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

Abstract

The present application relates to a light emitting element (10) comprising a conversion material (14) adapted to convert a first radiation in a first spectral band into a second radiation in a second spectral band, the second spectral band being different from the first spectral band, and a standing wave generator in the first spectral band, the standing wave generator comprises a two-dimensional photonic crystal (26) adapted to generate a standing wave in the first spectral band, the photonic crystal (26) being at least partially composed of a light emitting diode (12) adapted to emit in the first spectral band.

Description

Field of the Invention

[0001] The present application relates to a light-emitting element and an optoelectronic device comprising the light-emitting element.

[0002] Technical Background of the Invention

[0003] In the field of optoelectronics, there is a desire to produce very small devices. This is especially true of pixels in color displays.

[0004] In a color display, each pixel includes multiple sub-pixels, each sub-pixel is configured to emit a specific color, so that the color emitted by the pixel can be changed by controlling which sub-pixel(s) is activated or changing the current applied to each sub-pixel, thereby changing the relative emission intensity of each sub-pixel.

[0005] Semiconductor structures, such as light emitting diodes (LEDs), are often used for various purposes, such as lighting, because of their potentially good light-emitting efficiency. Due to this potential high efficiency, LEDs have been proposed for use in making efficient displays. LED structures are usually in the form of a stack of planar semiconductor layers. When current flows through the stack, light is emitted.

[0006] Therefore, in order to reduce the size of the pixel, it is known how to grow native pixels containing LEDs made of GaN / InGaN on the same wafer. A native pixel is a pixel whose emitted color is the desired color.

[0007] However, the efficiency of such pixels is not high, as this type of LED only has a satisfactory quantum efficiency for the blue color. In fact, the quantum efficiency for green is typically 30%, while the quantum efficiency for red drops to less than 5%.

[0008] It is therefore known how to use a color conversion module to obtain other colors from a blue LED or an ultraviolet LED. Quantum dots are an example of a converter that is often used in a conversion module. The quantum dots are usually inserted into a matrix.

[0009] However, for pixels of the order of a few micrometers, the absorption of the quantum dots is too low to guarantee a complete conversion of the blue radiation into red or green radiation. Therefore, in order to obtain a red pixel or a green pixel, the unconverted radiation must be filtered. This filtering means a significant loss of the radiation emitted by the LED. For example, for a pixel with a size of 5μm x 5μm, the loss is 60%.

[0010] It is conceivable that this loss could be compensated by increasing the number of quantum dots.

[0011] The first way to increase the number of quantum dots is to increase the concentration of quantum dots in the matrix. The result of this is that too high a concentration will lead to a loss of mechanical properties of the matrix, making it incompatible with the technology used to manufacture pixels.

[0012] The second way to increase the number of quantum dots is to increase the size of the substrate, especially the thickness of the substrate.

[0013] However, this increase also faces many problems.

[0014] First, it is technically difficult to make pixels of very high thickness.

[0015] A thicker substrate means a longer optical path length for the radiation converted by the quantum dots. This increase results in greater reabsorption losses.

[0016] Another problem is related to crosstalk between two pixels. This is usually prevented by inserting opaque walls at the edge of the color conversion module. The thicker the matrix, the higher the height of the wall and thus the higher the absorption losses of the wall, even to the point where the losses exceed the absorption gain associated with the increased number of quantum dots. SUMMARY OF THE INVENTION

[0018] Therefore, a small-sized light-emitting element is needed to overcome the above disadvantages.

[0019] To this end, the present specification describes a light emitting element that includes a conversion material suitable for converting first radiation within a first spectral band into second radiation within a second spectral band, the second spectral band being different from the first spectral band. The light emitting element also includes a standing wave generator within the first spectral band, the standing wave generator including a two-dimensional photonic crystal suitable for generating a standing wave within the first spectral band, the photonic crystal being at least partially composed of a light emitting diode suitable for emitting within the first spectral band.

[0020] In contrast to the prior art, in particular documents FR3068173A and US2022 / 102324A1, the nanowires constituting the light source are part of a photonic crystal and are partly used to produce a photonic crystal. More precisely, the photonic crystal here is a combination of a medium and nanowires.

[0021] Furthermore, because photonic crystals have a different role to play in generating standing waves, standing waves can be generated efficiently due to the difference in the previous structure.

[0022] This allows the manufacture of light-emitting elements (usually pixels) that are small in size and have good conversion efficiency, and can therefore emit a satisfactory amount of light.

[0023] According to other specific embodiments, the light emitting element has one or more of the following features, which can be used alone or in all technically possible combinations:

[0024] -The photonic crystal is completely composed of a light-emitting diode and a medium surrounding the light-emitting diode.

[0025] -The light emitting diode comprises an active layer, and the photonic crystal comprises at least one active layer. In this way, light can be effectively injected into the photonic crystal to form a standing wave.

[0026] -The photonic crystal part is formed by each active layer of the light-emitting diode.

[0027] -The photonic crystal comprises the entirety of each light emitting diode.

[0028] - The light emitting diode is located in a medium, which is a conversion material. The above is used to reduce the size of the light emitting element.

[0029] -Conversion materials are based on photonic crystals. The above facilitates the manufacture of light-emitting components.

[0030] The photonic crystal has multiple bandgap widths, and the photonic crystal has a pitch and fill factor suitable for the light emitting diode to emit at 90° at the band edge of the first bandgap width. The above can increase the probability that the conversion material absorbs photons in the first spectral band.

[0031] The photonic crystal has a plurality of bandgap widths, the photonic crystal having a pitch and a fill factor suitable for the light emitting diode to emit at 90° at a band edge of a bandgap width different from the first bandgap width. In this way, a higher efficiency of the light emitting element can be obtained by increasing the directivity of the converted radiation.

[0032] -The spacing and filling factor of the photonic crystal are also suitable for the conversion material to emit at the band edge of the 0° bandgap width, and the bandgap width of the conversion material emission is smaller than the bandgap width of the light-emitting diode emission. The above content enables the photonic crystal to obtain more precise vertical emission, so that the light-emitting element has better performance.

[0033] - The photonic crystal is surrounded by walls forming a cavity, at least one wall being made of a material selected from the following: transparent conductive oxides (such as indium tin oxide or zinc oxide doped with gallium or aluminum), metals (such as silver or aluminum), graphene and combinations thereof. In this way, it is possible to obtain walls with good optical properties, thereby improving the efficiency of the photonic crystal.

[0034] - The conversion material is a polymer matrix comprising quantum dots. The above facilitates the manufacture of light emitting components.

[0035] Each light-emitting diode comprises an active medium made of a first material, the active medium being surrounded by a layer made of a second material, the first material comprising InGaN and the second material comprising GaN. In this way, a light-emitting element with good performance can be obtained while maintaining ease of manufacture.

[0036] -The photonic crystal consists of a central part and a peripheral part. Each part brings together a group of light-emitting diodes, and only the central part of the photonic crystal has energy supply. This can reduce energy consumption.

[0037] The present description also relates to a light-emitting element, which includes a light-emitting diode suitable for emitting within a spectral band, and a two-dimensional photonic crystal including an active layer and at least the medium of the light-emitting diode and the active layer, wherein the crystal is suitable for generating a standing wave within the spectral band.

[0038] In addition, the present description proposes a light-emitting element comprising a two-dimensional photonic crystal suitable for generating a standing wave, the photonic crystal comprising an emission source of the light-emitting element.

[0039] The present specification also describes an optoelectronic device comprising at least one of the above-mentioned light-emitting elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The characteristics and advantages of the present application will become apparent upon reading the following description which is given by way of example only and not limitation, and with reference to the accompanying drawings, in which:

[0042] - Figure 1 is a cross-sectional schematic diagram of a pixel instance,

[0043] - Figure 2 is a schematic diagram of the energy band diagram, which illustrates Figure 1 An example of how a pixel works is shown,

[0044] - Figure 3 is Figure 2 Schematic diagram of the radiation emitted by certain elements of a pixel within the functional framework shown,

[0045] - Figure 4 is a schematic diagram of another pixel instance.

[0046] - Figure 5 is a schematic diagram of the energy band diagram, which illustrates Figure 1 Another example of how pixels work is shown,

[0047] - Figure 6 is a schematic diagram of the radiation emitted by certain elements of a pixel within the functional framework of the figure, and

[0048] - Figure 7 is a top-down schematic diagram of another pixel example.

[0049] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0050] Below, for ease of understanding, the present application will be explained as follows: first, the general principles of the present application will be explained through specific examples, second, how to conveniently apply the same principles to other examples will be explained in detail, and third, improvements or alternative implementations of the examples will be described.

[0051] In addition, to simplify the explanation, a “Definitions” section is inserted at the end to refer the reader to each term introduced below.

[0052] Specific examples

[0053] For specific examples, please refer to Figure 1 Let us consider the case of a red sub-pixel 10, hereinafter referred to as red pixel 10 (for simplicity).

[0054] exist Figure 1 In this case, the red radiation of the pixel 10 is obtained by converting the blue radiation from the nanowire 12 using the conversion material 14.

[0055] Nanowire 12 is a light emitting diode made of a material including InGaN, which is used to form an active layer 16 between GaN (typically nGaN or pGaN) layers 18. Nanowire 12 emits blue radiation. The emission spectrum 20 from nanowire 12 is Figure 2 This can be seen in the band diagram shown.

[0056] The nanowires 12 mainly extend along the longitudinal direction Z, and the lateral directions are referred to as a first lateral direction X and a second lateral direction Y, respectively.

[0057] For this example, the conversion material 14 is a matrix including quantum dots. Each quantum dot has an absorption spectrum 22 and an emission spectrum 24, such as Figure 2 As shown in the energy band diagram.

[0058] The groups of nanowires 12 are arranged in the conversion material 14 to form a photonic crystal 26 with a pitch a.

[0059] Since this arrangement of nanowires 12 is two-dimensional, the photonic crystal 26 is a two-dimensional photonic crystal.

[0060] The photonic crystal 26 forms a resonant cavity in a plane formed by two transverse planes X and Y, hereinafter indicated as transverse plane XY.

[0061] The emission curve 27 of the photonic crystal 26 corresponding to each propagation mode allowed by the photonic crystal 26 is Figure 2 The emission curve 27 is a curve showing the emission wavelength as a function of the emission angle.

[0062] The propagation modes of the photonic crystal 26 are separated by the bandgap width. Figure 2 Two bandgap widths B1 and B2 are schematically shown in FIG.

[0063] The positions of the two bandgap widths B1 and B2 are determined by the pitch a of the photonic crystal 26 , the diameter of the nanowire 12 , the material index of the nanowire 12 , the material index of the conversion material 14 , and the total thickness of the photonic crystal 26 .

[0064] Furthermore, the photonic crystal 26 is surrounded by two walls 28 and 30 , namely an upper wall 28 and a lower wall 30 , which define a cavity in the longitudinal direction Z.

[0065] One of the two walls 28 and 30 is a wall that can extract light, while the other is a reflecting wall.

[0066] To make the walls 28 and 30, it is possible to consider stacking together layers of different materials, which may be metals and / or dielectrics. Advantageously, a conductive material such as indium tin oxide (also known as ITO), a metal such as silver or aluminum is in direct contact with the upper and lower parts of the nanowires 12, thereby enabling electrical injection.

[0067] In fact, the photonic crystal 26 has the particularity that it can form a blue standing wave generator with a wavelength close to the forbidden band width at 90° in the transverse plane XY.

[0068] The term "generator" is to be understood as meaning that the photonic crystal 26 is here a primary light source, since standing waves are generated within the photonic crystal 26. More specifically, radiation sent to such a photonic crystal cannot generate standing waves, since the penetration of radiation into the photonic crystal 26 is very low.

[0069] This peculiarity is now explained by discussing the relevant physical phenomena in detail.

[0070] In a standing wave generator, the Purcell effect increases the spontaneous photon emission rate of the material in the resonant cavity compared to the material not in the resonant cavity. The above means that the nanowire 12 emits more photons in the transverse plane XY. Therefore, the Purcell effect produces angle selection and wavelength selection.

[0071] In the example described, the photonic crystal 26 acts on a specific band edge, namely the band edge of the first resonance band of the nanowire 12 at 90° (corresponding to a wave vector of π / a). The band edge corresponds to the wavelength range where the emission curve 27 of the photonic crystal is significantly flattened, typically a wavelength range of less than 25 nm, advantageously less than 10 nm, and even more advantageously less than 5 nm. Figure 2 , the above means that the emission occurs in the first resonance band of the nanowire 12, that is, the portion of the first resonance band indicated by the bold line.

[0072] More specifically, the emission ultimately generated by the nanowire 12 in the photonic crystal 26 is confined to the intersection between the emission spectrum 20 (primary emission) and the emission curve 27 of the photonic crystal 26, which is below the first bandgap width B1, i.e., it is mainly emitted at an angle of 90° as shown in the bold line (corresponding to the generation of a standing wave).

[0073] The result of this is that the emission of radiation in the photonic crystal 26 is confined only in the XY plane.

[0074] Thus, the photonic crystal 26 is adapted to generate a standing wave in the blue [range], the photonic crystal 26 being at least partially comprised of the nanowires 12 adapted to emit in the blue [range].

[0075] To obtain such performance of the photonic crystal 26, it is necessary to adjust the basic unit cell, spacing and filling factor of the photonic crystal.

[0076] The basic lattice and spacing of the photonic crystal 26 correspond to the arrangement of the nanowires 12 , while the filling factor is the ratio between the surface area occupied by the nanowires 12 and the total surface area of ​​the photonic crystal 26 and therefore depends on the size of the nanowires 12 , more precisely, on the diameter of the nanowires 12 .

[0077] To select a suitable arrangement and diameter for the nanowires 12, simulation techniques can be used for configurations that are easily experimentally feasible, followed by scaling.

[0078] For example, the applicant conducted tests using a photonic crystal that emits at a wavelength of 0.52 μm, has a hexagonal lattice, a filling factor of 50%, and extends over 1.5 μm. Based on the above, the applicant determined that the band edge is located at a reduction frequency of 0.43. By definition, the reduction frequency is the ratio of the spacing a to the wavelength.

[0079] Thus, it can be determined that for an emission wavelength of 450 nm, the appropriate spacing a is 193.5 nm.

[0080] Then numerical simulations can be performed. Thus, the applicant has shown that the absorption of quantum dots with an encapsulation material index of 1.55 reaches 96% with a pixel size of only 1.5 μm x 1.5 μm. Moreover, the absorption occurs over a relatively wide band of about 30 nm centered around a reduction frequency of 0.43.

[0081] Therefore, by restating what has just been proposed above, by simply choosing the arrangement and diameter of the nanowires 12 , the blue radiation emitted by the nanowires 12 will be forced to move in the transverse plane XY, thereby forming a standing wave within the conversion material 14 .

[0082] Therefore, there is no blue radiation in the other direction, so the radiation is no longer Lambertian reflection. The above clearly shows that Figure 3 In FIG. 1 , the blue radiation emitted by the nanowire under reference numeral 32 is schematically represented.

[0083] It can be seen that the presence of the photonic crystal 26 greatly increases the optical path length of the photons emitted by the nanowires 12 in the conversion material 14 because the photons travel back and forth in the conversion material 14 .

[0084] This increase in the optical path increases the probability of blue photons encountering the quantum dots, thereby greatly increasing the absorption of blue radiation by the quantum dots. Almost all of the light emitted by each nanowire 12 is absorbed.

[0085] Along the longitudinal direction Z, emission of red radiation showing Lambertian emission is obtained, such as Figure 3 As shown by the dotted line in FIG. , the reference numeral 36 is shown in the figure.

[0086] More specifically, by design, the thickness of each quantum dot is very small, and therefore the path of the converted light in the conversion material 14 is very small. This significantly prevents reabsorption losses.

[0087] Thus, without any increase in reabsorption losses and especially without any increase in wall height, the absorption of the quantum dots is greatly improved compared to increasing the thickness of the conversion material.

[0088] Therefore, the quantum efficiency of the proposed pixel 10 is greatly improved.

[0089] One consequence of this good quantum efficiency is that, unlike known conversion modules, the leakage of blue photons becomes very low, so that the thickness of the blue radiation cutoff filter is reduced or, if diffusion is negligible, is no longer necessary.

[0090] Furthermore, if the quantum efficiency is suitable, it may even be possible to consider reducing the number of quantum dots in the matrix. Such a reduction would reduce the manufacturing cost of the pixel 10 and the amount of environmentally harmful materials.

[0091] Furthermore, the pixel 10 is easier to manufacture than other known pixels, in particular it requires fewer components, such as blue filters or taller walls for preventing crosstalk.

[0092] Furthermore, the manufacturing can also employ relatively standard techniques that are compatible with the small size of the pixel 10 .

[0093] Extension of the principle to other examples

[0094] The principle of using a standing wave generator to improve the switching of a pixel 10 can have versions for many other instances without changing the principle itself.

[0095] In particular, what has just been said remains valid for other wavelengths.

[0096] In particular, the red pixel 10 may be a green pixel.

[0097] The radiation emitted by the nanowires 12 may be ultraviolet radiation.

[0098] This principle also applies to other conversion materials 14 .

[0099] A list of possible materials can be found in the Definitions section.

[0100] The materials used to constitute the nanowires may also be different from the pair of GaN and InGaN.

[0101] In particular, one can envision a semiconductor material that mainly includes at least one Group III element and one Group V element (such as gallium nitride GaN), hereinafter referred to as a III-V compound, or mainly includes at least one Group II element and one Group VI element (such as zinc oxide ZnO), hereinafter referred to as a II-VI compound, or mainly includes at least one Group IV element.

[0102] Furthermore, it is known how to produce active regions including confinement means, in particular single quantum wells or multiple quantum wells. A single quantum well is produced by inserting a layer of a second semiconductor material, such as an alloy of a III-V compound and a third element, in particular InGaN, between two layers of a first semiconductor material, such as a III-V compound, in particular GaN, doped p-type or n-type, respectively, the second semiconductor material having a different bandgap than the first semiconductor material. A multiple quantum well structure comprises a stack of semiconductor layers, the stack constituting an alternation of quantum well and barrier layers.

[0103] Other materials may also be used to form the upper wall 28 or the lower wall 30 .

[0104] Therefore, the upper wall 28 is made of zinc oxide (also called ZNO) doped with gallium or aluminum.

[0105] More generally, the upper wall 28 is made of a transparent conductive oxide (often referred to as TCO).

[0106] However, other materials such as graphene can also be considered.

[0107] The same material can also be used for the lower wall 30 .

[0108] Improved or alternative implementations

[0109] Improved or alternative embodiments are now proposed.

[0110] Reference Figure 4 , it can be imagined Figure 1 A variant of a medium red pixel 10 in which the conversion material 14 is located on the upper wall 28 .

[0111] This is achieved in particular by depositing a layer over the entire upper wall, which will be referred to hereinafter as conversion layer 15 .

[0112] In a variant, it is possible to envisage depositing quantum dots of different colors for adjacent pixels 10. Such a deposition can be obtained, for example, using selective lithography or etching techniques.

[0113] The medium 31 surrounding the nanowires may then be SiO 2 , for example.

[0114] In a variant, the medium 31 is TiO2, Al2O3 or Si3N4.

[0115] More generally, the material constituting the medium 31 is an oxide or a nitride that is transparent to the wavelengths emitted by the nanowires 12 and to the wavelengths emitted by the quantum dots.

[0116] However, its function is similar to Figure 1 The situation described is different.

[0117] The absorption of the standing wave by the conversion material 14 occurs only in one part, namely the evanescent part PE of the standing wave, which excites the quantum dots of the conversion layer 15 .

[0118] Since the standing wave has a certain range along the direction Z, there is an evanescent part PE.

[0119] The above means that the distance between the quantum dots and the nanowires 12 is small enough so that the overlap between the PE part of the standing wave and the conversion layer 14 is large enough.

[0120] Furthermore, to advantageously enhance the directional emission of quantum dots, the distance between conversion layer 15 and lower wall 30 is a multiple of λ / 2n, where λ is the emission wavelength of the quantum dots and n is the effective index of the group consisting of walls 28 and 30 and photonic crystal 26 .

[0121] For example, the distance can be defined here as the distance between the center of the conversion layer 15 and the last layer of the lower wall 30 and is obtained by simulation.

[0122] The above improves the red emission of quantum dots by increasing the number of photons emitted by the Purcell effect and the conversion efficiency, while making the emission of quantum dots more directional.

[0123] and Figure 1This embodiment of the red pixel 10 is less efficient than the embodiment shown, but the conversion layer 15 can be added separately when blue photons are generated, which makes the process of depositing this layer easier than adding a conversion matrix between the nanowires.

[0124] Furthermore, in this case, one of the last steps of the manufacturing process will be the deposition of the conversion layer 15, which means that the quantum dots undergo fewer technological processes that could affect their performance or reliability. Furthermore, a protective layer, in particular a protective layer against oxidation, can be deposited on the conversion layer 15 to improve its reliability. Such a protective layer is made of, for example, SiO2, TiO2 or Al2O3.

[0125] refer to Figure 5 and Figure 6 , it is also possible to use nth order resonance to emit the nanowire 12. The above is equivalent to using a wave vector of n*π / a instead of π / a.

[0126] In this case, from Figure 5 As can be seen in the band diagram shown, the wavelength of the quantum dot emission is aligned with the band edge at 0° (corresponding to the bandgap width denoted by B2).

[0127] This arrangement can be used to increase the internal quantum efficiency of the quantum dots (still the Purcell effect mentioned above) and make the emission of each quantum dot more directional (more concentrated in direction Z).

[0128] When the emission spectrum 20 of the nanowire 12 is aligned with the 90° resonant mode (corresponding to the bandgap denoted by B3), the preferred emission direction of the nanowire 12 is the transverse plane XY. It can be noted that the bandgap of the emission of the conversion material 14 (here the bandgap B2) is narrower than the bandgap of the emission of the nanowire 12 (here the bandgap B3).

[0129] In this example, the emission spectrum of the quantum dot is aligned with the 0° resonance mode, so the preferred emission direction of the quantum dot is along the direction Z. This is equivalent to the presence of two standing waves, the first standing wave in blue on the transverse plane XY and the second standing wave along the axis Z in red.

[0130] from Figure 6 The radiation pattern of the quantum dots when using this second-order resonant emission nanowire 12 can be seen in FIG.

[0131] Therefore, advantageously, the photonic crystal 26 has a pitch a and a fill factor suitable for causing the nanowires 12 to emit at a band edge of a bandgap different from the first bandgap (here, the third energy band B3).

[0132] By making the converted radiation more directional, such an embodiment preserves the Figure 1The advantages of the illustrated embodiment of the red pixel 10 contribute to further improving the efficiency of the pixel 10 under consideration.

[0133] Figure 7 An embodiment is shown which is compatible with all the embodiments of the red pixel 10 just presented.

[0134] In the illustrated example, the photonic crystal 26 includes a central portion 42 and a peripheral portion 44 , each portion 42 or 44 grouping groups of nanowires 14 together.

[0135] As mentioned above, the central portion 42 is supplied with energy for emitting standing waves.

[0136] The peripheral portion 44 surrounds the central portion 42 and is not supplied with energy. The nanowires 12 of the peripheral portion 44 act as mirrors for the standing waves.

[0137] In the peripheral portion 44, if multiple wavelengths need to be reflected, a variable pitch may be used, for example, the pitch increases from the ends toward the center region.

[0138] The above makes it possible to dispense with external mirrors, or to use them in conjunction with them if desired.

[0139] We therefore propose a series of implementations that exploit the idea of ​​a standing wave generator made of photonic crystals to better excite the conversion material. These implementations can be combined when technically feasible.

[0140] In all cases, it is possible to produce small pixels 10 with good conversion efficiency, thereby emitting a satisfactory amount of light.

[0141] The above can be used to advantage in many applications.

[0142] More specifically, these pixels could be used in optoelectronic devices such as display screens, light projectors or glasses for immersion in virtual reality.

[0143] In the example of a display screen, the optoelectronic device can be integrated into an electronic device such as a mobile phone, tablet computer or laptop computer. In another embodiment, the display screen is integrated into a dedicated display device such as a television or desktop computer monitor.

[0144] When the screen is a full-color screen, each pixel includes a plurality of pixels of different colors, which can be the pixels just described.

[0145] However, according to the prior art, it is also possible to envision the coexistence of pixels, especially when the efficiency is not obvious (such as at the edge of the screen).

[0146] definition

[0147] blue : The average wavelength of blue radiation ranges from 430nm to 470nm.

[0148] quantum dots : A quantum dot is a structure in which quantum confinement occurs in all three spatial dimensions.

[0149] An example of a quantum dot is a particle P having a maximum dimension less than or equal to 5 times the electron wavelength of the charge carriers in the conversion material.

[0150] To give an order of magnitude, an example of a quantum dot is a particle P made of a semiconductor conversion material with a maximum dimension in the range of 1 nm-200 nm.

[0151] The quantum dots may be selected from Group II-VI, Group III-V, Group IV-VI semiconductor nanocrystals or mixtures thereof.

[0152] 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, HgSTe.

[0153] III-V semiconductor nanocrystals may include, but are not limited to, GaN, GaP, GaAs, AlN, AlP, AlAs, InN, InP, InAs, InGaN, GaNPs, GaNAs, GaPAs, AlNPs, AlNAs, AlPAs, and InAlPAs.

[0154] IV-VI semiconductor nanocrystals may include, but are not limited to: SbTe, PbSe, GaSe, PbS, PbTe, SnS, SnTe, PbSnTe. Also contemplated are chalcopyrite semiconductor nanocrystals selected from: CuInS2, CuInSe2, CuGaS2, CuGaSe2, AgInS2, AgInSe2, AgGaS2, and AgGaSe2.

[0155] Another example of a quantum dot is a particle P having a core made of a semiconductor conversion material and a shell surrounding the core, the core having a maximum dimension in the range of 1 nm to 200 nm.

[0156] The core may include, for example, a nanocrystal, such as the nanocrystals described above.

[0157] The outer shell may be composed of ZnS, CDS, ZnSe, CdSe or any mixture thereof.

[0158] The quantum dots may also be protected from oxidation by using a metal oxide protective layer, a metal nitride protective layer, an oxynitride protective layer, or a mixture thereof.

[0159] The metal oxide protective layer can be selected from but is not limited to: Al2O3, SiO2, TiO2, ZrO2, B2O3, Co2O3, Cr2O3, CuO, Fe2O3, Ga2O3, HfO2, In2O3, MgO, Nb2O5, NiO, SnO2 and Ta2O5.

[0160] The metal nitride may be, for example, BN, AlN, GaN, InN, Zr3N4, CuZN, etc.

[0161] The oxynitride protective layer may include, but is not limited to, SiON.

[0162] The thickness of the protective layer may be 1 nm-400 nm, preferably 1 nm-100 nm.

[0163] The particles P may be combined with a photosensitive resin. Photosensitive resins are useful in many electronics manufacturing techniques for defining patterns on semiconductor surfaces, particularly because specific areas of the resin can be cured while other areas can be removed to define the pattern, the areas to be removed or cured being determined by exposure to a wavelength of light to which the resin is sensitive. Such photosensitive resins are particularly useful for protecting covered areas from deposition or etching of material.

[0164] It should be noted that the shapes of quantum dots can vary. Examples of different shapes of quantum dots can be called nanorods, nanowires, tetrahedrons, nanopyramids, nanocubes, etc.

[0165] It should be noted that each particle P may contain more than one quantum dot, for example, by integrating the quantum dots into porous silica microspheres, or by aggregating multiple quantum dots.

[0166] Photonic Crystals : A periodic structure of dielectric, semiconductor or metal dielectric material that modifies the propagation of electromagnetic waves, just as the periodic potential in a semiconductor crystal affects the motion of electrons by creating allowed energy bands and forbidden bands. The wavelengths that can propagate in the crystal are called modes, and their energy wave vectors represent the energy bands. In this structure, the phenomenon that there is no propagation mode of electromagnetic waves within a certain frequency or wavelength range is called the bandgap width.

[0167] Energy band diagram : The band diagram shows the energy of the bands, expressed as a function of reduced frequency and the value of the wave vector.

[0168] Light Emitting Diode (LED) :

[0169] The LED structure is a semiconductor structure including a plurality of semiconductor regions forming a PN junction and configured such that when current flows through different semiconductor regions, the LED structure emits light.

[0170] An example of an LED structure is a two-dimensional structure including an n-type doped layer, a p-type doped layer and at least one emission layer. In this case, each emission layer is inserted between the n-type doped layer and the p-type doped layer along the normal direction D.

[0171] In one embodiment, the bandgap value of each emission layer is strictly smaller than the bandgap value of the n-type doped layer and also strictly smaller than the bandgap 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 emission layer is an InGaN layer.

[0172] For example, the emissive layer is undoped. In other embodiments, the emissive layer is doped.

[0173] The quantum well is a specific example of an emission layer, and its bandgap value is smaller than the bandgap values ​​of the n-type doped layer and the p-type doped layer.

[0174] Doping : Doping refers to the presence of impurities in a material that provide free charge carriers. Impurities are atoms of elements, for example, that are not naturally present in the material.

[0175] When the impurity increases the density of holes in the material compared to the undoped material, the doping is p-type. For example, a layer of gallium nitride (GaN) is p-doped by adding magnesium atoms (Mg).

[0176] When the impurity increases the volume density of free electrons in the material compared to the undoped material, the doping is n-type, such as n-doping a gallium nitride (GaN) layer by adding silicon (Si) atoms.

[0177] Converting Materials : The conversion material is configured to convert the first radiation emitted by the light emitter into the 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.

[0178] The second radiation has a second wavelength range. The second range is different from the first range. More specifically, the second radiation has a second average wavelength, which is different from the first average wavelength. The second average wavelength is, in particular, strictly greater than the first average wavelength.

[0179] The conversion material may be a semiconductor material.

[0180] For example, the conversion material may be selected from: CdSe, CdTe, ZnSe, ZnTe, InP, InPZnS, Ag2S, CuInS, CuInSe, AgInS2, AgInSe2 or InPZn x Se x-y S y However, it is also conceivable that other types of materials may be used.

[0181] In other embodiments, the conversion material is a non-semiconductor material, such as an inorganic garnet. For example, the conversion material is a doped yttrium aluminum garnet. However, it is also conceivable to use other types of non-semiconductor conversion materials, in particular other garnets.

[0182] More specifically, the conversion material may be an inorganic phosphorus.

[0183] Yttrium aluminum garnet particles (such as YAG:CE), terbium aluminum garnet particles, TAG (such as TAG:Ce), silicate particles (such as SrBaSiO4:Eu), sulfide particles (such as SrGa2S4:Eu, SrS:Eu, CaS:Eu, etc.), nitride particles (such as Ca2Si5N8:Eu, Ba2Si5N8:Eu, etc.), oxynitride particles (such as Ca2Si5N8:Eu, Ba2Si5N8:Eu, etc.), and fluoride particles (such as K2SiF6:Mn, Na2SiF6:Mn, etc.) are all examples of inorganic phosphors.

[0184] Many other conversion materials can also be used, such as doped aluminates, doped nitrides, doped fluorides, doped sulfides or doped silicates.

[0185] The conversion material can be doped with, for example, rare earth elements, alkaline earth elements or transition metal elements. For example, cerium is sometimes used to dope yttrium aluminum garnet.

[0186] The conversion material comprises, for example, a group of particles P made of the conversion material. The particles P are sometimes referred to as "luminophores".

[0187] Semiconductor Materials : The term "bandgap width value" should be understood as the bandgap width value between the valence band and the conduction band of a material.

[0188] The unit of the bandgap value is, for example, electron volt (eV).

[0189] Among the allowed energy bands of electrons in a material, the valence band is defined as the band with the highest energy and is completely filled at a temperature less than or equal to 20 Kelvin (K).

[0190] Each valence band has a first energy level defined. The first energy level is the highest energy level in the valence band.

[0191] Among the allowed energy bands of electrons in a material, the conduction band is defined as the energy band with the lowest energy but not completely filled when the temperature is less than or equal to 20K.

[0192] Each conduction band has a second energy level defined. The second energy level is the highest energy level in the conduction band.

[0193] Therefore, each bandgap value is measured between the first and second energy levels of the material.

[0194] A semiconductor material is a material whose bandgap value is strictly greater than zero and less than or equal to 6.5 eV.

[0195] A direct bandgap semiconductor is an example of a semiconductor material. A material is said to have a "direct bandgap" when the minimum of the conduction band and the maximum of the valence band correspond to the same value of the charge carrier momentum. A material is said to have an "indirect bandgap" when the minimum of the conduction band and the maximum of the valence band correspond to different values ​​of the charge carrier momentum.

[0196] Each semiconductor material may be selected from, for example, group III-V semiconductors (particularly nitrides of group III elements), group II-VI semiconductors or group IV-IV semiconductors.

[0197] The III-V semiconductors include, in particular, InAs, GaAs, AlAs and alloys thereof, InP, GaP, AlP and alloys thereof, and nitrides of the III-group elements.

[0198] Group II-VI semiconductors include CdTe, HgTe, CdSe, HgSe and their alloys.

[0199] Group IV-IV semiconductors include, in particular, Si, Ge and alloys thereof.

[0200] Nanowires : Nanowires are a specific example of three-dimensional structures.

[0201] A three-dimensional structure is a structure extending along a main direction. A three-dimensional structure has a length measured along the main direction. A three-dimensional structure also has a maximum lateral dimension measured along a lateral direction perpendicular to the main direction, where the lateral direction is the direction perpendicular to the main direction in which the structure has the largest dimension.

[0202] The maximum lateral dimension is, for example, less than or equal to 10 micrometers (μm), and the length is greater than or equal to the maximum lateral dimension. The maximum lateral dimension is preferably less than or equal to 2.5 μm.

[0203] In particular, the maximum lateral dimension is greater than or equal to 10 nm.

[0204] In specific embodiments, the length is greater than or equal to twice the largest lateral dimension, such as greater than or equal to five times the largest lateral dimension.

[0205] The main direction is, for example, the normal direction D. In this case, the length of the three-dimensional structure is referred to as the "height", the maximum dimension of the three-dimensional structure on a plane perpendicular to the normal direction D being less than or equal to 10 μm.

[0206] The maximum dimension of a three-dimensional structure on a plane perpendicular to the normal direction D is usually referred to as the "diameter", which has nothing to do with the cross-sectional shape of the three-dimensional structure.

[0207] Each three-dimensional structure is, for example, a microfilament. A microfilament is a three-dimensional cylindrical structure.

[0208] In a specific embodiment, the microfilament is a cylinder extending along a normal direction D. In this case, the diameter of the base of the cylinder is less than or equal to half the length of the microfilament.

[0209] Microwires with a maximum lateral dimension less than 1 μm are called "nanowires".

[0210] Another example of a three-dimensional structure is a pyramid extending along the normal direction D of the substrate.

[0211] Another example of a three-dimensional structure is a cone extending along the normal direction D.

[0212] Another example of a three-dimensional structure is a truncated cone or a truncated pyramid extending along the normal direction D.

[0213] Standing Wave :Standing waves refer to the phenomenon that multiple waves with the same frequency and amplitude propagate in opposite directions simultaneously in the same physical medium. The elements of the standing wave pattern are fixed in time. What is observed at each observation point is not the propagating wave, but standing wave vibrations of different intensities. These characteristic fixed points are called pressure nodes.

[0214] Pixel : Many display screens have groups of light emitters that form the image displayed on the screen. Each of these emitters plays the role of a picture element or "pixel", from the English "Picture Element" (especially when the screen is monochrome), or a part of such a picture element, called a "sub-pixel" (especially when the screen is color, each pixel includes sub-pixels of different colors, whose selective illumination can change the color of the pixel). In the description, the red pixel is a sub-pixel in the above sense.

[0215] Quantum Well:A quantum well is a structure in which at least one type of charge carrier is quantum confined in one direction. When the size of the structure along that direction is comparable to or smaller than the de Broglie wavelength of the carriers (usually electrons and / or holes), quantum confinement effects occur, resulting in energy levels known as "energy subbands".

[0216] In such a quantum well, carriers can have only discrete energy values, but generally move easily in a plane perpendicular to the direction in which confinement occurs. The energy values ​​(also known as "energy levels") available to carriers increase as the size of the quantum well decreases along the direction in which confinement occurs.

[0217] In quantum mechanics, the "de Broglie wavelength" is the wavelength of a particle when the particle is viewed as a wave. The de Broglie wavelength of an electron is also called the "electron wavelength." The de Broglie wavelength of a charge carrier depends on the material the quantum well is made of.

[0218] An example of a quantum well is an emissive layer whose thickness is strictly less than 5 times the electron wavelength of the electrons in the semiconductor material constituting the emissive layer.

[0219] Another example of a quantum well is an emitting layer whose thickness is strictly less than 5 times the de Broglie wavelength of an exciton in the semiconductor constituting the emitting layer. An exciton is a quasiparticle consisting of an electron and a hole.

[0220] In particular, the thickness of the quantum well is typically in the range of 1 nm to 50 nm.

[0221] radiation : Every type of radiation consists of groups of electromagnetic waves.

[0222] Every electromagnetic wave is defined by a wavelength.

[0223] Each group corresponds to a wavelength range or spectral band. A wavelength range includes groups of wavelengths of an electromagnetic wave group. The average wavelength of a spectral band can be defined as the average value of the ends of the spectral band.

[0224] red : The average wavelength of red radiation ranges from 600nm-720nm.

[0225] UV rays : The average wavelength of ultraviolet radiation ranges from 350nm to 430nm.

[0226] green : The average wavelength of green radiation ranges from 500nm to 560nm.

Claims

1. A light emitting element (10), comprising: a conversion material (14) adapted to convert a first radiation within a first spectral band into a second radiation within a second spectral band, the second spectral band being different from the first spectral band, and A standing wave generator within the first spectral band, the standing wave generator comprising a two-dimensional photonic crystal (26) suitable for generating a standing wave within the first spectral band, the photonic crystal (26) being at least partially constituted by a light emitting diode (12) suitable for emitting within the first spectral band.

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

3. The light-emitting element according to claim 1 or 2, wherein the light-emitting diode (12) comprises an active layer (16), and the photonic crystal (26) comprises at least one of the active layers (16).

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

5. The light-emitting element according to any one of claims 1 to 4, wherein the photonic crystal (26) includes the entirety of each of the light-emitting diodes (12).

6. The light-emitting element according to any one of claims 1 to 5, wherein the light-emitting diode (12) is located in a medium, and the medium is the conversion material (14).

7. The light-emitting element according to any one of claims 1 to 5, wherein the conversion material (14) is located on the photonic crystal (26).

8. The light-emitting element according to any one of claims 1 to 7, wherein the photonic crystal (26) has a plurality of bandgap widths, and the photonic crystal (26) has a spacing (a) and a filling factor suitable for enabling the light-emitting diode (12) to emit at 90° at the band edge of a first bandgap width.

9. A light-emitting element according to any one of claims 1 to 7, wherein the photonic crystal (26) has multiple bandgap widths, and the photonic crystal (26) has a spacing (a) and a filling factor suitable for enabling the light-emitting diode (12) to emit at 90° at a band edge of a bandgap width different from the first bandgap width.

10. According to the light-emitting element of claim 9, the spacing (a) and the filling factor of the photonic crystal (26) are also suitable for making the conversion material emit at the band edge of the 0° bandgap width, and the bandgap width emitted by the conversion material (14) is smaller than the bandgap width emitted by the light-emitting diode (12).

11. A light-emitting element according to any one of claims 1 to 10, wherein the photonic crystal (26) is surrounded by walls (28, 30) to form a cavity, and at least one of the walls (28, 30) is made of a material selected from the following: transparent conductive oxides, such as indium tin oxide or zinc oxide doped with gallium or aluminum; metals, such as silver or aluminum; graphene; and combinations thereof.

12. The light-emitting element according to any one of claims 1 to 11, wherein the conversion material (14) is a polymer matrix comprising quantum dots.

13. The light-emitting element according to any one of claims 1 to 12, wherein each of the light-emitting diodes (12) comprises an active medium (16) made of a first material, the active medium (16) being surrounded by a layer (18) made of a second material, the first material comprising InGaN, the second material comprising GaN.

14. A light-emitting element according to any one of claims 1 to 13, wherein the photonic crystal (26) has a central part (42) and a peripheral part (44), each part (42, 44) brings together a plurality of the light-emitting diodes (12), and only the central part (42) of the photonic crystal (26) is supplied with energy.

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

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