Preparation method of light-emitting element based on super-smooth interface composite functional transparent conductive layer

Abstract

This invention relates to a method for fabricating a light-emitting element based on an ultra-smooth interface composite functional transparent conductive layer, comprising the following steps: (1) providing a substrate and performing epitaxial growth; (2) growing a composite functional layer with a thickness of 5-10 nm on the surface of the epitaxial structure; (3) polishing the composite functional layer to ensure that the surface roughness Ra < 0.2 nm; (4) defining the photonic crystal pattern and etching photonic crystal pre-holes in the composite functional layer; (5) depositing the composite transparent conductive layer: firstly, using an atomic layer deposition system (ALD), filling the photonic crystal pre-holes with an ITO material of an indium-tin weight ratio of 90:10, and then growing a second ITO layer with a thickness of 30 nm and an indium-tin weight ratio of 95:5 as a current diffusion layer by sputtering or ion beam deposition, and finally performing high-temperature thermal annealing; this invention optimizes the light extraction efficiency and current diffusion performance of the device by combining fundamental planarization of the substrate interface with the precise fabrication of nanophotonic structures.

Description

Technical Field

[0001] This invention relates to the field of semiconductor optoelectronic devices, and more specifically to a method for fabricating a light-emitting element based on an ultra-smooth interface composite functional transparent conductive layer. Background Technology

[0002] In the fabrication of gallium nitride-based light-emitting devices (such as LEDs), the industry commonly uses transparent conductive layers to improve current spread, and also employs photonic crystals interspersed within semiconductor layers to enhance light extraction efficiency. However, in actual production, due to lattice mismatch and thermal mismatch during the growth of the InGaN / GaN multiple quantum well structure, stress-induced indium atom migration and aggregation occur on the surface of the gallium nitride epitaxial layer. This results in a three-dimensional island-like growth pattern on the surface of the P-type gallium nitride cap layer, causing its surface roughness Ra > 5~20 nm (e.g., ...). Figure 1 This highly undulating surface morphology, besides significantly hindering the uniform growth of the subsequent transparent conductive layer, also greatly affects the performance of photonic crystals, mainly in the following aspects: 1) Rough substrate affects optical performance: Rough interfaces become light scattering centers, increasing the haze of the transparent conductive layer. Also, because dry etching processes have morphological reproducibility, the rough morphology of the substrate will lead to damage to the optical structure and uneven size, significantly reducing its light extraction efficiency.

[0003] 2) Existing solutions have limitations: They only focus on planarization technology and the matching and optimization of the film values ​​of the transparent conductive layer itself. There is no relevant research to explore the fundamental impact of substrate roughness on the electrical performance degradation of the transparent conductive layer. The interface undulations not only form a scattering barrier for charge carriers, increasing the sheet resistance and contact resistance of the transparent conductive layer, but also prevent the ultrathin transparent conductive layer from achieving perfect two-dimensional layered growth, resulting in defects and discontinuous coverage, which ultimately affects the uniform injection and spread of current.

[0004] 3) Performance Bottleneck: In conventional technical approaches, optical extraction optimization and electrical performance optimization are often independent or even contradictory. For example, introducing air-hole photonic crystals sacrifices current paths, while increasing ITO thickness to improve conductivity introduces light absorption. Existing technologies lack an integrated solution that can simultaneously and synergistically improve optical efficiency and electrical performance.

[0005] Therefore, there is a need for an innovative solution that can address the root cause at the substrate interface, provide an ideal growth template for high-performance photonic structures, and efficiently integrate light extraction and current expansion functions. Summary of the Invention

[0006] To address the aforementioned issues, this invention aims to provide a method for fabricating light-emitting elements based on an ultra-smooth interface composite functional transparent conductive layer. This method solves the technical challenges of photonic crystal structure failure caused by substrate roughness and the difficulty in synergistically optimizing light extraction and current spreading performance, thereby achieving a breakthrough improvement in the optoelectronic performance of the device.

[0007] To achieve the above objectives, the present invention provides the following technical solution: The method for fabricating a light-emitting element based on an ultra-smooth interface composite functional transparent conductive layer specifically includes the following steps: (1) Provide a substrate for epitaxial growth; (2) A composite functional layer with a thickness of 5~10 nm is grown on the surface of the epitaxial structure; (3) Polish the composite functional layer to ensure that the surface roughness Ra < 0.2 nm; (4) Define the photonic crystal pattern and etch photonic crystal pre-holes in the composite functional layer; (5) Composite transparent conductive layer: Using an atomic layer deposition system (ALD), ITO material with an indium-tin weight ratio of 90:10 is used to fill the pre-hole of the photonic crystal. Its tin-rich design can achieve good ohmic contact with P-type gallium nitride. Then, a second ITO layer with a thickness of 30nm and an indium-tin weight ratio of 95:5 is grown by sputtering or ion beam deposition as a current diffusion layer. The indium-rich properties can better improve conductivity and light transmittance. Finally, high-temperature thermal annealing is performed. (6) Subsequent processes: Continue to complete the standard procedures of electrode preparation, cutting and packaging of light-emitting elements.

[0008] Preferably, the composite functional layer is made of aluminum indium gallium nitride or magnesium nitride.

[0009] Preferably, the polishing process in step (3) is as follows: 1) First step polishing: Use diamond or cubic boron nitride abrasive with a particle size of ≤0.5μm, combined with a weak oxidant polishing slurry and a medium hardness porous polishing pad to perform preliminary rough polishing to remove larger undulations; 2) Second polishing step: Use alumina abrasive with a particle size of ≤0.3μm, combined with alkaline polishing liquid and soft polishing pad, to perform intermediate fine polishing to further smooth the surface; 3) Third step polishing: Use silica abrasive with a particle size of <0.15μm, combined with alkaline polishing liquid and soft polishing pad, to perform final ultra-fine polishing to achieve an atomically flat surface.

[0010] Preferably, step (3) polishing can be repeated, with a total number of polishing operations not less than three. Ultrasonic cleaning is required for each polishing step to reduce cross-contamination of abrasive particles.

[0011] Preferably, the composite functional layer has a thickness of 2–3 nm after polishing.

[0012] Preferably, the depth of the photonic crystal pre-hole in step (4) is 30~50nm.

[0013] Preferably, the precursor source of the ALD atomic deposition system in step (5) is cyclopentadienyl indium, tetra(dimethylamino)tin combined with ozone and hydrogen peroxide.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. Optical aspects: (1) The light scattering at the interface of the transparent conductive layer is greatly reduced, the haze is significantly reduced, and the light transmittance is improved, thereby improving the light output efficiency.

[0015] (2) The precise and ordered photonic crystal structure can effectively improve the light extraction efficiency by about 30%~50%.

[0016] 2. Electrical aspects: Reduced interface roughness decreases carrier scattering, the resistivity of the transparent conductive layer decreases by 20%, improving current spread and reducing operating voltage.

[0017] 3. In terms of process: The uniformity and density of the transparent conductive layer are improved, reducing holes and defects and enhancing device reliability.

[0018] 4. Enhanced overall performance and integrated functionality: The photonic crystal structure filled with ITO itself constitutes part of the transparent conductive layer, realizing monolithic integration of the "current spreading layer" and the "light extraction structure". This eliminates the need for additional material layers or complex processes, simplifying the device structure and improving reliability. Attached Figure Description

[0019] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings: Figure 1 The results are based on the surface roughness measurements of existing P-type gallium nitride epitaxial layers. Figure 2 This is a process flow diagram of the present invention. Detailed Implementation

[0020] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0021] like Figure 2 As shown, the method for fabricating a light-emitting element based on an ultra-smooth interface composite functional transparent conductive layer of the present invention specifically includes the following steps: 1. Provide a substrate: Prepare a light-emitting element structure with a p-type gallium nitride epitaxial layer, with an initial surface roughness Ra≈12nm.

[0022] 2. Growth of composite functional layer: A composite functional layer with a thickness of 5~10nm (either aluminum indium gallium nitride or magnesium nitride) is grown on the surface of p-type gallium nitride using MOCVD. This composite functional layer not only serves as a protective layer and planarization transition layer for subsequent polishing (the final thickness after polishing is 2~3nm), but also, because its work function is about 5~5.5eV, it can serve as an ohmic contact layer between p-type gallium nitride and transparent conductive film, which is beneficial to reducing contact resistance.

[0023] 3. Multi-step chemical mechanical polishing: 1) First step polishing: Use diamond or cubic boron nitride abrasive with a particle size of ≤0.5μm, combined with a weak oxidizing agent polishing slurry (H2O2) and a medium hardness porous polishing pad to perform preliminary rough polishing to remove larger undulations.

[0024] 2) Second polishing step: Use alumina abrasive with a particle size of ≤0.3μm, combined with alkaline polishing liquid and soft polishing pad, to perform intermediate fine polishing to further smooth the surface.

[0025] 3) Third step polishing: Use silica abrasive with a particle size of <0.15μm, combined with alkaline polishing liquid and soft polishing pad, to perform final ultra-fine polishing to achieve an atomically flat surface.

[0026] The above polishing steps can be repeated, with a total of no less than three polishing cycles. Ultrasonic cleaning is required after each polishing step to reduce cross-contamination of the abrasive.

[0027] 4. Cleaning and Inspection: After polishing, clean the sample and use an atomic force microscope (AFM) to inspect the surface roughness to ensure that Ra < 0.2 nm.

[0028] 5. Definition of photonic crystal pattern: A circle formed by using photoresist as a mask to create a triangular lattice arrangement. Pivot array (500nm period, 30% duty cycle). For structures requiring high aspect ratio holes, SiN can be selected. x Alternatively, materials such as SiO2 can be used as hard masks. The arrangement of photonic crystals (such as square or hexagonal) and the shape of the holes (such as cylinders, cones, or polygonal prisms) can be adjusted according to design requirements.

[0029] 6. Use dry etching technology to etch out the pre-hole of the photonic crystal, with a preferred depth of 30~50nm.

[0030] 7. Deposition of composite transparent conductive layer: Utilizing the excellent conformal filling capability of the ALD atomic deposition system, the above-mentioned holes are filled with ITO as a photonic crystal at a temperature below 150 degrees Celsius using cyclopentadienyl indium, tetra(dimethylamino)tin, ozone, and hydrogen peroxide as the precursor source. The indium-tin weight ratio is 90:10. Then, a 30nm thick ITO layer (indium-tin weight ratio of 95:5) is grown by sputtering or ion beam deposition. Finally, high-temperature thermal annealing is performed to optimize the ITO lattice recombination.

[0031] 8. Subsequent processes: Continue with standard procedures such as electrode preparation, cutting, and packaging for the light-emitting elements. LED chip structures are not limited to flip-chip, vertical, upright, or high-voltage configurations.

[0032] The light-emitting device prepared by this invention can achieve the following effects: 1. This invention provides an ultra-smooth substrate surface. Without a substrate with Ra<0.2nm, no matter how sophisticated the photonic crystal design or how pure the ITO material, the optoelectronic properties of the device will be affected by interface scattering and structural distortion. 2. The newly added photonic crystal structure is characterized by filling with ITO with different indium-tin ratios, which can transform the conventional two-dimensional planar conductivity into a "vertical" conductivity channel, realizing the three-dimensional expansion of current. Furthermore, by using different indium-tin ratios, the work function of P-type gallium nitride can be further matched, which is a core design point in spatial distribution in the field of LED applications. 3. Since the new photonic crystal is built on a smooth substrate, it is preferable to use ALD (Alternating Current Deposition) to fill the holes in order to maintain a flat morphology; In summary, this invention provides an ideal environment for photonic crystals through atomic-level smoothing technology, constructs vertical conductive channels in the holes of photonic crystals using ALD filling technology, and combines ITO design with spatial composition gradient to achieve, for the first time, the synergistic optimization of the two physical paths of 'light guidance + electrical conduction' in three-dimensional space within a single functional layer, solving the problem of mutual constraints between light extraction and current expansion in traditional LEDs.

[0033] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. It will be apparent to those skilled in the art that various modifications can be easily made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A method for fabricating a light-emitting element based on an ultra-smooth interface composite functional transparent conductive layer, characterized in that: Includes the following steps: (1) Provide a substrate for epitaxial growth; (2) A composite functional layer with a thickness of 5~10 nm is grown on the surface of the epitaxial structure; (3) Polish the composite functional layer to ensure that the surface roughness Ra < 0.2 nm; (4) Define the photonic crystal pattern and etch photonic crystal pre-holes in the composite functional layer; (5) Deposition of composite transparent conductive layer: First, using an atomic layer deposition system, ITO material with an indium-tin weight ratio of 90:10 is used to fill the pre-hole of the photonic crystal. Then, a second ITO layer with a thickness of 30 nm and an indium-tin weight ratio of 95:5 is grown as a current diffusion layer by sputtering or ion beam deposition. Finally, high-temperature thermal annealing is performed. (6) Subsequent processes: Continue to complete the standard procedures of electrode preparation, cutting and packaging of light-emitting elements.

2. The method for fabricating a light-emitting element based on an ultra-smooth interface composite functional transparent conductive layer as described in claim 1, characterized in that: The composite functional layer is made of aluminum indium gallium nitride or magnesium nitride.

3. The method for fabricating a light-emitting element based on an ultra-smooth interface composite functional transparent conductive layer as described in claim 1 or 2, characterized in that: The specific polishing process in step (3) is as follows: 1) First step polishing: Use diamond or cubic boron nitride abrasive with a particle size of ≤0.5μm, combined with a weak oxidant polishing slurry and a medium hardness porous polishing pad to perform preliminary rough polishing to remove larger undulations; 2) Second polishing step: Use alumina abrasive with a particle size of ≤0.3μm, combined with alkaline polishing liquid and soft polishing pad, to perform intermediate fine polishing to further smooth the surface; 3) Third step polishing: Use silica abrasive with a particle size of <0.15μm, combined with alkaline polishing liquid and soft polishing pad, to perform final ultra-fine polishing to achieve an atomically flat surface.

4. The method for fabricating a light-emitting element based on an ultra-smooth interface composite functional transparent conductive layer as described in claim 3, characterized in that: The total number of polishing steps (3) shall not be less than three times. The polishing steps can be repeated. Each polishing step requires ultrasonic cleaning to reduce cross-contamination of abrasives.

5. The method for fabricating a light-emitting element based on an ultra-smooth interface composite functional transparent conductive layer as described in claim 4, characterized in that: The composite functional layer has a thickness of 2-3 nm after polishing.

6. The method for fabricating a light-emitting element based on an ultra-smooth interface composite functional transparent conductive layer as described in claim 1, characterized in that: The depth of the photonic crystal pre-hole in step (4) is 30~50nm.

7. The method for fabricating a light-emitting element based on an ultra-smooth interface composite functional transparent conductive layer as described in claim 1, characterized in that: The precursor source for the ALD atomic deposition system in step (5) is cyclopentadienyl indium, tetra(dimethylamino)tin combined with ozone and hydrogen peroxide.

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