JPH03190285A - Radiation detector - Google Patents

Abstract

PURPOSE:To obtain a high-quality and sufficient detection efficiency by forming a semiconductor layer consisting of a deposited film which is sensitive to radiation on the surface of a substrate with conductivity, forming an electrode on the surface of the semiconductor layer, and then placing the surface of the semiconductor layer in approximately parallel to the incidence direction of radiation. CONSTITUTION:A CdTe layer 2 is deposited on the surface of a conductive glass substrate 3 by the sputter method and then a Pt thin film is vacuum- deposited onto the surface of the CdTe layer 1 for forming an electrode 2. This detector is placed so that the substrate surface is in parallel to the incidence direction of radiation 7 and the edge surface of the CdTe layer 1 becomes the incidence surface of the radiation. When a high electric field is applied between the conductive glass substrate 3 and the electrode 2, charge which is generated due to mutual operation between the radiation and the CdTe layer 1 is moved by this electric field and is collected by the electrode to turn into signal so that this signal is amplified by an amplifier for enabling the radiation to be detected. Thus, even if a high-energy radiation enter, it can fully be absorbed, thus obtaining a high-quality and sufficient detection effect.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a radiation detector used in medical radiation inspection equipment and industrial non-destructive testing equipment.

The sensitivity of conventional art radiation detectors depends on how much sensitive layer the semiconductor material used has and how much radiation it can absorb.

The absorption efficiency η of radiation by a semiconductor is as follows, where k is the linear absorption coefficient of the semiconductor material, 77=1−exp (−to−d). However, d is the thickness of the sensitive layer. Therefore, if the semiconductor material is the same, it will largely depend on the thickness of the sensitive layer. When the semiconductor material is cadmium telluride, the absorption coefficients for 60 keV and 100 keV gamma rays are approximately 36 cm-' and 9 cm, respectively.
-'. Using this value to find the thickness d at which the absorption efficiency η is 0.7, it is 0.033 cm at 60 keV, 1
At 00 keV, 0.134 cm is required. High-energy radiation requires a thicker sensitive layer.

As shown in FIG. 6, the radiation detector is composed of a semiconductor layer 10 serving as a sensitive layer and electrodes 11 and 12 for extracting charges generated by the interaction between the radiation and the semiconductor. A bulk material is generally used for the semiconductor layer 10 so as to form a thick sensitive layer.

Problems to be Solved by the Invention When a bulk semiconductor is used in a radiation detector, it is difficult to cut and process the semiconductor after electrode formation, which poses a manufacturing problem. In addition, bulk semiconductors used in radiation detectors are of high resistance in order to suppress leakage current flowing into the detector, but high-quality bulk semiconductors with high resistance and carrier mobility are difficult to manufacture, and It's also expensive.

Due to these problems, it has been considered to use a thin film semiconductor for the semiconductor layer, but current thin film manufacturing techniques cannot deposit a film thick enough to obtain high quality and sufficient detection efficiency.

Means to solve problems The radiation detector of the present invention is constructed as follows.

The radiation detector of the first invention forms a radiation-sensitive semiconductor layer made of a deposited film on the surface of a conductive substrate,
Further, an electrode is formed on the surface of the semiconductor layer, and the surface of the semiconductor layer is arranged substantially parallel to the incident direction of radiation.

Further, the radiation detector of the second invention comprises forming an electrode on the surface of the substrate, forming a radiation-sensitive semiconductor layer made of a deposited film on the surface of the electrode, and further forming an electrode on the surface of the semiconductor layer. This is a configuration in which the surface of the semiconductor layer is arranged approximately parallel to the incident direction of radiation.

Furthermore, a radiation detector according to a third aspect of the present invention is provided by forming a radiation-sensitive semiconductor layer made of a deposited film on the surface of the substrate, and further forming electrode pairs at intervals on the surface of the semiconductor layer. The surface of the radiation source is arranged substantially parallel to the direction of incidence of radiation.

In the first aspect of the invention, the surface of the semiconductor layer of the radiation detector is arranged approximately parallel to the incident direction of radiation, the end face of the semiconductor layer is used as the radiation incident surface, and a high electric field is created between the conductive substrate and the electrode. When , an electric charge is generated due to the interaction between the semiconductor layer and the radiation. This charge is moved by the electric field and collected on the electrode. Even if the thickness of the semiconductor layer is not large, the length of the semiconductor layer in the radiation incident direction, that is, the radiation absorption length can be increased, so that high-energy radiation can be sufficiently absorbed. In this first invention, the substrate serves as an electrode.

The second invention is different from the first invention in that an electrode is formed on the surface of the substrate, but the semiconductor layer located between the electrode and the electrode formed on the surface side is formed in the direction of incidence of radiation. On the other hand, since they are arranged in the same positional relationship as in the first invention, high-energy radiation can be sufficiently absorbed even if the thickness of the semiconductor layer is not large.

The third invention is different from the first and second inventions in that electrode pairs are formed on the surface of the semiconductor layer, but since the distance between the electrode pairs can be appropriately selected, the radiation incident position It is possible to reduce variations in the signal pulse height caused by the radiation and increase the energy resolution. Therefore, it can sufficiently absorb high-energy radiation.

Embodiments Embodiment 1 An embodiment of the present invention is shown in FIG. In this detector, a CdTe layer 1 is deposited on the surface of a conductive glass substrate 3 by sputtering, and a PTL film is further vacuum-deposited on the surface of the CdTe layer 1 to form an electrode 2. This detector was installed so that the substrate surface was parallel to the incident direction of the radiation 7, and the Cd
The end face of the Te layer 1 was used as a radiation incident surface. When a high electric field is applied between the conductive glass substrate 3 and the electrode 2, radiation and C(
Charges generated by the JTeTeO2 interaction move due to this electric field and are collected at the electrodes to become a signal. This signal was amplified by an amplifier (not shown) to detect radiation.

Although the width of the radiation incident surface cannot be made large because it depends on the thickness of the CdTe layer, even if high-energy radiation were incident, it could be sufficiently absorbed.

The semiconductor layer sensitive to radiation includes Ga in addition to the CdTe layer.
As, HgI, CdSe can be used, and the metal film as an electrode includes Au, In, Mo other than the pt group.
, AI, Cr, etc. In addition to the sputtering method and vacuum evaporation method, methods for forming these semiconductor layers and electrodes include hot wall epitaxy method, metal-organic chemical vapor deposition method (M
OCVD), molecular beam epitaxy (MBE), liquid phase epitaxy (LPE), etc.

A detector using any combination of the semiconductor layer, the electrode, and these formation methods is made by depositing a CdTe layer 1 on the surface of the conductive glass substrate 3 by sputtering, and forming the electrode 2 by vacuum-depositing a PT thin film on the surface of the CdTe layer 1. Like the one that formed it, it was able to absorb enough high-energy radiation.

Embodiment 2 Another embodiment of the present invention is shown in FIGS. 2 and 3. This embodiment is an example of a multi-channel radiation detector array. Second
The figure shows a substrate 3 used in the detector of this embodiment, in which a plurality of electrodes 4 made of Ag--Pd films are formed on the ceramic surface. The electrodes 4 are electrically connected to the back surface of the substrate 3 through through holes 5, respectively. Furthermore, Cd is applied to the surface of this substrate 3.
By forming TeJil 1 and electrode 2, a multi-channel radiation detector shown in FIG. 3 was manufactured. The substrate 3 is placed parallel to the incident direction of radiation, and a high voltage is applied to each channel from the back side of the substrate 3 through the through hole 5.
I got the signal from. Radiation between 20 and 120 KeV could be detected.

FIG. 4 shows an embodiment of the multi-channel detector of the present invention. On a substrate 3 having the same structure as shown in FIG. 2, a CdTe layer was formed in a pattern divided into channels, and electrodes 2 were vapor-deposited. As in this example, since even the sensitive layer portion of each channel consisting of a CdTe layer is formed separately, there is no crosstalk between channels, and the spatial resolution can be improved.

Furthermore, for this reason, it is extremely difficult to divide and form the semiconductor of the sensitive layer portion at minute pitches using bulk materials, but this can be easily done using thin film manufacturing technology. To pattern the CdTe layer as shown in FIG.
CdTe is deposited on the entire surface of the substrate by evaporating the e-layer using a metal mask or by any of the methods described in Example 1.
After forming a layer, it is also possible to fabricate a pattern by etching with bromine-methanol or the like, and similar results were obtained in both cases.

Embodiment 3 FIG. 5 is a diagram showing another embodiment of the multi-channel radiation detector of the present invention. CdT on the surface of the substrate 3 made of quartz
The e-layer 1 was formed into a pattern. Subsequently, CdTe layer 1
Electrodes 2.6 were formed on the surface. A high voltage was applied to electrode 2, and electrode 6 was used for signal extraction and connected to an amplifier system.

For the substrate, insulating materials such as alumina could be used in addition to quartz. In this case too, the CdTe layer l and the electrode 2.6
could be formed by any of the methods described above. In this example, since the electrodes 2.6 are formed on the same surface of the CdTe layer 1, there is no need to form an electrode layer on the substrate, and the electrode layer can be easily formed. Furthermore, the travel distance of the charges generated by radiation is not dependent on the layer thickness of the CdTe layer (in this example, the distance between the electrodes can be appropriately selected). According to the relationship, the signal pulse height depends on the transit time, that is, the position of incidence of the charge. However, according to this embodiment, since the electrode position can be appropriately selected, such a phenomenon can be alleviated, and detection with high energy resolution can be achieved. Replaced. Also, the above CdT
The e layer does not necessarily have to be divided into channels as shown in FIG. 5, and the electrode 2 for high voltage application may be used as a common electrode without being divided, and only the electrode 6 may be divided.

As a result of the above effects of the invention, high-energy radiation can be sufficiently absorbed by a relatively thin semiconductor layer made of a deposited film, which is advantageous in terms of cost and processability, without using bulk semiconductor materials that are expensive and have poor processability. A radiation detector with high detection efficiency was obtained. In addition, the energy resolution with little variation in signal pulse height depending on the radiation incident position is shown in FIG. 1. FIG. 1 is a perspective view of an embodiment of the present invention. FIG. 4 and 5 are perspective views of other embodiments of the present invention, respectively, and FIG. 6 is a perspective view of a conventional radiation detector.

Claims (7)

[Claims] (1) A radiation-sensitive semiconductor layer made of a deposited film is formed on the surface of a conductive substrate, and an electrode is further formed on the surface of the semiconductor layer, so that the surface of the semiconductor layer is aligned with the radiation incident direction. A radiation detector characterized in that the radiation detectors are arranged substantially in parallel. (2) An electrode is formed on the surface of the substrate, a radiation-sensitive semiconductor layer made of a deposited film is formed on the surface of the electrode, and an electrode is further formed on the surface of the semiconductor layer, so that the surface of the semiconductor layer is A radiation detector characterized in that it is arranged substantially parallel to the incident direction of radiation. (3) The radiation detector according to claim 2, wherein the electrodes formed on both sides of the semiconductor layer are divided into a plurality of pairs. (4) The radiation detector according to claim 2, wherein the semiconductor layer is divided into a plurality of channels, and a pair of electrodes are formed on both sides of each channel. (5) A radiation-sensitive semiconductor layer made of a deposited film is formed on the surface of the substrate, and electrode pairs are further formed at intervals on the surface of the semiconductor layer, so that the surface of the semiconductor layer is directed in the direction of incidence of radiation. A radiation detector characterized in that it is arranged substantially parallel to. (6) The radiation detector according to claim 5, wherein the semiconductor layer is divided into a plurality of channels, and electrode pairs are formed at intervals on the surface of each channel. (7) The semiconductor layer sensitive to radiation is cadmium telluride,
The radiation detector according to any one of claims 1 to 6, characterized in that it is made of mercury iodide, gallium arsenide, or cadmium selenide.