilibrium negative charges will induce the P-type doped elements to be ionized into holes to neutralize their electric field, further limiting electron overflow.

[0062] In the embodiments disclosed herein, the growth temperature of each sublayer in the composite P-type layer may remain constant or vary, and the growth pressure may remain constant or vary.

[0063] In one possible implementation, step 209 may include: A first AlN sublayer with a thickness of 2-200 nm is grown in a pure hydrogen atmosphere with a temperature range of 1250~1300℃ (e.g. 1255℃) and a pressure range of 40~60mbar (e.g. 50mbar). A first AlGaN sublayer with a thickness ranging from 2 to 200 nm is grown in a nitrogen-hydrogen mixed atmosphere with a temperature range of 1200–1250 °C (e.g., 1235 °C) and a pressure range of 40–60 mbar (e.g., 50 mbar). For example, a p-type AlGaN sublayer is grown in this atmosphere. 0.14 Ga 0.86 N-layer, Mg doping concentration is 7*10 19 cm -3 ; A first P-type doped GaN sublayer with a thickness ranging from 2 to 200 nm was grown under a pure nitrogen atmosphere at a temperature range of 1200–1250 °C (e.g., 1230 °C) and a pressure range of 180–220 mbar (e.g., 200 mbar), with a Mg doping concentration of 5 × 10⁻⁶. 20 cm -3 ; Under a nitrogen-hydrogen mixed atmosphere with a temperature range of 1200–1240 °C (e.g., 1230 °C) and a pressure range of 40–60 mbar (e.g., 50 mbar), a second P-type doped AlGaN sublayer with a thickness range of 2–200 nm is grown, for example, P-type Al 0.4 Ga 0.6 The N and Mg doping concentrations are 5*10 20 cm -3 .

[0064] The first AlN sublayer grows close to the electron blocking layer, which helps reduce electron overflow and enhances electron confinement. AlN has a wide bandgap of 6.2 eV, and the effective mass of holes is greater than that of electrons. However, the mobility of holes is much lower than that of electrons. If the AlN sublayer is too thick, it will restrict the effective flow of holes to the light-emitting region, reduce the effective radiative recombination of holes and electrons, and thus reduce the luminous efficiency. A thinner first AlN sublayer can avoid the problems caused by an excessively thick AlN sublayer. The GaN sublayer is slightly thicker than the AlGaN sublayer. The high Mg doping of the GaN sublayer can provide a large number of holes and also play a role in current spreading, which can reduce the on-state voltage Vf and improve the device's anti-static capability. The two AlGaN sublayers can also effectively play a role in current spreading.

[0065] For example, the thickness of the first AlN sublayer ranges from 2 to 20 nm, the thickness of the first AlGaN sublayer ranges from 5 to 100 nm, the thickness of the first GaN sublayer ranges from 100 to 200 nm, and the thickness of the second AlGaN sublayer ranges from 5 to 100 nm.

[0066] For example, the thickness of the first AlN sublayer ranges from 5 to 15 nm, the thickness of the first AlGaN sublayer ranges from 5 to 50 nm, the thickness of the first GaN sublayer ranges from 100 to 150 nm, and the thickness of the second AlGaN sublayer ranges from 5 to 50 nm.

[0067] In one example, the thickness of the first AlGaN sublayer and the thickness of the second AlGaN sublayer can be the same. For example, the thickness of the first AlN sublayer is 10 nm, the thickness of the first AlGaN sublayer is 50 nm, the thickness of the first GaN sublayer is 120 nm, and the thickness of the second AlGaN sublayer is 50 nm.

[0068] In other examples, the thicknesses of the first AlGaN sublayer and the second AlGaN sublayer may also be different.

[0069] In this embodiment, the first AlN sublayer, the first AlGaN sublayer, the first GaN sublayer, and the second AlGaN sublayer are all In-doped layers. The In doping concentration is relatively small; the incorporation of a small amount of In can further activate Mg and increase the hole concentration.

[0070] In this embodiment, the carrier gas used during the growth of the first GaN sublayer is pure nitrogen. Using pure nitrogen to grow the GaN sublayer can open the Mg-H bonds passivated by the carrier gas H2, activate Mg, improve hole injection efficiency, and also improve quantum efficiency.

[0071] In one possible implementation of this disclosure, the Al composition remains unchanged during the growth of the first AlGaN sublayer and the second AlGaN sublayer.

[0072] In another possible implementation of this disclosure, the Al composition of the first AlGaN sublayer and the second AlGaN sublayer changes with growth time during the growth process.

[0073] In one example, the Al component first decreases in gradient and then increases in gradient.

[0074] In other examples, the Al component can increase linearly, decrease linearly, increase linearly then decrease linearly, increase with a gradient, or decrease with a gradient, etc. Figures 3 to 7 These are just a few examples, which will not be elaborated upon here.

[0075] The first AlGaN sublayer is followed by another AlGaN sublayer. One approach is to reduce stress accumulation caused by the lattice constant mismatch between AlN and AlGaN through variations in the Al composition, thereby reducing the significant polarization effect caused by stress accumulation. Specifically, a gradient decrease followed by a gradient increase in Al composition, or a linear decrease in Al composition, can effectively reduce stress accumulation. Al atoms have high migration energies and are not easily able to achieve lateral expansion. Al atoms tend to occupy their initial adsorption sites and are less likely to migrate to lower-energy lattice sites, making them prone to parasitic reactions. Variations in the Al composition can alleviate these parasitic reactions, reduce the defect density of the material, improve crystal quality, and obtain epitaxial wafers with smooth surfaces.

[0076] In another possible implementation of this disclosure, the composite P-type layer includes, in addition to a first AlN sublayer, a P-type doped first AlGaN sublayer, a P-type doped first GaN sublayer, and a P-type doped second AlGaN sublayer, a superlattice structure sequentially stacked on the second AlGaN sublayer, the superlattice structure including a second AlN sublayer, a P-type doped third AlGaN sublayer, a P-type doped second GaN sublayer, and a P-type doped fourth AlGaN sublayer.

[0077] The first AlGaN sublayer is the same as the second AlN sublayer, the first AlGaN sublayer is the same as the third AlGaN sublayer, the first GaN sublayer is the same as the second GaN sublayer, and the second AlGaN sublayer is the same as the fourth AlGaN sublayer.

[0078] The composition and fabrication methods of the above sublayers can be referenced from the implementation methods without superlattices.

[0079] In this implementation, unlike the implementation without a superlattice, the thickness of each sublayer is smaller. For example, the thicknesses of the four sublayers in one cycle are 5nm, 12nm, 30nm, and 15nm, respectively.

[0080] The superlattice structure can have 2-5 periods, for example, 2 periods.

[0081] Step 210: Grow a P-type GaN contact layer on the P-type GaN layer.

[0082] For example, the growth temperature of the P-type GaN contact layer is 1120°C, the thickness is 50 nm, and the growth pressure is 180~220 mbar (e.g., 200 mbar).

[0083] Step 210 is an optional step, meaning that the light-emitting diode may not include a P-type GaN contact layer.

[0084] After the above steps are completed, the temperature of the reaction chamber is lowered to 650-850℃ and annealed in a nitrogen atmosphere for 5-15 minutes, and then gradually lowered to room temperature to end the epitaxial growth of the light-emitting diode.

[0085] The fabrication of light-emitting diodes also includes structures such as electrodes and passivation layers, and this disclosure does not limit the methods for fabricating these structures.

[0086] In the light-emitting diode provided in this embodiment, the second semiconductor layer is implemented using a composite layer. The first AlN sublayer is grown close to the light-emitting layer, which reduces electron overflow and enhances electron confinement. A p-type doped first AlGaN sublayer, a p-type doped first GaN sublayer, and a p-type doped second AlGaN sublayer are grown in a stacked manner. The second AlGaN sublayer has a higher Al content, while the first AlGaN sublayer has a lower Al content. The high-Al-content AlGaN has a greater polarization intensity than the low-Al-content AlGaN, resulting in a net negative polarization charge at their interface. This net non-equilibrium negative charge induces the p-type dopant elements to ionize and release holes to neutralize their electric field, further confining electron overflow. Additionally, the Al in the AlGaN sublayer reduces light absorption by the GaN sublayer. Through this implementation, both quantum recombination in the light-emitting layer and light absorption by the semiconductor layer are increased, thereby improving luminous efficiency. The first AlN sublayer being undoped of Mg, the first AlGaN sublayer being lightly doped of Mg, and the first GaN sublayer and the second AlGaN sublayer being highly doped of Mg can enhance current diffusion and improve the electrical performance of the device. Furthermore, the first GaN sublayer is grown with pure nitrogen gas, which can open the Mg-H bonds that are passivated by the carrier gas H2, activate Mg, improve hole injection efficiency, and also improve the quantum efficiency of the light-emitting diode.

[0087] Figure 8 This is a schematic diagram of the structure of a light-emitting diode provided in an embodiment of the present disclosure. The light-emitting diode adopts the following... Figure 1 or Figure 2 It was made using the method shown. Figure 8 As shown, the light-emitting diode includes a substrate 1, and a buffer layer 2, an AlN transition layer 3, an undoped AlGaN layer 4, a first semiconductor layer 5, a light-emitting layer 6, and a second semiconductor layer 7, which are sequentially stacked on the substrate 1.

[0088] In one possible implementation of this disclosure, the composite P-type layer includes a first AlN sublayer, a P-type doped first AlGaN sublayer, a P-type doped first GaN sublayer, and a P-type doped second AlGaN sublayer stacked sequentially on a P-type electron blocking layer, wherein the Al content in the second AlGaN sublayer is higher than the Al content in the first AlGaN sublayer.

[0089] For example, the first AlN sublayer is an undoped AlN sublayer, or the first AlN sublayer is a Mg-doped AlN sublayer with a Mg doping concentration of 1*10⁻⁶. 18 -2*10 19 cm -3 ; The first AlGaN sublayer is a Mg-doped AlGaN sublayer with a Mg doping concentration of 1*10⁻⁶. 19 -2*10 20 cm -3 ; The first GaN sublayer is a Mg-doped GaN sublayer with a Mg doping concentration of 1*10⁻⁶. 19 -5*10 21 cm -3 ; The second AlGaN sublayer is a Mg-doped AlGaN sublayer with a Mg doping concentration of 1*10⁻⁶. 19 -9*10 20 cm -3 .

[0090] In the implementation of undoped AlN sublayers, the AlN layer is undoped, the first AlGaN sublayer is a low-doped Mg layer, and the first GaN sublayer and the second AlGaN sublayer are high-doped Mg layers, which can enhance current diffusion and improve the electrical performance of the device.

[0091] For example, the first AlGaN sublayer is Al x Ga 1-x N layers, 0 <x<0.2; The second AlGaN sublayer is Al y Ga 1-y N layers, x <y,0.2<y<1。

[0092] For example, the first AlGaN sublayer is Al 0.14 Ga 0.86 N, the second AlGaN sublayer is Al 0.4 Ga 0.6 N. The second AlGaN sublayer has a higher Al content, while the first AlGaN sublayer has a lower Al content. The high-Al-content AlGaN has a greater polarization intensity than the low-Al-content AlGaN. A net negative polarization charge will be generated at the interface between the two. These net non-equilibrium negative charges will induce the P-type doped elements to be ionized into holes to neutralize their electric field, further limiting electron overflow.

[0093] In the embodiments disclosed herein, the growth temperature of each sublayer in the composite P-type layer may remain constant or vary, and the growth pressure may remain constant or vary.

[0094] In one possible implementation, the thickness of the first AlN sublayer ranges from 2 to 200 nm; the thickness of the first AlGaN sublayer ranges from 2 to 200 nm, for example, P-type Al... 0.14 Ga 0.86 N-layer, Mg doping concentration is 7*10 19 cm -3 The thickness of the first GaN sublayer ranges from 2 to 200 nm, and the Mg doping concentration is 5*10⁻⁶. 20 cm -3 The thickness of the second AlGaN sublayer ranges from 2 to 200 nm, for example, p-type Al... 0.4 Ga 0.6 The N and Mg doping concentrations are 5*10 20 cm -3 .

[0095] For example, the thickness of the first AlN sublayer ranges from 2 to 20 nm, the thickness of the first AlGaN sublayer ranges from 5 to 100 nm, the thickness of the first GaN sublayer ranges from 100 to 200 nm, and the thickness of the second AlGaN sublayer ranges from 5 to 100 nm.

[0096] For example, the thickness of the first AlN sublayer ranges from 5 to 15 nm, the thickness of the first AlGaN sublayer ranges from 5 to 50 nm, the thickness of the first GaN sublayer ranges from 100 to 150 nm, and the thickness of the second AlGaN sublayer ranges from 5 to 50 nm.

[0097] In one example, the thickness of the first AlGaN sublayer and the thickness of the second AlGaN sublayer can be the same. For example, the thickness of the first AlN sublayer is 10 nm, the thickness of the first AlGaN sublayer is 50 nm, the thickness of the first GaN sublayer is 120 nm, and the thickness of the second AlGaN sublayer is 50 nm.

[0098] In other examples, the thicknesses of the first AlGaN sublayer and the second AlGaN sublayer may also be different.

[0099] In this embodiment, the first AlN sublayer, the first AlGaN sublayer, the first GaN sublayer, and the second AlGaN sublayer are all In-doped layers. The In doping concentration is relatively small; the incorporation of a small amount of In can further activate Mg and increase the hole concentration.

[0100] In this embodiment, the carrier gas used during the growth of the first GaN sublayer is pure nitrogen. Using pure nitrogen to grow the GaN sublayer can open the Mg-H bonds passivated by the carrier gas H2, activate Mg, improve hole injection efficiency, and also improve quantum efficiency.

[0101] In one possible implementation of this disclosure, the Al composition remains unchanged during the growth of the first AlGaN sublayer and the second AlGaN sublayer.

[0102] In another possible implementation of this disclosure, the Al composition of the first AlGaN sublayer and the second AlGaN sublayer changes with growth time during the growth process.

[0103] In one example, the Al component first decreases in gradient and then increases in gradient.

[0104] In other examples, the Al component can increase linearly, decrease linearly, increase linearly then decrease linearly, increase with a gradient, or decrease with a gradient, etc. Figures 3 to 7 These are just a few examples, which will not be elaborated upon here.

[0105] In another possible implementation of this disclosure, the composite P-type layer includes, in addition to a first AlN sublayer, a P-type doped first AlGaN sublayer, a P-type doped first GaN sublayer, and a P-type doped second AlGaN sublayer, a superlattice structure sequentially stacked on the second AlGaN sublayer, the superlattice structure including a second AlN sublayer, a P-type doped third AlGaN sublayer, a P-type doped second GaN sublayer, and a P-type doped fourth AlGaN sublayer.

[0106] The first AlGaN sublayer is the same as the second AlN sublayer, the first AlGaN sublayer is the same as the third AlGaN sublayer, the first GaN sublayer is the same as the second GaN sublayer, and the second AlGaN sublayer is the same as the fourth AlGaN sublayer.

[0107] The composition and fabrication methods of the above sublayers can be referenced from the implementation methods without superlattices.

[0108] In this implementation, unlike the implementation without a superlattice, the thickness of each sublayer is smaller. For example, the thicknesses of the four sublayers in one cycle are 5nm, 12nm, 30nm, and 15nm, respectively.

[0109] The superlattice structure can have 2-5 periods, for example, 2 periods.

[0110] 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 method for fabricating a light-emitting diode, characterized in that, The preparation method includes: A buffer layer is grown on the substrate; An AlN transition layer is grown on the buffer layer; An undoped AlGaN layer, a first semiconductor layer, a light-emitting layer, and a second semiconductor layer are grown on the AlN transition layer. The second semiconductor layer includes a first AlN sublayer, a P-type doped first AlGaN sublayer, a P-type doped first GaN sublayer, and a P-type doped second AlGaN sublayer, which are sequentially stacked on the light-emitting layer. The Al content in the second AlGaN sublayer is higher than that in the first AlGaN sublayer.

2. The preparation method according to claim 1, characterized in that, The first AlN sublayer is an undoped AlN sublayer, or the first AlN sublayer is a Mg-doped AlN sublayer with a Mg doping concentration of 1*10⁻⁶. 18 -2*10 19 cm -3 ; The first AlGaN sublayer is a Mg-doped AlGaN sublayer with a Mg doping concentration of 1*10⁻⁶. 19 -2*10 20 cm -3 ; The first GaN sublayer is a Mg-doped GaN sublayer with a Mg doping concentration of 1*10⁻⁶. 19 -5*10 21 cm -3 ; The second AlGaN sublayer is a Mg-doped AlGaN sublayer with a Mg doping concentration of 1*10⁻⁶. 19 -9*10 20 cm -3 .

3. The preparation method according to claim 1 or 2, characterized in that, The first AlGaN sublayer is Al x Ga 1-x N layers, 0 <x<0.2; The second AlGaN sublayer is Al y Ga 1-y N layers, x <y,0.2<y<1。 4. The preparation method according to claim 1 or 2, characterized in that, During the growth of the first AlGaN sublayer and the second AlGaN sublayer, the Al composition changes with the growth time.

5. The preparation method according to claim 4, characterized in that, The Al component first decreases in gradient and then increases in gradient.

6. The preparation method according to claim 1 or 2, characterized in that, The thickness of the first AlN sublayer ranges from 2 to 200 nm, the thickness of the first AlGaN sublayer ranges from 2 to 200 nm, the thickness of the first GaN sublayer ranges from 2 to 200 nm, and the thickness of the second AlGaN sublayer ranges from 2 to 200 nm.

7. The preparation method according to claim 1 or 2, characterized in that, The first AlN sublayer, the first AlGaN sublayer, the first GaN sublayer, and the second AlGaN sublayer are all In-doped layers.

8. The preparation method according to claim 1 or 2, characterized in that, The carrier gas used during the growth of the first GaN sublayer is pure nitrogen.

9. The preparation method according to claim 1 or 2, characterized in that, The second semiconductor layer further includes a superlattice structure sequentially stacked on the second AlGaN sublayer. The superlattice structure includes a second AlN sublayer, a P-type doped third AlGaN sublayer, a P-type doped second GaN sublayer, and a P-type doped fourth AlGaN sublayer.

10. A light-emitting diode, characterized in that, The light-emitting diode is prepared using the method described in any one of claims 1 to 9.

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