EP3900057A1

EP3900057A1 - Color uniformity in converted light emitting diode using nanostructures

Info

Publication number: EP3900057A1
Application number: EP19858667.9A
Authority: EP
Inventors: Antonio LOPEZ-JULIA; Venkata Ananth TAMMA
Original assignee: Lumileds Holding BV
Current assignee: Lumileds Holding BV
Priority date: 2018-12-21
Filing date: 2019-12-20
Publication date: 2021-10-27
Also published as: TW202032822A; WO2020128629A1; TWI788612B

Abstract

A nanostructure layer is disclosed. The nanostructure layer includes an array of nanostructure material configured to receive a first light beam at a first angle of incidence and to emit the first light beam at a second angle greater than the first angle, the nanostructure material each having a largest dimension of less than l000nm.

Description

COLOR UNIFORMITY IN CONVERTED LIGHT EMITTING DIODE USING

NANOSTRUCTURES

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit of priority to European Patent Application

19156833.6 filed February 13, 2019 and to U.S. Patent Application 16/230,811 filed December 21, 2018, each of which is incorporated herein by reference in its entirety.

BACKGROUND

[0002] A typical light-emitting diode (LED) experiences color over source or angle based non-uniformity of emission. In such LEDs, color often varies within a given LED, most significantly as a function of the angle of emitted light from, for example, an active layer that is part of the LED’s semiconductor structure. This color-over-angle (CoA) effect can lead to general non-uniformity and may also lead to more noticeable visual phenomenon such as“yellow rings” at large angles in the far-field of a white LED.

[0003] CoA based non-uniformity can also occur as a result of limited interaction of light emitted by an active layer with a wavelength converting layer. Such limited interaction can occur as a result of light emitted through the wavelength converting at an angle at or close to normal such that the light emission interacts with a minimal number of particles within the wavelength converting layer.

SUMMARY

[0004] A nanostructure layer is disclosed. The nanostructure layer includes an array of nanostructure material configured to receive a first light beam at a first angle of incidence and to emit the first light beam at a second angle greater than the first angle, with respect to normal, the nanostructure material each having a largest dimension of less than lOOOnm.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] A more detailed understanding can be had from the following description, given by way of example in conjunction with the accompanying drawings wherein:

[0006] FIG. 1A is a diagram of light emitting device with a nanostructure layer;

[0007] FIG. IB is a diagram showing light emission with and without a nanostructure layer; [0008] FIG. 1C is a diagram showing light emission with a nanostructure layer;

[0009] FIG. ID is a chart showing transmission as a function of angle;

[0010] FIG. IE is flow diagram for light emission with a nanostructure layer;

[0011] FIG. IF is a structure with a nanostructure layer;

[0012] FIG. 1G is another structure with a nanostructure layer;

[0013] FIG. 1H is another structure with a nanostructure layer;

[0014] FIG. II is a diagram of different nanoantennas;

[0015] FIG. 1 J is a multi nanostructure material array;

[0016] FIG. IK is another is a diagram of different nanoantennas;

[0017] FIG. 2A is a diagram showing an Light Emitting Diode (LED) device;

[0018] FIG. 2B is a diagram showing multiple LED devices; and

[0019] FIG. 3 is a diagram of an example application system.

DETAILED DESCRIPTION

[0020] Examples of different light illumination systems and/or light emitting diode implementations will be described more fully hereinafter with reference to the

accompanying drawings. These examples are not mutually exclusive, and features found in one example may be combined with features found in one or more other examples to achieve additional implementations. Accordingly, it will be understood that the examples shown in the accompanying drawings are provided for illustrative purposes only and they are not intended to limit the disclosure in any way. Like numbers refer to like elements throughout.

[0021] It will be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms may be used to distinguish one element from another. For example, a first element may be termed a second element and a second element may be termed a first element without departing from the scope of the present invention. As used herein, the term "and/or" may include any and all combinations of one or more of the associated listed items.

[0022] It will be understood that when an element such as a layer, region, or substrate is referred to as being "on" or extending "onto" another element, it may be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" or extending "directly onto" another element, there may be no intervening elements present. It will also be understood that when an element is referred to as being "connected" or "coupled" to another element, it may be directly connected or coupled to the other element and/or connected or coupled to the other element via one or more intervening elements. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present between the element and the other element. It will be understood that these terms are intended to encompass different orientations of the element in addition to any orientation depicted in the figures.

[0023] Relative terms such as "below," "above," "upper,", "lower," "horizontal" or "vertical" may be used herein to describe a relationship of one element, layer, or region to another element, layer, or region as illustrated in the figures. It will be understood that these terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures.

[0024] Semiconductor light emitting devices or optical power emitting devices, such as devices that emit ultraviolet (UV) or infrared (IR) optical power, are among the most efficient light sources currently available (hereinafter“LEDs”). These LEDs, may include light emitting diodes, resonant cavity light emitting diodes, vertical cavity laser diodes, edge emitting lasers, or the like. Due to their compact size and lower power requirements, for example, LEDs may be attractive candidates for many different applications. For example, they may be used as light sources (e.g., flash lights and camera flashes) for hand-held battery-powered devices, such as cameras and cell phones. They may also be used, for example, for automotive lighting, heads up display (HUD) lighting, horticultural lighting, street lighting, torch for video, general illumination (e.g., home, shop, office and studio lighting, theater/stage lighting and architectural lighting), augmented reality (AR) lighting, virtual reality (VR) lighting, as back lights for displays, and IR spectroscopy. A single LED may provide light that is less bright than an incandescent light source, and, therefore, multi junction devices or arrays of LEDs (such as monolithic LED arrays, micro LED arrays, etc.) may be used for applications where more brightness is desired or required.

[0025] Improvement of color uniformity in LEDs that include one or more wavelength converting layers is disclosed. It will be understood that although white LEDs, blue pump light, and phosphor particles are used herein, they are used as examples only. Notably, disclosure related to white LEDs may be applied to LEDs of one or more other color spectra. Disclosure related to blue pump light may be related to light emitted at one or more other wavelengths. Disclosure related to phosphor particles may be applied to one or more other particles types, layers, or material in general that may provide wavelength converting properties.

[0026] Typically, in white LED applications, a pump light (e.g., blue pump) is provided by an active semiconductor layer and the pump light is used to excite particles in a wavelength converting layer which may be a material containing color converters, such as phosphors. The white spectrum in such an LED may be achieved based on contributions from unconverted, residual, blue pump and converted phosphor light. As an example, a portion of blue pump light emitted by an active layer may traverse through a wavelength converter and may not collide with any wavelength converting particles such that it passes thorough the wavelength converter unaltered. A different portion of the blue pump light emitted by the active layer may traverse through the wavelength converter and may collide with one or more wavelength converting particles (e.g., phosphor particles) such that the resulting light from the collision(s) is a wavelength converted light and may be a more yellow light than the blue pump light that collided with the one or more wavelength converting particles. The combined blue pump light and the converted yellow light may result in the white light output of the LED.

[0027] In the example provided above, the spectrum of the converted light can vary depending on the application and can be narrowband or broadband. Similarly, in some cases, the blue light may be chosen to be completely converted to achieve certain colors in the light output by an LED. The wavelength converting layer may broadly be classified as powdered phosphors which consist of micron sized converter particles packed into a silicone film or converters doped into a slab of ceramic material. The light scattering properties of both types of phosphors vary with powdered phosphors being inherently a volume scattering medium whereas the ceramic phosphors can include surface and volume scattering to promote light absorption and conversion.

[0028] The scattering within a wavelength converting layer may dictate the path length of the light traversing and getting absorbed within the wavelength converting layer and can lead to over-conversion or under-conversion of blue pump light within the phosphor material. As an example, a high amount of scattering within a wavelength converting layer may correspond to a higher path length, resulting in more collisions (or potential collisions) with wavelength converting particles within the wavelength converting layers. Due to the scattering and conversion properties specific to each type of wavelength converting layer and also to the architecture of the LED package chosen, color over source issues may be experienced in the near or far field. Color over source can be characterized by the lack of color uniformity (relative spectral distribution of different components) over the light emitting surface of a wavelength converting material. Color over source, when projected into the far-field using projection optical elements, results in far-field light spots having color non-uniformity over different angles. Color over source is often referred to as color over angle, which both generally pertain to the same phenomenon. Color non-uniformity can cause undesired optical effects and result in sub-optimal LED performance.

[0029] The subject matter disclosed herein is directed to techniques and material to improve color mixing and color uniformity over the surface of a wavelength converting layer by use of photonic nanostructure layers made of nanostructure material such as metasurfaces or metamaterials (e.g., Huygen’s metasurfaces), photonic crystals and/or subwavelength scatterers.

[0030] A nanostructure layer may be implemented with nanostructure material such as meta-molecules (e.g., that create meta-surfaces), photonic crystals, subwavelength scatterers, among others. As used herein, photonic crystals, subwavelength scatterers and meta-surfaces may be periodic arrangements of symmetric or asymmetric meta-molecules and/or nanoantennas. A meta-molecule nanostructure layer may include an array of meta molecules. A nanoantenna nanostructure layer may include one or more nanoantennas. Nanostructured layers, as disclosed herein, may incorporate the design of LED devices with nano scale optical antennas placed on an LED surface (e.g., a sapphire substrate).

[0031] Photonic crystals, subwavelength scatterers and/or meta-surfaces in a nanostructure layer may be purely plasmonic, composed of metal nanoparticles, or metallo- dielectric, composed of metals and dielectric nanoparticles, or purely dielectric, composed of dielectric nanoparticles, typically high index dielectrics. The photonic crystals and/or meta-surfaces in a nanostructure layer may be fabricated using top-down or bottom-up fabrication methods and may utilize nanoparticle self-assembly to provide advantages for manufacturing and scalability. Photonic crystals can be fabricated for one, two, or three dimensions. One-dimensional photonic crystals can be made of layers deposited or stuck together. Two-dimensional ones can be made by photolithography, or by drilling holes in a suitable substrate. Fabrication methods for three-dimensional ones include drilling under different angles, stacking multiple 2D layers on top of each other, direct laser writing, or, for example, instigating self-assembly of spheres in a matrix and dissolving the spheres. The meta-molecules within photonic crystals and/or meta-surfaces in the nanostructure layer may be held together by different techniques including, but not limited to, molecular linkers, DNA, and the like. Alternatively, they may be fabricated by top-down fabrication techniques, such as nano-imprint lithography, nano-sphere lithography, or the like, and individual meta-molecules released using lift-off techniques. A nanostructure layer may be encapsulated by dielectrics such as silicon dioxide or aluminum dioxide to prevent degradation of meta-molecule properties over time.

[0032] The design and optimization for steering light in LEDs using a nanostructure layer is disclosed. By way of example and in order to provide concrete description, a flip chip of chip scale package (CSP) LED with a sapphire substrate is described, although the principles and teaching herein may be applied to any applicable LED design. A sapphire based CSP emitter with a smooth light escape surface (LES) may allow deposition of a nanostructured layer such that light emitted by an active layer of the LED is incident upon the nanostructured layer via the sapphire substrate.

[0033] According to the subject matter disclosed herein, a nanostructure layer may increase color uniformity by increasing the angle of incident of a light beam that is incident upon the nanostructure layer by steering the incident light towards a higher angle with respect to normal (e.g., from less than 10 degrees to greater than 90 degrees). Alternatively or in addition, the nanostructure layer may increase color uniformity by allowing light above a cutoff angle to pass through the nanostructure layer such that only light incident upon the nanostructure layer at angles that are more likely to increase light path length pass through the nanostructure layer.

[0034] Fig. 1A illustrates an LED device 100 including a nanostructure layer 110 on an LED device that includes an epitaxial grown semiconductor layers 130 and substrate 120. The epitaxial grown semiconductor layers 130 may include a first contact 137 and a second contact 138 separated by a gap 133 which may be an airgap or may be filled with dielectric material. A p-type layer 134 may be proximate to an active layer 135 and an n-type layer 139. The active layer 135 may be configured to emit light distal from the contacts 137 and 138 such that light beams emitted from the active layer 135 are generally emitted towards the substrate 120. The LED device 100 is presented in a simplified form for ease of understanding of the invention, knowing that one possessing an ordinary skill in the pertinent arts would understand the other elements included within an LED.

[0035] The epitaxial grown semiconductor layers 130 may be formed from any applicable material configured to emit photons when excited including sapphire, SiC, GaN, Silicone and may more specifically be formed from a III-V semiconductors including, but not limited to, AIN, A1P, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, II-VI semiconductors including, but not limited to, ZnS, ZnSe, CdSe, CdTe, group IV

semiconductors including, but not limited to Ge, Si, SiC, and mixtures or alloys thereof. These example materials may have indices of refraction ranging from about 2.4 to about 4.1 at the typical emission wavelengths of LEDs in which they are present.

[0036] For example, Aluminum nitride (AIN) may be used and is a wide band gap (6.01-6.05 eV at room temperature) material. AIN may have refractive indices of about 1.9- 2.2 (e.g., 2.165 at 632.8 nm). Ill-Nitride semiconductors, such as GaN, may have refractive indices of about 2.4 at 500 nm, and Ill-Phosphide semiconductors, such as InGaP, may have refractive indices of about 3.7 at 600 nm. An example gallium nitride (GaN) layer may take the form of a layer of pGaN. As would be understood by those possessing an ordinary skill the pertinent arts, GaN is a binary III/V direct bandgap semiconductor commonly used in light-emitting diodes. GaN may have a crystal structure with a wide band gap of 3.4 eV that makes the material ideal for applications in optoelectronics, high-power and high-frequency devices. GaN can be doped with silicon (Si) or with oxygen to create an n-type GaN and with magnesium (Mg) to create a p-type GaN as is used in the present example. The active layer 135 is the region where light is emitted as electroluminescence occurs. Contacts 137 and/or 138 coupled to the LED device 100 may be formed from a solder, such as AuSn, AuGa, AuSi or SAC solders.

[0037] As shown in Fig. 1A, substrate 120 may be located between the semiconductor layers 130 and the nanostructured layer 110. The substrate may be a CSP emitter with a smooth LES that enables deposition of the nanostructured layer 110. The substrate 120 may comprise sapphire which is an aluminum oxide (A1203) also known as corundum and can exhibit properties including being very hard, strong, easy to machine flat, a good electrical insulator, and an excellent thermal conductor. Sapphire is generally transparent when produced synthetically with the blue color in naturally occurring sapphires (and the red in rubies, which are another form of corundum) comes from impurities in the crystal lattice. In other LEDs, the sapphire may be replaced with gallium nitride (GaN). The semiconductor layers 130 may be in the region where light is emitted as electroluminescence occurs.

[0038] As shown in Fig. 1A, the sidewalls of the substrate 120 may be covered by sidewall material 140. The sidewall material 140 may also cover one or more layers of the semiconductor layers 130 such that either the same sidewall material 140 covers the substrate 120 and the semiconductor layers 130 or a different material may cover the sidewalls of the substrate 120 than the semiconductor layers 130. The sidewall material 140 may be any applicable reflecting or scattering material. According to an embodiment, the sidewall material 140 may be a distributed Bragg reflector (DBR).

[0039] The nanostructured layer 110 may include photonic materials incorporated into photonic crystals and/or meta-surfaces which may include meta-molecule and/or nanoantennas such that the largest dimension for a meta-molecule or nanoantennas is less than lOOOnm. The nanoantennas can be implemented as an array of nanoparticles located in the nanostructure layer, as further disclosed herein. The nanoantennas may be arranged in either periodic or a-periodic patterns, as further disclosed herein. In analogy with chemical molecules composed of atoms, a meta-surface is composed of meta-molecule with the meta molecules combined together and interacting to give the meta-surface unique optical properties. The size of individual meta-surfaces may be sub-wavelength or may be formed at the same order of wavelength of use.

[0040] The nanostructured layer 110 can also include nanoantennas that are distributed throughout a host dielectric medium. The sizes of the nanoantennas may be a sub wavelength of order of wavelength.

[0041] As disclosed herein, to promote a longer light path for light that traverses through wavelength converting layer 102, a nanostructure layer 110 may create an angular filter that transmits lights at angles greater than an angular cut-off angle and reflects radiation below the angular cut-off angle, with respect to normal. As a result, only light beams that are incident upon the nanostructure layer 110 at a high angle (e.g., not normal or close to normal) traverses through the nanostructure layer 110. Given the high angle, the light path of such light beams is longer than, for example, light beams that would otherwise be incident upon the wavelength converting layer 102 at a lower (e.g., at normal or near normal) angle.

[0042] As disclosed herein, light beams incident upon a nanostructure layer 110 of Fig.

1 A may reflect back into the substrate 120 such that the reflected beams are incident upon the sidewall material 140 and/or a back reflector 125 located below the active layer 135 and distal from the surface of the substrate 120 that faces the nanostructured layer 110. The back reflector 125 may be a plasmonic layer including planar metal mirrors, a distributed Bragg reflector (DBR) and/or other known LED reflectors. The back reflector 125 is designed to re-reflect the light beams that are reflected back into the substrate 120. The back reflector 125 may reflect light beams before or after the light beams bounce off sidewall material 140 or may reflect light beams directly reflected by the nanostructured layer 110.

[0043] Fig. IB shows an example of light steering via a nanostructure layer. LED device 111 A is shown with a substrate 120A and wavelength converting layer 102A. Light beam 112A and 113A traverse through the substrate 120A and are incident upon the wavelength converting layer 102A at angles QIA and 02A respectively. LED device 11 IB is shown with a substrate 120B, wavelength converting layer 102B, as well as a nanostructure layer 110B in accordance with the disclosed subject matter. Light beam 112B and 113B traverse through the substrate 120B with the same optical properties (e.g., angle, frequency, direction) as light beams 112A and 113 A as they traversed through substrate 120A which is similar to or the same as substrate 120B. Light beams 112B and 113B are incident upon the wavelength converting layer 102B after traversing through the nanostructure layer 110B. As shown, light beams 112B and 113B are steered within the nanostructure layer 110B such that they are incident upon the wavelength converting layer 102B at angles QIB and 02B respectively. It will be noted that angles 0IB and 02B are greater than angles 0IA and 02A with respect to normal. To clarify, the nanostructure layer 110B steers light beams incident upon the nanostructure layer 110B such that the enter the wavelength converting layer 102B at an angle greater than if the nanostructure layer 110B did not steer the light beams (i.e., the example of wavelength converting layer 102A). As a result, the path length of light emitted through the wavelength converting layer 102B is greater than the path length of light emitted through wavelength converting layer 102A, and, accordingly, the light beams

112B and 113B are more likely to collide with particles within wavelength converting layer

102B, effectively increasing the chance of conversion, providing color uniformity.

[0044] According to an embodiment, as disclosed herein, the nanostructure layer 110 of

Fig. 1 A may reflect light beams incident upon the nanostructure layer 110 at an angle less than a cutoff angle. An example visual representation of this phenomenon is shown in Fig.

1C by light beams 122 and 123. Light beams 122 and 123 may traverse the substrate 120 and be incident upon the nanostructure layer 121. Nanostructure layer 121 may be configured such that light beams incident at an angle below a given cutoff angle are reflected back and light beams above the cutoff angle are transmitted through the nanostructure layer (e.g., into a wavelength converting layer). Light beams 122 may be incident at an angle 03 of incidence which may be angle below a cut off angle (i.e., closer to normal) such that the nanostructure layer reflects the light beams 122, as shown. Light beams 123 may be incident upon nanostructure layer 121 at an angle 04 of incident which is higher than the cut off angle (i.e., is further away from normal) and may traverse through the nanostructure layer 121 as shown. According to the disclosed subject matter, the light beams 123 may experience light steering within the nanostructure layer 121. As disclosed herein, light beams reflected back into the substrate 120 may experience one or more bounces within the substrate and/or on a back reflector such that they may be incident upon the nanostructure layer 121 a second time after being reflected into the substrate 120 by the nanostructure layer 121. A light beam that is reflected into the substrate by the

nanostructure layer 121 at a first time may experience one or more bounces within the substrate (e.g., at the sidewall material, back reflector, etc.) and may be incident upon the nanostructure layer 121 at a second time after the first time. The angle of incidence of the light beam, at the second time, may be higher than the cut off angle and, accordingly, the light beam may pass through the nanostructure layer 121.

[0045] Fig. ID shows the phi averaged transmission 127 versus angle plot for a nanostructure layer from the example light beam interaction with nanostructure layer 121, as described for Fig. 1C. As shown, the configuration of the nanostructure layer 121 enables a unity or near unity transmission after cutoff angle of approximately 45 degrees and does not permit transmission (e.g., reflects light beams) before the cutoff angle.

[0046] Fig. IE shows an example process 1400 of a beam transmission through substrate 120 and nanostructure layer 110 of Fig. 1A (note that this process could also apply to the nanostructure layer 121 of Figs. 1C and ID). At step 1410, a first light beam may be incident upon the nanostructure layer 110 after traversing through substrate 120. The first light beam may be incident at an angle below the nanostructure layer 110’s cutoff angle. At step 1420, the first light beam may be reflected back into the substrate 120 based on the interaction with the nanostructure layer 110 at an angle below the cutoff angle. At step 1430, a second light beam maybe incident upon the nanostructure layer 110 through the substrate 120. The second light beam may be incident at an angle above the nanostructure layer 110’s cutoff angle. At step 1440, the second light beam may be emitted through the nanostructure layer 110 based on its interaction with the nanostructure layer 110 at an angle above the cutoff angle. According to an embodiment, as discussed herein, the first light beam may bounce off one or more inside surfaces of the substrate, sidewall material and/or back reflector and may then be incident upon the nanostructure layer 110 at an angle above the cutoff angle. The first light beam may then be emitted through the nanostructure layer 110 based on the angle of incident above the cutoff angle.

[0047] Nanostructure layer configurations will be discussed further herein.

[0048] Figs. 1F-1H shows different configurations of nanostructure layers 1 IOC, 110D, and 110E in accordance with subject matter herein. Fig. IF shows a substrate 131, an adhesive layer 136, and a wavelength converting layer 132. A nanostructure layer 1 IOC is disposed within the wavelength converting layer 132 between a first surface and a second surface of the wavelength converting layer 132 such that the first surface and second surface are planar to the substrate 131. Fig. 1G shows a substrate 131, an adhesive layer 136, and a wavelength converting layer 132. A nanostructure layer 110D is disposed on a surface of the wavelength converting layer 132, the surface proximate to the substrate 131. Fig. 1G shows a substrate 131, an adhesive layer 136, and a wavelength converting layer 132. A nanostructure layer 110E is disposed between the substrate 131 and wavelength converting layer 132 such that it is disposed within the adhesive layer 136.

[0049] As disclosed herein, photonic nanostructure layer is structured such that is transmits radiation incident upon a wavelength converting layer after bending the angle of light towards a chosen direction (e.g., to a greater angle than the angle of incident). For example, for an application with ceramic phosphors, light incident normally on a nanostructure layer may bend to larger deflection angle within the phosphor layer, with respect to normal. This results in the light path length for such light to increase, causing increased conversion and improvement in color mixing and color uniformity. The deflection angle of the nanostructure layer and the distribution of nanostructures within thee nanostructure layer can be chosen to optimize the color mixing and color uniformity, as disclosed herein.

[0050] A nanostructure layer configured in accordance with a Huygen’s metasurface can include of nano-cylinders, nano-cones or nano-cuboids arranged in either hexagonal or rectangular lattice. The lattice period can be sub-wavelength or larger than wavelength. These nanostructures can be chosen to satisfy a first Kerker’s conditions so that the magnetic and electric dipole radiation cancels in the backward direction yielding a large forward scatter. For nanoantenna including either a vertical dimer and/or coaxial dimer, interfering modes may be provided within respective meta-molecules that provide better control of the scattered modes using structural parameters. [0051] Figure II illustrates various cross-sections of some different possible nanoantennas. The nanoantenna may be formed from nano-cylinders 191, nano-cones 192, or nano-cone 193 and 195 with vertical or coaxial dimers, arranged in either hexagonal or rectangular lattice. The lattice period may be sub-wavelength or larger than wavelength.

The nanoantennas may be Huygen’s meta-molecules and/or support waveguide modes.

Each photonic crystal or meta-surface may present a certain amount of beam bending properties such that incident beams can be shaped to the required angular distribution.

[0052] As an alternative configuration example, Fig. IK shows sub-wavelength gratings formed from asymmetric scatterers 167 and 172. Asymmetric scatterer 168 includes two nano-cylinders 164 and 166 with a height H on a substrate 162. As shown, the scatterer 168 is asymmetric such that the nano-cylinders 165 and 166 are not the same size/shape. Array of scatterers 168 may create a nano-scatter layer such that the array includes multiple copies of scatterer 168. Scatterer 172 is an L-shaped scatterer with one side of the scatterer 172 larger than another side of the scatterer 172. Array of scatterers 168 may create a nano scatter layer such that the array includes multiple copies of scatterer 168 and/or 172. These sub wavelength scatterers may scatter light incident at normal incidence to large oblique angles. Asymmetric nanostructures (e.g., 168, 172) can be chosen to be arrayed in a 2- dimensional grating. The design and placement of these nanostructures may be directed to achieve the best possible color mixing and color uniformity.

[0053] Further, the nanoantennas may be configured in an arrangement that establishes a given cutoff angle such that light incident above the cutoff angle passes through the nanoantennas, and thus the nanostructure layer, and light incident below the cutoff angle does not pass or is reflected back.

[0054] Nanoantennas may be formed or arrayed as single nano-photonic structures such that the same nanoantenna is repeated numerous times to form a nanostructured layer.

Alternatively or in addition, nanoantennas may be formed or arrayed as multi nanostructure material such that an array of nanoantennas is repeated numerous times to form a nanostructured layer. Figure 1J illustrates an example multi nanostructure material 1300.

As shown, the multi nanostructure material 1300 includes nano-cylinders 1301 and 1302 such that the different nano-cylinders 1301 and 1302 have one or more different properties when compared to each other. As a visual example, as shown in Fig. 1 J, nano-cylinder 1301 is smaller in volume than the nano-cylinder 1302. These multi nanostructures may be arrayed such that a nanostructure layer 110 includes multiple iterations of multi nanostructure materials 1300. Each small multi nanostructure material 1300 of a nanostructure layer 110 may provide beam bending to the light incident on nanostructure layer 110. By suitably placing a multitude of different nano-cylinders 1301, with different beam bending properties, within a multi nanostructure material 1300 within nanostructure layer 110, light incident upon nanostructure layer 110 may be shaped to present a certain amount of beam bending properties or to obtain a predetermined or preferred angular distribution. The design and placement within nanostructure layer 110 of Fig. 1A may be selected by an optimizer to obtain the best possible flux from the LED device 100 of Fig.

1 A.

[0055] The design of photonic crystals and/or meta-surfaces may be dictated by the required beam bending or angular distribution and the placement of the same can be determined based on an optimizer to obtain the best possible color mixing and color uniformity.

[0056] Referring again to Figure 1A, side reflectors 140, back reflector 125, or side reflectors 140 and back reflector 125 may be non-specularly reflective nanostructured layers designed to further enhance directional light output through nanostructured layer 110 into wavelength converting layer 102 at desired increased (e.g., oblique) angles.

[0057] For example, side reflectors 140 and/or back reflector 125 may be

nanostructured layers designed such that, compared to a specular reflector, they increase the fraction of light rays incident on them that is directly reflected to nanostructured layer 110 in a desired range of (e.g., large) angles of incidence, or indirectly reflected to

nanostructured layer 110 (via one or more additional reflections) in the desired range of angles of incidence. The desired range of angles of incidence on nanostructured layer 110 may be, for example, angles of incidence greater than a cutoff angle as described above. Such nanostructured side reflectors and back reflector may optionally be used in combination with each other.

[0058] Side reflectors 140 and back reflectors 125 as just described may take the form of a nanostructured photonic layer designed to steer angular radiation. Such a

nanostructured side or back reflector may include or consist of a photonic crystal, metamaterial, metasurface or subwavelength gratings of asymmetric scattering elements

(also referred to herein as nanoantennas), by way of non-limiting example only. The main function of such a nanostructured side or back reflector is to reflect radiation incident upon it from a given angular range to a chosen angular range. This restricted angular range may be chosen to direct as much light as possible from the rear surface or sides of the LED toward nanostructured layer 110 at desired angles of incidence.

[0059] Such a nanostructured back or side reflector may comprise scattering elements formed into, or arrayed, into unit cells. Each unit cell may provide beam bending to the light incident on the side reflector. By suitably arranging a multitude of different unit cells with different beam bending properties, the light may be shaped to the required angular distribution.

[0060] In such a nanostructured side or back reflector the reflective beam-benders (unit cells) may arranged in a periodic two-dimensional pattern or grating, for example, and may be formed of background material encapsulating or otherwise containing one or more scattering elements and positioned adjacent to substrate 120. The plurality of scattering elements may be surrounded by the background material. A specular reflector may be adjacent to the background material distal to substrate 120. Asymmetrical scattering may be achieved, for example, by using asymmetric scattering elements designed to link the reflected fields from the specular reflector to the scattered fields from scattering elements. Interference between these fields causes light to be scattered in a particular direction. The arrangement of scattering elements may produce a spatial gradient of phase.

[0061] A unit cell for a periodic array of beam benders in a nanostructured side reflector may be rectangular in dimensions and include a series of layers including a specular reflector, one or more scattering elements, and background material as described above. Periodicity may be centered on a wavelength in use, such as for example the peak wavelength emitted by the LED (e.g., 450 nm). In the unit cell, one or more scattering elements may be positioned adjacent to substrate layer 120 distal to the specular reflector and / or one or more scattering elements may be places in contact, or near contact, with the specular reflector.

[0062] The scattering elements may be of any suitable height and width and may be formed, for example, from silicon (Si) or titanium oxide (TiCh), or a combination thereof. The background material may be a low refractive index material, such as magnesium fluoride (MgF2), for example. The specular reflector, if present, may be a metal mirror, for example a gold or silver mirror, a dielectric mirror, or a Bragg reflector, for example.

[0063] The scattering elements may take the form of any of the scattering elements described herein. A scattering element may comprise a single light scatterer (a single dipole), or an array of light scatterers (dipoles) that may be configured analogously to a yagi-uda antenna, for example.

[0064] A scattering element may be designed as two interfering Huygen’s meta-atoms. The scattering elements may be selected to satisfy the first Kerker’s conditions so that the magnetic and electric dipole radiation cancel in the backward direction yielding a large forward scatter, referred to as Huygen’s meta-atoms. A scattering element may be formed as a two-dimensional scatterer, such as a grating, for example, or a three-dimensional scatter. An example three-dimensional scatter may be a nano-cylinder. Other geometrical scatterers may also be employed includes L-shaped scatterers, for example.

[0065] The scattering elements may be formed, for example, from nano-cylinders, nano cones, or nano-cuboids arranged for example in either a hexagonal or a rectangular lattice. The lattice period may be sub-wavelength or larger than wavelength. In the cases of a nano- cylinder vertical dimer and coaxial dimer, interfering modes within the meta-atom or nanoantenna provide additional control of the scattered modes using structural parameters.

[0066] The scattering elements may also be formed from photonic metamaterial (PM), also known as an optical metamaterial, which is a type of electromagnetic metamaterial that interacts with light, covering terahertz (THz), infrared (IR) or visible wavelengths. The materials employ a periodic, cellular structure. The subwavelength periodicity distinguishes photonic metamaterials from photonic band gap or photonic crystal structures. The cells are on a scale that is magnitudes larger than atoms, yet much smaller than the radiated wavelength, and are on the order of nanometers. In metamaterials, cells take the role of atoms in a material that is homogeneous at scales larger than the cells, yielding an effective medium model.

[0067] FIG. 2A is a diagram of an LED device 200 in an example embodiment. The

LED device 200 may include one or more epitaxial layers 202, an active layer 204, and a substrate 206. In other embodiments, an LED device may include a wavelength converter layer and/or primary optics. As shown in FIG. 2A, the active layer 204 may be adjacent to the substrate 206 and emit light when excited. The epitaxial layers 202 may be proximal to the active layer 204 and/or one or more intermediate layers may be between the active layer

204 and epitaxial layers 202. The substrate 206 may be proximal to the active layer 204 and/or one or more intermediate layers may be between the active layer 204 and substrate

206. The active layer 204 emits light into the substrate 206. A nanostructure layer may be placed on the substrate 206 such that light incident upon the nanostructure layer is bent by the nanostructure layer or is filtered by the nanostructure layer such that only light beams above a cutoff angle, with respect to normal, are emitted through the nanostructure layer.

[0068] FIG. 2B shows a cross-sectional view of a lighting system 220 including an LED array 210 with pixels 201A, 201B, and 201C. The LED array 210 includes pixels 201A, 201B, and 201C each including a respective substrate 206B active layer 204B and an epitaxial layer 202B. Pixels 201A, 201B, and 201C, in the LED array 210 may be formed using array segmentation, or alternatively using pick and place techniques and may, for example, emit light at different peak wavelengths such as red, green, and blue. The spaces 203 shown between one or more pixels 201 A, 20 IB, and 201 C may include an air gap or may be filled by a material such as a metal material which may be a contact (e.g., n- contact). According to some embodiments, secondary optics such as one or more lenses and/or one or more waveguides may be provided.

[0069] The LED device 200 or pixels 201A, 201B, and 201C may be single wavelength emitters and may be powered individually or via as an array. The LED device 200 or pixels 201A, 201B, and 201C may be part of an illumination system that includes one or more electronics boards, power modules, sensors, connectivity and control modules, LED attach regions, or the like. Pixels in an array may be powered based on different channel signals and their operation may be determined by a microcontroller.

[0070] FIG. 3 shows an example system 550 which includes an application platform 560 and LED systems 552 and 556. The LED system 552 produces light beams 561 shown between arrows 561a and 561b. The LED system 556 may produce light beams 562 between arrows 562a and 562b. As an example embodiment, the LED system 552 and 556 may be part of an automobile and may emit infrared (IR) light communication beams such that an oncoming vehicle in the path of the light beams 561 and/or 562 is able to receive communication from the automobile. In example embodiments, the system 550 may be a mobile phone of a camera flash system, indoor residential or commercial lighting, outdoor light such as street lighting, an automobile, a medical device, AR/VR devices, and robotic devices.

[0071] The application platform 560 may provide power to the LED systems 552 and/or 556 via a power bus via line 565 or other applicable input, as discussed herein. Further, application platform 560 may provide input signals via line 565 for the operation of the LED system 552 and LED system 556, which input may be based on a user

input/preference, a sensed reading, a pre-programmed or autonomously determined output, or the like. One or more sensors may be internal or external to the housing of the application platform 560.

[0072] In various embodiments, application platform 560 sensors and/or LED system 552 and/or 556 sensors may collect data such as visual data (e.g., LIDAR data, IR data, data collected via a camera, etc.), audio data, distance based data, movement data, environmental data, or the like or a combination thereof. The data may be collected based on emitting an optical signal by, for example, LED system 552 and/or 556, such as an IR signal and collecting data based on the emitted optical signal. The data may be collected by a different component than the component that emits the optical signal for the data collection.

Continuing the example, sensing equipment may be located on an automobile and may emit a beam using a vertical-cavity surface-emitting laser (VCSEL). The one or more sensors may sense a response to the emitted beam or any other applicable input.

[0073] Although features and elements are described above in particular combinations, one of ordinary skill in the art will appreciate that each feature or element can be used alone or in any combination with or without the other features and elements. In addition, the methods described herein may be implemented in a computer program, software, or firmware incorporated in a computer-readable medium for execution by a computer or processor. Examples of computer-readable media include electronic signals (transmitted over wired or wireless connections) and computer-readable storage media. Examples of computer-readable storage media include, but are not limited to, a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs).

Claims

WHAT IS CLAIMED IS:

1. A light emitting device comprising:

a semiconductor diode structure;

a substrate transparent to light emitted by the semiconductor diode structure and comprising a top surface, an oppositely positioned bottom surface, and side surfaces connecting the top and bottom surfaces, the bottom surface disposed on or adjacent the semiconductor diode structure;

a wavelength converting structure comprising a top surface and an oppositely positioned bottom surface disposed on or adjacent the top surface of the substrate; and

a nanostructured metasurface comprising a plurality of nanoantennas, the metasurface positioned between the top surface of the substrate and the top surface of the wavelength converting structure and configured to:

transmit into the wavelength converter at an angle greater than their angle of incidence on the metasurface light rays that are emitted by the semiconductor diode structure and are incident on the metasurface from the substrate side of the metasurface; or reflect light rays that are emitted by the semiconductor diode structure and are incident on the metasurface from the substrate side of the metasurface at an angle less than or equal to a cutoff angle, and transmit into the wavelength converter light rays that are emitted by the semiconductor diode structure and are incident on the metasurface from the substrate side of the metasurface at an angle greater than the cutoff angle; or

reflect light rays that are emitted by the semiconductor diode structure and are incident on the metasurface from the substrate side of the metasurface at an angle less than or equal to a cutoff angle, and transmit into the wavelength converter at an angle greater than their angle of incidence on the metasurface light rays that are emitted by the semiconductor diode structure and are incident on the metasurface from the substrate side of the metasurface at an angle greater than the cutoff angle.

2. The light emitting device of claim 1, wherein the metasurface is disposed on or adjacent the bottom surface of the wavelength converter.

3. The light emitting device of claim 1, wherein the metasurface is disposed within the wavelength converter.

4. The light emitting device of claim 1, wherein the nanoantennas are arranged in a periodic lattice.

5. The light emitting device of claim 1, wherein the nanoantennas each have a largest dimension less than a wavelength of light emitted by the semiconductor diode structure.

6. The light emitting device of claim 1, wherein at least one nanoantenna is asymmetric.

7. The light emitting device of claim 1, wherein at least one nanoantenna comprises two or more light scattering objects.

8. The light emitting device of claim 7, wherein the light scattering objects are symmetric objects.

9. The light emitting device of claim 8, wherein the light scattering objects are arranged asymmetrically.

10. The light emitting device of claim 1, wherein the metasurface is configured to transmit into the wavelength converter at an angle greater than their angle of incidence on the metasurface light rays that are emitted by the semiconductor diode structure and are incident on the metasurface from the substrate side of the metasurface.

11. The light emitting device of claim 10, wherein the metasurface is disposed on or adjacent the bottom surface of the wavelength converter.

12. The light emitting device of claim 10, wherein the metasurface is disposed within the wavelength converter.

13. The light emitting device of claim 10, wherein the nanoantennas are arranged in a periodic lattice.

14. The light emitting device of claim 10, wherein the nanoantennas each have a largest dimension less than a wavelength of light emitted by the semiconductor diode structure.

15. The light emitting device of claim 10, wherein at least one nanoantenna is asymmetric.

16. The light emitting device of claim 10, wherein at least one nanoantenna comprises two or more light scattering objects.

17. The light emitting device of claim 16, wherein the light scattering objects are symmetric objects.

18. The light emitting device of claim 17, wherein the light scattering objects are arranged asymmetrically.

19. The light emitting device of claim 1, wherein the metasurface is configured to reflect light rays that are emitted by the semiconductor diode structure and are incident on the metasurface from the substrate side of the metasurface at an angle less than or equal to a cutoff angle, and transmit into the wavelength converter light rays that are emitted by the semiconductor diode structure and are incident on the metasurface from the substrate side of the metasurface at an angle greater than the cutoff angle.

20. The light emitting device of claim 19, wherein the metasurface is disposed on or adjacent the bottom surface of the wavelength converter.

21. The light emitting device of claim 19, wherein the metasurface is disposed within the wavelength converter.

22. The light emitting device of claim 19, wherein the nanoantennas are arranged in a periodic lattice.

23. The light emitting device of claim 19, wherein the nanoantennas each have a largest dimension less than a wavelength of light emitted by the semiconductor diode structure.

24. The light emitting device of claim 19, wherein at least one nanoantenna is asymmetric.

25. The light emitting device of claim 19, wherein at least one nanoantenna comprises two or more light scattering objects.

26. The light emitting device of claim 25, wherein the light scattering objects are symmetric objects.

27. The light emitting device of claim 26, wherein the light scattering objects are arranged asymmetrically.

28. The light emitting device of claim 1, wherein the metasurface is configured to reflect light rays that are emitted by the semiconductor diode structure and are incident on the metasurface from the substrate side of the metasurface at an angle less than or equal to a cutoff angle, and transmit into the wavelength converter at an angle greater than their angle of incidence on the metasurface light rays that are emitted by the semiconductor diode structure and are incident on the metasurface from the substrate side of the metasurface at an angle greater than the cutoff angle

29. The light emitting device of claim 28, wherein the metasurface is disposed on or adjacent the bottom surface of the wavelength converter.

30. The light emitting device of claim 28, wherein the metasurface is disposed within the wavelength converter.

31. The light emitting device of claim 28, wherein the nanoantennas are arranged in a periodic lattice.

32. The light emitting device of claim 28, wherein the nanoantennas each have a largest dimension less than a wavelength of light emitted by the semiconductor diode structure.

33. The light emitting device of claim 28, wherein at least one nanoantenna is asymmetric.

34. The light emitting device of claim 28, wherein at least one nanoantenna comprises two or more light scattering objects.

35. The light emitting device of claim 34, wherein the light scattering objects are symmetric objects.

36. The light emitting device of claim 35, wherein the light scattering objects are arranged asymmetrically.