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] This disclosure relates to a photodetector.

Background Art

[0002] Patent Document 1 describes an electron tube. This electron tube includes an input panel 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 panel, and a semiconductor element fixed to the vacuum side of the stem and having an electron incident portion for injecting electrons emitted from the photocathode. The semiconductor element is configured as a back-illuminated semiconductor element in which the front surface is positioned on the stem side, the back surface is positioned on the input panel side, and the electron incident portion is formed in a thin plate shape with respect to a peripheral portion disposed on the outer periphery of the electron incident portion.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Currently, in a photodetector such as the electron tube described in Patent Document 1, for example, for the purpose of detecting a plurality of wavelength components spectrally separated by a spectroscope, there is a requirement to configure an electron incident portion including a plurality of channels for the semiconductor element. On the other hand, since the trajectory of electrons from the photocathode toward the electron incident portion has a certain spread, a configuration for suppressing crosstalk between channels is required.

[0005] An object of this disclosure is to provide a photodetector capable of suppressing crosstalk between channels.

Means for Solving the Problems

[0006] The photodetector according to this disclosure is a photodetector that [1] "an incident plate 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 and for detecting the photoelectrons emitted from the photocathode, wherein the semiconductor element has a first portion having an electron incident surface which is the surface facing the photocathode and includes a plurality of channels arranged spaced apart from each other along a second direction intersecting the first direction, the incident plate is flat, and when the distance between the photocathode and the electron incident surface in the first direction is distance b, the spacing between the channels in the second direction is spacing Δch, and the voltage applied between the photocathode and the electron incident surface is voltage V, the photodetector satisfies the following equation (1)." Distance b [mm] / Spacing Δch [mm] < 14.4 × Voltage V [kV] + 60 …(1)

[0007] In this photodetector, the semiconductor elements for detecting photoelectrons emitted from the photocathode have a first portion having an electron incident surface containing multiple channels arranged spaced apart from each other. This photodetector satisfies equation (1) above, where distance b is the distance between the photocathode and the electron incident surface, spacing Δch is the spacing between channels in the channel arrangement direction (second direction), and voltage V is the voltage applied between the photocathode and the electron incident surface. As a result, crosstalk between channels is suppressed by appropriately setting the voltage V between the photocathode and the electron incident surface and the spacing Δch between channels according to the spread of electron trajectories corresponding to the distance b from the photocathode to the electron incident surface. In particular, since the incident plate of this photodetector is flat, it is easy to manufacture and easy to set the distance b between the photocathode and the electron incident surface to satisfy each equation.

[0008] In photodetectors such as the electron tube described in Patent Document 1, if a relatively thick portion (the surrounding portion) is formed around the electron incident portion in the semiconductor element, distortion may occur in the equipotential surface between the photocathode and the electron incident portion, extending from the electron incident portion to the surrounding portion. In that case, the electron collection efficiency of channels in the region where the equipotential surface is distorted (for example, channels near the surrounding portion) may decrease compared to the electron collection efficiency of channels in the region where the equipotential surface is not distorted (for example, channels other than those near the surrounding portion). Therefore, it is desirable to suppress the decrease in electron collection efficiency of channels located on the surrounding portion side, even when distortion of the equipotential surface occurs near the surrounding portion.

[0009] Therefore, the photodetector according to the present disclosure may be [2] "the photodetector according to [1] above, wherein the semiconductor element is provided on both ends of the electron incident surface in the second direction and has a second portion which is thicker than the first portion as it protrudes toward the photocathode side from the electron incident surface, and when the distance from the end of the electron incident surface on one side of 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 of the second direction to the starting end of the second portion is distance w, the photodetector according to [1] above satisfies the following formula (2) or formula (3)." 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 at least on both ends of the electron incident surface in the direction of channel arrangement, and has a second portion that is thicker than the first portion as it protrudes toward the photocathode side from 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 beginning of the second portion is distance w, this photodetector satisfies equation (2) or equation (3) above. 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 part, the decrease in electron collection efficiency in the outermost channel is suppressed.

[0011] The photodetector relating to this disclosure may also be [3] "a photodetector according to [1] or [2] above that satisfies formula (4) below." 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 relating to this disclosure may also be the photodetector described in [3] above, which satisfies formula (5) below. In this case, crosstalk between channels can be suppressed more reliably. Distance b [mm] / Spacing Δch [mm] < 12.4 × Voltage V [kV] + 51.5 … (5)

[0013] The photodetector relating to this disclosure may also be the photodetector described in [4] above, satisfying formula (6) below. In this case, crosstalk between channels can be suppressed even more reliably. Distance b [mm] / Spacing Δch [mm] < 12 × Voltage V [kV] + 50 ... (6)

[0014] The photodetector according to this disclosure may also be [6] "a photodetector according to any one of [1] to [5] above, comprising a side tube sealed at one end by the incident plate, 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 side." In this case, by setting the dimensions of each part of the side tube, incident plate, and base member, it is possible to achieve, 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 [1] to [6] above, provided with an insulating film having a thickness of 100 nm or less on at least the surface facing the photoelectric surface in the semiconductor element". In this case, at least the insulating film formed on the surface of the semiconductor element suppresses the return (ion feedback) of the gas that has been generated and ionized by the injection of photoelectrons into the semiconductor element to the photoelectric surface.

Advantages 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] It is a schematic cross-sectional view of the photodetector according to the present embodiment. [Figure 2] It is a top view showing a part of the photodetector shown in FIG. 1. [Figure 3] It is a partially enlarged view of the photodetector shown in FIG. 1. [Figure 4] It is a partially enlarged view of the semiconductor element shown in FIG. 2. [Figure 5] It is a graph showing the relationship between the voltage V and the distance b when the crosstalk between channels is 0% for each value of the channel interval Δch. [Figure 6] It is a graph showing the relationship between the voltage V and the distance b when the channel interval Δch is 50 μm for each value of the crosstalk. [Figure 7] It is a graph showing the relationship between the voltage V and the distance b when the channel interval Δch is 100 μm for each value of the crosstalk. [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] It is a graph showing the relationship between the distance e and the collection efficiency when the distance e is greater than the distance b for each value of the distance w.

Best Mode for Carrying Out the Invention

[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 may be denoted by the same reference numerals, and redundant descriptions may be omitted. In each figure, a Cartesian coordinate system may be shown that consists of an axis defining a first direction D1, an axis defining a second direction D2 that intersects the first direction D1, and an axis defining a third direction that intersects 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. In FIG. 1, the hatching is omitted. The photodetector 1 shown in FIGS. 1 and 2 is, for example, an HPD (Hybrid Photo Detector), and can be used, for example, in a fluorescence microscope, a flow cytometer, a time-resolved measurement device, etc.

[0020] The photodetector 1 includes an incident panel 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 incident panel 2 includes a front surface 2a and a back surface 2b on the opposite side of the front surface 2a. It is made of a light-transmissive material such as glass, for example, and transmits the light incident from the front surface 2a toward the back surface 2b. The incident panel 2 is formed, for example, in a circular flat plate shape (that is, a disk shape). That the incident panel 2 is in a flat plate shape means that, for example, with respect to the direction (first direction D1) from the front surface 2a to the back surface 2b of the incident panel 2, the thickness of a relatively thick portion is within the 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 incident panel 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 the incident light transmitted through the incident panel 2.

[0022] The side tube 3 is formed in a tubular shape (here, a circular tube) with both ends open, using an insulating material such as ceramic. One end of the side tube 3 is sealed by the incident plate 2. The stem 4 is formed in a plate shape (here, a disc shape) using 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. A metal member, which also serves as a connecting member, is interposed between one end of the side tube 3 and the incident plate 2, and between the other end of the side tube 3 and the stem 4. A voltage can be applied to both ends via this metal member, for example, such that the stem 4 side is at GND potential relative to the photocathode 2s (the photocathode 2s has 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 the surface facing the photocathode 2s, and is formed in the shape of a rectangular parallelepiped block that protrudes convexly from the stem 4 toward the photocathode 2s, for example, using an insulating material such as ceramic. Multiple pins 6 (for example, the same number as the channels ch described later) are provided through the base member 5 so that each can output an electrical signal detected by the semiconductor element 10 to the outside. For example, one end of the pin 6 reaches the surface of the base member 5 opposite to the stem 4 (top surface 5a), and the other end of the pin 6 protrudes from the surface of the base member 5 on the stem 4 side toward the outside of the side tube 3. The base member 5 may be formed integrally with the stem 4, and 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 positioned 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 such that the back surface 10r (i.e., the electron incident surface 11s described later) faces the photocathode 2s (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 photoelectrons incident from the photocathode 2s, causing multiplication by electron implantation and further multiplication by avalanche multiplication. The semiconductor element 10 may also be a PD (Photodiode), SiPM (Silicon photomultiplier), or SPAD (Single photon avalanche diode). In this embodiment, the semiconductor element 10 is a back-illuminated semiconductor element.

[0025] The semiconductor element 10 has a first part 11 and a second part 12. The first part 11 has an electron incident surface 11s which is the surface facing the photocathode 2s. The electron incident surface 11s includes a plurality of channels ch arranged spaced apart from each other along a second direction D2 which intersects a first direction D1. In other words, the electron incident surface 11s is the photoelectron detection surface of the semiconductor element 10 and includes a sensitive region which is the plurality of channels ch and a dead region which surrounds each individual channel ch. The dead region includes a partition between adjacent channels ch (a portion corresponding to the region indicated by the interval Δch described later) and a region provided between the outermost channel ch and the second part 12 described later (a region corresponding to the region indicated by the distance w described later). The semiconductor element 10 detects photoelectrons in each of the plurality of channels ch. The second part 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 so as to surround 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 of the electron incident surface 11s. A potential is applied between the photocathode 2s and the electron incident surface 11s such that photoelectrons emitted from the photocathode 2s move toward the electron incident surface 11s with a desired acceleration. In this embodiment, a voltage is applied so that the electron incident surface 11s side is at GND potential (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 pin 6. Preferably, the insulating film 7 is formed with a thickness of about 100 nm or less using a metal oxide (e.g., aluminum oxide), and in this embodiment, it is formed with a thickness of about 30 nm or less. As a result, the insulating film 7 does not affect the incidence of photoelectrons on the electron incident surface 11s or the electrical connection of the pin 6. The insulating film 7 can be formed, for example, by performing film deposition by ALD (Atomic Layer Deposition) on a unit consisting of the semiconductor element 10, the base member 5, the stem 4, and the pin 6.

[0027] Next, the relationships between the various parts of the photodetector 1 will be explained. Figure 3 is a magnified view of a part of the photodetector shown in Figure 1. Figure 4 is a magnified view of a part of the semiconductor element shown in Figure 2. Figure 4(a) is a magnified perspective view of region A1 in Figure 2, and Figure 4(b) is a schematic magnified cross-sectional view of region A2 in Figure 2. Figure 4(b) shows the equipotential surface Sv corresponding to the voltage applied between the photocathode 2s and the electron incident surface 11s.

[0028] As shown in Figures 3 and 4, in the following explanation, the distance between the photocathode 2s and the electron incident surface 11s in the first direction D1 is denoted as distance b, and the spacing between the channels ch in the second direction D2 is denoted as spacing Δch. Furthermore, the voltage applied between the photocathode 2s and the electron incident surface 11s is denoted as voltage V, the distance from the end of the electron incident surface 11s on one side of the second direction D2 (one end of the second direction D2) to the end of the second part 12 (one end of the second direction D2) is denoted as distance e, and the distance from the end of the outermost (farthest end) channel ch on one side of the second direction D2 (one end of the second direction D2) to the starting end of the second part 12 (the end of the portion of the first part 11 located on one side of the second direction D2 on the electron incident surface 11s side) is denoted as distance w.

[0029] Distance w is the distance from the end of the outermost channel ch (one end in the second direction D2) to the rising portion of the second part 12. Distance e may be the distance to the end of a component (e.g., wiring) that is at the same potential (or approximately the same potential) as the electron incident surface 11s, if such a component is provided further outside the end of the second part 12. Furthermore, distances e and w may be set similarly for the other side of the second direction D2, and may also be set similarly for the third direction D3 if the channels ch are arranged along the third direction D3. Channel ch is an electron collection unit, which is a semiconductor region inside the semiconductor element 10, and the interval Δch is the interval between these electron collection units. If a guard ring, which is another semiconductor region, is formed at the edge of the electron collection unit, the interval Δch may be the distance between 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 and suppressing a decrease in the electron collection efficiency of the outermost channel.

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

[0032] As shown in Figure 5, when suppressing crosstalk between channels ch to 0%, a certain relationship was found between voltage V and distance b for each interval Δch. Furthermore, as shown in Figures 6 and 7, the relationship between voltage V and distance b shown in Figure 5 shows a similar trend even when the allowable crosstalk is set to values ​​from 0% to 20%. Therefore, in photodetector 1, when suppressing crosstalk to about 20%, the following equation (1) is satisfied. In other words, in photodetector 1, by satisfying the following equation (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, Figure 8 is a graph showing the relationship between distance b, normalized by distance e, and the collection efficiency of the outermost channel for each distance e. As shown in Figure 8, even when the conditions for collection efficiency are most stringent at distance e = 1 [mm], it was confirmed that a collection efficiency of 80% or more can be obtained in the range of distance b from approximately 1 [mm] to 4 [mm]. Therefore, in photodetector 1, when the collection efficiency of electrons in the outermost channel ch is to be 80% or more, and distance e is smaller than distance b, the following equation (2) is satisfied. In other words, in photodetector 1, by satisfying the following equation (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, Figure 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. Figure 9 illustrates the cases for distances W = 0 [mm], 0.2 [mm], 0.4 [mm], 0.5 [mm], 0.6 [mm], 0.8 [mm], and 1 [mm]. As shown in Figure 9, in the photodetector 1, when distance e is greater than distance b, a collection efficiency of 95% or more is obtained for each distance e when distance w is 0.2 [mm] or greater. Therefore, in the photodetector 1, the decrease in electron collection efficiency is suppressed by satisfying the following equation (3). Distance b[mm] < distance e[mm], and distance w[mm] > 0.2[mm]...(3)

[0035] Furthermore, equation (1) above is required to suppress crosstalk between channels to about 20%. Therefore, in order to further suppress crosstalk between channels in the photodetector 1, equations (4) to (6) below can be satisfied. In the photodetector 1, by satisfying equation (4) below, crosstalk can be suppressed to about 10%, by satisfying equation (5) below, crosstalk can be suppressed to about 3%, and by satisfying equation (6) below, 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] For example, distance b can be 0 to 20 mm. Preferably, distance b is 0.5 mm to 10 mm, and more preferably 1 mm to 6 mm. For example, voltage V can be 0.1 kV to 8 kV. Preferably, voltage V is 1 kV to 7 kV, and more preferably 2 kV to 6 kV. For example, spacing Δch can be 0.01 mm to 0.5 mm. Preferably, spacing Δch is 0.01 mm to 0.3 mm, and more preferably 0.03 mm to 0.2 mm.

[0037] The distance e can be, for example, 0.1 [mm] to 10 [mm]. It is preferable that the distance e be between 1 [mm] and 5 [mm], and more preferably between 1 [mm] and 3 [mm]. The distance w can be, for example, 0 [mm] to 10 [mm]. It is preferable that the distance w be between 0 [mm] and 1 [mm], and more preferably between 0 [mm] and 0.3 [mm]. The crosstalk can be around 20%, preferably around 10%, and more preferably around 3% or 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 part 11 having an electron incident surface 11s which includes a plurality of channels ch arranged spaced apart from each other. In the photodetector 1, the distance b between the photocathode 2s and the electron incident surface 11s, the spacing Δch between the channels ch in the channel arrangement direction (second direction), and the voltage V applied between the photocathode 2s and the electron incident surface 11s satisfy equation (1) above. As a result, crosstalk between channels ch is suppressed by appropriately setting the voltage V between the photocathode 2s and the electron incident surface 11s and the spacing Δch between the channels ch according to the spread of the electron trajectory corresponding to the distance b from the photocathode 2s to the electron incident surface 11s. In particular, in the photodetector 1, since the incident surface plate 2 is flat, it is easy to manufacture and easy to set the distance b between the photocathode 2s and the electron incident surface 11s to satisfy each equation. Furthermore, if the incident plate 2 is not flat, the distance b can be adjusted by, for example, making the photocathode 2s formation region protrude towards the semiconductor element 10 (for example, making only the photocathode 2s formation region convexly thicker). In that case, the incident plate 2 becomes thicker, increasing the likelihood of crosstalk within the incident plate 2. Therefore, it is preferable that the incident plate 2 is flat and has a thickness sufficient to maintain mechanical strength (for example, 1 mm or more).

[0039] Furthermore, in the photodetector 1, the semiconductor element 10 is provided at least on both ends of the electron incident surface 11s in the direction of channel ch arrangement, and has a second portion 12 that is thicker than the first portion 11 by protruding toward the photocathode 2s side from the electron incident surface 11s. 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 beginning of the second portion 12 satisfy equation (2) or equation (3) above. 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 electron collection efficiency in the outermost channel ch is suppressed. As described above, the photodetector 1 can suppress crosstalk between channels ch and the decrease in electron collection efficiency.

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

[0041] Furthermore, the photodetector 1 comprises a side tube 3 sealed at one end by an incident plate 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 mounted on the base member 5 such that the electron incident surface 11s faces the photocathode 2s. Therefore, by setting the dimensions of each part of the side tube 3, incident plate 2, and base member 5, it is possible to achieve, for example, a distance b that satisfies the above formula.

[0042] Furthermore, the photodetector 1 is provided on at least the surface of the semiconductor element 10 facing the photocathode 2s and includes an insulating film 7 having a thickness of 100 nm or less. Therefore, the insulating film 7 formed at least on the surface of the semiconductor element 10 suppresses the return of ionized gas generated when photoelectrons are injected into the semiconductor element 10 back to the photocathode 2s (ion feedback).

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

[0044] For example, the photodetector 1 does not need to have an insulating film 7. Also, if we focus solely on suppressing crosstalk between channels, the photodetector 1 does not need to satisfy equations (2) and (3) above. In this case, the semiconductor element 10 does not need to have the second part 12. In other words, in this embodiment, the semiconductor element 10 is a back-illuminated semiconductor element, but a front-illuminated semiconductor element may also be used.

[0045] Furthermore, in this embodiment, the photocathode 2s is exemplified as including a photoelectric conversion layer made of a thin film of a compound semiconductor, but the photocathode 2s may also include a photoelectric conversion layer containing an alkali metal. Also, in this embodiment, the base member 5 is exemplified as being formed in the shape of a rectangular parallelepiped block that protrudes convexly from the stem 4 toward the photocathode 2s, made of an insulating material such as ceramic, but the base member 5 may also be a plate-shaped member made of an insulating material such as ceramic. In this case, a fixing part for fixing the base member 5 in a desired position may be provided on the stem 4. [Explanation of Symbols]

[0046] 1...Photodetector, 2...Induction plate, 3...Side tube, 4...Stem, 5...Base member, 7...Insulating film, 10...Semiconductor element, 11...First part, 11s...Electron incidence surface, 12...Second part, b,e,w...Distance, ch...Channel, V...Voltage.

Claims

1. An incident surface plate having a photocathode formed on it that emits photoelectrons in response to incident light, A semiconductor element is arranged to face the photocathode along a first direction and to detect the photoelectrons emitted from the photocathode, Equipped with, The semiconductor element has a first portion having an electron incident surface which is a surface facing the photocathode and includes a plurality of channels arranged spaced apart from each other along a second direction intersecting the first direction, The incident plate is flat, When the distance between the photocathode and the electron incident surface in the first direction is distance b, the spacing between the channels in the second direction is spacing Δch, and the voltage applied between the photocathode and the electron incident surface is voltage V, then the following equation (1) is satisfied, Distance b [mm] / Spacing Δch [mm] < 14.4 × Voltage V [kV] + 60 ... (1) The distance b is between 0.5 mm and 20 mm. Multiple channels are facing one of the photocathodes, Photodetector.

2. The following equation (4) is satisfied: Distance b [mm] / Spacing Δch [mm] < 13.2 × Voltage V [kV] + 55 (4) The photodetector according to claim 1.

3. The following equation (5) is satisfied: Distance b [mm] / Spacing Δch [mm] < 12.4 × Voltage V [kV] + 51.5 ... (5) The photodetector according to claim 2.

4. The following equation (6) is satisfied: Distance b [mm] / Spacing Δch [mm] < 12 × Voltage V [kV] + 50 ... (6) The photodetector according to claim 3.

5. The aforementioned semiconductor device performs electron multiplication. The photodetector according to claim 1.

6. The aforementioned semiconductor element is a back-illuminated type. The photodetector according to claim 1.

7. The semiconductor device is one of the following: an avalanche diode, a photodiode, a SiPM, or a SPAD. The photodetector according to claim 1.

8. The distance b is between 0.5 mm and 10 mm. The photodetector according to claim 1.

9. The distance b is between 1 mm and 6 mm. The photodetector according to claim 8.

10. The voltage V is between 0.1 [kV] and 8 [kV]. The photodetector according to claim 1.

11. The aforementioned voltage is between 1 kV and 7 kV. The photodetector according to claim 10.

12. The aforementioned voltage is between 2 kV and 6 kV. The photodetector according to claim 11.

13. The aforementioned interval Δch is 0.01 [mm] to 0.5 [mm]. The photodetector according to claim 1.

14. The aforementioned interval Δch is 0.01 [mm] to 0.3 [mm]. The photodetector according to claim 13.

15. The aforementioned interval Δch is 0.03 [mm] to 0.2 [mm]. The photodetector according to claim 14.

16. The semiconductor element includes a front surface and a back surface, One of the aforementioned front surface and the aforementioned back surface faces the photocathode, The surface facing the photocathode has the electron incident surface which includes a plurality of channels, The photodetector according to claim 1.

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