Gan-based direct white light-emitting LED epitaxial thin film structure and preparation method therefor

Abstract

A GaN-based direct white light-emitting LED epitaxial thin film structure and a preparation method therefor. The structure mainly comprises a sapphire patterned substrate, a buffer layer, a uGaN layer, a rough porous layer, an n-GaN layer, a yellow light quantum well layer, an electron blocking layer, and a p-type layer. The rough porous layer is composed of an InGaN layer and a GaN layer which grow alternately. A porous structure is formed by H2 etching treatment at a specific temperature, and blue light emitting is realized. The yellow light quantum well layer is responsible for light emitting in a yellow band. Direct white light emitting can be realized without fluorescent powder, so that the production process is simplified, the cost is reduced, and the stability and controllability of a light source are improved. The present invention can be widely applied to lighting, display, backlight and other fields, and has significant market potential and practical value.

Description

A GaN-based self-emitting white LED epitaxial thin film structure and its preparation method

[0001] This application claims priority to Chinese Patent Application No. 202410803746.X, filed on June 20, 2024, with the State Intellectual Property Office of China, entitled "A GaN-based self-emitting white LED epitaxial thin film structure and its preparation method", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention relates to the field of semiconductor lighting technology, specifically to a GaN (gallium nitride) based self-emitting white LED epitaxial thin film structure and its preparation method. Background Technology

[0003] Current white LED light sources primarily rely on the combination of LED chips and phosphors to produce white light. This technology has several common applications. First, blue-band LED chips are often combined with yellow phosphors; second, UV LEDs in the ultraviolet band utilize a mixture of yellow and blue phosphors with phosphor adhesive to create a two-color phosphor colloid; third, especially near-ultraviolet UVA band UV LED chips, combine red, green, and blue phosphors with phosphor adhesive to form a three-color phosphor colloid. Regardless of the specific approach, the core principle is to use an LED chip to excite the phosphor, thereby producing white light.

[0004] However, this method of generating white light by combining LED chips with phosphors has many drawbacks and limitations. First, this technology requires both LED chips and phosphors to be used, resulting in relatively high costs for the light source device. Its operating mechanism involves the LED chip emitting light to excite the phosphor, but the light power is affected by the excitation efficiency, leading to a certain loss in device power consumption.

[0005] Secondly, the most widely used solution currently is to combine blue-band LED chips with yellow phosphors. However, the LED chip light source produced by this method inevitably contains a high proportion of blue light. This high-intensity blue light can cause potentially irreparable damage to the human eye; therefore, it is not the preferred solution for healthy lighting.

[0006] Furthermore, when UV LEDs or other LED chips in different wavelength bands are combined with corresponding phosphors, a combination of multiple phosphors and precise proportions are required. This not only increases costs but also places higher demands on the stability and yield of the manufacturing process.

[0007] In recent years, industry professionals have been striving to create a low-cost, stable light source device by enabling LED chips to emit white light independently. However, achieving simultaneous red, green, and blue light from a single epitaxial wafer of an LED presents significant technical challenges. Furthermore, using a splicing method would result in unsatisfactory yield, process stability, and manufacturing costs for the light source device. Summary of the Invention

[0008] This invention proposes a novel and feasible GaN-based self-emitting white LED solution, which mainly involves the innovative structural design of epitaxial layered thin films. Through the uniquely designed epitaxial structure, light emission in both blue and yellow wavelengths is generated simultaneously, and then superimposed to produce a white light source.

[0009] The technical solution adopted in this invention is as follows:

[0010] A GaN-based self-emitting white LED epitaxial thin film structure, characterized in that it comprises:

[0011] Sapphire patterned substrate;

[0012] A buffer layer consisting of AlN (aluminum nitride) and GaN is sequentially grown on a patterned sapphire substrate;

[0013] A uGaN (undoped gallium nitride) layer grown on a buffer layer;

[0014] A rough porous layer is grown on a uGaN layer. This rough porous layer consists of alternating InGaN (indium gallium nitride) and GaN layers. The InGaN layer forms a porous structure under H2 etching, and the GaN layer serves as a quantum barrier layer.

[0015] n-GaN layer (n-type gallium nitride layer) grown on a roughened porous layer.

[0016] The yellow quantum well layer grown on the n-GaN layer emits light with a wavelength between 580 nm and 600 nm.

[0017] An electron blocking layer (EBL) grown on a yellow quantum well layer is composed of AlGaN (aluminum gallium nitride).

[0018] A Mg-doped p-GaN layer (p-type gallium nitride layer) and a p-type contact layer are grown on an electron blocking layer.

[0019] During the preparation of the roughened porous layer, the growth temperature of the InGaN layer is controlled at 720℃~760℃, and the growth thickness is controlled in the range of 2nm~6nm.

[0020] During the preparation of the roughened porous layer, the growth temperature of the GaN layer is controlled at 800℃~900℃, and the growth thickness is controlled in the range of 2nm~4nm.

[0021] The fine structure of the yellow light quantum well layer consists of an InN layer, an InGaN quantum well layer, and a combined quantum barrier layer of AlGaN and GaN stacked sequentially, with the overall number of cycles of the multi-quantum well layer designed to be in the range of 5 to 8.

[0022] The thickness of the InN layer is controlled between 0.5 and 1.0 nm.

[0023] The thickness of the InGaN quantum well layer is controlled at 3-5 nm, and the molar content of In is 30%.

[0024] The AlGaN thickness in the aforementioned light quantum well layer is controlled at 3-5 nm, and the molar content of Al is 10-15%.

[0025] The thickness of GaN in the aforementioned yellow quantum well layer is controlled at 9-12 nm.

[0026] The above-mentioned method for preparing the epitaxial thin film structure of GaN-based self-emitting white LED includes the following steps:

[0027] Prepare a patterned sapphire substrate;

[0028] A buffer layer combining AlN and GaN is sequentially grown on a patterned sapphire substrate;

[0029] A uGaN layer is grown on the buffer layer;

[0030] A roughened porous layer is prepared on a uGaN layer;

[0031] An n-GaN layer is grown on a roughened porous layer;

[0032] A yellow quantum well layer with emission wavelengths of 580 nm to 600 nm was fabricated on an n-GaN layer;

[0033] An electron blocking layer (EBL) composed of AlGaN is grown on a yellow quantum well layer;

[0034] A Mg-doped p-GaN layer and a p-type contact layer are grown on an electron blocking layer.

[0035] The step of preparing the roughened porous layer includes:

[0036] An InGaN layer was grown at a controlled temperature range of 720℃ to 760℃, with the growth thickness controlled in the range of 2nm to 6nm.

[0037] The growth process is paused, and H2 is introduced to etch InGaN, forming a microstructure of pores.

[0038] GaN layers with a thickness ranging from 2 nm to 4 nm are grown on the porous microstructure, and the growth temperature is controlled in the range of 800℃ to 900℃.

[0039] The above process is repeated until a coarsened porous GaN layer with a thickness ranging from 30 nm to 150 nm is formed.

[0040] This invention includes steps for testing and verifying the obtained LED epitaxial thin film structure. By means of EL light emission test, PL spectral analysis and other means, it is confirmed whether the structure successfully realizes the self-emitting white light function and evaluates its light emission performance and stability. It also includes steps for controlling the wavelength and intensity of the blue emission peak by adjusting the growth temperature of the coarsening porous layer and the time length of H2 etching.

[0041] In the special design of this invention, although the roughened porous layer is located below the p-GaN layer, p electrode, n-GaN layer and N electrode, its unique structure and position design enable carriers to achieve effective recombination within it. The periodic InGaN and GaN-type quantum well structure designed in the roughened porous layer, while working with H2 etching to desorb InN material and form a loose porous stress-relieving layer, combined with the growth of GaN-type layers, is essentially a set of light-emitting quantum well structures that form a crystal barrier. By controlling multiple growth conditions such as growth temperature, In doping amount, and H2 etching time, a certain amount of In component residue can be retained in the formation of the porous loose layer. In fact, the roughened porous layer still retains the periodic cyclic structure of InGaN / GaN material.

[0042] Specifically, the roughened porous layer is an InGaN / GaN-type quantum well composite structure that can emit light upon current injection. Because the P-electrode and N-electrode of an LED chip are not physically perpendicular, when an external electric field is applied, the current flows through the P-electrode, then through the quantum well, and flows to the N-electrode via the lower end or below the n-GaN layer. During this process, by controlling the applied electric field strength within a certain range, current can pass through the specially designed roughened layer, inducing carrier recombination and light emission. In this invention, the roughened layer being positioned below the n-GaN layer is a special and deliberate design.

[0043] The technological advancements and beneficial effects achieved by the above-mentioned technical solutions mainly include:

[0044] Innovative Structural Design: This invention successfully realizes a GaN-based self-emitting white LED epitaxial film through a unique structural design. This structure combines the emission of both blue and yellow wavelengths, which, when superimposed, can produce a stable white light source. This eliminates the dependence on phosphors in traditional LED lighting, effectively reducing costs and improving the stability and reliability of the light source.

[0045] Highly efficient spectral modulation: By precisely controlling the growth conditions and etching process of the coarsened porous layer, this invention achieves precise control over the blue emission band. This precise spectral modulation capability not only improves the luminous performance of LEDs but also enhances their controllability, making the lighting effect more in line with user needs.

[0046] Simplified process flow: Traditional white LEDs usually require phosphors to achieve the white light effect, while the self-emitting white LED structure of this invention simplifies this step, reduces production links, improves production efficiency, reduces production costs, and reduces light decay problems caused by phosphor aging.

[0047] Environmentally friendly and energy-saving: By reducing the use of phosphors, this invention also has certain advantages in terms of environmental protection, reducing the potential environmental impact during production and use. At the same time, the high-efficiency white LEDs also contribute to energy conservation and emission reduction, aligning with the current trend of green environmental protection and sustainable development.

[0048] Broad application prospects: The self-emitting white LED epitaxial thin film structure of the present invention can be widely used in lighting, display, backlight and other fields. Its stable light-emitting performance and tunable spectral characteristics enable it to meet the needs of different application scenarios and have broad market prospects. Attached Figure Description

[0049] Figure 1 shows a schematic diagram of the epitaxial barrier thin film structure of the present invention.

[0050] Figure 2 is a schematic diagram of the fine structure design of the coarsened porous layer involved in this invention.

[0051] Figure 3 is a schematic diagram of the yellow light quantum well structure designed in this invention.

[0052] The left image in Figure 4 shows the epitaxial wafer grown according to the design structure of this invention, and the right image shows its corresponding PL spectrum and mapping diagram.

[0053] Figure 5 shows the effect of the porous layer on the emission wavelength of the LED structure.

[0054] Figure 6 shows the changes in wavelength and intensity of the blue emission peak when the growth temperature of the coarsened porous layer and the H2 etching time are adjusted. Detailed Implementation

[0055] The preferred embodiments of the present invention are given below with reference to the accompanying drawings to illustrate the technical solution of the present invention in detail.

[0056] Example

[0057] An embodiment of the present invention provides a method for fabricating a GaN-based self-emitting white light LED epitaxial thin film structure (as shown in Figure 1), the specific steps of which are as follows:

[0058] Step 1: Substrate Preparation

[0059] First, prepare a sapphire patterned substrate 100. This substrate has good thermal stability and mechanical strength, making it suitable for the growth of GaN-based LEDs.

[0060] Step 2: Grow a Buffer layer of 200

[0061] A buffer layer consisting of AlN and GaN layers is sequentially grown on a patterned sapphire substrate. This layer primarily serves to mitigate the lattice mismatch between the substrate and the subsequent GaN layer, thereby improving crystal quality.

[0062] Step 3: Grow a 300m thick uGaN layer

[0063] A uGaN layer is grown on the buffer layer, which serves as the basis for subsequent structures.

[0064] Step 4: Prepare a roughened porous layer 400

[0065] A roughened porous layer is prepared on the uGaN layer (its structure is shown in Figure 2). This step is one of the key innovations of this invention, and specifically includes the following sub-steps:

[0066] An InGaN layer was grown at a controlled temperature range of 720℃ to 760℃, with the growth thickness controlled in the range of 2nm to 6nm.

[0067] The growth process is paused, and a program is set to etch InGaN using H2. During this process, the InN material is gradually desorbed and carried away by the introduced H2, thus forming a porous microstructure.

[0068] Based on this, a GaN layer with a thickness ranging from 2 nm to 4 nm is grown at a growth temperature controlled within the range of 800℃ to 900℃. This layer not only isolates the porous structure but also provides a quantum barrier layer to block charge carriers for the subsequent luminescence of the porous structure under an external electric field.

[0069] The above process is repeated until a coarsened porous GaN layer with a thickness ranging from 30 nm to 150 nm is formed.

[0070] Step 5: Grow an n-GaN layer 500

[0071] An n-GaN layer is grown on a roughened porous layer to serve as the n-type region of the LED.

[0072] Step 6: Fabricate the yellow quantum well layer 600 (its structure is shown in Figure 3).

[0073] A yellow quantum well layer with an emission wavelength of 580 nm to 600 nm was fabricated on an n-GaN layer. Its fine structure consists of an InN layer (indium nitride layer), an InGaN quantum well layer, and a combined quantum barrier layer of AlGaN and GaN stacked sequentially. The overall number of cycles of the multi-quantum well layer is designed in the range of 5 to 8 to ensure that the luminescence intensity reaches the required level while the overall crystal quality remains controllable.

[0074] Step 7: Growth of Electron Blocking Layer (EBL) 700 and p-type Layer

[0075] An electron blocking layer (EBL) 700 composed of AlGaN is grown on the yellow quantum well layer to prevent electron leakage into the p-type region. Subsequently, a Mg-doped p-GaN layer 800 and a p-contact layer 900 are grown.

[0076] The left image in Figure 4 shows the EL emission pattern of the epitaxial wafer grown according to the design structure of this invention, using In ball die casting as a temporary electrode, where obvious white emission is visible. The right image shows its corresponding PL spectrum and mapping diagram, where a clear blue emission peak is visible around 450 nm and a yellow emission peak is visible around 590 nm.

[0077] Step 8: Testing and Verification

[0078] After completing the above preparation steps, process layer structures such as LED chip electrodes (p-PAD901, n-PAD501) were fabricated, and the resulting LED epitaxial thin film structure was tested and verified. EL emission testing and PL spectral analysis were used to confirm whether the structure successfully achieved self-emitting white light, and its luminescent performance and stability were evaluated.

[0079] To further design and control the stability of the present invention, a series of designs were carried out on the fine-structured coarsened porous layer, a key innovation of this invention. As shown in Figure 5, to demonstrate the light emission phenomenon of the fine-structured coarsened porous layer of this invention, the coarsened porous layer was removed from the overall LED structure. It can be seen that as the porous layer was removed, the blue light peak disappeared, and the peak wavelength of the yellow light-emitting quantum well above also shortened significantly, shifting from nearly 600nm to around 570nm. This further verifies the two important functions of the specially designed coarsened porous layer of this invention as described above: generating blue light emission and providing a substrate for stress relief of the yellow light-emitting quantum well above.

[0080] Figure 6 shows that by adjusting the growth temperature of the coarsened porous layer and the H2 etching time, the wavelength and intensity of the blue emission peak can be clearly and regularly controlled, proving the precise controllability and structural stability of this design.

[0081] This embodiment successfully fabricates a GaN-based self-emitting white LED epitaxial film through a unique structural design. This structure can simultaneously generate light in both blue and yellow wavelengths, which are then superimposed to produce a white light source. This eliminates the need for phosphors, reducing costs and improving the stability of the light source. Furthermore, by precisely controlling the growth conditions and etching process of the coarsened porous layer, precise control over the blue emission wavelength is achieved, further enhancing the LED's luminous performance and controllability.

Claims

1. A GaN-based self-emitting white LED epitaxial thin film structure, characterized in that, include: Sapphire patterned substrate; A buffer layer consisting of AlN and GaN grown sequentially on a patterned sapphire substrate; uGaN layer grown on a buffer layer; A roughened porous layer is grown on a uGaN layer. This roughened porous layer consists of alternating InGaN and GaN layers. The InGaN layer forms a porous structure under H2 etching, and the GaN layer serves as a quantum barrier layer. n-GaN layer grown on a roughened porous layer; The yellow quantum well layer grown on the n-GaN layer emits light with a wavelength between 580 nm and 600 nm. An electron blocking layer grown on a yellow quantum well layer, the composition of which is AlGaN; A Mg-doped p-GaN layer and a p-type contact layer grown on an electron blocking layer.

2. The GaN-based self-emitting white LED epitaxial thin film structure according to claim 1, characterized in that, During the preparation of the roughened porous layer, the growth temperature of the InGaN layer is controlled at 720℃~760℃, and the growth thickness is controlled in the range of 2nm~6nm.

3. The GaN-based self-emitting white LED epitaxial thin film structure according to claim 2, characterized in that, During the preparation of the roughened porous layer, the growth temperature of the GaN layer is controlled at 800℃~900℃, and the growth thickness is controlled in the range of 2nm~4nm.

4. The GaN-based self-emitting white LED epitaxial thin film structure according to claim 3, characterized in that, The fine structure of the yellow light quantum well layer consists of an InN layer, an InGaN quantum well layer, and a combined quantum barrier layer of AlGaN and GaN stacked sequentially, with the overall number of cycles of the multi-quantum well layer designed to be in the range of 5 to 8.

5. The GaN-based self-emitting white LED epitaxial thin film structure according to claim 4, characterized in that, The thickness of the InN layer is controlled between 0.5 and 1.0 nm.

6. The GaN-based self-emitting white LED epitaxial thin film structure according to claim 4, characterized in that, The thickness of the InGaN quantum well layer is controlled at 3-5 nm, and the molar content of In is 30%.

7. The GaN-based self-emitting white LED epitaxial thin film structure according to claim 4, characterized in that, The AlGaN thickness in the yellow quantum well layer is controlled at 3-5 nm, and the molar content of Al is 10-15%.

8. The GaN-based self-emitting white LED epitaxial thin film structure according to claim 4, characterized in that, The thickness of GaN in the yellow light quantum well layer is controlled at 9-12 nm.

9. The method for preparing the GaN-based self-emitting white light LED epitaxial thin film structure according to any one of claims 1-8, characterized in that, Includes the following steps: Prepare a patterned sapphire substrate; A buffer layer combining AlN and GaN is sequentially grown on a patterned sapphire substrate; A uGaN layer is grown on the buffer layer; A roughened porous layer is prepared on a uGaN layer; An n-GaN layer is grown on a roughened porous layer; A yellow quantum well layer with emission wavelengths of 580 nm to 600 nm was fabricated on an n-GaN layer; An electron blocking layer composed of AlGaN is grown on a yellow quantum well layer; A Mg-doped p-GaN layer and a p-type contact layer are grown on an electron blocking layer.

10. The method according to claim 9, characterized in that, The step of preparing the roughened porous layer includes: a) Grow an InGaN layer at a controlled temperature range of 720℃~760℃, with the growth thickness controlled in the range of 2nm~6nm. b) The growth process is paused, and H2 is introduced to etch the InGaN, forming a microstructure of pores; c) A GaN layer with a thickness of 2 nm to 4 nm is grown on the microstructure of the pores, and the growth temperature is controlled in the range of 800℃ to 900℃. The growth process is repeated in steps a), b), and c) until a coarsened porous layer with a thickness ranging from 30 nm to 150 nm is formed.

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