Light-emitting element with standing wave generator and associated optoelectronic device

Abstract

The present invention relates to a light-emitting element (10), - a conversion material (14) suitable for converting a first emission in a first spectral band into a second emission in a second spectral band, the second spectral band being distinct from the first spectral band, - a standing wave generator in a first spectral band, comprising a two-dimensional photonic crystal (26) suitable for generating a standing wave in the first spectral band, the photonic crystal (26) being at least partially formed by a light-emitting diode (12) suitable for emitting in the first spectral band, and relates to a light-emitting element (10) comprising the same.

Description

Technical Field

[0001] The present invention relates to a light-emitting element and an optoelectronic device including such a light-emitting element.

Background Art

[0002] In the field of optoelectronics, it is desired to fabricate very small devices. This is particularly true in the case of pixels for color display devices.

[0003] In a color display device, each pixel includes a plurality of sub-pixels, and each sub-pixel is configured to emit a specific color. Thereby, the color emitted from the pixel can be changed by controlling which sub-pixels are activated or by changing the current applied to each sub-pixel to change the relative emission intensity of each sub-pixel.

[0004] Semiconductor structures such as light-emitting diodes (LEDs) are generally used for various purposes such as lighting due to their potentially good light-emitting efficiency. LEDs have been proposed for the manufacture of high-efficiency display devices due to their potentially high efficiency. An LED structure typically takes the form of a stack of flat semiconductor layers. When current flows through the stack, light is emitted.

[0005] Regarding this, a method of growing native pixels containing LEDs made of GaN / InGaN on the same wafer to reduce the size of pixels is known. A native pixel is a pixel whose emission is inherently of a desired color.

[0006] However, such pixels are not efficient because only the blue quantum efficiency of such types of LEDs is satisfactory. In fact, the green quantum efficiency is generally 30%, while for red, the quantum efficiency drops below 5%.

[0007] Therefore, methods are known for using color conversion modules to obtain other colors from blue or UV LEDs. Quantum dots are a common example of the converters used in conversion modules. Quantum dots are often inserted into a matrix.

[0008] However, for pixels of only a few micrometers, the absorption of the quantum dot is too small to guarantee a complete conversion from blue radiation to red or green radiation. As a result, unconverted radiation must be filtered out to obtain a red or green pixel. Such filtering means that a significant amount of radiation is lost from the LED. For example, a 60% loss is observed in a 5μm x 5μm pixel.

[0009] Such losses can be compensated for by increasing the number of quantum dots.

[0010] A first method for increasing the number of quantum dots is to increase the density of quantum dots in the matrix. Such a proposal leads to the fact that excessively high densities result in a loss of the matrix's mechanical properties, making the matrix incompatible with the techniques used in pixel fabrication.

[0011] A second way to increase the number of quantum dots is to increase the size of the matrix, especially its thickness.

[0012] However, in this case as well, such an increase leads to several problems.

[0013] Firstly, manufacturing pixels with extremely large thicknesses is technically difficult.

[0014] A thicker matrix means a longer optical path length for the radiation converted by the quantum dots. As a result of this increase, reabsorption losses become greater.

[0015] Another problem relates to the presence of crosstalk between two pixels. Crosstalk is usually prevented by inserting opaque walls at the edges of the color conversion module. As the thickness of the matrix increases, the height of the walls increases, and therefore the absorption loss in the larger walls increases, and furthermore, it becomes so large that the loss outweighs the absorption gain associated with the increasing number of quantum dots. [Prior art documents] [Patent Documents]

[0016] [Patent Document 1] French Patent Application Publication No. 3068173 [Patent Document 2] U.S. Patent Application Publication No. 2022 / 102324 [Overview of the project] [Problems that the invention aims to solve]

[0017] Therefore, a small-sized light-emitting element is needed to overcome the aforementioned drawbacks. [Means for solving the problem]

[0018] For this purpose, this specification describes a light-emitting element comprising a conversion material suitable for converting a first emission in a first spectral band to a second emission in a second spectral band, wherein the second spectral band is distinct from the first spectral band. The light-emitting element further comprises a standing wave generator in a first spectral band, comprising a two-dimensional photonic crystal suitable for generating standing waves in a first spectral band, wherein the photonic crystal is at least partially formed by light-emitting diodes suitable for emission in a first spectral band.

[0019] In contrast to the prior art, particularly document FR3068173A and US Patent Application No. 2022 / 102324 (A1), the nanowires forming the light-emitting source are part of the photonic crystal and are used to fabricate part of the photonic crystal. More precisely, in this case, the photonic crystal is a combination of a medium and the nanowires.

[0020] In addition, this photonic crystal has a different role because it serves to generate a standing wave that efficiently occurs due to the differences in the previous structure.

[0021] In this way, it is possible to fabricate a light-emitting element, generally a pixel, that is small, has good conversion efficiency, and thus emits a satisfactory amount of light.

[0022] According to other specific embodiments, the light-emitting element has one or more of the following features, which are selected individually or according to all technically possible combinations. - The photonic crystal is formed only by the light-emitting diode and the medium surrounding the light-emitting diode. - The light-emitting diode includes an active layer, and at least one active layer is included in the photonic crystal. This makes it possible to efficiently inject light into the photonic crystal to form a standing wave. - The photonic crystal is partially formed from each active layer of the light-emitting diode. - The photonic crystal includes all of each light-emitting diode. - The light-emitting diode is in a medium, and the medium is a conversion material. The above content is used to miniaturize the light-emitting element. - The conversion material is based on a photonic crystal. This facilitates the fabrication of the light-emitting element according to the above content. - The photonic crystal has a plurality of band gaps, and the photonic crystal has a pitch and a filling factor suitable for causing the light-emitting diode to emit at 90° at the band edge of the first band gap. According to the previous content, the probability of photon absorption within the first spectral band by the conversion material is increased. - The photonic crystal has several band gaps, and the photonic crystal has a pitch and a filling factor suitable for causing the light-emitting diode to emit at 90° at the band edge of a band gap different from the first band gap. In this way, better efficiency of the light-emitting element can be obtained by enhancing the directivity of the converted radiation. - The pitch and filling factor of the photonic crystal are also suitable for causing the conversion material to emit at the band edge of the 0° band gap, and the band gap emitted by the conversion material is smaller than the band gap emitted by the light-emitting diode. According to the previous content, it is possible to achieve more accurate vertical emission of the photonic crystal, resulting in better performance of the light-emitting element. - The photonic crystal is surrounded by walls forming a cavity, and at least one of the walls is made of a material selected from the list consisting of transparent conductive oxides such as indium tin oxide or zinc oxide doped with gallium or aluminum, metals such as Ag or Al, graphene, and combinations of the said elements. In this way, it is possible to obtain walls with good optical properties, and thus improve the efficiency of the photonic crystal. - The conversion material is a polymer matrix comprising quantum dots. According to the previous content, the fabrication of the light-emitting element becomes easier. - Each light-emitting diode includes an active medium made of a first material surrounded by a layer made of a second material, the first material includes InGaN, and the second material includes GaN. In this way, it is possible to obtain good performance of the light-emitting element while maintaining easy fabrication. - The photonic crystal consists of a central and peripheral portion, each portion being a collection of sets of light-emitting diodes, and energy is supplied only to the central portion of the photonic crystal. In this way, energy consumption can be reduced.

[0023] This specification also relates to a light-emitting element comprising a light-emitting diode having an active layer adapted to emit within a certain spectral band, and a two-dimensional photonic crystal formed from at least a medium and the active layer of the light-emitting diode, adapted to generate standing waves within its spectral band.

[0024] To express it more clearly in another way, this specification proposes a light-emitting element comprising a two-dimensional photonic crystal adapted to generate standing waves, wherein the photonic crystal comprises an emission source for the light-emitting element.

[0025] This specification also describes optoelectronic devices comprising at least one of the light-emitting elements described above.

[0026] The features and advantages of the present invention are given merely as examples, but are not limited thereto. They will become clear from reading the following description and referring to the accompanying drawings. [Brief explanation of the drawing]

[0027] [Figure 1] This is a schematic cross-sectional view of an example of a pixel. [Figure 2] Figure 1 is a schematic diagram of a band diagram illustrating an example of how the pixels shown function. [Figure 3] Figure 2 is a schematic diagram of the radiation emitted from a specific element of a pixel within the functional framework shown. [Figure 4] This is a schematic diagram of another example of a pixel. [Figure 5] Figure 1 is a schematic diagram of a band diagram showing another example of how pixels function. [Figure 6]This is a schematic diagram of radiation emitted from a specific element of a pixel within the functional framework of the figure. [Figure 7] This is a schematic top view of another example of a pixel. [Modes for carrying out the invention]

[0028] Hereafter, in order to facilitate understanding, the present invention will be described as follows: firstly, by explaining its general principle through specific examples; secondly, by providing details on how the principle can be easily applied to other examples; and thirdly, by describing improved or alternative embodiments of those examples.

[0029] Furthermore, to simplify the explanation, a "Definitions" section has been inserted at the end, and readers are encouraged to refer to this section for each term introduced thereafter.

[0030] Presentation of specific examples For a specific example, please refer to Figure 1, and it is proposed to consider the case of a red subpixel 10, which will hereafter be simply referred to as red pixel 10 (for simplicity).

[0031] In the case shown in Figure 1, the red radiation from pixel 10 is obtained by converting the blue radiation from nanowire 12 using conversion material 14.

[0032] The nanowire 12 is a light-emitting diode made of a material containing InGaN to form an active layer 16 between layers 18 of GaN, typically nGaN or pGaN. The nanowire 12 emits blue radiation. The emission spectrum 20 from the nanowire 12 can be seen in the band diagram shown in Figure 2.

[0033] The nanowire 12 extends primarily along the longitudinal direction Z. The transverse directions are referred to as the first transverse direction X and the second transverse direction Y, respectively.

[0034] In this example, the conversion material 14 is a matrix comprising quantum dots. Each quantum dot has an absorption spectrum 22 and an emission spectrum 24 as shown in the band diagram of Figure 2.

[0035] A set of nanowires 12 is arranged in the conversion material 14 to form a photonic crystal 26 with pitch a.

[0036] Since such an arrangement of nanowires 12 is two-dimensional, the photonic crystal 26 is a two-dimensional photonic crystal.

[0037] The photonic crystal 26 forms a resonant cavity in a plane formed by two transverse directions, X and Y, which will hereafter be referred to as the transverse plane XY.

[0038] The emission curves 27 of the photonic crystal 26, corresponding to each propagation mode enabled by the photonic crystal 26, are schematically shown on the band diagram in Figure 2. The emission curve 27 is a curve that represents the emitted wavelength as a function of the emission angle.

[0039] The propagation modes of the photonic crystal 26 are separated by band gaps. Figure 2 schematically shows the two band gaps B1 and B2.

[0040] The positions of the two band gaps B1 and B2 are determined by the pitch a of the photonic crystal 26, the diameter of the nanowire 12, the refractive index of the nanowire 12 material and the refractive index of the conversion material 14, and the total thickness of the photonic crystal 26.

[0041] Furthermore, the photonic crystal 26 is surrounded by two walls 28 and 30, namely an upper wall 28 and a lower wall 30, and the two walls 28 and 30 form a cavity along the longitudinal direction Z.

[0042] One of the two walls 28 and 30 is a wall that allows light extraction, while the other wall is a reflective wall.

[0043] To fabricate walls 28 and 30, it is possible to construct a laminate of layers of different materials, which are metals and / or dielectrics. Advantageously, conductive materials such as indium tin oxide (also known as ITO), and metals such as Ag or Al, can be in direct contact with the top and bottom of the nanowires 12 to allow for electrical injection.

[0044] In fact, the photonic crystal 26 has the special property of forming a blue standing wave generator in the transverse XY plane for wavelengths close to the band gap at 90°, as described herein.

[0045] With regard to the term "generator," it should be understood herein that the photonic crystal 26 is a primary source in the sense that standing waves are generated within the photonic crystal 26 itself. More specifically, because the penetration of radiation into the photonic crystal 26 is very small, the radiation emitted onto such a photonic crystal does not enable the generation of standing waves.

[0046] Such peculiarities will be explained in detail next by discussing the physical phenomena involved.

[0047] In a standing wave generator, the Purcell effect increases the rate of spontaneous photon emission from materials within the resonant cavity compared to materials outside the cavity. This means that nanowire 12 emits more photons in the XY cross-sectional plane. Consequently, the selection of angle and wavelength is a result of the Purcell effect.

[0048] In the example described here, the photonic crystal 26 operates at a specific band edge, namely, the band edge of the first resonant band of the nanowire 12 at 90° (corresponding to the wave vector π / a). The band edge corresponds to a wavelength range where the emission curve 27 of the photonic crystal becomes remarkably flattened, typically spanning wavelengths less than 25 nm, preferably less than 10 nm, and preferably even less than 5 nm. Referring to Figure 2, what this means is that the emission occurs on the portion of the first resonant band of the nanowire 12 indicated by the thicker line of the first resonant band.

[0049] More precisely, the emission ultimately produced within the photonic crystal 26 by the nanowire 12 is limited to the intersection of the emission spectrum 20 (primary emission) and the emission curve 27 of the photonic crystal 26, located below the first band gap B1, that is, limited primarily to angular emission at 90° (corresponding to the generation of standing waves), represented by a thicker line portion.

[0050] The result is that the emission of radiation within the photonic crystal 26 is restricted to the XY plane only.

[0051] The photonic crystal 26 is thus suitable for generating standing waves in the blue [range], and the photonic crystal 26 is at least partially formed by nanowires 12 that are suitable for emitting in the blue [range].

[0052] To obtain such behavior in the photonic crystal 26, it is necessary as a prerequisite to adapt the basic unit cell, pitch, and packing density of the photonic crystal.

[0053] The elementary lattice and pitch of the photonic crystal 26 correspond to the arrangement of the nanowires 12, while the packing density is the ratio of the surface area occupied by the nanowires 12 to the total surface area of ​​the photonic crystal 26, and is therefore determined by the size of the nanowires 12, or more precisely, the diameter of the nanowires as used herein.

[0054] To select the appropriate arrangement and diameter of the nanowires 12, simulation techniques can be used to obtain a configuration that is easy to implement experimentally, and then homothety transformations are used.

[0055] For example, the applicant conducted tests using a photonic crystal that emits light at 0.52 μm, has a hexagonal lattice, a 50% packing density, and extends over 1.5 μm. Based on the results, the applicant determined that the band edge is located at a reduced frequency of 0.43. By definition, the reduced frequency is the ratio of pitch a to wavelength.

[0056] In this way, for emission at 450 nm, it is possible to determine that the appropriate pitch a is 193.5 nm.

[0057] Next, numerical simulations can be performed. Thus, the applicant has shown that even though the pixels are only 1.5 μm × 1.5 μm in size, it is possible to obtain 96% absorption with quantum dots containing an encapsulation material with a refractive index of 1.55. In addition, the absorption occurs over a relatively broad band of about 30 nm centered around a converted frequency of 0.43.

[0058] By reconstructing what has just been shown through a simple selection of the arrangement and diameter of the nanowires 12, the blue radiation emitted from the nanowires 12 is forced to move within the XY transverse plane, thereby generating a standing wave in the conversion material 14.

[0059] Therefore, there is no blue radiation in the other direction, and thus the radiation is no longer Lambertian. This is clearly illustrated in Figure 3, which schematically represents the blue radiation emitted from the nanowire under reference number 32.

[0060] As a result, the presence of the photonic crystal 26 significantly increases the length of the optical path through which photons emitted from the nanowire 12 into the conversion material 14 travel, because the photons travel back and forth within the conversion material 14.

[0061] Such an increase in the optical path increases the probability that blue photons will encounter quantum dots, resulting in a significant increase in the absorption of blue radiation by the quantum dots. The absorption of all light emitted from each nanowire 12 becomes almost perfect.

[0062] Within the dotted line in Figure 3, as indicated by reference numeral 36, a red emission exhibiting Lambertian emission is obtained along the longitudinal direction Z.

[0063] More specifically, the design ensures that the thickness of each quantum dot is very small, and therefore the path of converted light in the conversion material 14 is very small. This greatly prevents reabsorption losses.

[0064] This results in a very large increase in absorption by quantum dots, without any increase in reabsorption loss, and especially without any increase in wall height, compared to an increase in the thickness of the conversion material.

[0065] This significantly increases the quantum efficiency of pixel 10 as proposed here.

[0066] Such good quantum efficiency results in less blue photon leakage compared to known conversion modules, which means that the thickness of the blue radiation cutoff filter can be reduced, or if diffusion is negligible, the cutoff filter may no longer be necessary.

[0067] Furthermore, in cases of appropriate quantum efficiency, it may even be possible to attempt to reduce the number of quantum dots in the matrix. Such a reduction would decrease the manufacturing cost of each pixel and the amount of environmentally harmful material used.

[0068] Furthermore, the fabrication of pixel 10 is easier than that of other known pixels, particularly insofar as it requires fewer elements, such as the presence of a blue filter or a high wall to prevent crosstalk.

[0069] In addition, the production process may involve relatively standard techniques that are compatible with the small pixel size of 10.

[0070] Extension of this principle to other examples The present principle, which uses a standing wave generator to improve the conversion of pixel 10, can have many other example versions without modifying the present principle.

[0071] In particular, the information I have just explained remains valid for other wavelengths as well.

[0072] In particular, the red pixel 10 can be a green pixel.

[0073] The radiation emitted from the nanowire 12 can be classified as ultraviolet radiation.

[0074] This principle is also applicable to other conversion materials 14.

[0075] A list of possible materials can be found in the definitions section.

[0076] The materials used to form the nanowires can also be different from the GaN and InGaN pair.

[0077] In particular, it is possible to design semiconductor materials that primarily contain at least one element from Group III and one element from Group V, hereafter referred to as III-V compounds (e.g., gallium nitride GaN), or semiconductor materials that primarily contain at least one element from Group II and one element from Group VI, hereafter referred to as II-VI compounds (e.g., zinc oxide ZnO), or semiconductor materials that primarily contain at least one element from Group IV.

[0078] Methods for fabricating active zones equipped with confinement mechanisms, particularly single or multiple quantum wells, are also known. Single quantum wells are fabricated by inserting a layer of a second semiconductor material, such as an alloy of a III-V compound and a third element, particularly InGaN, whose band gap is different from that of the first semiconductor material, between two layers of a first semiconductor material, such as a III-V compound, particularly GaN, which are p-doped or n-doped, respectively. Multiple quantum well structures comprise a laminate of semiconductor layers that form an alternating arrangement of quantum wells and barrier layers.

[0079] Other materials may also be considered for constructing the upper wall 28 or the lower wall 30.

[0080] Therefore, the upper wall 28 is made of zinc oxide (also known as ZNO) doped with gallium or aluminum.

[0081] More generally, the upper wall 28 is made of a transparent conductive oxide (often abbreviated as TCO).

[0082] However, other materials such as graphene can be taken into consideration.

[0083] The same material can also be used for the bottom wall 30.

[0084] Improved or Alternative Embodiments Next, we propose an improved or alternative embodiment.

[0085] Referring to Figure 4, it is possible to envision a modified form of the red pixel 10 shown in Figure 1, in which the conversion material 14 is positioned on the upper wall 28.

[0086] The above is achieved, in particular, by depositing layers across the entire upper wall. Hereafter, these layers will be referred to as the transformation layer 15.

[0087] In one variant, it is possible to attempt to deposit quantum dots of different colors for adjacent pixels 10. Such deposits can be obtained, for example, using selective lithography or selective etching techniques.

[0088] In that case, the medium 31 surrounding the nanowire is, for example, SiO2.

[0089] In one variant, the medium 31 is TiO2, Al2O3, or Si3N4.

[0090] More generally, the material forming the medium 31 is an oxide or nitride that transmits wavelengths emitted from the nanowires 12 and quantum dots.

[0091] Nevertheless, its function differs from that of the case described in Figure 1.

[0092] In this case, the absorption of the standing wave by the conversion material 14 occurs on only one part, which is the evanescent part PE of the standing wave, and this evanescent part PE excites the quantum dots of the conversion layer 15.

[0093] The evanescent portion PE exists because the standing wave has a specific length (extent) along the direction Z.

[0094] What the above means is that the distance between the quantum dot and the nanowire 12 is small enough that the overlap between the PE portion of the standing wave and the conversion layer 14 is sufficiently large.

[0095] Furthermore, in order to favorably improve the directional emission of quantum dots, the distance between the conversion layer 15 and the lower wall 30 is a multiple of λ / 2n, where λ is the emission wavelength of the quantum dots and n is the effective refractive index of the set formed by the walls 28 and 30 and the photonic crystal 26.

[0096] For example, this distance can be defined in this specification as the distance between the center of the transformation layer 15 and the final layer of the bottom wall 30, and can be obtained by simulation.

[0097] Based on the above, the red emission from quantum dots is improved by increasing the number of photons emitted by the Purcell effect, enhancing the conversion efficiency, and enabling more directional emission from quantum dots.

[0098] Such an embodiment of the red pixel 10 is not as efficient as the embodiment shown in Figure 1, but it allows the conversion layer 15 to be added independently of the generation of blue photons, thereby making the process of depositing this layer easier than incorporating the conversion matrix between nanowires.

[0099] Furthermore, in such cases, one of the final steps in the fabrication process is the deposition of the conversion layer 15, which means that there are fewer technical processes that the quantum dots undergo that could affect their performance or reliability. In addition, to further enhance the reliability of the conversion layer 15, a protective layer, particularly against oxidation, can be deposited on the conversion layer 15. Such a protective layer may be made of, for example, SiO2, TiO2, or Al2O3.

[0100] Referring to Figures 5 and 6, it is also possible to use a resonance of order n for the emission of the nanowire 12. The above corresponds to using the wave vector n*π / a instead of the wave vector π / a.

[0101] In such a situation, as can be seen in the band diagram shown in Figure 5, the wavelength emitted from the quantum dot is position-matched to the band edge at 0° (corresponding to the band gap labeled B2).

[0102] Using such positional alignment, it is possible to obtain an increase in the internal quantum efficiency of the quantum dots (again, the aforementioned Purcell effect), and to obtain much more directional emission from each quantum dot (more focused in direction Z).

[0103] When the emission spectrum 20 of the nanowire 12 is position-matched with the 90° resonance mode (corresponding to the band gap denoted as B3), the preferred emission direction of the nanowire 12 is the transverse plane XY. It is noteworthy that the band gap emitted by the conversion material 14 (band B2 in this specification) is narrower than the band gap emitted by the nanowire 12 (band B3 in this specification).

[0104] In the current case, since the emission spectrum of the quantum dot is position-matched with the 0° resonant mode, the preferred emission direction of the quantum dot is therefore along direction Z. The above corresponds to the existence of two standing waves: the first blue one in the transverse plane XY and the second red one along axis Z.

[0105] The emission pattern of the quantum dot when secondary resonance is used in this way for the emission of nanowire 12 can be seen in Figure 6.

[0106] Therefore, advantageously, the photonic crystal 26 has a pitch a and packing density suitable for causing the nanowire 12 to emit at the band edge of a third band B3, which is different from the first band gap.

[0107] Such embodiments retain the advantages of the embodiment of the red pixel 10 according to Figure 1 by adding to it better directivity of the converted radiation, which contributes to a further increase in the efficiency of the pixel 10 under consideration.

[0108] Figure 7 shows one embodiment of the red pixel 10 that is compatible with all the embodiments presented so far.

[0109] In the above example, the photonic crystal 26 includes a central portion 42 and a peripheral portion 44, where each portion 42 or 44 is an assembly of sets of nanowires 14.

[0110] The central section 42 is powered, and as explained above, the central section 42 emits standing waves.

[0111] The peripheral portion 44 surrounds the central portion 42, and the peripheral portion 44 is not powered. In this case, the nanowires 12 of the peripheral portion 44 act as mirrors for standing waves.

[0112] In the peripheral portion 44, if it is desired to reflect multiple wavelengths, a variable pitch can be considered, for example, a pitch that increases from the edge toward the central zone.

[0113] Based on the above, it is possible to use the system without an external mirror, although it can be combined with other components if desired.

[0114] In summary, we have presented a set of embodiments that utilize the idea of ​​using a standing wave generator formed by a photonic crystal to better excite the conversion material. Where technically possible, such embodiments can be combined together.

[0115] In either case, it is possible to fabricate a small pixel 10 that has good conversion efficiency and therefore emits a satisfactory amount of light.

[0116] The above content can be advantageously applied to many fields of study.

[0117] More specifically, these pixels can be used in optoelectronic devices such as display screens, light projectors, or even glasses used for virtual reality immersion.

[0118] In the case of a display screen, the optoelectronic device can be incorporated into an electronic device such as a mobile phone, tablet, or laptop. In another embodiment, the display screen is incorporated into a dedicated display device such as a television receiver or a desktop computer monitor.

[0119] When the screen is a full-color screen, each pixel contains multiple pixels of different colors. Such pixels can be the pixels described above.

[0120] However, when efficiency is not particularly critical (for example, at the edges of the screen), it is possible to attempt to coexist pixels using conventional techniques.

[0121] definition Blue: Blue radiation has an average wavelength that falls between 430 nm and 470 nm.

[0122] Quantum dots: Quantum dots are structures in which quantum confinement occurs in all three spatial dimensions.

[0123] An example of a quantum dot is a particle P in a conversion material that has a maximum size less than or equal to the product of the electron wavelength of the charge carrier multiplied by 5.

[0124] To give an example of size, particle P, made from semiconductor conversion material, has the largest dimensions between 1 nm and 200 nm and is an example of a quantum dot.

[0125] Quantum dots can be selected from group II-VI semiconductor nanocrystals, group III-V semiconductor nanocrystals, group IV-VI semiconductor nanocrystals, or mixtures thereof.

[0126] Group II-VI semiconductor nanocrystals may include, but are not limited to, CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, and HgSTe.

[0127] III-V semiconductor nanocrystals may include, but are not limited to, GaN, GaP, GaAs, AlN, AlP, AlAs, InN, InP, InAs, InGaN, GaNP, GaNAs, GaPAs, AlNP, AlNAs, AlPAs, and InAlPAs.

[0128] Group IV-VI semiconductor nanocrystals may include, but are not limited to, SbTe, PbSe, GaSe, PbS, PbTe, SnS, SnTe, and PbSnTe. Chalcopyrite semiconductor nanocrystals selected from the group consisting of CuInS2, CuInSe2, CuGaS2, CuGaSe2, AgInS2, AgInSe2, AgGaS2, and AgGaSe2 may also be considered.

[0129] Another example of a quantum dot is particle P, which has a core and a shell surrounding the core, with the core being made of a semiconductor conversion material and having a maximum size that falls between 1 nm and 200 nm.

[0130] The core may include, for example, nanocrystals such as the nanocrystals described above.

[0131] The shell can consist of ZnS, CDS, ZnSe, CdSe, or any mixture thereof.

[0132] Quantum dots can also be protected from oxidation by using a protective layer of metal oxide, metal nitride, oxynitride, or a mixture thereof.

[0133] The metal oxide protective layer can be selected from the group consisting of Al2O3, SiO2, TiO2, ZrO2, B2O3, Co2O3, Cr2O3, CuO, Fe2O3, Ga2O3, HfO2, ln2O3, MgO, Nb2O5, NiO, SnO2, and Ta2O5, although this is not limited to these materials.

[0134] Metal nitrides can be, for example, BN, AlN, GaN, lnN, Zr3N4, CuZn, etc.

[0135] The oxynitride protective layer may, but is not limited to, contain silicon (SiON).

[0136] The thickness of the protective layer is in the range of 1 to 400 nm, with a preference for the range of 1 to 100 nm.

[0137] Particles P are incorporated, for example, into a photosensitive resin. Photosensitive resins are used in many electronics fabrication techniques to define patterns on semiconductor surfaces, more specifically, to define patterns by solidifying specific zones of the resin while leaving the possibility of removing other zones, since the zones to be removed or solidified are defined by exposure using wavelengths of light to which the resin is sensitive. Such photosensitive resins are used more specifically to protect the coated zones from material deposition or etching.

[0138] It should be noted that quantum dots can take on a variety of shapes. Examples of quantum dots with different shapes are sometimes called nanorods, nanowires, tetrapods, nanopyramids, and nanocubes.

[0139] For example, by integrating quantum dots within porous silica microspheres, or by aggregating multiple quantum dots, each particle P can possess more than one quantum dot.

[0140] Photonic crystal: A periodic structure in a dielectric, semiconductor, or metallic dielectric material that modifies the propagation of electromagnetic waves in the same way that a periodic potential in a semiconductor crystal influences electron movement by creating allowable and forbidden energy bands. The wavelengths that can propagate within the crystal are called modes, and their energy wave vector representation forms a band. In such a structure, if there are no electromagnetic wave propagation modes within a certain range of frequency or wavelength, it is called a band gap.

[0141] Band diagram: A band diagram shows the energy of a band as a function of the converted frequency, which is a function of the value of the wave vector.

[0142] Light-emitting diode (LED): An LED structure is a semiconductor structure that comprises multiple semiconductor regions forming a PN junction, and is configured to emit light when an electric current flows through different semiconductor zones.

[0143] An example of an LED structure is a two-dimensional structure comprising an n-type doped layer, a p-type doped layer, and at least one emissive layer. In such a case, each emitting layer is inserted between the n-type doped layer and the p-type doped layer along the normal direction D.

[0144] In one embodiment, each light-emitting layer has a band gap value that is strictly smaller than the band gap value of the n-type doped layer and strictly smaller than the band gap value of the p-type doped layer. For example, the n-type doped layer and the p-type doped layer are GaN layers, and each light-emitting layer is an InGaN layer.

[0145] The light-emitting layer is, for example, not doped. In other embodiments, the light-emitting layer is doped.

[0146] A quantum well is a specific example of a light-emitting layer having a band gap value smaller than the band gap values ​​of the n-type doped layer and the p-type doped layer.

[0147] Doping: Doping is defined as the presence of impurities in a material that provide free charge carriers. Impurities are, for example, atoms of elements that are not originally present in the material.

[0148] Doping is p-type when impurities increase the hole density in a material compared to an undoped material. For example, a layer of gallium nitride (GaN) is p-type doped by adding magnesium atoms (Mg).

[0149] When impurities increase the volume density of free electrons in a material compared to an undoped material, doping is n-type; for example, a layer of gallium nitride (GaN) is n-doped by adding silicon (Si) atoms.

[0150] Conversion material: The conversion material is configured to convert the first radiation emitted from the light source into a second radiation. In other words, the conversion material is configured to be excited by the first radiation and to emit the second radiation in response.

[0151] The second radiation has a second range of wavelengths, distinct from the first range. More specifically, the second location has a second mean wavelength, which is different from the first mean wavelength. The second mean wavelength is, in particular, strictly greater than the first mean wavelength.

[0152] The conversion material is, for example, a semiconductor material.

[0153] For example, the conversion materials are CdSe, CdTe, ZnSe, ZnTe, InP, InPZnS, Ag2S, CuInS, CuInSe, AgInS2, AgInSe2, or even InPZn x Se x-y S y It is selected from the group consisting of [the specified group]. However, other types of materials are also possible.

[0154] In other embodiments, the conversion material is a non-semiconductor material such as inorganic garnet. For example, the conversion material is doped yttrium aluminum garnet. However, other types of non-semiconductor conversion materials, particularly other garnets, are also conceivable.

[0155] More specifically, the conversion material can be an inorganic phosphor.

[0156] Examples of inorganic phosphors include yttrium aluminum garnet particles (e.g., YAG:CE), terbium aluminum garnet particles (TAG, e.g., TAG:Ce), silicate particles (e.g., SrBaSiO4:Eu), sulfide particles (e.g., SrGa2S4:Eu, SrS:Eu, CaS:Eu, etc.), nitride particles (e.g., Sr2Si5N8:Eu, Ba2Si5N8:Eu, etc.), oxynitride particles (e.g., Ca-α-SiAlON:Eu, SrSi2O2N2:Eu, etc.), and fluoride particles (e.g., K2SiF6:Mn, Na2SiF6:Mn, etc.).

[0157] Many other conversion materials can be used, such as doped aluminates, doped nitrides, doped fluorides, doped sulfides, or doped silicates.

[0158] The conversion material is doped with, for example, rare earth elements, alkaline earth elements, or transition metal elements. Cerium may be used, for example, to dope yttrium aluminum garnet.

[0159] The conversion material comprises, for example, a set of particles P made from the conversion material. These particles P are sometimes called "luminescent phosphophores."

[0160] Semiconductor materials: The term "band gap value" should be understood as the band gap value between the valence band and conduction band of a material.

[0161] The band gap value is measured, for example, in units of electron volts (eV).

[0162] Of the allowable energy bands of electrons in a material, the valence band is defined as the band with the highest energy when it is completely filled at temperatures below 20 Kelvin (K).

[0163] For every valence band, a first energy level is defined. This first energy level is the highest energy level in the valence band.

[0164] In a material, the conduction band is defined as the band with the lowest energy when electrons are not completely filled at temperatures below 20K.

[0165] For all conduction bands, a second energy level is defined. This second energy level is the highest energy level in the conduction band.

[0166] Therefore, all band gap values ​​are measured between the first and second energy levels of the material.

[0167] Semiconductor materials are materials that have a bandgap value that is strictly greater than zero and less than or equal to 6.5 eV.

[0168] A direct bandgap semiconductor is an example of a semiconductor material. A material is considered to have a "direct bandgap" when the minimum value of the conduction band and the maximum value of the valence band correspond to the same value of momentum of the charge carrier. A material is considered to have an "indirect bandgap" when the minimum value of the conduction band and the maximum value of the valence band correspond to different values ​​of momentum of the charge carrier.

[0169] Each semiconductor material can be selected from, for example, the group consisting of III-V semiconductors, particularly nitrides of Group III elements, II-VI semiconductors, or further IV-IV semiconductors.

[0170] III-V semiconductors include, in particular, InAs, GaAs, AlAs and their alloys, InP, GaP, AlP and their alloys, and nitrides of element III.

[0171] Semiconductors II-VI include CdTe, HgTe, CdSe, HgSe, and their alloys.

[0172] IV-IV semiconductors include, in particular, Si, Ge, and their alloys.

[0173] Nanowires: Nanowires are an example of identifying three-dimensional structures.

[0174] A three-dimensional structure is a structure that extends along its principal direction. A three-dimensional structure has a length measured along its principal direction. A three-dimensional structure also has a maximum transverse dimension measured along a transverse direction perpendicular to the principal direction, which is the direction perpendicular to the principal direction along which the dimensions of the structure are greatest.

[0175] The maximum transverse dimension is, for example, 10 micrometers (μm) or less, and the length is greater than or equal to the maximum transverse dimension. The maximum transverse dimension is advantageously 2.5 μm or less.

[0176] The maximum horizontal dimension is particularly large, exceeding 10 nm.

[0177] In certain embodiments, the length is at least twice the maximum width, for example, at least five times the maximum width.

[0178] The primary direction is, for example, the vertical direction D. In such cases, the length of the three-dimensional structure is called the "height," and the maximum dimension of the three-dimensional structure in a plane perpendicular to the vertical direction D is 10 μm or less.

[0179] The maximum dimension of a three-dimensional structure in a plane perpendicular to the vertical direction D is often called the "diameter," regardless of the cross-sectional shape of the three-dimensional structure.

[0180] All three-dimensional structures are, for example, microwires. Microwires are three-dimensional cylindrical structures.

[0181] In a particular embodiment, the microwire is a cylinder extending along a vertical direction D. The microwire is, for example, a cylinder with a circular base. In such a case, the diameter of the base of the cylinder is less than or equal to half the length of the microwire.

[0182] Microwires with a maximum horizontal dimension of less than 1 μm are called "nanowires."

[0183] A pyramidal structure extending vertically along direction D from the substrate is another example of a three-dimensional structure.

[0184] A cone extending along the vertical direction D is another example of a three-dimensional structure.

[0185] A frustum of a cone or pyramidal pyramid extending along a vertical direction D is yet another example of a three-dimensional structure.

[0186] Standing waves: Standing waves are a phenomenon that occurs when multiple waves of the same frequency and amplitude propagate simultaneously in opposite directions through the same physical medium, forming a diagram in which the wave components are fixed in time. In the diagram, instead of seeing the propagating waves, standing oscillations of different intensities are observed at each observation point. These characteristic fixed points are called pressure nodes.

[0187] Pixel: Many display screens have a set of light-emitting elements used to form the image displayed on the screen. Each such light-emitting element can function as an image element, or a "pixel" (derived from the English "picture element"), especially when the screen is monochrome, or as a part of such an image element, called a "subpixel" (especially when the screen is a color screen and each pixel contains subpixels of a different color, and the color of the pixel can be changed by selectively illuminating the subpixels). In this specification, a red pixel was more or less a subpixel in the sense described above.

[0188] Quantum wells: A quantum well is a structure in which quantum confinement occurs in one direction for at least one type of charge carrier. The quantum confinement effect occurs when the size of the structure along such a direction becomes comparable to or smaller than the de Broglie wavelength of the carrier, which is usually electrons and / or holes, thereby resulting in energy levels called "energy subbands."

[0189] In such quantum wells, the carrier can only have discrete energy values, but generally tends to move in a plane perpendicular to the direction in which confinement occurs. As the dimensions of the quantum well decrease along the direction in which confinement occurs, the available energy values ​​for the carrier, also known as "energy levels," increase.

[0190] In quantum mechanics, the "de Broglie wavelength" is the wavelength of a particle when it is considered a wave. The de Broglie wavelength of an electron is also called the "electron wavelength." The de Broglie wavelength of a charge carrier is determined by the material from which the quantum well is made.

[0191] An example of a quantum well is a light-emitting layer having a thickness that is strictly less than the product of the electron wavelength of the electrons in the semiconductor material forming the light-emitting layer and 5.

[0192] Another example of a quantum well is a luminescent layer in a semiconductor that forms the luminescent layer, having a thickness strictly less than the product of the de Broglie wavelength of an exciton and 5. An exciton is a quasiparticle comprising an electron and a hole.

[0193] In particular, quantum wells often have thicknesses that fall between 1 nm and 50 nm.

[0194] Radiation: All radiation includes a set of electromagnetic waves.

[0195] Wavelengths are defined for all electromagnetic waves.

[0196] Each set corresponds to a wavelength range or spectral band. A wavelength range is a group of wavelengths that a set of electromagnetic waves possesses.

[0197] The average wavelength of a spectral band can be defined as the average of the wavelengths at both ends of the spectral band.

[0198] Red: Red radiation has an average wavelength that falls between 600 nm and 720 nm.

[0199] Ultraviolet radiation: Ultraviolet radiation has an average wavelength that falls between 350 nm and 430 nm.

[0200] Green: Green radiation has an average wavelength that falls between 500 nm and 560 nm. [Explanation of Symbols]

[0201] 10 red subpixels, red pixels 12 nanowires 14 Conversion Materials 15 Conversion Layer 16 Active layer 18 GaN layer 20 Emission spectrum 22 Absorption Spectrum 24 Emission Spectrum 26 Photonic Crystals 27 Release curve 28 Upper wall 30 Lower wall, bottom wall 31 Medium 42 Central part 44 Peripheral area a pitch B1 First band gap B2 band gap, band B3 Third Band

Claims

1. A conversion material (14) suitable for converting a first emission in a first spectral band to a second emission in a second spectral band, wherein the second spectral band is distinct from the first spectral band, A standing wave generator in the first spectral band, comprising a two-dimensional photonic crystal (26) suitable for generating standing waves in the first spectral band, wherein the photonic crystal (26) is at least partially formed by light-emitting diodes (12) suitable for emission in the first spectral band, the light-emitting diodes (12) are nanowires extending mainly along the longitudinal direction (Z), the photonic crystal (26) forms a resonant cavity in a transverse plane formed by two directions (X, Y) traversing the longitudinal direction (Z), and the photonic crystal (26) is suitable for generating standing waves in the first spectral band in the transverse plane, and A light-emitting element (10) including the element.

2. The light-emitting element according to claim 1, wherein the photonic crystal (26) is formed only by a light-emitting diode (12) and a medium (14, 31) surrounding the light-emitting diode (12).

3. The light-emitting element according to claim 1, wherein the light-emitting diode (12) comprises an active layer (16), and at least one active layer (16) is contained within the photonic crystal (26).

4. The light-emitting element according to claim 3, wherein the photonic crystal (26) is partially formed from each active layer (16) of the light-emitting diode (12).

5. The light-emitting element according to claim 1, wherein the photonic crystal (26) includes all of the light-emitting diodes (12).

6. The light-emitting element according to claim 1, wherein the light-emitting diode (12) is in a medium, and the medium is the conversion material (14).

7. The light-emitting element according to claim 1, wherein the conversion material (14) is located on the photonic crystal (26).

8. The light-emitting element according to claim 1, wherein the photonic crystal (26) has a plurality of band gaps, and the photonic crystal (26) has a pitch (a) and packing density suitable for emission by the light-emitting diode (12) at the band edge at 90° of the first band gap.

9. The light-emitting element according to claim 1, wherein the photonic crystal (26) has a plurality of band gaps, and the photonic crystal (26) has a pitch (a) and packing density suitable for emission by the light-emitting diode (12) at a band edge at 90° of a band gap different from the first band gap.

10. The light-emitting element according to claim 9, wherein the pitch (a) and packing density of the photonic crystal (26) are suitable for the conversion material to emit at the band edge at 0° of the band gap, and the band gap at which the emission of the conversion material (14) occurs is smaller than the band gap at which the emission of the light-emitting diode (12) occurs.

11. The light-emitting element according to claim 1, wherein the photonic crystal (26) is surrounded by walls (28, 30) that form a cavity, and at least one of the walls (28, 30) is made of a material selected from a list consisting of transparent conductive oxides such as indium tin oxide or zinc oxide doped with gallium or aluminum, metals such as Ag or Al, graphene, and combinations of the elements.

12. The light-emitting element according to claim 1, wherein the conversion material (14) is a polymer matrix comprising quantum dots.

13. The light-emitting element according to claim 1, wherein each light-emitting diode (12) comprises an active medium (16) made of a first material, surrounded by a layer (18) made of a second material, the first material comprises InGaN, and the second material comprises GaN.

14. The light-emitting element according to claim 1, wherein the photonic crystal (26) has a central portion (42) and a peripheral portion (44), and each portion (42, 44) is made up of a plurality of light-emitting diodes (12), and energy is supplied only to the central portion (42) of the photonic crystal (26).

15. A photoelectronic device comprising at least one light-emitting element (10) according to any one of claims 1 to 14.

Images