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  • H01L22/00—Testing or measuring during manufacture or treatment; Reliability measurements, i.e. testing of parts without further processing to modify the parts as such; Structural arrangements therefor
  • H01L22/10—Measuring as part of the manufacturing process
  • H01L22/12—Measuring as part of the manufacturing process for structural parameters, e.g. thickness, line width, refractive index, temperature, warp, bond strength, defects, optical inspection, electrical measurement of structural dimensions, metallurgic measurement of diffusions
• • H—ELECTRICITY
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  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/02104—Forming layers
  • H01L21/02365—Forming inorganic semiconducting materials on a substrate
  • H01L21/02367—Substrates
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  • H01L21/02365—Forming inorganic semiconducting materials on a substrate
  • H01L21/02367—Substrates
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  • H01L21/02381—Silicon, silicon germanium, germanium
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  • H01L21/02104—Forming layers
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  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
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  • H01L21/02365—Forming inorganic semiconducting materials on a substrate
  • H01L21/02436—Intermediate layers between substrates and deposited layers
  • H01L21/02439—Materials
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  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/02104—Forming layers
  • H01L21/02365—Forming inorganic semiconducting materials on a substrate
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  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/02104—Forming layers
  • H01L21/02365—Forming inorganic semiconducting materials on a substrate
  • H01L21/02518—Deposited layers
  • H01L21/02521—Materials
  • H01L21/02524—Group 14 semiconducting materials
  • H01L21/02527—Carbon, e.g. diamond-like carbon
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  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
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  • H01L21/02365—Forming inorganic semiconducting materials on a substrate
  • H01L21/02656—Special treatments
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• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y40/00—Manufacture or treatment of nanostructures

Definitions

• GRAPHIC EPITAXIE ON SIC HAVING OPENED GAP AND MOBILITY COMPARABLE TO THAT OF GRAPHENE STANDARD A GAP
• the invention relates to the field of the microelectronics industry and in particular the use of graphene and its carrier transport properties for this industry.
• Graphene existing in the form of semi-infinite crystalline monolayers of carbon atoms organized in sp2 formation, has, like the carbon nanotubes better known to the general public, very interesting mechanical, electrical and electronic properties.
• graphene has an electron mobility of up to 250000 cm 2 / Vs at room temperature and 200000 cm 2 / Vs at high temperature.
• carbon nanotubes have a mobility approaching 100000 cm 2 / Vs at room temperature
• silicon has an electron mobility close to 1400 cm 2 / Vs and the mobility of electrons in copper is of the order of 4400 cm 2 / Vs
• Graphene is a material formed of an atomic plane of carbon atoms C in structure sp2 characterized by a hexagonal structure often likened to a "honeycomb" shape 11 as illustrated in three dimensions in FIG. 1A. Its atomic structure and its electronic properties were predicted more than 60 years ago. Experimentally, its existence has been demonstrated only much later, firstly by means of an epitaxy allowing a self-organized formation on the surface of silicon carbide (SiC) by sublimation of silicon present on the surface of SiC in a furnace or in ultra-vacuum, then by epitaxy on metal surfaces, or by exfoliation of graphite.
• SiC silicon carbide
• the substrate 1 can therefore be considered as insulating if it is not doped.
• the methods used by the silicon technology are then applicable to the epitaxial graphene layer 2 on a SiC substrate 1, for example lithography.
• the exfoliated graphene that would have to be transferred to an insulating substrate "sheet by sheet” so as to cover a substrate before being able to integrate into microelectronic technology.
• Such a process is not very compatible with the industrial production of structures.
• the epitaxial graphene layer 2 present on a metal substrate 1, by the very nature of the conductive substrate, is little or not compatible with applications in electronics. Indeed, a conductive substrate forms a conductive plane under graphene, in electrical contact with graphene and any electron initially present in the epitaxial graphene layer 2 could be captured by the underlying metal and circulate.
• Graphene is often considered as a semiconductor with zero or almost zero gap, that is to say that it is a material having a valence band and a conduction band in which the valence band is either in contact with the conduction band, or it is separated by a very small gap, less than 0.05 eV and often considered as zero.
• the semiconductor material with a smaller gap that can be used in microelectronics has a gap of the order of 0.1 eV.
• the mobility of electrons in graphene is close to 250000 cm 2 / Vs. This exceptional mobility is due to characteristics of the valence band form of graphene, forming a Dirac cone. This leads the electrons to behave, during an electron transport, like Dirac fermions with zero mass.
• ARPES angle-resolved photoemission spectroscopy
• ARPES angle-resolved photoemission spectroscopy
• the semiconductors are divided into three classes: the semiconductors with a small gap, between 0.1 eV and 0.7 eV, such as InSb, InAs or GaSb, the semiconductors with a medium gap, included between 0.7 eV and 2 eV, such as silicon, GaAs or InP and wide-gap semiconductors, greater than 2 eV, such as GaP, SiC, ZnO, GaN, AlN, the BN or the diamond, etc.
• the semiconductors with a small gap between 0.1 eV and 0.7 eV, such as InSb, InAs or GaSb
• the semiconductors with a medium gap included between 0.7 eV and 2 eV, such as silicon, GaAs or InP and wide-gap semiconductors, greater than 2 eV, such as GaP, SiC, ZnO, GaN, AlN, the BN or the diamond, etc.
• the gap of graphene could be opened by hydrogenation in the particular case of exfoliated graphene leading to the formation of "graphane” [2].
• the formation of grape requires hydrogenation along two sides of the graphene plane and therefore can not be applied to graphene present on a substrate.
• the grapephide thus obtained is an insulator and the electrons have a mobility of 10 cm 2 / Vs. This shows that the advantages of graphene, in particular its carrier transport property, disappear after such hydrogenation.
• the mesh parameter is reduced by 5% to 10% under the action of hydrogen. Such a reduction in the mesh parameter, which does not pose a problem for an exfoliated graphene sheet, free of any substrate, would lead to the appearance of significant stresses if the graphene layer was bonded to a substrate.
• microscopy and tunneling spectroscopy show that a hydrogenation of an epitaxial graphene layer 2 present on an iridium substrate 1 makes it possible to open the graphene gap by 0.45 eV.
• the substrate is metallic, it is not easy to use such a product in a microelectronic production line.
• Two different studies concern the hydrogenation of an epitaxial graphene layer 2 on a SiC substrate under two hydrogenation conditions.
• One of the studies presents a method for producing an insulating graphene [4] in which a gap opening of less than 0.1 eV further leads to a curvature of the electronic state dispersion of graphene. Such a method can not therefore be used to produce a semiconductor graphene on SiC, because of the small opening of the gap and the loss of the electron mobility properties.
• the second study [5] carried out with graphene partially present on a 1 SiC substrate, uses a hydrogenation with a total dose of 1200 Langmuirs; a Langmuir is a metering unit for a gas of 10 ⁇ 6 torr.s, that is 0.133 mPa.s. It has been observed that although the electronic and transport properties are modified locally, the hydrogenation does not cause any change in the graphene gap.
• the inventors have produced a thick-gap semiconductor graphene layer epitaxially grown on a Sic substrate because this method, epitaxy of graphene, is one of the least expensive and one of the easiest to implement if it is desired to great Graphene surfaces, especially if a semiconductor substrate is desired.
• the prior art leads to think that the hydrogenation of graphene induces a curvature of the dispersion of electronic states and therefore a loss of the property of exceptional mobility of the electrons, the inventors have obtained at least one layer of graphene semiconductor on an SiC substrate by means of a hydrogenation with a large gap opening and a rectilinear electronic state dispersion.
• the invention is based on the use of relatively low dose hydrogenation.
• the invention therefore firstly relates to a method of manufacturing a structure comprising a substrate, and at least one semiconductor modified graphene layer, that is to say having a gap of between 0.2 eV and 1.8.
• eV for example up to 1.3 eV, measured by tunneling spectroscopy, and that it has a dispersion of electronic states, observed by angle resolved photoemission spectroscopy (ARPES or ARUPS), as it appears either as a valence band forming a Dirac cone or as a rectilinear electronic dispersion of states; said modified graphene layer being present on said substrate; the method comprising the following steps:
• an initial structure comprising at least one non-metallic substrate capable of supporting a layer of graphene, forming a layer of graphene on the substrate,
• Said method is characterized in that the step of hydrogenation of the graphene layer is carried out with an adequate exposure dose previously evaluated according to a given reaction frame.
• the appropriate exposure dose is low, measured in a few hundred or thousands of Langmuirs.
• the evaluation of the adequate exposure dose was made by taking measurements of the number of graphene layers and the gap value of graphene, for example by the STS method, for initial structures having a layer of graphene subjected to exposure doses in a range of doses from 100 Langmuirs and up to at least 1100 Langmuirs or up to 4000 Langmuirs or 5000 Langmuirs by sampling in said range. It is then possible to identify at least one hydrogenation cycle of graphene.
• the appropriate exposure dose is chosen for a value between two successive sampled doses, at least one of which has made it possible to measure a gap greater than 0.2 eV on at least one layer of modified graphene.
• the exposure doses are preferably obtained with a hydrogen pressure less than or substantially equal to 10 ⁇ 4 Pascals or less or substantially equal to 10 ⁇ 6 Pascals or 10 ⁇ 7 Pascals.
• the invention relates in particular to a method of manufacturing a structure comprising a substrate, and at least one layer of semiconductor-modified epitaxial graphene, the epitaxial graphene layer having a gap of between 0.2 eV and 1.8 eV, measured by tunneling spectroscopy, and having a dispersion of electronic states, observed by angle-resolved photoemission spectroscopy (ARPES or ARUPS) which is either a valence band forming a Dirac cone or a linear (so-called linear) electronic state dispersion, called the modified graphene layer, present on the said substrate.
• the method comprises the following steps:
• an initial structure comprising at least one non-metallic substrate capable of supporting a layer of graphene
• the process is characterized in that the step of hydrogenation of the graphene layer is carried out with an exposure dose of between 100 Langmuirs and 4000 Langmuirs, ie between 13 mPa.s and 533 mPa.s.
• An exposure dose given in Langmuirs corresponds to a given pressure during a given time.
• the exposure time may vary from one fabricated structure to another.
• the doses used may vary according to the form of the frame, which may modify the relationship between a used exposure dose and the gap opening of the corresponding modified graphene layer.
• Those skilled in the art will be able to carry out the tests necessary to calibrate the process according to the invention as a function of the particularities of the reaction chamber which it uses.
• the hydrogenation step advantageously makes it possible to introduce hydrogen atoms added at a surface of the substrate, allowing the formation of the modified graphene layer.
• the hydrogenation step takes place after the formation of the graphene layer.
• the hydrogenation then makes it possible to modify the graphene layer to make the graphene semiconductor or to form a new layer of graphene, the latter being advantageously made of semiconductor graphene.
• the exposure dose during the hydrogenation can be between 100 and 1100 Langmuirs, to be adapted according to the frame used, the graphene layer becoming the graphene layer modified, having a non-zero gap, semiconductor.
• the modified graphene layer has a gap between 0.2 eV and 1.8 eV, measured by tunneling spectroscopy, and that it has a dispersion of electronic states, observed by angle resolved photoemission spectroscopy. (ARPES or ARUPS) which presents itself as a band of valence forming a Dirac cone is like a rectilinear electronic dispersion of states.
• Such a method makes it possible to subject the initial structure to an optimum dose of atomic hydrogen, with added hydrogen atoms interposing between the graphene layer and the substrate. Indeed, as will be described later, the inventors have observed that there is a threshold exposure dose allowing maximum opening of the gap for a graphene layer. So there is a minimum exposure dose below which we do not open the gap of the graphene layer and a maximum dose beyond which the gap has become too small for the graphene layer to be considered as semiconductor and usable in microelectronics. Such a method therefore has as a first advantage vis-à-vis the state of the art to choose an exposure dose giving gap opening of interest to the microelectronics industry.
• the exposure dose during the hydrogenation is between 200 and 500 Langmuirs, to be adapted according to the frame used.
• This dose of exposure is lower than the threshold dose and however allows a gap opening of interest to the microelectronics industry.
• This exposure dose therefore makes it possible to obtain a given gap opening which will then be able to increase further if the opening of the gap is considered insufficient.
• At least one surface layer of the substrate is Sic.
• the exposure dose is then between 1300 and 4000 or 5000 Langmuirs, to adapt according to the frame used.
• at least one last carbon plane is decoupled from the SiC surface layer and forms, following the hydrogenation, at least one additional modified graphene layer.
• the exposure dose during the hydrogenation is between 1300 Langmuirs and 2500 Langmuirs.
• the exposure dose during the hydrogenation is between 1300 Langmuirs and 2500 Langmuirs.
• it forms a layer of graphene modified gap almost zero.
• a last carbon plane is further decoupled from the SiC substrate and forms an additional modified graphene layer.
• At least one additional modified graphene layer is in semiconductor graphene, with gap greater than 0.2 eV with at least one Dirac cone-shaped valence band or a rectilinear electronic dispersion of states.
• this second advantageous mode of the process of the invention can be used a structure which does not initially comprise a graphene layer, the hydrogenation forming a modified graphene layer on the SiC substrate.
• a modified graphene bilayer can be formed.
• this step induces the formation of the graphene layer.
• an additional graphene layer is formed such that the initial layer is made of quasi-metallic graphene and the additional layer forms a first layer of modified graphene, semiconductor.
• the exposure dose is further increased.
• the dose of exposure can be between 2500 and 4000 or 5000 Langmuirs, to adapt according to the frame used.
• two additional modified graphene layers can be formed on the substrate. If there was an initial graphene layer, it is separated from the substrate by the two additional modified graphene layers.
• At least one of the additional modified graphene layers is in semiconductor graphene, with a gap greater than 0.2 eV and with at least one Dirac cone-shaped valence band or a rectilinear electronic dispersion of states. If there are several that are in semiconductive graphene, they may have different gaps.
• a heterostructure diode comprising a metal-acting surface zone formed of the initial graphene layer superimposed on two semiconductor layers having different gaps formed from the two additional modified graphene layers.
• Such a diode takes advantage of the effects of a diode with heterostructure, effects of electronic mobility peculiar to graphene and the fact of being composed of a superposition of three atomic planes.
• graphene when it is semiconductor, retains its electronic mobility properties characterized by a Dirac cone-shaped valence band or at least by a rectilinear electronic dispersion of states. .
• the substrate is advantageously Sic. It is indeed a very interesting material in microelectronics: it is a material with a large gap which also has a high thermal conductivity. Finally, it is relatively easy to form a graphene layer epitaxially grown from SiC.
• the added hydrogen atoms form a buffer plane between the modified graphene layer and the SiC substrate. A majority of the added hydrogen atoms are bonded to the SiC of the substrate. This buffer plane electronically decouples the graphene layer modified vis-à-vis the substrate.
• the semiconductor substrate is made of SiC material. It can be a SiC substrate in any polytype of SiC, in any crystalline orientation.
• the graphene layer may be present on a silicon face or a carbon face of the SiC substrate. This allows a simplification in the choice of substrate. In addition, this makes it possible to choose the face of the SiC substrate, silicon or carbon, independently of a desire to use a modified graphene layer according to the invention. This therefore guarantees an increased flexibility of use.
• the SiC substrate can come from a silicon substrate. It can even be a silicon substrate having a SiC surface layer. In such a structure, applied to the invention, the SiC surface layer is between the graphene layer and the silicon substrate.
• the substrate may come from a silicon substrate and comprise at least one surface layer of SiC. This allows the formation of SiC layers of large area, obtained by surface treatment, for example by carburation, of a standard SiC substrate.
• the growth of graphene can take place alternately on SiC having a cubic crystal lattice (3C) and or a hexagonal crystal lattice (6H or 4H).
• the process is advantageously characterized in that the structure, during the hydrogenation step or subsequent thereto, is subjected to at least one thermal treatment of temperature of between 200 ° C. and 400 ° C., preferably between 250 ° C and 350 ° and preferably close to 300 ° C.
• the method according to the invention has the advantage, by means of heat treatment, of diffusing the hydrogen atoms added to the surface of the substrate. If the graphene layer is formed before the hydrogenation step, the heat treatment makes it possible to diffuse the added hydrogen atoms more rapidly and more uniformly through the graphene layer. The heat treatment also makes it possible to homogenize a density of hydrogen atoms added to the surface of the substrate and to react them preferentially with the substrate so as not to degrade the modified graphene layer. This part of the process makes it possible to preserve, in the modified graphene layer, an important property of standard graphene: an exceptional electronic mobility. This step of the method makes it easier to open the gap without modifying the dispersion of electronic states in the valence band of the graphene.
• Said electronic state dispersion remains rectilinear and forms a Dirac cone. If there is no graphene layer previously in the hydrogenation stage, the heat treatment makes it possible to remove atoms from a last silicon plane present on the surface of the substrate and makes it possible to homogenize an interaction between the last silicon plane and the added hydrogen atoms.
• the heat treatment may comprise an annealing occurring during the hydrogenation stage called hydrogenation annealing.
• the hydrogenation anneal then has a temperature of between 200 ° C. and 400 ° C., preferably between 250 ° C. and 350 ° C. and advantageously close to 300 ° C. This step makes it possible to diffuse the added hydrogen atoms and to diffuse them directly during their deposition on the structure. Any damaging interaction between the added hydrogen atoms and the graphene layer is therefore limited.
• the process may be such that the heat treatment comprises an annealing which takes place after the hydrogenation step, called post-hydrogenation annealing, of a temperature of between 200 ° C. and 400 ° C, preferably between 250 ° C and 350 ° and preferably close to 300 ° C, and which has a duration of between one minute and twenty minutes, preferably five minutes. It is then possible to carry out an identical post-hydrogenation annealing for any dose of exposure. In addition, for the same dose the exposure time may vary from one structure to another. The post-hydrogenation annealing then makes it possible to dissociate the duration of the annealing from the exposure time.
• Annealing post ⁇ hydrogenation can be applied there was a hydrogenation annealing during the hydrogenation step or the hydrogenation was held at room temperature.
• the atomic hydrogen gas can be produced by a cold plasma. There is no hydrogenation annealing during the hydrogenation step and post-hydrogenation annealing is applied.
• the hydrogenation step before the hydrogenation step, there was formation of the graphene layer and it was subjected to an oxidation step inducing the opening of a gap in the graphene layer.
• This oxidation step preceding the provision of an initial structure, forms defects, which reduce the electronic mobility properties of the graphene layer.
• the hydrogenation step of the process according to the passive invention defects formed by oxidation.
• the structure may initially comprise electronic traps, said critical defects, between the substrate and the graphene layer.
• These electronic traps can be pieces of carbon nanotubes or other carbon constructions with pendant bonds.
• Critical defects then cause the standard graphene layer of the initial structure to have a reduced electron mobility.
• the hydrogenation stage of the process according to the invention passes the critical defects and thus makes it possible to have a modified graphene layer having significant electron mobility.
• the invention also relates to a structure comprising at least one semiconductor or insulator substrate, and at least one layer of graphene on this substrate, characterized in that the graphene layer is a modified graphene layer, called the first modified graphene layer, semiconductor.
• the first modified graphene layer has a gap between 0.25 eV and 1.8 eV, measured by tunneling spectroscopy.
• the modified graphene layer has a dispersion of electronic states, observed by angle resolved photoemission spectroscopy (ARPES or ARUPS) which is either a valence band forming a Dirac cone or a dispersion of states electronic rectilinear.
• ARPES or ARUPS angle resolved photoemission spectroscopy
• the first modified graphene layer is substantially electronically decoupled from the substrate. This allows an independence of the graphene layer vis-à-vis any doping or doping variation in the substrate.
• the first layer of modified graphene may be an epitaxial graphene layer.
• the invention also relates to a structure further comprising a second layer of modified graphene, with a metallic behavior or a quasi-zero gap.
• the second modified graphene layer is then separated from the substrate by the first modified graphene layer, the first graphene layer having a gap greater than 0.2eV.
• the invention also relates to a structure comprising at least a third layer of modified graphene interposed between the first layer of modified graphene and the second layer of modified graphene.
• the third layer of modified graphene is in semiconductor graphene with a gap greater than 0.2 eV and with at least one Dirac cone-shaped valence band or a rectilinear electronic state dispersion.
• the third layer of graphene preferably has a gap different from that of the first layer of graphene, and advantageously less than this.
• the substrate is preferably a semiconductor substrate so as to integrate the structure according to the invention in conventional microelectronic lines.
• the substrate advantageously comprises a SiC surface layer.
• the layer or layers of modified graphene may have a "p" type doping.
• FIGS. 1A and 1B illustrate a standard graphene layer on a substrate according to the state of the art, in three-dimensional view and in section,
• FIG. 2 illustrates a modified structure according to the invention, comprising at least one semiconductor modified graphene layer
• FIGS. 3A to 3D are graphs of gap measurement of graphene layers by STS according to a first, a second, a third embodiment of the invention and according to the state of the art,
• FIG. 4 is a graph of the density of electronic states obtained by ARPES observation
• FIGS. 5A and 5B are maps obtained by STS of graphene layer surfaces present on a substrate, an insert in each figure representing an enlargement of FIG. part of each of the figures,
• FIG. 5C is a diagram illustrating an interaction between two hexagonal networks
• FIGS. 6A and 6B illustrate modified structures according to the invention in which there are several layers of modified graphene,
• FIG. 7A is a graph of gap measurement by STS of a modified structure according to the invention in which there are several layers of modified graphene,
• FIGS. 7B to 7D are graphs of gap measurement of graphene layers according to the state of the art and of structures each comprising several layers of modified graphene,
• FIGS. 8A to 8C illustrate steps of a method according to the invention for obtaining a modified structure according to the invention
• FIGS. 8D and 8E illustrate variants of the method according to the invention
• FIGS. 9A to 9C illustrate a first advantageous mode of a method according to the invention, this embodiment making it possible to provide an alternative initial structure before starting the method according to the invention
• FIG. 10 illustrates a map obtained by STM of an initial structure comprising critical defects.
• FIG. 11 illustrates a measurement of low energy electron diffraction of a structure having undergone a characteristic exposure dose of a second advantageous mode of the process according to the invention
• FIGS. 12A to 12C illustrate the second advantageous mode of the method according to the invention
• FIGS. 13A to 13C illustrate a third advantageous mode of the method according to the invention.
• Standard graphene, epitaxial or not, is a material having a very important property of electron mobility as presented above.
• the invention relates first of all to obtaining a modified structure 201 (201 must also be indicated in FIG. 2, as is done below for the structures 601 , 801 etc.) such as a semiconductor-modified epitaxial graphene layer 23 is present on a semiconductor or insulator substrate 21.
• the modified epitaxial graphene layer 23, referred to as the modified graphene layer has properties of a standard epitaxial graphene layer.
• the property of Electronic mobility is maintained in the modified graphene layer 23 present in the structure 201 according to the invention.
• the standard epitaxial graphene and modified epitaxial graphene layers are referred to as such since the graphene component thereof is generally formed by epitaxial growth. However, in some cases, particularly when the invention makes it possible to form an additional graphene layer, the graphene layer in question is not formed by epitaxial growth.
• this figure represents an advantageous embodiment of the invention in which, as will be explained below, added hydrogen atoms H are bonded to the substrate 21 by chemical bonds 24.
• the structure 100 according to the invention comprises a modified graphene layer 3 having a gap between 0.20 eV and 1.8 eV, preferably between 0.25 eV and 1.5 eV, for example 1 eV.
• the gap of the modified epitaxial graphene layer 3 may be 0.25 eV or 1.3 eV or 0.40 eV as illustrated in respective figures 3A and 3B and 3C.
• FIGS. 3A, 3B, 3C and 3D represent, in ordinates, a logarithm of a measured intensity I, in nanoamperes, flowing in a graphene layer obtained by epitaxial, present on a Sic substrate, as a function of an applied voltage U, in volts, on the abscissa.
• Each figure is obtained by studying the epitaxial graphene layer by means of a method called tunnel scanning spectroscopy (STS). This method makes it possible to measure the gap (7A, 7B, 7C) of a test material, in this case semiconductor graphene.
• the voltage U applied to a test material allows, if it is a semiconductor material comprising two energy bands, a valence band and a conduction band, separated by a gap, to provide energy to electrons present in the valence band and pass them into the conduction band across the gap. This leads to the flow of a current.
• FIG. 3A illustrates a measurement obtained by STS of the gap 7A of a modified graphene layer present in a structure according to a first particular embodiment of the invention.
• the gap 7A difference between the smallest positive voltage U1 allowing the passage of the current and the smaller negative voltage U2 allowing the passage of the current, is measured substantially equal to 1.3 eV. Since the zero voltage is at 0.33 V from the smallest negative voltage U2 allowing the passage of current, the Fermi level is at 0.33 V above the valence band, ie, expressed in electrons-volts 0.33 eV. Thus, since the Fermi level is closer to the valence band than to the conduction band, the modified graphene layer can be considered to be "p" doped.
• a modified graphene layer having a gap of 1.3 eV is obtained (FIG. 3A ), behaving as a p-doped semiconductor material.
• FIG. 3B illustrates a measurement obtained by STS of the gap 7B of a modified graphene layer present in a structure according to a second particular embodiment of the invention.
• the gap 7B the difference between the smallest positive voltage U1 allowing the passage of the current and the smaller negative voltage U2 allowing the passage of the current, is measured substantially equal to 0.25 eV.
• the two previously described structures, according to the first and second embodiments of the invention, comprise a modified graphene layer present on a silicon face of an SiC substrate.
• FIG. 3C illustrates a measurement obtained by STS of the gap 7C of a modified graphene layer present in a structure according to a third particular embodiment of the invention.
• the gap 7C difference between the smallest positive voltage Ul allowing the passage of the current and the smaller negative voltage U2 allowing the flow of current, is measured substantially equal to 0.40 eV.
• This structure according to a third embodiment of the invention comprises a modified graphene layer present on a carbon face of an SiC substrate in which defects are present between the substrate and the modified graphene layer.
• Figure 3D illustrates this measurement of the gap of a standard epitaxial graphene layer.
• an intensity is produced for any voltage U applied. It is therefore considered that the gap is zero.
• the Fermi level located at the zero voltage level, is closer to the valence band than to the conduction band.
• the modified graphene layer is advantageously "p" type doping.
• the different structures of the invention comprising a graphene layer modified with a different gap, make it possible to open up the use of semiconductor graphene to various applications, each requiring a different opening gap and all of which can benefit from the exceptional properties of mobility. graphene, preserved in a structure according to the invention.
• the inventors have made observations of the dispersion of electronic states in the modified graphene layer present in the graphene layer. a structure according to the invention. These observations were made using a measurement according to the ARPES method mentioned above.
• ARPES In the ARPES method, also known as ARUPS, photons are sent to a surface of a sample, and in response, electrons, called photoelectrons, are "photo-emitted" with a given kinetic energy, in a given direction.
• a measurement of the kinetic energy of the photoelectrons provides information on the electronic properties of the sample and in particular of its surface.
• the photoemission measures only occupied electronic states and not empty electronic states, and in a semiconductor, we mainly explore only the states below the Fermi level, so the band of valence. To probe the conduction band, it is possible to use a reverse photoemission. In some cases, if the Fermi level is in the conduction band, the ARPES or ARUPS method can be used to visualize a part of the conduction band below the Fermi level.
• a measurement of the direction in which the photoelectron is emitted from the surface of the sample makes it possible to know its atomic structure according to the principle of photoelectron diffraction. This also makes it possible to know the dispersion of the electronic states along the directions of the Brillouin zone, k, and thus to determine the Fermi surface and the shape of the valence band, in Dirac cone in the case of graphene.
• This method of observing the position of the valence band in a modified graphene layer can be done in a synchrotron on any light line or using a plasma discharge ultraviolet lamp and using an analyzer. It is possible, for example, to make such an observation at the SOLEIL synchrotron, in particular on the lines of light called TEMPO or Cassiochere and by using a SCIENTA analyzer manufactured by the company VG-SCIENTA.
• the ARPES method is known to those skilled in the art.
• FIG. 4 illustrates the results obtained during an observation of a structure according to the first embodiment of the invention by the ARPES method. Only half of the dispersion of the electronic states of the modified graphene layer has been measured; which is sufficient because there is always a perfect symmetry in the valence band. An overview of the valence band and the conduction band can therefore be easily deduced. In this figure we read on the abscissa the variation of k, direction in the Brillouin zone, in the reciprocal lattice. On the ordinates we read the kinetic energy of the photoelectrons. Two important pieces of information about the characteristics of the modified graphene layer are:
• the curve of the dispersion of electronic states 43 in a modified graphene layer according to the invention is entirely rectilinear; no curvature is observed. This means that the valence band forms a perfect Dirac cone.
• the level of Fermi F is identifiable in this figure taking into account the kinetic energy giving a white signal for any value of k. It is observed secondly that the dispersion of electronic states 43 in the modified graphene layer is separated from the Fermi level F by a value of 0.6 eV. The variations between this value and the value obtained by STS, explained above, are due to a difference in surface size analyzed between the two measurement methods.
• the ARPES method observes a larger area than the STS and integrates points of the modified graphene layer with different dopings or with different gap openings.
• the substrate may be an insulator but is preferably a semiconductor and advantageously a large gap semiconductor.
• the semiconductor substrates provide a high quality, which is not necessarily the case of an insulator, and may allow the manufacture of conventional microelectronic elements.
• a large gap substrate allows the carriers to remain confined in the epitaxial graphene layer and do not disperse in the substrate.
• the substrate is preferably SiC. It is indeed a very advantageous material: it is a material with a large gap; it also has a high thermal conductivity and finally it is easy to form a standard graphene layer from SiC.
• the substrate may be formed of any known SiC polytype, and in particular it may be one of the hexagonal, rhombohedral or cubic polytypes of SiC, for example: 4H-SiC or 6H-SiC or 2H-SiC or 3C-SiC or 3C-SiC.
• Polytypes are known names that identify an organization of silicon and carbon planes within an SiC monocrystal.
• the substrate may also comprise only one SiC layer present on the surface of a main substrate composed mainly of another material, for example silicon.
• the modified graphene may be present on the carbon face or on the silicon face of the SiC substrate.
• the plane directly below the modified graphene layer, embedded in a crystal lattice Sic is respectively composed of carbon or silicon.
• On the silicon face of the SiC substrate there is generally a rotation of an angle of 30 ° between the atomic lattice of the epitaxial graphene layer and the crystal lattice of the SiC substrate. Such a rotation is not limiting for the invention.
• all the surface orientations are usable for a substrate according to the invention: for example the surfaces of the type (0001), (000-1), (11-20), (1-102), (-110-2 ), (0-33-8), (1-100) for the hexagonal polytypes and the (100), (110) or (111) type surfaces for the face-centered cubic SiC polytype.
• FIGS. 5A and 5C illustrate this advantageous characteristic of epitaxial graphene present on a structure according to the invention.
• Figs. 5A and 5C are each a surface map of an epitaxial graphene layer present on a SiC substrate of 4H-SiC polytype. These maps were obtained by tunneling microscopy (STM). Tunneling microscopy allows a topology of a surface to be observed by measuring an electronic interaction between atoms of the surface and a tunnel-effect point. It is possible to see in the inset of Figure 5A an enlargement of a portion of the map of Figure 5A. This inset illustrates a "honeycomb" structure 51 of hexagonal mesh characteristic of a graphene layer epitaxied on SiC. Furthermore, outside the box of this same FIG.
• an STM map is obtained by observing, by STM, a standard epitaxial graphene layer present on an SiC substrate, a regular moiré of light C1 spots and of darker areas S.
• Regular moiré is a distinctive sign of an electronic interaction between two networks of atoms with similar but not superimposed links to each other. It is characteristic of standard graphene present on an SiC substrate.
• FIG. 5B from the thesis defense document of Institut Varchon "Electronic and structural properties of graphene on silicon carbide", supported on December 8, 2008, illustrates this phenomenon by representing the superposition of two hexagonal networks having a disorientation one relative to each other by an angle ⁇ .
• AA and AB are circles respectively identifying one of the points where the interaction is strong between the networks, comparable to a clear spot C1 in Figure 5A, and one of the points where the interaction is the weakest between the networks, comparable to a darker area S in Figure 5A.
• a period D is then observed between the points where the interaction is strong and a half-angle ⁇ defining a symmetry in the moiré.
• Microscopy The tunneling effect measures the electron interaction between the surface atoms and the probe, and thus a measurement by STM is influenced by any electronic coupling between the surface composed of the graphene layer and the SiC substrate.
• FIG. 5C is an STM map of a structure according to the first embodiment of the invention, comprising a modified graphene layer present on an SiC substrate, with a gap measured by STS as being equal to 1.3 eV.
• the inset of this figure shows that there is indeed a network in the form of a "honeycomb" 11 hexagonal mesh identical to those observable in Figure 5A for a standard epitaxial graphene.
• Figure 5C out of the box, does not have regular moiré. Only a few irregularities of intensity appear. The disappearance of regular moiré indicates that for a structure according to the invention there is no regular interaction between the modified graphene layer and the SiC substrate.
• a structure 201 according to the invention there is preferably atomic hydrogen present, in the form of hydrogen atoms, called added hydrogen atoms H, between the layer modified graphene 23 and the substrate 21.
• the hydrogen atoms H which may be protium, isotope X H of hydrogen, or deuterium, isotope 2 H of hydrogen, or a mixture of these two isotopes, form a buffer plane comprising atomic hydrogen.
• the added hydrogen atoms H are bonded to atoms of the substrate 21 by the chemical bonds 24 and some added hydrogen atoms H are placed where there would be electronic bonds between the substrate 21 and the substrate layer. standard graphene if it were not a modified graphene layer 23.
• the added hydrogen atoms H interact with few carbon atoms of the modified graphene layer.
• the buffer plane electronically decouples the graphene layer modified vis-à-vis the substrate.
• a structure 601 according to the invention may comprise a set of several layers 63, 63 'of modified graphene, present on each other above the substrate 1 ( Figure 6A).
• the set of several modified epitaxial graphene layers 63, 63 'according to the invention is semiconductor with an open gap and with a rectilinear dispersion of the electronic states.
• a first modified graphene layer 63 is made of semiconductor graphene with a gap of the same order of magnitude as in the modified graphene layer present in the previously presented structure, by example between 0.25 eV and 1.8 eV, for example up to 1.3 eV.
• the first modified graphene layer 63 comprises a valence band having a Dirac cone shape and is located between the substrate 61 and a second modified graphene layer 63 '.
• the second modified graphene layer 63 ' may have a quasi-metallic behavior, with, for example, a zero gap.
• the invention also relates to an alternative to the aforementioned structure, comprising, in addition to the substrate 61, the first modified graphene layer 63 and the second modified graphene layer 63 'a modified third graphene layer 63' '( Figure 6B).
• the third modified graphene layer 63 '' is interposed between the first modified graphene layer 63 and the second modified graphene layer 63 '.
• the modified third graphene layer 63 '' is preferably made of semiconductor graphene having a Dirac cone-shaped valence band.
• the third modified graphene layer 63 '' has a gap which is preferably different from that of the first modified graphene layer 63, and for example it may be smaller.
• the different layers of graphene are preferably decoupled electronically from each other.
• FIG. 7A illustrates a measurement by STS of the gap 7 'of graphene in a structure comprising two superimposed layers of modified graphene present on the carbon face of a substrate Sic in a structure according to the invention, without defects between the layer of modified graphene and the substrate. It is observed that the gap 7 'is open and has a value close to 0.95 eV. Between the energy level of the valence band U2 and the Fermi level (zero abscissa), a measurable difference between 0.25 eV and 0.35 eV is observed. The different layers can be decoupled electronically from each other.
• FIGS. 7B to 7D are figures obtained by the ARPES method and showing the shape of the valence band of structures comprising one or more layers of graphene.
• the valence band V has a Dirac cone shape: the electronic dispersion of the valence band V is measured in the form of two rectilinear curves, starting from the weakest energies towards the strongest energies , which join to stronger energies without any curvature of one or other of the curves.
• Figure 7C is a measure by method
• FIG. 6A shows two valence bands VI and V2 and a conduction cone C representing at least one conduction band.
• a first valence band is separated from the C conduction bands and is at least 0.4 eV from the Fermi F level. This measurement is in agreement with the variation observed by the STS method, with some variations.
• the first valence band VI forming a Dirac cone, indicates that the first layer of modified graphene is in semiconductor graphene and that the electronic mobility properties of standard graphene are retained.
• a second valence band V2 forms a Dirac cone, situated to the right in the figure than the first valence band VI and ending in the conduction cone C. It can be deduced that there is no separation between the band valence and the conduction band and that the second layer of graphene has a metallic behavior.
• FIG. 7D is a measurement by the ARPES method of the structure according to the invention illustrated in FIG. 6B.
• a third Dirac cone-shaped valence band V3 is observed between the first and the second valence band VI and V2.
• the first valence band VI is then clearly separated from the conduction cone C.
• the first valence band is located at 0.4 eV of the Fermi level F and the third valence band is located at approximately 0.2 eV from the level of Fermi F. This means that the first and third layer of modified graphene are well in semiconductor graphene with different gaps.
• FIGS. 7B to 7D there is observed a gap between valence bands and the Fermi level and not directly a gap value such as that shown in FIGS. 7A.
• FIG. 7A shows that the gap is larger than the difference between the valence band and the Fermi level.
• the invention relates to a first advantageous embodiment of a method according to the invention.
• This first advantageous mode of the method makes it possible to produce a structure according to the invention.
• the first advantageous mode of the method according to the invention comprises two major steps illustrated in FIGS. 8A to 8E:
• This hydrogenation step can take place under ultrahigh vacuum and an atomic hydrogen gas 85 is brought into contact with the initial structure 800.
• this step the initial structure 800 is exposed to a dose of exposure to gas 85 of atomic hydrogen, called exposure dose, between 100 Langmuirs and 1100 Langmuirs.
• a langmuir is a unit of measurement for a dose of a gas of value equal to 10 ⁇ 6 torr.s, ie 0.133 mPa.s.
• exposure to a gas with an exposure dose of 1 langmuir may be indifferently exposure to a gas at a pressure of 0.001 mPa for 133 seconds or exposure to a gas at a pressure of 0.133 mPa for one second .
• the hydrogenation step according to the invention is advantageously carried out with an exposure dose of between 200 Langmuirs and 800 Langmuirs or even more preferably with an exposure dose of between 200 Langmuirs and 500 Langmuirs.
• the added hydrogen atoms H predominantly create chemical bonds 84 with the substrate 81.
• the hydrogen atoms added to the hydrogenation stage advantageously form a buffer layer composed of atomic hydrogen between the substrate. 81 and the modified graphene layer 83.
• the modified graphene layer 83 according to the invention is a graphene layer having a gap open value of between 0.25 eV, for example when the exposure dose is 1100 Langmuirs, and 1.8 eV, or preferably between 0.25 eV and 1.5 eV.
• the opening of the gap measured by STS, is substantially 1.3 eV or 0.95 eV if respectively a single layer of graphene modified 83 is present on the silicon face of a substrate SiC 81 or if several layers of modified graphene 83 are present on the carbon face of a substrate 81 Sic.
• These two gap values give the layer (s) of modified graphene 83 a gap value of the same order of magnitude as that of silicon.
• a particular embodiment of the hydrogenation step is to use a hydrogen pressure of 10 ⁇ 7 pascals for a time to obtain the desired dose, for example 100 minutes for a dose of 500 Langmuirs.
• This pressure value in an experimental reaction frame of CEA-Saclay, made it possible to obtain the aforementioned gap values, at the aforementioned exposure doses.
• the gap of the modified graphene layer 83 increases. If, on the other hand, the exposure dose is increased from 800 Langmuirs to 1100 Langmuirs, the gap of the modified graphene layer 83 decreases. Between these values, if a dose of 500 Langmuirs is applied, the The gap of the modified graphene layer 83 is larger than for the two above-mentioned exposure doses. It is therefore possible, by controlling the atomic hydrogen gas exposure dose 85, to control the value of the opening of the gap in the modified graphene layer 83.
• a gap opening is optimal only in relation to a desired application.
• the modified graphene layers 83 obtained by the process according to the invention which have gaps having these values then have optimal gap openings for the desired applications.
• Some of these applications concern the fabrication of transistors or diodes or other microelectronics or nanoelectronics devices.
• the method according to the invention makes it possible to coordinate the opening of the gap of the modified graphene layer 83 with a predetermined application.
• the added hydrogen atoms H are subjected to a heat treatment having a temperature between 200 ° C and 400 ° C, preferably between 250 ° C and 350 ° and for example close to 300 ° C.
• the heat treatment may be an annealing of the structure carried out during the hydrogenation step, and called hydrogenation annealing 86, as shown in Figure 8B.
• the initial structure 800 comprising the substrate 81 and the standard graphene layer 82, is maintained at the desired temperature, for example by means of a heating plate, throughout the hydrogenation step.
• the heat treatment may consist of an annealing occurring after the hydrogenation step, and called post-hydrogenation annealing 86 '. It may follow a stage of hydrogenation at room temperature illustrated in FIG. 8D, identical to FIG. 8B except for the absence of hydrogenation annealing 86. Then, the initial structure 800, on which are present added hydrogen atoms , may be subjected to post-hydrogenation annealing 86 ', as shown in Figure 8E.
• the post-hydrogenation annealing 86 has a temperature between 200 ° C and 400 ° C, preferably between 250 ° C and 350 ° and in particular close to 300 ° C, and has a duration of a few minutes, for example included between one minute and 20 minutes, preferably five minutes. It can for example take place in a furnace or in a reaction chamber where the hydrogenation took place.
• the post-hydrogenation annealing 86 ' can be carried out in addition of the hydrogenation step comprising a hydrogenation anneal 86 as illustrated in FIG. 8B.
• the hydrogenation annealing 86 and the post-hydrogenation annealing 86 ' are intended to facilitate the diffusion of the added hydrogen atoms H through the standard graphene layer 82 towards the substrate 81. They are also intended to enable homogeneous distribution of the added hydrogen atoms H on the substrate 81 and thus to have a density of added hydrogen atoms H substantially constant on the substrate 81. These anneals are not necessary to open the gap of the graphene layer modified, but to obtain a uniform gap opening over the entire layer. An absence of annealing may make it possible to obtain a variation of the opening of the gap on the surface of the structure, certain points having a first gap value and other points having other gap values.
• the atomic hydrogen H used during the hydrogenation stage is preferably formed by dissociation of dihydrogen with a tungsten filament heated to a high temperature, for example of the order of 1400 ° C. or 2000 ° C., or greater than 2000. C., the filament being advantageously placed at a short distance from the initial structure 800.
• the tungsten filament used may have a diameter of 0.25 mm and a current of 3.7 A may be circulated therein. way to reach the desired temperature.
• the atomic hydrogen gas 85 by means of a cold plasma.
• the substrate 81 is made of SiC, in particular one of the polytypes mentioned above, and the standard graphene layer 82 can be present on any type of SiC surface orientation.
• modified graphene layer 3 may alternatively be present on the silicon face or the carbon face of the SiC substrate 81.
• the hydrogenation described above takes place in a reaction chamber having a frame of a given shape.
• the relationship between the exposure doses and the gap opening of the modified graphene layer 83 may vary.
• the substrate 81 may be 3C-SiC, that is to say that the SiC has a cubic mesh face-centered instead of a hexagonal mesh.
• the substrate 81 made of 3C-SiC may be made from a conventional silicon substrate. This means that the initial structure 800, comprising a standard graphene layer 82 on an SiC substrate 801 is then advantageously manufactured according to the following steps:
• Sublimation and / or conventional carburation between 1200 ° C. and 1300 ° C., of silicon present on the surface of the substrate to obtain at least one surface layer 91 of SiC (FIG. 9B) above the silicon substrate 90, or formation of SiC by any other known method, ultra-high vacuum oven, sublimation under pressure of a neutral gas, etc.
• the silicon substrate 90, and therefore the surface layer 91 of SiC may be oriented (100), (110) or (111).
• Such a method is advantageous because it is easy to obtain silicon substrates 90 of large area. It is therefore possible to relatively easily produce substrates coated with a surface layer 91 of large and high quality SiC. It then becomes relatively easy to use epitaxial graphene modified in microelectronics.
• the gap is closed compared to the gap obtained by the first mode.
• the invention therefore also relates to a second advantageous mode of the method according to the invention, illustrated in FIGS. 12A to 12C.
• This second advantageous mode of the process according to the invention is a variant of the first advantageous mode of the process according to the invention in which doses of hydrogen gas exposures are different.
• an initial structure 1201 within the meaning of the invention comprises at least one initial graphene layer 123 located on a surface layer 121 of SiC, as illustrated in FIG. 12A, there is under the initial graphene layer 123 a last plane of carbon atoms, said last carbon plane 122 of the substrate Sic (sometimes called "buffer layer”), immediately located under the initial graphene layer 123.
• the last plane of carbon 122 may be located above a last plane of silicon atoms, called the last plane of silicon. 124. Conversely, if the initial graphene layer 123 is on a silicon face of the SiC substrate, the last plane of carbon may be located under a last silicon plane 124, the last silicon plane 124 being between the graphene layer 123 and the last carbon plan 122.
• the initial structure 1201 may comprise, as announced above, a surface layer 121 of SiC present on a substrate 120 of any other material compatible with the manufacture of the surface layer 121 of SiC.
• the substrate 120 is also SiC. There is then no difference between the surface layer 121 and the substrate 120.
• the hydrogenation carried out in this embodiment of the process according to the invention imposes on the initial structure 1201 a dose of exposure to hydrogen gas of between 1500 Langmuirs and 2500 Langmuirs, for example 2000 Langmuirs or 2200 Langmuirs, or greater at 2500 Langmuirs.
• the dose can go up to 4000 Langmuirs or 5000 Langmuirs.
• the exposure doses allowing an identical result vary.
• the structure whose gap is measured in FIG. 7A was obtained with the frame CEA Grenoble cited above and an exposure dose of 2200 Langmuirs.
• the structure whose gap was measured from FIG. 7C was, as previously announced, obtained with the aforementioned SOLEIL frame, with an exposure dose of 500 Langmuirs. There is therefore a factor close to 4.4 between the effect of the doses of these two frames.
• FIGS. 6B and 7D The structure illustrated in FIGS. 6B and 7D was obtained by means of a method according to the invention with an exposure dose of 1000 Langmuirs, in the SOLEIL frame, at a pressure of 10 ⁇ 6 Pa. This means that relatively at CEA, it would be necessary to have an exposure dose of 4400 Langmuirs.
• modified graphene By further increasing the dose, with a pressure between approximately 10 ⁇ 5 Pa at 10 ⁇ 8 Pa, it is possible to obtain the formation of other layers of modified graphene, for example fourth and fifth layers of graphene from carbon planes of the Sic substrate. Part of the modified graphene layers are then semiconductors within the meaning of the invention.
• the above-mentioned annealing 126 may be a hydrogenation annealing and / or a post-hydrogenation annealing. It can therefore be carried out respectively during the hydrogenation and / or following it.
• the annealing (s) have a temperature of between 200 ° C. and 400 ° C., preferably between 250 ° C. and 350 ° C. and in particular close to 300 ° C.
• the post-hydrogenation annealing if it takes place, preferably has a duration of a few minutes, for example between one minute and 20 minutes, preferably five minutes. It may, for example, take place in an oven or in the reaction chamber where the hydrogenation took place.
• a new carbon plane and a new silicon plane are defined as the last carbon plane and the last silicon plane.
• a third modified graphene layer is then formed on a substrate 1201 having at least one surface layer 121, 129 in SiC and at the surface of which a new carbon plane and a new silicon plane are defined as being the last plane of carbon. and the last plane of silicon.
• a hydrogenation at low pressure between 10 ⁇ 5 Pa at 10 ⁇ 8 Pa, preferably comprising or followed a hydrogenation annealing and / or a post hydrogenation annealing as described above, it It is possible to observe with increasing exposure doses a cycle of the hydrogenation of a layer of graphene.
• the initial graphene layer acquires a quasi-metallic behavior.
• the new gap-modified graphene layer that also evolves as a function of a second cycle of the hydrogenation of a graphene layer, similar to the first cycle.
• the second cycle of the hydrogenation of a graphene layer has exposure dose values, calculated from the formation of the new modified graphene layer that may be different from the exposure dose values of the first one. cycle.
• a third layer of modified graphene may be formed before the end of the second cycle mentioned above.
• the third layer of modified graphene also has a gap that changes with a third cycle of the hydrogenation of a graphene layer similar to the second cycle.
• the exposure dose values calculated from the formation of the third layer of graphene may be different from those of the second cycle. This can occur many times by further increasing the dose, the layers of graphene farthest from the substrate getting all the quasi-metallic behavior, and new layers of graphene being formed, initially at zero gap, then in graphene semiconductor as the exposure dose increases.
• the first advantageous mode of the invention aims to obtain a semiconductor graphene layer forming a gap in an initial graphene layer, following the first cycle of the hydrogenation of a graphene layer.
• the second advantageous mode of the method according to the invention aims to obtain a semiconductor graphene layer by creating one or more new layers of modified graphene. This is then at least one of the new layers of modified graphene which is in semiconductor graphene.
• the initial graphene layer being disoriented by 30 ° to the substrate, this means that there is a new layer of graphene.
• the double layer of modified graphene therefore has a low energy electron diffraction structure, which does not have a 6A / 3X6A / 3 satellite.
• the double layer is thus again quasi-metallic, or zero-gap semiconductor. This is very interesting because it is very difficult to make a double layer of uniform graphene on a large surface.
• the new modified graphene layer 123 has an interface with the new SiC surface layer 129 substantially free of defects. Indeed, since the new modified graphene layer 123 'comes from the last carbon plane 122 of the surface layer 121, there is an almost perfect alignment between a crystal lattice characteristic of the new modified graphene layer 123' and a network crystalline characteristic of the new surface layer 129.
• the first advantageous mode of the method for manufacturing a structure comprising a modified graphene layer present on a substrate can also be used with an imperfect initial structure as illustrated in FIG. 10, reproducing an STM observation of such a structure.
• the method according to the invention can be applied. Si substrate surface defects do not cause any mobility reduction in standard epitaxial graphene, nor in a modified graphene layer. It is not these defects that can be critical.
• critical defects 102 are likely to be present. These defects can be in particular electron traps. They reduce the mobility of electrons in the standard graphene layer by means of dangling bonds. They can include carbon nanotube tips or carbon chains with pendant bonds that create interface states that deform the Dirac cone shape of the valence band of the standard epitaxial graphene layer. This situation is generally quite frequent at the interface between a substrate and a graphene layer obtained according to conventional methods.
• Another possible application of the first advantageous mode of the method according to the invention is to choose an initial structure 800 in which the standard graphene layer 82 has undergone, previously to the hydrogenation step according to the invention, an oxidation so as to open the gap of the standard graphene layer 82.
• an oxidation so as to open the gap of the standard graphene layer 82.
• the application of the process according to the invention to such an initial structure 800 makes it possible to modify the opening of the gap obtained by the oxidation step and to passivate the electron traps.
• the modified graphene layer 83 is then such that the dispersion of the electronic states is rectilinear and the modified graphene layer 83 thus has the mobility of a standard graphene layer 82 without defects.
• the initial structure 800 of a method according to the invention may comprise several superimposed layers of modified epitaxial graphene 83. After application of the method according to the invention, it is observed that the gap is open and has a value close to 0.95 eV.
• the second embodiment makes it possible to obtain a modified graphene layer and makes it possible to passivate a majority of critical defects that may be present between the initial graphene layer and the surface layer. from Sic.
• the valence band finds a Dirac cone shape.
• FIGS. 13A to 13C the inventors propose a third embodiment of the method according to the invention, illustrated in FIGS. 13A to 13C.
• the method according to the invention in its first and second advantageous modes, requires providing an initial structure comprising at least one substrate on which is present, on the surface, an initial epitaxial graphene layer.
• the inventors propose the third advantageous mode of the process according to the invention making it possible to do without this necessity in order to obtain a structure comprising a semiconductor modified graphene layer.
• a starting structure 1301 comprising at least one silicon carbide layer Sic and having no initial epitaxial graphene layer.
• the silicon carbide layer may be silicon-faced or carbon-faced SiC, as shown in FIG. 13A.
• This layer may be in itself an autonomous substrate or may be a surface layer 131 present on a substrate 120 made of another material, for example silicon.
• On a free surface of this layer are present two last atomic planes: a last plane of carbon 132 and a last silicon plane 134.
• the last atomic plane is respectively the last carbon plane 132 or the last silicon plane 134.
• a hydrogenation 135 and a heat treatment 136 are carried out under operating conditions similar to the second advantageous mode of a method according to the invention described above (FIG. 13B).
• the hydrogenation is preferably carried out with a hydrogen gas exposure dose of between 1500 Langmuirs and 2500 Langmuirs or greater than 2500 Langmuirs, for example 2000 Langmuirs or 2200 Langmuirs or 3000 Langmuirs. These values are to be considered under the conditions of pressures of 10 ⁇ 7 Pa in the experimental building of the CEA.
• those skilled in the art will have to make adjustments to the aforementioned values and for example use an exposure dose of up to 4000 Langmuirs or 5000 Langmuirs.
• the aforementioned heat treatment 136 may be a hydrogenation annealing and / or a post-hydrogenation annealing. It can therefore be carried out during the hydrogenation and / or as a result thereof.
• the annealing or annealing has a temperature between 200 ° C and 400 ° C, preferably between 250 ° C and 350 ° and in particular close to 300 ° C, and have a duration of a few minutes, for example between one minute and 20 minutes, advantageously five minutes. They can for example take place in an oven.
• added hydrogen atoms H penetrate under the last carbon plane 132, forming a buffer plane of added hydrogen atoms H and decoupling the last carbon plane of the superficial layer 131.
• the atoms of hydrogen can evacuate or disorganize part of the last silicon plane 138.
• This modified graphene layer 123 being on the surface behaves as if the graphene was substantially doped p.
• an initial SiC substrate which does not comprise an initial graphene layer at the surface
• a hydrogenation step makes it possible to decouple the last carbon plane from the SiC surface to form a graphene monolayer modified electronically decoupled from the substrate.
• This increase of the exposure dose can be made during the hydrogenation step of the third advantageous mode or can be carried out in an additional step.
• the doses of exposure to hydrogen that must then be used are to be evaluated according to the frame and the pressures used.

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