Blue-green double-wave epitaxial structure and growth method thereof

Abstract

The invention discloses a blue-green double-wave epitaxial structure and a growth method thereof. The method aims at solving the problems that in the prior art, a blue light trap crystal is poor in quality, the overall luminous intensity is low, and the blue-green peak intensity ratio is uncontrollable. The method comprises the following steps: growing a high-temperature front-stage well on an N-type GaN layer; growing a first active region on the high-temperature preceding-stage well; growing a stress release layer on the first active region; and growing a second active region on the stress release layer. The high-temperature preceding stage trap is arranged in front of the green light trap to inhibit a V-shaped pit and improve the growth quality of the green light trap, the low-temperature and large-thickness stress release layer is arranged between the green light trap and the blue light trap to prevent dislocation from entering the blue light trap, and hole injection of the green light trap and the blue light trap is cooperatively regulated and controlled. According to the invention, the overall luminous intensity of the device can be obviously improved, and the blue-green peak intensity ratio can be effectively regulated and controlled.

Description

Technical Field

[0001] This invention relates to the field of semiconductor optoelectronic technology, and in particular to a blue-green dual-wave epitaxial structure of a GaN-based light-emitting diode (LED) and its growth method. Background Technology

[0002] GaN-based light-emitting diodes (LEDs) have been widely used in general lighting, backlighting displays, automotive lighting, and other fields due to their high efficiency in electro-optical conversion, high brightness, long lifespan, and low energy consumption. With increasing attention to lighting quality and visual health, such as to meet the needs of healthy lighting and reduce the potential harm of high-energy blue light to the human eye, developing LED technologies with superior spectral characteristics has become an important development direction, giving rise to blue-green dual-wave, triple-wave, and even full-spectrum LED technologies.

[0003] Among them, blue-green dual-wave LEDs integrate two active regions with different indium (In) contents in a single epitaxial structure to emit blue light and green light respectively, thereby achieving blue-green dual-color light emission. They are often used to build lighting systems with high color rendering index (CRI) or backlight systems with wide color gamut (WCG).

[0004] like Figure 1 As shown, a mainstream blue-green dual-wave LED epitaxial structure consists of an N-type GaN layer, a stress-relieving layer, a high-indium green quantum well (MQW1), a low-indium blue quantum well (MQW2), and a P-type layer, which are grown sequentially along the epitaxial growth direction.

[0005] However, this existing technical solution has the following significant drawbacks: 1. Poor crystal quality and insufficient luminescence intensity: Due to the high indium content, the high-indium green light trap (MQW1) typically requires a lower growth temperature, which inevitably leads to significant piezoelectric polarization and high density of lattice defects (such as dislocations). When a blue light trap (MQW2) is subsequently grown on it, these dislocations originating from the green light trap continue to extend upwards, resulting in an increased defect density and a sharp deterioration in crystal quality in the blue light trap (MQW2). This results in a severe deficiency in the internal quantum efficiency (IQE) and luminescence intensity of the blue light trap, ultimately affecting the overall luminescence performance of the chip.

[0006] 2. Uncontrollable blue-green peak intensity ratio (BGR): In Figure 1In this structure, the stress-relieving layer preceding the green light trap is typically also the layer forming V-pits. The opening of the V-pits gradually increases in size along the growth direction with increasing thickness. During electroluminescence in the device, the hole injection depth is highly sensitive to the morphology of the V-pits and varies with the applied current. This leads to an unstable hole distribution ratio between the green and blue light traps, ultimately causing an uncontrollable shift in the peak intensity ratio of green and blue light, making it difficult to meet the spectral stability requirements of different application scenarios.

[0007] Therefore, in view of the technical problems of poor blue light trap crystal quality, insufficient overall luminescence intensity, and uncontrollable blue-green peak intensity ratio in the above-mentioned background technology, there is an urgent need to provide a novel epitaxial growth method for blue-green dual-wave epitaxial structures. Summary of the Invention

[0008] The primary objective of this invention is to provide a method for growing blue-green dual-wave epitaxial structures, aiming to solve the technical problems in the prior art, such as poor crystal quality and low luminous intensity of blue light traps due to dislocation extension in green light traps, and uncontrollable blue-green peak intensity ratio due to improper control of V-shaped pit morphology.

[0009] The second objective of this invention is to provide a blue-green dual-wave epitaxial structure prepared by the above method.

[0010] To achieve the above objectives, the present invention provides the following technical solution: On one hand, the present invention provides a method for epitaxial growth of a blue-green dual-wave epitaxial structure, characterized in that the method includes the following steps: A high-temperature front-end well is grown on an N-type GaN layer; A first active region is grown on the high-temperature front-end well, and the first active region is adapted to emit green light; A stress-relieving layer is grown on the first active region; A second active region is grown on the stress-relieving layer, the second active region being adapted to emit blue light.

[0011] Preferably, the step of growing the high-temperature pre-well includes: a well growth temperature of 820 °C to 840 °C; and / or a barrier growth temperature of 900 °C to 950 °C.

[0012] Preferably, the high-temperature pre-stage well has a well thickness of 1.0 nm to 2.2 nm; the high-temperature pre-stage well has a barrier thickness of 15 nm to 18 nm; and / or, the Si doping concentration of the barrier of the high-temperature pre-stage well is 3.5 × 10⁻⁶. 18 cm -3 Up to 4.5 × 10 18 cm -3 .

[0013] Preferably, the step of growing the stress-relieving layer includes: growing at a growth temperature of 700 °C to 880 °C; and / or, the thickness of the stress-relieving layer is 400 nm to 700 nm; and / or, the growth pressure is 200 TORR.

[0014] Preferably, the stress relief layer is used to transform dislocations from the first active region and / or below it into V-shaped pits to reduce the dislocation density entering the second active region.

[0015] Preferably, the stress relief layer is also used to increase the opening of the V-shaped pit formed during the growth of the first active region, so as to increase the hole injection capability of the first active region.

[0016] Preferably, the thickness of the stress relief layer is set according to a predetermined application current to regulate the peak intensity ratio between the first active region and the second active region.

[0017] On the other hand, the present invention provides a blue-green dual-wave epitaxial structure, characterized in that the structure comprises, along the epitaxial growth direction, the following components in sequence: N-type GaN layer; High-temperature front-end well disposed on the N-type GaN layer; A first active region is disposed on the high-temperature front end well, the first active region being adapted to emit green light; A stress relief layer disposed on the first active region; A second active region is disposed on the stress relief layer, the second active region being adapted to emit blue light.

[0018] Preferably, the high-temperature pre-stage trap has a trap thickness of 1.0 nm to 2.2 nm and a barrier thickness of 15 nm to 18 nm; and / or, the stress relief layer has a thickness of 400 nm to 700 nm.

[0019] Preferably, the structure further includes an LTP layer (Low Temperature P-GaN), an EBL (electron blocking layer), a P-GaN layer, and a P-GaN contact layer sequentially disposed on the second active region.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Improved Overall Luminescence Intensity: This invention enhances the crystal quality and luminescence efficiency of the two active regions through a dual defect management mechanism. First, a high-temperature pre-MQW is introduced before the green light trap (MQW1). Utilizing the high atomic migration rate during high-temperature growth (820℃ to 950℃), the formation of V-shaped pits is effectively suppressed, and some stress is released, providing a high-quality C-plane growth substrate for MQW1, thereby enhancing the photoluminescence intensity of MQW1 itself. Second, a stress-relieving layer (SRL) is placed between MQW1 and MQW2, and grown at a low temperature (700℃ to 880℃) and a large thickness (400nm to 700nm). This SRL layer acts as a "dislocation barrier," intentionally transforming dislocations extending from the bottom layer and MQW1 into V-shaped pits, causing the dislocations to terminate at the sidewalls of the V-shaped pits. This effectively prevents dislocations from entering the upper blue light trap (MQW2), significantly reducing nonradiative recombination in MQW2 and improving the internal quantum efficiency of blue light.

[0021] 2. Effective control of the blue-green peak intensity ratio (BGR) is achieved: This invention places the SRL between two active regions, enabling it to synergistically control hole injection. On one hand, during growth, the SRL further enlarges the opening of the V-shaped pit formed by MQW1, enhancing the hole injection capability into MQW1 and increasing green light intensity. On the other hand, the V-shaped pit formed by the SRL also provides a hole injection path for MQW2. More importantly, the uncontrollable BGR drift problem in the prior art is solved. In this invention, the thickness of the SRL layer (400nm to 700nm) becomes an active, designable, and controllable parameter. By adjusting this thickness, the geometry of the V-shaped pit can be precisely controlled, thereby controlling the hole injection ratio in MQW1 and MQW2. This allows the blue-green peak intensity ratio to be preset and optimized according to the target application current, achieving stable and controllable BGR characteristics. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of a blue-green dual-wave epitaxial structure in the prior art.

[0023] Figure 2 This is a schematic diagram of the blue-green dual-wave epitaxial structure of the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the following description will be provided in conjunction with the appendix. Figure 2 The present invention will be described in further detail below.

[0025] It should be understood that the specific embodiments of the present invention are for illustrative purposes only and are not intended to limit the invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0026] Example

[0027] This embodiment provides a method for epitaxial growth of a blue-green dual-wave epitaxial structure, such as... Figure 2 As shown, epitaxial growth is performed on a PSS sapphire substrate using a metal-organic chemical vapor deposition (MOCVD) system. The method specifically includes the following steps: Step S1: Provide a PSS sapphire substrate 100 and grow a conventional LED structure thereon, including a buffer layer 200, a U-GaN (undoped gallium nitride) layer 300 up to an N-GaN (N-type GaN) layer 400.

[0028] Step S2: On the N-type GaN layer, a high-temperature pre-well (PreMQW) 500 is epitaxially grown.

[0029] The growth parameters of the high-temperature pre-well are as follows: MO source: TEGa (triethylgallium) and TMIn (trimethylindium) are used as metal sources.

[0030] Trap growth: The trap thickness is preferably 1.0 nm to 2.2 nm, and 1.8 nm can be selected in this embodiment; the trap growth temperature is preferably 820 ℃ to 840 ℃, and 830 ℃ can be selected in this embodiment.

[0031] Barrier growth: The barrier thickness is preferably 15 nm to 18 nm, and 17 nm can be selected in this embodiment; the barrier growth temperature is preferably 900 ℃ to 950 ℃, and 930 ℃ can be selected in this embodiment; the Si doping concentration of the barrier is preferably 3.5 × 10⁻⁶. 18 cm -3 Up to 4.5 × 10 18 cm -3 In this embodiment, 4.0 × 10 can be selected. 18 cm -3 .

[0032] This high-temperature growth step takes advantage of the high atomic migration rate at high temperatures, making it less likely for V-shaped pits to form due to accumulation. At the same time, it releases some stress, providing a high-quality C-face for the subsequent growth of MQW1, which is beneficial for enhancing the intensity of green light.

[0033] Step S3: On the high-temperature pre-stage well (PreMQW), grow the first active region (MQW1) 600, which is a green quantum well with high indium composition.

[0034] Step S4: On the first active region (MQW1), an epitaxial stress relief layer (SRL) 700 is grown.

[0035] The growth parameters of the stress relief layer are as follows: Growth method: Low temperature growth.

[0036] MO source: TMGa (trimethylgallium) and TMIn (trimethylindium) are used as metal sources.

[0037] Carrier gas: N2.

[0038] Reacting gas: NH3.

[0039] Growth temperature: preferably 700 ℃ to 880 ℃, and 760 ℃ can be selected in this embodiment.

[0040] Thickness: preferably 400 nm to 700 nm, and 550 nm can be selected in this embodiment.

[0041] Growth stress: preferably 200 TORR.

[0042] This step is crucial to the invention. This low-temperature, thick SRL layer plays multiple synergistic roles: (a) transforming dislocations from MQW1 and the underlying layer into V-shaped pits, preventing them from entering MQW2 and reducing nonradiative recombination in MQW2; (b) increasing the opening of existing V-shaped pits on MQW1, enhancing hole injection into MQW1, and increasing green light emission intensity; and (c) providing additional hole injection paths for MQW2.

[0043] Specifically, the thickness (400nm to 700nm) can be adjusted according to the target application current of the chip. If the target application current is large, the thickness can be adjusted appropriately to optimize the blue-green peak intensity ratio at high current.

[0044] Step S5: On the stress relief layer (SRL), a second active region (MQW2) 800, i.e., a blue light trap with low indium composition, is grown. Due to the dislocation barrier effect of the SRL, the MQW2 grown in this step has a lower defect density and higher crystal quality.

[0045] Step S6: On the second active region (MQW2), LTP layer 900, EBL 1000, P-GaN layer 1100 and P-GaN contact layer 1200 are grown sequentially to complete the growth of the epitaxial structure.

[0046] Step S7: Standard chip fabrication processes can then be performed, such as fabricating P electrodes on the P-GaN contact layer and N electrodes on the N-GaN layer. This epitaxial structure can be used to fabricate either conventional or flip-chip chips.

[0047] The blue-green dual-wave LED device prepared using the method of this embodiment is superior to existing technologies ( Figure 1 The device described above exhibits significant improvements in blue light quantum efficiency, overall luminous intensity, and stability of the blue-green peak intensity ratio. Table 1 compares the overall luminous intensity of existing devices and the device of this invention. Table 2 compares the peak intensity of the device of this invention.

[0048] Table 1 structure Blue light intensity / mW Green light intensity / mW Overall brightness / mW Figure 1 structure A * 1.0 B * 1.0 C * 1.0 Figure 2 structure A * 1.15 B * 1.05 C * 1.2 As can be seen from the comparative data in Table 1, compared with the existing technology structure ( Figure 1 The blue-green dual-wave epitaxial structure proposed in this invention (structure) Figure 2 The proposed structure achieves comprehensive improvements in blue light, green light, and overall brightness, with blue light brightness increased by approximately 15%, green light brightness by approximately 5%, and overall brightness by approximately 20%. This indicates that the invention significantly improves the luminous efficiency of both the upper and lower active regions by introducing a high-temperature pre-well before the green quantum well to improve the quality of the crystal growth substrate and by setting a low-temperature, thick stress-relieving layer between the green and blue quantum wells to effectively block dislocation propagation and optimize the hole injection path. In particular, the significant reduction in the defect density of the blue quantum well leads to a greater enhancement in its luminous intensity, further improving the overall luminous performance of the device. Therefore, the data in Table 1 fully demonstrate the significant overall improvement in optoelectronic performance of the proposed structure and its clear technological contribution.

[0049] The structure of this invention maintains a stable overall brightness within a wide current range of 0.9–1.1 over a wide current range of 30 mA to 150 mA, indicating high stability of the blue-green peak intensity ratio under different driving currents. Because this invention incorporates a stress-relieving layer of adjustable thickness between the two types of quantum wells, it can effectively stabilize the injection ratio of holes between the green and blue light wells by controlling the geometric opening of the V-shaped pits while suppressing dislocations, thus achieving consistency in spectral output under varying current. This spectral stability not only overcomes the inherent defect of blue-green peak intensity ratio drift with driving current in existing technologies but also makes the structure of this invention more suitable for lighting and display applications requiring high spectral consistency and stability. This fully demonstrates the significant advantages of this invention in terms of controllable blue-green peak intensity ratio and spectral stability.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for growing blue-green dual-wave epitaxial structures, characterized in that, The method includes the following steps: A high-temperature front-end well is grown on an N-type GaN layer; A first active region is grown on the high-temperature front-end well, and the first active region is adapted to emit green light; A stress-relieving layer is grown on the first active region; A second active region is grown on the stress-relieving layer, the second active region being adapted to emit blue light.

2. The method according to claim 1, characterized in that, The steps for growing the high-temperature pre-well include: The trap growth temperature is 820 °C to 840 °C; and / or, the barrier growth temperature is 900 °C to 950 °C.

3. The method according to claim 2, characterized in that, The high-temperature pre-well has a well thickness of 1.0 nm to 2.2 nm; the barrier thickness of the high-temperature pre-well is 15 nm to 18 nm; and / or, the Si doping concentration of the barrier of the high-temperature pre-well is 3.5 × 10⁻⁶. 18 cm -3 Up to 4.5 × 10 18 cm -3 .

4. The method according to any one of claims 1 to 3, characterized in that, The step of growing the stress-relieving layer includes: growing at a growth temperature of 700 °C to 880 °C; and / or having a thickness of 400 nm to 700 nm; and / or having a growth pressure of 200 TORR.

5. The method according to claim 1 or 4, characterized in that, The stress relief layer is used to transform dislocations from the first active region and / or below it into V-shaped pits, thereby reducing the dislocation density entering the second active region.

6. The method according to claim 1, 4, or 5, characterized in that, The stress relief layer is also used to increase the opening of the V-shaped pit formed during the growth of the first active region, so as to increase the hole injection capability of the first active region.

7. The method according to claim 4, characterized in that, The thickness of the stress relief layer is set according to a predetermined application current to regulate the peak intensity ratio between the first active region and the second active region.

8. A blue-green dual-wave epitaxial structure, characterized in that, The structure, along the epitaxial growth direction, comprises, in sequence: N-type GaN layer; High-temperature front-end well disposed on the N-type GaN layer; A first active region is disposed on the high-temperature front-end well, the first active region being adapted to emit green light; A stress relief layer disposed on the first active region; A second active region is disposed on the stress relief layer, the second active region being adapted to emit blue light.

9. The structure according to claim 8, characterized in that, The high-temperature pre-stage well has a well thickness of 1.0 nm to 2.2 nm and a barrier thickness of 15 nm to 18 nm; and / or, the stress relief layer has a thickness of 400 nm to 700 nm.

10. The structure according to claim 8 or 9, characterized in that, The structure further includes an LTP layer, an EBL layer, a P-GaN layer, and a P-GaN contact layer sequentially disposed on the second active region.

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