GaN-based blue-green light LED epitaxial structure and preparation method thereof, and GaN-based blue-green light LED

Abstract

The invention discloses a GaN-based blue-green light LED epitaxial structure and a preparation method thereof, and a GaN-based blue-green light LED. The GaN-based blue-green light LED epitaxial structure comprises a substrate, and a buffer layer, a 3D layer, a U-GaN layer, an N-GaN layer, a multi-quantum well layer, an electron blocking layer and a P-GaN layer which are stacked on the substrate in sequence; wherein the multi-quantum well layer comprises a shallow well transition layer, a first quantum well layer, a second quantum well layer, a stress release layer and a third quantum well layer which are stacked in sequence; the growth temperature of the first quantum well layer is greater than the growth temperature of the second quantum well layer and greater than the growth temperature of the third quantum well layer, and the number of cycles of alternate stacking of the second quantum well layer is greater than the number of cycles of alternate stacking of the third quantum well layer; the stress release layer is an AlGaN layer or an AlN layer and a GaN layer, wherein the AlN layer and the GaN layer are periodically and alternately stacked. According to the invention, the turn-on voltage of the GaN-based blue-green light LED can be effectively improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a GaN-based blue-green LED epitaxial structure and its fabrication method, and a GaN-based blue-green LED. Background Technology

[0002] A light-emitting diode (LED) is a light-emitting device based on a semiconductor PN junction. When a forward bias voltage is applied to the PN junction, electrons and holes recombine and release energy in the form of photons, thereby emitting light. Due to its advantages such as low energy consumption, long lifespan, small size, fast response, and environmental friendliness, LEDs have been widely used in many fields such as displays, lighting, backlighting, and communications.

[0003] Turn-on voltage (or forward voltage, Vf) is a core performance parameter of LEDs, defined as the minimum forward bias voltage required for an LED to begin emitting light. The turn-on voltage is primarily determined by the band gap of the semiconductor material. Theoretically, for an LED made of a specific material, the turn-on voltage is a fixed value. However, in practical manufacturing and applications, factors such as the polarization electric field of multiple quantum well layers, carrier overflow, and nonradiative recombination of carriers can cause the turn-on voltage to be too low, resulting in poor interference immunity and difficulties in matching multiple devices in series and parallel. Changing the material system of the multiple quantum well layers can increase the turn-on voltage, but this is costly and inevitably alters key performance indicators such as the emission wavelength, internal quantum efficiency, and reliability of the device. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a GaN-based blue-green LED epitaxial structure and its preparation method, and a GaN-based blue-green LED, which effectively and flexibly improves its turn-on voltage without significantly changing the LED material system, emission wavelength and core photoelectric performance.

[0005] To address the aforementioned issues, this invention discloses a GaN-based blue-green LED epitaxial structure, comprising a substrate and a buffer layer, a 3D layer, a U-GaN layer, an N-GaN layer, a multiple quantum well layer, an electron blocking layer, and a P-GaN layer sequentially stacked on the substrate. The multi-quantum-well layer comprises a shallow-well transition layer, a first quantum well layer, a second quantum well layer, a stress-relieving layer, and a third quantum well layer stacked sequentially. The growth temperature of the first quantum well layer is greater than that of the second quantum well layer and also greater than that of the third quantum well layer. The number of alternating stacking periods of the second quantum well layer is greater than that of the third quantum well layer. The stress-relieving layer is an AlGaN layer or a periodically alternating stack of AlN and GaN layers.

[0006] As an improvement to the above technical solution, the stress relief layer is a Si-doped AlGaN layer with a thickness of 2nm~20nm and a Si doping concentration of 1×10⁻⁶. 16 atoms / cm 3 ~1×10 19 atoms / cm 3 Along the epitaxial growth direction, the proportion of Al component increases from 0.15 to 0.25.

[0007] As an improvement to the above technical solution, the stress relief layer is a periodically alternating AlN layer and GaN layer, with the number of alternating stacking periods being 2 to 10, the thickness of the AlN layer being 1 nm to 10 nm, and the thickness of the GaN layer being 1 nm to 10 nm. The GaN layer is a Si-doped GaN layer with a Si doping concentration of 1×10⁻⁶. 16 atoms / cm 3 ~1×10 19 atoms / cm 3 .

[0008] As an improvement to the above technical solution, the shallow well transition layer comprises periodically alternating layers of In... a Ga 1-a An N-type quantum well layer and a first GaN barrier layer; the first quantum well layer comprises periodically alternating layers of In. b Ga 1-b An N-type quantum well layer and a second GaN barrier layer; the second quantum well layer comprises periodically alternating layers of In. c Ga 1-c An N-type quantum well layer and a third GaN barrier layer; the third quantum well layer comprises periodically alternating layers of In. d Ga 1-d The N-type potential well layer and the fourth GaN potential barrier layer; wherein, 0.01≤a≤b≤c≤d≤0.5.

[0009] As an improvement to the above technical solution, the growth temperature of the second quantum well layer is equal to the growth temperature of the third quantum well layer.

[0010] As an improvement to the above technical solution, the number of alternating stacked shallow well transition layers is 1~20, a is 0.01~0.1, and the thickness is 1nm~5nm. The first GaN barrier layer is a Si-doped GaN barrier layer with a Si doping concentration of 5×10⁻⁶. 17 atoms / cm 3 ~5×10 19 atoms / cm 3 The thickness is 10nm~50nm; The first quantum well layer has an alternating stacked period of 1 to 20, a b of 0.1 to 0.2, and a thickness of 1 nm to 5 nm. The second GaN barrier layer is a Si-doped GaN barrier layer with a Si doping concentration of 5 × 10⁻⁶. 16 atoms / cm 3 ~5×10 18 atoms / cm 3 The thickness is 5nm~30nm; The second quantum well layer has an alternating stacked period of 6-20, c of 0.2-0.5, and a thickness of 2nm-5nm. The third GaN barrier layer is a Si-doped GaN barrier layer with a Si doping concentration of 1×10⁻⁶. 17 atoms / cm 3 ~5×10 18 atoms / cm 3 The thickness is 5nm~20nm.

[0011] The third quantum well layer has an alternating stacked period of 3-6, a d of 0.2-0.5, and a thickness of 2nm-5nm. The fourth GaN barrier layer is a Si-doped GaN barrier layer with a Si doping concentration of 1×10⁻⁶. 17 atoms / cm 3 ~5×10 18 atoms / cm 3 The thickness is 5nm~20nm.

[0012] Accordingly, this invention also discloses a method for fabricating a GaN-based blue-green LED epitaxial structure, which includes the following steps: A substrate is provided on which a buffer layer, a 3D layer, a U-GaN layer, an N-GaN layer, a multiple quantum well layer, an electron blocking layer and a P-GaN layer are sequentially grown. The multi-quantum-well layer comprises a shallow-well transition layer, a first quantum well layer, a second quantum well layer, a stress-relieving layer, and a third quantum well layer stacked sequentially. The growth temperature of the first quantum well layer is greater than that of the second quantum well layer and also greater than that of the third quantum well layer. The number of alternating stacking periods of the second quantum well layer is greater than that of the third quantum well layer. The stress-relieving layer is an AlGaN layer or a periodically alternating stack of AlN and GaN layers.

[0013] As an improvement to the above technical solution, the growth temperature of the stress relief layer is 700℃~950℃, the growth pressure is 100 torr~500 torr, and the V / Ⅲ ratio is 2000~20000.

[0014] As an improvement to the above technical solution, in the shallow well transition layer, the In a Ga 1-a The growth temperature of the N-well layer is 750℃~950℃, the growth pressure is 100 torr~500 torr, and the V / III ratio is 500~10000; the growth temperature of the first GaN barrier layer is 750℃~950℃, the growth pressure is 100 torr~500 torr, and the V / III ratio is 500~10000. In the first quantum well layer, the In b Ga 1-b The growth temperature of the N-type potential well layer is 750℃~950℃, the growth pressure is 100 torr~500 torr, and the V / III ratio is 2000~20000; the growth temperature of the second GaN barrier layer is 750℃~1000℃, the growth pressure is 100 torr~500 torr, and the V / III ratio is 2000~20000. In the second quantum well layer, the In c Ga 1-c The growth temperature of the N-type potential well layer is 700℃~850℃, the growth pressure is 100 torr~500 torr, and the V / III ratio is 2000~20000; the growth temperature of the third GaN barrier layer is 800℃~950℃, the growth pressure is 100 torr~500 torr, and the V / III ratio is 2000~20000.

[0015] In the third quantum well layer, the In d Ga 1-d The growth temperature of the N-type potential well layer is 700℃~850℃, the growth pressure is 100 torr~500 torr, and the V / III ratio is 2000~20000; the growth temperature of the fourth GaN barrier layer is 800℃~950℃, the growth pressure is 100 torr~500 torr, and the V / III ratio is 2000~20000.

[0016] Accordingly, the present invention also discloses a GaN-based blue-green LED, comprising the above-described GaN-based blue-green LED epitaxial structure.

[0017] Implementing this invention has the following beneficial effects: The GaN-based blue-green LED epitaxial structure provided by this invention includes a multi-quantum-well layer comprising a shallow-well transition layer, a first quantum well layer, a second quantum well layer, a stress-relieving layer, and a third quantum well layer stacked sequentially. The stress-relieving layer is an AlGaN layer or a periodic stacked structure composed of AlN and GaN layers. Placing the stress-relieving layer between the second and third quantum well layers, which have a lower growth temperature, effectively reduces epitaxial defects in the low-temperature grown quantum well layer, lowers the GaN epitaxial dislocation density, thereby improving the surface morphology of the GaN epitaxial layer, releasing epitaxial stress, effectively reducing the polarization electric field of the third quantum well layer, alleviating quantum well band bending, increasing the band gap, blue-shifting the wavelength, and increasing the LED's turn-on voltage. Furthermore, the second quantum well layer has a greater number of alternating stacked periods than the third quantum well layer, and the stress-relieving layer is located relatively close to the P-GaN layer in the multi-quantum-well layer, which can further improve the LED's turn-on voltage. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a GaN-based blue-green LED epitaxial structure provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the multi-quantum-well layer in the GaN-based blue-green LED epitaxial structure provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the multi-quantum-well layer in the GaN-based blue-green LED epitaxial structure provided in another embodiment of the present invention; Figure 4 This is a flowchart of a method for fabricating a GaN-based blue-green LED epitaxial structure according to an embodiment of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in further detail below.

[0020] like Figures 1-3 As shown, this invention discloses a GaN-based blue-green LED epitaxial structure, including a substrate 1 and a buffer layer 2, a 3D layer 3, a U-GaN layer 4, an N-GaN layer 5, a multi-quantum well layer 6, an electron blocking layer 7, and a P-GaN layer 8 sequentially stacked on the substrate 1. The multi-quantum well layer 6 includes a shallow well transition layer 61, a first quantum well layer 62, a second quantum well layer 63, a stress relief layer 64, and a third quantum well layer 65 sequentially stacked. The growth temperature of the first quantum well layer 62 is higher than that of the second quantum well layer 63 and also higher than that of the third quantum well layer 65. The number of alternating stacking periods of the second quantum well layer 63 is greater than that of the third quantum well layer 65. The stress relief layer 64 is an AlGaN layer, or a periodically alternating stacked AlN layer 641 and GaN layer 642.

[0021] The relatively small lattice constant of AlN means that when an AlN layer is deposited on top of a GaN layer, the AlN layer tends to shrink to accommodate its smaller lattice constant. This shrinkage is constrained by the underlying GaN layer, thus generating compressive stress. This compressive stress from AlN effectively alleviates the tensile stress caused by GaN growth. The second and third quantum well layers have lower growth temperatures and typically higher In content, resulting in greater lattice mismatch between their potential well and barrier layers, making them more prone to accumulating significant compressive stress. The first quantum well layer has a higher growth temperature, which to some extent repairs defects in the underlying layer. Simultaneously, the addition of a stress-relieving layer between the second and third quantum well layers further reduces epitaxial defects caused by the first and second quantum well layers, improves the surface morphology of the GaN epitaxial layer, and releases epitaxial stress. In particular, it can suppress the migration and phase separation of In atoms in the third quantum well layer, ensuring the compositional uniformity of the potential well layer and effectively reducing the polarization electric field of the third quantum well layer. This alleviates the quantum well bandgap bending, increases the band gap, and causes a blue shift in wavelength, thus increasing the LED turn-on voltage. Furthermore, the number of alternating stacked cycles of the second quantum well layer is greater than that of the third quantum well layer. Since the 3 to 6 quantum wells closest to the P-layer structure often affect the luminous performance of LEDs, and the stress relief layer is located in the multi-quantum well layer relatively close to the P-GaN layer, the LED turn-on voltage is significantly improved. By adopting the multi-quantum well layer structure provided by this invention, the LED turn-on voltage can be effectively and flexibly improved without significantly changing the LED material system, emission wavelength, and core optoelectronic performance.

[0022] It is understood that the growth temperature of the first quantum well layer 62 is higher than that of the second quantum well layer 63 and the third quantum well layer 65. Specifically, this refers to the growth temperature of the potential well layers; that is, the potential well layer of the first quantum well layer 62 is grown at a relatively high temperature, while the potential well layers of the second quantum well layer 63 and the third quantum well layer 65 are grown at relatively low temperatures. Furthermore, the growth temperature of the barrier layer is generally higher than that of the potential well layer. In one embodiment, to achieve better growth quality by matching the growth of the potential well layer, the growth temperature of the barrier layer of the first quantum well layer 62 may also be higher than that of the barrier layers of the second quantum well layer 63 and the third quantum well layer 65.

[0023] In one implementation, such as Figure 2 As shown, the stress relief layer 64 is a Si-doped AlGaN layer with a thickness of 2nm to 20nm, exemplarily 5nm, 10nm, 14nm, 16nm, or 18nm, but not limited to these, and the Si doping concentration is 1×10⁻⁶. 16 atoms / cm 3 ~1×10 19 atoms / cm 3An example is 5×10 16 atoms / cm 3 1×10 17 atoms / cm 3 5×10 17 atoms / cm 3 1×10 18 atoms / cm 3 Or 5×10 18 atoms / cm 3 However, it is not limited to this. Along the epitaxial growth direction, the Al composition ratio increases from 0.15 to 0.25, the lattice constant of the stress relief layer changes gradually, avoiding stress concentration. The gradually changing energy band can slow down the movement speed of electrons, so that electrons are uniformly injected into the third quantum well layer, while weakening the QCSE effect, releasing compressive stress, and reducing the polarization built-in electric field.

[0024] In another implementation, such as Figure 3 As shown, the stress relief layer 64 consists of periodically alternating AlN layers 641 and GaN layers 642. The number of alternating stacking periods of the stress relief layer 64 is 2 to 10, exemplarily 3, 5, 7, 8, or 9, but not limited to these. Preferably, the number of alternating stacking periods of the stress relief layer 64 is 5 to 10. The thickness of the AlN layer 641 is 1 nm to 10 nm, exemplarily 2 nm, 4 nm, 5 nm, 6 nm, or 8 nm, but not limited to these. The thickness of the GaN layer 642 is 1 nm to 10 nm, exemplarily 2 nm, 4 nm, 5 nm, 6 nm, or 8 nm, but not limited to these. Preferably, the thickness of the AlN layer 641 is 1 nm to 5 nm, and the thickness of the GaN layer 642 is 1 nm to 5 nm. Based on the stress relief layer 64 with the above composition, the crystal quality of the epitaxial structure can be further optimized, improving the luminous efficiency of the LED under high current.

[0025] In a preferred embodiment, the GaN layer is a Si-doped GaN layer with a Si doping concentration of 1×10⁻⁶. 16 atoms / cm 3 ~1×10 19 atoms / cm 3 An example is 5×10 16 atoms / cm 3 1×10 17 atoms / cm 3 5×10 17 atoms / cm 3 1×10 18 atoms / cm 3 Or 5×10 18 atoms / cm 3However, it is not limited to this. The GaN layer is a Si-doped GaN layer, which can provide electrons to the third quantum well layer 65, thereby improving the electron-hole recombination efficiency in the third quantum well layer 65.

[0026] It is understood that the shallow well transition layer 61, the first quantum well layer 62, the second quantum well layer 63, and the third quantum well layer 65 are all formed by periodically alternating layers of potential well layers and potential barrier layers. In one embodiment, the shallow well transition layer 61 includes periodically alternating layers of In... a Ga 1-a The first quantum well layer 611 and the first GaN barrier layer 612. The first quantum well layer 62 comprises periodically alternating layers of In. b Ga 1-b An N-type quantum well layer 621 and a second GaN barrier layer 622. The second quantum well layer 63 comprises periodically alternating layers of In. c Ga 1-c The N-type quantum well layer 631 and the third GaN barrier layer 632. The third quantum well layer 65 comprises periodically alternating layers of In. d Ga 1-d An N-type potential well layer 651 and a fourth GaN barrier layer 652 are defined, where 0.01 ≤ a ≤ b ≤ c ≤ d ≤ 0.5. Based on the above structure, the shallow well transition layer 61 and the first quantum well layer 62 can effectively buffer the compressive strain of the second quantum well layer 63 and the third quantum well layer 65, reduce the polarization electric field strength, and increase the electron-hole recombination probability. In a preferred embodiment, the second quantum well layer 63 and the third quantum well layer 65 have the same growth temperature and the same In composition ratio. That is, the quantum well layer with a relatively lower growth temperature is divided into a second quantum well layer and a third quantum well layer, and a stress relief layer 64 is set between them, which can further increase the epitaxial crystal quality and reduce the polarization electric field strength. Based on the above combination of layered structures, the second quantum well layer 63 and the third quantum well layer 65 can use a higher In composition, effectively solving the Green Gap problem.

[0027] In one embodiment, the shallow well transition layer 61 is grown in alternating cycles of 1 to 20, exemplarily 5, 8, 10, 15, or 18, but is not limited thereto. a Ga 1-a The In composition ratio α of the N-well layer 611 is 0.01~0.1, exemplarily 0.02, 0.04, 0.05, 0.06 or 0.08, but not limited thereto; the thickness is 1nm~5nm, exemplarily 1.5nm, 2nm, 2.5nm, 3nm or 4nm, but not limited thereto; the first GaN barrier layer 612 is a Si-doped GaN barrier layer with a Si doping concentration of 5×10⁻⁶. 17 atoms / cm 3 ~5×10 19atoms / cm 3 An example is 7.5 × 10 17 atoms / cm 3 1×10 18 atoms / cm 3 5×10 18 atoms / cm 3 9×10 18 atoms / cm 3 Or 1×10 19 atoms / cm 3 However, it is not limited to this; the thickness is 10nm to 50nm, with examples of 15nm, 20nm, 25nm, 30nm, or 40nm, but not limited to this. Preferably, In a Ga 1-a The thickness of the N-type quantum well layer 611 is 3nm~4nm, and the thickness of the first GaN barrier layer 612 is 30nm~40nm. The shallow well transition layer 61 can effectively buffer the compressive strain of the second quantum well layer 63 and the third quantum well layer 65, reduce the polarization electric field intensity, alleviate the quantum well band bending, increase the quantum barrier height, and improve the LED turn-on voltage.

[0028] The number of alternating growth cycles of the first quantum well layer 62 is 1 to 20, exemplarily 5, 8, 10, 15, or 18, but not limited to these. b Ga 1-b The In composition percentage (b) of the N-well layer 621 is 0.1~0.2, exemplarily 0.12, 0.14, 0.15, 0.16, or 0.18, but not limited thereto; the thickness is 1nm~5nm, exemplarily 1.5nm, 2nm, 2.5nm, 3nm, or 4nm, but not limited thereto; the second GaN barrier layer 622 is a Si-doped GaN barrier layer with a Si doping concentration of 5×10⁻⁶. 16 atoms / cm 3 ~5×10 18 atoms / cm 3 An example is 1×10 17 atoms / cm 3 5×10 17 atoms / cm 3 1×10 18 atoms / cm 3 2.5×10 18 atoms / cm 3 Or 4×10 18 atoms / cm 3However, it is not limited to this; the thickness is 5nm to 30nm, with examples of 8nm, 10nm, 15nm, 20nm, or 25nm, but not limited to this. Preferably, In b Ga 1-b The thickness of the N-type quantum well layer 621 is 2nm~3nm, and the thickness of the second GaN barrier layer 622 is 10nm~15nm. The In in the first quantum well layer 62... b Ga 1-b The N-well layer 621 is grown at high temperature, resulting in high atomic mobility, which is more suitable for two-dimensional material growth. This significantly reduces defects and makes it easier to obtain high-quality InGaN materials. Meanwhile, In... b Ga 1-b The lower proportion of In component in the N-potential well layer 621 reduces the lattice mismatch stress between InGaN and GaN materials, significantly improving the quality of the subsequently grown second quantum well layer 63 and third quantum well layer 65, thereby enhancing the luminous efficacy and yield of the LED.

[0029] The number of alternating growth cycles of the second quantum well layer 63 is 6 to 20, exemplarily 8, 10, 12, 15, or 18, but not limited to these. c Ga 1-c The In composition ratio c of the N-well layer 631 is 0.2~0.5, exemplarily 0.25, 0.3, 0.35, 0.4 or 0.45, but not limited thereto; the thickness is 2nm~5nm, exemplarily 2.5nm, 3nm, 3.5nm, 4nm or 4.5nm, but not limited thereto; the third GaN barrier layer 632 is a Si-doped GaN barrier layer with a Si doping concentration of 1×10⁻⁶. 17 atoms / cm 3 ~5×10 18 atoms / cm 3 An example is 2.5 × 10 17 atoms / cm 3 5×10 17 atoms / cm 3 6×10 17 atoms / cm 3 7.5×10 17 atoms / cm 3 Or 1×10 18 atoms / cm 3 However, it is not limited to this; the thickness is 5nm to 20nm, with examples of 8nm, 10nm, 12nm, 15nm, or 18nm, but it is not limited to this. Preferably, In c Ga 1-cThe thickness of the N-well layer 631 is 2nm~4nm, and the thickness of the third GaN barrier layer 632 is 8nm~13nm.

[0030] The third quantum well layer 65 is grown with alternating growth cycles of 3 to 6, exemplarily 4 or 5. d Ga 1-d The In composition ratio d of the N-well layer 651 is 0.2~0.5, exemplarily 0.25, 0.3, 0.35, 0.4 or 0.45, but not limited thereto; the thickness is 2nm~5nm, exemplarily 2.5nm, 3nm, 3.5nm, 4nm or 4.5nm, but not limited thereto; the fourth GaN barrier layer 652 is a Si-doped GaN barrier layer with a Si doping concentration of 1×10⁻⁶. 17 atoms / cm 3 ~5×10 18 atoms / cm 3 An example is 2.5 × 10 17 atoms / cm 3 5×10 17 atoms / cm 3 6×10 17 atoms / cm 3 7.5×10 17 atoms / cm 3 Or 1×10 18 atoms / cm 3 However, it is not limited to this; the thickness is 5nm to 20nm, with examples of 8nm, 10nm, 12nm, 15nm, or 18nm, but it is not limited to this. Preferably, In d Ga 1-d The thickness of the N-well layer 651 is 2nm~4nm, and the thickness of the fourth GaN barrier layer 652 is 8nm~13nm.

[0031] Furthermore, the GaN-based blue-green LED epitaxial structure may also include a hole injection layer and a contact layer. Specifically, the hole injection layer is disposed between the third quantum well layer 65 and the electron blocking layer 7. The hole injection layer is a low-temperature P-GaN layer with a thickness of 10nm~100nm, exemplary of 20nm, 40nm, 50nm, 60nm or 80nm, but not limited to these, and the Mg doping concentration is 1×10⁻⁶. 18 atoms / cm 3 ~1×10 21 atoms / cm 3 An example is 2.5 × 10 17 atoms / cm 3 5×10 17 atoms / cm 36×10 17 atoms / cm 3 7.5×10 17 atoms / cm 3 Or 9×10 17 atoms / cm 3 However, this is not the only possibility. The hole injection layer can inject holes into the third quantum well layer 65, improving luminescence efficiency. A contact layer is disposed on the P-GaN layer 8. The contact layer is a heavily doped P-GaN layer with a thickness of 1 nm to 20 nm, exemplarily 8 nm, 10 nm, 12 nm, 15 nm, or 18 nm, but not limited to these. The Mg doping concentration is 1 × 10⁻⁶. 18 atoms / cm 3 ~1×10 22 atoms / cm 3 An example is 2.5 × 10 17 atoms / cm 3 5×10 17 atoms / cm 3 6×10 17 atoms / cm 3 7.5×10 17 atoms / cm 3 Or 9×10 17 atoms / cm 3 However, this is not the only benefit. The contact layer can optimize the ohmic contact between the epitaxial structure and the LED electrode.

[0032] In addition to the structure described above, the other layered structures of the present invention have the following characteristics: Substrate 1 can be a sapphire substrate, a silicon substrate, or a SiC substrate, but is not limited to these. A patterned sapphire substrate is preferred.

[0033] Buffer layer 2 can be an AlN layer or an AlGaN layer, but is not limited to these.

[0034] The 3D layer 3 can be a GaN layer with a thickness of 0.5 μm to 2 μm. The 3D layer 3 can cover the substrate pattern, reduce dislocation defects at the bottom of the epitaxial structure, release the bottom stress of the epitaxial structure, and thus improve the crystal quality of the subsequently grown epitaxial structure.

[0035] The thickness of U-GaN layer 4 is 0.5μm~2μm.

[0036] The N-GaN layer 5 can be a Si-doped GaN layer with a Si doping concentration of 1×10⁻⁶. 18 atoms / cm 3 ~1×10 21 atoms / cm 3The thickness is 0.5μm~1.5μm.

[0037] Electron blocking layer 7 can be a P-AlGaN layer with an Al content of 0.05~0.3%, a thickness of 20nm~130nm, and a Mg doping concentration of 1×10⁻⁶. 18 atoms / cm 3 ~1×10 21 atoms / cm 3 .

[0038] Among them, the P-GaN layer 8 can be a Mg-doped GaN layer with a Mg doping concentration of 5 × 10⁸. 18 atoms / cm 3 ~5×10 20 atoms / cm 3 The thickness is 10nm~150nm.

[0039] Correspondingly, such as Figure 4 As shown, this invention also discloses a method for fabricating a GaN-based blue-green LED epitaxial structure, which includes the following steps: S1, Provide a substrate 1.

[0040] S2. A buffer layer 2, a 3D layer 3, a U-GaN layer 4, an N-GaN layer 5, a multiple quantum well layer 6, an electron blocking layer 7, and a P-GaN layer 8 are sequentially grown on substrate 1. The epitaxial structure can be grown using MOCVD, MBE, PVD, or VPE, but is not limited to these methods. Specifically, S2 includes the following steps: S21. Grow a buffer layer 2 on substrate 1.

[0041] Specifically, in one embodiment, the buffer layer is an AlN buffer layer and an AlGaN buffer layer stacked sequentially, and the growth of the buffer layer includes the following steps: The AlN buffer layer was grown by PVD at a temperature of 500℃~700℃ and a power of 2500W~5000W. During growth, Ar was used as the sputtering gas, N2 as the precursor, and Al as the sputtering target. Then, the layer was treated in an H2 atmosphere or N2 atmosphere at a temperature of 1000℃~1200℃ for a time of 1min~10min.

[0042] AlGaN buffer layers were grown on AlN buffer layers by MOCVD at growth temperatures of 500℃~900℃, growth pressures of 100 torr~600 torr, and V / III ratios of 50~1000.

[0043] S22. Grow a 3D layer 3 on the buffer layer 2.

[0044] Specifically, in one embodiment, a 3D layer is grown by MOCVD at a growth temperature of 700℃~950℃, a growth pressure of 100 torr~400 torr, and a V / III ratio of 800~2000.

[0045] S23. Grow a U-GaN layer 4 on the 3D GaN layer 3.

[0046] Specifically, in one embodiment, a U-GaN layer is grown by MOCVD at a growth temperature of 1050℃~1250℃, a growth pressure of 150 torr~500 torr, and a V / III ratio of 800~2500.

[0047] S24. Grow an N-GaN layer 5 on the U-GaN layer 4.

[0048] Specifically, in one embodiment, an N-GaN layer is grown by MOCVD at a growth temperature of 1050℃~1150℃, a growth pressure of 150 torr~500 torr, and a V / III ratio of 500~2500.

[0049] S25. A multi-quantum well layer 6 is grown on the N-GaN layer 5.

[0050] Specifically, in one embodiment, the multi-quantum-well layer 6 includes a shallow well transition layer 61, a first quantum well layer 62, a second quantum well layer 63, a stress-relieving layer 64, and a third quantum well layer 65 stacked sequentially. The growth of the multi-quantum-well layer 6 includes the following steps: S251. A shallow well transition layer 61 is grown on the N-GaN layer 5.

[0051] In through periodic growth via MOCVD a Ga 1-a The process continues with an N-well layer and a first GaN barrier layer until a shallow well transition layer is obtained. Specifically, In... a Ga 1-a The growth temperature of the N-type well layer is 750℃~950℃, the growth pressure is 100 torr~500 torr, and the V / III ratio is 500~10000; the growth temperature of the first GaN barrier layer is 750℃~950℃, the growth pressure is 100 torr~500 torr, and the V / III ratio is 500~10000.

[0052] S252. Grow the first quantum well layer 62 on the shallow well transition layer 61.

[0053] In through periodic growth via MOCVD b Ga 1-b The process continues with an N-type potential well layer and a second GaN barrier layer until the first quantum well layer is obtained. Specifically, In... b Ga1-b The growth temperature of the N-type potential well layer is 750℃~950℃, the growth pressure is 100 torr~500 torr, and the V / III ratio is 2000~20000; the growth temperature of the second GaN barrier layer is 750℃~1000℃, the growth pressure is 100 torr~500 torr, and the V / III ratio is 2000~20000.

[0054] S253, Grow a second quantum well layer 63 on the first quantum well layer 62.

[0055] In through periodic growth via MOCVD c Ga 1-c The process continues with an N-type potential well layer and a third GaN barrier layer until a second quantum well layer is obtained. Specifically, In... c Ga 1-c The growth temperature of the N-type potential well layer is 700℃~850℃, the growth pressure is 100 torr~500 torr, and the V / III ratio is 2000~20000; the growth temperature of the third GaN barrier layer is 800℃~950℃, the growth pressure is 100 torr~500 torr, and the V / III ratio is 2000~20000.

[0056] S254. A stress-relieving layer 64 is grown on the second quantum well layer 63.

[0057] AlGaN layers are periodically grown by MOCVD, or AlN and GaN layers are periodically grown until a stress-relieving layer is obtained.

[0058] In one embodiment, an AlGaN layer is grown by MOCVD at a growth temperature of 700°C to 950°C, a growth pressure of 100 torr to 500 torr, and a V / III ratio of 2000 to 20000.

[0059] In another embodiment, AlN and GaN layers are periodically grown by MOCVD. The growth temperature of the AlN layer is 700℃~850℃, the growth pressure is 100 torr~500 torr, and the V / III ratio is 2000~20000. The growth temperature of the GaN layer is 800℃~950℃, the growth pressure is 100 torr~500 torr, and the V / III ratio is 2000~20000.

[0060] S255, A third quantum well layer 65 is grown on the stress relief layer 64.

[0061] In through periodic growth via MOCVD d Ga 1-d The process continues with an N-type quantum well layer and a fourth GaN barrier layer, until the third quantum well layer is obtained. Specifically, In... d Ga1-d The growth temperature of the N-type potential well layer is 700℃~850℃, the growth pressure is 100 torr~500 torr, and the V / III ratio is 2000~20000; the growth temperature of the fourth GaN barrier layer is 800℃~950℃, the growth pressure is 100 torr~500 torr, and the V / III ratio is 2000~20000.

[0062] S26, an electron blocking layer 7 on the multi-quantum well layer 6.

[0063] Specifically, in one embodiment, a P-AlGaN layer is grown by MOCVD as an electron blocking layer at a growth temperature of 900℃~1000℃, a growth pressure of 50 torr~300 torr, and a V / III ratio of 500~10000.

[0064] S27. Grow a P-GaN layer 8 on the electron blocking layer 7.

[0065] Specifically, in one embodiment, a P-GaN layer is grown by MOCVD at a growth temperature of 850°C to 1050°C, a growth pressure of 100 torr to 500 torr, and a V / III ratio of 500 to 3500.

[0066] In a preferred embodiment, a hole injection layer is further grown on the multi-quantum well layer 6.

[0067] Specifically, in one embodiment, a low-temperature P-GaN layer is grown by MOCVD as a hole injection layer, with a growth temperature of 650℃~850℃, a growth pressure of 100 torr~500 torr, and a V / III ratio of 500~10000.

[0068] In a preferred embodiment, a contact layer is further grown on the P-GaN layer 8.

[0069] Specifically, in one embodiment, a heavily doped P-GaN layer is grown by MOCVD as a contact layer, with a growth temperature of 650°C to 950°C, a growth pressure of 100 torr to 500 torr, and a V / III ratio of 10000 to 20000.

[0070] The present invention will be further described below with reference to specific embodiments: Example 1 This embodiment provides a GaN-based blue-green LED epitaxial structure, including a substrate and a buffer layer, a 3D layer, a U-GaN layer, an N-GaN layer, a multiple quantum well layer, an electron blocking layer and a P-GaN layer sequentially stacked on the substrate.

[0071] The substrate is sapphire. The buffer layer consists of an AlN buffer layer and an AlGaN buffer layer stacked sequentially on the substrate. The AlN buffer layer has a thickness of 17 nm, and the AlGaN buffer layer has a thickness of 25 nm. The 3D layers are GaN layers with a thickness of 1.5 μm, U-GaN layers with a thickness of 1.5 μm, and N-GaN layers with a thickness of 2 μm. The Si doping concentration is 5.5 × 10⁻⁶. 19 atoms / cm 3 .

[0072] The multi-quantum-well layer comprises a shallow well transition layer, a first quantum well layer, a second quantum well layer, a stress-relieving layer, and a third quantum well layer stacked sequentially.

[0073] The shallow well transition layer has a periodic structure with three periods, each period consisting of sequentially stacked In layers. 0.1 Ga 0.9 N-potential well layer and first GaN barrier layer, In 0.1 Ga 0.9 The thickness of the N-well layer is 3.5 nm, the thickness of the first GaN barrier layer is 35 nm, and the Si doping concentration is 7.5 × 10⁻⁶. 17 atoms / cm 3 .

[0074] The first quantum well layer has a periodic structure with 6 periods, and each period consists of sequentially stacked In... 0.2 Ga 0.8 N-potential well layer and second GaN barrier layer, In 0.2 Ga 0.8 The thickness of the N-well layer is 2 nm, the thickness of the second GaN barrier layer is 10 nm, and the Si doping concentration is 1 × 10⁻⁶. 17 atoms / cm 3 .

[0075] The second quantum well layer has a periodic structure with 6 periods, and each period consists of sequentially stacked In... 0.25 Ga 0.75 N-potential well layer and third GaN barrier layer, In 0.25 Ga 0.75 The thickness of the N-well layer is 3.5 nm, the thickness of the third GaN barrier layer is 11 nm, and the Si doping concentration is 5 × 10⁻⁶. 17 atoms / cm 3 .

[0076] The stress relief layer has a periodic structure with 5 periods, each period consisting of sequentially stacked AlN and GaN layers. The AlN layer has a thickness of 1 nm, and the GaN layer has a thickness of 1 nm.

[0077] The third quantum well layer has a periodic structure with four periods, each period consisting of sequentially stacked In... 0.25 Ga 0.75 N-potential well layer and fourth GaN barrier layer, In 0.25 Ga 0.75 The thickness of the N-well layer is 3.5 nm, the thickness of the fourth GaN barrier layer is 11 nm, and the Si doping concentration is 5 × 10⁻⁶. 17 atoms / cm 3 .

[0078] The electron blocking layer is a P-AlGaN layer with an Al content of 0.25%, a thickness of 35 nm, and a Mg doping concentration of 1.3 × 10⁻⁶. 18 atoms / cm 3 .

[0079] The P-GaN layer is 20 nm thick, and the Mg doping concentration is 3.2 × 10⁻⁶. 19 atoms / cm 3 .

[0080] The fabrication method of the GaN-based blue-green LED epitaxial structure in this embodiment is as follows: (1) Provide a substrate.

[0081] (2) An AlN buffer layer was grown on the substrate using PVD at a growth temperature of 540℃ and a power of 4300W. During growth, Ar was used as the sputtering gas, N2 as the precursor, and Al as the sputtering target. After growth, the substrate was loaded into an MOCVD machine and treated at 1150℃ for 2 minutes in an N2 atmosphere. Then, an AlGaN buffer layer was grown at 750℃, 400 torr, and a V / III ratio of 250.

[0082] (3) The 3D layer was grown at 900℃, 200 torr, and V / Ⅲ ratio of 800.

[0083] (4) U-GaN layers were grown at 1150℃, 300 torr, and a V / Ⅲ ratio of 1000.

[0084] (5) N-GaN layers were grown at 1100℃, 300 torr, and V / III ratio of 1000.

[0085] (6) In was grown at 900℃, 300 torr, and a V / III ratio of 10000. 0.1 Ga 0.9 An N-type well layer is formed, and then the first GaN barrier layer is grown at 950℃, 300 torr, and a V / Ⅲ ratio of 10000. This process is repeated for three cycles to grow a shallow well transition layer.

[0086] In was grown at 800℃, 300 torr, and a V / III ratio of 10000. 0.2 Ga 0.8 An N-type quantum well layer is formed, and then a second GaN barrier layer is grown at 900°C, 300 torr, and a V / III ratio of 10000. This process is repeated for six cycles to grow the first quantum well layer.

[0087] In was grown at 780℃, 300 torr, and a V / III ratio of 10000. 0.25 Ga 0.75 An N-type quantum well layer is formed, and then a third GaN barrier layer is grown at 850 °C, 300 torr, and a V / Ⅲ ratio of 10000. This process is repeated for six cycles to grow a second quantum well layer.

[0088] An AlN layer was grown at 800℃, 300 torr, and a V / III ratio of 10000. Then, a GaN layer was grown at 800℃, 300 torr, and a V / III ratio of 10000. This cyclic growth process was repeated for 5 cycles to grow a stress-relief layer.

[0089] In was grown at 780℃, 300 torr, and a V / III ratio of 10000. 0.25 Ga 0.75 An N-type quantum well layer is formed, and then a fourth GaN barrier layer is grown at 850 °C, 300 torr, and a V / Ⅲ ratio of 10000. This process is repeated for four cycles to grow the third quantum well layer.

[0090] (7) P-AlGaN layers were grown at 900℃, 200 torr, and V / III ratio of 800.

[0091] (8) A P-GaN layer was grown at 950℃, 300 torr, and V / Ⅲ ratio of 1200, and then annealed at 800℃ for 5 min to obtain the final product.

[0092] Example 2 This embodiment provides a GaN-based blue-green LED epitaxial structure, which differs from Embodiment 1 in that the GaN layer in the stress relief layer is a Si-doped GaN layer with a Si doping concentration of 2 × 10⁻⁶. 18 atoms / cm 3 Everything else is the same as in Example 1.

[0093] Example 3 This embodiment provides a GaN-based blue-green LED epitaxial structure, which differs from Embodiment 1 in that the stress relief layer is an AlGaN layer, with the Al content increasing from 0.15 to 0.25 along the epitaxial growth direction, and a thickness of 10 nm. Correspondingly, the stress relief layer is prepared by growing it at 800°C, 300 torr, and a V / III ratio of 10000. All other conditions are the same as in Embodiment 1.

[0094] Comparative Example 1 This comparative example provides a GaN-based blue-green LED epitaxial structure, which differs from Example 1 in that it does not include a stress-relieving layer. Correspondingly, the fabrication method does not include the preparation of the stress-relieving layer. All other aspects are the same as in Example 2.

[0095] Comparative Example 2 This comparative example provides a GaN-based blue-green LED epitaxial structure, which differs from Example 1 in that a stress relief layer is disposed between the first quantum well layer and the second quantum well layer. Correspondingly, the fabrication method of the multiple quantum well layers includes sequentially growing a shallow well transition layer, a first quantum well layer, a stress relief layer, a second quantum well layer, and a third quantum well layer. The rest is the same as in Example 2.

[0096] Comparative Example 3 This comparative example provides a GaN-based blue-green LED epitaxial structure, which differs from Example 1 in that the second quantum well layer has 4 periods and the third quantum well layer has 6 periods. All other aspects are the same as in Example 1.

[0097] The epitaxial structures obtained in Examples 1-3 and Comparative Examples 1-3 were fabricated into 55mil × 55mil flip-chip structures. The chips were lit up at a test current of 700mA, and their luminous intensity was measured. Simultaneously, their turn-on voltage Vf was measured at 1μA. The specific results are shown in the table below:

[0098] The above description is a preferred embodiment of the invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the invention, and these improvements and modifications are also considered to be within the scope of protection of the invention.

Claims

1. A GaN-based blue-green LED epitaxial structure, characterized in that, It includes a substrate and a buffer layer, a 3D layer, a U-GaN layer, an N-GaN layer, a multiple quantum well layer, an electron blocking layer and a P-GaN layer sequentially stacked on the substrate; The multi-quantum-well layer comprises a shallow-well transition layer, a first quantum well layer, a second quantum well layer, a stress-relieving layer, and a third quantum well layer stacked sequentially. The growth temperature of the first quantum well layer is greater than that of the second quantum well layer and also greater than that of the third quantum well layer. The number of alternating stacking periods of the second quantum well layer is greater than that of the third quantum well layer. The stress-relieving layer is an AlGaN layer or a periodically alternating stack of AlN and GaN layers.

2. The GaN-based blue-green LED epitaxial structure as described in claim 1, characterized in that, The stress relief layer is a Si-doped AlGaN layer with a thickness of 2nm~20nm and a Si doping concentration of 1×10⁻⁶. 16 atoms / cm 3 ~1×10 19 atoms / cm 3 Along the epitaxial growth direction, the proportion of Al component increases from 0.15 to 0.

25.

3. The GaN-based blue-green LED epitaxial structure as described in claim 1, characterized in that, The stress relief layer is a periodically alternating stack of AlN and GaN layers, with 2 to 10 alternating stacking periods. The thickness of the AlN layer is 1 nm to 10 nm, and the thickness of the GaN layer is 1 nm to 10 nm. The GaN layer is a Si-doped GaN layer with a Si doping concentration of 1×10⁻⁶. 16 atoms / cm 3 ~1×10 19 atoms / cm 3 .

4. The GaN-based blue-green LED epitaxial structure as described in claim 1, characterized in that, The shallow well transition layer comprises periodically alternating layers of In. a Ga 1-a An N-type quantum well layer and a first GaN barrier layer; the first quantum well layer comprises periodically alternating layers of In. b Ga 1-b An N-type quantum well layer and a second GaN barrier layer; the second quantum well layer comprises periodically alternating layers of In. c Ga 1-c An N-type quantum well layer and a third GaN barrier layer; the third quantum well layer comprises periodically alternating layers of In. d Ga 1-d The N-type potential well layer and the fourth GaN potential barrier layer; wherein, 0.01≤a≤b≤c≤d≤0.

5.

5. The GaN-based blue-green LED epitaxial structure as described in claim 4, characterized in that, The growth temperature of the second quantum well layer is equal to the growth temperature of the third quantum well layer.

6. The GaN-based blue-green LED epitaxial structure as described in claim 4, characterized in that, The shallow well transition layers have an alternating stacking period of 1 to 20, a of 0.01 to 0.1, and a thickness of 1 nm to 5 nm. The first GaN barrier layer is a Si-doped GaN barrier layer with a Si doping concentration of 5 × 10⁻⁶. 17 atoms / cm 3 ~5×10 19 atoms / cm 3 The thickness is 10nm~50nm; The first quantum well layer has an alternating stacked period of 1 to 20, a b of 0.1 to 0.2, and a thickness of 1 nm to 5 nm. The second GaN barrier layer is a Si-doped GaN barrier layer with a Si doping concentration of 5 × 10⁻⁶. 16 atoms / cm 3 ~5×10 18 atoms / cm 3 The thickness is 5nm~30nm; The second quantum well layer has an alternating stacked period of 6-20, c of 0.2-0.5, and a thickness of 2nm-5nm. The third GaN barrier layer is a Si-doped GaN barrier layer with a Si doping concentration of 1×10⁻⁶. 17 atoms / cm 3 ~5×10 18 atoms / cm 3 The thickness is 5nm~20nm. The third quantum well layer has an alternating stacked period of 3-6, a d of 0.2-0.5, and a thickness of 2nm-5nm. The fourth GaN barrier layer is a Si-doped GaN barrier layer with a Si doping concentration of 1×10⁻⁶. 17 atoms / cm 3 ~5×10 18 atoms / cm 3 The thickness is 5nm~20nm.

7. A method for fabricating a GaN-based blue-green LED epitaxial structure, used to fabricate the GaN-based blue-green LED epitaxial structure as described in any one of claims 1 to 6, characterized in that, Includes the following steps: A substrate is provided on which a buffer layer, a 3D layer, a U-GaN layer, an N-GaN layer, a multiple quantum well layer, an electron blocking layer and a P-GaN layer are sequentially grown. The multi-quantum-well layer comprises a shallow-well transition layer, a first quantum well layer, a second quantum well layer, a stress-relieving layer, and a third quantum well layer stacked sequentially. The growth temperature of the first quantum well layer is greater than that of the second quantum well layer and also greater than that of the third quantum well layer. The number of alternating stacking periods of the second quantum well layer is greater than that of the third quantum well layer. The stress-relieving layer is an AlGaN layer or a periodically alternating stack of AlN and GaN layers.

8. The method for fabricating the GaN-based blue-green LED epitaxial structure as described in claim 7, characterized in that, The stress relief layer is grown at a temperature of 700℃ to 950℃, a growth pressure of 100 torr to 500 torr, and a V / III ratio of 2000 to 20000.

9. The method for fabricating the GaN-based blue-green LED epitaxial structure as described in claim 7, characterized in that, In the shallow well transition layer, the In a Ga 1-a The growth temperature of the N-well layer is 750℃~950℃, the growth pressure is 100 torr~500 torr, and the V / III ratio is 500~10000; the growth temperature of the first GaN barrier layer is 750℃~950℃, the growth pressure is 100 torr~500 torr, and the V / III ratio is 500~10000. In the first quantum well layer, the In b Ga 1-b The growth temperature of the N-type well layer is 750℃~950℃, the growth pressure is 100 torr~500 torr, and the V / III ratio is 2000~20000; the growth temperature of the second GaN barrier layer is 750℃~1000℃, the growth pressure is 100 torr~500 torr, and the V / III ratio is 2000~20000. In the second quantum well layer, the In c Ga 1-c The growth temperature of the N-type potential well layer is 700℃~850℃, the growth pressure is 100 torr~500 torr, and the V / III ratio is 2000~20000; the growth temperature of the third GaN barrier layer is 800℃~950℃, the growth pressure is 100 torr~500 torr, and the V / III ratio is 2000~20000. In the third quantum well layer, the In d Ga 1-d The growth temperature of the N-type potential well layer is 700℃~850℃, the growth pressure is 100 torr~500 torr, and the V / III ratio is 2000~20000; the growth temperature of the fourth GaN barrier layer is 800℃~950℃, the growth pressure is 100 torr~500 torr, and the V / III ratio is 2000~20000.

10. A GaN-based blue-green LED, characterized in that, Including the GaN-based blue-green LED epitaxial structure as described in any one of claims 1 to 6.

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