Photodetector

Abstract

Provided is a photodetector comprising: an incident surface plate on which there is formed a photoelectric surface for emitting photoelectrons in accordance with incident light; and a semiconductor element for detecting the photoelectrons emitted from the photoelectric surface, the semiconductor element being disposed so as to face the photoelectric surface along a first direction. The semiconductor element has a first portion having an electron incident surface facing the photoelectric surface, the electron incident surface including a plurality of channels that are arranged separated from each other along a second direction intersecting the first direction. The incident surface plate is formed in a flat plate shape. The photodetector satisfies formula (1), where a distance b is the distance between the photoelectric surface and the electron incident surface in the first direction, an interval Δch is the interval between the channels in the second direction, and a voltage V is the voltage applied between the photoelectric surface and the electron incident surface.

Description

Photodetector

[0001] The present disclosure relates to photodetectors.

[0002] Patent Document 1 describes an electron tube. This electron tube includes an input faceplate provided on one side of a 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 incident 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 facing the stem and its back surface facing the input faceplate, and the electron incident portion being thin-plate shaped relative to a peripheral portion located around the electron incident portion.

[0003] Japanese Patent Application Publication No. 11-040086

[0004] Currently, in photodetectors such as the electron tube described in Patent Document 1, there is a demand for configuring an electron incident section including multiple channels in a semiconductor element in order to detect multiple wavelength components dispersed by a spectroscope, for example. However, because the trajectory of electrons traveling from the photocathode toward the electron incident 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.

[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 disposed opposite the photocathode along a first direction and configured to detect the photoelectrons emitted from the photocathode, the semiconductor element having a first portion having an electron incident surface facing the photocathode and including a plurality of channels arranged at a distance from one another along a second direction intersecting the first direction, the faceplate being flat, and satisfying the following formula (1): 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 one another. This photodetector satisfies the above formula (1) when the distance between the photocathode and the electron incident surface is distance b, the channel spacing in the channel arrangement direction (second direction) is distance Δch, and the voltage applied between the photocathode and the electron incident surface is voltage V. This suppresses crosstalk between channels by appropriately setting the inter-channel spacing Δch in accordance with the voltage V between the photocathode and the electron incident surface and the expansion of electron trajectories corresponding to the distance b from the photocathode to the electron incident surface. In particular, this photodetector has a flat faceplate, which makes it easy to manufacture and to set the distance b between the photocathode and the electron incident surface so as to satisfy the formulas.

[0008] In a photodetector such as the electron tube described in Patent Document 1, if a semiconductor element has a relatively thick portion (the peripheral portion) formed around the electron incident portion, distortion may occur in the equipotential surface between the photocathode and the electron incident portion from the electron incident portion to the peripheral portion. In this case, the electron collection efficiency of channels in the region where the equipotential surface is distorted (e.g., channels near the peripheral portion) may be lower than the electron collection efficiency of channels in the region where the equipotential surface is not distorted (e.g., channels other than those near 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 channels located on the peripheral portion side.

[0009] Therefore, the photodetector according to the present disclosure may be [2] "the photodetector according to the above [1], wherein the semiconductor element has a second portion provided on at least both ends of the electron incident surface in the second direction, and formed thicker than the first portion by protruding further than the electron incident surface toward the photocathode, and the following formula (2) or formula (3) is satisfied, where e is the distance from an end of the electron incident surface to an end of the second portion on one side in the second direction, and w is the distance from an end of the outermost channel on one side in the second direction to a start of the second portion." 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 element is provided on both ends of the electron incident surface in at least the channel arrangement direction, and has a second portion that protrudes further toward the photocathode than the electron incident surface and is thereby formed to be thicker than the first portion. When the distance from the end of the electron incident surface to the end of the second portion is defined as distance e and the distance from the end of the outermost channel to the start of the second portion is defined as distance w, this photodetector satisfies formula (2) or formula (3) above. This prevents a decrease in electron collection efficiency in the outermost channel 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.

[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 so that the electron incident surface faces the photocathode." In this case, by setting the dimensions of the side tube, faceplate, and base member, it is possible to achieve, for example, the 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], which includes 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).

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

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

[0018] A photodetector according to one embodiment will be described below with reference to the drawings. In the description of the drawings, identical or corresponding elements are denoted by the same reference numerals, and redundant description may be omitted. Each drawing may also show a Cartesian coordinate system including 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 the front surface 2a. It is made of a light-transmitting material such as glass, and transmits light incident on 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-like). The faceplate 2 being flat means, for example, that 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 approximately 130% of the thickness of a relatively thin portion.

[0021] The photocathode 2s is provided on the rear 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 made of an insulating material such as ceramic and has a tubular (circular) shape with both ends open. One end of the side tube 3 is sealed by the faceplate 2. The stem 4 is made of an insulating material such as ceramic and has a plate-like (disk-like) shape, and seals the other end of the side tube 3. This allows a vacuum region to be formed inside the side tube 3. Metal members, made of, for example, Kovar, which also serve as connecting members, are interposed 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. A voltage can be applied to both ends via these metal members, for example, so that the stem 4 side is at GND potential relative 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 positioned within the side tube 3. The base member 5 has a top surface 5a that faces the photocathode 2s and is formed in the shape of a rectangular parallelepiped block made of an insulating material such as ceramic, protruding convexly from the stem 4 toward the photocathode 2s. A plurality of pins 6 (e.g., the same number as the channels ch described below) penetrate the base member 5 so that each pin can output an electrical signal detected by the semiconductor element 10 to the outside. For example, one end of each pin 6 extends to the surface of the base member 5 opposite the stem 4 (top surface 5a), and the other end of each pin 6 protrudes from the surface of the base member 5 facing the stem 4 to the outside of the side tube 3. The base member 5 may be formed integrally with the stem 4, or the pins 6 and the semiconductor element 10 may be electrically connected via other conductive members 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 disposed on the top surface 5a of the base member 5 so that the back surface 10r (i.e., the electron incident surface 11s described below) 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 pins 6 by, for example, bump connection. The semiconductor element 10 is, for example, an avalanche diode (AD). In this case, the semiconductor element 10 receives photoelectrons from the photocathode 2s, causing 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 device 10 has a first portion 11 and a second portion 12. The first portion 11 has an electron incident surface 11s, which is a surface facing the photocathode 2s. The electron incident surface 11s includes multiple channels arranged at a distance from one another along a second direction D2 intersecting the first direction D1. In other words, the electron incident surface 11s is a photoelectron detection surface of the semiconductor device 10 and includes sensitive regions, which are multiple channels, and insensitive regions surrounding each channel. The insensitive regions include partitions between adjacent channels (corresponding to the regions indicated by the spacing Δch described below) and regions between the outermost channel and the second portion 12 described below (corresponding to the region indicated by the distance w described below). The semiconductor device 10 detects photoelectrons in each of the multiple channels. 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 protrudes further toward the photocathode 2s than the electron incident surface 11s, and is thereby thicker than the first portion 11. A potential is applied between the photocathode 2s and the electron incident surface 11s so that 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 can be formed, for example, from a metal oxide (e.g., aluminum oxide) to a thickness of approximately 100 nm or less, and in this embodiment, it is formed to a thickness of approximately 30 nm or less. This prevents the insulating film 7 from affecting the incidence of photoelectrons on the electron incident surface 11s or the electrical connection of the pins 6. The insulating film 7 can be formed, for example, by performing film formation by atomic layer deposition (ALD) 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) also shows an equipotential surface Sv corresponding 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 2 s and the electron incident surface 11 s in the first direction D1 is referred to as distance b, and the spacing between the channels ch in the second direction D2 is referred to as distance Δch. Furthermore, the voltage applied between the photocathode 2 s and the electron incident surface 11 s is referred to as voltage V, the distance from the end of the electron incident surface 11 s on one side in the second direction D2 (the end on one side in the second direction D2) to the end of the second portion 12 (the end on one side in the second direction D2) is referred to as distance e, and the distance from the end of the outermost (edgemost) channel ch on one side in the second direction D2 (the end on the electron incident surface 11 s side) to the start of the second portion 12 (the end of the first portion 11 located on one side in the second direction D2) is referred to as 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. Furthermore, if a member (e.g., wiring, etc.) having the same potential (or approximately the same potential) as the electron incident surface 11s is provided further outward than the end of the second portion 12, the distance e may be the distance to the end of that member. Furthermore, the distances e and w may be set similarly on the other side in the second direction D2, or may be set similarly in the third direction D3 when the channels ch are arranged along the third direction D3. Furthermore, the channel ch is an electron collector that is a semiconductor region inside the semiconductor element 10, and the spacing Δch is the spacing between the electron collectors. If guard rings that are separate semiconductor regions are formed around the edges of the electron collectors, the spacing 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 the 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 means that photoelectrons emitted from a region of photocathode 2s facing one channel in the first direction D1 are incident on another channel adjacent to the one channel.

[0032] As shown in FIG. 5, it was found that when suppressing crosstalk between channels ch to 0%, there is a certain relationship between voltage V and distance b for each spacing Δch. Furthermore, as shown in FIGS. 6 and 7, the relationship between voltage V and distance b shown in FIG. 5 tends to be similar even when the allowable crosstalk is set to values ​​from 0% to 20%. Therefore, in the photodetector 1, when suppressing crosstalk 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, when the distance e is 1 mm, it was confirmed that a collection efficiency of 80% or more can be obtained when the distance b is in the range of approximately 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 the distance e is smaller than the 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 distance e and collection efficiency for each value of distance w when distance e is greater than distance b. FIG. 9 illustrates the cases where 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 distance e is greater than distance b and distance w is 0.2 [mm] or greater, a collection efficiency of 95% or greater is achieved for each distance e. Therefore, in the photodetector 1, a decrease in electron collection efficiency is suppressed by satisfying the following formula (3): distance b [mm] < distance e [mm] and distance w [mm] > 0.2 [mm] (3)

[0035] Note that the above formula (1) is required to suppress crosstalk between channels to about 20%. Therefore, in order to further suppress crosstalk between channels in the photodetector 1, the following formulas (4) to (6) can be satisfied. In the photodetector 1, by satisfying the following formula (4), crosstalk can be suppressed to about 10%, by satisfying the following formula (5), crosstalk can be suppressed to about 3%, and by satisfying the following formula (6), 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 may be, for example, 0 mm to 20 mm. The distance b may be, for example, 0.5 mm to 10 mm, or may be, for example, 1 mm to 6 mm. The voltage V may be, for example, 0.1 kV to 8 kV. The voltage V may be, for example, 1 kV to 7 kV, or may be, for example, 2 kV to 6 kV. The gap Δch may be, for example, 0.01 mm to 0.5 mm. The gap Δch may be, for example, 0.01 mm to 0.3 mm, or may be, for example, 0.03 mm to 0.2 mm.

[0037] The distance e can be, for example, 0.1 mm to 10 mm. The distance e may be 1 mm to 5 mm, or may be 1 mm to 3 mm. The distance w can be, for example, 0 mm to 10 mm. The distance w may be 0 mm to 1 mm, or may be 0 mm to 0.3 mm. The crosstalk can be about 20%, about 10%, 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 includes a first portion 11 having an electron incident surface 11s including a plurality of channels arranged at a distance from one another. In the photodetector 1, the distance b between the photocathode 2s and the electron incident surface 11s, the spacing Δch between the channels in the arrangement direction of the channels (the second direction), and the voltage V applied between the photocathode 2s and the electron incident surface 11s satisfy the above-described formula (1). This suppresses crosstalk between the channels by appropriately setting the spacing Δch between the channels in accordance with the voltage V between the photocathode 2s and the electron incident surface 11s and the expansion of the electron trajectories corresponding to the distance b from the photocathode 2s to the electron incident surface 11s. In particular, the photodetector 1 has a flat faceplate 2, which facilitates fabrication and facilitates setting the distance b between the photocathode 2s and the electron incident surface 11s to satisfy the formulas. Furthermore, if 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, by making only the area where the photocathode 2s is formed thick and convex). In this case, the thickness of the faceplate 2 increases the possibility that the incident light itself will crosstalk within the faceplate 2. For this reason, the faceplate 2 can be flat and have a thickness that allows it to maintain mechanical strength (for example, 1 mm or more).

[0039] Furthermore, in the photodetector 1, the semiconductor element 10 is provided on both ends of the electron incident surface 11s in at least the arrangement direction of the channels ch, and has second portions 12 that protrude further toward the photocathode 2s than the electron incident surface 11s and are thicker than the first portions 11. In the photodetector 1, the distance e from the end of the electron incident surface 11s to the end of the second portions 12 and the distance w from the end of the outermost channel ch to the beginning of the second portion 12 satisfy the above formula (2) or (3). This prevents a decrease in electron collection efficiency in the outermost channel ch 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. As described above, the photodetector 1 can prevent crosstalk between channels ch and a decrease in electron collection efficiency.

[0040] Furthermore, the photodetector 1 can satisfy the above formulas (4) to (6), which makes it possible to reliably suppress crosstalk between channels.

[0041] The photodetector 1 also includes a side tube 3, one end of which is sealed by a faceplate 2, a stem 4 that seals the other end of the side tube 3, and an insulating base member 5 that is 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. Therefore, by setting the dimensions of the side tube 3, faceplate 2, and base member 5, it is possible to achieve a distance b that satisfies the above formula, for example.

[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 has described 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 does not need to have the insulating film 7. Furthermore, when focusing only on suppressing crosstalk between channels ch, the photodetector 1 does not need to satisfy the above formulas (2) and (3). In this case, the semiconductor element 10 does not need to 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] Furthermore, 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. Furthermore, in this embodiment, the base member 5 is formed into a rectangular parallelepiped block shape made of an insulating material such as ceramic and protruding convexly from the stem 4 toward the photocathode 2s, but the base member 5 may also 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.

[0046] 1...photodetector, 2...faceplate, 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. 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): distance b [mm] / spacing Δch [mm] < 14.4 × voltage V [kV] + 60... (1), where 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.

2. The photodetector according to claim 1, wherein the semiconductor element has a second portion that is provided on at least both ends of the electron incident surface in the second direction and protrudes further toward the photocathode than the electron incident surface to be thicker than the first portion, and wherein, 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 distance e, and a distance from an end of the outermost channel on one side in the second direction to a start of the second portion is distance w, the following formula (2) or (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).

3. The photodetector according to claim 1 or 2, wherein the following formula (4) is satisfied: distance b [mm] / spacing Δch [mm]<13.2×voltage V [kV]+55 (4).

4. The photodetector according to claim 3, which satisfies the following formula (5): distance b [mm] / spacing Δch [mm]<12.4×voltage V [kV]+51.5 (5).

5. The photodetector according to claim 4, which satisfies the following formula (6): distance b [mm] / spacing Δch [mm]<12×voltage V [kV]+50 (6).

6. The photodetector according to claim 1, comprising: a side tube having one end sealed by the incident 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 so that the electron incident surface faces the photocathode.

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

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