Radiant energy – Invisible radiant energy responsive electric signalling – Semiconductor system
Reexamination Certificate
2000-09-27
2003-01-28
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Semiconductor system
Reexamination Certificate
active
06512233
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The invention relates to a radiation detector and a radiation image taking device to be used in a field of medical treatment, industry or atomic energy, more particularly, a structure of a radiation sensitive semiconductor film to be provided to the radiation detector of this type, wherein radiation is directly converted into a carrier formed of a pair of electron and hole (hereinafter referred to “a pair of electron-hole”).
A conventional radiation detector is structured such that a semiconductor film for producing a carrier formed of a pair of electron-hole sensitive to radiation to be detected is sandwiched by a bias electrode and detecting electrodes, and by applying a bias voltage between these electrodes, and the carriers, specifically, small number of carriers, produced in the semiconductor film are taken out from the detecting electrodes. As the radiation sensitive semiconductor film, it is desirable to select a semiconductor film having a good radiation conversion efficiency as much as possible. As the semiconductor film of this type, a monocrystalline semiconductor film is preferable, and especially monocrystals of CdTe and CdZnTe are used since they operate at a room temperature and have a high sensitivity.
However, the conventional radiation detector having the structure as described above has the following problems.
Since the radiation detector is used in place of an image intensifier for detecting X-rays in the medical treatment field, a radiation detector having a large area has been desired. However, it is very difficult to obtain a monocrystalline semiconductor film of CdTe or CdZnTe necessary for the radiation detector having the large area. Thus, there has been proposed a radiation detector having a large area by bonding together crystals with small areas in a tile style or arrangement to thereby obtain the radiation detector with the large area. However, it is very complicated to produce the radiation sensitive layer of the large area by bonding the monocrystals of the small area in the tile style, which results in poor work efficiency and poor economy. Also, since the carriers are not accumulated on joint portions for bonding the crystals, when an image is outputted, vertical stripes and horizontal stripes appear on the joint portions for bonding the crystals to thereby lower the quality of the picture image.
Further, in order to raise a catching rate of radiations, such as X-rays, although it is desired to make a radiation sensitive layer thick, since a growing speed of the monocrystals of CdTe and CdZnTe is very slow, it takes a long time to obtain a necessary thickness of the radiation sensitive layer, which results in a poor productivity of the radiation detector.
The present invention has been made in view of the above problems, and an object of the invention is to provide a radiation detector and radiation image taking device having a large area.
Another object of the invention is to provide a radiation detector and radiation image taking device as stated above, wherein a semiconductor film having a thickness sufficient for catching radiation can be produced in a short time.
Further objects and advantages of the invention will be apparent from the following description of the invention.
SUMMARY OF THE INVENTION
In order to attain the above objects, the present invention has the structures as follows.
According to a first aspect of the invention, in a radiation detector, a semiconductor film for producing a carrier formed of a pair of electron-hole sensitive to radiation to be detected is disposed between a bias electrode and detecting electrodes, and when a bias voltage is applied between the bias electrode and the detecting electrodes, the carrier produced in the semiconductor film can be taken out from the detecting electrodes, wherein the semiconductor film is a polycrystalline film of CdTe (cadmium telluride).
According to a second aspect of the invention, in a radiation detector, a semiconductor film for producing a carrier formed of a pair of electron-hole sensitive to radiations to be detected is disposed between a bias electrode and detecting electrodes, and when a bias voltage is applied between the bias electrode and the detecting electrodes, the carrier produced in the semiconductor film can be taken out from the detecting electrodes, wherein the semiconductor film is a polycrystalline film of CdZnTe (cadmium zinc telluride).
According to a third aspect of the invention, in a radiation detector, a semiconductor film for producing a carrier formed of a pair of electron-hole sensitive to radiations to be detected is disposed between a bias electrode and detecting electrodes, and when a bias voltage is applied between the bias electrode and the detecting electrodes, the carrier produced in the semiconductor film can be taken out from the detecting electrodes, wherein the semiconductor film has a laminate structure of a polycrystalline film of CdTe (cadmium telluride) and a polycrystalline film of CdZnTe (cadmium zinc telluride).
According to a fourth aspect of the invention, in the radiation detector of the third aspect, the polycrystalline film of CdZnTe (cadmium zinc telluride) constituting the semiconductor film is disposed on an incident side of radiation.
According to a fifth aspect of the invention, in the radiation detector of the third aspect, the polycrystalline film of CdTe (cadmium telluride) constituting the semiconductor film is disposed on an incident side of radiation.
According to a sixth aspect of the invention, in the radiation detector of any one of the first, third through fifth aspects of the invention, the polycrystalline film of CdTe (cadmium telluride) is obtained by heating a sintered material of CdTe power under a reduced pressure to sublimate.
According to a seventh aspect of the invention, in the radiation detector of any one of the second through fifth aspects of the invention, the polycrystalline film of CdZnTe (cadmium zinc telluride) is obtained by heating a mixed sintered material of CdTe power and ZnTe powder under a reduced pressure to sublimate.
According to an eighth aspect of the invention, in the radiation detector of any one of the second through fifth aspects of the invention, the polycrystalline film of CdZnTe (cadmium zinc telluride) is obtained by heating a mixed sintered material of CdTe power and Zn powder under a reduced pressure to sublimate.
According to a ninth aspect of the invention, in the radiation detector of any one of the first through eighth aspects, a carrier injection preventing layer for preventing the carrier from being injected to the semiconductor film is formed between the bias electrode and the semiconductor film and/or between the semiconductor film and the detecting electrodes.
According to a tenth aspect of the invention, in the radiation detector of the ninth aspect, the carrier injection preventing layer is an n-type or p-type semiconductor layer for making a hetero-junction between the semiconductor film and itself.
According to an eleventh aspect of the invention, in the radiation detector of the ninth aspect, the carrier injection preventing layer is made of a material capable of forming a Schottky barrier on an interface between the semiconductor film and itself.
According to a twelfth aspect of the invention, in the radiation detector according to any one of the first to eleventh aspects, the detecting electrodes are separately disposed on a one-dimension or two-dimensions, and the bias electrode is a single common electrode.
A thirteenth aspect of the invention is a radiation image taking device including the radiation detector according to the twelfth aspect; and a switching matrix board having a plurality of charge storage capacitors connected separately to the respective detecting electrodes, and a plurality of charge read-out switching elements connected to the respective charge storage capacitors.
Next, functions of the radiation detectors and the radiation image taking device of the invention will be explai
Sato Toshiyuki
Tokuda Satoshi
Hannaher Constantine
Kanesaka & Takeuchi
Lee Shun
Shimadzu Corporation
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