Method for growing a bulk single crystal, bulk Ba2ScNbO6 single crystal, single-crystal Ba2ScNbO6 substrate, growth setup, (multi-)layer structure and its use

Abstract

A method for growing a bulk single crystal, comprising the following steps: - introducing a starting material into a crucible, - melting the starting material in the crucible by heating the starting material, - arranging a heat-insulating lid at a distance above a melting surface of the melt such that at least a central part of the melting surface is covered by the lid, and - growing the bulk single crystal from the melt from the crucible wall towards the central part of the crucible by controlling the cooling of the melt with the heat-insulating lid arranged above the melting surface.

Description

TECHNICAL AREA

[0001] The invention relates to a growing method and a growing setup for growing a bulk single crystal and their uses. BACKGROUND OF THE INVENTION

[0002] To fabricate electronic components, a stack of crystal layers is often grown layer by layer on a single-crystal substrate. To grow the crystal layers as epitaxial films with a well-defined crystallographic orientation relative to the single-crystal substrate, it is typically necessary that the lattice parameters of the substrate are compatible with the corresponding lattice parameters of the crystal layers.

[0003] To manufacture an electronic component, a suitable single-crystal substrate must therefore typically be selected which has a lattice parameter that approximately matches - e.g. with lattice matching better than 1% - the lattice parameters of the crystal layers to be grown on the substrate.

[0004] A widely used technique for growing bulk single crystals, from which single-crystal substrates can be produced, is the Czochralski method. In the Czochralski method, a starting material is melted in a crucible, and a seed crystal is immersed in the melt. To grow a bulk single crystal, the seed crystal is rotated and simultaneously slowly pulled upwards. This allows large bulk single crystals in the form of cylindrical blocks (ingots) or semiconductor bars (boules) of a semiconductor material to be grown and subsequently processed, for example, into substrates used in the electronics industry for the manufacture of electronic devices. However, the Czochralski method does not work for all materials. SUMMARY OF THE INVENTION

[0005] One objective of the invention is to provide an alternative method for growing a bulk single crystal and an alternative growth setup for growing a bulk single crystal.

[0006] Regarding the growth method, this goal is achieved through a process for growing a bulk single crystal, which includes the following steps. - Introducing a starting material into a crucible - Melting the starting material in the crucible by heating the starting material - Arranging a heat-insulating lid at a distance above a melting surface of the molten metal such that at least a central part of the melting surface is covered by the lid, and - Growing the volume single crystal from the melt by controlling the cooling of the melt with the heat-insulating lid arranged over the melt surface.

[0007] Of these process steps, the step "arranging a heat-insulating lid" can be performed before, during, or after melting the starting material. However, it is essential that the heat-insulating lid be placed over the melt during the growth of the bulk single crystal from the melt.

[0008] Within the scope of this invention, a volume single crystal is a single crystal with a volume of at least 5 mm × 5 mm × 5 mm (length × width × height).

[0009] The heat-insulating lid is designed to block thermal radiation emitted by at least the portion of the melt surface covered by the lid. Because the lid is positioned at a distance above the melt surface, the temperature distribution within the crucible can be influenced. By positioning the heat-insulating lid above the melt surface, it is therefore possible to control the temperature distribution within the melt.

[0010] The invention incorporates the understanding that the fabrication of electronic components typically requires single-crystal substrates with standard wafer sizes, e.g., 5 mm × 5 mm or 10 mm × 10 mm, or 1-inch, 2-inch, 3-inch, 4-inch, 6-inch, and 8-inch wafers, which are chemically stable, structurally compatible with the crystal layers to be grown on the substrate, and exhibit good structural quality. In particular, the requirement of good structural quality for the single-crystal substrate can be difficult to meet with certain substrate materials. However, good structural quality of the substrate is necessary to enable the growth of crystal layers with equally high crystal quality on it and thus prevent defects that would impair the functionality of the layer.

[0011] However, for various materials, no suitable single-crystal substrate with high structural quality is available. As a result, many materials with advantageous properties have not yet been used in the electronics industry. Indeed, the availability of suitable single-crystal substrates for the production of electronic devices often represents a significant bottleneck.

[0012] The inventive method for growing a bulk single crystal enables the growth of bulk single crystals with high structural quality, which have a size that allows the production of single crystal substrates in standard wafer sizes.

[0013] A particular advantage of this method is that it allows for the convenient growth of bulk single crystals that are not easily grown using the widely employed Czochralski method. Such bulk single crystals, which cannot be easily grown in a Czochralski process, such as oxide crystals exhibiting intense infrared absorption and very low thermal conductivity at high temperatures, typically suffer from growth instabilities such as diameter variations, foot formation, or lateral growth across the melt surface followed by spiraling shortly after seeding in a Czochralski process.

[0014] The inventive method for growing a bulk single crystal thus provides access to the production of single-crystal substrates from materials that were previously unavailable to the electronics industry in a suitable size and required structural quality. As an advantageous consequence of this invention, additional single-crystal substrates will become available on which crystal layers can be grown from materials for which the electronics industry previously had no structurally and chemically compatible substrate available.

[0015] This is achieved by positioning the heat-insulating lid at a distance above the melt to grow the bulk single crystal. By arranging the heat-insulating lid so that at least a central part of the melt surface is covered by the lid, thermal insulation is achieved that blocks the heat radiation emitted from the melt surface and thus influences and shapes the temperature distribution in the melt within the crucible. The heat-insulating lid allows the temperature distribution in the melt to be controlled during the growth of the bulk single crystal. By influencing the temperature distribution in the melt with the heat-insulating lid, a bulk single crystal with high structural quality and a size suitable for producing single-crystal substrates with standard wafer dimensions can be grown from the melt.

[0016] By positioning the heat-insulating lid during bulk single-crystal growth such that at least a central portion of the melt surface is covered by the lid, the bulk single-crystal grows towards the central part of the crucible. During controlled cooling of the melt, melt crystals germinate on the crucible wall, and grain selection and continuous grain enlargement progress as the growth front moves towards the central part of the crucible.

[0017] This growth behavior is in contrast to what is generally known and therefore expected for the growth of bulk single crystals using generally known growth methods - such as the widely used Czochralski method - in which the bulk single crystal grows from the central part of the crucible towards the crucible wall without touching it during the entire growth process.

[0018] Preferred variants of the method for growing a single crystal according to the invention are described below.

[0019] Preferably, the cooling of the melt is passively controlled by reducing the heat supplied by a heating element over a predefined period. For example, the power supplied to the heating element by a generator can be continuously or stepwise reduced over a predefined period so that the heat coupled into the crucible decreases. This causes the melt to cool, and the bulk single crystal grows from the crucible wall towards the central part of the crucible. The cooling rate of the melt is determined by the heat loss from the crucible and the melt over time, the material from which the crucible is made, the crucible geometry, the geometry of the heat-insulating lid, and the general thermal insulation close to the crucible. The predefined period over which the supplied heat is reduced can be, for example, 10 to 50 hours.

[0020] In addition to or as an alternative to passively controlled cooling of the melt, cooling can also be actively controlled. Active cooling can be achieved, for example, by directing an inert gas stream, such as an argon gas stream, onto the melt. Active cooling involves, for example, the use of a sensor in a feedback loop, such as a temperature sensor to measure the local temperature near the surface of the melt. The advantage is that active and automated cooling, for example, in a feedback loop, can be controlled and adjusted based on a parameter that is repeatedly measured by a suitable sensor.

[0021] It is preferred that the distance at which the heat-insulating lid is arranged above the melt surface is between 1 mm (i.e., just not touching the melt) and 100 mm. In particular, it is advantageous if the distance at which the heat-insulating lid is arranged above the melt surface is 10 mm or at least between 5 mm and 20 mm. By adjusting the distance at which the heat-insulating lid is arranged above the melt surface, a suitable temperature distribution within the melt can be created, and thus the distance can be used as a control parameter for controlling the growth of the bulk single crystal, e.g., the growth rate and direction of crystal growth.

[0022] It is preferred that the distance between the lid and the melt surface be kept constant during the growth of the bulk single crystal. However, it can also be advantageous to vary the distance during the growth of the bulk single crystal in order to adjust the temperature distribution in the melt, e.g., for different growth stages. Furthermore, it is advantageous that the lid is arranged parallel or at least approximately parallel to the melt surface so that the distance between the lid and the melt surface is constant across the area of ​​the heat-insulating lid. In some growth scenarios, however, it is advantageous for the lid to be inclined with respect to the melt surface in order to achieve a specific temperature distribution in the melt.

[0023] The heat-insulating cover can be attached to a bracket, and the distance between the heat-insulating cover and the melting surface can be adjusted by vertically moving the bracket relative to the melting surface. Such an arm can be moved manually or automatically.

[0024] For the described growth process, it is not necessary for the heat-insulating lid to be positioned exactly in the center of the crucible. The growth process also works if at least a central part of the melt surface is covered by the lid. In this case, the heat-insulating lid, and especially its rim, can be in contact with the crucible wall.

[0025] Preferably, the starting material is provided in powder form with a purity of 99.99%. However, impurities in the 1% range and dopants in the 5% range are also acceptable.

[0026] The starting material can consist of only one or two chemical species, but in most cases it is composed of several. It is advantageous to produce a powder mixture from the starting material, for example, by weighing, mixing, and calcining the powders of the different chemical species.

[0027] If the starting material is in powder form, it is preferred that the powder be a dried powder.

[0028] To improve the filling of the crucible with the starting material and the melting of the starting material within the crucible, it is further preferred that the powder be compacted before being introduced into the crucible if the starting material is in powder form. Compacting the powder typically reduces the number of heating / cooling cycles required to fill the crucible before crystal growth can begin. For example, the powder, e.g., a powder mixture, can be pressed. Advantageously, one or more rods, flakes, or spheres can be produced from the powder by cold isostatic pressing. Cold isostatic pressing can be performed, for example, at 0.2 GPa. When a rod is produced, it typically extends above the top of the crucible and sinks into the crucible upon melting.Such a rod of compacted powder preferably has a total mass calculated to fill the crucible when melted, and a shape that fits into the crucible but extends upwards and out of the crucible.

[0029] The starting material can also be introduced into the crucible as loose powder and subsequently compacted inside the crucible before melting. The pressing is then uniaxial. Preferably, the powder is compressed before being introduced into the crucible to prevent potential damage to the crucible.

[0030] However, compacting the starting material is not necessary to grow a bulk crystal from the melt. Therefore, the powder could be placed directly into the crucible and heated to melt it. Filling the crucible can then involve several steps of adding more powder.

[0031] It is preferred that the crucible be arranged in an inert gas atmosphere, preferably at ambient pressure. The inert gas atmosphere can be argon or nitrogen. However, it is also possible for the growth process to operate in a vacuum or under high pressure, e.g., up to several hundred atmospheres, at which argon becomes a superfluid. Preferably, the inert gas atmosphere is established before heating the crucible and is present throughout the melting process and during crystal growth. Typically, a few percent oxygen is acceptable. If iridium or another oxidizing material is used as the crucible material, it is preferred that most of the air be replaced by an inert gas such as argon.

[0032] In various variants of the growth process according to the invention, the starting material comprises oxygen in combination with at least one cation species that can assume several oxidation states, and the grown bulk single crystal comprises an oxide containing at least one cation species that can assume several oxidation states, or preferably at least one of titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, niobium, molybdenum, tungsten or tantalum, and the bulk single crystal comprises an oxide, preferably an oxide of titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, niobium, molybdenum, tungsten or tantalum.

[0033] Specifically for these materials, it is not possible to grow bulk single crystals of sufficient quality using known methods. Therefore, the invention provides, for the first time, bulk single crystals of these materials and a method for growing them. The invention is based on the finding that bulk single crystals of these materials can be grown using a heat-insulating lid, which is positioned at a distance above a melt surface such that, during the cooling of the melt and thus during growth, at least a central part of the melt surface is covered by the lid.

[0034] Particularly preferred is that the starting material contains at least Ba, Sc, Nb and O and that the resulting bulk single crystal is a bulk Ba2ScNbO6 single crystal.

[0035] The production of bulk Ba₂ScNbO₆ single crystals is particularly preferred, as these bulk Ba₂ScNbO₆ single crystals can be processed into Ba₂ScNbO₆ single-crystal substrates. Such Ba₂ScNbO₆ single-crystal substrates are not yet available in the electronics industry in the required size and structural quality.

[0036] A bulk Ba₂ScNbO₆ single crystal is a double perovskite with cubic symmetry. The lattice parameter of a bulk Ba₂ScNbO₆ single crystal lies within 1% of the lattice parameter of various perovskites—such as BaSnO₃—for which, until now, no suitable substrate was available in the electronics industry for the fabrication of electronic components containing crystal layers of these materials with the low defect densities required for high performance. Thus, the invention provides a bulk Ba₂ScNbO₆ single crystal for the fabrication of a substrate that then enables the production of electronic components from materials that were previously unavailable in high-quality form in the electronics industry, but which are in demand due to their expected high performance.

[0037] Preferably, the starting material, comprising at least Ba, Sc, Nb, and O, is provided in dried powder form with a purity of 99.99%. In addition to Ba, Sc, Nb, and O, the starting material may contain MgO and / or CaO in a proportion of less than 5 mol%. MgO and / or CaO can thus be added as dopants to reduce free support absorption at high temperatures through a mechanism known as compensation doping. When one or both of these dopants are added to the starting material, the resulting bulk single crystal is a bulk Ba₂ScNbO₆ single crystal doped with Mg and / or Ca.

[0038] If the starting material contains at least Ba, Sc, Nb and O and the bulk single crystal to be grown is a bulk Ba2ScNbO6 single crystal, then the method for growing a bulk single crystal according to the invention accordingly comprises the steps - Introducing a starting material containing at least Ba, Sc, Nb and O into a crucible, - Melting the starting material in the crucible by heating the starting material, - Arranging a heat-insulating lid at a distance above a melting surface of the molten metal such that at least a central part of the melting surface is covered by the lid, and - Growing the bulk Ba2ScNbO6 single crystal from the melt by controlling the cooling of the melt with the heat-insulating lid arranged over the melt surface.

[0039] In one embodiment, the step "introducing a starting material" comprises the following sub-steps: - Producing a powder mixture from the starting material, which contains at least Ba, Sc, Nb and O, - Compacting the powder mixture, which contains at least Ba, Sc, Nb and O, and - Transferring the compacted powder mixture into the crucible.

[0040] The step of "producing a powder mixture from the starting material, which contains at least Ba, Sc, Nb and O" can include weighing, mixing and calcining the starting material. Calcining the starting material – preferably in dried powder form – can be carried out, for example, in air at 1300°C for 12 hours.

[0041] The sub-step “compacting the powder mixture containing at least Ba, Sc, Nb and O” may include producing one or more rods from the powder mixture by cold isostatic pressing at 0.2 GPa.

[0042] To melt the starting material, which contains at least Ba, Sc, Nb, and O, it is sufficient to heat the crucible to a temperature at least as high as the melting point of a bulk Ba₂ScNbO₆ single crystal. For example, the crucible can be heated to a temperature of at least 2165 ± 30 °C. To be significantly above the melting point, the crucible can be heated to a temperature of at least 2195 °C, for example, to a temperature of 2200 °C.

[0043] For the growth of a bulk Ba2ScNbO6 single crystal, it is advantageous if an inert gas atmosphere in which the crucible is arranged has a pressure of 1 atm or even higher than 1 atm in order to reduce the effective evaporation rate of BaO.

[0044] A Ba₂ScNbO₆ single crystal grown according to the method described herein can be at least partially surrounded by a multicrystalline or polycrystalline matrix that grows near the crucible wall in the initial phase of the growth process according to the invention. Therefore, the method for growing a bulk Ba₂ScNbO₆ single crystal can, in particular, comprise the following step: - Separation of the bulk Ba₂ScNbO₆ single crystal from a multicrystalline or polycrystalline matrix that at least partially surrounds the bulk Ba₂ScNbO₆ single crystal. Separation, in one embodiment, comprises cutting and / or grinding and / or splitting to isolate the volume of the Ba₂ScNbO₆ single crystal.

[0045] In particular, a slice of the bulk Ba₂ScNbO₆ single crystal can be cut to produce a Ba₂ScNbO₆ single crystal substrate. Slices with a lateral diameter of 6 mm or greater can be cut from a Ba₂ScNbO₆ single crystal grown using the method described here. The method also makes it possible to grow a Ba₂ScNbO₆ single crystal from which a slice with a lateral diameter of 8 mm or greater, or even 10 mm or greater, can be cut. A slice cut from a Ba₂ScNbO₆ single crystal can be further processed into a Ba₂ScNbO₆ single crystal substrate for use in the electronics industry.

[0046] Advantageously, a Ba₂ScNbO₆ single-crystal substrate with a lateral diameter of 6 mm or greater is produced from the disk. A substrate with a lateral diameter of 8 mm or greater can be produced from a disk with a lateral diameter of 8 mm or greater. A substrate with a lateral diameter of 10 mm or greater can be produced from a disk with a lateral diameter of 10 mm or greater.

[0047] The invention also relates to a Ba₂ScNbO₆ single crystal with a cross-sectional area equal to or greater than 6 mm × 6 mm. The invention further relates to a Ba₂ScNbO₆ single crystal with a cross-sectional area equal to or greater than 8 mm × 8 mm, in particular equal to or greater than 10 mm × 10 mm. The bulk Ba₂ScNbO₆ single crystal can be realized independently of other aspects described herein and thus constitutes a separate invention.

[0048] The bulk Ba₂ScNbO₆ single crystal according to the invention has cubic symmetry and a lattice parameter of 412 pm. Therefore, a bulk Ba₂ScNbO₆ single crystal has a compatible lattice parameter with many materials of interest to the electronics industry, such as BaSnO₃, which also exhibits the perovskite structure with identical Ba-O layers. In fact, Ba₂ScNbO₆ and BaSnO₃ are lattice-matched to a greater than 0.1%. Furthermore, Ba₂ScNbO₆ has a dielectric constant of 16 and a band gap of 3.6 eV and thus possesses material properties that are often required for a suitable substrate in the electronics industry. The bulk Ba₂ScNbO₆ single crystal has a melting point of 2165 ± 30 °C in an inert gas atmosphere at ambient pressure.

[0049] Preferably, the bulk Ba₂ScNbO₆ single crystal has a composition of 66.7 mol% ± 5% BaO, 16.7 mol% ± 5% SC₂O₃, and 16.7 mol% ± 5% Nb₂O₅. However, the melt from which the bulk Ba₂ScNbO₆ single crystal was grown, e.g., using the bulk single crystal growth method according to the invention, need not have the same composition as the bulk Ba₂ScNbO₆ single crystal. Related crystal growth methods, e.g., top-seed solution growth (TSSG), can be used to provide a melt containing Ba, Sc, Nb, and O from which the bulk Ba₂ScNbO₆ single crystal can be grown using the bulk single crystal growth method according to the invention. A flux of another species, e.g. based on Cu2O or PbO / PbF2, may be present in the melt, but preferably a flux is used that incorporates only minimally into the bulk single crystal grown from the melt.Other species that can replace MgO include, for example, CaO, but the proportion of such dopants is preferably limited to less than 5 mol%.

[0050] The invention also relates to a single-crystal Ba₂ScNbO₆ substrate with a lateral diameter of 6 mm or greater. The invention further relates to a single-crystal Ba₂ScNbO₆ substrate with a lateral diameter of 8 mm or greater, in particular 10 mm or greater. In particular, the invention also relates to a single-crystal Ba₂ScNbO₆ substrate with standard wafer sizes, e.g., with lateral dimensions of 4 inches or 6 inches. Such single-crystal Ba₂ScNbO₆ substrates can be produced from the bulk Ba₂ScNbO₆ single crystal according to the invention with a corresponding cross-sectional area.

[0051] The invention also relates to a (multi-)layer structure comprising a single-crystal Ba2ScNbO6 substrate according to the invention and one or more crystal layers grown on the Ba2ScNbO6 substrate. This (multi-)layer structure can be realized independently of other aspects described herein and thus constitutes a separate invention.

[0052] The single-crystal Ba2ScNbO6 substrate according to the invention has a lattice parameter that makes it a suitable substrate for various materials in the electronics industry, in particular for materials for which no suitable substrate was previously available in the sizes and structural quality required to maintain the functionality of these materials.

[0053] A particular advantage is that the single-crystal Ba2ScNbO6 substrate has a lattice parameter that corresponds to the lattice parameter of various perovskites. For example, the one or more crystal layers grown on the single-crystal Ba2ScNbO6 substrate can contain at least one of the perovskites BaSnO3, LaInO3, BiScO3, PbZrO3, SrZrO3, SrHfO3, PrInO3, LaScO3, SrSnO3, BaHfO3, LaLuO3, CeLuO3, PrLuO3, NdLuO3, CeYbO3, PrYbO3, or BaZrO3.

[0054] The one or more crystal layers grown on the single-crystal Ba2ScNbO6 substrate can also consist of at least one of the perovskite solid solutions PbZr 1-x Ti x O3 (PZT), PbCa 1-x Ti x O3 (PCT) or Ba 1-x Sr x exhibit SnO3, where x is a number between 0 and 1.

[0055] The one or more crystal layers can also be at least one of the relaxor-ferroelectric mixed crystals PbMg. 1 / 3 Note 2 / 3O3-PbTiO3 (PMN-PT), PbZn 1 / 3 Note 2 / 3 O3-PbTiO3 (PZN-PT) and PbIn 1 / 2 Note 1 / 2 O3-PbMg 1 / 3 Note 2 / 3 exhibit O3-PbTiO3 (PIN-PMN-PT).

[0056] If the multilayer structure has several crystal layers grown in different layers on the Ba2ScNbO6 substrate, the multilayer structure can, for example, include at least one of the perovskites listed above and / or at least one of the perovskite solid solutions listed above and / or at least one of the relaxor-ferroelectric solid solutions listed above.

[0057] A particularly advantageous feature is that the multilayer structure incorporates a BaSnO3 crystal layer grown directly on the single-crystal Ba2ScNbO6 substrate. With its highly lattice-matched single-crystal Ba2ScNbO6 substrate, the BaSnO3 crystal layer exhibits excellent properties for use in electronic components. Furthermore, the BaSnO3 crystal layer grown directly on the single-crystal Ba2ScNbO6 substrate has an average thread disclocation density (TDD) of less than 10⁻⁶. 8 Displacements per cm 2 and / or an electron mobility of more than 190 cm⁻¹ 2 V -1 s -1 and / or a full width at half maximum (FWHM) of its rocking curve that is less than or equal to 23 arcsec (0.006°).

[0058] Due to its high electron mobility - which exceeds 300 cm³ with degenerative doping 2 V -1 s -1Due to its ability to operate at room temperature, its excellent transparency, chemical stability, and the fact that it is free of indium, the transparent conductive oxide (TCO) BaSnO3 offers a variety of material properties that are advantageous for electronic devices. For example, field-effect transistors (FETs) made of BaSnO3 have been shown to achieve peak field-effect mobilities of 61 cm⁻¹ at room temperature. 2 V -1 s -1 and I on / I off -ratios of up to 10 9 work.

[0059] Until now, multilayer structures with a BaSnO3 crystal layer have not been used in the electronics industry because no suitable substrate was available that would allow the fabrication of a multilayer structure with a BaSnO3 crystal layer of the required crystal quality. Due to the lack of suitable substrates, according to the prior art, thin films of BaSnO3 can only be grown on currently available substrates with high dislocation densities (TDD), which leads to significantly reduced electron mobilities. With the invention, multilayer structures made of a BaSnO3 crystal layer are now available on a large scale with consistent functionality and thus advantageous properties.

[0060] The invention includes the realization that the possibility of growing Ba2ScNbO6 single crystals, for example, using the growth method according to the invention, and thus providing a Ba2ScNbO6 single-crystal substrate with the required structural compatibility and structural quality, enables the production of multilayer structures from a BaSnO3 crystal layer with high structural quality and thus retained functionality. For example, a BaSnO3 crystal layer with an average total dislocation density (TDD) of less than 10 can be grown directly on a Ba2ScNbO6 single-crystal substrate. 8 Displacements per cm 2 and an electron mobility of more than 190 cm 2 V -1 s -1BaSnO3 crystals are grown to produce a multilayer structure. The high structural quality results in a full width at half maximum (FWHM) of the rocking curve of the BaSnO3 crystal layer that is equal to or even less than 23 arcseconds (0.006°). These values ​​are achieved, for example, for a 250 nm thick undoped BaSnO3 crystal layer followed by a 130 nm thick La-doped BaSnO3 layer, which is doped to achieve a free electron concentration of 3 × 10⁻⁶. 19 cm -3 has, on a Ba2ScNbO6 single crystal substrate.

[0061] A particular advantage of the (multi-)layer structure with a BaSnO3 crystal layer grown epitaxially on a Ba2ScNbO6 single-crystal substrate is that the BaSnO3 crystal layer can have a thickness of, for example, 380 nm and more, while still maintaining an average dislocation density (TDD) of less than 10 8 Displacements per cm 2 and an electron mobility of more than 190 cm 2V -1 s -1 has. In such a (multi-)layer structure, the crystal layer grown as an epitaxial BaSnO3 film on Ba2ScNbO6 is perfectly adequate even if a BaSnO3 crystal layer with a thickness of more than one micrometer is grown.

[0062] The invention further relates to an electronic device having the (multi-)layer structure according to the invention. The electronic device can be a device selected from: a field-effect transistor with a conventional gate dielectric (a MOSFET), a field-effect transistor with a ferroelectric gate dielectric (a ferroelectric FET), a field-effect transistor with an antiferroelectric gate dielectric (an antiferroelectric FET), a transducer, a receiver, an amplifier, a sensor, and an actuator. Due to the high bandgap of BaSnO3, the aforementioned components can be completely transparent, i.e., a transparent transistor, transparent transducer, transparent sensor, etc.

[0063] Transparent MOSFETs based on BaSnO3 have been shown to have better electrical performance than all previous transparent MOSFETs.

[0064] Ferroelectric FETs require no current to maintain their logic states, making them relevant for memory and instant-on computing systems. The logic state can be read non-destructively based on the conductivity of the semiconductor channel. These ferroelectric FETs were first proposed over 60 years ago, but their realization was thwarted by material integration problems. An abrupt ferroelectric-to-semiconductor interface is crucial for the performance of these devices; unfortunately, direct growth of ferroelectrics on mainstream semiconductors is accompanied by extensive interdiffusion or chemical reactions that degrade the properties of the oxide, the underlying semiconductor, or both, leading to electrically active defects at the semiconductor / oxide interface. Such defects render these devices unusable.The invention makes it possible to meet this long-standing challenge and enable a new generation of hyperfunctional oxide electronics by using BaSnO3 as a high-mobility channel layer in ferroelectric FETs, since BaSnO3 is structurally and chemically compatible with many ferroelectric and multiferroic oxides.

[0065] FETs containing ferroelectric or antiferroelectric gate dielectrics also have the potential to produce low-energy transistors that can exceed the 60 mV / decade subthreshold limit of conventional transistors.

[0066] The ability to produce highly mobile BaSnO3 channel layers made possible by this invention enables the production of “smart FETs” by integrating the exceptional functionalities of chemically and structurally compatible perovskite oxides to produce particularly sensitive temperature, pressure or magnetic field sensors.

[0067] Regarding the growth setup, the objective of the invention is achieved by a growth setup for growing a bulk single crystal from a melt. The growth setup comprises - a melting pot - a heating element that is arranged and designed to melt a starting material located in the crucible into a melt, and - a heat-insulating lid for covering at least a central part of a melt surface of a melt located in the crucible.

[0068] The growth setup according to the invention is suitable for carrying out the growth process according to the invention for growing a bulk single crystal. The growth setup according to the invention shares the advantages of the growth process according to the invention.

[0069] An advantage of the growing setup according to the invention is that, compared to other growing setups, it requires only a small number of components, e.g., compared to a Czochralski setup, which also requires a scale to measure the weight of the growing crystal (or the crucible from which it is pulled) and the crystal rotation.

[0070] Another advantage of the growing setup according to the invention is that, by using the heat-insulating lid, even high-quality bulk single crystals can be grown conveniently, which are difficult or impossible to grow using the Czochralski technique.

[0071] In particular, by varying, for example, the geometry of the heat-insulating lid, the lid material, and / or the lid size, and / or by varying the arrangement of the heat-insulating lid relative to the crucible, the growth setup can be adapted to the needs for growing a specific bulk single crystal. Furthermore, for growing a specific bulk single crystal in a growth process, the distance to the melt and / or the inclination of the lid relative to the melt surface can be varied appropriately.

[0072] It is advantageous if the heat-insulating cover is a closure or has a closure and is designed such that the proportion of the melt surface covered by the heat-insulating cover can be adjusted by opening and closing the closure. A heat-insulating cover that is a closure or has a closure can be designed in various ways.

[0073] In one embodiment, the clasp has two discs arranged one above the other, sharing the same center point. Both discs can have the same diameter or different diameters. Furthermore, the two discs are positioned so that they can be rotated relative to each other, allowing the clasp to be opened and closed by rotating the discs relative to each other.

[0074] Both disks can have a multitude of, for example, uniformly shaped perforations, with the perforations of both disks being distributed along the circumference of circles of the same diameter. In other embodiments, perforations can be arranged, for example, in certain quadrants of a disk, while other quadrants are solid throughout.

[0075] In various other embodiments of a heat-insulating lid featuring a closure, the closure is achieved by one or more windows that can be opened or closed. By selecting the opening angle of one or more windows, the amount of heat radiation emitted from the melt surface per unit of time can be controlled. It is also possible to implement a heat-insulating lid with a closure by means of a heat-insulating lid with a plurality of perforations, each of which can be closed by a corresponding lid. Such a lid for closing a plurality of perforations can also be manufactured in one piece, so that the plurality of perforations can be opened and closed in a single step.

[0076] It is preferred that the heat-insulating lid be made of a material that is rigid and can withstand the hot environment, including potential thermal shock. Preferably, the heat-insulating lid is made of the same material as the crucible (iridium in the case of Ba₂ScNbO₆) or of the same chemical elements as the starting material from which a bulk single crystal is to be grown. For example, particularly when growing a bulk Ba₂ScNbO₆ single crystal, the heat-insulating lid can be made from a disc-shaped piece of Ba₂ScNbO₆.

[0077] The outer diameter of the heat-insulating lid should be smaller than the inner diameter of the crucible, especially below the covered crucible tip (below the perforated Ir disk). This ensures that when growing a bulk single crystal, only a fraction of the melt surface is covered by the lid, which is positioned at a distance above the melt surface. An area between the lid and the crucible wall remains uncovered, preventing thermal radiation from being blocked. The ratio of covered to uncovered melt surface areas can be used as an additional parameter to shape a temperature distribution within the melt that is optimal for growing a specific bulk single crystal.

[0078] In one embodiment, the heat-insulating lid is arranged so that it is centered on the crucible in such a way that the uncovered melt surface area surrounding the covered center radiates the heat from the melt evenly.

[0079] A heat-insulating lid can also be relatively thick to ensure good thermal insulation. Alternatively, the heat-insulating lid can also consist of several stacked lids, in one version even with small gaps between the lids.

[0080] In particular, a heat-insulating lid designed to completely cover the crucible may have a closure for adjusting the proportion of the melt surface that is covered by the heat-insulating lid during the growth of a bulk single crystal.

[0081] Preferably, the crucible is covered with a perforated disc. The perforated disc can be placed on the crucible after the insulating lid has been fitted. A support for the heat-insulating lid, e.g., an arm attached to the heat-insulating lid, can then extend through the punched hole in the perforated disc. A support extending through the punched hole can be moved vertically with respect to the perforated disc and the crucible to adjust the distance of the attached heat-insulating lid above a molten surface. Preferably, the crucible is embedded in thermal insulation, the thermal insulation being close to or in contact with the crucible. The thermal insulation can be arranged below, beside, and / or above the crucible.

[0082] For example, the crucible can be embedded in a ZrO2 and Al2O3 insulation, with Al2O3 preferably being used at lower growth temperatures or in cooler areas of the growing setup.

[0083] The crucible can be made of iridium or platinum. Generally, any crucible designed to hold a starting material and its melt can be used. Consequently, the crucible must have a higher melting point than the material being melted. Therefore, a suitable crucible is preferably designed to withstand high heating temperatures, e.g., at least 2200°C, and also cooling. Furthermore, the crucible should be made of a material that does not react with the starting material.

[0084] The crucible of the growth setup can be made in various shapes and sizes. A larger crucible allows for the growth of a larger bulk single crystal. Thus, the size of the crucible can be chosen according to the desired size of the bulk crystal to be grown. Generally, a cylindrical shape is preferable, as it allows for convenient and uniform heating. Preferred diameter-to-height ratios for the crucible are in the range of 0.3–2. For example, the crucible could have an inner diameter of 28 mm and a height of 42 mm.

[0085] It can also be advantageous if the crucible is a skull crucible formed from a powder containing at least the same chemical elements as the starting material from which the bulk single crystal is to be grown. For example, if the starting material contains at least Ba, Sc, Nb, and O, and the bulk single crystal to be grown is a Ba₂ScNbO₆ single crystal, the skull crucible can be made from a powder containing at least Ba, Sc, Nb, and O. When using a skull crucible, the starting material typically melts in the central part of the crucible by heating the crucible with a heating element. The outside of the skull crucible is cooled, for example, with a water-cooled vessel, to prevent the crucible itself from melting. The advantage of the skull crucible is that the crucible no longer needs to have a higher melting point than the material to be melted.

[0086] The heating element can be an induction heating element, preferably comprising at least one induction heating coil for heating a starting material located in the crucible. When using an induction heating coil, heating is achieved by high-frequency (HF) induction. Preferably, the induction heating coil is wound around the thermal insulation next to the crucible. List of characters

[0087] Preferred embodiments of the invention are described below with reference to the figures. The figures show: Fig. Figure 1 shows a flowchart illustrating a process for growing a bulk single crystal; Fig. Figure 2 shows a flowchart illustrating a process for growing a bulk Ba2ScNbO6 single crystal; Fig. Figure 3: schematically shows an embodiment of a growth setup for growing a bulk single crystal; Fig. Figure 4: schematically shows an embodiment of a heat-insulating lid with a locking function in the open state a) and in the closed state b); Fig. Figure 5: schematically shows another embodiment of a heat-insulating lid with a locking function in the open state a) and in the closed state b); Fig. 6: shows in a) a graphical grayscale intensity representation of a selected Bragg reflection produced by the bulk Ba2ScNbO6 single crystal shown in a photograph in b), and in c) the sum spectra acquired within the area of ​​the bulk Ba2ScNbO6 single crystal; Fig. Figure 7 shows a chemo-mechanically polished (001)-oriented Ba2ScNbO6 single crystal substrate with a lateral extent of 10 mm; Fig. Figure 8 shows a transmission electron microscope (TEM) image of a structure that has a Ba2ScNbO6 single crystal substrate and a BaSnO3 crystal layer epitaxially grown on it; Fig. Figure 9: schematically shows a disc of another embodiment of a heat-insulating lid with a locking function; Fig. Figure 10: schematically shows a disc of another embodiment of a heat-insulating lid with a locking function; Fig. Figure 11: schematically shows a disc of another embodiment of a heat-insulating lid with a locking function. DETAILED DESCRIPTION

[0088] Fig. Figure 1 shows a flowchart illustrating a process for growing a bulk single crystal. The growth process can be carried out, for example, using a growth setup such as the one described in relation to Fig. 3 is described.

[0089] In a first step S1 A starting material is placed in a crucible. The starting material is provided in dried powder form with a purity of 99.99%. In various other embodiments of the process, the starting material contains impurities in the 1% range and dopants in the 5% range. It is advantageous if a powder mixture is prepared from the starting material before it is placed in the crucible, e.g., by weighing, mixing, and calcining the powders of the different chemical species.

[0090] Here, the starting material is introduced into the crucible as loose powder. Before melting, the loose powder can be compacted inside the crucible. However, in various other embodiments, it is preferred that the starting material be compacted before being introduced into the crucible. Compacting the starting material before introducing it into the crucible is often preferred because it allows the crucible to be filled more effectively with starting material and the starting material to be melted more efficiently within the crucible.

[0091] The starting material can, for example, contain oxygen in combination with a cation species that can assume multiple oxidation states. In particular, it is advantageous if the starting material contains at least Ba, Sc, Nb, and O.

[0092] After introduction, the starting material is processed in step S2The starting material is melted in the crucible by heating it, for example with a heating element. If the starting material is introduced into the crucible in a compacted form, for example in the form of a cylindrical rod, the rod sinks to the lower part of the crucible as it melts.

[0093] After the starting material has been melted into a molten state, in step S3A heat-insulating lid is arranged at a distance above a molten surface of the melt to block the radiation emitted by the molten surface. In particular, the heat-insulating lid is arranged above the molten surface such that at least a central part of the molten surface is covered by the lid. Preferably, the lid is arranged close to the molten surface, e.g., at a distance between 1 mm and 10 mm. However, in various embodiments, it is advantageous if the heat-insulating lid is arranged above the molten surface at a distance between 1 mm and 100 mm. In further embodiments, the heat-insulating lid can also be arranged above the molten or unmelted starting material before or during the melting of the starting material.

[0094] The heat-insulating lid, positioned at a distance above the melting surface, is used in step S4 A bulk single crystal is grown from the melt. Crystals germinate on the crucible wall, resulting in grain selection and continuous grain enlargement towards the central part of the crucible, so that the bulk single crystal grows from the crucible wall towards the central part of the crucible.

[0095] Crystal growth is achieved by controlled cooling of the melt using a heat-insulating lid positioned over the melt surface. Controllable cooling of the melt can be passive, e.g., by reducing the heat supplied by a heating element over a predefined period, and / or active, e.g., by directing a stream of inert gas onto the melt surface.

[0096] When carrying out the above-described process steps for growing a bulk single crystal, the crucible is preferably arranged in an inert gas atmosphere, e.g. argon or nitrogen atmosphere, preferably under ambient pressure.

[0097] Fig. Figure 2 shows a flowchart illustrating a process for growing a bulk Ba₂ScNbO₆ single crystal. The process for growing a bulk Ba₂ScNbO₆ single crystal can be carried out, for example, using a growth setup, as shown in relation to Fig. 3 described. This refers to Fig. The breeding method described in section 2 represents a variant of the one described in Fig. 1 described breeding procedure.

[0098] In the flowchart in Fig. In the growth process described in section 2, a starting material containing at least Ba, Sc, Nb, and O is provided in dried powder form with a purity of 99.99%. The starting material may also contain dopants, e.g., MgO and / or CaO, with a content of less than 5 mol%. The starting material is then processed in step 1. B1The starting material is introduced into the crucible. In various embodiments, a powder mixture containing at least Ba, Sc, Nb, and O is prepared from the starting material before it is introduced into the crucible. One way to prepare the powder mixture from the starting material is to weigh, mix, and calcine the dried powders. Calcination of the starting material can be carried out, for example, in air at 1300°C for 12 hours. The powder mixture produced from the starting material is then introduced into the crucible. Often, it is advantageous, particularly for the filling process and the subsequent melting, to compact the starting material or a powder mixture produced from it. For example, the starting material can be compacted into a cylindrically shaped rod, which is then introduced into the crucible. One possible way to compact the starting material is to use cold isostatic presses with a pressure of 0.2 GPa.

[0099] The starting material in the crucible is then processed in step B2 The starting material is melted by heating it. To melt the starting material, the crucible is heated to at least the melting point of a bulk Ba₂ScNbO₆ single crystal. To be significantly above the melting point of a bulk Ba₂ScNbO₆ single crystal, the crucible can be heated to a temperature of, for example, 2200°C.

[0100] After the starting material has been melted, the following step takes place: B3A heat-insulating lid is arranged at a distance above a melt surface of the molten material to block the radiation emitted by the melt surface. In particular, the heat-insulating lid is arranged above the melt surface such that at least a central part of the melt surface is covered by the lid. Preferably, the lid is arranged close to the melt surface, e.g., at a distance between 1 mm and 10 mm. In various embodiments, however, it is advantageous if the heat-insulating lid is arranged above the melt surface at a distance between 1 mm and 100 mm. In further embodiments, the heat-insulating lid can also be arranged before or during the melting of the starting material, either over the molten material or over the unmelted starting material.

[0101] The melt in the crucible is then cooled – passively and / or actively – in a controllable manner to grow a bulk Ba₂ScNbO₆ single crystal (B4). During the growth of the bulk Ba₂ScNbO₆ single crystal, the heat-insulating lid is placed over the melt surface to block the thermal radiation emitted from the melt surface and to create a specific temperature distribution that promotes crystal growth. Such a temperature distribution favorable for crystal growth can include a temperature gradient with lower (colder) temperatures near the crucible wall and higher (hotter) temperatures in the central part of the crucible.

[0102] With the related to Fig. 1 described breeding methods and in particular with regard to Fig. In the variant of this growth method described in section 2, a bulk Ba₂ScNbO₆ single crystal with a volume greater than 5 mm × 5 mm × 5 mm (length × width × height) can be grown. Consequently, from the variants described in section 2, the following can be grown: Fig. 1 and Fig. The volume Ba2ScNbO6 single crystal substrates grown using the 2 described methods are produced and used in the electronics industry for the manufacture of electronic components.

[0103] Fig. Figure 3 schematically shows a breeding setup. 300 Longitudinal section for growing a bulk single crystal. The growth setup 300 can be used to carry out the tasks related to Fig. 1 and Fig. The 2 described breeding methods are used.

[0104] The breeding setup includes a pot 302 , which is incorporated into thermal insulation 304 is embedded. The thermal insulation 304It can contain, for example, ZrO2 and Al2O3. The crucible itself can be made of, for example, iridium or platinum. Preferably, the crucible 302 a cylindrical shape. The crucible 302 However, it can also be realized in other forms, e.g., the crucible 302 have a hemispherical shape or the crucible 302 It can be cubic in shape. Larger crucibles allow for the growth of larger bulk single crystals. Therefore, for growing a bulk single crystal of a specific size, a suitable crucible is preferably chosen that is not too large, in order to conserve the energy required to melt the starting material. For example, to grow a bulk single crystal with a volume of approximately 15 mm × 15 mm × 15 mm (length × width × height), a crucible with an inner diameter of 30 mm and a height of 50 mm can be used.

[0105] The crucible 302 is equipped with a perforated disc 303covered, preferably made of the same material as the pot 302 consists of, for example, iridium or platinum. The perforated disc 303 It serves to block the heat radiation emanating from the melting surface. The perforated disc 303 is optional and not strictly necessary to grow a bulk single crystal, e.g. by applying one of the methods related to the Fig. 1 or Fig. 2 described breeding methods.

[0106] The breeding setup 300 It also includes a heating element. 306 , which is arranged and designed for melting a starting material that is in the crucible 302 is located and is melted. In particular, the heating element has 306 an induction heating coil that surrounds the crucible 302 The material is wound. The heating of the starting material to a melt is therefore achieved primarily through high-frequency (HF) induction in the crucible and crucible lid.

[0107] In the breeding setup 300 a melt 308 shown. At a distance above the melt. 308 , which are in the crucible 302 It is located on a heat-insulating lid. 310 arranged, which at least partially covers the surface of the melt 308 covers. In particular, the heat-insulating lid 310 to influence and control the temperature distribution in the melt 308 arranged in the crucible 302 is positioned to promote crystal growth from the crucible wall towards the center of the crucible. The heat-insulating lid 310 may have a closure as described in relation to the Fig. 4a and Fig. 4b and the Fig. 5a and Fig. 5b as well as the Fig. 9, Fig. 10 and Fig. 11. A heat-insulating lid with a closure allows the proportion of the melt surface covered by the heat-insulating lid during the growth of a bulk single crystal to be adjusted. The heat-insulating lid 310 It can be produced from iridium, for example. This is especially true if the starting material contains Ba, Sc, Nb, and O, and the cultivation setup... 300 When used to grow a bulk Ba2ScNbO6 single crystal, the heat-insulating lid can be used 310 made from a disc-shaped piece of Ba2ScNbO6.

[0108] The heat-insulating lid 310 is used as a mount on an arm 312 attached, with which the heat-insulating lid 310 raised or closer to the surface of the melt 308 The arm extends vertically through the hole in the perforated disc. 303This allows the heat-insulating lid attached to the arm to be lifted. The arm can, for example, have a screw thread at its end outside the crucible and be moved manually. Alternatively, the arm can be lifted automatically, for example, with an electrically driven motor connected to it.

[0109] This growth setup is particularly useful for growing a bulk Ba2ScNbO6 single crystal, especially with regard to Fig. 2 described procedures.

[0110] The Fig. 4a, Fig. 4b and Fig. 5a, Fig. Figure 5b schematically shows two different embodiments of a heat-insulating lid with a locking function. The heat-insulating lids with a locking function, as described in relation to the Fig. 4a, Fig. 4b and Fig. 5a, Fig. 5b can be used as heat-insulating lids in a breeding setup, as described with reference to Fig. The closure described in section 3 can be used. By opening and closing the closure, the proportion of the melting surface covered by the thermal insulation can be adjusted. Accordingly, the amount of heat radiation that can escape from the crucible can be adjusted with the closure. The closure can be designed in different ways, whereby the Fig. 4a, Fig. 4b and Fig. 5a, Fig. 5b shows only simplified selected examples. In particular, the closure geometry of the heat-insulating lid can be adapted to specific breeding scenarios.

[0111] The heat-insulating lid 400 with the in the Fig. 4a and Fig. The locking mechanism shown in 4b has two superimposed discs. 402 , 404on, which have the same center point. Both discs can have the same diameter, but also different diameters, as in the Fig. 4a and Fig. Figure 4b shows both discs featuring numerous circular perforations. 406 , 408 , whereby the perforations 406 , 408 both discs 402 , 404 are distributed along the circumference of circles with the same diameter. Furthermore, the two disks are 402 , 404 arranged one above the other in such a way that they can be rotated relative to each other. As in Fig. As shown in 4a, the two discs 402 , 404 then arranged so that the perforations of one disc 402 with the perforations of the other disc 404 are congruent. Then the seal is open and the proportion of the melt surface covered by the thermal insulation is minimal. In Fig. 4b is the opposite, namely that the two disks 402 , 404 are arranged one above the other in such a way that the perforations 406 , 408 the two discs 402 , 404 They should not overlap, so that the proportion of the melting surface covered by the thermal insulation is maximized. Of course, the two discs can 402 , 404 They are arranged one above the other in such a way that there is an overlapping state between fully open and fully closed.

[0112] Even a heat-insulating lid that has a locking function can have multiple perforations, perforations of different sizes and shapes, and a variety of perforations arranged in different patterns. For example, in a pattern like the ones shown in the... Fig. 5a and Fig. 5b shown. Comparable to the heat-insulating lid. 400 , as he said with reference to the Fig. 4a and Fig. As described in 4b, the heat-insulating closure has 500 the Fig. 5a and Fig. 5b two discs 502 , 504 each of which has a multitude of perforations 506 , 508 exhibit. As with regard to the Fig. 4a and Fig. As described in 4b, the two discs 502 , 504 They are rotated relative to each other to close or open the clasp. This shows Fig. 5a the heat-insulating lid 500 with a closure in its open state and Fig. 5b shows the heat-insulating lid 500 with a closure in its closed state.

[0113] Here are the perforations 506 , 508 triangular in shape, with one of the points at the edge of the discs 502 , 504nearest. For a specific design of the melt's temperature distribution, it can be advantageous if each of the triangles is rotated by 180° so that the shortest edge is at the edge of the disks. 502 , 504 nearest.

[0114] In various other embodiments of a heat-insulating lid featuring a closure, the closure is achieved by one or more windows that can be opened or closed. By selecting the opening angle of one or more windows, the amount of thermal radiation emitted by the melting surface per unit of time can be controlled.

[0115] It is also possible to create a heat-insulating lid with a closure using a heat-insulating lid with a multitude of perforations, so that each perforation can be closed by a corresponding lid. Such a lid for closing multiple perforations can also be manufactured from a single piece, allowing the multiple perforations to be opened and closed in one step.

[0116] Fig. Figure 6 shows in a) a grayscale intensity graph of a selected Bragg reflection produced from the bulk Ba₂ScNbO₆ single crystal photographed in b). The measurement shown in a) was performed on the bulk Ba₂ScNbO₆ single crystal within the area indicated by the white box in b). The bulk Ba₂ScNbO₆ single crystal was prepared from the melt using an iridium crucible with the reference to Fig. It was grown using the 2 described methods and has a volume of 17 mm × 17 mm × 15 mm (length × width × height).

[0117] The area in a), surrounded by the white dashed lines, represents the single-crystal region of the bulk Ba₂ScNbO₆ single crystal. This in Fig. 6b) The bulk Ba₂ScNbO₆ single crystal shown is therefore part of a larger multicrystalline volume. Small differences in the intensity of the Bragg peak are related to topographic effects, since the bulk Ba₂ScNbO₆ single crystal was measured in its as-grown state. In c), the sum spectra recorded within the single-crystal region are shown.

[0118] Fig. Figure 7 shows a DIG (Differential Interference Contrast) microscopy image of a chemo-mechanically polished (001)-oriented Ba2ScNbO6 single crystal substrate with a surface area of ​​10× 10 mm. 2 The Ba2ScNbO6 single-crystal substrate was obtained from the in Fig. 6b) shown volume Ba2ScNbO6 single crystal produced.

[0119] Fig. Figure 8 shows transmission electron microscopy (TEM) images at different magnifications in a), b) and c) of a multilayer structure comprising a Ba2ScNbO6 single-crystal substrate and an epitaxially grown 250 nm thick undoped BaSnO3 crystal layer on it, followed by a 130 nm thick La-doped BaSnO3 layer, which is doped to achieve a free electron concentration of 3×10 19 cm -3In particular, in c), it is clearly evident that a high degree of structural perfection is present at the interface (indicated by the dashed line) between the Ba₂ScNbO₆ single-crystal substrate and the BaSnO₃ crystal layer of the multilayer structure. This is due to the high structural quality of the Ba₂ScNbO₆ single-crystal substrate itself. For the multilayer structure shown, which comprises the single-crystal Ba₂ScNbO₆ substrate and a 250 nm thick undoped BaSnO₃ crystal layer followed by a 130 nm thick La-doped BaSnO₃ layer, an average total dislocation density (TDD) of less than 10⁻⁶ is obtained. 8 Displacements per cm 2 and a full width at half maximum (FWHM) of its rocking curve, which is equal to 23 arcseconds (0.006°). Electrical transport measurements on this film, performed using the Hall effect method, show that the layer has a concentration of 3 × 10 19 electrons cm -3contains and that the mobility of these electrons at room temperature is 190 cm 2 V -1 s -1 exceeds. This mobility is higher than any previously reported in the literature and is an indication of the electron mobility that can be achieved in electronic devices that use these films, e.g. in a field-effect transistor.

[0120] The Fig. 9, Fig. 10 and Fig. Figure 11 shows exemplary embodiments of discs used as discs in an exemplary embodiment of a heat-insulating cover with a locking function. As shown in the Fig. 4a, Fig. 4b, Fig. 5a and Fig. 5b Each heat-insulating lid has two discs of identical shape which can be rotated against each other to open and close the lid. By appropriately designing the holes and openings in such lids and rotating them relative to each other, the temperature distribution of the melt can be controlled, which in turn affects nucleation and crystal growth in the crucible.

[0121] Fig. Figure 9 schematically shows one of two discs 900 with identical shape, functioning as heat-insulating lids with a locking function. The disc 900 It extends over three quadrants of a circle. The fourth quadrant 904, which forms an opening, is left open except for a small inner circle for attaching the disk, so that when it is positioned at a distance above a molten surface, the heat radiation emitted from the molten surface can escape through the opening when the fourth quadrants 904 Both disks are arranged in a way that at least partially overlaps. In one example, the disk closer to the melt remains fixed on top of the crucible, while the disk above it can be rotated relative to the other disk. In other examples, both disks can be rotated. When the two disks 900When the two discs, which form a heat-insulating cover, are arranged congruently, the opening is maximized. By further rotating the discs relative to each other, the area of ​​the opening decreases, thus reducing the amount of heat radiation that can escape. The closure can be achieved by arranging the two discs so that the opening is in the fourth quadrant. 904 the respective discs 900 is completely covered by the other disc. When the crucible, which is protected by the heat-insulating lid with the two discs, 900 If the area to be covered has an inner diameter of 42 cm, the discs of the heat-insulating cover can also have a diameter of 42 cm. Preferably, each of the discs 900 a thickness of 1.5 cm.

[0122] Fig. Figure 10 schematically shows one of two discs 910with identical shape, functioning as a heat-insulating lid with a locking function. The disc 910 is similarly constructed and functions like the one in Fig. Disc 9 is shown. Therefore, only differences from disc 9 are shown. 900 out of Fig. 9 described. In addition to the opening in the fourth quadrant. 914 The disc indicates 910 in the second quadrant 912 , which is opposite the opening in the fourth quadrant, a multitude of elongated, curved perforations 915 on, which in the radial direction of the disc 910 are arranged at regular intervals. A heat-insulating cover, which holds two of the discs shown. 910 Depending on the arrangement of the discs relative to each other, it can have a variety of opening states. For example, the opening and the perforations can 915either completely covered or uncovered by the other disc. It is also possible that only the perforations 915 Each disk is open when the opening of the fourth quadrant 914 the second quadrant of the other disk 912 with the perforations 915 overlaps. Furthermore, the disc has 910 a central opening 916 for mounting a bracket for the heat-insulating lid.

[0123] Fig. Figure 11 schematically shows another embodiment of one of two disks 920 with identical shape, functioning as heat-insulating lids with a locking function. The disc 920 is similarly constructed and functions like the one in Fig. Disc 9 is shown. Therefore, only differences from disc 9 are shown. 900 out of Fig. 9 described. The fourth quadrant 924 and the second quadrant 922In this embodiment, there are no openings or perforations. Instead, in the first quadrant... 921 and in the third quadrant 923 a multitude of elongated, curved perforations 925 arranged in the radial direction of the disc 920 are arranged at regular intervals, with the perforations 925 , which are closer to the center of the disc 920 lie, have a lesser thickness than the perforations 925 , which are further away from the center. Like the disc 910 in Fig. The disc has 10 920 a central opening 926 for mounting a bracket for the heat-insulating lid.

Claims

[1] A method for growing a bulk single crystal, the method comprising the following steps - Placing a starting material into a crucible, - Melting the starting material in the crucible by heating the starting material, - arranging a heat-insulating lid at a distance above a melt surface of the melt such that at least a central part of the melt surface is covered by the lid, and - Growing the bulk single crystal from the melt by controllable cooling of the melt with the heat-insulating lid arranged above the melt surface. [2] The method of claim 1, wherein the cooling of the melt is passively controlled by reducing the heat provided by a heating element over a predefined period of time and / or is actively controlled. [3] A method according to claim 1 or 2, wherein the distance at which the heat-insulating lid is arranged above the melt surface of the melt is between 1 mm and 100 mm, preferably between 5 mm and 20 mm, more preferably the heat-insulating lid is arranged at a distance of 10 mm above the melt surface. [4] Method according to at least one of claims 1 to 3, wherein the starting material is compacted before melting and preferably before introducing the starting material into the crucible. [5] Method according to at least one of claims 1 to 4, wherein the crucible is arranged in an inert gas atmosphere, preferably in an argon or nitrogen atmosphere. [6] A method according to at least one of claims 1 to 5, wherein the starting material comprises oxygen in combination with a cation species that can assume multiple oxidation states, and the bulk single crystal comprises an oxide containing at least one cation species that can assume multiple oxidation states, or more preferably at least one of the elements titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, niobium, molybdenum, tungsten or tantalum, and the bulk single crystal comprises an oxide, preferably an oxide of titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, niobium, molybdenum, tungsten or tantalum. [7] The method according to at least one of claims 1 to 6, wherein the starting material comprises at least Ba, Sc, Nb and O and wherein the bulk single crystal produced is a bulk Ba2ScNbO6 single crystal. [8] The method according to claim 7, wherein the starting material additionally comprises MgO and / or CaO in a proportion of less than 5 mol% and the bulk single crystal produced is a bulk Ba2ScNbO6 single crystal doped with Mg and / or Ca. [9] The method according to claim 7 or 8, further comprising separating the bulk Ba2ScNbO6 single crystal from a multicrystalline or polycrystalline matrix at least partially surrounding the Ba2ScNbO6 single crystal. [10] The method according to at least one of claims 7 to 9, further comprising cutting a slice of the bulk Ba2ScNbO6 single crystal. [11] The method of claim 10, further comprising producing a Ba2ScNbO6 substrate from the wafer having a diameter in lateral extent equal to or greater than 6 mm, preferably equal to or greater than 8 mm, more preferably equal to or greater than 10 mm. [12] Bulk Ba2ScNbO6 single crystal having a cross-sectional area equal to or larger than 6 mm × 6 mm, preferably equal to or larger than 8 mm × 8 mm, more preferably equal to or larger than 10 mm × 10 mm. [13] Single crystal according to claim 12 with cubic symmetry and a lattice parameter of 412 pm. [14] A single crystal according to claim 12 or 13, having a melting point of 2165 + / - 30 °C in an inert gas atmosphere at ambient pressure. [15] Single-crystal Ba2ScNbO6 substrate having a lateral diameter equal to or greater than 6 mm, preferably equal to or greater than 8 mm, more preferably equal to or greater than 10 mm. [16] A (multi-)layer structure comprising the single-crystalline Ba2ScNbO6 substrate according to claim 15 and one or more crystal layers grown on the Ba2ScNbO6 substrate. [17] (Multi-)layer structure according to claim 16, wherein the one or more crystal layers comprise a perovskite, preferably at least one of the perovskites BaSnO3, LaInO3, BiScO3, PbZrO3, SrZrO3, SrHfO3, PrInO3, LaScO3, SrSnO3, BaHfO3, LaLuO3, CeLuO3, PrLuO3, NdLuO3, CeYbO3, PrYbO3 or BaZrO3 and / or the one or more crystal layers comprise at least one of the perovskite solid solutions PbZr 1-x Ti x O3 (PZT), PbCa 1-x Ti x O3 (PCT), or Ba 1-x Sr x SnO3, where x is a number between 0 and 1, and / or the one or more crystal layers comprise at least one of the relaxor-ferroelectric mixed crystals PbMg 1 / 3 Nb 2 / 3 O3-PbTiO3 (PMN-PT), PbZn 1 / 3 Nb 2 / 3 O3-PbTiO3 (PZN-PT), and PbIn 1 / 2 Nb 1 / 2 O3-PbMg 1 / 3 Nb 2 / 3 O3-PbTiO3 (PIN-PMN-PT). [18] A (multi-)layer structure according to claim 16 or 17, wherein one of the one or more crystal layers is a BaSnO3 crystal layer grown directly on the Ba2ScNbO6 substrate, the BaSnO3 crystal layer having an average dislocation density of less than 10 8 Dislocations per cm 2 and / or an electron mobility of more than 190 cm 2 V -1 s -1 and / or has a full width at half maximum (FWHM) of its rocking curve that is less than or equal to 23 arcseconds (0.006°). [19] Electronic device with a (multi-)layer structure according to at least one of claims 16 to 18. [20] Growth setup for growing a bulk single crystal from a melt, comprising - a melting pot, - a heating element arranged and designed to melt a starting material in the crucible into a melt, and - a heat-insulating lid for covering at least a central part of a melt surface of a melt in the crucible. [21] The growth structure according to claim 20, wherein the heat-insulating lid has a closure and is designed such that the proportion of the melt surface covered by the heat-insulating lid can be adjusted by opening and closing the closure. [22] A growth structure according to claim 20 or 21, wherein the crucible is embedded in thermal insulation. [23] Growth structure according to claims 20 to 21, wherein the crucible is an iridium crucible. [24] Growth structure according to claims 20 to 22, wherein the crucible is a skull crucible formed from a powder containing at least the same chemical elements as the starting material from which the bulk single crystal is to be grown. [25] Growth structure according to at least one of claims 20 to 24, wherein the heating element is an induction heating element, preferably comprising at least one induction heating coil for heating a starting material located in the crucible. [26] Growth structure according to at least one of claims 20 to 25, wherein the heat-insulating lid is formed from iridium or from at least the same chemical elements as the starting material from which the bulk single crystal is to be grown. [27] Growth structure according to at least one of claims 20 to 26, wherein the crucible is covered with a perforated disc.

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