Optoelectronic device with axial three-dimensional light-emitting diode

Abstract

The present disclosure relates to an optoelectronic device (10) comprising an array (15) of axial light-emitting diodes (LEDs), each having an active region (20) configured to emit electromagnetic radiation whose emission spectrum includes a maximum at a first wavelength. The device further comprises a cladding (23) for each LED, the cladding (23) being made of a first material that surrounds the sidewalls of the LED over at least a portion of the LED and is transparent to the radiation, each cladding having a thickness greater than 10 nm. The device further comprises a layer (24) between the claddings, the layer (24) being made of a second material different from the first material that is transparent to the radiation, the second material being electrically insulating, and the array forming a photonic crystal.

Description

[Technical Field]

[0001] The present disclosure relates to optoelectronic devices, in particular display screens or image projection devices comprising light emitting diodes (LEDs) based on semiconductor materials, and methods for manufacturing the same. [Background technology]

[0002] LEDs based on semiconductor materials generally include an active region, which is the region of the LED from which most of the electromagnetic radiation provided by the LED is emitted. The structure and composition of the active region are tailored to provide electromagnetic radiation with desired characteristics.

[0003] Of particular interest herein are axial three-dimensional LEDs, i.e., optoelectronic devices having electroluminescent diodes each comprising a three-dimensional semiconductor element, extending along a preferred direction and with active regions at the axial ends of the three-dimensional semiconductor element.

[0004] Examples of three-dimensional semiconductor elements are semiconductor materials containing at least one element from group III and one from group V in majority, hereinafter referred to as III-V compounds, such as gallium nitride (GaN), semiconductor materials containing at least one element from group II and one from group VI in majority, hereinafter referred to as II-VI compounds, such as zinc oxide (ZnO), or microwires or nanowires comprising semiconductor materials containing at least one element from group IV in majority. Such devices are described, for example, in patent applications FR 2 995 729 and FR 2 997 558.

[0005] The formation of active regions comprising confinement means, in particular single or multiple quantum wells, is known. A single quantum well is produced by inserting a layer of a second semiconductor material (having a different bandgap than the first semiconductor material), such as an alloy of a III-V compound and a third element, in particular InGaN, between two layers (doped P-type and N-type, respectively) of a first semiconductor material, such as a III-V compound, in particular GaN. A multiple quantum well structure comprises a stack of semiconductor layers forming alternating quantum wells and barrier layers.

[0006] The wavelength of the electromagnetic radiation emitted by the active region of an optoelectronic device depends, inter alia, on the dimensions of the active region, particularly on the average diameter of the active region. Furthermore, the quantum efficiency of the active region depends, inter alia, on the crystalline quality of the layers that make up the active region. The crystalline quality of the layers that make up the active region tends to deteriorate as the average diameter of the active region increases.

[0007] The LEDs can be arranged in an LED array to form a photonic crystal. In particular, the photonic crystal allows for the light beam emitted by the LED array to be directed along a preferred direction. The photonic crystal also allows for filtering the wavelength of the radiation emitted by the LED array, for example, to facilitate the emission of a narrow spectrum of radiation. In particular, the properties of the photonic crystal depend on the pitch of the LEDs in the LED array and the average diameter of the LEDs.

[0008] One drawback is that the average LED diameter that allows for the emission of the desired radiation from each LED at the desired wavelength while still allowing for adequate crystal quality may differ from the average LED diameter that allows for obtaining a photonic crystal with the desired properties. Summary of the Invention

[0009] It is therefore an object of one embodiment to address all or some of the drawbacks of LED optoelectronic devices mentioned above.

[0010] It is another object of an embodiment for the active region of each LED to comprise a stack of layers of semiconductor material based on a III-V compound, a II-VI compound, or a Group IV semiconductor or compound.

[0011] It is a further object of an embodiment that the emission spectrum of the active region of an axial three-dimensional LED based on a III-V compound, a II-VI compound, or a Group IV semiconductor or compound has desired characteristics.

[0012] It is a further object of an embodiment that the optoelectronic device comprises an LED array that forms a photonic crystal with desired properties.

[0013] Another object of an embodiment is that the active region of the LED has good crystalline quality.

[0014] One embodiment provides an optoelectronic device comprising an array of axially aligned LEDs, each LED having an active region configured to emit electromagnetic radiation whose emission spectrum includes a maximum at a first wavelength. The device further comprises, for each LED, a cladding of a first material transparent to the aforementioned radiation and surrounding a sidewall of the LED over at least a portion of the LED, each cladding having a thickness greater than 10 nm. The device further comprises, between the claddings, a layer of a second material transparent to the aforementioned radiation but different from the first material, the second material being electrically insulating, such that the array forms a photonic crystal. The properties of the photonic crystal are advantageously selected so that the array of coated LEDs forms a resonant cavity, particularly to achieve coupling and enhance selectivity. This allows the intensity of radiation emitted by a group of coated LEDs of the array by the light-emitting surface of the optoelectronic device to be amplified at a particular wavelength compared to a group of coated LEDs that do not form a photonic crystal.

[0015] This makes it possible to separate the properties of the photonic crystal, which depend to a first approximation on the LED pitch and the average outer diameter of the cladding material and LED assembly, from the light-emitting properties of the LED active region, which depend to a first approximation on the average diameter of the LEDs in the absence of the cladding material.

[0016] According to one embodiment, each coating has a thickness greater than 20 nm, which allows the coating to change the optical properties of the photonic crystal compared to an LED array without the coating.

[0017] According to one embodiment, the refractive index of the first material at the first wavelength is strictly greater than the refractive index of the second material at the first wavelength, which allows the coating to change the optical properties of the photonic crystal compared to an LED array without the coating.

[0018] According to one embodiment, the difference between the refractive index of the first material at the first wavelength and the refractive index of the second material at the first wavelength is greater than 0.5 The greater the difference between the refractive index of the first material at the first wavelength and the refractive index of the second material at the first wavelength, the more efficient the photonic crystal is and the easier it is to change the properties of the photonic crystal by changing the thickness of the cladding material.

[0019] According to one embodiment, each LED comprises a semiconductor element made of a third material and at least partially surrounded by the aforementioned coating material, the difference between the refractive index of the first material and the refractive index of the third material being less than 0.5, preferably less than 0.3, which provides refractive index uniformity between the first and third materials, enabling efficient photonic crystal formation and simplifying the design of optoelectronic devices.

[0020] According to one embodiment, the first material is electrically insulating, and protection of the various parts of the LED from short circuits is achieved by the covering material.

[0021] According to one embodiment, the optoelectronic device further comprises, for each LED, an electrically insulating coating interposed between the covering and the LED, the coating having a thickness of less than 10 nm. Since protection against short circuits of the individual parts of the LED is achieved by the electrically insulating coating, the covering does not have to be an insulating material. This advantageously allows for greater freedom in the selection of the material from which the covering is made.

[0022] According to one embodiment, each LED comprises a portion of a III-V compound, a II-VI compound, or a group IV semiconductor or compound, which allows the LED to be manufactured according to known methods.

[0023] According to one embodiment, the first material is silicon nitride or titanium oxide, which allows the use of a first material whose refractive index at the first wavelength is close to the refractive index at the first wavelength of the material from which the LED is made.

[0024] According to one embodiment, the second material is silicon oxide, which makes it possible to obtain a large difference between the refractive index of the first material at a first wavelength and the refractive index of the second material at a second wavelength.

[0025] According to one embodiment, the photonic crystal is configured to form a resonant peak that amplifies the intensity of the aforementioned electromagnetic radiation at at least a second wavelength, which second wavelength is different from or equal to the first wavelength. Advantageously, when the resonant peak is at the first wavelength, the intensity of the radiation emitted at the first wavelength is increased and the emission spectrum is narrowed and centered around the first wavelength. Decoupling the dimensions of the array from the dimensions of each LED facilitates designing a photonic crystal that forms a resonant peak at the first wavelength.

[0026] According to one embodiment, an optoelectronic device comprises a support on which LEDs are mounted, each LED comprising a stack of a first semiconductor portion mounted on the support, an active region in contact with the first semiconductor portion, and a second semiconductor portion in contact with the active region.

[0027] According to one embodiment, the device comprises a reflective layer between the support and the first semiconductor portion of the LED, which improves light extraction from the optoelectronic device.

[0028] According to one embodiment, the reflective layer is metallic.

[0029] According to one embodiment, the second semiconductor part of the LED is covered with a conductive layer that is at least partially transparent to the radiation emitted by the LED.

[0030] One embodiment also provides a method for designing an optoelectronic device comprising axial LEDs each comprising an active region, the method comprising: Dimensioning the LEDs so that each active region emits electromagnetic radiation whose emission spectrum includes a maximum at a first wavelength; determining dimensions of the array of LEDs to obtain a photonic crystal; The array comprises, for each LED, a covering of a first material that is transparent to the aforementioned radiation and surrounds the sidewalls of the LED over at least a portion of the LED, each covering having a thickness greater than 10 nm, and further comprises a layer of a second material between the coverings that is different from the first material, and the second material is electrically insulating.

[0031] Also, one embodiment provides a method for manufacturing an optoelectronic device comprising an array of axial LEDs, each having an active region configured to emit electromagnetic radiation having an emission spectrum including a maximum at a first wavelength, wherein the device further comprises, for each LED, a coating made of a first material that is transparent to the aforementioned radiation and surrounds a sidewall of the LED over at least a portion of the LED, each coating having a thickness greater than 10 nm, wherein the device further comprises a layer between the coatings made of a second material different from the first material, the second material being electrically insulating, and wherein the array forms a photonic crystal.

[0032] According to one embodiment, forming the LED comprises: forming second semiconductor portions on the substrate separated from one another by the pitch of the array; forming an active region on each second semiconductor portion; forming a first semiconductor portion on each active region; forming a coating of a first material surrounding a sidewall of at least a portion of the first portion, the second portion, and / or the active region for each LED; forming a layer of a second material; Includes.

[0033] According to one embodiment, the method includes removing the substrate, thereby allowing a substrate compatible with the formation of the LED to be used. [Brief explanation of the drawings]

[0034] These and other features and advantages are described in detail in the following particular embodiments, given as non-limiting illustrations of the invention with reference to the accompanying drawings, in which:

[0035] [Figure 1] 1 is a schematic partial cross-sectional view of one embodiment of an optoelectronic device comprising an LED. [Figure 2] 2 is a schematic partial perspective view of the optoelectronic device shown in FIG. 1. [Figure 3] 2 is a diagram illustrating an example of an arrangement of LEDs in the optoelectronic device shown in FIG. 1. FIG. [Figure 4] 1. FIG. 4 is a diagram schematically illustrating another example of the arrangement of LEDs in the optoelectronic device shown in FIG. [Figure 5] 1 is a schematic partial cross-sectional view of another embodiment of an optoelectronic device comprising an LED. [Figure 6] Grayscale map of the light intensity emitted by an uncoated LED in a photonic crystal as a function of the wavelength and direction of the emitted radiation. [Figure 7]Grayscale map of the light intensity emitted by a photonic crystal coated LED as a function of the wavelength and direction of the emitted radiation. [Figure 8] 3 shows evolution curves of the light intensity of radiation emitted by an array of LEDs as a function of wavelength measured along a first direction for uncoated and coated LEDs. [Figure 9] FIG. 10 shows a curve of the light intensity of radiation emitted from the LED array as a function of wavelength measured along a second direction for a coated LED. [Figure 10A] 2A to 2C illustrate steps of an embodiment of a method for manufacturing the optoelectronic device shown in FIG. 1. [Figure 10B] 5A-5C illustrate other steps of the manufacturing method. [Figure 10C] 5A-5C illustrate other steps of the manufacturing method. [Figure 10D] 5A-5C illustrate other steps of the manufacturing method. [Figure 10E] 5A-5C illustrate other steps of the manufacturing method. [Figure 10F] 5A-5C illustrate other steps of the manufacturing method. [Figure 10G] 5A-5C illustrate other steps of the manufacturing method. DETAILED DESCRIPTION OF THE INVENTION

[0036] Similar features are designated by similar reference numerals in the various drawings. In particular, structural and / or functional features that are common among various embodiments may have the same reference numerals and may have the same structural, dimensional, and material properties. For clarity, only operations and elements useful for understanding the embodiments described herein are shown and described in detail. In particular, contemplated optoelectronic devices may include other components not described in detail.

[0037] In the following disclosure, unless otherwise specified, when referring to terms modifying absolute position such as "front," "back," "top," "bottom," "left," "right," or relative position such as "above," "below," "upper," "lower," or terms modifying orientation such as "horizontal," "vertical," etc., they refer to the optoelectronic device in the orientation shown in the figures or in its normal position of use.

[0038] Unless otherwise specified, the terms "about," "approximately," "substantially," and "to the extent of" refer to within 10%, preferably within 5%, of the relevant value. Additionally, the terms "insulator" and "conductor" are understood herein to mean "electrically insulating" and "electrically conductive," respectively.

[0039] In the following description, the internal transmittance of a layer is the ratio of the radiation intensity leaving the layer to the radiation intensity entering the layer. The absorptance of a layer is equal to the difference between 1 and the internal transmittance. In the remainder of this specification, a layer is said to be transparent to radiation if the absorption of radiation through the layer is less than 60%. In the remainder of this specification, a layer is said to be absorbing for radiation if the absorption of radiation in the layer is greater than 60%. When radiation has a generally "bell-shaped" spectrum, such as a Gaussian spectrum with a maximum, the wavelength of the radiation, or the central or dominant wavelength of the radiation, is referred to as the wavelength at which the maximum of the spectrum is reached. In the remainder of this specification, the refractive index of a material refers to the refractive index of the material for the wavelength range of radiation emitted by the optoelectronic device. Unless otherwise specified, the refractive index is considered to be substantially constant over the wavelength range of useful radiation, e.g., equal to the average refractive index over the wavelength range of radiation emitted by the optoelectronic device.

[0040] An axial LED refers to a three-dimensional structure that is elongated along a preferred direction, such as a cylinder, and has at least two dimensions, called minor dimensions, between 5 nm and 2.5 μm, preferably between 50 nm and 2.5 μm. The third dimension, called the major dimension, is at least one, preferably at least five, and more preferably at least ten times the largest minor dimension. In some embodiments, the minor dimension may be about 1 μm or less, preferably between 100 nm and 1 μm, and more preferably between 100 nm and 800 nm. In some embodiments, the height of each LED may be 500 nm or more, preferably between 1 μm and 50 μm.

[0041] 1 and 2 are schematic partial cross-sectional side and partial perspective views, respectively, illustrating one embodiment of an optoelectronic device 10 having an LED.

[0042] From bottom to top in FIG. 1, the optoelectronic device 10 comprises the following elements: · Support 12; a first electrode layer 14 mounted on the support 12 and having an upper surface 16; an array 15 of axial light-emitting diodes LEDs mounted on the upper surface 16: each axial LED comprises, from bottom to top in FIG. 1 , a lower semiconductor portion 18 (not shown in FIG. 2 ) in contact with the electrode layer 14, an active region 20 (not shown in FIG. 2 ) in contact with the semiconductor portion 18, and an upper semiconductor portion 22 (not shown in FIG. 2 ) in contact with the active region 20; an insulating covering 23 (not shown in FIG. 2) of each axial light-emitting diode LED: made of a first insulating material surrounding the side walls of the light-emitting diode LED over at least a part of the height of the light-emitting diode LED, the assembly comprising the light-emitting diode LED and the insulating covering 23 surrounding the light-emitting diode LED forming a coated electroluminescent diode LED', of which only the outline of the coated electroluminescent diode LED' is shown in FIG. 2; an insulating layer 24 of a second insulating material extending between the coated electroluminescent diodes LED' over the entire height of the coated electroluminescent diodes LED'; a second electrode layer 26 (not shown in FIG. 2 ) contacting the upper portion 22 of the light emitting diode LED and covering the light emitting diode LED; and A coating 28 (not shown in FIG. 2) covering the second electrode layer 26 and defining the light emitting surface 30 of the optoelectronic device 10 .

[0043] Each light emitting diode LED is said to be axial in that the active region 20 is an extension of the lower portion 18 and the upper portion 22 is an extension of the active region 20, and the assembly comprising the lower portion 18, the active region 20 and the upper portion 22 extends along an axis Δ, which is referred to as the axis of the axial LED. Preferably, the axis of the light emitting diode LED is parallel to and perpendicular to the face 16.

[0044] The support 12 may correspond to an electronic circuit. The electrode layer 14 may be a metal such as silver, copper, or zinc. By way of example, the electrode layer 14 has a thickness between 0.01 μm and 10 μm. The electrode layer 14 may completely cover the support 12. Alternatively, the electrode layer 14 may be divided into separate portions to allow separate control of groups of LEDs in the LED array. According to one embodiment, the surface 16 may be reflective, and the electrode layer 14 may exhibit specular reflection. According to another embodiment, the electrode layer 14 may exhibit Lambertian reflection. One way to achieve a surface exhibiting Lambertian reflection is to form irregularities on a conductive surface. For example, if the surface 16 corresponds to the surface of a conductive layer mounted on a base, the surface of the base can be textured before the deposition of the metal layer so that the surface 16 of the deposited metal layer has a relief.

[0045] The second electrode layer 26 is conductive and transparent. According to one embodiment, the electrode layer 26 is a transparent conductive oxide (TCO) layer such as indium tin oxide (or ITO), zinc oxide doped or undoped with aluminum or gallium, or graphene. By way of example, the electrode layer 26 has a thickness between 5 nm and 200 nm, preferably between 20 nm and 50 nm. The coating 28 may include an optical filter or multiple optical filters arranged next to each other.

[0046] 1 and 2, all of the light emitting diodes LED have the same height, for example, the thickness of the insulating layer 24 is selected to be equal to the height of the light emitting diodes LED so that the top surface of the insulating layer 24 is flush with the top surface of the LED.

[0047] According to one embodiment, the semiconductor portions 18 and 22 and the active region 20 are at least partially made of semiconductor materials. The semiconductor materials are selected from the group consisting of III-V compounds, II-VI compounds, and IV semiconductors or compounds. Examples of Group III elements include gallium (Ga), indium (In), or aluminum (Al). Examples of Group V elements include nitrogen (N), phosphorus (P), or arsenic (As). Examples of III-N compounds are GaN, AlN, InN, InGaN, AlGaN, or AlInGaN. Examples of Group II elements include Group IIA elements, including beryllium (Be) and magnesium (Mg), and Group IIB elements, including zinc (Zn), cadmium (Cd), and mercury (Hg). Examples of Group VI elements include Group VIA elements, including oxygen (O) and tellurium (Te). Examples of II-VI compounds are ZnO, ZnMgO, CdZnO, CdZnMgO, CdHgTe, CdTe, or HgTe. Generally, elements of III-V or II-VI compounds can be combined in different mole fractions. Examples of IV semiconductor materials are silicon (Si), carbon (C), germanium (Ge), silicon carbide (SiC) alloy, silicon germanium (SiGe) alloy, or germanium carbide (GeC) alloy. The semiconductor portions 18, 22 may contain dopants. As an example, for III-V compounds, the dopant may be selected from the group consisting of a Group II P-type dopant such as magnesium (Mg), zinc (Zn), cadmium (Cd), or mercury (Hg), a Group IV P-type dopant such as carbon (C), or a Group IV N-type dopant such as silicon (Si), germanium (Ge), selenium (Se), sulfur (S), terbium (Tb), or tin (Sn). Preferably, semiconductor portion 18 is P-doped GaN and semiconductor portion 22 is N-doped GaN.

[0048] For each light-emitting diode LED, the active region 20 may include a confinement means. By way of example, the active region 20 may include a single quantum well, which includes a semiconductor material different from the semiconductor material forming the semiconductor portions 18 and 22 and has a smaller bandgap than the material forming the semiconductor portions 18 and 22. The active region 20 may also include multiple quantum wells, which includes a stack of semiconductor layers forming alternating quantum wells and barrier layers.

[0049] 1 and 2, each light-emitting diode LED has a cylindrical shape with a circular base and a delta axis. However, each light-emitting diode LED may have a cylindrical shape with a delta axis and a polygonal base such as a square, rectangular, or hexagonal. Preferably, each light-emitting diode LED has a cylindrical shape with a hexagonal base.

[0050] The sum of the height h1 of the lower portion 18, the height h2 of the active region 20, the height h3 of the upper portion 22, the thickness of the electrode layer 26, and the thickness of the coating 28 is referred to as the height H of the light emitting diode LED.

[0051] The first insulating material constituting the insulating coating 23 is transparent to the wavelength of radiation emitted by the light-emitting diode LED. The refractive index of the first insulating material is strictly greater than the refractive index of the second insulating material. According to one embodiment, the coated electroluminescent diode LED' is arranged to form a photonic crystal. To have an effective photonic crystal, it is desirable to have a maximum refractive index gap between the first insulating material and the second insulating material. Preferably, from an optical point of view, the difference between the refractive index of the first insulating material and the refractive index of the material constituting the lower and upper portions 18 and 22 of the LED is as small as possible, so that the coating 23 forms an "extension" of the lower and upper portions 18 and 22 of the LED. The difference between the refractive index of the first insulating material and the refractive index of the second insulating material is preferably greater than 0.5, more preferably greater than 0.6, and ideally greater than 1. Preferably, the difference between the refractive index of the first insulating material and the refractive index of the material constituting the lower and upper portions 18 and 22 of the LED is less than 0.5, preferably less than 0.3. When the materials constituting the lower portion 18 and the upper portion 22 of the LED are GaN-based, the refractive index of the first insulating material is preferably between 2 and 2.5. According to one embodiment, the first insulating material constituting the insulating coating 23 is silicon nitride (Si3N4) or titanium oxide (TiO2). According to one embodiment, the insulating coating 23 extends over the entire lower portion 18, active region 20, and upper portion 22 of the corresponding light-emitting diode LED. According to another embodiment, the insulating coating 23 extends over only a portion of the lower portion 18, active region 20, and / or upper portion 22 of the corresponding light-emitting diode LED. The thickness of the insulating coating 23 is greater than 10 nm, preferably between 15 nm and 150 nm, and more preferably between 15 nm and 50 nm. In general, the thickness of the insulating coating 23 can vary significantly, depending in particular on the desired properties of the photonic crystal. According to one embodiment, the thickness of the insulating coating 23 is substantially constant. However, the insulating coating 23 does not have to be present over the entire height of the lower portion 18, and / or the active region 20, and / or the upper portion 22 of the light emitting diode LED.

[0052] According to one embodiment, the second insulating material constituting the insulating layer 24 is transparent to the wavelength of the radiation emitted by the light-emitting diode LED. The refractive index of the second material is less than 1.6, preferably between 1.3 and 1.56. The insulating layer 24 may be made of an inorganic material such as silicon oxide (SiO2). The insulating layer 24 may also be made of an organic material, for example, an insulating polymer of the benzocyclobutene (BCB) or parylene family.

[0053] According to one embodiment, the coated electroluminescent diodes LED' are arranged to form a photonic crystal. Although 12 coated electroluminescent diodes LED' are shown as an example in Figure 2, in practice the array 15 may comprise between 7 and 100,000 coated electroluminescent diodes LED'.

[0054] The coated electroluminescent diodes LED' of the array 15 are arranged in rows and columns (three rows and four columns are shown as an example in FIG. 2). The pitch "a" of the array 15 is the distance between the axis of a coated electroluminescent diode LED' and the axis of a nearby coated electroluminescent diode LED' in the same row or an adjacent row. The pitch a is substantially constant. More specifically, the pitch a of the array is selected so that the array 15 forms a photonic crystal. The photonic crystal formed is, for example, a two-dimensional photonic crystal.

[0055] The properties of the photonic crystal formed by the array 15 are advantageously selected so that the array 15 of coated electroluminescent diodes LED' forms a resonant cavity in a plane perpendicular to the Δ axis as well as a resonant cavity along the Δ axis, in particular to achieve coupling and enhance the selectivity, thereby enabling the intensity of radiation emitted through the light-emitting surface 30 by the group of coated electroluminescent diodes LED' of the array 15 to be amplified at certain wavelengths compared to a group of coated electroluminescent LEDs that do not form a photonic crystal.

[0056] 3 and 4 are cross-sectional views in a plane parallel to plane 16, which schematically show examples of arrangements of coated electroluminescent diodes LED' in array 15. In particular, Fig. 3 shows a so-called square mesh arrangement, and Fig. 4 shows a so-called hexagonal mesh arrangement.

[0057] 3 and 4 each show four rows of LEDs. In the arrangement shown in FIG. 3, each coated electroluminescent diode LED' is located at the intersection of a row and a column, with the rows perpendicular to the columns. Furthermore, in the arrangement shown in FIG. 3, the light-emitting diodes LED have a circular cross-section with a diameter D in a plane parallel to face 16, and the coated electroluminescent diodes LED' have a circular cross-section with a diameter D' in a plane parallel to face 16. In the arrangement shown in FIG. 4, the coated electroluminescent diodes LED' on one line are offset by half the pitch a from the coated electroluminescent diodes LED' on the previous and next lines. Furthermore, in the arrangement shown in FIG. 4, the light-emitting diodes LED have a hexagonal cross-section with an average diameter D in a plane parallel to face 16, and the coated LEDs have a hexagonal cross-section with an average diameter D' in a plane parallel to face 16. In the remainder of this specification, the average diameter of an element in a certain plane is referred to as the diameter of a disk having the same area as the area of ​​the cross-section of the element in that plane. In a variant, the cross section of the coated electroluminescent diode LED' may differ from the cross section of the light emitting diode LED contained therein. As an example, the coated electroluminescent diode LED' may have a circular cross section, while the light emitting diode LED contained therein has a hexagonal cross section.

[0058] In the case of a hexagonal or square array arrangement, the diameter D' may be between 0.05 μm and 2 μm, and the pitch a may be between 0.1 μm and 4 μm.

[0059] Furthermore, according to one embodiment, the height H of the LEDs is selected so that each light emitting diode LED forms a resonant cavity along the Δ-axis at a desired center wavelength λ of the radiation emitted by the optoelectronic device 10. According to one embodiment, the height H is selected to be substantially proportional to k×(λ / 2)×neff, where neff is the effective refractive index of the light emitting diode LED in the optical mode of interest, and k is a positive integer. The effective refractive index is defined, for example, in the book "Semiconductor Optoelectronic Devices: Introduction to Physics and Simulation" by Joachim Piprek.

[0060] If the LEDs are divided into groups of LEDs emitting at different central wavelengths, the height H of all the LEDs can nevertheless be the same, and the resonant cavity of each group of LEDs can be determined from the theoretical heights that can be obtained, for example, equal to the average of these theoretical heights.

[0061] According to one embodiment, the properties of the photonic crystal formed by the array of coated light-emitting diodes LED's 15 are selected to increase the light intensity emitted by the array of light-emitting diodes LED's 15 at at least one target wavelength. According to one embodiment, the active region 20 of each light-emitting diode LED has an emission spectrum with a maximum at a central wavelength different from the target wavelength. However, the emission spectrum of the active region 20 overlaps with the target wavelength, i.e., the energy of the emission spectrum of the active region 20 at the target wavelength is non-zero. This makes it possible to select an average diameter D of the light-emitting diode LED that allows the production of active regions 20 with suitable crystalline quality. The fact that for each light-emitting diode LED, the coating material 23 can cover the sidewalls of the light-emitting diode LED over only a portion of the height of the sidewalls allows for additional parameters, in addition to the thickness of the insulating coating material 23, to be used to select the desired properties of the photonic crystal.

[0062] FIG. 5 is a schematic partial cross-sectional view illustrating another embodiment of an optoelectronic device 35 including an LED. The optoelectronic device 35 includes all the elements of the optoelectronic device 10 shown in FIG. 1 and further includes, for each light-emitting diode (LED), an insulating coating 36 interposed between the encapsulant 23 and the light-emitting diode (LED). The insulating coating 36 may correspond to a layer having a thickness of less than 10 nm, preferably less than 5 nm. The coating 36 may correspond to a passivation layer. The coating 36 is transparent to the radiation emitted by the LED. The coating 36 is sufficiently thin so that it does not significantly affect the average refractive index of the assembly including the encapsulant 23, the coating 36, and the LED. Since the coating 36 prevents short circuits between different parts of the light-emitting diode (LED), the encapsulant 23 does not need to be an insulating material. This advantageously allows for greater freedom in the selection of the material from which the encapsulant 23 is made, which may be an insulating, conductive, or semiconducting material.

[0063] Simulations and tests were performed. In these simulations and tests, for each light-emitting diode LED, the lower semiconductor portion 18 was made of P-doped GaN. The upper semiconductor portion 22 was made of N-doped GaN. The refractive indexes of the lower and upper portions 18 and 22 were between 2.4 and 2.5. The active region 20 corresponded to a layer of InGaN. The height h2 of the active region 20 was equal to 40 nm. The electrode layer 14 was made of aluminum. The insulating layer 24 was made of a BCB-based polymer. The refractive index of the insulating layer 24 was between 1.45 and 1.56.

[0064] In the simulations and tests, the LED has a circular base. The height h3 is equal to between 300 nm and 350 nm, and the total height H is equal to 400 nm. Specular reflection at face 16 is taken into account. The pitch a of the photonic crystal is constant and equal to 300 nm.

[0065] 6 and 7 are grayscale maps of the light intensity of the radiation emitted by the LED array 15, plotted on the x-axis as a function of the angle between the light emission direction and a direction perpendicular to the light-emitting surface 30, and on the y-axis as a function of the ratio a / λ, where λ is the central wavelength of the radiation emitted by the LED. For FIG. 6, the LEDs are not surrounded by an insulating covering 23. For FIG. 7, each LED is surrounded by an insulating covering 23 made of TiO2 with a refractive index between 2.4 and 2.5 and a thickness of 25 nm. The corresponding values ​​of the central wavelength λ are further indicated on the right side of FIGS. 6 and 7. Each grayscale map contains bright regions corresponding to resonant peaks.

[0066] The inventors emphasize that Fig. 7 substantially corresponds to Fig. 6, shifted along the Y-axis. This means that the resonance peaks present in Fig. 6 are also present in Fig. 7, but are obtained at lower values ​​of the ratio a / λ. This indicates that the properties of the photonic crystal, which depend primarily on the pitch a and average diameter D' of the coated electroluminescent diodes LED', are substantially de-correlated from the wavelength λ, which depends on the average diameter D of the light-emitting diodes LED.

[0067] As an example, in Figure 6, a resonance peak is obtained when the emission angle is 10° and the ratio a / λ is equal to approximately 0.57, which corresponds to a wavelength λ of 530 nm and an average diameter D equal to 240 nm. This same resonance peak is obtained in Figure 7 when the ratio a / λ is equal to approximately 0.55 and corresponds to an average diameter D' equal to 260 nm. A thickness of 25 nm for the TiO2 insulating coating 23 would therefore correspond to an increase in the average diameter of the LED of approximately 20 nm.

[0068] Through further simulations, the inventors have shown that a thickness of 30 nm for the TiO2 insulating coating 23 corresponds to an increase in the average diameter of the LED of approximately 40 nm, and a thickness of 50 nm for the TiO2 insulating coating 23 corresponds to an increase in the average diameter of the LED of approximately 60 nm.

[0069] Note that the heights h1 and h3 can be varied to achieve optimization.

[0070] Simulations and tests were carried out with the following parameters: height h1 equal to 100 nm, height h3 equal to 300 nm, height h2 equal to 100 nm, pitch a of the photonic crystal equal to 300 nm, and average diameter D equal to 240 nm.

[0071] 8 shows an evolution curve C1 of the luminous intensity I (arbitrary units (au)) in a direction inclined by ±24° relative to the direction perpendicular to the light-emitting surface 30 as a function of the wavelength λ of the radiation emitted by an uncoated light-emitting diode LED, and an evolution curve C2 of the luminous intensity I of the radiation emitted by an array 15 of coated light-emitting diode LEDs. For curve C2, each insulating coating 23 has a thickness equal to 120 nm. FIG. 9 shows an evolution curve C3 similar to curve C2 for a direction inclined by ±5° relative to the direction perpendicular to the light-emitting surface 30.

[0072] As shown in Figure 8, a resonant peak P1 of curve C2 is obtained at a wavelength different from the central wavelength of the radiation emitted by the light-emitting diode LED. As shown in Figure 9, a resonant peak P3 with a high amplification factor of curve C3 is obtained at a wavelength different from the central wavelength of the radiation emitted by the light-emitting diode LED. In this way, directional radiation is obtained.

[0073] 10A-10G are schematic cross-sectional views of portions of structures obtained in successive steps of one embodiment of a method for manufacturing the optoelectronic device 10 shown in FIG.

[0074] FIG. 10A shows the resulting structure after the following formation steps:

[0075] A seed layer 40 is formed on a substrate 42. Then, light emitting diodes (LEDs) are formed from the seed layer 40. Specifically, the light emitting diodes (LEDs) are formed such that the upper portions 22 are in contact with the seed layer 40. The seed layer 40 is made of a material that promotes the growth of the upper portions 22. For each light emitting diode (LED), an active region 20 is formed on the upper portion 22, and a lower portion 18 is formed on the active region 20.

[0076] Furthermore, the light emitting diodes LED are arranged to form an array 15, i.e., to form rows and columns at a desired pitch of the array 15. Only one row is partially shown in Figures 10A to 10G.

[0077] A mask (not shown) may be formed on seed layer 40 before the LEDs are formed, so as to expose only a portion of seed layer 40 where the LEDs will be located. Alternatively, seed layer 40 may be etched before the LEDs are formed to form pads where the LEDs will be formed.

[0078] The growth method for light-emitting diodes (LEDs) can be chemical vapor deposition (CVD) or metalorganic chemical vapor deposition (MOCVD), also known as metalorganic vapor phase epitaxy (MOVPE). However, methods such as molecular beam epitaxy (MBE), gas source MBE (GSMBE), metalorganic MBE (MOMBE), plasma-assisted MBE (PAMBE), atomic layer epitaxy (ALE), or hydride vapor phase epitaxy (HVPE) can also be used. However, electrochemical methods, such as chemical bath deposition (CBD), hydrothermal processes, liquid aerosol pyrolysis, or electrodeposition can also be used.

[0079] The LED growth conditions are such that all light emitting diodes LEDs in array 15 are formed at substantially the same rate. Thus, the heights of semiconductor portions 22 and 18, as well as the height of active region 20, are substantially the same for all LEDs in array 15.

[0080] According to one embodiment, the height of semiconductor portion 22 is greater than the desired value h3 because it may be difficult to precisely control the height of upper portion 22, particularly due to the initiation of growth of upper portion 22 from seed layer 40. Also, forming semiconductor material directly on seed layer 40 may result in crystalline defects in the semiconductor material directly above seed layer 40. Therefore, it may be desirable to remove a portion of upper portion 22.

[0081] 10B shows the structure obtained after forming a coating 23 of a first insulating material, such as silicon nitride, over the light-emitting diode LED to obtain a coated light-emitting diode LED'. According to one embodiment, the coating 23 is formed by CVD. According to another embodiment, a layer of the first insulating material is deposited over the entire structure shown in FIG. 10A, the layer having a thickness greater than the height of the light-emitting diode LED. The layer of the first insulating material is then partially etched to define the coating 23.

[0082] 10C shows the resulting structure after the formation of a layer 24 of a second insulating material, such as silicon oxide. The layer 24 is formed by depositing a layer of filler material on the structure shown in FIG. 10B, for example, with a thickness greater than the height of the light-emitting diodes LEDs. The layer 24 of the second insulating material and the covering material 23 are then partially removed in a planarized manner to expose the upper surfaces of the semiconductor portions 18. The upper surfaces of the layer 24 and the covering material 23 are then made substantially flush with the upper surfaces of the semiconductor portions 18. In a variant, the method may include an etching step to partially etch the semiconductor portions 18.

[0083] FIG. 10D shows the structure obtained after depositing an electrode layer 14 on the structure obtained in the previous step.

[0084] FIG. 10E shows the structure obtained after attaching layer 14 to support 12, for example by metal-to-metal bonding, or thermocompression bonding, or soldering using a eutectic on the support 12 side.

[0085] 10F shows the resulting structure after removing substrate 42 and seed layer 40. Layer 24, cladding 23, and upper portion 22 are then etched so that each upper portion 22 has a desired height h3. Advantageously, this step allows for precise control of the height H of the LED and for removing portions of upper portion 22 that may have crystalline defects.

[0086] FIG. 10G shows the resulting structure after deposition of electrode layer 26.

[0087] The method may further include forming at least one optical filter over all or a portion of the structure shown in Figure 10G.

[0088] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these embodiments and variations may be combined, and other variations will be readily apparent to those skilled in the art. In particular, the coating 28 described above may include additional layers other than one or more optical filters. In particular, the coating 28 may include anti-reflection layers, protective layers, etc. Finally, practical implementation of the embodiments and variations described herein is within the capabilities of those skilled in the art based on the functional descriptions provided herein. Furthermore, the refractive index values ​​of the materials comprising the LED are described in the context of III-VI compound LEDs. Clearly, these numerical refractive index values ​​would need to be adapted if the LED were based on II-VI or IV semiconductors or compounds.

[0089] This patent application claims priority from French Patent Application No. 20 / 13521, which is incorporated herein by reference.

Claims

1. an optoelectronic device comprising an array of axial light emitting diodes, each of the axial light emitting diodes comprising an active region configured to emit electromagnetic radiation, the emission spectrum of the active region comprising a maximum at a first wavelength; the optoelectronic device further comprising, for each of the axial light emitting diodes, a cladding made of a first material that is transparent to the electromagnetic radiation and surrounds a sidewall of the axial light emitting diode over at least a portion of the axial light emitting diode, the cladding having a thickness greater than 10 nm; the optoelectronic device further comprising, between the claddings, a layer of a second material that is transparent to the electromagnetic radiation and different from the first material, the second material being electrically insulating; each of the axial light emitting diodes comprising a semiconductor element made of a third material and at least partially surrounded by the cladding; a difference between the refractive index of the first material and the refractive index of the third material being less than 0.5; and the array of cladded axial light emitting diodes forming a photonic crystal. Optoelectronic devices.

2. each of the coatings having a thickness greater than 20 nm; The optoelectronic device of claim 1 .

3. the refractive index of the first material at the first wavelength is greater than the refractive index of the second material at the first wavelength; 3. An optoelectronic device according to claim 1 or 2.

4. a difference between the refractive index of the first material at the first wavelength and the refractive index of the second material at the first wavelength is greater than 0.5; The optoelectronic device of claim 3 .

5. The difference between the refractive index of the first material and the refractive index of the third material is less than 0.

3. The optoelectronic device of claim 1 .

6. the first material is electrically insulating and is preferably silicon nitride or titanium oxide; The optoelectronic device of claim 1 .

7. Each of the axial light-emitting diodes further includes an electrically insulating coating interposed between the covering material and the axial light-emitting diode, and the thickness of the electrically insulating coating is less than 10 nm. The optoelectronic device of claim 1 .

8. the second material is silicon oxide; The optoelectronic device of claim 1 .

9. the photonic crystal is configured to form a resonant peak that amplifies the intensity of the electromagnetic radiation at at least a second wavelength, the second wavelength being different from or equal to the first wavelength; The optoelectronic device of claim 1 .

10. A support on which the axial light emitting diodes are mounted, each of the axial light emitting diodes comprising a laminate of a first semiconductor portion mounted on the support, an active region in contact with the first semiconductor portion, and a second semiconductor portion in contact with the active region. The optoelectronic device of claim 1 .

11. a reflective layer between the support and the first semiconductor portion of the axial light emitting diode; 11. An optoelectronic device according to claim 10.

12. the second semiconductor portion of the axial light-emitting diode is covered with a conductive layer that is at least partially transparent to the electromagnetic radiation emitted by the axial light-emitting diode.

11. An optoelectronic device according to claim 10.

13. 1. A method for designing an optoelectronic device comprising axial light emitting diodes each comprising an active region, the method comprising: determining a first target wavelength for the optoelectronic device; Dimensioning the axial light emitting diodes so that each active region emits electromagnetic radiation having an emission spectrum that includes the first target wavelength; determining dimensions of the array of axial light-emitting diodes to obtain a photonic crystal that forms a resonant peak that amplifies the intensity of the electromagnetic radiation at the first target wavelength, wherein for each axial light-emitting diode, a cladding of a first material that is transparent to the electromagnetic radiation and surrounds a sidewall of the axial light-emitting diode over at least a portion of the axial light-emitting diode, each of the claddings having a thickness greater than 10 nm, further comprising a layer of a second material between the claddings that is transparent to the electromagnetic radiation and different from the first material, the second material being electrically insulating, each of the axial light-emitting diodes comprising a semiconductor element made of a third material and at least partially surrounded by the cladding, a difference between the refractive index of the first material and the refractive index of the third material being less than 0.5, and the array of coated axial light-emitting diodes forming a photonic crystal; Including, method.

14. 1. A method for manufacturing an optoelectronic device comprising an array of axial light emitting diodes, each of the axial light emitting diodes comprising an active region configured to emit electromagnetic radiation, the emission spectrum of the active region comprising a maximum at a first wavelength, the optoelectronic device further comprising, for each of the axial light emitting diodes, a cladding made of a first material that is transparent to the electromagnetic radiation and surrounds a sidewall of the axial light emitting diode over at least a portion of the axial light emitting diode, the cladding having a thickness greater than 10 nm, the optoelectronic device further comprising, between the claddings, a layer made of a second material that is transparent to the electromagnetic radiation and different from the first material, the second material being electrically insulating, each of the axial light emitting diodes comprising a semiconductor element made of a third material and at least partially surrounded by the cladding, the refractive index of the first material differing from the refractive index of the third material being less than 0.5, and the array of cladded axial light emitting diodes forming a photonic crystal. method.

15. forming the axial light emitting diode forming second semiconductor portions on the substrate separated from one another by the pitch of the array; forming an active region on each of the second semiconductor portions; forming a first semiconductor portion on each of the active regions; forming a coating of a first material surrounding sidewalls of the first semiconductor portion, the second semiconductor portion, and / or at least a portion of the active region for each of the axial light emitting diodes; forming a layer of a second material; Including, 15. The method of claim 14.

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