Light emitting device including color conversion material and light extraction structure and method for manufacturing same

Abstract

The light-emitting element comprises a light-emitting diode configured to emit incident photons of blue or ultraviolet radiation, a color conversion material disposed on the light-emitting diode and configured to absorb the incident photons emitted by the light-emitting diode and generate converted photons having a peak wavelength longer than the peak wavelength of the incident photons, and at least one light extraction mechanism disposed between the light-emitting diode and the color conversion material.

Description

[Technical field]

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 278,571, filed November 12, 2021, which is incorporated herein by reference in its entirety. FIELD OF THE DISCLOSURE The present disclosure relates to light emitting devices, and in particular to light emitting diodes formed with color conversion materials within an optical cavity, and light extraction structures and methods for their manufacture. [Background technology]

[0002] Light-emitting elements are used in electronic displays, such as backlighting for liquid crystal displays in laptops and televisions. Light-emitting elements include light-emitting diodes (LEDs) and many other types of electronic devices configured to emit light.

[0003] For light-emitting devices such as light-emitting diodes (LEDs), the emission wavelength is determined by the bandgap of the LED's active region, along with size-dependent quantum confinement effects. The active region often contains one or more bulk semiconductor layers and / or quantum wells (QWs). For III-nitride LED devices, such as GaN-based devices, the material of the active region (e.g., bulk semiconductor layers or QW well layers) is InN. x Ga 1-x N, where 0 <x<1である。

[0004] The band gap of such III-nitride materials depends on the amount of In incorporated into the active region. More Indium will result in a smaller band gap and longer emission wavelength. As used herein, the term "wavelength" refers to the peak emission wavelength of the LED. It should be understood that the typical emission spectrum of a semiconductor LED is a narrow band of wavelengths centered around the peak wavelength. Summary of the Invention

[0005] An embodiment of the light-emitting element includes a light-emitting diode configured to emit incident photons of blue or ultraviolet radiation, a color conversion material disposed on the light-emitting diode and configured to absorb the incident photons emitted by the light-emitting diode and generate converted photons having a peak wavelength longer than the peak wavelength of the incident photons, and at least one light extraction mechanism disposed between the light-emitting diode and the color conversion material.

[0006] A further embodiment of the light-emitting element includes an optical cavity bounded by cavity walls, a light-emitting diode disposed within the optical cavity and configured to emit incident photons of blue or ultraviolet radiation, a color conversion material disposed over the light-emitting diode and configured to absorb the incident photons emitted by the light-emitting diode and generate converted photons having a peak wavelength longer than the peak wavelength of the incident photons, a reflective material disposed over the cavity walls, and a transparent material disposed over the metallic material. [Brief description of the drawings]

[0007] [Figure 1A] FIG. 1A is a side cross-sectional view of an intermediate structure that may be used in constructing a light-emitting device array, according to various embodiments. [Figure 1B] FIG. 1B is a side cross-sectional view of a further intermediate structure that may be used in constructing a light-emitting device array, according to various embodiments. [Figure 1C] FIG. 1C is a side cross-sectional view of a further intermediate structure that may be used in constructing a light-emitting device array, according to various embodiments. [Figure 1D] FIG. 1D is a side cross-sectional view of a light-emitting element array according to various embodiments. [Figure 1E] FIG. 1E is a side cross-sectional view of a further light emitting element array according to various embodiments. [Figure 2A] FIG. 2A is a top perspective view of a first patterned matrix having a plurality of vias formed therein, according to various embodiments. [Figure 2B]FIG. 2B is a top perspective view of a second patterned matrix, the first patterned matrix having a plurality of vias formed therein, according to various embodiments. [Diagram 3] FIG. 3 is a vertical cross-sectional view of a micro LED emitting a Lambertian radiation pattern according to various embodiments. [Figure 4] FIG. 4 is a vertical cross-sectional view of a comparative light-emitting element array according to a comparative embodiment. [Diagram 5] FIG. 5 is a side cross-sectional view of a further light emitting element array including a light extraction material layer according to various embodiments. [Figure 6A] FIG. 6A is a side cross-sectional view of a further light emitting element array including a light extraction material layer and light extraction features according to various embodiments. [Figure 6B] FIG. 6B is a side cross-sectional view of a further light-emitting element array including a light extraction material layer and light extraction features according to various embodiments. [Figure 6C] FIG. 6C is a side cross-sectional view of a further light emitting element array including a light extraction material layer and light extraction features according to various embodiments. [Figure 7A] FIG. 7A is a side cross-sectional view of a light-emitting element array in which each pixel is divided into multiple subcells, according to various embodiments. [Figure 7B] FIG. 7B is a side cross-sectional view of a further light-emitting element array in which each pixel is divided into multiple subcells, according to various embodiments. [Figure 7C] FIG. 7C is a top view of a light-emitting element array in which each pixel is divided into multiple subcells, according to various embodiments. [Figure 8] 8 and 10 are side cross-sectional views of additional light emitting element arrays in which the cavity walls may be configured to include a reflective material, according to various embodiments. [Figure 9A] FIG. 9A is a vertical cross-sectional view of the reflection pattern of photons hitting a reflective cavity wall having a metallic reflector, according to various embodiments. [Figure 9B]FIG. 9B is a vertical cross-sectional view of the reflection pattern of photons striking a reflective cavity wall having a transparent material formed on a metallic reflector, according to various embodiments. [Figure 10] 8 and 10 are side cross-sectional views of additional light emitting element arrays in which the cavity walls may be configured to include a reflective material, according to various embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] A display device, such as a direct-view display, may be formed from an array of pixels. Each pixel may include a collection of subpixels that emit light at a respective peak wavelength. For example, a pixel may include red, green, and blue subpixels. Each subpixel may include one or more light-emitting diodes that emit light at a particular wavelength. A conventional arrangement is to have red, green, and blue (RGB) subpixels within each pixel. Each pixel is driven by a backplane circuit such that any combination of colors within the color gamut may be displayed on the display for each pixel. A display panel may be formed by a process in which LED subpixels are soldered or otherwise electrically attached to bond pads on a backplane. The bond pads may be electrically driven by the backplane circuit and other driving electronics.

[0009] Various embodiments provide light emitting devices configured to generate highly efficient red, green, blue, and / or other color pixelated light from shorter wavelength excitation sources using photonically excited quantum dots in a vertical cavity structure. Micro-scale light emitting diodes (micro LEDs) in examples are less than 100 microns in length and width, e.g., 5-20 microns, and can be used in display devices. This new technology allows for the ultimate black level to be achieved by using individual LEDs at each pixel location in a display device. Additionally, each pixel can be configured to generate a single color of light. The backplane on which the individual LEDs are mounted may include a substrate (e.g., plastic, glass, semiconductor, etc.) with thin film transistor (TFT) structures, silicon CMOS, or other driver circuitry configured to apply voltage or current independently to each LED. For example, the backplane may include TFTs on a glass or plastic substrate, or bulk silicon transistors (e.g., transistors in CMOS configuration) on a bulk silicon substrate or on a silicon-on-insulator (SOI) substrate. It should be noted that although micro-LEDs are described in the following embodiments, other types of LEDs (e.g., nanowire or other nanostructured LEDs) or macro-LEDs having sizes (e.g., width and length) greater than 100 microns can be used in place of or in addition to micro-LEDs.

[0010] In some embodiments, the size of each micro LED may be smaller than the pitch of pixels used in a particular display device, such as a direct view display device or other display device. For example, a 300 ppi display may have pixels with a pitch of about 85 microns, while a typical micro LED for such a display may be about 20 microns wide. Micro LEDs that include indium doped GaN material (i.e., LEDs that emit colors that depend on the indium doping of GaN) may suffer from degradation in efficiency and uniformity as LED size decreases (e.g., sizes below 10 microns) due to the difficulties associated with indium doping of the GaN crystal structure. Thus, longer peak wavelength emitting III-nitride micro LEDs (e.g., red LEDs) that utilize higher indium content in the active region may have poor efficiency and uniformity due to degraded indium doping.

[0011] Some of the embodiments of the present disclosure may include photonic emitters based on LEDs having an undoped GaN active region (e.g., a micro-LED having a GaN light-emitting active layer) or a low indium-doped InGaN active region (e.g., a micro-LED having a low indium content InGaN light-emitting active layer) coupled with a photonically excited color conversion material. Such LEDs may be ultraviolet (UV)-emitting or blue light-emitting micro-LEDs having a peak emission wavelength in the ultraviolet (UV)-emitting or blue light spectral region (e.g., 370-460 nm, e.g., 390-420 nm, e.g., 400-410 nm). As used herein, the blue light spectral region includes the colors blue and violet as perceived by a human observer.

[0012] In some embodiments, the color conversion material may include quantum dots. The quantum dots may be configured to absorb photons generated by the GaN-based LED and generate light of various colors depending on the properties of the quantum dots (e.g., the size and material composition of the quantum dots). Such structures may avoid problems associated with indium doping of small GaN structures. Alternatively, the color conversion material may include inorganic phosphors or organic dyes.

[0013] In the size range appropriate for augmented reality (AR) displays (e.g., smart glasses) and other applications (i.e., sizes below 10 microns), the use of undoped or low indium-doped GaN LED active regions and photo-pumped quantum dots to produce a variety of colors can provide display devices with better uniformity across an array of micro-LEDs. Such arrays may also exhibit higher efficiency than systems with colored LEDs based on relatively highly indium-doped GaN (e.g., red LEDs with more indium than blue LEDs). Improved efficiency and uniformity can be achieved because quantum dots can be manufactured with a high degree of uniformity in size and material composition. These uniform quantum dots have correspondingly uniform (i.e., narrow spectral linewidth) emission characteristics.

[0014] Extraction of light emitted by micro-LEDs can become increasingly challenging as pixel pitch and micro-LED size become smaller. In the disclosed embodiments, light extraction of quantum dot-generated photons (e.g., along a particular direction) is improved while maintaining high efficiency by avoiding loss of photons to absorbing surfaces. The disclosed system can also prevent or reduce excitation photons from escaping the device, thereby ensuring the purity of the color emitted by a given micro-LED. This can be achieved by forming reflective optical cavity walls that include a light extraction material layer and other light extraction structures such as microlenses, distributed Bragg reflectors (DBRs), textured or corrugated interfaces, as described in more detail below.

[0015] 1A is a vertical cross-sectional view of an intermediate structure 100a that may be used to form a light-emitting device array, according to various embodiments. The intermediate structure 100a may include a plurality of micro LEDs 102 formed on a substrate 104. As discussed above, the micro LEDs 102 may include micro LEDs having peak emission wavelengths in the UV-emitting or blue light spectral region (e.g., UV or blue-emitting micro LEDs, also referred to as UV or blue LEDs). Such LEDs may include an undoped GaN active region configured to emit ultraviolet (UV) photons and / or photons in the blue spectral region.

[0016] In an embodiment, the micro LED 102 may have at least one electrode 103 located on the top of the LED and facing away from the substrate 104. The electrode 103 may consist of an anode electrode or a cathode electrode. In an embodiment, the micro LED 102 may consist of a vertical LED with a second electrode (not shown for clarity) located between the substrate 104 and the bottom surface of the micro LED 102. In another embodiment, the micro LED may include a horizontal LED with both electrodes located on the same side of the LED (e.g., the top or bottom side of the LED).

[0017] The substrate 104 may be a backplane having electrical circuitry (e.g., TFT circuitry and / or CMOS circuitry) configured to provide voltage and current to the micro-LEDs 102 via electrodes (including the electrodes 103) and thereby control light emission by the micro-LEDs 102. The backplane may be an active matrix or passive matrix backplane substrate for driving LEDs. As used herein, "backplane substrate" refers to any substrate configured to have multiple elements attached thereto. In an embodiment, the backplane may include a substrate including silicon, glass, plastic, and / or other materials that can provide structural support to at least the elements attached thereto. In an embodiment, the backplane substrate may be a passive backplane substrate in which a metal interconnect structure (not shown) including metallization lines is present, for example in a cross-lattice pattern, and there is no dedicated active element (e.g., TFT) for each LED. In another embodiment, the backplane substrate may be an active backplane substrate, which includes a metal interconnect structure as a cross-grid of conductive lines and may further include dedicated active elements (e.g., CMOS transistors or TFTs) for each LED at one or more intersections of the cross-grid of conductive lines.

[0018] 1B is a vertical cross-sectional view of a further intermediate structure 100b that may be used to form a light-emitting device array, according to various embodiments. The intermediate structure 100b may include a plurality of optical cavities 106 formed above the micro LEDs 102. Each optical cavity may be bounded by a cavity wall 108. The optical cavities 106 may be formed using a reflective material having mechanical properties suitable for forming a high aspect ratio cavity (e.g., diameter less than 5 microns, such as 1-2 microns, height greater than 10 microns, such as 20-30 microns) with a relatively thin cavity wall 108. The cavity wall 108 may have a thickness less than 10 microns, such as 0.5-5 microns, including 1-2 microns. The cavity wall 108 may form an insulating matrix.

[0019] The matrix material may be selected to be compatible with both thermal evaporation process steps and solvent-based fluid deposition and evaporation. One such matrix material is alumina, but silica, titania, or other insulating metal oxide materials may also be used. A variety of materials commonly used in the manufacture of microelectromechanical (MEMS) devices can be used to form optical cavities 106 bounded by cavity walls 108 made of an electrically insulating material (e.g., alumina). Such materials have a relatively high refractive index and are suitable for forming structures with high aspect ratios. A layer of such matrix material (not shown in FIG. 1B) can be grown or deposited on an array of micro-LEDs 102 disposed on a substrate 104, and techniques such as etching or other microfabrication approaches can be used to create optical cavities 106 in the material. FIG. 2A is a top perspective view of a matrix 200a having multiple cylindrical optical cavities 106 bounded by cavity walls 108. FIG. 2B is a top perspective view of a matrix 200 b having a plurality of hexagonal optical cavities 106 bounded by cavity walls 108 .

[0020] In an embodiment, a voltage may be applied to the anode or cathode electrodes 103 of the micro-LEDs 102, thereby forming one side of the etching bias. For example, if the matrix 200a or 200b (i.e., the cavity walls 108) comprises alumina, porous alumina may be formed by anodization. In this embodiment, an aluminum metal layer may be deposited on the micro-LEDs 102 and then electrochemically anodized to form a porous anodic alumina matrix having optical cavities (i.e., pores) 106 bounded by the anodized alumina cavity walls 108. The substrate 104 including the aluminum layer may be placed in an acid electrolyte (e.g., oxalic acid, chromic acid, sulfuric acid, and / or phosphoric acid) and a voltage may be applied to the electrodes 103 and / or external electrodes of the micro-LEDs 102 to form a porous anodic alumina matrix including optical cavities (i.e., pores) 106 bounded by the alumina cavity walls 108. The optical cavities 106 may be arranged in a hexagonal array in an anodic alumina matrix.

[0021] FIG. 1C is a vertical cross-sectional view of a further intermediate structure 100c that may be used to form a light-emitting device array, according to various embodiments. The intermediate structure 100c may include a light extraction material layer 110 and a color conversion material (112a, 112b, 112c, 112d) formed in the optical cavity 106 above the array of micro LEDs 102. The light extraction material layer 110 may have a refractive index lower than that of the material forming the cavity wall 108. For example, the light extraction material layer 110 may have a refractive index less than 1.7, such as 1.3-1.5 for an alumina cavity wall 108. A low refractive index of the light extraction material layer 110 may cause excitation photons (i.e., photons generated by the micro LEDs 102) to be reflected from the cavity wall 108 rather than being absorbed by or transmitted through the cavity wall 108. Such reflection prevents loss of photons and increases the quantum efficiency of the device.

[0022] A variety of polymeric materials can be used as the light extraction material layer 110. One such polymer is Jet-144 (i.e., an inkjet compatible polymer), which has a refractive index of 1.44, and can be deposited into the optical cavity 106 using an inkjet system. The thickness of the cavity wall 108 can be configured to be as thick as possible to increase the probability that photons that do not reflect from the cavity wall 108 are absorbed (i.e., extinguished) and do not enter an adjacent cavity.

[0023] The light extraction material layer 110 can be deposited using a variety of techniques, including inkjet, vacuum, pressure, and / or gravity deposition. After deposition, the polymer may be crosslinked, for example, by exposure to ultraviolet (UV) radiation. In other embodiments, the solvent in which the polymer is dissolved may be driven off by evaporation, leaving behind residual crosslinked polymer as the light extraction material layer 110 in each cavity. In various embodiments, the light extraction material layer 110 may be formed with a variety of thicknesses and may or may not additionally include light scattering materials, such as ZrO2, TiO2 or SiO2 nano- or microbeads, textured or corrugated interfaces, as described in more detail below. The light extraction material layer 110 may partially fill the optical cavities 106, leaving an empty cavity space above the light extraction material layer 110 in each cavity.

[0024] Color conversion materials (112a, 112b, 112c, 112d) may then be formed in the optical cavity 106 (see, e.g., FIG. 1B) and on the light extraction material layer 110 (see, e.g., FIG. 1C). The color conversion materials (112a, 112b, 112c, 112d) may include quantum dots corresponding to a variety of different colors. In this example, the color conversion materials (112a, 112b, 112c, 112d) may include a plurality of first quantum dots 112a, a plurality of second quantum dots 112b, a plurality of third quantum dots 112c, and a plurality of fourth quantum dots 112d, which are configured to convert UV excitation photons into photons having a first, second, third, and fourth color, respectively. The second and third colors may be composed of different peak wavelengths within the green spectral range. Alternatively, only three quantum dot colors may be used.

[0025] The quantum dots may each be formed as nanocrystals having a diameter of 1-10 nm, such as 2-8 nm nanocrystals of a compound semiconductor material, such as a III-V semiconductor material (e.g., indium phosphide, as described in U.S. Pat. No. 9,884,763 B1, which is incorporated herein by reference in its entirety), a II-VI semiconductor material (e.g., ZnSe, ZnS, ZnTe, CdS, CdSe, etc., core-shell quantum dots, as described in U.S. Patent Publication 2017 / 0250322 A1, which is incorporated herein by reference in its entirety), and / or a I-III-VI semiconductor material (e.g., AgInGaS / AgGaS core-shell quantum dots, as described in U.S. Pat. No. 10,927,294 B2, which is incorporated herein by reference in its entirety). The quantum dots can emit different colors of light (e.g., red, green, blue) depending on their diameter. Larger dots emit longer wavelengths of light and smaller dots emit shorter wavelengths of light. The quantum dots may be suspended in a material (e.g., a polymer such as polyimide) that has a refractive index different from (e.g., higher than) the refractive index of the light extraction material layer 110. By way of example, the refractive index of the polyimide material may be between 1.6 and 1.75, e.g., about 1.7.

[0026] Quantum dots corresponding to different colors can be selectively deposited in each cavity. For example, a first cavity can be formed by etching a first via in a matrix material. A first quantum dot corresponding to a first color can then be introduced into the first cavity and a layer of protective material can be formed over the first quantum dot. This process can then be repeated to form a second cavity, a third cavity, etc., and introduce a second quantum dot, a third quantum dot, etc., into each cavity, respectively.

[0027] In other embodiments, photoresist may be deposited on all cavities except the first cavities. A first layer of quantum dots configured to generate a first color (e.g., red) may then be deposited in the first cavities corresponding to the subpixels having the first color. The polymer in which the first quantum dots are suspended may then be crosslinked by evaporation or exposure to UV light. The process may then be repeated for other optical cavities, respectively depositing quantum dots configured to generate other colors of light (e.g., green and blue).

[0028] Alternatively, the color conversion material (112a, 112b, 112c, 112d) may include an inorganic phosphor or an organic dye. An optional organic planarization layer may be formed on the color conversion material. The color conversion material and the optional organic planarization layer may partially fill the optical cavity 106.

[0029] 1D is a vertical cross-sectional view of a light-emitting element array 100d, according to various embodiments. As shown, the array 100d may include a color selector 114 formed in and / or on the optical cavity 106. The color selector 114 may include a color filter array and / or a distributed Bragg reflector. In some embodiments, the color selector 114 may be formed in the optical cavity and may extend to the top of the cavity wall 108 such that the optical cavity 106 is completely filled with the material.

[0030] The color conversion materials (112a, 112b, 112c, 112d) may be configured to absorb and convert excitation photons 118 to emitted converted photons (e.g., visible light such as red, green, or blue) 120. In some embodiments, the color conversion materials (112a, 112b, 112c, 112d) may not have a sufficient thickness and / or density to completely convert all excitation photons 118 to converted photons 120. In this manner, the color selector 114 formed on the color conversion materials (112a, 112b, 112c, 112d) absorbs and / or reflects all or a portion of the excitation photons 118 not converted by the color conversion materials (112a, 112b, 112c, 112d) without absorbing and / or reflecting the converted photons 120 emitted by the color conversion materials.

[0031] Each micro LED 102 may be configured to emit excitation photons 118 within a common or target wavelength range. For example, a GaN-based micro LED 102 may emit excitation photons 118 having a wavelength of about 400-410 nm, such as about 405 nm (i.e., in the blue or near ultraviolet portion of the electromagnetic spectrum). The micro LEDs 102 may exhibit high uniformity and high efficiency. However, slight variations in wavelength of such micro LEDs 102 may not be easily visible. Furthermore, leakage of excitation photons 118 through the color conversion material (112a, 112b, 112c, 112d) may minimize degradation of color purity of the converted photons 120.

[0032] In an embodiment, the color selector 114 includes a color filter array including organic dyes embedded in an organic polymer. The dyes may be configured to absorb the ultraviolet light of the excitation photons 118 but not the blue, green, or red light of the conversion photons. Optionally, different dyes may be provided on each colored subpixel (e.g., red, green, and blue subpixels). For example, a first dye filter material configured to transmit primarily red light may be provided on the red subpixels, a second dye filter material configured to transmit primarily green light may be provided on the green subpixels, and a third dye filter material configured to transmit primarily blue light may be provided on the blue subpixels. The color filters may be formed using further photolithography steps. In various embodiments, a thin film encapsulation (TFE) layer or layer stack may then be applied over the color filter material to provide protection against air or moisture ingress to the quantum dot layer of the color conversion material. In an embodiment, the TFE may include a three-layer stack of two silicon nitride layers separated by a polymer layer.

[0033] In an alternative embodiment, the color selector 114 may include a DBR formed on the color conversion material (112a, 112b, 112c, 112d). The DBR may be configured to reflect excitation photons 118 transmitted through the color conversion material back into the optical cavity 106 as reflected photons 122 (e.g., ultraviolet or deep blue photons) and transmit converted photons 120 from the optical cavity 106. The DBR may be formed as an alternating multi-layer stack of materials (not shown) having different refractive indices. For example, the DBR may be formed as a stack of N alternating layers of TiO2 (n=2.5) and SiO2 (n=1.5), where N is 2 or greater. In other embodiments, various other materials having respective refractive indices may be used to create the DBR.

[0034] In an embodiment where the DBR includes TiO2 and SiO2 and N=2, the bandwidth may be 164 nm and the maximum reflectance R may be 84% at a center wavelength of 405 nm. In an embodiment where the DBR stack includes a larger number of layers (i.e., N>2), the reflectance may be increased. Therefore, the probability that a UV excitation photon 118 passes through the DBR may be decreased. UV photons 122 that are reflected from the DBR back to the optical cavity 106 may circulate through the color conversion material (112a, 112b, 112c, 112d), thereby also increasing the probability that they are converted to a converted photon 120 having a desired wavelength (e.g., green, blue, or red). In this way, any UV reflected photon 122 that is not initially absorbed by the color conversion material (112a, 112b, 112c, 112d) may eventually be absorbed and converted to a converted photon 120 having a desired emission wavelength. This process, sometimes referred to as "photon recycling," may increase the quantum efficiency of the device.

[0035] If the micro-LED 102 includes a short-wavelength blue-emitting LED, the DBR 114 blocks the short-wavelength blue light (i.e., excitation photons 118) of the micro-LED 102 but allows the long-wavelength converted photons 120 emitted from the blue quantum dots of the color conversion material to pass through. Alternatively, the DBR 114 can be omitted on the sub-pixels that emit blue light.

[0036] The DBR can be formed by deposition (e.g., evaporation) of a multi-layer stack (not shown) over every subpixel. In this way, the DBR provides additional protection against moisture and oxygen ingress to the quantum dot layer. Higher values ​​of N further improve the reflectivity of the DBR and its protection from moisture and oxygen, improving the performance and durability of the overall system.

[0037] In additional various embodiments, other materials may be used for various components of the device. For example, the DBR may include a wide range of materials, each with its own refractive index, such as nitrides (TiN, AlN, TiN, etc.), polysilicon, etc. Some embodiments may include multiple layers of quantum dots, multiple DBR structures, etc. The light extraction material layer 110 described above may be omitted in some embodiments, or multiple light extraction material layers 110 may be used. By using a more effective DBR 114, the layer thickness and density of the color conversion material (112a, 112b, 112c, 112d) may be reduced. In further embodiments, the optical cavity 106 may be formed in various ways. For example, the optical cavity 106 may be formed in a separate matrix layer that is attached to the array of micro LEDs 102 after the optical cavity 106 is formed. In further embodiments, a light collimating element may be included to mitigate performance degradation due to lateral photon propagation.

[0038] FIG. 1E is a vertical cross-sectional view of a further light-emitting element array 100e according to various embodiments. As shown therein, the light-emitting element array 100e includes a microlens 124 formed over the optical cavity 106. Each microlens 124 can help improve light extraction from each micro LED structure, thereby improving the efficiency of the array 100e. In general, extraction of light emitted by a micro LED can become increasingly difficult as pixel pitch and micro LED size become smaller. In this regard, the color conversion material (112a, 112b, 112c, 112d) may be selected to be thick enough to convert all of the excitation photons 118 into converted photons 120, each having a particular color. The thickness of the color conversion material (112a, 112b, 112c, 112d) may be very large compared to the lateral dimensions of the subpixels. In such a structure, photons may travel diffusively rather than ballistically from the micro LED subpixels. These diffusively moving photons can spread to adjacent sub-pixels and cause optical crosstalk.

[0039] Embodiments of the present disclosure improve light extraction of photons (e.g., along a particular direction) generated by the quantum dots while maintaining high efficiency by avoiding loss of photons to absorbing surfaces. As described above, this may be achieved by forming a matrix structure that includes reflective cavity walls 108, including a light extraction material layer 110, and / or including a color selector 114, such as a DBR.

[0040] The use of quantum dots as color conversion materials (112a, 112b, 112c, 112d) for micro LED displays may involve deposition and patterning of high density quantum dot layers with very small feature sizes. Sub-pixels with aspect ratios greater than 1:1 may be used to allow sufficient absorption of excitation photons 118 (see, e.g., FIG. 1D and FIG. 1E) in the quantum dot layer. Such sub-pixels may also be separated by cavity walls 108 formed of an opaque matrix material to prevent color crosstalk in the display (i.e., photons from one micro LED propagating to an adjacent sub-pixel).

[0041] Various embodiments include a matrix, such as matrix 200a or 200b (see, e.g., FIG. 2A and FIG. 2B), which allows better light extraction from each subpixel and may mitigate photonic color crosstalk. Using the matrix as a template to sequentially open vias corresponding to different color subpixels allows deposition and curing of quantum dot inks without relying on high-resolution photopatternable resin compositions. In other embodiments, other techniques can be used to fabricate the LED structures.

[0042] FIG. 3 is a vertical cross-sectional view of an intermediate structure 300 showing the radiation pattern of a micro LED 102 formed on a substrate 104, according to various embodiments. The micro LED 102 may be configured to emit a Lambertian radiation pattern. In this regard, the intensity of the emitted radiation (i.e., the number of photons per unit time per unit area) varies with the cosine of the emission angle with respect to a direction normal to the emission surface. Each of the various arrows in FIG. 3 has a length proportional to the intensity of the emitted radiation in the direction of the arrow. For example, radiation emitted at an angle θ has an intensity given by I=I0cos(θ), where I0 is the intensity emitted normal to the surface. Circle 308 illustrates the continuous angular cosine dependence of the radiation emitted from the top surface of the micro LED 102. As shown here, the emitted intensity is greatest in a direction normal to the top surface, decreases away from the direction normal to the surface, and is zero in a direction parallel to the surface (i.e., emission from the top surface parallel to the top surface is zero).

[0043] 4 is a vertical cross-sectional view of a comparative light emitting element array 400 according to a comparative embodiment. The light emitting element array 400 may include a plurality of LEDs 102a formed within a plurality of cavities bounded by cavity walls 108. The LEDs 102a may be coupled to a substrate (e.g., a backplane) 104, which may include electrical circuitry configured to control the LEDs 102. Each cavity may include a color conversion material 112.

[0044] The light-emitting element array 400 may be similar to the intermediate structure 100c described above (see FIG. 1C). However, in contrast to the intermediate structure 100c, the light-extracting material layer 110 is omitted in the light-emitting element array 400. In this comparative embodiment, the LEDs 102a may be selected to have a large upper light-emitting surface to enlarge the contact area between the LEDs 102a and the color conversion material. Such a large contact area may improve the coupling between the emitted photons and the color conversion material. However, the larger area of ​​the LEDs 102a increases the sub-pixel size and increases the device cost.

[0045] In embodiments of the present disclosure, smaller micro LEDs 102 may be used in conjunction with a light extraction material layer 110 and various light extraction mechanisms, as described in more detail below with reference to Figures 5-7C. Smaller on-micro LEDs 102 reduce the size of each sub-pixel, lowering device cost.

[0046] 5 is a vertical cross-sectional view of a light emitting element array 500 including a light extraction material layer 110 according to various embodiments. The light emitting element array 500 may include a plurality of micro LEDs 102 formed in a plurality of cavities bounded by cavity walls 108. The micro LEDs 102 may be coupled to a substrate (e.g., a backplane) 104, which may include electrical circuitry configured to control the micro LEDs 102. Each cavity may include a color conversion material 112 and a light extraction material layer 110. The cavity walls 108 may include an angled surface 402 that enhances the reflective properties of the cavity walls 108. The angled surface 402 may include a reflective surface (e.g., a metal surface such as an aluminum surface).

[0047] A high refractive index material may be selected for the light extraction material layer 110, which may act as a waveguide for the photons emitted by the micro-LED. The waveguiding effect of the light extraction material layer may act to broaden the angular distribution of the emitted photons, thereby making the distribution of photons more uniform. As described above, the uniform distribution of emitted photons may be more effectively coupled to the color conversion material 112 than in the absence of the light extraction material layer 110.

[0048] The light extraction material layer 110 may be selected to have a refractive index close to that of the micro-LED 102. In various embodiments, the micro-LED may include GaN, which has a refractive index in the range of about 2.4 to 2.5. Thus, the light extraction material layer 110 may be selected to have a similar refractive index (or a broader range, such as from about 1.5 to about 2.5) such that photons emitted from the micro-LED are coupled into the waveguide mode of the light extraction material layer 110. Additionally, the material selected for the light extraction material layer 110 may be selected to be transparent and have a small extinction coefficient (i.e., to avoid absorption of photons). In various embodiments, various transparent polymer resins can be used for the light extraction material layer 110.

[0049] Additionally, in various embodiments, the light extraction material layer 110 may be a composite material having a high refractive index matrix with light extraction and scattering mechanisms. For example, the matrix may include an epoxy or UV curable polymer, and the light extraction and scattering mechanisms may include a plurality of scattering particles dispersed throughout the matrix. The scattering particles may include a material having a high refractive index, such as TiO2, ZrO2, or AlN, and the particles may be formed as nanoparticles (e.g., having a diameter of 1 nm to 1 micron). Other embodiments include particles of other materials and other sizes. Photons interacting with the nanoparticles may undergo multiple scattering, which may result in a random spatial distribution of the photons. As discussed above, a more uniform photon distribution may lead to more efficient conversion of photons by the color conversion material 112. Various transparent polymer binders or resins may be selected for the matrix in combination with the high refractive index nanoparticles to form the light extraction material layer 110.

[0050] However, the difference in refractive index between the light extraction material layer 110 and the color conversion material 112 may reduce the coupling between the light extraction material layer 110 and the color conversion material 112. In this regard, some of the photons may be trapped in the light extraction material layer 110 due to total internal reflection caused by the difference in refractive index between the light extraction material layer 110 and the color conversion material 112. Photons incident on the interface between the light extraction material layer 110 and the color conversion material 112 at an angle greater than a critical angle (which depends on the difference in refractive index) may be internally reflected and, as a result, trapped within the light extraction material layer 110. To address this issue, in further embodiments, various light extraction features may be included to improve the coupling between the light extraction material layer 110 and the color conversion material 112, as described in more detail below with reference to Figures 6A to 7C.

[0051] 6A is a vertical cross-sectional view of a further light emitting element array 600a including a light extraction material layer 110 and a light extraction feature 602 according to various embodiments. The light emitting element array 600 may include a number of micro LEDs 102 formed in a number of cavities bounded by cavity walls 108. The micro LEDs 102 may be coupled to a substrate 104, which may include electrical circuitry configured to control the micro LEDs 102. Each cavity may include a color conversion material 112 and a light extraction material layer 110. The cavity walls 108 may include angled surfaces 402 that improve the reflective properties of the cavity walls 108. As mentioned above, a high refractive index material may be selected for the light extraction material layer 110 that may act as a waveguide for photons emitted by the micro LEDs.

[0052] The light extraction features 602 can be formed by roughening the top surface of the light extraction material layer 110 prior to deposition of the color conversion material 112. In this manner, the interface between the light extraction material layer 110 and the color conversion material 112 is roughened to include features 602 that include peaks and valleys at the interface. Photons incident on the light extraction features 602 may be more likely to transmit from the light extraction material layer 110 to the color conversion material 112. In this regard, the light extraction features 602 exhibit multiple surfaces that have a range of angles relative to the normal to the interface between the light extraction material layer 110 and the color conversion material 112, which may make it more difficult to meet the criterion for total internal reflection (i.e., photons incident at angles greater than the critical angle relative to the normal to the interface). In this manner, the presence of the light extraction features 602 may increase the transmission of photons from the light extraction material layer 110 to the color conversion material 112. In this manner, light extraction efficiency may be increased.

[0053] 6B and 6C are vertical cross-sectional views of further light emitting element arrays (600b, 600c) each including a light extraction material layer 110 and a light extraction feature (604, 606) according to various embodiments. The light emitting element arrays (600b, 600c) may each include a number of micro LEDs 102 formed in a number of cavities bounded by cavity walls 108. The micro LEDs 102 may be coupled to a substrate 104, which may include electrical circuitry configured to control the micro LEDs 102. Each cavity may include a color conversion material 112 and a light extraction material layer 110. The cavity walls 108 may include angled surfaces 402 that improve the reflective properties of the cavity walls 108. As mentioned above, a high refractive index material may be selected for the light extraction material layer 110 that may act as a waveguide for photons emitted by the micro LEDs.

[0054] The light extraction features (604, 606) of the arrays (600b, 600c) may include corrugated structures formed on the light extraction material layer 110. For example, the light extraction features (604, 606) may each form a nanoscale photonic crystal. The light extraction features 604 of the array 600b may be formed by patterning the surface of the light extraction material layer 110 to form a periodic array of nanoscale features. Various patterning techniques, such as nanoimprint lithography, may be used to generate the light extraction features 604 of the array 600b. The light extraction features 604 may include a periodic (i.e., regular) array of battlement-shaped protrusions and recesses etched or stamped into the top surface of the light extraction material layer 110.

[0055] The light extraction features 606 of the array 600c may be formed by depositing a second material on the light extraction material layer 110 and patterning the second material to form the light extraction features 606. The second material may be selected to have a refractive index different from that of the light extraction material layer 110. For example, the second material may be selected to have a refractive index intermediate that of the light extraction material layer 110 and the color conversion material 112. This allows the presence of the light extraction features 606 to act to reduce a discontinuity in refractive index between the light extraction material layer 110 and the color conversion material 112. Various patterning techniques, such as nanoimprint lithography, may be used to generate the light extraction features 606 of the array 600c. The light extraction features 606 may include a periodic (i.e., regular) array of battlement-shaped protrusions and recesses formed on the top surface of the light extraction material layer 110.

[0056] The periodic variation in refractive index caused by the spatial variation of the light extraction features (604, 606) can change the coupling between optical modes in the light extraction material layer 110 and the color conversion material 112. In this manner, the presence of the light extraction features (604, 606) can increase the transmission of photons from the light extraction material layer 110 to the color conversion material 112, thereby increasing the light extraction efficiency.

[0057] As will be described in more detail with reference to Figures 7A-7C below, in additional embodiments, various additional geometric shapes may be used in forming the light extraction features. Various embodiments of the light emitting element arrays in which each subpixel is divided into multiple subcells are shown in Figures 7A-7C. In this regard, Figure 7A is a vertical cross-sectional view of a first light emitting element array 700a, Figure 7B is a vertical cross-sectional view of a second light emitting element array 700b, and Figure 7C is a top view of a third light emitting element array 700c. In each array (700a, 700b, 700c), a plurality of partition structures 608 may be formed on the light extraction material layer 110. However, unlike the cavity walls 108 that may extend through the light extraction material layer 110 and form the boundaries of each subpixel of the display device, the partition structures 608 may be disposed on the top surface of the light extraction material layer 110 and be bounded by the cavity walls 108 in each subpixel. A subpixel may include a single color (e.g., red, green, or blue) light-emitting region of a light-emitting element, while a pixel may include multiple subpixels (e.g., three or four pixels such as a red subpixel, a green subpixel, and a blue subpixel). The partition structure 608 may include a metal (e.g., aluminum), a metal oxide (e.g., aluminum oxide), or a polymeric material.

[0058] As shown, in the first array 700a, the partition structures 608 may have a height approximately equal to that of the surrounding color conversion material 112, while in the second array 700b, the partition structures 608 may have a height less than that of the color conversion material 112. As shown in FIG. 7C, the partition structures 608 may be formed as a periodic lattice having a first plurality of parallel structures extending along a first direction (e.g., shown from left to right in FIG. 7C) and a second plurality of parallel structures extending along a second direction (e.g., shown from top to bottom in FIG. 7C). Thus, each subpixel may be divided into four or more regions (e.g., subcells), such as, for example, 9-12 regions.

[0059] The partitioning structure 608 may be selected to have a refractive index different from the refractive index of the light extraction material layer 110 and the color conversion material 112. For example, the partitioning structure 608 may be selected to have a refractive index less than that of the light extraction material layer 110 and greater than that of the color conversion material 112. In this manner, the partitioning structure 608 can function as a waveguide to couple photons from the light extraction material layer 110 to the color conversion material 112.

[0060] Thus, each partition structure 608 divides the color conversion material 112 into multiple separate regions. In this embodiment, the partition structure 608 has a tapered shape, and therefore divides the color conversion material 112 into multiple tapered regions, each of which can function as a long and thin tapered light source. Such a long and thin tapered light source may have improved coupling efficiency compared to a thick and short light source. This phenomenon can be enhanced by selecting the refractive index of the material surrounding each partition structure 608 (i.e., the color conversion material 112) to be lower than the refractive index of the partition structure 608, as described above.

[0061] In various embodiments, the micro LEDs 102 may include organic light emitting diodes (OLEDs). Such OLEDs may have very thin active layers, so that each OLED may essentially act as a two-dimensional structure (i.e., in a plane parallel to the top surface of the substrate 104 in FIG. 7A and FIG. 7B). The efficiency of such OLEDs may be approximately constant, independent of the size of the light emitting area (e.g., the size of the top surface emitting surface in FIG. 3). However, in a display system in which a micro LED 102 and a color conversion material 112 are combined, the light extraction efficiency may depend on the shape of the light source due to the thickness of the element. In various embodiments, the thickness of each micro LED 102 may be on the order of a few microns (e.g., less than 20 microns), and the light extraction efficiency may vary depending on the emission angle (e.g., see FIG. 3), the type of material used for the partition structure 608, and the refractive index of the material surrounding the partition structure 608 (e.g., the color conversion material 112).

[0062] As discussed above, the light extraction efficiency of a long, tapered light source (e.g., tapered regions of color conversion material 112 separated by partition structures 608) may be greater than a short, thick light source (e.g., color conversion material 112 without partition structures 608). For example, a light source having a thin, tapered color conversion material 112 may be formed by dividing each pixel into multiple subcells, as shown in Figures 7A-7C. As shown in Figure 7C, one subpixel may be divided into 12 subcells. In other embodiments, division of various subpixels into subcells may be included. Furthermore, in other embodiments, each subcell may be bounded by structures having various cross-sectional shapes, such as circles, squares, polygons, or other irregular shapes. In other embodiments, subcells having many different shapes (e.g., circles, squares, polygons, or other irregular shapes) may be included.

[0063] By creating multiple subcells at a given subpixel size, multiple elongated light sources are created. The light extraction efficiency may depend not only on the shape but also on the refractive index of the encapsulation material surrounding the sidewalls of each partition structure 608. Thus, as described above, the light extraction efficiency can be increased by configuring the color conversion material 112 to have a lower refractive index than the partition structures 608 and the light extraction material layer 110.

[0064] 8 is a side cross-sectional view of a further light emitting element array 800 in which the cavity walls 108 are configured to include a reflective material, according to various embodiments. The light emitting element array 800 may include a number of micro LEDs 102 formed in a number of cavities bounded by the cavity walls 108. The micro LEDs 102 may be coupled to a substrate 104, which may include electrical circuitry configured to control the micro LEDs 102. Each cavity may include a color conversion material 112.

[0065] Similar to other embodiments described above, the cavity wall 108 may include an angled surface 402 that may improve the reflective properties of the cavity wall 108. Additionally, the cavity wall 108 may include a reflective material. For example, the cavity wall 108 may be covered by a metallic material 802 in some embodiments. In further embodiments, a transparent material 804 may be formed over the metallic material 802, as shown in FIG. 8. The reflective material may increase light extraction efficiency by reflecting photons to the color conversion material 112.

[0066] FIG. 9A is a vertical cross-sectional view of a reflection pattern of photons hitting a reflective cavity wall 108 having a metallic material (i.e., metallic reflector) 802 on its surface. FIG. 9B is a vertical cross-sectional view of a reflection pattern of photons hitting a reflective cavity wall 108 having a transparent material 804 formed on the metallic material (i.e., metallic reflector) 802 in region 9B of FIG. 8 according to various embodiments. The color conversion material 112 may include a plurality of discrete color converters 902 (e.g., quantum dots). Each of the plurality of discrete color converters 902 may emit converted photons in all directions. Some of the emitted photons 904 may hit the metallic material 802 and be reflected back to the color conversion material 112. Other photons 906 may be emitted by the discrete color converters 902 at an angle such that the photons 906 do not hit the metallic material 802 and therefore exit the color conversion material 112 without being reflected.

[0067] Metallic reflectors (e.g., metal material 802) can be used in lighting applications and optical components. Metallic materials 802 are generally quite reflective, with aluminum reflectors having reflectivities of over 85% and silver reflectors having reflectivities of over 90%. However, photons propagating in a material with a relatively high refractive index (e.g., color conversion material 112) may not be easily extracted and may undergo multiple reflections before exiting the material. Because the metal material 802 is not perfectly reflective, photons may be absorbed with each reflection. Thus, the reflectivity decreases exponentially with each reflection. Thus, as shown in FIG. 9A, the effective reflectivity of the metal material 802 covering the cavity wall 108 may be significantly lower than the reflectivity of the metal material 802 in air. As will be described in more detail with reference to FIG. 9B, it is possible to increase the reflectivity by covering the metal material 802 with a transparent material (e.g., DBR, etc.) such that a portion of the incident photons undergo total internal reflection with substantially no loss.

[0068] As shown in FIG. 8 and FIG. 9B, the metal material 802 may be coated with a transparent material 804. The transparent material 804 may be selected to be a low refractive index material, a total internal reflector (TIR), an omnidirectional reflector (ODR), or a DBR. Photons 908 incident at a small angle relative to a direction normal to the cavity wall 108 may be reflected by the metal material 802. Other photons 910 incident at a larger angle may be reflected by the transparent material 804 without interacting with the metal material 802. In this regard, photons 910 incident at angles equal to or greater than the critical angle may undergo total internal reflection from the transparent material 804. Thus, these photons 910 do not undergo the exponential attenuation that they would experience in the absence of the transparent material 804. In this manner, the proportion of reflected photons that experience attenuation due to reflection from the metal material 802 may be reduced. As such, the overall reflectivity of the cavity wall 108 may be increased.

[0069] The efficiency of total internal reflection can be configured to approach 100%. In this way, even if a photon undergoes multiple total internal reflections, the loss (i.e., attenuation) of the photon is negligibly small. The boundary conditions of the electric field associated with the photon dictate that the electric field penetrates to a certain depth within the transparent material 804. Within the transparent material 804, the electric field is an evanescent wave with an amplitude that decreases exponentially with distance from the surface of the transparent material 804. To prevent absorption by the metallic material 802, the transparent material 804 may be selected to have a thickness greater than the penetration depth. For example, in one embodiment, to avoid absorption of the photons, the transparent material 804 may be selected to be about 1 micron or more thick, for example, 1-10 microns thick.

[0070] As discussed above, the transparent material 804 may be formed as a DBR. In this regard, the DBR may be formed as multiple layers having alternating refractive indices. By appropriately selecting the refractive indices of the alternating layers, the DBR may be configured to have a high reflectivity, and when disposed on the metal material 802, may form a reflective structure having a significantly higher reflectivity than a single metal layer alone. In an example embodiment, the DBR may include alternating layers of TiO2 and SiO2. Further, the number of alternating layers and the thickness of each individual layer may be optimized to achieve a high reflectivity at a wavelength corresponding to the central wavelength of the micro LED 102. In this manner, the DBR may be configured to reflect ultraviolet and / or blue light emitted by the micro LED 102. In this manner, the DBR may increase the probability that the reflected photons are converted to longer wavelength photons by the color conversion material 112. A variety of materials, including dielectric materials, polymers, resins, etc., having various refractive indices may be used to construct the transparent material 804.

[0071] In the embodiment shown in Figure 8, the light extraction material layer 110 may be omitted. In another embodiment shown in Figure 10, the light extraction material layer 110 is used in combination with the transparent material 804 described above. Figure 10 is a side cross-sectional view of a further light emitting element array 1000 including both the light extraction material layer 110 and the transparent material 804 disposed on the metal material 802 on the cavity wall 108.

[0072] The foregoing description of the embodiments of the present disclosure is provided to enable any person skilled in the art to make or use the disclosed embodiments. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments without departing from the spirit or scope of the present disclosure. Thus, the present disclosure is not intended to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the following claims and the principles and novel features disclosed herein.

Claims

1. A light-emitting element, a light emitting diode configured to emit incident photons of blue or ultraviolet radiation; a color conversion material disposed on the light emitting diode and configured to absorb the incident photons emitted by the light emitting diode and generate converted photons having a peak wavelength longer than the peak wavelength of the incident photons; at least one light extraction feature disposed between the light emitting diode and the color conversion material; A light-emitting element comprising:

2. an optical cavity bounded by cavity walls, the light emitting diode being disposed within the optical cavity; The light-emitting device according to claim 1 .

3. the at least one light extraction feature comprises a first light extraction material layer disposed within the optical cavity between the light emitting diode and the color conversion material. The light-emitting device according to claim 2 .

4. the light emitting diode includes a Group III nitride active region; the first light extraction material layer has a first refractive index in the range of 1.5 to 2.5; The light-emitting device according to claim 3 .

5. the first light extraction material layer comprises a light extraction feature including a rough interface between the first light extraction material layer and the color conversion material; The light-emitting device according to claim 3 or 4.

6. the first light extraction material layer comprises a light extraction mechanism including a periodic array of nanoscale features including nanoscale photonic crystals that couple an optical mode of the first light extraction material layer with an optical mode of the color conversion material. The light-emitting device according to claim 3 or 4.

7. further comprising a second light extraction material layer disposed over the first light extraction material layer and including a corrugated height profile. The light-emitting device according to claim 3 or 4.

8. the second light extraction material layer includes a second refractive index different from the first refractive index of the first light extraction material layer; The light-emitting device according to claim 7 .

9. a plurality of partition structures formed on the first light extraction material layer that divide the optical cavity into a plurality of subcells; the color conversion material is formed within the plurality of subcells; The light-emitting device according to claim 3 or 4.

10. Each of the plurality of partition structures includes a tapered shape. The light-emitting device according to claim 9 .

11. the first light extraction material layer includes a plurality of light scattering nanoparticles dispersed in a matrix; The light-emitting device according to claim 3 or 4.

12. The plurality of light-scattering nanoparticles are TiO ２ , ZrO ２ or AlN nanoparticles, the matrix comprises an epoxy or a UV curable polymer; The light-emitting device according to claim 11 .

13. a reflective material formed on the cavity wall; and a transparent material formed on the reflective material. The light-emitting device according to claim 3 or 4.

14. the transparent material is configured to cause total internal reflection of photons incident at an angle greater than a critical angle relative to a direction normal to a surface of the transparent material. The light-emitting device according to claim 13 .

15. the transparent material has a thickness greater than a penetration depth of an evanescent field associated with a reflected photon; the reflective material includes a metallic material formed on the cavity wall; The light-emitting device according to claim 13 .

16. the transparent material comprises a distributed Bragg reflector; The light-emitting device according to claim 13 .

17. A light-emitting element, an optical cavity bounded by cavity walls; a light emitting diode disposed within the optical cavity and configured to emit incident blue or ultraviolet photons; a color conversion material disposed over the light emitting diode and configured to absorb incident photons emitted by the light emitting diode and generate converted photons having a peak wavelength longer than the peak wavelength of the incident photons; a reflective material disposed on the cavity wall; a transparent material disposed over the reflective material; A light-emitting element comprising:

18. the transparent material is configured to cause total internal reflection of photons incident at an angle greater than a critical angle relative to a direction normal to a surface of the transparent material. The light-emitting device according to claim 17 .

19. the transparent material has a thickness greater than a penetration depth of an evanescent field associated with a reflected photon; the reflective material includes a metallic material formed on the cavity wall; The light-emitting device according to claim 17 or 18.

20. the transparent material comprises a distributed Bragg reflector; The light-emitting device according to claim 17 or 18.

Images