JP6236609B2 - Photon output device and photon output method - Google Patents

Description

  The present invention relates to a photon output device, and more particularly to a technique for efficiently generating and outputting a single photon used in quantum cryptography communication or the like.

  In recent years, with the spread of remittance by digital communication, electronic commerce, and the like, there is an increasing demand for technology for improving safety, protecting important information communicated from eavesdropping and tampering by a third party. One effective technique for improving security is cryptography. As the encryption method, there are mainly a public key encryption method and a secret key encryption method. These details are described in Shinichi Ikeno and Kenji Koyama, “Modern Cryptography” (The Institute of Electronics, Information and Communication Engineers). In the public key cryptosystem, the transmitting side holds a public key, encrypts confidential information using the public key, the receiving side holds the secret key, and decrypts the confidential information using the secret key.

  In order to update the public key and the private key of the public key cryptosystem, each receiving side usually generates a key pair of the public key and the private key, and normally sends the public key to the transmitting side. Since it is not necessary to send the private key, there is no worry of being known to the third party at the time of transmission, and even if the public key is known to the third party, it is considered that confidential information will not be decrypted. No confidentiality management is required. Also, since the public key does not need to be managed confidentially even when stored, the burden on the distribution side is small.

  The security of the public encryption key method is secured based on a mathematical theory that it is not easy to generate a decryption key from an encryption key. In order to obtain a decryption key from an encryption key in a commonly used RSA encryption method, it is necessary to perform a very difficult operation of factoring a very large integer that is an encryption key. For example, even if this calculation is performed using the latest supercomputer, since it takes an unrealistic time, it is considered impossible to generate a decryption key from an encryption key.

  However, if a high-performance computer that can perform prime factorization of large integers in a relatively short period of time appears in the future, it will be possible to generate a decryption key from an encryption key. The encryption key method may become unusable.

  On the other hand, in the secret key encryption method, the transmitting side and the receiving side keep the same common key secretly, the transmitting side encrypts confidential information using the common key, and the receiving side decrypts confidential information using the common key. . In order to update the common key of the secret key cryptosystem, for example, a new common key must be generated on either the transmission side or the reception side, and the new common key must be transmitted to the other side secretly. When a new common key is known to a third party, confidential information is decrypted and known to the third party, so confidentiality management at the time of key transmission must be thoroughly implemented.

  As a safety measure, it is desirable to update the key used for encryption and decryption regularly or frequently as necessary. Further, it has been theoretically proved that an encryption method called Vernam encryption, in which a secret key having the same length as that of confidential information before encryption is disposable at once, is theoretically absolutely safe.

  Therefore, expectations for quantum cryptography communication are increasing as a means for secretly transmitting this common key. In quantum cryptography communication, information is given to one of the quantum states of a single photon, and the single photon is transmitted as a transmission medium. There are various types of photon quantum states such as photon polarization (direction of light wave), phase, and spin.

  There is a quantum mechanical principle that when an observer measures one of the quantum states of a single photon, it influences other quantum states. It is believed that legitimate communicators can know that there has been a possibility of wiretapping. Therefore, if there is a possibility of eavesdropping, the transmitted common key is discarded, and if encrypted communication is performed using only the transmitted common key when there is no possibility of eavesdropping, communication safety Sex is secured.

  The outline of the principle of quantum cryptography communication will be described below.

  First, each time a sender tries to send 1-bit information, the sender randomly determines whether to transmit using a quantum state of type A or B using a quantum state of B, and selects the selected type of quantum state. A single photon whose state corresponds to the 1-bit information to be transmitted is transmitted. At this time, in the same single photon, the quantum state of the type not selected is uncertain due to the quantum mechanical principle, and it is impossible to know what the state is without changing the quantum state.

  The receiver randomly determines whether to measure a quantum state of type A or a quantum state of B for a single photon sent, and measures the selected type of quantum state to measure 1 bit. Get the information. If the quantum state of the type selected at this time is measured, the other quantum states change, so that it is not possible to correctly know the type of quantum state that was not selected.

  After that, the sender and the receiver make an answer as to whether or not they have made the same selection, and if the same selection is made, the obtained information is retained as valid information, and if the same selection has not been made Discards the information obtained. By repeating such communication for each bit, a predetermined amount of information can be communicated. Here, if there is no eavesdropper, the information is communicated correctly.

  However, when there is an eavesdropper, the eavesdropper changes the quantum state of a single photon, and information is erroneous with a certain probability.

  Since the eavesdropper cannot know the type of quantum state selected by the sender at the time of eavesdropping, whether the quantum state of type A or the type of quantum state B is measured as in the case of the receiver. One-bit information is obtained by randomly determining and measuring the selected type of quantum state. Here, if an eavesdropper happens to make the same selection as the sender, the eavesdropper can get the correct information and retransmit a single photon with the selected quantum state in the same state. , Legitimate correspondents will not know that they are eavesdropping.

  However, it is impossible to make the same selection as the sender by chance, and a selection different from the receiver is usually made with a probability of 50%. When an eavesdropper makes a different selection from the recipient, another 50% (a total of 25%) of the 50% of the different selections is incorrect information. Here, even if a single photon is transmitted again, a single photon in a state corresponding to wrong information is transmitted with a probability of 50%. Such a single photon will also give the receiver the wrong information if the receiver makes the same choice as the sender. Therefore, even if an eavesdropper eavesdrops on all the information that the sender tried to send, 25% of the information is wrong information, and by eavesdropping, 25% of the information received by legitimate receivers. % Is changed to wrong information.

  Therefore, if the sender and the receiver communicate a predetermined amount of information and then extract some bits at random and check whether or not the correct information is transmitted, it is confirmed that it is 100% correct. If it is determined that there is no possibility of wiretapping, the information received at this time can be used with confidence as a common key.

  Here, for quantum cryptography communication, a photon output device capable of repeatedly outputting a single photon is indispensable. For example, as a conventional method for generating a single photon, a first method (for example, Patent Document 1) based on photoexcitation in which a quantum dot is irradiated with light having a short wavelength, or a quantum device using a semiconductor pn junction is used. There is a second method (for example, Patent Document 2) that generates single photons by injecting electric charges into dots and recombining electrons and holes. Patent Document 3 discloses a technique related to a light-emitting element that is closely related to the invention of the present application.

JP 2004-253657 A WO2011009465 JP 2008-078611 A

  However, in the first method, since the wavelength of the excitation pulse light has to be accurately adjusted in order to generate a high-quality single photon, an expensive light source device is required, the device scale is increased, and the cost is increased. Get higher.

  Further, in the second method, problems such as emission of unnecessary wavelengths are likely to occur, and it is difficult to obtain high-quality single photons. In addition, as far as the inventors of the present application know, there is no example of operation at room temperature as far as the inventor of the present application knows, and a separate cooling facility is required. .

  As described above, a technique for efficiently generating a single photon has not been established yet, and development of a new technique is desired. Therefore, the present invention provides a photon output device, a photon output method, and a method of manufacturing a semiconductor used for the photon output device that can efficiently generate and output a single photon without requiring a light source device or a cooling facility. For the purpose.

  A photon output device according to the present invention includes a semiconductor having a PIN structure including a p-type diamond layer, an n-type diamond layer, and an i-type diamond layer provided between the p-type diamond layer and the n-type diamond layer. A light emitting element; and an optical element that allows passage of photons generated in the i-type diamond layer.

  In one embodiment, the optical element transmits photons generated at a predetermined position of the i-type diamond layer, and is generated at another position of the i-type diamond layer, the p-type diamond layer and the n-type diamond layer. Cut the photons.

  In one embodiment, the photon output device further includes a current injection unit that applies a voltage to the semiconductor having the PIN structure and injects a current into the light emitting element.

  In one embodiment, a nitrogen-vacancy complex defect center in which nitrogen and vacancies are adjacent is formed in the i-type diamond layer.

  In one embodiment, nitrogen is ion-implanted in the i-type diamond layer.

  In one embodiment, the optical element includes an objective lens and a pinhole arranged near the focal point of the objective lens.

  In one embodiment, the optical element outputs a single photon to the outside.

  In one embodiment, the concentration of impurities in the i-type diamond layer is 0.1 ppb or less.

  In one embodiment, a main surface of the i-type diamond layer is smaller than a main surface of at least one of the p-type diamond layer and the n-type diamond layer, and the main surface of the i-type diamond layer. There is a region exposed to the outside air, and the optical element outputs photons that have passed through the region exposed to the outside air to the outside.

  In one embodiment, a region exposed to the outside air of the i-type diamond layer is cleaned.

  In one embodiment, in the light emitting device, the i-type diamond layer is laminated on a surface of a material substrate to be the p-type diamond layer, and the n-type diamond layer is laminated on a part of the i-type diamond layer. An electrode is formed on the n-type diamond layer, and a region exposed to the outside air corresponds to a portion where the n-type diamond layer is not laminated on the i-type diamond layer. However, the region exposed to the outside air is cleaned stepwise by a plurality of different methods after the formation of the electrode.

  In one embodiment, the photon output device operates at room temperature.

  A photon output method according to the present invention includes a semiconductor having a PIN structure including a p-type diamond layer, an n-type diamond layer, and an i-type diamond layer laminated between the p-type diamond layer and the n-type diamond layer. A preparation step of preparing a light emitting element; a light emitting step of causing the light emitting element to emit light; and a photon passing step of allowing photons generated in the i-type diamond layer in the light emitting step to pass through the optical element.

  In one embodiment, the light emitting step includes a step of injecting a current into the light emitting element by applying a voltage to the semiconductor having the PIN structure.

  A semiconductor manufacturing method according to the present invention includes a PIN structure semiconductor comprising a p-type diamond layer, an n-type diamond layer, and an i-type diamond layer laminated between the p-type diamond layer and the n-type diamond layer. The manufacturing method includes an implantation step of ion-implanting nitrogen into the i-type diamond layer.

  According to the present invention, by using a PIN structure semiconductor as the light-emitting element, current injection can be easily performed taking advantage of the characteristics of the semiconductor, and at the same time, it is a clean film in which very little light is emitted. By adopting a mechanism in which light emitted from the i-type diamond layer is observed, only a photon generated from one impurity or the like can be output relatively easily.

It is a figure which shows schematic structure of the photon output device 1 of this Embodiment. It is a figure which shows the outline of an example of the optical element 20 in this Embodiment. It is a figure which shows the outline of another example of the optical element 20 in this Embodiment. (A) is a figure which shows light emission from the light emitting element in the photon output device of a comparative example, (b) is a partially expanded view of (a). 3 is a diagram showing an outline of a method for manufacturing the light emitting element 10. FIG. 3 is a diagram showing an outline of a method for manufacturing the light emitting element 10. FIG. 3 is a diagram showing an outline of a method for manufacturing the light emitting element 10. FIG. 3 is a diagram showing an outline of a method for manufacturing the light emitting element 10. FIG. 3 is a diagram showing an outline of a method for manufacturing the light emitting element 10. FIG. 3 is a diagram showing an outline of a method for manufacturing the light emitting element 10. FIG. 3 is a diagram showing an outline of a method for manufacturing the light emitting element 10. FIG. 3 is a diagram showing an outline of a method for manufacturing the light emitting element 10. FIG. (A) is a figure which shows light emission by the photoexcitation of the photon output device of this Embodiment, (b) is a figure which shows light emission by the current injection of the photon output device of this Embodiment. It is a figure which shows the outline of the evaluation system at the time of evaluating the light emitting element 10 in this Embodiment. (A) is a graph which shows the anti-bunching in the photon output device of this embodiment light-emitted by optical excitation, (b) is a graph which shows the anti-bunching in the photon output device of this embodiment light-emitted by current injection. .

(Embodiment)
<Overview>
The embodiment is the world's first photon output device capable of outputting a single photon from an i-type diamond layer by current injection at room temperature for the first time by injecting current utilizing the characteristics of a semiconductor having a PIN structure. It is.

<Configuration>
FIG. 1 is a diagram showing an outline of the photon output device 1 of the present embodiment. As shown in FIG. 1, the photon output device 1 of the present embodiment is a system that outputs photons, and includes a light emitting element 10, an optical element 20, and a current injection unit 30. The light-emitting element 10 is a semiconductor having a PIN structure including three layers of a p-type diamond layer 11, an n-type diamond layer 12, and an i-type diamond layer 13 provided between the p-type diamond layer 11 and the n-type diamond layer 12. including.

  The p-type diamond layer 11 is a semiconductor layer in which diamond is doped with a p-type dopant. For example, the p-type diamond layer 11 is formed based on a diamond substrate to which about 10 20 boron (element symbol B) is added per cubic centimeter.

  The n-type diamond layer 12 is a semiconductor layer in which diamond is doped with an n-type dopant. For example, the n-type diamond layer 12 has a thickness of about 500 nm, and about 10 18 phosphorus (element symbol P) is added per cubic centimeter.

  The i-type diamond layer 13 is an intrinsic semiconductor layer made of diamond that is almost non-doped and contains almost no p-type or n-type dopant. For example, the i-type diamond layer 13 has a film thickness of about 10 μm, and the impurity concentration is suppressed to 0.1 ppb (parts per billion, parts per billion) or less. Further, a small amount of nitrogen (element symbol N) is intentionally ion-implanted from the main surface side (upper surface in FIG. 1) on the n-type diamond layer 12 side, and the ion-implanted nitrogen and vacancies are then combined. Annealed to let you.

  In the present embodiment, the main surface of the n-type diamond layer 12 is smaller than the main surface of the i-type diamond layer 13, and a part of the main surface of the i-type diamond layer 13 is exposed to the outside air. . The reason why a part of the main surface of the i-type diamond layer 13 is exposed to the outside air is that photons (arrow A in FIG. 1) generated from a predetermined position in the i-type diamond layer 13 are present. This is because, when outputting to the outside, the photons that have passed through the region exposed to the outside air are output to the outside, thereby making it easier to extract the photons.

  Here, the predetermined position in the i-type diamond layer 13 refers to a nitrogen-vacancy complex defect center (hereinafter referred to as “NV center”) in which nitrogen and vacancies are adjacent at the molecular structure level. ) Is arbitrarily selected at the manufacturing stage. In the present embodiment, the NV center existing immediately below any position in the region where the i-type diamond layer 13 is exposed to the outside air is selected as the predetermined position in the i-type diamond layer 13. .

  Here, the reason why the impurity concentration in the i-type diamond layer 13 is suppressed to 0.1 ppb or less is that in order to see each photon generated from a single photon generation source one by one, adjacent single photon generation sources This is because it is considered necessary to make the interval of about 300 nm or more, and if the concentration is calculated by calculating backward from this, the impurity concentration becomes about 0.1 ppb. Therefore, in the i-type diamond layer 13, the average interval between the single photon generation sources is 300 nm or more apart, and it is possible to see one photon generated from the single photon generation source one by one.

  Incidentally, it is only silicon and diamond that can reduce the concentration of impurities in the semiconductor to 0.1 ppb or less with the current technology, and it is impossible with compound semiconductors. Further, in the p-type diamond layer 11 and the diamond layer 12, since the impurity concentration is an order of magnitude higher than that in the i-type diamond layer 13, various emission centers exist at high concentrations, and everywhere is shining. It seems that it is impossible to see each photon generated from a single photon source like the i-type diamond layer 13 one by one.

  In the present embodiment, the main surface of the n-type diamond layer 12 is made smaller than the main surface of the i-type diamond layer 13 for ease of manufacturing, but not the n-type diamond layer 12 but the p-type diamond layer 11. The main surface may be smaller than the main surface of the i-type diamond layer 13. In short, the main surface of at least one of the p-type diamond layer 11 and the n-type diamond layer 12 is made smaller than the main surface of the i-type diamond layer, and one of at least one main surface of the i-type diamond layer 13 is reduced. What is necessary is just to expose the area | region of a part with respect to external air.

  In the present embodiment, the PIN structure is stacked in the vertical direction with respect to the emission direction, and photons are output from the main surface of the i-type diamond layer 13 to the outside. The photons may be output to the outside from the cross section of the i-type diamond layer.

  The light-emitting element 10 further includes an electrode 14 formed on a part of the main surface of the p-type diamond layer 11 that is not in contact with the i-type diamond layer 13 (the surface below the p-type diamond layer 11 in FIG. 1). And an electrode 15 formed on the entire main surface of the n-type diamond layer 12 that is not in contact with the i-type diamond layer 13 (the upper surface of the n-type diamond layer 12 in FIG. 1). In FIG. 1, one electrode 14 and one electrode 15 are provided in one light-emitting element 10 in order to avoid an excessively complicated drawing, but the electrode 14 and / or the electrode 15 are A plurality may be provided as necessary.

  Each of the electrode 14 and the electrode 15 is a metal film provided for facilitating electrical connection by wire bonding or the like. When a voltage is applied between the electrode 14 and the electrode 15, the light emitting element A voltage can be applied to the PIN structure semiconductor in FIG. For example, the electrode 14 has a circular pattern with a radius of 400 μm, and the electrode 15 has a circular pattern with a radius of 200 μm. Each of the electrodes 14 has three layers of titanium 30 nm, platinum 30 nm, and gold 100 nm in order from the lower layer.

  Here, in the electrode 14 and the electrode 15, the bottom layer is made of titanium because it has good contact properties with diamond, and platinum is laminated thereon to prevent oxidation of titanium. In order to improve the quality, gold is laminated. Note that the electrodes 14 and 15 are not necessarily required because they are provided to improve electrical reliability and facilitate processing.

  A method for manufacturing the light emitting element 10 will be described separately below.

  The optical element 20 passes photons generated at the predetermined position in the i-type diamond layer 13. Thus, the photons emitted from the light emitting element 10 pass through the optical element 20 and are output to the outside of the photon output device 1. For this reason, such an optical element 20 is also called an output unit.

  FIG. 2 is a diagram showing an outline of an example of the optical element 20 in the present embodiment. As shown in FIG. 2, the optical element 20 includes an objective lens 21 and a pinhole 22 disposed in the vicinity of the focal point of the objective lens 21, and uses the same principle as that of a confocal laser microscope, and the inside of the i-type diamond layer 13. The photons (arrow A in FIG. 2) emitted from a three-dimensional narrow region including the predetermined position are selectively output to the outside. For example, here, only a region having a circular field of view of about 350 nm and a depth direction of about 1 μm can be seen. Even if light enters from outside this region, what is the opening of the pinhole 22? Since the focal point is set at a different position, the light is blocked by the pinhole 22 and eliminated, and only light emitted from this region passes. For this reason, photons generated in a specific region of the i-type diamond layer 13 can be output to the outside with high resolution.

  The optical element 20 shown in FIG. 2 includes the objective lens 21 and the pinhole 22, but the present embodiment is not limited to this. When the distance between the NV centers in the i-type diamond layer 13 is relatively large, the optical element 20 may include the objective lens 21 without including the pinhole.

  Alternatively, instead of the objective lens 21 and the pinhole 22, a transmission optical fiber may be optically directly connected to the surface of the i-type diamond layer 13 closest to the predetermined position in the i-type diamond layer 13. Good. FIG. 3 shows a schematic diagram of a configuration using an optical fiber 23 as the optical element 20. The optical fiber 23 has a core 23a and a clad 23b surrounding the core 23a. Photons generated at the emission center of the i-type diamond layer 13 propagate in the core 23a.

  Such a connection method is particularly effective when outputting photons generated from a shallow point in the i-type diamond layer 13 that is relatively close to the outside air. The optical fiber 23 can control the range of the region where photons that can pass through the optical fiber 23 are generated by adjusting the diameter of the core 23 a and / or the distance between the i-type diamond layer 13 and the optical fiber 23.

  Thus, the optical element 20 faces the exposed part of the i-type diamond layer 13 without the p-type diamond layer 11 and the n-type diamond layer 12 interposed therebetween. For this reason, the optical element 20 allows photons generated at a predetermined position of the i-type diamond layer 13 to pass therethrough, and photons generated at another position of the i-type diamond layer 13, the p-type diamond layer 11 and the n-type diamond layer 12. Can be cut.

  The current injection unit 30 is a current source that applies a voltage between the electrode 14 and the electrode 15 to inject a current into the light emitting element 10. When a current is appropriately injected at room temperature by the current injection unit 30, photons are generated from the predetermined position in the i-type diamond layer 13. For example, the current injection unit 30 injects a forward current of about 1 to 20 mA into the light emitting element 10.

  In addition, since it is not uncommon to provide a power supply portion outside the own device in other general devices, the photon output device 1 of the present embodiment also includes the current injection unit 30 outside the own device, and the light emitting element 10 A configuration including the optical element 20 may be used.

  Here, advantages of the photon output device 1 according to the present embodiment as compared with the photon output device of the comparative example will be described. The photon output device of the comparative example has a light emitting element and a current injection part, but does not have an optical element. Although details are omitted, the light-emitting element in the photon output device of the comparative example includes a p-type diamond layer, an n-type diamond layer, and an i-type diamond layer provided between the p-type diamond layer and the n-type diamond layer. It has a PIN structure semiconductor consisting of layers.

  Hereinafter, light emission from the light emitting element in the photon output device of the comparative example will be described with reference to FIG. FIG. 4A is a diagram showing light emission from the light emitting element in the photon output device of the comparative example, and FIG. 4B is a partially enlarged view of FIG. In this photon output device, electrodes are provided at two locations, and it is understood from FIGS. 4A and 4B that light is emitted in the vicinity of the two electrodes.

  As described above, the i-type diamond layer emits light from the NV center, but the p-type diamond layer and the n-type diamond layer emit light using the doped impurity as the emission center. For this reason, the concentration of the emission center of the p-type diamond layer and the n-type diamond layer is several orders of magnitude higher than the concentration of the emission center from the i-type diamond layer. Therefore, the light emitted from the light emitting element includes a light emitting component from the i-type diamond layer, and most of the light emitted from the light emitting element is emitted from the p-type diamond layer and the n-type diamond layer. On the other hand, the photon output device 1 of the present embodiment allows photons generated in the i-type diamond layer 13 of the light emitting element 10 to pass through the optical element 20, so that photons can be output to the outside with high spatial resolution. it can.

<Manufacturing method>
5-12 is a figure which shows the outline of the manufacturing method of the light emitting element 10. FIG. Hereinafter, a method for manufacturing the light emitting element 10 will be described in order with reference to FIGS.

  (1) As shown in FIG. 5, a p-type diamond substrate 101 as a base of the p-type diamond layer 11 is prepared and set in a CVD apparatus (Chemical Vapor Deposition system) 100. The p-type diamond substrate 101 finally becomes the p-type diamond layer 11 shown in FIG.

  In this embodiment, a commercially available p-type diamond (manufactured by TISNCM Research Institute in Russia) synthesized by a high temperature high pressure method (HPHT: High Temperature Treatment Treatment) was purchased and used. The CVD apparatus 100 used in this embodiment is an ASTeX microwave plasma CVD apparatus sold by Seki Technotron Co., Ltd. in Japan, and has the same type of CVD apparatus or an equivalent function. Anyone can manufacture the light emitting element 10 by purchasing another CVD apparatus having the above and adjusting it so as to have the same characteristics as in the present embodiment or using the same conditions.

(2) As shown in FIG. 6, methane gas (CH ₄ ) and hydrogen gas (H ₂ ) are supplied to the CVD reaction chamber using the CVD apparatus 100, and the i-type diamond 103 is formed by chemical vapor deposition. The thickness is controlled over the entire surface of the mold diamond substrate 101 to a thickness of about 10 μm.

(3) As shown in FIG. 7, a CVD apparatus 100 is used to mix a small amount of phosphine (PH ₃ ) with methane gas and hydrogen gas and supply them to the CVD reaction chamber. The diamond 102 is laminated on the entire surface of the i-type diamond 103 layer so as to have a thickness of about 500 nm.

  (4) As shown in FIG. 8, a stack of n-type diamonds 102 is taken out from the CVD apparatus 100, a part of the n-type diamond 102 layer is removed by dry etching with oxygen gas, and the i-type diamond 103 layer is removed. A part of the area is exposed to the outside air. In the present embodiment, the n-type diamond layer 12 shown in FIG. 1 is formed by removing the layer of the n-type diamond 102 around the circle having a diameter of 200 microns.

  (5) As shown in FIG. 9, the region of the i-type diamond 103 layer exposed to the outside air corresponds to a portion of the n-type diamond 102 layer that has been removed by dry etching. Nitrogen ions are implanted into the substrate. Here, if nitrogen is ion-implanted into the i-type diamond, vacancies can be formed together. For example, about 10 to the 9th power of nitrogen per square centimeter is ion-implanted into the region exposed to the outside air at 180 keV.

  Here, the ion implantation is not performed only in the region that is selectively exposed to the outside air, and the n-type diamond layer 12 is not particularly masked during the ion implantation. At the same time, nitrogen is also ion-implanted into the n-type diamond layer 12. However, since the amount of nitrogen implanted here is extremely small compared to the amount of dopant doped in the n-type diamond layer 12, the characteristics of the n-type diamond layer 12 are hardly changed even when nitrogen is ion-implanted. It is done. In addition, by spatially controlling the position where the nitrogen ions are implanted, the position where the NV center is formed can be arbitrarily arranged like a lattice.

  (6) As shown in FIG. 10, annealing is performed to combine nitrogen and vacancies. It is known that vacancies move at around 600 ° C. When nitrogen and vacancies are combined, a stable state is obtained. Therefore, if nitrogen is ion-implanted and then annealed at about 800 ° C. for about 1 hour, the vacancy moved and the nearby nitrogen and vacancies joined together to form an NV center. Here, for example, annealing is performed at 800 ° C. for about 2 hours to form the i-type diamond layer 13 shown in FIG.

  (7) As shown in FIG. 11, the electrode 15 is formed on the entire portion of the n-type diamond layer 12 exposed to the outside air, and the electrode is formed on a portion of the p-type diamond layer 11 exposed to the outside air. 14 is formed. Here, unnecessary portions are masked by photolithography, and after only titanium, platinum, and gold are sequentially deposited on the necessary portions, the unnecessary portions of the mask are removed by photolithography to form the electrodes 14 and 15. To do. Also, here, after the electrodes 14 and 15 are formed, annealing is performed in an argon gas at 420 ° C. for about 30 minutes in order to improve the characteristics of each electrode.

  (8) As shown in FIG. 12, the region exposed to the outside air is cleaned by irradiating hydrogen molecules with hydrogen atoms using a hot filament, and oxygen is further removed using plasma. Impurities such as organic substances on the surface are removed by irradiation with atoms and cleaning. Further, the surface of the region exposed to the outside air while suppressing damage to each electrode by cleaning the region exposed to the outside air stepwise by a plurality of different methods as described above. The impurities can be sufficiently removed.

  In the child output device 1 shown in FIG. 1, the light emitting element 10 generates photons by current injection from the current injection unit 30, but the present embodiment is not limited to this. The light emitting element 10 may generate photons by photoexcitation.

  FIG. 13A is a diagram showing a confocal microscope fluorescence image of photons generated in the i-type diamond layer 13 by photoexcitation. Even when photoexcitation is performed, light emission from the i-type diamond layer 13 is observed through the optical element 20. FIG. 13B shows a confocal microscope fluorescence image of photons generated in the i-type diamond layer 13 by current injection. In either case, it is understood that a single photon is similarly output from the NV center.

<Evaluation method>
Here, whether or not photons are output from a single photon generation source as intended from the light-emitting element 10 for both the case of photoexcitation using a YAG laser and the case of injecting a current, The evaluation will be based on academic proof called anti-bunching. Anti-bunching is indicated by an intensity correlation observed when the probability of detecting another individual photon in the vicinity of one photon detected by the photon correlation method is small. In the case of the NV center, after one photon is emitted after excitation, the state returns from the excited state to the ground state. Therefore, another individual photon cannot be emitted until the state returns to the excited state again. The probability that a photon exists is reduced and anti-bunching is observed.

  FIG. 14 is a diagram showing an outline of an evaluation system when the operation of the light emitting element 10 in the present embodiment is evaluated. In the evaluation system shown in FIG. 14, the light emitting element 10 is installed on the piezo stage 200, and the sample stage 200 (piezo stage) is finely moved in advance, and photons emitted from a three-dimensional narrow area including the position of the evaluation target. It adjusts so that only can be detected selectively.

In the case of optical excitation (1) Laser light is output from the YAG laser generator 201, reflected by the dichroic mirror 202, the direction of travel is changed, passes through the objective lens 203, and is focused at a predetermined position in the light emitting element 10. tie.

  (2) Since the light emitted here is different in energy and wavelength from the laser light, only the light that is condensed by the objective lens 203 and passes through the dichroic mirror 202 and emitted from a narrow region by the pinhole 204 is used. Pass selectively.

  (3) The light that has passed through the pinhole 204 is put into a beam splitter 205, and detected by two APDs (avalanche photodiodes) 206, respectively. Here, the APD 206 is a photon counting module that outputs one TTL signal when one photon is detected.

  (4) Signals output by detecting photons in the two APDs 206 are input to the personal computer 207 and processed. The personal computer 207 measures the time difference between the two signals output from the two APDs 206 and counts the time difference in the order of several ns to create a histogram.

(5) The histogram counted for each time difference is normalized so that the vertical axis has a scale from 0 to 1, and it is determined whether the dip at the time difference of zero is smaller than 0.5. If the dip at the zero time difference is smaller than 0.5, it is proof that photons are output from one single photon source.
When Injecting Current (1) Using the current injection unit 30, a voltage is applied between the electrode 14 and the electrode 15 to inject current into the light emitting element 10.

  (2) to (5) The same as (2) to (5) in the case of photoexcitation.

<Evaluation results>
FIG. 15A is a graph showing the anti-bunching in the photon output device 1 of the present embodiment that emits light by photoexcitation, and FIG. 15B shows the anti-bunching in the photon output device 1 of the present embodiment that emits light by current injection. It is a graph which shows bunching. In the case of photoexcitation, the dip at the time difference of zero was about 0.35. In the case of injecting current, the dip at the time difference of zero was about 0.45.

  In addition, the emission intensity in the case of injecting current was comparable to that in the case of photoexcitation. Therefore, it was found that, in both cases of photoexcitation and current injection, photons are output from one single photon source in a three-dimensional narrow area adjusted in advance. . Therefore, it was verified that single photons generated from such a single photon generation source can be selectively output. In light excitation, when the distance between the NV centers in the i-type diamond layer 13 is short, photons generated from adjacent NV centers may not be distinguished from each other due to the limit of the wavelength of light. On the other hand, in the current injection, when a microfabricated electrode is used, even if the distance between the NV centers is relatively short, the photons generated from the adjacent NV centers can be distinguished by controlling the electrode for injecting the current. .

<Summary>
As described above, according to the present embodiment, single photons can be output from the i-type diamond layer by current injection at room temperature, so that single photons can be generated and output very efficiently. Can do. Therefore, it can be used for various devices that require a single photon in fields such as quantum cryptography communication and distributed processing quantum computers, and can greatly contribute to practical use.

  The present invention can be applied to various devices in fields such as quantum cryptography communication and distributed processing quantum computers. According to the present invention, a single photon can be efficiently generated and output without the need for a light source device or a cooling facility, and the cost of the apparatus can be greatly reduced without increasing the scale of the apparatus. Extremely high.

DESCRIPTION OF SYMBOLS 1 Photon output device 10 Light emitting element 11 p-type diamond layer 12 n-type diamond layer 13 i-type diamond layer 14 Electrode 15 Electrode 20 Optical element 21 Objective lens 22 Pinhole 30 Current injection part

Claims (10)

A PIN structure semiconductor comprising a p-type diamond layer, an n-type diamond layer, and a single-structure i-type diamond layer implanted between the p-type diamond layer and the n-type diamond layer and implanted with nitrogen ions. A light emitting device comprising:
A current injection unit that applies a voltage to the PIN structure semiconductor to inject a current into the light emitting element;
An optical element that passes photons generated in the i-type diamond layer by current injection by the current injection unit;
The optical element passes photons generated at a predetermined position of the i-type diamond layer, and cuts photons generated at another position of the i-type diamond layer, the p-type diamond layer, and the n-type diamond layer. , Photon output device.   The photon output device according to claim 1, wherein a nitrogen-vacancy complex defect center in which nitrogen and vacancies are adjacent is formed in the i-type diamond layer.   3. The photon output device according to claim 1, wherein the optical element includes an objective lens and a pinhole disposed near a focal point of the objective lens.   The photon output device according to claim 1, wherein the optical element outputs a single photon to the outside.   The photon output device according to claim 4, wherein the impurity concentration in the i-type diamond layer is 0.1 ppb or less. The main surface of the i-type diamond layer is smaller than the main surface of at least one of the p-type diamond layer and the n-type diamond layer,
The main surface of the i-type diamond layer has a region exposed to the outside air,
The photon output device according to claim 1, wherein the optical element outputs photons that have passed through a region exposed to the outside air to the outside.   The photon output device according to claim 6, wherein a region exposed to the outside air of the i-type diamond layer is cleaned. In the light emitting element,
The i-type diamond layer is laminated on the surface of the material substrate to be the p-type diamond layer,
The n-type diamond layer is laminated on a part of the i-type diamond layer,
An electrode is formed on the n-type diamond layer;
The region exposed to the outside air corresponds to a portion where the n-type diamond layer is not laminated on the i-type diamond layer, and the region exposed to the outside air is the electrode. 8. The photon output device according to claim 7, wherein after the formation, the photon output device is cleaned stepwise by a plurality of different methods.   The photon output device according to claim 1, wherein the photon output device operates at room temperature. A PIN structure comprising a p-type diamond layer, an n-type diamond layer, and a single-structure i-type diamond layer laminated between the p-type diamond layer and the n-type diamond layer and implanted with nitrogen ions A preparation step of preparing a light-emitting element including the semiconductor;
A light emitting step of causing the light emitting element to emit light by applying a voltage to the semiconductor having the PIN structure and injecting a current into the light emitting element;
Photons generated at a predetermined position of the i-type diamond layer in the light emitting step are passed through an optical element, and photons generated at another position of the i-type diamond layer, the p-type diamond layer, and the n-type diamond layer. A photon passing step of causing the optical element to cut the photon.