Scintillators and electron detectors

Abstract

The scintillator (1A) according to the present invention is characterized by comprising: a supporting substrate (10); a light-emitting layer (14) formed on the substrate (10) and having an electron concentration of 2×10 19 cm ‑3 Above 2×10 20 cm ‑3 The following form is composed of ZnO to which impurities are added and generates scintillation light in response to the incidence of radiation; a protective layer (16) is formed on the light-emitting layer (14) and is composed of a material having a band gap larger than that of ZnO; and a metal layer (18) is formed on the protective layer (16). The supporting substrate (10) is composed of a material that transmits the scintillation light generated on the light-emitting layer (14). In addition, the metal layer (18) functions as a reflection layer that reflects the scintillation light from the light-emitting layer (14). Thus, a scintillator suitable for detecting radiation such as electrons and an electron detector using the scintillator can be realized.

Description

[0001] This application is filed on December 9, 2016 、Application No. 201680076533.5 、The name of the invention is Scintillator and electronic detectors A divisional application for a patent application. Technical Field

[0002] The present invention relates to a scintillator used for detecting radiation such as electrons, and an electron detector using the scintillator. Background Art

[0003] A photodetector such as a photomultiplier tube used in a scanning electron microscope (SEM) or a time-of-flight mass spectrometer (TOF-MS) has a structure in which a scintillator that converts accelerated electrons into light is provided in front of the photodetector.

[0004] For example, in a scanning electron microscope, secondary electrons from an object to be observed are accelerated at an accelerating voltage of about 12 kV and made incident on a scintillator, and a photodetector is used to convert the scintillation light generated on the scintillator into an electrical signal to obtain an image. For such a device, it is necessary to increase the electron scanning speed in order to improve throughput, but at the same time, it is also necessary to shorten the fluorescence lifetime (afterglow characteristics) of the scintillation light generated on the scintillator.

[0005] In addition, in the case of a time-of-flight mass spectrometer, a micro channel plate (MCP) is used to convert ions to be analyzed by mass spectrometry into electrons, and a scintillator is used to further convert the electrons into light, and a photodetector is used to convert the generated scintillation light into an electrical signal, thereby performing mass spectrometry of the ions by time difference measurement. For such a device, the fluorescence lifetime of the scintillation light on the scintillator is also required to be short.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2013-212969

[0009] Patent Document 2: Japanese Patent Application Publication No. 2014-144992

[0010] Patent Document 3: Japanese Patent Application Publication No. 2012-1662

[0011] Patent Document 4: Japanese Patent Application Publication No. 2011-141134

[0012] Patent Document 5: Japanese Patent Application Publication No. 2010-280826

[0013] Patent Document 6: Japanese Patent Application Publication No. 2010-280533

[0014] Patent Document 7: Japanese Patent Application Publication No. 2009-286856

[0015] Patent Document 8: Japanese International Publication No. WO2005 / 114256

[0016] Non-patent literature

[0017] Non-patent document 1: T.Shimizu et al., "Response Time-Shortened Zinc OxideScintillator for Accurate Single-Shot Synchronization of Extreme UltravioletFree-Electron Laser and Short-Pulse Laser", Applied Physics Express Vol.4 (2011) pp.062701-1-062701-3

[0018] Non-patent document 2: Y.Hiragino et al., "Improved transport properties for ZnO films on Al203(1120) by MOCVD", Physica Status Solidi C Vol.ll No.7-8(2014)pp.1369-1372 Summary of the invention

[0019] Technical problem to be solved by the invention

[0020] As mentioned above, scintillators used in scanning electron microscopes and time-of-flight mass spectrometers require high-speed responsiveness due to a short fluorescence lifetime. However, for general scintillators that have been put into practical use, the fluorescence lifetime of the scintillation light is about 20 nsec, and its high speed is not sufficient. In addition, for example, for plastic scintillators (body), the fluorescence lifetime is about 2.4 nsec, but there are problems such as rapid deterioration of the scintillator.

[0021] It is also known that ZnO (zinc oxide) can be used as a high-speed response scintillator having a fluorescence lifetime of less than 1 nsec by adding impurities (see, for example, Patent Documents 1 to 8 and Non-Patent Document 1). However, existing ZnO scintillators are mainly used for bulk single crystals and crystals produced by liquid phase epitaxy, and have problems in terms of impurity control, processability, thickness control, cost, productivity, etc.

[0022] In addition, the existing ZnO scintillator uses a thick crystal for the purpose of measuring α particles. For example, when such a scintillator is used for measuring low-energy electron beams with a small penetration depth, strong fluorescence cannot be obtained due to self-absorption. In addition, although there is a proposal to use a ZnO scintillator with nanoparticles, such a scintillator has many defects and cannot obtain a sufficient amount of fluorescence.

[0023] The present invention is the result of unremitting efforts to solve the above-mentioned technical problems, and an object of the present invention is to provide a scintillator suitable for detecting radiation such as electrons, and an electron detector using the scintillator.

[0024] Solutions to technical problems

[0025] In order to achieve the above-mentioned object, the scintillator according to the present invention is characterized by comprising: (1) a supporting substrate; (2) a light-emitting layer formed on the supporting substrate and having an electron concentration of 2×10 19 cm -3 Above 2×10 20 cm -3 The following forms are composed of ZnO to which impurities are added and which generates scintillation light in response to the incidence of radiation such as electrons; (3) a protective layer, which is formed on the light-emitting layer and is composed of a material having a band gap larger than that of ZnO; (4) a metal layer, which is formed on the protective layer; the supporting substrate is composed of a material that transmits the scintillation light generated in the light-emitting layer, and the metal layer is constructed in a form that acts as a reflection layer that reflects the scintillation light from the light-emitting layer.

[0026] In the above-mentioned scintillator, a light-emitting layer composed of ZnO doped with impurities is formed on a supporting substrate and the electron concentration in the light-emitting layer is set to 2×10 19 cm -3 Above 2×10 20 cm -3As follows. By setting the electron concentration in the light-emitting layer, the fluorescence lifetime becomes shorter because it becomes the target of carrier recombination, and the luminescence efficiency becomes higher. In addition, by compensating for defects in the crystal, electrons fill the lower part of the conduction band and the effective band gap becomes larger, thereby suppressing the occurrence of self-absorption.

[0027] In addition, in the above structure, a protective layer for protecting hygroscopic ZnO is formed on the ZnO light-emitting layer, and the material of the protective layer is a material having a band gap greater than that of ZnO. By providing such a protective layer, it is possible to prevent the electrons or holes generated on the light-emitting layer from flowing out to the outside, and thus the luminous efficiency can be improved. In addition, a metal layer is further formed on the protective layer. The metal layer acts as a reflection layer that reflects the scintillation light from the light-emitting layer, thereby improving the utilization efficiency of the scintillation light in the detection of radiation. According to the above, it can be suitable for the detection of radiation such as electrons, and a scintillator with high-speed responsiveness can be realized.

[0028] The radiation to be detected by the above-mentioned scintillator includes particles such as electrons, protons, neutrons, α particles, and ions, as well as electromagnetic waves such as γ rays, X rays, and light.

[0029] The electron detector of the present invention is composed of a scintillator having the above structure that outputs scintillation light generated on a light-emitting layer in response to the incidence of electrons, and a photodetector that detects the scintillation light output from the scintillator. According to such an electron detector, electrons can be suitably detected using a scintillator having high-speed response.

[0030] Effects of the Invention

[0031] According to the scintillator and the electron detector of the present invention, a scintillator having an electron concentration of 2×10 19 cm -3 Above 2×10 20 cm -3 The following form consists of a light-emitting layer composed of ZnO to which impurities are added, a protective layer composed of a material having a band gap larger than that of ZnO, and a metal layer that acts as a reflection layer for the scintillation light from the light-emitting layer, thereby making it possible to be suitable for detecting radiation such as electrons, and to realize a scintillator with high-speed responsiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a side cross-sectional view schematically showing a scintillator structure according to one embodiment.

[0033] Figure 2Graphs showing the fluorescence lifetimes of (a) a ZnO scintillator and (b) a plastic scintillator.

[0034] Figure 3 : is an energy band diagram showing the layer structure in the scintillator.

[0035] Figure 4 This is a graph showing the band gap of materials constituting the protective layer.

[0036] Figure 5 It is a side view showing the structure of an electron detector according to one embodiment.

[0037] Figure 6 This is a schematic diagram showing the structure of a scanning electron microscope.

[0038] Figure 7 This is a schematic diagram showing the structure of a time-of-flight mass spectrometer.

[0039] Figure 8 This is a graph showing the wavelength dependence of the light emission intensity related to the scintillator.

[0040] Fig. 9 This is a graph showing the dependence of luminous efficiency on electron concentration.

[0041] Fig.10 This is a graph showing the dependence of luminous efficiency on the electron acceleration voltage. DETAILED DESCRIPTION

[0042] The following is a detailed description of the embodiments of the scintillator and the electron detector according to the present invention with reference to the accompanying drawings. In the description of the accompanying drawings, the same symbols are used to mark the same elements, and repeated descriptions are omitted. In addition, the dimensional ratios of the accompanying drawings are not necessarily consistent with the objects being described.

[0043] Figure 1 1 is a side cross-sectional view schematically showing a scintillator structure according to an embodiment. The scintillator 1A according to the present embodiment is a scintillator used for detecting radiation such as electrons, and is composed of a supporting substrate 10, a buffer layer 12, a light-emitting layer 14, a protective layer 16, and a metal layer 18. In addition, the radiation to be detected by the scintillator 1A according to the present embodiment generally includes particles such as electrons, protons, neutrons, α particles, and ions, as well as electromagnetic waves such as γ rays, X-rays, and light, and the scintillator 1A can be suitably used for detecting electrons with an energy of -5keV to 20keV, as described later.

[0044] The support substrate 10 is a substrate made of a material that transmits the scintillation light (fluorescence) generated on the light-emitting layer 14 with sufficient transmittance. For example, an a-plane sapphire substrate can be suitably used as the support substrate 10. The light-emitting layer 14 is formed on the support substrate 10 and generates scintillation light in response to the incidence of radiation such as electrons. In addition, the light-emitting layer 14 involved in this embodiment has an electron concentration of 2×10 19 cm -3 Above 2×10 20 cm -3 The following form is composed of ZnO (zinc oxide) to which impurities are added. The impurities added to the light emitting layer 14 are, for example, added at a concentration of 2×10 19 cm -3 ~4×10 20 cm -3 Doped Ga.

[0045] Figure 1 In the illustrated structural example, a buffer layer 12 composed of ZnO is further formed between the support substrate 10 and the light emitting layer 14, and the light emitting layer 14 is formed on the buffer layer 12. The buffer layer 12 is composed of, for example, ZnO to which no impurities are added.

[0046] The protective layer 16 for protecting ZnO in the hygroscopic light-emitting layer 14 is formed on the ZnO light-emitting layer 14 to which impurities are added. In addition, the protective layer 16 is composed of a material having a band gap larger than that of ZnO. By using such a material, the protective layer 16 has a function of improving the detection characteristics and detection efficiency of radiation by the scintillator 1A including the ZnO light-emitting layer 14. Specifically, for example, SiO2 can be used appropriately as a material constituting the protective layer 16.

[0047] Furthermore, a metal layer 18 that functions as a reflection layer for reflecting scintillation light from the light emitting layer 14 is further formed on the protective layer 16. As a material constituting the metal layer 18, for example, Al can be preferably used.

[0048] Next, the effects of the scintillator 1A according to the present embodiment will be described below.

[0049] Figure 1 In the scintillator 1A shown, a light emitting layer 14 made of ZnO doped with impurities (e.g., Ga) at a predetermined concentration is formed on a supporting substrate 10. As described above, the ZnO scintillator doped with impurities is a scintillator having a very short fluorescence lifetime of scintillation light, e.g., less than 1 ns, and high-speed responsiveness.

[0050] Here, Figure 2 The graphs show the fluorescence lifetimes of (a) a ZnO scintillator and (b) a plastic scintillator. Figure 2The curve (a) shows the time waveform of the scintillation light generated on the ZnO scintillator. Figure 2 The curve (b) shows the time waveform of the scintillation light generated by the plastic scintillator as a comparative example. As shown in these curves, it can be understood that the 90%-10% afterglow characteristic corresponding to the fluorescence lifetime of the plastic scintillator is 2.17ns, while the 90%-10% afterglow characteristic of the ZnO scintillator is 0.517ns and can have high-speed response.

[0051] By controlling the fluorescence lifetime of the scintillation light generated in the light-emitting layer 14 to less than 1 ns, it is possible to set the scanning speed to more than 300 MHz in, for example, a scanning electron microscope for semiconductor inspection. In addition, in terms of a time-of-flight mass spectrometer, the resolution of mass spectrometry can be relatively improved compared to the existing plastic scintillator.

[0052] In the above-mentioned scintillator 1A, the electron concentration in the ZnO light-emitting layer 14 to which the impurity is added is set to 2×10 19 cm -3 Above 2×10 20 cm -3 By setting the electron concentration in the ZnO light-emitting layer 14 and increasing the electron concentration by adding impurities to ZnO, the excited carriers become the target of recombination when the excitation intensity is weak, so the fluorescence lifetime of the scintillation light is shortened, and the luminous efficiency is improved.

[0053] In the light-emitting layer 14 of the above structure, defects in the ZnO crystal are compensated by impurity addition, thereby suppressing the generation of defective light emission with a long fluorescence lifetime. In addition, by sufficiently increasing the electron concentration, electrons fill the lower part of the conduction band and the effective band gap becomes larger, thereby suppressing the occurrence of self-absorption.

[0054] In the above structure, the protective layer 16 for protecting the hygroscopic ZnO is formed on the ZnO light-emitting layer 14, and the material of the protective layer 16 is a material having a band gap larger than that of ZnO (e.g., SiO2). By providing such a protective layer 16 relative to the light-emitting layer 14, the light-emitting efficiency on the light-emitting layer 14 can be further improved. In addition, the band gap of ZnO is 3.4 eV, and it is necessary to use a material having a band gap larger than 3.4 eV as the material constituting the protective layer 16.

[0055] In addition, in the above structure, a metal layer 18 is further formed on the protective layer 16. The metal layer 18 functions as a reflection layer that reflects the scintillation light from the ZnO light-emitting layer 14, thereby improving the output efficiency of the scintillation light from the back side of the support substrate 10 that serves as the light output surface. In summary, it is possible to detect radiation such as electrons, and it is possible to realize a scintillator 1A with high-speed responsiveness.

[0056] Figure 3 Yes means Figure 1 The energy band diagram of the layer structure in the scintillator 1A shown in FIG. Figure 3 For the sake of simplicity, the energy band diagram does not consider the band bending caused by surface energy levels or charge transfer, and only shows the energy size. In addition, the expansion of electron distribution caused by thermal energy is also ignored in this energy band diagram. Figure 3 As shown, by providing a protective layer 16 of a material having a band gap larger than that of ZnO for the ZnO light-emitting layer 14, electrons or holes generated in the light-emitting layer 14 are prevented from flowing out to the outer metal layer 18, thereby improving the light-emitting efficiency relative to the incident radiation such as electrons.

[0057] In addition, as described above, the light-emitting layer 14 has a sufficiently high electron concentration due to the addition of impurities, thereby increasing the probability of recombination between holes and electrons generated by the incidence of radiation and improving the light emission efficiency. Figure 3 As shown, the electrons are retained in the conduction band. In this case, the energy level of the lower part of the conduction band is filled with electrons, and absorption and excitation by radiation incidence etc. can only occur with higher energy than this. In addition, since the emission of scintillation light occurs between the electrons in the lower part of the conduction band and the holes retained in the upper part of the valence band, its energy becomes smaller than the absorbed energy. Therefore, according to the light-emitting layer 14 with set electron concentration as described above, the occurrence of self-absorption can be suppressed.

[0058] In the scintillator 1A having the above structure, the light emitting layer 14 preferably has a thickness of 0.5 μm or more and 3.0 μm or less. The scintillator 1A having such a thickness of the ZnO light emitting layer 14 doped with impurities can be used for detecting electrons with energies of about -5 keV to 20 keV in, for example, a scanning electron microscope and a time-of-flight mass spectrometer.

[0059] Here, assuming that electrons are the radiation to be detected, the penetration depth of electrons into ZnO is about 1 μm under the condition of an acceleration voltage of 10 kV. For example, the acceleration voltage of electrons in a scanning electron microscope and a time-of-flight mass spectrometer is about 5 kV to 20 kV. In this case, it is appropriate to set the thickness of the light-emitting layer 14 within the range of 0.5 μm to 3.0 μm as described above. If the thickness of the light-emitting layer 14 is thicker than this range, the luminous efficiency decreases due to self-absorption.

[0060] In the light emitting layer 14, the impurity added to ZnO preferably includes at least one impurity selected from Ga, Al, and In, and the impurity added to ZnO is particularly preferably Ga. Ga, Al, and In are all good donor impurities that provide conduction electrons to ZnO.

[0061] In the scintillator 1A having the above structure, the buffer layer 12 made of ZnO is formed between the support substrate 10 and the ZnO light emitting layer 14. By forming the ZnO light emitting layer 14 doped with impurities on the ZnO buffer layer 12, the light emitting layer 14 can be formed on the substrate 10 appropriately.

[0062] The buffer layer 12 and the light-emitting layer 14 on the supporting substrate 10 can be formed by, for example, an MOCVD method having good controllability in thin film formation. In addition, when the ZnO buffer layer 12 is disposed between the supporting substrate 10 and the light-emitting layer 14, the buffer layer 12 preferably has a thickness of 20 nm to 400 nm. That is, in order to prepare a base for ZnO crystals, the thickness of the buffer layer 12 is preferably 20 nm or more. In addition, because of self-absorption and the susceptibility to defective luminescence, the thickness of the buffer layer 12 is preferably 400 nm or less. In addition, if such a ZnO buffer layer 12 is not required, a structure without a buffer layer is also possible.

[0063] For the protective layer 16 formed on the light-emitting layer 14 and composed of a material having a band gap greater than that of ZnO, the material constituting the protective layer 16 is preferably a material comprising at least one selected from SiO2, Al2O3, MgO, CaF2, BeO, MgF2 and LiF, and the material of the protective layer 16 is particularly preferably a chemically stable material, namely SiO2.

[0064] Figure 4 is a graph showing the band gap of the material constituting the protective layer 16. Figure 4 As shown, the above materials for the protective layer 16 are all considered to have a band gap greater than that of ZnO. For example, the band gap of SiO2 is 7.9 eV, while the band gap of ZnO is 3.4 eV. In addition, the protective layer 16 preferably has a layer thickness of 10 nm to 200 nm.

[0065] Regarding the support substrate 10 made of a material that transmits scintillation light, for example, a sapphire substrate, a quartz substrate, or a glass substrate can be used. Specifically, as the material of such a support substrate 10, for example, there are a-plane sapphire, c-plane sapphire, quartz glass, UV-transmitting glass (350nm or more), borosilicate glass, etc. In addition, the support substrate 10 preferably uses an a-plane sapphire substrate in order to appropriately form the ZnO light-emitting layer 14 on the support substrate 10.

[0066] The metal layer 18 formed on the protective layer 16 is preferably made of Al. In addition, metals other than Al may be used as the material of the metal layer 18. In addition, when the metal layer 18 is made of Al, for example, it is preferable that the thickness of the metal layer 18 is 10 nm or more and 50 nm or less in order to ensure the function as a reflective layer.

[0067] Next, the structures of an electron detector, a scanning electron microscope, and a time-of-flight mass spectrometer using the scintillator 1A having the above structure will be described below.

[0068] Figure 5 2A is a side view showing the structure of an electron detector according to an embodiment. The electron detector 2A according to this embodiment is composed of a scintillator 1A, a photodetector 20, and a light guide 22. The scintillator 1A includes a support substrate 10, a buffer layer 12, a light emitting layer 14, a protective layer 16, and a metal layer 18, and is configured to Figure 1 Same. Also, in Figure 5 2 shows a cross-sectional structure of a scintillator 1A.

[0069] The photodetector 20 is optically connected to the back side of the support substrate 10 of the scintillator 1A, which is the light output surface, through the light guide 22. Thus, the scintillation light generated on the light emitting layer 14 of the scintillator 1A in response to the incidence of electrons and output to the buffer layer 12 side passes through the support substrate 10 and the light guide 22, reaches the photodetector 20, and is detected. In addition, the scintillation light generated on the light emitting layer 14 and output to the protective layer 16 side is reflected by the metal layer 18 functioning as a reflective layer, and then similarly passes through the support substrate 10 and the light guide 22, reaches the photodetector 20, and is detected.

[0070] According to the electron detector 2A having such a structure, the electrons can be suitably detected using the scintillator 1A having high-speed response. As the light detector 20 for detecting the scintillation light output from the scintillator 1A, for example, a photomultiplier tube can be used. In addition, a light detection element other than a photomultiplier tube can be used as the light detector 20. In addition, as for the light guide 22 used for guiding the scintillation light between the scintillator 1A and the light detector 20, if it is not necessary, a structure without the light guide can be used.

[0071] In addition, when the scintillator 1A is used in such an electron detector 2A, the metal layer 18 in the scintillator 1A, in addition to having the function of a reflection layer that reflects the scintillation light, can also be made into a structure that acts as an accelerating electrode for accelerating electrons of the detection object that are incident on the scintillator 1A from the outside.

[0072] Figure 6 This is a schematic diagram showing the structure of a scanning electron microscope. Figure 6 In the illustrated configuration example, a scintillator 30, a light guide 34, and an electron detector composed of a photodetector 32 are provided relative to an observation object 36. In this device, electron beams are irradiated to the observation object 36, secondary electrons released from the object 36 are accelerated with a predetermined voltage and made incident on the scintillator 30, and scintillation light generated on the scintillator 30 is detected by the photodetector 32 through the light guide 34, thereby outputting an electrical signal. In such a configuration, the scintillator 30 that converts electrons from the object 36 into light can be used. Figure 1 In such a structure, the metal layer 18 of the scintillator 1A can be used as an electrode for accelerating electrons released from the observation object 36 .

[0073] Figure 7 This is a schematic diagram showing the structure of a time-of-flight mass spectrometer. Figure 7 In the illustrated structural example, an electron detector composed of a scintillator 30, a light guide 34, and a photodetector 32 is provided with respect to a microchannel plate (MCP) 38. In this device, ions to be the subject of mass spectrometry analysis are converted into electrons on the MCP 38, and the electrons released from the MCP 38 are made incident on the scintillator 30, and the scintillation light generated on the scintillator 30 is detected by the photodetector 32 via the light guide 34, thereby outputting an electrical signal. In such a structure, the scintillator 30 that converts the electrons from the MCP 38 into light can be used. Figure 1 The scintillator 1A is shown.

[0074] The structure of the scintillator 1A according to the above-described embodiment will be further described together with its specific configuration example. For the formation of a ZnO film by MOCVD, for example, refer to Non-Patent Document 2 [Y. Hiragino et al., Physica Status Solidi C Vol. 11 No. 7-8 (2014) pp. 1369-1372].

[0075] In this configuration example, an a-plane sapphire substrate with a thickness of 500 μm is used as the support substrate 10, and a buffer layer 12 of a ZnO thin film without impurities is formed on the substrate 10 with a film thickness of 250 nm by MOCVD. In the formation of the ZnO film, diethyl zinc is used as a zinc (Zn) raw material, and tert-butyl alcohol is used as an oxygen (O) raw material. In addition, the growth temperature is 575° C. and the growth pressure is 1000 hPa.

[0076] Furthermore, the MOCD method is also used to form a light-emitting layer 14 composed of a ZnO single crystal thin film to which Ga is added on the ZnO buffer layer 12 described above. Here, triethylgallium is used as a gallium (Ga) raw material. In addition, a protective layer 16 composed of a SiO2 film with a film thickness of 10nm is formed by the EB evaporation method on the ZnO light-emitting layer 14 to which impurities are added. In addition, an Al metal layer 18 with a layer thickness of 50nm is formed on the SiO2 protective layer 16 by the vacuum evaporation method. In addition, the area of ​​the scintillator 1A can be arbitrarily set according to the purpose of the scintillator, but it is set to 10mm×10mm here.

[0077] Figure 8 : is a graph showing the wavelength dependence of the luminous intensity of the scintillator of the above-mentioned configuration example. Figure 8 For the curve, the horizontal axis represents the wavelength (nm) and the vertical axis represents the luminous intensity (counts) of the scintillation light. Here, the thickness of the light-emitting layer 14 is 1.2 μm and the electron concentration is 6.7×10 19 cm -3 The luminescence spectrum of cathode luminescence (cathodoluminescence) under electron beam excitation (6 kV) under the condition of . From this luminescence spectrum, it can be understood that the luminescence on the ZnO luminescent layer 14 is only the band-end luminescence with a short fluorescence lifetime, and there is no defect luminescence with a long fluorescence lifetime, which shows good characteristics.

[0078] Fig. 9 Graph showing the electron concentration dependence of the luminous efficiency of the scintillator under electron beam excitation conditions. Fig. 9 For the curve, the horizontal axis represents the electron concentration (carrier concentration) (cm -3), the vertical axis represents the luminous efficiency (photon / electron).

[0079] As shown in the curve, it can be seen that the luminescence intensity increases with the increase of the electron concentration in the luminescent layer 14. However, if the electron concentration exceeds 10 20 cm -3 If the electron concentration in the light-emitting layer 14 is too high, the luminous efficiency will drop sharply. This is because the electron concentration in the light-emitting layer 14 is high, and the energy of carrier recombination is absorbed by nearby electrons due to the Auger effect. If this aspect is taken into consideration, the electron concentration in the light-emitting layer 14 is preferably 2×10 19 cm -3 Above 2×10 20 cm -3 The electron concentration is preferably set within the following range. 19 cm -3 Above 2×10 20 cm -3 the following.

[0080] In addition, the above phenomenon related to the luminescence intensity is not the effect of the concentration of the impurities added to ZnO, but the effect of the electron concentration obtained by the impurities. Therefore, the impurities added to ZnO are not limited to Ga (gallium), but can also be group III elements Al (aluminum), In indium, etc. that are good donor impurities for ZnO.

[0081] Fig.10 This is a graph showing the dependence of the luminous efficiency of the scintillator under electron beam excitation conditions on the electron acceleration voltage. Fig.10 In the graph, the horizontal axis represents the accelerating voltage (kV) of the electron beam, and the vertical axis represents the luminous efficiency (photon / electron). Fig.10 In the figure, curve G1 represents the luminous efficiency under the structural condition without ZnO buffer layer 12, curve G2 represents the luminous efficiency under the structural condition with ZnO buffer layer 12, and curve G3 represents the luminous efficiency under the structural condition with buffer layer 12 and further provided with SiO2 protective layer 16 with a thickness of 10 nm. In addition, curve G5 represents the luminous efficiency on a plastic scintillator as a comparative example.

[0082] As shown in the graph, it can be understood that in the scintillator 1A having the above structure, the luminous efficiency is improved by forming the ZnO luminescent layer 14 on the supporting substrate 10 via the buffer layer 12. In addition, by providing a protective layer 16 composed of a material having a larger band gap than ZnO on the opposite side of the supporting substrate 10 with respect to the luminescent layer 14 in addition to the buffer layer 12, the luminous efficiency is further significantly increased.

[0083] In addition, the energy shielding effect from the light emitting layer 14 to the outside by the SiO2 protective layer 16 becomes stronger as the layer thickness increases, but if the protective layer becomes larger than a certain degree, the effect will disappear. If this aspect is taken into consideration, the thickness of the protective layer 16 is preferably set within the range of 10 nm to 200 nm as described above. In addition, as for materials having a band gap larger than that of ZnO constituting the protective layer 16, Al2O3, MgO, CaF2, BeO, MgF2, LiF, etc. can be used in addition to SiO2 as described above.

[0084] The scintillator and electron detector involved in the present invention are not limited to the above-mentioned embodiments and configuration examples, and various modifications are possible. For example, the scintillator with the above-mentioned structure is not limited to the above-mentioned electron detector, and can also be applied to other radiation detection detectors.

[0085] The scintillator according to the above embodiment comprises: (1) a supporting substrate; and (2) a light emitting layer formed on the supporting substrate and having an electron concentration of 2×10 19 cm -3 Above 2×10 20 cm -3 The following forms are composed of ZnO to which impurities are added and which generates scintillation light in response to the incidence of radiation such as electrons; (3) a protective layer, which is formed on the light-emitting layer and is composed of a material having a band gap larger than that of ZnO; (4) a metal layer, which is formed on the protective layer; the supporting substrate is composed of a material that transmits the scintillation light generated on the light-emitting layer, and the metal layer is constructed in a form that acts as a reflection layer that reflects the scintillation light from the light-emitting layer.

[0086] The radiation to be detected by the above-mentioned scintillator includes particles such as electrons, protons, neutrons, α particles, and ions, as well as electromagnetic waves such as γ rays, X rays, and light.

[0087] In the scintillator of the above structure, the light-emitting layer preferably has a layer thickness of 0.5 μm or more and 3.0 μm or less. A scintillator provided with a ZnO light-emitting layer doped with impurities of such a layer thickness can be applied to the detection of electrons with energies of -5 keV to 20 keV, such as scanning electron microscopes and time-of-flight mass spectrometers. In addition, in the light-emitting layer, the impurities added to ZnO are preferably impurities containing at least one selected from Ga, Al and In, and the impurities added to ZnO are particularly preferably Ga.

[0088] In the scintillator having the above structure, a buffer layer composed of ZnO can be formed between the support substrate and the light-emitting layer. In this way, the light-emitting layer can be suitably formed by forming a ZnO light-emitting layer doped with impurities on the ZnO buffer layer.

[0089] The ZnO buffer layer and the light-emitting layer on the supporting substrate can be formed by MOCVD (Metal Organic Chemical Vapor Deposition) method. In addition, when the ZnO buffer layer is provided between the supporting substrate and the light-emitting layer, the buffer layer preferably has a layer thickness of 20 nm to 400 nm.

[0090] For the protective layer composed of a material having a band gap larger than that of ZnO, the material constituting the protective layer is preferably a material containing at least one selected from SiO2, Al2O3, MgO, CaF2, BeO, MgF2 and LiF, and the material constituting the protective layer is particularly preferably a chemically stable material, namely SiO2. In addition, the protective layer preferably has a layer thickness of not less than 10 nm and not more than 200 nm.

[0091] The supporting substrate made of a material that transmits scintillation light is preferably a sapphire substrate, a quartz substrate, or a glass substrate. In addition, the supporting substrate is particularly preferably an a-plane sapphire substrate.

[0092] Regarding the metal layer formed on the protective layer, the material constituting the metal layer is preferably Al. In addition, when the material of the metal layer is Al, it is preferred that the metal layer has a layer thickness of 10 nm or more and 50 nm or less.

[0093] The electron detector involved in the above embodiment is composed of a scintillator having the above structure that outputs scintillation light generated in the light-emitting layer in response to the incidence of electrons, and a photodetector that detects the scintillation light output from the scintillator. According to such an electron detector, electrons can be appropriately detected using a scintillator having high-speed response. In addition, in this case, the metal layer in the scintillator can also be made into a structure that functions as an accelerating electrode that accelerates the electrons incident on the scintillator.

[0094] Possibility of Industrial Application

[0095] The present invention can be utilized as a scintillator that can be suitably used for detecting radiation such as electrons, and an electron detector using the scintillator.

[0096] Explanation of symbols

[0097] 1A.Scintillator

[0098] 2A. Electronic detector

[0099] 10. Support substrate

[0100] 12. ZnO buffer layer

[0101] 14. ZnO light-emitting layer with impurities added

[0102] 16. Protective layer

[0103] 18.Metal layer

[0104] 20. Light detector

[0105] 22. Light guide

[0106] 30. Flasher

[0107] 32. Light detector

[0108] 34. Light guide

[0109] 36. Observe the object

[0110] 38.Microchannel plate

Claims

1. A method for forming a scintillator, characterized in that: include: Using a sapphire substrate as a supporting substrate; A buffer layer composed of ZnO without adding impurities is formed on the sapphire substrate by using MOCVD method; The buffer layer was formed by MOCVD with an electron concentration of 2×10 19 cm -3 Above 2×10 20 cm -3 The following forms a light-emitting layer composed of ZnO to which impurities are added and which generates scintillation light in response to incident radiation; and forming a protective layer composed of a material having a larger band gap than ZnO on the radiation incident side of the light emitting layer, The sapphire substrate is an a-plane sapphire substrate.

2. The method for forming a scintillator according to claim 1, wherein: In the light-emitting layer, the impurity added to ZnO is Ga.

3. The method for forming a scintillator according to claim 1, wherein: The protective layer is formed by using a vapor deposition method.

4. The method for forming a scintillator according to claim 2, wherein: The protective layer is formed by using a vapor deposition method.

5. The method for forming a scintillator according to any one of claims 1 to 4, wherein: A metal layer is further formed on the protective layer.

6. The method for forming a scintillator according to claim 5, wherein: The metal layer is formed by using an evaporation method.

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