Photodetector

Abstract

To provide a photodetector capable of reducing the crosstalk between channels.SOLUTION: A photodetector 1 comprises: a tabular incident surface plate 2 on which a photoelectric surface 2s for emitting photoelectrons in accordance with incident light is formed; and a semiconductor element 10 for detecting the photoelectrons emitted from the photoelectric surface 2s, the semiconductor element being disposed to face the photoelectric surface 2s. The semiconductor element 10 has a first portion 11 having an electron incident surface 11s facing the photoelectric surface 2s, the electron incident surface including a plurality of channels ch that are arranged separated from each other. A distance b between the photoelectric surface 2s and the electron incident surface 11s, an interval Δch between the channels ch, and a voltage V applied between the photoelectric surface 2s and the electron incident surface 11s satisfy the formula (1): distance b [mm] / interval Δch [mm]<14.4×voltage V [kV]+60.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to photodetectors. [Background technology]

[0002] Patent Document 1 describes an electron tube. This electron tube includes an input faceplate provided on one side of the side tube and having a photocathode that emits electrons in response to incident light, a stem provided on the other side of the side tube and defining a vacuum region together with the input faceplate, and a semiconductor element fixed to the vacuum side of the stem and having an electron incidence portion that allows electrons emitted from the photocathode to be incident. The semiconductor element is configured as a back-illuminated semiconductor element with its front surface positioned on the stem side and its back surface positioned on the input faceplate side, and with the electron incidence portion formed in a thin plate shape relative to a peripheral portion disposed on the outer periphery of the electron incidence portion. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-040086 Summary of the Invention [Problem to be solved by the invention]

[0004] Currently, in photodetectors such as the electron tube described in Patent Document 1, there is a demand for configuring an electron entrance section including multiple channels in a semiconductor element in order to detect multiple wavelength components dispersed by a spectrometer, for example. However, since the trajectory of electrons traveling from the photocathode to the electron entrance section has a certain degree of spread, a configuration is required to suppress crosstalk between channels.

[0005] An object of the present disclosure is to provide a photodetector capable of suppressing crosstalk between channels. [Means for solving the problem]

[0006] The photodetector according to the present disclosure is [1] "a photodetector comprising: a faceplate having a photocathode formed thereon that emits photoelectrons in response to incident light; and a semiconductor element arranged to face the photocathode along a first direction for detecting the photoelectrons emitted from the photocathode, wherein the semiconductor element has a first portion having an electron incident surface that faces the photocathode and includes a plurality of channels arranged at a distance from each other along a second direction intersecting the first direction, the faceplate is flat, and satisfies the following formula (1): b is the distance between the photocathode and the electron incident surface in the first direction, Δch is the spacing between the channels in the second direction, and V is the voltage applied between the photocathode and the electron incident surface." Distance b [mm] / Spacing Δch [mm] < 14.4 × Voltage V [kV] + 60…(1)

[0007] In this photodetector, a semiconductor element for detecting photoelectrons emitted from the photocathode has a first portion having an electron incident surface including a plurality of channels arranged at a distance from each other. This photodetector satisfies the above formula (1) when the distance between the photocathode and the electron incident surface is the distance b, the interval between the channels in the channel arrangement direction (second direction) is the interval Δch, and the voltage applied between the photocathode and the electron incident surface is the voltage V. This allows the interval Δch between the channels to be appropriately set according to the voltage V between the photocathode and the electron incident surface and the spread of the electron trajectory according to the distance b from the photocathode to the electron incident surface, thereby suppressing crosstalk between the channels. In particular, in this photodetector, since the incident faceplate is flat, it is easy to manufacture and it is easy to set the distance b between the photocathode and the electron incident surface so as to satisfy each formula.

[0008] Here, in a photodetector such as the electron tube described in Patent Document 1, when a relatively thick portion (the above-mentioned peripheral portion) is formed around the electron incidence portion in the semiconductor element, there is a risk of distortion occurring in the equipotential surface between the photocathode and the electron incidence portion from the electron incidence portion to the peripheral portion. In this case, the electron collection efficiency of the channel in the region where the equipotential surface is distorted (e.g., the channel near the peripheral portion) may be lower than the electron collection efficiency of the channel in the region where the equipotential surface is not distorted (e.g., the channel other than the peripheral portion). Therefore, even if distortion of the equipotential surface occurs near the peripheral portion, it is desirable to suppress the decrease in the electron collection efficiency of the channel located on the peripheral portion side.

[0009] Therefore, the photodetector according to the present disclosure may be [2] "the photodetector described in [1] above, wherein the semiconductor element has a second portion provided on at least both ends of the electron incident surface in the second direction, and protruding toward the photocathode further than the electron incident surface to be thicker than the first portion, and wherein when the distance from the end of the electron incident surface on one side in the second direction to the end of the second portion is distance e, and the distance from the end of the outermost channel on one side in the second direction to the start of the second portion is distance w, the following formula (2) or the following formula (3) is satisfied." Distance b[mm] / 4<distance e[mm]<distance b[mm]…(2) Distance b [mm] < distance e [mm] and distance w [mm] > 0.2 [mm]…(3)

[0010] In this photodetector, the semiconductor elements are provided at least on both ends of the electron incident surface in the arrangement direction of the channels, and have a second portion formed to be thicker than the first portion by protruding further toward the photocathode than the electron incident surface. When the distance from the end of the electron incident surface to the end of the second portion is distance e and the distance from the end of the outermost channel to the start of the second portion is distance w, this photodetector satisfies the above formula (2) or (3). As a result, even if distortion occurs from the electron incident surface to the second portion with respect to the equipotential surface between the photocathode and the electron incident portion, a decrease in the electron collection efficiency in the outermost channel is suppressed.

[0011] The photodetector according to the present disclosure may be [3] "the photodetector according to the above [1] or [2], which satisfies the following formula (4)." In this case, crosstalk between channels can be reliably suppressed. Distance b [mm] / Spacing Δch [mm] < 13.2 × Voltage V [kV] + 55…(4)

[0012] The photodetector according to the present disclosure may be [4] "the photodetector according to the above [3], which satisfies the following formula (5)." In this case, crosstalk between channels can be more reliably suppressed. Distance b [mm] / Spacing Δch [mm] < 12.4 × Voltage V [kV] + 51.5 … (5)

[0013] The photodetector according to the present disclosure may be [5] "the photodetector according to the above [4], which satisfies the following formula (6)." In this case, crosstalk between channels can be more reliably suppressed. Distance b [mm] / Spacing Δch [mm] < 12 × Voltage V [kV] + 50…(6)

[0014] The photodetector according to the present disclosure may be [6] "the photodetector according to any one of the above [1] to [5], comprising a side tube one end of which is sealed by the faceplate, a stem sealing the other end of the side tube, and an insulating base member provided on the stem, wherein the semiconductor element is provided on the base member such that the electron incident surface faces the photocathode." In this case, by setting the dimensions of the side tube, the faceplate, and the base member, it is possible to realize, for example, a distance b that satisfies the above formula.

[0015] The photodetector according to the present disclosure may be [7] "the photodetector according to any one of the above [1] to [6], comprising an insulating film having a thickness of 100 nm or less, provided on at least a surface of the semiconductor element facing the photocathode." In this case, the insulating film formed on at least the surface of the semiconductor element prevents ionized gas generated by photoelectrons being bombarded into the semiconductor element from returning to the photocathode (ion feedback). Effect of the Invention

[0016] According to the present disclosure, it is possible to provide a photodetector capable of suppressing crosstalk between channels. [Brief description of the drawings]

[0017] [Figure 1] 1 is a schematic cross-sectional view of a photodetector according to an embodiment of the present invention. [Diagram 2] 2 is a top view showing a portion of the photodetector shown in FIG. 1. [Diagram 3] FIG. 2 is an enlarged view of a portion of the photodetector shown in FIG. [Figure 4] 3 is a partially enlarged view of the semiconductor element shown in FIG. 2. [Diagram 5] 13 is a graph showing the relationship between voltage V and distance b when crosstalk between channels is 0%, for each value of inter-channel spacing Δch. [Figure 6] 1 is a graph showing the relationship between voltage V and distance b for each crosstalk value when the channel spacing Δch is 50 μm. [Figure 7] 1 is a graph showing the relationship between voltage V and distance b for each crosstalk value when the channel spacing Δch is 100 μm. [Figure 8] FIG. 8 is a graph showing the relationship between the distance b normalized by the distance e and the collection efficiency of the outermost channel for each distance e. [Figure 9] 13 is a graph showing the relationship between distance e and collection efficiency for each value of distance w when distance e is greater than distance b. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, a photodetector according to an embodiment will be described with reference to the drawings. In the description of the drawings, the same or corresponding elements are given the same reference numerals, and duplicated descriptions may be omitted. In addition, each drawing may show an orthogonal coordinate system consisting of an axis defining a first direction D1, an axis defining a second direction D2 intersecting the first direction D1, and an axis defining a third direction intersecting the first direction D1 and the second direction D2.

[0019] Fig. 1 is a schematic cross-sectional view of a photodetector according to this embodiment. Fig. 2 is a top view showing a part of the photodetector shown in Fig. 1. Hatching is omitted in Fig. 1. The photodetector 1 shown in Figs. 1 and 2 is, for example, a HPD (hybrid photodetector), and can be used, for example, in a fluorescence microscope, a flow cytometer, a time-resolved measurement device, etc.

[0020] The photodetector 1 includes a faceplate 2, a photocathode 2s, a side tube 3, a stem 4, a base member 5, pins 6, an insulating film 7, and a semiconductor element 10. The faceplate 2 includes a front surface 2a and a back surface 2b opposite to the front surface 2a. The faceplate 2 is made of a light-transmitting material such as glass, and transmits light incident from the front surface 2a toward the back surface 2b. The faceplate 2 is formed, for example, in a circular flat plate shape (i.e., disk shape). The faceplate 2 being flat means that, for example, the thickness of a relatively thick portion of the faceplate 2 in the direction from the front surface 2a to the back surface 2b (first direction D1) is within a range of about 130% of the thickness of a relatively thin portion.

[0021] The photocathode 2s is provided on the back surface 2b of the faceplate 2. The photocathode 2s includes a photoelectric conversion layer made of a thin film of a compound semiconductor such as GaAs, and emits photoelectrons in response to incident light that has passed through the faceplate 2.

[0022] The side tube 3 is formed in a tubular shape (here, circular tube shape) with both ends open, for example, from an insulating material such as ceramic. One end of the side tube 3 is sealed by the faceplate 2. The stem 4 is formed in a plate shape (here, disk shape) from an insulating material such as ceramic, and seals the other end of the side tube 3. This allows a vacuum region to be formed inside the side tube 3. Between one end of the side tube 3 and the faceplate 2, and between the other end of the side tube 3 and the stem 4, metal members that also serve as connecting members made of, for example, Kovar, are interposed, and a voltage can be applied to both ends via the metal members, for example, so that the stem 4 side is at GND potential with respect to the photocathode 2s (so that the photocathode 2s is at a negative potential and the stem 4 side is at ground potential).

[0023] The base member 5 is provided on the stem 4 so as to be located inside the side tube 3. The base member 5 has a top surface 5a which is a surface facing the photocathode 2s, and is formed in a rectangular block shape protruding from the stem 4 toward the photocathode 2s in a convex manner by an insulating material such as ceramic. A plurality of pins 6 (for example, the same number as the channels ch described later) are provided penetrating the base member 5 so that each of them can output an electric signal detected by the semiconductor element 10 to the outside. For example, one end of the pin 6 reaches the surface (top surface 5a) of the base member 5 opposite the stem 4, and the other end of the pin 6 protrudes from the surface of the base member 5 on the stem 4 side to the outside of the side tube 3. The base member 5 may be formed integrally with the stem 4, and the pin 6 and the semiconductor element 10 may be electrically connected via another conductive member such as wiring.

[0024] The semiconductor element 10 is for detecting photoelectrons emitted from the photocathode 2s. The semiconductor element 10 is disposed on the top surface 5a of the base member 5 so as to face the photocathode 2s along the first direction D1. More specifically, the semiconductor element 10 includes a back surface 10r and a front surface 10s, and is provided on the top surface 5a of the base member 5 so that the back surface 10r (i.e., an electron incident surface 11s described later) faces the photocathode 2s (so that the front surface 10s faces the top surface 5a of the base member 5). The semiconductor element 10 is electrically connected to the pin 6 by bump connection, for example. The semiconductor element 10 is, for example, an AD (Avalanche diode). In this case, the semiconductor element 10 receives the photoelectrons from the photocathode 2s, and causes multiplication by electron bombardment and further multiplication by avalanche multiplication. The semiconductor element 10 may be a photodiode (PD), a silicon photomultiplier (SiPM), or a single photon avalanche diode (SPAD). In this embodiment, the semiconductor element 10 is a back-illuminated semiconductor element.

[0025] The semiconductor element 10 has a first portion 11 and a second portion 12. The first portion 11 has an electron incident surface 11s that faces the photocathode 2s. The electron incident surface 11s includes a plurality of channels ch that are arranged at a distance from each other along a second direction D2 that intersects with the first direction D1. In other words, the electron incident surface 11s is a photoelectron detection surface in the semiconductor element 10, and includes a sensitive region that is a plurality of channels ch and an insensitive region that surrounds each of the channels ch. The insensitive region includes a partition portion (a portion corresponding to a region indicated by a distance Δch described later) between adjacent channels ch and a region (a region corresponding to a region indicated by a distance w described later) between the outermost channel ch and the second portion 12 described later. The semiconductor element 10 detects photoelectrons in each of the plurality of channels ch. The second portion 12 is provided at least on both ends of the electron incident surface 11s in the second direction D2. In this embodiment, the second portion 12 is formed in a rectangular frame shape surrounding the electron incident surface 11s when viewed from the first direction D1. The second portion 12 is formed to be thicker than the first portion 11 by protruding toward the photocathode 2s side beyond the electron incident surface 11s. A potential is applied between the photocathode 2s and the electron incident surface 11s such that the photoelectrons emitted from the photocathode 2s move toward the electron incident surface 11s with a desired acceleration, and in this embodiment, a voltage is applied so that the electron incident surface 11s side is at GND potential (so that the photocathode 2s is at a negative potential and the electron incident surface 11s side is at ground potential).

[0026] The insulating film 7 is provided on at least the surface of the semiconductor element 10 facing the photocathode 2s. In this embodiment, the insulating film 7 is formed on the surfaces of the semiconductor element 10, the base member 5, the stem 4, and the pins 6. The insulating film 7 is preferably formed to a thickness of about 100 nm or less using a metal oxide (e.g., aluminum oxide), for example, and is formed to a thickness of about 30 nm or less in this embodiment. This prevents the insulating film 7 from affecting the incidence of photoelectrons on the electron incidence surface 11s and the electrical connection of the pins 6. The insulating film 7 can be formed, for example, by performing film formation by ALD (Atomic Layer Deposition) on a unit consisting of the semiconductor element 10, the base member 5, the stem 4, and the pins 6.

[0027] Next, the relationship between the various parts of the photodetector 1 will be described. Fig. 3 is a partially enlarged view of the photodetector shown in Fig. 1. Fig. 4 is a partially enlarged view of the semiconductor element shown in Fig. 2. Fig. 4(a) is an enlarged perspective view of region A1 in Fig. 2, and Fig. 4(b) is a schematic enlarged cross-sectional view of region A2 in Fig. 2. Fig. 4(b) shows an equipotential surface Sv according to the voltage applied between the photocathode 2s and the electron incident surface 11s.

[0028] 3 and 4, in the following description, the distance between the photocathode 2s and the electron incident surface 11s in the first direction D1 is defined as the distance b, and the interval between the channels ch in the second direction D2 is defined as the interval Δch. In addition, the voltage applied between the photocathode 2s and the electron incident surface 11s is defined as the voltage V, the distance from the end of the electron incident surface 11s on one side of the second direction D2 (the end on one side of the second direction D2) to the end of the second portion 12 (the end on one side of the second direction D2) is defined as the distance e, and the distance from the end of the outermost (endmost) channel ch on one side of the second direction D2 (the end on the electron incident surface 11s side of the portion of the first portion 11 located on one side of the second direction D2) to the start of the second portion 12 (the end on the electron incident surface 11s side of the portion of the first portion 11 located on one side of the second direction D2) is defined as the distance w.

[0029] The distance w is the distance from the end of the outermost channel ch (the end on one side in the second direction D2) to the rising portion of the second portion 12. When a member (e.g., wiring, etc.) having the same potential (or approximately the same potential) as the electron incident surface 11s is provided further outside than the end of the second portion 12, the distance e may be the distance to the end of the member. Furthermore, the distance e and the distance w may be set similarly on the other side of the second direction D2, and when the channels ch are arranged along the third direction D3, they may be set similarly in the third direction D3. The channel ch is an electron collector that is a semiconductor region inside the semiconductor element 10, and the interval Δch is the interval between the electron collectors. When a guard ring that is another semiconductor region is formed on the edge of the electron collector, the interval Δch may be the distance between the guard rings.

[0030] In the photodetector 1, the distance b, voltage V, distance e, and distance w set as described above satisfy a certain relationship from the viewpoint of suppressing crosstalk between channels ch and suppressing a decrease in the electron collection efficiency of the outermost channel ch.

[0031] Fig. 5 is a graph showing the relationship between voltage V and distance b for each value of channel spacing Δch when crosstalk between channels is 0%. Fig. 6 is a graph showing the relationship between voltage V and distance b for each value of crosstalk when the channel spacing Δch is 50 μm. Furthermore, Fig. 7 is a graph showing the relationship between voltage V and distance b for each value of crosstalk when the channel spacing Δch is 100 μm. Note that crosstalk between channels ch means that photoelectrons emitted from a region of photocathode 2s facing one channel ch in the first direction D1 are incident on another channel ch adjacent to the one channel ch.

[0032] As shown in FIG. 5, it was found that when crosstalk between channels ch is suppressed to 0%, there is a certain relationship between voltage V and distance b for each interval Δch. Furthermore, as shown in FIG. 6 and FIG. 7, the relationship between voltage V and distance b shown in FIG. 5 has a similar tendency even when the allowable crosstalk is set to each value of 0% to 20%. Therefore, in the photodetector 1, when crosstalk is suppressed to about 20%, the following formula (1) is satisfied. In other words, in the photodetector 1, by satisfying the following formula (1), crosstalk between channels ch can be suppressed to about 20%. Distance b [mm] / Spacing Δch [mm] < 14.4 × Voltage V [kV] + 60…(1)

[0033] On the other hand, Fig. 8 is a graph showing the relationship between the distance b normalized by the distance e and the collection efficiency of the outermost channel for each distance e. As shown in Fig. 8, even when the condition for collection efficiency is the strictest, that is, distance e = 1 [mm], it was confirmed that a collection efficiency of 80% or more can be obtained when distance b is in the range of about 1 [mm] to 4 [mm]. Therefore, in the photodetector 1, when the collection efficiency of electrons in the outermost channel ch is set to 80% or more and distance e is smaller than distance b, the following formula (2) is satisfied. In other words, in the photodetector 1, by satisfying the following formula (2), the collection efficiency of electrons in the outermost channel ch is ensured to be 80% or more. Distance b[mm] / 4<distance e[mm]<distance b[mm]…(2)

[0034] On the other hand, FIG. 9 is a graph showing the relationship between the distance e and the collection efficiency for each value of the distance w when the distance e is greater than the distance b. FIG. 9 illustrates the cases of distance W=0 [mm], 0.2 [mm], 0.4 [mm], 0.5 [mm], 0.6 [mm], 0.8 [mm], and 1 [mm]. As shown in FIG. 9, in the photodetector 1, when the distance e is greater than the distance b and the distance w is 0.2 [mm] or greater, a collection efficiency of 95% or greater is obtained for each distance e. Therefore, in the photodetector 1, by satisfying the following formula (3), a decrease in the electron collection efficiency is suppressed. Distance b [mm] < distance e [mm] and distance w [mm] > 0.2 [mm]…(3)

[0035] The above formula (1) is required to suppress the crosstalk between channels ch to about 20%. Therefore, in order to suppress the crosstalk between channels ch to a lower level, the photodetector 1 can satisfy the following formulas (4) to (6). In the photodetector 1, by satisfying the following formula (4), the crosstalk can be suppressed to about 10%, by satisfying the following formula (5), the crosstalk can be suppressed to about 3%, and by satisfying the following formula (6), the crosstalk can be suppressed to about 0%. Distance b [mm] / Spacing Δch [mm] < 13.2 × Voltage V [kV] + 55…(4) Distance b [mm] / Spacing Δch [mm] < 12.4 × Voltage V [kV] + 51.5 … (5) Distance b [mm] / Spacing Δch [mm] < 12 × Voltage V [kV] + 50…(6)

[0036] The distance b can be, for example, 0 [mm] to 20 [mm]. The distance b is preferably 0.5 [mm] to 10 [mm], and more preferably 1 [mm] to 6 [mm]. The voltage V can be, for example, 0.1 [kV] to 8 [kV]. The voltage V is preferably 1 [kV] to 7 [kV], and more preferably 2 [kV] to 6 [kV]. The interval Δch can be, for example, 0.01 [mm] to 0.5 [mm]. The interval Δch is preferably 0.01 [mm] to 0.3 [mm], and more preferably 0.03 [mm] to 0.2 [mm].

[0037] The distance e may be, for example, 0.1 mm to 10 mm. The distance e is preferably 1 mm to 5 mm, and more preferably 1 mm to 3 mm. The distance w may be, for example, 0 mm to 10 mm. The distance w is preferably 0 mm to 1 mm, and more preferably 0 mm to 0.3 mm. The crosstalk may be about 20%, preferably about 10%, and more preferably about 3% or about 0%.

[0038] As described above, in the photodetector 1 according to this embodiment, the semiconductor element 10 for detecting photoelectrons emitted from the photocathode 2s has a first portion 11 having an electron incident surface 11s including a plurality of channels ch arranged while being spaced apart from each other. In the photodetector 1, the distance b between the photocathode 2s and the electron incident surface 11s, the interval Δch between the channels ch in the arrangement direction (second direction) of the channels ch, and the voltage V applied between the photocathode 2s and the electron incident surface 11s satisfy the above formula (1). As a result, the interval Δch between the channels ch is appropriately set according to the voltage V between the photocathode 2s and the electron incident surface 11s and the spread of the electron trajectory according to the distance b from the photocathode 2s to the electron incident surface 11s, thereby suppressing crosstalk between the channels ch. In particular, in the photodetector 1, the incident faceplate 2 is flat, so that it is easy to manufacture and it is easy to set the distance b between the photocathode 2s and the electron incident surface 11s so as to satisfy each formula. Furthermore, when the faceplate 2 is not flat, it is possible to adjust the distance b by, for example, protruding the area where the photocathode 2s is formed toward the semiconductor element 10 (for example, making only the area where the photocathode 2s is formed thick in a convex shape). In that case, the thicker faceplate 2 increases the possibility that the incident light itself will crosstalk within the faceplate 2. For this reason, it is preferable that the faceplate 2 is flat and has a thickness that allows mechanical strength to be maintained (for example, 1 mm or more).

[0039] In addition, in the photodetector 1, the semiconductor element 10 is provided at least on both ends of the electron incident surface 11s in the arrangement direction of the channels ch, and has a second portion 12 formed thicker than the first portion 11 by protruding from the electron incident surface 11s toward the photocathode 2s. In the photodetector 1, the distance e from the end of the electron incident surface 11s to the end of the second portion 12 and the distance w from the end of the outermost channel ch to the start of the second portion 12 satisfy the above formula (2) or (3). As a result, even if distortion occurs from the electron incident surface 11s to the second portion 12 with respect to the equipotential surface Sv between the photocathode 2s and the electron incident surface 11s, the decrease in the electron collection efficiency in the outermost channel ch is suppressed. As described above, the photodetector 1 can suppress crosstalk between channels ch and a decrease in the electron collection efficiency.

[0040] Moreover, the photodetector 1 can satisfy the above formulas (4) to (6). In this case, crosstalk between channels can be reliably suppressed.

[0041] The photodetector 1 also includes a side tube 3 having one end sealed by a faceplate 2, a stem 4 sealing the other end of the side tube 3, and an insulating base member 5 provided on the stem 4. The semiconductor element 10 is provided on the base member 5 so that the electron incident surface 11s faces the photocathode 2s. For this reason, by setting the dimensions of the side tube 3, the faceplate 2, and the base member 5, it is possible to achieve, for example, a distance b that satisfies the above formula.

[0042] Furthermore, the photodetector 1 includes an insulating film 7 having a thickness of 100 nm or less, which is provided on at least the surface of the semiconductor element 10 facing the photocathode 2s. Therefore, the insulating film 7 formed on at least the surface of the semiconductor element 10 prevents ionized gas generated by photoelectrons being bombarded into the semiconductor element 10 from returning to the photocathode 2s (ion feedback).

[0043] The above embodiment describes one aspect of the photodetector according to the present invention. Therefore, the photodetector according to the present invention is not limited to the above embodiment and can be modified as desired.

[0044] For example, the photodetector 1 may not have the insulating film 7. Furthermore, when only focusing on suppressing crosstalk between channels ch, the photodetector 1 may not satisfy the above formulas (2) and (3). In this case, the semiconductor element 10 may not have the second portion 12. That is, although a back-illuminated semiconductor element is used as the semiconductor element 10 in this embodiment, a front-illuminated semiconductor element may also be used.

[0045] In this embodiment, the photocathode 2s includes a photoelectric conversion layer made of a thin film of a compound semiconductor, but the photocathode 2s may include a photoelectric conversion layer containing an alkali metal. In this embodiment, the base member 5 is formed in a rectangular parallelepiped block shape that protrudes from the stem 4 toward the photocathode 2s in a convex manner using an insulating material such as ceramic, but the base member 5 may be a plate-like member made of an insulating material such as ceramic. In this case, the stem 4 may be provided with a fixing portion for fixing the base member 5 at a desired position. [Explanation of symbols]

[0046] 1...photodetector, 2...incident plate, 3...side tube, 4...stem, 5...base member, 7...insulating film, 10...semiconductor element, 11...first part, 11s...electron incident surface, 12...second part, b,e,w...distance, ch...channel, V...voltage.

Claims

1. an incident face plate having a photocathode that emits photoelectrons in response to incident light; a semiconductor element disposed opposite the photocathode along a first direction, the semiconductor element detecting the photoelectrons emitted from the photocathode; Equipped with the semiconductor element has a first portion having an electron incidence surface facing the photocathode, the first portion including a plurality of channels arranged at a distance from one another along a second direction intersecting the first direction; The entrance plate is flat, When the distance between the photocathode and the electron incident surface in the first direction is a distance b, the interval between the channels in the second direction is a distance Δch, and the voltage applied between the photocathode and the electron incident surface is a voltage V, the following formula (1) is satisfied: Distance b [mm] / interval Δch [mm] < 14.4 × voltage V [kV] + 60 ... (1) Photodetector.

2. the semiconductor element has a second portion provided on at least both ends of the electron incident surface in the second direction, protruding further toward the photocathode than the electron incident surface and formed to be thicker than the first portion; When a distance from an end of the electron incident surface to an end of the second portion on one side in the second direction is a distance e, and a distance from an end of the outermost channel to a start of the second portion on one side in the second direction is a distance w, the following formula (2) or the following formula (3) is satisfied: Distance b [mm] / 4<distance e [mm]<distance b [mm]...(2) Distance b [mm] < distance e [mm], and distance w [mm] > 0.2 [mm]... (3) 2. The photodetector of claim 1.

3. Satisfying the following formula (4): Distance b [mm] / interval Δch [mm] < 13.2 × voltage V [kV] + 55 (4) 2. The photodetector of claim 1.

4. Satisfying the following formula (5): Distance b [mm] / interval Δch [mm] < 12.4 × voltage V [kV] + 51.5 ... (5) 4. The photodetector of claim 3.

5. Satisfying the following formula (6): Distance b [mm] / interval Δch [mm] < 12 × voltage V [kV] + 50 ... (6) 5. The photodetector of claim 4.

6. a side tube having one end sealed by the entrance faceplate; a stem that seals the other end of the side tube; an insulating base member provided on the stem; Equipped with the semiconductor element is provided on the base member such that the electron incident surface faces the photocathode.

2. The photodetector of claim 1.

7. an insulating film having a thickness of 100 nm or less, the insulating film being provided on at least a surface of the semiconductor element facing the photocathode; The photodetector according to any one of claims 1 to 6.

Images