Resonant cavity light emitting diode based on birefringent crystal, preparation method and application thereof

Abstract

The invention relates to a resonant cavity light-emitting diode based on birefringent crystals, a preparation method and application thereof. The light-emitting diode comprises a substrate layer, a reflecting layer, a p-GaN layer, an active layer, an n-GaN layer, a terminal electrode layer and a high-contrast grating layer which are sequentially stacked. Wherein the active layer is configured to be of a birefringent quantum well structure, so that light waves passing through the active layer generate orthogonal linearly polarized light; and the high-contrast grating layer is used for filtering the orthogonal linearly polarized light, so that the light-emitting diode radiates linearly polarized light in a single direction. In the process of preparing the light-emitting diode, an inverted mounting process is adopted, an active microcavity structure (a p-GaN layer, an active layer and an n-GaN layer), a reflecting layer and a substrate layer are sequentially deposited on a sapphire substrate, then after the sapphire substrate is stripped and removed, a high-contrast grating layer and a terminal electrode layer are prepared on one side, deviating from the reflecting layer, of the active microcavity structure through deposition etching, and the high-contrast grating layer and the terminal electrode layer are prepared on the other side of the active microcavity structure. Therefore, the preparation of the light-emitting diode is completed.

Description

Technical Field

[0001] The present invention relates to the technical field of diodes, and particularly to a resonant cavity light emitting diode based on a birefringent crystal, a preparation method thereof, and an application thereof. Background Art

[0002] Linearly polarized light refers to a light beam whose electric field vibrates in a single direction, and plays a key role in multiple fields such as liquid crystal display technology, optical fiber communication, optical detection, microscope imaging, and 3D display. At present, the main way to obtain polarized light is to obtain linearly polarized light by filtering non-polarized light sources through polarizers. However, this method has deficiencies such as being difficult to integrate and miniaturize, and having low utilization rate of light sources. In order to achieve high integration and miniaturization of linearly polarized light sources, researchers prepare a layer of metal grating or dielectric film high-contrast grating on the surface of traditional light emitting diodes, and obtain TM (transverse magnetic mode) polarized light whose electric field vibration direction is perpendicular to the grating slit by suppressing TE (transverse electric mode) polarized light whose electric field vibration direction is parallel to the grating slit. Although this method improves the integration degree, it has a low utilization rate of photons radiated by the active microcavity structure, and will also have an adverse impact on the line width and purity of the obtained polarized light. Therefore, there is an urgent need for a new method to improve the quality of polarized light. Summary of the Invention

[0003] The present invention aims to provide a resonant cavity light emitting diode based on a birefringent crystal, a preparation method thereof, and an application thereof, so as to solve the technical problem that the existing method for obtaining polarized light has a low utilization rate of photons radiated by the active microcavity structure, and will also have an adverse impact on the line width and purity of the obtained polarized light.

[0004] The present invention discloses a resonant cavity light emitting diode based on a birefringent crystal, which includes a substrate layer, a reflective layer, a p-GaN layer, an active layer, an n-GaN layer, and an end electrode layer stacked in sequence; the reflective layer is embedded in the substrate layer, and the upper surface of the reflective layer is flush with the upper surface of the substrate layer and is covered by the p-GaN layer; the high-contrast grating layer and the end electrode layer are jointly deposited on the upper surface of the n-GaN layer, and the end electrode layer is located on the periphery of the high-contrast grating layer;

[0005] Wherein the active layer is configured as a birefringent quantum well structure, so that the light wave passing through the active layer generates orthogonally polarized light; the high-contrast grating layer is used to filter the orthogonally polarized light, so that the light emitting diode emits linearly polarized light in a single direction.

[0006] In one embodiment, the reflective layer includes a distributed Bragg reflector, which is composed of two dielectric films with different refractive indices stacked in an alternating manner, wherein the thickness of each dielectric film is 1 / 4 of the central wavelength; or, the reflective layer includes a metal film; the two emission wavelengths of the light-emitting diode are located in a high reflection band formed by the reflective layer, and the reflectivity of the reflective layer is not less than 80%.

[0007] In one embodiment, the high contrast grating layer is made of dielectric material, has a height of 40-80 nm, a width of 60-100 nm, and a period of 100-200 nm, and selectively transmits linearly polarized light perpendicular to the slit direction of the high contrast grating layer.

[0008] In one of the embodiments, the high-contrast grating layer is made of dielectric material, and the high-contrast grating layer selectively transmits linearly polarized light perpendicular to the slit direction of the high-contrast grating layer.

[0009] In one of the embodiments, in a direction perpendicular to the light emitting surface of the light emitting diode, the reflective layer and the high-contrast grating layer are arranged in alignment and form a resonant cavity structure, and the light field forms a light field standing wave in the resonant cavity structure, and the antinode position of the light field standing wave overlaps with the active layer.

[0010] Second aspect

[0011] The present invention discloses a method for preparing a resonant cavity light emitting diode based on a birefringent crystal, comprising the following steps:

[0012] S10, preparing an active microcavity structure: growing and depositing an n-GaN layer, an active layer and a p-GaN layer layer by layer on a surface of a sapphire substrate to form the active microcavity structure;

[0013] S20, preparing a reflective layer: depositing a reflective layer on a side of the p-GaN layer away from the active layer;

[0014] S30, preparing a substrate layer: depositing the substrate layer on the same side of the p-GaN layer after the reflective layer is deposited, the substrate layer is epitaxially grown along the side of the p-GaN layer, and the surface of the reflective layer is flush with the surface of the substrate layer and both are covered by the stacked p-GaN layer;

[0015] S40, removing the sapphire substrate: removing the sapphire substrate by a laser lift-off process, and flattening the surface of the n-GaN layer after the sapphire substrate is removed by chemical mechanical polishing;

[0016] S50, preparing a high-contrast grating layer: depositing a metal film or a dielectric film on the surface of the n-GaN layer, and selectively etching the metal film or the dielectric film by photolithography and etching processes, to finally form the high-contrast grating layer;

[0017] S60, preparing a terminal electrode layer: depositing the terminal electrode layer on the surface of the n-GaN layer by using a magnetron sputtering technique, so that the high-contrast grating layer and the terminal electrode layer are deposited together on the upper surface of the n-GaN layer, and the terminal electrode layer is located at the periphery of the high-contrast grating layer, so as to complete the preparation of the light-emitting diode;

[0018] The active layer is configured as a birefringent quantum well structure, so that the light waves passing through the active layer generate orthogonal linear polarized light; the high-contrast grating layer is used to filter the orthogonal linear polarized light, so that the light-emitting diode radiates linear polarized light in a single direction.

[0019] In one of the embodiments, the thickness of the birefringent quantum well structure is simulated by simulation software, and the light emission of the simulated birefringent quantum well structure is adjusted to a desired wavelength, and the active layer is deposited according to the simulation result.

[0020] In one of the embodiments, in step S20, the reflective layer adopts a distributed Bragg reflector, which is composed of two dielectric films with different refractive indices stacked in an alternating manner, wherein the thickness of each dielectric film is 1 / 4 of the central wavelength; or, the reflective layer adopts a metal film.

[0021] In one of the embodiments, in a direction perpendicular to the light emitting surface of the light emitting diode, the reflective layer and the high-contrast grating layer are deposited in alignment to form a resonant cavity structure, and the light field distribution of the light emitting diode is simulated using simulation software, so that the optical cavity mode of the light emitting diode is at the light emission wavelength of the active layer, and the light field forms a light field standing wave in the resonant cavity structure, and the antinode position of the light field standing wave overlaps with the active layer.

[0022] In one embodiment, the birefringent quantum well structure uses a semiconductor material with birefringence properties.

[0023] In one of the embodiments, the terminal electrode layer is made of at least one electrode material selected from Au, Ni, Cr, and Ti.

[0024] In one embodiment, the substrate layer is made of metal or semiconductor material.

[0025] The third aspect

[0026] The present application provides an application of a resonant cavity light emitting diode based on a birefringent crystal, and the light emitting diode prepared by any one of the above preparation method embodiments is applied to 3D display.

[0027] It can be seen from the above technical solutions that the embodiments of the present invention have at least the following advantages and positive effects:

[0028] The embodiment of the present invention provides a resonant cavity light emitting diode based on a birefringent crystal and a preparation method thereof, wherein the light emitting diode comprises a substrate layer, a reflective layer, a p-GaN layer, an active layer, an n-GaN layer, an end electrode layer and a high-contrast grating layer which are stacked in sequence. The active layer is configured as a birefringent quantum well structure so that the light wave passing through the active layer generates orthogonal linear polarized light; the high-contrast grating layer is used to filter the orthogonal linear polarized light so that the light emitting diode radiates linear polarized light in a single direction. On the other hand, the high-contrast grating layer and the reflective layer together form a resonant cavity structure, further restricting the movement of photons to compress the spectrum and obtain a narrow line width and a light beam with good direction. Moreover, due to the effect of the resonant cavity structure, the light beam forms a light field standing wave in the resonant cavity structure, and the antinode position of the light field standing wave overlaps and couples with the active layer to generate a certain gain, thereby improving the utilization rate of photons and improving the light output power of the entire light emitting diode. Therefore, the present invention combines the resonant cavity structure with the high-contrast grating, improves the internal photon efficiency of the device, narrows the line width of the emission spectrum, and obtains a light wave with a single linear polarization orientation. In addition, the present invention has the characteristics of simple structure, high integration, concentrated light beam direction, and easy control of the polarization direction of the emitted light. It proposes a new device structure for obtaining linearly polarized light and has broad application prospects in the fields of realizing 3D display, optical communication, and optical detection.

[0029] For example, the light emitting diode of the present application is applied to 3D display, which can provide a highly integrated polarized light source for naked-eye 3D display, and the 3D display device has the advantages of high integration and simple structure. The present invention provides a new light source structure for near-eye 3D display, and the optical resonant cavity structure can realize the collimation and directionality of the radiated light, improve the light efficiency and brightness; the integrated structural design has the advantages of high integration and low manufacturing cost, and is conducive to realizing the thinness of the product in terms of application. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0031] Figure 1Schematic diagram of the overall structure of a resonant cavity light emitting diode based on a birefringent crystal in an embodiment of the present application;

[0032] Figure 2 is Figure 1 Schematic diagram of the reflectivity of the distributed Bragg reflector in the light emitting diode shown in the corresponding wavelength band;

[0033] Figure 3 is Figure 1 Schematic diagram of the structure of the high-contrast grating layer and the light beam propagation direction in the light emitting diode shown;

[0034] Figure 4 is Figure 1 Schematic diagram of the optical wave in which the optical field standing wave in the resonant cavity structure and the active layer in the light emitting diode shown are coupled to each other;

[0035] Figure 5 is Figure 1 Flow chart of the preparation of the resonant cavity light emitting diode based on a birefringent crystal shown;

[0036] Figures 6 to 10 is Figure 1 Schematic diagram of the intermediate structure of each preparation step of the light emitting diode shown;

[0037] Figure 11 Schematic diagram of the overall structure of an optical radiation component of the present application.

[0038] Explanation of reference numerals is as follows:

[0039] 10. Resonant cavity light emitting diode based on a birefringent crystal; 100. Substrate layer; 200. Reflective layer; 210. Distributed Bragg reflector; 300. p-GaN layer; 400. Active layer; 410. Birefringent quantum well structure; 500. n-GaN layer; 600. Terminal electrode layer; 700. High-contrast grating layer; 800. Protective layer; 101. Active microcavity structure; 102. Resonant cavity structure; 20. Sapphire substrate; 30. Optical radiation component. Detailed implementation mode

[0040] Typical -GaN implementation modes reflecting the features and advantages of the present invention will be described in detail in the following description. It should be understood that the present invention can have various variations in different implementation modes, all of which do not depart from the scope of the present invention, and the descriptions and illustrations therein are essentially for illustrative purposes and not for limiting the present invention.

[0041] In addition, 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 quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the said features. In the description of this application, "a plurality of" means two or more unless otherwise specifically defined.

[0042] In the description of this application, it should be noted that unless otherwise clearly stipulated and defined, the terms "mounted", "installed", and "connected" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0043] Linearly polarized light refers to a light beam in which the electric field vibrates in a single direction and plays a key role in many fields such as liquid crystal display technology, optical fiber communication, optical detection, microscope imaging, and 3D display. At present, the main way to obtain polarized light is to filter non-polarized light sources through polarizers to obtain linearly polarized light. However, this method has deficiencies such as being difficult to integrate and miniaturize, and having low utilization rate of light sources. In order to achieve high integration and miniaturization of linearly polarized light sources, researchers prepare a layer of metal grating or dielectric film high-contrast grating on the surface of traditional light-emitting diodes, and obtain TM (transverse magnetic mode) polarized light with the electric field vibration direction perpendicular to the grating slits by suppressing TE (transverse electric mode) polarized light with the electric field vibration direction parallel to the grating slits. Although this method can improve the integration degree, it has a low utilization rate of photons radiated by the active microcavity structure and will also have an adverse impact on the line width and purity of the obtained polarized light. Therefore, there is an urgent need for a new method to improve the quality of polarized light.

[0044] Based on this, referring to Figure 1 , this application provides a resonant cavity light-emitting diode 10 of a birefringent crystal, which can achieve better polarized light purity and integration to improve the display effect of the light-emitting diode 10. Specifically, the light-emitting diode 10 adopts a vertical structure and includes a substrate layer 100, a reflective layer 200, a p-GaN layer 300, an active layer 400, an n-GaN layer 500, and a terminal electrode layer 600 stacked in sequence from bottom to top. Among them, the p-GaN layer 300, the active layer 400, and the n-GaN layer 500 form an active microcavity structure 101. In Figure 1In it, the reflective layer 200 is embedded in the substrate layer 100. The upper surface of the reflective layer 200 is flush with the upper surface of the substrate layer 100, and both upper surfaces are covered by the p-GaN layer 300 in a stacked manner. The light-emitting diode 10 further includes a High Contrast Grating (HCG) layer 700. The end electrode layer 600 and the high contrast grating layer 700 are co-deposited on the upper surface of the n-GaN layer 500, and the end electrode layer 600 is located on the periphery of the high contrast grating layer 700. Among them, the active layer 400 is configured as a birefringent quantum well structure 410, so that the light wave passing through the active layer 400 generates orthogonally linearly polarized light; the high contrast grating layer 700 is used to filter the orthogonally linearly polarized light, so that the light-emitting diode 10 emits polarized light in a single direction.

[0045] It should be noted that a birefringent semiconductor material refers to a material in which, in a crystal structure, there are different refractive indices in two directions (generally orthogonal directions), resulting in the birefringence phenomenon. When a beam of light passes through a birefringent semiconductor material, due to the different refractive indices, the refraction angles are different, and two different refracted light beams will be generated. One of the refracted light beams is always in the plane of the incident light beam and follows the law of refraction, that is, the ratio of the sine of the incident angle to the sine of the refraction angle is a constant. Usually, this refracted ray is called the ordinary ray or o-ray: the other refracted light beam is not in the same plane as the incident light beam, and the ratio of the sine of the incident angle to the sine of the refraction angle is not a constant and does not follow the law of refraction. Usually, this refracted light beam is called the extraordinary ray or e-ray. Optionally, the birefringent semiconductor material includes ZnO, GaN, CdS, and the doping ratio ranges of x and y are: 0 ≤ x ≤ 1, 0 ≤ y ≤ 1. Preferably, the birefringent semiconductor material is selected as semi-polar GaN or non-polar GaN, and the active microcavity structure is In x Ga (1-x) N / Al y Ga (1-y) N quantum well structure; where x and y respectively represent the doping ratios of In and Al in In x Ga (1-x) N and Al y Ga (1-y) N. By changing the doping ratios of In and Al in the active microcavity structure between 0 and 1 respectively, the wavelength of the light-emitting diode can be changed to cover the wavelength range of 200 - 1700 nm. The principle is that by changing the doping ratio, the bandgap width of the semiconductor material can be changed, and the bandgap width determines the radiation wavelength. It should be noted that GaN materials, as the third-generation semiconductor materials, are widely used in light-emitting devices. The growth of GaN materials mainly uses metal organic chemical vapor deposition technology (MOCVD). And GaN grown along different crystal planes can be divided into polar, semi-polar, and non-polar, among which semi-polar and non-polar GaN have birefringent properties.

[0046] Preferably, in combination with reference Figure 1 and Figure 2 , in one embodiment, the reflective layer 200 includes a distributed Bragg reflector (DBR) mirror 210, which is composed of a combination of two different refractive index dielectric films stacked alternately, where the thickness of each dielectric film is 1 / 4 of the central wavelength, and the dielectric film combination is SiO2 / TiO2. It should be noted that the distributed Bragg reflector 210 is composed of dielectric thin films with different refractive indices, and the optical thickness of each thin film is 1 / 4 of the target wavelength. According to the thin film optical principle, the reflected light of the target wavelength at the thin film interface has the same phase and interferes with each other to enhance, thus generating a high reflectivity. Therefore, the design with the thickness of each dielectric film being 1 / 4 of the central wavelength can reduce the reflection loss of light on the distributed Bragg reflector 210 and improve the device performance. According to the optical propagation principle, the optical thickness of a single dielectric film must be 1 / 4 of the central wavelength to minimize the loss and improve the reflectivity and the quality of the resonant cavity. The reason for using the SiO2 / TiO2 dielectric film combination is that: the refractive index difference between SiO2 and TiO2 is large, and it is easy to obtain a high reflectivity ( Figure 4 as shown); the absorption of visible light by both is small, which helps to improve the light output power of the light-emitting diode 10; the preparation process of the SiO2 / TiO2 dielectric film combination is mature, easy to obtain, and has a low cost. Optionally, in other embodiments of the present application, the dielectric film combination can be any of the dielectric film combinations of SiO2 / TiO2 or SiO2 / Ti2O5, or SiO2 / Ti3O5. Additionally, optionally, in the present application, the reflective layer 200 can also use a metal mirror with a high reflectivity.

[0047] Preferably, in one embodiment, the two emission wavelengths of the light-emitting diode 10 are located in the high reflection band formed by the reflective layer 200, and the reflectivity of the reflective layer needs to reach more than 99%. It should be noted that the spectrum of the electrically injected device should be located within the high reflection band (high reflection region) to form an obvious resonance effect. For the distributed Bragg reflector 210, the greater the refractive index difference between the two dielectric film materials, the easier it is to achieve a high reflectivity. The higher the reflectivity, the smaller the loss of light during reflection, and the more obvious the resonance effect.

[0048] It should be noted, reference Figure 3, the high-contrast grating layer 700 is a sub-wavelength grating with high-refractive-index grating teeth completely surrounded by a low-refractive-index medium (such as air). This structure enables the high-contrast grating layer 700 to generate a strong waveguide coupling phenomenon on the incident / emitting surface. The guided-mode resonance effect can make the leaky mode excited by the grating waveguide layer completely coincide with the evanescent wave diffraction mode, achieving zero-order diffraction, thereby achieving broadband high-reflection characteristics. Moreover, the high-contrast grating layer 700 has different reflection and transmission characteristics for light of different polarization states. For TE-polarized light and TM-polarized light, the high-contrast grating layer 700 can exhibit different reflectivities, that is, it shows a high reflectivity for one polarization light while suppressing the other polarization light. This polarization selectivity enables the HCG to be used for polarization control and polarization beam splitting. Optionally, the height range of the high-contrast grating layer 700 is 40 - 80 nm, the width range is 60 - 100 nm, and the period range is 100 - 200 nm. Its specific dimensions can be calculated according to the wavelength of the radiation spectrum.

[0049] Preferably, continuing to refer to Figure 3 , in one embodiment, the high-contrast grating layer 700 is prepared from a dielectric material and selectively transmits TM-polarized light whose electric field direction is perpendicular to the slit direction of the high-contrast grating layer 700, while the TE-polarized light parallel to the slit direction of the high-contrast grating layer 700 is suppressed in the resonant cavity, that is, the TE-polarized light is filtered out, so that the light-emitting diode 10 emits unidirectional TM-polarized light. It should be noted that in other embodiments, according to the display requirements of the light-emitting diode 10, by changing the structural parameters of the high-contrast grating layer 700, the high-contrast grating layer 700 can also filter out the TM-polarized light and make the light-emitting diode 10 emit unidirectional TE-polarized light.

[0050] It is worth noting that in combination with referring to Figure 1 and Figure 4 , in the direction perpendicular to the light-emitting surface of the light-emitting diode 10, the reflective layer 200 and the high-contrast grating layer 700 form a resonant cavity structure 102. The light beam forms an optical field standing wave in the resonant cavity structure 102, and the antinode position of the optical field standing wave overlaps with the active layer 400. On the one hand, the resonant cavity structure 102 can further restrict the movement of photons to compress the radiation spectrum and obtain a beam with a narrow linewidth and good directivity; on the other hand, the antinode position of the optical field standing wave overlaps with the active layer 400 and is coupled with the active microcavity structure to generate a certain gain, thereby further improving the utilization rate of photons to improve the output power of the entire light-emitting diode 10 and enhancing the light efficiency and display effect of the light-emitting diode 10.

[0051] In the second aspect

[0052] In combination with referring to Figure 1 , Figures 5 to 10The present application provides a method for preparing a resonant cavity light emitting diode based on a birefringent crystal, the preparation method adopts a flip chip process, and comprises the following steps:

[0053] S10, preparing an active microcavity structure 101, and gradually growing and depositing an n-GaN layer 500, an active layer 400, and a p-GaN layer 300 on the surface of a sapphire substrate 20 to form an active microcavity structure 101 (such as Figure 6 shown);

[0054] S20, preparing a reflective layer 200, depositing the reflective layer 200 on the side of the p-GaN layer 300 away from the active layer 400 (eg Figure 7 shown);

[0055] S30, preparing a substrate layer 100, depositing the substrate layer 100 on the same side surface of the p-GaN layer 300 after the reflective layer is deposited, the substrate layer 100 is epitaxially extended along the side of the p-GaN layer 300, the surface of the reflective layer 200 is flush with the surface of the substrate layer 100 and both are covered by the stacked p-GaN layer 300 (such as Figure 8 shown);

[0056] S40, removing the sapphire substrate 20, using a laser lift-off process to remove the original sapphire substrate 20, and using chemical mechanical polishing to flatten the surface of the n-GaN layer 500 after the sapphire substrate 20 is removed (eg Figure 9 shown);

[0057] S50, preparing a high contrast grating layer 700, depositing a metal film or a dielectric film on the surface of the n-GaN layer 500, and selectively etching the metal film or the dielectric film using a photolithography and etching process, and finally forming a high contrast grating layer 700 (such as Figure 10 shown);

[0058] S60, preparing the terminal electrode layer 600, using magnetron sputtering technology to deposit the terminal electrode layer 600 on the surface of the n-GaN layer 500, so that the terminal electrode layer 600 and the high-contrast grating layer 700 are deposited together on the upper surface of the n-GaN layer 500, and the terminal electrode layer 600 is located at the periphery of the high-contrast grating layer 700, so as to complete the preparation of the light-emitting diode 10 (such as Figure 1 shown);

[0059] The active layer 400 is configured as a birefringent quantum well structure 410, so that the light waves passing through the active layer 400 generate orthogonal linear polarized light; the high-contrast grating layer 700 is used to filter the orthogonal linear polarized light, so that the light-emitting diode 10 radiates linear polarized light in a single direction.

[0060] Optionally, in step S10, the growth and deposition process adopts MOCVD technology; the active layer 400 adopts Inx Ga (1-x) N / Al y Ga (1-y) N (where 0 ≤ x ≤ 1, 0 ≤ y ≤ 1) birefringent crystal material, the n-GaN layer 500 and the p-GaN layer 300 are both semi-polar or non-polar materials and have birefringence properties. It should be noted that the birefringent quantum well structure 410 (active layer 400) can use other semiconductor materials with birefringence properties, such as ZnO, CdS, GaN, etc. Additionally, the thickness of the birefringent quantum well structure 410 can be simulated by simulation software, and the light emission of the simulated birefringent quantum well structure 410 can be adjusted to the desired wavelength, and the thickness of the active layer 400 can be deposited according to the simulation results.

[0061] Optionally, in step S20, first, the deposition process uses electron beam-induced deposition (EBID) technology; the reflective layer 200 is a distributed Bragg reflector 210 composed of an alternating stack of two dielectric films with different refractive indices. Specifically, 12 pairs of SiO2 / TiO2 are deposited on the surface of the p-GaN layer 300 by photolithography and EBID technology to form the distributed Bragg reflector 210. Additionally, the material and the film thickness of each layer of the distributed Bragg reflector 210 are determined by the simulation results, so as to control the reflection band of the distributed Bragg reflector 210 to be between the emission wavelengths of the light-emitting diode 10. The optical thickness of each layer is 1 / 4 of the central wavelength, the designed central wavelength is 520 nm, and the reflectivity reaches 99%.

[0062] Optionally, in step S30, the method of depositing the substrate layer 100 uses electroplating Cu process to form a Cu substrate. The metal Cu substrate not only plays a role in supporting the epitaxial wafer but also plays a role as a p-type electrode. It should be noted that in other embodiments, the substrate layer 100 can also use other metal or semiconductor materials to achieve the functions of conductivity and support.

[0063] Optionally, in step S50, a 60-nm SiO2 thin film (dielectric thin film) can be deposited on the surface of the n-GaN layer 500, and finally a SiO2 / Air high-contrast grating layer 700 is formed. The SiO2 / Air high-contrast grating layer 700 selectively transmits TM polarized light, and the light-emitting diode 10 emits TM linearly polarized light with a polarization degree of 92%. In a specific embodiment, the height of the high-contrast grating layer 700 is 60 nm, the width is 80 nm, and the period is 150 nm. It should be noted that the high-contrast grating layer 700 needs to satisfy sufficient reflectivity, and a metal material or a dielectric material can be used according to the radiation wavelength of the active microcavity structure 101. Therefore, in other embodiments, a SiO2 / Air grating can be used, or a SiO2 / TiO2 grating or other metal gratings can be used.

[0064] Optionally, in step S60, the end electrode layer 600 functions as an n-type electrode, and at least one of the electrode materials such as Au, Ni, Cr, and Ti can be used. In one embodiment, the end electrode layer 600 is a Cr / Au electrode.

[0065] In a third aspect

[0066] With reference to Figure 1 and Figure 11 , the present application provides an application of a resonant cavity light-emitting diode based on a birefringent crystal. Applying the light-emitting diode prepared by the previous preparation method to 3D display can provide a highly integrated polarized light source for naked-eye 3D display. Specifically, in one embodiment, a plurality of light-emitting diodes 10 are arranged in an array to form a light radiation component 30 (display device). The light radiation component 30 includes two resonant cavity light-emitting diodes 10 that can emit mutually orthogonal linearly polarized lights, and the orientation of the linearly polarized light is determined by the structure of the top high-contrast grating layer 700. The light radiation component 30 is applied to the display device as the same pixel point. The resonant cavity light-emitting diodes 10 with the same grating orientation are connected in series with each other and are connected in parallel with the resonant cavity light-emitting diodes 10 with the other orientation. The switching component controls the current path to realize the electrical excitation of different resonant cavity light-emitting diodes. At 3 / 4 of the cycle of each image, the switching component judges whether it is necessary to change the orientation of the polarized light, and emits linearly polarized lights in different directions by changing the current path, so as to realize the rapid switching of the linearly polarized light received by the eyes. As a display device, the light radiation component 30 has various usage methods and can be applied to far-field 3D display or near-field naked-eye 3D display.

[0067] The present application provides a resonant cavity light emitting diode 10 based on a birefringent crystal, a preparation method and an application thereof, wherein the light emitting diode 10 comprises a substrate layer 100, a reflective layer 200, a p-GaN layer 300, an active layer 400, an n-GaN layer 500, an end electrode layer 600 and a high-contrast grating layer 700 stacked in sequence. The active layer 400 is configured as a birefringent quantum well structure 410, so that the light waves passing through the active layer 400 generate orthogonal linear polarized light; the high-contrast grating layer 700 is used to filter the orthogonal linear polarized light, so that the light emitting diode 10 radiates linear polarized light in a single direction. On the other hand, the high-contrast grating layer 700 and the reflective layer 200 together constitute a resonant cavity structure 102, which further limits the movement of photons in the cavity, thereby compressing the spectrum and obtaining a narrow line width and a beam with good direction. Moreover, due to the effect of the resonant cavity structure 102, the light beam forms a light field standing wave in the resonant cavity, and the antinode position of the light field standing wave overlaps and couples with the active layer 400, generating a certain gain, thereby improving the utilization rate of photons and improving the light output power of the entire light emitting diode 10. Therefore, the present invention combines the resonant cavity structure 102 with the high-contrast grating layer 700, improves the photon efficiency in the light emitting diode, narrows the line width of the emission spectrum, and obtains a light wave with a single linear polarization orientation. In addition, the present invention has the characteristics of simple structure, high integration, concentrated light beam direction, and easy control of the polarization direction of the emitted light. It proposes a new device structure (light emitting diode 10) for obtaining linearly polarized light, and has broad application prospects in the fields of realizing 3D display, optical communication, and optical detection. For example, the light emitting diode of the present application is applied to 3D display, which can provide a highly integrated polarized light source for naked-eye 3D display, and the 3D display device has the advantages of high integration and simple structure. The present invention provides a new light source structure for near-eye 3D display. The optical resonant cavity structure can realize the collimation and directionality of the radiated light, and improve the light efficiency and brightness. The integrated structural design of the display device has the advantages of high integration and low manufacturing cost, and is conducive to realizing the lightweight and thinness of the product in terms of application.

[0068] Although the present invention has been described with reference to several typical embodiments, it should be understood that the terms used are illustrative and exemplary rather than limiting. Since the present invention can be embodied in many forms without departing from the spirit or essence of the invention, it should be understood that the above embodiments are not limited to any of the foregoing details, but should be broadly interpreted within the spirit and scope defined by the appended claims, so all changes and modifications within the scope of the claims or their equivalents should be covered by the appended claims.

Claims

1. A resonant cavity light-emitting diode based on a birefringent crystal, characterized in that, The light emitting diode comprises a substrate layer, a reflective layer, a p-GaN layer, an active layer, an n-GaN layer and a terminal electrode layer which are stacked in sequence; the reflective layer is embedded in the substrate layer, the upper surface of the reflective layer is flush with the upper surface of the substrate layer and both are covered by the stacked p-GaN layer; the light emitting diode further comprises a high-contrast grating layer, the high-contrast grating layer and the terminal electrode layer are deposited together on the upper surface of the n-GaN layer, and the terminal electrode layer is located at the periphery of the high-contrast grating layer; The active layer is configured as a birefringent quantum well structure, so that the light waves passing through the active layer generate orthogonal linear polarized light; the high-contrast grating layer is used to filter the orthogonal linear polarized light, so that the light-emitting diode radiates linear polarized light in a single direction.

2. The resonant cavity light emitting diode based on a birefringent crystal according to claim 1, characterized in that, The reflective layer includes a distributed Bragg reflector, which is composed of two dielectric films with different refractive indices stacked in an alternating manner, wherein the thickness of each dielectric film is 1 / 4 of the central wavelength; or, the reflective layer includes a metal film; the two emission wavelengths of the light-emitting diode are located in the high reflection band formed by the reflective layer, and the reflectivity of the reflective layer is not less than 80%.

3. The resonant cavity light emitting diode based on a birefringent crystal according to claim 1, wherein The high-contrast grating layer is made of dielectric material, has a height of 40-80nm, a width of 60-100nm, and a period of 100-200nm, and selectively transmits linearly polarized light perpendicular to the slit direction of the high-contrast grating layer.

4. The resonant cavity light emitting diode based on a birefringent crystal according to claim 1, wherein, In a direction perpendicular to the light emitting surface of the light emitting diode, the reflective layer and the high-contrast grating layer are arranged in alignment and form a resonant cavity structure, and the light field forms a light field standing wave in the resonant cavity structure, and the antinode position of the light field standing wave overlaps with the active layer.

5. A preparation method of a resonant cavity light emitting diode based on a birefringent crystal, characterized in that, The steps include: S10, preparing an active microcavity structure: growing and depositing an n-GaN layer, an active layer and a p-GaN layer layer by layer on a surface of a sapphire substrate to form the active microcavity structure; S20, preparing a reflective layer: depositing a reflective layer on a side of the p-GaN layer away from the active layer; S30, preparing a substrate layer: depositing the substrate layer on the same side of the p-GaN layer after the reflective layer is deposited, the substrate layer is epitaxially grown along the side of the p-GaN layer, and the surface of the reflective layer is flush with the surface of the substrate layer and both are covered by the stacked p-GaN layer; S40, removing the sapphire substrate: removing the sapphire substrate by a laser lift-off process, and flattening the surface of the n-GaN layer after the sapphire substrate is removed by mechanical polishing; S50, preparing a high-contrast grating layer: depositing a metal film or a dielectric film on the surface of the n-GaN layer, and selectively etching the metal film or the dielectric film by photolithography and etching processes, to finally form the high-contrast grating layer; S60, preparing a terminal electrode layer: depositing the terminal electrode layer on the surface of the n-GaN layer by using a magnetron sputtering technique, so that the high-contrast grating layer and the terminal electrode layer are deposited together on the upper surface of the n-GaN layer, and the terminal electrode layer is located at the periphery of the high-contrast grating layer, so as to complete the preparation of the light-emitting diode; wherein the active layer is configured as a birefringent quantum well structure, so that light waves passing through the active layer generate orthogonal linearly polarized light; The high contrast grating layer is used to filter the orthogonal linear polarized light, so that the light emitting diode radiates linear polarized light in a single direction.

6. The manufacturing method of the resonant cavity light emitting diode based on a birefringent crystal according to claim 5, characterized in that, The thickness of the birefringent quantum well structure is simulated by simulation software, and the light emission of the simulated birefringent quantum well structure is adjusted to a desired wavelength, and the active layer is deposited according to the simulation result.

7. The manufacturing method of the resonator light-emitting diode based on a birefringent crystal according to claim 5, characterized in that, In step S20, the reflective layer adopts a distributed Bragg reflector, which is composed of two dielectric films with different refractive indices stacked in an alternating manner, wherein the thickness of each dielectric film is 1 / 4 of the central wavelength; or, the reflective layer adopts a metal film.

8. The preparation method of the resonant cavity light-emitting diode based on a birefringent crystal according to claim 5, characterized in that, In a direction perpendicular to the light emitting surface of the light emitting diode, the reflective layer and the high-contrast grating layer are deposited in alignment to form a resonant cavity structure, and the light field distribution of the light emitting diode is simulated using simulation software, so that the optical cavity mode of the light emitting diode is at the light emission wavelength of the active layer, and the light field forms a light field standing wave in the resonant cavity structure, and the antinode position of the light field standing wave overlaps with the active layer.

9. The manufacturing method of a resonant cavity light emitting diode based on a birefringent crystal according to claim 5, characterized in that, The birefringence quantum well structure adopts a semiconductor material with birefringence property; And / or, the terminal electrode layer uses at least one electrode material of Au, Ni, Cr, and Ti; And / or, the substrate layer is made of metal or semiconductor material.

10. Application of a resonant cavity light emitting diode based on a birefringent crystal, characterized in that, The luminescent diode prepared by any one of the preparation methods of claims 5 to 9 is applied to 3D display.

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