Linearly polarized light emitting diode based on double-layer superstructure grating structure and preparation process thereof

Abstract

The application discloses a linear polarization light emitting diode based on a double-layer super-structured grating structure and a preparation process, which comprises an LED epitaxial wafer, which comprises, from bottom to top, a substrate, an undoped epitaxial layer, an n-type epitaxial layer, a quantum well layer and a p-type epitaxial layer; a metal composite super-structured grating layer, which comprises a resin grating layer arranged on the lower surface of the substrate and a first metal layer covering the resin grating layer; and a metal-dielectric composite super-structured grating layer, which comprises a p-type epitaxial grating layer arranged on the upper surface of the p-type epitaxial layer and a second metal layer covering the p-type epitaxial grating layer. The application can realize polarization emission, can efficiently recycle mode energy, can reduce energy loss while ensuring the polarization extinction ratio of the device, and can realize high-efficiency polarization emission of the LED.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor technology and optical metamaterials, and particularly relates to a linearly polarized light-emitting diode based on a double-layer metagrating structure and its fabrication process. Background Technology

[0002] Nitride-based light-emitting diodes (LEDs), especially Micro-LEDs, are widely used in lighting, display, and communication. Among them, LEDs that can emit linearly polarized light play a key role in many high-value-added fields such as LCD backlights, 3D displays, information encryption, and biomedical diagnostics. However, traditional LEDs are usually unpolarized, especially gallium nitride (GaN)-based LEDs, which have weak anisotropy and are difficult to polarize, usually requiring additional waveplates for induction. However, waveplates are bulky, difficult to integrate, and result in polarized light loss, thicker panels, and higher costs.

[0003] To address this issue, integrating subwavelength metal grating structures onto the LED surface has become a common approach, enabling transverse magnetic (TM) mode linear polarization light emission by controlling the grating parameters. However, this method sacrifices LED light extraction efficiency, and transverse electrical (TE) mode reflection results in at least 50% mode energy loss, leading to a reduction in luminous efficiency. This contradiction between polarization emission and luminous efficiency has constrained the development of linearly polarized LEDs. Although attempts have been made to improve efficiency and polarization degree through resonant coupling of multiple quantum wells with metal nanostructures, or to utilize metal nanostructures with half-wave plate functionality to convert TE mode to TM mode, the efficiency improvement has remained limited.

[0004] Therefore, there is an urgent need to design new structures that can achieve polarized emission while efficiently recovering lost mode energy, reducing energy loss while maintaining the device's polarization extinction ratio, thus achieving efficient polarized emission of LEDs. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a linearly polarized light-emitting diode based on a double-layer metagrating structure and its fabrication process. This invention can achieve polarized emission and efficiently recover lost mode energy, reducing energy loss while ensuring the polarization extinction ratio of the device, thus achieving efficient polarized emission of the LED.

[0006] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution:

[0007] According to a first aspect of the present invention, a linearly polarized light-emitting diode based on a double-layer metagrating structure is provided, comprising:

[0008] LED epitaxial wafer, comprising, from bottom to top, a substrate, an undoped epitaxial layer, an n-type epitaxial layer, a quantum well layer and a p-type epitaxial layer;

[0009] A metal composite meta-grating layer includes a resin grating layer disposed on the lower surface of a substrate, and a first metal layer covering the resin grating layer;

[0010] A metal-dielectric composite meta-grating layer includes a p-type epitaxial grating layer disposed on the upper surface of the p-type epitaxial layer, and a second metal layer covering the p-type epitaxial grating layer.

[0011] In one possible implementation of the first aspect, the grating height of the resin grating layer is 40 nm to 60 nm, the period is 100 nm to 150 nm, and the duty cycle is 0.5 to 0.7.

[0012] In one possible implementation of the first aspect, the thickness of the first metal layer is 20 nm to 40 nm.

[0013] In one possible implementation of the first aspect, the material of the first metal layer is one of Al, Ag, Au or Cu.

[0014] In one possible implementation of the first aspect, the grating height of the p-type epitaxial grating layer is 100 nm to 150 nm, the period is 200 nm to 1 μm, and the duty cycle is 0.4 to 0.6.

[0015] In one possible implementation of the first aspect, the thickness of the second metal layer is 150 nm to 300 nm.

[0016] In one possible implementation of the first aspect, the material of the second metal layer is one of Al, Ag, Au or Cu.

[0017] In one possible implementation of the first aspect, the angle between the grating orientation of the metal composite metagrating layer and the grating orientation of the metal dielectric composite metagrating layer is 45° to 50°.

[0018] In one possible implementation of the first aspect, the linearly polarized light-emitting diode further includes:

[0019] The negative electrode is located on the n-type epitaxial layer;

[0020] The positive electrode is located on the p-type epitaxial layer.

[0021] According to a second aspect of the present invention, a fabrication process for a linearly polarized light-emitting diode based on a double-layer metagrating structure is provided, comprising:

[0022] 1) Photoresist is uniformly coated on the surface of the p-type epitaxial layer of the LED epitaxial wafer;

[0023] 2) A photoresist grating layer is fabricated on the photoresist using laser interference lithography;

[0024] 3) A metal mask layer is deposited on the photoresist grating layer by vapor deposition;

[0025] 4) Remove the photoresist grating layer using an organic solvent to obtain a metal mask grating layer;

[0026] 5) Based on the metal mask grating layer, a p-type epitaxial grating layer is etched on the surface of the p-type epitaxial layer;

[0027] 6) Remove the metal mask grating layer on the surface of the p-type epitaxial grating layer, and then deposit the second metal layer onto the surface of the p-type epitaxial grating layer and into the groove to obtain a metal dielectric composite metagrating layer;

[0028] 7) Deposit organic resin on the substrate surface of the LED epitaxial wafer;

[0029] 8) A resin grating layer was prepared on an organic resin using ultraviolet nanoimprinting technology;

[0030] 9) The first metal layer is vapor-deposited onto the surface of the resin grating layer to obtain a metal composite metagrating layer.

[0031] Compared with the prior art, the present invention has at least the following beneficial effects:

[0032] This invention provides a linearly polarized light-emitting diode (LED) based on a dual-layer metagrating structure, integrating a metal composite metagrating layer with polarization selection function and a metal dielectric composite metagrating layer capable of recovering energy from loss modes. Unlike traditional linearly polarized LEDs, the metal dielectric composite metagrating layer of this invention converts the reflected, dissipated TE mode into a TM mode that can be extracted a second time, allowing for secondary radiation. For upward-radiated photons, the metal dielectric composite metagrating layer also decouples the captured mode, providing additional momentum to the captured mode and avoiding energy loss due to momentum mismatch. Furthermore, the polarization selection function of the metal composite metagrating layer maximizes the TM mode output. The continuous mode conversion and decoupling process of the captured mode continuously recovers the mode energy lost during polarization emission. Therefore, the synergistic effect of the dual-layer metagrating structure overcomes the bottleneck problem of low efficiency in traditional polarized light sources, achieving a dual improvement in polarization luminous efficiency and polarization extinction ratio, representing the realization of a high-efficiency, high-polarization polarized light source. A metallic composite metagrating layer for achieving polarized emission extracts the TM mode and reflects the TE mode. The physical mechanism of this polarized emission can be explained by equivalent medium theory, treating the structure as a negative uniaxial refractive index crystal, leading to anomalous transmission processes for both TM and TE modes. In this invention, the metallic composite metagrating layer allows the TM mode to pass through with high transmittance, while the TE mode is reflected due to the excited free electron oscillation effect, thus achieving polarization selection of the TM mode. The metallic dielectric composite metagrating layer for loss mode energy recovery has dual functions of mode conversion and mode decoupling. First, acting as a reflective half-wave plate, it converts the TE mode reflected back into the device into a TM mode that can be extracted a second time. This is due to the π phase difference achieved by the significant difference in the equivalent refractive index of the orthogonal electric field components after reflection. Furthermore, momentum compensation can be achieved by introducing grating momentum, significantly modulating the dispersion curves of air, GaN, and the trapped modes. The momentum modulation process relies on the Bragg scattering mechanism of the metallic composite metagrating layer. By increasing or decreasing the initial momentum to establish suitable momentum-matching conditions, the decoupling output of the trapped modes is promoted. After momentum compensation, the trapped modes can couple with free photons in GaN, thereby effectively recovering the light energy loss from the back reflection surface and significantly improving the output efficiency of the TM mode. Therefore, the dual function of the metallic composite metagrating layer enables efficient recovery of energy from lossy modes during polarization emission. The metallic composite metagrating layer is fabricated using cost-effective and easily processed laser interferometry, replacing expensive and time-consuming traditional metasurface fabrication processes such as electron beam lithography, ion beam etching, and nanoimprinting, thus overcoming the challenges of large-area mass production and device integration.

[0033] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings used in the description of the specific embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0035] Figure 1 This is a schematic diagram of the structure of a linearly polarized light-emitting diode based on a double-layer metagrating structure in an embodiment of the present invention;

[0036] Figure 2 This is a schematic diagram illustrating the propagation and evolution of TM and TE modes in a linearly polarized light-emitting diode based on a double-layer metagrating structure in an embodiment of the present invention.

[0037] Figure 3 Comparison of electric field distributions in TM mode excited by TM dipole and TE dipole for three different linearly polarized light-emitting diodes (including the linearly polarized light-emitting diode based on a double-layer metagrating structure in the embodiments of the present invention).

[0038] Figure 4 This is a process flow diagram of a linearly polarized light-emitting diode based on a double-layer metagrating structure in an embodiment of the present invention;

[0039] Figure 5 These are scanning electron microscope images of the metal composite metagrating layer (corresponding to a in the figure) and the metal dielectric composite metagrating layer (corresponding to b in the figure) in the embodiments of the present invention.

[0040] Figure 6 This is a schematic diagram of the structure of a linearly polarized light-emitting diode based on a double-layer metagrating structure that integrates a positive electrode and a negative electrode in an embodiment of the present invention.

[0041] Figure 7 The diagram shows a comparison of the current-voltage characteristics of four different linearly polarized light-emitting diodes (including the linearly polarized light-emitting diode based on the double-layer metagrating structure in the embodiments of the present invention). The inset shows a microscope photograph (left) and a polarization illumination image (right) of the linearly polarized light-emitting diode based on the double-layer metagrating structure in the embodiments of the present invention.

[0042] Figure 8 The figure shows the polarization-dependent electroluminescence spectrum of a linearly polarized light-emitting diode based on a double-layer metagrating structure in an embodiment of the present invention. The inset is a schematic diagram of the test method.

[0043] Figure 9 The figure shows a comparison of the electroluminescence intensity of four different linearly polarized light-emitting diodes with different emission angles in TM mode (including the linearly polarized light-emitting diode based on the double-layer metagrating structure in the embodiment of the present invention). The inset is a schematic diagram of the test method.

[0044] Figure 10 A comparison of the polarization extinction ratio of four different linearly polarized light-emitting diodes (LEDs) with different emission angles (including the linearly polarized LED based on a double-layer metagrating structure in the embodiments of this invention).

[0045] Figure 11 This is an extended application of polarization-controlled encrypted display based on a linearly polarized light-emitting diode with a double-layer metagrating structure in the embodiments of the present invention.

[0046] The components are as follows: 1. Metal composite metagrating layer; 2. Substrate; 3. Undoped epitaxial layer; 4. n-type epitaxial layer; 5. Quantum well layer; 6. p-type epitaxial layer; 7. Metal dielectric composite metagrating layer; 8. First metal layer; 9. Resin grating layer; 10. p-type epitaxial grating layer; 11. Second metal layer; 12. Photoresist; 13. Photoresist grating layer; 14. Metal mask layer; 15. Metal mask grating layer; 16. Negative electrode; 17. Positive electrode; 18. Step; 19. Negative electrode contact layer; 20. Negative electrode conductive layer; 21. Positive electrode contact layer; 22. Positive electrode conductive layer; 23. Positive electrode region; 24. Negative electrode region; 25. Current spread region; 26. Polarization control encrypted display design layout; 27. Top panel; 28. Middle panel; 29. ​​Bottom panel; 30. Polarizer. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] like Figure 1As shown, this embodiment of the invention provides a linearly polarized light-emitting diode based on a dual-layer metagrating structure, including an LED epitaxial wafer, a metal composite metagrating layer 1, and a metal dielectric composite metagrating layer 7. The LED epitaxial wafer includes, from bottom to top, a substrate 2, an undoped epitaxial layer 3, an n-type epitaxial layer 4, a quantum well layer 5, and a p-type epitaxial layer 6. The metal composite metagrating layer 1 includes a resin grating layer 9 disposed on the lower surface of the substrate 2, and a first metal layer 8 covering the resin grating layer 9. The metal dielectric composite metagrating layer 7 includes a p-type epitaxial grating layer 10 disposed on the upper surface of the p-type epitaxial layer 6, and a second metal layer 11 covering the p-type epitaxial grating layer 10.

[0049] In other words, the linearly polarized light-emitting diode based on the dual-layer metagrating structure includes, from bottom to top, a metal composite metagrating layer 1, a substrate 2, an undoped epitaxial layer 3, an n-type epitaxial layer 4, a quantum well layer 5, a p-type epitaxial layer 6, and a metal dielectric composite metagrating layer 7. The metal composite metagrating layer 1 is disposed on the lower surface (light-emitting surface) of the substrate 2 and consists of a resin grating layer 9 and a first metal layer 8 covering it; the metal dielectric composite metagrating layer 7 is disposed on the surface of the p-type epitaxial layer 6 and consists of a p-type epitaxial grating layer 10 and a second metal layer 11 covering it.

[0050] For example, substrate 2 is a sapphire substrate, and the materials of undoped epitaxial layer 3, n-type epitaxial layer 4, quantum well layer 5 and p-type epitaxial layer 6 are GaN, GaAs, InGaN or AlGaN; wherein, when the linearly polarized light-emitting diode is applied to the ultraviolet or deep ultraviolet band, the material is AlGaN; when the linearly polarized light-emitting diode is applied to the blue light band, the material is GaN; when the linearly polarized light-emitting diode is applied to the green light band, the material is InGaN; and when the linearly polarized light-emitting diode is applied to the red light band, the material is GaAs.

[0051] In one possible implementation, the grating height of the resin grating layer 9 is 40 nm to 60 nm, the period is 100 nm to 150 nm, and the duty cycle is 0.5 to 0.7. The thickness of the first metal layer 8 is 20 nm to 40 nm, and the material of the first metal layer 8 is one of Al, Ag, Au, or Cu. This height parameter creates a separated first metal layer 8, generating destructive interference of the TM mode at the gap, forming an interference effect in the resonant cavity, thereby enhancing the transmission efficiency of the TM mode and relaxing the height requirement of the first metal layer 8 for polarization emission. Therefore, this structural parameter is chosen to improve the extraction effect of the TM mode, maximizing both transmission efficiency and polarization degree.

[0052] In one implementation, the p-type epitaxial grating layer 10 has a grating height of 100 nm to 150 nm, a period of 200 nm to 1 μm, and a duty cycle of 0.4 to 0.6. The second metal layer 11 has a thickness of 150 nm to 300 nm, and the material of the second metal layer 11 is one of Al, Ag, Au, or Cu. The phase difference of the reflected electric field component is only related to parameters such as grating height, period, and duty cycle. By adjusting these parameters, the nanoscale metal composite metagrating layer 1 can achieve a reflective waveplate effect for different wavelengths. Due to its extensive periodic distribution and direct integration with the p-type epitaxial grating layer 10, it can be used for mode conversion between TE and TM modes and decoupling of trapped modes, thereby achieving polarization emission with high efficiency and reducing energy loss.

[0053] In one implementation, the grating orientation of the metallic composite metagrating layer 1 is at an angle of 45° to 50° relative to the grating orientation of the metallic dielectric composite metagrating layer 7. The metallic composite metagrating layer 1 acts as a reflective half-wave plate, converting the reflected TE mode into an extractable TM mode. Its grating orientation angle allows for a π-phase difference after the orthogonal electric field components are reflected. This phase difference arises from the significant difference in the equivalent refractive index of the different electric field components, thus achieving the mode conversion effect.

[0054] More preferably, the angle between the grating orientation of the metal composite metagrating layer 1 and the grating orientation of the metal dielectric composite metagrating layer 7 is 45°.

[0055] In one possible implementation, the linearly polarized light-emitting diode further includes a negative electrode 16 and a positive electrode 17, wherein the negative electrode 16 is located on the n-type epitaxial layer 4; and the positive electrode 17 is located on the p-type epitaxial layer 6.

[0056] For example, the metal materials of the negative electrode 16 and the positive electrode 17 are Ti / Al, Ti / Au, Ni / Al or Ni / Au, wherein the thickness of Ti or Ni is 100 nm to 150 nm, and the thickness of Al or Au is 300 nm to 400 nm.

[0057] See appendix Figure 2 This demonstrates the propagation and recycling process of TM and TE modes within the structure. Figure 2 The polarization mode with the electric field direction perpendicular to the metal composite metagrating layer 1 is defined as the TM mode, while the electric field direction of the TE mode is parallel to the metal composite metagrating layer 1. The polarization extinction ratio ER is commonly used to evaluate the polarization performance of the device.

[0058]

[0059] In the above formula, I TM and ITE These represent the total radiative intensity in TM and TE modes, respectively. (See attached image.) Figure 2 In this process, electrons and holes recombine in the quantum well layer 5 to generate photons. The photon radiation process often exhibits a mixture of TM and TE modes, propagating in various directions. For downward-radiated photons, the TM mode is extracted and radiated outward by the metal composite metagrating layer 1, composed of the first metal layer 8 and the resin grating layer 9, while the TE mode is reflected back into the structure, resulting in energy waste in the polarization device. However, unlike conventional linearly polarized light-emitting diodes (LEDs), the metal dielectric composite metagrating layer 7 converts the reflected TE mode into a TM mode that can be extracted a second time, allowing it to be re-radiated through the metal composite metagrating layer 1. For upward-radiated photons, the metal dielectric composite metagrating layer 7 also promotes the decoupling radiation of the trapped TM mode by providing momentum to the trapped mode. The continuous mode conversion and decoupling process recovers the mode energy lost during polarization emission, thereby improving the radiation efficiency and polarization extinction ratio of the linearly polarized LED.

[0060] Appendix Figure 3 Images (a), (b), and (c) illustrate mode transitions for three different structures, where the electric field intensity of the TM electric field distribution represents the mode transition effect of the TE dipole excitation. (See appendix...) Figure 3 In (a) and (b) of the above, there is no electric field intensity distribution; therefore, there is no mode conversion, and 50% of the TE mode is wasted. Meanwhile, in the attached... Figure 3 (c) in the figure shows a clear electric field intensity distribution. Therefore, the metal dielectric composite metagrating layer 7 induces mode conversion, converting the TE mode blocked by the metal composite metagrating layer 1 into a TM mode that can be extracted a second time.

[0061] Appendix Figure 3 (d), (e), and (f) illustrate mode decoupling with three different structures, where the electric field intensity of the TM electric field distribution represents the mode decoupling effect of the TM dipole excitation. (See appendix...) Figure 3 In (d), only a small fraction of the TM modes are radiated into the air through the metallic composite metagrating layer 1; in the attached... Figure 3 In (e), the upward-radiating TM mode is reflected by the silver mirror and radiates again through the metallic composite metagrating layer 1. However, the momentum mismatch effect induced by the planar structure causes the radiation mode to be trapped and dissipated as heat, thus limiting the radiation of the TM mode. (See attached diagram.) Figure 3 In (f), the radiation intensity of the TM mode is greatly improved. This is due to the momentum compensation achieved by the introduction of grating momentum. The appropriate momentum matching conditions are established by Bragg scattering, which decouples the initially captured TM mode and finally radiates it into the air through the metal composite metagrating layer 1.

[0062] like Figure 4 As shown, this invention provides a fabrication process for a linearly polarized light-emitting diode based on a double-layer metagrating structure, specifically including the following steps:

[0063] 1) Photoresist 12 is uniformly coated on the surface of the p-type epitaxial layer 6 of the LED epitaxial wafer.

[0064] Specifically, the photoresist 12 is a positive photoresist of S1805, with a spin coating thickness of 300 nm to 400 nm.

[0065] It should be noted that the surface of the LED epitaxial wafer needs to be cleaned before applying photoresist 12.

[0066] 2) A photoresist grating layer 13 is prepared on the photoresist 12 using laser interference lithography.

[0067] Specifically, the laser interference lithography technique is used to achieve a photoresist grating layer 13 with a period of 200 nm ~ 1 μm, a height of 100 nm, and a duty cycle of 0.4 ~ 0.6.

[0068] Laser interference lithography can precisely control the period and shape of the photoresist grating layer 13 by adjusting the beam angle, exposure time, and development time, so that it can be transformed from a sinusoidal pattern into a rectangular pattern.

[0069] In one embodiment, laser interference lithography can be replaced by nanoimprint lithography.

[0070] 3) A metal mask layer 14 is deposited on the photoresist grating layer 13 by vapor deposition.

[0071] Specifically, the metal mask layer 14 is made of Ni or Cr and has a thickness of 25 nm to 30 nm; the evaporation method is electron beam evaporation or thermal evaporation.

[0072] 4) Remove the photoresist grating layer 13 using an organic solvent to obtain the metal mask grating layer 15.

[0073] Specifically, the organic solvent is methylpyrrolidone or acetone.

[0074] 5) Based on the metal mask grating layer 15, a p-type epitaxial grating layer 10 is etched on the surface of the p-type epitaxial layer 6.

[0075] Specifically, a p-type epitaxial grating layer 10 is etched onto the surface of the p-type epitaxial layer 6. During the process, Cl2 and BCl3 are used as etching gases for surface etching. The etching rate and sample morphology are controlled by adjusting the ratio of Cl2 to BCl3; the etching depth of the p-type epitaxial grating layer 10 is controlled by adjusting the etching time, with an etching depth of 100 nm to 150 nm.

[0076] 6) Remove the metal mask grating layer 15 from the surface of the p-type epitaxial grating layer 10, and then deposit the second metal layer 11 onto the surface of the p-type epitaxial grating layer 10 and into the groove to obtain the metal dielectric composite metagrating layer 7.

[0077] Specifically, the material of the second metal layer 11 is Al, Ag, Au, or Cu, and the metal thickness is 150 nm to 300 nm. The deposition method is electron beam evaporation or thermal evaporation. The dielectric material of the metal-dielectric composite metagrating layer 7 is GaN, GaAs, InGaN, or AlGaN.

[0078] 7) Deposit organic resin on the surface of substrate 2 of the LED epitaxial wafer.

[0079] 8) A resin grating layer was prepared on an organic resin using ultraviolet nanoimprinting technology.

[0080] Specifically, the grating height of the resin grating layer 9 is 40 nm ~ 60 nm, the period is 100 nm ~ 150 nm, and the duty cycle is 0.5 ~ 0.7.

[0081] Specifically, the height of the resin grating layer 9 is 40 nm to 60 nm, the period is 100 nm to 150 nm, and the duty cycle is 0.5 to 0.7.

[0082] In one embodiment, the nanoimprint process can be replaced by the laser interference lithography process.

[0083] 9) The first metal layer 8 is vapor-deposited onto the surface of the resin grating layer 9 to obtain the metal composite metagrating layer 1.

[0084] Specifically, the material of the first metal layer 8 is one of Al, Ag, Au or Cu, and the thickness is 20 nm to 40 nm.

[0085] See appendix Figure 5 Image (a) is a scanning electron microscope (SEM) image of the metal composite metagrating layer 1 with a period of 100 nm and a duty cycle of 0.6; (See attached image.) Figure 5(b) is a scanning electron microscope planar and cross-sectional view of the metal-dielectric composite meta-grating layer 7, which was obtained by depositing a second metal layer 11 with a thickness of 200 nm on the surface of the p-type epitaxial grating layer 10.

[0086] See appendix Figure 6 This illustration shows a schematic diagram of a linearly polarized light-emitting diode based on a double-layer metagrating structure integrating a negative electrode 16 and a positive electrode 17 in an embodiment of the present invention. Step 18 is prepared by photolithography and ICP etching, and metal is deposited to obtain a negative electrode contact layer 19, a negative electrode conductive layer 20, a positive electrode contact layer 21, and a positive electrode conductive layer 22.

[0087] The metal materials of the negative electrode contact layer 19 and the positive electrode contact layer 21 are Ti or Ni, and the metal materials of the negative electrode conductive layer 20 and the positive electrode conductive layer 22 are Al or Au. The thickness of Ti or Ni is 100 nm to 150 nm, and the thickness of Al or Au is 300 nm to 400 nm; the evaporation method used is electron beam evaporation or thermal evaporation.

[0088] See appendix Figure 7 The figure shows a comparison of the current-voltage characteristics of four different linearly polarized light-emitting diodes (LEDs) with different structures. For the linearly polarized LED based on the double-layer metagrating structure in this embodiment, although the ICP etching process causes potential etching damage and thinning of the p-type epitaxial layer 6, which may affect its current diffusion effect, the current-voltage characteristic curves of the device integrating the metal composite metagrating layer 1 and the metal dielectric composite metagrating layer 7 show that its series resistance and threshold voltage are only slightly higher than other structures, and no leakage current is observed. Therefore, the linearly polarized LED with the integrated double-layer metagrating structure ensures sufficient carrier mobility and excellent electrical performance.

[0089] See appendix Figure 7 The left-hand inset shows a microscope image of a linearly polarized light-emitting diode based on a double-layer metagrating structure, revealing the positive electrode region 23, negative electrode region 24, and current-spreading region 25 obtained through device fabrication. Figure 7 The illustration on the right shows polarization illumination images of a linearly polarized light-emitting diode based on a double-layer metagrating structure at different polarization rotation angles (0°, 90°), demonstrating a significant change in polarization emission intensity and indicating high-polarization linearly polarized emission.

[0090] See appendix Figure 8 The diagram shows the polarization electroluminescence spectrum of a linearly polarized light-emitting diode based on a double-layer metagrating structure in an embodiment of the present invention. A polarization rotation angle of 0° corresponds to the TM mode, while a rotation angle of 90° corresponds to the TE mode. The electroluminescence spectrum curves show obvious polarization emission characteristics, with the electroluminescence intensity decreasing sharply with increasing rotation angle.

[0091] See appendix Figure 9 This is a comparison of the electroluminescence intensity of four different linearly polarized light-emitting diodes (LEDs) in TM mode at different emission angles. (See attached image.) Figure 9 As can be seen, the device integrating the metal composite metagrating layer 1 and the metal dielectric composite metagrating layer 7 exhibits a higher TM mode electroluminescence intensity. Within an emission angle range of ±60°, the TM mode electroluminescence intensity induced by the metal dielectric composite metagrating layer 7 increases by a factor of 2. This is attributed to the energy recovery mechanism of the loss mode, including the dual functions of mode switching and mode decoupling.

[0092] See appendix Figure 10 This paper presents a comparison of the polarization extinction ratios (ERs) of four different linearly polarized light-emitting diodes (LEDs) at various emission angles. The ER is calculated by comparing the electroluminescence intensity of the TM mode with that of the TE mode. (See attached image.) Figure 10 In the comparison, the linearly polarized light-emitting diode without the integrated metal composite metagrating layer 1 has an ER value of 1 dB, representing unpolarized emission. Among the two types of linearly polarized light-emitting diodes with the integrated metal composite metagrating layer 1, the device with the integrated metal dielectric composite metagrating layer 7 achieves an ER value of 23.5 dB at an emission angle of 0°. Within an emission angle range of ±60°, the average ER value of the linearly polarized light-emitting diode with the integrated metal dielectric composite metagrating layer 7 is 21.9 dB, significantly higher than the comparative structure.

[0093] See appendix Figure 11 This invention demonstrates an exploration of the extended application of polarization-controlled encrypted displays using linearly polarized light-emitting diodes based on a dual-layer metagrating structure, as described in embodiments of the present invention. (Appendix) Figure 11 Image (a) shows the polarization-controlled encrypted display design layout 26 composed of linearly polarized light-emitting diode pixels and the corresponding scanning electron microscope planar view, where each display unit consists of 30 pixels arranged in a 5 × 6 grid, integrating two orthogonal polarization emission modes. (See appendix) Figure 11 (b) illustrates the polarization-controlled encrypted display design panel, where the top panel 27 represents a pixel overlay of two images, while the middle panel 28 and bottom panel 29 display two switchable images (“36” and “48”). (See appendix) Figure 11(c) illustrates a schematic diagram of a polarization-controlled encrypted display based on two orthogonal polarization emission modes. By rotating the polarizer 30 in the middle position, the grating direction of the metal composite metagrating layer 1 of the linearly polarized light-emitting diode based on a double-layer metagrating structure is aligned with the x-axis or y-axis respectively, thereby displaying the separate characters "36" and "48". This exploratory application aims to realize a polarization-controlled encrypted display based on an electroluminescent device. Given that the designed linearly polarized light-emitting diode has high luminous efficiency, polarization extinction ratio, and resolution, it can greatly promote the development of self-driven polarization-controlled encrypted display applications.

[0094] Compared with the prior art, the linearly polarized light-emitting diode based on a dual-layer metagrating structure provided by the present invention simultaneously improves the polarization extinction ratio and polarization luminous efficiency of the linearly polarized light-emitting diode by simultaneously integrating a metal composite metagrating layer 1 with polarization selection function and a metal dielectric composite metagrating layer 7 with loss mode energy recovery mechanism.

[0095] This invention relates to a metallic dielectric composite metagrating layer 7 for loss mode energy recovery, which possesses dual functions of mode conversion and mode decoupling. First, acting as a half-wave plate, it converts the TE modes reflected back into the device into TM modes that can be extracted a second time. Second, the Bragg scattering mechanism of the metallic dielectric composite metagrating layer 7 provides momentum to the captured TM modes, promoting their decoupling and radiation. This dual function enables efficient recovery of loss mode energy during polarization emission.

[0096] The metal dielectric composite meta-grating layer 7 of this invention is prepared by laser interference lithography, which is cost-effective and easy to process. It replaces the expensive and time-consuming traditional metasurface manufacturing processes, such as electron beam lithography, ion beam etching and nanoimprinting, thereby overcoming the challenges of large-area mass production and device integration. It has great advantages in terms of process difficulty and economic cost.

[0097] This invention relates to the design and fabrication process of a linearly polarized light-emitting diode based on a double-layer metagrating structure, which overcomes the bottleneck problem of low efficiency in traditional linearly polarized light-emitting diodes and promotes their application and development in information encryption, 3D display, optical communication and many other fields.

[0098] In the description of this invention, it should be understood that the terms "upper", "lower", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0099] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0100] In this invention, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0101] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0102] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which 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. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0103] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A linearly polarized light-emitting diode based on a double-layer metagrating structure, characterized in that, include: LED epitaxial wafer, comprising a substrate (2), an undoped epitaxial layer (3), an n-type epitaxial layer (4), a quantum well layer (5) and a p-type epitaxial layer (6) arranged sequentially from bottom to top; The metal composite meta-grating layer (1) includes a resin grating layer (9) disposed on the lower surface of the substrate (2) and a first metal layer (8) covering the resin grating layer (9). The metal dielectric composite meta-grating layer (7) includes a p-type epitaxial grating layer (10) disposed on the upper surface of the p-type epitaxial layer (6), and a second metal layer (11) covering the p-type epitaxial grating layer (10).

2. A linearly polarized light-emitting diode based on a double-layer metagrating structure according to claim 1, characterized in that, The resin grating layer (9) has a grating height of 40 nm ~ 60 nm, a period of 100 nm ~ 150 nm, and a duty cycle of 0.5 ~ 0.

7.

3. A linearly polarized light-emitting diode based on a double-layer metagrating structure according to claim 1, characterized in that, The thickness of the first metal layer (8) is 20 nm ~ 40 nm.

4. A linearly polarized light-emitting diode based on a double-layer metagrating structure according to claim 3, characterized in that, The material of the first metal layer (8) is one of Al, Ag, Au or Cu.

5. A linearly polarized light-emitting diode based on a double-layer metagrating structure according to claim 1, characterized in that, The p-type epitaxial grating layer (10) has a grating height of 100 nm ~ 150 nm, a period of 200 nm ~ 1 μm, and a duty cycle of 0.4 ~ 0.

6.

6. A linearly polarized light-emitting diode based on a double-layer metagrating structure according to claim 1, characterized in that, The thickness of the second metal layer (11) is 150 nm ~ 300 nm.

7. A linearly polarized light-emitting diode based on a double-layer metagrating structure according to claim 6, characterized in that, The material of the second metal layer (11) is one of Al, Ag, Au or Cu.

8. A linearly polarized light-emitting diode based on a double-layer metagrating structure according to claim 1, characterized in that, The angle between the grating orientation of the metal composite meta-grating layer (1) and the grating orientation of the metal dielectric composite meta-grating layer (7) is 45°~50°.

9. A linearly polarized light-emitting diode based on a double-layer metagrating structure according to claim 1, characterized in that, Linearly polarized light-emitting diodes also include: The negative electrode (16) is located on the n-type epitaxial layer (4); The positive electrode (17) is located on the p-type epitaxial layer (6).

10. The fabrication process of a linearly polarized light-emitting diode based on a double-layer metagrating structure as described in any one of claims 1 to 9, characterized in that, include: 1) Photoresist (12) is uniformly coated on the surface of the p-type epitaxial layer (6) of the LED epitaxial wafer. 2) A photoresist grating layer (13) is prepared on the photoresist (12) using laser interference lithography. 3) A metal mask layer (14) is deposited on the photoresist grating layer (13) by vapor deposition. 4) Remove the photoresist grating layer (13) using an organic solvent to obtain the metal mask grating layer (15). 5) Based on the metal mask grating layer (15), a p-type epitaxial grating layer (10) is etched on the surface of the p-type epitaxial layer (6). 6) Remove the metal mask grating layer (15) on the surface of the p-type epitaxial grating layer (10), and then deposit the second metal layer (11) onto the surface of the p-type epitaxial grating layer (10) and the groove to obtain the metal dielectric composite meta grating layer (7). 7) Deposit organic resin on the surface of the substrate (2) of the LED epitaxial wafer; 8) A resin grating layer was prepared on an organic resin using ultraviolet nanoimprinting technology (9); 9) The first metal layer (8) is vapor deposited onto the surface of the resin grating layer (9) to obtain the metal composite meta grating layer (1).

Images