Color LED with integrated optical filter element

Abstract

A red LED includes a semiconductor LED layer having an active InGaN layer, the intrinsic emission spectrum of which has an L value in the range of 580 nm to 620 nm. Dom The filter is located above the semiconductor LED layer to filter out shorter wavelengths of the intrinsic emission spectrum and reduce the wavelength of the LED. Dom Shift 5nm to 20nm towards longer wavelengths.

Description

Technical Field

[0001] This invention generally relates to the manufacture of LEDs with integrated color filter elements. By directly forming passive optical filter elements into the LED structure, the performance characteristics of broadband color LEDs can be improved, and this LED structure can be formed as part of a micro-LED array or display system. Background Technology

[0002] Semiconductor light-emitting devices (LEDs) with a wide range of optical emission characteristics can be fabricated. For example, InGaN-based LEDs can emit light of any color in the visible spectrum, making them attractive for display applications. However, InGaN-based LEDs are characterized by some unique properties, including a tendency for the centroid wavelength of the emission spectrum (Lc) to shift to shorter wavelengths as the operating current density increases. This property is partly due to the shielding of the internal electric field by injected carriers. A second property is the tendency for the full width at half maximum (FWHM) of the spectrum to broaden, especially over a longer Lc range. For the InGaN spectrum in the red light range, the FWHM can be as broad as 50-70 nm. It should be noted that the FWHM of InGaN red LEDs can be very broad, resulting in a considerable portion of the output power being emitted in the infrared range. This property is partly due to the increased inhomogeneity of the InGaN quantum well (QW) as the indium concentration increases.

[0003] These characteristics of the InGaN spectrum are significant. The shift in Lc with the driving current makes it difficult to control the optical output power and emission color independently. Larger currents are needed to increase output power, but these also lead to color changes. For example, green LEDs emit a bluish-green appearance at higher currents, while red LEDs emit a yellowish appearance. When operating an LED with a fixed current, the broad emission spectrum has additional significance. The human eye is more sensitive to green and yellow light than to blue and red light. This means that a small portion of the spectrum of a red or blue LED extending into the yellow-green range has a disproportionately large impact on the color perceived by the eye (dominant wavelength). Although >90% of the radiative flux emitted by an InGaN LED with an Lc of 625 nm is in the red range, its dominant wavelength (Lc) is much larger. Dom The color is orange because a small "tail" of its spectrum extends to shorter wavelengths. The wide FWHM and shift of Lc with current density has so far hindered the adoption of red InGaN LEDs in many applications.

[0004] Several attempts have been made to provide improved InGaN spectra. For example, U.S. Patent 10,361,341 to Danesh et al. discloses improved InGaN spectra at low current densities (1.2 A / cm²). 2The spectrum of a red InGaN LED measured at [current density value] represents the minimum required operating conditions, given the shift in (Lc) with increasing current density. However, many applications require much higher current densities to achieve the desired flux.

[0005] InGaN LEDs (especially LED displays with high color gamut) require improved structures and components. Such displays may require peak or dominant wavelengths up to 625 nm. Dom In existing technologies, 620nm L Dom Using InGaN at low drive current densities is nearly impossible, and at even higher current densities it is impossible. This limitation hinders the manufacture of displays with high color gamuts, which have all three emitters (e.g., RGB) made of the same InGaN material system. Due to the complexity of integrating LEDs from different material systems into the same display, it is preferable to use InGaN for all three colors rather than using GaAs-based materials or other LED materials for the red pixels in the display. Summary of the Invention

[0006] According to an embodiment of the present invention, the red LED includes a semiconductor LED layer having an active InGaN layer, the intrinsic emission spectrum of which has an L... Dom Within the range of 580nm to 620nm, the filter is located above the semiconductor LED layer to filter out the shorter wavelengths of the intrinsic emission spectrum and reduce the wavelength of the LED. Dom Shift 5nm to 20nm towards longer wavelengths.

[0007] In another embodiment, the blue LED includes a semiconductor LED layer with an active InGaN layer that emits an intrinsic spectrum with a dominant wavelength greater than 470 nm and a color saturation of less than 93%. A filter is located above the semiconductor LED layer to filter out the longer wavelengths of the emitted intrinsic spectrum and increase the color saturation by at least 3 percentage points.

[0008] In another embodiment, the infrared LED includes a semiconductor LED layer having an active InGaN layer that emits an intrinsic spectrum with a centroid WL in the range of 640 nm to 740 nm. A filter is located above the semiconductor LED layer to filter out the shorter wavelength portions of the emitted intrinsic spectrum and increase the centroid WL by 10 nm to 100 nm.

[0009] In another embodiment, the green LED includes a semiconductor LED layer having an active InGaN layer that emits an intrinsic spectrum with a dominant wavelength less than 535 nm and a color saturation of less than 90%. A filter is located above the semiconductor LED layer to filter out the shorter wavelengths of the emitted intrinsic spectrum and increase the color saturation by at least 3 percentage points.

[0010] In some embodiments, the filter may be located above the semiconductor layer and may be directly integrated, contact positioned, or located on an intermediate transparent layer relative to the semiconductor LED layer.

[0011] In some embodiments, a transparent conductive layer is attached to a semiconductor LED layer, and a filter is attached to the transparent conductive layer.

[0012] In some embodiments, a transparent sapphire layer is attached to a semiconductor LED layer on a first side, and a filter is attached to the transparent sapphire layer on a second side.

[0013] In some embodiments, the filter includes an absorbing material.

[0014] In some embodiments, the filter includes a II-VI semiconductor.

[0015] In some embodiments, the filter comprises at least one metallic material.

[0016] In some embodiments, the filter includes a wavelength-selective mirror.

[0017] In some embodiments, the LED is a microLED.

[0018] In some embodiments, LEDs form part of an RGB display. Attached Figure Description

[0019] Non-limiting and non-exhaustive embodiments of this disclosure are described with reference to the following figures, wherein similar reference numerals throughout the figures refer to similar parts unless otherwise stated.

[0020] Figure 1 A filter not shown to scale, which is directly integrated with a semiconductor layer including an active light-emitting region;

[0021] Figure 2A The image is not to scale and is intended to show a filter formed on a transparent conductive layer that is formed on a semiconductor layer including an active light-emitting region.

[0022] Figure 2B The image is not to scale and is intended to show a filter formed on a transparent substrate, which is on a semiconductor layer including an active light-emitting region.

[0023] Figure 3AThe graph shows the optical reflectivity versus wavelength for a selected metal.

[0024] Figure 3B The graphs showing the electroluminescence (EL) intensity versus wavelength of LEDs with unfiltered ITO / Ag electrodes and filtered ITO / Cu electrodes are presented.

[0025] Figure 4A The transmission characteristics from sapphire through an interference filter to air are shown. This interference filter has multiple TiO2 and SiO2 layers to suppress the shorter wavelength emission of an InGaN red LED.

[0026] Figure 4B Unfiltered LED and its use are shown. Figure 4A A graph showing the EL intensity versus wavelength of the LED in the intermediate filter;

[0027] Figure 5A The transmission characteristics from sapphire through an interference filter to air are shown. This interference filter has multiple SiN atoms. x And a SiO2 layer to suppress the shorter wavelength emission of InGaN red LEDs;

[0028] Figure 5B Unfiltered LED and its use are shown. Figure 5A A graph showing the EL intensity versus wavelength of the LED in the intermediate filter;

[0029] Figure 6A The transmission characteristics of a filter with an integrated LED semiconductor layer are shown.

[0030] Figure 6B Unfiltered LED and its use are shown. Figure 6A A graph showing the EL intensity versus wavelength of the LED in the intermediate filter;

[0031] Figure 7A The reflective properties of a composite mirror (ITO / dielectric stack / Ag) are shown, which is designed to filter out the longer portion of the blue LED emission.

[0032] Figure 7B Unfiltered LED and its use are shown. Figure 7A A graph showing the EL intensity versus wavelength of the LED in the intermediate filter;

[0033] Figure 8A The transmission characteristics from sapphire through an interference filter to air are shown. This interference filter has multiple SiN atoms. x A SiO2 layer is used to suppress the longer wavelength emission of the InGaN blue LED;

[0034] Figure 8B Unfiltered LED and its use are shown. Figure 8A A graph showing the EL intensity versus wavelength of the LED in the intermediate filter;

[0035] Figure 9A The transmission characteristics of sapphire to air are shown in a filter coating that transmits the infrared portion of the emission spectrum of an InGaN LED and blocks the visible portion of the emission spectrum of an InGaN LED.

[0036] Figure 9B Unfiltered LED and its use are shown. Figure 9A A graph showing the EL intensity versus wavelength of the LED in the intermediate filter;

[0037] Figure 10A The transmission characteristics of sapphire to air are shown for a filter coating that transmits the green portion of the InGaN LED emission spectrum and blocks the blue portion; and

[0038] Figure 10B Unfiltered LED and its use are shown. Figure 10A A graph showing the EL intensity versus wavelength of the LED in the middle filter. Detailed Implementation

[0039] Figure 1 This is a non-scale illustration of a filter located above a semiconductor layer including the active light-emitting region. In some embodiments, the filter may be an absorption filter, while in other embodiments, a mirror filter may be used. Figure 1 As shown, LED 100 includes a substrate 110 supporting a semiconductor LED layer 120 and a filter 130 formed to contact the semiconductor LED layer 120 to block light of a selected wavelength. At least some of the light emitted from the semiconductor layer 120 must pass through the filter 130. The filter 130 may be directly integrated with the semiconductor layer 120 (as shown), formed to contact the semiconductor layer; or it may be located on one or more intermediate transparent layers.

[0040] The substrate 110 can be formed of patterned or unpatterned sapphire, silicon, or silicon carbide, capable of supporting the epitaxially grown or deposited semiconductor LED layer 120. In one embodiment, the semiconductor p-layer can be sequentially grown or deposited on the n-layer, forming an active region at the junction between the layers. Semiconductor materials capable of forming high-brightness light-emitting devices can include, but are not limited to, group III-V semiconductors, particularly binary, ternary, and quaternary alloys of gallium, aluminum, indium, and nitrogen (also known as group III nitride materials). In one embodiment, an n-type GaN layer, a red-emitting InGaN QW active region, and a p-type GaN layer can be grown.

[0041] After the epitaxial growth of the semiconductor LED layer 120, conventional wafer fabrication processes for manufacturing flip-chip (TFFC) LED products can be used. After dicing the photoelectrochemical surface texture of the substrate 110 to form a tile comprising one or more LEDs, the tile can be cleaned and then loaded into an RF sputtering deposition cavity. In one embodiment, the filter 130 absorbing the desired wavelength may include a CdSe composition approximately equal to... 0.4 S 0.6 The polycrystalline II-VI semiconductor alloy can be used, and an 800 nm thick layer can be deposited on the tile using an alloy target to conformally coat the textured GaN light-emitting surface. Typically, the absorption filter coating has a transmittance of more than 60% for light wavelengths greater than 610 nm and a transmittance close to zero for light wavelengths less than 600 nm.

[0042] Various light-absorbing materials from group II-VI semiconductors can also be used. Typically, such light-absorbing materials have a direct band gap that provides high absorption and a sharp cutoff wavelength in the spectral range between green and near-infrared. For example, alternative compositions may include those with a similar structure to CdSe. 0.4 S 0.6 Cd with similar optical properties 0.2 Zn 0.8 The thickness of coatings for group II-VI semiconductors can range from a useful range of 200-2000 nm. The optimal thickness depends on both the material chosen and the deposition conditions. These coatings can be fabricated using physical vapor deposition techniques such as sputtering, thermal evaporation, or electron beam evaporation. Some materials can also be deposited from a wet chemical bath, although bath methods may not allow for precise control of composition and optical properties. Small (< 0.1%) concentrations of impurities (e.g., Cr or Fe) can be added to increase the resistivity of group II-VI materials and prevent short circuits in the semiconductor LED layer.

[0043] In some embodiments, metallic reflective compositions can be used as an alternative to using absorptive group II-VI semiconductor filters. While Cu is particularly well-suited for preferentially reflecting the longer wavelengths of the emission spectrum of InGaN red LEDs, any metal with a property of decreasing reflectivity as wavelengths shorter than red can be used. Some alternatives include Au, Au-Cu alloys, and conductive metal nitride compounds (e.g., TiN, HfN, ZrN, CrN, and / or mixtures thereof). In one example, Cu can be deposited directly on p-GaN, or it can be deposited after a 2-10 nm thick Ni layer is deposited on p-GaN, as Cu directly on p-GaN has less than ideal electrical properties. The Ni layer can be annealed in a separate process step prior to Cu deposition.

[0044] In another embodiment, a reflective filtering element (i.e., a wavelength-selective mirror filter) can be integrated at the end of chip or tile fabrication. Following epitaxial growth, the wafer fabrication processes used in conventional chip-scale packaged LED products can support a high-reflectivity thin-film side coating deposited via atomic layer deposition (ALD). In this embodiment, prior to the die attachment step, ALD is used to uniformly and conformally deposit a dielectric mirror on the outer side of the chip, which serves as the light-emitting surface. The material used for the mirror is a combination of six layers of TiO2 (high refractive index) and five layers of SiO2 (low refractive index) deposited in an alternating sequence. The optical interference generated by the corresponding thickness values ​​of 50 nm and 80 nm is useful for filtering the emission of InGaN red LEDs.

[0045] In some applications, only one emitting surface of the LED (instead of five surfaces) needs to filter the emitted light. Some applications may use LED arrays so tightly packed together that light escaping from the sidewalls is blocked by adjacent LEDs. Dielectric mirrors can be deposited using any of a variety of physical or chemical vapor deposition techniques, including plasma-assisted deposition, and materials from a wide range of dielectric oxides and nitrides can be used. As another example, a mirror design effective for filtering InGaN red LEDs consists of 11 layers of SiN. x It consists of 10 layers of SiO2 with thicknesses of 70 nm and 93 nm, respectively. By simply adjusting the thickness of the dielectric layer, this dielectric mirror coating can also be used to suppress the long-wavelength portion of blue LED emission. The transmission characteristics of the coating used to filter blue light involve using 5 layers of SiN... x It consists of four layers of SiO2 with thicknesses of 73 nm and 97 nm, respectively. Advantageously, the reflective filter exhibits low optical loss for light within the desired wavelength range. Light of the desired wavelength that is not absorbed by the reflective filter undergoes another transformation to escape from the die.

[0046] In another embodiment, the reflective filtering element (i.e., a wavelength-selective mirror filter) can be integrated within the semiconductor LED layer 120. In this embodiment, the filter 130 includes a coalescing layer that provides a two-dimensional surface for the growth of the epitaxial reflective layer. Forty Al layers with thicknesses of 70 nm and 65 nm are grown on the coalescing layer. 0.84 In 0.16 Alternating sequences of N and GaN. Advantageously, Al... 0.84 In 0.16 Nitrogen (N) has a low refractive index, is n-type conductive and approximately lattice-matched to GaN, and is thermally stable relative to the growth of subsequent epitaxial layers required to complete the LED structure. 0.84 In 0.16The reflectivity characteristics of N / GaN dielectric mirrors are suitable for suppressing the short-wavelength portion of emission from red InGaN LEDs. Note that although Al... 0.84 In 0.16 The N and GaN compositions have particularly favorable lattice matching and reflection properties, but mirror-based filters can be made from Al with different refractive indices. x In y Ga 1-x-y N and Al a In b Ga 1-a-b Any layer pair of components selected from N is made.

[0047] Using Al integrated into the epitaxial layer 0.84 In 0.16 The advantage of N / GaN filter mirrors (as discussed above) is that, in terms of die manufacturing, the epitaxial wafer is an "insertion replacement" that does not require additional post-epitaxy manufacturing process steps.

[0048] In some embodiments, applying post-growth techniques to increase the refractive index contrast between GaN and other epitaxial layers can be used to produce mirrors with narrower stopbands and better angular characteristics. For example, this can be achieved by etching Al onto an LED mesa. 0.84 In 0.16 This is achieved by selectively photoelectrochemically oxidizing the layers after the edges of the N-layer (or other Al-containing layers). For process conditions that keep GaN and InGaN constant, Al... 0.84 In 0.16 N (and other Al-containing layers) can be oxidized to Al2O3 with a low refractive index.

[0049] In other embodiments, the layer sequence grown for the mirror may include a highly n-type doped GaN layer and a lightly n-type doped GaN layer. After etching the edges of the buried layer to expose the LED mesa, post-growth electrochemical processing can preferentially introduce high porosity into the highly n-type doped layer. Because porous layers have a much lower refractive index than non-porous layers, Al layers grown as discussed above can be grown. 0.84 In 0.16 N / GaN mirrors exhibit better reflective properties. Advantageously, the porous GaN layer can also be n-type conductive, unlike oxidized Al layers discussed earlier. 0.84 In 0.16 N layers. The conductivity of the mirror filter can optionally be provided in vertically injected LEDs, but is not necessary for LEDs using lateral current injection.

[0050] Figure 2AThe image shows a filter located above a semiconductor layer including the active light-emitting region, but in this embodiment, it directly contacts the intermediate transparent conductive layer that acts as the anode of the underlying semiconductor layer. In some embodiments, the filter may be an absorptive filter, while in other embodiments, a mirror filter may be used. Figure 2A As shown, LED 200 includes a substrate 210 supporting a semiconductor LED layer 220 and a transparent conductive layer 240. A filter 230 is formed in contact with the transparent conductive layer 240 to suppress light of a selected wavelength. As will be understood, the substrate and the semiconductor LED layer may include, for example, [details about the substrate and the semiconductor LED layer]. Figure 1 Examples discussed.

[0051] Figure 2B This is a non-scale illustration of a filter located on an intermediate transparent substrate layer above a lower semiconductor layer, which includes an active light-emitting region. Similar to... Figure 2A In one embodiment, the filter can be an absorptive filter, while in other embodiments, a reflective filter can be used. For example... Figure 2B As shown, LED 200B includes a substrate 210B, which may be formed of transparent sapphire or other suitable material supporting the growth of semiconductor LED layer 220B. A filter 230B is formed in contact with the substrate 210B to suppress light of a selected wavelength. The substrate 210B is located between the filter 230B and the semiconductor LED layer 220B (i.e., the filter is attached to a first side, and the semiconductor LED layer is on the opposite second side). As will be understood, the substrate and the semiconductor LED layer may include, for example, [details about the substrate and semiconductor LED layer]. Figure 1 Examples discussed.

[0052] In one embodiment, after the epitaxial growth of the semiconductor LED layer 220, conventional wafer fabrication processes for manufacturing flip-chip (TFFC) LED products can be used. An anode contact can be formed with the semiconductor LED layer 220. In one embodiment, a bilayer of indium tin oxide (ITO) and Cu can be formed, where ITO acts as a transparent conductor and Cu acts as a reflective filter. The ITO and Cu layers can be deposited using physical vapor deposition techniques such as electron beam evaporation, thermal evaporation, or sputtering. To improve their properties, the ITO layer can be annealed in a separate step prior to Cu deposition. The ITO thickness is typically in the range of 5-50 nm, and the Cu thickness is in the range of 100-500 nm, with the most preferred values ​​being about 20 nm and about 200 nm, respectively. In some embodiments, a very thin (1-5 nm) layer of another metal (e.g., Al, Ni, Ti, or Cr) can be deposited on top of the ITO before Cu to improve its adhesion to the ITO.

[0053] While implementations using ITO offer optimal electrical and optical properties, in some embodiments, ITO may be replaced by transparent conductive oxides—such as ZnO, indium zinc oxide (IZO), conductive graphene, or other compositions capable of forming ohmic electrical contacts with p-GaN.

[0054] In another embodiment, a reflective filtering element (i.e., a mirror filter) can be deposited on the anode contacts provided by transparent conductive ITO or other layers. For example, a dielectric mirror can be deposited on ITO, and an array of vias is etched through the dielectric mirror to allow contact with the ITO. Ag metal can be deposited on the dielectric mirror with vias, enabling electrical contact between Ag and ITO. The dielectric mirror in this example can be designed to have poor reflectivity for the wavelengths to be suppressed and high reflectivity for the wavelengths to be retained. The first layer of the mirror can be a thick (500 nm) SiO2 layer, followed by five alternating TiO2 layers and four SiO2 layers (with thicknesses of 40 nm and 68 nm, respectively). Advantageously, this type of composite mirror has 1) filtering capabilities that are not limited by the properties of the available metals, and 2) optical losses in the wavelength range to be retained can be very low.

[0055] In another embodiment, the composite mirror can be made of a metal coating on top of alternating stacks of ITO layers with different physical densities (and therefore different refractive indices). The ITO layers with different porosity densities can be deposited using, for example, a deposition cavity having two ITO evaporation sources positioned at different angles relative to the substrate wafer. An advantage of this approach is that the mirror is composed entirely of conductive material and does not require patterned vias, thus simplifying the process.

[0056] The aforementioned structures and processes can be used to provide filtering over a selected bandwidth and possess a variety of performance characteristics depending on the specific choices of materials, layer thickness, number of layers, and layer order. Generally, red and green LEDs benefit from filters that block shorter wavelengths, while blue LEDs benefit from filters that block longer wavelengths. In practice, red LEDs benefit by shifting the dominant wavelength to a desired longer wavelength setpoint. Even considering the red light loss in the filter, this approach yields a higher external quantum efficiency (EQE) than it could be achieved by designing LEDs to emit true red light. DomThis eliminates the need for filters. Instead, broadband direct-light blue LEDs benefit from maximized brightness of the longer wavelengths while maintaining acceptable color saturation, as the portion of the spectrum “tailing” into the green range is blocked. Green LEDs, on the other hand, can benefit from increased color saturation due to the filtering out of the shorter wavelengths of their spectrum, particularly in applications where high color saturation is desired across a wide range of operating currents. While the discussion focuses on visible LEDs, it should be noted that long-pass filters can be applied to InGaN red LEDs, effectively converting them into infrared LEDs. See below. Figures 3A to 8B The text shows some selected examples of red and blue filtering using various types of absorptive and reflective filters.

[0057] Figure 3A The graph shows the optical reflectivity of the selected metals as a function of wavelength. As is clear from the graph, among these elements, Cu is particularly well-suited for enhancing the reflection of red light relative to shorter wavelengths.

[0058] Figure 3B The graphs showing the electroluminescence (EL) intensity versus wavelength of LEDs with unfiltered ITO / Ag electrodes and filtered ITO / Cu electrodes are presented.

[0059] Figure 4A To illustrate the transmission characteristics from sapphire through an interference filter to air, a graph is shown. This interference filter has multiple TiO2 and SiO2 layers to suppress shorter wavelength emission from an InGaN red LED. The graph shows the filter cutoff shifting to shorter wavelengths as the incident angle increases from 0 degrees to 15 degrees, and then to 25 degrees. As will be understood, the filter performance is only related to angles less than the critical angle for total internal reflection.

[0060] Figure 4B Unfiltered LED and its use are shown. Figure 4A A graph showing the EL intensity versus wavelength of the LED in the middle filter.

[0061] Figure 5A To illustrate the transmission characteristics from sapphire through an interference filter to air, the interference filter has multiple SiN... x A SiO2 layer is used to suppress shorter wavelength emission from InGaN red LEDs. The results show that the filter cutoff shifts to shorter wavelengths as the incident angle increases from 0 degrees to 15 degrees, and then to 25 degrees. Similarly, the filter performance is only related to angles less than the total internal reflection critical angle.

[0062] Figure 5B Unfiltered LED and its use are shown. Figure 5A A graph showing the EL intensity versus wavelength of the LED in the middle filter.

[0063] Figure 6A The graph shows the transmission characteristics of a filter with an integrated LED semiconductor layer. Graph 600 shows that as the incident angle increases from 0 degrees to 15 degrees and then to 25 degrees, the blocked wavelength shifts to shorter wavelengths.

[0064] Figure 6B Unfiltered LED and its use are shown. Figure 6A A graph showing the EL intensity versus wavelength of the LED in the middle filter.

[0065] Figure 7A A graph illustrating the reflectivity of a composite mirror (ITO / dielectric stack / Ag) designed to filter out the longer portion of blue LED emission is shown. Different incident angles (0°, 15°, and 25°) are indicated. The reflectivity near 500 nm decreases sharply over the 0-15° angle range and decreases slightly around 25°.

[0066] Figure 7B Unfiltered LED and its use are shown. Figure 7A A graph showing the EL intensity versus wavelength of the LED in the middle filter.

[0067] Figure 8A To illustrate the transmission characteristics from sapphire through an interference filter to air, the interference filter has multiple SiN... x A SiO2 layer is used to suppress longer wavelength emission from the InGaN blue LED. The results show that as the incident angle increases from 0 degrees to 15 degrees, and then to 25 degrees, the filter cutoff shifts towards shorter wavelengths. Similarly, the filter performance is only related to angles less than the total internal reflection critical angle.

[0068] Figure 8B Unfiltered LED and its use are shown. Figure 8A A graph showing the EL intensity versus wavelength of the LED in the middle filter.

[0069] Figure 9A A graph illustrating the transmission characteristics from sapphire to air of a filter coating that transmits the infrared portion of the InGaN LED emission spectrum and blocks the visible portion. The filter coating on the sapphire may include 95 nm SiN... x Nine layers of SiO2 and SiN, with thicknesses of 126 nm and 95 nm respectively. xAlternating layers, and a final SiO2 layer with a thickness of 175 nm. In fact, for LEDs with an intrinsic emission spectrum where the centroid WL is in the 640-740 nm range, the centroid WL can be increased by 10-100 nm by filtering out the shorter wavelength portion of the emission spectrum. It is shown that as the incident angle increases from 0 degrees to 15 degrees, and then to 25 degrees, the filter cutoff shifts to shorter wavelengths. Similarly, the filter performance is only related to angles less than the critical angle for total internal reflection.

[0070] Figure 9B Unfiltered LED and its use are shown. Figure 9A A graph showing the EL intensity versus wavelength of the LED in the middle filter.

[0071] Figure 10A A graph illustrating the transmission characteristics from sapphire to air of a filter coating that transmits the green portion of the InGaN LED emission spectrum and blocks the blue portion. The filter coating on the sapphire may include 60 nm SiN... x The layers consist of eight SiO2 and SiN layers with thicknesses of 82 nm and 60 nm, respectively. x Alternating layers, and a final SiO2 layer with a thickness of 115 nm. In fact, by using this filter or located in an L... Dom Other suitable filters applied above LEDs with inherent emission spectra less than 535 nm and color saturation less than 90% can filter out the shorter wavelength portions of the spectrum, increasing color saturation by at least 3 percentage points. This is illustrated as the filter cutoff shifts towards shorter wavelengths when the incident angle increases from 0 degrees to 15 degrees, and then to 25 degrees. Similarly, the filter performance is only related to angles less than the critical angle for total internal reflection.

[0072] Figure 10B Unfiltered LED and its use are shown. Figure 10A A graph showing the EL intensity versus wavelength of the LED in the middle filter.

[0073] As will be understood, although the examples described are for TFFC LEDs, the structures and methods are not limited to TFFC LEDs. Optically absorbing or mirror-based bandpass filters can be coated on any outer surface of the light-emitting LED. This structure and method are applicable to microLED arrays, microLED displays, RGB displays, or larger LEDs suitable for general lighting, flash lighting, or automotive lighting.

[0074] In some embodiments, the encapsulated LED or microLED may have sidewalls or a surrounding area surrounded by a reflective or absorbent material. Reflective metal or dielectric mirrors, along with the reflective or absorbent materials, may be used. Such materials may include organic, inorganic, or organic / inorganic binder and filler materials. For example, organic / inorganic binders and fillers may be, for instance, silicone resins with embedded reflective titanium dioxide (TiO2) or other reflective / scattering particles. Inorganic binders may include sol-gels (e.g., sol-gels of TEOS or MTMS) or liquid glasses (e.g., sodium silicate or potassium silicate) (also known as water glass). In some embodiments, the binder may include fillers with modifiable physical properties. Fillers may include inorganic nanoparticles, silica, glass particles or fibers, or other materials capable of improving optical or thermal properties.

[0075] The LED can be packaged and optionally includes a connecting submount or printed circuit board for powering and controlling the light generation by the semiconductor LED. In some embodiments, the printed circuit board may also include vias, heat sinks, ground planes, electrical traces, and flip-chip or other mounting systems. The submount or printed circuit board can be formed of any suitable material, such as ceramic, silicon, aluminum, etc. If the submount material is conductive, an insulating layer is formed on the substrate material, and a pattern of metal electrodes is formed on the insulating layer. The submount acts as a mechanical support, provides an electrical interface between the electrodes and the power supply on the LED, and provides heat dissipation.

[0076] In other embodiments, primary or secondary optics may be attached to or positioned near the packaged LED. Optical components may include concave or convex lenses, microlens arrays, graded-index lenses, reflectors, scattering elements, beam equalizers, diffusers, or other light-focusing or blurring optics. Protective layers, transparent layers, thermal layers, or other encapsulation structures may be used as required by the specific application.

[0077] The systems and methods discussed herein for providing absorptive or reflective filters are particularly well-suited for microLED displays. A variety of emerging display applications—including wearable devices, head-mounted displays, and large-area displays—require miniaturized chips composed of high-density arrays of microLEDs (µLEDs or uLEDs) with lateral dimensions as low as less than 100µm × 100µm. MicroLEDs (uLEDs) typically have dimensions of about 50µm in diameter or width and are used to fabricate color displays by closely aligning microLEDs with wavelengths including red, blue, and green.

[0078] Beyond displays, microLEDs and conventional LEDs with filtering elements can be used to support a variety of beam manipulations or other applications that benefit from fine-grained intensity, spatial, and temporal control of light distribution. This can include, but is not limited to, precise spatial patterning of emitted light from pixel blocks or individual pixels. Depending on the application, the emitted light can be spectrally distinct, time-adaptive, and / or environmentally responsive. Arrays of emitting pixels can provide pre-programmed light distributions with various intensity, spatial, or temporal patterns. Associated optics can be distinct at the pixel, pixel block, or device level. Example microLED pixel arrays may include a central block with shared control of high-intensity pixels having associated common optics, while edge pixels may have individual optics. Common applications supported by emitting pixel arrays, besides flashlights, include video lighting, automotive headlights, architectural and area lighting, and street lighting.

[0079] For example, luminescent pixel arrays can be used to selectively and adaptively illuminate buildings or areas to improve visual displays or reduce lighting costs. Additionally, luminescent pixel arrays can be used to project media facades for decorative motion or video effects. Combined with tracking sensors and / or cameras, selectively illuminating areas around pedestrians is possible. Pixels with distinctly different spectra can be used to adjust the color temperature of the lighting, as well as to support horticultural lighting at specific wavelengths.

[0080] Street lighting is a significant application that can greatly benefit from the use of luminescent pixel arrays. A single type of luminescent array can be used to simulate various streetlight types, allowing switching between Type I linear streetlights and Type IV semi-circular streetlights, for example, by appropriately activating or deactivating selected pixels. Furthermore, street lighting costs can be reduced by adjusting beam intensity or distribution based on environmental conditions, the presence or absence of pedestrians identified by facial recognition, or usage time. For example, when no pedestrians are present, light intensity and distribution area can be reduced. If the pixels in the luminescent pixel array are spectrally distinct, the color temperature of the light can be adjusted according to corresponding daytime, dusk, or nighttime conditions.

[0081] Vehicle headlights are another application of light-emitting arrays that require precise light color control, a large number of pixels, and high data refresh rates. Motor vehicle headlights that actively illuminate only selected portions of the road can be used to reduce problems associated with glare or blindness to oncoming drivers. Using an infrared camera as a sensor, the light-emitting pixel array activates only those pixels needed to illuminate the road, while deactivating pixels that could glare pedestrians or drivers of oncoming vehicles. In some embodiments, pedestrians, animals, or signs outside the road can be selectively illuminated to improve driver environmental awareness. If the pixels in the light-emitting pixel array are spectrally distinct, the color temperature of the light can be adjusted according to the corresponding daytime, dusk, or nighttime conditions. Example

[0082] Various embodiments are listed below. It will be understood that, within the scope of the invention, the embodiments listed below can be combined with all aspects and other embodiments.

[0083] Example (a). A red LED includes: a semiconductor LED layer having an active InGaN layer, the intrinsic emission spectrum of which has an L value between 580 nm and 620 nm. Dom ; and a filter located above the semiconductor LED layer, used to filter shorter wavelengths of the intrinsic emission spectrum and to reduce the L Dom Shift 5nm to 20nm towards longer wavelengths.

[0084] Example (b). The LED according to Example (a) wherein the filter is located above the semiconductor layer and is directly integrated, contact positioned, or located on an intermediate transparent layer relative to the semiconductor LED layer.

[0085] Example (c). The LED according to Examples (a) to (b) further includes a transparent conductive layer attached to the semiconductor LED layer, wherein a filter is attached to the transparent conductive layer.

[0086] Example (d). The LED according to Examples (a) to (c) further includes a transparent sapphire layer attached to the semiconductor LED layer on a first side, wherein a filter is attached to the transparent sapphire layer on a second side.

[0087] Example (e). The LED according to Examples (a) to (d) wherein the filter includes an absorbing material.

[0088] Example (f). The LED according to Examples (a) to (e), wherein the filter comprises a group II-VI semiconductor.

[0089] Example (g). The LED according to Examples (a) to (f) wherein the filter comprises at least one metallic material.

[0090] Example (h). The LED according to Examples (a) to (g) wherein the filter includes a wavelength selective reflector.

[0091] Example (i). The LED according to Examples (a) to (h), wherein the LED is a micro LED.

[0092] Example (j). The LED according to Examples (a) to (i), wherein the LED forms part of an RGB display.

[0093] Example (k). A blue LED includes: a semiconductor LED layer having an active InGaN layer that emits an intrinsic spectrum with a dominant wavelength greater than 470 nm and a color saturation of less than 93%; and a filter located above the semiconductor LED layer for filtering out longer wavelengths of the emitted intrinsic spectrum and increasing the color saturation by at least 3 percentage points.

[0094] Example (l). The LED according to Example (k) wherein the filter is located above the semiconductor layer and is directly integrated, contact positioned, or located on an intermediate transparent layer relative to the semiconductor LED layer.

[0095] Example (m). The LED according to Examples (k) to (l) further includes a transparent conductive layer attached to the semiconductor LED layer, wherein a filter is attached to the transparent conductive layer.

[0096] Example (n). The LED according to Examples (k) to (m) further includes a transparent sapphire layer attached to the semiconductor LED layer on a first side, and wherein a filter is attached to the transparent sapphire layer on a second side.

[0097] Example (o). The LED according to Examples (k) to (n), wherein the filter includes an absorbing material.

[0098] Example (p). The LED according to Examples (k) to (o) wherein the filter comprises a group II-VI semiconductor.

[0099] Example (q). The LED according to Examples (k) to (p) wherein the filter comprises at least one metallic material.

[0100] Example (r). The LED according to Examples (k) to (q) wherein the filter includes a wavelength selective reflector.

[0101] Example (s). The LED according to Examples (k) to (r), wherein the LED is a micro LED.

[0102] Example (t). The LED according to Examples (k) to (s), wherein the LED forms part of an RGB display.

[0103] Example (u). An infrared LED includes: a semiconductor LED layer having an active InGaN layer that emits an intrinsic spectrum with a centroid WL in the range of 640-740 nm; and a filter located above the semiconductor LED layer for filtering out the shorter wavelength portion of the emitted intrinsic spectrum and increasing the centroid WL by 10-100 nm.

[0104] Example (v). The LED according to Example (u) wherein the filter is located above the semiconductor layer and is directly integrated, contact positioned, or located on an intermediate transparent layer relative to the semiconductor LED layer.

[0105] Example (w). The LED according to Examples (u) to (v) further includes a transparent conductive layer attached to the semiconductor LED layer, wherein a filter is attached to the transparent conductive layer.

[0106] Example (x). The LED according to Examples (u) to (w) further includes a transparent sapphire layer attached to the semiconductor LED layer on a first side, wherein a filter is attached to the transparent sapphire layer on a second side.

[0107] Example (y). The LED according to Examples (u) to (x) wherein the filter includes an absorbing material.

[0108] Example (z). The LED according to Examples (u) to (y) wherein the filter comprises a group II-VI semiconductor.

[0109] Example (aa). The LED according to Examples (u) to (z) wherein the filter comprises at least one metallic material.

[0110] Example (bb). The LED according to Examples (u) to (aa) wherein the filter includes a wavelength selective reflector.

[0111] Example (cc). The LED according to Examples (u) to (bb), wherein the LED is a micro LED.

[0112] Example (dd). The LED according to Examples (u) to (cc), wherein the LED forms part of an RGB display.

[0113] Example (ee). A green LED includes: a semiconductor LED layer having an active InGaN layer that emits an intrinsic spectrum with a dominant wavelength of less than 535 nm and a color saturation of less than 90%; and a filter located above the semiconductor LED layer for filtering out shorter wavelengths of the emitted intrinsic spectrum and increasing the color saturation by at least 3 percentage points.

[0114] Example (ff). According to Example (ee), the LED is located above the semiconductor layer and is directly integrated, contact positioned, or located on an intermediate transparent layer relative to the semiconductor LED layer.

[0115] Example (gg). The LED according to Examples (ee) to (ff) further includes a transparent conductive layer attached to the semiconductor LED layer, wherein a filter is attached to the transparent conductive layer.

[0116] Example (hh). The LED according to Examples (ee) to (gg) further includes a transparent sapphire layer attached to the semiconductor LED layer on a first side, and wherein a filter is attached to the transparent sapphire layer on a second side.

[0117] Example (ii). The LED according to Examples (ee) to (hh), wherein the filter includes an absorbing material.

[0118] Example (jj). The LED according to Examples (ee) to (ii) wherein the filter comprises a group II-VI semiconductor.

[0119] Example (kk). The LED according to Examples (ee) to (jj) wherein the filter comprises at least one metallic material.

[0120] Example (ll). The LED according to Examples (ee) to (kk) wherein the filter includes a wavelength selective reflector.

[0121] Example (mm). The LED according to Examples (ee) to (ll), wherein the LED is a micro LED.

[0122] Example (nn). An LED according to Example (a), Example (k), Example (u) or Example (ee), wherein the filter is located above the semiconductor layer and is directly integrated, contact positioned, or located on an intermediate transparent layer relative to the semiconductor LED layer.

[0123] Example (oo). The LED according to Example (a), Example (k), Example (u) or Example (ee) further includes a transparent conductive layer attached to the semiconductor LED layer, and wherein a filter is attached to the transparent conductive layer.

[0124] Implementation scheme (pp). The LED according to embodiment (a), embodiment (k), embodiment (u) or embodiment (ee) further includes a transparent sapphire layer attached to the semiconductor LED layer on a first side, and wherein the filter is attached to the transparent sapphire layer on a second side.

[0125] Example (qq). The LED according to Example (a), Example (k), Example (u) or Example (ee), wherein the filter includes an absorbing material.

[0126] Example (rr). An LED according to Example (a), Example (k), Example (u), or Example (ee), wherein the filter comprises a group II-VI semiconductor.

[0127] Example (ss). An LED according to Example (a), Example (k), Example (u), or Example (ee), wherein the filter comprises at least one metallic material.

[0128] Example (tt). An LED according to Example (a), Example (k), Example (u), or Example (ee), wherein the filter includes a wavelength selective reflector.

[0129] Example (uu). An LED according to Example (a), Example (k), Example (u), or Example (ee), wherein the LED is a micro LED.

[0130] Example (vv). An LED according to Example (a), Example (k) or Example (u), wherein the LED forms part of an RGB display.

[0131] The invention has been described in detail, and those skilled in the art will appreciate that, given this disclosure, modifications can be made to the invention without departing from the spirit of the inventive concept described herein. Therefore, it is intended that the scope of the invention is not limited to the specific embodiments illustrated and described.

Claims

1. A red LED, comprising: A semiconductor LED layer having an active InGaN layer, wherein the emission spectrum of the active InGaN layer has a peak wavelength in the range of 580 nm to 620 nm; and A filter located above the semiconductor LED layer, the filter comprising one or more of an absorbing material, a polycrystalline II-VI semiconductor alloy, at least one metallic material, and a wavelength-selective mirror, and configured to filter shorter wavelengths of the emission spectrum of the active InGaN layer and shift the peak wavelength to longer wavelengths by 5 nm to 20 nm. The red LED has a higher external quantum efficiency than the contrasting red LED, which includes a semiconductor LED layer with an active InGaN layer but does not include the filter, and the contrasting red LED directly emits the peak wavelength shifted to the longer wavelength.

2. The red LED of claim 1, wherein the filter is located above the semiconductor layer and is directly integrated, contact positioned, or located on an intermediate transparent layer relative to the semiconductor LED layer.

3. The red LED of claim 1 further includes a transparent conductive layer attached to the semiconductor LED layer, wherein the filter is attached to the transparent conductive layer.

4. The red LED of claim 1, further comprising a transparent sapphire layer attached to the semiconductor LED layer on a first side, wherein the filter is attached to the transparent sapphire layer on a second side.

5. The red LED according to claim 1, wherein the filter is an absorption filter.

6. The red LED according to claim 1, wherein the filter is an absorption filter comprising the polycrystalline II-VI group semiconductor alloy.

7. The red LED according to claim 1, wherein the at least one metallic material comprises a metallic reflective composition.

8. The red LED according to claim 1, wherein the wavelength selective reflector comprises a reflective metal or dielectric reflector.

9. The red LED according to claim 1, wherein the LED is a micro LED.

10. The red LED of claim 1, wherein the LED forms part of an RGB display.

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