Photodetector

Abstract

Provided is a photodetector that can protect a semiconductor photodetector element from reflected electrons generated inside a vacuum housing. 【Solution means】The photodetector 1 includes a vacuum housing 2 having a window portion 12, a photoelectric surface (first photoelectric conversion layer) 3 that emits electrons E in response to the incidence of light L1, and a phosphor layer (second photoelectric conversion layer) 4 that generates light L2 in response to the incidence of electrons E emitted from the photoelectric surface 3. A semiconductor photodetector element 5 is disposed on the opposite side of the photoelectric surface 3 with the phosphor layer 4 interposed therebetween, and detects the light L2 generated in the phosphor layer 4. The semiconductor photodetector element 5 is disposed at a distance from the phosphor layer 4.

Description

Technical Field

[0001] The present disclosure relates to a photodetector.

Background Art

[0002] In high-energy physics experiments such as cosmic ray detection experiments and accelerator experiments, photodetectors capable of detecting single photons are used. As a conventional photodetector, there is a so-called hybrid photodetector (HPD) in which a photocathode and a semiconductor element such as an avalanche photodiode are arranged inside a vacuum housing. In a hybrid photodetector, electrons emitted from the photocathode are directly detected by the semiconductor element, but the gain required for detecting single photons is high, and therefore it is necessary to drive the semiconductor element at a high voltage.

[0003] In order to drive the semiconductor photodetection element at a lower voltage, a photodetector that once converts electrons emitted from the photocathode into light and detects the converted light with the semiconductor photodetection element has been studied. As such a photodetector, for example, the pixel sensor described in Patent Document 1 can be mentioned. In this conventional photodetector, a photocathode and a semiconductor photodetection element provided with a phosphor layer on the surface are arranged inside a vacuum housing.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a photodetector such as the above-described Patent Document 1, some of the electrons emitted from the photocathode can be reflected inside the vacuum housing and become reflected electrons. An electric field is formed inside the vacuum housing such that the electrons emitted from the photocathode are focused on the phosphor layer. For this reason, it is conceivable that the reflected electrons that deviate from the trajectory toward the phosphor layer travel again toward the phosphor layer. When the reflected electrons deviate from the phosphor layer and collide with the semiconductor photodetection element and the surrounding wiring portions, etc., there is a risk that the semiconductor photodetection element will be damaged.

[0006] The present disclosure has been made to solve the above problems, and an object thereof is to provide a photodetector that can protect a semiconductor photodetection element from reflected electrons generated inside a vacuum housing.

Means for Solving the Problems

[0007] The gist of the present disclosure is as follows.

[0008] [1] A vacuum housing having a window portion for incident light to be detected, a first photoelectric conversion layer disposed inside the vacuum housing and emitting electrons in response to the incidence of the light, and disposed inside the vacuum housing, A second photoelectric conversion layer that generates light in response to the incidence of the electrons emitted from the first photoelectric conversion layer, and is disposed on the opposite side of the first photoelectric conversion layer with the second photoelectric conversion layer interposed therebetween inside the vacuum housing, A semiconductor photodetection element that detects light generated by the second photoelectric conversion layer, wherein the semiconductor photodetection element is disposed at a distance from the second photoelectric conversion layer.

[0009] In this photodetector, the semiconductor photodetection element is disposed at a distance from the second photoelectric conversion layer. As a result, when some of the electrons emitted from the first photoelectric conversion layer are reflected inside the vacuum housing and become reflected electrons, even if the reflected electrons that deviate from the trajectory toward the second photoelectric conversion layer travel again toward the phosphor layer due to the electric field inside the vacuum housing, the possibility of the reflected electrons colliding with the semiconductor photodetection element can be reduced. Therefore, in this photodetector, the semiconductor photodetection element can be protected from the reflected electrons generated inside the vacuum housing.

[0010] [2] The photodetector according to [1], wherein an inner housing surrounding the semiconductor photodetector is disposed inside the vacuum housing. In this case, the inner housing can physically block the reflected electrons heading toward the semiconductor photodetector. Therefore, it is possible to more reliably prevent the reflected electrons from colliding with the semiconductor photodetector.

[0011] [3] The photodetector according to [2], wherein the inner housing defines the separation length of the semiconductor photodetector from the second photoelectric conversion layer. In this case, the separation length between the second photoelectric conversion layer and the semiconductor photodetector can be formed as designed. Therefore, it is possible to more reliably reduce the possibility of the reflected electrons colliding with the semiconductor photodetector.

[0012] [4] The photodetector according to [2] or [3], wherein the inner housing has a hole portion that communicates the inner space of the vacuum housing and the inner space of the inner housing. In this case, when evacuating the vacuum housing, the inner housing can be evacuated simultaneously through the hole portion. Thereby, deterioration of the first photoelectric conversion layer due to residual gas inside the vacuum housing and the inner housing can be suppressed.

[0013] [5] The photodetector according to [4], wherein the semiconductor photodetector is disposed at the bottom of the inner housing, and the hole portion is disposed around the semiconductor photodetector at the bottom. According to such a configuration, the hole portion of the inner housing and the semiconductor photodetector can be sufficiently close to each other. Therefore, even when the inner housing has a hole portion, it is possible to suppress the reflected electrons from passing through the hole portion and colliding with the semiconductor photodetector.

[0014] [6] A chip tube, which serves as an exhaust port of the vacuum housing and an inlet for an alkali used for alkalization of the first photoelectric conversion layer, is provided at the bottom of the vacuum housing. The chip tube is arranged at a position that does not overlap with the inner housing when viewed from the front of the window portion. The photodetector according to [4] or [5]. According to such a configuration, a sufficient space can be formed between the hole portion of the inner housing and the chip tube. Therefore, even when the inner housing has a hole portion, it is possible to suppress the alkali introduced from the chip tube from adhering to the semiconductor photodetection element through the hole portion. This contributes to the suppression of noise (such as dark current) caused by the adhesion of alkali to the semiconductor photodetection element.

[0015] [7] The inner housing is composed of a conductive material. The photodetector according to any one of [2] to [6]. In this case, the inside of the inner housing can be made into a non-electric field environment, and the formation of an electric field that directs reflected electrons toward the semiconductor photodetection element can be suppressed. Therefore, even if the reflected electrons travel inside the inner housing, the possibility of the reflected electrons colliding with the semiconductor photodetection element can be sufficiently reduced.

[0016] [8] In the second photoelectric conversion layer, a metal layer is arranged on the surface facing the first photoelectric conversion layer side. The photodetector according to any one of [2] to [7]. In this case, among the light generated in the second photoelectric conversion layer, the component traveling toward the first photoelectric conversion layer can be reflected by the metal layer and made to travel to the semiconductor photodetection element. Therefore, an improvement in the detected light amount at the semiconductor photodetection element can be achieved.

[0017] [9] The metal layer is electrically connected to the inner housing. The photodetector according to [8]. In this case, it becomes possible to supply power to the metal layer together with the inner housing. By supplying power to the metal layer, the metal layer can function as an electrode that forms an electric field for guiding the electrons emitted from the first photoelectric conversion layer to the second photoelectric conversion layer.

[0018]

[10] The area of the first photoelectric conversion layer is larger than the area of the second photoelectric conversion layer, and the area of the second photoelectric conversion layer is larger than the area of the semiconductor photodetector element. The photodetector according to any one of [1] to [9]. In this case, by reducing the area of the semiconductor photodetector element, the response characteristics of the semiconductor photodetector element can be improved. When reducing the area of the semiconductor photodetector element, it is necessary to sufficiently secure the area of the first photoelectric conversion layer in order to improve the light collection efficiency. However, by making the area of the second photoelectric conversion layer interposed between the first photoelectric conversion layer and the semiconductor photodetector element larger than the area of the semiconductor photodetector element, it becomes unnecessary to focus the electrons emitted from the first photoelectric conversion layer into a minute region. Since precise control of the electron orbits is not required, complication of the design of the photodetector can be avoided.

[0019]

[11] The vacuum housing is made of a conductive material, and a focusing electrode for focusing the electrons emitted from the first photoelectric conversion layer onto the second photoelectric conversion layer is disposed inside the vacuum housing. The focusing electrode has the same potential as the vacuum housing. The photodetector according to any one of [1] to

[10] . With such a configuration, the electrons emitted from the first photoelectric conversion layer can be efficiently guided toward the second photoelectric conversion layer.

[0020]

[12] A light guiding member for guiding the light generated in the second photoelectric conversion layer to the semiconductor photodetector element is disposed between the second photoelectric conversion layer and the semiconductor photodetector element. The photodetector according to any one of [1] to

[11] . In this case, the light generated in the second photoelectric conversion layer can be efficiently guided toward the semiconductor photodetector element. Further, even when ions are generated by the collision of the residual gas inside the vacuum housing and electrons, the ions passing through the second photoelectric conversion layer and heading toward the semiconductor photodetector element can be physically blocked by the light guiding member. Therefore, the semiconductor photodetector element can be protected from ion collisions.

Advantages of the Invention

[0021] According to the present disclosure, the semiconductor photodetector element can be protected from reflected electrons generated inside the vacuum housing.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0023] Hereinafter, with reference to the drawings, a preferred embodiment of a photodetector according to one aspect of the present disclosure will be described in detail.

[0024] FIG. 1 is a schematic cross-sectional view showing the configuration of a photodetector according to an embodiment of the present disclosure. The photodetector 1 shown in FIG. 1 is configured as a photodetector capable of detecting single photons in high-energy physics experiments such as cosmic ray detection experiments and accelerator experiments. As shown in FIG. 1, the photodetector 1 includes a vacuum housing 2. Inside the vacuum housing 2, a photocathode (first photoelectric conversion layer) 3, a phosphor layer (second photoelectric conversion layer) 4, a semiconductor photodetector element 5, an inner housing 6, a light guide member 7, and a focusing electrode 8 are arranged.

[0025] The vacuum housing 2 is composed of, for example, a side tube 11, a window portion 12, and a stem 13. The internal space S1 of the vacuum housing 2 is defined by the side tube 11, the window portion 12, and the stem 13 and is maintained in a vacuum state. The degree of vacuum in the internal space S1 is, for example, 10 -6 Pa to 10 -5 about Pa.

[0026] The side tube 11 is the part that forms the base of the vacuum housing 2. The side tube 11 has, for example, a cylindrical shape with both ends open in the axial direction. Examples of the constituent material of the side tube 11 include iron-nickel (FeNi) alloy, stainless steel (FeCrNi) alloy, kovar (FeCoNi) alloy, ceramic, glass, etc. The side tube 11 may be made of a conductive material. When the photodetector 1 is used in high-energy physics experiments and it is necessary to exclude the presence of radioactive isotopes, it is preferable to use an iron-nickel (FeNi) alloy that does not contain cobalt (Co). In this embodiment, the side tube 11 is made of an iron-nickel (FeNi) alloy which is a conductive material.

[0027] The window portion 12 is the part that allows the light L1 to be detected to enter the vacuum housing 2. The window portion 12 is provided in a disk shape so as to close one end of the side tube 11 in the axial direction. Examples of the constituent material of the window portion 12 include glass materials such as synthetic quartz. For the joining of the window portion 12 and the side tube 11, for example, an aluminum (Al) seal or a brazing material is used. When the constituent material of the window portion 12 is synthetic quartz, it is preferable to perform thermocompression bonding with an aluminum (Al) seal.

[0028] The stem 13 is the part that forms the bottom of the vacuum housing 2. The stem 13 is provided in a disk shape so as to close the other end of the side tube 11 in the axial direction. Examples of the constituent material of the stem 13 include kovar metal, etc. A plurality of stem pins 14 are inserted through the stem 13. The stem pins 14 include a power supply pin 14A for supplying power to the vacuum housing 2 (photoelectric surface 3), a power supply pin 14B for supplying power to the semiconductor photodetector element 5, an output pin 14C for taking out a signal from the semiconductor photodetector element 5, a ground pin 14D for setting the internal housing 6 described later to the ground potential, a power supply pin 14E for supplying power to the focusing electrode 8 described later, etc. These stem pins 14 and the stem 13 are electrically insulated by an insulating material 15 such as glass.

[0029] Further, a chip tube 16 is provided on the stem 13. The chip tube 16 is a part used as an exhaust port of the vacuum housing 2 and an inlet for an alkali used for alkalization of the photoelectric surface 3 in the manufacturing process of the photodetector 1. The chip tube 16 is arranged at a position closer to the side tube 11 outside the arrangement position of the stem pin 14. Thereby, the chip tube 16 is arranged at a position where it does not overlap with the inner housing 6 in a front view of the window portion 12. Note that when the size of the photodetector 1 is small, the arrangement of the chip tube 16 may be omitted.

[0030] The photoelectric surface 3 is a part that emits electrons E in response to the incidence of light L1. The photoelectric surface 3 is arranged inside the vacuum housing 2. In the present embodiment, the photoelectric surface 3 is provided in a circular shape on the inner surface of the window portion 12 (the surface facing the internal space S1). Further, the photoelectric surface 3 is a transmissive alkali photoelectric surface. Examples of the alkali used for the photoelectric surface 3 include potassium (K), cesium (Cs), sodium (Na), and the like.

[0031] The phosphor layer 4 is a part that generates light L2 in response to the incidence of electrons E emitted from the photoelectric surface 3. Examples of the material for forming the phosphor layer 4 include compound semiconductors such as GaN and ZnO. In the phosphor layer 4, a metal layer 18 is arranged on the surface facing the photoelectric surface 3. Examples of the constituent material of the metal layer 18 include aluminum (Al). The metal layer 18 has a function of reflecting a component of the light L2 generated in the phosphor layer 4 that travels toward the photoelectric surface 3 by the metal layer 18 and causing it to travel to the semiconductor photodetector element 5. Further, by supplying power to the metal layer 18, the metal layer 18 can also function as an electrode that forms an electric field for guiding the electrons E emitted from the photoelectric surface 3 to the phosphor layer 4.

[0032] The semiconductor light detection element 5 is a part that detects the light L2 generated in the phosphor layer 4. Examples of the semiconductor light detection element 5 include SiPM (Silicon Photomultiplier), APD (Avalanche Photodiode), PD (Photodiode), and the like. The semiconductor light detection element 5 outputs a signal corresponding to the amount of the detected light L2 to the outside of the photodetector 1 via the output pin 14C.

[0033] In the present embodiment, the area of the photocathode 3 is larger than the area of the phosphor layer 4, and the area of the phosphor layer 4 is larger than the area of the semiconductor light detection element 5. That is, when the area of the photocathode 3 is P1, the area of the phosphor layer 4 is P2, and the area of the semiconductor light detection element 5 is P3, the relationship of P1 > P2 > P3 is satisfied. By reducing the area P3 of the semiconductor light detection element 5, the response characteristics of the semiconductor light detection element 5 can be improved. When reducing the area P3 of the semiconductor light detection element 5, it is necessary to sufficiently secure the area P1 of the photocathode 3 in order to improve the collection efficiency of the light L1. However, by making the area P2 of the phosphor layer 4 intervening between the photocathode 3 and the semiconductor light detection element 5 larger than the area P3 of the semiconductor light detection element 5, it becomes unnecessary to focus the electrons E emitted from the photocathode 3 into a minute region. Since precise control of the electron orbits is not required, complication of the design of the photodetector 1 can be avoided.

[0034] The inner housing 6 is a housing provided so as to surround the semiconductor light detection element 5 inside the vacuum housing 2. The inner housing 6 is disposed closer to the stem 13 at the central portion in the axial direction of the side tube 11 in the inner space S1 of the vacuum housing 2. The inner space S2 of the inner housing 6 is separated from the inner space S1 of the vacuum housing 2 by the inner housing 6. The inner housing 6 is made of, for example, a conductive material. Examples of the conductive material include, for example, (FeNi) alloy similar to the side tube 11 of the vacuum housing 2. When the photodetector 1 is used in a high-energy physics experiment and it is necessary to eliminate the presence of radioactive isotopes, it is preferable to use an iron-nickel (FeNi) alloy that does not contain cobalt (Co).

[0035] The inner housing 6 is composed of, for example, side tubes 21, a window portion 22, and a bottom portion 23. The side tube 21 has a cylindrical shape with a diameter slightly larger than that of the semiconductor photodetector element 5, for example. The window portion 22 is provided at one end of the side tube 21 (the end facing the photoelectric surface 3). An inward cylindrical portion 24 protruding toward the inside of the side tube 21 is provided at the central portion of the window portion 22. The cylindrical portion 24 is formed such that its diameter gradually decreases toward the inside of the side tube 21, for example. Both one end (the end facing the photoelectric surface 3) and the other end (the end facing the semiconductor photodetector element 5) of the cylindrical portion 24 are open. The size of the opening on one end side of the cylindrical portion 24 is, for example, approximately the same as the size of the semiconductor photodetector element 5. When the cylindrical portion 24 is viewed from the photoelectric surface 3 side, the semiconductor photodetector element 5 can be seen through the cylindrical portion 24.

[0036] The phosphor layer 4 described above is joined to the outer surface of the window portion 22 of the inner housing 6 so as to close the opening at one end of the cylindrical portion 24. Further, the metal layer 18 provided on the phosphor layer 4 projects outward from the edge of the phosphor layer 4 and is joined to the window portion 22 of the inner housing 6. For example, a conductive adhesive can be used for the joining of the phosphor layer 4 and the window portion 22 and the joining of the metal layer 18 and the window portion 22. Therefore, the phosphor layer 4 and the inner housing 6 are electrically connected to each other, and the metal layer 18 and the inner housing 6 are electrically connected to each other.

[0037] The bottom portion 23 is provided in a disk shape so as to close the other end of the side tube 21 (the end facing the stem 13). The power supply pin 14B and the output pin 14C described above are inserted through the bottom portion 23. These stem pins 14 and the bottom portion 23 are electrically insulated by an insulating material 25 such as glass. Further, the ground pin 14D described above is electrically connected to the bottom portion 23. The semiconductor photodetector element 5 described above is disposed on the inner surface of the bottom portion 23 in a state of being axially spaced from the phosphor layer 4 and the side tube 11. The semiconductor photodetector element 5 is joined to the central portion of the inner surface of the bottom portion 23 so as to face the phosphor layer 4 through the cylindrical portion 24. The semiconductor photodetector element 5 is electrically connected to the power supply pin 14B and the output pin 14C inserted through the bottom portion 23.

[0038] The separation length T between the phosphor layer 4 and the semiconductor photodetector 5 is defined by the internal housing 6. In the example of FIG. 1, the separation length T is the distance between the surface of the phosphor layer 4 on the side of the semiconductor photodetector 5 and the surface of the semiconductor photodetector 5 on the side of the phosphor layer 4, and is mainly defined by adjusting the axial length of the side tube 11. For the bonding between the semiconductor photodetector 5 and the bottom 23, for example, an inorganic adhesive can be used. The adhesive may be either a conductive adhesive or a non-conductive adhesive. As an example of the adhesive, a nano metal paste such as a nano silver paste can be mentioned. By applying and baking the nano metal paste in the bonding region, the solvent volatilizes and the metal nanoparticles remain, and the metal nanoparticles aggregate and melt with each other, so that the materials to be bonded can be bonded together.

[0039] The internal housing 6 has a hole 26 that communicates the internal space S1 of the vacuum housing 2 and the internal space S2 of the internal housing 6. Due to the hole 26, the degree of vacuum in the internal space S2 of the internal housing 6 is approximately the same as the degree of vacuum in the internal space S1 of the vacuum housing 2. In the present embodiment, the hole 26 is arranged around the semiconductor photodetector 5 at the bottom 23. There is no particular limitation on the number of holes 26 arranged, but a plurality of holes 26 may be arranged around the semiconductor photodetector 5 with a predetermined phase angle. The position of the hole 26 is, for example, closer to the center than the insertion positions of the power supply pin 14B and the output pin 14C. As a result, the position of the hole 26 is closer to the semiconductor photodetector 5 than the insertion positions of the power supply pin 14B and the output pin 14C in a front view of the window portion 12.

[0040] The light guide member 7 is a part that guides the light L2 generated in the phosphor layer 4 to the semiconductor light detection element 5. The light guide member 7 is disposed between the phosphor layer 4 and the semiconductor light detection element 5. In the present embodiment, the light guide member 7 is disposed within the cylindrical portion 24 of the internal housing 6. Various configurations can be applied to the light guide member 7. The light guide member 7 may be constituted by, for example, synthetic quartz on which a light reflecting film such as an aluminum (Al) film is vapor-deposited on the surface, or may be constituted by a metal reflector formed on the inner wall surface of the cylindrical portion 24. When the light L2 from the phosphor layer 4 advances to the semiconductor light detection element 5 with a sufficient light quantity, the arrangement of the light guide member 7 may be omitted. In this case, the cylindrical portion 24 may be omitted, and a simple opening may be provided in the window portion 22.

[0041] The focusing electrode 8 is a part that forms an electric field for focusing the electrons E emitted from the photocathode 3 onto the phosphor layer 4. The focusing electrode 8 has, for example, a circular frame shape, and is disposed so as to surround the phosphor layer 4 at a position slightly closer to the photocathode 3 than the phosphor layer 4 of the window portion 12. The power supply pin 14E described above is electrically connected to the focusing electrode 8. Examples of the constituent material of the focusing electrode 8 include an iron-nickel (FeNi) alloy, a stainless steel (FeCrNi) alloy, and a kovar (FeCoNi) alloy. When the size of the photocathode 3 is not so much larger than the size of the phosphor layer 4, the arrangement of the focusing electrode 8 may be omitted. In this case, the power supply pin 14E can also be omitted accordingly.

[0042] When detecting the light L1 in the above-described photodetector 1, a negative high voltage (for example, about -3 kV) is applied to the vacuum housing 2 (photocathode 3) via the power supply pin 14A, and a drive voltage (for example, about several tens to several hundreds of kV) is applied to the semiconductor light detection element 5 via the power supply pin 14B. Further, a negative high voltage approximately equal to that of the vacuum housing 2 (photocathode 3) is applied to the focusing electrode 8 via the power supply pin 14E. The internal housing 6, the phosphor layer 4, and the metal layer 18 that are electrically connected to the ground pin 14D all have a ground potential.

[0043] When light L1 to be detected enters the window portion 12 of the photodetector 1 in this state, electrons E are emitted from the photocathode 3 in response to the incidence of the light L1. The electrons E emitted from the photocathode 3 are guided to the phosphor layer 4 by an electric field formed by the cooperation of the focusing electrode 8 and the metal layer 18. When the electrons E enter the phosphor layer 4, light L2 is generated in the phosphor layer 4 in response to the incidence of the electrons E. The light L2 generated in the phosphor layer 4 is guided by the light guiding member 7 and enters the semiconductor photodetector element 5. In the semiconductor photodetector element 5, a signal corresponding to the amount of the detected light L2 is generated. The signal is output to the outside of the photodetector 1 via the output pin 14C. Note that the polarity of the voltage applied to the photodetector 1 is not limited to this, and it is sufficient that the relationship holds in which the electrons E emitted from the photocathode 3 are directed toward the phosphor layer 4. For example, it is sufficient that the potential of the phosphor layer 4 is relatively positive with respect to the photocathode 3.

[0044] In the operation of the photodetector 1, a part of the electrons E emitted from the photocathode 3 may be reflected inside the vacuum housing 2 (for example, on the surface of the phosphor layer 4 or the like) to become reflected electrons Er. Inside the vacuum housing 2, an electric field is formed by the cooperation of the focusing electrode 8 and the metal layer 18 so that the electrons emitted from the photocathode 3 are focused on the phosphor layer. Therefore, it is conceivable that the reflected electrons Er that deviate from the trajectory toward the phosphor layer 4 travel again toward the phosphor layer 4. When the reflected electrons Er deviate from the phosphor layer 4 and collide with the semiconductor photodetector element 5 and the surrounding wiring portions or the like, there is a possibility that the semiconductor photodetector element 5 may be damaged.

[0045] On the other hand, in the photodetector 1, the semiconductor photodetector element 5 is disposed at a distance from the phosphor layer 4. Thereby, when a part of the electrons E emitted from the photocathode 3 are reflected inside the vacuum housing 2 to become reflected electrons Er, even if the reflected electrons Er that deviate from the trajectory toward the phosphor layer 4 travel again toward the phosphor layer 4 due to the electric field inside the vacuum housing 2, the possibility of the reflected electrons Er colliding with the semiconductor photodetector element 5 can be reduced. Therefore, in the photodetector 1, the semiconductor photodetector element 5 can be protected from the reflected electrons Er generated inside the vacuum housing 2.

[0046] In this embodiment, an inner housing 6 that surrounds the semiconductor photodetector 5 is disposed inside the vacuum housing 2. Thereby, the reflected electrons Er heading toward the semiconductor photodetector 5 can be physically blocked by the inner housing 6. Therefore, it is possible to more reliably prevent the reflected electrons Er from colliding with the semiconductor photodetector 5.

[0047] In this embodiment, the inner housing 6 defines the separation length T of the semiconductor photodetector 5 from the phosphor layer 4. According to such a configuration, the separation length between the phosphor layer 4 and the semiconductor photodetector 5 can be formed as designed. Therefore, the possibility of the reflected electrons Er colliding with the semiconductor photodetector 5 can be more reliably reduced.

[0048] In this embodiment, the inner housing 6 has a hole portion 26 that communicates the internal space S1 of the vacuum housing 2 and the internal space S2 of the inner housing 6. Thereby, evacuation of the inner housing 6 can be simultaneously performed through the hole portion 26 during evacuation of the vacuum housing 2. Thereby, deterioration of the photocathode 3 due to residual gas inside the vacuum housing 2 and the inner housing 6 can be suppressed.

[0049] In this embodiment, the semiconductor photodetector 5 is disposed at the bottom 23 of the inner housing 6, and the hole portion 26 is disposed around the semiconductor photodetector 5 at the bottom 23. According to such a configuration, the hole portion 26 of the inner housing 6 and the semiconductor photodetector 5 can be sufficiently close to each other. Therefore, even when the inner housing 6 has the hole portion 26, it is possible to suppress the reflected electrons Er from passing through the hole portion 26 and colliding with the semiconductor photodetector 5.

[0050] In this embodiment, a chip tube 16 serving as an exhaust port of the vacuum housing 2 and an inlet for an alkali used for alkalization of the photoelectric surface 3 is provided at the bottom 23 of the vacuum housing 2. And the chip tube 16 is arranged at a position where it does not overlap with the inner housing 6 in a front view of the window portion 12. According to such a configuration, a sufficient interval can be formed between the hole portion 26 of the inner housing 6 and the chip tube 16. Therefore, even when the inner housing 6 has the hole portion 26, it is possible to suppress the alkali introduced from the chip tube 16 from adhering to the semiconductor photodetector 5 through the hole portion 26. This contributes to suppressing noise (such as dark current) caused by the adhesion of the alkali to the semiconductor photodetector 5.

[0051] In this embodiment, the inner housing 6 is made of a conductive material. Thereby, the inside of the inner housing 6 can be made into a non-electric field environment, and the formation of an electric field that causes the reflected electron Er to face the semiconductor photodetector 5 can be suppressed. Therefore, even if the reflected electron Er travels inside the inner housing 6, the possibility of the reflected electron Er colliding with the semiconductor photodetector 5 can be sufficiently reduced.

[0052] In this embodiment, in the phosphor layer 4, a metal layer 18 is disposed on the surface facing the photoelectric surface 3 side. Thereby, among the light generated in the phosphor layer 4, the component directed toward the photoelectric surface 3 can be reflected by the metal layer 18 and made to travel to the semiconductor photodetector 5. Therefore, an improvement in the detected light amount at the semiconductor photodetector 5 can be achieved.

[0053] In this embodiment, the metal layer 18 is electrically connected to the inner housing 6. Thereby, it becomes possible to supply power to the metal layer 18 together with the inner housing 6. By supplying power to the metal layer 18, the metal layer 18 can function as an electrode that forms an electric field for guiding the electron E emitted from the photoelectric surface 3 to the phosphor layer 4.

[0054] In this embodiment, the area P1 of the photocathode 3 is larger than the area P2 of the phosphor layer 4, and the area P2 of the phosphor layer 4 is larger than the area P3 of the semiconductor photodetector 5. In this case, by reducing the area P3 of the semiconductor photodetector 5, the response characteristics of the semiconductor photodetector 5 can be improved. When reducing the area P3 of the semiconductor photodetector 5, it is necessary to ensure a sufficient area P1 of the photocathode 3 for improving the collection efficiency of the light L1. However, by making the area P2 of the phosphor layer 4 intervening between the photocathode 3 and the semiconductor photodetector 5 larger than the area P3 of the semiconductor photodetector 5, it becomes unnecessary to focus the electrons E emitted from the photocathode 3 into a minute region. Since precise control of the electron orbits is not required, the complication of the design of the photodetector 1 can be avoided.

[0055] In this embodiment, the vacuum housing 2 is made of a conductive material. Inside the vacuum housing 2, a focusing electrode 8 for focusing the electrons E emitted from the photocathode 3 onto the phosphor layer 4 is disposed, and the focusing electrode 8 has the same potential as the vacuum housing 2. With such a configuration, the electrons E emitted from the photocathode 3 can be efficiently guided toward the phosphor layer 4. Also, such a technical effect can be realized with a simple configuration. Note that the focusing electrode 8 and the vacuum housing 2 do not necessarily have the same potential, and different potentials may be applied to each other. In this case, more precise control of the electron orbits becomes possible.

[0056] In this embodiment, between the phosphor layer 4 and the semiconductor photodetector 5, a light guide member 7 for guiding the light L2 generated in the phosphor layer 4 to the semiconductor photodetector 5 is disposed. By using the light guide member 7, the light L2 generated in the phosphor layer 4 can be efficiently guided toward the semiconductor photodetector 5. Also, even when ions are generated due to the collision between the residual gas inside the vacuum housing 2 and the electrons E, the ions passing through the phosphor layer 4 and heading toward the semiconductor photodetector 5 can be physically blocked by the light guide member 7. Therefore, the semiconductor photodetector 5 can be protected from the collision of ions.

[0057] Ions generated by the collision of residual gas and electrons E can be a cause of defects in the photodetector 1. For example, when negatively charged ions (negative ions) are generated, it is conceivable that electrons E emitted from the photocathode 3 collide with the semiconductor photodetection element 5 in the same orbit as the orbit toward the phosphor layer 4. In this case, the phosphor layer 4 or the semiconductor photodetection element 5 may be damaged, and there is a risk that the characteristics will deteriorate. Even if it does not ionize, if water, hydrocarbons, etc. adhere to the semiconductor photodetection element 5 as residual gas, the characteristics may deteriorate. Therefore, by physically protecting the semiconductor photodetection element 5 with the light guide member 7, deterioration of the characteristics of the semiconductor photodetection element 5 can be suppressed.

[0058] Subsequently, embodiments of the present disclosure will be described.

[0059] FIGS. 2(a), 2(b), 3(a), and 3(b) are diagrams showing simulation results of electron orbits from the photocathode toward the phosphor layer. In FIGS. 2(a) and 2(b), in a photodetector having the same configuration as the above-described photodetector 1, when the diameter of the photocathode was 3 inches and the diameter of the phosphor layer was changed, the probability that electrons emitted from the photocathode entered the phosphor layer was calculated. Here, the voltage applied to the photocathode and the focusing electrode was set to -2 kV, and the phosphor layer was set to the ground potential. As a result, when the diameter of the phosphor layer was 6 mm, the incidence probability of electrons on the phosphor layer was less than 75%, but when the diameter of the phosphor layer was 8 mm or more, the incidence probability of electrons on the phosphor layer exceeded 90% in all cases. In FIGS. 3(a) and 3(b), the voltage applied to the photocathode and the focusing electrode was set to -3 kV, and other conditions were the same as those in FIGS. 2(a) and 2(b). As a result, when the diameter of the phosphor layer was 6 mm, the incidence probability of electrons on the phosphor layer was less than 75%, but when the diameter of the phosphor layer was 8 mm or more, the incidence probability of electrons on the phosphor layer exceeded 90% in all cases.

[0060] From these results, it can be seen that when electrons emitted from the photocathode are once converted into light by the phosphor layer, electrons can be incident on the phosphor layer with high efficiency at an applied voltage of about -2 kV to -3 kV. When electrons are directly focused on the fine regions of the semiconductor photodetector element, the gain required to detect a single electron is about 1×10 5 and a voltage of about 10 kV is also required to be applied to the semiconductor detector element. However, in the configuration in which the phosphor layer is interposed between the photocathode and the semiconductor photodetector element as in the present disclosure, driving at a lower voltage becomes possible.

[0061] FIGS. 4(a) and 4(b) are diagrams showing the simulation results of the trajectories of the reflected electrons generated on the surface of the phosphor layer. In this simulation, the trajectories of the reflected electrons generated in the half portion of the phosphor layer (the right half portion in FIG. 4(a)) were calculated. Here, as the initial trajectories of the reflected electrons, as shown in FIG. 4(a), those traveling perpendicularly from the surface of the phosphor layer 4 (reflected electron A), those traveling at an inclination of 30° from the direction perpendicular to the surface of the phosphor layer 4 (reflected electron B), and those traveling at an inclination of 60° from the direction perpendicular to the surface of the phosphor layer 4 (reflected electron C) were set.

[0062] As shown in FIG. 4(b), the reflected electron A traveled toward the vicinity of the center of the photocathode and then reversed toward the phosphor layer, resulting in a trajectory mainly toward the left half portion of the phosphor layer. The reflected electron B traveled toward the vicinity of the edge of the photocathode and then reversed toward the phosphor layer, resulting in a trajectory mainly toward the right half portion of the phosphor layer. Among the reflected electrons C, the electrons traveling at an inclination of 60° to the right from the direction perpendicular to the surface of the phosphor layer 4 drew a curve convex toward the photocathode and returned to the phosphor layer, resulting in a trajectory mainly toward the right half portion of the phosphor layer and the right side surface portion of the inner housing. Among the reflected electrons C, the electrons traveling at an inclination of 60° to the left from the direction perpendicular to the surface of the phosphor layer 4 mainly had a trajectory toward the left half portion and the back surface of the inner housing.

[0063] From these results, it was confirmed that by arranging the semiconductor photodetector away from the second photoelectric conversion layer, the possibility of reflected electrons colliding with the semiconductor photodetector can be reduced. Also, by arranging the internal housing surrounding the semiconductor photodetector inside the vacuum housing, it was confirmed that the reflected electrons heading towards the semiconductor photodetector can be physically blocked by the internal housing, and the semiconductor photodetector can be suitably protected.

Explanation of Reference Signs

[0064] 1... Photodetector, 2... Vacuum housing, 3... Photoelectric surface (first photoelectric conversion layer), 4... Phosphor layer (second photoelectric conversion layer), 5... Semiconductor photodetector, 6... Internal housing, 7... Light guide member, 8... Focusing electrode, 16... Chip tube, 18... Metal layer, 23... Bottom, 26... Hole, L1... Light to be detected, L2... Light generated in the phosphor layer, T... Separation length, S1... Internal space of the vacuum housing, S2... Internal space of the internal housing.

Claims

1. a vacuum housing having a window through which light to be detected enters; a first photoelectric conversion layer disposed inside the vacuum enclosure and emitting electrons in response to the incidence of the light; a second photoelectric conversion layer disposed inside the vacuum enclosure and configured to generate light in response to the electrons emitted from the first photoelectric conversion layer; a semiconductor light-detecting element disposed inside the vacuum enclosure on the opposite side of the first photoelectric conversion layer with the second photoelectric conversion layer interposed therebetween, the semiconductor light-detecting element detecting light generated in the second photoelectric conversion layer; The semiconductor photodetector element is disposed apart from the second photoelectric conversion layer.

2. 2. The photodetector according to claim 1, further comprising an inner housing disposed within said vacuum housing and surrounding said semiconductor photodetector element.

3. The photodetector of claim 2 , wherein the inner housing defines a distance of the semiconductor photodetector element from the second photoelectric conversion layer.

4. 3. The photodetector according to claim 2, wherein the internal housing has a hole that communicates the internal space of the vacuum housing with the internal space of the internal housing.

5. the semiconductor light detecting element is disposed on a bottom of the internal housing, 5. The photodetector according to claim 4, wherein said hole is disposed at said bottom around said semiconductor photodetector element.

6. a tip tube serving as an exhaust port of the vacuum housing and an inlet for an alkali used for alkalinizing the first photoelectric conversion layer is provided at a bottom of the vacuum housing; The photodetector according to claim 4 , wherein the tip tube is disposed at a position not overlapping with the inner housing when viewed from the front of the window portion.

7. The photodetector of claim 2 , wherein the inner housing is constructed from a conductive material.

8. The photodetector according to claim 2 , wherein a metal layer is disposed on a surface of the second photoelectric conversion layer facing the first photoelectric conversion layer.

9. The photodetector of claim 8 , wherein the metal layer is in electrical communication with the inner housing.

10. The area of ​​the first photoelectric conversion layer is larger than the area of ​​the second photoelectric conversion layer, 10. The photodetector according to claim 1, wherein an area of ​​the second photoelectric conversion layer is larger than an area of ​​the semiconductor photodetector element.

11. the vacuum housing is made of a conductive material, a focusing electrode that focuses the electrons emitted from the first photoelectric conversion layer onto the second photoelectric conversion layer is disposed inside the vacuum enclosure; 10. The photodetector according to claim 1, wherein the focusing electrode is at the same potential as the vacuum enclosure.

12. The photodetector according to any one of claims 1 to 9, wherein a light-guiding member is disposed between the second photoelectric conversion layer and the semiconductor photodetection element, the light-guiding member guiding the light generated in the second photoelectric conversion layer to the semiconductor photodetection element.

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