EP2313897A1

EP2313897A1 - Semiconductor-based magnetic material

Info

Publication number: EP2313897A1
Application number: EP09800114A
Authority: EP
Inventors: Pascal Pochet; Emmanuel Arras
Original assignee: Commissariat a lEnergie Atomique CEA; Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2008-07-22
Filing date: 2009-07-21
Publication date: 2011-04-27
Also published as: FR2934412B1; US20110186948A1; WO2010010250A1; FR2934412A1

Abstract

Magnetic material based on at least one magnetic 3d transition metal element and at least one Group IVA semiconductor element, this material being homogeneous and having a Curie temperature (Tc) of 350 K or higher. Method for the production and uses thereof, especially in spintronics.

Description

SEMICONDUCTOR MAGNETIC MATERIAL

The subject of the invention is a novel magnetic material based on at least one magnetic 3d transition metal element and at least one semiconductor element of the group (IVA), chosen from among germanium, silicon and their alloys, this material being homogeneous, crystalline, and having a Curie temperature (Tc) equal to or greater than 350 K. It also relates to a process for its production and uses, especially in spintronics. The diamond structure of this material also offers many possibilities for the co-integration of magnetic functions (magnetic sensors, magnetic memories, etc.) in conventional microelectronics. According to a preferred embodiment, the invention relates to the synthesis of a homogeneous magnetic material based on germanium and manganese, magnetic above ambient temperature.

The injection into a semiconductor of a spin-polarized carrier current, which is characterized by an excess of one of the two carrier populations present (for example that of spin-up or spin-up), has recently is the subject of several publications. By way of example, mention may be made of the electronic components described in the article Datta and Das, Applied Physics Letters, 56, 665, 1990 and in Vutic et al., Reviews of Modem Physics, Volume 76, 323, April 2004. ).

The implementation of this injection of a spin polarized current is of great interest in microelectronics, but its development is hampered by the lack of suitable materials to constitute the current injection electrode.

Indeed, if the usual ferromagnetic metals, such as iron and many of its alloys, have some of the required qualities such as a high spin polarization and a ferromagnetic behavior at room temperature, their electrical resistance is several orders of magnitude different from that of the semiconductors, which generates great implementation difficulties and requires tunneling current injection (see A. Fert and H. Jaffres, Physical Review B 64, 184420). This has the disadvantage of requiring the growth of a difficult hybrid hetero-structure to achieve, of the semiconductor / tunnel-effect barrier / ferromagnetic metal type. In contrast, there exist so-called diluted magnetic semiconductors (abbreviated DMS in English, for "Diluted Magnetic Semiconductors") which do not have the disadvantage of having a resistivity very different from that of ordinary semiconductors. These DMS typically consist of a semiconductor matrix of groups III-V, IV or II-VI in which are diluted magnetic impurities such as manganese, iron, chromium, cobalt, vanadium or nickel.

In the case of a dilution of manganese, which is an acceptor in the semiconductor III-V or IV ₅ charge carriers are constituted by holes. When the concentration of manganese and the density of holes (naturally created by the presence of manganese or voluntarily introduced by co-doping) are sufficiently high in the

DMS, the latter can become ferromagnetic and the exchange coupling between manganese ions is induced by the holes. The first synthesized ferromagnetic DMS was

InMnAs 1992 (H. Ohno et al, Phys Rev. Lett 68, 2664 (1992)). Since then, many other ferromagnetic DMS have been manufactured such as GaMnAs (H. Ohno et al,

Science 281, 951 (1998)), ZnMnTe (D. Ferrand et al., Phys Rev. B 63, 085201 (2001)), ZnCrTe (H. Saito et al, Phys Rev. Lett 90, 207202 ( 2003)) or GaMnN (ML Reed et al, Appl Phys Lett 79, 3473 (2001)).

A major disadvantage of these DMS is that they all presently have a Curie temperature Tc (temperature up to which the semiconductor has ferromagnetic properties) less than or equal to the ambient temperature (typically <

About 300 K). For example, see K. K. Edmonds et al., Phys.

Rev. Lett. 92, 037201, 2004, which discloses a semiconductor of formula GaMnAs having a Curie temperature of only about 159 K, and to the article H. Saito et al., Phys. Rev. Lett. 90, 207202, 2003, which describes DMS corresponding to the formula Zm- _x Cr _x Te and having a Curie temperature substantially equal to 300 K (± 10 K), when x =

0.20.

Another disadvantage of these DMS lies in the undesirable but frequent formation of small ferromagnetic metal precipitates within the semiconductor matrix, which does not plead in favor of truly ferromagnetic properties for these DMS and makes the crystal growth step very difficult to achieve.

It should further be noted that the use of these materials based on gallium or tellurium is very difficult to design on silicon substrates, the basic material of the microelectronics industry. Patent Application US Pat. No. 6,946,301 discloses a non-equilibrium thermal evaporative fabrication method of an amorphous ferromagnetic semiconductor of the GeMn type, which has a Curie temperature of up to 250 K, for a manganese d about 35%. The patent application US Pat. No. 6,307,241 teaches, in its sole exemplary embodiment, to manufacture a ferromagnetic semiconductor of type III-V (GaAs) with a Curie temperature Tc greater than 400 K, by the technique of ion implantation of manganese ions (Mn ⁺ ) followed by annealing. As is known to those skilled in the art (see in particular the article Magnetooptical Study of Mn ions Implanted in Ge, Franco D'Orazio et al., IEEE Transactions on Magnetics, Vol 38, No. 5, September 2002), it should be noted that this implantation technique is not adapted to the manufacture of magnetic materials based on a semiconductor element of group IVA (typically based on germanium) of Tc> 350 K, it being specified that the phase thus obtained, of type Ge ₃ Mn ₅ , has a Tc no more than 300 K.

A major disadvantage of these known magnetic semiconductors lies in their relatively low Curie temperature, which is generally limited to about 300 K. Moreover, when the measured Curie temperature is close to 300 K, it is difficult to exclude the presence of the Ge ₃ Mn ₅ metal phase, whose Curie temperature is precisely close to 300 K.

A solution recently proposed by Jamet et al. (Jamet et al., Nature Materials 5, 653-659, 2006, WO2007 / 090946) consists of synthesizing an alloy of germanium and manganese constituting a magnetic semiconductor having a Curie temperature higher than room temperature. This material is characterized by a spatial modulation of the manganese composition, a modulation that allows the appearance of the magnetic semiconductor phase in the manganese-rich regions. These manganese enriched regions do not have a composition similar to that of the known compounds of the phase diagram of the Ge-Mn binary alloy. They can then be used for a variety of spintronic applications. However, this spatial inhomogeneity, at the origin of the good properties of this material, also limits its implementation in devices that would rather require a homogeneous phase, such as for example an injection electrode of a spin polarized current, which is of great interest in microelectronics, or as the FET spin transistor, Qbit spin or MRAM type information storage devices. V. Ko et al, AIP Conf. Proc. 893, 1229 (2007) described a ferromagnetic compound with a Tc above 400 ° C DMS type and formula Si _o.75 Geo. ₂₅ with 8 and 12% of average Mn concentration obtained after Mn ⁺ ion implantation followed by annealing at 800 or 900 ° C. This material was found to be inhomogeneous and composed small precipitates ferromagnetic metal within the semiconductor die after analysis of samples by EXAFS and TEM (transmission electron microscopy) ( "Correlation of structural and magnetic properties of ferromagnetic Mn-implanted If _1- _x Ge _x film" Ko V. , et al., J. Appl Phys 103, 053912 (2008)). The same type of material was produced by implantation of Mn ⁺ in Si _x Ge _x for x varying from 0 to 0.5: the material obtained was also nonhomogeneous, with Mn ₄ Si ₇ metal precipitates for x 0.2 and of Mn ₇ Ge _{3 type} for x> 0.2 (see Ko, et al., J. Appl Phys 103, 053912 (2008)). The presence of these small metal precipitates within the semiconductor matrix does not make it possible to obtain truly ferromagnetic properties for these materials. US-5,296,048 discloses a semiconductor material belonging to the family of groups III-V or materials of group IV, which is associated with a transition element or a rare earth in an amount sufficient to impart to the material magnetic properties. The materials described herein are diluted semiconductors (DMS), when a Group IV material is employed, the magnetic element is present at a maximum concentration of less than 1%.

The document M. Bolduc et al, Physical Review B71, 033302 (2005) describes an Mn / Si material with a Curie temperature greater than 400K. The materials described in this document are diluted semiconductors (DMS), the magnetic element is present at a maximum concentration of less than 0.8%. E.S.Demidov et al, JETP Letters, Vol. 83, 25/08/06, 568-

It describes magnetic semiconductor materials based on Ge or Si and Mn or Fe. In these materials, the magnetic element is present at a concentration of between 13 and 15%. These materials are obtained by a method (laser ablation) distinct from that of the invention. And the resistivity values measured by the authors (between 10 ^"4 and 10 ^{" 6} Ohm.m) allow to assume the presence of metal precipitates.

The present invention proposes to prepare a new crystalline homogeneous magnetic material, in particular a dilute solid solution of Mn in Ge, which is not described in the equilibrium phase diagram (at atmospheric P, the Temperature / Concentration diagram). this material. Indeed, in the case of GeMn, the solubility limit of Mn in Ge is much lower than 0.1 at%. Beyond this limit one should obtain the precipitation of a phase rich in Mn (MnπGeg or Mn5Ge3) in a matrix of Ge. The material of the invention exists in a concentration range around 20-45 at. % of Mn. This concentration is lower than that of rich precipitates in Mn cited above (respectively 58 and 62.5 at.%). In the prior art, the embodiments relate to crystalline materials whose concentration of Mn is less than 15 at%. Furthermore, extensive analyzes of such materials (TEM) have revealed the precipitation of a second phase Mn] \ Ges or Mn5Ge3, these materials are therefore not homogeneous.

Crystalline materials, unlike amorphous materials, have a long-range order in their structure. The crystalline materials may be distinguished from amorphous materials by diffraction experiments X-rays ₅ for example on a solid material or a powder: a crystal gives rise to diffraction peaks spatially localized while a large bumps product amorphous compound . The first hump corresponds to the correlations between a given atom and its nearest neighbors, the second corresponds to the correlations between this atom and its nearest neighbors. The width of the bumps increases with the order of the neighbors, which means that the correlations become weaker and weaker: the local order for a given atom does not exceed the 5 ^th or 6 ^th neighbors. In addition to the aforementioned advantages, the material, insofar as it is crystalline, allows an epitaxial recovery for the crystalline layers that would subsequently be deposited on its surfaces to prepare complete electronic or spintronic devices, such recovery would be much more difficult to implement if the material was amorphous. Moreover, the crystalline structure of the material makes it possible to ensure a spin diffusion length, a key parameter in spintronics, which is large and comparatively higher than that expected in amorphous materials.

An object of the present invention is to provide a substantially homogeneous crystalline magnetic material which makes it possible to overcome the aforementioned drawbacks of both metals (the material of the invention has a resistivity of approximately 10 ^-3 Ohm.m, against less than 10 ^"7 Ohm.m for metals) and known DMS (the material of the invention has a Curie temperature greater than or equal to 350 K), and this goal is achieved using a magnetic material based at least one element of group IVA, preferably Ge and / or Si, comprising at least one transition element selected from the group consisting of manganese, iron, cobalt, nickel, vanadium and chromium, the properties of the material being obtained by stabilizing the transition element, in particular manganese, in the interstitial position of the diamond mesh. This position of the transition element, in particular manganese, in the semiconductor network is induced by the maintenance of the material under deformation during its preparation. Another object is to propose a magnetic material whose Tc is controllable, the Tc can go beyond the ambient temperature. In addition, according to a variant of the invention, it is possible to prepare a material comprising localized zones according to a predetermined pattern whose magnetism and Tc are controlled and different from those of the other parts of the material. The possibility of obtaining on the same device magnetic zones whose Tc can be different can also be exploited to produce a device whose response is a function of temperature, such as a flat magnetic memory for example.

For this purpose, a new synthetic process has been developed, this synthesis route making it possible to obtain a film of a homogeneous material, alloy of a semiconductor, advantageously germanium, and a transition element, advantageously manganese. this film being magnetic at room temperature and having properties comparable to those of the manganese enriched phase of the alloys produced by following the method described in WO2007 / 090946. This synthetic route makes it possible to obtain an alloy of germanium and of manganese, magnetic, in the form of a film of homogeneous composition. The synthesized material object of the invention is characterized by a high Curie temperature. When it is composed of Ge and Mn, its composition and structure are different from those of the known compounds of the phase diagram of the Ge-Mn binary alloy (Ge ₃ Mn ₅ or Ge ₈ Mn ₁ )). And in particular, the transition element is predominantly in the interstitial position in the crystal lattice of the semiconductor (diamond type mesh). A certain proportion of the transition element in the substitutional position is, however, necessary to obtain a magnetic material with non-zero resting magnetization. In addition, the Curie temperature of this material is controlled by the proportion of the transition element in the substitutional position (relative to the interstitial position) (see FIG.

I) -

In an alloy based on: on the one hand a crystalline material A and on the other hand an element B, the element B can occupy at least 2 different types of position in the network of A (see FIG. Ic). In the case presented, crystalline material A is germanium (Figure 1a), and element B is manganese. We can find the element B:

In substitutive position (figure Ib), each atom of B comes to take the place of an atom of A. It is about a form of classic alloy of substitution. But a classical alloy of a transition element such as Mn, in a semi- Conductor, such as Ge, does not make it possible to obtain Curie temperatures higher than the ambient temperature.

In the interstitial position (FIG. 1c), the mesh of the atoms A is conserved, and each atom of B is placed in the interstices of the crystal A (for example octahedral or tetrahedral sites in the case of the diamond mesh). This is a form of so-called insertion alloy. This type of alloy is normally observed with small B-elements, for example hydrogen, boron, carbon or nitrogen.

Advantageously, in the material of the invention, between 15 and 45% of the transition element is in substitutional position (relative to the total amount ^~~ of transition element), and preferably between 20 and 35%.

The magnetic material of the invention can be obtained by means of a novel process which comprises several variants and whose characteristics are as follows:

The method for manufacturing the magnetic material according to the invention comprises at least one molecular beam epitaxy step comprising a simultaneous deposition of at least one transition element selected from the group consisting of manganese, iron, cobalt, nickel, vanadium and chromium and at least one other element selected from group IVA of the periodic table, on a substrate selected according to criteria which are defined below. The temperature of the substrate during deposition is subject to adjustment.

However, this growth temperature is much lower than the growth temperatures of between 550 ° C. and 600 ^° C., which are commonly used in the epitaxy of Group IV semiconductor materials. This procedure makes it possible to stabilize metastable phases rich in magnetic elements such as manganese. The choice of the substrate constitutes an essential characteristic of the process of the invention. The substrate is advantageously constituted by a binary or ternary semiconductor alloy, possibly quaternary, with a diamond or zinc-blende structure (possibly of Wurtzite type). The atoms involved in the constitution of the substrate may in particular be chosen from the following elements: Al, In, Ga, As, Sb, P, C, Si, Ge.

Preferably, the substrate used to implement this process is based on one or more atoms selected from the group consisting of (In, Ga, As, Sb, P) or (Si, Ge, C) and alloys of these, for example: In _1-x Ga _x As, GaAs _1-x Sb _x , In _1-x Ga _x P, Si _1-x Ge _x , and x is a number such that

O ≤ x ≤ l or Sii- _xy Ge _x C _y and x and y represent numbers such that

O <x, O <y, O <x + y <1.

According to a first variant, the manufacturing method of the magnetic material according to the invention comprises at least one step of molecular beam epitaxy comprising a simultaneous deposition of at least one transition element selected from the group consisting of manganese, iron , cobalt, nickel, vanadium and chromium and at least one other element selected from group IVA of the periodic table, on a substrate whose mesh mismatch with the element (s) chosen in group IVA of the periodic table is between 0.1 and 10% in absolute value, and whose temperature during crystal growth is between 80 ° C and 200 ° C, preferably between 100 ° C and 150 ° C , leading to obtaining a thin layer of said group IVA semiconductor, in which are inserted the magnetic element (s) atoms.

The support is chosen so that its mesh parameter is 0.1 to 10% higher or lower than that of the semiconductor (element chosen in group IVA) used for the material of the invention. advantageously between 1 and 5%, and preferably between 2 and 4% when the group IVA element is Germanium and the transition element is Manganese.

The expansion or contraction of the substrate can be modulated to manage the relative stability of the interstitial defects with respect to the substituents as follows: In equilibrium germanium, out of stress, it is the substitutional position that is stable. To obtain the magnetic structure in germanium, which constitutes the material according to the invention, it is necessary to promote the formation of interstitials with respect to the substituents. The stabilization of such a structure is obtained in the Ge thanks to a dilation stress which stabilizes the interstitial with respect to the substitutional (mesh parameter of the upper substrate of 0.1 to 10% compared to that of the Ge). This constraint is obtained through the use of a substrate having a mesh parameter greater than that of Ge, in particular an expansion of 2 to 4%, and in particular of about 3%, gives good results. In silicon, the situation is reversed: it is the interstitial that is stable at equilibrium and the substitutional is less stable, it is therefore necessary to use a substrate for slightly contracting the silicon (substrate mesh parameter 0.1 to 10% lower than that of Si), and preferably a mesh parameter substrate 0.5 to 5% lower than that of Si.

In the case where the element of the group IVA is an alloy Si] _-x Ge _x , the same procedure is used for the choice of the substrate ie the interstitial is stabilized with respect to the substitutional, but without excess. For this purpose, a mesh parameter substrate smaller than that of the Si _1-x Ge _x alloy is used if the interstitial is stable at equilibrium and a mesh parameter substrate greater than that of the Si- ₁ alloy. _x Ge _x if the substitutional is stable at equilibrium. In the literature we find a theoretically established limit at about x <0.25 (x≈0.16) for this change in stability (Da Silva Phys Rev. B 70, 193205

(2004)).

When the element of group IVA is an alloy Si _1-x Ge _x with 0.25 <x <1, it is necessary to dilate using in the method of the invention a substrate with a mesh parameter greater than 0.1 to 10 % than that of Si _-x Ge _x so as to promote the interstitial position of the transition member and to obtain the material according to the invention.

When the element of group IVA is an alloy Sii _-x Ge _x with 0 <x <

0.16, it is necessary to contract using in the method of the invention a mesh parameter substrate 0.1 to 10% lower than that of Si _1-x Ge _x to reduce the stability of the interstitial compared to the substitutional and to obtain the material according to the invention.

The mesh parameter of a substitution alloy such as those used as substrates in the present invention can be calculated using methods well known to those skilled in the art and described in particular in a first approximation by the law of Végard which indicates that in the case of alloys in which there is miscibility throughout the concentration scale, the parameter of the elementary mesh of the alloy varies linearly between the respective parameters of the two pure compounds.

The mesh parameters of the various semiconductor alloys can be found for example on: http://www.ioffe.rssi.ru/SVA/NSM/Semicond/ or on: http://www.semiconductors.co.uk/ home.htm or in Semiconductor Materials,

Lev I. Berger, (CRC Press, Boca Raton, 1997) or in "Fundamentals of

Semiconductors, "Peter Y. Yu and Manuel Cardona, (Springer, 2005). When the group IVA element is an Si _1-x Ge _x alloy, as discussed above, either compression or expansion is chosen depending on the germanium x concentration.

A suitable substrate can be obtained easily in each case: it is possible to use a substrate of formula Si _1-2 Ge ₂ (whose mesh parameter varies from 5.43 to 5.66 Å for z increasing from 0 to 1). a substrate of formula Ini _y Ga _y P (whose lattice parameter varies from 5.44 to 5.86 Å for descending it from 1 to 0).

In a second embodiment, the manufacturing process of the magnetic material according to the invention comprises at least one epitaxy step by molecular beam ^"comprising simultaneous deposition of at least one transition element selected from the group consisting of manganese, iron, cobalt, nickel, vanadium and chromium and at least one other element selected from group IVA of the Periodic Table, on a substrate whose mesh mismatch with the element (s) chosen (s) ) in group IVA of the periodic table is less than 1% in absolute value, preferably less than 0.5%, and whose temperature during crystal growth is between 80 ° C and 200 ° C, preferably between 100 ° C and 150 ° C, leading to obtaining a thin layer of said group IVA semiconductor, in which are inserted the magnetic element (s) atoms (s).

This variant is used when the element of group IVA is an alloy Si _1-x Ge _x with 0.16 <x <0.25. Growth can then be made directly on a Si substrate _-y Ge _y with x ≈ y, as the relative stability compared to interstitials substitutional allows unconstrained to obtain the magnetic phase of the present invention material. However, a slight positive or negative constraint can be advantageously applied to favor the good ratio of substitutes with respect to the interstitials because it is this ratio which controls the curie temperature and the total magnetization of the structure.

The position of the atoms of the transition element with respect to the semiconductor network can be observed as a function of their concentration either by X-ray diffraction for concentrations greater than 10% by volume, or by EXAFS (for Extended X-Ray Absorption Fine Structure or X-ray absorption of fine structures) for all concentrations (but this method requires a synchrotron) or more simply by the RBS technique (for Rutherford Backscattering Spectrometry or Rutherford Backscattering Spectrometry) for all concentrations

The RBS technique involves examining the energy distribution of highly energetic He ⁺ ions (> 2 MeV) backscattered by the near-surface region of the sample. The composition and the depth distribution of the elements present in the sample can be deduced from it. Quantitative data of the crystallinity of the material can also be obtained.

More precisely, the so-called "channeling" technique can be used, an example of which is given in the following publication, which measures the rate of interstitials and substitutions in a GeMn network with nanocolumns: "Dopant segregation and giant magnetoresistance in manganese-doped germanium AP Li et al., Phys. Rev. B 75, 201201 (2007).

According to the prior art, it is accepted that in germanium, it is the substitutional position which is more stable than the interstitial position (for example Da Silva Phys Rev. B 70, 193205 (2004)). Moreover, it is also accepted that in the DMS, it is necessary to favor this position of substitution of Ge by Mn if it is desired to obtain a ferromagnetic compound (for example in GaMnAs: KM Yu et al, Phys Rev B 65 201303 (2002), AH MacDonald Nat Mat 4,195 (2005)). Finally, it is also admitted that in the DMS, the presence of the interstitials decreases and limits the curie temperature of the material (for example in GaMnN: KM Yu et al, Phys Rev B 65, 201303 (2002) AH MacDonald Nat Mat 4,195 (2005)). Also, the method and the material of the invention are contrary to the knowledge of those skilled in the art on DMS since it has been shown that by maximizing the concentration of manganese in the interstitial position, one obtains a magnetic material at room temperature. The manganese is stabilized in this position by the tension imposed by the substrate. Moreover, this method makes it possible to obtain a large value of the magnetization as shown in the curve of FIG. 3: the moment of the interstitial is always greater than that of the substitutional; it increases to its saturation value during the stretching of the mesh. On the other hand, to have a ferromagnetic coupling between these interstitial manganese, it is necessary to have a small proportion of manganese in substitutional position. In the structure obtained (Figure 1- d) interstitial manganese are second neighbors to each other, while substitutions are first neighbors of at least 2 interstitial manganese, which leads to a substitution ratio of about 20% compared to total of Mn. This implies that the tension applied for the stabilization of such a structure is obtained in Germanium thanks to a dilation stress which stabilizes the interstitial with respect to the substitutional (Figure 2). This constraint is obtained through the use of a substrate having a mismatch as previously described. However, this constraint should not be too great to also allow for the existence of a few manganese atoms in the substitutional position as described above. This last point explains why in silicon for which the interstitial position is stable out of stress, it is necessary to grow on a substrate compressing silicon in order to reduce the stability of the interstitial compared to the substitutional.

T0 ^{~ "~} The use of a compressive stress for stabilizing dilute magnetic semiconductors in silicon has recently been proposed by ZZ Zhang, et al. (" First-principles study of transition metal impurities in Si "Phys. B 77, 155201 (2008)) However, in this electronic structure calculation work, the objective of the constraint is to stabilize the manganese in the substitutional position and not in the interstitial position as in the present invention. to choose the optimal mesh mismatch between the substrate and silicon when it is used as element of group IVA: <4% for V, <-4% for Cr, <-2% for Mn, <-3% for Fe <-3% for Co and <-3% for Ni.

The key parameters in the process of the invention are:

The choice of the substrate (the expansion or contraction of the substrate with respect to the element of group IVA in the case of the first variant, or on the contrary the choice of a mesh parameter substrate that is substantially identical with respect to the group IVA element in the case of the second variant)

the flow of the group IVA element, advantageously germanium, and the flow of the transition element, advantageously manganese, during the deposition

(concentration),

the thickness of the deposition layer (as well as the possible Ge buffer layer), which is chosen so as to avoid the relaxation of the deposit,

the temperature of the substrate during the deposition.

The maximum deposition thickness to avoid a relaxation of the deposition of magnetic material depends on the composition of this material (choice of atoms and their proportions), its concentration and the expansion of the support. It can be determined using methods well known to those skilled in the art, such as the method de Matthews-Blakesîee, a description of which is given for example in F. Tinjod doctoral thesis UJF Grenoble 2003.

Advantageously, the atomic fraction of the element (s) magnetic (s) in the material is preferably between 15% and 60% relative to the entire material, preferably between 20 and 45% and results from the relative concentration of the magnetic elements and the elements of group IVA during the deposition: the deposition of the elements is done by using an average ratio [rate of deposition of the magnetic element (s) / speeds of deposition of the set of elements] which is between 15% and 60%, advantageously between 20 and 45%. Preferably, the at least one of the magnetic element (s) is manganese, chromium or vanadium and advantageously manganese.

Also preferentially, the other element (s) of Group IVA deposited simultaneously are germanium, silicon or one of their alloys.

Even more preferentially, the transition element and the element of group IVA deposited simultaneously are respectively manganese and germanium and / or silicon, for obtaining a magnetic material GeMn or SiMn or SiGeMn, or, in variant, of GeMnX, SiMnX or SiGeMnX type where X is a metal or an alloy of a metal that can be chosen for example from iron, cobalt, nickel, vanadium or chromium, preferably from chromium and vanadium . In the case where Ge is chosen as the semiconductor element and Mn as the transition element, a homogeneous layer of magnetic GeMn is obtained with the appropriate set of parameters above the ambient temperature with a manganese concentration that can go from 15 to 60%, advantageously from 20 to 45%. The thickness of GeMn is advantageously between 0.1 nm and 1 μm, preferably between 0.3 nm and 1 μm.

Advantageously, the method according to the invention further comprises a deposit on the substrate of a "buffer" layer of germanium, prior to the simultaneous deposition of germanium and manganese to obtain the thin layer, so as to obtain a surface as smooth as possible at the atomic scale for two-dimensional growth of the germanium-manganese film. In the case where the element of group IVA is Si or an alloy of Ge and Si, the buffer layer is respectively made of Si or the same Ge / Si alloy. And the thickness of the buffer layer, when such a layer is present, is calculated so as to avoid relaxation of the semiconductor. The person skilled in the art can rely on the method of Matthews-Blakeslee, a description of which is given, for example, in F. Tinjod PhD Thesis UJF Grenoble 2003, to calculate this maximum thickness.

In more detail, in the case where the transition element is manganese and the semiconductor is germanium, the synthesis of the magnetic material is carried out as in the case of the method of WO2007 / 090946 by Jets Epitaxy

Molecular (MBE) at low temperature. In this embodiment under ultra-vacuum, legermanium and manganese are evaporated from solid sources on a substrate.

The main difference with the method of the prior art comes from the choice of the substrate on which the growth by EJM is carried out. In the process of the invention, the crystal lattice mismatch between germanium and the substrate is essential. The substrate is thus chosen so as to have a mesh parameter several percent higher than that of germanium. It is possible to choose a substrate or support having a mesh parameter mismatch with respect to Germanium of between 1 and 7%, advantageously between 2 and 4%. For example, the compound (Ga _{1 -X} In _x ) As can be used as a substrate, the indium concentration fixing the mismatch of the mesh parameters: about -0.1% for x = 0 to about + 7% for x = l.

To a substrate (Gay _-x In _x) As, the disagreement (D) is given so as estimated by the formula:

D = 40 x / 5.66.

The growth procedure is carried out according to a standard method well known to those skilled in the art: a) deoxidation of the substrate or desorption of the protective layer to obtain a sufficiently "clean" surface to allow to carry out a 2D epitaxy next the rules of those skilled in the art (chemical cleaning, plasma treatment). b) application of a method which makes it possible, if necessary, to smooth the surface to be epitaxially treated and / or to make a diffusion barrier. It is possible, for example, to deposit a germanium buffer layer epitaxially with the substrate, of a sufficiently small thickness to avoid its relaxation, for example of a thickness between

0.1 nm and 100 nm This critical thickness depends on the mismatch according to the rules well known to those skilled in the art. c) deposition of a layer of GeMn on the Ge buffer layer implemented

Voltage by the substrate or directly onto the substrate in the absence of the buffer layer. The thickness of the layer is also controlled so as to remain below the critical relaxation thickness, and in particular it is between 0.1 nm and 1 μm. This thickness also depends on the initial mesh clash. The deposit of GeMn

^"TO ^~ is carried out at low temperature (<200 ⁰ C) with partial pressures of germanium and manganese in the flow at the substrate between, respectively, 0.8. ^10" and 8.10 ^"Torr and between 0.1.10 ^'9 and 100.10 ^"9 Torr. Thus, the deposition rate is of the order of 0.01 to 0.1 nm / s. The relative concentration of manganese is

Between about 15 and 60%, advantageously between 20 and 45%, depending on the respective ratio of the two partial pressures used. Under these growth conditions, the deposit is obtained in the form of a thin layer in which the manganese is distributed substantially homogeneously. In particular, manganese occupies interstitial positions of the germanium diamond mesh. This stabilization is favored by the voltage applied by the substrate during the growth of the layer. This material has a Curie temperature greater than 350 K. Neither its composition nor its structure resemble the known compounds of the GeMn phase diagram.

These modulations of the process parameters have of course

The effect of modifying both the thickness of the GeMn layer that can be envisaged without relaxation, the magnetization at rest of the material and its Curie temperature, while at the same time leading to the production of magnetic GeMn layers beyond the ambient temperature . By way of example, the evolution of the Curie temperature and the idle magnetization (relative to the manganese concentration) as a function of the relative concentration of the substituent relative to the total number of manganese atoms in germanium. The growth parameters can therefore be adjusted according to the applications to find the compromise between a high Curie temperature and a strong magnetization at rest. The operating point is determined by following the total concentration of manganese as well as the ratio of Mn substitutions / interstitials which can be for example measured by RBS.

The invention is based on the stabilization of manganese interstitial position of the diamond mesh of germanium. The rate of expansion to stabilize this interstitial position with respect to the substitutional position is defined from results of calculations based on the electronic structure of the solids and presented in FIG. 2. A stability inversion of about 1% is noted. of dilatation. Preferably, a margin of 1-2% is applied to ensure this stabilization in the samples prepared. In addition, the rate can be judiciously adjusted to obtain a compromise between the stability of these interstitials and the critical relaxation thickness of the Ge and GeMn buffer layers.

In more detail, the material of the invention is in the form of a film consisting of a crystalline homogeneous alloy of an element chosen from group IVA of the periodic table, advantageously germanium and a transition element, advantageously manganese. It has a Curie temperature (Tc) greater than or equal to 350 K. These very high values of Curie temperatures, which can be measured via a "SQUID" type magnetometer (ie "Superconducting Quantum Interference Device", or quantum energy detector with superconductors), have never been achieved to date for films of homogeneous Group IVA semiconductor compositions mixed with magnetic elements.

The magnetic material of the invention also has an extraordinary Hall effect ("EHE" abbreviated) at a temperature above 300 K and can reach at least 350 K.

These very high temperature values where this "EHE" effect is manifested, temperatures measured via a magneto-transport bench equipped with a cryostat and a superconducting coil, have never been reached to date for composition films. homogeneous group IVA semiconductors mixed with magnetic elements.

Compared to the materials described in WO2007 / 090946, the material of the invention is distinguished by its homogeneous nature. This characteristic can be observed in several ways: if two random samples are taken from the material and the concentration of the transition element is evaluated, it is within a range of values of + 5% around an average value. And a study of the material by X-ray diffraction shows that the atomic structure of the material is substantially homogeneous. Finally, the physical properties of the material (magnetization, conductivity, mesh parameter) are substantially identical at any point on the surface of the film of material: this homogeneity allows the injection of spins at any point on the surface of the material, which is not possible with the material described in WO2007 / 090946.

The homogeneity of the material has the advantage that the injection surface of the spins is larger. This spin injection function and its associated surface are important for applications such as the FET spin transistor or the Qbit spin. Similarly, if the material is used as a magnetic layer in a device ^'MRAM type information storage or in a spin valve, the ability to implement homogeneous film form is required, in particular at a possible stage of lithography. The advantage of such a material lies in its ability to be easily epitaxied on semiconductors (Si, Ge, ... diamond mesh) without introducing extensive defects. It also has the advantage of being able to be located via the stress transmitted by the substrate (processes' glued shot ^{1 in} particular) for example for the co-integration of magnetic functions (magnetic sensors, magnetic memories, etc.) in conventional microelectronics.

The material of the invention can be used for a variety of applications, either as a source of a spin polarized carrier current in silicon or germanium, or as a magnetic element in devices of the spin valve or tunnel junction type. magnetic, or conventionally as a magnetic region (easily localizable) source of a magnetic field for applications in high density magnetic recording. Devices using DMS and for which the materials of the invention could advantageously replace DMS are described in: Vutic et al., Reviews of Modem Physics, Volume 76, 323, April 2004.

Another object of the invention is a plate, also called "wafer" comprising a support as described above and at least one layer of a magnetic material of the invention. It optionally comprises an intermediate buffer layer as described above. This plate results from the implementation of the method of the invention and can be used in an electromagnetic device for the applications described above. In the case where this plate results from the application of the method of the invention on a support having a mesh parameter mismatch with the element of group IVA, two distinct configurations can be distinguished:

According to a first variant of this aspect of the invention, this support 5 has a constraint, or disagreement of mesh parameter with respect to the element of group IVA, which is constant. This results in a homogeneous deposit on the entire surface of this support.

According to a second variant, this support has a mesh parameter mismatch with respect to the element of group IVA, which varies according to a TU ^{~ "} predetermined pattern.Thus, the film is grown on a substrate having one or more areas where the stress (mesh parameter mismatch with respect to the semiconductor) is homogeneous and others where the stress is distributed inhomogeneously.This makes it possible to grow on a substrate zones of homogeneous magnetic film according to a predetermined pattern. To the devices described in WO2007 / 090946, the dimensions and the distribution of the magnetic film areas in the deposit are then controlled and not random.

According to this variant, if we denote by Rs the surface ratio of the areas where a stress is applied and the total surface area of the substrate, the total concentration of manganese can range from 15% xRs to 60% xRs and preferably from 20% xRs to

20 45% xRs. During the growth by EJM _3, the manganese is preferentially concentrated in line with the constrained zones according to the chosen scheme. The characteristics of the deposition in these zones are the same as those described for deposition on a uniform substrate.

And in particular, the total concentration of manganese in these zones is then preferably between 20 and 45% with a ratio of substitutionally preferably between 20 and

25 35%.

One well known way to obtain such a substrate is to use "glued turned" substrates which by creating a dislocation network make it possible to locate the quantum boxes whose growth is also sensitive to the deformation. This method is explained for example by A. Bourret. Surf. Sci. 432, p. 37, (1999).

Other methods of locating constraints are also possible: implantations, engravings, etc. In particular, one can refer to M. Hanbuckenet al, "Nanosciences: Nanotechnologies and Nanophysics", p. 50, Belin Edition by M. Lahmani, C. Dupas and P. Houdy (2004). This variant can be very interesting for the co-integration of magnetic functions (magnetic sensors, magnetic memories, etc.) in conventional microelectronics or for the production of different Tc zone plates according to a predetermined pattern.

An electronic component according to the invention may advantageously be of the diode type for the injection or the collection of spins in or from another semiconductor, respectively, or of a magnetic field-sensitive element type, and this component advantageously comprises a material magnetic device according to the invention as defined above.

^"1ii ^~ According to a first embodiment of the invention, ^it" is a diode-type component for injecting or collecting spins in or from another semiconductor e.g. Group IVA, such illustrated in Figure 4, and comprising:

a first thin layer (1) formed of a plate comprising a magnetic material according to the invention deposited on a substrate,

A second thin layer (2) formed of a semiconductor based on Group IV, III-V or II-VI elements or one of their alloys, in contact with which said first thin layer is applied; . If the first layer is p-doped, the production of an Esaki diode by adding a strongly doped layer n between the first and the second layer makes it possible to transform the polarized holes into polarized electrons (whose

Depolarization length is greater)

a carrier current source (3) coupled to the first layer for, in a first case, selectively extracting a spin polarized current and for injecting it into the second layer or, in a second case, for selectively extracting a stream of spin-polarized carriers from the second layer and inject it into the

First layer, so that the magnetic phase according to the invention of the first semiconductor emits or receives this spin-polarized current to or from the second semiconductor, respectively according to the first or second case. The fact that the material is not semiconductor but just bad conductor is enough to avoid depolarization. (A. Fert and H. Jaffres, Physical Review B 64, 184420).

According to a second embodiment of the invention, the component is sensitive to a magnetic field and it may be a magnetic field sensor, which comprises a thin layer formed of a magnetic material according to the invention such that defined above, for the detection or measurement of the said field by measuring a magnetoresistance to a magnetic field applied perpendicular to the thin layer or in the plane thereof.

It is noted that this component makes it possible to overcome the phenomenon of

"Super-paramagnetism" which characterizes diluted systems based on nanoparticles, and

5 that the magnetoresistance measured according to the invention remains high even at ambient temperature unlike these diluted systems, which gives this component according to the invention excellent capacity for measuring magnetic fields

A first use according to the invention of a magnetic material as defined above consists in injecting or collecting by contact a stream of spiral-polarized carriers in or from another semiconductor based on Si, Ge ₅ . .. (groups ^" IV, III-V, II-VI) or an alloy thereof, at a temperature equal to or greater than 350 K and which may be equal to or greater than 400 K.

A second use according to the invention of a magnetic material as defined above consists in measuring a magnetic field by measuring a magnetoresistance effect in said semiconductor, at a temperature equal to or greater than 350 K and able to be equal to or greater than 400 K.

Note that the magnetic material according to the invention can also be used as a magnetic element in spin valve type devices, or as a magnetized region source of a magnetic field for applications in high density magnetic recording. .

The magnetic material of the invention can also be used for the manufacture of a flat MRAM type magnetic memory (the stacking of the magnetic layers, is not vertical as in a conventional MRAM but they are deposited one to next to each other on a silicon-based conduction channel, for example), especially in the case where it has different Tc areas.

1: magnetic element Mn in the crystal lattice of germanium (a), in substitutional (b) and interstitial position (c) and arrangement of the phase according to the structure of the material of the invention (d)

Figure 2: Evolution of the formation energy of the two point defects

Elemental manganese in germanium (substitutional site, tetrahedral interstitial site) as a function of expansion with respect to the equilibrium mesh parameter of germanium. Figure 3: Evolution of the magnetic moment carried by the manganese as a function of the dilation with respect to the equilibrium mesh parameter of the germanium.

Figure 4: Schematic representation of a diode-like component for injecting spins into another semiconductor.

Figure 5: Evolution of the Curie temperature evaluated from the exchange integral as a function of the relative concentration of Mn substitution in GeMn for an interstitial manganese concentration fixed at 1/3 of the total number of atoms.

Claims

1. Magnetic material characterized in that it is in the form of a film consisting of a crystalline homogeneous alloy of a member selected from group IVA of the periodic table and a transition element selected from the group consisting of manganese, iron, cobalt, nickel, vanadium and chromium, the atomic fraction of the magnetic element (s) being between 20 and 45% relative to the entire material.

Material according to claim 1, wherein the transition element is manganese and the element selected from group IVA is germanium.

^"10 3. Material according to claim ^, wherein the thickness of GeMn is between 0.1 nm and 1 micron.

4. Material according to any one of claims 1 to 3 which is deposited on a substrate selected from compounds of the formula: In _1-x Ga _x As, GaAs _1-x Sb _x, In _1-x Ga _x P, If _1-X Ge _x 15 and x represents a number such that

O ≤ x ≤ 1 or Si _1-xy Ge _x C _y and x and y represent numbers such that 0 <x, 0 <y, 0 <x + y <1.

Material according to any one of claims 1 to 4, which has a Curie temperature (Tc) greater than or equal to 350 K.

6. Material according to any one of claims 1 to 5, which has an extraordinary Hall effect at a temperature greater than 300 K.

The material of any one of claims 1 to 6, wherein between 15 and 45% of the transition element is in substitutional position with respect to the total amount of transition element.

An electronic component comprising at least one layer of a material according to any one of claims 1 to 7.

The component of claim 8 of the diode type for injecting or collecting spins in or from another semiconductor.

10. Component according to claim 8 of the magnetic field sensor type.

11. A method of manufacturing a magnetic material according to any one of claims 1 to 7, comprising at least one step of molecular beam epitaxy comprising a simultaneous deposition of at least one transition element selected from the group consisting of manganese, iron, cobalt, nickel, vanadium and chromium and at least one other element selected from group IVA of the Periodic Table, on a substrate whose mesh mismatch with the element (s) ) selected from group IVA of the Periodic Table is between 0 ₅ and 10%, in absolute value, and whose temperature during crystal growth is between 80 ° C and 200 ° C.

The method of claim 11, wherein the group member

IVA of the Periodic Table is selected from Ge, Si and their alloys of formula Si ₁ _x Ge _x with 0 <x <0.16 and 0.25 <x <1.

A method according to any one of claims 11 and 12, wherein the group IVA element is Ge and the transition element is Mn the Ge mesh parameter mismatch with the support being between 2 and 4%

The method of claim 13 which comprises the steps of: a) deoxidizing the substrate or desorbing the protective layer; b) deposition of a Ge buffer layer, of a thickness between 0.1 nm and 100 nm; c) deposition of a layer of GeMn, the thickness of the layer being between 0.1 nm and 1 micron, the GeMn deposition being carried out at a temperature <200 ° C. with partial pressures of germanium and manganese in the flux at the substrate level between 0.8. 10 ^"8 and 8.10 ^{" 8} Torr for Ge and between 0.1.10 ^{~ 9} and ¹⁰⁰ OJ ^"9 Torr for Mn, and a relative concentration of manganese between 15 and

60%.

15. A method of manufacturing a magnetic material according to any one of claims 1 to 7, comprising at least one step of molecular beam epitaxy comprising a simultaneous deposition of at least one transition element selected from the group consisting of manganese, iron, cobalt, nickel, vanadium and chromium and at least one other element selected from the group IVA of the periodic table which is a Si alloy _-x Ge _x with 0.16 <x < 0.25 on a substrate whose mesh cleavage with the element (s) chosen in group IVA of the classification Periodic is less than 1% in absolute value, preferably less than 0.5%, and whose temperature during the growth of the crystals is between 80 ° C and 200 ° C, preferably between 100 ° C and 150 ° C.

16. A method according to any one of claims 11 to 15, wherein the substrate is made of a binary or ternary or optionally quaternary semiconductor alloy of diamond or zinc-blende structure.

17. The method of claim 16, wherein the atoms involved in the constitution of the substrate are chosen from the following elements:

Al, In, Ga, As, Sb, N, P, C, Si, Ge. (T ^"""18. A method according to any one of claims 11 to 17, wherein the deposition of the elements is done by using an average ratio [deposition rate of the one or member (s) Magnetic (s) / gear deposit of all elements] which is between 20 and 45%.

19. A plate obtainable by the process of any one of claims 11 to 18, comprising a substrate and at least one layer of a material according to any one of claims 1 to 7.

The plate of claim 19 wherein the substrate has a mesh parameter mismatch with respect to the group IVA element, and this mismatch is constant over its entire surface. 0

The plate of claim 19 wherein the substrate has a mesh parameter mismatch with respect to the group IVA element which varies according to a predetermined pattern.

22. Use of a material according to any one of claims 1 to 7 as a magnetic field source region of a magnetic field for applications in high density magnetic recording.

23. Use of a material according to any one of claims 1 to 7 for the manufacture of a flat magnetic memory.