JP2635683B2 - Radiation detection element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a radiation detecting element that detects radiation such as α-rays, β-rays, γ-rays, and X-rays.

(Prior Art) Conventionally, various types of radiation detecting devices have been known, and FIG. 5 shows an example thereof. In the figure, 51
And 52 are metal electrodes (metal films) composed of Mo and Ta, respectively.
It has a role of strongly interacting with radiation to emit secondary particles such as photoelectrons to the amorphous silicon (a-Si) film 53 and to collect electron-hole pairs generated in the a-Si film. Since Mo is a Schottky electrode and Ta is an ohmic electrode, a detection signal can be obtained by connecting the Mo electrode to the current amplifier 54 in a non-biased state as shown in the figure. That is, operation in the PV (Photo-voltaic) mode can be performed.

(Problems to be Solved by the Invention) The conventional radiation detecting element shown in FIG. 2 has the following problems. That is, a metal electrode having the same thickness is a
-Since they are arranged at equal intervals across the Si film, in a situation where the incident radiation particles lose their energy, the electron-hole pairs are necessarily effectively formed in the a-Si film. Does not occur. The reason is that the energy of the secondary particles generated from the metal electrode decreases along the incident direction of the radiation, the energy lost in the metal increases, and the effective energy addition to the a-Si film is hindered. That's why.

An object of the present invention is to provide a radiation detecting element that solves the above problems.

[Configuration of the invention]

(Means for Solving the Problems) A first aspect of the present invention is to provide a semiconductor (a-Si) film in which at least a metal electrode or a semiconductor film is configured to be thick on a radiation incident side and thin on a side facing the incident side. In this way, effective energy addition to the steel is not hindered.

According to a second aspect of the present invention, one of the metal films formed on both sides of the semiconductor film is formed in a comb shape so that the effective energy addition to the semiconductor (a-Si) film is not hindered, and the time change Fast radiation can also be measured.

(Operation) As in the first invention, by reducing the thickness of the metal film along the incident direction of the radiation, the semiconductor of the secondary radiation particles is effective against the incident radiation particles whose energy is attenuated. The incidence on the (a-Si) film occurs. That is, for radiation particles having a small energy, it is more effective to reduce the metal film thickness so that the secondary radiation particles are more effectively incident on the semiconductor (a-Si) film and the electron-hole pairs are generated. . Also, the energy of the secondary radiation particles decreases along the incident direction,
The range in the a-Si film becomes shorter, and the thickness of the a-Si film can be gradually reduced.

As in the second aspect, by forming one of the metal films formed on both sides of the semiconductor film in a comb shape, the capacitance between the electrodes is reduced, and radiation with a fast time change can be measured. Further, if one of the metal films of the semiconductor film is comb-shaped in the same manner as in the first invention, there is a portion without the metal film, and radiation with low energy reaches the next semiconductor layer.

(Embodiment) An embodiment of the present invention will be described with reference to FIG. The structure is Mo
The thickness of the electrode (Mo metal film) 11 and the thickness of the Ta electrode (Ta metal film) 12 gradually decrease in the radiation incident direction.
The thickness of the Si film (semiconductor film) 13 is similarly reduced. The incident radiation interacts with the Mo electrode 11 and the Ta electrode 12 to emit secondary radiation particles into the a-Si film, and the energy is attenuated. In this process, the electron-positive electrons are stored in the a-Si film 13. A hole pair is generated, and the Ta electrode 12 has an ohmic property and the Mo electrode 11 has a Schottky property.
A signal can be detected by operation.

Next, the metal electrodes 11, 12 and a-Si
How the thickness of the film 13 is gradually reduced will be described with reference to a design example shown below. First, the Mo electrode 11 and
The thicknesses of the Ta electrode 12 and the a-Si film 13 are respectively (d ₁ , d ₃ ,
.. Dn _-1 ), (d ₂ , d ₄ ,... Dn) and (a ₁ , a ₂ , a ₃ ... An), and the total energy decay constant of radiation including secondary radiation particles is α ₁ (Mo ), Α ₂ (Ta) and α ₃ (a-
si). Next, let the initial energy of radiation be Eo,
Energy E absorbed in each layer (d ₁ , a ₁ , d ₂ , a ₂ … dn, an)
(D ₁ ), E (a ₁ ), E (d ₂ ), E (a ₂ )... E (dn), E (an) are calculated as follows.

E (d ₁ ) = Eo ｛1−exp (−α ₁ d ₁ )｝ E (a ₁ ) = {Eo−E (d ₁ )｝ ｛1−exp (−α ₃ a ₁ )} E (d ₂ ) = {Eo−E (d ₁ ) −E (a ₁ )} 1 −exp (−α ₂ d ₂ )} E (dn) = {Eo−E (d ₁ ) −E (a ₁ ). (Dn _-1 )｝ ｛1-exp
(−αndn)｝ E (an) = {Eo−E (d ₁ ) −E (a ₁ )... E (dn ₋₁ ) E (an ₋₁ )} 1 −exp (−αn ₋₁ an)} Through the above calculations, the thickness to be obtained is given by the following equation in consideration of the equilibrium of the absorbed energy.

d ₁ : d ₂ : d ₃ …: dn = E (d ₁ ): E (d ₂ ): E (d ₃ )… E (dn) a ₁ : a ₂ : a ₃ …: an = E (a ₁ ): E (a ₂ ): E (a ₃ )... E (an) FIG. 3 shows an example of a calculation result based on the above equation. The third
The figure is based on FIG. ₂ and the thicknesses of a ₁ , a ₂ and a ₃ are 20
μm, 15 μm, 12 μm, the thickness of d ₁ , d ₂ , d ₃ is 15 μm, 10 μm respectively
m, 6 μm.

In the above embodiment, the thickness of both the metal film and the a-Si film is decreased along the incident direction, but either the metal film or the a-Si film may be decreased along the incident direction. ,
Alternatively, only one of the metal films may be reduced.

Next, another embodiment of the present invention will be described with reference to FIG. The basic structure is a comb-shaped during periodic lamination of Ta electrode 12 and a-Si film 13.
The Mo electrode 45 is inserted. The incident radiation mainly interacts with the Ta electrode 12, and secondary radiation particles such as photoelectrons are generated by energy conversion. Next, secondary radiation particles generate electron-hole pairs in the a-Si film 13 and are collected by the comb-shaped Mo electrode 45 as signal charges.

Since the Ta electrode 12 has ohmic properties and the Mo electrode 45 has Schottky properties, PV (Ph-oto-vl
c) The signal can be detected by the operation. This fourth
In the radiation detecting element configured as shown in the drawing, the same effect as in the above-described embodiment occurs because the absorption of the radiation passing through portions other than the comb portion of the comb-shaped electrode 45 is reduced. Further, by forming at least one of the electrodes in a comb shape, the electric capacity is reduced, and a sensor with good time response can be obtained.

In the above embodiment, one interdigital electrode between the Ta electrodes
Although 12 is provided, two or more interdigital electrodes can be inserted between the Ta electrodes. It is more effective to combine this embodiment with the above-described embodiment.

〔The invention's effect〕

As described above, according to the present invention, it is possible to obtain a radiation detecting element having excellent electron-hole pair generation efficiency in an a-Si film. Further, if one of the electrodes is formed in a comb shape, in addition to the above effects, the electric capacity is reduced, and the time response is improved.

[Brief description of the drawings]

1 to 3 are diagrams for explaining one embodiment of the present invention, FIG. 4 is a diagram for explaining another embodiment of the present invention,
FIG. 5 is a diagram for explaining a conventional example. 11,12 Metal film, 13 Semiconductor film 14 Current amplifier 45 Comb-shaped Mo electrode

Claims (5)

(57) [Claims] 1. A radiation detecting element comprising a metal film and a semiconductor film alternately laminated, wherein at least one of the metal film and the semiconductor film is thicker on the radiation incident side and thinner on the side facing the incident side. A radiation detection element characterized in that: 2. The radiation detecting element according to claim 1, wherein the semiconductor film is an amorphous silicon film, and the thickness of the semiconductor film is sequentially reduced along the radiation incident direction. 3. The radiation detecting element according to claim 1, wherein the thickness of the metal film is gradually reduced along the radiation incident direction. 4. A radiation detecting element in which a metal film and a semiconductor film are alternately stacked, wherein one of the metal films formed on both sides of the semiconductor film is formed in a comb shape. Radiation detection element. 5. The radiation detecting element according to claim 4, wherein the material of the comb-shaped metal film is made of Mo.