Method for producing tin defect centers in a diamond substrate and diamond substrate

Abstract

Method for producing tin defect centers (2) in a diamond substrate (4), wherein the diamond substrate (4) has a surface (6) with (100) or (110) orientation, - wherein a p-doped diamond layer (8) is grown onto the surface (6), - wherein tin ions (14) are implanted into the grown diamond layer (8) by means of ion implantation with an implantation energy which is dimensioned such that at least a part of the tin ions (14) penetrate the diamond layer (8) and enter the diamond substrate (4) due to the lattice guidance effect, - wherein the diamond substrate (4) and the grown diamond layer (8) are heated in a heating process, so that defects (16) in the diamond lattice combine with the implanted tin ions (16) to form tin-defect centers (2), and - whereby the accumulated diamond layer (8) is essentially completely removed.

Description

[0001] The invention relates to a method for producing tin defect centers in a diamond substrate, wherein the diamond substrate has a (100) or (110) surface. The invention further relates to a diamond substrate with at least one tin defect center.

[0002] So-called spin impurities or spin defects in solids are among the best-known and most studied quantum systems. In particular, color centers in diamonds, such as the negatively charged nitrogen vacancy center (NV), have proven to be versatile, atom-sized spin systems with a multitude of applications in quantum optics, information processing, and quantum sensing.

[0003] The zero-voiding (NV) center in diamonds is suitable for demonstrating and developing a variety of sensor protocols for static magnetic and electric fields, pressure, temperature, or fluctuating fields. However, the zero-phonon line (ZPL) of the NV center exhibits only a small fraction of the total fluorescence (approximately 4%) due to its large phonon sideband (PSB). Furthermore, the NV center is highly sensitive to external noise, leading to instability in the optical transition energy. These drawbacks could be overcome by using group IV vacancy centers in diamond.

[0004] Group IV defect centers in diamond exhibit particularly stable optical properties due to their crystallographic symmetry, which favors emission in the zero phonon line (ZPL). The negatively charged tin vacancy center (also called tin-vacancy center, SnV) is especially promising in this regard.

[0005] For investigation and application, the controlled generation of tin-defect centers in diamond is desired. In particular, the most deterministic positioning possible, at the nanometer scale, is preferred. This is typically achieved through ion implantation, in which tin ions are implanted into the diamond lattice with an implantation energy that controls the statistical depth distribution of the implanted tin ions. Furthermore, the implantation process also creates defects (vacancies) in the diamond lattice due to collisions between the tin ions and the diamond lattice. After implantation, the diamond is heated, causing the defects in the diamond lattice to diffuse and combine with the implanted tin ions to form tin-defect centers.

[0006] The fabrication of tin-deficient centers by ion implantation is disclosed, for example, in R. Fukuta et al., Japanese Journal of Applied Physics 60, 035501 (2021), in SD Tchernij et al., ACS Photonics 2017, 4 (10), 2580-2586, in T. I-wasaki et al., PRL 119, 253601 (2017), and in AE Rugar et al., Nano. Lett. 20, pp. 1614-1619 (2020).

[0007] Tin defect centers produced by ion implantation, however, generally exhibit comparatively poor optical properties. This is primarily due to residual damage in the diamond lattice (implantation defects) in the immediate vicinity of the implanted tin defect centers, which is not completely eliminated by thermal heating.

[0008] The invention is based on the objective of providing a particularly suitable method for producing tin-deficient centers in a diamond substrate. In particular, the aim is to produce tin-deficient centers with the best possible optical properties. The invention is further based on the objective of providing a particularly suitable diamond substrate.

[0009] The problem is solved according to the invention with respect to the method by the features of claim 1 and with respect to the diamond substrate by the features of claim 10. Advantageous embodiments and further developments are the subject of the dependent claims. The advantages and embodiments mentioned with respect to the method are also transferable to the diamond substrate and vice versa.

[0010] The method according to the invention is designed, suitable, and configured for the production of tin defect centers in a diamond substrate. The tin defect centers are generated, in particular, by means of ion implantation, so that the method, by appropriate selection of the implantation density and / or by the optional use of an implantation mask, is suitable for producing multiple tin defect centers as well as single tin defect centers or a single tin defect center in the diamond substrate.

[0011] In this and the following, a diamond substrate is understood to be a diamond material, i.e., a material consisting essentially of a diamond lattice. In particular, a diamond substrate is understood to be a synthetic single-crystal diamond material, which, for example, has been produced by chemical vapor deposition (CVD). The diamond substrate or diamond material preferably exhibits the highest possible purity and electronic quality, as well as the lowest possible number of lattice defects. The diamond material, for example, has a nitrogen and / or boron content of less than 10 ppb (parts per billion), in particular less than 5 ppb, preferably less than 1 ppb, and an isotopic content of 13 Carbon-14 of about 1.1% (natural abundance) or less.

[0012] The diamond substrate is preferably thin or flat; in particular, the diamond substrate has a thickness or height that is significantly less than its dimensions along a longitudinal and transverse direction. For example, the diamond material has dimensions of 2 mm (millimeters) by 2 mm by 50 µm (micrometers).

[0013] According to the invention, the diamond substrate has a (100)- or (110)-oriented surface. The notation (hkl) corresponds to the Miller indices for designating crystal faces or planes in a crystal lattice. The diamond structure of the diamond lattice has a face-centered cubic lattice, with the cube faces formed by the planes (100), (010), and (001). The surface of the diamond substrate is thus oriented parallel to the (100)- or (110)-crystal plane of the diamond lattice.

[0014] The surface of the diamond substrate is, for example, polished or ground. To reduce mechanical stress (strain), the diamond substrate can be treated by an etching process, in particular a reactive ion etching (RIE) process, preferably an oxygen etching process (O₂ RIE). To clean the diamond substrate or its surface, the diamond substrate is, for example, cleaned before and / or after the etching process, particularly in an acid solution of sulfuric acid (H₂SO₄), nitric acid (HNO₃), and perchloric acid (HClO₄).

[0015] In a first process step, the preferably etched and / or cleaned (100) or (110) surface of the diamond substrate is overgrown with a diamond layer. In other words, a diamond layer is grown onto the surface. The grown diamond layer has the same lattice orientation as the diamond substrate, i.e., (100) or (110).

[0016] The diamond or growth layer is grown onto the surface of the diamond substrate, particularly in a growth or epitaxy process, for example, a CVD process, preferably in a homoepitaxial diamond synthesis, i.e., as an epitaxial layer (epilayer). The growth layer is also made of a diamond material, wherein the diamond material of the growth layer is doped or impregnated with foreign atoms, i.e., atoms that are not carbon. According to the invention, a p-doped diamond layer, i.e., a diamond layer with p-type doping, is grown. Foreign atoms are thus introduced into the diamond layer as acceptors, which create freely moving positive vacancies or holes, or defect electrons, in the diamond lattice of the diamond layer.

[0017] The growth layer is grown, for example, on the surface of the diamond material using a microwave CVD process (MW-CVD) at a power of 1000 W (watts), a temperature of 800 °C to 900 °C (degrees Celsius), and a pressure of approximately 30 torr. The doping of the growth layer preferably takes place in situ during the growth or epitaxy process by adding doping sources. These doping sources are added, for example, by introducing a process gas or a solid, such as a boron rod, into the CVD plasma.

[0018] In a second process step, tin ions (e.g., Sn) are added. + , Sn 2+ , ...) are implanted into the grown diamond layer by means of ion implantation. Preferably, the following are used: 119 Sn ions are implanted because they possess a nuclear spin, allowing for an interaction between tin-vacancy center electrons and the 119Sn nuclear spin is enabled, which is desirable for applications in quantum communication or quantum computing applications, for example.

[0019] The tin ions are implanted with an implantation energy dimensioned such that at least a portion of the tin ions completely penetrate the diamond layer and enter the diamond lattice of the diamond substrate due to the lattice guidance effect. In particular, the implantation energy is selected such that the projected or predicted depth distribution for tin ions is localized within the diamond layer without the lattice guidance effect.

[0020] Lattice channeling, also known as the lattice channeling effect, is a physical phenomenon in ion beam physics in which an ion can penetrate a single crystal almost undisturbed due to linear regions without lattice atoms in certain crystal lattices. By implanting into a (100) or (110) plane of the diamond lattice, such atom-free channels are created for guiding the tin ions, allowing them to penetrate deeper into the diamond lattice (statistically speaking) at the same implantation energy than with other implantation directions. This results in a reduction of the defect density in the vicinity of the implanted tin ions at their resting position.

[0021] Following the implantation process, the diamond, i.e., the diamond substrate and the diamond layer, undergoes a third process step: heating. During this heating process, the defects (vacancies) created in the diamond lattice during implantation combine with the implanted tin ions, thus forming tin-vacancy centers. Heating takes place at high temperatures under vacuum.

[0022] During implantation, lattice defects or vacancies are created. During the annealing or bake-out process, these vacancies can combine to form divacancies, i.e., two adjacent lattice defects, which are comparatively thermally stable. Due to p-doping, the defects exhibit a doubly positively charged state (2+) during bake-out, thus significantly reducing the formation of divacancies due to the Coulomb repulsion of the vacancies. The charging of the defects in the V + - or V 2+This condition occurs particularly in the area of ​​the interface between the substrate and the p-doped diamond layer grown on it. This provides more defects for combination with the implanted tin ions, thus reducing the number of lattice defects and increasing the number of generated tin-defect centers, and therefore the yield.

[0023] Finally, in a third process step, the grown diamond layer is essentially completely removed. This results in a particularly suitable method for producing tin-vacancy centers in a diamond substrate. Under optical excitation, the generated tin-vacancy centers stabilize in a (singly) negatively charged state, which is particularly advantageous with regard to the application of spin manipulation.

[0024] The invention is based on the understanding that, in ion implantation, the near-surface layers of the implanted surface exhibit numerous implantation defects (lattice defects, etc.). According to the invention, the grown diamond layer, in addition to its function of electrically charging the defects, also serves as a sacrificial layer for the ion implantation, so that the majority of the implantation defects are removed along with the diamond layer. The remaining tin defect centers thus result essentially from the lattice-guided tin ions, which are located at a distance from the majority of the implantation defects. As a result, the generated tin defect centers have an improved lattice environment within the diamond lattice of the diamond substrate, thereby enhancing the properties, particularly the optical properties, of the generated tin defect centers.

[0025] In the third process step, preferably at least the diamond layer is removed. In particular, a layer thickness corresponding to the implantation depth of non-lattice-guided tin ions is ablated or removed, so that preferably only tin defect centers remain, which are formed by lattice-guided tin ions in the diamond substrate.

[0026] In a suitable further development process, the grown diamond layer is removed by an etching process, in particular by means of a reactive ion etching (RIE) process, preferably an oxygen etching process (O₂ RIE). In contrast to mechanical removal, for example by polishing, this results in less strain and damage to the diamond lattice of the diamond substrate. The etching parameters depend on the etching system used. For example, with a high-frequency power of 30 W and a pressure of 10 mTorr (millitors), an etching rate of 5 nm / min (nanometers per minute) is achieved, so that removing a diamond layer 20 nm thick takes approximately 4 minutes. This removes the diamond material of the diamond layer essentially completely, and the remaining diamond substrate is subsequently wet-chemically cleaned, for example in an acid solution of H₂SO₄, HNO₃, and HClO₄.

[0027] In an advantageous embodiment, a fourth process step, particularly after temperature treatment and wet chemical cleaning of the surface, involves treating the surface of the diamond substrate with hydrogen (H). Specifically, the diamond substrate is exposed to a radio frequency (RF) or microwave hydrogen plasma. The treatment parameters (H gas pressure, RF or MW power, substrate temperature, treatment duration, application of an additional negative DC bias to the substrate) are preferably selected such that atomic hydrogen diffuses into the diamond substrate to a depth below the profile of the implanted tin defect centers. The hydrogen saturates or passivates existing defects and implantation damage in the diamond lattice of the diamond substrate, thereby improving the lattice quality and thus the stability and optical properties of the tin defect centers.

[0028] In an alternative version, the diamond substrate (and the diamond layer) is exposed to a hydrogen atmosphere for annealing after heating.

[0029] In a suitable design, the diamond layer is grown with a thickness of less than 50 nm (nanometers). In particular, a diamond layer of 20 nm to 30 nm is grown. The diamond layer thickness and the implantation energy are preferably matched such that the lattice-guiding extension of the depth distribution (so-called "channeling tail") for the tin ions extends into the underlying diamond substrate. In a suitable design, for example, an implantation energy of less than 100 keV (kiloelectronvolts), particularly between 30 keV and 60 keV, for example 40 keV, is used.

[0030] To ensure a sufficient lattice guidance effect, the tin ions are implanted in a suitable configuration with an implantation angle of less than 3°. Here, the implantation angle is defined as the implantation direction relative to the normal of the implanted surface. In other words, the implantation direction preferably deviates by less than 3° from the direction perpendicular to the (100) / (110) surface. This ensures that as many implanted tin ions as possible penetrate into the diamond lattice of the diamond substrate due to the lattice guidance effect. In particular, this reduces the local density of defects in the lattice.

[0031] In a preferred embodiment, boron atoms (B) are used as foreign atoms for the p-doping of the diamond layer. The number of boron atoms (N) A ) in the grown diamond material of the diamond layer, for example, is about 10 20up to 10 21 cm -3 (per cubic centimeter). The diamond layer is thus particularly p+-doped. The diamond layer preferably exhibits a doping transition to the diamond material that is as steep or sharp as possible. In other words, a doping profile with a step-like appearance is achieved with respect to the diamond substrate. In a suitable dimension, the doping profile at the transition between the diamond layer and the diamond substrate exhibits a doping gradient ∂N A / ∂x of approximately 10 20 cm -2 nm -1 To achieve such a "sharp" doping profile, a solid doping source is used, for example.

[0032] For example, a 20 nm to 30 nm thick diamond layer with boron doping is grown, with tin ions implanted at approximately 40 keV. Due to the lattice guidance effect, the depth distribution of the tin ions statistically extends below the diamond layer, i.e., into the diamond substrate. In other words, the tin vacancy centers are at least partially generated within the diamond substrate. The tin vacancy centers, or rather the implanted tin ions, are thus preferentially located in a charge carrier-reduced environment.

[0033] The tin vacancy centers are partially located in the substrate where no boron doping atoms are present, but where free charge carriers diffuse out from the boron-doped layer. In particular, the implantation-induced defects are electrically charged by these charge carriers. For this reason, the formation of divacancy complexes is suppressed during heat treatment.

[0034] In other words, boron doping of the diamond layer creates the most abrupt possible planar p+-n junction on the (100)- / (110)-oriented diamond substrate. The diamond substrate has a low concentration of nitrogen or other donor impurities (N D < 10 ppb). The boron-doped diamond layer, deposited by epitaxial growth, has a thickness in the nanometer range and a high concentration of boron acceptors N A above the full activation limit of approximately 1020 cm -3 as well as a high gradient of the boron doping profile at the substrate interface in a range of approximately ∂NA / ∂x ~ 10 20 cm -2 nm -1 After implantation and the heating process, the p+ layer is selectively removed, at least at the Sn-implanted sites.

[0035] In a suitable design, a bake-out temperature between 1200 °C and 1600 °C, particularly between 1400 °C and 1500 °C, is used during the bake-out process. For example, the diamond is baked for two hours at a high vacuum of less than 10 -6The diamond layer is annealed at mbar (millibar) pressure. This annealing process reduces lattice defects resulting from the implantation process, whereby defects in the lattice diffuse to the implanted tin and form stable tin defect centers. After annealing, the diamond layer and the associated diamond substrate are preferably cleaned in an acid solution.

[0036] The diamond substrate according to the invention has a (100) or (110) oriented surface and at least one tin defect center, which is produced according to a method described above. This results in a diamond substrate with an optically particularly stable tin defect center in a defined position. This makes it a particularly suitable diamond substrate for applications in quantum optics, information processing, and quantum sensing.

[0037] An embodiment of the invention is explained in more detail below with reference to a drawing. The drawing shows, in schematic and simplified representations: Fig. 1 in successive representations a method for producing tin defect centers in a diamond substrate, and Fig. 2. Depth distributions for boron doping, implanted Sn ions, and defects in the diamond lattice created by implantation are shown in superimposed diagrams.

[0038] Corresponding parts and sizes are always marked with the same reference symbols in all figures.

[0039] The Fig. Figure 1 shows, in successive schematic representations, a manufacturing process for producing tin defect centers 2 in a diamond substrate 4. The tin defect centers 2 are only provided with reference numerals in the figures as examples.

[0040] In this exemplary embodiment, the (manufacturing) process essentially comprises six process steps: I, II, III, IV, V, and VI.

[0041] In process step I, the diamond substrate 4 is provided. The diamond substrate 4 is a synthetic single-crystal diamond material with a diamond lattice that has a (100) orientation on a substrate surface 6. In other words, the (substrate) surface 6 is (100) oriented. The diamond substrate, or its diamond material or diamond lattice, has, for example, a nitrogen and / or boron content of less than 10 ppb, in particular less than 5 ppb, preferably less than 1 ppb, and an isotopic content of 13 Carbon content of approximately 1.1% or less.

[0042] The surface 6 of the diamond substrate 4 is, for example, polished or ground. To reduce mechanical stress, the diamond substrate 4 can be treated in process step I by means of an etching process, in particular a reactive ion etching process (RIE), preferably an oxygen etching process (O₂ RIE). To clean the diamond substrate 4 or the surface 6, the diamond substrate 2 is, for example, cleaned before and / or after the etching process, particularly in an acid solution of sulfuric acid (H₂SO₄), nitric acid (HNO₃), and perchloric acid (HClO₄).

[0043] In process step II, the surface 6 of the diamond substrate 4 is overgrown with a diamond layer 8. The diamond lattice of the diamond layer 8 has the same orientation as the underlying diamond lattice of the diamond substrate 4, so that a surface 10 of the diamond layer also has a (100) orientation.

[0044] The diamond layer 8 is grown onto the surface 6 of the diamond substrate 4, particularly in a growth or epitaxy process, for example in a CVD process, preferably in a homoepitaxial diamond synthesis, i.e., as an epitaxial layer (epilayer) with a thickness of 12. The diamond layer 8 is a diamond material doped or impregnated with foreign atoms, i.e., atoms other than carbon. According to the process, the diamond layer 8 is p-doped (p+-doped). Foreign atoms are thus introduced into the diamond layer as acceptors, which create freely moving positive vacancies or holes, or defects, in the diamond lattice of the diamond layer 8.

[0045] The diamond layer 8 is grown, for example, on the surface 6 of the diamond material 4 using a microwave CVD process (MW-CVD) at a power of 1000 W, a temperature of 800 °C to 900 °C, and a pressure of approximately 30 torr, wherein the doping preferably takes place in situ during the growth or epitaxy process by adding doping sources. The doping sources are added, for example, by introducing a process gas or by introducing a solid, such as a boron rod, into the CVD plasma.

[0046] In process step III, tin ions 14 are implanted into the surface 8 by means of ion implantation. Preferably, in this process 119Tin ions 14 are implanted into the (100)-oriented surface 10 at an implantation angle of less than 3°. The implantation direction thus deviates by less than 3° from the normal of the surface 10. This results in the tin ions 14 being implanted along a lattice direction of the diamond lattice along which a lattice guidance effect is possible. The implantation energy of the tin ions 14 is selected such that the projected or predicted depth distribution for the tin ions 14 without a lattice guidance effect is localized within the diamond layer 8, and that at least part of the depth distribution for the tin ions 14 with a lattice guidance effect is localized in the diamond substrate 4. At least some of the tin ions 14 are thus located in the diamond substrate 4 after implantation. During ion implantation, the tin ions 14 create defects 16 in the diamond lattice of the diamond layer 8 and the diamond substrate 4.The tin ions 14 and the defects 16 are shown in the figures with reference symbols only as examples.

[0047] In process step IV, the diamond, i.e., the diamond substrate 4 and the diamond layer 8 grown on it, is baked out in a vacuum. A baking temperature between 1200 °C and 1600 °C, particularly between 1400 °C and 1500 °C, is used. For example, the diamond is baked out for two hours at a high vacuum of less than 10 -6 The diamond layer 8 is baked out at mbar. During the baking process, lattice defects due to the implantation process are reduced; in particular, defects 16 diffuse to the implanted tin ions 14 and form stable tin defect centers 2 with them. After the baking process, the diamond layer 8 and the associated diamond substrate 4 are preferably cleaned in an acid solution.

[0048] In process step V, the grown diamond layer 8 is substantially completely removed. In particular, the grown diamond layer 8 is removed by an etching process, especially by means of a reactive ion etching process (RIE), preferably by means of an oxygen etching process (O2 RIE). For this purpose, the diamond is exposed to a suitable plasma, the process parameters being selected such that a diamond layer with a thickness 17 approximately corresponding to the layer thickness 12 is removed.

[0049] It is possible that slightly less or more than the layer thickness 12 is etched, so that the resulting surface 6' of the diamond substrate 4 may differ from the original surface 6. "Slightly less or more" here refers in particular to a value or tolerance range of up to ± 10 nm, which results, for example, from starting and stopping the plasma. Preferably, slightly more than the layer thickness 12, for example up to 10 nm more, is etched. In other words, the diamond substrate 4 is also partially etched and removed. This ensures that the p-doped diamond layer 8 is completely removed. Furthermore, implantation defects of the diamond substrate 4 are also removed, thus further improving the quality of the resulting tin defect centers 2.Preferably, with layer thickness 17, those tin ions 16 which are in the non-lattice-guided part of the depth distribution are removed, so that after etching, preferably only the tin ions 16 or tin defect centers 2 from the lattice-guided part of the depth distribution remain.

[0050] In an optional process step VI, the surface 6' of the diamond substrate 4 is treated with hydrogen (H), the hydrogen-treated surface being designated by reference numeral 6''. In particular, the diamond substrate 4 is exposed to a radiofrequency (RF) or microwave hydrogen plasma. The treatment parameters (H gas pressure, RF or MW power, substrate temperature, treatment duration, application of an additional negative DC bias to the substrate) are preferably selected such that atomic hydrogen diffuses into the diamond substrate 4 to a depth below the profile of the implanted tin defect centers 2. The hydrogen saturates or passivates existing defects 16 and implantation defects in the diamond lattice of the diamond substrate 4, thereby improving the lattice quality—and thus the stability and optical properties—of the tin defect centers 2.

[0051] In an alternative embodiment, it is conceivable, for example, that process steps IV and VI are combined, and that the diamond substrate 4 (and the diamond layer 8) is exposed to a hydrogen atmosphere for annealing after heating.

[0052] The following is the selection of parameters for process steps II, III, IV, and V based on the Fig. 2 explained in more detail. Fig. 2 comprises three vertically stacked sections 18, 20, 22.

[0053] Sections 18, 20, and 22 each show a number-depth diagram. Along the x- or abscissa axis, a depth t, i.e., a distance to the surface 10, is plotted, particularly in nanometers (nm), while along the vertical ordinate axis (y-axis), a density is plotted. Section 18 shows the charge carrier density N in the diamond lattice, while Section 20 shows a tin density N. Snof implanted tin ions 16 in the diamond lattice, and section 22 shows a defect density Nv of defects 16.

[0054] Sections 18, 20, and 22 each show two vertical lines. The dashed line represents the layer thickness 12 of the grown, p- or boron-doped, diamond layer 8, while the dotted line corresponds to an etching depth, i.e., the layer thickness 17 removed during the etching process.

[0055] In the illustrated embodiment, the etching process extends deeper than the original diamond substrate, thus removing a portion of the original diamond substrate 4. Etching to a thickness of 17 removes the majority of the ion implantation-induced defects, which, according to Section 22, are concentrated in the near-surface layer, at least for the selected implantation energy range (< 100 keV). Such near-surface defects are a potential cause of optical disturbances in implanted tin defect centers located somewhat deeper. Etching to a thickness of 17 therefore improves the optical properties of the remaining tin defect centers 2.

[0056] Section 18 shows two dotted horizontal lines. The upper line corresponds to the density of acceptor foreign atoms N. Ain the p-doped diamond layer 8. The lower line shows the density of the intrinsic donor foreign atoms N D in the diamond lattice of the diamond substrate 4.

[0057] Section 18 shows a depth distribution 24 for the holes or defect electrons in the diamond lattice, section 20 shows a depth distribution 26 for the implanted tin ions 14, and section 22 shows a depth distribution 28 for the defects 16 resulting from the ion implantation.

[0058] The tin defect centers 2 are generated according to the procedure by ion implantation of tin ions 14 and subsequent heating. The ion implantation essentially results in the depth distribution 26 of the tin ions 14 and in the depth distribution 28 of the defects 16 generated by the implanted tin ions 14 within the diamond lattice.

[0059] The distribution maxima (peaks) of the depth distributions 26 and 28 are shifted relative to each other; in particular, the distribution maximum of the defects 16 is essentially located at the surface 10, and the distribution maximum of the tin ions 14 is located within the diamond lattice. The depth distributions 26 and 28 thus only partially overlap, meaning that tin defect centers 2 produced by ion implantation are generally embedded in a damaged diamond lattice and therefore exhibit poor optical properties.

[0060] One of the considerations underlying the invention is the exploitation of the lattice guidance effect in ion implantation, so that the distribution maxima of the depth distribution 26 of the tin ions 14 is located further away from the distribution maxima of the depth distribution 28 of the defects 16, and thus the tin defect centers 2 in the diamond lattice are generated further away from the majority of the implantation defects.

[0061] To reduce implantation damage, the diamond layer 8 is doped with acceptor foreign atoms. Due to intrinsic impurities (e.g., nitrogen) which act as donor foreign atoms, the diamond substrate 4 is essentially (slightly) n-doped. The charge carrier density N D The p-doped diamond layer 8 thus creates a planar p+-n junction at the interface between the diamond substrate 4 and the diamond layer 8, in which the number of acceptor foreign atoms N A much larger than the number of donor foreign atoms N D is dimensioned.

[0062] Boron atoms (B) are preferably used as foreign atoms for p-doping. The density of boron atoms (N) A ) in the grown diamond material of the diamond layer, for example, is about 10 20 up to 10 21 cm -3, and is therefore preferably above the full activation limit. The doping profile or depth distribution 24 exhibits a doping gradient ∂NA / ∂x of approximately 10 at the transition between the diamond layer 8 and the diamond substrate 4. 20 cm -2 nm -1 Due to the sharp doping profile, the holes diffuse from the p-doped diamond layer 8 into the intrinsic diamond substrate 4, particularly during the curing or heating step (process step IV), so that the depth distribution 24 extends into the diamond substrate 4. The thermally mobile holes are trapped at the defects, thus becoming positively charged (V + or V 2+ ).

[0063] Due to this p-doping, the defects 16 exhibit a doubly positively charged state (2+) during bake-out, thus significantly reducing the formation of di-vacancies due to the Coulomb repulsion of the defects 16. This makes more defects 16 available for combination with the implanted tin ions 14, thereby reducing the number of lattice defects and increasing the number of generated tin-vacancy centers 2, i.e., the yield.

[0064] As a matter of procedure, the implantation defects remaining after heating are removed as far as possible so that they do not have a negative impact on the tin defect centers 2. For this purpose, the diamond layer 8 is grown before implantation and then etched, so that a large proportion of the implantation defects are removed.

[0065] Because of the central importance of the lattice guidance effect for the process, the other parameters, in particular the layer thickness 12 of the diamond layer 8 and the implantation energy of the tin ion implantation, are essentially compromise solutions. The aim is to generate the tin defect centers 2 in a diamond region with minimal lattice damage, with the lattice guidance component of the depth distribution 26 and with maximum charge carrier density, so that the best possible optical properties are achieved.

[0066] All these steps aim to reduce the density of implantation defects caused by tin ion implantation (defect clusters) along the energy ion stop tracks. In this way, the optical and spin properties of the optical tin defect centers generated by this method are improved.

[0067] In the exemplary embodiment of the Fig.In process step II, a diamond layer 8 with a layer thickness 12 of approximately 15 nm and a boron doping with a charge carrier density N is formed. D of 5×10 20 cm -3 grown. In process step III, the tin ions 14 are implanted with an implantation energy of 40 keV, resulting in a depth distribution 26 between approximately 10 nm and 30 nm and a depth distribution 28 between 0 nm and 20 nm. In process step V, for example, a layer thickness 17 of approximately 19 nm is etched.

[0068] The claimed invention is not limited to the embodiments described above. Rather, other variants of the invention can also be derived by a person skilled in the art within the scope of the disclosed claims without departing from the subject matter of the claimed invention. In particular, all individual features described in connection with the various embodiments can also be combined in other ways within the scope of the disclosed claims without departing from the subject matter of the claimed invention.

[0069] Thus, the substrate surface 6 of the diamond substrate 4 can have a (110) orientation instead of a (100) orientation, which is also suitable for the tunneling effect (channeling effect) in the diamond lattice.

Claims

[1] Method for producing tin defect centers (2) in a diamond substrate (4), wherein the diamond substrate (4) has a surface (6) with (100) or (110) orientation, - wherein a p-doped diamond layer (8) is grown onto the surface (6), - wherein tin ions (14) are implanted into the grown diamond layer (8) by means of ion implantation with an implantation energy which is dimensioned such that at least a part of the tin ions (14) penetrate the diamond layer (8) and enter the diamond substrate (4) due to the lattice guidance effect, - wherein the diamond substrate (4) and the grown diamond layer (8) are heated in a heating process, so that defects (16) in the diamond lattice combine with the implanted tin ions (16) to form tin-defect centers (2), and - whereby the accumulated diamond layer (8) is essentially completely removed. [2] Method according to claim 1, characterized by , that the diamond layer (8) is removed by means of an etching process. [3] Method according to claim 1 or 2, characterized by , that the surface (6') of the diamond substrate (4) is treated with hydrogen after the removal of the grown diamond layer (8). [4] Method according to any one of claims 1 to 3, characterized by , that the diamond layer (8) is grown with a layer thickness (12) of less than 50 nm, in particular between 20 nm and 30 nm. [5] Method according to any one of claims 1 to 4, characterized by that an implantation energy of less than 100 keV, in particular between 30 keV and 60 keV, preferably 40 keV, is used. [6] Method according to any one of claims 1 to 5, characterized by , that the tin ions (14) are implanted with an implantation angle of less than 3°. [7] Method according to any one of claims 1 to 6, characterized by, that boron atoms are used for the p-doping of the diamond layer (8), with the boron doping having a concentration of about 10 20 up to 10 21 cm -3 exhibits. [8] Method according to claim 7, characterized by , that the boron doping starting from the boundary layer to the surface (6) has a doping gradient of about 10 20 cm -2 nm -1 exhibits. [9] Method according to any one of claims 1 to 8, characterized by , that a baking temperature between 1200 °C and 1600 °C, in particular between 1400°C and 1500°C, is used in the baking process. [10] Diamond substrate (4) having a (100) oriented surface, and having at least one tin defect center (2), produced according to a method according to any one of claims 1 to 9.

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