Optoelectronic device having axial three-dimensional light-emitting diodes

Abstract

The present disclosure relates to an optoelectronic device (5) comprising a matrix of axial light emitting diodes (LEDs). Each LED comprises an active layer (36) that emits electromagnetic radiation. The matrix forms a photonic crystal having at least first and second resonant peaks in a plane containing the active layer, each of the first and second peaks amplifying the radiation intensity at a first and second wavelength, respectively. Each light emitting diode (LED) comprises an elongated semiconductor element (26) having a first average diameter (D nw ), a second portion (30) extending the first portion and having a cross-sectional area that decreases with distance from the first portion, and a second portion (31) extending the second portion and having a second average diameter (D) strictly smaller than the first average diameter. top and an active layer (36) having a peak density (Pd) of 1.5 V, the active layer being at the position of the first peak and not at the position of the second peak.

Description

[Technical Field]

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

[0002] For certain applications, it is desirable to obtain light-emitting diodes that emit electromagnetic radiation having a narrow spectrum that is ideally substantially monochromatic, and / or light-emitting diodes whose emission is as directional as possible.

[0003] Axial photoelectron three-dimensional light-emitting diode (LED) devices may have such characteristics. An axial three-dimensional light-emitting diode is an LED comprising an elongated three-dimensional semiconductor element extending along a preferred direction, for example, a wire with a diameter in the micrometer or nanometer range, and having an active layer at the axial end of the three-dimensional semiconductor element, the active layer being the LED region from which most of the electromagnetic radiation provided by the LED is emitted.

[0004] However, for some applications where optoelectronic devices emitting a very narrow spectrum and / or highly directional radiation are desired, known three-dimensional axial LEDs may be insufficient. [Overview of the project]

[0005] Therefore, the objective of one embodiment is to address all or some of the drawbacks of the LED optoelectronic device described above.

[0006] Another objective of one embodiment is that the three-dimensional axial LED has a narrow emission spectrum.

[0007] A further objective of one embodiment is for the axial three-dimensional LED to emit directional radiation.

[0008] One embodiment provides a photoelectronic device comprising a matrix of axial LEDs. Each LED comprises an active layer configured to emit electromagnetic radiation, the matrix forming a photonic crystal configured to form at least first and second resonance peaks in a plane including the active layer. Each first resonance peak amplifies the intensity of the electromagnetic radiation at a first wavelength, and each second resonance peak amplifies the intensity of the electromagnetic radiation at a second wavelength. Each light-emitting diode (LED) comprises an elongated semiconductor element along an axis, the elongated semiconductor element having a first portion having a first average diameter, a second portion extending from the first portion and having a decreasing cross-sectional area as it moves away from the first portion, and an active layer extending from the second portion and having a second average diameter strictly smaller than the first average diameter, the active layer being located at the position of the first resonance peak but not at the position of the second resonance peak.

[0009] According to one embodiment, twice the ratio of the second average diameter to the first average diameter is between 0.5 and 1.8.

[0010] According to one embodiment, twice the ratio of the second average diameter to the first average diameter is between 0.6 and 1.4.

[0011] According to one embodiment, the first average diameter is between 0.05 μm and 2 μm.

[0012] According to one embodiment, the first average diameter is between 100 nm and 1 μm.

[0013] According to one embodiment, the height of the second portion measured along the axis is less than 10% of the height of the elongated semiconductor element measured along the axis.

[0014] According to one embodiment, the first portion of the elongated semiconductor element has a certain cross-section.

[0015] According to one embodiment, the axial LEDs are arranged in an array having a pitch between 0.1 μm and 4 μm.

[0016] According to one embodiment, the height of each elongated semiconductor element measured along the axis is between 100 nm and 50 μm.

[0017] Also, one embodiment provides a method for designing an optoelectronic device as defined above. The method includes the following steps: Step a: Considering that the elongated semiconductor element has a constant cross-section, determine, by simulation, the pitch and the first average diameter of the photonic crystal; Step b: Reduce the second average diameter without changing the first average diameter; Step c: Simulate the operation of an optoelectronic device having a second average diameter with a reduced active layer; and Step d: Repeat steps b and c until the active layer is at the position of the first resonance peak and disappears at the position of the second resonance peak.

Brief Description of the Drawings

[0018] The above and other features and advantages are described in detail in the following specific embodiments given as non-limiting examples of the invention with reference to the accompanying drawings.

[0019] [Figure 1] FIG. 1 is a schematic partial cross-sectional view of one embodiment of an optoelectronic device including an LED. [Figure 2] FIG. 2 is a schematic partial perspective view of the optoelectronic device shown in FIG. 1. [Figure 3] FIG. 3 is a schematic partial cross-sectional view corresponding to a detailed view of a part of the optoelectronic device shown in FIG. 1. [Figure 4] FIG. 4 is a schematic partial cross-sectional view of a comparative optoelectronic device used in a first simulation. [Figure 5] FIG. 5 is a grayscale map showing the light intensity emitted by the comparative optoelectronic device as a function of the wavelength of the emitted radiation and the emission angle indicating the presence of two emission modes. [Figure 6]This figure shows the evolution curves of the cumulative flux of radiation emitted by a comparative optoelectronic device and Lambertian radiation, respectively. [Figure 7] This figure shows a diagram comparing the radiation emitted by a comparative optoelectronic device with Lambertian radiation. [Figure 8] This is a grayscale map of the first mode amplification coefficients of a comparative optoelectronic device in a plane containing the active layer of an LED. [Figure 9] This is a grayscale map of the second mode amplification coefficients of a comparative optoelectronic device in a plane containing the active layer of an LED. [Figure 10] Figures 8 and 9 show schematic cross-sectional views of a portion of the LED in the optoelectronic device Figure 1, which has a high amplification region. [Figure 11] Figures 8 and 9 show schematic diagrams of a portion of the LED in the optoelectronic device shown in Figure 1, which has a high-gain region, viewed from above. [Figure 12] This is a grayscale map of the light intensity emitted by the photoelectronic device in Figure 1, obtained by simulation, corresponding to the wavelength of emitted radiation and the emission angle, for the case of the first diameter reduction coefficient of the LED. [Figure 13] This figure is similar to Figure 12, but for the case of the second reduction factor of the LED. [Figure 14] This figure is similar to Figure 6, but for the optoelectronic device shown in Figure 1, which has a second reduction coefficient. [Figure 15] This figure is similar to Figure 7, but for the optoelectronic device shown in Figure 1, which has a second reduction coefficient. [Figure 16] This is a grayscale map of the light intensity emitted by the comparative optoelectronic device, obtained during the first test period, corresponding to the wavelength and emission angle of the emitted radiation. [Figure 17] This figure shows the evolution curve of the light intensity emitted orthogonally to the light-emitting surface by the comparative optoelectronic device, obtained during the first test period, corresponding to the wavelength of the emitted radiation. [Figure 18]This is a grayscale map obtained during the second test period, showing the light intensity emitted orthogonally to the light-emitting surface by the photoelectronic device in Figure 1, corresponding to the wavelength of emitted radiation and the emission angle. [Figure 19] This figure shows the evolution curve of the light intensity emitted orthogonally to the light-emitting surface by the photoelectronic device in Figure 1, as it corresponds to the wavelength of the emitted radiation, obtained during the third test period. [Figure 20] This is a grayscale map of the light intensity emitted by the simulated photoelectronic device in Figure 1, corresponding to the wavelength and attenuation rate of the emitted radiation. [Figure 21] Figure 1 is a block diagram of one embodiment of a method for designing an optoelectronic device. [Modes for carrying out the invention]

[0020] Similar features are designated by similar reference numerals in various drawings. In particular, structural and / or functional features common among various embodiments may have the same reference numerals and may have identical structural, dimensional, and material properties. For clarity, only the operations and elements useful for understanding the embodiments described herein are illustrated and described in detail. In particular, the optoelectronic devices considered may include other components that are not detailed.

[0021] In the following disclosures, unless otherwise specified, when referring to terms that modify absolute positions, such as “front,” “back,” “top,” “bottom,” “left,” and “right,” terms that modify relative positions, such as “top,” “bottom,” “upper side,” and “lower side,” or terms that modify orientation, such as “horizontal” and “vertical,” it refers to the orientation shown in a diagram that is oriented in its normal use.

[0022] Unless otherwise specified, the expressions “approximately,” “approximately,” “substantially,” and “to the extent” refer to a range of 10%, preferably 5%, of the applicable value. Furthermore, the terms “insulator” and “conductor” are understood herein to mean “electrically insulating” and “conductive,” respectively.

[0023] In the following description, the internal transmittance of a layer is the ratio of the radiation intensity emanating from the layer to the radiation intensity entering the layer. The absorptance of a layer is equal to the difference between 1 and the internal transmittance. For the remainder of this specification, a layer is said to be transparent to radiation if the absorptance of radiation passing through the layer is less than 60%. For the remainder of this specification, a layer is said to be absorpting to radiation if the absorptance of radiation in the layer is greater than 60%. When radiation has a generally "bell-shaped" spectrum, such as a Gaussian spectrum with a maximum value, the wavelength of the radiation, or the central or dominant wavelength of the radiation, is called the wavelength at which the spectrum reaches its maximum value. For the remainder of this specification, the refractive index of a material refers to the refractive index of the material over the wavelength range of radiation emitted by the optoelectronic device. Unless otherwise specified, the refractive index is considered to be substantially constant over the useful wavelength range of radiation, for example, equal to the average refractive index over the wavelength range of radiation emitted by the optoelectronic device.

[0024] An axial LED refers to a three-dimensional structure with an elongated shape along a preferred direction, such as a cylindrical shape, and this three-dimensional structure has at least two dimensions called minor dimensions, between 5 nm and 2.5 μm, preferably between 50 nm and 2.5 μm. A third dimension, referred to as the major dimension, is at least 1 times, preferably 5 times, and more preferably 10 times, the largest minor dimension. In some embodiments, the minor dimension may be about 1 μm or less, preferably between 100 nm and 1 μm, and more preferably between 100 nm and 800 nm. In some embodiments, the height of each LED may be 500 nm or more, preferably between 1 μm and 50 μm.

[0025] Figure 1 is a schematic partial cross-sectional side view of one embodiment of a photoelectron LED device 5 in which the semiconductor element corresponds to a nanowire or microwire, thereby enabling the emission of a narrow spectrum and / or directional radiation.

[0026] Device 5 comprises the following elements: -Support 10: comprises a first electrode 12, a substrate 14 such as a semiconductor having parallel surfaces 16 and 18, a nucleation layer 20 covering surface 18, and an insulating layer 22 covering the nucleation layer 20 and including an opening 24 at a desired wire position, with surface 16 in contact with electrode 12, and one opening 24 is shown in Figure 1; - Matrix of light-emitting diode LEDs: Mounted on a support 10, one light-emitting diode LED is shown in Figure 1, each light-emitting diode LED comprises a wire 26 in contact with the nucleation layer 20 at one of the openings 24, the wire 26 being at least partially doped with a first conductivity type (e.g., N-type doping), and having a substantially cylindrical lower part 28, the lower part 28 in contact with the nucleation layer 20, extending to an upper part 30 whose cross-section decreases as it moves away from the substrate 14, the upper part 30 having a top surface 32, and each light-emitting diode LED further comprises a shell 34 covering the top surface 32 of the wire 26, the shell 34 comprising an active layer 36 and a semiconductor layer 38 doped with a second conductivity type (e.g., P-type doping); -Insulating layer 40: Covers the outer circumference of each wire 26 and each shell 34 and is transparent to radiation emitted by the active layer 36; -Conductive layer 42: Transparent to radiation emitted by the active layer 36, covering the insulating layer 40 and each shell 34, in contact with each shell 34, the conductive layer 42 forms a second electrode; and - Electrical insulating sealing layer 44: Transparent to radiation emitted by the active layer 36, covers the entire structure, and the sealing layer 44 has an upper surface 46 referred to as the light-emitting surface.

[0027] The active layer 36 is the layer from which most of the electromagnetic radiation provided by the light-emitting diode LED is emitted. The light-emitting diode LEDs may be connected in parallel to form an LED array. The array may consist of several to 1000 light-emitting diode LEDs.

[0028] Each light-emitting diode LED is said to be axial in that the active layer 36 is on the extension line of the wire 26 and the semiconductor layer 38 is on the extension line of the active layer 36. The assembly including the wire 26, the active layer 36, and the semiconductor layer 38 extends along an axis Δ called the axis of the wire 26 or the axis of the axial LED. Preferably, the axes of the light-emitting diodes LED are parallel and perpendicular to the plane 18.

[0029] The bottom surface of the wire 26 has a shape such as an ellipse, a circle, or a polygon (including, for example, a triangle, a rectangle, a square, or a hexagon). The cross-sectional area of the wire may be constant along the wire axis Δ or may vary along the wire axis. The average diameter of the lower part 28 of the wire 26 is D be and is so-called. In the case where the lower part 28 of the wire 26 has a circular cross-sectional shape, the average diameter is the diameter of the circle. In the case where the wire 26 has a cross-section other than circular, the average diameter corresponds to the diameter of a circle enclosing the same area as the cross-sectional area of the lower part 28. The average diameter of the upper surface 32 is D top and is also so-called. Preferably, the upper surface 32 is flat. Preferably, the upper surface 32 corresponds to a crystal plane perpendicular to the crystal growth direction c including the wire 26. When the upper surface 32 corresponds to a circle, the average diameter D<e000003>corresponds to the diameter of the circle. When the upper surface 32 is other than circular, the average diameter D top corresponds to the diameter of a circle enclosing the same area as the cross-sectional area of the upper surface 32. The ratio of the diameter D nw . to the diameter D top is called the diameter reduction rate SF twice and is so-called. Further, the height of the lower part 28 of the wire 26 measured along the axis Δ is H be and is so-called, and the height of the upper part 30 of the wire 26 measured along the axis is H nw . and is so-called.

[0030] The diameter D nw ​​It may be between 0.05 μm and 2 μm, preferably between 100 nm and 1 μm, more preferably between 100 nm and 800 nm. According to one embodiment, the diameter reduction ratio SF is less than 1.8, preferably less than 1.6, more preferably less than 1.4, and even more preferably less than 1.2. According to one embodiment, the diameter reduction ratio SF is greater than 0.5, preferably greater than 0.7, and more preferably greater than 0.8.

[0031] According to one embodiment, height H nw and H top The height of the wire 26 corresponding to the sum of these may be 100 nm or more, preferably between 500 nm and 50 μm, and more preferably between 1 μm and 50 μm. Height H top This is less than 10% of the height of the wire 26, preferably 8%, and more preferably 5%.

[0032] According to one embodiment, if the cross-sectional area of ​​the lower part 28 of the wire 26 is not constant along the axis Δ, the lower part 28 is defined as the portion from the bottom surface of the wire 26 to the contact portion with the support 10, where the variation in the average diameter of the cross-sectional area remains less than 10%. Also, the average diameter D of the lower part 28 of the wire 26 nw This may correspond to the average diameter of the straight portion of the lower part 28 at the joint between the lower part 28 and the upper part 30, or it may correspond to the average of the average diameters of the straight portion of the lower part 28 of the wire 26 along axis Δ.

[0033] In the embodiment shown in Figure 1, the upper part 30 has a frustoconical shape. In modified examples, the upper part 30 may have a flared, concave, or convex shape.

[0034] Figure 2 is a schematic partial perspective view of the optoelectronic device 5. In Figure 2, each light-emitting diode LED is schematically shown as a cylindrical shape. Layers 42 and 44 are not shown.

[0035] According to one embodiment, the light-emitting diodes (LEDs) are arranged to form a photonic crystal. Figure 2 shows, as an example, 12 light-emitting diodes (LEDs). In practice, the light-emitting diode (LED) matrix may comprise 7 to 100,000 light-emitting diodes (LEDs).

[0036] According to one embodiment, the light-emitting diodes (LEDs) are arranged in rows and columns (Figure 2 shows three rows and four columns as an example). The matrix pitch "a" is the distance between the axis of one LED and the axis Δ of a nearby LED in the same row or an adjacent row. The pitch a is substantially constant. According to one embodiment, the pitch a may be between 0.1 μm and 4 μm.

[0037] More specifically, the matrix pitch a is selected so that the matrix forms a photonic crystal. The resulting photonic crystal is, for example, a two-dimensional photonic crystal. In the arrangement example shown in Figure 2, referred to as a square arrangement, the light-emitting diodes (LEDs) are located at each intersection of rows and columns, with rows perpendicular to columns. According to another arrangement example, called a hexagonal arrangement, the LEDs in one row are offset by half a pitch a from the LEDs in the previous and next rows.

[0038] The properties of the photonic crystal formed by the matrix are advantageously selected, particularly to achieve coupling and enhance the selective effect, such that the LED matrix forms resonant cavities in the plane perpendicular to axis Δ and resonant cavities along axis Δ. This makes it possible to amplify the intensity of radiation emitted through the light-emitting surface 46 by the array of light-emitting diode LEDs with the matrix at a specific wavelength, compared to an array of light-emitting diode LEDs without a photonic crystal. It should be noted that the resonance peak of the photonic crystal may be different from the wavelength at which the emission spectrum of the isolated active layer 36 is maximized. Advantageously, one of the resonance peaks of the photonic crystal is at the same wavelength as, or close to, the wavelength at which the emission spectrum of the isolated active layer 36 is maximized.

[0039] The properties of the photonic crystal are determined by the geometric dimensions of the elements constituting the optoelectronic device 5 and the materials that make up these elements. As a first approximation, the properties of the photonic crystal may be set by the wire 26.

[0040] According to one embodiment, the wire 26 and shell 34 are made of a semiconductor material in at least part. The semiconductor material is selected from the group consisting of Group III-V compounds, Group II-VI compounds, and Group IV semiconductors or compounds. Examples of Group III elements include gallium (Ga), indium (In), or aluminum (Al). Examples of Group V elements include nitrogen (N), phosphorus (P), or arsenic (As). Examples of Group III-N compounds are GaN, AlN, InN, InGaN, AlGaN, or AlInGaN. Examples of Group II elements include Group IIA elements, including beryllium (Be) and magnesium (Mg), and Group IIB elements, including zinc (Zn), cadmium (Cd), and mercury (Hg). Examples of Group VI elements include Group VIA elements, including oxygen (O) and tellurium (Te). Examples of Group II-VI compounds are ZnO, ZnMgO, CdZnO, CdZnMgO, CdHgTe, CdTe, or HgTe. Generally, the elements of III-V or II-VI compounds can be combined in different mole fractions. Examples of Group IV semiconductor materials include silicon (Si), carbon (C), germanium (Ge), silicon carbide (SiC) alloys, silicon germanium (SiGe) alloys, or germanium carbide (GeC) alloys. The wire 26 and semiconductor layer 38 may be dopants. For example, in the case of III-V compounds, the dopants may be selected from the group consisting of Group II P-type dopants such as magnesium (Mg), zinc (Zn), cadmium (Cd) or mercury (Hg), Group IV P-type dopants such as carbon (C), or Group IV N-type dopants such as silicon (Si), germanium (Ge), selenium (Se), sulfur (S), terbium (Tb) or tin (Sn). Preferably, at least partially, the semiconductor layer 38 is P-doped GaN and the wire 26 is N-doped GaN.

[0041] The second electrode layer 42 is conductive and transparent. According to one embodiment, the electrode layer 42 is a transparent conductive oxide (TCO) layer such as indium tin oxide (or ITO), aluminum or gallium-doped or undoped zinc oxide, or graphene. As an example, the electrode layer 42 has a thickness between 5 nm and 200 nm, preferably between 20 nm and 50 nm. The insulating layer 22 or 40, or the coating 44, may be made of an inorganic material such as silicon oxide or silicon nitride. The insulating layer 40 and / or the coating 44 may be an organic material such as benzocyclobutene (BCB) based on an insulating polymer. The coating 44 may comprise one optical filter or multiple optical filters arranged adjacent to each other, as will be described in detail later.

[0042] The seed layer, or nucleation layer 20, is made of a material that promotes the growth of the wire 26. For example, the material comprising the seed layer 20 may be a nitride, carbide, or boride of a transition metal in the IV, V, or VI column of the periodic table, or a combination of these compounds. The seed layer 20 may be replaced by multiple separate seed pads, in which case each wire 26 is placed on one seed pad.

[0043] The support 10 may have a structure different from the structure described above. According to one embodiment, the support 10 may correspond to an electronic circuit having a surface electrode layer on which light-emitting diodes are mounted. The electrode layer 12 may be divided into separate parts to allow for separate control of LED groups of the LED matrix.

[0044] Figure 3 is an enlarged view of the shell 34. The shell 34 may comprise a stack of multiple semiconductor layers, including but not limited to: - An intermediate layer 50, such as GaN, covering the upper surface 32 of the upper part 30 of the wire 26; - An active layer 36 covering the intermediate layer 50, preferably in contact with the intermediate layer 50; -Optionally, a barrier layer 52 covering the active layer 36; -A conductive semiconductor layer 38 opposite to the lower part 28 of the wire 26 covering the barrier layer 52; and - A bonding layer 54 that covers the semiconductor layer 38, is covered by the electrode layer 42, and is in contact with the electrode layer 42.

[0045] The intermediate layer 50 is preferably a layer of the same semiconductor material as the upper part 28 of the wire 26, or a layer of GaInN, AlGaN, or AlGaInN type alloy. The purpose of the intermediate layer 50 is to provide a surface with properties suitable for the growth of the active layer 36. The thickness of the intermediate layer 50 may be in the range of 5 nm to 5 μm, preferably in the range of 10 nm to 2000 nm.

[0046] The active layer 36 may include confinement means such as multiple quantum wells. The active layer 36 is made up of alternating stacks of GaN layers 56 and InGaN layers 58, for example, as shown in Figure 3, two GaN layers 56 and two InGaN layers 58 are shown as an example. The GaN layers 56 may be doped with N-type or P-type, or they may not be doped. In another example, the active layer 36 may have a single quantum well comprising, for example, a single InGaN layer with a thickness greater than 10 nm between two GaN layers.

[0047] Methods for growing light-emitting diodes (LEDs) may include chemical vapor deposition (CVD), metal-organic chemical vapor deposition (MOCVD) (also known as metal-organic vapor epitaxy (MOVPE)), or remote plasma metal-organic vapor deposition (RP-MOCVD), or a combination of these methods. However, methods such as molecular beam epitaxy (MBE), gas-source MBE (GSMBE), metal-organic MBE (MOMBE), plasma-assisted MBE (PAMBE), atomic layer epitaxy (ALE), or hydride vapor deposition (HVPE) may also be used. However, electrochemical methods, such as chemical bath deposition (CBD), hydrothermal processes, liquid aerosol pyrolysis, or electrodeposition, may also be used.

[0048] The formation of the upper part 30 of the wire 26 may also be achieved by changing the growth conditions of the wire 26, for example, by changing the diameter D nw Initial growth conditions for obtaining the wire, and diameter D top The diameter reduction is achieved by gradually increasing the V / III ratio and decreasing the temperature between the final growth conditions for obtaining the wire.

[0049] According to one embodiment, the lower part 28 of the wire 26 is formed by MOCVD, and the upper part 30 of the wire 26 is formed by MBE.

[0050] Simulations and tests were performed. In these simulations and tests, the lower 28 and upper 30 were made of N-doped GaN, and in each light-emitting diode LED, the refractive indices of the lower 28 and upper 30 were between 2.4 and 2.5. The active layer 36 is an InGaN layer. The semiconductor layer 38 is made of P-doped GaN. The electrode layer 42 is made of TCO. The insulating layer 40 and encapsulating layer 44 are made of BCB-based polymer. The refractive index of the insulating layer 40 is between 1.45 and 1.56. An array of light-emitting diode LEDs distributed in a hexagonal mesh was considered. The height of the wire 26 is between 300 nm and 1 μm. The height of the upper 30 is between 20 nm and 300 nm. The thickness of the shell 34 is between 100 nm and 500 nm. The thickness of the electrode layer 42 is between 100 nm and 500 nm. The thickness of the encapsulating layer 44 is between 1 μm and 1 mm.

[0051] In the first simulation, the diameter reduction ratio SF of the optoelectronic device 5 is equal to 2.

[0052] Figure 4 shows the optoelectronic device 5 when the diameter reduction ratio SF is equal to 2. ′ This is a schematic partial cross-sectional view. The cross-sectional area of ​​the upper part 30 is substantially constant and is the same as the cross-sectional area of ​​the lower part 28 of the wire 26. Optoelectronic device 5 with this configuration ′ This is referred to as a comparative optoelectronic device.

[0053] Figure 5 is a grayscale map of the light intensity IL (arbitrary units) of radiation emitted from the light-emitting surface 46 of a comparative optoelectronic device, corresponding to the wavelength λ of the emitted radiation and the emission angle in a direction perpendicular to the light-emitting surface 46. Bright areas in the grayscale map correspond to resonance peaks. At small emission angles, the first emission mode M1 is observed at a wavelength of approximately 550 nm, and the second emission mode M2 ​​is observed at a longer wavelength. The optical gap OG corresponds to the wavelength difference between modes M1 and M2 at a given emission angle.

[0054] Figure 6 shows the evolution curve CA of the cumulative flux F (expressed as a percentage) of radiation emitted by a comparative photoelectron device in a cone with an axis perpendicular to the light-emitting surface 46, corresponding to the half-angle at the apex of the cone. Curve CB corresponds to the evolution of the cumulative flux of Lambertian radiation.

[0055] Figure 7 shows the emission pattern (curve DA) and Lambertian emission (DB) of a comparative optoelectronic device. The DA emission pattern consists of a primary lobe L1 substantially centered at 0° and a secondary lobe L2 substantially centered at + / -45°.

[0056] The first mode M1 corresponds to the radiant intensity peak centered at the principal frequency and is essentially involved in the formation of the L1 lobe in the radiation pattern. Mode M2 ​​not only broadens the emission spectrum of the light-emitting diode LED but also contributes to the formation of the secondary lobe L2. As can be seen in Figures 6 and 7, a significant portion of the radiant energy of the comparative optoelectronic device is lost in the secondary lobe L2. In particular, less than 20% of the flux is emitted in cones where the half-angle of the vertex is equal to 20°.

[0057] Figures 8 and 9 are grayscale maps of the amplification coefficients by the photonic crystals for the first and second modes, respectively, in a plane parallel to the light-emitting surface 46 and containing the active layer 36. Brighter areas correspond to areas with high amplification coefficients. The outlines of the LED wires 26 are shown by white dashed lines. As a first approximation, Figures 8 and 9 are substantially independent of the lateral dimensions of the active layer 36.

[0058] The inventors have determined that the average diameter D of the lower part 28 of the wire 26 is such that the active layer 36 is positioned at a location where the amplification coefficient of mode M1 is large and the amplification coefficient of mode M2 ​​is small. nw We demonstrated that by changing the lateral dimensions of the active layer 36 without altering the other components, it is possible to reduce the contribution of the second mode M2 ​​to mode M1 in the radiation emitted by the photoelectronic device 5. As a result, the photonic crystal essentially amplifies only photon generation by the first mode M1.

[0059] Figures 10 and 11 are schematic partial side and top views of the wire 26 and active layer 36 portion of the optoelectronic device 5 in Figure 1 with added regions Mx1 and Mx2, respectively. Each region Mx1 represents a region with a high amplification coefficient for the first mode M1 due to the photonic crystal, and each region Mx2 represents a region with a high amplification coefficient for the second mode M2 ​​due to the photonic crystal. As shown in Figures 10 and 11, by selecting a diameter reduction ratio SF, the active layer 36 can be positioned so that it does not exist in the Mx2 region.

[0060] A second simulation was performed. In the second simulation, the diameter reduction ratio SF was equal to 1.6.

[0061] Figure 12 is a grayscale map of the light intensity IL emitted from the light-emitting surface 46 of the optoelectronic device 5 in the second simulation, corresponding to the wavelength λ of the emitted radiation and the emission angle in a direction perpendicular to the light-emitting surface 46. Compared to the first simulation, the first mode M1 is shifted to the shorter wavelength side (blue shift). This increased the optical gap OG. Attenuation of the second mode M2 ​​was also observed.

[0062] A third simulation was performed. In the third simulation, the diameter reduction ratio was equal to 1.2.

[0063] Figure 13 is a grayscale map of the optical intensity IL of the radiation emitted from the light-emitting surface 46 of the optoelectronic device 5 in the third simulation, corresponding to the wavelength λ of the emitted radiation and the emission angle in a direction perpendicular to the light-emitting surface 46. Compared to the second simulation, the first mode M1 is further shifted towards shorter wavelengths (blue shift). This increases the optical gap OG. An increase in the quality factor of the first mode M1, i.e., a decrease in the broadening of the first mode, was also observed. Furthermore, a further attenuation of the second mode M2 ​​was observed.

[0064] Figure 14 shows the evolutionary curve CA′ of the cumulative flux (expressed as a percentage) of radiation emitted by the third simulated photoelectron device 5 in a cone with an axis perpendicular to the light-emitting surface 46, corresponding to the half-angle at the apex of the cone. Curve CB corresponds to the evolution of the cumulative flux of Lambertian radiation.

[0065] Figure 15 shows the emission pattern (curve DA′) of the third simulation of the optoelectronic device 5 and the emission pattern of Lambertian radiation (DB). The emission pattern DA′ essentially has a single lobe centered at 0°. There are essentially no secondary lobes.

[0066] As can be seen from Figures 14 and 15, the majority of the radiant energy of the photoelectron device 5 resides in a single lobe DA′. In particular, more than 80% of the radiation flux is emitted in the cone with a half-angle equal to 20°.

[0067] Tests were conducted. In the first test, an optoelectronic device with the characteristics of the first simulation was fabricated.

[0068] Figure 16 is a grayscale map of the normalized light intensity IL of the radiation emitted from the light-emitting surface 46 of the photoelectronic device 5 in the first test, corresponding to the wavelength λ of the emitted radiation and the emission angle in a direction perpendicular to the light-emitting surface 46.

[0069] Figure 17 shows the evolution curve of the light intensity IL of the radiation emitted from the light-emitting surface 46 of the photoelectronic device 5 in the first test, along a direction perpendicular to the light-emitting surface, corresponding to the wavelength λ.

[0070] Compared to the results of the first simulation, it was observed that at low angles, there was virtually no optical difference between the first and second modes. This is thought to be due to the fact that it may be difficult to form a perfectly cylindrical wire 26, and although the growth conditions should result in a cylindrical wire 26, a slight spreading at the top of the wire 26 may be observed.

[0071] In the second and third tests, optoelectronic devices 5 with the characteristics of the third simulation were fabricated. The reactors used to fabricate the optoelectronic devices were different in the second and third tests.

[0072] Figure 18 is a grayscale map of the optical intensity IL of the radiation emitted from the light-emitting surface 46 of the photoelectronic device 5 in the second test, corresponding to the wavelength λ of the emitted radiation and the emission angle in a direction perpendicular to the light-emitting surface 46. Compared to the first test, an increase in the optical gap OG between the first and second modes was observed, as predicted from the simulation.

[0073] Figure 19 shows the evolution curve of the light intensity IL of the radiation emitted by the light-emitting surface 46 of the photoelectronic device 5 in the third test, along a direction perpendicular to the light-emitting surface, with respect to wavelength λ. Compared to Figure 17, the emission peak of the first mode is narrower, and the second mode is absent.

[0074] Figure 20 is a grayscale map obtained by simulation of the light intensity emitted by the photoelectronic device 5 in Figure 1, corresponding to the wavelength λ of the emitted radiation and the attenuation rate SF, when the emission angle in the direction perpendicular to the light-emitting surface 46 is substantially equal to 0°. It is clearly visible that as the attenuation rate SF decreases, the second mode M2 ​​tends to disappear, the first mode M1 shifts to the shorter wavelength side, and the optical gap (OG) increases. When SF is 1.2 or less, the second mode M2 ​​becomes negligibly small. Figure 20 gives the impression that the first mode M1 disappears as the attenuation rate SF decreases. In reality, the first mode M1 becomes finer as the attenuation rate SF decreases, which means that the quality factor of the first mode M1 increases as the attenuation rate SF decreases.

[0075] Figure 21 is a block diagram of one embodiment of a method for designing an optoelectronic device.

[0076] In step 60, the features of the photonic crystal are determined to achieve the desired first characteristic of the emission spectrum. The features of the photonic crystal are the pitch a of the LED matrix and the diameter D of the wire 26. nw The following may be included. The desired first characteristic of the emission spectrum may include the desired dominant wavelength of the emission peak. According to one embodiment, determining the characteristics of the photonic crystal may include performing a series of computer simulations, each simulation being performed considering an LED with a diameter reduction ratio SF equal to 2. For example, pitch a and average diameter D nwThe simulation is performed using the initial values, and these values ​​are corrected according to predetermined criteria, such as the difference between the desired dominant wavelength and the dominant wavelength of the resonance peak in the simulation. This operation is repeated until an emission spectrum with the desired characteristics is obtained. The method proceeds to step 62.

[0077] In step 62, the diameter reduction ratio SF is reduced. The method is then explained in step 64.

[0078] Step 64 simulates the operation of an optoelectronic device with a new diameter reduction ratio SF. The method proceeds to Step 66.

[0079] Step 66 determines whether the method can be completed. According to one embodiment, it is determined whether a desired sub-characteristic of the emitted radiation is achieved. The desired sub-characteristic may include, for example, the emission spectral bandwidth and / or the directivity of the emitted radiation due to the absence of sub-lobes in the emission pattern. If the sub-characteristic of the emitted radiation is achieved, the method is completed. Otherwise, the method proceeds to step 62 to perform a further reduction of the attenuation rate SF.

[0080] Various embodiments and modifications have been described. Those skilled in the art will understand that specific features of these embodiments and modifications may be combined, and that other modifications are readily conceivable by those skilled in the art. Finally, the practical realization of the embodiments and modifications described herein is within the capabilities of those skilled in the art, based on the functional descriptions provided herein.

[0081] This patent application claims priority to French Patent Application No. 20 / 13518, which is deemed to be part of this specification.

Claims

1. A matrix of axial light-emitting diodes is provided, each light-emitting diode comprising an active layer configured to emit electromagnetic radiation, the matrix forming a photonic crystal configured to form at least first and second resonance peaks in a plane including the active layer, each first resonance peak amplifying the intensity of the electromagnetic radiation at a first wavelength, each second resonance peak amplifying the intensity of the electromagnetic radiation at a second wavelength, each light-emitting diode comprising an elongated semiconductor element along an axis, comprising a first portion having a first average diameter, a second portion extending from the first portion and having a cross-sectional area decreasing as it moves away from the first portion, and the active layer extending from the second portion and having a second average diameter strictly smaller than the first average diameter, the active layer being located at the position of the first resonance peak and not at the position of the second resonance peak. Optoelectronic devices.

2. The ratio of the second average diameter to the first average diameter (twice) is between 0.5 and 1.

8. The device according to claim 1.

3. The ratio of the second average diameter to the first average diameter (twice) is between 0.6 and 1.

4. The device according to claim 2.

4. The first average diameter is between 0.05 μm and 2 μm. The device according to claim 1.

5. The first average diameter is between 100 nm and 1 μm. The device according to claim 4.

6. The height of the second portion, measured along the axis, is less than 10% of the height of the elongated semiconductor element, measured along the axis. The device according to claim 1.

7. The first portion of the elongated semiconductor element has a certain cross-section The device according to claim 1.

8. The axial light-emitting diodes are arranged in an array having a pitch between 0.1 μm and 4 μm. The device according to claim 1.

9. The height of each elongated semiconductor element, measured along the aforementioned axis, is between 100 nm and 50 μm. The device according to claim 1.

10. Step a, taking into consideration that the elongated semiconductor element has a certain cross-section, determines the pitch of the photonic crystal and the first average diameter by simulation, Step b, which involves reducing the second average diameter without changing the first average diameter, Step c simulates the operation of the optoelectronic device having the active layer having a reduced second average diameter, Step d is repeated until the active layer is at the position of the first resonance peak and is no longer at the position of the second resonance peak. A method for designing an optoelectronic device according to claim 1, including the above.

Images