JPH10241555A - Transmission type photoelectric cathode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectric cathode with which the number of emitted electrons can be increased. SOLUTION: This transmission type photoelectric cathode 10 comprises a semiconductor substrate having a first and a second through holes 10b, 10c neighboring each other. The shortest distance DL between the inner faces of the first and the second through holes 10b, 10c is set so as to make electrons (e), which are generated in the semiconductor substrate 5 corresponding to the applied electromagnetic waves XR and proceeding in the direction to the first and the second through holes 10b, 10c, escape to either of the first and the second through holes 10b, 10c.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photocathode that generates and emits electrons in response to the incidence of electromagnetic waves such as X-rays and gamma rays.

[0002]

2. Description of the Related Art A conventional photocathode is disclosed in Japanese Patent Publication No. 5-0334.
No. 86 is described. This publication describes a reflective photocathode (photocathode) that emits electrons in response to incident light. Irregularities are formed on the surface of the photocathode, and by setting the width of the convex portion to approximately the electron diffusion length (1 μm), electrons generated in the convex portion can easily escape into the concave portion. I have.

[0003]

However, in a transmission type photocathode, even if such irregularities are formed on the surface of the photocathode, the generated electrons are not emitted to the surface opposite to the light incident surface. . The present invention has been made based on such a problem, and has as its object to provide a transmission-type photocathode capable of increasing the number of electrons emitted in response to an incident electromagnetic wave.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a transmission type photocathode according to the present invention is intended for a transmission type photocathode which emits electrons generated in response to an incident electromagnetic wave. A semiconductor member having first and second through-holes, wherein the shortest distance between the inner surfaces of the first and second through-holes is generated in the semiconductor member in response to an incident electromagnetic wave, and the direction of the first and second through-holes; It is set so that electrons that have progressed to can escape into at least one of the first and second through holes.

[0005] The shortest distance between the inner surfaces of the first and second through holes is:
The number of electrons emitted from the photocathode is increased because the electron traveling in the direction of the first and second through holes is set so as to escape into at least one of the first and second through holes. Can be done.

The semiconductor member is preferably formed by bundling a plurality of fibers made of a semiconductor material, and the first and second through holes are preferably defined by a gap between the fibers.
In this case, the first and second through holes can be easily formed by bundling the fibers.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A transmission type photocathode according to an embodiment will be described below. The same reference numerals are used for the same elements or elements having the same functions, and overlapping descriptions are omitted.

FIG. 1 shows an electron tube 10 such as an image intensifier (II tube) provided with the transmission type photocathode 10.
FIG. It should be noted that, in the figure, the description of the metal wiring and members supporting each element arranged in the II tube 100 is omitted. The II tube 100 includes a side tube 1 made of metal such as Kovar, and a glass face plate 2 that seals openings at both ends of the side tube 1 and a glass fiber 14 provided with a phosphor 3. 1 provides a vacuum environment (a reduced pressure environment of 10 ^-5 torr or less).
In the following description, the face plate 2 side is the upper side, and the glass fiber 14 side is the lower side.

A photocathode 10 is provided on the surface of the face plate 2 in the side tube 1.
Are fixed, and an electrode 13 is fixed on the surface of the phosphor 3 in the side tube 1. Between the photocathode 10 and the electrode 13, a grid electrode 11 for giving a potential for accelerating the electrons emitted from the photocathode 10 into a vacuum, and an MCP for multiplying and passing electrons passing through the grid electrode 11 An electron multiplier 12 such as a (micro channel plate) is arranged. Electrons reaching the electrode 13 constituting the anode are:
Since the light is converted into fluorescent light by the phosphor 3, the light image incident on the face plate 2 is output as a multiplied light image from the outer surface of the glass fiber 14.

FIG. 2 is a sectional view of the II-tube 100 shown in FIG.
It is A arrow sectional drawing. The photocathode 10 is formed with a plurality of through-holes including through-holes 10 a and 10 b whose cross section perpendicular to the longitudinal direction has a substantially circular shape, and the center of these through-holes is the face plate 2 of the photocathode 10. It is formed at a position that forms a vertex of a regular hexagon in the surface on the side. Also,
The shape of the outer periphery of the photocathode 10 is substantially circular, but may be rectangular.

FIG. 3 is a sectional view of the photocathode 10 shown in FIG.
It is arrow B sectional drawing. The photocathode 10 includes an upper electrode 4 and
A semiconductor substrate (semiconductor member) 5 having an upper electrode 4 formed on the upper surface thereof, and an insulating layer 6 formed on a lower surface of the semiconductor substrate 5
And a lower electrode 7 fixed to the lower surface of the semiconductor substrate 5 with an insulating layer 6 interposed therebetween. When the II tube 100 includes the grid electrode 11 shown in FIG. 1, the insulating layer 6 and the lower electrode 7 may be omitted. Note that Cs—O or the like may be deposited on the inner surface of the above-described through hole to lower the work function.

When an electromagnetic wave XR such as X-ray or γ-ray transmitted through the face plate 2 shown in FIG. 1 enters the semiconductor substrate 5 of the photocathode 10, electrons e are generated in the semiconductor substrate 5, and the generated electrons e Proceeds into the through holes 10a to 10d. Here, the semiconductor substrate 5 is formed between the adjacent first and second through holes 10.
b, 10c, and the first and second through holes 10b,
The shortest distance DL between the inner surfaces of 10c is the incident electromagnetic wave XR
The electrons e generated in the semiconductor substrate 5 according to the above and advanced in the directions of the first and second through holes 10b and 10c can escape into at least one of the first and second through holes 10b and 10c. Is set to This shortest distance DL
Is shorter than twice the diffusion length of the generated electrons. Here, the distance DL is 2 μm, and the diameter D ₁ of each of the through holes 10 a to 10 d is 1.4 μm. In this case, the semiconductor substrate 5
Through holes 10a-10 in a plane perpendicular to the thickness direction of
The ratio of the entire through hole including d is about 40%.
Note that the thickness of the semiconductor substrate 5 is 20 μm. The longitudinal direction of each of the through holes 10 a to 10 d intersects the thickness direction of the semiconductor substrate 5, and the electromagnetic wave XR perpendicularly incident on the surface of the semiconductor substrate 5 penetrates without passing through the semiconductor substrate 5. It is prevented from passing through the holes 10a to 10d.

As described above, according to the transmission type photocathode 10 according to the present embodiment, the thickness of the semiconductor substrate 5 is increased by providing the plurality of through holes 10a to 10d at intervals equal to or less than the shortest distance DL. be able to. That is, when incident light having a high transmittance and being hardly absorbed by a semiconductor substance such as X-rays and γ-rays is applied to the thin semiconductor substrate 5, the incident light is not sufficiently absorbed by the semiconductor substance. It is not possible to improve the detection sensitivity of an electron tube using the method. Increasing the thickness of the semiconductor substrate 5 allows the incident light to be sufficiently absorbed, but the diffusion length of the electrons is about 1 μm. I can't escape from inside. In the transmission type photocathode 10 according to the present embodiment, the generated electrons are が of the minimum distance DL.
If the electrons proceed only in the direction of the through holes 10a to 10d, the electrons can escape into the through holes 10a to 10d. The preferred thickness of the semiconductor substrate 5 is 3 μm or more. With such a thickness, the semiconductor substrate 5 constituting the photocathode 10 is formed.
The number of electrons generated in the semiconductor substrate 5 can be increased, and the number of electrons that can escape from the semiconductor substrate 5 can be increased. Preferred materials for the semiconductor substrate 5 having sensitivity to X-rays are GaAs, Si, InP, CdTe, C
dZnTe and PbO.

Next, a method for manufacturing the photocathode 10 will be described. First, a p-type GaAs semiconductor substrate 5 (wafer) having a thickness of 20 μm is prepared, and the surface of the semiconductor substrate 5 is polished and etched to a mirror surface. This semiconductor substrate 5
After a photoresist is applied on the surface of the substrate, a photomask such that portions corresponding to a plurality of through holes are removed from the semiconductor substrate 5 by development is arranged on the photoresist, and exposure and development are performed. Since the surface of the semiconductor substrate 5 corresponding to the plurality of through holes is exposed by this process, dry etching is performed from the exposed surface of the semiconductor substrate 5 toward the inside. As the dry etching, a plasma sputter etching method can be used. When etching is performed perpendicularly to the surface of the semiconductor substrate 5, the direction of an electric field that accelerates ions used for sputtering is set perpendicular to the surface of the semiconductor substrate 5. This etching may be performed by using a reactive ion beam etching (RIBE) method using reactive ions. As described above, when the longitudinal direction of the through hole intersects the direction (thickness direction) perpendicular to the surface of the semiconductor substrate 5, the acceleration electric field is applied obliquely to the thickness direction of the semiconductor substrate 5. I do. Incidentally, anisotropic etching by wet etching may be performed by appropriately selecting the surface direction of the semiconductor substrate 5 and an etching solution. In any case, the etching is performed until a through hole is formed in the semiconductor substrate 5.

Next, Al is vapor-deposited on the surface of the semiconductor substrate 5 to a thickness such that X-rays can be transmitted therethrough to form an Al upper electrode 4. After the formation of the upper electrode 4, the insulating layer 6 and the lower electrode 7 are sequentially formed on the lower surface of the semiconductor substrate 5. The process of forming the lower electrode 7 and the upper electrode 4 is the same. A lead electrode is attached to each of the electrodes 4 and 7, and is arranged in the side tube 1 shown in FIG.
After this step, Cs, O _{2 and the} like may be introduced into the side tube 1 in order to form a material for lowering the work function such as Cs—O so as to be in contact with the semiconductor substrate 5. In addition, GaAs X
When using a CdTe having a large X-ray absorption coefficient than (39cm ^-1) linear absorption coefficient (10.8 cm ^-1), the thickness of the semiconductor substrate 5 may be about 10 [mu] m. In order to have sensitivity to visible light, high-concentration p-type GaAs is used as the material of the semiconductor substrate 5 and the electrode 4 is
Or a transparent electrode covering the surface of the semiconductor substrate 5, and the thickness of the semiconductor substrate 5 is desirably 3 to 5 μm.

Further, as a material of the semiconductor substrate 5 for X-ray detection, CdZnTe, p-type CdTe, PbO or the like can be used.

The present invention relates to the transmission type photocathode 10 described above.
However, the shape and arrangement of the through holes may be described below.

FIG. 4 is a sectional view of the II tube 10 showing the photocathode 10 in which only the shape and arrangement of the through-holes are changed in the same manner as FIG. 2, and FIG. 5 is a sectional view of the photocathode 10 shown in FIG. C
It is arrow C sectional drawing. The cross section perpendicular to the longitudinal direction of the through holes 10e to 10h is rectangular, and the adjacent through holes 10e to 10h are rectangular.
The shortest distance DL of the inner surface of f, 10g is set in the same manner as described above. The long sides of all the through holes including these rectangular through holes 10e to 10h are parallel to the long sides of the adjacent through holes, and the short sides are parallel to the short sides of the adjacent through holes. The length X is set shorter than the shortest distance DL. Here, the shortest distance DL is 2 μm, the length X of the long side is 1.6 μm, and the length Y of the short side is 1 μm. Through hole 10 in a plane perpendicular to the thickness direction of semiconductor substrate 5
The ratio of the entire through hole including e to 10h is about 36%
It is. The thickness of the semiconductor substrate 5 is 10 μm.
That is, since the effective light receiving area increases as the proportion of the through holes decreases, the thickness of the semiconductor substrate 5 can be made smaller than that described above.

FIG. 6 is a plan view of the photocathode 10 in which the dimensions of the through holes are changed from those shown in FIG. Photocathode 10
Has a through hole 1 having a substantially circular cross section perpendicular to the longitudinal direction.
A plurality of through-holes including 0h to 10m are formed, and these through-holes are formed at positions such that the center thereof forms a vertex of a regular hexagon in the surface of the photocathode 10 on the face plate 2 side. Here, the distance between the centers of the through holes 10i and 10l located at the opposing vertices of the hexagon is 2 μm,
The diameter D ₂ of the through hole 10i is 0.9 .mu.m. When the setting is performed in this manner, the ratio of the entire through hole including the through holes 10h to 10m in a plane perpendicular to the thickness direction of the semiconductor substrate 5 is about 49%.

FIG. 7 shows a photocathode 10 in which through holes 10n, 10p to 10t are arranged on each side of the hexagon in addition to the through holes 10h to 10m arranged at the vertices of the hexagon shown in FIG. FIG. The distance between the centers of the through holes 10i, 10l located at the opposite vertices of the hexagon is 2 μm,
The diameter D ₃ of the through hole 10i is 0.4 .mu.m. When the setting is performed in this manner, the proportion of the entire through hole in a plane perpendicular to the thickness direction of the semiconductor substrate 5 is about 24%.

FIG. 8 shows a semiconductor photocathode 10 in which the proportion of the entire through-hole in a plane perpendicular to the thickness direction of the semiconductor substrate 5 is reduced to about 10% and the effective light receiving area is increased to 90%. It is a top view. This semiconductor substrate 5
Is formed by bundling the fibers F such that the axis of each fiber F is located at the vertex of the regular hexagon. This fiber F is made of a semiconductor material and has a through hole 10.
u to 10z are defined by the gap between the fibers F.
In this case, the through holes 10u to 10z can be easily formed by bundling the fibers F, and the effective light receiving area can be significantly increased.

[0022]

As described above, the transmission type photocathode of the present invention can increase the number of emitted electrons, so that the detection sensitivity of an electron tube using the same can be improved.

[Brief description of the drawings]

FIG. 1 is a front view of an electron tube showing a partly broken electron tube.

FIG. 2 is a sectional view of the electron tube shown in FIG.

FIG. 3 is a sectional view of the photocathode shown in FIG.

FIG. 4 is a cross-sectional view of another electron tube.

5 is a cross-sectional view of the photocathode shown in FIG. 4 taken along the line CC.

FIG. 6 is a plan view of another photocathode.

FIG. 7 is a plan view of another photocathode.

FIG. 8 is a plan view of another photocathode.

[Explanation of symbols]

 10 photocathode, 10a, 10b ... through-hole.

Claims (2)

[Claims] 1. A transmission type photocathode for emitting electrons generated in response to an incident electromagnetic wave, comprising a semiconductor member having adjacent first and second through holes, wherein the first and second semiconductor members have adjacent through holes.
The shortest distance between the inner surfaces of the through holes is generated in the semiconductor member in response to the incident electromagnetic wave, and electrons traveling in the directions of the first and second through holes are at least one of the first and second through holes. A transmissive photocathode characterized in that it is set so that it can escape into either one of them. 2. The semiconductor device according to claim 1, wherein the semiconductor member is formed by bundling a plurality of fibers made of a semiconductor material, and the first and second through holes are defined by a gap between the fibers. Transmission type photocathode.