Light-emitting device

Abstract

To provide a light emitting device that has narrowed angle light distribution characteristics and also emits high efficiency and high output mixed-color light.SOLUTION: A light emitting device includes: a semiconductor light-emitting structural layer 20 having a photonic crystal layer; an optical filter 40 placed on the emitting surface of the semiconductor light-emitting structural layer 20; and a nano-antenna phosphor 30 placed on the optical filter 40. The nano-antenna phosphor 30 has a phosphor plate 31, which is a wavelength converter, and an antenna array 32, which is formed on the phosphor plate 31 and comprises a plurality of nano-antennas 32A.SELECTED DRAWING: Figure 1B

Description

[Technical Field]

[0001] The present invention relates to a light-emitting device, and more particularly to a light-emitting device including a light-emitting element having a photonic crystal and a phosphor. [Background technology]

[0002] In recent years, efforts toward autonomous driving of vehicles and moving objects such as automobiles have progressed rapidly, and the requirements for lighting fixtures such as headlamps are also changing. For example, headlamps are expected to have value not as a single lamp but as a lamp system that incorporates sensors and other elements. However, while automobile headlamps sometimes use LED (Light Emitting Diode) elements arranged in parallel to achieve high output, there is a problem in that it is difficult to find space to install sensors and other elements.

[0003] Generally, with LEDs that emit spontaneous light, the light emission distribution is Lambertian, which causes the light distribution to spread, resulting in loss of light that escapes the lens inside the headlamp. In order to reduce light loss and further increase the amount of light, it is necessary to make the lens larger (i.e., increase the numerical aperture (NA)), but this is not desirable from the perspective of headlamp space. In order to increase the amount of LED light taken in without changing the NA of the lens, it is necessary to narrow the light emission distribution angle of the LED light source itself.

[0004] As a technique for forming a small, narrow-angle white light source, a configuration has been disclosed in which laser light is irradiated onto a phosphor having nanoantennas formed on the surface.

[0005] For example, Patent Document 1 discloses an illumination device in which photons from a photon emitter are emitted from a plasmonic antenna array. Patent Document 2 discloses a wavelength conversion device having a wavelength converter that converts the wavelength of incident laser light and an antenna array formed on the emission surface of the wavelength converter.

[0006] However, there is a further demand for a light source that has a narrow-angle light distribution and high light output. Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a light emitting device that has narrow-angle light distribution characteristics and emits mixed color light with high efficiency and high output. [Means for solving the problem]

[0008] A light emitting device according to one embodiment of the present invention comprises: a semiconductor light-emitting structure layer having a photonic crystal layer; The device comprises a wavelength converter placed on the emission surface of the semiconductor light-emitting structure layer and converting the wavelength of the emitted light from the semiconductor light-emitting structure layer to generate wavelength-converted light, and a nanoantenna phosphor consisting of an antenna array in which a plurality of nanoantennas are periodically arranged on the wavelength converter. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 6381645 [Patent Document 2] Patent No. 6789536 [Brief explanation of the drawings]

[0010] [Figure 1A] 1 is a plan view schematically showing the upper surface of a light emitting device 10 according to a first embodiment of the present invention. [Figure 1B] FIG. 1B is a cross-sectional view schematically showing a cross-sectional structure taken along line AA shown in FIG. 1A. [Figure 2] 10 is a diagram showing the results of a simulation of the incidence angle (θ) dependency of the reflectance of the optical filter 40. FIG. [Figure 3A] FIG. 1 is a diagram showing the dispersion relationship with the wave number kx (= k sin θ) on the horizontal axis and the normalized frequency a / λ on the vertical axis. [Figure 3B] FIG. 10 is an enlarged view showing the maximum value portion of the TE0 mode. [Figure 4A] FIG. 2 is a cross-sectional view of a nanoantenna phosphor 30. [Figure 4B] FIG. 2 is a top view of the nanoantenna phosphor 30. [Figure 5A] 10 is a graph showing the simulation results of the relationship between the emission angle (θem) of the antenna array 32 and wavelength when the period P is 360 nm. [Figure 5B] 10 is a graph showing the simulation results of the relationship between the emission angle (θem) of the antenna array 32 and wavelength when the period P is 400 nm. [Figure 5C] 10 is a graph showing the simulation results of the relationship between the emission angle (θem) of the antenna array 32 and wavelength when the period P is 440 nm. [Figure 5D] 10 is a graph showing the simulation results of the relationship between the emission angle (θem) of the antenna array 32 and wavelength when the period P is 480 nm. [Figure 6A] 10 is a diagram showing the light distribution characteristics of blue light from the LED structure layer 20. FIG. [Figure 6B] 10 is a diagram showing the light distribution characteristics of fluorescent light (yellow light) from the nanoantenna phosphor 30. FIG. [Figure 6C] 1 is a diagram showing the light distribution characteristics of white light from the light emitting device 10. FIG. [Figure 7] 1 is a diagram schematically illustrating narrow-angle LED light generated by an LED structure layer 20. FIG. [Figure 8] FIG. 10 is a cross-sectional view schematically showing the cross-sectional structure of a light-emitting device 50 according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] In the following, preferred embodiments of the present invention will be described, but these may be modified and combined as appropriate. In the following description and accompanying drawings, substantially the same or equivalent parts are designated by the same reference numerals.

[0012] [First embodiment] FIG. 1A is a plan view schematically showing the upper surface of a light emitting device 10 according to a first embodiment of the present invention, and FIG. 1B is a cross-sectional view schematically showing the cross-sectional structure taken along line AA shown in FIG. 1A.

[0013] 1A and 1B, the light emitting device 10 includes a semiconductor light emitting structure layer 20, a nanoantenna phosphor 30, and an optical filter 40. In the light emitting device 10 of this embodiment, the optical filter 40 is disposed on the light emitting surface of the semiconductor light emitting structure layer 20, and the nanoantenna phosphor 30 is disposed on the optical filter 40.

[0014] (1) Semiconductor light-emitting structure layer The semiconductor light emitting structure layer (hereinafter referred to as the LED structure layer) 20 has a first semiconductor layer 21 having a photonic crystal layer 21P, an active layer 23, and a second semiconductor layer 25.

[0015] In this embodiment, the LED structure layer 20 is described as being made of a nitride-based semiconductor layer (GaN-based semiconductor layer), but may be made of a semiconductor light-emitting structure layer of another crystal system that operates as an LED.

[0016] Furthermore, the composition, layer thickness, impurities, doping concentration, etc. of each layer of the semiconductor structure layer shown below are merely examples, and can be appropriately selected, modified, etc. according to the desired characteristics.

[0017] The LED structural layer 20 will be described in detail below with reference to FIGS. 1A and 1B.

[0018] The LED structure layer 20 is formed by sequentially growing an active layer 23 and a second semiconductor layer 25 on a first semiconductor layer 21. For example, the LED structure layer 20 can be formed by MOCVD (metal organic chemical vapor deposition) or MBE (molecular beam epitaxy).

[0019] First semiconductor layer 21 has photonic crystal layer 21P formed on lower layer 21A made of n-GaN, an n-type semiconductor layer. Photonic crystal layer 21P has minute air holes 22 formed two-dimensionally and periodically in a plane parallel to first semiconductor layer 21, and is a structural layer whose refractive index changes periodically.

[0020] On photonic crystal layer 21 P, buried layer 21 B is formed to bury photonic crystal layer 21 P. Buried layer 21 B is made of n-GaN, an n-type semiconductor layer, and has a thickness of 120 nm.

[0021] More specifically, in this embodiment, holes 22 in photonic crystal layer 21P are arranged at square lattice positions, have a cylindrical shape, a lattice constant (period) of 185 nm, a height of 240 nm, and a diameter of 92.5 nm.

[0022] Here, when the lattice constant of the photonic crystal is a, the emission wavelength is λ (in a vacuum), and the refractive index of the matrix is ​​neff, the relationship is such that a≠mλ / neff (m is a natural number) is satisfied in the case of a square lattice two-dimensional photonic crystal, and a≠mλ×2 / (3 / 2×neff) (m is a natural number) is satisfied in the case of a triangular lattice two-dimensional photonic crystal.

[0023] In this case, λ is valid not only for the peak wavelength but also for any wavelength λw (in vacuum) within the full width at half maximum (FWHM) of the emission spectrum of the active layer 23. In other words, if the emission spectrum peak is 450 nm and the full width at half maximum is 10 nm, λ is considered to be in the range of 445 nm to 455 nm (445 nm≦λw≦455 nm). The present invention is preferably a light-emitting device that emits non-resonant LED light. By forming only photonic crystals that satisfy these conditions, the angle of the non-resonant light is narrowed.

[0024] However, even if a = mλ / neff is satisfied in the case of a square lattice two-dimensional photonic crystal, or a = mλ × 2 / (3 / 2 × neff) is satisfied in the case of a triangular lattice two-dimensional photonic crystal, the light can remain non-resonant and be narrow-angle light as long as the supplied current value is equal to or less than a certain value. In this case, by supplying a current value that does not generate resonant light from a power supply (not shown) connected to the light-emitting device 10, the light-emitting device can be made to emit non-resonant LED light for both narrow-angle light components (emission angle within 20°) and wide-angle light components (emission angle greater than 20°).

[0025] A light emitting layer 23A is formed on the first semiconductor layer 21. The light emitting layer 23A is a five-layer multiple quantum well structure layer (hereinafter referred to as an MQW layer) in which GaN barrier layers and InGaN well layers are alternately stacked.

[0026] A spacer layer 23B is formed on the light emitting layer 23A. The spacer layer 23B is made of GaN and has a thickness of 6 nm.

[0027] A second semiconductor layer 25 is formed on the spacer layer 23B. More specifically, the second semiconductor layer 25 is made of an electron blocking layer 25A and a p-GaN layer 25B, which is a p-type semiconductor layer, formed on the electron blocking layer 25A.

[0028] The electron blocking layer 25A is made of AlGaN and has a thickness of, for example, 10 nm, and the p-GaN layer 25B has a thickness of, for example, 116 nm.

[0029] In this specification, a layer consisting of the light emitting layer 23A and the spacer layer 23B is referred to as an active layer (core layer) 23. The first semiconductor layer 21 and the second semiconductor layer 25 sandwiching the active layer 23 from both sides function as a first cladding layer and a second cladding layer, respectively.

[0030] The first semiconductor layer (first cladding layer) 21 includes a photonic crystal layer 21P, i.e., voids 22, and therefore has a smaller refractive index than the base semiconductor (GaN in this embodiment), and therefore has a smaller effective refractive index than the active layer (core layer) 23.

[0031] In addition, the electron blocking layer 25A is made of a semiconductor (in this embodiment, AlGaN) that has a larger band gap and a smaller refractive index than the active layer 23 (i.e., the spacer layer 23B of the active layer 23), and the effective refractive index of the second semiconductor layer (second cladding layer) 25 is smaller than the effective refractive index of the active layer 23.

[0032] The first semiconductor layer 21 and the second semiconductor layer 25 have a function similar to that of the cladding of an optical fiber, that is, a function of confining light guided through the active layer (core layer) 23. The first semiconductor layer 21 may be composed of a plurality of semiconductor layers having different compositions. The second semiconductor layer 25 may also be composed of a plurality of semiconductor layers having different compositions.

[0033] Furthermore, the first semiconductor layer 21 is an n-type semiconductor layer, and the second semiconductor layer 25 is a p-type semiconductor layer (opposite conductivity type to the first semiconductor layer 21), but the first semiconductor layer 21 and the second semiconductor layer 25 may have an i-layer or an undoped layer. For example, the electron blocking layer 25A in the second semiconductor layer 25 may be configured as an undoped layer.

[0034] A p-electrode 28A is provided on the p-GaN layer 25B. The p-electrode 28A is formed, for example, as a Ni / Au structure (Au is the surface layer) made of Ni (nickel) formed on the p-GaN layer 25B and Au (gold) formed on the Ni.

[0035] The p-electrode 28A can be a metal layer that is in ohmic contact with the p-GaN layer 25B. For example, it can be configured using an ITO electrode with high reflectivity / Ag reflective film. Alternatively, a semiconductor layer (e.g., a highly doped layer) that can easily make ohmic contact with the metal layer may be provided on the p-GaN layer 25B.

[0036] Furthermore, an n-electrode 28B is provided on the exposed surface of first semiconductor layer 21 where buried layer 21B is partially exposed by etching. N-electrode 28B is in ohmic contact with first semiconductor layer 21. N-electrode 28B has, for example, an Al (aluminum) / Pt (platinum) / Au structure (Au is the surface layer).

[0037] 1A, light emitting device 10 is placed on a substrate or block provided with a wiring circuit, with p-electrode 28A and n-electrode 28B facing downward. When current is applied between p-electrode 28A and n-electrode 28B, light emitting device 10 emits light.

[0038] (2) Optical filter In the light emitting device 10 of this embodiment, an optical filter 40 is inserted between the emission surface of the LED structure layer 20 and the incidence surface S1 of the nanoantenna phosphor 30. The optical filter 40 is provided in close contact with the emission surface of the LED structure layer 20 and the incidence surface S1 of the nanoantenna phosphor 30.

[0039] The optical filter 40 has a filter film 40A, which is a dichroic mirror, formed on a light-transmitting sapphire substrate 40B. The filter film 40A can be formed, for example, of a multilayer film (SiO2 / NbO5 film) in which SiO2 and NbO5 are alternately stacked, or an SiO2 / TiO2 multilayer film.

[0040] The optical filter 40 is configured as a short-pass filter (SPF) that transmits the light (blue light) emitted from the LED structure layer 20 and reflects the wavelength-converted light (yellow light) from the phosphor plate 31.

[0041] First, the angle of incidence on the optical filter 40 for allowing the light emitted from the LED structure layer 20 to efficiently enter the nanoantenna phosphor 30 will be described.

[0042] Fig. 2 is a diagram showing the results of a simulation of the dependency of the reflectance of the optical filter 40 on the angle of incidence (θ). Fig. 2 shows the reflectance when the angle of incidence of light incident on the optical filter 40 is θ = 30°, 15°, and 0°. Note that here, the emission wavelength (λ) of the LED structure layer 20 that emits narrow-angle light is considered to be 450 nm ± 5 nm.

[0043] When the incident angle θ is 30°, 99% or more of the incident light is reflected by the filter film 40A of the optical filter 40. However, when θ is 15° (=θth) or less, the reflectance in the above wavelength range is almost 0%, and the blue LED light of the LED structure layer 20 can be efficiently incident on the nanoantenna phosphor 30. In other words, it can be seen that an LED structure layer 20 having a photonic crystal that can efficiently emit narrow-angle light with θth≦15° is effective.

[0044] Furthermore, the depth of the holes in the photonic crystal is 100 nm, which has almost no effect on the physical size, making it possible for the first time to realize a compact, narrow-angle white light source using a nanoantenna phosphor and an LED as a light source.

[0045] That is, in this embodiment, as described above, the emission spectrum of the active layer 23 has a full width at half maximum of 10 nm, and the characteristics of the filter film 40A (SPF) of the optical filter 40 are set so that light within this full width at half maximum passes through the optical filter 40 with a reflectance of 0%.

[0046] In this way, the characteristics of the LED structure layer 20 and the optical filter 40 are set so that light within the full width at half maximum of the emission spectrum of the LED structure layer 20 passes through the optical filter 40 with a reflectance of 0%.

[0047] In the above case, it is preferable that the transmittance of the incident light at the peak wavelength for incident light with an incident angle θ of 30° or more (blue light in the above example) is less than 10%.It is also preferable that the transmittance of the incident light at the peak wavelength for incident light with an incident angle θ of 15° or less is 90% or more.

[0048] (3) Narrow-angle structure of photonic crystal Next, we will explain the structure for narrowing the angle of the photonic crystal using a blue LED with a wavelength λ=450 nm (full width at half maximum 10 nm) as an example.

[0049] We will calculate the band gap in a photonic crystal, and for information on calculation methods, please refer to references such as "Introduction to Photonic Crystals" (author: Kazuaki Sakoda, Morikita Publishing).

[0050] Photonic crystals have the ability to exclude light of a certain frequency from within the crystal, and the frequency range can be freely set. This range is called the photonic band gap.

[0051] Here, the dispersion relation is calculated from the photonic band gap calculation. The refractive index of the photonic crystal medium is n = 2.5 (e.g., GaN), the refractive index of the medium (air) of the photonic crystal air holes is n = 1, and the lattice constant a (or period) and the diameter d of the air holes are d / a = 0.5. The dispersion relation of the TE mode (Transverse Electric mode) is calculated when the air holes are arranged in a square lattice.

[0052] Figure 3A shows the dispersion relationship, with the horizontal axis representing the wave number kx (= k sin θ) and the vertical axis representing the normalized frequency a / λ. Here, the diffraction angle is θ, and the wave number k = 2π / λ. Here, we focus on the lowest-order TE0 of the multiple TE modes.

[0053] Fig. 3B is an enlarged view of the maximum value portion of the TE0 mode. As shown in Fig. 2B, matching the normalized frequency to the optical mode edge (white circle in the figure) corresponds to extracting narrow-angle light in the 0° direction.

[0054] Here, considering the incidence on nanoantenna phosphor 30, we consider the design of photonic crystal layer 21P, assuming that narrow-angle light is allowed up to θ=-15° to 15° (i.e., the emission angle is within 30°). Figure 3B plots the diffraction lines obtained at θ=-10° and θ=10° as representative design values ​​within the range where an effect is expected.

[0055] The lattice constant design value of 185 nm is obtained from the normalized frequency of 0.415 at the point where the optical mode (TE0) and the diffraction line intersect (black circle in the figure). Therefore, photonic crystal layer 21P can be configured by arranging air holes 22 in a square lattice with air hole diameter d = 92.5 nm and lattice constant a = 185 nm, and can be arranged in an in-plane area of, for example, 1 mm square.

[0056] The hole arrangement in photonic crystal layer 21P is not limited to a square lattice, but may be selected appropriately from a triangular lattice or a hexagonal lattice, etc., and can be obtained in a similar manner.

[0057] The design value may be determined from the intersection of the diffraction lines and the theoretical value, but may also be determined after actually fabricating a number of photonic crystal structures with slightly different lattice constants and determining the conditions.

[0058] For example, by forming an LED having a photonic crystal and measuring the on-axis PL (Photoluminescence) intensity, it is possible to obtain the optimal values ​​for the lattice constant a and the diameter d of the holes 22 so that the peak intensity value is within the desired range.

[0059] The angle of the narrow-angle light emitted by the photonic crystal is determined by determining the hole arrangement, lattice constant a, and diameter d of the holes 22 of the photonic crystal.

[0060] (4) Nanoantenna phosphor (4.1) Structure of nanoantenna phosphor Fig. 4A is a cross-sectional view of nanoantenna phosphor 30. Fig. 4B is a top view of nanoantenna phosphor 30. Fig. 4A is a cross-sectional view taken along line VV in Fig. 4B. As shown in Fig. 4A, nanoantenna phosphor 30 has a phosphor plate 31, which is a wavelength converter, and an antenna array 32 formed on phosphor plate 31 and consisting of a plurality of nanoantennas 32A (hereinafter also simply referred to as antennas 32A).

[0061] The phosphor plate 31 has an incident surface S1 onto which primary light L1, which is light from the LED structure layer 20 that has passed through the optical filter 40, is incident, and an exit surface S2 from which secondary light L2 is emitted. In this embodiment, the phosphor plate 31 has a parallel plate shape, with one of its main surfaces serving as the incident surface S1 and the other main surface serving as the exit surface S2. That is, the primary light L1 is incident from the incident surface S1, which is one of the main surfaces (the back surface) of the phosphor plate 31, and is emitted from the exit surface S2, which is the other main surface (the front surface) of the phosphor plate 31.

[0062] The secondary light L2 emitted from the exit surface S2 of the phosphor plate 31 includes wavelength-converted light L21, the wavelength of which has been converted by the phosphor plate 31, and transmitted light L22 (primary light whose wavelength has not been converted) that has passed through the phosphor plate 31. That is, the phosphor plate 31 converts the wavelength of part of the primary light L1 incident from the incident surface S1 to generate the wavelength-converted light L21. In this embodiment, the phosphor plate 31 is disposed so that the incident surface S1 is perpendicular to the optical axis of the incident light L1.

[0063] Hereinafter, the primary light L1 may be referred to as light incident on the phosphor plate 31. In other words, the phosphor plate 31 includes an incident surface S1 and an exit surface S2, and is configured to convert the wavelength of the incident light L1 incident on the incident surface S1 to generate wavelength-converted light L21, and to emit the wavelength-converted light L21 and transmitted light L22 from the exit surface S2. In this embodiment, the phosphor plate 31 is disposed parallel to the LED structure layer 20.

[0064] In this embodiment, the phosphor plate 31 is a ceramic phosphor plate made of a single phase of yttrium aluminum garnet (YAG:Ce) with cerium as the luminescent center.

[0065] As described above, the LED structure layer 20 uses an InGaN-based semiconductor as a light-emitting layer, and the primary light L1 is blue light with a wavelength of approximately 450 nm. The wavelength-converted light L21 is yellow light with a wavelength of approximately 460 to 750 nm, and the secondary light L2 is white light obtained by mixing the yellow light and blue light.

[0066] Although various phosphors can be used as the phosphor of the phosphor plate 31, a single-phase phosphor is preferable, because a single-phase phosphor can extract the incident excitation light as it is as narrow-angle light without scattering it.

[0067] Furthermore, in order to achieve stable whitening (color mixing), the phosphor plate 31 preferably has a thickness T within the range of 40 to 200 μm.

[0068] A light-reflecting film may be provided on the side surface of the phosphor plate 31. For example, the light-reflecting film is a film of white paint provided on the side surface of the phosphor plate 31. The light-reflecting film may be replaced with a light-absorbing film such as black paint.

[0069] Next, the antenna array 32 will be described. In this embodiment, the antenna array 32 is formed on the emission surface S2 of the phosphor plate 31. The antenna array 32 has a wavelength longer than the peak wavelength of the light emitted from the LED structure layer 20. small period Distributed by The antenna 32A has a plurality of antennas 32A placed thereon.

[0070] In this embodiment, each of the antennas 32A is a columnar or conical metal protrusion (pillar) capable of exciting surface plasmons. Also, in this embodiment, each of the antennas 32A has a cylindrical shape and is made of a material having a plasma frequency in the ultraviolet to visible light range, such as Au (gold), Ag (silver), Cu (copper), Pt (platinum), Pd (palladium), Al (aluminum), or Ni (nickel), or an alloy or laminate containing these materials.

[0071] 4B, in this embodiment, each of the antennas 32A has substantially the same antenna height H and antenna width (diameter) W1. When the antenna 32A has a columnar or cone-like shape, the antenna width W1 refers to the maximum width of the antenna 32A.

[0072] In this embodiment, the multiple antennas 32A are arranged in a hexagonal lattice pattern with a period P on the emission surface S2 of the phosphor plate 31. The antenna array 32 is formed within a square area with a vertical and horizontal width (array width) of W2 at the center of the emission surface S2.

[0073] In this embodiment, the antenna width W1 is 150±20 nm, and the array width W2 is 6 mm. The YAG:Ce phosphor has a refractive index of approximately 1.82 and emits light with a wavelength of 460 nm to 750 nm. Here, the optical wavelength is calculated as (emission wavelength / refractive index).

[0074] When light is irradiated onto each antenna 32A of the antenna array 32, localized surface plasmon resonance on the surface of the antenna 32A increases the electric field intensity near the antenna 32A. Furthermore, by setting the arrangement period P of the antennas 32A to approximately the optical wavelength of the wavelength-converted light L21, the localized surface plasmon resonance of adjacent individual antennas 32A causes resonance via optical diffraction, resulting in a further increase in electric field intensity and improving the light extraction efficiency of the wavelength-converted light L21. In this specification, "approximately the optical wavelength" within the phosphor plate 31 refers to, for example, a wavelength band that is 50 nm above and below the emission wavelength band of the phosphor within the phosphor plate 31.

[0075] As a result, the wavelength-converted light L21 from the phosphor plate 31 is amplified and emitted with a narrow light distribution angle (low etendue) from the antenna array 32. In other words, the antenna array 32 has the function of amplifying the light within the phosphor plate 31 and narrowing the emission direction of the secondary light L2 (wavelength-converted light L21).

[0076] (4.2) Narrowing angle structure of nanoantenna phosphor Next, we will explain the structure for narrowing the angle of the nanoantenna phosphor 30. Here, since plasmon resonance occurs in sync with the diffraction mode, the period P of the antennas 32A (pillars) in the antenna array 32 is determined by simulating the relationship between the diffraction angle (emission angle) and wavelength and calculating the region where light increases within an emission angle of 30°.

[0077] Here, the relationship between the emission angle and wavelength was simulated under the condition that the period P was 360 nm to 480 nm, using the antenna array 32 in which the antennas 32A were arranged in a hexagonal lattice as a model.

[0078] 5A to 5D show simulation results of the wavelength of wavelength-converted light versus the emission angle (θem) of the antenna array 32. The period P is shown as a parameter. More specifically, FIGS. 5A to 5D show the YAG(1,0) component of the diffraction order (1,0) (shown by a solid line in the figures) and the diffraction order (-1,0) (shown by a dashed dotted line in the figures) that represent the directivity characteristics when the period P of the antenna 32A is 360 nm, 400 nm, 440 nm, and 480 nm, respectively.

[0079] Here, the diffraction order (-1,0) is a line that represents emission from the nanoantenna phosphor 30 to the atmosphere, and is referred to as Air(-1,0) here. If a propagation mode exists on the upper left side of the figure, with the Air(-1,0) line as the boundary, this indicates that the propagation mode is light that can be extracted to the atmosphere.

[0080] Furthermore, if the optical mode exists in the range to the lower right of the figure, with the Air (-1,0) line as the boundary, the light is evanescent light, and it is safe to assume that the light does not leave the nanoantenna phosphor 30.

[0081] Also, in Figures 5A to 5D, the fluorescence from phosphor plate 31 is dominated by light with wavelengths of 500 nm to 650 nm, so the condition is that diffracted light within this wavelength range (shown by dotted lines in the figures) is emitted within an angle of 30°.

[0082] In order for light to be emitted from the nanoantenna phosphor 30, taking into consideration the above-mentioned Air(-1,0) line, it is possible to extract light from the YAG(1,0) component (area surrounded by dashed lines) within the range surrounded by dotted lines.

[0083] It was found that when the period P is in the range of 400 nm to 440 nm, much of the light is extracted within an angle of 30°. Therefore, when the emission angle range of the wavelength-converted light by the antenna array 32 is set to a predetermined range, for example, within 30°, it is desirable that the period P of the antenna 32A be in the range of 400 nm to 440 nm. It was found that under conditions other than the above period, the region of the diffraction lines related to light extraction is significantly reduced.

[0084] That is, the period P of the antenna 32A can be determined based on the angular range of emission of the wavelength-converted light by the antenna array 32.

[0085] Although the antenna array 32 in which the antennas 32A are arranged in a hexagonal lattice has been described, the lattice structure of the antenna array 32 is not limited to this. For example, an antenna array having a periodic structure such as a square lattice or a triangular lattice may also be used.

[0086] (5) Light distribution characteristics of the light-emitting device 10 The light distribution characteristics of the light emitting device 10 will be described below. Figures 6A and 6B respectively show the light distribution characteristics of blue light from the LED structure layer 20 and the light distribution characteristics of fluorescent light (yellow light) from the nanoantenna phosphor 30. Figure 6C also shows the light distribution characteristics of white light from the light emitting device 10, i.e., the light distribution characteristics of combined light of blue light and fluorescent light (yellow light).

[0087] 6A to 6C show the Lambertian light distribution characteristics (broken lines in the figures) from a conventional LED and phosphor.

[0088] As shown in Fig. 6A, the blue light from the LED structure layer 20 increases in light within ±15°, forming a narrow-angle light distribution relative to the Lambertian. Also, as shown in Fig. 6B, it can be seen that the yellow light obtained when the nanoantenna phosphor 30 is excited also has the function of narrowing the angle relative to the Lambertian.

[0089] As shown in FIG. 6C, it can be seen that a narrow-angle light distribution characteristic is also obtained for the combined light (white light) from light emitting device 10.

[0090] More specifically, in a conventional Lambertian light distribution, the luminous flux (output ratio) within ±30° is 25%, but in the light emitting device 10, the luminous flux within ±30° is 40%, which is a 15% improvement over the Lambertian light distribution. It was also found that the central luminance increased by more than 20%.

[0091] That is, narrow-angle white light can be generated only by combining the narrow-angle blue light and narrow-angle yellow light formed by the LED structure layer 20 having the photonic crystal 21P and the nanoantenna phosphor 30.

[0092] (6) Mechanism and configuration of the light-emitting device 10 The above describes in detail the light emitting device 10 of the present invention, but the light emitting device 10 may be configured so that narrow-angle light is formed by a photonic crystal and that the narrow-angle light is efficiently incident on the nanoantenna phosphor.

[0093] Fig. 7 is a diagram schematically illustrating narrow-angle LED light generated by the LED structure layer 20. More specifically, as shown in Fig. 7, in the light-emitting device 10 of the present invention, the LED structure layer 20 is a photonic crystal LED having a photonic crystal layer 21P embedded therein, and is configured to generate narrow-angle LED light (narrow-angle blue light).

[0094] More specifically, the period of holes 22 in photonic crystal layer 21P is determined according to the incident angle dependency of the reflectance of filter film 40A of optical filter 40. That is, angle θth at which the reflection angle of filter film 40A (e.g., a dichroic mirror) is 0 (zero) is calculated, and the period of holes 22 in photonic crystal layer 21P is determined so that the diffraction angle θ of the photonic crystal satisfies θ≦θth.

[0095] That is, the LED structure layer 20 is configured to generate narrow-angle light LN having an angle θth (θth=15° in the above embodiment) or less. The narrow-angle light LN0 passes through the optical filter 40, which is an SPF, and enters the nanoantenna phosphor 30 with high incidence efficiency.

[0096] The wavelength-converted light (yellow light) is incident on the phosphor plate 31 of the nanoantenna phosphor 30 and is wavelength-converted by the phosphor, and is then emitted as narrow-angle light LN1 by the nanoantenna 32A. The wavelength-converted light is also reflected by the optical filter 40 in the emission direction.

[0097] Therefore, narrow-angle white light is emitted by the narrow-angle blue light and narrow-angle yellow light that have passed through phosphor plate 31, and light emitting device 10 functions as a narrow-angle white light source.

[0098] Although the photonic crystal layer 21P has been described as having a single lattice structure, it may have a multiple lattice structure such as a double lattice structure.

[0099] Although the optical filter 40 is configured by a dichroic mirror in the above example, the present invention is not limited to this. It may be configured by an optical filter such as a short-pass filter (SPF) that transmits light from the LED structure layer 20 and reflects wavelength-converted light from the phosphor plate 31.

[0100] In this case, the light extraction efficiency can be improved by using an optical filter 40 that has small angle dependency of reflectance for light emitted from the LED structure layer 20. Specifically, a wide-band bandpass filter with small incident angle dependency may be used.

[0101] [Second embodiment] FIG. 8 is a cross-sectional view schematically showing the cross-sectional structure of a light-emitting device 50 according to the second embodiment of the present invention.

[0102] The light emitting device 50 of the second embodiment differs from the light emitting device 10 of the first embodiment in that the optical filter 40 is not provided.

[0103] More specifically, the light emitting device 50 has an LED structure layer 20 and a nanoantenna phosphor 30 disposed on the LED structure layer 20. The LED structure layer 20 and the nanoantenna phosphor 30 have the same configuration as those of the light emitting device 10 of the first embodiment.

[0104] That is, the LED structure layer 20 has a photonic crystal layer 21P, and is configured to emit light at a predetermined narrow angle (for example, within 15° with respect to the normal direction of the LED structure layer 20).

[0105] As described in the light emitting device 10 of the first embodiment, the angle of the narrow angle light can be determined by the hole arrangement of the photonic crystal, the lattice constant a, and the diameter d of the holes 22.

[0106] In this embodiment, the narrow-angle light from the LED structure layer 20 is directly incident on the nanoantenna phosphor 30. The narrow-angle structure of the nanoantenna phosphor 30 is preferably set according to the angle of the narrow-angle light from the photonic crystal layer 21P.

[0107] As described in the first embodiment of the light-emitting device 10, the plasmon resonance of the nanoantenna phosphor 30 occurs in sync with the diffraction mode, and therefore the period P of the antenna 32A in the antenna array 32 can be determined by simulating the relationship between the diffraction angle and wavelength and calculating the region where light increases within a predetermined emission angle (e.g., 30°).

[0108] The light emitting device 50 having the above-described configuration can realize a mixed-color light source having narrow-angle light distribution characteristics and high light output.

[0109] In the above-described embodiment, the semiconductor light-emitting structure layer is a photonic crystal light-emitting diode made of a nitride semiconductor, but the present invention is not limited to this and can also be applied to photonic crystal light-emitting diodes made of semiconductors of other crystal systems.

[0110] Although the phosphor plate is made of a phosphor that converts blue light into yellow light in the above description, the present invention is not limited to this. A phosphor can be selected and applied appropriately depending on the wavelength of the photonic crystal light-emitting diode used.

[0111] Furthermore, the numerical values ​​in the above examples are merely examples and can be appropriately modified and applied depending on the composition of the semiconductor used, the emission wavelength, etc. [Explanation of symbols]

[0112] 10, 50: Light emitting device, 20: Semiconductor light emitting structure layer, 21: First semiconductor layer, 21P: Photonic crystal layer, 22: Air hole, 23: Active layer, 23A: Light emitting layer, 23B: Spacer layer, 25: Second semiconductor layer, 28A: P electrode, 28B: N electrode, 30: Nanoantenna phosphor, 31: Phosphor plate, 32: Antenna array, 32A: Nanoantenna, 40: Optical filter, 40A: Filter film, 40B: Light-transmitting substrate

Claims

1. a semiconductor light-emitting structure layer having a photonic crystal layer; a wavelength converter placed on the light emitting surface of the semiconductor light emitting structure layer and converting the wavelength of the emitted light from the semiconductor light emitting structure layer to generate wavelength-converted light; and a nanoantenna phosphor comprising an antenna array on the wavelength converter in which a plurality of nanoantennas are periodically arranged; an optical filter disposed between the semiconductor light-emitting structure layer and the nanoantenna phosphor; The light emitting device, wherein the optical filter transmits the emitted light from the semiconductor light emitting structure layer and reflects the wavelength-converted light from the nanoantenna phosphor.

2. The light emitting device according to claim 1 , wherein the plurality of nanoantennas are arranged on the wavelength converter at a period smaller than a peak value of the wavelength of the emitted light from the semiconductor light emitting structure layer.

3. The light emitting device according to claim 1 , wherein the period of the plurality of nanoantennas is set based on the range of angles at which the wavelength-converted light is emitted by the antenna array.

4. 2. The light-emitting device according to claim 1, wherein the optical filter has a transmittance of less than 10% at a peak value of the wavelength of the emitted light for the emitted light having an incident angle of 30° or more from the semiconductor light-emitting structure layer, and a transmittance of 90% or more at a peak value of the wavelength of the emitted light for the emitted light having an incident angle of 15° or less.

5. the semiconductor light emitting structure layer has a light distribution characteristic in which the radiated light of the semiconductor light emitting structure layer has a larger radiated light component of 15° or less compared to a Lambertian light distribution characteristic, The light emitting device according to claim 1 , wherein the nanoantenna phosphor has a light distribution characteristic in which the emitted light of the nanoantenna phosphor has a larger component of light emitted at an angle of 15° or less than a Lambertian light distribution characteristic.

6. 2. The light emitting device according to claim 1, wherein the wavelength conversion material is a single-phase phosphor.

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