How diamonds are made

Abstract

To provide: a diamond including nitrogen-hole centers and having improved coherence T2; a sensor element including the same; and a method for manufacturing the diamond having the improved T2.SOLUTION: A method for manufacturing a diamond comprises: a phosphorus doped CVD step S1 of doping phosphorus when manufacturing a diamond by a chemical vapor phase deposition method to manufacture a phosphorus doped n type diamond; and an ion implantation step S2 of ion-implanting nitrogen ions into the phosphorus doped n type diamond to manufacture a diamond including nitrogen-hole centers by including the nitrogen-hole centers in the crystal structure of the phosphorus doped n type diamond.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention , conclusion A method for producing diamond containing nitrogen-vacancy centers in the crystal structure. Regarding This is what we do. [Background technology]

[0002] Patent Document 1 describes a single crystal CVD diamond component having a nitrogen vacancy defect (nitrogen-vacancy center, hereafter also referred to as NV center). This NV center (Nitrogen Vacancy center) is a pair of a carbon vacancy (a position where a carbon atom is missing) and an adjacent substitutional nitrogen atom (a nitrogen atom that exists in place of a carbon atom) in the diamond crystal lattice.

[0003] As described in Patent Document 1, negatively charged NV centers (NV - ) has various desirable characteristics. For example, NV - The electron spin state of the NV center can be placed in a specific electron spin state even at non-cryogenic temperatures (e.g., room temperature of about 300 K). In other words, the quantum state of the NV center can be artificially changed from the outside.

[0004] Also, N.V. - The electronic structure of the NV center contains emissive and non-emissive electron spin states, making it possible to read the electron spin state of the defect through photons. In other words, the quantum state of the NV center can also be read from the outside. Since the quantum state can be artificially changed and read, the NV center can be used as a quantum bit, whose quantum state can be written / read.

[0005] Further, NV - Since the electron spin state of exhibits an extremely long coherence time T2 (also called the transverse relaxation time, spin coherence time, or decoherence time), the above quantum state can be written / read stably. Therefore, it has been proposed that the NV center can be applied to various applications.

[0006] For example, diamonds containing NV centers can be used as quantum information elements in solid-state quantum information processing by applying the above-mentioned use as quantum bits, as well as in measuring devices and sensor elements such as magnetometers, nuclear magnetic resonance devices, and magnetic resonance imaging devices.

[0007] As an example of a method for forming such NV centers, Patent Document 1 gives a method of implanting nitrogen ions after synthesis of a diamond material, which provides NV centers near the surface of the diamond. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2016-539900 A Summary of the Invention [Problem to be solved by the invention]

[0009] Patent Document 1 discloses that an NV center with a long coherence time can be provided by positioning the NV center near a surface with low surface roughness and low surface damage in a growth state. However, as a specific example, Patent Document 1 discloses that T2 for an NV center formed by implantation into a surface with low roughness and low damage in a growth state is about 65.1 μs. Although this is longer than T2 of only about 16.6 μs for an NV center formed by implantation into a polished surface, it cannot be said that it is suitable for use in quantum information devices, etc. Thus, in practice, it has been difficult to obtain a long T2.

[0010] In view of these problems, the present invention ,stomach To provide a method for producing diamond in which T2 of NV centers (nitrogen-vacancy centers) incorporated into the crystal structure of diamond by on-implantation is improved. of This will be the task. [Means for solving the problem]

[0019] In order to solve the above problems, a method of manufacturing diamond as one example of an embodiment of the present invention comprises the steps of: manufacturing diamond by chemical vapor deposition, doping the diamond with phosphorus to an n-type to produce phosphorus-doped n-type diamond; and then implanting nitrogen ions into the phosphorus-doped n-type diamond to include nitrogen-vacancy centers in the crystal structure of the phosphorus-doped n-type diamond, so that the concentration of the nitrogen-vacancy centers relative to the concentration of nitrogen atoms is 5% or more. The phosphorus doping in the production of the phosphorus-doped n-type diamond by chemical vapor deposition is carried out such that the phosphorus concentration in the phosphorus-doped n-type diamond is 1×10 15 cm -3 Greater than or equal to 1×10 18 cm -3 Do the following: It is something.

[0021] In the method for producing diamond, when nitrogen ions are implanted into the phosphorus-doped n-type diamond, 15 It is preferred to use N ions.

[0022] Furthermore, in this method for manufacturing diamond, when nitrogen ions are implanted into the phosphorus-doped n-type diamond, it is preferable to adjust the acceleration energy of the nitrogen ions so that the nitrogen ions are implanted to a depth of 1 μm or less from the crystal surface of the phosphorus-doped n-type diamond. Effect of the Invention

[0023] This issue Ming Diamonds produced by this method exhibit a longer coherence time T2 than conventional diamonds, even at room temperature. Such diamonds exhibit excellent properties as sensor elements in terms of optimum operating temperature range and sensitivity, and are also suitable for use in quantum information elements, measuring devices, etc. [Brief description of the drawings]

[0024] [Figure 1]FIG. 1 is a diagram showing the flow of each step in a method for producing diamond as one embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing the concentration distribution of nitrogen atoms in phosphorus-doped n-type diamond produced by the diamond production method shown in FIG. [Diagram 3] 2 is a graph showing the results of measuring the T2 value of phosphorus-doped n-type diamond produced by the diamond production method shown in FIG. [Figure 4] 2 is a table showing a comparison of the T2 values ​​of phosphorus-doped n-type diamonds produced by the diamond production method shown in FIG. 1 with the T2 values ​​of conventional non-doped diamonds. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The flow of each step in the method for producing diamond as one example of an embodiment of the present invention is shown in Figure 1. As shown in Figure 1, the production method of this embodiment includes a phosphorus-doping CVD step S1, an ion implantation step S2, and a heat treatment step S3.

[0026] In the phosphorus-doped CVD step S1, diamond doped with phosphorus to n-type, that is, phosphorus-doped n-type diamond is manufactured. In the phosphorus-doped CVD step S1 of this embodiment, a chemical vapor deposition (CVD) method is carried out to deposit a diamond film on the surface of a diamond crystal substrate as a substrate under an atmosphere containing a carbon compound (e.g., methane) and a phosphorus compound (e.g., phosphine). Here, being doped with phosphorus to n-type means that phosphorus atoms are distributed in the crystal structure to a sufficient extent that diamond functions as an n-type semiconductor (the mobility of electrons as carriers is sufficient).

[0027] The phosphorus-doped n-type diamond manufactured by the above-mentioned phosphorus-doped CVD step S1 contains a predetermined concentration of phosphorus depending on the conditions of the CVD method (concentration of the phosphorus compound, etc.). In this embodiment, the phosphorus concentration contained in the phosphorus-doped n-type diamond is 1×10 15 cm -3Greater than or equal to 1×10 18 cm -3 It is assumed that the phosphorus-doped CVD step S1 is performed as follows.

[0028] Then, the phosphorus-doped n-type diamond produced by the phosphorus-doped CVD step S1 is subjected to an ion implantation step S2. In the ion implantation step S2 of this embodiment, 15 Nitrogen atoms are incorporated into phosphorus-doped n-type diamond by applying acceleration energy to N ions and implanting them into the phosphorus-doped n-type diamond. Here, it is preferable to adjust the acceleration energy so that nitrogen ions are implanted to a depth of 1 μm or less from the crystal surface of the phosphorus-doped n-type diamond. More preferably, nitrogen atoms are implanted at a density of 1.0×10 to a depth of 30 nm or less from the crystal surface. 11 pieces / cm 3 Greater than or equal to 1.0×10 18 pieces / cm 3 The acceleration energy of the nitrogen ions may be adjusted so that they are distributed at the following concentrations:

[0029] Next, the phosphorus-doped n-type diamond that has nitrogen atoms incorporated therein by the ion implantation process S2 is subjected to a heat treatment process S3 so that the nitrogen atoms incorporated therein are accommodated at the lattice points of the diamond crystal lattice. In the heat treatment process S3 of this embodiment, an annealing process is performed. As a result, the crystal structure of the phosphorus-doped n-type diamond contains nitrogen-vacancy centers (NV centers).

[0030] The diamond produced in the above manner is a diamond that is n-type phosphorus-doped and contains nitrogen-vacancy centers (NV centers) in the crystal structure, and phosphorus atoms are distributed in a wider range than nitrogen atoms. Specifically, phosphorus atoms are distributed evenly throughout the diamond, and nitrogen atoms are distributed locally compared to phosphorus atoms. In this embodiment, nitrogen atoms are distributed to a depth of 1 μm or less from the crystal surface. Here, if ion implantation is used, it is possible to include NV centers in the diamond crystal structure so that the concentration of NV centers relative to the concentration of nitrogen atoms is 5% or more.

[0031] The NV center contained in the diamond produced in this way shows a longer T2 even at room temperature compared to the NV center formed by implanting nitrogen ions into a diamond that is not doped with phosphorus (non-doped). In addition, the NV center formed by nitrogen atoms incorporated by ion implantation is located near the surface of the diamond (within the range of nm order), so it reacts with high sensitivity to changes in the external environment (for example, magnetic field). Due to the long T2 of the NV center near the surface, the diamond produced by this embodiment is more suitable for use in measuring devices and sensor elements than conventional ones. Furthermore, if the concentration of NV centers relative to the concentration of nitrogen atoms near the crystal surface is 5% or more, many NV centers will react in one detection, and the sensitivity of the sensor element or measuring device will be higher. In contrast, when the NV center is included in the diamond crystal structure by only the CVD method, the concentration of the NV center relative to the concentration of nitrogen atoms is only about 3%. Therefore, by including the NV center in the crystal structure of phosphorus-doped n-type diamond by ion implantation, a diamond suitable for use in a sensor element or measuring device can be obtained compared to the case of only performing the CVD method. EXAMPLES

[0032] An example of a method for producing diamond according to the present invention will be described in more detail below. First, a diamond of type IIa with a density of 3.513 g / cm 3A diamond film is homoepitaxially grown on the (111) plane of the diamond substrate while being doped with phosphorus by chemical vapor deposition (CVD) (phosphorus-doped CVD step S1).

[0033] In the phosphorus-doped CVD step S1, a diamond film is grown in an atmosphere containing a carbon compound (here, methane CH3) and a phosphorus compound (here, phosphine PH3), thereby producing a phosphorus-doped n-type diamond. Note that the amount of the phosphorus compound is small relative to the carbon compound so that the phosphorus atoms are distributed to such an extent that the phosphorus-doped n-type diamond produced functions as an n-type semiconductor. Here, the phosphorus concentration in the phosphorus-doped n-type diamond is 5×10 16 cm -3 Concentration (1×10 15 cm -3 Greater than or equal to 1×10 18 cm -3 The phosphorus-doped CVD step S1 is performed so as to obtain the following example.

[0034] When the phosphorus-doped n-type diamond film on the diamond substrate grows to a sufficient thickness (700 nm in this example), the phosphorus-doped CVD step S1 is terminated and the ion implantation step S2 is started. In the ion implantation step S2, the implantation energy of the nitrogen ions is adjusted so that the nitrogen atoms in the phosphorus-doped n-type diamond have a concentration distribution as shown in Figure 2 (the vertical axis is a logarithmic scale). By adjusting the implantation energy at this time, the concentration of NV centers relative to the concentration of nitrogen atoms in the finally obtained diamond crystal structure is set to 5% or more.

[0035] in particular 15 N ions are used, and the implantation energy is 10 keV and the implantation dose is 1.0 × 10 9 pieces / cm 2 As a result, as shown in Figure 2, a concentration of 1.0 × 10 11 pieces / cm 3 (1E+11atoms / cm 3 ) or more and 1.0×10 15 pieces / cm3 The following concentration (1.0×10 11 pieces / cm 3 Greater than or equal to 1.0×10 18 pieces / cm 3 Within the following range 15 N atoms are distributed. If we limit the depth to 1 nm or more and 20 nm or less, 15 The concentration of N atoms is 1.0×10 13 pieces / cm 3 Greater than or equal to 1.0×10 15 pieces / cm 3 The following is the result.

[0036] 15 The reason for using N ions is that they have a low natural abundance. 15 By artificially incorporating N atoms into diamond, it is possible to distinguish whether the nitrogen-vacancy centers (NV centers) that are ultimately included in the crystal structure are naturally occurring or artificially created by ion implantation. 14 Either by N atoms or artificially injected 15 Whether the NV center is caused by N atoms can be determined by the difference in optical and electromagnetic properties of the NV center. In addition, since each NV center can be measured separately, it is also possible to measure artificially created NV centers and naturally occurring NV centers by comparing them.

[0037] 15 When the N ions are sufficiently implanted, the ion implantation step S2 is terminated, and the heat treatment step S3 is started. Typically, annealing is performed at 600° C. or higher.

[0038] By the phosphorus-doped CVD step S1, ion implantation step S2, and heat treatment step S3, phosphorus-doped n-type diamond containing NV centers in the crystal structure is manufactured. When the echo intensity of this diamond (one of the NV centers contained therein) was measured by the Hahn Echo method to examine the T2 value, the results shown in Figure 3 were obtained. Note that for the sake of simplicity, the plot of the actual measured values ​​is omitted, and only the fitting curve obtained based on the actual measured values ​​is shown.

[0039] The diamond produced in this example has 13 Since C atoms are included, the echo intensity shown in Fig. 3 is 13 The effect of Rabi oscillation of C nuclear spin is shown. Specifically, the echo intensity is measured as a decaying oscillation, but the actual decay of the echo intensity can be expressed as a curve passing through the peak value of the oscillation (an exponential function shown by the two-dot chain line in Figure 3). The T2 value calculated from this curve is about 476.74 μs, as shown in Figure 3.

[0040] Figure 4 shows a table comparing the T2 values ​​when nitrogen ions are implanted into phosphorus-doped n-type diamond and when nitrogen ions are implanted into non-phosphorus-doped (non-doped) diamond. This is the result of investigating the T2 of five of the NV centers in each of the phosphorus-doped n-type diamond sample and the non-doped diamond sample. Here, for the sake of simplicity, the table shows only the estimated values ​​based on the measurement results, and the standard deviation (estimated error) of the estimated values ​​is omitted. Note that Figure 3 shows the measurement results for the measurement object "3" in Figure 4.

[0041] As shown in FIG. 4, the T2 value of the non-doped diamond is less than 200 μs for all the measurement objects (NV centers). On the other hand, the T2 value of the phosphorus-doped n-type diamond is 400 μs or more for all the measurement objects (NV centers). Thus, the diamond manufactured by the manufacturing method of this embodiment shows a T2 value that is dramatically improved compared to the non-doped diamond. All of these measurements were performed at room temperature (about 300 K).

[0042] Diamonds with such a long T2 are said to have a stable quantum state, and are suitable for use as quantum information devices at room temperature. The magnetic sensitivity (detection limit and resolution) of the NV center is inversely proportional to the square root of T2 (T2 -1 / 2 Since the T2 of a diamond is proportional to the T2 of the magnetic field, the longer the T2, the more suitable it is for use as a magnetic field sensor element.

[0043] In addition, the diamond manufactured by the manufacturing method of this embodiment has nitrogen ions implanted near the crystal surface by ion implantation, so NV centers are present near the crystal surface. Therefore, these NV centers have high sensitivity to environmental changes (for example, magnetic field changes) outside the crystal, and are suitable for use in sensor elements and measuring devices. In addition, the magnetic field sensitivity of the sensor element as a whole is inversely proportional to the square root of the number of NV centers that react in one detection. Therefore, diamonds with a high concentration of NV centers of 5% or more relative to the concentration of nitrogen atoms have a large number of NV centers that react in one detection, and are more suitable for use in sensor elements and measuring devices.

[0044] In this embodiment, the natural ratio is low. 15 N atoms were incorporated near the crystal surface of diamond by ion implantation, 15 N atoms are distributed locally. Diamonds with this type of distribution can only be produced artificially, so the distribution near the crystal surface is 15 By examining the distribution of N atoms, it is possible to confirm whether the diamond was produced by the production method of this embodiment. 15 N atoms are 1.0×10 11 pieces / cm 3 Greater than or equal to 1.0×10 15 pieces / cm 3 Diamonds having the following concentration distribution and doped with n-type phosphorus are considered to be diamonds manufactured by the manufacturing method of this embodiment. 15 Not limited to N atoms 14 In phosphorus-doped n-type diamond, in which the concentration of NV centers is 5% or more relative to the concentration of nitrogen atoms, even in the case of N atoms, it is believed that ion implantation was performed after phosphorus doping by the CVD method.

[0045] In addition, the NV center incorporated into the diamond crystal structure by ion implantation does not have the axis connecting the nitrogen atom and the vacancy (nitrogen-vacancy axis, NV axis) oriented perpendicular to a specific orientation plane (it does not align in a specific direction). More specifically, each NV center randomly takes one of the four possible directions for the NV axis. In other words, the NV axis faces one of the four directions with a probability of about 25% each. In contrast, the NV axis of the NV center incorporated into the crystal structure by the CVD method tends to be oriented in a specific direction. Specifically, it is known that in homoepitaxial growth on the (111) face of diamond, the NV axis of the NV center included in the crystal structure faces the (111) direction with a probability of nearly 100%, and in homoepitaxial growth on the (110) face, the NV axis faces only two of the four directions with a probability of about 50% each. Therefore, diamonds having NV centers whose NV axes are not oriented in a specific direction (pointing in four directions with a probability of approximately 25% each) are considered to be N ion implanted diamonds.

[0046] In addition, when NV centers are incorporated into the diamond crystal structure by ion implantation, it is possible to prevent hydrogen from being incorporated into the diamond crystal structure. Specifically, when the diamond is analyzed by secondary ion mass spectrometry (SIMS), the hydrogen concentration is below the background level (e.g., 2×10 17 cm -3 The amount of remaining hydrogen can be reduced to a level where only a small amount of hydrogen is detected (below the background level in SIMS). In contrast, when NV centers are incorporated into the diamond crystal structure by the CVD method, hydrogen is incorporated into the crystal structure, and the diamond contains more remaining hydrogen than the background level in SIMS. Therefore, diamonds that have NV centers and in which the amount of remaining hydrogen contained in the crystal structure is below the background level in secondary ion mass spectrometry are considered to be diamonds that have been implanted with N ions.

[0047] By the way, since phosphorus has electron spin, it was previously thought that phosphorus atoms in diamond crystal become magnetic noise for NV center by phosphorus doping, and shorten T2. ​​However, as mentioned above, T2 of phosphorus doped n-type diamond produced by the present invention is improved compared to conventional. It is considered that phosphorus atoms play a role of reducing magnetic noise.

[0048] One of the sources of magnetic noise is a "divacancy defect" consisting of multiple vacancies. If there are many divacancy defects, the number of magnetic noise sources increases, and T2 is shortened. In phosphorus-doped n-type diamond, a single vacancy, i.e., a monovacancy, carries a (negative) charge. Since the monovacancies are charged, they repel each other due to Coulomb force, making it difficult for multiple vacancies to gather together. This suppresses the generation of "divacancy defects," and is thought to result in a reduction in magnetic noise sources.

[0049] At the end of the ion implantation step S2, the phosphorus-doped n-type diamond contains phosphorus atoms, nitrogen atoms, and vacancies in addition to carbon atoms. However, since monovacancies are annealed out at 600°C, if annealing is performed at, for example, 900°C in the heat treatment step S3, the monovacancies will eventually disappear from the phosphorus-doped n-type diamond. On the other hand, complex defects due to nitrogen-vacancy centers (NV centers) are stable even at 1500°C, so the magnetic noise source is ultimately reduced in the crystal structure of the phosphorus-doped n-type diamond, and the NV centers remain.

[0050] In the above embodiment, the method for manufacturing diamond is comprised of the phosphorus-doped CVD step S1, the ion implantation step S2, and the heat treatment step S3, but other steps may be included. For example, since part of the diamond may be graphitized in the heat treatment step S3, a step of cleaning with acid and removing graphite by annealing in oxygen may be performed.

[0051] In the above embodiment, the diamond substrate is of type IIb, but it may be of type Ia, type Ib, or type IIb. The surface on which the diamond film is grown is not limited to the (111) surface, but may be, for example, the (001) surface.

[0052] In the above embodiment, the nitrogen ions implanted in the ion implantation step S2 are 15 Although N ions are used, this is not limited to this. If there is no need to distinguish artificially implanted nitrogen atoms from others, 14 N ions may be implanted. [Explanation of symbols]

[0053] S1 Phosphorus doped CVD process S2 ion implantation process S3 Heat treatment process

Claims

1. When producing diamond by chemical vapor deposition, phosphorus is doped to n-type to produce phosphorus-doped n-type diamond, and then implanting nitrogen ions into the phosphorus-doped n-type diamond to include nitrogen-vacancy centres in the crystal structure of the phosphorus-doped n-type diamond such that the concentration of nitrogen-vacancy centres relative to the concentration of nitrogen atoms is 5% or more; The method for producing diamond, wherein the phosphorus doping in producing the phosphorus-doped n-type diamond by chemical vapor deposition is carried out so that the phosphorus concentration contained in the phosphorus-doped n-type diamond is 1×10 15 cm −3 or more and 1×10 18 cm −3 or less.

2. When nitrogen ions are implanted into the phosphorus-doped n-type diamond, １５ The method for producing diamond according to claim 1 , wherein N ions are used.

3. 3. The method for producing diamond according to claim 1 or 2, wherein when nitrogen ions are implanted into the phosphorus-doped n-type diamond, the acceleration energy of the nitrogen ions is adjusted so that the nitrogen ions are implanted to a depth of 1 μm or less from the crystal surface of the phosphorus-doped n-type diamond.

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