Optoelectronic device with reflector and method for manufacturing same

Abstract

The present application relates to an optoelectronic device (1) comprising at least one first light source (100) configured to emit a first light beam (101) emitting at least at a first wavelength λ1 and emitted at least in a direction referred to as the first emission direction (110), the optoelectronic device further comprising at least one first reflector (150) bordering the first light source (100), configured to reflect, in a first reflection direction (120), first light rays (111) of the first wavelength λ1 emitted in the first emission direction (110), the at least one first reflector (150) comprising a plurality of first passive nanowires (151).

Description

[0001] OPTOELECTRONIC DEVICE WITH REFLECTOR AND METHOD FOR MANUFACTURING SAME

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The present invention relates in particular to the field of microelectronics and optoelectronics technologies. It finds particularly advantageous but non-limiting application in LED-based display systems (from the English “Light-Emitting Diode”).

[0004] STATE OF THE ART

[0005] A display screen generally comprises a plurality of pixels arranged on a so-called basal plane and emitting independently of one another. Each color pixel generally comprises at least three components for emitting and / or converting a luminous flux, also called sub-pixels. These sub-pixels each emit a luminous flux in substantially a single color (typically red, green and blue). The color of a pixel perceived by an observer comes from the superposition of the different luminous fluxes emitted by the sub-pixels.

[0006] Typically, an LED or micro-LED emits the luminous flux associated with a sub-pixel. A major issue with these technologies concerns the directivity of the light emitted by the LEDs. Indeed, even if the LED is configured to emit mainly in a direction normal to the basal plane, some rays of the beam are emitted in directions too grazing to be extracted from the sub-pixel and do not contribute to the luminous intensity perceived by the observer.

[0007] Many light extraction solutions have been disclosed in the prior art. One of them concerns the extraction of laser light using a textured surface. This solution is shown schematically in Figure 1. A waveguide 30 in which laser radiation 41 propagates consists on the one hand of a region 31 used as a DFB laser cavity (from the English “Distributed FeedBack laser”). This region 31 is electrically injected - it is the active zone of the guide - and has a high coupling coefficient allowing propagation with few losses. The waveguide is also constituted by a region 32 allowing the extraction at the surface 42 of a portion of the laser radiation. Region 32 is a passive zone of the guide; it is not electrically injected. It has a lower coupling coefficient than the active zone.The waveguide 30 is a simple layer structured in a periodic network whose height and pitch are configured for the confinement (at the active zone 31) or the extraction (at the passive zone 32) of the laser radiation 41. The laser radiation comes from a lateral region not shown in FIG. 1.

[0008] This solution is commonly used for laser extraction but is not compatible with incoherent light sources such as LEDs. In addition, while this solution provides good extraction efficiency, it is incompatible with light extraction occurring in the same region as the light emission, as is the case in pixel-based display screens.

[0009] Another solution, this time adapted to LED-based pixels, consists of forming a composite mirror around each sub-pixel. However, the formation of such a mirror, at a very low height, requires complex masking and deposition steps to be carried out without degrading surrounding LEDs and without bringing contamination.

[0010] There is therefore a need for a light extraction solution compatible with the structure of LED-based pixels, the implementation of which does not alter the quality of the pixels and which offers better extraction performance than current structures.

[0011] SUMMARY OF THE INVENTION

[0012] To achieve this objective, a first object relates to an optoelectronic device comprising a substrate having an upper face extending along a plane called the basal plane defined by a first direction and a second direction, at least one first light source arranged on the upper face and configured to emit a first light beam emitting at least at a first wavelength λi, said first light beam being emitted at least along a direction called the first emission direction, a first emission direction vector of which has a non-zero component along at least one of the first direction and the second direction.

[0013] The device is characterized in that it further comprises at least one first reflector at least partially bordering the first light source, configured to reflect in a first reflection direction the first light rays of first wavelength λ emitted in the first emission direction, and in that the at least one first reflector comprises a plurality of first passive nanowires extending from the upper face of the substrate.

[0014] The first reflector formed from first passive nanowires makes it possible to efficiently reflect the first light rays and thus extract the light emitted by the first light source.

[0015] A second subject matter relates to a method for manufacturing an optoelectronic device comprising a first light source and a first reflector itself comprising a plurality of first passive nanowires. This method comprises the following steps:

[0016] - Provide a substrate having an upper face, extending along a plane called the basal plane defined by a first direction and a second direction and comprising a nucleation layer allowing the nucleation and growth of the first passive nanowires,

[0017] - Growing the first passive nanowires from the upper face of the substrate so as to form the first reflector, the first reflector being configured to reflect in a first reflection direction the first light rays of first wavelength λ emitted in the first emission direction,

[0018] - Forming the first light source on the upper face of the substrate, the first light source being configured to emit a first light beam emitting at least at the first wavelength λi, said first light beam being emitted at least in a direction called the first emission direction, a first emission direction vector of which has a non-zero component in at least one of the first direction and the second direction.

[0019] According to an advantageous embodiment, the first light source comprises at least one first active nanowire, the formation of which is carried out simultaneously with the formation of the first passive nanowires. Forming the passive and active nanowires during the same manufacturing steps makes it possible to limit the degradation of the quality of the pixels. This solution is made possible in particular by the fact that the first active nanowires (forming the first light source) and the first passive nanowires (forming the first reflector) can be based on the same material. This was not the case in particular in the described solution consisting of depositing composite mirrors around the sub-pixels.

[0020] BRIEF DESCRIPTION OF THE FIGURES

[0021] The aims, objects, as well as the characteristics and advantages of the invention will emerge more clearly from the detailed description of an embodiment thereof which is illustrated by the following accompanying drawings in which:

[0022] Figure 1 shows a diffraction grating used in the prior art for surface laser emission.

[0023] Figure 2A represents a top view of an embodiment of the device which is the subject of the invention. In particular, a light source and a reflector surrounding it are visible.

[0024] Figures 2B to 2E represent top views of other embodiments of the device that is the subject of the invention. They illustrate different variants concerning the number and arrangement of nanowires that the light source of the device can comprise.

[0025] Figure 3 represents a sectional view of an embodiment of the device according to the invention comprising a single light source. In particular, a light source comprising active nanowires and emitting a light beam and a reflector comprising passive nanowires are visible.

[0026] Figure 4 represents a sectional view of an embodiment of the device according to the invention comprising two adjacent light sources separated by a transition zone.

[0027] Figure 5 shows a sectional view of an embodiment in which the reflector has a decoupler function.

[0028] The drawings are given as examples and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate the understanding of the invention and are not necessarily to the scale of practical applications. In particular, the dimensions of each of the elements are not representative of reality.

[0029] DETAILED DESCRIPTION OF THE INVENTION

[0030] Before commencing a detailed review of embodiments of the invention, optional features that may optionally be used in combination or alternatively are set forth below: According to one embodiment, the first light source is an incoherent light source.

[0031] According to one embodiment, the first passive nanowires have a diameter that gradually decreases or increases as they move away from the at least one first light source. This makes it possible to avoid symmetry breaks and edge effects around the first light source and therefore around the sub-pixel formed by the first light source.

[0032] According to one embodiment, the first passive nanowires are arranged according to a first constant pi pitch according to at least one of the first direction and the second direction.

[0033] According to one embodiment, the first passive nanowires are arranged in a progressively increasing or decreasing pitch moving away from the at least one first light source. This makes it possible to avoid symmetry breaks and edge effects around the first light source and therefore around the sub-pixel formed by the first light source.

[0034] According to one embodiment, the at least one first light source comprises at least one first active nanowire having a first diameter <p Oi and comprising a first active region configured to emit the first light rays of first wavelength λi.

[0035] According to one embodiment, the first diameter <p Oi of the at least one first active nanowire is less than 5 pm.

[0036] In one example, the first passive nanowires and the at least one first active nanowire are based on the same material. In this embodiment, the first passive nanowires and the at least one first active nanowire can be formed by epitaxy in the same epitaxy reactor, which is advantageous in terms of process simplicity, costs and time.

[0037] According to another example, the first passive nanowires and the at least one first active nanowire are based on distinct materials. The first passive nanowires can then be formed by etching a material previously deposited next to, or even all around, depending on the desired shape for the first reflector, the at least one first active nanowire.

[0038] In one example, the reflector, and thus typically the first passive nanowires, and the light source are based on the same material.

[0039] According to one embodiment, the at least one first reflector completely surrounds, according to a projection on the basal plane, the first light source. This makes it possible to create a closed cavity around the first light source and to further improve the light extraction.

[0040] According to one embodiment:

[0041] - The first emission direction vector has a non-zero component in the first direction,

[0042] - The first emission direction vector has an orthogonal projection in a transverse plane defined by the first direction and a third direction normal to the basal plane, called the first projected emission vector v emiXZ , forming a first emission angle a emXZ with the third direction,

[0043] - A first reflection direction vector of the first reflection direction has an orthogonal projection in the transverse plane, called the first projected reflection vector v re / -iXZ , forming a first angle of reflection a ref xz with the third direction,

[0044] - The plurality of passive nanowires is configured to reflect the first light rays such that the first emission angle has em XZ and the first angle of reflection has ref xz are distinct.

[0045] According to one example, the first angle of reflection has ref xz is less than 40°, preferably less than 20°.

[0046] According to one embodiment, the device further comprises at least one second light source adjacent to the first light source, configured to emit a second light beam emitting at a second wavelength λ2, said second light beam being emitted at least in a direction called the second emission direction, a second emission direction vector of which has a non-zero component in at least one of the first direction and the second direction, said first and second light sources being separated by a transition zone comprising the at least one first reflector and at least one second reflector, the at least one second reflector being configured to reflect in a second reflection direction second light rays of second wavelength λ2, said at least one second reflector comprising a plurality of second passive nanowires extending from the upper face of the substrate.

[0047] According to one embodiment, the second light source is an incoherent light source.

[0048] According to one embodiment, the second passive nanowires have a diameter that gradually decreases or increases away from the at least one second light source. According to one embodiment, the second passive nanowires are arranged according to a second constant pitch P2 according to at least one of the first direction and the second direction.

[0049] According to one embodiment, the second passive nanowires are arranged in a progressively increasing or decreasing pitch moving away from the at least one second light source.

[0050] According to one embodiment, the at least one second light source comprises at least one second active nanowire having a second diameter q>02 and comprising a second active region configured to emit the second light rays of second wavelength λ2.

[0051] According to one embodiment, the second diameter q>02 of the at least one second active nanowire is less than 5 pm.

[0052] According to one embodiment of the method according to the invention:

[0053] - the first light source comprises at least one first active nanowire,

[0054] - the nucleation layer allows the nucleation and growth of at least one active nanowire,

[0055] - the step of forming the first light source comprises a step of growing the at least one first active nanowire from the upper face of the substrate so as to form the first light source.

[0056] According to one embodiment of the method according to the invention, the step of growing the first passive nanowires and the step of growing the at least one first active nanowire are carried out simultaneously.

[0057] A wire or nanowire is understood to mean a 3D structure of elongated shape in the longitudinal direction. The longitudinal dimension of the 3D structure, along z in the figures, is greater, and preferably much greater, than the transverse dimensions of the 3D structure, in the xy plane in the figures. The longitudinal dimension is for example at least five times, and preferably at least ten times, greater than the transverse dimensions.

[0058] Diameter is understood to mean the largest transverse dimension of the nanowire. In the present invention, the 3D structures do not necessarily have a circular cross-section. The 3D structures may in particular have a hexagonal or polygonal cross-section. In particular, in the case of 3D structures based on GaN, this cross-section may be hexagonal. The diameter then corresponds to an average diameter calculated from the diameter of a circle inscribed in the polygon of the cross-section and the diameter of a circumscribed circle of this polygon.

[0059] In the context of the invention, the diameter of the nanowires is typically between 50 nm and 1.5 μm, preferably between 50 nm and 1 μm, preferably between 50 nm and 600 nm and advantageously substantially equal to 50 nm.

[0060] The longitudinal dimension, along z, of the nanowires is commonly referred to as the height of the nanowires. In the context of the invention, the height of the nanowires is typically between 220 nm and 5 pm, preferably substantially equal to 260 nm.

[0061] In this patent application, the terms "light-emitting diode", "LED" or simply "diode" are used synonymously. An "LED" can also be understood as a "micro-LED".

[0062] In the following, the following abbreviations relating to a material M are possibly used:

[0063] Mi refers to the intrinsic or unintentionally doped material M, according to the terminology usually used in the field of microelectronics for the suffix -i.

[0064] Mn refers to the material M doped N, N+ or N++, according to the terminology usually used in the field of microelectronics for the suffix -n.

[0065] Mp refers to the material M doped P, P+ or P++, according to the terminology usually used in the field of microelectronics for the suffix -p.

[0066] A substrate, a layer, a device, "based" on a material M, is understood to mean a substrate, a layer, a device comprising this material M only or this material M and possibly other materials, for example alloying elements, impurities or doping elements. Thus, a 3D structure based on gallium nitride (GaN) may for example comprise gallium nitride (GaN or GaN-i) or doped gallium nitride (GaN-p, GaN-n). An active region based on gallium-indium nitride (InGaN) may for example comprise gallium-aluminium nitride (AIGaN) or gallium nitride with different aluminium and indium contents (GalnAIN). In the context of the present invention, the material M is generally crystalline.

[0067] A reference frame, preferably orthonormal, comprising the x, y, z axes is shown in the attached figures.

[0068] The terms "substantially", "approximately", "of the order of" mean, when they refer to a value, "within 10%" of that value or, when they refer to an angular orientation, "within 10°" of that orientation. Thus, a direction substantially normal to a plane means a direction presenting an angle of 90±10° with respect to the plane.

[0069] To determine the geometry of 3D structures and the compositions of the different elements (wire, active region, collar for example) of these 3D structures, we can carry out Scanning Electron Microscopy (SEM) or Transmission Electron Microscopy (TEM) analyses or even STEM (Scanning Transmission Electron Microscopy).

[0070] TEM or STEM are particularly well suited to the observation and identification of quantum wells - whose thickness is generally of the order of a few nanometers - in the active region. Different techniques listed below in a non-exhaustive manner can be implemented: dark field and bright field imaging, weak beam imaging, and wide-angle diffraction (HAADF) (acronym for "High Angle Annular Dark Field").

[0071] The chemical compositions of different elements can be determined using the well-known EDX or X-EDS method, an acronym for "energy dispersive x-ray spectroscopy" which means "energy dispersive analysis of X-ray photons".

[0072] This method is well suited for analyzing the composition of small optoelectronic devices such as nanowire-based LEDs (3D LEDs). It can be implemented on metallurgical sections within a Scanning Electron Microscope (SEM) or on thin sections within a Transmission Electron Microscope (TEM).

[0073] The optical properties of the various elements, and in particular the main emission wavelengths of GaN-based 3D LEDs and / or InGaN-based active regions, can be determined by spectroscopy.

[0074] Cathodoluminescence (CL) and photoluminescence (PL) spectroscopies are well suited to optically characterize the 3D structures described in the present invention.

[0075] The techniques mentioned above make it possible in particular to determine whether an LED optoelectronic device comprises one or more lateral reflectors formed by nanowires, according to a principle of the present invention.

[0076] The optoelectronic device 1 which is the subject of the invention comprises a substrate 2 having an upper face 20 extending along a plane defined by a first direction and a second direction. These two directions correspond in FIGS. 2A to 2E, 3 and 4 to the directions carried by the x and y axes of the orthogonal reference frame shown. The substrate 2 may be in the form of a stack comprising, along the z direction, a support 21, a surface layer called the nucleation layer 22 and a masking layer 23.

[0077] The support 21 can be made of sapphire to limit the mesh parameter mismatch with GaN, or silicon to reduce costs and for technological compatibility issues. In the latter case, it can be in the form of a wafer with a diameter of 200 mm or 300 mm. It serves in particular as a support for 3D structures.

[0078] The nucleation layer 22 may be based on AlN. It may alternatively be based on other metal nitrides, for example GaN or AIGaN. It may be formed on the silicon support 21 by epitaxy, preferably by vapor phase epitaxy with organometallic precursors MOVPE (acronym for “MetalOrganic Vapor Phase Epitaxy”). According to one example, the nucleation layer 22 has a thickness of between 1 nm and 10 pm (1 nm = 10 9m). It preferably has a thickness of the order of a few hundred nanometers, for example approximately 100 nm or 200 nm, to a few microns, for example of the order of 2 μm. It may also have a thickness of less than 100 nm. This makes it possible to limit the mechanical stresses induced by this layer 22 on the support 21. This makes it possible to avoid a detrimental curvature of the support 21. Such a thickness also makes it possible to limit the appearance of structural defects in the nucleation layer 22. In particular, the growth of this nucleation layer 22 can be pseudomorphic, that is to say that the epitaxial stresses (linked in particular to the difference in lattice parameters between Si and AIN, GaN or AIGaN) can be elastically released during growth. The crystalline quality of this nucleation layer 22 can thus be optimized.

[0079] The optoelectronic device 1 further comprises a first light source 100 arranged on the upper face 20 of the substrate 2. This first light source 100 typically comprises at least one active nanowire 130, as shown in FIG. 2A. Such a nanowire 130 advantageously extends from the possible nucleation layer 22 and through an opening of the possible masking layer 23 of the substrate 2. The first light source 100 advantageously comprises a plurality of first active nanowires 130, as shown in FIGS. 2B to 2E.

[0080] The first active nanowires 130 may be arranged in different configurations, some of which are illustrated in FIGS. 2B to 2E. The arrangement of the first active nanowires 130 advantageously has at least one plane of symmetry other than a plane of symmetry parallel to the basal plane. It is preferably configured so that the electromagnetic field within the first light source has maximums at the level of the active nanowires.

[0081] An active nanowire 130 comprises an active region 131 and is electrically connected. This active region 131 is the site of radiative recombinations of electron-hole pairs making it possible to obtain light radiation having a main wavelength. The active region 131 typically comprises a plurality of quantum wells, for example formed by emissive layers based on GaN, InN, InGaN, AIGaN, AIN, AlInGaN, GaP, AIGaP, AlInGap, AIGaAs, GaAs, InGaAs, AIIIAs, or a combination of several of these materials.

[0082] The first light source 100 typically comprises a layer based on a transparent conductive oxide, commonly referred to as TCO (Transparent Conductive Oxide), the thickness of which is preferably between 100 and 300 nm. The nanowires are typically arranged in the longitudinal direction between a mirror layer based on a metallic material, typically AI, and the TCO layer. This arrangement of the nanowires between the mirror layer and the TCO layer possibly makes it possible to create a Fabry-Perot cavity in the longitudinal direction.

[0083] The first light source 100 is advantageously sized to have dimensions of the order of those of a sub-pixel of a display device, preferably between 1 pm and 150 pm, typically between 4 and 150 pm.

[0084] The first light source 100 is configured to emit a first light beam 101. Advantageously, the first light beam 101 is configured to be emitted mainly in a direction normal to the substrate 2, i.e. extending parallel to the z axis shown in FIGS. 2A to 4, called the longitudinal direction. The light beam 101 however comprises a multitude of rays propagating in as many emission directions. The emission is for example omnidirectional. The rays of the beam are typically emitted according to a Lambertian or orthotropic profile, i.e. the luminance of the light source 100 is angularly uniform, but the emitted light intensity depends on the emission direction. The light intensity of the beam typically varies according to Lambert's law:

[0085] I = I oCOS(0) with I the luminous intensity along an emission direction, lo the luminous intensity at the source and 0 the angle of the emission direction relative to the normal to the source surface, here the longitudinal direction. It is understood that any other emission profile is possible and that the first light source 100 is not limited to a Lambertian source.

[0086] Whatever the emission profile of the first light source 100, the first light beam 101 is such that it emits at least one first light ray 111 of wavelength λi called first wavelength λi in a first emission direction 110. In practice, the first light beam 101 typically emits a plurality of rays whose wavelengths form a continuum. The first emission direction 110 is characterized by the fact that any direction vector of this first emission direction 110 has a non-zero component in the first direction x and / or the second direction y. In other words, the first emission direction 110 is not parallel to the longitudinal direction.

[0087] As mentioned in the introduction, an objective of the present application is to redirect light rays deviating from the longitudinal direction so that they contribute to the light intensity perceived by the user.

[0088] The present invention therefore provides the presence of at least one first reflector 150 arranged on the upper face 20 of the substrate 2 and at least partly bordering the first light source 100. The first reflector 150 is configured to reflect the first light ray 111 propagating in the first emission direction 110. The first light ray 111 is reflected in a first reflection direction 120 of which any direction vector has a non-zero component in the first direction x and / or the second direction y.Depending on the presence or absence of other reflectors around the light source 100, the extent of the first reflector 150 around the first light source 100 and the height of the at least one first reflector 150, the first light ray 111 can then be returned towards another wall of the reflector 150 or a wall of another reflector and be reflected again, or no longer be reflected by the device 1. Thus, advantageously, and possibly after several reflections against the first reflector 150 and / or other reflectors, the first light ray 111 is extracted from the device 1 and contributes to the total intensity perceived by the observer.

[0089] According to one embodiment, the first reflector 150 functions as a mirror, that is to say that the first emission direction 110 and the first reflection direction 120 are symmetrical with respect to a plane normal to a plane of the first reflector 150. This plane of the first reflector 150 can be defined in several ways and can in particular be defined locally. For example, if the passive nanowires 151 of the first reflector 150 are arranged in rectilinear rows, the plane of the first reflector 150 is defined as the plane comprising the axes of symmetry along z of the passive nanowires 151 of the row of passive nanowires 151 bordering the first light source 100.If the first passive nanowires 151 of the first reflector 150 are arranged in rows forming circular arcs, the plane of the first reflector 150 can be defined at the point of incidence of the first light ray 111 with the first reflector 150 as the plane tangent to the circular arc defined by the row of first passive nanowires 151 bordering the first light source 100.

[0090] According to another embodiment, the first reflector 150 does not function as a mirror but as a decoupler. In this example, the first light ray 111 is not reflected symmetrically by the first reflector 150. This embodiment is illustrated in Figure 5. This figure more particularly envisages a case in which the first passive nanowires 151 are arranged in parallel rectilinear rows and oriented in the y direction. Figure 5 is a sectional view along the xz plane of the reflection of the first light ray 111 by the first reflector 150. The first light ray 111 propagates along a first emission direction 110 that can be defined by a first emission direction vector. This first emission direction vector admits in the xz plane an orthogonal projection denoted v emiXZ'. In the same way, after reflection, the first light ray 111 propagates along a first reflection direction 120 which can be defined by a first reflection direction vector admitting in the xz plane an orthogonal projection noted v re / -iXZ . These two orthogonal projections respectively form a first emission angle a em XZ and a first angle of reflection has ref xz with the z direction. In the previously described case of a first reflector 150 acting as a mirror, these angles are equal. On the contrary, in a decoupling function, the first reflector allows the first light ray to be deflected so that a em XZ has ref xz . With the aim of optimizing light extraction, the first reflector 150 is configured so that the first reflection direction is close to the z direction. Thus, the first reflection angle is preferably less than 20°, and even more advantageously less than 10°.

[0091] This same decoupling phenomenon can be predicted in the yz plane.

[0092] As mentioned previously, the first light source 100 typically emits a plurality of light beams corresponding to a continuum of wavelengths. Thus, the first reflector 150 is advantageously configured to reflect a plurality of wavelengths. Typically, it makes it possible to reflect all of the wavelengths included in a given range. For example, if the first light source 100 is part of a blue-colored sub-pixel, the first reflector 150 can be configured to reflect the wavelengths between 430 nm and 470 nm. For the first reflector 150 to reflect a plurality of wavelengths, it is advantageously provided that the diameter of the first passive nanowires 151 and the pitch between neighboring first passive nanowires 151 change with the distance from the first light source 100.

[0093] Advantageously, the first reflector 150 is arranged on the substrate 2 so as to completely surround the first light source 100 in the xy plane. This embodiment illustrated in FIGS. 2A to 2E makes it possible to reflect a greater number of light rays which, without the presence of a reflector, would not have been extracted from the device 1, and therefore to further improve the directivity of the first light beam 101. Preferably, by completely surrounding the first light source 100, the at least one first reflector 150 forms a rectangular-shaped cavity around the first light source 100. Such a cavity is similar to the association of two Fabry-Perot type cavities arranged in orthogonal directions. This cavity advantageously has a width W of less than 1 pm (1 pm = 10' 6 m).

[0094] The first reflector 150 advantageously comprises a plurality of first passive nanowires 151 extending from the upper face 20 of the substrate 2. The term “passive nanowire” means a nanowire that does not emit light radiation. The passive nanowires 151 are typically nanowires similar to active nanowires but are not electrically connected. The first passive nanowires 151 may in particular be electrically insulated from the first active nanowires 130 that can form the first light source 100. Thus, the first active nanowires 130 can be traversed by a current and generate a light beam without the passive nanowires 151 themselves being electrically connected.

[0095] The first passive nanowires 151 preferably form a photonic crystal extending over the substrate 2, for example a Bragg mirror. The photonic crystal formed by all of the first passive nanowires 151 of the first reflector 150 can be described by several parameters and in particular:

[0096] - no network,

[0097] - the filling rate, also called opening rate or density, generally between 10 and 90%,

[0098] - the type of mesh (hexagonal, square, etc.),

[0099] - the refractive index of a possible filling material between the nanowires, commonly called “filler”, preferably between 1 and 1.7, and

[0100] - the dimensions of the nanowires.

[0101] In the case where the first reflector is used as a mirror, the characteristics of the first photonic crystal reflector 150 are defined so that the spectral stop band, sometimes referred to as the English term “stopband”, of the first photonic crystal reflector 150 comprises the first wavelength λi. In particular, the pitch and the diameter of the first passive nanowires 151 of the first reflector 150 must be adjusted as a function of the first wavelength λi.

[0102] In the case where the first reflector is used as a decoupler, these characteristics are adjusted according to the reflection angles that one wishes to impose. More precisely, these characteristics are defined so that the optical modes supported by the photonic crystal of the first reflector 150 at the first wavelength λi are above the light cone defined by the following relation:

[0103] Pair ~ ~ with f> a tr the propagation constant of the light beam in air, œ the pulsation of the incident light beam and c the speed of light. If an incident light beam has an orientation outside the extraction cone, it will be entirely reflected and there will be no refracted ray (total reflection phenomenon).

[0104] To avoid a total reflection phenomenon, the top of the nanowires can be covered by a layer inducing a certain topography and therefore an associated diffusion phenomenon. This layer is called a diffusive layer. It makes it possible to avoid or limit the total reflection phenomenon. The incident beam can thus be reflected then diffused or refracted. For low angles of incidence, successive reflections of the incident beam between the mirrors can occur before diffusion or refraction. The extraction of low incidence beams is thus improved. The diffusive layer can typically be based on TiC>2. According to one possibility, the topography of the vertices, for example having a pyramidal shape, acts as such a diffusive layer and improves light extraction.

[0105] The different wires (first active nanowires 130, first passive nanowires 151) are preferably formed through a masking layer 23 partially masking the nucleation layer 22 and comprising preferably circular openings defined so as to obtain the different wire diameters and the different desired arrangements or networks. Each opening in the masking layer 23 in fact allows localized growth of a 3D structure from the nucleation layer 22.

[0106] The masking layer 23 is preferably made of a dielectric material, for example silicon nitride Si3N4. It can be deposited by chemical vapor deposition CVD (acronym for “Chemical Vapor Deposition”) on the nucleation layer 22. The openings can be made for example by UV or DUV lithography (acronym for Deep UV), by electron beam lithography or by NIL (acronym for Nanoinprint lithography). It can be removed after growth of the different wires, for example by selective etching.

[0107] The device described makes it possible to obtain a cavity effect even for very small sub-pixels. This effect is in fact obtained for cavity widths as small as 1 pm. The device advantageously makes it possible to decorrelate the characteristics specific to the source, such as the emission wavelength, from the characteristics specific to the extraction or shaping of the light emitted by this source. By using different nanowires for the source and the reflectors, it is thus possible to form a substantially independent emissive part and a resonant cavity. The possible combinations between the source and the reflectors are thus more numerous. This makes it possible to envisage a large number of technological configurations, depending on the intended applications.

[0108] According to an advantageous embodiment, the optoelectronic device 1 comprises a second light source 200 arranged on the upper face of the substrate and adjacent to the first light source 100. The two light sources 100, 200 can be likened to two adjacent sub-pixels of a display screen. These may be two sub-pixels belonging to the same pixel or two sub-pixels each belonging to a separate pixel.

[0109] The second light source 200 is configured to emit a second light beam 201 being, like the first light beam 101, advantageously configured to be mainly emitted in the longitudinal direction. The second light beam 201 is for example omnidirectional and typically has a Lambertian profile. The second light beam 201 emits at least one second light ray 211 of wavelength λ2 called second wavelength λ2 in a second emission direction 210. This second emission direction 210 is characterized by the fact that any direction vector of this second emission direction 210 has a non-zero component in the first direction x and / or the second direction y.

[0110] The second light source 200 preferably comprises at least one second active nanowire 230 extending from the upper face 20 of the substrate 2. It is bordered by a second reflector 250 advantageously comprising a plurality of second passive nanowires 251 extending from the upper face 20 of the substrate 2. The second passive nanowires form a photonic crystal that can be described in the same way as the photonic crystal formed by the first passive nanowires 151.

[0111] The second active nanowires 230 and the second passive nanowires 251 are preferably also formed through openings in the optional masking layer 23, as described for the first active nanowires 130 and the first passive nanowires 151.

[0112] The second reflector 250 is configured to reflect the second light ray 211 propagating along the second emission direction 210. The second light ray 211 is reflected along a second reflection direction 220, any direction vector of which has a non-zero component along the first direction x and / or the second direction y. As described for the device with a single light source, the second light ray 211 is thus extracted from the device 1 and contributes to the total intensity perceived by the observer.

[0113] The characteristics of the first photonic crystal reflector 150 adapt mutatis mutandis to the second photonic crystal reflector 250. In particular, if the second reflector 250 is used as a mirror, the latter are defined so that the spectral stop band, sometimes referred to by the English term "stopband", of the second photonic crystal reflector 250 comprises the second wavelength λ2. In particular, the pitch and the diameter of the second passive nanowires 251 of the second reflector 250 must be adjusted as a function of the second wavelength λ2.

[0114] Similar to the first reflector 150, the first reflector may be configured to be used as a decoupler.

[0115] The first light source 100 and the second light source 200 are separated by a transition zone comprising the first reflector 150 and the second reflector 250. This transition zone thus makes it possible to isolate the first light source 100 from the rays emitted by the second light source 200, and vice versa.

[0116] The first passive nanowires 151 and / or the second passive nanowires 251 may advantageously have a diameter and / or a pitch between nanowires 151, 251 that progressively increases or decreases as they move away from the first light source and / or the second light source respectively. By progressive variation of the diameter of the nanowires 151, 251 or of the pitch between these nanowires 151, 251, it is meant, depending on the arrangement of the nanowires 151, 251 in the xy plane, that these parameters vary in limited proportions between neighboring nanowires. Typically, it is expected that the nanowires 151, 251 have a diameter of between 3% and 13% of that of their nearest neighbor. In the case where the nanowires 151, 251 are arranged in parallel rows, it is typically provided that the pitch between a row and one of the two rows adjacent to it is between 2% and 4% of that separating this same row and the other of the two rows adjacent to it.

[0117] It is conceivable to ensure that the first reflector 150 and the second reflector 250 cover disjointed zones within the transition zone. In this case, it is advantageous to provide that these disjointed zones are adjacent and that the first passive nanowires 151 of the first reflector 150 bordering the second reflector and the second passive nanowires 251 of the second reflector 250 bordering the first reflector 150 have substantially equal diameters.

[0118] It is also conceivable that a portion of the first reflector 150 coincides with a portion of the second reflector 250.

[0119] The at least one first light source 100 may also be a so-called bidirectional light source (embodiment not shown) with a planar type electroluminescent zone emitting the first light rays of first wavelength λi in the first emission direction 110 as described previously. In a known manner, for example, the light source 100 comprises at least one stack of semiconductor layers and a covering layer, the covering layer comprising one or more radiation-emitting layers equivalent to the first active region 131. The different layers are superimposed, structured, and are substantially planar. The stack extends from the upper face 20 of the substrate 2 so as to form, in a known manner, a luminescent mesa.In this embodiment, the stack of layers to form the first light source 100 and the first passive nanowires 151 as described previously to form the first reflector 150 can be formed successively in the same epitaxy reactor or according to separate known methods. They can be based on the same material or based on different materials. The first passive nanowires 151 can also be formed by etching a material previously deposited next to the at least one first light source 100, or even all around, depending on the desired shape for the first reflector 150. The stack of semiconductor layers and covering layer can for example have a height taken along z of between 1 and 3 pm. The emitting layer(s), corresponding to the first active region 131, advantageously have(s) a height along z of between 200 and 1000 nm.

[0120] The characteristics of this embodiment described with reference to the first light source 100 can be applied mutatis mutandis to other light sources, in particular the second light source 200.

[0121] As illustrated by the previous examples, the devices according to the invention make it possible to improve the directivity of the beam emitted by an LED type light source, and therefore to improve light extraction.

[0122] The invention is however not limited to the embodiments previously described.

[0123] In particular, the number, shape and arrangement of each element of the device can be adapted according to display needs.

Claims

CLAIMS 1. Optoelectronic device (1) comprising: • a substrate (2) having an upper face (20) extending along a plane called the basal plane defined by a first direction (x) and a second direction (y), • at least one first light source (100) arranged on the upper face (20) and configured to emit a first light beam (101) emitting at least at a first wavelength λi, said first light beam (101) being emitted at least in a direction called the first emission direction (110) of which a first emission direction vector has a non-zero component in at least one of the first direction (x) and the second direction (y), said device (1) being characterized in that: • it further comprises at least one first reflector (150) at least partially bordering the first light source (100), configured to reflect in a first reflection direction (120) first light rays (111) of first wavelength λi emitted in the first emission direction (110), • the at least one first reflector (150) comprises a plurality of first passive nanowires (151) extending from the upper face (20) of the substrate.

2. Optoelectronic device (1) according to the preceding claim, wherein the first light source (100) is an incoherent light source.

3. Optoelectronic device (1) according to any one of the preceding claims, in which the first passive nanowires (151) have a diameter which gradually decreases or increases as they move away from the at least one first light source (100).

4. Optoelectronic device (1) according to any one of the preceding claims, wherein the first passive nanowires (151) are arranged according to a first constant pitch pi in at least one of the first direction (x) and the second direction (y).

5. Optoelectronic device (1) according to any one of claims 1 to 3, wherein the first passive nanowires (151) are arranged in a pitch which gradually increases or decreases away from the at least one first light source (100).

6. Optoelectronic device (1) according to any one of the preceding claims, wherein the at least one first light source (100) comprises at least one first active nanowire (130) having a first diameter <p Oi and comprising a first active region (131) configured to emit the first light rays (111) of first wavelength λi.

7. Optoelectronic device (1) according to the preceding claim, in which the first diameter <p Oi of the at least one first active nanowire is less than 5 pm.

8. Optoelectronic device (1) according to any one of claims 6 and 7, wherein the first passive nanowires (151) and the at least one first active nanowire (130) are based on the same material.

9. Optoelectronic device (1) according to any one of the preceding claims, in which the at least one first reflector (150) completely surrounds, according to a projection on the basal plane, the first light source (100).

10. Optoelectronic device (1) according to any one of the preceding claims, in which: • The first emission direction vector has a non-zero component in the first direction (x), • The first emission direction vector has an orthogonal projection in a transverse plane defined by the first direction (x) and a third direction (z) normal to the basal plane, called the first projected emission vector v em XZ , forming a first emission angle a emXZ with the third direction (z), • A first reflection direction vector of the first reflection direction (120) has an orthogonal projection in the transverse plane, called the first projected reflection vector v re / -iXZ ', forming a first angle of reflection a ref xz with the third direction (z), • The plurality of passive nanowires (151) is configured to reflect the first light rays (111) such that the first emission angle aem,xz et I e first angle of reflection a ref xz are distinct.

11. Optoelectronic device (1) according to the preceding claim in which the first angle of reflection has ref xz is less than 40°, preferably less than 20°.

12. Optoelectronic device (1) according to any one of the preceding claims, further comprising at least one second light source (200) adjacent to the first light source (100), configured to emit a second light beam (201) emitting at a second wavelength λ2, said second light beam (201) being emitted at least in a direction called second emission direction (210) of which a second emission direction vector has a non-zero component in at least one of the first direction (x) and the second direction (y), said first and second light sources (100, 200) being separated by a transition zone (1000) comprising the at least one first reflector (150) and at least one second reflector (250), the at least one second reflector (250) being configured to reflect in a second reflection direction (220) second light rays (211) of second wavelength λ2, said at least one second reflector (250) comprising a plurality of second passive nanowires (251) extending from the upper face of the substrate (20).

13. Optoelectronic device (1) according to the preceding claim, wherein the second light source is an incoherent light source.

14. Optoelectronic device (1) according to any one of the two preceding claims, in which the second passive nanowires (251) have a diameter which gradually decreases or increases as they move away from the at least one second light source (200).

15. Optoelectronic device (1) according to any one of the three preceding claims, wherein the second passive nanowires (251) are arranged according to a second constant pitch P2 according to at least one of the first direction (x) and the second direction (y).

16. Optoelectronic device (1) according to any one of claims 12 to 14, wherein the second passive nanowires (251) are arranged in a pitch which gradually increases or decreases away from the at least one second light source (200).

17. Optoelectronic device (1) according to any one of claims 12 to 16, wherein the at least one second light source (200) comprises at least one second active nanowire having a second diameter q>02 and comprising a second active region configured to emit the second light rays of second wavelength λ2.

18. Optoelectronic device (1) according to the preceding claim, in which the second diameter q>02 of the at least one second active nanowire is less than 5 pm.

19. Method for manufacturing an optoelectronic device (1) comprising a first light source (100) and a first reflector (150) itself comprising a plurality of first passive nanowires (151), comprising the following steps: • Provide a substrate (2) having an upper face (20), extending along a plane called the basal plane defined by a first direction (x) and a second direction (y) and comprising a nucleation layer (22) allowing the nucleation and growth of the first passive nanowires (151), • Growing the first passive nanowires (151) from the upper face (20) of the substrate (2) so as to form the first reflector (150), the first reflector (150) being configured to reflect in a first reflection direction (120) the first light rays (111) of first wavelength λi emitted in the first emission direction (110), • Forming the first light source (100) on the upper face (20) of the substrate (2), the first light source (100) being configured to emit a first light beam (101) emitting at least at the first wavelength λi, said first light beam (101) being emitted at least in a direction called the first emission direction (110) of which a first emission direction vector has a non-zero component in at least one of the first direction (x) and the second direction (y).

20. Manufacturing method according to the preceding claim in which: • the first light source (100) comprises at least one first active nanowire (130), • the nucleation layer (22) allows the nucleation and growth of at least one active nanowire (130), • the step of forming the first light source (100) comprises a step of growing the at least one first active nanowire (130) from the upper face (20) of the substrate (2) so as to form the first light source (100).

21. Manufacturing method according to the preceding claim in which the step of growing the first passive nanowires (151) and the step of growing the at least one first active nanowire (130) are carried out simultaneously.

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