Methods to improve the brightness of Micro LED chips

Abstract

This application relates to the field of optoelectronic devices, specifically disclosing a method for improving the brightness of Micro LED chips. The method for improving the brightness of Micro LED chips includes the following steps: Step 1: Forming an N-GaN semiconductor layer on a semiconductor substrate using metal-organic chemical vapor deposition (MOCVD); Step 2: Etching the plane of the N-GaN semiconductor layer away from the semiconductor substrate to obtain a prismatic N-GaN semiconductor layer; Step 3: Forming a quantum well on the etched prismatic N-GaN semiconductor layer using MOCVD; Step 4: Forming a P-GaN semiconductor layer on the quantum well using MOCVD; Step 5: Etching the plane of the P-GaN semiconductor layer away from the semiconductor substrate to form a prismatic shape on the surface of the P-GaN semiconductor layer that intersects the prismatic shape on the surface of the P-GaN semiconductor layer. This application has the advantage of improving light recycling efficiency, thereby increasing the brightness of Micro LED chips.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic devices, and in particular to a method for improving the brightness of Micro LED chips. Background Technology

[0002] Light-emitting diodes, or Micro LEDs for short, are commonly used light-emitting devices that release energy through the recombination of electrons and holes, and are widely used in the lighting field. LEDs have advantages such as small size, long lifespan, rich colors, reliable performance, and low power consumption. With Micro LED displays receiving increasing attention, they have become an internationally recognized next-generation display technology, and improving the brightness of Micro LEDs has gradually become a research hotspot in the field of electronics.

[0003] However, Micro LED currently faces several challenging technical problems: low luminous efficiency, low power, and high cost, all of which seriously affect and restrict its application in general lighting and its wider market promotion and popularization. Therefore, increasing luminous efficiency, improving brightness and power, and reducing costs have become urgent technical challenges that Micro LED needs to solve.

[0004] To achieve higher brightness in Micro LEDs, improving both the internal and external quantum efficiency of the device is crucial. However, the refractive index differences between substrate materials, epitaxial materials, and air largely limit the light extraction efficiency of the chip, causing total internal reflection at the interfaces of materials with different refractive indices generated in the active region, preventing light from being extracted from the chip. Currently, academia and industry have proposed various methods to improve light extraction efficiency, including flip-chip technology, reflective layers (metallic reflective layers, distributed Bragg reflective layers, total internal reflection layers), patterned substrates, surface roughening, photonic crystals, transparent substrates, three-dimensional vertical structures, laser lift-off, optimization of ohmic electrode shapes, geometrical chip shapes, substrate transfer, and process improvements (packaging, heat dissipation, and phosphor selection for white light). However, all of these methods suffer from high construction costs, insignificant increases in light extraction efficiency, or limitations in the application areas of Micro LEDs. Summary of the Invention

[0005] To improve the brightness of Micro LED chips, this application provides a method for improving the brightness of Micro LED chips.

[0006] This application provides a method for improving the brightness of Micro LED chips, which employs the following technical solution:

[0007] A method for improving the brightness of a Micro LED chip includes the following steps:

[0008] Step 1: Generate an N-GaN semiconductor layer on a semiconductor substrate using metal-organic chemical vapor deposition;

[0009] Step 2: Etch the plane of the N-GaN semiconductor layer away from the semiconductor substrate to obtain a prismatic N-GaN semiconductor layer;

[0010] Step 3: Use metal-organic chemical vapor deposition to generate quantum wells on the etched prismatic N-GaN semiconductor layer;

[0011] Step 4: Generate a P-GaN semiconductor layer on the quantum well using metal-organic chemical vapor deposition;

[0012] Step 5: Etch the plane of the P-GaN semiconductor layer away from the semiconductor substrate to generate a prism on the P-GaN semiconductor layer that intersects the prism on the N-GaN semiconductor layer.

[0013] When light travels from a material with a high refractive index to a material with a low refractive index, total internal reflection occurs at their interface. For GaN-based Micro LEDs, the refractive index of GaN is approximately 2.5, while the external environment of a Micro LED is mostly air, which has a refractive index of approximately 1. Light emitted from the active layer inside the Micro LED will undergo total internal reflection at the interface between the GaN material and the air. Furthermore, the GaN material itself absorbs a significant portion of the reflected light, thus greatly reducing the external light extraction efficiency of the Micro LED.

[0014] By adopting the above technical solution, since metal-organic chemical vapor deposition is used to generate prisms on the P-GaN semiconductor layer that are orthogonal to the prisms on the N-GaN semiconductor layer, when the light source passes through the incident surface and the transparent substrate layer and passes through the fine prism structure on the N-GaN and P-GaN semiconductor layers, on the one hand, the incident angle at the interface is constantly changing while the light is constantly being reflected. This will cause the light that was originally at an incident angle greater than the critical angle of total internal reflection to couple out of the device as the incident angle changes to be less than the critical angle of total internal reflection, thereby improving the light extraction efficiency. On the other hand, the orthogonal prism structure controls the light intensity distribution through refraction, total internal reflection, and light accumulation, so that the light scattered by the light source is concentrated in front, thereby changing the light propagation path and enabling the unused light source to be recycled and reused, improving the light recycling rate and emission efficiency, and further improving the brightness of the Micro LED chip.

[0015] Optionally, the semiconductor substrate may be sapphire.

[0016] By adopting the above technical solutions, firstly, the production technology of sapphire substrates is mature and the device quality is good; secondly, sapphire substrates can maintain good stability in organometallic chemical vapor deposition methods that require high temperatures, and can be used in high-temperature operation processes; thirdly, sapphire has high mechanical strength and hardness, and is easy to handle and clean; finally, because sapphire has a wide optical transmission band, it has good light transmittance from near-ultraviolet light to mid-infrared light, which can improve the brightness of Micro LED chips and is widely used in optical components, infrared devices, high-strength laser lens materials, and photomask materials.

[0017] Optionally, the etching depth of the N-GaN semiconductor layer in step two is 2000A-4000A.

[0018] Optionally, the etching depth of the P-GaN semiconductor layer in step five is 30 Å-50 Å.

[0019] By adopting the above technical solution, the prism structure etched on the N-GaN semiconductor layer and the P-GaN semiconductor layer can reduce the light loss caused by reflection at the interface when light is emitted from inside the chip to outside the chip, thereby improving the light extraction efficiency of Micro LED.

[0020] Optionally, in steps two and five, the apex angle of the prism on the N-GaN semiconductor layer and the apex angle of the prism on the P-GaN semiconductor layer are both 90°-110°.

[0021] By adopting the above technical solution, the emission angle of light after prism refraction can be maintained at about 70°. Together with the light circulating through reflection, the total amount of light refracted in the prism can reach 40%-70%, thereby reducing light loss and further improving the light extraction efficiency of Micro LED.

[0022] Optionally, in steps two and five, an ethylene glycol solution of potassium hydroxide or an ethylene glycol solution of sodium hydroxide may be used for etching.

[0023] By adopting the above technical solution, since GaN crystals have a hexagonal zinc ore structure, the ethylene glycol solutions of potassium hydroxide and sodium hydroxide have different corrosion rates on each crystal, thereby forming orthogonal prismatic structures on the N-GaN semiconductor layer and the P-GaN semiconductor layer.

[0024] Optionally, in step two, the concentration of the ethylene glycol solution of potassium hydroxide or the ethylene glycol solution of sodium hydroxide is 0.8-1.8 mol / L, and the etching temperature is 80-120℃.

[0025] By adopting the above technical solution, the etching depth of the N-GaN semiconductor layer can be maintained between 2000A and 4000A, thereby reducing the negative impact on the light intensity and antistatic performance of Micro LED when the etching depth is too high or too low, thus improving the light intensity of Micro LED without affecting the overall performance of Micro LED chip.

[0026] Optionally, in step five, the concentration of the ethylene glycol solution of potassium hydroxide or the ethylene glycol solution of sodium hydroxide is 0.2-0.6 mol / L, and the etching temperature is 70-100℃.

[0027] By adopting the above technical solution, the etching depth of the P-GaN semiconductor layer can be maintained at 30A-50A, thereby reducing the negative impact on the light intensity and antistatic performance of Micro LED when the etching depth is too high or too low, thus improving the light intensity of Micro LED without affecting the overall performance of Micro LED chip.

[0028] In summary, this application has the following beneficial effects:

[0029] 1. By etching mutually orthogonal prism structures in the N-GaN and P-GaN semiconductor layers, light will undergo refraction, total internal reflection, and light accumulation when passing through the fine prism structure on the surface of the prism layer. This will concentrate the scattered light towards the front, change the light propagation path, and thus improve the light extraction efficiency of the Micro LED chip.

[0030] 2. By controlling the apex angle of the prism structure to be maintained at 90°-110°, the refracted light can reach 40%-70%, improving the light recycling rate and greatly increasing the emitted light, thereby improving the brightness of the Micro LED chip. Attached Figure Description

[0031] Figures 1-5 This is a schematic diagram illustrating the implementation of key steps in this plan.

[0032] Figure 6 This is a schematic diagram of the intersecting prism structures on the N-GaN semiconductor layer and the P-GaN semiconductor layer of this application.

[0033] Figure 7 This is a schematic diagram of the light refraction principle in the prismatic structure of this application.

[0034] Explanation of reference numerals in the attached figures:

[0035] 1. Semiconductor substrate; 2. N-GaN semiconductor layer; 21. Rhombus on N-GaN semiconductor layer; 3. Quantum well; 4. P-GaN semiconductor layer; 41. Rhombus on P-GaN semiconductor layer; 5. Top corner. Detailed Implementation

[0036] The present application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0037] Example

[0038] Example 1

[0039] The method to improve the brightness of Micro LED chips involves the following steps:

[0040] Step 1: An N-GaN semiconductor layer is grown on a sapphire substrate using metal-organic chemical vapor deposition.

[0041] Step 2: Use an ethylene glycol solution with a concentration of 0.8 mol / L potassium hydroxide to etch the N-GaN semiconductor layer on a plane away from the semiconductor substrate at 120°C to obtain a prismatic N-GaN semiconductor layer; wherein the etching depth on the N-GaN semiconductor layer is 2000 Å, and the apex angle of the prismatic shape is 90°-110°.

[0042] Step 3: Use metal-organic chemical vapor deposition to generate quantum wells on the etched prism-shaped N-GaN semiconductor layer;

[0043] Step 4: Generate a P-GaN semiconductor layer on the quantum well using metal-organic chemical vapor deposition;

[0044] Step 5: Use an ethylene glycol solution with a concentration of 0.2 mol / L sodium hydroxide to etch the plane of the P-GaN semiconductor layer away from the semiconductor substrate at 100°C, forming a prism on the P-GaN semiconductor layer that intersects the prism on the N-GaN semiconductor layer; wherein the etching depth on the P-GaN semiconductor layer is 30 Å, and the apex angle of the prism is 90°-110°.

[0045] Example 2

[0046] The method to improve the brightness of Micro LED chips involves the following steps:

[0047] Step 1: An N-GaN semiconductor layer is grown on a sapphire substrate using metal-organic chemical vapor deposition.

[0048] Step 2: Use an ethylene glycol solution with a concentration of 1.8 mol / L potassium hydroxide to etch the N-GaN semiconductor layer on a plane away from the semiconductor substrate at 80°C to obtain a prismatic N-GaN semiconductor layer; wherein the etching depth on the N-GaN semiconductor layer is 4000 Å, and the apex angle of the prismatic shape is 90°-110°.

[0049] Step 3: Use metal-organic chemical vapor deposition to generate quantum wells on the etched prism-shaped N-GaN semiconductor layer;

[0050] Step 4: Generate a P-GaN semiconductor layer on the quantum well using metal-organic chemical vapor deposition;

[0051] Step 5: Use an ethylene glycol solution with a concentration of 0.6 mol / L sodium hydroxide to etch the plane of the P-GaN semiconductor layer away from the semiconductor substrate at 70°C, forming a prism on the P-GaN semiconductor layer that intersects the prism on the N-GaN semiconductor layer; wherein the etching depth on the P-GaN semiconductor layer is 50 Å, and the apex angle of the prism is 90°-110°.

[0052] Example 3

[0053] The method to improve the brightness of Micro LED chips involves the following steps:

[0054] Step 1: An N-GaN semiconductor layer is grown on a sapphire substrate using metal-organic chemical vapor deposition.

[0055] Step 2: Use an ethylene glycol solution with a concentration of 1.3 mol / L potassium hydroxide to etch the N-GaN semiconductor layer on a plane away from the semiconductor substrate at 100°C to obtain a prismatic N-GaN semiconductor layer; wherein the etching depth on the N-GaN semiconductor layer is 3000 Å, and the apex angle of the prismatic shape is 90°-110°.

[0056] Step 3: Use metal-organic chemical vapor deposition to generate quantum wells on the etched prism-shaped N-GaN semiconductor layer;

[0057] Step 4: Generate a P-GaN semiconductor layer on the quantum well using metal-organic chemical vapor deposition;

[0058] Step 5: Use an ethylene glycol solution with a concentration of 0.4 mol / L sodium hydroxide to etch the plane of the P-GaN semiconductor layer away from the semiconductor substrate at 85°C, forming a prism on the P-GaN semiconductor layer that intersects the prism on the N-GaN semiconductor layer; wherein the etching depth on the P-GaN semiconductor layer is 40 Å, and the apex angle of the prism is 90°-110°.

[0059] Example 4

[0060] The method to improve the brightness of Micro LED chips involves the following steps:

[0061] Step 1: An N-GaN semiconductor layer is grown on a sapphire substrate using metal-organic chemical vapor deposition.

[0062] Step 2: Use an ethylene glycol solution with a concentration of 1.2 mol / L potassium hydroxide to etch the N-GaN semiconductor layer on a plane away from the semiconductor substrate at 90°C to obtain a prismatic N-GaN semiconductor layer; wherein the etching depth on the N-GaN semiconductor layer is 3000 Å, and the apex angle of the prismatic shape is 90°-110°.

[0063] Step 3: Use metal-organic chemical vapor deposition to generate quantum wells on the etched prism-shaped N-GaN semiconductor layer;

[0064] Step 4: Generate a P-GaN semiconductor layer on the quantum well using metal-organic chemical vapor deposition;

[0065] Step 5: Use a 0.5 mol / L sodium hydroxide solution in ethylene glycol to etch the plane of the P-GaN semiconductor layer away from the semiconductor substrate at 80°C, generating a prism on the P-GaN semiconductor layer that intersects the prism on the N-GaN semiconductor layer; wherein the etching depth on the P-GaN semiconductor layer is 45 Å, and the apex angle of the prism is 90°-110°.

[0066] Example 5

[0067] The method for improving the brightness of Micro LED chips differs from that in Example 3 in that the etching depth of the N-GaN semiconductor layer is 1500 Å.

[0068] Example 6

[0069] The method for improving the brightness of Micro LED chips differs from that in Example 3 in that the etching depth of the N-GaN semiconductor layer is 4500 Å.

[0070] Example 7

[0071] The method for improving the brightness of Micro LED chips differs from that in Example 3 in that the etching depth of the P-GaN semiconductor layer is 20 Å.

[0072] Example 8

[0073] The method for improving the brightness of Micro LED chips differs from that in Example 3 in that the etching depth of the P-GaN semiconductor layer is 60 Å.

[0074] Example 9

[0075] The method for improving the brightness of Micro LED chips differs from that in Example 3 in that the tip angle of the N-GaN semiconductor layer surface is 85°.

[0076] Example 10

[0077] The method for improving the brightness of Micro LED chips differs from that in Example 3 in that the tip angle of the N-GaN semiconductor layer surface is 115°.

[0078] Example 11

[0079] The method for improving the brightness of Micro LED chips differs from that in Example 3 in that the tip angle of the P-GaN semiconductor layer surface is 85°.

[0080] Example 12

[0081] The method for improving the brightness of Micro LED chips differs from that in Example 3 in that the tip angle of the P-GaN semiconductor layer surface is 115°.

[0082] Example 13

[0083] The method for improving the brightness of Micro LED chips differs from that in Example 3 in that the prism tip angle on the N-GaN semiconductor layer is 85° and the prism tip angle on the P-GaN semiconductor layer is 115°.

[0084] Example 14

[0085] The method for improving the brightness of Micro LED chips differs from that in Example 3 in that the prism tip angle on the N-GaN semiconductor layer is 115° and the prism tip angle on the P-GaN semiconductor layer is 85°.

[0086] Comparative Example

[0087] Comparative Example 1

[0088] The method for improving the brightness of Micro LED chips differs from that in Example 3 in that there is no prism structure on the N-GaN semiconductor.

[0089] Comparative Example 2

[0090] The method for improving the brightness of Micro LED chips differs from that in Example 3 in that there is no prism structure on the P-GaN semiconductor.

[0091] Comparative Example 3

[0092] The method for improving the brightness of Micro LED chips differs from that in Example 3 in that the prisms generated on the P-GaN semiconductor layer do not intersect obliquely with the prisms on the N-GaN semiconductor layer.

[0093] Comparative Example 4

[0094] The method for improving the brightness of Micro LED chips differs from that in Example 3 in that the prisms generated on the P-GaN semiconductor layer are not parallel to the prisms on the N-GaN semiconductor layer.

[0095] Detection methods

[0096] I. Brightness Test

[0097] Brightness tests were conducted on the Micro LEDs prepared using Examples 1-14 and Comparative Examples 1-4, according to standard condition B of CIE 2017, "Methods of Measurement for Micro LEDs". Five parallel samples were used in each group, and the average brightness of each group was calculated. Brightness tests were also conducted on commercially available Micro LED chips without prismatic structures, again according to standard condition B of CIE 2017, with five samples used. The average brightness was calculated, and the percentage increase in brightness of the Micro LED chips prepared using Examples 1-14 and Comparative Examples 1-4 compared to commercially available Micro LED chips without prismatic structures was calculated and recorded in Table 1.

[0098] Table 1

[0099] object Brightness increase percentage (%) object Brightness increase percentage (%) Example 1 20.2 Example 10 15.1 Example 2 20.4 Example 11 15.5 Example 3 20.5 Example 12 15.3 Example 4 20.3 Example 13 10.3 Example 5 18.5 Example 14 10.1 Example 6 17.3 Comparative Example 1 9.6 Example 7 18.9 Comparative Example 2 9.8 Example 8 17.8 Comparative Example 3 8.3 Example 9 15.2 Comparative Example 4 8.5

[0100] Combining Examples 1-8 and Table 1, it can be seen that excessively high or low etching depths will negatively affect the brightness of the Micro LED chip. This is because excessively high or low etching depths will increase the light loss caused by reflection at the interface when light is emitted from inside the chip to the outside of the chip, thus negatively affecting the brightness of the Micro LED chip.

[0101] Combining Examples 3, 9-14 and Table 1, it can be seen that whether the apex angle of the prism generated on the P-GaN semiconductor layer is too large or too small, or the apex angle of the prism generated on the N-GaN semiconductor layer is too large or too small, it will have a negative impact on the brightness of the Micro LED chip. This is because when the apex angle value of the prism structure deviates from the range, the prism structure cannot exert the refraction effect, most of the emitted light cannot be reused, the scattered light source cannot be concentrated, and thus the brightness of the Micro LED chip decreases significantly.

[0102] Based on Example 3, Comparative Examples 1-4 and Table 1, it can be seen that only when prism structures are generated on both the P-GaN semiconductor layer and the N-GaN semiconductor layer can the brightness of the Micro LED chip be significantly improved. Furthermore, the brightness improvement effect of the Micro LED chip is most significant when the prism structures generated on the P-GaN semiconductor layer and the N-GaN semiconductor layer intersect each other.

[0103] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for improving the brightness of a Micro LED chip, characterized in that: Includes the following steps: Step 1: Generate an N-GaN semiconductor layer on a semiconductor substrate using metal-organic chemical vapor deposition; Step 2: Etch the plane of the N-GaN semiconductor layer away from the semiconductor substrate to obtain a prismatic N-GaN semiconductor layer; Step 3: Use metal-organic chemical vapor deposition to generate quantum wells on the etched prismatic N-GaN semiconductor layer; Step 4: Generate a P-GaN semiconductor layer on the quantum well using metal-organic chemical vapor deposition; Step 5: Etch the plane of the P-GaN semiconductor layer away from the semiconductor substrate to generate a prism on the P-GaN semiconductor layer that is perpendicular to the prism on the N-GaN semiconductor layer; The semiconductor substrate is selected from sapphire. In step two, the etching depth of the N-GaN semiconductor layer is 2000Å-4000Å; In step five, the etching depth of the P-GaN semiconductor layer is 30 Å-50 Å. In steps two and five, the apex angle of the prism on the N-GaN semiconductor layer and the apex angle of the prism on the P-GaN semiconductor layer are both 90°-110°.

2. The method for improving the brightness of a Micro LED chip according to claim 1, characterized in that: In steps two and five, an ethylene glycol solution of potassium hydroxide or an ethylene glycol solution of sodium hydroxide is used for etching.

3. A method for improving the brightness of a Micro LED chip according to claim 2, characterized in that: In step two, the concentration of the ethylene glycol solution containing potassium hydroxide or sodium hydroxide is 0.8-1.8 mol / L, and the etching temperature is 80-120℃.

4. A method for improving the brightness of a Micro LED chip according to claim 2, characterized in that: In step five, the concentration of the ethylene glycol solution containing potassium hydroxide or sodium hydroxide is 0.2-0.6 mol / L, and the etching temperature is 70-100℃.

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