Patent Application
20240321843
The present disclosure relates generally to optoelectronic devices based on semiconductor materials and methods for their manufacture. The present invention relates more specifically to optoelectronic devices comprising light-emitting diodes formed by three-dimensional elements, in particular semiconductor microwires or nanowires.
By optoelectronic devices comprising light-emitting diodes, devices are understood that are adapted to effect the conversion of an electric signal into electromagnetic radiation, and in particular devices dedicated to the emission of electromagnetic radiation, in particular light. Examples of three-dimensional elements adapted to the realisation of light-emitting diodes are micowires or nanowires comprising a semiconductor material based on a compound predominantly comprising at least one element from group III and one element from group V (for example gallium nitride GaN), called III-V compound in the following.
The light extraction efficiency (LEE) of an optoelectronic device is generally defined by the ratio between the number of photons that escape from the optoelectronic device and the number of photons emitted by the light-emitting diodes. It is desirable that the extraction efficiency of an optoelectronic device is as high as possible.
A drawback of the existing optoelectronic devices is that a fraction of the photons emitted within each light-emitting diode does not escape from the light-emitting diode.
Thus, one object of an embodiment is to at least partially address the drawbacks of the optoelectronic devices comprising light-emitting diodes, in particular comprising microwires or nanowires, described in the foregoing and methods for their manufacture.
A further object of an embodiment is to increase the extraction efficiency of the optoelectronic device.
A further object of an embodiment is to reduce the proportion of the light that does not escape from each light-emitting diode.
A further object of an embodiment is to reduce the proportion of the light emitted by a light-emitting diode that is absorbed/trapped by the adjacent light-emitting diodes.
One embodiment provides an optoelectronic device comprising:
A further embodiment provides an optoelectronic device comprising:
According to an embodiment, the dielectric layer is placed between the electrically conductive layer and the encapsulation block or the electrically conductive layer is placed between the dielectric layer and the encapsulation block.
According to an embodiment, each semiconductor element is a III-V compound.
According to an embodiment, each semiconductor element comprises gallium nitride.
According to an embodiment, the average diameter of each semiconductor element is comprised between 200 nm and 2 μm and the average diameter of each encapsulation block is comprised between 3 μm and 30 μm.
According to an embodiment, the device comprises, moreover, for at least one light-emitting diode, a photoluminescent layer covering the encapsulation block.
According to an embodiment, the device comprises lenses covering the encapsulation blocks, the interstices of air being present between the lenses.
According to an embodiment, the device comprises, moreover, an angular filter covering the lenses.
According to an embodiment, the angular filter comprises a layer at least partially opaque to the visible light and spanned by openings.
A further embodiment provides a method for manufacturing an optoelectronic device comprising a support comprising a face and light-emitting diodes lying on the face and comprising semiconductor elements in the form of wires, cones or truncated cones. The method comprises the formation, for each light-emitting diode or each group of light-emitting diodes, of an encapsulation block at least partially transparent to the radiation emitted by the light-emitting diodes and covering the light-emitting diode or the group of light-emitting diodes, the maximum thickness of the encapsulation block being comprised between 1 μm and 30 μm, interstices of air being present between the encapsulation blocks covering adjacent light-emitting diodes or adjacent groups of light-emitting diodes, and the formation of an electrically conductive layer covering the encapsulation blocks and in contact with each light-emitting diode, wherein the refractive index of the encapsulation block covering at least one of the light-emitting diodes or one of the groups of light-emitting diodes is comprised between 1.3 and 1.6.
A further embodiment provides a method for manufacturing an optoelectronic device comprising a support comprising a face and light-emitting diodes lying on the face and comprising semiconductor elements in the form of wires, cones or truncated cones, the method comprising the formation, for each light-emitting diode or each group of light-emitting diodes, of an encapsulation block at least partially transparent to the radiation emitted by the light-emitting diodes and covering the light-emitting diode or the group of light-emitting diodes, the maximum thickness of the encapsulation block being comprised between 1 μm and 30 μm, interstices of air being present between the encapsulation blocks covering adjacent light-emitting diodes or adjacent groups of light-emitting diodes, and the formation of an electrically conductive layer covering the encapsulation blocks and in contact with each light-emitting diode. The optoelectronic device comprises, for at least one of the encapsulation blocks, a conformal dielectric layer covering the encapsulation block, and at least partially transparent to the radiation emitted by the light-emitting diodes, the refractive index of the encapsulation block being comprised between 1.8 and 2.2, the thickness of the dielectric layer being comprised between 200 nm and 5 μm, and the refractive index of the dielectric layer being comprised between 1.3 and 1.6.
According to an embodiment, the method comprises the formation of lenses covering the encapsulation blocks.
According to an embodiment, the method comprises the formation of a monobloc structure comprising the lenses, each lens comprising a slot and comprising the fixation of the monobloc structure to the support, the encapsulation blocks being inserted into the slots.
The foregoing features and advantages, as well as others, will be described in detail in the following description of specific embodiments given by way of illustration and not limitation with reference to the accompanying drawings, in which:
Like features have been designated by like references in the various figures. In particular, the structural and/or functional features that are common among the various embodiments may have the same references and may have identical structural, dimensional and material properties. For the sake of clarity, only the operations and elements that are useful for an understanding of the described embodiments herein have been illustrated and described in detail. In particular, the means of biasing the light-emitting diodes of an optoelectronic device are well known and have not been described.
In the following disclosure, unless indicated otherwise, when reference is made to absolute positional qualifiers, such as the terms “front”, “back”, “top”, “bottom”, “left”, “right”, etc., or to relative positional qualifiers, such as the terms “above”, “below”, “higher”, “lower”, etc., or to qualifiers of orientation, such as “horizontal”, “vertical”, etc., reference is made to the orientation shown in the figures or to an optoelectronic device in a normal position of usage. Moreover, “component mainly constituted by a material” or “compound based on a material” are understood to mean that a compound comprises a proportion that is greater than or equal to 95% of said material, this proportion preferably being greater than 99%. Unless otherwise specified, the expressions “around”, “approximately”, “substantially” and “in the order of” signify within 10%, and preferably within 5%. In the following disclosure, “conductive layer” is understood to mean an electrically conductive layer and “isolating layer” is understood to mean an electrically isolating layer.
The present disclosure relates to optoelectronic devices comprising three-dimensional elements, for example elements in the form of wires, cones or truncated cones, in particular microwires or nanowires.
The term “microwire” or “nanowire” designates a three-dimensional structure with an elongated form in a privileged direction at least two dimensions of which, called minor dimensions, are comprised between 5 nm and 2.5 μm, preferably between 50 nm and 2.5 μm, the third dimension, called the major dimension, being at least equal to once, preferably at least 5 times and even more preferably at least 10 times, greater than the minor dimensions. In certain embodiments, the minor dimensions can be less than or equal to approximately 1.5 μm, preferably comprised between 100 nm and 1.5 μm, more preferably between 100 nm and 800 nm. In certain embodiments, the height of each microwire or nanowire can be greater than or equal to 500 nm, preferably comprised between 1 μm and 50 μm.
In the following disclosure, the term “wire” is used to signify “microwire or nanowire”. Preferably, the mean line of the wire that transects the barycentres of the cross sections, in planes perpendicular to the privileged direction of the wire, is substantially rectilinear and is called “axis” of the wire in the following.
According to a further embodiment, the isolating layer 32 is not present. According to a further embodiment, the isolating layer 32 is placed between the conductive layer 30 and the encapsulation block 25.
In the present embodiment, the light-emitting diodes DEL are connected in parallel and form a set of light-emitting diodes. As a variant, the electrodes 24 and 30 can be arranged in order to connect the light-emitting diodes in different manners.
According to an embodiment, the isolating layer 32 is in contact with air 34. The front face 36 of the optoelectronic device 5 is the face seen by an observer and comprises in particular the faces exposed to the air 34 of the encapsulation blocks 25 when the layer 32 is not present, or the faces exposed to the air 34 of the layer 32 when the layer 32 is present. In particular, an interstice of air 37 is placed between each pair of adjacent light-emitting diodes.
According to an embodiment, the material composing the encapsulation block 25 has an optical refractive index, also called refractive index, for the wavelengths of the radiation emitted by the light-emitting diodes DEL, strictly lower than the refractive index of the material composing the wire 16 and strictly greater than the refractive index of the material composing the isolating layer 32. The optical refractive index is a dimensionless number that characterises the optical properties of a medium, in particular absorption and diffusion. The refractive index is equal to the real part of the complex optical index. The refractive index can be determined, for example, by ellipsometry. Unless otherwise indicated, when the following disclosure refers to a refractive index, this is a refractive index for the wavelengths of the radiation emitted by the light-emitting diodes DEL. According to an embodiment, the material composing the isolating layer 32 has an optical refractive index strictly lower than the refractive index of the material composing the encapsulation block 25 and strictly greater than the refractive index of air.
The support 10 can correspond to a monobloc structure or comprise a base covered by a conductive layer. The upper face 12 is electrically conductive and is for example metal, for example made of aluminium, of silver, of copper or of zinc. The support 10 can comprise various conductive areas electrically isolated from one another. By this means, it is possible to address the various light-emitting diodes independently. According to an embodiment, the face 12 can be reflective. The support 10 can thus have a specular reflection. According to a further embodiment, the support 10 can thus have a Lambertian reflection. In order to obtain a surface having a Lambertian reflection, one possibility is to create irregularities on a conductive surface. For instance, when the face 12 corresponds to the face of a conductive layer lying on a base, a texturing of the surface of the base can be realised before the deposition of the metal layer so that the face 12 of the metal layer, once deposited, exhibits reliefs.
The wires 16 are, at least partly, formed from at least one semiconductor material. The wires 16 can be, at least partly, formed from semiconductor materials predominantly comprising a III-V compound, for example a III-N compound. Examples of elements from group III comprise gallium (Ga), indium (In) or aluminium (Al). Examples of III-N compounds are GaN, AlN, InN, InGaN, AlGaN or AlInGaN. Further elements from group V can also be used, for example, phosphorus or arsenic. Generally speaking, the elements in the III-V compound can be combined with various mole fractions. The wires 16 can comprise a dopant. For instance, for III-V compounds, the dopant can be chosen from the group comprising a p-type dopant from group II, for example magnesium (Mg), zinc (Zn), cadmium (Cd) or mercury (Hg), a p-type dopant from group IV, for example carbon (C) or an n-type dopant from group IV, for example silicon (Si), germanium (Ge), selenium (Se), sulphur (S), terbium (Tb) or tin (Sn).
The cross section of the wires 16 can have various shapes, such as, for example, an oval, circular or polygonal shape, in particular triangular, rectangular, square or hexagonal. Thus, it is understood that, when the “diameter” in a cross section of a wire or a layer deposited on this wire is mentioned here, this is a variable associated with the surface area of the desired structure in this cross section, corresponding, for example, to the diameter of the disk having the same surface area as the cross section of the wire. The height of each wire 16 can be comprised between 250 nm and 50 μm. Each wire 16 can have a semiconductor structure elongated along an axis substantially perpendicular to the face 12. Each wire 16 can have a general cylindrical shape. The axes of two adjacent wires 16 can be distant by 0.5 μm to 10 μm and preferably by 1.5 μm to 6 μm. For instance, the wires 16 can be distributed regularly, in particular in accordance with a hexagonal or square array.
The casing 22 can comprise a stack of a plurality of layers comprising in particular:
The active layer is the layer from which the majority of the radiation provided by the light-emitting diode DEL is emitted. According to an example, the active layer can comprise confining means, such as a single quantum well or multiple quantum wells. It is, for example, constituted by an alternation of layers of GaN and of InGaN having respective thicknesses from 5 to 20 nm (for example 8 nm) and from 1 to 10 nm (for example 2.5 nm). The layers of GaN can be doped, for example n-type or p-type doped. According to a further example, the active layer can comprise a sole layer of InGaN, for example with a thickness greater than 10 nm.
The intermediate layer, for example p-type doped, can correspond to a semiconductor layer or to a stack of semiconductor layers and allow the formation of a p-n or pin junction, the active layer being comprised between the p-type intermediate layer and the n-type wire 16 of the p-n or pin junction. The coupling layer can correspond to a semiconductor layer or to a stack of semiconductor layers and allows the formation of an ohmic contact between the intermediate layer and the electrode 24. For instance, the coupling layer can be very heavily doped with the type opposite that of the wire 16, until a degeneration of the one or more semiconductor layers, for example p-typed doped at a concentration greater than or equal to 1020 atoms/cm3. The stack of semiconductor layers can comprise a layer for blocking electrons formed from a ternary alloy, for example made of aluminium gallium nitride (AlGaN) or of aluminium indium nitride (AlInN) in contact with the active layer and the intermediate layer, in order to ensure a good distribution of the electric carriers in the active layer.
Each electrode 24, 30 is adapted to bias the active layer of the light-emitting diode DEL and to let through the electromagnetic radiation emitted by the light-emitting diode DEL. The material forming each electrode 24, 30 can be a conductive and transparent material such as indium tin oxide (or ITO), pure zinc oxide, aluminium-doped zinc oxide, gallium-doped zinc oxide, graphene, or silver nanowires. For instance, each electrode layer 24, 30 has a thickness comprised between 5 nm and 200 nm, preferably between 30 nm and 100 nm.
Each isolating layer 14, 28 and 32 can be made of a dielectric material, for example made of silicon oxide (SiO2), of silicon nitride (SixNy, where x is approximately equal to 3 and y is approximately equal to 4, for example Si3N4), of silicon oxynitride (in particular with the general formula SiOxNy, for example Si2ON2), of aluminium oxide (Al2O3), of hafnium oxide (HfO2) or of diamond. For instance, the thickness of each isolating layer 14 and 28 is comprised between 5 nm and 500 nm, for example equal to approximately 30 nm. The layer 32 can, moreover, be made of an organic material, for example an organic polymer, or of an inorganic polymer, for example silicon. For instance, the thickness of the isolating layer 32, when it is present, is comprised between 200 nm and 5 μm, for example equal to approximately 1 μm.
The encapsulation block 25 can be made of an organic material or an inorganic material at least partially transparent to the radiation emitted by the light-emitting diode DEL. The maximum thickness of the encapsulation block 25, measured perpendicularly to the face 12, is preferably comprised between 1 μm and 30 μm. The width of the encapsulation block 25 can correspond to the diameter of the circle circumscribing the encapsulation block in a top view. According to an embodiment, the width of the encapsulation block 25 is comprised between 3 μm and 30 μm. According to an embodiment, the upper face 26 is flat and parallel to the face 12. According to an embodiment, the lateral wall 18 is perpendicular to the face 12. As a variant, the lateral wall 18 can be inclined with respect to the face 12.
The encapsulation block 25 can be realised from an at least partially transparent organic material. The encapsulation block 25 can comprise a matrix of an at least partially transparent organic or inorganic material in which particles of a dielectric material are possibly distributed. The refractive index of the dielectric material composing the particles is strictly higher than the refractive index of the material composing the matrix. According to an example, the encapsulation block 25 comprises a matrix made of silicone, also known as polysiloxane, or a matrix made of an epoxide polymer and comprises, moreover, particles of a dielectric material distributed in the matrix. The particles are composed of any type of material with which it is possible to obtain relatively spherical nanocale particles and having an adapted refractive index. For instance, the particles can be composed of titanium oxide (TiO2), of zirconium oxide (ZrO2), of zinc sulphide (ZnS), of lead sulphide (PbS) or of amorphous silicon (Si). What is known as the average diameter of a particle is the diameter of the sphere with the same volume. The average diameter of the particles of the dielectric material is comprised between 2 nm and 250 nm. The concentration by volume of the particles with respect to the total weight of the encapsulation layer 34 is comprised between 1% and 50%. According to a further example, the encapsulation block 25 can be composed of one of the materials described in the foregoing in relation to the isolating layers 14, 28 and 32.
When the layer 32 is not present, the encapsulation block has a refractive index comprised between 1.3 and 1.6. When the layer 32 is present, the encapsulation block 25 has a refractive index comprised between 1.8 and 2.2 and the isolating layer 32 has a refractive index comprised between 1.3 and 1.6.
The optoelectronic device according to the embodiment described in the foregoing advantageously makes it possible to increase the overall extraction efficiency of the optoelectronic device 5, i.e. escaping from the optoelectronic device 5 via the front face 36. In order to be perceived by an observer looking at the optoelectronic device 5, the light must leave the encapsulation blocks 25 via the front face 36. In order to improve the extraction efficiency of the optoelectronic device 5, a surface processing, known as texturing, can be applied to the front face 36 so as to form relief patterns on the face 36.
Simulations were performed for the optoelectronic device 5 illustrated in
The photoluminescent layer 42 can comprise luminophores adapted, when they are excited by the light emitted by the associated light-emitting diode DEL, to emit light at a wavelength different from the wavelength of the light emitted by the associated light-emitting diode DEL. The thickness of the photoluminescent layer 42 can be comprised between 4 μm and 40 μm.
According to an embodiment, the photoluminescent layer 42 comprises particles of at least one photoluminescent material. An example of a photoluminescent material is the yttrium aluminium garnet (YAG) activated by the trivalent cerium ion, also known as YAG:Ce or YAG:Ce3+. The average size of the particles of the classic photoluminescent materials is generally greater than 5 μm.
According to an embodiment, each photoluminescent layer 42 comprises a matrix in which nanoscale single-crystalline particles of a semiconducting material are dispersed, also called semiconductor nanocrystals or nanoluminophore particles in the following. The internal quantum efficiency QYint of a photoluminescent material is equal to the ratio between the number of photons emitted and the number of photons absorbed by the photoluminescent substance. The internal quantum efficiency QYint of the semiconductor nanocrystals is higher than 5%, preferably higher than 10%, more preferably higher than 20%.
According to an embodiment, the average size of the nanocrystals is in the range of 0.5 nm and 1000 nm, preferably from 0.5 nm to 500 nm, even more preferably from 1 nm to 100 nm, in particular from 2 nm to 30 nm. For dimensions less than 50 nm, the photoconversion properties of the semiconductor nanocrystals essentially depend on quantum confinement phenomena. The semiconductor nanocrystals thus correspond to quantum dots (in the case of a confinement in the three dimensions) or to quantum wells (in the case of a confinement in two dimensions).
According to an embodiment, the semiconductor material of the semiconductor nanocrystals is chosen from the group comprising cadmium selenide (CdSe), indium phosphide (InP), cadmium sulphide (CdS), zinc sulphide (ZnS), zinc selenide (ZnSe), cadmium telluride (CdTe), zinc telluride (ZnTe), cadmium oxide (CdO), zinc cadmium oxide (ZnCdO), cadmium zinc sulphide (CdZnS), cadmium zinc selenide (CdZnSe), silver indium sulphide (AgInS2), perovskites of the type PbScX3, where X is a halogen atom, in particular iodine (I), bromine (Br) or chlorine (Cl), and a mixture of at least two of these compounds. According to an embodiment, the semiconductor material of the semiconductor nanocrystals is chosen from the materials cited in the publication by Blevenec and al. in Physica Status Solidi (RRL)-Rapid Research Letters Volume 8, No. 4, pages 349-352, April 2014.
According to an embodiment, the dimensions of the semiconductor nanocrystals are chosen in accordance with the desired wavelength of the radiation emitted by the semiconductor nanocrystals. For instance, CdSe nanocrystals the average size of which is in the order of 3.6 nm are adapted to convert blue light into red light and CdSe nanocrystals the average size of which is in the order of 1.3 nm are adapted to convert blue light into green light. According to a further embodiment, the composition of the semiconductor nanocrystals is chosen in accordance with the desired wavelength of the radiation emitted by the semiconductor nanocrystals.
The matrix is made of a material at least partly transparent to the radiation emitted by the light-emitting diode DEL and to the radiation emitted by the photoluminescent particles. The matrix is, for example, made of silica. The matrix is, for example, made of any at least partly transparent polymer, in particular of silicone, of epoxy or of polyacetic acid (PLA). The matrix can be made of an at least partly transparent polymer used with three-dimensional printers, such as PLA. According to an embodiment, the matrix contains from 2% to 90%, preferably from 10% to 60%, by weight nanocrystals, for example approximately 30% by weight nanocrystals. The matrix can further contain scattering particles, in particular TiO2 particles, having, for example, a diameter comprised between 100 nm and 300 nm.
Simulations were performed for the optoelectronic device 40 illustrated in
The lens 56 can be realised from an organic or inorganic material, in particular the materials described in the foregoing in order to form the encapsulation block 25 and/or the matrix of the photoluminescent layer 42. With the lens 56, it is possible to improve the directivity of the light emitted by the optoelectronic device 55. The thickness Zmax of the lens 56 corresponds to the maximum distance between the electrode layer 30 and the face 58. The width Ymax of the lens 56 corresponds to the maximum distance of the lens 56 measured parallel to the face 12 of the support 10. According to an embodiment, the thickness Zmax is comprised between 8 μm and 50 μm. According to an embodiment, the width Ymax is comprised between 8 μm and 50 μm. Preferably, the refractive index of the lens 56 is comprised between 1.4 and 1.5.
According to an embodiment, the support 10 is reflective for the radiation emitted by the light-emitting diode DEL and the lateral wall of the lens 56, on a lower portion of the lens 56, is surrounded by a layer reflective for the radiation emitted by the light-emitting diode DEL.
Simulations were performed for the optoelectronic device 55 illustrated in
Preferably, each light-emitting diode DEL is covered with a lens 56 as illustrated in
1) Formation of the light-emitting diodes DEL (
2) Fixation of the structure obtained in the preceding step to a handle 79, removal of the substrate 70 and of the nucleation layer 72 and partial cutting out of the obtained structure, on the side of the isolating layer 74, in order to delimit the encapsulation blocks 25 and the isolating layers 28 (
3) Fixation to the support 10 of light-emitting diodes of the structure obtained in the preceding step (
4) Formation of the isolating layer 14 (
5) Formation of the electrode layer 30, for example by conformal deposition (
6) Possible formation for the light-emitting diodes DEL not comprising a photoluminescent layer 42 of the layer 32 covering the electrode layer 30 (
7) Formation of the photoluminescent layers 42 for the other light-emitting diodes DEL (
8) Formation of the isolating layer 43, for example by conformal deposition (
9) Formation of the filters 44 (
In the case of optoelectronic devices comprising lenses 56 covering the light-emitting diodes, the lenses 56 can be formed by the deposition of a layer of the material composing the lenses on the light-emitting diodes and the etching of this layer or the forming of this layer in order to obtain the lenses 56.
1)′ Formation of the light-emitting diodes DEL in a manner analogous to what was described in the foregoing in step 1) in relation to
2)′ Partial cutting out of the obtained structure, on the side of the isolating layer 74, in order to delimit the encapsulation blocks 25, the isolating layers 28 and portions 88 of the nucleation layer 72 (
3)′ Fixation to the support 10 of light-emitting diodes of the structure obtained in the preceding step (
4)′ Selective freeing of the substrate 70 of the light-emitting diodes DEL fixed to the support 10 and removal of the portions 80 of the nucleation layer.
The subsequent steps of the method can correspond to the steps described in the foregoing in relation to
Various embodiments and variants have been described. Those skilled in the art will understand that certain features of these embodiments can be combined and other variants will readily occur to those skilled in the art. In particular, the structure of the light-emitting diode DEL of optoelectronic device 50 illustrated in
Finally, the practical implementation of the embodiments and variants described herein is within the capabilities of those skilled in the art based on the functional description provided hereinabove.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1871254 | Oct 2018 | FR | national |
This Application is continuation of U.S. patent application Ser. No. 17/287,087, filed Apr. 20, 2021, which is a national stage filing under 35 U.S.C. § 371 of International Patent Application Serial No. PCT/EP2019/078320, filed Oct. 18, 2019, which claims priority to French patent application FR18/71254, filed Oct. 22, 2018. The entire contents of these applications are incorporated herein by reference in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 17287087 | Apr 2021 | US |
| Child | 18676771 | US |
