Method and device for producing a layer, substrate provided therewith and its use

Abstract

Process for producing a layer on a substrate by metal-organic vapor phase epitaxy, which comprises at least one compound of the formula M 1 a SC 1-a Containing or consisting of N, where M 1 is selected from Al or Ga or In and 0.01 ≤ 1-a ≤ 0.295, characterized in that a precursor containing scandium is used with a molar flow (ṅ) of at least 10 -6 mol / min into a reaction chamber (1) for metal-organic vapor phase epitaxy, in which the precursor is present in a bubbler (2) whose temperature is between 120°C and 200°C, wherein the precursor contains or consists of a cyclopentadiene, and the cyclopentadiene contains scandium.

Description

The invention relates to a method for producing a layer on a substrate by metalorganic vapor phase epitaxy (MOCVD or MOVPE) which contains or consists of at least one compound of empirical formula M 1a Sc 1-a N, wherein M 1 is selected from Al or Ga or In and Sc is scandium and 0.01≤1-a≤0.295 is selected. The invention further relates to a layer produced by this method, to a wafer having this layer, to the use of this layer in various components and to an apparatus for producing such layers.Components based on AlScN are considered to be the next generation of power electronics or optoelectronics. With AlScN in combination with further heteroepitaxially deposited binary or ternary Group 13 nitrides, high electron mobility transistors (HEMT) with high power, higher cut-off frequency and / or high efficiency can be obtained.According to the prior art, AlScN layers can be produced by means of sputtering. However, the crystal quality of these layers is not sufficient for electronic applications. Since no smooth surfaces are obtained, no semiconductor heterostructures with defined boundary surfaces can be produced, so that no transistors or LED structures can be produced.Alternatively, the prior art discloses to produce Al a Sc 1-a N by means of molecular beam epitaxy (MBE). With this method, high Sc contents in the ternary compound can be obtained. The crystal quality is also sufficiently good for the production of microelectronic components. However, the method is complicated and not suitable for producing large amounts of the material for the mass market. The productivity in this method is too low, so that it cannot be used industrially. Although the method has become established in research and development, the growth rates for industrial processes are too slow.Saidi, C., et al.: "Growth of Scandium-doped GaN by MOVPE". Superlattices and Microstructures, 60, 2013, 120-128 describe the growth of scandium-doped GaN by MOVPE. Furthermore, Kieske, Daniel David, et al. (Sandia Report, 2009) describe the production of ScGaN and YGaN layers by MOCVD. However, according to the teaching of both publications, only an Sc content of about 1·10 18 at. / cm 3 is achieved. These known layers are Sc-doped GaN and not a ternary Al a Sc 1-a N compound.Chinese Patent Publication CN 108899403 A mentions the production of ScAlN / AlGaN-based p-doped multilayer systems for LEDs by MOCVD. However, the patent specification does not contain any technical teaching that can be revised. The only embodiment disclosed in the figures uses In x Ga 1-x N / Al z Ga 1-z N superlattices as semiconductor active layers. Process parameters which could be used for the production of Al a Sc 1-a N-layers are not described in this Chinese patent publication in a manner which can be revised by the person skilled in the art.From J. Wang et al.: Study of Defects in GaN In Situ doped with Eu 3+ Ion Grown by OMVPE. Journal of Electronic Materials, Vol. 45 No. 4, 2016 discloses doping an epitaxially deposited layer of GaN with Eu. This resulted in defects with activation energies of 0.108 eV, 0.287 eV and 0.485 eV.D. D. Kolske et al.: Issues Associated with the Metalorganic Chemical Vapor Deposition of ScGaN and YGaN Alloys, Sandia Report SAND2009-4419, July 2009, discloses the potential of ScGaN and YGaN for producing optoelectronic components. However, these alloys could not be produced. Only a slight doping of GaN with scandium or yttrium was achieved in each case.From the laid-open specification CN 101 736 400 A a method for growing a crystalline thin film based on GaN is known. The method is characterized in that trimethylborine or trimethylaluminium is proportionally doped in a starting material formula of the GaN crystal film, and boron or aluminium is incorporated as trivalent ions into the GaN crystal lattice.In "Metal-Organic Chemical Vapor Deposition of Aluminum Scandium Nitride", St. Leone et al., Phys. Status Solidi RRL 2020, 14, 1900535, the deposition of aluminum scandium nitride by means of MOCVD is described.Starting from the prior art, the object of the present invention is thus to specify a reproducible production process for high-quality M 1a Sc 1-a N layers which is suitable for industrial production and with which ternary or quaternary compounds or alloys and not just a doping of a binary or ternary compound are obtained. Furthermore, a device suitable for this purpose is intended to be provided.The object is achieved according to the invention by a method according to claim 1, a substrate having at least one layer according to claim 11, a use according to claim 13 and a device according to claim 14. Advantageous further developments of the invention are found in the dependent claims.According to the invention, a method for producing a layer on a substrate by organometallic vapor phase epitaxy is proposed, wherein the layer contains or consists of at least one compound of empirical formula M 1a SC 1-a N, wherein M 1 is selected from Al or Ga or In and 0.01≤1-a<0.295, and a precursor is fed with a molar flow of at least 10 -6 mol / min into a reaction chamber (1) for organometallic vapor phase epitaxy, which contains or consists of Sc.For the purposes of the present description, an element of group 13 denotes an element of the boron group or of the earth metals, i.e. in particular Ga, In and / or Al. The numbering of the groups of the periodic table is carried out in the present description with Arabic numerals 1 to 18 and thus follows the valid IUPAC convention.According to the invention, it has been recognized that by means of a molar flow of more than about 10 -6 mol / min of the precursor containing Sc, high crystal quality layers with a high Sc content of (1-a) >0.01 or >0.05 or >0.1 or >0.2 can be obtained by means of MOCVD. The at least one precursor containing Sc may be solid or liquid. It can have a vapor pressure of less than or equal to 0.1 mmHg or 0.13 mbar at room temperature.Metal organic vapor phase epitaxy (hereinafter also referred to as MOCVD) is an epitaxy method for forming crystalline layers. Organometallic compounds can be used as starting materials (precursors) for scandium in the layers. These organometallic compounds may, in some embodiments of the invention, be supplied from bubbles which correspond in structure to gas scrubbing bottles. In the bubbler, a saturated vapor forms over the liquid or the solid. If a carrier gas flows through the bubbler, the organometallic compound is transported into the reaction chamber, in which deposition on a substrate then takes place. The carrier gas can be selected from hydrogen or nitrogen or an inert gas, for example a noble gas.The determination of the molar flux ṅ of the precursor containing Sc can be made by the following formula:Here, Vb denotes the flow of the carrier gas, p sc the partial pressure of the scandium, p total the total pressure inside the nebulizer, T the temperature of the nebulizer and R the universal gas constant. The temperature T of the bubbler and the flow Vb of the carrier gas can be measured or controlled by associated regulating devices. The total pressure p total can be measured, for example, by a capacitive manometer or a spring manometer. The partial pressure p sc of the scandium can be determined from the temperature T of the bubbler if the vapor pressure curve is known or has been determined for the precursor used. The determination of the vapor pressure curve can be carried out in a manner known per se or approximately data of a similar compound can be used.In some embodiments, the layer produced according to the invention may further comprise a metal M 3 which is different from M 1 and is selected from the group 3rd or the group 13th of the periodic table, such that the layer comprises or consists of at least one compound of the empirical formula M 1a M 3b SC 1-a-b N, wherein M 1 is selected from Al or Ga or In and Sc is scandium and 0.705≤a<0.99 is selected and 0.705≤b<0.99 is selected, wherein 0.01≤1-a-b≤0.295. For example, this layer can contain or consist of InGaScN.The substrates used for the process according to the invention may be any substrates suitable for the uses indicated above and below. Examples thereof are sapphire, silicon and / or silicon carbide. Upon deposition of the layer, the substrate may be heated, for example, to a temperature of about 700° C. to about 1400° C. In other embodiments, the substrate may be heated to a temperature of about 900° C. to about 1300° C. In still other embodiments, the substrate may be heated to a temperature of about 700° C. to about 1300° C. In other further embodiments, the substrate may be heated to a temperature of about 1000° C. to about 1300° CWith the MOCVD, epitaxial layers of high crystalline quality can also be produced on wafers or substrates having a large diameter of more than 50 mm or more than 75 mm or more than 100 mm or more than 150 mm. M 1a SC 1-a N, for example AlScN, can be generated with a growth rate of about 0.02 nm / s to about 0.15 nm / s or of about 0.01 nm / s to about 0.5 nm / s. A complete HEMT structure can be produced by the method of the invention in about 2.5 h to about 4 h or in about 2.75 h to about 3.5 h, in contrast to the known MBE method which requires about 7 h to about 8 h. However, unlike sputter deposition, high quality layers can be formed. The quality of the layers produced can be determined by the line width of the Bragg reflections in the omega scan, which can be between about 0.01 ° and about 0.3 0 or between about 0.03° and about 0.07° FWHM for the layers produced according to the invention.The deposition can be carried out homoepitaxially or heteroepitaxially using the method proposed according to the invention. In particular, it is also possible to produce multilayer systems or superlattices from layers of different composition which each contain or consist of a different binary or ternary or quaternary compound of at least one element of group 13 and nitrogen. In some embodiments of the invention, multilayers bz. Heterojunctions contain at least two different compounds, each crystallizing in wurtzite structure and having different band gap energy. For example, multilayers of GaN / AlScN or InGaN / AlScN or AlGaN / AlScN can be produced, at the interfaces of which a two-dimensional electron gas can form.In some embodiments of the invention, it is possible to grow the layers in a reaction chamber on multiple substrates in parallel. This allows the throughput to be increased.In some embodiments of the invention, the pressure in the reaction chamber during the deposition of the layer according to the invention, which contains or consists of M 1a M 3b SC 1-a-b N or M 1a Sc 1-a N, can be between about 40 mbar and about 150 mbar.In some embodiments of the invention, the parameter a may be selected such that 0.7 ≤ a ≤ 0.95. In other embodiments of the invention, the parameter a can be selected such that the following applies: 0.7≤a≤0.9. In yet other embodiments of the invention, the parameter a can be selected such that the following applies: 0.8≤a≤0.95. correspondingly high contents of Sc are achieved by the method according to the invention, which are of particular importance for modern performance or optoelectronics.According to the invention, M is 1 selected from aluminum or indium or gallium. The method according to the invention is thus suitable for producing corresponding layers or multilayer systems for optical or power electronics. Examples of the compounds of the formula M 1a SC 1-a N are ScN, Al a Sc 1-a N and Ga a Sc 1-a N, where a is selected as above.In one embodiment, the layer as defined above is an alloy. This makes it clear that it differs from those known layers in which the constituent Sc represents only one doping. Both the above Saidi et al. and Kolske et al. publications which studied the epitaxial growth of GaScN by MOCVD, only doping and no alloy could be obtained. Further, the layer may be an epitaxial layer. The layer material is thus substantially monocrystalline, unlike layers which have been produced by the sputtering process and are therefore polycrystalline.According to the invention, scandium is used as precursor for Sc, which is coordinated with two or more cyclopentadienyl rings (Cp), for example Cp 3 S C. One or more of the cyclopentadienyl rings may be substituted with C1-C5 alkyl groups, especially methyl or n-butyl. These precursors have the advantage of a higher vapor pressure over analogous molecules in which the metal atoms are coordinated with alkyl compounds such as methyl or ethyl. By substitution with the above C1-C5 alkyl group, the vapor pressure is increased. Cp 3 Sc or the corresponding methyl-substituted cyclopentadienyl (MeCp) 3 Sc are particularly suitable for Sc.The elements M 1 and N present in the layer can be introduced into the reaction chamber for the MOCVD method in a manner known per se. For example, the precursor for nitrogen can be selected from ammonia, hydrazine, phenylhydrazine, dimethylhydrazine or tertiarybutylamine. Examples of M 1 are Al and Ga, so that the precursors known per se, trimethylaluminum or triethylaluminum or trimethylgallium and triethylgallium, can be used. The handling of these precursors is known to the person skilled in the art, for example from the production of AlGaN, GaN and AlN layers by means of MOCVD methods.In some embodiments of the invention, the bubbler containing the precursor for Sc is heated to a temperature of about 120° C. to about 200° C., or about 150° C. to about 200° C., or about 150° C. to about 175° C. In this way, the molar flux of more than 10 -6 mol / min can be achieved, thereby making it possible to incorporate the correspondingly large amounts of Sc into the layer.For carrying out the MOCVD process, the bubbler in which the precursors are contained is connected by a line to the reaction chamber in which the deposition of the layer on a substrate takes place. In one embodiment of the process according to the invention, the temperature of this line is adjusted to about 120° C. to about 200° C., or about 150° C. to about 200° C., or about 150° C. to about 175° C., or about 120° C. to about 160° C. The temperature of the conduit may be adjusted to correspond to the temperature in the bubbler with a deviation from +0°C to +10°C or from +0°C to +5°C.In some embodiments of the invention, the pressure in the line may be set to more than 0.15 bar, or to about 0.15 bar to about 0.3 bar, or to about 0.17 bar to about 0.26 bar. The process according to the invention can thus be operated in a particularly advantageous manner and particularly advantageous layers can be produced.The present invention further relates to a layer as can be produced by the method according to the invention, in particular a layer of this type on a substrate or wafer and / or as part of a multilayer system or a semiconductor heterostructure. It can be determined by X-ray structure analysis that the layer obtainable according to the invention is different from layers as obtained by the sputtering method. The layers according to the invention can be used for electronic or optoelectronic components, for example as active layers of HEMT, LED, optical detectors or semiconductor lasers.An MOVCD reactor is generally equipped with mass flow controllers, pressure controllers, valves and / or gas injection systems which enable precise control of the quantity of gas supplied to the reaction chamber of the precursors and thus ensure high reproducibility of the epitaxial growth process. No components are currently known which withstand temperatures above 70° C. Since the bubbler and optionally the corresponding conduit for the precursor for Sc can be heated to a temperature of about 120° C. to about 200° C., or about 150° C. to about 200° C., or about 150° C. to about 175° C., or about 120° C. to about 160° C., known components cannot be used. According to the invention, it is therefore proposed to use mechanical or pneumatic valves which do not have any electronic components which are impaired by high temperatures.The present invention further provides an apparatus for producing a layer which comprises or consists of M 1a SC 1-a N, where M 1, Sc and a are as defined above in connection with the process according to the invention. The apparatus for producing at least one layer by means of MOCVD contains at least one reaction chamber and at least one heatable substrate holder for receiving the substrate to be coated, and furthermore contains at least one bubbleer, which is connected to the reaction chamber via a line, wherein furthermore a heating device is present, with which the bubbleer (2) and the line (3) can be heated to more than 140° C.According to the invention, the line further comprises a pressure measuring device. The pressure measuring device can be used to control the pressure of the precursor in the line and, if appropriate, to adjust it by regulating the carrier gas flow.In one embodiment, the conduit further includes an optional check valve. The check valve prevents contamination by reflux of other gases, for example carrier gas and other precursors, into the line or the bubbler for the precursor for Sc.The invention is explained in more detail below with reference to figures without limiting the general concept of the invention. This shows FIG. 1 shows an exemplary structure of a layer system obtainable using the method according to the invention FIG. 2 shows a SIMS analysis of an Al a Sc 1-a N layer grown on a GaN / Al 2 O 3- wafer, wherein the parameter a=0.705. FIG. 3 shows an optical microscopy image of an Al 0,775 Sc 0,225 N epitaxial layer. FIG. 4 shows an optical microscopy image of an Al 0,8 Sc 0,2 N epitaxial layer. FIG. 5 shows an AFM analysis of a Ga 0,999 SC 0,001 N epitaxial layer:Area 10 x 10 μm 2 with RMS=0.33 nm (right);Area 2 x 2 μm 2 with RMS=0.15 nm (left). FIG. 6 shows an AFM analysis of an Al 0,887 Sc 0,113 N epitaxial layer:Area 10 x 10 μm 2 with RMS=0.33 nm (right);Area 2 x 2 μm 2 with RMS=0.32 nm (left). FIG. 7 shows an HRXRD analysis of a 300 nm thick Al 0,8 SC 0,2 N epitaxial layer deposited on a GaN / Al 2 O 3- substrate. Fig. 8 shows a block diagram of a device according to the invention. FIG. 9 shows a source according to the invention in a second embodiment, which can generate a molar flow (ṅ) of at least 10 -6 mol / min for a precursor.FIG. 1 shows an exemplary structure of a layer system obtainable using the method according to the invention.The layer system is deposited on a wafer or a substrate 20, which contains sapphire, for example. In other embodiments of the invention, silicon carbide or sapphire, or AlN or GaN or other material may be used.An optional nucleation layer 21 is then produced by means of MOCVD, which contains or consists of GaN and can optionally be doped with iron. The nucleation layer can have a thickness of approximately 2 μm.A buffer layer 22 follows, which may also contain or consist of GaN. The buffer layer may have a thickness of about 200 nm or about 20 nm to about 50 nm.Finally, an optional heteroepitaxial layer 23 is provided which contains or consists of AlN. The layer 24 according to the invention is then produced, which contains or consists of Al a Sc 1-a N, has a thickness of about 20 nm and whose content of scandium is selected to be (1-a)>0.01 or (1-a)>0.05 or (1-a)>0.1 or (1-a)>0.2. The heteroepitaxial layer 23 and the layer 24 according to the invention each have a wurtzite structure, but different band gap energies.The termination is formed by a cap layer 25, which in turn can contain GaN or AlN or Si 3 N 4. The cap layer may have a thickness of about 3 nm or from about 0.1 nm to about 10 nm.The layer system illustrated with reference to FIG. 1 is to be understood merely as an example. Of course, modifications are possible which result from the present application. Thus, individual layers or all layers can be provided with optional dopants in order to obtain a predeterminable electrical conductivity. In addition, further layers may be inserted, which are not shown in FIG. 1, or some of the layers shown may also be omitted.To produce quantum well structures, the layer sequence of the layers 23 and 24 can be repeated a number of times, for example between in each case 1 and in each case approximately 10 to approximately 20 or approximately 15 to approximately 30 or approximately 20 to approximately 50 layers 23 and 24 can be deposited alternately one above the other.Finally, other materials may be chosen. For example, layer 24 may also contain GaScN or InGaScN instead of AlScN. GaN or AlGaN can also be selected for the layer 23. The example shown in FIG. 1 is intended merely to illustrate the basic idea of the invention.Using an apparatus described below in connection with Fig. 7, the following examples were carried out, the results of which are illustrated in Figs. 2 to 6.Epitaxial growth experiments were performed to deposit Al a Sc 1-a N- or Ga a Sc 1-a N-layers in a multi-wafer MOCVD reactor with either 4" (101.6 mm) diameter sapphire or silicon carbide substrates. The typical structure consisted of a 1.5 μm GaN epitaxial layer on sapphire, followed by a 50-150 nm thick AlScN or GaScN layer which was finally coated with a few nm thick AlN or GaN layer.In other embodiments, Al a Sc 1-a N layers were deposited directly on a 50 nm thick GaN layer deposited on an Al 2 O 3- substrate to perform high resolution X-ray diffraction analysis. The HRXRD measurements were performed with a Cu radiation source and a two-beam Ge(220) monochromator, which provides monochromatic Cu-Kα1radiation. The diffracted X-ray radiation was analyzed using a triaxial Ge(220) analyzer.In the following embodiments, epitaxial growth of Al a Sc 1-a N and Ga a Sc 1-a N is shown. Various epitaxial growth parameters such as temperature, pressure, ratio of the molar flow of the precursor for nitrogen to the molar flow of the precursors for Al and Sc were studied. The composition of the AlScN layers was analyzed by secondary ion mass spectrometry (SIMS), using O 2+- or Cs +- ions with 5 keV energy as the primary ion beam, to identify various atoms (Sc, Al, Ga, N, C, O,... ) in the epitaxial layers. To assess the morphology of these layers, optical microscopy with Nomarski differential interference contrast (NDIC) and atomic force microscopy in tapping mode (AFM) was used.1. Exemplary EmbodimentIn a first exemplary embodiment, a layer system was produced according to the basic principle illustrated with reference to FIG. 1. The layer system contains a nucleation layer 21 containing GaN, a buffer layer 22, a heteroepitaxial layer 23 containing AlN, a layer 24 according to the invention containing Al a Sc 1-a N and a cap layer 25 which in turn contains AlN. In the table below, the manufacturing conditions for the nucleation layer and the first part of the buffer layer are not given. For the other layers, the growth time for the respective layer, the substrate temperature, the total pressure in the reaction chamber and the molar flow of the precursors of metal organics (MO, the precursors for Ga or Al), Cp 3 Sc (Sc) and NH 3 are given in the table below.GaN (22)05:0011802001.67E-0403, 57E-01AlN(23)03:001000402.28E-0501.52E-02AlScN (24)01:30:001000404, 87E-063.60E-061, 52E-02AlN(25)03:001000402.28E-0501.52E-02In Fig. 2, the result of a SIMS measurement is calculated on the above-mentioned. This is shown in the drawing as a layer system. The layer according to the invention has an Sc content of 29.5%, i.e. the layer contains Al 0,705 Sc 0,295 N. This concentration has not yet been obtained by means of MOCVD and it is clear that the method and apparatus according to the invention have succeeded in generating a high molar flow of Cp 3 Sc and introducing it into the MOCVD reactor. As a result, epitaxial growth of AlScN by means of MOCVD is shown for the first time.2. Exemplary EmbodimentIn a second exemplary embodiment, a layer system was produced according to the basic principle illustrated with reference to FIG. 1. The layer system contains at least one nucleation layer 21 and a buffer layer 22, each containing GaN, a heteroepitaxial layer 23 containing AlN, a layer 24 according to the invention containing Al 0,775 Sc 0,225 N and a cap layer 25, which in turn contains AlN. In the table below, the manufacturing conditions for the nucleation layer and the first part of the buffer layer are not given. The table below gives the growth time for the respective layer, the substrate temperature, the total pressure in the reaction chamber and the molar flow of the precursors organometallics (MO), Cp 3 Sc (Sc) and NH 3.GaN (22)05:0011802001.67E-0403, 57E-01AlN (23)03:001000401, 55E-0501.52E-02AlScN (24)02:00:001000404,87E-062, 49E-061.52E-02AlN (25)03:001000401, 55E-0501.52E-02FIG. 3 shows the result of an optical microscopy on the layer thus obtained. It is evident that, with an Sc content of 22.5% (Al 0,775 Sc 0,225 N), a crack-free layer having a thickness above 100 nm could be deposited.3. Exemplary EmbodimentIn a third exemplary embodiment, a layer system was produced according to the basic principle illustrated with reference to FIG. 1. The layer system contains a nucleation layer 21 and a buffer layer 22, each containing GaN, a heteroepitaxial layer 23 containing AlN, a layer 24 according to the invention containing Al 0,8 Sc 0,2 N and a cap layer 25, which in turn contains GaN. In the table below, the manufacturing conditions for the nucleation layer and the first part of the buffer layer are not given. The table below gives the growth time for the respective layer, the substrate temperature, the total pressure in the reaction chamber and the molar flow of the precursors organometallics (MO), Cp 3 Sc (Sc) and NH 3.GaN:Fe (21)20:0011802001.67E-0403, 57E-01GaN (22)40:0011802001.67E-0403, 57E-01AlN (23)00:301000402.28E-0504.90E-02AlScN (24)23:001000404,87E-063, 60E-064.90E-02GaN (25)00:201000404,18E-0501, 78E-01FIG. 4 shows the result of an optical microscopy on the layer thus obtained. It is evident that, at an Sc content of 20% (Al 0,8 Sc 0,2 N), a crack-free layer having a thickness above 100 nm could be deposited.4. Embodiment Not According to the InventionIn a fourth exemplary embodiment not according to the invention, a layer system was produced according to the basic principle illustrated with reference to FIG. 1. The layer system includes at least a nucleation layer 21 and a buffer layer 22 each containing GaN (only the second part of the buffer layer 22 is shown in the table below), a heteroepitaxial layer 23 containing AlN and a layer 24 containing Ga a Sc 1-a N with a=0.999. The growth time for the respective layer, the substrate temperature, the total pressure in the reaction chamber and the molar flow of the precursors metal organics (MO), Cp 3 Sc (Sc) and NH 3. are given.GaN (22)05:0011802001.67E-0403, 57E-01AlN (23)02:001000402.28E-0501.52E-02GaScN (24)02:00:001000401.67E-053, 60E-064.90E-02In FIG. 5, the result of an AFM measurement is shown. The measurement yields an RMS roughness of 0.33 nm over an area of 10 μm x 10 μm. On a smaller area of area 2 x 2 μm 2 the RMS roughness is only 0.15 nm. The measurements confirm the high crystal quality of the layer thus obtained. The composition of the layer 24 is Ga 0,999 Sc 0,001 N.5. Exemplary EmbodimentIn a fifth exemplary embodiment, a layer system was produced according to the basic principle illustrated with reference to FIG. 1. The nucleation layer 21 contains AlN. The buffer layer 22, the heteroepitaxial layer 23, and the cap layer 25 are omitted in this example. The following table shows the growth conditions for the nucleation layer 21 containing AlN and a layer 24 according to the invention containing Al 0,887 Sc 0,113 N. The growth time for the respective layer, the substrate temperature, the total pressure in the reaction chamber and the molar flow of the precursors metal organics (MO), Cp 3 Sc (Sc) and NH 3. are given in each case.AlN (21)01:301000402.28E-0501.52E-02AlScN (24)01:30:001000404,87E-061,68E-061.52E-02The result of an AFM measurement is shown in FIG. 6. The measurement yields an RMS roughness of 0.33 nm over an area of 10 μm x 10 μm. On a smaller area of area 2 x 2 μm 2 the RMS roughness is 0.32 nm. The measurements confirm the high crystal quality of the layer thus obtained. The composition of the layer 24 according to the invention is Al 0,887 Sc 0,113 N.6. Exemplary EmbodimentIn a sixth exemplary embodiment, a layer system was produced on an Al 2 O 3- substrate according to the basic principle illustrated with reference to FIG. 1. The nucleation layer 21 contains GaN. The following table shows the growth conditions for the buffer layer 22, the heteroepitaxial layer 23, the layer 24 of the present invention containing Al 0,8 Sc 0,2 N, the cap layer 25 containing GaN. In the exemplary embodiment shown, the buffer layer 22 is composed of two layers, the sub-layer lying closer to the substrate being doped with iron. The growth time for the respective layer, the substrate temperature, the total pressure in the reaction chamber and the molar flow of the precursors metal organics (MO), Cp 3 Sc (Sc) and NH 3. are given in each case. In the production of the Al 0,8 Sc 0,2 N layer, pulsed growth is used, i.e. the sources Al and Sc are alternately opened and closed, so that scandium is initially introduced for 5 s and aluminum is subsequently introduced for 2 s, the sequence being repeated cyclically until the layer thickness of 12 nm is reached.GaN:Fe (22)20:0011802001.67E-0403, 57E-01GaN (22)40:0011802001.67E-0403, 57E-01AlN (23)00:301000402.28E-0504.90E-02AlScN (24)23:001000404,87E-063, 60E-064.90E-02GaN (25)00:201000404,18E-0501.78E-01On the 12 nm Al 0,8 Sc 0,2 N layer 24 thus obtained, HRXRD (High Resolution X-ray Diffraction) measurement was performed, the result of which is shown in FIG. 7. The phase analysis shows that pure Al 0,8 Sc 0,2 N was deposited in wurtzite structure with high crystal quality. This is indicated by the presence of thin AlScN layer thickness edges for the reflection region 0002, 0004 and 0006.To analyze the lattice parameter of the AlScN layer, reciprocal spatial imaging measurements (RSMs) of the 0002 and 1124 reflection regions were performed on the same sample. The estimated lattice parameters for the AlScN layer 24 are a=138.21 pm and c= 498.80 pm and for the GaN buffer layer 22 a=138.21 pm and c=159.14 pm. The identical lattice parameter a of the AlScN layer and the GaN buffer layer demonstrates that pseudomorphic growth was achieved for the AlScN layer by MOCVD. In addition, both the RSMs of the 0002 and 1124 reflection regions exhibit well resolved thickness boundaries which confirm the high structural quality of the AlScN layer.As can be seen from the exemplary embodiments, the method according to the invention can be used to enable successful epitaxial growth of Al a Sc 1-a N- and Ga a Sc 1-a N-layers with 0.705<a<0.999 with high crystalline quality and good morphology. This makes it possible to produce HEMT structures or optoelectronic components (emitters and detectors) with increased performance compared to previously nitride-based electronics.FIG. 8 schematically shows an apparatus according to the invention. The method according to the invention is also explained in more detail again with reference to this device. The explanation of the device and the method is carried out by way of example on the connection Al a Sc 1-a N. The preparation of other compounds can be carried out in an analogous manner. It is expressly pointed out that individual process conditions explained here should not be understood as being suitable for carrying out the method according to the invention only in conjunction with the other process conditions.The device according to the invention has a reaction chamber 1. The reaction chamber can have a wall made of an aluminum alloy or a stainless steel. The reaction chamber 1 can be gas-tight in order to evacuate it by means of a vacuum pump, not shown. The reaction chamber can have a cover or an opening, not shown, so that the reaction chamber can be quickly discharged and loaded with new substrates after the production process is completed.In the reaction chamber 1 there is at least one substrate holder 17, which is provided for receiving at least one substrate 20. The substrate holder 17 can have a heating device with which the substrate can be heated to a temperature of from about 700° C. to about 1400° C., or from about 900° C. to about 1300° C., or from about 700° C. to about 1300° C., or from about 1000° C. to about 1300° C. The substrate holder 17 can be configured to move or rotate the substrate in the reaction chamber 1 in order to thus enable a uniform layer structure of the epitaxial layer. In some embodiments of the invention, the substrate holder may be configured to receive a plurality of substrates.Furthermore, at least one gas inlet 18 is located in the reaction chamber 1, In various embodiments of the invention, the gas inlet 18 can have different designs, for example a vertical and / or a horizontal arrangement of nozzles. According to the invention, it is proposed to provide the gas inlet 18 with a heating device 185, so that the latter can be heated during operation to a temperature of more than 80° C. or more than 90° C. more than 110° C. The heating device 185 can contain an induction heater or a resistance heater or a heat transfer medium can flow through the gas inlet 18, which heat transfer medium is kept at a predeterminable temperature in a thermostatically controlled manner. The heat transfer medium can be selected from water and / or glycol or an oil.Gaseous precursors are supplied to the gas inlet 18 via a collecting line 13. In the collecting line 13 there may be a changeover valve which is designed to connect all or some lines for supplying the precursors temporarily to an exhaust line 10 and temporarily to the gas inlet 18. For example, the precursor can be discharged from the bubbler 2 as exhaust gas through the exhaust gas line 10 if, due to the layer structure, scandium is not necessary, because a layer containing no scandium is just being produced in the reaction chamber 1.The device according to the invention has at least one bubbler 15 known per se, in which at least one organometallic compound, for example trimethylgallium (TMGa) or trimethylaluminium (TMAl), is located during operation of the device. The structure of the bubbler 15 corresponds to that of a gas scrubbing bottle, i.e. a saturated vapor forms above the solid or liquid precursor, which vapor is discharged from the bubbler 15 by a carrier gas and transported into the reaction chamber 1.The carrier gas may be an active gas or an inert gas. In some embodiments, hydrogen or nitrogen may be used. The carrier gas may be supplied at a flow rate of from about 0.01 slm to about 3 slm or from about 5 slm to about 10 slm. The flow of carrier gas can be kept constant by means of a second mass flow controller 14.The bubbler 15 is in contact with a heating or cooling device 19 which may contain, for example, a water or oil bath, the temperature of which is controlled to a predeterminable desired value. Typical set points of temperature are between about -5°C and about 50°C. For TMGa temperatures from -5°C to 20°C are common. For other precursors, for example for Al or In, the typical temperature is 10° C. to 20° C. For dopants such as Mg or Fe, a temperature of 15° C. to 50° C. can be chosen.The molar flow of precursor supplied to the reaction chamber via the line 16 can be influenced by the temperature of the heating or cooling device 19 and the quantity of carrier gas. In addition, the pressure in the line 16 may be controlled by an electronic pressure regulator.In the same manner as described above, a plurality of similar blowers 15 with associated mass flow controllers and lines may be provided to supply different precursors for the component M 1 or M 3 simultaneously or sequentially.In addition, ammonia can be supplied to the reaction chamber as a precursor for nitrogen in gaseous form via a first mass flow controller 12 and the line 11. In addition, hydrogen and / or nitrogen can be introduced into the reaction chamber as a carrier gas or as a flushing gas.The device according to the invention further comprises a bubbler 2 which is connected via a line 3 to the reaction chamber 1 in which the MOCVD deposition takes place. In the illustrated embodiment, the bubbler 2 contains 3 Sc as a precursor for the Sc content in the layer to be grown. However, other precursors for Sc may also be included in the bubbler 2, as described above.The bubbler 2 has a heating device 4, for example an electrical resistance heater, an induction heater or a water or oil bath. With this heater, the temperature in the bubbler 2 can be controlled and adjusted, thereby achieving the molar flow of 10 -6 mol / min or more for the precursor. In some embodiments of the invention, the temperature in the bubbler 2 is about 120° C. to about 200° C., or about 150° C. to about 200° C., or about 150° C. to about 175° C., or about 120° C. to about 160° C.A carrier gas, for example hydrogen or nitrogen or a noble gas, is introduced into the bubbler 2 via a feed line 7. The amount of carrier gas is between about 1 slm and about 6 slm (standard litres per minute, the following applying in SI units). The amount of carrier gas can be controlled by a third mass flow controller 8. The pressure of the carrier gas in the supply line 7 can be about 1 bar. The carrier gas is introduced into the precursor-having nebulizer 2 through the supply line 7, so that the precursor is discharged from the nebulizer 2 through the line 3 and introduced into the reaction chamber 1.According to the invention, it is proposed to provide the line 3 with a first tube-accompanying heater 9 and optionally also the supply line 7 with a second tube-accompanying heater 7, which bring the respective lines to an elevated temperature. For this purpose, for example, an induction heater or a resistance heater can be used. A resistance heater may comprise a heating wire parallel to the line and / or heat a metallic line by direct current flow. The line 3 and the supply line 7 can be brought to a temperature which corresponds approximately to the temperature of the bubbler 2 or which is selected to be higher by approximately 10° C. The first tube accompanying heater 9 can optionally also heat the pressure measuring device 5 and the optional nonreturn valve 6.A pressure measuring device 5 can be present in the line 3, with which the total pressure in the line 3 and thus within the bubbler is determined. The pressure measuring device 5 can be a gas-type-independent pressure measuring device, for example a capacitive manometer or a spring manometer. The pressure in the line 3 and thus in the bubbler 2 can be about 0.15 bar to 0.3 bar or 0.17 bar to 0.26 bar.Furthermore, the line 3 can have an optional nonreturn valve 6, with which it can be ensured that other gases, for example carrier gas and other precursors, do not flow back from the reaction chamber 1 into the line 3. Such a check valve 6 can be a mechanical valve which, in contrast to electronic pressure regulators, also operates without faults at elevated temperatures up to 150° C. or up to 200° C.According to the invention, it has been found that the molar flux ṅ of the precursor which contains Sc can be determined by the following formula:Here, Vb denotes the flow of the carrier gas H 2, p sc the partial pressure of the scandium, p total the measured total pressure within the nebulizer, T the temperature of the nebulizer and R the universal gas constant. The temperature T of the bubbler and the flow Vb of the carrier gas can be controlled by associated control devices 8 and 4. The partial pressure p sc of the scandium can be determined from the temperature T of the bubbler if the vapor pressure curve is known or has been determined for the precursor used. The determination of the vapor pressure curve can be carried out in a manner known per se or approximately data of a similar compound can be used, for example (MeCp) 3 Y.The device according to the invention thus enables for the first time the operation of a bubbler at temperatures of more than 50° C. without damaging the pressure regulator or mass flow regulator due to occurring overtemperatures. As a result, precursors with low vapor pressure can also be used for the first time in an MOCVD method.FIG. 9 shows a source according to the invention in a second embodiment, which can generate a molar flow (ṅ) of at least 10 -6 mol / min for a precursor. Identical components of the invention are provided with identical reference numerals, so that the following description is limited to the essential differences.As can be seen from Figure 9, the source of precursor for Sc consists of a plurality of bubbles which are simultaneously operated in parallel. In the example shown, two blowers 2 aand 2 bare present, which are supplied with carrier gas via their own supply line 7 aand 7 band their own associated mass flow controllers 8 aand 8 b. A separate temperature control via the heating devices 4 aand 4 ballows precise control of the molar flow of the precursor delivered in each case.In some embodiments of the invention, the number of parallel-operated blowers can also be greater than 2 and between 2 and about 15, or between 2 and about 10, or between 2 and 6.In order to reduce the complexity of the apparatus, in some embodiments components of a plurality of blowers can be used, for example a plurality of blowers 2 aand 2 bmay also be located in a single heating device 4 or may be supplied with carrier gas by only one supply line 7.Of course, the invention is not limited to the embodiments shown in the figures. The foregoing description is, therefore, not to be considered as limiting, but illustrative. The following claims are to be understood as providing a said feature in at least one embodiment of the invention. This does not exclude the presence of further features. If the description or the claims define "first" and "second" features, this serves to distinguish similar features without specifying a ranking.

Claims

A method for producing a layer on a substrate by organometallic vapor phase epitaxy which contains or consists of at least one compound of the formula M 1a SC 1-a N, wherein M 1 is selected from Al or Ga or In and is selected from 0.01 ≤ 1-a ≤ 0.295, characterized in that a precursor which contains scandium is fed into a reaction chamber (1) for organometallic vapor phase epitaxy with a molar flow (ṅ) of at least 10 -6 mol / min, by the precursor being present in a bubbler (2) whose temperature is between 120°C and 200°C, wherein the precursor contains or consists of a cyclopentadiene, and the cyclopentadiene contains scandium.Method according to claim 1, characterised in that a carrier gas flows through the bubbler (2) containing the cyclopentadiene at a flow rate of 5 slm to 10 slm.Method according to one of Claims 1 to 2, characterized in that a multilayer system is deposited heteroepitaxially, which contains at least one single layer of the composition M 1a SC 1-a N and at least one single layer of a binary or ternary Group 13 nitride, wherein a two-dimensional electron gas is formed or can be formed at its interface.Process according to any one of Claims 1 to 3, characterized in that the cyclopentadiene of the precursor is substituted by a C1 to C5 alkyl.Method according to one of Claims 1 to 4, characterized in that the pressure in the reaction chamber (1) is between 40 mbar and 150 mbar.Method according to one of Claims 1 to 5, characterized in that the substrate has a temperature of 700°C to 1400°C or of 900°C to 1300°C or of 700°C to 1300°C or of 1000°C to 1300°C.Process according to any of Claims 1 to 6, characterized in that the cyclopentadiene which comprises scandium is present in a bubbler (2) whose temperature is 150°C to 200°C or 150°C to 175°C or 120°C to 160°C.Method according to one of Claims 1 to 7, characterized in that the bubbler (2) is connected to the reaction chamber (1) via a line (3), the difference between the temperature of the line (3) and the temperature of the bubbler (2) corresponding to +0°C to +10°C.Method according to claim 8, characterised in that the pressure in the line (3) is 0.15 bar to 0.3 bar or 0.17 bar to 0.26 bar.Method according to one of Claims 1 to 9, characterized in that a carrier gas having a temperature of 90°C to 200°C or of 120°C to 200°C or of 150°C to 200°C or of 150°C to 175°C or of 120°C to 160°C is fed to the bubbler.Substrate having at least one heteroepitaxial layer (23) and at least one layer (24) which contains or consists of at least one compound of the formula M 1a SC 1-a N, wherein M 1 is selected from Al or Ga or In and is selected from 0.01 ≤ 1-a ≤ 0.295, wherein a graded transition layer having a thickness of 10 nm to 20 nm is present between the heteroepitaxial layer (23) and the layer (24).Substrate according to Claim 11, characterized in that the layer 24 furthermore contains a metal M 3 which is different from M 1 and is selected from the 3rd group or the 13th group of the periodic table, such that the layer contains or consists of at least one compound of the empirical formula M 1a M 3b SC 1-a-b N, where 0.705 ≤ a ≤ 0.99 and 0.705 < b ≤ 0.99 is selected and 0.01 ≤ 1-a-b ≤ 0.295 applies.Use of the substrate according to one of Claims 11 or 12 for producing an optoelectronic component and / or an electronic component and / or an acousto-optical and / or acousto-electronic component.Device for producing at least one layer by means of MOCVD, comprising at least one reaction chamber (1) and at least one heatable substrate holder (17) for receiving the substrate (20) to be coated and at least one gas inlet (18), characterized in that the device further comprises at least one bubbler (2) which is connected to the reaction chamber via a line (3), wherein a heating device is furthermore present, by means of which the bubbler (2) and the line (3) can be heated to 120°C to 200°C, and at least one pressure measuring device is present, by means of which the pressure in the line (3) can be determined, wherein the bubbler is connected to a feed line (7) through which a carrier gas can be fed, wherein a mass flow controller (8) is present in the feed line (7).Device according to claim 14, characterised in that the bubbler (2) and the line (3) can be heated to 150°C to 200°C or 150°C to 175°C or 120°C to 160°C.Device according to claim 14 or 15, characterised in that the supply line (7) can be heated between the mass flow regulator (8) and the inlet to the bubbler (2).Device according to one of Claims 14 to 16, characterized in that the gas inlet (18) can be heated.Device according to one of Claims 14 to 17, characterized in that it contains a plurality of parallel blowers (2) which each have a heating device with which the blower (2) can be heated to 120°C to 200°C or 150°C to 200°C or 150°C to 175°C or 120°C to 160°C.Device according to claim 18, characterised in that the plurality of parallel blowers (2) is between 2 and 15 or between 2 and 10 or between 2 and 6.

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