Nanowires, nanowire photonic elements, and nanowire light-emitting devices

Abstract

A nanowire (10) of the present invention is a columnar semiconductor and comprises a hollow portion (12) along the central axis direction of the columnar semiconductor, the central axis of the columnar semiconductor and the central axis of the hollow portion being substantially aligned. The nanowire (10) generates a vector beam. Further, the nanowire may have a nanowire diameter at least twice and not more than four times the upper limit value of a nanowire diameter at which light is present in single mode. Further, the columnar semiconductor may have a circular or polygonal horizontal cross section.　Thus, the present invention can provide a nanowire capable of generating a vector beam with high efficiency.

Description

Technical Field

[0001] The present invention relates to a nanowire that generates a vector beam, a nanowire optical element, and a nanowire light-emitting device.

Background Art

[0002] In recent years, devices for generating vector beams have been actively researched and developed. A vector beam has a doughnut-shaped electric field distribution and is expected to be applied to the capture of nanomaterials, laser processing, super-resolution microscopy, etc.

[0003] Normally, a vector beam is generated by reflecting, transmitting, etc. the light of a light source with a hologram, a crystal having a refractive index distribution, a plurality of wave plates, etc. Since this vector beam generation device is configured by combining bulk-sized optical elements, it becomes large. Therefore, in order to miniaturize and reduce the power consumption of this generation device, it is important to directly generate a vector beam from the light source and further miniaturize the light source itself.

[0004] In addition, vector beam generation using nanostructures such as metasurfaces is also being performed. In this case, it can be miniaturized compared to a generation device having a configuration that combines bulk optical elements, but the structure becomes complicated.

[0005] On the other hand, a small laser using a nanowire has been realized (Non-Patent Document 1). A semiconductor nanowire is an extremely fine semiconductor nanomaterial with a diameter of several tens of nm to several μm and a length of several μm. In addition, the structure is simple, it can be grown on a substrate in large quantities at once, and a group III-V semiconductor etc. can be directly formed on a silicon substrate. Therefore, generation of a vector beam by a laser using a nanowire is desired.

Prior Art Documents

Non-Patent Documents

[0006]

Non-Patent Document 1

[0007] However, when using nanowire lasers to generate vector beams, selecting the modes present in the nanowires becomes a challenge. Typically, in columnar structures with circular or polygonal cross-sections, such as nanowires, electric field modes similar to those in optical fibers are formed. Therefore, in nanowires, the ground mode is a Gaussian beam rather than a vector beam, while higher-order modes are vector beams with a donut-shaped electric field distribution. As a result, it is not possible to efficiently extract vector beams from nanowires.

[0008] Therefore, in order to efficiently extract a vector beam from a nanowire, it is necessary to ensure that a Gaussian beam does not exist and a vector beam exists in the ground mode of the nanowire. [Means for solving the problem]

[0009] To solve the problems described above, the nanowire according to the present invention is a columnar semiconductor having a hollow portion in the direction of the central axis of the columnar semiconductor, the central axis of the columnar semiconductor and the central axis of the hollow portion substantially coincide, generating a vector beam, and the nanowire diameter is 150 nm or more and 300 nm or less. On the surface of nanowires It is characterized by not containing quantum dots. Furthermore, the nanowire according to the present invention is a columnar semiconductor, having a hollow portion in the direction of the central axis of the columnar semiconductor, the central axis of the columnar semiconductor and the central axis of the hollow portion substantially coincide, generating a vector beam, and the nanowire diameter being 2 times or more and 4 times or less the upper limit of the nanowire diameter in which light exists in single mode. Furthermore, the nanowire according to the present invention is a columnar semiconductor, having a hollow portion in the direction of the central axis of the columnar semiconductor, the central axis of the columnar semiconductor and the central axis of the hollow portion substantially coincide, generating a vector beam, and having metal in at least a part of the hollow portion. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide nanowires, nanowire optical elements, and nanowire light-emitting devices that generate vector beams with high efficiency. [Brief explanation of the drawing]

[0011] [Figure 1A] Figure 1A is a schematic external view of a nanowire according to the first embodiment of the present invention. [Figure 1B] Figure 1B is a schematic external view of an example of a nanowire according to the first embodiment of the present invention. [Figure 2A] Figure 2A is a schematic horizontal cross-sectional view of a nanowire according to the first embodiment of the present invention. [Figure 2B] Figure 2B is a light intensity distribution diagram in a horizontal cross-section of a nanowire according to the first embodiment of the present invention. [Figure 3] Figure 3 shows the dispersion relationship in a nanowire without a hollow section. [Figure 4A] Figure 4A shows the light intensity distribution in a horizontal cross-section of a nanowire without a hollow section. [Figure 4B] Figure 4B shows the light intensity distribution in a horizontal cross-section of a nanowire without a hollow section. [Figure 5] Figure 5 shows the dispersion relationship in a nanowire according to the first embodiment of the present invention. [Figure 6A] FIG. 6A is a diagram showing the light intensity distribution in a horizontal cross-section of a nanowire according to the first embodiment of the present invention. [Figure 6B] FIG. 6B is a diagram showing the light intensity distribution in a horizontal cross-section of a nanowire according to the first embodiment of the present invention. [Figure 6C] FIG. 6C is a diagram showing the light intensity distribution in a horizontal cross-section of a nanowire according to the first embodiment of the present invention. [Figure 7A] FIG. 7A is a diagram showing the light intensity distribution in a horizontal cross-section of a nanowire according to the first embodiment of the present invention. [Figure 7B] FIG. 7B is a diagram showing the light intensity distribution in a vertical cross-section of a nanowire according to the first embodiment of the present invention. [Figure 8] FIG. 8 is a schematic external view of a nanowire according to the second embodiment of the present invention. [Figure 9] FIG. 9 is a diagram showing the dispersion relationship in a nanowire according to the second embodiment of the present invention. [Figure 10A] FIG. 10A is a diagram showing the light intensity distribution in a horizontal cross-section of a nanowire according to the second embodiment of the present invention. [Figure 10B] FIG. 10B is a diagram showing the light intensity distribution in a horizontal cross-section of a nanowire according to the second embodiment of the present invention. [Figure 11A] FIG. 11A is a diagram showing the light intensity distribution in a horizontal cross-section of a nanowire according to the second embodiment of the present invention. [Figure 11B] FIG. 11B is a diagram showing the light intensity distribution in a vertical cross-section of a nanowire according to the second embodiment of the present invention. [Figure 12A] FIG. 12A is a schematic horizontal cross-sectional view showing an example of a nanowire according to the second embodiment of the present invention. [Figure 12B] FIG. 12B is a schematic vertical cross-sectional view showing an example of a nanowire according to the second embodiment of the present invention. [Figure 13A] FIG. 13A is a schematic horizontal cross-sectional view showing an example of a nanowire according to the second embodiment of the present invention. [Figure 13B]Figure 13B is a schematic vertical cross-sectional view showing an example of a nanowire according to a second embodiment of the present invention. [Figure 14A] Figure 14A is a schematic horizontal cross-sectional view showing an example of a nanowire according to a modified embodiment of the present invention. [Figure 14B] Figure 14B is a schematic vertical cross-sectional view showing an example of a nanowire according to a modified embodiment of the present invention. [Figure 15A] Figure 15A is a schematic horizontal cross-sectional view showing an example of a nanowire according to a modified embodiment of the present invention. [Figure 15B] Figure 15B is a schematic vertical cross-sectional view showing an example of a nanowire according to a modified embodiment of the present invention. [Figure 16] Figure 16 is a diagram showing the configuration of a nanowire light-emitting device according to a third embodiment of the present invention. [Figure 17A] Figure 17A is a light intensity distribution diagram illustrating the operation of a nanowire light-emitting device according to a third embodiment of the present invention. [Figure 17B] Figure 17B is a light intensity distribution diagram illustrating the operation of a nanowire light-emitting device according to a third embodiment of the present invention. [Figure 18A] Figure 18A is a light intensity distribution diagram illustrating the operation of a nanowire light-emitting device according to a third embodiment of the present invention. [Figure 18B] Figure 18B is a light intensity distribution diagram illustrating the operation of a nanowire light-emitting device according to a third embodiment of the present invention. [Figure 19A] Figure 19A is a light intensity distribution diagram illustrating the operation of a nanowire light-emitting device according to a third embodiment of the present invention. [Figure 19B] Figure 19B is a light intensity distribution diagram illustrating the operation of a nanowire light-emitting device according to a third embodiment of the present invention. [Modes for carrying out the invention]

[0012] <First Embodiment> A nanowire according to the first embodiment of the present invention will be described with reference to Figures 1A to 7B.

[0013] <Nanowire composition> The nanowire 10 according to this embodiment is composed of a nanowire having a hollow portion 12, as shown in Figure 1A. More specifically, the main body 11 of the nanowire 10 is a columnar GaN whose cross-section in the horizontal plane (XY plane in the figure) (hereinafter referred to as "horizontal cross-section") is a regular hexagon. The length r1 from the center to the vertex of the regular hexagon in the horizontal cross-section is 200 nm. The length in the central axis direction (Z direction in the figure) should be 200 nm or more. Here, the regular hexagonal horizontal cross-sectional shape is due to the hexagonal crystal structure of GaN.

[0014] The hollow portion 12 has a circular horizontal cross-section, is positioned approximately at the center of the nanowire 10 body 11 in the central axis direction (Z direction), and penetrates the nanowire 10 body 11. In other words, the central axis A of the nanowire 10 body 11 11 and the central axis A of the hollow part 12 These are approximately identical. The radius r2 of the horizontal cross-section of the hollow portion 12 is 108 nm. Here, "approximately center" includes the exact center and includes a range of machining tolerances. Similarly, "approximately identical" includes the exact identical and includes a range of machining tolerances.

[0015] Furthermore, the nanowire 20 may be composed of columnar GaN with a circular horizontal cross-sectional shape, as shown in Figure 1B.

[0016] Here, we have shown an example where the nanowire body is made of GaN, but it is not limited to this, and other semiconductors such as GaAs, InP, and SiGe may also be used. Furthermore, it may have a layered structure made of multiple materials, such as multiple quantum wells (MQW).

[0017] Furthermore, the horizontal cross-sectional shape of the nanowire 10 is not limited to a regular hexagon or a circle; it may also be a polygon. Here, a symmetrical circle or regular polygon is preferable. In addition, the length from the center to the vertex in a polygon or the radius in a circle (hereinafter referred to as "nanowire diameter") r1 in the horizontal cross-section of the nanowire 10 is preferably between 150 nm and 300 nm.

[0018] Furthermore, the horizontal cross-sectional shape of the hollow portion 12 is not limited to a circle; it may also be a regular hexagon or a polygon. Here, a symmetrical circle or regular polygon is preferable. Also, in the horizontal cross-section of the hollow portion 12, the length from the center to the vertex in a polygon or the radius (hereinafter referred to as "hollow diameter") r2 in a circle only needs to be sufficient to confine light within the nanowire 10. For example, the lower limit may be a few nanometers, and the upper limit may be such that the thickness of the side surface of the main body 11 of the nanowire 10 is approximately 10 nm.

[0019] The nanowire 10 according to this embodiment is fabricated, for example, as follows.

[0020] First, a GaN buffer layer is grown on a sapphire substrate, and then hexagonal GaN is deposited as a hexagonal prismatic nanowire crystal (the main body).

[0021] Next, in the nanowire crystal (main body), hollow portions (holes) 12 are formed by dry etching or sublimation (a top-down selective-area sublimation method) using a pattern created by electron beam lithography.

[0022] Finally, the nanowire 10 having a hollow portion is separated from the GaN buffer layer.

[0023] Figures 2A and 2B show an example of the simulation results of the electric field distribution of the nanowire 10 according to this embodiment. For the simulation, a nanowire made of GaN is used, and the refractive index of GaN is set to 2.022. As shown in Figure 2A, the horizontal cross-sectional shape of the nanowire body 11 is a regular hexagon, and the nanowire diameter r1 is set to 200 nm. The horizontal cross-sectional shape of the hollow portion 12 is a perfect circle, and the hollow diameter r2 is set to 0.54 times the nanowire diameter r1 (108 nm).

[0024] The simulation was performed using a two-dimensional finite element method simulation (product name: COMSOL Multiphysics, manufacturer: COMSOL Inc.).

[0025] Figure 2B shows the light intensity (electric field) distribution in nanowire 10. The arrows in the figure indicate the direction of the electric field at a specific phase.

[0026] In the nanowire 10, the light (electric field) is distributed in a donut shape. This indicates that the nanowire 10 can generate a vector beam with a donut-shaped electric field distribution as its ground mode.

[0027] Next, the operation of the nanowire 10 according to this embodiment will be described.

[0028] First, we will describe the optical mode distribution of the nanowire 30 without a hollow section. Figure 3 shows the simulation results of the dispersion relation of the optical modes of the nanowire 30 without a hollow section. The horizontal axis is the nanowire diameter r1, and the vertical axis is the effective mode refractive index. The nanowire material is GaN, and the wavelength is around 400 nm. In the figure, the inset shows the horizontal cross-section of the nanowire 30 used in the simulation.

[0029] As the nanowire diameter r1 increases, the number of optical modes present in the nanowire 30 increases, with 22 modes present when the nanowire diameter r1 is 0.2 μm. Furthermore, the effective mode refractive index of each mode increases with increasing nanowire diameter r1.

[0030] Furthermore, modes 1 and 2 exist in a degenerate state across the entire nanowire diameter (0.04 μm to 0.20 μm). Because modes 1 and 2 are degenerate, they are plotted overlapping in the figure.

[0031] Furthermore, across the entire nanowire diameter, the degenerate modes 1 and 2 exhibit the highest effective mode refractive index and are therefore the ground modes, existing as single modes down to a nanowire diameter r1 of 0.075 μm.

[0032] Figures 4A and 4B show the light intensity distributions for Mode 1 and Mode 3 in a horizontal cross-section of nanowire 30 with a nanowire diameter r1 of 0.20 μm, respectively. Here, the light intensity distribution for Mode 2 is the same as that for Mode 1.

[0033] In mode 1, as shown in Figure 4A, the light intensity is high at the center of the nanowire 30. Therefore, mode 1 is a Gaussian beam, not a vector beam. Thus, the ground modes, the degenerate modes 1 and 2, are Gaussian beams.

[0034] On the other hand, as shown in Figure 4B, mode 3 exhibits a donut-shaped mode distribution and is a vector beam of so-called azimuthal polarization modes.

[0035] Here, across the entire nanowire diameter, degenerate modes 1 and 2 exhibit a Gaussian beam distribution. On the other hand, mode 3 shows a donut-shaped mode distribution (vector beam).

[0036] Thus, the nanowire 30, which does not have a hollow section, has a mode distribution similar to that of a typical optical fiber, and the vector beam always exists in a higher-order mode rather than the ground mode, making it impossible to efficiently extract the vector beam.

[0037] Next, the light intensity distribution of the hollow nanowire 10 related to this implementation will be described. Figure 5 shows the simulation results of the dispersion relations of the modes in nanowire 10. The horizontal axis represents the nanowire diameter r1, and the vertical axis represents the effective mode refractive index.

[0038] In the figure, the inset shows the horizontal cross-sectional shape of the nanowire 10 used in the simulation. The diameter (hollow diameter) r2 of the hollow portion 12 located at the center of the nanowire 10 was set to 0.54 times that of the nanowire r1.

[0039] As the nanowire diameter r1 increases, the number of optical modes present in the nanowire 10 increases, with 31 modes present when the nanowire diameter r1 is 0.3 μm. Furthermore, the effective mode refractive index of each mode increases with increasing nanowire diameter r1.

[0040] Furthermore, modes 1 and 2 exist in a degenerate state across the entire nanowire diameter range (0.02 μm to 0.30 μm), and a single mode exists up to a nanowire diameter r1 of 0.075 μm (75 nm). Here, since modes 1 and 2 are degenerate, they are plotted overlapping in the figure.

[0041] Furthermore, within the range of nanowire diameter r1 up to approximately 0.15 μm (150 nm), the degenerate modes 1 and 2 exhibit the highest effective modal refractive index, while above approximately 0.15 μm (150 nm), mode 3 exhibits the highest effective modal refractive index. Thus, at a nanowire diameter r1 of approximately 0.15 μm (150 nm), the ground mode changes (reverses) from the degenerate modes 1 and 2 to mode 3.

[0042] Figures 6A, B, and C show the light intensity distributions for modes 1, 2, and 3 in a horizontal cross-section of nanowire 10 with a nanowire diameter r1 of 0.20 μm, respectively. The arrows in the figures indicate the direction of the electric field at a specific phase.

[0043] As shown in Figures 6A and 6B, in modes 1 and 2, the high-intensity light region is divided into two parts, and the electric field distribution is split. In this case, the light is not distributed in the central region, and there is no light in the air region of the hollow part 12 of the nanowire 10.

[0044] On the other hand, as shown in Figure 6C, in mode 3, the light exhibits a donut-shaped distribution, which is a vector beam of the so-called azimuthal polarization mode.

[0045] Here, across the entire nanowire diameter, modes 1 and 2 show split electric field distributions, while mode 3 shows a donut-shaped mode distribution (vector beam).

[0046] Based on the above, the ground mode of nanowire 10 becomes mode 3, i.e., the vector beam mode, when the nanowire diameter r1 is approximately 0.15 μm (150 nm) or larger.

[0047] As mentioned above, in modes 1 and 2, the arrangement of hollow sections in small-diameter nanowires causes the electric field distribution to split, preventing light from existing in the air region of the hollow section. Furthermore, increased light leakage into the air reduces the effective refractive index. As a result, the effective refractive index of mode 3 becomes larger than that of modes 1 and 2, leading to a reversal of the ground mode.

[0048] Thus, this ground mode inversion occurs in a nanowire diameter region of approximately twice the upper limit of the nanowire diameter r1 (75 nm) where light exists in single mode (150 nm). Therefore, it is desirable for the nanowire diameter to be at least twice the upper limit of the nanowire diameter where light exists in single mode. Furthermore, it is desirable for the nanowire diameter to be four times or less the upper limit of the nanowire diameter where light exists in single mode.

[0049] Based on the above, with the nanowire 10, the vector beam exists in ground mode at a nanowire diameter greater than a predetermined diameter, and the vector beam can be efficiently extracted.

[0050] Next, we will describe the resonance characteristics of mode 3, which is the ground mode in the nanowire 10.

[0051] Figures 7A and 7B show the results of a three-dimensional simulation of the electric field (light intensity) distribution in mode 3 in nanowire 10, and are horizontal and vertical cross-sectional views, respectively. Here, "vertical cross-section" refers to the cross-section in the vertical plane (XZ plane in the figure). The arrows in the figure indicate the direction of the electric field at a specific phase.

[0052] Furthermore, the nanowire diameter r1 is set to 200 nm and the hollow diameter r2 to 108 nm.

[0053] As shown in Figure 7A, the electric field distribution in mode 3 has the shape of a vector beam. Also, as shown in Figure 7B, the electric field (light) is confined in the vertical direction (Z direction). Thus, in the nanowire 10, a resonator structure is formed for the ground mode of the vector beam due to end-face reflection.

[0054] Furthermore, the Q-factor of the resonator of this nanowire 10 is approximately 1500, providing the optical confinement necessary for laser oscillation.

[0055] <Effects> The nanowire 10 according to this embodiment has a hollow core structure with a hollow portion (hole) in the center. With the nanowire according to this embodiment, there is no mode in which light is confined in the hollow portion, so the concentration of light in the center can be suppressed. As a result, under predetermined conditions of nanowire diameter r1 and hollow diameter r2, the ground mode of the nanowire can be made into a vector beam, and a vector beam can be generated with high efficiency.

[0056] In this embodiment, the hollow-core optical fiber has a hollow portion, similar to the nanowire according to this embodiment. However, since the electric field is confined and propagated within the hollow portion of the hollow-core optical fiber, its effects differ from those of the nanowire according to this embodiment.

[0057] Furthermore, in the nanowire according to this embodiment, a vector beam can be generated by injecting light from an external source. Also, as described later, by forming a p-type layer and an n-type layer in the nanowire, a vector beam can be emitted by injecting an external current. In addition, by forming a resonator structure, laser oscillation can be achieved with the vector beam.

[0058] <Second Embodiment> A nanowire according to a second embodiment of the present invention will be described with reference to Figures 8 to 13B.

[0059] <Nanowire composition> In the nanowire 40 according to this embodiment, as shown in Figure 8, the portion corresponding to the hollow portion in the nanowire according to the first embodiment is filled with metal 42, and the metal-filled portion penetrates the nanowire body 41. Here, gold is used as the metal 42, but other metals such as aluminum or silver may also be used. The other configurations are the same as in the first embodiment.

[0060] The nanowire 40 according to this embodiment is manufactured, for example, in the same manner as in the first embodiment, by processing a hollow portion into a nanowire crystal (main body), and then inserting and fixing a cylindrical metal 42 into the hollow portion.

[0061] Figure 9 shows the simulation results of the dispersion relations of the modes of the nanowire 40. The horizontal axis represents the nanowire diameter r1, and the vertical axis represents the effective mode refractive index. The diameter r2 of the metal 42 placed at the center of the nanowire 40 was set to 0.54 times the nanowire diameter r1.

[0062] As the nanowire diameter r1 increases, the number of optical modes present in the nanowire 40 also increases, and when the nanowire diameter r1 is 0.3 μm, there are 22 modes. Here, modes 2 and 3 are degenerate and are therefore plotted overlapping in the figure.

[0063] Furthermore, in the region where the nanowire diameter r1 is approximately 0.11 μm (110 nm), only mode 1 exists, and in this region, mode 1 is a single mode and is the ground mode.

[0064] Furthermore, when the nanowire diameter r1 is 0.125 to 0.14 μm, modes 6 and 7 are degenerate and represent the ground mode, and when the nanowire diameter r1 is 0.14 to 0.25 μm, mode 8 is the ground mode.

[0065] Figures 10A and 10B show the light intensity distribution for Mode 1 in a horizontal cross-section of nanowire 40 with a nanowire diameter r1 of 0.10 μm, and the light intensity distribution for Mode 8 in a horizontal cross-section of nanowire 40 with a nanowire diameter r1 of 0.15 μm, respectively. Here, the arrows in the figures indicate the direction of the electric field at a specific phase.

[0066] As shown in Figure 10A, Mode 1 exhibits a donut-shaped distribution and is a vector beam of the azimuthal polarization mode. Thus, in Mode 1, light cannot exist in the central part where metal 42 is located, and therefore a vector beam exists as the ground mode rather than a Gaussian beam.

[0067] Thus, with nanowire 40, a single-mode vector beam can be generated with a nanowire diameter r1 of approximately 0.09 μm (90 nm) to 0.11 μm (110 nm).

[0068] As shown in Figure 10B, in mode 8, the electric field exhibits a donut-shaped distribution with a radial distribution, and is a vector beam of radial polarization mode.

[0069] Thus, when the nanowire diameter r1 is 0.14 to 0.25 μm, a plasmomic mode vector beam in which the electric field is concentrated in the central metal 42 can be generated in the ground mode.

[0070] Here, across the entire nanowire diameter, Mode 1 represents the mode of an azimuthally polarized vector beam, and Mode 8 represents the mode of a radially polarized vector beam.

[0071] Next, we will describe the resonance characteristics of Mode 1, which is the ground mode in the nanowire 40.

[0072] Figures 11A and 11B show the results of a three-dimensional simulation of the electric field (light intensity) distribution in mode 1 in nanowire 40, which are horizontal and vertical cross-sectional views, respectively. The arrows in the figures indicate the direction of the electric field at a specific phase. Here, the nanowire diameter r1 is 100 nm and the hollow diameter r2 is 54 nm.

[0073] As shown in Figure 11A, the electric field distribution in mode 1 has the shape of a vector beam. Also, as shown in Figure 11B, the electric field (light) is confined in the vertical direction (Z direction). Thus, in the nanowire 40, a resonator structure is formed for the ground mode of the vector beam due to end-face reflection.

[0074] Furthermore, the Q-factor of the resonator of this nanowire 40 is approximately 60, providing the optical confinement necessary for laser oscillation. This Q-factor can be improved by placing an insulating film (for example, SiO2) between the nanowire and the metal.

[0075] Similarly, a resonator structure is also formed for mode 8, which is the ground mode, when the nanowire diameter r1 is 0.14 to 0.25 μm.

[0076] In this embodiment, an example is shown in which the entire hollow portion of the nanowire is filled with metal, but the invention is not limited to this, and metal may be placed only in a part of the hollow portion.

[0077] For example, metal microspheres 52 may be arranged in the hollow portion, as shown in Figures 12A and 12B, for example, a commercially available metal sphere made of gold with an outer diameter of several tens to 100 nm may be used for the metal microspheres 52. In this configuration, a vector beam distribution is formed around the metal microspheres 52.

[0078] Alternatively, as shown in Figures 13A and 13B, multiple metal microspheres 62 may be arranged in the hollow portion of the nanowire 60. In this configuration, an electric field distribution can be formed periodically in the central axis direction (Z direction), and an effect similar to that of a nano-sized antenna can be obtained.

[0079] <Effects> Similar to the first embodiment, the nanowire according to this embodiment does not have a mode in which light is confined to the central metal, thus suppressing the concentration of light at the center. As a result, under predetermined conditions, the ground mode of the nanowire can be made into a vector beam, and a vector beam can be generated with high efficiency.

[0080] Furthermore, since the nanowire according to this embodiment can generate a vector beam in the ground mode in a single mode, it is suitable for signal transmission in optical fibers and waveguides in optical communications and the like.

[0081] Furthermore, it provides the same effects as the first embodiment.

[0082] <Modified examples of nanowires> A modified example of the embodiment of the present invention, the nanowire 70, may have a periodic grating structure 73 in the central axis direction (Z direction) on the outer periphery of a nanowire (body 71) having a hollow portion 72, as shown in Figures 14A and B. Alternatively, as shown in Figures 15A and B, the nanowire 80 may have a periodic grating structure 83 in the central axis direction (Z direction) on the outer periphery of a nanowire (body 81) having a metal 82 in the center.

[0083] The periodic structures (gratings) 73 and 83 of the nanowires can be formed, for example, by etching a nanowire that periodically has materials with different etching rates arranged in the central axis direction (Z direction) under predetermined etching conditions.

[0084] According to this modified nanowire, optical confinement can be achieved as a resonator, and the Q factor can be improved.

[0085] <Third Embodiment> A nanowire light-emitting device according to a third embodiment of the present invention will be described with reference to Figures 16 to 19B.

[0086] <Configuration of Nanowire Light-Emitting Device> The nanowire light-emitting device 90 according to this embodiment is configured using a nanowire laser. As shown in Figure 16, the nanowire light-emitting device 90 includes nanowires 91 on a sapphire substrate 93 via nanowire base ends 92.

[0087] The nanowire 91 is made of GaN with a pin structure, and has p-type GaN91_1 at one end (e.g., the top side) and n-type GaN91_3 at the other end (e.g., the base end side), with i-type GaN91_2 between the p-type GaN91_1 and the n-type GaN91_3. Other configurations of the nanowire 91 are the same as in the first embodiment.

[0088] Furthermore, the nanowire base end 92 is made of n-type GaN.

[0089] Furthermore, an insulating layer 94 is provided on the side surface of the nanowire 91.

[0090] Furthermore, a transparent electrode 95 (p-type electrode) is positioned to cover the end face of one (for example, p-type GaN91_1), and an n-type electrode 96 is provided at the base end 92 of a nanowire that is electrically connected to the end face of the other (for example, n-type GaN91_3).

[0091] Current is injected from an external power supply 97 connected to the transparent electrode (p-type electrode) 95 and the n-type electrode 96, respectively, and laser light (dotted arrows m1 and m2 and solid arrow m3 in the figure) is emitted from one end (for example, the top side).

[0092] Here, the nanowire laser comprises at least a nanowire 91, a p-type electrode 95, and an n-type electrode 96.

[0093] Furthermore, an NA lens 98 is positioned near the exit end face of the nanowire 91 so that the laser light is incident on it. The NA lens 98 allows only the ground mode light (solid arrow m3 in the figure) to be focused and extracted (output) from the laser light (dotted arrows m1 and m2 and solid arrow m3 in the figure) of the multimode nanowire 91. Here, other than an NA lens, an NA optical element such as a high NA fiber may also be used.

[0094] <Method for fabricating nanowire lasers> An example of a method for fabricating the nanowire laser used in this embodiment will be described.

[0095] First, an n-type GaN buffer layer is grown on a sapphire substrate 93 as the nanowire base end 92, and then hexagonal pin-structured GaN is deposited as a regular hexagonal prismatic nanowire crystal (main body).

[0096] Next, a nanowire 91 having a hollow portion is fabricated by dry etching using a pattern created by electron beam lithography on the nanowire crystal (main body).

[0097] Next, an insulating layer 94 is formed on the side surface of the nanowire using an ALD (Atomic Layer Deposition) apparatus.

[0098] Next, the insulating layer attached to the upper surface of the nanowire during ALD is removed by dry etching to expose the upper surface of the nanowire 91.

[0099] Next, a transparent electrode 95 made of ITO or the like is formed to cover the upper surface of the nanowire 91 using sputtering or the like.

[0100] Finally, an n-type electrode 96 is formed on the nanowire base end 92.

[0101] <Operation of Nanowire Light-Emitting Device> The operation of the nanowire light-emitting device 90 according to this embodiment will be explained with reference to Figures 17A to 19B.

[0102] Figures 17A and 17B show the near-field and far-field images of Mode 1 in the nanowire 10 (corresponding to nanowire 91 in this embodiment) according to the first embodiment, respectively. Similarly, Figures 18A to 19B show the near-field and far-field images of Modes 2 and 3 in the nanowire 10, respectively. To compare the near-field and far-field images, the near-field and far-field images for each mode are shown on the same scale. The arrows in the figures indicate the direction of the electric field at a specific phase.

[0103] In near-field images, modes 1-3 have similar diameters, modes 1 and 2 tend to show a splitting of the electric field distribution, and mode 3 shows a donut-shaped electric field distribution (Figures 17A, 18A, 19A).

[0104] On the other hand, in the far-field image, the electric fields of modes 1 and 2 are clearly split (Figures 17B and 18B), while mode 3 shows a donut-shaped electric field distribution (Figure 19B). Here, in the far-field image, the electric fields of modes 1 and 2 are more widely distributed than those of mode 3. That is, the divergence angle of the electric fields (light) of modes 1 and 2 in the direction of emission is greater than that of mode 3.

[0105] Therefore, by using an NA lens 98 positioned at a predetermined distance from the emission end of the nanowire laser (for example, the distance at which a far-field image is acquired) relative to the emitted light, it is possible to exclude light of modes 1 and 2 (dotted arrows m1 and m2 in Figure 16) and focus and extract (output) only light of mode 3 (solid arrow m3 in Figure 16), thereby extracting (outputting) only vector mode light (mode 3).

[0106] Thus, by using a lens with an appropriate numerical aperture (NA) for the emission of light from a nanowire containing multimode light, it is possible to extract (output) only the light (modes) of the vector beam.

[0107] In particular, as shown in the first embodiment, when a ground mode vector beam is generated with a predetermined nanowire diameter, higher-order modes are also induced. In such cases, the higher-order modes can be excluded by using an appropriate NA lens, and only the ground mode vector beam can be extracted (output).

[0108] <Effects> According to the nanowire light emission device of this embodiment, the ground mode vector beam can be efficiently extracted.

[0109] Furthermore, the nanowire light emission device according to this embodiment enables the realization of an ultra-compact vector beam generation device.

[0110] In this embodiment, the nanowire configuration according to the first embodiment was used, but the nanowire configuration according to the second embodiment and its modified form may also be used.

[0111] In the embodiments of the present invention, an example was shown in which the hollow portion or the metal filling the hollow portion penetrates the nanowire body. However, the invention is not limited to this, and penetration is not required. The metal should be thick enough to generate a vector beam in the ground mode and its length should be approximately the wavelength considering the effective refractive index, and it should be placed in the hollow portion.

[0112] In the embodiments of the present invention, an example was shown in which a laser is used as the optical element of the nanowire, but other optical elements such as light-emitting diodes (LEDs) or semiconductor optical amplifiers (SOAs) may also be used.

[0113] In the embodiments of the present invention, examples of the structure, dimensions, materials, etc. of each component in the configuration and manufacturing method of nanowires, nanowire optical elements, and nanowire light-emitting devices are shown, but the invention is not limited to these examples. It is sufficient as long as the nanowires, nanowire optical elements, and nanowire light-emitting devices perform their functions and produce effects. [Industrial applicability]

[0114] This invention can be applied to the capture of nanomaterials, laser processing, super-resolution microscopy, and the like. [Explanation of Symbols]

[0115] 10 nanowires 11 Nanowire body 12 Hollow part

Claims

1. A columnar semiconductor, The columnar semiconductor has a hollow portion in the direction of its central axis, The central axis of the columnar semiconductor and the central axis of the hollow portion substantially coincide, generating a vector beam. The nanowire diameter is between 150 nm and 300 nm. The surface of the nanowire does not contain quantum dots. Nanowires characterized by the following features.

2. A columnar semiconductor, The columnar semiconductor has a hollow portion in the direction of its central axis, The central axis of the columnar semiconductor and the central axis of the hollow portion substantially coincide, generating a vector beam. The nanowire diameter is more than twice and less than four times the upper limit of the nanowire diameter in which light exists in single mode. Nanowires characterized by the following features.

3. A columnar semiconductor, The columnar semiconductor has a hollow portion in the direction of its central axis, The central axis of the columnar semiconductor and the central axis of the hollow portion substantially coincide, generating a vector beam. At least a portion of the hollow section is made of metal. Nanowires characterized by the following features.

4. The horizontal cross-section of the columnar semiconductor is circular or polygonal. The nanowire according to any one of claims 1 to 3.

5. The aforementioned metal is a metal microsphere. The nanowire according to claim 3.

6. It has a periodic structure on its side. The nanowire according to any one of claims 1 to 5, characterized by the features described above.

7. The nanowire according to any one of claims 1 to 6 is provided with electrodes electrically connected to one end and the other end, One end is a p-type semiconductor, and the other end is an n-type semiconductor. A nanowire optical element characterized by the following features.

8. The nanowire optical element according to claim 7, An NA optical element is disposed near one end face of the aforementioned nanowire optical element. Equipped with, The NA optical element collects only the light of the vector beam mode from the light emitted from one end face of the nanowire optical element. A nanowire light-emitting device characterized by the following features.

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