Classifications

• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
  • C30B25/02—Epitaxial-layer growth
  • C30B25/18—Epitaxial-layer growth characterised by the substrate
  • C30B25/183—Epitaxial-layer growth characterised by the substrate being provided with a buffer layer, e.g. a lattice matching layer
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
  • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
  • C23C16/30—Deposition of compounds, mixtures or solid solutions, e.g. borides, carbides, nitrides
  • C23C16/301—AIII BV compounds, where A is Al, Ga, In or Tl and B is N, P, As, Sb or Bi
  • C23C16/303—Nitrides
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
  • C30B25/02—Epitaxial-layer growth
  • C30B25/10—Heating of the reaction chamber or the substrate
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
  • C30B29/10—Inorganic compounds or compositions
  • C30B29/40—AIIIBV compounds wherein A is B, Al, Ga, In or Tl and B is N, P, As, Sb or Bi
  • C30B29/403—AIII-nitrides

Definitions

• the field of the invention is that of the epitaxial growth of a crystalline layer into a III-N compound from a graphene layer, the epitaxy then being van der Waals type.
• the invention applies in particular to the production of an electronic or optoelectronic device comprising such an epitaxial crystalline layer.
• the epitaxy of a crystalline material from a nucleation layer or a growth substrate corresponds to the growth of this material so that its crystal lattice has a relationship of epitaxy with that of the underlying material.
• the epitaxial material has an alignment of the crystallographic orientations of its crystal lattice, in at least one direction lying in the plane of the material and at least one direction orthogonal to the plane of the material, with those of the crystalline lattice of the nucleating material.
• the plane of the epitaxial material is here parallel to the nucleation plane. This results in the fact that there is an agreement of orientation and crystallographic position between the crystal lattice of the epitaxial material and that of the nucleation material.
• the epitaxial material when the crystalline material has a mesh parameter different from that of the nucleation material, the epitaxial material then has a deformation of its crystal lattice, so that it then undergoes mechanical stresses in tension or in compression.
• the thickness of the epitaxial material exceeds a value called critical thickness, the mechanical stresses can relax in a plastic way, thus resulting in the formation of structural defects such as dislocations of mesh mismatch.
• the epitaxial growth of a crystalline layer in a III-N compound for example gallium nitride GaN or indium gallium nitride InGaN, can be carried out, inter alia, from a sapphire (AI2O3) or silicon substrate.
• a sapphire AI2O3
• GaN has a 15% mesh clash with sapphire, as well as significant difference in the coefficient of thermal expansion.
• the epitaxial GaN then has mechanical stresses which, from a critical thickness of the layer, can plastically relax by forming dislocations.
• Such structural defects are capable of degrading the optical and / or electronic properties of a microelectronic or optoelectronic device comprising such an epitaxial layer.
• the article by Kim et al. titled Principle of direct van der Waals epitaxy of single-crystalline films on epitaxial graphene, Nat. Comm. 2014, 5: 4836 discloses the formation of a crystalline layer of GaN by chemical vapor deposition from a graphene layer, which is formed on a SiC silicon carbide substrate.
• the epitaxial growth is said to be of the van der Waals type insofar as the epitaxial GaN layer does not have epitaxial relationships with the graphene layer.
• Kim 2014 also shows that the crystalline quality of the epitaxial GaN layer can be improved when the nucleation and growth phases are carried out at high temperature, respectively at 1100 ° C. and 1250 ° C.
• the object of the invention is to provide a layer of interest in an 111-INI compound having improved crystalline quality by van der Waals epitaxy from a graphene layer.
• the subject of the invention is a process for manufacturing a layer of interest in a 111-INI crystalline compound by epitaxy from a graphene layer, characterized in that it comprises, prior to a nucleation phase of the layer of interest, a step of heat treatment of the graphene layer in which it is subjected to a first temperature greater than or equal to 1050 ° C and an ammonia flow.
• the manufacturing method implicitly comprises a step of obtaining a layer of graphene resting on a support layer.
• the layer of interest is a layer made of a crystalline material forming a III-N compound.
• a 111-INI compound is an alloy formed of nitrogen and at least one element of column III of the periodic table of elements.
• the nucleation phase of the layer of interest can be carried out at a second temperature below 1050 ° C.
• the method may include, following the nucleation phase, a growth phase of the layer of interest made at a third temperature above the second temperature and below 1050 ° C.
• the ammonia may be a precursor of the nitrogen of the 111-INI compound during nucleation and growth phases of the 111-INI compound of the layer of interest.
• the graphene layer may be previously performed on a support layer made of hexagonal silicon carbide.
• the graphene layer may consist of from one to at most five sheets of graphene.
• the 111 -INI compound may be selected from GaN, AIGaN, InGaN, and ANnGaN.
• the crystalline compound 111-INI can be epitaxially grown by chemical vapor deposition with organometallic compounds.
• the 111-INI compound may be ln x iGai-xiN with an atomic proportion of indium xl greater than or equal to 5%.
• the invention also relates to a method of producing an optoelectronic device, comprising the production of a layer of interest from the method according to any one of the preceding characteristics, then the realization from the layer. of interest of N and P doped layers between which an active zone is located, the active zone comprising at least one quantum well made based on the 111-INI compound.
• the 111-INI compound of the layer of interest may be InGaN with an atomic proportion of indium greater than or equal to 5%, and the active zone may be made from InGaN with an atomic proportion. indium greater than or equal to 15%.
• FIG. 1A illustrates an example of temperature evolution for different steps of the method of manufacturing a layer of interest in a 111-INI compound according to one embodiment
• FIG. 1B is a diagrammatic sectional view of FIG. an example of a layer of interest obtained by the manufacturing method
• FIG. 2 is a schematic and partial sectional view of an optoelectronic device comprising a layer of interest obtained by the manufacturing method according to one embodiment
• FIGS. 3A, 3B, 3C respectively illustrate X-ray diffraction spectra, photoluminescence spectra, and Raman spectra for a GaN layer of interest obtained by the manufacturing method according to one embodiment and for different layers of GaN reference;
• FIGS. 4A and 4B respectively show a scanning electron microscope view (FIG. 4A) of nucleation pads obtained during a manufacturing method according to one embodiment of the invention, and a Fourier transform (FIG. 4B) performed from the view illustrated in Fig.4A;
• FIGS. 5A and 5B respectively illustrate a scanning electron microscope view (FIG. 5A) of nucleation pads obtained during a manufacturing process that does not include a heat treatment step prior to the nucleation step, and a Fourier transform (FIG. 5B) made from the view illustrated in FIG. 5A;
• FIGS. 6A and 6B respectively illustrate a scanning electron microscope view (FIG. 6A) of nucleation pads obtained during a manufacturing process comprising a step of thermal annealing of the graphene layer without submitting it to a ammonia flow, and a Fourier transform (Fig. 6B) made from the view illustrated in Fig. 6A;
• FIG. 7 illustrates Raman spectra for a graphene layer obtained on a support layer, for the same graphene layer after an annealing step and finally for the same graphene layer after the annealing and heat treatment steps.
• van der Waals epitaxy also called van der Waals epitaxy
• van der Waals epitaxy is a heteroepitaxy technique by which a three-dimensional crystalline layer is bonded to a layer of one or more sheets of a material.
• the two-dimensional material may be selected from graphene, boron nitride, transition metal chalcogenides, among others. This is, in the context of the invention, a graphene layer.
• the van der Waals epitaxy makes it possible in particular to overcome the mismatch that may exist between the two-dimensional material and the epitaxial layer, this mismatch being derived from the difference between the mesh parameters of the two materials, thereby allowing obtain a crystalline epitaxial layer relaxed or almost relaxed.
• Such a crystal layer obtained by van der Waals epitaxy then has a reduced density of structural defects such as disordered mesh dislocations, thus optimizing the optical and / or electronic properties of a microelectronic or optoelectronic device comprising such a layer of interest.
• FIG. 1A illustrates an example of temperature evolution for different stages of the manufacturing process
• FIG. 1B illustrates an example of a layer of interest thus obtained.
• the temperature considered in Figure 1A corresponds to the temperature of the support layer at its upper face on which rests the graphene layer. It also corresponds to the temperature of the graphene layer because of the very small thickness of the latter. The temperature is usually measured, directly or indirectly, through a thermocouple and / or infrared laser pyrometer.
• a three-dimensional orthogonal direct reference mark ( ⁇ , ⁇ , ⁇ ) is defined here, in which the X and Y axes form a plane parallel to the main plane along which the layer of interest extends, and where the Z axis is oriented in a direction orthogonal to the main plane of the layer.
• a support layer 1 is first provided in order to subsequently form the graphene layer 2.
• the support layer 1 may be formed of a thick layer of the same material, by example be a bulk substrate (bulk substrate), or be formed of a stack of layers of different materials such as a SOI type substrate (for Silicon On Insulator, in English). It can be made of an electrically insulating material, for example sapphire (Al2O3), or be made of a semiconductor material based on a III-V compound, a II-VI compound or a IV compound, by example silicon or silicon carbide.
• a III-V compound is an alloy formed of at least one element of column III and at least one element of column V of the periodic table.
• the choice of the material of the support layer 1 depends in particular on the technique chosen for producing the graphene layer.
• the graphene layer obtained on a growth substrate can be transferred to the support layer.
• the support layer 1 is a solid substrate of hexagonal SiC.
• the upper face of the support layer 1 may have a surface pattern in the form of steps or steps which may have a width of the order of a few tens of nanometers to a few microns, for example between 10 nm and ⁇ , preferably equal to about 100 nm, and a difference in height of the order of a few nanometers, for example between 1 and 10 nm, for example equal to about 1 nm.
• a graphene layer 2 is formed on the support layer 1.
• it can be formed by graphitization on the SiC support layer, or be formed by deposition on a growth substrate. and then transferred to the support layer 1.
• the graphene layer 2 is made by graphitization of the support layer 1 in hexagonal SiC according to operating conditions that are identical or similar to those described in the article by Kim 2014 mentioned previously.
• the graphene layer 2 thus covers a surface of the support layer 1.
• Graphene is a two-dimensional crystalline material formed of a single sheet of carbon atoms arranged in hexagon to form a planar structure of monoatomic thickness.
• a sheet here corresponds to a monoatomic layer. It is said to be two-dimensional insofar as it is formed of one or more sheets of carbon atoms arranged so as to form a hexagonal two-dimensional crystal lattice.
• the graphene layer 2 can have a single sheet of graphene or a few sheets of graphene stacked on top of each other, for example not more than five sheets. When it is formed of at most five sheets of carbon atoms, it is then said to be made of graphene.
• the graphene layer 2 When it is formed of a stack of more than five sheets of carbon atoms, it is said to be made of graphite.
• the graphene layer 2 has a thickness of preferably between 0.3 nm and 1.8 nm.
• the graphene layer 2 can also reproduce this structuring with identical or similar dimensions.
• an annealing is carried out by carrying the graphene layer 2 at a temperature of the order of a few hundred degrees Celsius, for example at 800 ° C, for a duration of the order of a few minutes.
• the graphene layer is not subjected to any ammonia and precursor stream of III-III of the III-INI component of the layer of interest 3. It can be subjected to a nitrogen environment (N 2 ) or hydrogen (H 2 ).
• This step provides a surface treatment of the graphene layer in order to remove any impurities present, in particular the adsorbates.
• a heat treatment is carried out by carrying the graphene layer at a temperature T t t greater than or equal to a threshold value Tth equal to 1050 ° C under a stream of ammonia N H3.
• the flow of ammonia can be between 1000 and 15000 sccm (standard cubic centimeter per minute), for example equal to 7300 sccm.
• the duration of the heat treatment may be a few minutes, for example of the order of 4 or 5 min.
• the pressure may be a few hundred millibars, for example of the order of 600 to 800 mbar.
• the carrier gas may be nitrogen (N 2 ) or hydrogen (H 2 ).
• the heat treatment temperature T t t remains lower than the melting temperature of the graphene layer 2 and that of the support layer 1.
• the threshold temperature Tth may be greater, or less than or equal to, a maximum value Tn m ax of nucleation of the compound 111-INI of the layer of interest 3.
• Tn m ax a maximum value of nucleation of the compound 111-INI of the layer of interest 3.
• the threshold temperature Tth is greater than the maximum temperature Tn m ax nucleation, it is irrelevant that the graphene layer 2 is also subjected to a flow of the precursor of the element III, for example a flow of trimethylgallium TMGa or triethylgallium TEGa in the case where the element III is gallium.
• the 111-INI compound can not nucleate from the graphene layer 2, since, by definition, from the maximum nucleation temperature, the probability of The desorption of the atoms III is greater than their adsorption probability on the graphene layer 2.
• the threshold temperature Tth is less than or equal to the maximum temperature Tn m ax of nucleation
• the graphene layer 2 n is not subject to a flow of the precursor of the element III during this heat treatment step, thereby to avoid the nucleation of the III-N compound.
• the graphene layer 2 may be subjected to a heat treatment temperature T tt of 1075 ° C. for 5 min, under a pressure of 600 mbar, under a stream of ammonia of 7300 sccm. Under these conditions, it appears that the heat treatment temperature T tt is greater than the maximum temperature Tn m ax of nucleation of the compound III-N, the latter being in this example gallium nitride GaN. Also, it is possible to also subject the graphene layer 2 to a stream of gallium precursor, for example TMGa. The ratio of the flux of N H3 to the flow of TMGa may be here equal to 1340.
• the growth of the layer of interest 3 in compound III-N is carried out by van der Waals epitaxy from the graphene layer 2. It may comprise, as described herein, a nucleation phase followed by a proper growth phase, these two phases being distinguished from each other by the growth conditions and in particular by the value of the growth temperature. Alternatively, the growth step may not have distinct phases of nucleation and growth.
• the growth can be carried out by conventional epitaxy techniques such as chemical vapor deposition (CVD for Chemical Vapor Deposition, in English) for example organometallic (MOCVD, for Metal-Organic Chemical Vapor Deposition).
• CVD chemical vapor deposition
• MOCVD Metal-Organic Chemical Vapor Deposition
• MBE Molecular Beam Epitaxy
• HVPE hydride vapor phase epitaxy
• ALE Atomic Layer Epitaxy
• ALD for Atomic Layer Deposition
• the growth process is a chemical MOCVD deposition of a GaN gallium nitride layer of interest 3 on the graphene layer 2 which rests on a support layer 1 of hexagonal SiC.
• nucleation of the III-N compound is carried out from the graphene layer 2 by epitaxial growth MOCVD.
• the temperature is then lowered to a value Tn lower than the maximum nucleation temperature Tn m ax.
• the temperature Tn is also lower than the threshold temperature Tth of 1050 ° C.
• the compound III-N then nucleated directly on the graphene layer 2 and is bonded thereto by weak van der Waals bonds and not by covalent bonds.
• the compound III-N can thus form nucleation or nucleation pads, distinct from one another, in contact or not in pairs, distributed spatially on the surface of the graphene layer 2 in a random manner (see FIG. 4A as an example).
• the nucleation pads of the compound III-N are directly in contact with the graphene layer 2, in the sense that there is no intermediate material located between the compound III-N and the graphene layer 2.
• the compound III-N intended to form the layer of interest 3 is made of a crystalline alloy comprising nitrogen and at least one element of column III of the periodic table.
• the compound III-N may thus be, for illustrative purposes, chosen from among binary alloys such as gallium nitride GaN, aluminum nitride AlN, or even indium nitride InN, ternaries such as indium nitride and gallium InGaN or aluminum and gallium aluminum nitride AIGaN, or even the quaternary such as aluminum nitride, indium and gallium AlInGaN.
• the nucleation temperature Tn is here equal to 950 ° C.
• the NHs / TMGa ratio of the ammonia flux on the gallium precursor stream is equal here to 1180 and the pressure is equal to 300 mbar.
• the duration of this phase can be a few minutes, for example 5min.
• a plurality of GaN nucleation blocks (see FIG. 4A) is thus obtained by van der Waals growth directly from the graphene layer 2.
• the actual growth of the layer of interest 3 formed of the compound III-N is carried out, with the aim of obtaining a layer extending substantially continuously over the coating layer. graphene 2 and having a substantially constant final thickness.
• the temperature is increased to a so-called growth value Te, greater than the nucleation value Tn, in particular to increase the growth rate in the XY plane relative to the growth rate along the Z axis.
• the growth temperature Te is also lower than the threshold temperature Tth of 1050 ° C.
• the N / III ratio of the nitrogen precursor stream to the element III precursor stream, as well as the pressure, may remain unchanged.
• the duration of this phase can be from a few minutes to a few tens of minutes or more, depending on the desired final thickness of the layer interest.
• the final thickness can be between a few hundred nanometers to a few microns, or even a few tens or hundreds of microns.
• the growth temperature Te is here equal to 1030 ° C.
• the NHs / TMGa ratio of the ammonia flux on the gallium precursor stream is equal here to 1180 and the pressure is equal to 300 mbar.
• the duration of this phase can be equal to 2h. This gives a layer of interest in GaN of a thickness of about one micron.
• the layer of interest 3 has a crystal lattice which is not not mechanically constrained by that of the graphene layer 2, nor by that of the support layer 1.
• the effective mesh parameter of the layer of interest 3 is substantially equal to its value in the natural state. This then results in a good relaxation of the mechanical stresses in the layer of interest 3 along its entire thickness, thus leading to a low density of structural defects such as dislocations of mesh cleavage resulting from a possible plastic relaxation of the stresses.
• the mismatch between the 111-INI compound of the layer of interest 3 and the graphene layer 2 does not substantially cause mechanical stresses in the layer of interest 3. It is then possible to achieve a layer of interest 3 whose thickness is then no longer limited by the critical thickness from which a plastic relaxation of the mechanical stresses usually appears.
• the 111-INI compound is a ternary or a quaternary, for example, InGaN
• the atomic proportion of indium depends on the desired optical and / or electronic properties of the layer of interest 3. It is the same for the ternary AIGaN and the quaternary AlInGaN.
• FIG. 2 schematically and partially illustrates an example of an optoelectronic device comprising such a layer of interest in a III-N compound, for example in InGaN.
• the optoelectronic device here comprises the stack illustrated in FIG. 1B, namely the support layer 1, the graphene layer 2, and the InGaN layer of interest 3.
• it is a planar light emitting diode, but this device can be any other type of microelectronic or optoelectronic device.
• the layer of interest 3 obtained by van der Waals epitaxy forms, in this example, a buffer layer (in English) in ln x iGai- x iN with an atomic proportion of indium xl greater than or equal to 5 %, for example equal to about 18%.
• a value of the proportion of indium x1 is usually accessible only to the extent that the layer of interest 3 is substantially relaxed or for a thickness less than the critical thickness.
• the layer of interest is relaxed, its thickness is not limited by the value of the critical thickness. It can therefore be greater than or equal to 10 nm, which is the order of magnitude of the critical thickness of InGaN. It can thus be, for purely illustrative purposes, between 10 nm and 20 ⁇ m, for example between 500 nm and ⁇ , for example equal to about 5 ⁇ m.
• a first layer 4, doped according to a first type of conductivity, for example doped n, covers the layer of interest 3. It is made of a material based on the compound III-N, that is to say it is an alloy formed of at least the same elements as those of the compound III-N of the layer of interest 3. Preferably, it is made of n-doped InGaN, with an atomic proportion of indium substantially equal to xl, here at 18%, and has a thickness which may be, for purely illustrative purposes, between 10 nm and 20 ⁇ m, for example between 500 nm and ⁇ ⁇ m, for example equal to approximately 5 ⁇ m.
• the first doped layer 4 and the layer of interest 3 may not be distinct from each other and may thus form a single layer. In this case, the layer of interest 3 can be doped by incorporation of dopants during its growth stage.
• An active zone 5 is located between the two doped layers 4, 6. It is here a layer at which is emitted the bulk of the light radiation emitted by the light emitting diode. It comprises at least one quantum well made of a semiconductor compound whose bandgap energy is less than that of the two doped layers 4, 6. It can thus comprise a single quantum well or multiple quantum wells each interposed between barrier layers. .
• the layers forming the quantum wells, and preferably the barrier layers are made of a semiconductor material based on the compound III-N, and preferably InGaN as the compound III-N, with different atomic proportions for the quantum wells and barrier layers.
• the barrier layers may thus be made of InGaN with an atomic proportion of indium of between approximately 15% and 23%, for example equal to approximately 18%
• the quantum wells may also be made of InGaN with an atomic proportion of indium of between approximately 22% and 30%, for example equal to approximately 25%, making it possible here to obtain an emission wavelength of between 495 nm and 560 nm, for example equal to 500 nm.
• the light-emitting diode is then able to emit light radiation in the green, with a good light output insofar as the internal quantum efficiency is improved by limiting the mesh mismatch at the interfaces between the layers 3, 4, 5, 6, thus resulting in a reduced density of dislocation-like defects in the doped layers 4, 6 and the active zone 5.
• An electron-blocking layer (not shown) can be located between the active zone 5 and the second doped layer 6. It can be formed of a III-N ternary compound, for example AIGaN or AlInN, advantageously doped p. It makes it possible to increase the rate of radiative recombinations in the active zone.
• First and second polarization electrodes are in electrical contact respectively with the first doped layer 4 and the second doped layer 6. They make it possible to apply an electrical potential difference to the optoelectronic device. Depending on their positioning, they may be made of an electrically conductive material and transparent to the light radiation emitted by the diode, for example indium tin oxide ITO. Thus, when a difference in electrical potential is applied to the pn junction in a forward direction, the diode emits light radiation whose emission spectrum has a peak intensity at a wavelength here equal to about 500 nm.
• the layer of interest 3 has an improved crystalline quality, which makes it possible to limit the density of structural defects also in the doped layers 4, 6 and in the active zone 5, thus also improving the performances optoelectronic diode electroluminescent.
• Figures 3A to 3C illustrate different characterizations of a layer of interest 3 obtained by the manufacturing method according to one embodiment. These examples of characterizations of the layer of interest 3 make it possible to demonstrate the absence or the virtual absence of mechanical stresses, thus reflecting the relaxed state of the layer of interest 3.
• the layer of interest 3 is made of GaN, from a graphene layer 2 resting on a hexagonal SiC support layer, with the operating conditions mentioned above with reference to the preferred example.
• FIG. 3A illustrates a comparison of the X-ray diffraction pattern of the layer of interest 3 obtained by the fabrication method according to one embodiment with those of three GaN reference layers.
• the value of the angular position is compared with the angle ⁇ of the line [002] of the GaN layer of interest 3 with respect to the reference layers.
• the curve C1 illustrates the X-ray diffraction intensity of the layer of interest 3 in epitaxially grown GaN from the graphene layer obtained by the manufacturing method according to one embodiment.
• Curve C2 is relative to a solid GaN reference layer thus relaxed, the C4 curve to a GaN reference layer epitaxially grown directly from a sapphire support layer, and finally the C3 curve to a GaN reference layer.
• the curve C1 of the layer of interest 3 has a peak intensity for a value 2 ⁇ substantially equal to that of the C2 curve relative to the relaxed GaN.
• the C4 curve of GaN epitaxied from sapphire shows that GaN undergoes mechanical stresses in compression
• the C3 curve of GaN epitaxied from SiC indicates that GaN undergoes mechanical stresses in tension.
• the layer of interest 3 obtained from the manufacturing method according to one embodiment has a virtual absence of mechanical stresses: the GaN is here substantially relaxed. Its effective mesh parameter is then substantially equal to its natural mesh parameter (3.189), and corresponds neither to that of the SiC material (3.080) of the support layer 1 nor to that of the graphene (2.460).
• FIG. 3B illustrates a comparison of the photoluminescence spectrum of the layer of interest 3 obtained by the manufacturing method according to one embodiment with those of two GaN reference layers.
• the curve C1 illustrates the photoluminescence intensity of the layer of interest 3 in epitaxially grown GaN from the graphene layer 2 obtained by the manufacturing method according to one embodiment.
• Curve C2 is relative to a solid GaN reference layer thus relaxed, and curve C3 to a GaN reference layer epitaxially grown directly from a sapphire support layer. It also emerges here that the curve C1 of the layer of interest 3 has a photoluminescence peak for a value of energy that is closer to that of the peak of the layer C2. (GaN relaxed) than that of the peak of the C3 curve (GaN in compression).
• the layer of interest 3 actually has a relaxed or substantially relaxed state.
• FIG. 3C illustrates a comparison of the Raman spectrum of the E line (2, 2 of the layer of interest 3 obtained by the manufacturing method according to one embodiment with those of three GaN reference layers.
• the curve C1 illustrates the evolution of the diffused light intensity of the epitaxial GaN layer of interest 3 from the graphene layer 2 obtained by the manufacturing method according to one embodiment.
• the layer of interest 3 actually has a relaxed or substantially relaxed state.
• the inventors have thus demonstrated that the heat treatment step implemented before the growth step of the layer of interest 3, and therefore before the nucleation phase of the III-N compound, makes it possible to obtain an improvement in the crystalline quality of the III-N compound.
• the crystalline quality of the III-N compound can be demonstrated from the analysis of the presence and orientation of crystalline planes of the nucleation pads obtained following the nucleation phase.
• the nucleation pads of the compound III-N may each have a substantially pyramidal or frustoconical shape with inclined faces, more precisely with semi-polar faces, the latter connecting a hexagonal base to the top of the pad. This corresponds to the wurtzite (hexagonal) phase of the crystalline structure in which the III-N compounds are the most stable thermodynamically.
• FIG. 4A is a scanning electron microscope (SEM) view of an example of compound nucleation pads III-N obtained following the nucleation stage of the method according to one embodiment.
• FIG. 4B shows the Fast Fourier Transform (FFT) of the pixilated MEB view shown in FIG. 4A.
• the compound III-N is GaN epitaxially grown from the graphene layer 2, which rests on a support layer 1 of hexagonal SiC.
• the manufacturing method according to this embodiment thus comprises the heat treatment step during which the graphene layer 2 is subjected to a higher temperature. or equal to 1050 ° C., here about 1075 ° C., under a stream of ammonia of 7300 sccm.
• the nucleation phase is then carried out at a nucleation temperature of 960 ° C.
• the N / III ratio is 1180, for an NH 3 flux of 7300 sccm and a TMGa flux of 277 ⁇ . ⁇ ⁇ _1 . It emerges that the seedlings each have a predominantly pyramidal shape with a hexagonal base, whose half-polar faces, substantially flat, connect the base to the top of the stud.
• the Fourier transform of the SEM view has six main lines, each corresponding to one of the semi-polar faces of the seed pads. The fact that the contrast associated with the lines is important (significant signal-to-noise ratio) reflects the good crystalline quality of the nucleation pads, and consequently of the layer of interest 3 obtained subsequently.
• FIG. 5A is a scanning electron microscope (SEM) view of an example of nucleation blocks of compound III-N obtained as a result of the nucleation phase of a manufacturing process in which the step Heat treatment is not implemented.
• FIG. 5B shows the Fast Fourier Transform (FFT) of the pixellated MEB view shown in FIG. 5A.
• the compound III-N is GaN epitaxially grown from the graphene layer 2, which rests on a support layer 1 of hexagonal SiC.
• the manufacturing method thus comprises a nucleation phase without prior heat treatment step in the sense of the invention. As before, the nucleation phase is carried out at a nucleation temperature of 960 ° C.
• the N / III ratio is 1180, for an NH 3 flux of 7300 sccm and a TMGa flux of 277 ⁇ . ⁇ _1 . It follows that the sprouting blocks do not have the same crystalline structure from one plot to another. In addition, none of the studs has a substantially pyramidal shape with a hexagonal base, with substantially flat semi-polar faces. Consequently, the Fourier transform of the SEM view does not have distinguishable main lines, which reflects the low crystalline quality of the nucleation pads, and therefore the layer of interest 3 that can be obtained subsequently.
• FIG. 6A is a scanning electron microscope (SEM) view of an example of nucleation blocks of compound III-N obtained following the nucleation phase of a manufacturing process in which a preliminary step heat treatment is implemented, but without ammonia flow.
• Figure 6B shows the Fast Fourier Transform (FFT) of the pixilated MEB view shown in Fig. 6A.
• the compound III-N is GaN epitaxially grown from the graphene layer 2, which rests on a support layer 1 of hexagonal SiC.
• the manufacturing method here comprises a heat treatment step during which the graphene layer is subjected to a temperature greater than or equal to 1050 ° C., here approximately 1075 ° C., but is distinguished from the thermal treatment in the sense of the invention.
• the layer of graphene is not subjected concomitantly to a stream of ammonia.
• the nucleation phase is then carried out at a nucleation temperature of 960 ° C.
• the N / III ratio is 1180, for an NH 3 flux of 7300 sccm and a TMGa flux of 277 ⁇ . ⁇ ⁇ _1 .
• the seed pads also do not have the same crystalline structure from one pad to the other, and do not have a substantially pyramidal shape with a hexagonal base, with substantially flat semi-polar faces.
• the Fourier transform of the SEM view does not therefore have distinguishable main lines, which confirms the poor crystalline quality of the nucleation pads, and consequently of the layer of interest that can then be obtained.
• the inventors have thus shown that the fact of carrying out a heat treatment step at a temperature greater than or equal to a threshold temperature of 1050 ° C. under ammonia makes it possible to improve the crystalline quality of the nucleation pads of the compound III. N, and therefore as a consequence of the layer of interest 3 obtained subsequently.
• These germination pads have mainly the same crystalline structure of hexagonal-based pyramidal type whose semi-polar faces are substantially flat.
• the fact of carrying out a heat treatment step above the threshold temperature of 1050 ° C., but without ammonia flow does not make it possible to obtain seedlings of good crystalline quality.
• the fact of subjecting the graphene layer to an ammonia flux but at a temperature below the threshold temperature of 1050 ° C. also makes it possible to obtain good quality seeds of the compound III-N crystalline.
• FIG. 7 is a comparison of the Raman spectrum of the graphene layer 2 obtained after the heat treatment step of the manufacturing method according to one embodiment, with those of two reference graphene layers.
• Curve D1 illustrates the Raman spectrum for the graphene layer 2 used in the manufacturing method according to one embodiment, as obtained after its forming step.
• Curve D2 illustrates the Raman spectrum for the same graphene layer 2 used in the manufacturing method according to one embodiment, after an annealing step at 800 ° C (without ammonia flow).
• the curve D3 illustrates the Raman spectrum for the same layer of graphene 2 used in the manufacturing method according to one embodiment, after the annealing step at 800 ° C. (without ammonia flow) and after the step of heat treatment at 1075 ° C under ammonia.
• the Raman spectrum of a graphene layer has a peak coming from the D modes around 1350 cm -1 , a peak coming from the G modes around 1600 cm 1 and a peak coming from the 2D modes. around 2700 cm 1.
• the peak from the D modes is useful for evaluating the crystalline quality of the graphene layer: the higher the intensity, the more the graphene layer has defects in its crystalline structure.
• the peak resulting from the 2D modes gives essentially information on the number of sheets of carbon atoms: the more the graphene layer comprises sheets, the more the peak widens.
• the graphene layer 2 initially has a low peak of the D modes (Dl curve), and a more pronounced peak after the annealing step (curve D2), reflecting a possible degradation of the structure crystalline layer of the graphene layer induced by the annealing step.
• curve D3 after the heat treatment step (curve D3), it has a very low density of structural defects insofar as the spectrum no longer has a peak resulting from the modes D.
• the heat treatment step in which the layer of graphene 2 is subjected to an ammonia flow and at a temperature greater than or equal to 1050 ° C thus seems to induce an improvement in the crystalline quality of the graphene layer.

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