JP4347094B2 - Radiation detector and manufacturing method thereof - Google Patents

Description

  The present invention relates to a radiation detector and a method for manufacturing the same, and more particularly to a radiation detector made of diamond having high detection sensitivity.

  In recent years, in devices that detect ultraviolet rays, γ-rays, etc., it has been noted that diamond is used as a semiconductor material, which has a large band gap energy and is excellent in thermal conductivity, heat resistance, radiation resistance, and chemical resistance. Has been. According to this detector, a radiation detector with excellent environmental resistance can be manufactured.

  That is, conventional semiconductors such as Si used in conventional radiation detectors are semiconductors having a band gap of 3 eV or less, and the impurity level in the band gap that generates carriers is the lower end of the conduction band (when the carrier is an electron). ) Or an energy difference of 0.1 eV or less from the upper end of the valence band (in the case of the same hole). On the other hand, diamond with a band gap of about 5.5 eV has a similar impurity level with an energy difference of 0.3 eV or more, so that detection sensitivity and detection characteristics are not easily affected by temperature, and between constituent atoms The bond strength is stronger than that of conventional semiconductors and has excellent environmental resistance.

  In addition, since the conventional semiconductor has such a shallow impurity level, the dark current at room temperature (current signal due to carriers mainly generated by the thermal activation process in the case where no radiation is irradiated) is relatively high. For this reason, there has been a problem that the minimum detection sensitivity at room temperature most expected to be used cannot be improved. Or, in order to improve the detection sensitivity of radiation detectors using conventional semiconductors, it is necessary to suppress the dark current by cooling the detector to a very low temperature. Therefore, the radiation detector is complicated and difficult to downsize.

  Furthermore, since conventional semiconductors have high sensitivity to visible light, when detecting radiation other than visible light such as ultraviolet rays, a filter for blocking visible light has to be attached. This filter complicates the manufacturing process and lowers the intensity of radiation to be detected, particularly ultraviolet rays, so that there is a problem that the radiation detection sensitivity is reduced.

  In contrast, diamond has a light absorption upper limit wavelength that is sufficiently shorter than the visible light wavelength region, so it does not respond to visible light in a high-quality sample in which the deep level in the band gap is sufficiently suppressed. There is no need to install. Therefore, the manufacturing process can be simplified and radiation can be detected without reducing the detection sensitivity.

  In addition, conventional semiconductors such as silicon have at least 10 core electrons, whereas diamond, which is a light element semiconductor, has only two core electrons, so There is a feature that the probability of malfunction caused by shell electron excitation is greatly reduced.

  Furthermore, since the atomic number of the carbon atoms constituting the diamond is close to the average atomic number of the human body (it is equivalent to a living body), the radiation dose in the human body can be evaluated in a pseudo manner with good accuracy by using a diamond radiation detector. . That is, it can be used as a human body equivalent detector in which the behavior of radiation irradiated to the human body in the human body is substantially the same as the behavior of the irradiated radiation in the detector.

  Therefore, a detector using diamond is expected to be applied as a radiation detector that can withstand an environment such as high temperature or high radiation irradiation, or a biological equivalent detector.

  Radiation detectors using diamond have been studied for practical use, and some have already been put to practical use as ultraviolet detectors. Non-patent document 1 discloses a radioactive substance detector.

  As a known detector structure using diamond, a structure in which an electrode is deposited on a thin film diamond is generally known. More specifically, (i) a structure in which a comb-shaped counter electrode is arranged on a base layer made of a diamond thin film, and (ii) a flat plate in the vertical direction of the base layer made of a high-temperature / high-pressure synthetic diamond crystal (see Non-Patent Document 2). It is roughly divided into a structure in which electrodes are arranged. The structure (i) is suitable when a large detection area is required, for example, when detecting radiation with high sensitivity, and the structure (ii) is suitable when a relatively thick detection layer is required, for example, the energy of radiation. This is advantageous when performing decomposition detection. This difference in the application object is due to limitations in the conventional diamond manufacturing technology, that is, limitations such as high quality of the diamond thin film, high speed diamond film formation, and large area of high pressure synthetic diamond cannot be achieved. Therefore, if any high quality diamond film and high speed diamond film formation are realized, any radiation can be detected by any of the above detector structures.

  On the other hand, examples of a method for synthesizing a high-quality diamond base layer include a plasma CVD method disclosed in Patent Document 1 and Non-Patent Documents 3 and 4. According to this, it is shown that a high-quality thin film diamond can be obtained, although an increase in the film forming speed cannot be achieved.

  Therefore, in order to obtain a high-performance diamond detector, diamond applied to the bulk substrate of the detector is a high-temperature, high-pressure synthetic diamond that takes special time to grow and suppresses impurities and defects as much as possible by such a method. Can be considered. When such a diamond is not used, when a detector is manufactured by directly depositing an electrode on a bulk substrate, the signal intensity is generally low and the reproducibility is not good.

  However, impurity control and defect control in the high-temperature / high-pressure synthesis process that enables high-sensitivity detection requires huge and expensive manufacturing equipment and high running costs. At present, both technically and economically Not realistic.

Therefore, the present inventors are further developing a method for increasing the growth rate while maintaining high quality of diamond (see Non-Patent Documents 5, 6 and 7).
Japanese Patent Application No. 9-337740 (released on June 15, 1999) "Nuclear Instruments and Methods In Physics Research Section A" (Netherlands), 2002, Vol. 476, p.694-700 "Journal of Crystal Growth", (Netherlands), 2002, 237-239, p.1281-1285 "Journal of Crystal Growth", (Netherlands), 1998, 183, p.338-346 "Physica status solidi" (Germany), 1999, 174, p.101-115 "Journal of Crystal Growth", (Netherlands), 2002, Vol. 235, p.287-292 “Physica status solidi”, (Germany), 2003, 198, 2, p.395-406 "Proceedings of the 17th Diamond Symposium", New Diamond Forum, 2003, p.4-5

  As described above, an ultraviolet detector using a diamond thin film conventionally used for a detector, for example, a polycrystalline diamond thin film having a thickness of about 5 μm deposited on Si of a base substrate, is caused by ultraviolet rays. The carriers (electrons and holes) are mostly disappeared while diffusing in the diamond thin film near Si, which is not particularly good in quality, and the signal current is reduced, so that the detection sensitivity is greatly reduced. there were. This decrease in detection sensitivity can be solved by improving the quality of diamond. However, even if high-quality diamond is used, the radiation detector with the conventional structure cannot be said to have sufficient detection sensitivity like other radiation detectors, and new radiation detection that enables further high-sensitivity detection. Development of the vessel was required.

  That is, if the base diamond is sufficiently high in quality, a radiation detector using diamond has a dark current at room temperature (typically about 1 nA in Si) that is greatly reduced. It is expected that the minimum detection sensitivity will be greatly improved as compared to detectors using, so that even finer intensity radiation can be detected.

  However, since the number of electron-hole pairs formed for one incident radiation (one quantum) is roughly inversely proportional to the band gap energy, radiation detection is performed under conditions where the detector is cooled and the dark current is sufficiently reduced. When the sensitivity is compared, that is, when the detection signal intensity determined by the material-specific physical properties is compared, the detector using diamond is almost equal to the detector using a semiconductor other than diamond such as Si (ultraviolet light) The sensitivity is about 100 mA / W) or smaller.

  Therefore, in the diamond radiation detector, if the output signal intensity can be increased, it becomes more excellent than the radiation detector made of other materials. In other words, if a radiation detector with excellent sensitivity characteristics, that is, a low minimum detection radiation dose and a large signal intensity can be developed using a diamond thin film, the environmental resistance that is a material characteristic of diamond, and the ultra-high temperature at room temperature. Due to the low dark current characteristics, it is expected to become a high-sensitivity radiation detector for a wide range of applications.

  The present invention has been devised in view of the above-mentioned problems, and its purpose is a radiation detector using diamond, which can be operated at room temperature and has excellent environmental resistance, and is much more sensitive than conventional products. It is to realize a radiation detector having characteristics.

  A radiation detector according to the present invention has a base layer made of diamond and at least two electrodes in contact with the base layer, and a voltage is applied to the electrodes to cause current amplification in the base layer. An electric field portion is locally formed, and radiation applied to the base layer between the electrodes is detected based on a current collected by at least one of the electrodes.

  According to this, a very weak current is generated in the base layer due to the radiation applied to the base layer between the electrodes, and this very weak current is locally generated in the base layer formed by voltage application between the electrodes. In the high electric field part, the current is amplified significantly and then detected by at least one of the electrodes, so that the radiation detector is very sensitive.

  Note that “the high electric field portion is locally formed” means that the entire base layer does not become a high electric field portion but a high electric field is formed only in a part of the base layer. It does not necessarily mean that the intensity is spatially uniform in the high electric field part. “Current amplification” means current amplification by a collision ionization mechanism of carriers under a high electric field. The “high electric field portion” is a region where a high electric field necessary for causing this current amplification is formed.

  In the radiation detector according to the present invention, in order to solve the above problems, at least one end of the electrode is a thin film electrode region having a film thickness of less than 100 nm, and a voltage is applied to the electrode. Thus, the high electric field portion is formed in a local region of the base layer in contact with the thin film electrode region.

  In order to solve the above-described problem, the radiation detector according to the present invention has an end face protrusion with a minimum curvature radius of 100 nm or less, wherein the electrode protrudes in an in-plane direction of the surface of the base layer at at least one end thereof. The high electric field portion is formed in a local region of the base layer at a tip portion of the end face projection by applying a voltage to the electrode.

  In order to solve the above problems, the radiation detector according to the present invention has at least one of the electrodes extending in the in-plane direction of the surface of the base layer, and a minimum curvature radius of 100 nm on the electrode surface on the side in contact with the base layer. The high electric field portion is formed in a local region of the base layer that is in contact with the tip of the surface protrusion by applying a voltage to the electrode.

  In order to solve the above problems, the radiation detector according to the present invention has a recess having a minimum radius of curvature of 100 nm or less on the surface of the base layer in contact with the electrode, and the electrode is formed along the recess. The high electric field portion is formed in a local region of the base layer that is in contact with the tip of the surface protrusion by applying a voltage to the electrode.

  In order to solve the above problems, the radiation detector according to the present invention further includes a cap layer made of diamond, which is laminated so as to cover at least the high electric field portion, and applies a voltage to the electrode. Thus, a high electric field portion is also locally formed in the cap layer.

  In order to solve the above problems, a radiation detector according to the present invention has a cap layer made of diamond, which is laminated so as to cover at least the surface of the base layer located between the electrodes. A high electric field portion is also locally formed in the cap layer by applying a voltage to the cap layer.

In order to solve the above problems, the radiation detector according to the present invention is characterized in that an electric field of 10 ⁵ V / cm or more is formed in the high electric field portion by applying a voltage to the electrodes.

  In order to solve the above problems, the radiation detector according to the present invention is characterized in that the high electric field part is formed with a width of 5 μm or less in the electric field direction by applying a voltage to the electrode. Yes.

  The “electric field direction” is a direction of a force received by a positive charge in a high electric field portion generated by applying a voltage to the electrode.

In order to solve the above problems, the radiation detector according to the present invention is characterized in that a portion of the electrode that generates a high electric field portion is made of a conductive material having a carrier density of 10 ¹⁶ / cm ³ or more. Yes.

  Here, the “portion that generates the high electric field portion” is a portion that contributes to the generation of the high electric field portion, and specifically refers to the above-described thin film electrode region, end surface protrusion, and surface protrusion.

In order to solve the above problems, the radiation detector according to the present invention is characterized in that an electrical resistance between the electrodes is 10 ⁵ Ω or more when a voltage that generates the high electric field is applied.

  In order to solve the above problems, the radiation detector according to the present invention is characterized in that a response speed of a pulse current detected with respect to radiation irradiation is 10 μs or less in the electrode.

  The “pulse current response speed” indicates the time from the time of radiation irradiation until the pulse current flowing in response thereto is detected.

  The radiation detector according to the present invention is characterized by detecting any one of ultraviolet rays, α particles, β particles, γ particles, neutrons, and X-rays in order to solve the above problems.

  In order to solve the above problems, a manufacturing method of a radiation detector according to the present invention includes a base layer forming step of forming a base layer made of diamond, and a high electric field part that causes current amplification in the base layer by applying a voltage. An electrode forming step of forming at least two electrodes on the surface of the base layer.

  The method of manufacturing a radiation detector according to the present invention is characterized in that, in order to solve the above-described problem, in the electrode formation step, the electrode is formed by a vapor deposition method.

The method of manufacturing a radiation detector according to the present invention is characterized in that, in the electrode forming step, the electrode is formed by a chemical vapor deposition method in order to solve the above problems.
The method of manufacturing a radiation detector according to the present invention is characterized in that, in the electrode forming step, the electrode is formed by an ion implantation method in order to solve the above problems.

  The method of manufacturing a radiation detector according to the present invention is characterized in that, in the electrode forming step, the electrode is formed by a lithography method in order to solve the above problems.

  The method of manufacturing a radiation detector according to the present invention is characterized in that, in the electrode forming step, the electrode is patterned by masking in order to solve the above problems.

  In order to solve the above-mentioned problems, the manufacturing method of the radiation detector according to the present invention is characterized in that, in the electrode forming step, the electrode is formed by scanning the material in a beam shape.

In the method of manufacturing a radiation detector according to the present invention, in order to solve the above-described problem, the base layer forming step is performed by growing a diamond crystal on a base substrate by a microwave plasma chemical vapor deposition method. In the wave plasma chemical vapor deposition method, the methane / hydrogen ratio of the raw material is 1% or higher, the reaction pressure is 100 Torr or higher, and the power density expressed by input power / plasma emission volume is 15 W / cm ³ or higher. It is characterized in that it is performed at a temperature at which the temperature of the underlying substrate is 1000 ° C. or higher.

  In order to solve the above-mentioned problems, the manufacturing method of the radiation detector according to the present invention is characterized in that the input microwave power is set to 1000 W or more in the microwave plasma chemical vapor deposition method.

  In the manufacturing method of the radiation detector according to the present invention, in order to solve the above problems, the base layer forming step is performed by placing a base substrate on a base holder, and the base substrate is made of diamond, platinum. , Platinum alloy, molybdenum, molybdenum alloy, tantalum, tantalum alloy, tungsten, tungsten alloy, iron, iron alloy, iridium, iridium alloy, nickel, nickel alloy, silicon, metal silicide, quartz, boron nitride, aluminum nitride, silicon carbide, It is characterized by being a substrate made of at least one of gallium nitride and carbon nitride, or a substrate in which polycrystalline diamond or highly oriented diamond is grown on the surface of these substrates. Further, the base holder is made of platinum, platinum alloy, molybdenum, molybdenum alloy, tantalum, tantalum alloy, tungsten, tungsten alloy, iron, iron alloy, iridium, iridium alloy, nickel, nickel alloy, silicon, metal silicide, It is characterized in that at least one substrate surface is covered with diamond.

  In order to solve the above problems, the manufacturing method of the radiation detector according to the present invention is such that the base layer forming step is performed by placing the base substrate on a base holder, and the base layer is formed during diamond crystal synthesis. The temperature of the substrate is maintained at 50 ° C. or higher than the temperature of the base holder.

  In the manufacturing method of the radiation detector according to the present invention, in order to solve the above-described problem, the base layer forming step is performed in a reaction vessel, and the reaction vessel is resistant to microwave plasma. It is characterized by that.

  In the manufacturing method of the radiation detector according to the present invention, in order to solve the above-mentioned problem, the base layer forming step is performed in a reaction vessel, and the space in which the diameter of the reaction vessel is formed by microwave plasma. It is characterized by being 1 cm or more larger than the diameter.

  As described above, the radiation detector according to the present invention has a base layer made of diamond and at least two electrodes in contact with the base layer. By applying a voltage to the electrodes, the radiation detector is locally applied to the base layer. A high electric field portion is generated, and radiation applied to the base layer between the electrodes is detected based on a current collected by at least one of the electrodes.

  When a high electric field portion is locally formed in the base layer by applying a voltage to the electrode, carriers that have reached the high electric field portion are given large energy by the high electric field. Therefore, if the carriers generated by the radiation to be detected (for example, ultraviolet rays and particle beams) obtain a sufficiently high energy in the high electric field part, they will collide one after another with the valence electrons of the base layer diamond, and by the impact ionization mechanism A secondary carrier is generated each time. In this way, carriers generated by radiation can cause significant current amplification.

  This current amplification remarkably increases the signal intensity of radiation detection, so that even when extremely weak radiation is incident, it becomes a radiation detector with extremely high detection sensitivity that can be collected as a detectable level of current.

  The high electric field part is locally formed in the base layer. This is because when the high electric field part is formed over the entire base layer, the current amplification spreads over the entire base layer in an avalanche. This is because the base layer between the electrodes to which a voltage is applied is broken down, so that it does not function as a detector. In other words, by adjusting the formation region of the high electric field portion to make it local, the occurrence of current amplification can be stopped locally, and the detection sensitivity can be increased with good controllability while preventing the detector from being destroyed.

  In addition, when the high electric field portion is formed only locally, there is an advantage that the voltage to be applied to the detector can be kept low.

  In order to generate a high electric field portion locally in the base layer, for example, the film thickness of the end portion of the electrode is set to less than 100 nm, and the high layer portion is formed in a region of the base layer in contact with the electrode end portion on the side where the electrodes face each other. The electric field portion may be formed locally. That is, by setting the film thickness of the electrode end portion to less than 100 nm, when a voltage is applied to the electrode, the electric field concentrates in the vicinity of the electrode end surface, and the electrode end portion on the opposite side of the electrode in the base layer A local high electric field portion can be formed in a region along the line.

  In addition, a voltage can be applied to the electrodes by forming at least one electrode end on the side where the electrodes are opposed to each other to form an end surface protrusion having a minimum curvature radius of 100 nm or less protruding in the in-plane direction of the base layer surface. For example, the action of increasing the electric field occurs in the local region of the base layer that is in contact with the tip of the electrode end surface protrusion, and is locally in the base layer region along the tip of the electrode end surface protrusion on the opposite side of the electrode. A high electric field part can be formed.

  Similarly, at least one electrode on the side where the electrodes face each other extends in the in-plane direction of the surface of the base layer, and a surface protrusion having a minimum curvature radius of 100 nm or less is formed on the electrode surface on the side in contact with the base layer. However, when a voltage is applied to the electrode, there is an effect that the electric field is locally increased in the region of the base layer in contact with the surface protrusion, and the local layer region in contact with the tip of the surface protrusion on the opposite side of the electrode is locally applied. High electric field portion can be formed.

  Furthermore, even if a recess having a minimum curvature radius of 100 nm or less is formed on the surface of the base layer in contact with the electrode, and the electrode is formed along the surface of the base layer having the recess, a voltage is applied to the electrode. When the is added, a similar electric field increasing action occurs, and a local high electric field portion can be formed in the region of the base layer in contact with the surface protrusion on the side where the electrode faces.

  Furthermore, in the radiation detector according to the present invention, a cap layer made of diamond is laminated so as to cover at least the high electric field portion, and the high electric field portion is not only on the base layer side but also in the cap layer. If formed, the radiation detection sensitivity can be further increased.

  The high electric field portion in the cap layer is also formed by laminating the cap layer so as to cover at least the electrode portion that forms the high electric field. Specifically, the electrode portion that forms a high electric field is a thin-film electrode region on the side where the electrodes face each other when having an electrode end having a thickness of less than 100 nm, and the minimum curvature radius is 100 nm or less. This is the tip of the protrusion.

  In addition, in the radiation detector according to the present invention, if the structure has a cap layer made of diamond laminated so as to cover at least the surface of the base layer located between the electrodes, the detection characteristics thereof are It can be made more uniform and stable regardless of the atmospheric gas type, contributing to improved controllability and longer life of the detector. The reason for this is that when a voltage is applied to the electrode without a cap layer on the surface of the base layer located between the electrodes, the high electric field part on the surface of the base layer is exposed to the surface and tends to be somewhat unstable, whereas This is because a high electric field is not applied to the detector surface, and a high electric field portion can be formed only inside the detector without such instability.

The radiation detector according to the present invention can generate the current amplification satisfactorily by forming an electric field of 10 ⁵ V / cm or more in the high electric field portion.

  In the radiation detector according to the present invention, the high electric field portion is preferably formed with a width of 5 μm or less in the electric field direction. According to this, the detection sensitivity can be appropriately increased with good controllability without causing dielectric breakdown of the detector due to excessive current amplification.

Furthermore, in the radiation detector according to the present invention, the portion that generates the high electric field portion of the electrode is made of a conductive material having a carrier density of 10 ¹⁶ / cm ³ or more, so that the high electric field portion can be satisfactorily obtained. Can be formed.

Further, the radiation detector according to the present invention has an electrical resistance of 10 ⁵ Ω or more in an operating environment between the electrodes when a voltage that generates the high electric field is applied. The detection sensitivity can be improved.

  The radiation detector according to the present invention not only can improve the detection sensitivity of the radiation detector by making the response speed of the pulse current flowing with respect to radiation irradiation 10 μs or less in the electrode. The response speed can be improved.

  Since the radiation detector according to the present invention has a short cutoff wavelength of 220 nm, it can detect radiation without being influenced by long wavelength photons such as visible light of sunlight. Accordingly, the radiation to be detected is suitable for detecting ultraviolet rays, α rays, β rays, γ rays, neutron rays, X rays, and the like.

  As described above, the manufacturing method of the radiation detector according to the present invention forms an electrode on the surface of the base layer by forming at least two electrodes that locally form a high electric field portion on the base layer by applying a voltage. The manufacturing method of the radiation detector which has this.

  According to this, the radiation detector which can form a high electric field part locally in the said base layer can be manufactured by applying a voltage to an electrode. With such a high electric field part, the carriers formed by the above-described current amplification mechanism, that is, the radiation to be detected have sufficient energy, and the valence electrons of diamond in the base layer Is excited, and another secondary carrier is produced one after another, so that it becomes a radiation detector with high detection sensitivity capable of detecting even very weak radiation. The reason why the high electric field portion is locally formed is to prevent the dielectric breakdown of the detection element and to remarkably improve the controllability of the element by locally suppressing the occurrence of the current amplification described above. It is.

  The electrode for locally forming a high electric field part as described above can be formed by vapor deposition, chemical vapor deposition, ion implantation, lithography, or pattern formation by masking or beam-like material on the base layer surface. In this method, a thin film electrode having a thickness of less than 100 nm or a patterned electrode having a protruding fine structure with a radius of curvature of 100 nm or less is formed on the surface of the base layer.

In the method of manufacturing a radiation detector according to the present invention, the base layer forming step is performed by synthesizing a diamond crystal by a microwave plasma chemical vapor deposition method. In this case, the ratio of methane / hydrogen as a raw material is 1% or more, the reaction pressure is 100 Torr or more, and the power density represented by “input power / volume of plasma emission region” is 15 W / cm ³ or more. The temperature of the substrate is 950 ° C. or higher.

  According to this, high quality diamond crystals can be synthesized at high speed. In a radiation detector in which an electrode is attached to a base layer made of diamond, for example, it is desirable to form the base layer using diamond such that the main structure of the room temperature spectrum of cathodoluminescence is a peak due to band edge emission. However, such high-quality diamond was extremely slow in the synthesis rate, and industrial production was difficult. However, by synthesizing diamond using the microwave plasma chemical vapor deposition method under the above conditions, it is possible to synthesize the base layer by crystal growth at high speed while maintaining high quality diamond. The method of producing the film is very suitable for the synthesis of the base diamond of the radiation detector.

  In the microwave plasma chemical vapor deposition method, diamond can be synthesized more satisfactorily by setting the input microwave power to 1000 W or more.

  In the method for manufacturing a radiation detector according to the present invention, in the base layer forming step, the base substrate is diamond, platinum, platinum alloy, molybdenum, molybdenum alloy, tantalum, tantalum alloy, tungsten, tungsten alloy, iron, iron alloy. , Iridium, iridium alloy, nickel, nickel alloy, silicon, metal silicide, quartz, boron nitride, aluminum nitride, silicon carbide, gallium nitride, carbon nitride, or many of these on the substrate surface Since it is a substrate on which crystal diamond or highly oriented diamond is grown, high-quality diamond crystals can be synthesized.

  Furthermore, in the manufacturing method of the radiation detector according to the present invention, in the base layer forming step, the base holder is platinum, platinum alloy, molybdenum, molybdenum alloy, tantalum, tantalum alloy, tungsten, tungsten alloy, iron, iron alloy, iridium. Further, since the substrate surface made of at least one of iridium alloy, nickel, nickel alloy, silicon, and metal silicide is covered with diamond, high-quality diamond crystals can be synthesized.

  In addition, when the diamond crystal is synthesized, the temperature of the base substrate is kept higher by 50 ° C. or more than the temperature of the base holder, so that high-quality diamond crystals can be synthesized, so that a highly sensitive radiation detector can be manufactured. . If the temperature rise of the base substrate is less than 50 ° C. compared to the base holder, carbon atoms easily attach to the base holder and diamond nuclei or diamond crystallites grow, and one of the diamond nuclei or diamond crystallites grows. Since the part is peeled off from the base holder and mixed with the diamond on the base substrate, the quality is deteriorated.

  Moreover, a diamond crystal can be satisfactorily synthesized by performing the base layer forming step in a reaction vessel resistant to microwave plasma.

  Moreover, a diamond crystal can be satisfactorily synthesized by performing the above-mentioned base layer forming step in a reaction vessel that is 1 cm or more larger than the diameter of the space in which the microwave plasma is created.

[Embodiment 1]
An embodiment of the present invention will be described below with reference to FIGS.

  1A and 1B are diagrams showing a configuration of a radiation detector 1 according to the present invention. FIG. 1A is a plan view and FIG. 1B is a cross-sectional view.

  The radiation detector 1 includes a diamond base layer 11 and electrodes 12 and 13, and generates current when receiving radiation to be detected. The diamond base layer 11 is provided on the surface of a substrate (not shown) made of a non-conductive high-pressure synthetic bulk.

  Here, the diamond base layer 11 photoelectrically converts the radiation to be detected to flow a photocurrent, and the electrodes 12 and 13 output this photocurrent.

The diamond used as the material of the diamond base layer 11 has a main structure of room temperature cathodoluminescence spectrum relating to band edge emission and desirably has a certain high quality, so that a detection signal generated upon receiving radiation can flow well. be able to. Further, it is preferable to use diamond having a resistance between the electrodes 12 and 13 of 10 ⁵ Ω or more, preferably 10 ⁸ Ω or more, more preferably 10 ¹¹ Ω or more. Thereby, dark current is suppressed and the detection sensitivity of the radiation detector can be improved.

  The shape of the diamond base layer 11 may be appropriately selected depending on the use, but for example, a 3 mm × 3 mm shape is used. The thickness may be set to an appropriate thickness according to the type and energy of radiation in order to achieve high sensitivity. In general, the thickness is preferably about 20 μm or more. The upper limit of the thickness is preferably 100 μm or less in normal radiation detection, and the lower limit is 10 μm or more, preferably 20 μm or more, more preferably 30 μm or more.

  This is because carriers generated by radiation travel through the diamond base layer 11 and reach the electrodes 12 and 13. At this time, if the diamond base layer 11 is too thick, a part of the carrier is trapped during travel, This is because the signal intensity decreases and the energy resolution and response speed decrease. Further, if the diamond base layer 11 is too thin, there is a problem that radiation passes through the base layer without generating carriers, or the generated carriers flow out of the base layer and disappear during diffusion of the base layer.

As a material for the electrodes 12 and 13, it is preferable to use a conductive material having a carrier density of 10 ¹⁶ / cm ³ or more, more preferably a conductive material having a carrier density of 10 ²¹ / cm ³ or more. Examples of such electrodes 12 and 13 include an electrode in which titanium and gold are laminated, and a laminated electrode made of titanium, platinum and gold. If such a material is used, the carrier signal generated by radiation can be amplified well and detected with high sensitivity.

  In the present embodiment, the thickness of the electrode is less than 100 nm. Thus, as shown in FIG. 1B, when a voltage is applied to the electrode 12, the diamond base layer 11 has a high width of about 1 μm along the electrode end of the electrode 12 facing the electrode 13 side. An electric field part 14 is formed. The thickness of the electrode is more preferably less than 100 nm, and further preferably 40 nm or less.

  The high electric field portion 14 may be formed along one of the electrodes 12 and 13 by applying a voltage to one of the electrodes 12 and 13. You may form along. However, when the diamond base layer 11 has a very high quality diamond, the formation of the high electric field portion 14 at two locations may lead to the destruction of the detector. In such a case, the high electric field portion 14 It is better not to provide more than one place.

  That is, in the case of diamond of normal quality, the lifetime of holes in the diamond is longer than the lifetime of electrons. Therefore, among the carriers generated in the diamond base layer 11 upon receiving radiation, the hole current mainly has a high electric field portion 14. Current amplification. In such a case, if a local high electric field portion is formed on the opposite sides of the two electrodes, the positive hole current amplification occurs on the positive electrode side and the electronic current amplification occurs on the cathode side. If the distance is sufficiently longer than the electron diffusion distance, the holes formed by the carrier amplification on the cathode side cancel the electrons formed by the carrier amplification on the positive electrode side. Not formed, current amplification in the local high electric field portion operates stably.

  On the other hand, when the crystal quality of the diamond base layer 11 is very high, the lifetime of electrons becomes sufficiently long in addition to the lifetime of holes, and the current amplification of the electron current also occurs in the high electric field portion 14. In this case, if the local high electric field portions 14 are formed on opposite sides of the two electrodes, the above-described cancellation is not performed, and a positive feedback circuit for carrier amplification is formed, thereby preventing current amplification. It cannot be done, and the element is destroyed instantly. For this reason, when the crystal quality of the diamond base layer 11 is very high, it is necessary to have a configuration in which the high electric field portion 14 is formed only on one electrode.

  In addition, the high electric field part 14 to form should just be formed in a part of diamond base layer 11. FIG. The size (width) of the high electric field portion 14 depends on the distance between the electrodes and the diffusion distance of carriers, but is usually 5 μm or less, preferably 1 μm or less. According to this, in the diamond base layer 11, the high electric field part 14 can stop generation | occurrence | production of electric current locally, and can raise detection sensitivity, preventing destruction of a detection element.

The high electric field portion 14 is desirably formed with a high electric field of 10 ⁵ V / cm or more by applying an appropriate voltage to the electrodes 12 and 13, and the maximum electric field in the high electric field portion is 10 ⁶ V / cm. It is more desirable to set it to cm or more. Thereby, the detection sensitivity can be remarkably enhanced by utilizing the current amplification phenomenon by the carrier impact ionization mechanism.

  That is, when the carrier generated upon receiving radiation reaches such a high electric field portion 14, high energy sufficient to cause the impact ionization phenomenon can be obtained. Then, the carriers that have obtained high energy collide with the valence electrons of diamond in the diamond base layer 11 to produce secondary carriers one after another. As a result, the signal intensity of the carrier generated by the radiation is remarkably increased, so that a current signal large enough to detect even very weak incident radiation can be generated.

  The shape of the electrodes 12 and 13 is a rectangular shape as shown in FIG. 1, but is not limited to this, and the electrodes 21 and 22 are formed of the diamond base layer 11 and the electrode as shown in FIG. May be formed in a shape (comb shape) in which the electrodes are branched from each other. In this case, the distance between the electrodes 12 and 13 is reduced, and the carriers generated by the radiation can be reliably detected. Further, the formed high electric field portion 24 can be formed in the region of the diamond base layer 11 in contact with the electrode ends on the opposite sides of the electrodes 21 and 22 as shown in the cross-sectional view of FIG. The inter-electrode distance when the electrodes 12 and 13 are comb-shaped is preferably 100 μm or less, and more preferably 50 μm or less, as shown in Examples described later.

  In the present embodiment, as shown in FIG. 3, a cap layer 15 made of diamond may be laminated on the surface of the diamond base layer 11 on which the electrodes 12 and 13 are formed. According to this, since the high electric field portion 14 extends not only to the diamond base layer 11 but also to the cap layer 15, the detection sensitivity is further enhanced.

  Next, a method for manufacturing the radiation detector 1 of the present embodiment will be described.

  First, the base layer forming step for forming the diamond base layer 11 will be described. The method for producing the diamond base layer 11 is not particularly limited as long as it is a method capable of producing a diamond having a quality sufficient to perform a radiation detection function. However, in order to increase detection sensitivity, a higher quality and thicker film is used. Diamond is preferred.

  As a conventional single-crystal diamond synthesis method, there is a high-pressure synthesis method described in Non-Patent Document 2, which can be synthesized at a high growth rate of about 100 μm / h, but impurities such as nitrogen and catalyst metals are present in the diamond in ppm. Since it mixes in the level and crystal quality deteriorates, it cannot be adopted as a diamond synthesis method for electronic devices.

  On the other hand, according to the chemical vapor deposition method (CVD method), a carbon-containing gas such as methane, acetylene, or carbon monoxide is selected from hydrogen, argon, oxygen, nitrogen, or the like in the plasma CVD apparatus shown in FIG. Or by introducing a gas selected from hydrogen, argon, oxygen, nitrogen, or the like by installing a solid carbon source such as graphite in the reaction vessel 52. A diamond crystal can be grown on the base substrate 51. In this method, diamond with very few defects and impurities can be synthesized by adjusting the conditions (for example, the raw material concentration described in Patent Document 1 or the conditions described in Non-Patent Documents 3 and 4). However, the above CVD method has a very slow growth rate of 0.3 μm / h at the maximum, and it takes at least 60 hours or more to grow the diamond base layer 11 to a preferable thickness of 20 μm. Since it becomes extremely low, it becomes a barrier to practical use.

Therefore, in the microwave plasma CVD method, the ratio of raw material methane / hydrogen (volume ratio of methane to hydrogen) is 1% or more, the pressure in the reaction vessel is 50 Torr (67 hPa) or more, and expressed as input power / plasma emission volume. The power density is 15 W / cm ³ or more, and the temperature of the base substrate 51 is 50 ° C. higher than the temperature of the base holder 53 on which the base substrate 51 to be described later is placed at the time of diamond crystal synthesis. The crystal growth rate can be increased while maintaining the above. By this method, it is possible to manufacture the diamond base layer 11 of a radiation detector with higher detection sensitivity and higher productivity and practical use.

  Among the above conditions, the methane / hydrogen ratio of the raw material is preferably 1% or more and 70% or less, and more preferably 4% or more and 32% or less.

  The pressure in the reaction vessel is preferably 50 Torr (67 hPa) or more, more preferably 120 Torr (160 hPa) or more, and more preferably 160 Torr (210 hPa) or less.

Furthermore, the power density represented by input power / plasma emission volume is preferably 15 W / cm ³ or more, and more preferably 30 W / cm ³ or more. On the other hand, when the density is lower than 15 W / cm ³ , the non-diamond component and the non-epitaxial diamond phase contained in the produced diamond increase, which is not preferable.

  If the condition is out of the above range, high quality diamond cannot be synthesized at high speed, which is not preferable.

  In addition, the lower limit of the temperature of the base substrate 51 during diamond crystal synthesis is preferably 700 ° C. or higher, more preferably 1000 ° C. or higher, and the upper limit is preferably 1300 ° C. or lower, preferably 1200 ° C. or lower. It is more preferable that If the temperature of the base substrate 51 is lower than 700 ° C., a film mainly composed of a carbon film other than the crystalline diamond phase is formed, which is not preferable. On the other hand, if the temperature is too high, it becomes difficult to satisfactorily synthesize diamond crystals.

  Note that the microwave plasma CVD apparatus (apparatus shown in FIG. 4) used in the present embodiment is composed of a reaction vessel 52 having a gas inlet 54 through which a raw material is introduced, and a base holder 53 installed therein. In the reaction vessel 52, plasma is generated. Here, when the base substrate 51 on which the diamond base layer 11 is laminated is directly placed on the base holder 53 in the reaction vessel 52 of the plasma CVD apparatus, the heat of the base substrate 51 heated by the plasma is efficiently transmitted to the base holder 53. If the base substrate 51 is maintained at the appropriate temperature, the temperature of the base holder 53 as well as the base substrate 51 is included in the region temperature appropriate for high-speed diamond growth.

  In this case, diamond nuclei are frequently generated in the base holder 53 and grow into microcrystals, and part of the diamond nuclei or diamond microcrystals peel from the base holder 53 and move onto the base substrate 51. The growth of the non-epitaxial diamond phase on the underlying substrate 51 is unavoidable, and the crystal quality of the diamond base layer 11 is degraded.

  Therefore, the temperature of the base substrate 51 and the temperature of the base holder 53 are maintained at appropriate temperatures, that is, the base substrate 51 is maintained at a temperature at which diamond crystals are easy to grow, and the base holder 53 is maintained at a temperature at which diamond crystals are difficult to grow. There is a need. For this purpose, it is preferable to provide an appropriate heat conduction adjusting plate 55 between the base holder 53 and the base substrate 51. The temperature difference between the base substrate 51 and the base holder 53 can be adjusted by adjusting the thickness and contact area of the heat conduction adjusting plate 55. As a result, the base substrate 51 and the base holder 53 can be maintained at appropriate temperatures, and flat and high-quality diamond can be manufactured on the base substrate 51. The heat conduction adjusting plate 55 needs to be shaped and arranged so as to be covered by the base substrate 51 when viewed from the plasma irradiation direction.

  As another method for controlling the thermal contact between the base substrate 51 and the base holder 53, the base substrate 51 is not brought into contact with the base holder 53 by jetting high-pressure gas from directly under the base substrate 51 or electromagnetic field force. There is also a way to hold it up. In any case, the temperature of the base holder 53 is preferably lowered by 50 ° C. or more compared to the temperature of the base substrate 51, and more preferably a temperature difference of 100 ° C. or more is maintained. When this temperature difference is less than 50 ° C., the diamond peeled off from the base holder 53 and the amount of movement to the base substrate 51 increase as described above, and the quality of the diamond formed on the base substrate 51 deteriorates. Invite.

  Moreover, as the base substrate 51, a diamond thin film is easily generated, and a good diamond thin film can be obtained by using a material that does not cause the diamond film to peel in the growth temperature region. Specifically, diamond, platinum, platinum alloy, molybdenum, molybdenum alloy, tantalum, tantalum alloy, tungsten, tungsten alloy, iron, iron alloy, iridium, iridium alloy, nickel, nickel alloy, silicon, metal silicide, quartz, nitriding It is preferably a substrate made of at least one of boron, aluminum nitride, silicon carbide, gallium nitride, and carbon nitride, or a substrate in which polycrystalline diamond or highly oriented diamond is grown on the surface of these substrates. Diamond is more desirable.

  In addition, when any of the above-described base substrates 51 is used, preferable conditions in the plasma CVD method are the same as those described above.

  Furthermore, if a substance having a melting point of 2000 ° C. or higher is used as the base holder 53, the base holder material and the vapor pressure of impurities contained in the material at the temperature at the time of diamond growth can usually be sufficiently low. Can be prevented from mixing into the diamond during production. As the material of the base holder 53 that satisfies such requirements, platinum, platinum alloy, molybdenum, molybdenum alloy, tantalum, tantalum alloy, tungsten, tungsten alloy, iron, iron alloy, iridium, iridium alloy, nickel, nickel alloy, silicon, It is preferable to use metal silicide, quartz, boron nitride, aluminum nitride, silicon carbide, gallium nitride, or carbon nitride. Furthermore, by using the base holder 53 while being covered with diamond, it is possible to effectively suppress the separation of the diamond nuclei generated on the base holder 53 and the grown microcrystals.

  On the other hand, the reaction vessel 52 is preferably made of a material having resistance to microwave plasma. In addition, the reaction vessel 52 is preferably 1 cm or more larger than the diameter of the space in which the microwave plasma is created. According to this, the microwave plasma CVD method can be favorably advanced.

  Next, an electrode forming step for forming the electrodes 12 and 13 on the surface of the diamond base layer 11 thus manufactured will be described.

  The material of the electrodes 12 and 13 is not particularly limited as long as it is a conductive metal or a low-resistance semiconductor, but it is particularly a metal as an electrode for forming a high electric field in the diamond base layer 11. More specifically, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, which reacts with diamond to generate carbides, or platinum, gold, which is not easily oxidized in the atmosphere, Palladium, nickel, or graphite made from diamond suitable for fine structure formation is preferred, and two or more of these may be laminated, for example, titanium / gold may be laminated.

  The method for forming the electrodes 12 and 13 is not particularly limited as long as it is a method capable of forming a metal having a film thickness of less than 100 nm. However, a vapor deposition method, a chemical vapor deposition method, an ion implantation method, a lithography method, and the like. Etc.

  In the case of the vapor deposition method, the material metal is heated and evaporated, or the material metal is deposited on the diamond base layer 11 by ion sputtering. According to this, the electrodes 12 and 13 can be accurately formed with a thin film thickness of nanometer order. This method is particularly suitable when the electrodes 12 and 13 are flat and have a simple shape.

In the case of the ion implantation method, electrodes 12 and 13 are formed by ionizing and accelerating a metal serving as an electrode material and implanting it into the diamond base layer 11. According to this, by controlling the ion energy, the ion irradiation amount, and the ion implantation region, it is possible to form an electrode layer with a thin film thickness of nanometer order controlled to an arbitrary shape. For example, an electrode layer with a thickness of 30 nm can be formed by implanting ionized gallium with an acceleration voltage of 30 kV and an irradiation amount of 10 ¹⁵ / cm ² .

  The pattern formation of the electrodes 12 and 13 is performed by forming an electrode material by, for example, the above-described vapor deposition method, chemical vapor deposition method or ion implantation method after covering the diamond base layer 11 with a mask having a desired shape. A desired shape can be obtained.

  Alternatively, the pattern may be formed using a usual lithography method. Specifically, after forming a flat layer made of a metal as an electrode material on the surface of the diamond base layer 11, a desired pattern mask pattern such as a photosensitive resin is placed on the flat layer and etched. There is a method of transferring a pattern by applying. First, a pattern mask having a desired pattern shape is formed on the diamond base layer 11, and a flat layer made of an electrode material is further formed thereon. Then, an unnecessary portion of the flat layer is lifted off, thereby forming a desired pattern. There is also a method of forming patterned electrodes.

On the other hand, as a pattern forming method that does not use a mask, in the ion implantation method using a useful focused beam, a focused ion beam of a desired material focused to several tens of nanometers or less is scanned and implanted into a desired location, thereby obtaining a desired pattern. Shaped electrodes can be formed.
[Embodiment 2]
Another embodiment of the present invention will be described with reference to FIG.

  The configuration and manufacturing method of the radiation detector 4 of this embodiment are the same as those of the first embodiment except that the electrodes 42 and 43 are formed instead of the electrodes 12 and 13. The materials of the electrodes 42 and 43 are the same as those of the first embodiment, and the area and thickness may be appropriately selected depending on the use. However, as shown in FIG. It is formed so as to have an end face protrusion 45 having a radius of curvature of 100 nm or less on the diamond base layer 11 surface (cross section extending in the thickness direction). That is, each of the electrodes 42 and 43 is formed with an end face protrusion 45 along the diamond base layer 11 from the opposite surface toward the other electrode. Thereby, when a voltage is applied to the electrodes 42 and 43, the high electric field portion 44 having a width of about 5 μm along the end portions (end portions of the end surface protrusions 45) of the electrodes 42 and 43 facing each other. Can do. The curvature of the protrusion is preferably 100 nm or less, and more preferably 10 nm or less.

  At this time, if the radius of curvature of the end face protrusion 45 is 100 nm or less, the film thickness may be the same as the other electrode portions and may be constant, or the film thickness of the end face protrusion 45 may become thinner toward the tip. Good.

  The high electric field section 44 causes a current amplification phenomenon as in the first embodiment, and realizes the radiation detector 4 with high detection sensitivity.

In order to form the electrodes 42 and 43 having such end face protrusions 45, it is preferable to form the electrodes by the above-described lithography method, vapor deposition method or ion implantation method. .
[Embodiment 3]
Another embodiment of the present invention will be described with reference to FIG.

  The radiation detector 3 includes a diamond base layer 31, electrodes 32 and 33, and a diamond cap layer 38, and generates a current when receiving radiation to be detected. 6A is a plan view of the stage where the electrodes 32 and 33 are stacked on the diamond base layer 31. FIG.

  Here, the diamond base layer 31 photoelectrically converts the radiation to be detected and causes a photocurrent to flow on the surface, and the electrodes 32 and 33 formed on the surface output this photocurrent.

  The material of the diamond base layer 31 is the same as that of the first embodiment, and the area and thickness of the diamond base layer 31 may be appropriately selected according to use, but as shown in the cross-sectional view along BB ′ in FIG. At least one of the regions where the electrodes 32 and 33 are formed, preferably the entire surface of the electrode end region on the side where the electrodes 32 and 33 are opposed, the concave portion 31a having a radius of curvature of 100 nm or less on the surface of the diamond base layer 31 and the convex It has a part 31b.

  The curvature of the protrusion is preferably 100 nm or less, and more preferably 10 nm or less.

  Therefore, by laminating the electrodes 32 and 33 on the diamond base layer 31, a surface protrusion 32a is formed on the surface of the recess 31a shown in FIG. 6, and a surface protrusion 32b is formed on the surface of the protrusion 31b. Further, a diamond cap layer 38 is laminated on the diamond base layer 31 so as to cover the electrodes 32 and 33.

  In such a radiation detector 3, when a voltage is applied to the electrodes 32 and 33, a high electric field portion 34 having a width of about 5 μm is formed on the diamond base layer 31 in contact with the end portion of the surface projection 31 b, and the end of the surface projection 32 b is formed. A high electric field portion 35 having a width of about 5 μm is formed on the diamond cap layer 38 in contact with the portion. The high electric field portions 34 and 35 cause electronic amplification in the same manner as in the first embodiment, thereby realizing the radiation detector 3 with high detection sensitivity.

  The materials of the diamond base layer 31 and the electrodes 32 and 33 are the same as those in the first embodiment.

  In the present embodiment, the diamond cap layer 38 is laminated as an example, but the diamond cap layer 38 may not be laminated.

  In order to create such a concave portion 31a or convex portion 31b in the diamond base layer 31, a pattern is preferably formed by lithography, followed by oxygen, hydrogen, fluorine, hydrocarbon, nitrogen, argon, krypton, xenon. The diamond base layer 31 may be processed by irradiating it with an ion beam or plasma containing a gas comprising at least one of sulfur, selenium.

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

In a reaction vessel of a plasma CVD apparatus (AX-5250 manufactured by ASTeX), methane was 3.4 × 10 ⁻² Pa · m ³ / s and hydrogen was 8.1 × 10 ⁻¹ Pa · m ³ / s. Supplying at a flow rate, maintaining the pressure in the reaction vessel at 120 Torr (about 160 hPa), on a 3 mm × 3 mm × 0.5 mm base substrate made of high-pressure synthetic diamond under the condition of a processing time of 10 hours, A 20 μm thick diamond was formed.

  Using the above diamond as a base layer, two laminated electrodes (that is, the film thickness of the electrode is 40 nm) in which titanium 20 nm and gold 20 nm are laminated are formed on one surface of the detector S1 by using a photolithography method. It was created. At this time, the electrode was shaped like a comb as shown in FIG. Note that the width e of the comb-shaped electrode was 17 μm, and the distance to the adjacent electrodes (distance between the electrodes: the width of d in FIG. 7) was 20 μm.

In this detector S1, the applied voltage in the case of irradiating ultraviolet rays having a wavelength of 220 nm at 7.1 × 10 ⁻¹¹ W (2.8 × 10 ⁻⁹ W / cm ² ) while changing the voltage applied to the electrodes. FIG. 8 is a graph showing the relationship between the detection current and the detection current.

According to this, the current that flows when the voltage is 10 V or less was about 10 ⁻¹¹ A, but when it exceeds 10 V, it suddenly increases and reaches 10 ⁻⁷ A when the applied voltage is 50 V. That is, it can be seen that when a voltage of 10 V or higher is applied in the detector S1, the detected current increases rapidly and clear current amplification is performed. Further, the maximum light receiving sensitivity here was 7.4 × 10 A / W.

When a voltage of 10 V is applied in the detector S1, the maximum local electric field in the high electric field portion can be approximately expressed as “applied voltage” ÷ “electrode film thickness”, so that 2.5 × 10 ⁶ V A high electric field of about / cm is considered to be generated locally. Therefore, when a local electric field of about 2 × 10 ⁶ V / cm or more is generated in the detector S1, it can be determined that the detection current is suddenly increased, that is, the current is amplified.

  In addition, since the electric field formed in this example is given as a monotonically decreasing function of the distance as the electrode end face is the largest and away from the electrode end face, the high electric field portion locally exists only in the vicinity of the electrode end face, It can be judged.

In the same detector S2 as the detector S1 except that the distance between the electrodes is set to 50 μm, ultraviolet light having a wavelength of 220 nm is changed to 7.1 × 10 ⁻¹¹ W (2.8 × 10 ⁻⁹ W) while changing the voltage applied to the electrodes. / Cm ² ) and the current was measured. The relationship between the applied voltage and the detected current at this time is shown in the graph of FIG.

According to this, the current that flows when the voltage is 6 V or less was about 2 × 10 ⁻¹² A, but when it exceeds 6 V, it suddenly rises, and when a voltage of 50 V is applied, it reaches 10 ⁻⁷ A. That is, it can be seen that when a voltage of 6 V or higher is applied in the detector S2, the detected current increases rapidly and clear current amplification is performed. In addition, the maximum light receiving sensitivity here was 7.0 × 10 ² A / W.

When a voltage of 6 V is applied in the detector S2, the maximum local electric field is similarly calculated as 1.5 × 10 ⁶ V / cm. At this time, the high electric field portion necessary for current amplification is locally Is considered to have occurred. Therefore, when an electric field of about 10 ⁶ V / cm or more is generated in the detector S2, it can be said that the detected current increased rapidly and current amplification was performed.

  Also in this example, the high electric field portion was locally formed. Further, since the width of the high electric field portion is narrower than S1, it was found that when the applied voltage is the same, the distance between the electrodes tends to become narrower.

In the same detector S3 as the detector S1 except that the distance between the electrodes is set to 100 μm, ultraviolet light having a wavelength of 220 nm is changed to 7.1 × 10 ⁻¹¹ W (2.8 × 10 ⁻⁹ W) while changing the voltage applied to the electrodes. / Cm ² ), and current and applied voltage were measured. The relationship between the applied voltage and the detected current at this time is shown in the graph of FIG.

According to this, the current that flows when the voltage is 10 V or less was about 10 ⁻¹² A, but when it exceeds 10 V, it suddenly increases, and when a voltage of 50 V is applied, it reaches 10 ⁻⁹ A. That is, it can be seen that when a voltage of 10 V or higher is applied in the detector S3, the detected current increases rapidly and clear current amplification is performed. The maximum light receiving sensitivity here was 9.3 A / W.

Note that when a voltage of 10 V is applied to the detector S3, the maximum local electric field is calculated to be about 2.5 × 10 ⁶ V / cm. When a local electric field of 10 ⁶ V / cm or more is generated, it can be determined by the impact ionization mechanism, that is, that current amplification has been performed.
[Comparative Example 1]
An electrode in which titanium 50 nm and gold 50 nm were stacked (that is, the film thickness of the stacked electrode was 100 nm) was formed on the surface of the diamond base layer of Example 1 by using a photolithography method, and detector S4 was manufactured. At this time, the shape of the electrode was a comb shape. The width of the comb-shaped electrode was 17 μm, and the distance between the electrodes was 50 μm.

In this detector S4, ultraviolet rays having a wavelength of 220 nm were irradiated with 7.1 × 10 ⁻¹¹ W (2.8 × 10 ⁻⁹ W / cm ² ) while changing the voltage applied to the electrodes, and the current was measured. The relationship between the applied voltage and the detected current obtained at this time is shown in the graph of FIG.

  According to this, it is understood that no clear current amplification is performed even when the applied voltage is increased to 50V. Further, the maximum light receiving sensitivity here was 0.11 A / W.

  The detector S2 was irradiated with an ultraviolet laser having a pulse width of about 30 ps, and the temporal change in current was measured. The relationship between time and detected current at this time is shown in the graph of FIG. The applied voltage at this time is 50V. According to this, after laser irradiation, it can be seen that the detected current first increases rapidly, and then the time constant decreases at 15 ns according to the extended exponential function.

  In the electrode, the pulse response speed of the current flowing with respect to radiation irradiation is 10 μs or less.

  In the radiation detector of the present invention, the high electric field portion is locally provided on the base layer of diamond to be detected, so that high detection sensitivity is maintained. Therefore, high-sensitivity radiation that can be used in various environments by utilizing the environmental resistance (high hardness, excellent thermal conductivity, heat resistance, radiation resistance, and chemical resistance) that is a characteristic of diamond. This is a realization of the detector.

  Diamond responds to ultraviolet rays, α rays, β rays, γ rays, neutron rays, and X rays, and is less susceptible to damage from ultraviolet rays, X rays, or radioactive particles than other materials. The radiation detector of this embodiment can be suitably used as a radiation detector that detects ultraviolet rays, α rays, β rays, γ rays, neutron rays, and X rays.

  In addition, when the radiation detector of the present embodiment is used as an ultraviolet sensor, it is used for a semiconductor exposure apparatus, an industrial process monitoring using ultraviolet rays, an environmental monitor for monitoring harmful ultraviolet rays, a flame light detector, etc. it can.

  Alternatively, it can be used as a detector for radiation irradiation for medical purposes, an accelerator experiment, and a space experiment utilizing the radiation resistance (characteristic of being hardly damaged by radioactively active particles).

  Moreover, since it has heat resistance in addition to radiation resistance, it can also be used in nuclear reactors and fusion reactors. It can also be used for excimer laser monitors, biosensors, nuclear fuel processing, and gas sensors.

  Furthermore, since it is insensitive to visible light, it operates with high sensitivity even under visible light, and can be applied to detectors used in normal environments. Moreover, since the atomic number of carbon of diamond is close to the average atomic number of the human body (biological equivalent), it can be used as a human body equivalent detector in medical irradiation.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates an embodiment of the present invention, in which (a) is a plan view of a radiation detector, and (b) is a cross-sectional view taken along the plane A-A ′. FIG. 7 shows still another embodiment of the present invention, in which (a) is a plan view of a radiation detector and (b) is a cross-sectional view taken along the plane A-A ′. It is sectional drawing of the radiation detector which concerns on other embodiment of this invention. 1 is a plasma CVD apparatus according to an embodiment of the present invention. It is a top view of the radiation detector concerning other embodiments of the present invention. FIG. 7 shows still another embodiment of the present invention, wherein (a) is a plan view of a radiation detector, and (b) is a cross-sectional view taken along the B-B ′ plane. It is a top view which shows the radiation detector which concerns on the Example of this invention. It is a graph which shows the result of having measured the electric current, irradiating a fixed ultraviolet-ray and changing the voltage applied to an electrode in the radiation detector which concerns on the Example of this invention. It is a graph which shows the result of having measured the electric current in the radiation detector of the comparative example of this invention, irradiating fixed ultraviolet-ray and changing the voltage applied to an electrode. It is a graph which shows the result of having irradiated the ultraviolet laser with a pulse width of about 30 ps, and having measured the time change of the electric current in the radiation detector of the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Radiation detector 2 Radiation detector 3 Radiation detector 4 Radiation detector 11 Base layer (diamond base layer)
12 electrode 13 electrode 14 high electric field part 15 cap layer (diamond cap layer)
22 electrode 23 electrode 24 high electric field part 31 base layer (diamond base layer)
31a Concave part 31b Convex part 32 Electrode 32a Surface protrusion 32b Surface protrusion 33 Electrode 34 High electric field part 35 High electric field part 38 Cap layer (diamond cap layer)
42 Electrode 43 Electrode 44 High electric field portion 45 End projection 51 Base substrate 52 Reaction vessel 53 Base holder 54 Gas inlet 55 Heat conduction adjusting plate

Claims (25)

A base layer of diamond,
And at least two electrodes in contact with the base layer,
By applying a voltage to the electrode, a high electric field part that causes current amplification is locally formed in the base layer,
Detecting radiation applied to the base layer between the electrodes based on a current collected by at least one of the electrodes ;
The radiation detector according to claim 1, wherein the electrode has at least one end portion having a thickness of less than 100 nm . At least one end of the electrode is a thin film electrode region having a film thickness of less than 100 nm,
The radiation detector according to claim 1, wherein the high electric field portion is formed in a local region of the base layer in contact with the thin film electrode region by applying a voltage to the electrode. The electrode is formed with an end surface protrusion that protrudes in the in-plane direction of the surface of the base layer and has a minimum radius of curvature of 100 nm or less at at least one end thereof.
2. The radiation detector according to claim 1, wherein the high electric field portion is formed in a local region of the base layer in contact with a tip portion of the end surface protrusion by applying a voltage to the electrode. At least one of the electrodes has a surface protrusion that extends in the in-plane direction of the surface of the base layer and has a minimum curvature radius of 100 nm or less on the electrode surface on the side in contact with the base layer.
The radiation detector according to claim 1, wherein the high electric field portion is formed in a local region of the base layer in contact with a tip portion of the surface protrusion by applying a voltage to the electrode. The surface in contact with the electrode in the base layer has a recess with a minimum curvature radius of 100 nm or less,
The electrode includes a surface protrusion formed along the recess of the base layer;
The radiation detector according to claim 1, wherein the high electric field portion is formed in a local region of the base layer in contact with a tip portion of the surface protrusion by applying a voltage to the electrode. Furthermore, it has a cap layer made of diamond laminated so as to cover at least the high electric field part,
The radiation detector according to claim 1, wherein a high electric field portion is locally formed in the cap layer by applying a voltage to the electrode.   The radiation detector according to any one of claims 1 to 6, further comprising a cap layer made of diamond, which is laminated so as to cover at least a surface of the base layer located between the electrodes. . The radiation detector according to any one of claims 1 to 7, wherein an electric field of 10 ⁵ V / cm or more is formed in the high electric field portion by applying a voltage to the electrode.   9. The radiation detector according to claim 1, wherein the high electric field portion is formed with a width of 5 μm or less in the electric field direction by applying a voltage to the electrode. 10. The radiation detector according to any one of claims 1 to 9, wherein a portion of the electrode that generates a high electric field portion is made of a conductive material having a carrier density of 10 ¹⁶ / cm ³ or more. . 11. The radiation detector according to claim 1, wherein an electric resistance between the electrodes when a voltage causing the high electric field portion is applied is 10 ⁵ Ω or more.   The radiation detector according to claim 1, wherein a response speed of a pulse current detected with respect to radiation irradiation is 10 μs or less in the electrode.   The radiation detector according to any one of claims 1 to 12, wherein any one of ultraviolet rays, α rays, β rays, γ rays, neutron rays, and X rays is detected. A base layer forming step for forming a base layer made of diamond;
By a voltage being applied to, at least two electrodes to locally form a high field region to cause current amplification to the base, possess an electrode forming step of forming on the surface of the substrate, and
The base layer forming step is performed by growing a diamond crystal on a base substrate by a microwave plasma chemical vapor deposition method, and is performed by placing the base substrate on a base holder,
In the above microwave plasma chemical vapor deposition method, the ratio of raw material methane / hydrogen is 1% or more, the reaction pressure is 100 Torr or more, and the power density expressed by input power / plasma emission volume is 15 W / cm ³ or more. The temperature of the base substrate during crystal synthesis is 950 ° C. or higher, and
A method for producing a radiation detector, characterized in that, when synthesizing a diamond crystal, it is carried out under a condition that the temperature of the base substrate is maintained at 50 ° C. or higher than the temperature of the base holder .   15. The method of manufacturing a radiation detector according to claim 14, wherein in the electrode forming step, the electrode is formed by a vapor deposition method.   The method of manufacturing a radiation detector according to claim 14, wherein in the electrode forming step, the electrode is formed by a chemical vapor deposition method.   The method of manufacturing a radiation detector according to claim 14, wherein in the electrode formation step, the electrode is formed by an ion implantation method.   The method of manufacturing a radiation detector according to claim 14, wherein, in the electrode forming step, the electrode is formed by a lithography method.   The method of manufacturing a radiation detector according to claim 14, wherein in the electrode forming step, the electrode is patterned by masking.   The method of manufacturing a radiation detector according to claim 14, wherein in the electrode forming step, the electrode is formed by scanning the material in a beam shape. In the said microwave plasma chemical vapor deposition method, input microwave power shall be 1000 W or more, The manufacturing method of the radiation detector of Claim 14 characterized by the above-mentioned. The base substrate is diamond, platinum, platinum alloy, molybdenum, molybdenum alloy, tantalum, tantalum alloy, tungsten, tungsten alloy, iron, iron alloy, iridium, iridium alloy, nickel, nickel alloy, silicon, metal silicide, quartz, nitriding It is a substrate made of at least one of boron, aluminum nitride, silicon carbide, gallium nitride, and carbon nitride, or a substrate in which polycrystalline diamond or highly oriented diamond is grown on the surface of these substrates. The manufacturing method of the radiation detector of Claim 14 . The base holder is at least one of platinum, platinum alloy, molybdenum, molybdenum alloy, tantalum, tantalum alloy, tungsten, tungsten alloy, iron, iron alloy, iridium, iridium alloy, nickel, nickel alloy, silicon, and metal silicide. The method of manufacturing a radiation detector according to claim 14 , wherein the surface of the substrate made of diamond is covered with diamond. The base layer forming step is performed in a reaction vessel,
The method for manufacturing a radiation detector according to any one of claims 14 to 23 , wherein the reaction vessel is resistant to microwave plasma. The base layer forming step is performed in a reaction vessel,
The method of manufacturing a radiation detector according to any one of claims 14 to 24 , wherein a diameter of the reaction vessel is 1 cm or more larger than a diameter of a space in which microwave plasma is generated.

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