Light emitting device

Abstract

A light-emitting device of one embodiment of the present application includes an element main body and a lens layer. The element main body includes a light-emitting layer, a light exit surface, and a reflective layer that reflects light emitted from the light-emitting layer toward the light exit surface. The lens layer is provided on the light exit surface, extracts a predetermined polarized light from light emitted from the light exit surface, and has a focal distance equivalent to an optical path length of light that reaches the light exit surface from the light-emitting layer via the reflective layer with respect to the light emitted from the light exit surface.

Description

Technical Field

[0001] This invention relates to a light-emitting device that emits light with a predetermined polarization state. Background Technology

[0002] Circularly polarized light holds promise for applications in various fields such as optical communication, 3D displays, magnetic recording devices, and polarization imaging. However, previous methods of generating circularly polarized light by combining multiple optical elements have resulted in large-scale optical systems, which struggle to meet the demands of increasingly thin and high-resolution 3D displays, in vivo imaging, and miniaturized magnetic recording devices. Therefore, there is a need to develop a single, current-driven circularly polarized light-emitting element.

[0003] For example, Patent Document 1 discloses an illumination unit in which the light-emitting surface of its LED (Light Emitting Diode) is composed of a nanostructure such as a photonic crystal or a columnar structure that converts the emitted light into circularly polarized light. Furthermore, Non-Patent Document 1 discloses a bifocal superlens composed of a nanostructure, which has a different focal length depending on the rotation direction of the incident circularly polarized light.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Publication No. 2022-532642.

[0007] Non-patent literature

[0008] Non-patent document 1: T. Shengnan et al., "Dielectric longitudinal bifocalmetalens with adjustable intensity and high focusing efficiency" Opt.Express. 27, 680 (2019). Summary of the Invention

[0009] The problem the invention aims to solve

[0010] For example, GaN (gallium nitride) semiconductor devices are known as LEDs, which have an n-type semiconductor layer, an active layer, and a p-type semiconductor layer sequentially stacked on a sapphire substrate, and allow light radiated from the active layer to exit through a transparent electrode layer formed on the surface of the p-type semiconductor layer. The distance between the active layer and the light-emitting surface (transparent electrode layer) of such semiconductor devices is approximately several hundred nanometers. On the other hand, the focal length of the superlens described in Non-Patent Document 1 is 2μm to 4μm. Therefore, even if such a superlens is simply placed on the light-emitting surface of the LED, it is impossible to efficiently extract collimated light with the target polarization characteristics. Furthermore, there is a problem that it is impractical to manufacture LEDs according to the focal length of a superlens, and it is extremely difficult to manufacture a superlens with a focal length of approximately several hundred nanometers.

[0011] In view of the above, the object of the present invention is to provide a light-emitting device that can easily fabricate a lens layer and emit collimated light with desired polarization characteristics.

[0012] Solution for solving the problem

[0013] One embodiment of the present invention provides a light-emitting device having an element body and a lens layer.

[0014] The main body of the aforementioned element has a light-emitting layer, a light-emitting surface, and a reflective layer that reflects light radiated from the light-emitting layer toward the light-emitting surface.

[0015] The lens layer is disposed on the light emitting surface, and a predetermined polarized light is extracted from the emitted light from the light emitting surface. The lens layer has a focal length relative to the emitted light that is equivalent to the optical path length from the light emitting layer through the reflective layer to the light emitting surface.

[0016] According to the above-described light-emitting device, since the lens layer has a focal length relative to the emitted light that is equivalent to the optical path length from the light-emitting layer through the reflective layer to the light-emitting surface, it is possible to emit collimated light with the desired polarization characteristics. Furthermore, since the focal length of the lens layer can be designed with a distance (optical distance) equivalent to the optical path length from the light-emitting layer through the reflective layer to the light-emitting surface, the lens layer can be easily fabricated compared to designing the focal length with a distance (optical distance) equivalent to the optical path length when the light radiated from the light-emitting layer directly reaches the light-emitting surface.

[0017] The light-emitting layer can also be disposed between the light-emitting surface and the reflective layer.

[0018] The main body of the aforementioned element may also have: a first conductive semiconductor layer formed between the light-emitting layer and the light-emitting surface; and a second conductive semiconductor layer formed between the light-emitting layer and the reflective layer, wherein the reflective layer may be a distributed Bragg reflector (DBR).

[0019] Alternatively, the main body of the aforementioned element may also have: a first conductive semiconductor layer formed between the light-emitting layer and the reflective layer; and a second conductive semiconductor layer formed between the light-emitting layer and the light-emitting surface, wherein the reflective layer may be an electrode film stacked on the first conductive semiconductor layer.

[0020] The main body of the above-mentioned components can also be gallium nitride semiconductor components.

[0021] The aforementioned lens layer can also be a superlens composed of nanostructures of dielectric material.

[0022] The aforementioned lens layer can also be configured to extract right-handed or left-handed circularly polarized light from the emitted light.

[0023] Invention Effects

[0024] According to the present invention, the lens layer can be easily fabricated, and collimated light with desired polarization characteristics can be emitted. Attached Figure Description

[0025] Figure 1 This is a schematic side sectional view showing the structure of the light-emitting device according to the first embodiment of the present invention.

[0026] Figure 2 This is a diagram of the light path inside the aforementioned light-emitting device.

[0027] Figure 3 This is a simulation result showing the normalized electric field intensity of right-handed and left-handed circularly polarized light, respectively, with and without the introduction of DBR.

[0028] Figure 4 The diagram shows the light distribution and circular polarization degree (P) of the superlens with a focal length of 1 μm (without DBR) and 10 μm (with DBR), respectively. CP A simulation result.

[0029] Figure 5 This is a schematic side sectional view showing the structure of the light-emitting device according to the second embodiment of the present invention.

[0030] Figure 6 This is a diagram of the light path inside the aforementioned light-emitting device. Detailed Implementation

[0031] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0032] <First Implementation>

[0033] Figure 1This is a schematic side sectional view showing the structure of the light-emitting device 100 according to the first embodiment of the present invention. Figure 2 This is a diagram of the light path inside the light-emitting device 100.

[0034] [Overall Structure]

[0035] like Figure 1 As shown, the light-emitting device 100 of this embodiment has an element body 10 and a lens layer 31.

[0036] (Component body)

[0037] The main body 10 is composed of an InGaN-based blue light-emitting diode. The main body 10 has a structure in which a buffer layer 16, a reflective layer 12, an n-type semiconductor layer 13 (first conductive semiconductor layer), an active layer 14 (light-emitting layer), a p-type semiconductor layer 15 (second conductive semiconductor layer), a transparent conductive film 17, and a p-type electrode layer 19 are sequentially stacked on a substrate 11.

[0038] The substrate 11 is a sapphire substrate with a thickness of 300 μm and a face orientation of (0001).

[0039] The reflective layer 12 is, for example, an AlInN / GaN-based distributed Bragg reflector (DBR), which is formed on the substrate 11 via a buffer layer 16 by epitaxial growth. The buffer layer 16 is a 20nm thick GaN layer, which is also formed on the substrate 11 by epitaxial growth.

[0040] The n-type semiconductor layer 13 is a 1.6 μm thick GaN (n-GaN) layer formed on the reflective layer 12 by epitaxial growth. An n-type electrode layer 18, for example made of gold (Au), is attached to the n-type semiconductor layer 13. The n-type electrode layer 18 is formed on the n-type semiconductor layer 13 by, for example, sputtering.

[0041] The active layer 14 has, for example, an InGaN / GaN-based multiple quantum well (MQW) structure. The active layer 14 has a thickness of 75 nm and is formed on the n-type semiconductor layer 13 by epitaxial growth.

[0042] The p-type semiconductor layer 15 is a 100 nm thick GaN (p-GaN) layer formed on the active layer 14 by epitaxial growth.

[0043] The transparent conductive film 17 is, for example, an ITO film with a thickness of 30 nm, formed on the p-type semiconductor layer 15 by, for example, sputtering. The p-type electrode layer 19 is, for example, a gold (Au) electrode film, formed on the transparent conductive film 17 by, for example, sputtering. The p-type electrode layer 19 has an opening 19a, and the area of ​​the transparent conductive film 17 exposed through the opening 19a forms the light emitting surface 10a of the element body 10.

[0044] (Lens layer)

[0045] Lens layer 31 is disposed on the light emitting surface 10a of the element body 10. Lens layer 31 is a superlens made of a nanostructure of dielectric material, which can extract a specified polarized light (right-hand circularly polarized light in this embodiment) from the light emitted from the light emitting surface 10a.

[0046] As the dielectric material constituting the lens layer 31, a material with high transmittance (low absorption) and a refractive index of, for example, 1.4 or higher is used relative to the emitted light. In this embodiment, GaN, which has a relatively high refractive index and a relatively wide band gap, is used as the dielectric material, but ZrO2, Si3N4, HfO2, SiO2, etc., can also be used.

[0047] The lens layer 31 is composed of an array of GaN nanopillar arrays (two-dimensionally arranged nanostructure elements, such as elliptical cylinders), on the light emitting surface 10a. In this embodiment, the height, period, ellipticity, and orientation of each nanostructure element are set so that only right-handed circularly polarized light can be collimated and emitted. The height is, for example, 800 nm, and the period is, for example, 200 nm.

[0048] The lens layer 31 is formed on the surface of the transparent conductive film 17 that forms the light emitting surface 10a by sputtering. The patterning method of the lens layer 31 is not particularly limited, and known methods such as photolithography and lift-off can be used.

[0049] In the light-emitting device 100 of this embodiment, where the lens layer 31 is disposed on the transparent conductive film 17, the distance between the lens layer 31 and the active layer 14 is about 200 nm, which is very close. Therefore, it is very difficult to design a lens layer 31 with such a close focal length.

[0050] Therefore, in this embodiment, the focal length of the lens layer 31 is set relative to the emitted light, and is the optical path length from the active layer 14 through the reflective layer 12 to the light emitting surface 10a (refer to...). Figure 2 The distance is equivalent to that of the light ray L1. Specifically, for example, the lens layer 31 is designed with a focal length of 3.5 μm for right-hand circularly polarized light and 0 μm for left-hand circularly polarized light. As a design method for the lens layer 31, simulations based on the finite-difference time-domain method (FDTD) can be cited as an example.

[0051] Therefore, the focal length of the lens layer 31 can be extended to about a few μm, making it easy to design a lens layer 31 with the active layer 14 as the focal point, and as described later, it can efficiently emit collimated light with the right-hand circular polarization characteristic of the target.

[0052] [effect]

[0053] In the light-emitting device 100 of this embodiment configured as described above, by applying a positive voltage between the n-type electrode layer 18 and the p-type electrode layer 19, electrons moving from the n-type semiconductor layer 13 to the active layer 14 recombine with holes moving from the p-type semiconductor layer 15 to the active layer 14 to emit light (light-emitting recombination).

[0054] like Figure 2 As shown, the light radiated from the active layer 14 includes radiated light L1, which is reflected back by the reflective layer 12 and incident on the light emitting surface 10a, and radiated light L2, which is directed directly from the active layer 14 toward the light emitting surface 10a. A portion of the radiated light L2 passes through the lens layer 31 and is emitted to the outside as left-handed polarized light Lcp. On the other hand, most of the radiated light L2 is reflected toward the active layer 14 at the interface with the lens layer 31 and the p-type electrode layer 19, and then reflected back by the reflector 12, re-incidentally into the lens layer 31.

[0055] As described above, the focal length of the lens layer 31 is set to a distance equivalent to the optical path length from the active layer 14 through the reflective layer 12 to the light emitting surface 10a. Thus, right-handed circularly polarized light is extracted from the re-incident light of the radiated light L1 and the radiated light L2 through the lens layer 31 and emitted to the outside as collimated light Rcp.

[0056] As described above, in the lens layer 31 of this embodiment, since the virtual focus is set to have a focal length that is equivalent to the optical path length from the active layer 14 through the reflective layer 12 to the light emitting surface 10a, collimated light with the desired polarization characteristics (right-hand circularly polarized light) can be emitted.

[0057] Furthermore, since the focal length of the lens layer 31 can be designed with a distance (optical distance) equivalent to the optical path length from the active layer 14 through the reflective layer 12 to the light emitting surface, the lens layer 31 can be easily manufactured compared to the case where the focal length is designed with a distance (optical distance) equivalent to the optical path length when the light radiated from the active layer 14 directly reaches the light emitting surface 10a.

[0058] Furthermore, since the lens layer 31 is formed of inorganic material, it is possible to construct a circularly polarized light-emitting element that emits light with high circular polarization degree with long element life and stable emission.

[0059] The inventors designed a GaN superlens with a focal length of 3.5 μm for right-hand circularly polarized light and 0 μm for left-hand circularly polarized light. A dipole light source with a wavelength of 450 nm was placed at the center of the InGaN / GaN MQW (active layer 14), and the light distribution and circular polarization degree were calculated.

[0060] Figure 3The figure shows the normalized electric field strengths of right-handed and left-handed circularly polarized light, respectively, with and without a DBR (reflector 12). In this figure, (A) shows the case without a DBR, and (B) shows the case with a DBR. Furthermore, in the figure, I... R I represents the normalized electric field strength of right-handed circularly polarized light. L This represents the normalized electric field strength of left-handed circularly polarized light.

[0061] As shown in the figure, with the DBR imported, it is clear that only right-handed circularly polarized light is collimated due to the effect of the virtual focus. Furthermore, it was confirmed that the proportion of right-handed circularly polarized light is very high when the effective degree of circular polarization relative to the radiation angle is 0.78 (see reference). Figure 3 (B)

[0062] then, Figure 4 Figures (A) and (B) show the light distribution and circular polarization degree (P) of the superlens when the focal length (f) is 1 μm (~400 nm in GaN, without DBR) and 10 μm (~4 μm in GaN, with DBR), respectively. CP As shown in the figure, by setting the DBR, the virtual focal length of the superlens can be extended, thus enabling the efficient output of collimated light with right-hand circularly polarized components (see reference). Figure 4 (B)

[0063] <Second Implementation>

[0064] Figure 5 This is a schematic side sectional view showing the structure of the light-emitting device 200 according to the second embodiment of the present invention. Figure 6 This is a diagram of the light path inside the light-emitting device 200.

[0065] like Figure 5 As shown, the light-emitting device 200 of this embodiment has an element body 20 and a lens layer 32.

[0066] The main body 20 is composed of an InGaN-based blue light-emitting diode. The main body 20 has a structure in which a buffer layer 26, an n-type semiconductor layer 23 (first conductive semiconductor layer), an active layer 24 (light-emitting layer), a p-type semiconductor layer 25 (second conductive semiconductor layer), and a p-type electrode layer 29 (reflective layer) are sequentially stacked on a substrate 21.

[0067] The substrate 21 is a sapphire substrate with a thickness of 300 μm and a face orientation of (0001). The back side of the substrate 21 forms the light emitting surface 20a of the element body 20.

[0068] The n-type semiconductor layer 23 is a 1.6 μm thick GaN (n-GaN) layer, formed on the substrate 21 via a buffer layer 26 by epitaxial growth. The buffer layer 26 is a 20 nm thick GaN layer, also formed on the substrate 21 by epitaxial growth. An n-type electrode layer 28, for example made of gold (Au), is connected to the n-type semiconductor layer 23. The n-type electrode layer 28 is formed on the n-type semiconductor layer 23 by, for example, sputtering.

[0069] The active layer 24 has, for example, an InGaN / GaN-based multiple quantum well (MQW) structure. The active layer 24 has a thickness of 75 nm and is formed on the n-type semiconductor layer 23 by epitaxial growth.

[0070] The p-type semiconductor layer 25 is a 100 nm thick GaN (p-GaN) layer formed on the active layer 24 by epitaxial growth. The p-type electrode layer 29 is, for example, a gold (Au) electrode film formed on the p-type semiconductor layer 25 by, for example, sputtering.

[0071] A lens layer 32 is disposed on the light emitting surface 20a of the element body 20. The lens layer 32 is a superlens composed of a nanostructure of dielectric material, capable of extracting a predetermined polarized light (in this embodiment, right-handed circularly polarized light) from the emitted light at the light emitting surface 20a. In this embodiment, the focal length of the lens layer 32 is set relative to the emitted light, and is the optical path length from the active layer 24 through the p-type electrode layer 29 to the light emitting surface 20a (see reference). Figure 6 The light rays (L3) are at a considerable distance.

[0072] The dielectric material constituting the lens layer 32 is made of the same material as in the first embodiment described above. The lens layer 32 is composed of an array of nanostructure elements (GaN nanopillar array) arranged in two dimensions on the light emitting surface 20a, such as elliptical cylindrical nanostructure elements. In this embodiment, the height, period, ellipticity, and orientation of each nanostructure element are set so that only right-handed circularly polarized light can be collimated and emitted.

[0073] The lens layer 32 is formed on the back side of the substrate 21 that forms the light emitting surface 20a by sputtering. The patterning method of the lens layer 32 is not particularly limited, and known methods such as photolithography and lift-off can be used.

[0074] In the light-emitting device 200 of this embodiment configured as described above, as follows: Figure 6 As shown, the light radiated from the active layer 24 includes radiation light L3 that is reflected back by the p-type electrode layer 29 and incident on the light emitting surface 20a, and radiation light L4 that is directed directly from the active layer 24 toward the light emitting surface 20a.

[0075] As described above, the focal length of the lens layer 32 is set to a distance equivalent to the optical path length from the active layer 24 through the p-type electrode layer 29 to the light exit surface 10a. Thus, right-handed circularly polarized light is extracted from the re-incident light of the radiation light L1 and radiation light L2 through the lens layer 31 and emitted to the outside as collimated light Rcp.

[0076] As described above, in the lens layer 32 of this embodiment, since the virtual focal point is set to a focal length that is equivalent to the optical path length from the active layer 24 through the p-type electrode layer 29 to the light emitting surface 20a, collimated light with the desired polarization characteristics (right-hand circularly polarized light) can be emitted. Furthermore, since the lens layer 32 is disposed on the back side of the substrate 21, it is relatively easy to design a focal length that achieves the target lens function, thereby facilitating the fabrication of the lens layer 32.

[0077] The embodiments of the present invention have been described above, but the present invention is not limited to the embodiments described above, and various modifications can be made.

[0078] For example, in the above embodiments, a light-emitting device that emits collimated light of right-hand circularly polarized light has been described as an example, but it is not limited thereto. The present invention can also be applied to light-emitting devices that emit collimated light of other polarization states such as left-hand circularly polarized light, linearly polarized light, and ellipsoidally polarized light.

[0079] Furthermore, in the above embodiments, an InGaN-based blue semiconductor light-emitting element (LED) was used as an example to illustrate the element body, but it is not limited to this. The present invention can also be applied to light-emitting elements that can emit light in other wavelength regions. In addition, the element body is not limited to inorganic light-emitting elements, but can also be an organic light-emitting element (OLED).

[0080] Explanation of reference numerals in the attached figures

[0081] 10, 20: Main body of the component;

[0082] 10a, 20a: light exit surface;

[0083] 11, 21: substrate;

[0084] 12: Reflective layer;

[0085] 13, 23: n-type semiconductor layers;

[0086] 14, 24: Active layer (light-emitting layer);

[0087] 15, 25: p-type semiconductor layers;

[0088] 29: p-type electrode layer (reflective layer);

[0089] 31, 32: Lens layer;

[0090] 100, 200: Light-emitting devices.

Claims

1. A light-emitting device, comprising: The element body includes a light-emitting layer, a light-emitting surface, and a reflective layer that reflects light radiated from the light-emitting layer toward the light-emitting surface; and A lens layer disposed on the light emitting surface extracts a predetermined polarized light from the emitted light from the light emitting surface. The lens layer has a focal length relative to the emitted light that is equivalent to the optical path length from the light emitting layer through the reflective layer to the light emitting surface.

2. The light-emitting device according to claim 1, wherein, The light-emitting layer is disposed between the light-emitting surface and the reflective layer.

3. The light-emitting device according to claim 2, wherein, The main body of the component also has: A first conductivity type semiconductor layer is formed between the light-emitting layer and the light-emitting surface; and A second conductive semiconductor layer is formed between the light-emitting layer and the reflective layer. The reflective layer is a distributed Bragg reflector (DBR).

4. The light-emitting device according to claim 2, wherein, The main body of the component also has: A first conductivity type semiconductor layer is formed between the light-emitting layer and the reflective layer; and A second conductive semiconductor layer is formed between the light-emitting layer and the light-emitting surface. The reflective layer is an electrode film stacked on the first conductive semiconductor layer.

5. The light-emitting device according to claim 1, wherein, The main body of the component is a gallium nitride-based semiconductor component.

6. The light-emitting device according to claim 1, wherein, The lens layer is a superlens composed of nanostructures of dielectric material.

7. The light-emitting device according to claim 6, wherein, The lens layer extracts right-handed or left-handed circularly polarized light from the emitted light.

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