Epitaxial structure for improving light emitting efficiency and preparation method thereof

Abstract

The application discloses an epitaxial structure for improving light-emitting efficiency and a preparation method thereof. The epitaxial structure comprises, from bottom to top, a substrate, an N-type semiconductor layer, a first current expansion layer, an active layer, a second current expansion layer and a P-type semiconductor layer which are sequentially stacked. The first current expansion layer is an InGaN-GaN-AlGaN composite layer, and two-dimensional electron gas is generated at a heterojunction interface of InGaN / GaN and GaN / AlGaN. The second current expansion layer is an InGaN-GaN-AlGaN composite layer with gradually changed In and Al components. By arranging the double-layer InGaN-GaN-AlGaN current expansion layer structure, electron leakage is reduced, hole injection is increased, carrier transport is balanced, and the light-emitting efficiency of the device is improved.

Description

Technical Field

[0001] This invention belongs to the field of light-emitting diode technology, and specifically relates to an epitaxial structure for improving luminous efficiency and its preparation method. Background Technology

[0002] III-V GaN-based materials, with their excellent physical and chemical properties such as wide bandgap, high breakdown electric field, and high electron saturation velocity, have attracted widespread attention and application in the electrical and optical fields, as exemplified by the mainstream Micro-LED and Mini-LED technologies currently on the market. However, in practical LED structure design, due to significant differences in the physical properties of electrons and holes (such as differences in mobility caused by different relative masses), carrier transport imbalance is difficult to avoid. Specifically, electrons with smaller relative masses have higher mobility and are prone to overflow and leakage; while holes with larger relative masses have lower mobility, often resulting in insufficient injection efficiency. This carrier injection imbalance severely restricts the improvement of device luminous efficiency. Therefore, suppressing electron overflow and improving hole injection has become a key path to optimize LED luminous efficiency.

[0003] It is worth noting that while traditional electron blocking layers prevent electron leakage, they also hinder hole injection, resulting in low luminous efficiency. Therefore, developing novel carrier control structures that can enhance hole injection while maintaining electron confinement has become a key technological path to overcome the bottleneck of LED efficiency. Summary of the Invention

[0004] The purpose of this invention is to provide an epitaxial structure and its fabrication method for improving luminescence efficiency. By setting a double-layer InGaN-GaN-AlGaN current extension layer structure, electron leakage is reduced, hole injection is increased, carrier transport is balanced, and the luminescence efficiency of the device is improved.

[0005] To achieve the above objectives, the present invention provides the following technical solution: An epitaxial structure for improving luminous efficiency includes a substrate, an N-type semiconductor layer, a first current spreading layer, an active layer, a second current spreading layer, and a P-type semiconductor layer stacked sequentially from bottom to top. The first current spreading layer is an InGaN-GaN-AlGaN composite layer, wherein the InGaN / GaN and GaN / AlGaN generate a two-dimensional electron gas at the heterojunction; the second current spreading layer is an InGaN-GaN-AlGaN composite layer with graded In and Al compositions.

[0006] Optionally, the InGaN of the second current spreading layer is an In type with an In composition that gradually changes towards the P-type semiconductor layer. x Ga 1-xN layer, wherein x gradually increases from 0 to x₁, then gradually decreases back to 0, with 0<x₁<0.1; the GaN of the second current spreading layer is a GaN layer; the AlGaN of the second current spreading layer is Al with a gradient Al component along the growth direction y Ga 1-y N layer, wherein y gradually increases from 0 to y₁, then gradually decreases back to 0, with 0<y₁<1.

[0007] Optionally, said In x Ga 1-x N layer is intermittently doped with Mg.

[0008] Optionally, the In in the second current spreading layer x Ga 1-x N layer, GaN layer and Al y Ga 1-y The thicknesses of the N layer are 10-30 nm, 1-10 nm and 10-30 nm respectively, and all include endpoint values.

[0009] Optionally, the active layer comprises quantum barrier layers, quantum well layers and GaN protective layers which are alternately stacked and grown periodically, the quantum well layer is an InGaN layer, the quantum barrier layer is a GaN layer, and the In x Ga 1-x The In component of the N layer is smaller than the In component of the quantum well layer.

[0010] Optionally, the InGaN of the first current spreading layer is In z Ga 1-z N layer, wherein z≥0.3, is N-type doped with a doping concentration of 1-5×10 18 cm -3 , including endpoint values; the GaN of the first current spreading layer is a GaN layer; the AlGaN of the first current spreading layer is Al w Ga 1-w N layer, wherein w≥0.3.

[0011] Optionally, the In in the first current spreading layer z Ga 1-z N layer, GaN layer and Al w Ga 1-w The thicknesses of the N layer are 10-30 nm, 5-10 nm and 10-30 nm respectively, and all include endpoint values.

[0012] Optionally, both the InGaN-GaN-AlGaN composite layer structures of the first current spreading layer and the second current spreading layer have 2-5 periods, including endpoint values.

[0013] Optionally, a buffer layer is further provided between the substrate and the N-type semiconductor, and the buffer layer is an undoped GaN layer; an SSL layer is further provided between the first current spreading layer and the active layer, the SSL layer is a superlattice structure of InGaN / GaN grown for 5 to 10 periods, inclusive of endpoint values, and V-pits are formed by utilizing the growth difference of Ga on different polar planes.

[0014] The present invention further provides a preparation method of an epitaxial structure for improving luminous efficiency, comprising: growing an N-type semiconductor layer on a substrate; growing a first current spreading layer on the N-type semiconductor layer, wherein the first current spreading layer is an InGaN-GaN-AlGaN composite layer, and two-dimensional electron gas is generated at the heterointerfaces of InGaN / GaN and GaN / AlGaN therein; growing an active layer on the first current spreading layer; growing a second current spreading layer on the active layer, wherein the second current spreading layer is an InGaN-GaN-AlGaN composite layer with graded In component and graded Al component; growing a P-type semiconductor layer on the second current spreading layer.

[0015] Optionally, growing the second current spreading layer on the active layer comprises: introducing a Ga source, an In source and NH3, wherein within time t1, the flow rates of NH3 and the In source are gradually increased first and then gradually decreased to form In x Ga 1-x N layer, wherein x is gradually increased from 0 to x1, and then gradually decreased to 0, 0<x1<0.1; after time t' of introducing the Ga source, the In source and NH3, Mg is intermittently doped within time T', wherein T'<t1 and t'>0; then closing the In source and growing a GaN layer; then continuously introducing an Al source, the flow rate of the Al source is gradually increased first and then gradually decreased, while introducing NH3 with a flow rate trend opposite to that of the Al source to form Al y Ga 1-y N layer, wherein y is gradually increased from 0 to y1, and then gradually decreased to 0, 0<y1<1.

[0016] Optionally, the active layer comprises quantum barrier layers, quantum well layers and a GaN protective layer which are alternately stacked and grown periodically, the quantum well layer is an InGaN layer, the quantum barrier layer is a GaN layer, and the In x Ga 1-x N layer has an In component lower than that of the quantum well layer.

[0017] Optionally, the InGaN of the first current spreading layer is In z Ga 1-zN layers, where z ≥ 0.3; the first current-spreading layer is a GaN layer; the first current-spreading layer is an AlGaN layer. w Ga 1-w N layers, where w ≥ 0.3.

[0018] Optionally, a buffer layer is also grown between the substrate and the N-type semiconductor, the buffer layer being an undoped GaN layer; an SSL layer is also grown between the first current spreading layer and the active layer, the SSL layer being a superlattice structure of InGaN / GaN grown over 5-10 cycles, utilizing the growth difference of Ga on different polar faces to form V-shaped pits.

[0019] After adopting the above solution, the beneficial effects of the present invention are as follows: 1. The first current spreading layer near the N-type region is an InGaN-GaN-AlGaN composite layer. This reset layer structure utilizes the two-dimensional electron gas formed at the heterojunction between InGaN / GaN and GaN / AlGaN to increase the current spreading capability and improve the device's anti-static capability. At the same time, the band structure of InGaN-GaN-AlGaN is beneficial for hysteresis electrons, which can slow down the electron migration rate, reduce electron overflow, and thus reduce carrier transport imbalance. It also plays a role in blocking electrons, which is conducive to the injection of holes from the P-type layer into the deeper MQW (active layer) region and improves the device's luminous efficiency.

[0020] 2. The second current-spreading layer near the P-type region is an InGaN-GaN-AlGaN composite layer with graded In composition and graded Al composition. The graded In composition of InGaN can reduce the valence band barrier height and promote hole injection, while the graded Al composition of AlGaN can increase the conduction band barrier height and reduce electron leakage.

[0021] 3. In the second current extension, the In composition and Al composition both gradually increase and then gradually decrease, and the lattice difference between the two materials can be used to control the in-plane tensile stress of InGaN-GaN and the in-plane compressive stress of GaN-AlGaN, so as to weaken the polarization electric field, reduce band bending, increase the overlap of electron-hole wave functions, and improve radiative recombination luminescence.

[0022] 4. In the second current-extended InGaN, while the In composition is gradually changed, Mg is also intermittently doped. This can improve hole injection without introducing new impurities, maintain the crystal quality of the material, and improve the luminous efficiency of the device.

[0023] 5. While gradually introducing the In source and Al source into the second current extension layer, the flow rate of NH3 is also gradually introduced, during the growth of In. x Ga 1-xIn the N-layer, the gradual change trend of NH3 flux is the same as that of the In source, which makes the high V / III ratio created by the high NH3 flux beneficial to maintaining the crystal quality of InGaN and maximizing the preservation of material crystal quality; while in the growth of Al y Ga 1-y In the N-layer, the gradual change trend of NH3 flow rate is opposite to that of Al source, which reduces the pre-reaction during AlGaN growth. At the same time, the low V / III ratio created by the low NH3 flow rate is beneficial to the growth of AlGaN material system.

[0024] 6. By designing a double-layer InGaN-GaN-AlGaN structure, this invention can achieve complementary benefits in reducing electron leakage, increasing hole injection, and balancing carrier transport, resulting in higher combined benefits.

[0025] 7. The InGaN-GaN-AlGaN composite layer structure of the first current spreading layer and the second current spreading layer can also be used to construct a multi-period structure, further expanding the above-mentioned beneficial effects. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the epitaxial structure of the present invention; Figure 2 This is a schematic diagram of the InGaN-GaN-AlGaN conduction band of the second current extension layer of the present invention; Figure 3 This is a schematic diagram of the growth process of the InGaN-GaN-AlGaN in the second current extension layer of the present invention. Figure 4 This is a process flow diagram of the preparation method of the present invention.

[0027] Label Explanation: 1. Substrate; 2. Buffer layer; 3. N-type semiconductor layer; 4. First current spreading layer; 5. SSL layer; 6. Active layer; 7. Second current spreading layer; 8. P-type semiconductor layer. Detailed Implementation

[0028] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application, and all range values ​​of this application include endpoint values.

[0029] Please refer to Figure 1, the present invention provides an epitaxial structure for improving luminous efficiency, comprising a substrate 1, a buffer layer 2, an N-type semiconductor layer 3, a first current spreading layer 4, an SSL layer 5, an active layer 6, a second current spreading layer 7, and a P-type semiconductor layer 8 which are stacked in sequence from bottom to top; wherein the first current spreading layer 4 is an InGaN-GaN-AlGaN composite layer, the composite layer structure can further block dislocations and improve crystal quality, wherein the InGaN / GaN and GaN / AlGaN also generate two-dimensional electron gas at the heterogeneous interface (a sufficiently large component difference is required to form two-dimensional electron gas at the interface), which can increase the current spreading capability and improve the antistatic capability of the device; meanwhile, the band offset characteristic of InGaN-GaN-AlGaN is favorable for retarding electrons, can slow down the migration rate of electrons, reduce electron overflow, thereby reducing carrier transport imbalance, also plays a role in blocking electrons, which is favorable for holes in the P-type layer to inject into a deeper region of MQW (active layer 6), and improves the luminous efficiency of the device.

[0030] Optionally, InGaN of the first current spreading layer 4 is In z Ga 1-z N layer, wherein z≥0.3, it is N-type doped, and the doping concentration is 1-5×10 18 cm -3 ; GaN of the first current spreading layer 4 is an undoped GaN layer; AlGaN of the first current spreading layer 4 is Al w Ga 1-w N layer, wherein w≥0.3.

[0031] Optionally, In in the first current spreading layer 4 is In z Ga 1-z N layer, GaN layer and Al w Ga 1-w The thicknesses of the N layers are 10-30 nm, 5-10 nm and 10-30 nm respectively.

[0032] Furthermore, the second current spreading layer 7 is an InGaN-GaN-AlGaN composite layer with graded In component and graded Al component, wherein InGaN with graded In component can reduce the valence band barrier height and promote hole injection, while AlGaN with graded Al component can increase the conduction band barrier height and reduce electron leakage.

[0033] Specifically, the In component of InGaN of the second current spreading layer 7 is graded towards the P-type semiconductor layer 8, that is, In x Ga 1-x N layer, wherein x gradually increases from 0 to x1, then gradually decreases to 0, 0<x1<0.1, and In x Ga 1-xThe forbidden band width of the N-layer decreases as x increases, and the conduction band change of the second current spreading layer 7 is as Figure 2 shown; the GaN of the second current spreading layer 7 is a non-graded GaN layer; the AlGaN of the second current spreading layer 7 is Al with Al composition graded along the growth direction y Ga 1-y N layer, wherein y gradually increases from 0 to y1, then gradually decreases to 0, 0<y1<1, and Al y Ga 1-y The forbidden band width of the N layer increases as y increases, and the conduction band change is as Figure 2 shown. Through the adjustment of the above graded composition and the lattice difference between the two materials, the in-plane tensile stress of the InGaN-GaN interface and the in-plane compressive stress of the GaN-AlGaN interface can be regulated, so as to weaken the polarization electric field, reduce energy band bending, increase the overlap of electron-hole wave functions, and improve radiative recombination luminescence.

[0034] Optionally, the In x Ga 1-x N layer is intermittently doped with Mg, and Mg has a lower activation energy in In x Ga 1-x N, which is favorable for the incorporation of Mg, and can avoid introducing new impurities on the premise of improving hole injection, maintain the crystal quality of the material, and improve the luminous efficiency of the device.

[0035] Optionally, the In x Ga 1-x N layer, GaN layer and Al y Ga 1-y The thicknesses of the N layer are 10-30 nm, 1-10 nm and 10-30 nm, respectively.

[0036] Optionally, the InGaN-GaN-AlGaN composite layer structure of the first current spreading layer 4 and the second current spreading layer 7 can also be constructed into a multi-period structure to further expand the above beneficial effects. In a preferred embodiment, the InGaN-GaN-AlGaN composite layer structure is constructed with 2-5 periods.

[0037] Optionally, the active layer 6 comprises quantum barrier layers, quantum well layers and GaN protection layers which are alternately stacked and grown periodically, with a growth period of 5-10 cycles, the quantum well layer is an InGaN layer, the quantum barrier layer is a GaN layer, and the In content in the In x Ga 1-x N layer shall be less than the In composition of the quantum well layer, so as to reduce the absorption of light emitted from the quantum well layer by the In x Ga 1-x N layer, and further improve the luminous efficiency of the device.

[0038] Optionally, the quantum barrier layer is grown at a temperature of 800-900℃, has a thickness of 10-20 nm, and a doping concentration of 3-8 × 10⁻⁶. 17 cm -3 The quantum well layer is grown at a temperature of 700-800℃ and has a thickness of 1-4nm; the GaN protective layer has a growth thickness of 10-20Å.

[0039] Optionally, the SSL layer 5 is a short-period superlattice structure of InGaN / GaN grown over 5-10 cycles. It utilizes the growth differences of Ga on different polar faces to form V-pits, which can reduce the nonradiative recombination probability, enhance hole injection enhancement, and optimize electrical performance. The growth temperature of the SSL layer 5 is 800-850℃.

[0040] Optionally, the type of substrate 1 is not limited in this application. For example, substrate 1 includes any one of sapphire, silicon carbide, silicon, gallium nitride, and aluminum nitride. In this embodiment, c-plane sapphire substrate 1 is preferred.

[0041] Optionally, the buffer layer 2 is an undoped GaN layer with a thickness of 2.0-2.5 μm and a growth temperature of 1000-1100℃. The function of the buffer layer 2 is to reduce the lattice mismatch between the sapphire substrate 1 and the subsequent growth materials by growing a high-quality GaN layer.

[0042] Optionally, an undoped GaN low-temperature nucleation layer (not shown in the figure) with a thickness of 15-25 nm and a growth temperature of 800-900 °C is also grown between the buffer layer 2 and the sapphire substrate 1.

[0043] Optionally, the N-type semiconductor layer 3 is an N-type Si-doped GaN layer with a doping concentration of 1-5 × 10⁻⁶. 19 cm -3 The function of the N-type semiconductor layer 3 is to provide N-type contacts.

[0044] Optionally, the p-type semiconductor layer 8 is a p-type Mg-doped GaN layer with a doping concentration of 5-10×10⁻⁶. 18 cm -3 The growth temperature is 850-900℃. The purpose of growing the P-type semiconductor layer 8 is to provide P-type contacts.

[0045] This invention also provides a method for preparing an epitaxial structure with improved luminescence efficiency. Specifically, it employs metal-organic chemical vapor deposition (MOCVD) to grow a low-temperature nucleation layer, a buffer layer 2, an N-type semiconductor layer 3, a first current spreading layer 4, an SSL layer 5, an active layer 6, a second current spreading layer 7, and a P-type semiconductor layer 8 sequentially from bottom to top on a substrate 1. The substrate 1 includes, but is not limited to, a sapphire substrate 1. This embodiment uses a sapphire substrate 1 as an example, with trimethyl / ethyl gallium™Ga / TEGa, trimethylaluminum™Al, and ammonia NH3 as the Ga source, Al source, and N source, respectively, and N2 as the carrier gas. The N-type and P-type doping sources are silane SiH4 and magnesium pyrocene CP2Mg, respectively.

[0046] Please refer to Figure 4 The preparation method specifically includes the following steps: S1. Growing a low-temperature nucleation layer on substrate 1, including: The sapphire substrate 1 is placed in the MOCVD reaction chamber and hydrogenated with high-purity hydrogen gas at a high temperature of 1100℃ for 5-10 minutes. Then, the temperature is lowered to 800-900℃ and a TEGa source and an N source are introduced to grow a 15-25nm thick low-temperature nucleation layer of undoped GaN.

[0047] S2. A buffer layer 2 is grown on the low-temperature nucleation layer, comprising: After the low-temperature nucleation layer is grown, the temperature is raised to 1000-1100℃, the TEGa source is turned off, and the TMGa source is introduced to grow a 2.0-2.5μm undoped GaN buffer layer 2. The purpose of growing the buffer layer 2 is to reduce the lattice mismatch between the sapphire substrate 1 and the subsequent growth materials by growing a high-quality GaN layer.

[0048] S3. Growing an N-type semiconductor layer 3 on the buffer layer 2, including: After the buffer layer 2 is grown, silane is introduced to grow a 1-2 μm thick Si-doped N-type semiconductor layer 3 with a doping concentration of 1-5 × 10⁻⁶. 19 cm -3 The purpose of growing the N-type semiconductor layer 3 is to provide N-type contacts.

[0049] S4. Growing a first current spreading layer 4 on the N-type semiconductor layer 3, including: After growing the N-type semiconductor layer 3, an In source is then introduced to grow 10-30 nm of In. z Ga 1-z N layers, where z ≥ 0.3, with a doping concentration of 1-5 × 10⁻⁶. 18 cm -3 Then, the silane and In sources are turned off, and a 5-10 nm thick GaN layer is grown. Next, an Al source is introduced to grow a 10-30 nm thick Al layer. w Ga1-w The N-layer composite structure, with w≥0.3, can further block dislocations and improve crystal quality. At the same time, the two-dimensional electron gas generated at the heterojunction of InGaN / GaN and GaN / AlGaN can increase the current spread capability. In addition, the band structure of InGaN-GaN-AlGaN can also delay electrons, reduce electron overflow, and alleviate carrier transport imbalance.

[0050] Optionally, the InGaN-GaN-AlGaN composite layer structure of the first current extension layer 4 can be constructed into a multi-period structure, preferably 2-5 periods, to further amplify the above-mentioned beneficial effects.

[0051] S5. Grow an SSL layer 5 on the first current extension layer 4, including: After the first current-extended layer 4 is grown, the temperature is lowered to 800-850℃, and In source and Ga source are introduced to alternately grow InGaN / GaN for 5-10 cycles. The SSL layer 5 is a short-cycle superlattice structure of InGaN / GaN. It utilizes the difference in Ga growth on different polar faces to form V-pits, which can reduce the probability of nonradiative recombination, enhance hole injection enhancement, and optimize electrical performance.

[0052] S6. Grow an active layer 6 on top of SSL layer 5, including: After growing the SSL layer 5, the temperature was lowered to 800-900℃, and TEGa (Ga source) and SiH4 were introduced simultaneously to grow a 10-20 nm thick layer with a doping concentration of 3-8 × 10⁻⁶. 17 cm -3 The quantum barrier layer (QB) is a GaN layer. The temperature is then lowered to 700-800℃, and TEGa and TMIn are introduced while SiH4 and H2 are turned off to grow a 1-4 nm thick quantum well layer (QW), an InGaN layer. A Ga source is then introduced to grow a 10-20 Å GaN protective layer. Finally, H2 is turned on, and the temperature is raised to the growth temperature of QB. This growth process is repeated for 5-10 cycles to complete the entire growth process of the active layer 6.

[0053] S7. A second current extension layer 7 is grown on the active layer 6, including: The second current extension layer 7 begins to grow on the last quantum barrier layer, as shown below. Figure 3 As shown, a Ga source and an In source are first introduced. During time t1, the flow rates of NH3 and In source gradually increase and then gradually decrease, forming an In vapor deposition layer with a gradually varying In composition, which is 10 nm to 30 nm thick. x Ga 1-xN layer, wherein x gradually increases from 0 to x1, then gradually decreases to 0, with 0<x1<0.1. The high V / III ratio created by high NH₃ flow is conducive to maintaining the crystal quality of the InGaN layer; and, after t' time of introducing the Ga source, In source and NH₃, Mg is intermittently doped within T' time. The activation energy of Mg in InGaN is relatively low, which facilitates the incorporation of Mg. Intermittent Mg doping can also avoid introducing new impurities on the premise of improving hole injection, maintain the crystal quality of the material, and improve the luminous efficiency of the device. In addition, T'<t1 and t'>0, which can ensure that Mg does not penetrate into the active region to form non-radiative recombination centers.

[0054] Then turn off the In source, grow a GaN layer with a thickness of 1-10 nm, continue to introduce the Al source, the flow rate of the Al source first gradually increases and then gradually decreases, while introducing NH₃ with a flow rate trend opposite to that of Al. The purpose is to reduce pre-reaction when growing AlGaN. Meanwhile, the low V / III ratio created by low NH₃ flow is conducive to the growth of the AlGaN material system. Grow Al with a thickness of 10-30 nm and gradient Al composition y Ga 1-y N, wherein y gradually increases from 0 to y1, then gradually decreases to 0, with 0<y1<1.

[0055] Through the above adjustment of gradient composition, combined with the lattice difference between the two materials, the in-plane tensile stress of InGaN-GaN and the in-plane compressive stress of GaN-AlGaN can be regulated, so as to weaken the polarization electric field, reduce energy band bending, increase the overlap of electron-hole wave functions, and improve radiative recombination luminescence Optionally, the In in the second current spreading layer 7 x Ga 1-x The In composition of the N layer shall be lower than the In composition of the quantum well layer, so as to reduce the absorption of light emitted from the quantum well layer by the In x Ga 1-x N layer, further improving the luminous efficiency of the device.

[0056] Optionally, the InGaN-GaN-AlGaN composite layer structure of the second current spreading layer 7 can be constructed into a multi-period structure, preferably 2-5 periods, so as to further expand the above beneficial effects.

[0057] S8, growing a P-type semiconductor layer 8 on the second current spreading layer 7, comprising: After completing the growth of the second current spreading layer 7, introduce the P-type doping source bis(cyclopentadienyl)magnesium (CP₂Mg), anneal at 850-900°C for 20-30 minutes in N₂ atmosphere, grow a P-type semiconductor layer 8 with a doping concentration of 1-5×10 19 cm -3 , the pressure for the whole reaction growth is 100-300 torr, and the purpose of growing the P-type semiconductor layer 3 is to provide P-type contact.

[0058] As described above, the epitaxial structure fabricated using this method, through the design of a bilayer InGaN-GaN-AlGaN structure, achieves several advantages. Firstly, an InGaN-GaN-AlGaN composite layer is inserted near the N-type region. This layer utilizes the two-dimensional electron gas generated at the heterojunction to increase current spread, while its bandgap properties retard electrons and reduce electron overflow. Secondly, a compositionally graded InGaN-GaN-AlGaN composite layer is inserted near the P-type region. This reduces the valence band barrier height, increases hole injection, and modulates stress to weaken the polarization field in the active region, effectively improving the device's luminous efficiency. Furthermore, the bilayer InGaN-GaN-AlGaN structure offers complementary advantages in reducing electron leakage, increasing hole injection, and balancing carrier transport, resulting in greater combined benefits.

[0059] It is worth noting that the thicknesses of the substrate 1, buffer layer 2, N-type semiconductor layer 3, first current spreading layer 4, SSL layer 5, active layer 6, second current spreading layer 7, and P-type semiconductor layer 8 shown in the accompanying drawings are merely examples and do not represent their actual thicknesses. Furthermore, the actual proportions between the substrate 1, buffer layer 2, N-type semiconductor layer 3, first current spreading layer 4, SSL layer 5, active layer 6, second current spreading layer 7, and P-type semiconductor layer 8 are not as shown in the drawings and are for reference only.

[0060] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0061] 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 for improving luminous efficiency, characterized in that: It includes a substrate, an N-type semiconductor layer, a first current spreading layer, an active layer, a second current spreading layer, and a P-type semiconductor layer, which are stacked sequentially from bottom to top; Wherein, the first current spreading layer is an InGaN-GaN-AlGaN composite layer, and two-dimensional electron gas is generated at the heterointerfaces of InGaN / GaN and GaN / AlGaN therein; the second current spreading layer is an InGaN-GaN-AlGaN composite layer with graded In component and Al component, and the InGaN of the second current spreading layer is In with the In component graded towards the P-type semiconductor layer x Ga 1-x N layer, wherein x gradually increases from 0 to x1, then gradually decreases to 0, with 0<x1<0.1; the GaN of the second current spreading layer is a GaN layer; the AlGaN of the second current spreading layer is Al with the Al component graded along the growth direction y Ga 1-y N layer, wherein y gradually increases from 0 to y1, then gradually decreases to 0, with 0<y1<1.

2. The epitaxial structure for improving luminous efficiency as described in claim 1, characterized in that: The In x Ga 1-x N-layer discontinuous Mg doping.

3. The epitaxial structure for improving luminous efficiency as described in claim 1, characterized in that: In the second current spread layer x Ga 1-x N-layer, GaN layer and Al y Ga 1-y The thicknesses of the N layers are 10-30 nm, 1-10 nm, and 10-30 nm, respectively, and all include the endpoint values.

4. The epitaxial structure for improving luminous efficiency as described in claim 1, characterized in that: The active layer comprises alternatingly stacked, periodically grown quantum barrier layers, quantum well layers, and GaN protective layers. The quantum well layers are InGaN layers, and the quantum barrier layers are GaN layers. x Ga 1-x The In composition of the N-layer is smaller than that of the quantum well layer.

5. The epitaxial structure for improving luminous efficiency as described in claim 1, characterized in that: The first current-spreading layer of InGaN is In z Ga 1-z The N-layer, where z ≥ 0.3, is N-type doped with a doping concentration of 1-5 × 10⁻⁶. 18 cm -3 This includes endpoint values; the first current-spreading layer is a GaN layer; the first current-spreading layer is an AlGaN layer. w Ga 1-w N layers, where w ≥ 0.

3.

6. The epitaxial structure for improving luminous efficiency as described in claim 5, characterized in that: In the first current spread layer z Ga 1-z N-layer, GaN layer and Al w Ga 1-w The thicknesses of the N layers are 10-30 nm, 5-10 nm, and 10-30 nm, respectively, and all include the endpoint values.

7. The epitaxial structure for improving luminous efficiency as described in claim 1, characterized in that: Both the first and second current-spreading layers of the InGaN-GaN-AlGaN composite layer have 2-5 cycles, including endpoint values.

8. The epitaxial structure for improving luminous efficiency as described in claim 1, characterized in that: A buffer layer, which is an undoped GaN layer, is also provided between the substrate and the N-type semiconductor. An SSL layer, which is a superlattice structure of InGaN / GaN grown over 5-10 cycles, including endpoint values, is also provided between the first current spreading layer and the active layer. The SSL layer is a superlattice structure of InGaN / GaN grown over 5-10 cycles, which includes endpoint values ​​and utilizes the growth difference of Ga on different polar faces to form V-shaped pits.

9. A method for preparing an epitaxial structure with improved luminescence efficiency as described in any one of claims 1-8, characterized in that, include: An N-type semiconductor layer is grown on a substrate; A first current spreading layer is grown on an N-type semiconductor layer. The first current spreading layer is an InGaN-GaN-AlGaN composite layer, wherein the InGaN / GaN and GaN / AlGaN generate a two-dimensional electron gas at the heterojunction. An active layer is grown on the first current-spreading layer; Growing a second current spreading layer on the active layer, wherein the second current spreading layer is an InGaN-GaN-AlGaN composite layer with graded In composition and Al composition, and the InGaN of the second current spreading layer is In with In composition graded towards the P-type semiconductor layer x Ga 1-x N layer, wherein x gradually increases from 0 to x1, then gradually decreases to 0, 0<x1<0.1; the GaN of the second current spreading layer is a GaN layer; the AlGaN of the second current spreading layer is Al with Al composition graded along the growth direction y Ga 1-y N layer, wherein y gradually increases from 0 to y1, then gradually decreases to 0, 0<y1<1; A P-type semiconductor layer is grown on the second current spreading layer.

10. The method for preparing an epitaxial structure with improved luminescence efficiency as described in claim 9, characterized in that, Growing a second current-spreading layer on the active layer includes: Introduce a Ga source, an In source and NH₃, wherein within time t1, the flow rates of NH₃ and the In source gradually increase first and then gradually decrease to form In with a gradient In component x Ga 1-x N layer, wherein x gradually increases from 0 to x1, then gradually decreases to 0, with 0<x1<0.1; after time t' of introducing the Ga source, the In source and NH₃, Mg is intermittently doped within time T', wherein T'<t1 and t'>0; then closing the In source to grow a GaN layer; subsequently continuing to introduce an Al source, wherein the flow rate of the Al source gradually increases first and then gradually decreases, while introducing NH₃ with a flow rate trend opposite to that of the Al source to form Al with a gradient Al component y Ga 1-y N layer, wherein y gradually increases from 0 to y1, then gradually decreases to 0, with 0<y1<1.

11. The method for preparing an epitaxial structure with improved luminescence efficiency as described in claim 10, characterized in that: The active layer comprises alternatingly stacked, periodically grown quantum barrier layers, quantum well layers, and GaN protective layers. The quantum well layers are InGaN layers, and the quantum barrier layers are GaN layers. x Ga 1-x The In composition of the N-layer is smaller than that of the quantum well layer.

12. The method for preparing an epitaxial structure with improved luminescence efficiency as described in claim 9, characterized in that: The first current-spreading layer of InGaN is In z Ga 1-z N layers, where z ≥ 0.3; the first current-spreading layer is a GaN layer; the first current-spreading layer is an AlGaN layer. w Ga 1-w N layers, where w ≥ 0.

3.

13. The method for preparing an epitaxial structure with improved luminescence efficiency as described in claim 9, characterized in that: A buffer layer, which is an undoped GaN layer, is also grown between the substrate and the N-type semiconductor. An SSL layer, which is a superlattice structure of InGaN / GaN grown over 5-10 cycles, is also grown between the first current spreading layer and the active layer. The SSL layer is formed by utilizing the growth difference of Ga on different polar faces to create V-shaped pits.

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