Method for manufacturing an optoelectronic device

Abstract

A method for manufacturing a vertical nanostructured optoelectronic device, comprising an active zone (AZ) designed to emit ultraviolet photons from radiative electron-hole pair recombination, or designed to generate electron-hole pairs from absorbed ultraviolet photons; the vertical nanostructures being made of n-type doped gallium nitride (GaN) and formed on selective epitaxial zones (SAGs) by epitaxial growth; the method comprising a step of selective etching of the vertical nanostructures retaining a remaining portion (30) of each vertical nanostructure, adapted to maintain the mechanical strength of lateral zones (41) of an electron transport layer made of a type III-N aluminum alloy (Al). Figure 5

Description

Title of the invention: Method for manufacturing an optoelectronic device technical field

[0001] The invention relates to the technical field of manufacturing an optoelectronic device. More specifically, the optoelectronic device may be an electroluminescent device or a photodetector. The electroluminescent device is designed to emit ultraviolet (UV) photons from radiative recombination of electron-hole pairs. The photodetector is designed to generate electron-hole pairs from absorbed ultraviolet photons.

[0002] The invention finds its application in particular in the manufacture of light sources, displays, detectors for imaging (e.g. biology) etc. State of the art

[0003] Conventionally, a planar UV-emitting light-emitting diode (LED) comprises successively a sapphire substrate (Al₂O₃), a thick layer of aluminum nitride (AIN), and a stack of thin films made of an IILN-type alloy. The stack successively comprises an electron transport layer, an active region, and a hole transport layer. The active region, conventionally containing quantum wells, is designed to emit ultraviolet photons from radiative recombination of electron-hole pairs. Such a planar LED has a low efficiency (on the order of 10%) due to the thin-film technology. In particular, the presence of structural and point defects reduces the internal quantum efficiency.

[0004] In this respect, a nanowire LED for UV emission represents an interesting alternative to a planar LED. Indeed, the absence of structural defects (such as dislocations) makes it possible to envision a significant increase in efficiency. The industrial-scale growth of aluminum nitride (AIN) (or aluminum-gallium nitride (AlGaN) nanowires by metal-organic vapor phase epitaxy (MOVPE) is not yet fully controlled, due to the low diffusion of aluminum (Al) atoms. In contrast, the organized growth of gallium nitride (GaN) nanowires by MOVPE is perfectly controlled.

[0005] Thus, it is known from the prior art, in particular from the document V. Grenier et al., “UV-A to UV-B electroluminescence of core-shell GaN / AlGaN wire hetero-structures”, Appl. Phys. Lett., 121, 131102, 2022, to fabricate a nanowire LED for UV emission by performing epitaxial growth of the LED stack (electron transport layer, active region, hole transport layer) around gallium nitride (GaN) nanowires. This is referred to as core-shell type epitaxial growth, where the core is formed by a nanowire and the shell is formed by the stack extending around the nanowire.

[0006] However, such a prior art method is not entirely satisfactory insofar as: (i) the gallium nitride GaN core absorbs a large part of the UV photons emitted by the active zone, the band gap of gallium nitride being smaller than the energy of the UV photons emitted; (ii) Epitaxial growth of the LED stack (based on AlGaN aluminum nitride) generates elastic stresses along the tensile nanowire which promotes the formation of cracks extending perpendicularly to the nanowire. Description of the invention

[0007] The invention aims to remedy, in whole or in part, the aforementioned drawbacks. To this end, the invention relates to a method for manufacturing an optoelectronic device, comprising the following steps: a) use: - a substrate, made of a material allowing epitaxial growth of gallium nitride GaN; - a dielectric layer, formed on the substrate, and delimiting areas of selective epitaxy; - vertical nanostructures, made of n-type doped gallium nitride GaN, formed on areas of selective epitaxy by epitaxial growth; b) form an electron transport layer, made of a type III-N alloy containing aluminium Al, around each vertical nanostructure by epitaxy; the electron transport layer having a top zone and lateral zones; c) expose the vertical nanostructures by removing the upper zone of the electron transport layer; d) perform selective etching of the exposed vertical nanostructures so as to: - etch a portion of each exposed vertical nanostructure; - retain a remaining part of each exposed vertical nanostructure, adapted to maintain mechanical strength of the lateral areas of the electron transport layer; step d) being carried out with an etching agent allowing selective etching of the gallium nitride GaN compared to type III-N alloy containing aluminium Al; (e) form a stack, made in a type III-N alloy comprising aluminium Al, on the lateral areas of the electron transport layer by epitaxy; the stack comprising successively an active area and a hole transport layer; the active area being designed to emit ultraviolet photons from radiative recombinations of electron-hole pairs, or designed to generate electron-hole pairs from absorbed ultraviolet photons.

[0008] Thus, such a process according to the invention makes it possible to reduce the absorption of UV photons emitted by the active zone compared to the prior art, thanks to steps c) and d) which lead to partial etching of the vertical nanostructures (core). The selectivity of the partial etching of the gallium nitride (GaN) core with respect to the shell (electron transport layer) is achieved thanks to the presence of aluminum (Al) in the type III-N alloy of the electron transport layer.

[0009] Furthermore, such a process according to the invention makes it possible to reduce elastic stresses along the vertical nanostructures compared to the prior art, because step e) of stack formation by epitaxy is carried out with a partially etched core, and not with the initial core, which limits the formation of cracks extending perpendicularly to the vertical nanostructures. Cracks can be avoided during stack formation if the elastic energy of the lateral zones of the electron transport layer is limited to 4 J / m².

[0010] The invention also relates to a method for manufacturing an optoelectronic device, comprising the following steps: a) use: - a substrate, made of a material allowing epitaxial growth of gallium nitride GaN; - a dielectric layer, formed on the substrate, and delimiting areas of selective epitaxy; - vertical nanostructures, made of n-type doped gallium nitride GaN, formed on the zone of selective epitaxy by epitaxial growth; b') to form a stack, made of a type III-N alloy containing aluminum Al, around each vertical nanostructure by epitaxy; the stack comprising successively: - an electron transport layer; - an active zone, designed to emit ultraviolet photons from radiative recombinations of electron-hole pairs, or designed to generate electron-hole pairs from absorbed ultraviolet photons; - a layer for transporting holes; the stack having a top zone and lateral zones; c') Expose the vertical nanostructures: - by removing the top area of ​​the stack; or - by the formation, intentional or unintentional, of at least one orifice passing through the stack; d) perform selective etching of the exposed vertical nanostructures so as to: - etch a part of each exposed vertical nanostructure; - retain a remaining part of each exposed vertical nanostructure, adapted to maintain mechanical strength of the lateral areas of the stack; step d) being carried out with an etching agent permitting selective etching of gallium nitride GaN compared to the type III-N alloy containing aluminium Al.

[0011] Thus, such a process according to the invention makes it possible to reduce the absorption of UV photons emitted by the active zone compared to the prior art, thanks to steps c') and d) which lead to partial etching of the vertical nanostructures (core). The selectivity of the partial etching of the gallium nitride (GaN) core with respect to the shell (stack) is obtained thanks to the presence of aluminum (Al) in the type III-N alloy of the stack.

[0012] The method according to the invention may include one or more of the following features.

[0013] According to one feature of the invention, step c) is carried out so that the removal of the upper zone of the electron transport layer is achieved by reactive ion etching.

[0014] Thus, an advantage provided by such a technique is to allow both anisotropy and selectivity of the engraving.

[0015] According to one feature of the invention, step c') is carried out so that the removal of the upper area of ​​the stack is achieved by reactive ion etching.

[0016] Thus, an advantage provided by such a technique is to allow both anisotropy and selectivity of the engraving.

[0017] According to one feature of the invention, step c') is performed such that: - the intentional formation of said at least one orifice traversing the stack is obtained by photolithography followed by engraving; - the unintentional formation of said at least one orifice traversing the stack is obtained by cracks generated during the epitaxy of step b').

[0018] According to one feature of the invention, the type III-N alloy is selected from a ternary aluminum-gallium nitride alloy AlGaN, a quaternary aluminum-indium-gallium nitride alloy AlInGaN, a quinary nitride alloy aluminum-boron-indium-gallium AlBInGaN.

[0019] According to one feature of the invention, the type III-N alloy comprises aluminium Al in an atomic proportion greater than or equal to 5%.

[0020] Thus, one advantage provided is to improve the selectivity of the partial etching of vertical nanostructures.

[0021] According to one feature of the invention, the selective engraving is carried out during step d): - by thermal annealing under an atmosphere containing dihydrogen (H2) and ammonia (NH3); or - by plasma etching; or - by chemical etching.

[0022] According to one feature of the invention, step a) is carried out so that the vertical nanostructures are chosen from nanowires, nanotubes, nanoribbons, nanopillars, nanoneedles, nanocones, nanostraws, nanowalls.

[0023] According to one feature of the invention, step a) is carried out so that the substrate is made of a material selected from silicon Si, silicon carbide SiC, gallium nitride GaN, aluminium nitride AIN, sapphire A12O3.

[0024] Thus, an advantage provided by such substrates is to allow epitaxial growth of gallium nitride GaN.

[0025] According to one feature of the invention, step a) is carried out so that the dielectric layer is made of a material selected from silicon dioxide SiO2 and silicon nitride Si3N4.

[0026] According to one feature of the invention, the electron transport layer comprises n-type dopants, preferably silicon atoms Si or germanium atoms Ge.

[0027] Thus, one advantage provided is to increase the electrical conductivity of the electron transport layer.

[0028] According to one feature of the invention, the hole transport layer comprises p-type dopants, preferably magnesium Mg atoms.

[0029] Thus, one advantage provided is to increase the electrical conductivity of the hole transport layer.

[0030] According to one feature of the invention, the active zone comprises at least one quantum well comprising successively: - a first barrier layer, made of a ternary alloy of aluminium-gallium nitride AlxGai_xN; - an active layer, made of a ternary aluminum-gallium nitride alloy AlyGai yN with "y" strictly greater than "x", designed to emit ultraviolet photons from radiative electron-hole pair recombination, or designed to generate electron-hole pairs from absorbed ultraviolet photons; - a second barrier layer, made of a ternary aluminum-gallium nitride alloy AlxGabxN; said at least one quantum well which can be one-dimensional, two-dimensional or three-dimensional.

[0031] According to one feature of the invention, the active zone comprises at least one quantum well comprising successively: - a first barrier layer, made of an aluminum-gallium nitride alloy AlGaN; - an active layer, made in a quaternary alloy of aluminium-indium-gallium nitride AlInGaN or in a quinary alloy of aluminium-boron-indium-gallium nitride AlBInGaN, designed to emit ultraviolet photons from radiative recombinations of electron-hole pairs, or designed to generate electron-hole pairs from absorbed ultraviolet photons; - a second barrier layer, made of an AlGaN aluminum-gallium nitride alloy; said at least one quantum well which can be one-dimensional, two-dimensional or three-dimensional.

[0032] Definitions

[0033] - By "substrate", we mean a self-supporting physical support, made of a material a base from which an optoelectronic device can be formed. A substrate can be a "slice", also called a "wafer" which is generally in the form of a disc cut from an ingot of crystalline material.

[0034] - By "dielectric", it is meant that the layer is made of a material exhibiting an electrical conductivity at 300 K less than or equal to 106 S / cm.

[0035] - By "selective epitaxial zone" (SAG for "Selective Area Growth" in language In English, epitaxial growth refers to localized areas on the substrate surface, delimited by the dielectric layer, that have undergone epitaxial growth, while the rest of the substrate surface has not, the dielectric layer forming a growth mask. This is also called zone-selective epitaxy. Each localized area on the substrate surface that has undergone epitaxial growth forms a growth seed, from which a vertical nanostructure can grow. Homoepitaxy occurs when the growth seed and the vertical nanostructure are made of the same material. Heteroepitaxy occurs when the growth seed and the vertical nanostructure are made of different materials.

[0036] - By "exposing the vertical nanostructures", we mean an action of exposing partially vertical nanostructures so that the vertical nanostructures have at least one free surface.

[0037] - By "nanostructure" we mean a structure of which at least one of its dimensions is on the nanometric scale, that is to say between 0.1 nm and 10000 nm.

[0038] - By "vertical nanostructure", we mean a nanostructure extending along a The direction corresponding to the normal to the substrate surface on which the dielectric layer is formed, i.e., the vertical direction under normal operating conditions of the optoelectronic device. As a non-limiting example, the vertical nanostructure can be columnar, meaning that the vertical nanostructure can have an aspect ratio strictly greater than 1. The aspect ratio is the ratio between the height (thickness) and the width of the vertical nanostructure. The height (thickness) is the dimension along the normal to the substrate surface on which the dielectric layer is formed.

[0039] - By "type IIIN alloy", we mean an alloy between at least one element of the column III of the periodic table of elements (PTE) and nitrogen N. The alloy can be binary in the presence of a single element from column III of the PTE and nitrogen N. The alloy can be ternary in the presence of two elements from column III of the PTE and nitrogen N. The alloy can be quaternary in the presence of three elements from column III of the PTE and nitrogen N, etc.

[0040] - By "upper zone" is meant the highest zone of the transport layer of electrons along the normal to the surface of the substrate on which the dielectric layer is formed. Similarly, the highest area of ​​the stack formed during step b') along the normal to the surface of the substrate on which the dielectric layer is formed is understood to be.

[0041] - By "lateral zone" is meant a zone bordering one side of the transport layer of electrons. Similarly, we understand a zone bordering one side of the stack formed during step b'). The lateral zones of the electron transport layer are connected to each other by the upper zone of the electron transport layer. Likewise, the lateral zones of the stack formed during step b') are connected to each other by the upper zone of the stack.

[0042] - By "selective etching of a material A with respect to a material B", we mean that material A can be etched without attacking material B. In practice, the etching agent is usually chosen so that the etching speed of material A is at least 3 times (preferably at least 5 times, more preferably at least 10 times) the etching speed of material B.

[0043] - By "maintaining mechanical strength", it is meant that the lateral areas of the electron transport layer resists rupture at the end of step d) in response to mechanical stress. Similarly, it is understood that the lateral zones of the stack formed during step b') resists breakage at the end of step d) in response to mechanical stress.

[0044] - By "comprising successively an element A, an element B etc.", it is understood that Elements A and B are arranged consecutively in a defined order along the normal to a surface receiving elements A and B. For example, the surfaces receiving the stacking formed in step e) are the surfaces of the lateral regions of the electron transport layer. The surfaces receiving the stacking formed in step b') are the (top, lateral) surfaces of each of the vertical nanostructures around which the stacking extends.

[0045] - By "ultraviolet" (UV), we mean photons emitted or absorbed in at least one of the following spectral ranges: (i) UV-A: [315 nm; 400 nm] (ii) UV-B: [280 nm; 315 nm] (iii) UV-C: [100 nm; 280nm]

[0046] - By "thermal annealing" is meant a heat treatment comprising: (i) a phase of gradual temperature increase (heat ramp) until reaching a temperature known as the annealing temperature; (ii) a holding phase (plateau) at the annealing temperature, for a period called the annealing time; (iii) a cooling phase. A thermal budget is an energy input of a thermal nature, determined by the choice of a value for the annealing temperature and the choice of a value for the annealing time.

[0047] - By "type n dopants" we mean species (e.g. impurities) which, when introduced in the matrix of the type III-N alloy, donate an electron to the conduction band.

[0048] - By "p-type doping agents" we mean species (e.g., impurities) which, when introduced in the III-N type alloy matrix, accept an electron from the valence band (i.e. give a hole to the valence band).

[0049] - The expression "quantum well" can refer to a single-division quantum well dimensional, a two-dimensional quantum well (also called a quantum wire), a three-dimensional quantum well (also called a quantum box). Brief description of the drawings

[0050] Other features and advantages will become apparent in the detailed description of different embodiments of the invention, the description being accompanied by examples and references to the accompanying drawings.

[0051] [Fig-1] is a schematic cross-sectional view, illustrating a step a) of a process according to the invention.

[0052] [Fig.2] is a schematic cross-sectional view, illustrating a step b) of a process according to the invention.

[0053] [Fig.3] is a schematic cross-sectional view, illustrating a step c) of a process according to the invention.

[0054] [Fig.4] is a schematic cross-sectional view, illustrating a step d) of a process according to the invention carried out after step c) illustrated in [Fig.3].

[0055] [Fig.5] is a schematic cross-sectional view, illustrating a step e) of a process according to the invention.

[0056] [Fig.6] is a schematic cross-sectional view, illustrating a step b') of a process according to the invention.

[0057] [Fig.7] is a schematic cross-sectional view, illustrating a first mode of implementation of a step c') of a process according to the invention, with a suppression of the upper zone of the stack.

[0058] [Fig.8] is a schematic cross-sectional view, illustrating a step d) of a process according to the invention carried out after step c') illustrated in [Fig.7].

[0059] [Fig.9] is a schematic cross-sectional view, illustrating a second embodiment of a step c') of a method according to the invention, with an intentional formation of at least one orifice through the stack.

[0060] [Fig. 10] is a schematic cross-sectional view, illustrating a step d) of a process according to the invention carried out after step c') illustrated in [Fig.9].

[0061] [Fig. 11] is a schematic cross-sectional view, illustrating a third embodiment of a step c') of a method according to the invention, with an unintentional formation of holes through the stack.

[0062] [Fig. 12] is a schematic cross-sectional view, illustrating a step d) of a process according to the invention carried out after step c') illustrated in [Fig.11].

[0063] [Fig. 13] is a partial schematic cross-sectional view, illustrating an optoelectronic device obtained by a process according to the invention, the active area of ​​the stack being detailed in particular.

[0064] It should be noted that the drawings described above are schematic and are not necessarily to scale for the sake of legibility and to simplify their understanding. In particular, only one nanostructure is shown, and the views are enlarged for the reasons mentioned above. The sections are cut along the normal to the surface of the substrate on which the dielectric layer is formed. Detailed description of the implementation methods

[0065] Identical elements or elements performing the same function shall bear the same references for the different embodiments, for the sake of simplification.

[0066] 1st object: active zone formed after partial etching of the nanostructures

[0067] An object of the invention is a method for manufacturing an optoelectronic device, comprising the following steps: a) use: - a substrate 1, made of a material allowing epitaxial growth of gallium nitride GaN; - a dielectric layer 2, formed on the substrate 1, and delimiting zones of selective epitaxy S AG; - 3 vertical nanostructures, made of n-type doped gallium nitride GaN, formed on the S AG selective epitaxial zones by epitaxial growth; b) form an electron transport layer 4, made in a type III-N alloy containing aluminium Al, around each vertical nanostructure 3 by epitaxy; the electron transport layer 4 having a top zone 40 and lateral zones 41; c) expose the vertical s 3 nanostructures by removing the upper zone 40 of the electron transport layer 4; d) perform selective etching of the 3 exposed vertical nanostructures so as to: - etch a portion of each exposed vertical nanostructure 3; - retain a remaining part 30 of each exposed vertical nanostructure 3, adapted to retain mechanical strength of the lateral areas 41 of the electron transport layer 4; step d) being carried out with an etching agent allowing selective etching of gallium nitride GaN compared to the type III-N alloy containing aluminium Al; e) forming a stack, made of a type III-N alloy comprising aluminum Al, on the lateral regions 41 of the electron transport layer 4 by epitaxy; the stack comprising successively an active zone ZA and a hole transport layer 5; the active zone ZA being designed to emit ultraviolet photons from radiative recombination of electron-hole pairs, or designed to generate electron-hole pairs from absorbed ultraviolet photons.

[0068] Step a)

[0069] The substrate 1 used in step a) is made of a material allowing epitaxial growth of gallium nitride GaN. Step a) is advantageously carried out such that the substrate 1 is made of a material selected from silicon Si, silicon carbide SiC, gallium nitride GaN, aluminum nitride AIN, sapphire Al2O3.

[0070] The dielectric layer 2, formed on the substrate 1, delimits zones of selective epitaxial growth (SAG). Step a) is advantageously carried out so that the dielectric layer electrical 2 is made from a material chosen from silicon dioxide SiO2 and silicon nitride Si3N4.

[0071] The vertical 3-nanomenal nanostructures are made of n-type doped gallium nitride (GaN). The n-type dopants are preferably silicon (Si) or germanium (Ge) atoms. The vertical 3-nanomenal nanostructures are formed on the SAG selective epitaxial zones by epitaxial growth, preferably by metal-organic vapor-phase epitaxy. Step a) is advantageously carried out so that the vertical 3-nanomenal nanostructures are selected from nanowires, nanotubes, nanoribbons, nanopillars, nanoneedles, nanocones, nanostraws, and nanowalls.

[0072] Step b)

[0073] The electron transport layer 4 formed in step b) is made of an III-N type alloy comprising aluminum Al. The III-N type alloy is advantageously selected from a ternary aluminum-gallium nitride alloy AlGaN, a quaternary aluminum-indium-gallium nitride alloy AlInGaN, or a quinary aluminum-boron-indium-gallium nitride alloy AlBInGaN. The III-N type alloy advantageously comprises aluminum Al in an atomic proportion greater than or equal to 5%.

[0074] The electron transport layer 4 is formed in step b) around each vertical nanostructure 3 by epitaxy, preferably by metal-organic vapor-phase epitaxy. The electron transport layer 4 formed in step b) has a top zone 40 and lateral zones 4L

[0075] The electron transport layer 4 formed during step b) advantageously comprises n-type dopants, preferably silicon atoms Si or germanium atoms Ge.

[0076] Step c)

[0077] Step c) consists of exposing the vertical nanostructures 3 by removing the upper zone 40 of the electron transport layer 4 formed during step b).

[0078] Step c) is advantageously carried out so that the removal of the upper zone 40 of the electron transport layer 4 is achieved by reactive ion etching.

[0079] Step d)

[0080] Step d) consists of performing a selective etching adapted to partially etch the vertical nanostructures 3 exposed at the end of step c). The unetched portion 30 of each vertical nanostructure 3 has a volume adapted to maintain the mechanical strength of the lateral zones 41 of the electron transport layer 4 formed during step b). In other words, the remaining portion 30 (i.e., unetched) of each exposed vertical nanostructure 3 forms a pedestal allowing to maintain mechanical strength of the lateral zones 41 of the electron transport layer 4.

[0081] Step d) is carried out with an etching agent allowing selective etching of gallium nitride GaN (i.e. the material of the vertical nanostructures 3) compared to the type III-N alloy containing aluminium Al (i.e. the material of the electron transport layer 4).

[0082] Selective engraving is advantageously carried out during step d): - by thermal annealing (e.g., at a temperature of 1000°C) under an atmosphere containing dihydrogen (H2) and ammonia (NH3); or - by plasma etching (e.g., under a chlorine gas (Cl2)); or - by chemical etching (e.g. with potassium hydroxide KOH or with phosphoric acid H3PO4).

[0083] Step e)

[0084] The stack formed during step e) is made in an IILN type alloy comprising aluminium Al. The IILN type alloy is advantageously chosen from a ternary aluminium-gallium nitride alloy AlGaN, a quaternary aluminium-indium-gallium nitride alloy AlInGaN, a quinary aluminium-boron-indium-gallium nitride alloy AlBInGaN.

[0085] The stack is formed in step e) on the lateral regions 41 of the electron transport layer 4 by epitaxy, preferably by metal-organic vapor-phase epitaxy. The stack formed in step e) comprises successively an active region ZA and a hole transport layer 5.

[0086] The active zone ZA can be designed to emit ultraviolet photons from radiative recombination of electron-hole pairs. Alternatively, the active zone ZA can be designed to generate electron-hole pairs from absorbed ultraviolet photons.

[0087] According to a first embodiment, the active zone ZA comprises at least one quantum well comprising successively: - a first barrier layer Bl, made of a ternary alloy of aluminium-gallium nitride AlxGabxN; - an active CA layer, made in a ternary aluminum-gallium nitride alloy AlyGai yN with "y" strictly greater than "x", designed to emit ultraviolet photons from radiative recombinations of electron-hole pairs, or designed to generate electron-hole pairs from absorbed ultraviolet photons; - a second barrier layer B2, made of a ternary alloy of aluminium-gallium nitride AlxGai_xN.

[0088] Said at least one quantum well may be one-dimensional, two-dimensional or three-dimensional.

[0089] According to a second embodiment, the active zone ZA comprises at least one quantum well comprising successively: - a first barrier layer Bl, made of an aluminum-gallium nitride alloy AlGaN; - an active CA layer, made in a quaternary alloy of aluminium-indium-gallium nitride AlInGaN or in a quinary alloy of aluminium-boron-indium-gallium nitride AlBInGaN, designed to emit ultraviolet photons from radiative recombinations of electron-hole pairs, or designed to generate electron-hole pairs from absorbed ultraviolet photons; - a second barrier layer B2, made of an aluminum-gallium nitride alloy AlGaN.

[0090] Said at least one quantum well may be one-dimensional, two-dimensional or three-dimensional.

[0091] The hole transport layer 5 advantageously comprises p-type dopants, preferably magnesium Mg atoms.

[0092] 2nd object: active zone formed before partial etching of the nanostructures

[0093] The invention also relates to a method for manufacturing an optoelectronic device, comprising the following steps: a) use: - a substrate 1, made of a material allowing epitaxial growth of gallium nitride GaN; - a dielectric layer 2, formed on the substrate 1, and delimiting zones of selective epitaxy S AG; - 3 vertical nanostructures, made of n-type doped gallium nitride GaN, formed on the SAG selective epitaxial zone by epitaxial growth; b') to form a stack, made of an aluminum-containing IIIN alloy, around each vertical nanostructure 3 by epitaxy; the stack comprising successively: - an electron transport layer 4; - an active zone ZA, designed to emit ultraviolet photons from radiative recombinations of electron-hole pairs, or designed to generate electron-hole pairs from absorbed ultraviolet photons; - a layer for transporting holes 5; the stacking having a top zone ZS and side zones ZL; c') Expose the 3 vertical nanostructures: - by removing the top zone ZS of the stack; or - by the formation, intentional or unintentional, of at least one orifice O traversing the stack; d) perform selective etching of the 3 exposed vertical nanostructures so as to: - etch a portion of each exposed vertical nanostructure 3; - retain a remaining part 30 of each exposed vertical nanostructure 3, adapted to maintain mechanical strength of the lateral ZL zones of the stack; step d) being carried out with an etching agent permitting selective etching of gallium nitride GaN compared to the type III-N alloy containing aluminium Al.

[0094] Step a)

[0095] The substrate 1 used in step a) is made of a material that permits epitaxial growth of gallium nitride GaN. Step a) is advantageously carried out so that the substrate 1 is made of a material selected from silicon Si, silicon carbide SiC, gallium nitride GaN, aluminum nitride AIN, sapphire Al2O3.

[0096] The dielectric layer 2, formed on the substrate 1, delimits areas of selective epitaxial growth (SAG). Step a) is advantageously carried out so that the dielectric layer 2 is made of a material selected from silicon dioxide (SiO2) and silicon nitride (Si3N4).

[0097] The vertical 3-nanograms are made of n-type doped gallium nitride (GaN). The n-type dopants are preferably silicon (Si) or germanium (Ge) atoms. The vertical 3-nanograms are formed on the SAG selective epitaxial zones by epitaxial growth, preferably by metal-organic vapor-phase epitaxy. Step a) is advantageously carried out so that the vertical 3-nanograms are selected from nanowires, nanotubes, nanoribbons, nanopillars, nanoneedles, nanocones, nanostraws, and nanowalls.

[0098] Step b')

[0099] The stack formed in step b') is made of an IILN type alloy comprising aluminum Al. The IILN type alloy is advantageously chosen from a ternary aluminum-gallium nitride alloy AlGaN, a quaternary aluminum-indium-gallium nitride alloy AlInGaN, or a quinary aluminum-boron-indium-gallium nitride alloy AlBInGaN. The IILN type alloy advantageously comprises aluminum Al in an atomic proportion greater than or equal to 5%.

[0100] The stack is formed in step b') around each vertical nanostructure 3 by epitaxy, preferably by metal-organic vapor-phase epitaxy. The stack formed in step b') has an upper zone ZS and ZL lateral zones.

[0101] The stack formed during step b') successively comprises an electron transport layer 4, an active zone ZA, a hole transport layer 5.

[0102] The electron transport layer 4 advantageously comprises n-type dopants, preferably silicon atoms Si or germanium atoms Ge.

[0103] The active zone ZA can be designed to emit ultraviolet photons from radiative recombination of electron-hole pairs. Alternatively, the active zone ZA can be designed to generate electron-hole pairs from absorbed ultraviolet photons.

[0104] According to a first embodiment, the active zone ZA comprises at least one quantum well comprising successively: - a first barrier layer Bl, made of a ternary alloy of aluminium-gallium nitride AlxGabxN; - an active CA layer, made in a ternary aluminum-gallium nitride alloy AlyGai yN with "y" strictly greater than "x", designed to emit ultraviolet photons from radiative recombinations of electron-hole pairs, or designed to generate electron-hole pairs from absorbed ultraviolet photons; - a second barrier layer B2, made of a ternary alloy of aluminium-gallium nitride AlxGai_xN.

[0105] Said at least one quantum well may be one-dimensional, two-dimensional or three-dimensional.

[0106] According to a second embodiment, the active zone ZA comprises at least one quantum well comprising successively: - a first barrier layer Bl, made of an aluminum-gallium nitride alloy AlGaN; - an active CA layer, made in a quaternary alloy of aluminium-indium-gallium nitride AlInGaN or in a quinary alloy of aluminium-boron-indium-gallium nitride AlBInGaN, designed to emit ultraviolet photons from radiative recombinations of electron-hole pairs, or designed to generate electron-hole pairs from absorbed ultraviolet photons; - a second barrier layer B2, made of an aluminum-gallium nitride alloy AlGaN.

[0107] Said at least one quantum well may be one-dimensional, two-dimensional or three-dimensional.

[0108] The hole transport layer 5 advantageously comprises p-type dopants, preferably magnesium Mg atoms.

[0109] Step c')

[0110] Step c') consists of exposing the 3 vertical nanostructures.

[0111] According to a first embodiment, step c') is carried out by removing the upper zone ZS of the stack formed during step b'). Step c') is advantageously carried out so that the removal of the upper zone ZS of the stack is obtained by reactive ion etching.

[0112] According to a second embodiment, step c') is carried out by the intentional or unintentional formation of at least one orifice O through the stack formed in step b'). Step c') is advantageously carried out such that the intentional formation of said at least one orifice O through the stack is obtained by photolithography followed by etching (e.g., of the reactive ion etching type). Step c') is advantageously carried out such that the unintentional formation of said at least one orifice O through the stack is obtained by cracks F generated during the epitaxy of step b').

[0113] Step d)

[0114] Step d) consists of performing a selective etching adapted to partially etch the vertical nanostructures 3 exposed at the end of step c'). The unetched part 30 of each vertical nanostructure 3 has a volume adapted to maintain the mechanical strength of the lateral zones ZL of the stack formed during step b'). In other words, the remaining part 30 (i.e. unetched) of each exposed vertical nanostructure 3 forms a pedestal allowing the mechanical strength of the lateral zones ZL of the stack to be maintained.

[0115] Step d) is carried out with an etching agent allowing selective etching of gallium nitride GaN (i.e. the material of the vertical 3 nanostructures) with respect to the type IIIN alloy containing aluminium Al (i.e. the stacking materials).

[0116] Selective engraving is advantageously carried out during step d): - by thermal annealing (e.g., at a temperature of 1000°C) under an atmosphere containing dihydrogen (H2) and ammonia (NH3); or - by plasma etching (e.g., under a chlorine gas (Cl2)); or - by chemical etching (e.g. with potassium hydroxide KOH or with phosphoric acid H3PO4).

[0117] The invention is not limited to the embodiments described. A person skilled in the art is able to consider their technically operative combinations, and to substitute equivalents for them.

Claims

Demands

1. A method for manufacturing an optoelectronic device, comprising the steps: a) use: - a substrate (1), made of a material allowing epitaxial growth of gallium nitride GaN; - a dielectric layer (2), formed on the substrate (1), and delimiting areas of selective epitaxy (SAG); - vertical nanostructures (3), made of n-type doped gallium nitride GaN, formed on the selective epitaxial zones (SAG) by epitaxial growth; b) form an electron transport layer (4), made in a type III-N alloy comprising aluminium Al, around each vertical nanostructure (3) by epitaxy; the electron transport layer (4) having a top zone (40) and lateral zones (41); c) expose the vertical nanostructures (3) by removing the upper zone (40) of the electron transport layer (4); d) perform selective etching of the exposed vertical nanostructures (3) so as to: - etch a portion of each exposed vertical nanostructure (3); - retain a remaining part (30) of each exposed vertical nanostructure (3), adapted to retain mechanical strength of the lateral areas (41) of the electron transport layer (4); step d) being carried out with an etching agent allowing selective etching of gallium nitride GaN compared to the type III-N alloy containing aluminium Al; e) form a stack, made in a type III-N alloy comprising aluminium Al, on the lateral areas (41) of the electron transport layer (4) by epitaxy; the stack comprising successively an active zone (AZ) and a hole transport layer (5); the active zone (AZ) being designed to emit ultraviolet photons from radiative recombinations of electron-hole pairs, or designed to generate electron-hole pairs from absorbed ultraviolet photons.

2. A method for manufacturing an optoelectronic device, comprising the steps: a) use: - a substrate (1), made of a material allowing epitaxial growth of gallium nitride GaN; - a dielectric layer (2), formed on the substrate (1), and delimiting areas of selective epitaxy (SAG); - vertical nanostructures (3), made of n-type doped gallium nitride GaN, formed on the selective epitaxial zone (SAG) by epitaxial growth; b') form a stack, made in a type III-N alloy containing aluminium Al, around each vertical nanostructure (3) by epitaxy; the stack comprising successively: - an electron transport layer (4); - an active zone (AZ), designed to emit ultraviolet photons from radiative recombinations of electron-hole pairs, or designed to generate electron-hole pairs from absorbed ultraviolet photons; - a hole transport layer (5); the stacking having a top zone (ZS) and side zones (ZL); c') Expose the vertical nanostructures (3): - by removing the top zone (ZS) of the stack; or - by the formation, intentional or unintentional, of at least one orifice (O) passing through the stack; d) perform selective etching of the exposed vertical nanostructures (3) so as to: - etch a portion of each exposed vertical nanostructure (3); - retain a remaining part (30) of each exposed vertical nanostructure (3), adapted to retain mechanical strength of the lateral zones (ZL) of the stack; step d) being carried out with an etching agent permitting selective etching of gallium nitride GaN compared to the type III-N alloy containing aluminium Al.

3. A method according to claim 1, wherein step c) is carried out so that the removal of the upper zone (40) of the electron transport layer (4) is achieved by reactive ion etching.

4. A method according to claim 2, wherein step c') is carried out so that the removal of the top zone (ZS) of the stack is achieved by reactive ion etching.

5. A method according to claim 2, wherein step c') is carried out such that: - the intentional formation of said at least one orifice (0) through the stack is obtained by photolithography followed by etching; - the unintentional formation of said at least one orifice (0) through the stack is obtained by cracks (F) generated during the epitaxy of step b').

6. A process according to any one of claims 1 to 5, wherein the type III-N alloy is selected from a ternary aluminum-gallium nitride alloy AlGaN, a quaternary aluminum-indium-gallium nitride alloy AlInGaN, a quinary aluminum-boron-indium-gallium nitride alloy AlBInGaN.

7. A process according to any one of claims 1 to 6, wherein the type III-N alloy comprises aluminum Al in an atomic proportion greater than or equal to 5%.

8. A method according to any one of claims 1 to 7, wherein the selective etching is carried out in step d): - by thermal annealing under an atmosphere comprising di-hydrogen H2 and ammonia NH3; or - by plasma etching; or - by chemical etching.

9. A method according to any one of claims 1 to 8, wherein step a) is carried out so that the vertical nanostructures s (3) are selected from nanowires, nanotubes, nanoribbons, nanopillars, nanoneedles, nanocones, nanostraws, nanowalls.

10. A method according to any one of claims 1 to 9, wherein step a) is carried out so that the substrate (1) is made of a material selected from silicon Si, silicon carbide SiC, gallium nitride GaN, aluminium nitride AIN, sapphire A12O3.

11. A method according to any one of claims 1 to 10, wherein step a) is carried out so that the dielectric layer (2) is made of a material selected from silicon dioxide SiO2 and silicon nitride Si3N4.

12. A method according to any one of claims 1 to 11, wherein the electron transport layer (4) comprises n-type dopants, preferably silicon atoms Si or germanium atoms Ge.

13. A method according to any one of claims 1 to 12, wherein the layer of hole transport (5) involves p-type dopants, preferably magnesium Mg atoms.

14. A method according to any one of claims 1 to 13, wherein the active zone (AZ) comprises at least one quantum well successively comprising: - a first barrier layer (Bl), made of a ternary alloy of aluminium-gallium nitride AlxGabxN; - an active layer (AC), made of a ternary aluminum-gallium nitride alloy AlyGai yN with "y" strictly greater than "x", designed to emit ultraviolet photons from radiative recombinations of electron-hole pairs, or designed to generate electron-hole pairs from absorbed ultraviolet photons; - a second barrier layer (B2), made of a ternary alloy of aluminium-gallium nitride AlxGa[ xN; said at least one quantum well which can be one-dimensional, two-dimensional or three-dimensional.

15. A method according to any one of claims 1 to 13, wherein the active zone (AZ) comprises at least one quantum well successively comprising: - a first barrier layer (Bl), made of an aluminum-gallium nitride alloy AlGaN; - an active layer (AC), made in a quaternary alloy of aluminium-indium-gallium nitride AlInGaN or in a quinary alloy of aluminium-boron-indium-gallium nitride AlBInGaN, designed to emit ultraviolet photons from radiative recombinations of electron-hole pairs, or designed to generate electron-hole pairs from absorbed ultraviolet photons; - a second barrier layer (B2), made of an aluminum-gallium nitride alloy AlGaN; said at least one quantum well which can be one-dimensional, two-dimensional or three-dimensional.

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