JP2018204989A - Semiconductor radiation detector - Google Patents

Abstract

To provide a semiconductor radiation detector comprising a substrate 10 made of Si or GaAs and an active layer 20 for incident radiation 5 consisting of CdTe or CdZnTe laminated on a surface of the substrate 10.SOLUTION: A substrate 10 has a rectangular shape. An active layer 20 stacked in a rectangular shape on the substrate 10 has a long side 22 with one side being the same length as a substrate length 12 of the substrate 10, and a short side 21 of the other side being shorter than a substrate length 11 of the substrate 10. One surface of the laminate 23 of the short side 21 and the active layer 20 is a radiation receiving surface 25 of the incident radiation 5. A semiconductor radiation detector 1 comprises a power supply 6 which applies power to a second electrode 29 bonded to the active layer 20 as a negative electrode and to a first electrode 19 bonded to the substrate 10 as a positive electrode, and a detection part 7. It is possible to detect radiation of high photon energy (for example, Cs: 662 keV Sr: 514 keV) which was conventionally impossible.SELECTED DRAWING: Figure 1

Description

The present invention relates to a semiconductor radiation detector having a substrate made of Si or GaAs and an active layer for incident radiation made of CdTe or CdZnTe laminated on the surface of the substrate.

Conventionally, bulk CdTe single crystals by THM method are mainly used for CdTe radiation detectors. However, CdTe crystals are extremely soft and fragile and are difficult to handle. In addition, it is extremely expensive because it is difficult to obtain high-quality crystals that can be used in the detector.

On the other hand, Patent Document 1 describes a semiconductor radiation detector using a CdTe growth layer formed on a Si substrate. The CdTe growth layer on the Si substrate is extremely easy to handle because it grows on the Si substrate having high mechanical strength. Growth is also done by metalorganic vapor phase epitaxy, and the thickness of the growth layer and the electrical characteristics of the growth layer can be controlled, so the detector can be manufactured and designed with a high degree of freedom, and the area can be increased. There are features.

In this semiconductor radiation detector, the upper surface of the CdTe growth layer is used as a radiation receiving surface. The CdTe growth layer can be formed in a thickness range of 0.01 to 1 mm. That is, the thickness of the CdTe growth layer is limited to 1 mm.

Therefore, in the conventional semiconductor radiation detector described in Patent Document 1, the photon energy of the radiation can be detected only up to about 100 keV, and radiation having a larger photon energy can be detected because the transmittance of the CdTe growth layer is high. There wasn't.

JP 2005-159156 A

  An object of the present invention is to provide a semiconductor radiation detector capable of detecting radiation of high photon energy (for example, Cs: 662 keV, Sr: 514 keV, etc.), which has been impossible in the past.

The means for solving the problems of the present invention is that the CdTe growth layer of a semiconductor used in a semiconductor radiation detector is limited to a thickness of 1 mm, but the plane direction can be easily increased from several tens of mm to several hundreds of mm. The semiconductor radiation detector is realized by increasing the length of the CdTe growth layer that contributes to the detection of radiation to 1 mm or more by making the incident direction of the plane direction perpendicular to the thickness.
Specifically, the invention is as follows.
Invention 1 is a semiconductor radiation detector having a substrate (10) made of Si or GaAs and an active layer (20) for incident radiation (5) made of CdTe or CdZnTe laminated on the surface of the substrate (10). The substrate (10) has a rectangular shape, and the active layer (20) is on the substrate (10), and one side is a long side having the same length as the substrate length (12) of the substrate (10). (22) The other side is laminated in a rectangular shape having a short side (21) having a length smaller than the substrate length (11) of the substrate (10), and a lamination of the short side (21) and the active layer (20). One surface having the thickness (23) is used as a light receiving surface (25) for incident radiation (5), the second electrode (29) bonded to the active layer (20) is bonded to the negative electrode, and the substrate (10). It has a power source (6) for applying the first electrode (19) to the positive electrode and a detector (7). A semiconductor radiation detector (1), characterized in.
Invention 2 is that the laminate thickness (23) is 0.1 mm to 1 mm, the length of the short side (21) is 0.02 mm to 2 mm, and the length of the long side (22) is 10 mm to 200 mm. A semiconductor radiation detector (1) according to the first aspect of the invention.
Invention 3 arrange | positions two or more active layers (20) on a board | substrate (10) in parallel by the space | interval (31), and makes the 2nd electrode (29) of two or more active layers (20) into a negative electrode, The semiconductor radiation detector (2) according to invention 1 or 2, wherein the first electrode (19) is a common positive electrode.
Invention 4 provides the semiconductor radiation detector (2) according to claim 3, wherein the short side (21) is the same, the interval (31) is the same, and the interval (31) is longer than the short side (21). Insulating layer (30) having two insulating active layers (20) of one semiconductor radiation detector (2) and having an insulating function between active layers (2) of the other semiconductor radiation detector (2) It is a semiconductor radiation detector (3) characterized by being fitted via.
Invention 5 is a semiconductor radiation detector (4), wherein two or more semiconductor radiation detectors (3) described in Invention 4 are stacked.
In addition, the code | symbol in the parenthesis in the said and the claim shows the correspondence of the term described in the claim, and the specific substance etc. which are described in the below-mentioned embodiment, and become the example of the said term. is there.

It is possible to provide a semiconductor radiation detector capable of detecting high-photon energy radiation (for example, Cs: 662 keV, Sr: 514 keV, etc.), which has been impossible in the past.

The figure which shows the semiconductor radiation detector 1 of 1st Embodiment. The figure which shows the material thickness of CdTe material and the absorption rate of radiation The figure which shows the semiconductor radiation detector 2 of 2nd Embodiment. The figure which shows the semiconductor radiation detector 3 of 3rd Embodiment. The figure which shows the semiconductor radiation detector 4 of 4th Embodiment. Figure showing conventional example (structure and size of CdTe growth layer on Si substrate) The figure which shows the material thickness of CdTe material of the semiconductor radiation detector 102 of a prior art example, and the absorption factor of a radiation

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments, and changes, modifications, and improvements can be added without departing from the scope of the invention.

(Conventional example)
FIG. 6 shows the shape of a semiconductor layer 101 having a CdTe layer 120 stacked on a conventional Si substrate 110. Due to manufacturing restrictions, the CdTe layer 120 has a rectangular shape with a thickness of 0.1 mm to a maximum of 1 mm and a length of 200 mm on one side.
In the CdTe layer 120, an ultrathin CdTe layer 120b that is an n-type semiconductor is stacked on a Si substrate 110 that is an n-type semiconductor, and a CdTe layer 120a that is a p-type semiconductor is stacked thereon. In this lamination, a pn junction is formed in the CdTe layer 120. This is to reduce the dark current of the detector due to the influence of high-density dislocations existing at the growth interface between the Si substrate 110 and the CdTe layer 120. By growing the n-type CdTe layer 120b, dislocations at the pn junction portion are performed. Density can be reduced and detector dark current can be reduced. By applying a positive voltage to the n-type Si substrate 110 side and a negative voltage to the p-type CdTe layer side during detector operation, the depletion layer is spread over the entire p-type CdTe layer 120a and radiation photons are absorbed into the CdTe layer 120. The holes generated by the above are moved to the surface side of the p-type CdTe 120a and the electrons are moved to the n-type Si side to generate a detection current in the external circuit to detect incident radiation.
The p-type CdTe layer 120a has a thickness of 0.09 to 0.99 mm, the n-type CdTe layer 120b has a thickness of 0.01 mm, and the Si substrate 110 has a thickness of 0.52 mm.
The Si substrate 110 is made of Si or GaAs, and the CdTe layer 120 is made of CdTe or CdZnTe.

Patent Document 1 describes a semiconductor radiation detector 102 using a semiconductor layer 101. The irradiation direction of the radiation 105 on the semiconductor radiation detector 102 is the Z-axis direction in FIG. 6, and the surface (XY plane) of the CdTe layer 120 of the semiconductor radiation detector 102 becomes the light receiving surface 125. The thickness of the CdTe layer 120 is about 1 mm at the maximum.
FIG. 7 shows the material thickness and radiation absorption rate of the CdTe material of the semiconductor radiation detector 102 of the conventional example. The parameter is the photon energy (keV) of the radiation. (K) is 200 keV, (K) is 100 keV, (K) is 50 keV, (K) is 40 keV, (S) is 30 keV, (S) is 20 keV, (S) is 10 keV, (C) is 5 keV, ) Is 1 keV. From (ke) 5 keV to (ko) 40 keV, the difference between the material thickness and the radiation absorption rate is small.
At a thickness of 1 mm, the absorption rate is 100% at 50 keV or less. The absorption rate at 100 keV is 65%, and the absorption rate at 200 keV is 18%.
Here, in order to determine the presence or absence of radiation irradiation, an absorptance of 30 to 50% is necessary. Therefore, photon energy 100 keV can be detected, but radiation of 200 keV or more cannot be detected.

(First embodiment)
FIG. 1 shows a semiconductor radiation detector 1 of the first embodiment. The first embodiment includes a substrate 10 made of Si or GaAs and a growth layer made of CdTe or CdZnTe formed on the surface of the substrate 10, and this growth layer is a semiconductor having an active layer 20 for incident radiation 5. This is a radiation detector 1.
Further, in the semiconductor radiation detector 1, the substrate 10 has a rectangular shape, and the active layer 20 is formed on the substrate 10 with one side having a long side 22 having the same length as the substrate length 12 of the substrate and the other side. Are stacked in a rectangular shape having short sides 21 having a length smaller than the substrate length 11 of the substrate. One surface composed of the short side 21 and the laminated thickness 23 is a light receiving surface 25 for the incident radiation 5. In the case of FIG. 1, the incident radiation 5 is the X axis, and the light receiving surface 25 is the YZ plane.

In the active layer 20, an ultrathin active layer 20b that is an n-type semiconductor is stacked on the substrate 10, and an active layer 20a that is a p-type semiconductor is stacked thereon. The laminated thickness 23 of the active layer 20 is a value obtained by combining the active layer 20b and the active layer 20a.
An external circuit having a power source 6 and a detection unit 7 for applying the second electrode 29 electrically connected to the active layer 20a to the negative electrode and the first electrode 19 electrically connected to the lower surface of the substrate 10 to the positive electrode. It is composed. In the external circuit, the second electrode 29, the power supply 6, the detection unit 7, and the first electrode 19 are connected in series by the wiring 8 in this order. The order of the power source 6 and the detection unit 7 may be reversed.
The first electrode 19 and the second electrode 29 are formed by laminating a conductive metal such as gold on the active layer 20a and the substrate 10, respectively.
The active layer 20a has a very large electric resistance, so that almost no current flows even when applied by the power source 6. When the incident radiation 5 is irradiated onto the light receiving surface 25, the radiation is absorbed by the active layer 20 made of CdTe or CdZnTe, and a pair of electrons and holes is generated, and the electrons are applied to the positive electrode 19 side. In addition, the holes are attracted toward the p-type CdTe layer 120b (second electrode 29) applied to the negative electrode, and a current flows to the external circuit. The detector 7 detects this current and detects the incident radiation 5 incident on the light receiving surface 25.

FIG. 2 shows the material thickness of CdTe material and the absorption rate of radiation. The parameter is the photon energy (keV) of the radiation. (A) is 2000 keV, (b) is 1000 keV, (c) is 600 keV, (d) is 500 keV, (g) is 400 keV, (f) is 300 keV, (g) is 200 keV, (g) is 100 keV, ) Is 50 keV. At a material thickness of 150 mm, the absorption rate of photon energy of 2000 keV is about 98%, and at a material thickness of 200 mm, the absorption rate is 100% (not shown).

(Detection of radiation)
The material thickness corresponds to the long side 22. When the long side 22 is 100 mm, radiation having a photon energy of 600 keV or less is absorbed almost 100%. Therefore, the presence or absence of radiation can be determined from the current generated by the absorption.
When the long side 22 is 25 mm, the absorption rate of radiation with a photon energy of 600 keV is about 70%, the absorption rate of 1000 keV is about 58%, and the absorption rate of 2000 keV is about 45%. Can be determined. If the absorption rate is 30 to 50%, the presence or absence of radiation can be determined.
If the absorption rate is 50%, the long side 22 is about 4 mm and 200 keV, the long side 22 is about 12 mm and 600 keV, the long side 22 is about 20 mm and 1000 keV, and the long side 22 is about 27 mm and 2000 keV can be detected. The radiation detector 1 can be provided.

(Identify detected radiation elements)
When the long side 22 is 100 mm, radiation having a photon energy of 600 keV or less is absorbed almost 100%, but the number of electron-hole pairs generated in the CdTe layer 20a for each absorption of radiation photons varies depending on the photon energy. The number of electron-hole pairs is larger at 600 keV than at 100 keV. As a result, the peak value of the current pulse generated in the external circuit for every absorption of radiation photons increases with the photon energy. Therefore, if the relationship between the radiation photon energy and the pulse peak value generated in the external circuit is calibrated with a radiation source such as Cs (662 keV) or Sr (514 keV) in advance, the radiation photon energy can be identified by the pulse peak value, The radioactive element that is the radiation source can be identified. In order to increase the detection efficiency of radiation photons, the length of the long side 22 of the semiconductor radiation detector 1 is set so that the absorption efficiency is 30 to 50% or more with respect to the radiation photon energy to be measured. To do.

(About the size of the active layer 20)
The lamination thickness 23 is 0.1 mm or more and 1 mm or less. This is a stacking constraint.
The length of the short side 21 is 0.02 mm or more and 2 mm or less. 0.02 mm is the processing limit. 2 mm is for reducing the electric capacity of the active layer 20.
The length of the long side 22 is 2 mm or more and 200 mm or less. 2 mm is for detecting the photon energy of the incident radiation 5 of 10 keV or more. 200 mm is determined by the size of the Si substrate 10 currently used for CdTe layer growth. When detecting radiation of 2000 keV or more, it can be easily expanded up to about 200 mm (the maximum size of the current Si substrate).

According to the semiconductor radiation detector 1, high photon energy radiation (for example, Cs: 662 keV, Sr: 514 keV, etc.) irradiated on the light receiving surface 25 can be detected.

(Second Embodiment)
FIG. 3 shows a semiconductor radiation detector 2 according to the second embodiment. In the semiconductor radiation detector 2, two or more active layers 20 are arranged in parallel at intervals 31 on a substrate 10.
The first electrode 19 of the substrate 10 is a common positive electrode, and the second electrodes 29 of the two or more active layers 20 are negative electrodes. Here, the common first electrode 19 and two or more second electrodes 29 are applied in parallel. Therefore, between the first electrodes 19 common to the respective second electrodes 29, a power source 6 (not shown) and a detection unit 7 (not shown) are connected in series by a wiring 8 (not shown) by an external circuit. It is connected to the. A signal of the incident radiation 5 incident on the light receiving surface 25 of each active layer 20 is output from each detection unit 7. In the case of FIG. 3, the incident radiation 5 is the X axis, and the light receiving surface 25 is the YZ plane.

As a processing method of the interval 31, for example, a notch is made in the X direction with a wafer dicer, and the interval 31 is formed as a groove. The interval 31 is determined by the width of the blade of the wafer dicer. At present, the minimum value can be reduced from about 0.02 mm to 0.15 mm. Therefore, if it processes with the same blade, the space | interval 31 will become the same, and the space | interval 31 can also be made into a different value by selecting and processing a blade suitably. Similarly, the length of the short side 21 can be the same or different value.

According to the semiconductor radiation detector 2, it is possible to measure high photon energy radiation irradiated on the light receiving surfaces 25 of the two or more active layers 20 disposed on one substrate 10. In particular, by setting the width 31 to about 0.02 mm, it is possible to improve the resolution of the one-dimensional intensity distribution of radiation with high photon energy incident on the light receiving surface 25.

(Third embodiment)
FIG. 4 shows a semiconductor radiation detector 3 according to the third embodiment. The semiconductor radiation detector 3 includes two semiconductor radiation detectors 2 each having a plurality of short sides 21 having the same length, a plurality of intervals 31 having the same length, and a distance 31 having a length equal to or greater than the short side 21. The active layer 20 of one semiconductor radiation detector 2 is fitted between the active layers 20 of the other semiconductor radiation detector 2 via an insulating layer 30 having an insulating function. By making the interval 31 longer than the short side 21, there is a space between one active layer 20 and the other active layer 20. This space is the insulating layer 30. The insulating layer 30 is composed of a space, an insulator, and the like.
The semiconductor radiation detector 3 can detect the one-dimensional intensity distribution of high-photon energy radiation incident on the light receiving surface 25 with high resolution because the light receiving surfaces 25 of the radiation are one-dimensionally arranged at high density. In the case of FIG. 4, the incident radiation 5 is the X axis, and the light receiving surface 25 is the YZ plane.

(Fourth embodiment)
FIG. 5 shows a semiconductor radiation detector 4 of the fourth embodiment. The semiconductor radiation detector 4 has two or more semiconductor radiation detectors 3 stacked. In the case of FIG. 5, the incident radiation 5 is the X axis, and the light receiving surface 25 is the YZ plane.

According to the semiconductor radiation detector 4, it is possible to detect a two-dimensional intensity distribution of high photon energy radiation irradiated on the light receiving surface 25 arranged on a two-dimensional surface formed by stacking two or more semiconductor radiation detectors 3. A two-dimensional image detector can be constructed.

The semiconductor radiation detector of the present invention can be applied in nuclear power plant accident countermeasures, radioactive waste processing and management, non-destructive inspection of materials and mechanical products, high energy astronomy, and the like.
Currently, bulk CdTe single crystals by THM method are mainly used for CdTe radiation detectors. However, CdTe crystals are extremely soft and fragile and are difficult to handle. In addition, it is extremely expensive because it is difficult to obtain high-quality crystals that can be used in the detector. On the other hand, the CdTe growth layer on the Si substrate used in the present invention is extremely easy to handle because it grows on the Si substrate having high mechanical strength. Growth is also done by metalorganic vapor phase epitaxy, and the thickness of the growth layer and the electrical characteristics of the growth layer can be controlled, so the detector can be manufactured and designed with a high degree of freedom, and the area can be increased. There are features. Therefore, it is possible to realize a detector that not only can replace the current bulk CdTe single crystal but also far surpasses its characteristics.

DESCRIPTION OF SYMBOLS 1 Semiconductor radiation detector 2 Semiconductor radiation detector 3 Semiconductor radiation detector 4 Semiconductor radiation detector 5 Incident radiation 6 Power supply 7 Detection part 8 Wiring 10 Substrate 11 Substrate length 12 Substrate length 19 1st electrode (positive electrode)
20 active layer 20a n-type active layer 20b p-type active layer 21 short side 22 long side 23 laminated thickness 25 light receiving surface 29 second electrode (negative electrode)
30 Insulating layer 31 Active layer spacing 40 Base

Claims (5)

A semiconductor radiation detector having a substrate (10) made of Si or GaAs and an active layer (20) for incident radiation (5) made of CdTe or CdZnTe stacked on the surface of the substrate (10), The substrate (10) has a rectangular shape, and the active layer (20) has one side having a long side (22) having the same length as the substrate length (12) of the substrate (10) and the other side being The substrate (10) has a rectangular shape having a short side (21) having a length smaller than the substrate length (11), and is composed of a laminated thickness (23) of the short side (21) and the active layer (20). One surface is a light receiving surface (25) for the incident radiation (5), the second electrode (29) bonded to the active layer (20) is a negative electrode, and the first electrode is bonded to the substrate (10). Power supply (6) for applying (19) to the positive electrode and detector (7) Semiconductor radiation detector, characterized in Rukoto (1). The laminate thickness (23) is 0.1 mm to 1 mm, the length of the short side (21) is 0.02 mm to 2 mm, and the length of the long side (22) is 10 mm to 200 mm. Semiconductor radiation detector (1) according to claim 1, characterized in that it is characterized in that On the substrate (10), two or more active layers (20) are arranged in parallel at an interval (31), the second electrode (29) of the two or more active layers (20) is a negative electrode, 3. The semiconductor radiation detector (2) according to claim 1 or 2, characterized in that the first electrode (19) is a common positive electrode. The semiconductor radiation detector (2) according to claim 3, wherein the short side (21) is the same, the interval (31) is the same, and the interval (31) is longer than the short side (21). An insulating layer having an insulating function between two active layers (20) of the semiconductor radiation detector (2) and an active layer (2) of the other semiconductor radiation detector (2). 30) A semiconductor radiation detector (3), which is fitted via 30). A semiconductor radiation detector (4), wherein two or more semiconductor radiation detectors (3) according to claim 4 are stacked.