3D Light Emitting Diode and Associated Manufacturing Process

Abstract

3D Light-Emitting Diode and Associated Manufacturing Method. The invention relates to a light-emitting diode (1) and its manufacturing method, the diode comprising at least one radial 3D three-dimensional structure (20) including a core (21) having a first conductivity, and having a wire or pyramid shape with flanks (210) substantially parallel or oblique to the z-direction, an active region (22) configured to emit light radiation, the active region (22) including at least one radial portion (220) covering the flanks (210) of the core (21), a shell (23) having a second conductivity, the light-emitting diode (1) including a magnetic layer (33) having a polarization (M) along a principal direction substantially parallel to the z-direction, so as to increase the residence time at the active region (22) by at least one of the first and second carrier types. Figure for the abstract: Fig. 1

Description

Title of the invention: 3D light-emitting diode and associated manufacturing process. Technical field

[0001] The present invention relates to the field of optoelectronics. Its particularly advantageous application is the manufacture of optoelectronic devices having a three-dimensional (3D) structure, for example, light-emitting diodes based on nanowires. STATE OF THE ART

[0002] A light-emitting diode (LED) typically comprises carrier injection regions (electrons and holes) between which an active region is intercalated. The active region is where radiative recombinations of electron-hole pairs occur, resulting in light emission. This active region may include quantum wells, for example, InGaN-based wells.

[0003] LEDs exhibiting a three-dimensional structure (3D LEDs), typically in the form of nanowires or pyramids, can exhibit different architectures, particularly in the arrangement of the different constituent regions of the LED.

[0004] These different regions can be arranged radially around the longitudinal z-direction. Such an LED architecture is called radial or core-shell. A radial 3D LED typically has an inner part (the core) elongated along the z-axis and supported by a substrate, an active region surrounding the inner part, and an outer part (the shell) surrounding the active region. The inner part is generally used for electron injection and the outer part for hole injection. The active region typically has quantum wells extending parallel to the longitudinal z-direction in the case of nanowire-type radial 3D LEDs, or obliquely in the case of pyramidal radial 3D LEDs.

[0005] To improve the radiative recombination rate, i.e. the external quantum efficiency (EQE) of 3D LEDs, an existing solution consists of confining the carriers within the active region by adding one or more carrier-blocking layers around the active region.

[0006] In particular, an electron blocking layer (EBL) can be added between the hole injection region and the active region. This EBL prevents electrons from the electron injection region from passing through the active region without recombining. The EBL is configured to block electrons and allow holes to pass through.

[0007] In practice, the introduction of these EBL layers leads to other problems, including the appearance of structural defects, the appearance of electrical resistances in series, and / or an undesirable slowing of the carriers that must pass through these layers. From a technological point of view, the formation of EBL layers in 3D LED architectures is not sufficiently controlled.

[0008] There is therefore a need to design a radial 3D LED architecture with improved EQE. The present invention aims to meet this need and / or at least partially overcome the drawbacks mentioned above.

[0009] In particular, one object of the present invention is to provide a light-emitting diode with a radial 3D structure, of nanowire or pyramidal type, exhibiting an optimized EQE. Another object of the present invention is to provide a method for manufacturing such a light-emitting diode.

[0010] The other objects, features, and advantages of the present invention will become apparent from an examination of the following description and accompanying drawings. It is understood that other advantages may be incorporated. In particular, certain features and advantages of the device may be applied mutatis mutandis to the method, and vice versa. SUMMARY

[0011] To achieve this objective, according to a first aspect, a diode is planned electroluminescent comprising at least one three-dimensional radial 3D structure comprising: - a core exhibiting a first conductivity of a first type of carriers, the core having a wire or pyramid shape oriented along a z-direction, and having flanks substantially parallel or oblique to the z-direction, - an active region configured to emit light radiation of X wavelength, the active region comprising at least a so-called radial part covering the flanks of the core, - a shell having a second conductivity of a second type of carriers, the shell covering at least the radial part of the active region,

[0012] Advantageously, the diode includes at least one magnetic layer configured to have a bias along a principal direction substantially parallel to the z direction, so as to increase the residence time at the level of the active region of at least one of the first and second types of carriers.

[0013] Thus, the magnetic layer generates a magnetic field substantially along the axis of the 3D wire or pyramidal structure. In the active region, the velocity components perpendicular to the magnetic field of the charge carriers, and in particular of the electrons, are significant. The generated magnetic field perturbs This alters the electron trajectory, allowing electrons to remain in the active region, which includes quantum wells, for longer periods. The generated magnetic field can even trap charge carriers, particularly electrons, in the non-uniformities of quantum wells, which are typically indium-rich. It is therefore clear that this architecture improves the EQE (Electromagnetic Flux).

[0014] The core of the 3D structure is typically based on or made of n-GaN. The shell of the 3D structure is typically based on or made of p-GaN. The magnetic layer typically causes a modification of the trajectory of electrons propagating in the n-GaN core so as to maintain their residence time in the active region and to increase the possibilities of radiative recombination.

[0015] Another aspect relates to a method for making a light-emitting diode comprising at least one three-dimensional 3D structure, according to the first aspect, the method comprising: - to form the core by epitaxy on a growth substrate, by localized growth through an opening in a masking layer placed on the growth substrate, - to form the active region on the heart by epitaxy, - to form the shell on the active region by epitaxy, then - deposit at least one magnetic layer such that said magnetic layer has a polarization along a principal direction substantially parallel to the z direction.

[0016] The effects and advantages described above apply to the process in this respect. BRIEF DESCRIPTION OF THE FIGURES

[0017] The aims, objects, features and advantages of the invention will become clearer from the detailed description of an embodiment thereof, which is illustrated by the following accompanying drawings in which:

[0018] [Fig.1] Fig.1 illustrates a radial 3D wire-shaped LED comprising a magnetic layer, according to an embodiment of the present invention.

[0019] [Fig.2] Fig.2 illustrates a radial 3D wire-shaped LED comprising a magnetic layer, according to another embodiment of the present invention.

[0020] [Fig. 3] Figure 3 illustrates a pyramid-shaped radial 3D LED comprising a magnetic layer, according to an embodiment of the present invention.

[0021] [Fig.4A] [Fig.4B] [Fig.4C] Figures 4A to 4C illustrate different arrangements of magnetic layer patterns with several 3D structures, according to several embodiment examples.

[0022] [Fig.5] [Fig.6] [Fig.7] [Fig.8] [Fig.9] [Fig.10] [Fig.ll] [Fig.12] [Fig.13] [Fig.14] [Fig. 15] [Fig. 16A] Figures 5 to 16A schematically illustrate different stages of a method for producing a 3D LED comprising a magnetic layer, according to an example of an embodiment of the present invention.

[0023] [Fig.lôB] [Fig.lôC] [Fig.lôD] Figures 16B to 16D schematically illustrate two variants of the embodiment of the magnetic layer on the first contact of the 3D LED, according to an example of an embodiment of the present invention.

[0024] [Fig.17A] [Fig.17B] Figures 17A and 17B schematically illustrate a variant embodiment of the magnetic layer on the second contact of the 3D LED, according to an example of an embodiment of the present invention.

[0025] [Fig.18A] [Fig.18B] Figures 18A and 18B schematically illustrate another variant of the embodiment of the magnetic layer on the second contact of the 3D LED, according to an example of an embodiment of the present invention.

[0026] [Fig. 19] The [Fig. 19] schematically illustrates a variant embodiment of the magnetic layer, according to an example of an embodiment of the present invention.

[0027] [Fig.20] [Fig.21] Figures 20 and 21 illustrate field simulation results magnetic generated for a relative arrangement of the 3D structures and patterns of the magnetic layer as illustrated in [Fig.4A], according to an example embodiment of the present invention.

[0028] The drawings are given by way of example and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate understanding of the invention and are not necessarily to scale with practical applications. In particular, the dimensions of the different layers and parts of the 3D LED are not necessarily representative of reality. DETAILED DESCRIPTION

[0029] Before beginning a detailed review of embodiments of the invention, optional features which may possibly be used in association or alternatively are stated below.

[0030] According to one example, the carriers of the first type are electrons and the first conductivity is of type N, the carriers of the second type are holes and the second conductivity is of type P, at least one magnetic layer being configured so as to increase the residence time at the active region of the electrons that have propagated in the core.

[0031] According to one example, at least one magnetic layer extends in a principal extension plane substantially perpendicular to the z-direction and comprises motifs distributed according to a pitch p along at least one direction of its principal extension plane, so as to form a plurality of portions devoid of magnetic material, and preferably said motifs are distributed according to a first network of steps p, along two distinct directions of its main extension plan.

[0032] The magnetic layer thus exhibits a structure based on a pattern that repeats along at least one direction of its principal plane of extension. The magnetic layer is therefore discontinuous, along one and preferably two directions of its principal plane of extension. These two directions are then preferably perpendicular.

[0033] The discontinuity in the magnetic layer allows for the generation of local magnetic field maxima. This induces areas with strong induced fields. The perturbation effect on the trajectory of charge carriers is thus enhanced in the main extension plane of the magnetic layer.

[0034] According to one example, at least one magnetic layer has grooves, said grooves being devoid of magnetic material or the magnetic layer being formed at least in part by said grooves based on or made of a magnetic material

[0035] According to one example, at least one magnetic layer has a stud structure, said studs being devoid of magnetic materials or the magnetic layer being formed at least in part by said studs based on or made of a magnetic material.

[0036] According to one example, the diode comprises a plurality of 3D structures, the plurality of 3D structures being distributed according to the same pitch p as the patterns of the magnetic layer.

[0037] The plurality of 3D structures is thus arranged in coincidence with the patterns of the magnetic layer. The 3D structures are thus arranged in accordance with the local maxima of magnetic fields. More particularly, the 3D structures can thus be placed in the portions with strong induced fields, to further improve the EQE. The plurality of 3D structures can be distributed according to a second lattice with the same pitch p as the first lattice.

[0038] According to one example, at least one magnetic layer has a polarization, preferably a permanent polarization, between 0.1 T and 1.5 T, preferably substantially equal to 0.5 T.

[0039] This polarization range makes it possible to generate magnetic fields with intensities ranging from 100 Gauss to 5000 Gauss. During the development of the invention, it was found that this range was particularly well-suited for perturbing the trajectory of charge carriers in 3D LED structures. This is especially advantageous for 3D structures with a height along the z-direction on the order of pm, for example, between 0.1 pm and 5 pm.

[0040] According to one example, at least one magnetic layer is based on or made of a ferromagnetic material.

[0041] According to one example, at least one magnetic layer is based on or is made of a material comprising at least one element selected from cobalt, iron and nickel.

[0042] According to one example, at least one magnetic layer is based on or is made of a material selected from the group consisting of CoFeB, CoFe, NiW, NiFe.

[0043] According to one example, the at least one magnetic layer comprises a stack of sublayers, said stack comprising at least one first sublayer based on or made of a ferromagnetic material, arranged between two second sublayers based on or made of a non-magnetic metallic material. The magnetic properties may depend on the thicknesses of the sublayers. In particular, thin sublayers, for example with a thickness on the order of a few nanometers, may have a permanent polarization perpendicular to the principal plane of extension of the layer. By stacking thin sublayers separated by a non-magnetic material, it is possible to stack the polarizations of the magnetic sublayers.

[0044] According to one example, at least one magnetic layer has a thickness between 0.5 nm and 50 nm, preferably between 1 nm and 30 nm. According to another example, the magnetic layer has a thickness between 30 nm and 50 nm.

[0045] According to an example: - the sides of the core are approximately parallel to the z-direction, and - the radial part of the active region extends along an extension direction main substantially parallel to the z direction.

[0046] According to one example, the diode further comprises: - a first electrically conductive contact configured to inject carriers of the first type into the heart, - a second electrically conductive contact configured to inject carriers of the second type into the shell.

[0047] According to one example, the magnetic layer is underlying, along the z-direction, the first contact. According to an alternative or combinable example, the magnetic layer is above, along the z-direction, the second contact; preferably, the magnetic layer has a principal extension plane substantially parallel to the masking layer.

[0048] According to one example, the diode further comprises at least one electrically insulating layer interposed between the magnetic layer and the first contact.

[0049] According to one example, the diode further comprises at least one electrically insulating layer interposed between the magnetic layer and the second contact.

[0050] According to one example, the diode further comprises a masking layer having a so-called lower face, a so-called upper face, and openings, and the core passes through the masking layer at the level of said openings.

[0051] This structural characteristic of the 3D LED is typically linked to a Selective Area Growth (SAG) localized growth process for 3D structures. The presence of the masking layer is generally a residual element of the SAG localized growth implementation. Such a masking layer is not present in so-called planar 2D LEDs. LEDs structured in a mesa pattern by etching planar layers, according to a technological approach designated as "top-down," do not have a masking layer. The masking layer is generally specific to the implementation of a SAG process for the formation of 3D structures, according to a technological approach designated as "bottom-up." The presence of the masking layer is a means of differentiating between "bottom-up" 3D LEDs and "top-down" LEDs produced using planar technologies.

[0052] According to one example, the three-dimensional structure is obtained by localized growth through the openings of the masking layer.

[0053] The openings in the masking layer can be regularly distributed in the form of a network. A portion at the base of the core of the 3D structure is typically enclosed by the masking layer. The core can further expand above the enclosed portion and rest upon the masking layer.

[0054] According to one example, at least one magnetic layer surmounts, in the z direction, the masking layer.

[0055] According to one example, the radial part forms at least 80% of the active region.

[0056] In view of the effects and advantages previously presented, it is understood that the EQE can be improved without necessarily resorting to an EBL.

[0057] According to one example, the 3D LED further comprises a first-type carrier-blocking layer interposed between the shell and the active region. A synergistic effect between the perturbation of the carrier trajectory due to the magnetic layer on the one hand, and the carrier blocking due to the blocking layer on the other, can thus be obtained.

[0058] According to one example, the core and shell are based on or made of GaN, and the active region comprises quantum wells based on or made of InGaN.

[0059] In one example, the magnetic layer extends transversely, and in particular perpendicularly or obliquely, to said radial part. In another example, the main extension plane of the magnetic layer is transverse, and in particular perpendicularly or obliquely, to the main extension direction of the radial part of the active region.

[0060] According to one example, the process further comprises: - deposit a planarization layer on the growth substrate, on and around at least one 3D structure protruding from the growth substrate, so as to obtain a flat surface above at least one 3D structure, - to attach a manipulation substrate to said flat surface, - remove the growth substrate to expose the masking layer and a portion of the core through the masking layer.

[0061] According to one example, the process further comprises: - After removing the growth substrate, form the first contact with the exposed portion of the core, - following the formation of the first contact, deposit the magnetic layer on an underside of the masking layer.

[0062] The magnetic layer is thus arranged on the back face of the diode, which facilitates its deposition and structuring.

[0063] According to one example, the process further comprises, between the formation of the first contact and the deposition of the magnetic layer, the formation of an electrically insulating layer such that the electrically insulating layer is intercalated between the first contact and the magnetic layer.

[0064] According to one example, the process further comprises: - to form the second contact on the shell, for example by depositing a layer of transparent conductive oxide, and - deposit the magnetic layer on the second contact, preferably along a main extension plane substantially parallel to the masking layer.

[0065] These steps can be carried out prior to the deposition of the planarization layer. According to an alternative example, when the magnetic layer is deposited on the second contact, the process may be free from the deposition of a planarization layer.

[0066] The magnetic layer is thus arranged on the front face of the diode, around the 3D structures. According to this example, the growth substrate can be retained and serves as a contact with the n-type core. The fabrication process is therefore carried out on the front face, on the side of the 3D structures. The magnetic layer is deposited on the front face, on the second contact for example, or separated from the second contact by an insulating layer.

[0067] According to one example, the process further comprises, between the formation of the second contact and the deposition of the magnetic layer, the formation of an electrically insulating layer such that the electrically insulating layer is intercalated between the second contact and the magnetic layer.

[0068] According to one example, the manipulation substrate is based on a material transparent at the X wavelength. The manipulation substrate can thus be retained after the process. Alternatively, the manipulation substrate can be removed after the process, typically when the manipulation substrate is based on an opaque material such as silicon.

[0069] According to one example, the formation of the core and shell, and the formation of the active region, are carried out by organometallic precursor vapor phase epitaxy (MOVPE).

[0070] According to one example, the light-emitting diode comprises a plurality of 3D structures, and the core formation is such that two adjacent cores are separated from each other by a separation distance substantially less than 20 pm, preferably substantially between 1 pm and 5 pm. The diode cores are thus distributed over the substrate with a high surface density. This promotes radial growth of the portions above each core, particularly the active regions.

[0071] Except where incompatibility exists, technical features described in detail for a given embodiment may be combined with technical features described in the context of other embodiments described by way of example and without limitation, so as to form another embodiment which is not necessarily illustrated or described. Such an embodiment is obviously not excluded from the invention.

[0072] In the present invention, the device and method relate in particular to the architecture and fabrication of 3D-structured light-emitting diodes (LEDs). The invention can be implemented more broadly for various 3D-structured optoelectronic devices. The invention can therefore also be implemented in the context of laser or photovoltaic devices. In this patent application, the terms "light-emitting diode," "LED," or simply "diode" are used synonymously. An "LED" may also be understood to mean a "micro-LED."

[0073] Unless explicitly stated otherwise, it is specified that, within the framework of the present invention, the relative disposition of a third layer intercalated between a first layer and a second layer does not necessarily mean that the layers are directly in contact with each other, but means that the third layer is either directly in contact with the first and second layers, or separated from them by at least one other layer or at least one other element.

[0074] Thus, the terms and phrases "to bear upon" and "to cover" or "to re-cover" or even "on" do not necessarily mean "in contact with". Typically, the shell bears upon the active region either directly or indirectly, for example via an intercalated electron-blocking layer. The active region can bear upon the core either directly or indirectly, for example via an intercalated quantum barrier.

[0075] The LEDs according to the present invention are preferably based on III-V materials, in particular GaN-based materials. The different parts and regions of the LED typically have a hexagonal crystallographic structure. According to the Miller-Bravais system, (hkil) denotes a plane of the hexagonal structure, {hkil} a family of planes of the hexagonal structure, [hkil] a direction or vector of the hexagonal structure.

[0076] The external quantum efficiency EQE can be decomposed into three components: - the injection efficiency (IE) of carriers into the active region, - Internal quantum efficiency (IQE), which is the ratio between the number of radiative recombinations and the total number of recombinations, - Light extraction efficiency (LEE) which corresponds to the proportion of photons exiting the LED relative to the number of photons generated.

[0077] The term "3D structure" is understood in contrast to so-called planar or 2D structures, which have two dimensions in a plane much larger than the third dimension normal to the plane. Thus, the usual 3D structures used in the field of 3D LEDs can be in the form of a wire, nanowire, microwire, or even a pyramid. Such a 3D structure has an elongated shape or is oriented along the longitudinal direction z. The longitudinal dimension of the wire, along z in the figures, is greater, and preferably much greater, than the transverse dimensions of the wire, in the xy plane in the figures. The longitudinal dimension, particularly for a wire, is, for example, substantially between two and ten times greater than the transverse dimensions, preferably between three and five times the transverse dimensions.In the example of pyramids, the ratios of longitudinal dimensions to transverse dimensions can be fixed. This typically depends on the geometries of the GaN crystals. For example, for a pyramid, the ratio of the longitudinal dimension to a transverse dimension is substantially less than or equal to 0.9.

[0078] The 3D structures can also take the form of walls. In this case, only one transverse dimension of the wall is much smaller than the other dimensions, for example, three to five times smaller than the other dimensions. The 3D structures of the present application preferably have substantially vertical or oblique walls or flanks in the case of a pyramid shape. The vertical walls typically extend along crystallographic planes of type m {10-10}. They may be involved in a so-called radial growth mechanism. The 3D structures of the present application, and in particular wire-shaped structures, preferably have bases and vertices comprising substantially horizontal surfaces. These horizontal surfaces typically extend along crystallographic planes of type c (0001) or -c (000-1). They may be involved in a so-called axial growth mechanism.According to one possibility, the 3D structures appear as pyramids or nanopyramids. According to another possibility, the 3D structures appear as "elongated" pyramids or as a "pencil," typically a nanowire topped by a pyramid.

[0079] "Axial growth" means anisotropic growth occurring essentially or exclusively along the longitudinal direction z. "Radial growth" means isotropic growth covering, in particular, surfaces parallel to the longitudinal direction z.

[0080] The steps of the process as claimed are understood in a broad sense and may possibly be carried out in several sub-steps.

[0081] A substrate, layer, or device "based" on a material M means a substrate, layer, or device comprising only that material M or that material M and possibly other materials, for example alloying elements, impurities, or dopant elements.

[0082] In the following, the following abbreviations relating to a material M may be used: - aM refers to the material M in amorphous form, according to the terminology usually used in the field of microelectronics for the prefix a-. - pM refers to the material M in polycrystalline form, according to the terminology usually used in the field of microelectronics for the prefix p-.

[0083] Similarly, the following abbreviations relating to a material M may be used: - Mi refers to intrinsic or unintentionally doped material M, according to the terminology usually used in the field of microelectronics for the suffix -i. - Mn refers to the M-type material doped with N, N+ or N++, according to the terminology usually used in the field of microelectronics for the suffix -n. - Mp refers to the M material doped with P, P+ or P++, according to the terminology usually used in the field of microelectronics for the suffix -p.

[0084] A coordinate system, preferably orthonormal, comprising the x, y, z axes is shown in the figures. The z-axis is here parallel to the c-axis, i.e. to the crystallographic direction

[0001] .

[0085] In this patent application, the terms thickness for a layer and height for a structure or device will be preferred. The thickness is taken along a direction normal to the principal extension plane of the layer, and the height is taken perpendicular to the basal xy plane of the substrate. Thus, a layer typically has a thickness along z when it extends mainly along a plane xy, and an LED has a height along z. The relative terms "on", "surmounts", "under", "underlying" refer to positions taken along the z direction.

[0086] Dimensional values ​​are understood to be within manufacturing and measurement tolerances. The terms "approximately," "about," and "in the order of" mean, when referring to a value, "within 10%" of that value, or, when referring to an angular orientation, "within 10°" of that orientation. Thus, a direction that is substantially normal or perpendicular to a plane means a direction that is at an angle of 90 + 10° to the plane.

[0087] To determine the geometry of the 3D structures and the compositions of the different elements (wire, active region, slowing layer) of these 3D structures, one can carry out analyses of Scanning Electron Microscopy (SEM) or Transmission Electron Microscopy (TEM or TEM for the English acronym for "Transmission Electron Microscopy") or even Scanning Transmission Electron Microscopy (STEM) (English acronym for "Scanning Transmission Electron Microscopy").

[0088] TEM or STEM are particularly well suited to the observation and identification of quantum wells – whose thickness is generally on the order of a few nanometers – in the active region. Various techniques, listed below in a non-exhaustive manner, can be implemented: dark-field and bright-field imaging, weak beam imaging, and high-angle annular dark field (HAADF) diffraction.

[0089] The chemical compositions of the 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".

[0090] This method is well suited for analyzing the composition of small optoelectronic devices such as 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).

[0091] The techniques mentioned above make it possible in particular to determine whether an optoelectronic device with a 3D structure includes a magnetic layer within the meaning of the present invention, and / or a masking layer indicative of an implementation of localized growth, as described in the present invention.

[0092] Figures 1 and 2 illustrate an LED 1 comprising a 3D structure 20 in the form of a nanowire, according to two particular embodiments of the invention. The 3D structure 20 of the LED has a radial architecture, also called a core-shell architecture. Such a radial architecture may, in particular, comprise, from the inside to the outside of the nanowire along the y-direction: - a first part 21, or equivalently a core 21, having a diameter between 50 nm and 1.2 pm, typically on the order of 700 nm. This first part 21 forms the nucleus or core of the nanowire. It is preferably made of n-GaN, - an active region 22 with a thickness between 20 nm and 250 nm, typically on the order of 40 nm. The active region 22 covers the flanks 210 and the apex 211 of the core 21, respectively by a radial portion 220 and a summit portion 221. It is preferably made of InGaN. The active region 22 preferably comprises InGaN-i quantum wells alternating with GaN-i quantum barriers. The quantum wells may have a thickness between 1 nm and 15 nm and the quantum barriers may have a thickness between 3 nm and 20 nm, - optionally only, and not shown in the figures, an electron blocking layer (EBL) with a thickness between 10 nm and 100 nm, typically 30 nm. The EBL is preferably made of AlGaN. The EBL preferably covers the radial part 220 and the apex part 221 of the active region 22, - a second part 23, or equivalently a shell 23, with a thickness between 50 nm and 500 nm, typically on the order of 250 nm. The shell 23 covers the radial part 220 and the apex part 221 of the active region 22. It is preferably made of GaN-p. The shell 23 can directly cover the radial part 220 and the apex part 221 of the active region 22, or cover the EBL when an EBL is present.

[0093] Figure 3 illustrates an LED 1 comprising a pyramid-shaped 3D structure 20, according to another particular embodiment of the invention. In this example, the core 21 has a pyramidal shape with flanks 210 oblique to the z-direction. The active region 22 covers the flanks 210 of the core 21 by a radial portion 220. The shell 23 covers the radial portion 220 of the active region 22.

[0094] In the following, the 3D structure 20 is considered, for non-limiting purposes, to be in the form of a nanowire. The characteristics detailed below, unless otherwise specified, can be applied to a pyramidal form of the 3D structure 20.

[0095] The LED typically includes a masking layer 10 implemented during the nanowire growth process. This masking layer 10 may include several sublayers, for example, a layer 11 based on or made of silicon nitride and a layer 12 based on or made of oxide. The masking layer 10 includes openings 110 configured to promote local nanowire growth, as also illustrated in [Fig. 5]. During growth, the core 21 typically passes through the masking layer 10 at an opening 110, then extends essentially along z. According to one possibility, the cross-section in the xy plane of core 21 increases sharply at the exit of the opening 110. Core 21 can thus rest on the upper face 101 of the masking layer 10.

[0096] The LED may further comprise an electrically conductive first contact 31, configured to inject charge carriers into the core 21, as illustrated by the arrows Fl in Figures 1 to 3. In the illustrated example, the charge carriers injected by the first contact 31 are electrons. The first contact 31 may be metallic, for example, aluminum-based. Advantageously, this first contact 31 can also be used as an optical reflector to reflect the light emitted by the active region 22 back to the top side of the nanowire (i.e., the "front" side of the device). This improves the LED's light extraction efficiency. The first contact 31 is typically electrically insulated by a dielectric layer 40, for example, silicon oxide-based, located on the underside 102 of the masking layer 10 surrounding the first contact 31.

[0097] The LED may further include a second electrically conductive contact 32, configured to inject charge carriers into the shell 23. In the illustrated example, the charge carriers injected by the second contact 32 are holes. The second contact 32 is typically transparent to the wavelength of the light emitted by the active region 22. The second contact 32 is, for example, based on a transparent conducting oxide (TCO), for example, based on indium tin oxide (ITO).

[0098] According to one principle of the present invention, the 3D LED advantageously comprises a magnetic layer 33 configured to exhibit a polarization M, as illustrated in Figures 1 to 3. This polarization is oriented substantially parallel to the z-direction. Thus, it is understood that the polarization M is oriented along a principal non-perpendicular direction, and for example substantially parallel or oblique (and therefore forming, more particularly, a non-zero, non-right angle, for example strictly between 0° and 90°, 0° and 90° being excluded) with the radial portion 220 of the active region 22. The generated magnetic field thus perturbs the trajectory of the electrons. The electrons propagate along the arrow F2 in the core 21.At the p / n junction in the radial part 220 of the active region 22, their trajectory is perturbed by the generated magnetic field, as illustrated by the arrows F3, which slows down the electrons at the flanks 210 of the core 21 and the radial part 220 of the active region 22. Their residence time being increased, the recombination of electron-hole pairs is favoured at a plane m, thus favoring radiative recombination.

[0099] The magnetic layer 33 preferably has a polarization intensity between 0.1 T and 1.5 T, preferably substantially equal to 0.5 T. The structure The 3D 20 structure can have a height along the z-axis ranging from 100 nm to 5 pm. The 3D 20 structure can have at least one dimension in the xy-plane ranging from 300 nm to 3 pm. The described polarization ranges are indeed advantageously suited to generating a magnetic field that satisfactorily impacts the electron trajectory during propagation in the core 21. The polarization of the magnetic layer 33 can be permanent. It is possible that the polarization in the magnetic layer 33 will be induced by an additional magnetic source.

[0100] Since electrons are perturbed at a distance by the magnetic field, it is possible to position this magnetic layer 33 at different locations relative to the 3D structure 20. Electrical contact, in particular between the magnetic layer and the electrical contacts 31, 32, is not necessary. It is the relative orientation of the magnetic layer 33, and therefore its polarization M, with respect to the radial portion 220 of the active region 22 that primarily contributes to this effect, rather than its position relative to the 3D structure. Two examples are described below by way of non-limiting example. Other configurations can be considered.

[0101] According to a first particular example, illustrated in figures 1 and 3, the magnetic layer 33 is underlying, in the direction z, the 3D structure 20, and in particular the first contact 31. The magnetic layer 33 can be in direct electrical contact with the first contact 31 or through a layer distinct from this first contact 31, for example through an electrically insulating layer 40 described later.

[0102] According to a second particular alternative or combinable example to the previous one, and illustrated in [Fig.2], the magnetic layer 33 surmounts the upper face, in the direction z, of the masking layer 10. The magnetic layer 33 can, for example, surmount the second contact 32. Here again, the magnetic layer 33 can be in direct electrical contact with the second contact 32 or via a layer distinct from this second contact 32, for example via an electrically insulating layer 61 described later.

[0103] Preferably, the magnetic layer 33 is discontinuous. As illustrated, for example, by Figures 4A to 4C, the magnetic layer can therefore comprise portions 332 based on or made of a magnetic material, and portions 331 devoid of magnetic material (for example, based on or made of a non-magnetic material, such as a dielectric). These discontinuities allow for the generation of local magnetic field maxima. The portions 331 and 332 together preferably form a pattern that repeats at regular intervals in one, and preferably two, directions of the xy plane of principal extension of the magnetic layer 33. These local maxima are thus regularly distributed within the magnetic layer 33.

[0104] As illustrated in Figures 4A and 4B, for example, the magnetic layer 33 comprises a magnetic portion 332 in which non-magnetic cavities or studs 331 are formed. These cavities or studs form patterns 330 spaced according to a first lattice by pitches p and p' respectively in the y and x directions. p and p' are preferably, but not necessarily substantially, equal.

[0105] As illustrated in [Fig. 4C], the patterns 330 can be positively formed in magnetic material. Thus, magnetic material pads 332 can be distributed in the first lattice according to the steps p and p'. Each pad 332 can be surrounded by a portion 331 devoid of magnetic material.

[0106] Note that any shape, for example circular or polygonal, can be considered for the 330 patterns. The 330 patterns are not necessarily distributed in both directions x and y, although this is preferred. The 330 patterns can, for example, be grooves spaced by a pitch p along the y direction.

[0107] Preferably, the 3D structures 20 are arranged in coincidence with the motifs 330, so as to place the 3D structures 20 at the local maxima of the magnetic field. For this purpose, the 3D structures 20 can be distributed in a second lattice with the same spacing p, p' as the motifs 330 of the magnetic layer 33. Note that each 3D structure can be placed in a portion based on magnetic material 332 or in a portion devoid of magnetic material 331, as illustrated respectively in Figures 4A, 4C and [Fig. 4B].

[0108] Figures 5 to 18B illustrate different stages of a process for making a 3D structure LED 20 comprising a magnetic layer 33 as described above, according to several particular embodiment examples.

[0109] In the following, the 3D structures 20 are presented, by way of non-limiting example, in the form of nanowires. The internal architecture of these radial 3D structures 20 is not detailed with respect to the manufacturing process. Those skilled in the art know how to adapt the process to obtain pyramidal 3D structures.

[0110] As illustrated in [Fig. 5], the nanowires 20 are first formed on a growth substrate 4L. The substrate 41 can be silicon-based and serve as a support. The substrate 41 typically carries one or more layers 13, 14 based on or made of IILV materials or metal nitrides, particularly refractory metal nitrides. According to alternative examples, these layers 13 and 14 can be continuous (as illustrated) or etched and therefore discontinuous (not shown in the figures). A surface layer 13, called the nucleation layer, allows the nanowires 20 to grow. The nucleation layer 13 is preferably AlN-based. It can alternatively be based on other metal nitrides, for example GaN or AlGaN. It can be formed on the silicon support 41 by epitaxy, preferably by organometallic precursor vapor-phase epitaxy MOVPE (acronym for " MetalOrganic Vapor Phase Epitaxy). It advantageously has a thickness less than or equal to 200 nm, preferably less than or equal to 100 nm, for example on the order of 50 nm.

[0111] A masking layer 10 is preferably formed on the nucleation layer 13. It may comprise several sublayers based on dielectric material, for example, silicon nitride (Si3N4) and / or silicon oxide. The masking layer 10 may be formed by chemical vapor deposition (CVD). It partially masks the nucleation layer 13 and comprises openings 110, preferably circular, exposing areas of the nucleation layer 13. These openings 110 typically have at least one dimension, for example, a diameter, ranging from 30 nm to 500 nm. The openings 110 may be regularly distributed within the masking layer 10, for example, in the form of an ordered array.

[0112] Such a masking layer 10 allows localized growth of a 3D structure 20 at each opening 110. In particular, during a preliminary growth step called germination, a GaN-based seed forms at the opening 110 and then fills the opening 110. The subsequent growth of the nanowire 20 then takes place from this seed, in a localized manner.

[0113] During the formation of the nanowires 20, the cores 21, the active regions 22, and the shells 23 are successively formed by epitaxy, preferably by metal-organic vapor-phase epitaxy (MOVPE). The nanowires 20 typically have a characteristic diameter or dimension in the xy plane between 200 nm and 2 pm. The nanowires 20 preferably have a substantially horizontal apex, formed by a polar c(0001) or -c(000-1) plane. They have substantially vertical flanks, formed by non-polar m{10-10} planes.

[0114] As illustrated in [Fig. 6], after the formation of the nanowires 20 by localized growth through the masking layer 10, a dielectric layer 51 is conformally deposited on the nanowires 20 and on the exposed parts of the masking layer 10. The dielectric layer 51 is, for example, based on silicon dioxide SiO2. It can be formed by plasma-enhanced chemical vapor deposition (PECVD).

[0115] As illustrated in [Fig. 7], the dielectric layer 51 is then partially etched so as to expose the tops and sides of the nanowires 20 over almost their entire height. The etching typically corresponds to isotropic wet etching. After etching, the dielectric layer 51 remains on the masking layer 10. It preferably forms a ring at the base of the nanowires 20. This helps to reinforce the electrical insulation provided in part by the masking layer 10.

[0116] As illustrated in [Fig. 8], a layer based on a transparent electrically conductive material is continuously deposited on and between the nanowires 20. This continuous layer completely covers the exposed tips and sides of the nanowires 20. It forms the second electrical contact 32. It is typically based on a transparent conductive oxide, for example, ITO or ZnO. High-temperature annealing can be performed to obtain ohmic contact between the second electrical contact 32 and the shell 23 of each nanowire 20.

[0117] As illustrated in [Fig.9], a layer of metal 34 is then deposited on the continuous layer forming the second electrical contact 32. This layer of metal 34 is preferably based on a metal that reflects the wavelengths of the light emitted by the active region 22. It is typically based on aluminum.

[0118] As illustrated in [Fig. 10], the metal layer 34 is then partially etched, so as to expose the underlying continuous layer 32 over almost the entire height of the nanowires 20. The etching typically corresponds to isotropic etching. After etching, the metal layer 34 is retained on the second electrical contact 32 between the nanowires 20. It can form a ring at the base of the nanowires 20. It allows the formation of a power supply layer for the second electrical contact 32. It also allows the formation of a reflector for the light emitted by the active region 22. The light extraction efficiency of the LED is improved.

[0119] As illustrated in [Fig. 11], a passivation layer 61 can then be deposited on the exposed parts of the second electrical contact 32 and on the metal layer 34. This passivation layer 61 is, for example, based on an aluminum alloy, for example, based on Al2O3. It may be made of a dielectric material. It may be formed by plasma-assisted chemical vapor deposition (PECVD).

[0120] As illustrated in [Fig.12], the nanowires 20 protruding from the substrate 41 are then planarized by a planarization layer 62. This planarization layer 62 is typically deposited between and on the nanowires 20, and then polished by chemical-mechanical polishing (CMP) to obtain a flat surface 620 above the nanowires 20. This planarization layer 62 is typically electrically insulating and transparent.

[0121] A manipulation substrate 42, also called a "handle," is then bonded by molecular adhesion to the flat surface 620, on the "front face." This manipulation substrate 42 can be transparent, for example, glass-based. In this case, it can be retained in the final device after the manufacturing process. Alternatively, the manipulation substrate 42 is opaque, for example, silicon-based. In this case, it is typically removed at the end of the manufacturing process, after the steps dedicated to the "back face" or bottom face of the diode, along the z-direction, have been completed.

[0122] As illustrated in [Fig. 13], after bonding the handling substrate 42, the growth substrate 41 can be removed. This removal can be carried out in a known manner by a mechanical lapping step followed by a dry etching or wet etching step.

[0123] As illustrated in [Fig. 14], the layers 13, 14 based on III-V materials or metal nitrides, previously used for the germination / nucleation of the nanowires 20, are then removed from the back face, typically by one or more dry etchings. After the removal of the layers 13, 14, the lower face 102 of the masking layer 10 is exposed. The portions 200 of nanowires 20 enclosed by the masking layer 10, initially corresponding to the seeds formed during the germination / nucleation steps, are also exposed after the removal of the layers 13, 14.

[0124] As illustrated in [Fig. 15], according to one possibility, the first electrical contacts 31 are formed directly on the portions 200 of nanowires 20. They preferably cover all the free surfaces of the portions 200 and bear against the lower face 102 of the masking layer 10. The first electrical contacts 31 are preferably metallic, typically aluminum-based. They indirectly supply power to the nanowires 20. The first electrical contacts 31 also form reflectors on their rear or lower face, in order to redirect the light emitted by the nanowires towards the front or upper face of the diode.

[0125] As illustrated in [Fig. 10A], an electrically insulating layer 40, for example of dielectric material, can, according to a first example, be deposited on the back face on the lower face 102 and on the first electrical contacts 31. This layer is hereafter referred to as the dielectric layer 40. The dielectric layer 40 can be planarized, for example by chemical and / or mechanical polishing, to ensure the quality of the magnetic layer 33 which will subsequently be deposited.

[0126] The magnetic layer 33 can be deposited on the rear or lower face, so as to be underlying the dielectric layer 40. Whatever the embodiment, the deposition of the magnetic layer 33 can advantageously be carried out by various conventional physical or chemical vapor phase deposition techniques, for example by magnetron sputtering, for example by pulsed laser deposition (abbreviated PLD, from the English Pulse Laser Deposition) or by vacuum evaporation (thermal evaporation or electron beam assisted evaporation, for example).

[0127] Following the deposition of the dielectric layer 40, and regardless of the embodiment example, the process may include structuring the magnetic layer 33, for example by photolithography and / or by etching so as to form the patterns 330 previously described.

[0128] As illustrated in alternative to [Fig.10B], the magnetic layer 33 can be deposited directly on the first electrical contacts 31, prior to the deposition of the dielectric layer 40.

[0129] Figures 16A and 16B illustrate an example of an embodiment in which the portions 332 based on or made of a magnetic material are aligned with each 3D structure 20 along the z direction. Alternatively, and as illustrated in [Fig. 10C], the portions 332 based on or made of a magnetic material can be located between the nanowires 20, in projection in an xy plane.

[0130] As illustrated in [Fig. 10D], according to one possibility, a dielectric layer 43 is deposited on the rear face so as to cover the magnetic layer 33. Vias 310 can be formed within the dielectric layer 43, directly above the first electrical contacts 31. The first secondary electrical contacts 311 are then formed as pads on the dielectric layer 43, in contact with the previously filled vias 310. The filling of the vias 310 and the formation of the first secondary electrical contacts 311 can be carried out simultaneously in a single step.

[0131] According to an alternative or combinable embodiment with the fabrication of the magnetic layer 33 as previously described, the magnetic layer 33 can be deposited on the front face between the nanowires 20. For this purpose, following the step described in relation to [Fig. 10], for example, and as illustrated in Figures 17A and 17B, the magnetic layer 33 can be deposited on the metal layer 34. The passivation layer 61 can then be deposited. Here again, it can be envisaged that the magnetic layer 33 will be in direct contact with the metal layer 34, or via the passivation layer 61 when this passivation layer 61 is deposited prior to the magnetic layer 33 on the front face (see [Fig. 18A]). The deposition of the planarization layer 62 and the subsequent front-face steps can then be carried out as previously described and as illustrated in [Fig. 18B].

[0132] After the formation of the first electrical contacts 31, the nanowire-based LED 20 can be connected on the rear side, either directly to a power supply or to LED driver electronics, for example based on CMOS (Complementary Metal-Oxide-Semiconductor) technology. The manipulation substrate 42 can be removed, if necessary.

[0133] The magnetic layer 33 is now described in more detail. The magnetic layer 33 may be based on, or made of, a ferromagnetic material, for example, a ferromagnetic material comprising at least one of Co, Fe, and Ni, such as CoFeB, CoFe, NiW, NiFe. The magnetic layer 33 may be formed from a single magnetic monolayer. As illustrated, for example, in [Fig. 19], the magnetic layer 33 may comprise a stack of sublayers 333, 334. This stack may exhibiting a Metal / Ferromagnetic / Metal structure, in which a ferromagnetic sublayer 333 is sandwiched between two metallic and non-magnetic sublayers 334. The metallic and non-magnetic sublayers 334 may be based on or composed of at least one of Pt, Pd, Ru, Cr, or Ta. The sublayers 334, 334 may have thicknesses e333, e334 on the order of a few nanometers.

[0134] The magnetic layer preferably has a total thickness e33 ranging from one to several tens of nanometers, for example between 0.5 nm and 50 nm, preferably between 10 and 30 nm in order to generate a sufficient magnetic field in relation to the height of the 3D structure 20.

[0135] Figures 20 and 21 illustrate a simulation of the magnetic field that can be obtained for a nanowire arrangement as shown in [Fig. 4A], with a polarization of 0.5 T. In [Fig. 20], the locations of the nanowires are marked with a black cross. [Fig. 20] illustrates the magnetic field obtained at the surface of the magnetic layer 33, showing the local maxima of the magnetic field B obtained by the pattern structuring of the magnetic layer 33. [Fig. 21] shows the evolution along the z-direction of the magnetic field B along the axis of the nanowires with a polarization of 0.5 T, along the cross-sectional planes 70 and 71. A sufficient magnetic field can be generated in a significant portion of a 5 µm high nanowire LED, from a magnetization of 0.5 T of the magnetic layer 33 located at the base of the wire.

[0136] It is clear from the preceding description that the 3D LED according to the invention is more efficient than a conventional 3D LED.

[0137] The invention is not limited to the embodiments described above and extends to all embodiments covered by the invention. The present invention is not limited to the examples described above. Many other embodiments are possible, for example, by combining features described above, without departing from the scope of the invention. Furthermore, the features described with respect to one aspect of the invention can be combined with another aspect of the invention. Unless there is an incompatibility, technical features described in detail for a given embodiment can be combined with the technical features described in the context of other embodiments described by way of example and without limitation, so as to form another embodiment that is not necessarily illustrated or described. Such an embodiment is obviously not excluded from the invention.

Claims

Demands

1. Light-emitting diode (1) comprising at least one radial 3D three-dimensional structure (20) comprising: - a core (21) having a first conductivity of a first type of carriers, the core (21) having a wire or pyramid shape oriented along a direction z, and having flanks (210) substantially parallel or oblique to the direction z, - an active region (22) configured to emit light of wavelength X, the active region (22) comprising at least a so-called radial part (220) covering the flanks (210) of the core (21), - a shell (23) having a second conductivity of a second type of carriers, the shell (23) covering at least the radial part (220) of the active region (22),the light-emitting diode (1) being characterized in that it comprises at least one magnetic layer (33) configured to exhibit a polarization (M) along a principal direction substantially parallel to the z direction, so as to increase the residence time at the level of the active region (22) by at least one of the first and second types of carriers.

2. Diode (1) according to the preceding claim, wherein the carriers of the first type are electrons and the first conductivity is of type N, the carriers of the second type are holes and the second conductivity is of type P, at least one magnetic layer (33) being configured to increase the residence time at the active region (22) of the electrons that have propagated into the core (21).

3. Diode (1) according to any one of the preceding claims, wherein at least one magnetic layer (33) extends in a principal extension plane substantially perpendicular to the z direction and comprises motifs (330) distributed in a pitch p along at least one direction of its principal extension plane, so as to form a plurality of portions (331) devoid of magnetic material, and preferably said motifs (330) are distributed according to a first step network p, along two distinct directions of its main extension plane.

4. Diode (1) according to the preceding claim, comprising a plurality of 3D structures (20), the plurality of 3D structures (20) being distributed in the same pitch p as the patterns (330) of at least one magnetic layer (33).

5. Diode (1) according to any one of the preceding claims, wherein at least one magnetic layer (33) has a polarization, preferably permanent, of between 0.1 T and 1.5 T.

6. Diode (1) according to any one of the preceding claims, wherein at least one magnetic layer (33) is based on a ferromagnetic material.

7. Diode (1) according to any one of the preceding claims, wherein the at least one magnetic layer (33) comprises a stack of sublayers, said stack comprising at least a first sublayer (333) based on or made of a ferromagnetic material, disposed between two second sublayers (334) based on a non-magnetic metallic material.

8. Diode (1) according to any one of the preceding claims, wherein at least one magnetic layer (33) has a thickness (e33) of between 0.5 nm and 50 nm, preferably between 10 nm and 30 nm.

9. Diode (1) according to any one of the preceding claims, wherein: • the flanks (210) of the core (21) are substantially parallel to the z direction, and • the radial part (220) of the active region (22) extends along a principal extension direction substantially parallel to the z direction.

10. Diode (1) according to any one of the preceding claims, the diode further comprising: • a first electrically conductive contact (31) configured to inject carriers of the first type into the core (21), • a second electrically conductive contact (32) configured to inject carriers of the second type into the shell (23).

11. Diode (1) according to the preceding claim, wherein at least one magnetic layer (33) is underlying, along the z direction, the first contact (31).

12. Diode (1) according to the preceding claim, the diode (1) further comprising at least one electrically insulating layer (40) interposed between at least one magnetic layer (33) and the first contact (31).

13. Diode (1) according to any one of the preceding claims, further comprising a masking layer (10) having a face (102) referred to as lower, a face (101) referred to as upper, and openings (110), and in which the core (21) passes through the masking layer (10) at the level of said openings (110).

14. Diode (1) according to the preceding claim, wherein at least one magnetic layer (33) overlies, in the z direction, the masking layer (10).

15. Method of making a light-emitting diode (1) comprising at least one 3D three-dimensional structure (20) according to any one of the preceding claims, the method comprising: • forming the core (21) by epitaxy on a growth substrate (41), by localized growth through an opening (110) of a masking layer (10) disposed on said growth substrate (41), • forming by epitaxy the active region (22) on the core (21), • forming by epitaxy the shell (23) on the active region (22), then • depositing at least one magnetic layer (33) such that said magnetic layer (33) has a polarization (M) along a principal direction substantially parallel to the z direction.

16. A method according to the preceding claim, further comprising: • depositing a planarization layer (62) on the growth substrate (41), on and around at least one 3D structure (20) projecting from the growth substrate (41), so as to obtain a flat surface (620) above at least one 3D structure (20), • stick a manipulation substrate (42) onto said flat surface (620), • remove the growth substrate (41) so as to expose the masking layer (10) and a portion (200) of the core (21) through the masking layer (10).

17. Method according to the preceding claim, further comprising: • after removal of the growth substrate (41), forming the first contact (31) in contact with the exposed portion (200) of the core (21), • following the formation of the first contact (31), depositing the magnetic layer (33) on an underside (102) of the masking layer (10).

18. A method according to any one of the three preceding claims, further comprising: • forming the second contact (32) on the shell (23), by depositing a transparent conductive oxide layer, and • depositing the magnetic layer (33) on the second contact (32), along a principal extension plane substantially parallel to the masking layer (10).

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