Method for generating group iv-vacancy center, and method for producing diamond crystal having group iv-vacancy center

Abstract

In order to realize a production method, for forming a group IV-vacancy center, in which efficiency of the formation of the group IV-vacancy center is improved, a generation method for the group IV-vacancy (V) center according to the present invention includes: a preparation step (S11) for preparing a diamond that includes a group IV element and a vacancy; and a rapid thermal annealing step (S12) for forming the group IV-vacancy center in the diamond by performing rapid thermal annealing of the diamond at a target temperature of 800°C or higher.

Description

Method for generating group IV-vacancy centers and method for producing diamond crystals having group IV-vacancy centers

[0001] The present invention relates to a method for generating group IV-vacancy centers and a method for producing diamond crystals having group IV-vacancy centers.

[0002] Color centers are expected to be applied to a variety of devices (e.g., quantum information devices, quantum sensors). For this reason, development of technologies for efficiently producing materials having color centers (hereinafter referred to as "color center materials") (technologies for efficiently generating color centers) is underway (Patent Document 1, Non-Patent Documents 1 to 3). Examples of color centers include nitrogen-vacancy (NV) centers containing nitrogen elements and group IV-vacancy (V) centers containing group IV elements (group 14 elements in the new IUPAC notation, e.g., silicon, germanium, and tin).

[0003] U.S. Patent Publication No. 2021 / 0371741 A1

[0004] T. Yamamoto, et. al., "Extending spin coherence times of diamond qubits by high-temperature annealing", PHYSICAL REVIEW B 88, 075206(2013) Sorawis Sangtawesin, et. al., "Origins of Diamond Surface Noise Probed by Correlating Single-Spin Measurements with Surface Spectroscopy", PHYSICAL REVIEW X 9, 031052 (2019) Yasuyuki Narita, et. al., "Multiple Tin-Vacancy Centers in Diamond with Nearly Identical Photon Frequency and Linewidth", PHYSICAL REVIEW APPLIED 19, 024061 (2023)

[0005] In the prior art (Patent Document 1, Non-Patent Documents 1 to 3), the material (diamond) is gradually heated to a high temperature of, for example, 1000°C or higher, and heat-treated for a relatively long time. For example, the material is heated to 1000°C or higher over a period of 10 minutes to several hours, and this temperature is maintained for several hours to generate color centers in the material.

[0006] However, the inventors have studied methods for producing color center materials (methods for generating color centers) and found that the heat treatment conditions in the above-mentioned conventional techniques are not necessarily appropriate. As a result of various experiments, they have found that the formation of color centers proceeds more rapidly than generally assumed, and that it is therefore preferable to quickly transition to temperature conditions suitable for the formation of color centers.

[0007] An object of one aspect of the present invention is to provide a method for generating a group IV-vacancy center, which aims to form the group IV-vacancy center under more appropriate temperature conditions.

[0008] In order to solve the above problems, a method according to one aspect of the present invention is a method for generating a group IV-vacancy center, comprising: a preparation step of preparing a diamond containing a group IV element and a vacancy; and a rapid thermal annealing step of rapid thermal annealing the diamond at a target temperature of 800°C or higher to form a group IV-vacancy center in the diamond.

[0009] According to one aspect of the present invention, rapid thermal annealing allows for a rapid transition to an appropriate temperature condition, and facilitates the progression of the formation of group IV-vacancy centers under the appropriate temperature condition.

[0010] 1 is a flow diagram showing an example of a manufacturing method according to a first embodiment of the present invention. FIG. 1 is a schematic diagram showing the introduction of a group IV element and vacancies into a diamond. FIG. 2 is a graph showing an example of a rapid thermal annealing process. FIG. 3 is a schematic diagram showing the structure of a group IV-vacancy center. FIG. 4 is a schematic diagram showing the formation of a group IV-vacancy center in a diamond. FIG. 5 is a flow diagram showing an example of a manufacturing method according to a second embodiment of the present invention. FIG. 6 is a diagram showing the maximum luminescence intensity of a sample before and after acid washing. FIG. 7 is a diagram showing the repetition of heat treatment, PL measurement, and acid washing. FIG. 8 is a photograph of a HPHT-synthesized diamond crystal heat-treated under normal pressure. FIG. 9 is a photograph of a CVD-synthesized diamond crystal heat-treated under normal pressure. FIG. 10 is a photograph of a HPHT-synthesized diamond crystal heat-treated under high pressure. FIG. 11 is a photograph of a CVD-synthesized diamond crystal heat-treated under high pressure. FIG. 12 is a diagram showing an luminescence spectrum in a PL measurement of a HPHT-synthesized diamond crystal. FIG. 13 is a diagram showing an luminescence spectrum in a PL measurement of a synthetic diamond crystal. FIG. 14 is a graph showing the relationship between heat treatment time and luminescence intensity in a HPHT-synthesized diamond crystal. 1 is a diagram showing an emission spectrum in PL measurement, a diagram showing the maximum value of the emission intensity of the sample, a diagram showing an emission spectrum in PL measurement, a diagram showing the maximum value of the emission intensity of the sample, and a diagram showing the relationship between the position on the sample and the maximum value of the emission intensity.

[0011] [Embodiment 1] One embodiment of the present invention will be described in detail below. Fig. 1 is a flow diagram showing an example of a method for producing a color center material (a method for generating a color center) S10 according to embodiment 1 of the present invention.

[0012] Here, a method for manufacturing a diamond crystal having a group IV-vacancy center (a method for generating a group IV-vacancy center) will be described. As shown in Figure 1, the manufacturing method (generation method) S10 includes a preparation step (S11) and a rapid thermal annealing step (S12).

[0013] (1) Preparation Step S11 Preparation step S11 is a step of preparing a diamond containing a group IV element and vacancies. As will be described later, the group IV element and vacancies can be introduced into the diamond by implanting ions of the group IV element. The vacancies may also be formed by electron beam irradiation.

[0014] Diamond is, for example, synthetic diamond, for example, bulk (plate-like) or particle (powder-like) of synthetic diamond single crystal.Synthetic diamond can be produced by, for example, high-temperature high-pressure method (HPHT method), chemical vapor deposition method (CVD method) or detonation method.As synthetic diamond, for example, bulk of about several mm or powder-like particle of diameter about 5 nm to about 200 nm can be used.

[0015] It is desirable that diamond basically does not contain nitrogen. This is because nitrogen bonds with vacancies to become NV centers, consuming the vacancies necessary for the formation of group IV-vacancy centers. However, it is acceptable for diamond to contain a certain amount of nitrogen. As shown in Example 1 below, if the nitrogen content in diamond is about the same (for example, about 1 ppm) as the amount of group IV element implanted (for example, 5 ppm), group IV-vacancy centers can be formed.

[0016] Examples of Group IV elements include silicon (Si), germanium (Ge), and tin (Sn). A vacancy refers to a state in which carbon atoms that should be present in the diamond crystal lattice are missing. For example, Group IV elements and vacancies can be introduced into diamond by carrying out the following introduction process.

[0017] The preparation step S11 may include an introduction step of introducing a group IV element and vacancies into the diamond by implanting group IV ions into the diamond.

[0018] As mentioned above, vacancies can also be formed by irradiating diamond with electron beam.For example, by irradiating diamond containing group IV element with electron beam, diamond containing group IV element and vacancies can be formed.And, diamond containing group IV element can be formed by, for example, injecting group IV ions into diamond.That is, by injecting group IV ions into diamond and irradiating diamond with electron beam, group IV element and vacancies can be introduced into diamond.At this time, the injection of group IV ions and the irradiation of electron beam can be carried out in either order, or can be carried out simultaneously.

[0019] 2 is a schematic diagram showing the state in which a group IV element and a vacancy are introduced into a diamond. By ionizing a group IV element IV (group IV ion I) and accelerating it with an electric field or the like, the group IV ion I can be injected into the material (diamond S). By injecting the group IV ion I, the group IV element IV and a vacancy V can be introduced into the diamond S. A vacancy V is formed on the path along which the group IV ion I travels through the diamond S, and the group IV element IV is injected at the end of the path. The injection depth D at this time is preferably at least a certain depth (for example, on the order of μm). This is because there is a possibility that the surface of the diamond may be transformed into a non-diamond layer during the annealing process.

[0020] (2) Rapid Thermal Annealing Step S12 Rapid thermal annealing step S12 is a step of forming group IV-vacancy centers in the diamond by rapid thermal annealing (RTA) the diamond at a target temperature of 800°C or higher. As will be described later, by rapidly raising the temperature of the diamond, group IV-vacancy centers can be formed at an appropriate target temperature. If the rate of temperature rise is slow, the formation of group IV-vacancy centers will progress during the temperature rise, and there is a possibility that the formation of group IV-vacancy centers will be substantially completed before the target temperature is reached.

[0021] A heat treatment furnace capable of rapid thermal annealing can be used for the rapid thermal annealing step S12. Examples of such a heat treatment furnace include a heat treatment furnace that can rapidly heat a sample (e.g., diamond bulk and particles) by irradiating a stage inside the furnace with high-intensity light (e.g., infrared light, laser light) from a light source to heat the sample. The stage is heated by the light source, thereby heating the sample on the stage. Examples of the light source include an infrared lamp and a laser light source. An example of a heat treatment furnace is an infrared lamp heating device (a heat treatment furnace that uses an infrared lamp as a light source).

[0022] The rapid thermal annealing step S12 can be performed, for example, in a heat treatment furnace under atmospheric pressure and an inert gas (e.g., argon gas) atmosphere. However, the rapid thermal annealing step S12 may also be performed under a high pressure of about 6 to 10 GPa instead of atmospheric pressure.

[0023] 3 is a graph showing an example of the rapid thermal annealing step S12. The rapid thermal annealing step S12 includes a rapid thermal processing (RTP) step S121, a heat treatment step S122, and a temperature reduction step S123. Here, a preheating step S120 is performed before the rapid thermal annealing step S12.

[0024] That is, a preheating step S120 may be carried out between the preparation step S11 and the rapid thermal annealing step S12. This preheating step S120 is a heat treatment step in which the diamond is maintained at a temperature range of 200°C to 400°C (e.g., 300°C) in order to remove moisture and the like that may be contained in the diamond bulk and particles (powder) or in the heat treatment furnace. Since group IV-vacancy centers are not substantially formed in the temperature range of this preheating step S120, rapid thermal annealing does not need to be used in the preheating step S120.

[0025] In the rapid thermal process S121, the temperature of the diamond is rapidly raised by, for example, irradiating a high-intensity light from a light source onto a stage on which the diamond is placed. More specifically, in the rapid thermal process S121, the temperature of the diamond is rapidly raised to a high temperature (target temperature) of 800°C or higher by irradiating a high-intensity light from a light source onto a stage on which the diamond bulk and particles are placed.

[0026] The rapid thermal process S121 is a step of heating the diamond to a target temperature T2, and preferably includes a step of heating the diamond at a temperature rise rate At of at least 1000°C per minute or more from a temperature T1 exceeding at least 600°C to a target temperature T2 of 800°C or higher. By increasing the temperature rise rate At, it is possible to reduce the generation of group IV-vacancy centers before the target temperature T2 is reached. The target temperature T2 is generally in the range of 800 to, for example, 1800°C or 2500°C, but it is preferable to vary the target temperature T2 depending on the type of group IV element, as described below.

[0027] The reason why the temperature rise rate of ΔT°C or more per second is set from temperature T1 to target temperature T2 of 800°C or higher is that group IV-vacancy centers are formed within this temperature range. Conversely, if the temperature is lower than this temperature range, the temperature rise rate does not need to be so high. By passing through this temperature range quickly, it becomes easy to form group IV-vacancy centers with good properties through appropriate heat treatment at the set target temperature T2. If the temperature rise rate is low within this temperature range, the formation of group IV-vacancy centers may progress before the target temperature T2 is reached, making the set target temperature meaningless.

[0028] In the above, the temperature rise rate At from temperature T1 to target temperature T2 is considered. However, instead of or in addition to this, a temperature rise rate At0 from temperature T1 to a temperature (T2-ΔT) that is a predetermined value ΔT lower than target temperature T2 may be specified. For example, the temperature may be raised at a rate of 1000°C per minute or higher to a temperature (T2-ΔT) that is ΔT lower than target temperature T2. ΔT may be specified as 50°C, for example. Note that temperature ΔT can be set to prevent the sample temperature from temporarily exceeding or falling below the target temperature (overshoot / undershoot).

[0029] Just before the target temperature T2 is reached, the amount of light emitted from the light source is reduced. As a result, the rapid thermal annealing step S12 transitions from a rapid thermal process S121, in which the temperature rises rapidly, to a heat treatment step S122, in which the temperature is substantially fixed at the target temperature. In the heat treatment step S122, an appropriate heat treatment at the set target temperature T2 forms a group IV-vacancy center with good characteristics.

[0030] 4 is a schematic diagram showing the structure of a group IV-vacancy center. A lattice lacking a carbon atom (C) becomes a vacancy (V). A group IV-vacancy center is composed of two vacancies (V) and a group IV element (IV) located between these two vacancies (V).

[0031] Figure 5 is a schematic diagram showing the formation of a group IV-vacancy center in diamond. Vacancies V and group IV elements IV migrate due to heat treatment. In particular, vacancies V migrate at a high rate because carbon C, the source of vacancies V, has a smaller mass than the group IV element IV (e.g., silicon). In this way, group IV-vacancy centers are formed by the migration of vacancies V and group IV elements IV.

[0032] For example, as described above, the target temperature T2 is roughly in the range of 800 to 1800° C. or in the range of 800 to 2500° C. The target temperature T2 can be 1800° C. for silicon (Si), germanium (Ge), and tin (Sn). The time (heat treatment time) for the heat treatment step S122 can be in the range of 1 to 50 minutes, 5 to 50 minutes, and 100 minutes or more for silicon (Si), germanium (Ge), and tin (Sn), respectively.

[0033] After the heat treatment step S122, the irradiation of light from the light source onto the stage on which the diamond is placed is stopped, and the temperature of the diamond is lowered to approach room temperature (cooling down step S123). The diamond having group IV-vacancy centers is removed from the heat treatment furnace and can be used for various purposes.

[0034] As described above, in this embodiment, rapid thermal annealing allows for a rapid transition to an appropriate temperature condition (target temperature), and the formation of group IV-vacancy centers can be reliably promoted at the target temperature.

[0035] [Embodiment 2] Another embodiment of the present invention will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0036] 6 is a flow diagram showing an example of a manufacturing method (production method) S20 according to embodiment 2 of the present invention. As shown in FIG. 6, in this embodiment, an annealing step S21 is performed between the preparation step S11 and the rapid thermal annealing step S12.

[0037] In the annealing step S21, the diamond is treated at a temperature of 600° C. or more and less than 800° C. to form di-vacancies (V) in the diamond. ２ For example, the diamond is held at a target temperature in the range of 600 to 750°C for 10 to 100 hours. The annealing step S21 causes the vacancies dispersed in the diamond to move and form double vacancies (V ２ ) is formed.

[0038] The annealing step S21 can be performed, for example, under normal pressure or under a high pressure of about 6 to 10 GPa in an inert gas (eg, argon gas) atmosphere, similar to the rapid thermal annealing step S12.

[0039] Furthermore, the annealing step S21 and the rapid thermal annealing step S12 may be performed consecutively using a heat treatment furnace capable of rapid thermal annealing (for example, an infrared lamp heating device).

[0040] After the annealing step S21, a rapid thermal annealing step S12 is performed to form group IV-vacancy centers in the diamond.

[0041] By performing the annealing step S21, it is possible to increase the amount of group IV-vacancy centers produced compared to when the annealing step S21 is not performed. In the annealing step S21, the double vacancies (V ２ ) is believed to result in more efficient formation of group IV-vacancy centers.

[0042] It is not preferable to perform a normal heat treatment in which the temperature rise rate At to the target temperature T2 is relatively small instead of the rapid thermal annealing step S12 after the annealing step S21. ２ ) may be decomposed and return to normal pores during normal heat treatment.

[0043] As described above, in this embodiment, the annealing step S21 is performed before the rapid thermal annealing step S12 to form double voids (V ２ ) allows for more efficient formation of group IV-vacancy centers.

[0044] [Summary] The method according to aspect 1 of the present invention is a method for generating a group IV-vacancy center, and includes a preparation step of preparing a diamond containing a group IV element and a vacancy, and a rapid thermal annealing step of rapid thermal annealing the diamond at a target temperature of 800°C or higher to form a group IV-vacancy center in the diamond.

[0045] A method for producing diamond according to a second aspect of the present invention is the method for producing diamond according to the first aspect, further comprising the step of treating the diamond at a temperature of 600° C. or more and less than 750° C. between the preparation step and the rapid thermal annealing step to form di-vacancies (V) in the diamond. ２ ), wherein the rapid thermal annealing step forms group IV-vacancy centers from the divacancies.

[0046] A production method according to aspect 3 of the present invention is the same as that according to aspect 1 or 2, wherein the rapid thermal annealing step is a step of raising the temperature of the diamond to a target temperature of 800°C or higher, and includes a step of raising the temperature of the diamond from a temperature exceeding at least 600°C to the target temperature at a temperature increase rate of 1000°C or higher per minute.

[0047] A production method according to Aspect 4 of the present invention is any of Aspects 1 to 3, wherein the preparation step includes an introduction step of introducing a Group IV element and vacancies into the diamond by implanting Group IV ions into the diamond.

[0048] A production method according to Aspect 5 of the present invention is any of Aspects 1 to 3, wherein the preparation step includes an introduction step of implanting Group IV ions into the diamond and introducing Group IV elements and vacancies into the diamond by irradiating the diamond with an electron beam.

[0049] A sixth aspect of the present invention relates to a production method according to any one of the first to fifth aspects, wherein the Group IV element is Si, and in the rapid thermal annealing step, the diamond is held at a target temperature of about 1800°C for 1 minute or more and less than 50 minutes.

[0050] A production method according to Aspect 7 of the present invention is any of Aspects 1 to 5, wherein the Group IV element is Ge, and in the rapid thermal annealing step, the diamond is held at a target temperature of about 1800°C for 5 minutes or more but less than 50 minutes.

[0051] A production method according to an eighth aspect of the present invention is any of the first to fifth aspects, wherein the Group IV element is Sn, and in the rapid thermal annealing step, the diamond is held at a target temperature of about 1800°C for 100 minutes or more.

[0052] A manufacturing method according to Aspect 9 of the present invention is a method for manufacturing a diamond crystal having a group IV-vacancy center, and includes a preparation step of preparing a diamond containing a group IV element and a vacancy, and a rapid thermal annealing step of rapid thermal annealing the diamond at a target temperature of 800°C or higher to form a group IV-vacancy center in the diamond.

[0053] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0054] Example 1 corresponding to the first embodiment will be described below. As samples, synthetic diamond crystals produced by high pressure, high temperature (HPHT) and chemical vapor deposition (CVD) methods were used. The synthetic diamond produced by the HPHT method contains approximately 1 ppm of nitrogen. On the other hand, the synthetic diamond produced by the CVD method contains less than approximately 1 ppb (1 / 1000 of 1 ppm) of nitrogen, and the amount of nitrogen impurity varies in concentration.

[0055] (1) Preparation Step S11 Silicon (Si), germanium (Ge), and tin (Sn) were each ionized, accelerated to 18 MeV by an accelerator, and irradiated onto the sample. As a result, silicon and the like were implanted to a depth of 3 μm at a concentration of 5 ppm.

[0056] (2) Rapid Thermal Annealing Step S12: Then, in an argon gas atmosphere at normal pressure, a preheating step S120 and a rapid thermal annealing step S12 (rapid thermal process S121, heat treatment step S122, and temperature-lowering step S123) were performed using an infrared lamp heating device. In the rapid thermal process S121, the temperature of the sample reached 1800°C in a heating time of 1 minute. In the heat treatment step S122, the temperature was set to 1800°C, and the treatment time was changed in the range of 1 to 10 minutes.

[0057] More specifically, in the preheating step S120, the temperature was raised from room temperature to 300°C in 1 minute and held at 300°C for 10 minutes. In the rapid thermal process S121, the temperature was raised from 300°C to 1750°C in 30 seconds and then to 1800°C in 30 seconds. In the heat treatment step S122, the temperature was held at 1800°C for 1 to 10 minutes to perform heat treatment.

[0058] After the rapid thermal annealing step S12, the sample was subjected to photoluminescence (PL) measurement to examine the amount of color centers generated in the sample. PL measurement was performed using a Horiba, Ltd., microscopic laser Raman spectrometer, LabRAM HR Evolution, with a 532 nm laser (CW). The sample was then washed with acid. The sample was repeatedly subjected to heat treatment (preheating step S120, rapid thermal annealing step S12), PL measurement, and acid washing.

[0059] Figure 7 shows the maximum emission intensities of Samples 1 and 2 before and after acid cleaning. Sample 1 underwent rapid thermal annealing S12 (RTA) at 1800°C for 100 minutes. Sample 2 underwent RTA at 1800°C for 100 minutes followed by acid cleaning. In other words, the difference between Samples 1 and 2 is whether or not they were acid cleaned. Comparing the PL intensities of Samples 1 and 2 reveals that the PL intensity decreases if acid cleaning is not performed.

[0060] Figure 8 shows the repetition of heat treatment HT, PL measurement PL, and acid cleaning AC. As shown in Figure 7, the treatment was repeated 10 times. The heat treatment times for the first 10 times were 1 minute, 1 minute, 3 minutes, 5 minutes, 5 minutes, 10 minutes, 10 minutes, 10 minutes, and 10 minutes, respectively, and the cumulative heat treatment times were 1 minute, 2 minutes, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, and 60 minutes. The results show the relationship between heat treatment time and the amount of color centers generated.

[0061] Figures 9 and 10 show photographs of synthetic diamond crystals, respectively, heat-treated under atmospheric pressure by HPHT and CVD. Samples implanted with silicon (Si), germanium (Ge), and tin (Sn), respectively, were treated under the following conditions (1) and (2), and photographed with a bright-field microscope after acid washing. (1) No heat treatment. (2) Heat treatment at 1800°C under atmospheric pressure (cumulative heat treatment times of 50 and 100 minutes).

[0062] Note that in Figure 10, only one representative sample photograph is shown for the unheat-treated samples, because the CVD-synthesized diamond crystals are polished and laser-cut to a predetermined shape, so all the unheat-treated samples have identical micrographs.

[0063] As shown in FIGS. 9 and 10, the surface shape of the sample was not changed by the heat treatment (1800° C., 100 minutes) under atmospheric pressure.

[0064] Figures 11 and 12 show photographs of synthetic diamond crystals heat-treated under high pressure by HPHT and CVD, respectively. Samples implanted with silicon (Si), germanium (Ge), and tin (Sn) were treated under the following conditions (1) and (2), respectively, and photographed with a bright-field microscope after acid washing. (1) No heat treatment. (2) Heat treatment under high pressure (7.7 GPa) at 2100°C (cumulative heat treatment time: 20 minutes).

[0065] Here, the temperature was not raised to 300° C. and maintained at that temperature in the preheating step S120, and the temperature was not rapidly raised in the rapid thermal process S121.

[0066] 12, for the same reason as in FIG. 10, only a photograph of one typical sample without heat treatment is shown.

[0067] As shown in FIGS. 11 and 12, the surface shape of the sample was changed by heat treatment (2100° C., 20 minutes) under high pressure (7.7 GPa).

[0068] 13 shows the PL emission spectra of HPHT-synthesized diamond crystals, where SP1, SP2, and SP3 show the PL spectra from samples implanted with silicon (Si), germanium (Ge), and tin (Sn), respectively.

[0069] 13, ZPL (zero phonon lines) specific to the Si-V center, Ge-V center, and Sn-V center appear at wavelengths of 738 nm, 602 nm, and 619 nm, respectively. This indicates that the rapid thermal annealing step S12 and the annealing step S21 formed the Si-V center, Ge-V center, and Sn-V center. The greater the intensity of the PL spectrum, the higher the concentration of each color center and the higher the generation rate.

[0070] Fig. 14 is a diagram showing the emission spectrum in PL measurement of synthetic diamond crystal. The left and right columns correspond to synthetic diamond crystals by HPHT method and CVD method, respectively. SP4, SP5, SP6 correspond to samples implanted with silicon (Si), germanium (Ge), and tin (Sn), respectively. The heat treatment time was changed to 1 minute, 5 minutes, 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, 70 minutes, and 100 minutes. The PL measurement conditions of the sample were the same for synthetic diamond crystals by HPHT method and CVD method.

[0071] From FIG. 14, it can be seen that although there is a certain degree of difference in the intensity of the PL spectrum between the diamond crystals synthesized by the HPHT method and the CVD method, there is almost no difference in the shape of the PL spectrum.

[0072] Figure 15 is a graph showing the relationship between heat treatment time and luminescence intensity. Here, HPHT synthetic diamond crystals were used as samples, and the luminescence intensity of the PL spectrum (hereinafter also referred to as "PL intensity") was measured. SiV, GeV, and SnV respectively show the relationship between the PL intensity and heat treatment time in the ZPL of the Si-V center, Ge-V center, and Sn-V center. The time axes in the upper and lower graphs of Figure 15 are logarithmic and linear, respectively.

[0073] As shown in Figure 15, heat treatment for approximately 1 minute, approximately 50 minutes, and approximately 100 minutes or more is effective for the Si-V center, Ge-V center, and Sn-V center. As the mass number of group IV ions increases, the heat treatment time at which the PL intensity reaches its maximum increases. For SiV and GeV, the PL intensity decreased after reaching its maximum. It was found that in heat treatment at 1800°C, the heat treatment time at which the PL intensity reaches its maximum increases as the mass number of group IV ions increases.

[0074] 16 is a graph showing the relationship between heat treatment time and luminescence intensity for diamond crystals synthesized by the HPHT method and the CVD method. The PL measurement conditions for the samples were the same for the diamond crystals synthesized by the HPHT method and the CVD method.

[0075] It can be seen from FIG. 16 that the HPHT synthetic diamond has a greater PL intensity than the CVD synthetic diamond.

[0076] Example 2 corresponding to embodiment 2 will be described below. In example 2, synthetic diamond crystals made by CVD method are used as samples. This synthetic diamond contains nitrogen of about 1 ppb or less. In addition, in example 2, in order to measure the decrease of vacancies, experiments are also carried out using CVD (bulk) containing 8 ppm nitrogen as samples. The preparation process is the same as example 1, so detailed description is omitted.

[0077] In Example 2, an annealing step S21 at 600° C. for 100 hours was performed before the rapid thermal annealing step S12 to form di-vacancies (V) which are precursors of group IV-vacancy centers. ２Then, a rapid thermal annealing step S12 including a heat treatment step S122 at 1800°C for 1 minute was performed (sample a). Similarly, an annealing step S21 at 600°C for 10 hours was performed to form di-vacancies (V ２ After forming the layer 100, a rapid thermal annealing step S12 including a heat treatment step S122 at 1800° C. for 1 minute was performed (sample b).

[0078] For comparison, a sample c was also fabricated by performing the rapid thermal annealing step S12 (including the heat treatment step S122 at 1800° C. for 1 minute) without performing the annealing step S21.

[0079] FIG. 17 shows the emission spectra of samples a and b that were subjected to the annealing step S21, and sample c that was not subjected to the annealing step S21. (a) and (b) of FIG. 17 are an overall view and a partial enlarged view of the emission spectra, respectively. FIG. 18 shows the emission intensities in ZPL for samples a, b, and c. As shown in FIG. 17, by performing the annealing step S21, the double vacancies (V ２ ) increases the amount of Group IV-V centers produced.

[0080] In Example 2, double vacancies are formed by annealing step S21 at 600°C. Since double vacancies are formed by the combination of two vacancies, it should be possible to confirm that the number of vacancies decreases after annealing step S21. As a sample for a control experiment, a synthetic diamond crystal produced by the CVD method was used. This synthetic diamond contains approximately 8 ppm of nitrogen. The sample was subjected to 2 MeV, 10 １８ cm -２ After the annealing step S21, PL measurement was performed.

[0081] 19 shows PL spectra. Sample f1 was not subjected to the annealing step S21. On the other hand, sample f2 was subjected to the annealing step S21 at 600° C. for 10 hours, and sample f3 was subjected to the annealing step S21 at 600° C. for 100 hours.

[0082] As shown in Figure 19, a peak of charge-neutral vacancies (GR1 centers) appears at a wavelength of 741 nm. The PL intensity of the GR1 centers decreases as the heat treatment time at 600 °C increases (in the order of samples f1, f2, and f3). This trend can be interpreted as a decrease in GR1 and the formation of double vacancies due to annealing.

[0083] 20 is a diagram showing the maximum values ​​of the luminescence intensity of samples a, b, c, and A. Here, as a reproducibility experiment, samples a, b, and c of Example 2 were fabricated again. In addition to these samples a to c, sample A was fabricated under the following conditions: an annealing step S21 was performed at 700°C for 100 hours to form divacancies (Di-Vacancies: V2), and then a rapid thermal annealing step S12 including a heat treatment step S122 at 1800°C for 1 minute was performed to fabricate sample A.

[0084] It can be seen from FIG. 20 that the formation of double vacancies (V2) by performing the annealing step S21 increases the amount of group IV-V centers produced.

[0085] To investigate the uniformity of impurities and growth sectors in each sample, we measured the in-plane distribution of Ge-V center concentration in germanium-implanted samples that had been heat-treated at 1800°C for 50 minutes. Figure 21 shows the relationship between the position on the sample and the maximum PL intensity. Figure 21 includes four figures (HPHT_P and CVD_P on the left, and HPHT_I and CVD_I on the right). Figures HPHT_P and CVD_P are diagrams (photos) showing the position on the sample. Figures HPHT_I and CVD_I are graphs showing the relationship between the position on the sample (a1-c3, 1-5) and the PL intensity. Synthetic diamond crystals prepared by the HPHT and CVD methods were used as samples. The former and latter contained approximately 1 ppm and less than 1 ppb of nitrogen, respectively.

[0086] From Figures HPHT_I and CVD_I, it can be seen that the PL intensity of HPHT synthetic diamonds varies depending on the measurement position, whereas the PL intensity of CVD synthetic diamonds is almost constant regardless of the measurement position. This difference is thought to be due to the concentration distribution of impurities such as nitrogen, as follows.

[0087] That is, in HPHT synthetic diamond, (1) nitrogen is easily incorporated into the crystal during the synthesis process, so the nitrogen concentration is high, and (2) the amount of nitrogen incorporated varies depending on the growth sector. Since some of the nitrogen becomes NV centers, PL emission due to the NV centers can occur. The spectrum of this PL emission is superimposed on the PL spectrum of the group IV-vacancy center. As a result, it is thought that the PL intensity of HPHT synthetic diamond fluctuates, reflecting the nitrogen concentration distribution (variation in nitrogen concentration depending on the measurement position). On the other hand, in CVD synthetic diamond, the concentration of impurities such as nitrogen is uniform and low, so PL emission due to NV centers is virtually not generated, and only the PL emission of the group IV-vacancy center is measured.

[0088] S11 Preparation step S12 Rapid thermal annealing step S120 Preheating step S121 Rapid thermal process S122 Heat treatment step S123 Temperature reduction step S21 Annealing step

Claims

1. A method of producing a group IV-vacancy centre, comprising: a preparation step of preparing a diamond containing a group IV element and a vacancy; and a rapid thermal annealing step of forming a group IV-vacancy centre in the diamond by rapid thermal annealing the diamond at a target temperature of 800°C or higher.

2. The method includes, between the preparation step and the rapid thermal annealing step, treating the diamond at a temperature of 600° C. or higher and lower than 750° C. to form di-vacancies (V) in the diamond. ２ 2. The method of claim 1, further comprising the step of: annealing to form group IV-vacancy centers from divacancies during said rapid thermal annealing step.

3. The method according to claim 1 or 2, wherein the rapid thermal annealing step comprises: raising the temperature of the diamond to a target temperature of 800°C or more, and raising the temperature of the diamond from a temperature in excess of at least 600°C to the target temperature at a heating rate of 1000°C or more per minute.

4. A method according to any one of claims 1 to 3, wherein the preparation step includes an introduction step of introducing a group IV element and vacancies into the diamond by implanting group IV ions into the diamond.

5. A method according to any one of claims 1 to 3, wherein the preparation step includes an introduction step of introducing a Group IV element and vacancies into the diamond by implanting Group IV ions into the diamond and irradiating the diamond with an electron beam.

6. The method according to any one of claims 1 to 5, wherein the group IV element is Si, and in the rapid thermal annealing step, the diamond is held at a target temperature of around 1800°C for a period of at least 1 minute and less than 50 minutes.

7. A method according to any one of claims 1 to 5, wherein the group IV element is Ge, and in the rapid thermal annealing step, the diamond is held at a target temperature of around 1800°C for a period of at least 5 minutes and less than 50 minutes.

8. A method according to any one of claims 1 to 5, wherein the group IV element is Sn, and in the rapid thermal annealing step, the diamond is held at a target temperature of around 1800°C for 100 minutes or more.

9. A method for producing a diamond crystal having a Group IV-vacancy center, comprising: a preparation step of preparing a diamond containing a Group IV element and a vacancy; and a rapid thermal annealing step of forming a Group IV-vacancy center in the diamond by rapid thermal annealing the diamond at a target temperature of 800°C or higher.

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