LED epitaxial structure and preparation method thereof, and LED chip

Abstract

The invention provides an LED epitaxial structure and a preparation method thereof, and an LED chip, and relates to the technical field of semiconductor devices, the LED epitaxial structure comprises a substrate, and a buffer layer, an undoped GaN layer, an N-type GaN layer, a multi-quantum well layer, an electron blocking layer and a P-type GaN layer which are stacked on the substrate, and the multi-quantum well layer comprises a shallow quantum well layer and a main quantum well layer stacked on the shallow quantum well layer; the shallow quantum well layer comprises InxGa (1-x) N quantum well layers and shallow quantum barrier layers which are periodically and alternately stacked, In components x of the InxGa (1-x) N quantum well layers are gradually increased layer by layer, the main quantum well layer comprises InyGa (1-y) N quantum well layers and main quantum barrier layers which are periodically and alternately stacked, in each InyGa (1-y) N quantum well layer, In components y are gradually decreased according to the growth direction, and in each main quantum well layer, In components y are gradually decreased according to the growth direction. The technical problem that in the prior art, an In-doped multi-quantum well layer can cause the piezoelectric polarization effect and the crystal quality to be reduced, and consequently the internal quantum effect is reduced can be solved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor device technology, specifically to an LED epitaxial structure and its fabrication method, and an LED chip. Background Technology

[0002] As the core of next-generation lighting and display technologies, light-emitting diodes (LEDs) have luminous efficacy (luminous efficiency) and reliability as key performance indicators. Especially in high-end display applications such as Micro-LED, extreme requirements are placed on the wavelength uniformity, luminous efficacy, and reliability of LED chips.

[0003] Currently, nitride LEDs are typically epitaxially grown on c-plane sapphire substrates using metal-organic chemical vapor deposition (MOCVD). Their multiple quantum well layers often employ InGaN / GaN multiple quantum well (MQW) structures. However, such structures present two inherent challenges: First, the piezoelectric polarization effect: Due to the lattice and thermal mismatch between the InGaN quantum well layer and the GaN quantum barrier layer, a strong piezoelectric polarization effect is generated in the c-plane direction, which in turn forms a huge built-in electric field in the quantum well (quantum confinement Stark effect, QCSE). This electric field causes the wave functions of electrons and holes to be spatially separated, reducing the probability of radiative recombination, thus leading to a decrease in the luminous efficiency of LEDs, especially in the long wavelength (such as green light) region, where this effect is more significant.

[0004] Second, there is the issue of crystal quality with high In content: To achieve longer emission wavelengths (such as green light), it is necessary to increase the indium (In) content in the quantum well. However, the lattice mismatch between the InGaN layer and the GaN layer is greater with high In content, which generates higher stress and easily induces nonradiative recombination centers such as dislocations and defects, seriously impairing the device's lifespan and internal quantum efficiency. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide an LED epitaxial structure and its fabrication method, as well as an LED chip, in order to solve the technical problem that In-doped multiple quantum well layers lead to piezoelectric polarization effects and reduced crystal quality, resulting in a decrease in internal quantum effects.

[0006] A first aspect of the present invention is to provide an LED epitaxial structure, the LED epitaxial structure comprising a substrate and an epitaxial layer stacked on the substrate, the epitaxial layer comprising, in sequence, a buffer layer, an undoped GaN layer, an N-type GaN layer, a multiple quantum well layer, an electron blocking layer, and a P-type GaN layer. The multi-quantum-well layer includes a shallow quantum-well layer and a main quantum-well layer stacked on the shallow quantum-well layer; The shallow quantum well layer comprises periodically alternating layers of In. x Ga （1-x） N-quantum well layer and shallow quantum barrier layer, the In x Ga （1-x） The In composition x of the N-type quantum well layer gradually increases from the side closer to the N-type GaN layer to the side farther away from the N-type GaN layer. The main quantum well layer includes periodically alternating layers of In. y Ga （1-y） The N-quantum well layer and the master quantum barrier layer, wherein the In y Ga （1-y） The In composition y of the N quantum well layer gradually decreases from the side closer to the shallow quantum well layer to the side farther away from the shallow quantum well layer.

[0007] According to one aspect of the above technical solution, the period of the shallow quantum well layer is 5~14, and the In x Ga （1-x） The In composition x of the N quantum well layer gradually increases from 0.02~0.03 to 0.10~0.12.

[0008] According to one aspect of the above technical solution, the period of the main quantum well layer is 5~15. When the main quantum well layer is used in the epitaxial structure of a blue LED, in each In... y Ga （1-y） In the N quantum well layer, the In composition y gradually decreases from 0.18~0.25 to 0.10~0.18; When the main quantum well layer is used in the epitaxial structure of a green LED, in each of the In... y Ga （1-y） In the N quantum well layer, the In composition y gradually decreases from 0.25~0.35 to 0.15~0.25.

[0009] According to one aspect of the above technical solution, both the shallow quantum barrier layer and the main quantum barrier layer include one of GaN quantum barrier layer, AlGaN quantum barrier layer, and InAlGaN quantum barrier layer, with a thickness of 5nm~15nm.

[0010] According to one aspect of the above technical solution, the In y Ga （1-y） The thickness of the N quantum well layer is 2nm~5nm, and the In x Ga （1-x） The thickness of the N-quantum well layer is 1.5 nm to 3 nm.

[0011] A second aspect of the present invention is to provide a method for preparing an LED epitaxial structure, the method comprising: Provide a substrate; A buffer layer, an undoped GaN layer, and an N-type GaN layer are sequentially epitaxially grown on the substrate. A shallow quantum well layer and a main quantum well layer are epitaxially grown sequentially on the N-type GaN layer. The shallow quantum well layer comprises periodically alternating layers of In. x Ga （1-x） N-quantum well layer and shallow quantum barrier layer, the In x Ga （1-x） The In composition x of the N quantum well layers gradually increases with each layer. The main quantum well layer includes periodically alternating layers of In. y Ga （1-y） N quantum well layers and master quantum barrier layers, in each of the In... y Ga （1-y） In the N quantum well layer, the In composition y gradually decreases along the growth direction; An electron blocking layer and a P-type GaN layer are then epitaxially grown on the main quantum well layer.

[0012] Furthermore, the In x Ga （1-x） The growth steps of the N-quantum well layer include: The growth temperature is 700℃~800℃, and the growth pressure is 100~300 Torr. By increasing the trimethylindium source flow rate and / or decreasing the growth temperature, the In component x is increased layer by layer.

[0013] Furthermore, the In y Ga （1-y） The growth steps of the N-quantum well layer include: The growth temperature is 720℃~850℃, and the growth pressure is 100~300 Torr. y Ga （1-y） In the N quantum well layer, the In component y is continuously and gradually reduced by linearly decreasing the trimethylindium source flux and / or increasing the growth temperature.

[0014] Furthermore, the growth temperature of both the shallow quantum barrier layer and the main quantum barrier layer is 900℃~1050℃, and the growth pressure is 100~300 Torr.

[0015] A third aspect of the present invention is to provide an LED chip, the LED chip comprising the above-described LED epitaxial structure.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. In the main quantum well layer, each In y Ga （1-y）The continuous and gradually decreasing gradient change in the N-quantum well layer generates a built-in electric field opposite to the piezoelectric polarization field, which effectively counteracts the influence of the polarization field, weakens the quantum confinement Stark effect (QCSE), makes the quantum well band tend to be flat, significantly increases the overlap integral of the wave functions of electrons and holes, improves the probability of radiative recombination, and ultimately improves the internal quantum efficiency of the device.

[0017] 2. Increasing the In composition with the number of layers in the shallow quantum well layer will form a good stress transition region, gradually releasing the stress caused by lattice mismatch, effectively reducing the penetration dislocation density, improving the crystal quality of the active region, and reducing non-radiative recombination centers.

[0018] 3. By flexibly adjusting the gradient range, slope, and growth temperature of the In composition, it is applicable to both blue Micro-LEDs with extremely high wavelength uniformity requirements and green LEDs with low efficiency in traditional technology, thus having wide applicability. This solves the technical problem in existing technologies where In doping with multiple quantum well layers leads to piezoelectric polarization effects and reduced crystal quality, resulting in reduced internal quantum effects. Attached Figure Description

[0019] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a schematic diagram of the LED epitaxial structure in this invention; Figure 2 The energy band diagrams are shown for the multi-quantum well layers in Embodiment 1 and Comparative Example 1 of this invention. Component symbol explanation in the attached diagram: Substrate 1, buffer layer 2, undoped GaN layer 3, N-type GaN layer 4, multiple quantum well layer 5, shallow quantum well layer 50, main quantum well layer 51, electron blocking layer 6, P-type GaN layer 7. Detailed Implementation

[0020] To make the objectives, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. Several embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0021] Please see Figure 1The image shows an LED epitaxial structure provided by the present invention. The LED epitaxial structure includes a substrate 1 and an epitaxial layer stacked on the substrate 1. The epitaxial layer includes a buffer layer 2, an undoped GaN layer 3, an N-type GaN layer 4, a multiple quantum well layer 5, an electron blocking layer, and a P-type GaN layer 7, which are stacked sequentially. The multi-quantum-well layer 5 includes a shallow quantum well layer 50 and a main quantum well layer 51 stacked on top of the shallow quantum well layer 50; The shallow quantum well layer 50 includes In layers arranged in a periodically alternating stack. x Ga （1-x） N-quantum well layer and shallow quantum barrier layer, In x Ga （1-x） The In composition x of the N quantum well layers gradually increases with each layer. The main quantum well layer 51 includes periodically alternating layers of In y Ga （1-y） N quantum well layers and master quantum barrier layers, in each In y Ga （1-y） In the N quantum well layer, the In composition y gradually decreases along the growth direction.

[0022] The shallow quantum well layer 50 is used to alleviate lattice mismatch stress and reduce dislocation and defect density, thus forming a good stress transition region, gradually releasing the stress caused by lattice mismatch, effectively reducing the density of penetrating dislocations, improving the crystal quality of the active region, and reducing non-radiative recombination centers.

[0023] Furthermore, the period of the shallow quantum well layer 50 is 5~14, In x Ga （1-x） The In composition x of the N quantum well layer gradually increases from 0.02~0.03 to 0.10~0.12.

[0024] Furthermore, In x Ga （1-x） The thickness of the N-quantum well layer is 1.5 nm to 3 nm.

[0025] Furthermore, both the shallow quantum barrier layer and the main quantum barrier layer include one of GaN quantum barrier layer, AlGaN quantum barrier layer, and InAlGaN quantum barrier layer, with a thickness of 5nm~15nm.

[0026] It should be noted that in each In y Ga （1-y） In the N quantum well layer, the In component y gradually decreases along the growth direction. That is, the continuous and gradually decreasing gradient change in each layer will form an internal potential field that counteracts the piezoelectric polarization effect, making the potential energy height at the bottom of the conduction band and the top of the valence band in the quantum well tend to be flat.

[0027] In other words, traditional rectangular quantum wells, when solving the Schrödinger equation based on quantum mechanics, suffer from piezoelectric polarization, which causes severe band tilting and separation of electron and hole wave functions. However, the main quantum well layer 51 in this application generates a built-in electric field opposite to the piezoelectric polarization field, effectively counteracting the influence of the polarization field, reducing the quantum confinement Stark effect (QCSE), making the quantum well band more gradual, significantly increasing the overlap integral of electron and hole wave functions, improving the radiative recombination probability, and ultimately enhancing the internal quantum efficiency of the device.

[0028] Furthermore, the period of the main quantum well layer 51 is 5~15. When the main quantum well layer 51 is used in the epitaxial structure of a blue LED, in each In... y Ga （1-y） In the N quantum well layer, the In composition y gradually decreases from 0.18~0.25 to 0.10~0.18; When the main quantum well layer 51 is used in the epitaxial structure of a green LED, in each In y Ga （1-y） In the N quantum well layer, the In composition y gradually decreases from 0.25~0.35 to 0.15~0.25.

[0029] Furthermore, In y Ga （1-y） The thickness of the N-quantum well layer is 2nm~5nm.

[0030] In other words, by flexibly adjusting the gradient range, slope, and growth temperature of the In component, this LED epitaxial structure can be precisely tuned, making it suitable for both blue Micro-LEDs, which require extremely high wavelength uniformity, and green LEDs, which have lower efficiency due to traditional technology, thus exhibiting wide applicability.

[0031] Accordingly, the present invention also provides a method for preparing an LED epitaxial structure, the method comprising: steps S10 to S13.

[0032] Step S10: Provide a substrate; Specifically, the substrate is a patterned sapphire substrate, which is subjected to high-temperature thermal cleaning to remove surface contaminants.

[0033] Step S11: A buffer layer, an undoped GaN layer, and an N-type GaN layer are epitaxially grown sequentially on the substrate; Specifically, under a hydrogen atmosphere, the substrate is heated to 500℃~600℃ to grow a low-temperature GaN buffer layer with a thickness of 15nm~25nm.

[0034] Furthermore, the temperature was increased to 1000℃~1100℃ to grow an undoped GaN layer with a thickness of 1.5μm~2.5μm.

[0035] Furthermore, at 1000℃~1100℃, silane (SiH4) was introduced as an N-type dopant source to grow a Si-doped N-type GaN layer with a thickness of 1.5μm~2.5μm.

[0036] Step S12: A shallow quantum well layer and a main quantum well layer are epitaxially grown sequentially on the N-type GaN layer. The shallow quantum well layer comprises In layers stacked in a periodic alternating manner. x Ga （1-x） N-quantum well layer and shallow quantum barrier layer, the In x Ga （1-x） The In composition x of the N quantum well layers gradually increases with each layer. The main quantum well layer includes periodically alternating layers of In. y Ga （1-y） N quantum well layers and master quantum barrier layers, in each of the In... y Ga （1-y） In the N quantum well layer, the In composition y gradually decreases along the growth direction; Specifically, the In x Ga （1-x） The growth steps of the N-quantum well layer include: The growth temperature is 700℃~800℃ and the growth pressure is 100~300 Torr. The layer-by-layer increase of In component x is achieved by increasing the trimethylindium (TMIn) source flow rate and / or decreasing the growth temperature.

[0037] Furthermore, the In y Ga （1-y） The growth steps of the N-quantum well layer include: The growth temperature is 720℃~850℃, and the growth pressure is 100~300 Torr. y Ga （1-y） In the N quantum well layer, the In component y is continuously and gradually reduced by linearly decreasing the trimethylindium (TMIn) source flux and / or increasing the growth temperature.

[0038] Specifically, when the main quantum well layer is used in the epitaxial structure of blue LEDs, a faster TMIn flow rate reduction rate and / or a higher initial growth temperature are adopted; when the main quantum well layer is used in the epitaxial structure of green LEDs, a relatively slower TMIn flow rate reduction rate and / or a lower initial growth temperature are adopted.

[0039] Furthermore, the growth temperature of both the shallow quantum barrier layer and the main quantum barrier layer is 900℃~1050℃, and the growth pressure is 100~300 Torr.

[0040] Step S13: Continue epitaxial growth of an electron blocking layer and a P-type GaN layer on the main quantum well layer.

[0041] Specifically, an AlGaN layer with a thickness of 15nm to 25nm is grown at 800℃ to 950℃ as an electron blocking layer.

[0042] Furthermore, a Mg-doped P-type GaN layer with a thickness of 100 nm to 200 nm was grown at 900 °C to 1000 °C.

[0043] In addition, the present invention also provides an LED chip, the LED chip comprising the above-described LED epitaxial structure.

[0044] The technical solution of the present invention will now be described in detail with reference to specific embodiments.

[0045] Example 1 The first embodiment of the present invention provides an LED epitaxial structure, which includes a substrate and an epitaxial layer stacked on the substrate. The epitaxial layer includes a buffer layer, an undoped GaN layer, an N-type GaN layer, a multiple quantum well layer, an electron blocking layer, and a P-type GaN layer stacked sequentially. The multi-quantum-well layer includes a shallow quantum well layer and a main quantum well layer stacked on top of the shallow quantum well layer; Shallow quantum well layers consist of periodically alternating stacked In... x Ga （1-x） N-quantum well layer and shallow quantum barrier layer, In x Ga （1-x） The In composition x of the N quantum well layers gradually increases with each layer. The main quantum well layer comprises periodically alternating layers of In y Ga （1-y） N quantum well layers and master quantum barrier layers, in each In y Ga （1-y） In the N quantum well layer, the In composition y gradually decreases along the growth direction.

[0046] Furthermore, the period of the shallow quantum well layer is 9, In x Ga （1-x） The In composition x of the N quantum well layer gradually increases from 0.02 to 0.10.

[0047] Furthermore, In x Ga （1-x） The thickness of the N quantum well layer is 2.5 nm.

[0048] Furthermore, both the shallow quantum barrier layer and the main quantum barrier layer include one of GaN quantum barrier layer, AlGaN quantum barrier layer, and InAlGaN quantum barrier layer, with a thickness of 12nm.

[0049] Furthermore, the period of the main quantum well layer is 8, and the main quantum well layer is used in the epitaxial structure of blue LEDs, in each In y Ga （1-y） In the N quantum well layer, the In component y gradually decreases from 0.22 to 0.15.

[0050] Furthermore, In y Ga （1-y） The thickness of the N quantum well layer is 3.2 nm.

[0051] Accordingly, the present invention also provides a method for preparing an LED epitaxial structure, the method comprising: steps S10 to S13.

[0052] Step S10: Provide a substrate; Specifically, the substrate is a patterned sapphire substrate, which is subjected to high-temperature thermal cleaning to remove surface contaminants.

[0053] Step S11: A buffer layer, an undoped GaN layer, and an N-type GaN layer are epitaxially grown sequentially on the substrate; Specifically, a low-temperature GaN buffer layer with a thickness of 20 nm is grown by heating the substrate to 550°C in a hydrogen atmosphere.

[0054] Furthermore, the temperature was increased to 1050℃ to grow an undoped GaN layer with a thickness of 2μm.

[0055] Furthermore, at 1050°C, silane (SiH4) was introduced as an N-type dopant source to grow a Si-doped N-type GaN layer with a thickness of 2 μm.

[0056] Step S12: A shallow quantum well layer and a main quantum well layer are epitaxially grown sequentially on the N-type GaN layer. The shallow quantum well layer comprises In layers stacked in a periodic alternating manner. x Ga （1-x） N-quantum well layer and shallow quantum barrier layer, the In x Ga （1-x） The In composition x of the N quantum well layers gradually increases with each layer. The main quantum well layer includes periodically alternating layers of In. y Ga （1-y） N quantum well layers and master quantum barrier layers, in each of the In... y Ga （1-y） In the N quantum well layer, the In composition y gradually decreases along the growth direction; Specifically, the In x Ga （1-x） The growth steps of the N-quantum well layer include: The growth temperature was 760℃ and the growth pressure was 200 Torr. The layer-by-layer increase of In component x was achieved by increasing the trimethylindium (TMIn) source flow rate.

[0057] Furthermore, the In y Ga （1-y） The growth steps of the N-quantum well layer include: The growth temperature was 745℃, and the growth pressure was 200 Torr. (The last part, "in each In") y Ga （1-y） In the N quantum well layer, the In component y is continuously and gradually reduced by linearly decreasing the trimethylindium (TMIn) source flux and increasing the growth temperature. The TMIn flux is linearly reduced at a rate of 32 sccm / min and the growth time is 35 seconds, so that the In component y gradually changes from 0.22 at the beginning to 0.15 at the end.

[0058] Furthermore, the growth temperature of both the shallow quantum barrier layer and the main quantum barrier layer is 980°C, and the growth pressure is 200 Torr.

[0059] Step S13: Continue epitaxial growth of an electron blocking layer and a P-type GaN layer on the main quantum well layer.

[0060] Specifically, an Al layer with a thickness of 20 nm was grown at 870℃. 0.15 Ga 0.85 The N-layer acts as an electron blocking layer.

[0061] Furthermore, a Mg-doped P-type GaN layer with a thickness of 150 nm was grown at 950 °C.

[0062] Example 2 Embodiment 2 of the present invention also proposes an LED epitaxial structure. The difference between the LED epitaxial structure in this embodiment and the LED epitaxial structure in Embodiment 1 is that: The period of the shallow quantum well layer is 9, In x Ga （1-x） The In composition x of the N quantum well layer gradually increases from 0.02 to 0.12.

[0063] Furthermore, In x Ga （1-x） The thickness of the N quantum well layer is 2.8 nm.

[0064] Furthermore, the period of the main quantum well layer is 10, and the main quantum well layer is used in the epitaxial structure of green LEDs, in each In y Ga （1-y） In the N quantum well layer, the In component y gradually decreases from 0.3 to 0.2.

[0065] Furthermore, Iny Ga （1-y） The thickness of the N quantum well layer is 4 nm.

[0066] In x Ga （1-x） The growth steps of the N-quantum well layer include: The growth temperature was 735℃ and the growth pressure was 200 Torr. The layer-by-layer increase of In component x was achieved by increasing the trimethylindium (TMIn) source flow rate.

[0067] Furthermore, In y Ga （1-y） The growth steps of the N-quantum well layer include: The growth temperature was 720℃, and the growth pressure was 200 Torr. (The last part, "in each In") y Ga （1-y） In the N quantum well layer, the In component y is gradually reduced by linearly decreasing the trimethylindium (TMIn) source flux and increasing the growth temperature. The TMIn flux is linearly reduced at a rate of 25 sccm / min and the growth time is 55 seconds, so that the In component y gradually changes from 0.3 at the beginning to 0.2 at the end.

[0068] Comparative Example 1 Comparative Example 1 of the present invention also proposes an LED epitaxial structure. The difference between the LED epitaxial structure in this embodiment and the LED epitaxial structure in Example 1 is that: The period of the shallow quantum well layer is 9, In x Ga （1-x） The In composition x of the N quantum well layer is a constant composition of 0.05.

[0069] Furthermore, In x Ga （1-x） The thickness of the N quantum well layer is 2.5 nm.

[0070] Furthermore, the period of the main quantum well layer is 8, and the main quantum well layer is used in the epitaxial structure of blue LEDs, in each In y Ga （1-y） In the N quantum well layer, the In component y is a constant component of 0.18.

[0071] Furthermore, In y Ga （1-y） The thickness of the N quantum well layer is 3 nm.

[0072] In x Ga （1-x） The growth steps of the N-quantum well layer include: The growth temperature was 760℃ and the growth pressure was 200 Torr.

[0073] Furthermore, In y Ga （1-y） The growth steps of the N-quantum well layer include: The growth temperature was 760℃ and the growth pressure was 200 Torr.

[0074] Comparative Example 2 Comparative Example 2 of the present invention also proposes an LED epitaxial structure. The difference between the LED epitaxial structure in this embodiment and the LED epitaxial structure in Example 2 is that: The period of the shallow quantum well layer is 9, In x Ga （1-x） The In composition x of the N quantum well layer is a constant composition of 0.08.

[0075] Furthermore, In x Ga （1-x） The thickness of the N quantum well layer is 2.8 nm.

[0076] Furthermore, the period of the main quantum well layer is 10, and the main quantum well layer is used in the epitaxial structure of blue LEDs, in each In y Ga （1-y） In the N quantum well layer, the In component y is a constant component of 0.26.

[0077] Furthermore, In y Ga （1-y） The thickness of the N quantum well layer is 3 nm.

[0078] In x Ga （1-x） The growth steps of the N-quantum well layer include: The growth temperature was 735℃ and the growth pressure was 200 Torr.

[0079] Furthermore, In y Ga （1-y） The growth steps of the N-quantum well layer include: The growth temperature was 735℃ and the growth pressure was 200 Torr.

[0080] Please refer to Table 1 below, which shows the parameters corresponding to the above embodiments and comparative examples of the present invention.

[0081] Table 1

[0082] It should be noted that the peak emission wavelength was measured using photoluminescence (PL) spectroscopy. The sample was excited at 300K (room temperature) using a laser, and the emitted light signal was collected by a spectrometer. The wavelength at the point of maximum emission intensity was analyzed. The integrated intensity was measured by placing the sample in a 10K / 300K environment, performing PL measurements, and then integrating the spectrum to obtain the relative intensity. The internal quantum efficiency (IQE) was estimated using a model based on the ratio of the integrated PL intensity at 10K to that at 300K. Since the nonradiative recombination rate at the extremely low temperature of 10K is negligible, the IQE can be approximated as 100%. Therefore, at the same optical power, the IQE at 300K can be expressed as (PL intensity at 300K / PL intensity at 10K).

[0083] As shown in Table 1, the full width at half maximum (FWHM) of the PL spectrum in the embodiment is smaller than that in the comparative example, which verifies that the incremental In composition design of the shallow quantum well can effectively alleviate lattice mismatch stress. At the same time, the PL intensity of the embodiment at room temperature of 300K is significantly improved compared with the comparative example, and the internal quantum efficiency (IQE) is also improved, which verifies that the gradient In composition design of the main quantum well can significantly reduce the density of non-radiative recombination centers such as dislocations in the active region, thereby obtaining higher luminous efficiency.

[0084] Since the bandgap corresponding to the In composition of shallow quantum wells (0.08 for green light or 0.05 for blue light) cannot physically support the emission of visible light, the design of the main quantum well is crucial to determining the luminous efficacy of LEDs. The main quantum well design of this invention, especially the significant improvement in IQE achieved in Embodiment 2 of the green LED epitaxial structure, stems from the gradient In composition design of the main quantum well layer. This design, by counteracting the piezoelectric polarization field, makes the quantum well bandgap more gradual, greatly enhancing the overlap of wave functions between electrons and holes, thereby significantly improving the radiative recombination probability.

[0085] like Figure 2 As shown, (a) is the band structure of the multi-quantum well layer in Comparative Example 1 without considering the piezoelectric polarization effect (QCSE), (b) is the band structure of the multi-quantum well layer in Example 1 without considering the QCSE effect, (c) is the band structure of the multi-quantum well layer in Comparative Example 1 considering the QCSE effect, and (d) is the band structure of the multi-quantum well layer in Example 1 considering the QCSE effect. In other words, the conventional multi-quantum well layer in Comparative Example 1 does not have a gradient In composition doping. When the piezoelectric polarization effect is not considered, the band structure is rectangular and symmetrical. After considering the piezoelectric polarization effect, the piezoelectric polarization causes the band structure to be severely tilted, and the wave functions of electrons and holes are separated in space (the black wave function graphs do not overlap). This weakens the carrier recombination efficiency, which is a typical problem of conventional quantum wells.

[0086] In Embodiment 1 of this application, when In composition gradient doping is used, the band itself has a certain tilt when the piezoelectric polarization effect is not considered (due to the In composition gradient design). After considering the piezoelectric polarization effect, the band tilt interacts with the polarization field, causing the wave functions of electrons and holes to largely overlap (the black wave function graphs overlap significantly), which effectively improves the carrier recombination probability.

[0087] In summary, this invention, through a unique multi-quantum-well structure design, simultaneously achieves crystal quality optimization, radiative recombination efficiency improvement (high luminous efficacy), and enhancement of IQE for both blue and green light (wideband). Ultimately, it obtains high-quality, highly uniform LED epitaxial wafers suitable for both blue and green bands at the epitaxial wafer level, laying a solid foundation for the fabrication of high-performance, high-efficiency blue-green LED devices.

[0088] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0089] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. An LED epitaxial structure, characterized in that, The LED epitaxial structure includes a substrate and an epitaxial layer stacked on the substrate. The epitaxial layer includes a buffer layer, an undoped GaN layer, an N-type GaN layer, a multiple quantum well layer, an electron blocking layer, and a P-type GaN layer stacked sequentially. The multi-quantum-well layer includes a shallow quantum-well layer and a main quantum-well layer stacked on the shallow quantum-well layer; The shallow quantum well layer comprises periodically alternating layers of In. x Ga （1-x） N-quantum well layer and shallow quantum barrier layer, the In x Ga （1-x） The In composition x of the N quantum well layers gradually increases with each layer. The main quantum well layer includes periodically alternating layers of In. y Ga （1-y） N quantum well layers and master quantum barrier layers, in each of the In... y Ga （1-y） In the N quantum well layer, the In composition y gradually decreases along the growth direction.

2. The LED epitaxial structure according to claim 1, characterized in that, The shallow quantum well layer has a period of 5-14, and the In... x Ga （1-x） The In composition x of the N quantum well layer gradually increases from 0.02~0.03 to 0.10~0.

12.

3. The LED epitaxial structure according to claim 1, characterized in that, The period of the main quantum well layer is 5~15. When the main quantum well layer is used in the epitaxial structure of a blue LED, in each In... y Ga （1-y） In the N quantum well layer, the In composition y gradually decreases from 0.18~0.25 to 0.10~0.18; When the main quantum well layer is used in the epitaxial structure of a green LED, in each of the In... y Ga （1-y） In the N quantum well layer, the In composition y gradually decreases from 0.25~0.35 to 0.15~0.

25.

4. The LED epitaxial structure according to claim 1, characterized in that, Both the shallow quantum barrier layer and the main quantum barrier layer include one of GaN quantum barrier layer, AlGaN quantum barrier layer, and InAlGaN quantum barrier layer, with a thickness of 5nm~15nm.

5. The LED epitaxial structure according to claim 4, characterized in that, The In y Ga （1-y） The thickness of the N quantum well layer is 2nm~5nm, and the In x Ga （1-x） The thickness of the N-quantum well layer is 1.5 nm to 3 nm.

6. A method for fabricating an LED epitaxial structure, characterized in that, The preparation method is used to prepare the LED epitaxial structure according to any one of claims 1 to 5, and the preparation method includes: Provide a substrate; A buffer layer, an undoped GaN layer, and an N-type GaN layer are sequentially epitaxially grown on the substrate. A shallow quantum well layer and a main quantum well layer are epitaxially grown sequentially on the N-type GaN layer. The shallow quantum well layer comprises periodically alternating layers of In. x Ga （1-x） N-quantum well layer and shallow quantum barrier layer, the In x Ga （1-x） The In composition x of the N quantum well layers gradually increases with each layer. The main quantum well layer includes periodically alternating layers of In. y Ga （1-y） N quantum well layers and master quantum barrier layers, in each of the In... y Ga （1-y） In the N quantum well layer, the In composition y gradually decreases along the growth direction; An electron blocking layer and a P-type GaN layer are then epitaxially grown on the main quantum well layer.

7. The method for preparing an LED epitaxial structure according to claim 6, characterized in that, The In x Ga （1-x） The growth steps of the N-quantum well layer include: The growth temperature is 700℃~800℃, and the growth pressure is 100~300 Torr. By increasing the trimethylindium source flow rate and / or decreasing the growth temperature, the In component x is increased layer by layer.

8. The method for preparing an LED epitaxial structure according to claim 6, characterized in that, The In y Ga （1-y） The growth steps of the N-quantum well layer include: The growth temperature is 720℃~850℃, and the growth pressure is 100~300 Torr. y Ga （1-y） In the N quantum well layer, the In component y is continuously and gradually reduced by linearly decreasing the trimethylindium source flux and / or increasing the growth temperature.

9. The method for preparing an LED epitaxial structure according to claim 6, characterized in that, The growth temperature of both the shallow quantum barrier layer and the main quantum barrier layer is 900℃~1050℃, and the growth pressure is 100~300 Torr.

10. An LED chip, characterized in that, The LED chip includes the LED epitaxial structure described in any one of claims 1 to 5.

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