JPS61174778A - Semiconductor radiation detector - Google Patents

Abstract

PURPOSE:To detect radiation, by exposing a crystal semiconductor substrate in hydrogen plasma beforehand, introducing hydrogen, thereby detecting electron- hole pairs, which are generated by the radiation inputted in a depletion layer. CONSTITUTION:A P-type Si single crystal substrate 1 is placed on a lower electrode plate 13 and heated to about 200 deg.C. A voltage of about 560 V is applied in an hydrogen atmosphere of about 4torr, and hydrogen plasma is yielded between the upper and lower electrode plates 12 and 13. A large amount of hydrogen is implanted 2 from the surface of the single crystal substrate 1. For example, a Schottky barrier electrode 3 and an ohmic electrode 4 are attached. A reverse bias is applied, and a depletion layer is formed beneath the electrode 3. Incident quick neutrons hit the hydrogen and their speed is reduced. Thus a thermal neutron beam is formed. During this process, alpha rays are generated. The alpha rays are inputted in the depletion layer and electrons/hole pairs are formed, The pairs are counted as pulses, and, as a result, the neutron beam can be detected. In comparison with a conventional ionization chamber, the detector is rigid and can be operated by a low voltage.

Description

[Detailed description of the invention] [Technical field to which the invention pertains]

The present invention relates to a semiconductor radiation detector that detects neutron beams using hydrogen.

[Prior art and its problems]

Semiconductor radiation detectors have a diode structure such as a p-n junction type or a Shore-Key junction type. A reverse bias is applied to this junction to widen the depletion layer, radiation is incident into the depletion layer, and its trajectory is detected. Radiation is detected by counting the electron-hole pairs generated. In this method, α, β, γ,
It is possible to detect radiation that has an ionizing effect, such as X-rays. However, since neutron beams have no charge, they do not have any effect on the orbital electrons or the Coulomb field of the atomic nucleus other than nuclear reactions, and therefore no electron-hole pairs are generated.
The semiconductor radiation detector as described above is unsuitable for detecting neutron beams as it is. Semiconductor neutron beam detectors use the boron isotope 16B (
In addition to those using conversion of n, α), those using hydrogen are known. The principle of neutron beam detection using hydrogen is as follows. When a neutron beam collides with a nucleus with a large atomic number, it is simply bounced back and does not easily lose energy; however, when it collides with a hydrogen atom, most of its energy is transferred to the hydrogen atom. Therefore, the neutrons are decelerated and become thermal neutrons. This process produces excited hydrogen nuclei, which emit gamma rays and return to the ground state. By detecting the emitted gamma rays, neutron beams can be detected. However, it is not easy to fix hydrogen in a solid-state detection element, and it has not been easy to realize the above-mentioned principle. For example, as a semiconductor neutron detection element using this principle, there is one in which a plate containing a large amount of hydrogen, such as a polyethylene plate, is placed on the front surface of a semiconductor radiation detection element. but,
This is not practical because the structure becomes complicated and the detection efficiency is poor. Furthermore, a semiconductor neutron detector using hydrogenated amorphous silicon has been proposed because it contains a large amount of hydrogen. This is known from Japanese Patent Application Laid-Open No. 114382/1982, and a semiconductor neutron detection element using hydrogenated amorphous silicon or amorphous germanium was proposed, and a p-1-n structure was formed using an amorphous semiconductor. A prepared example is disclosed. Currently, amorphous silicon is used in various fields including solar cells, and is extremely easy to create. However, most of this amorphous silicon uses hydrogen to compensate for dangling bonds, and a large amount of It takes in hydrogen. The above proposal that focuses on this point is an extremely effective idea,
Another advantage is that hydrogen is fixed within the element itself. However, amorphous semiconductors have an extremely short lifetime and cannot function as a semiconductor radiation detector. That is, even if electron-hole pairs are generated in the depletion layer of an amorphous semiconductor by the incident radiation, their lifetime is extremely short and they cannot be taken out as a signal to the outside.

[Purpose of the invention]

In contrast, it is an object of the present invention to provide a semiconductor radiation detector that uses a crystalline semiconductor with a long lifetime, has hydrogen fixed in the semiconductor substrate itself, and has high efficiency in detecting neutron beams.

[Key points of the invention]

The present invention is a semiconductor radiation detector that detects radiation by detecting electron-hole pairs generated by radiation incident on a depletion layer spread within a crystalline semiconductor substrate. By introducing hydrogen into the interior, neutron detection can also be performed using the (n+γ) reaction, thereby achieving the above objective.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram of an apparatus for introducing hydrogen into a silicon single crystal substrate according to the present invention. This is a normal plasma generator that introduces hydrogen gas into a reaction tank and generates hydrogen plasma using a DC voltage. For this purpose, an upper electrode plate 12. A lower electrode plate 13 is arranged and connected to a DC power source 14, and a hydrogen gas cylinder 15. An exhaust system 17 and a vacuum gauge 18 are connected, and the lower electrode plate 13 is equipped with a heater 19. As shown in Figure 1, silicon single crystal [(specific resistance 10 k
Ω, P type) ■ is placed on the lower electrode plate 13 and heated to 200° C. by the heater 19. The internal pressure of the reaction tank 11, which has been evacuated by the exhaust system 17, is set to 4. Hydrogen is introduced from the hydrogen gas cylinder 15 to achieve Q Torr, and the electrode 12 is
, 13, 560V is applied using the voltage a[14]. This voltage application generates hydrogen plasma between the electrodes 8i12.13. Although the exact reason is not yet known, a large amount of hydrogen enters from the surface of the silicon single crystal plate 1 placed on the lower electrode plate 13. The concentration of hydrogen that entered was measured using a secondary ion mass spectrometer (SIMS). The results are shown in FIG. As you can see from this figure, the silicon single crystal surface has 1×102! Hydrogen is present at a high concentration of atoms/cd. A neutron beam is detected by the method described above using the hydrogen introduced into the silicon single crystal. For this purpose, we fabricated a radiation detector using a silicon single crystal containing hydrogen. An example is shown below. FIG. 3 shows a Schottky junction type detection element. A silicon single crystal plate 1 has a hydrogen penetration region 2 . A metal forming a Schottky barrier with the silicon single crystal plate 1 was attached as an electrode 3, while an ohmic electrode 4 was attached to the lower surface of the silicon single crystal plate. A reverse bias is applied between the two electrodes 3 and 4 to form a depletion layer from below the electrode 3. The incident fast neutron beam collides with hydrogen in the silicon single crystal plate 1 and transfers its energy to hydrogen atoms. For this reason, the neutrons are decelerated and become thermal neutrons. In this process, gamma rays are generated as described above. When this gamma ray enters the formed depletion layer, it generates electron-hole pairs, which are counted as a pulse, resulting in the detection of a neutron beam. Although FIG. 3 shows an element with the simplest structure, FIG. 4 is an improved version of FIG. 3. The embodiment shown in FIG. 4 is an example in which the method of infiltrating hydrogen into a silicon single crystal using hydrogen plasma described above is applied to both sides of a silicon single crystal. Therefore, as shown in FIG. 4, the structure is such that 8-14 hydrogen penetration regions 2 are provided above and below the element to increase the chances of r-ray generation. Figure 5 shows a p
This is characterized by the infiltration of boron at a high concentration by a low-temperature plasma doping method, and the other structure is the same as that of the embodiment shown in FIG. This low-temperature plasma doping method is a pass-) Myoii Anki 6?
It is disclosed in detail in the specification of Japanese Patent Application No. 4-6 Japanese Patent Application No. 58-93218. In the embodiment shown in FIG. 6, a high purity silicon plate (
An amorphous silicon layer 6 is deposited on the p-type (p-type, specific resistance 10 kΩ1 or more) 1 by plasma CVD method using monosilane gas, and monocrystalline silicon (c-3t) and amorphous silicon (a -5t). The conditions of plasma CVD for depositing the amorphous silicon layer 6 on the single crystal silicon substrate l are as follows. Gas used: Monosilane (Silt) 10% hydrogen base pressure: 10. OTorr applied voltage: 80
0V (DC) Electrode plate temperature: 200°C Under the above conditions, the amorphous silicon layer 6 with a thickness of approximately IIrm
is formed. In the detector structure shown in FIG. 6, the hydrogen penetration layer 2 is formed in advance by the method described above, and then an amorphous silicon layer is formed by the plasma CVD method. Electric 8ii4
and 7 are ohmic electrodes deposited by vacuum evaporation, electron beam evaporation, sputtering, or the like. FIG. 7 shows an improved version of the device shown in FIG. 6, with p for ohmic contact on the back side as in the case of FIG. Layer 5 is formed by low-temperature plasma doping of boron. Hydrogen penetration layer 2. The formation of the electrodes 4 and 7 is the same as the device shown in FIG. This improvement results in lower noise levels and improved temperature characteristics than the device shown in FIG. The detector shown in FIGS. 6 and 7 applies a reverse bias to the heterojunction between c-3t and a-5i between electrodes 4 and 7 to form a depletion layer in the single crystal silicon plate 1. spread. In addition to the plasma doping method described above, in which a large amount of hydrogen penetrates into single crystal silicon, amorphous silicon also contains hydrogen, and as mentioned above, fast neutron beams collide with this hydrogen. Gamma rays are generated by the reaction process, and the gamma rays enter a depletion layer spread in single crystal silicon to form electron-hole pairs, resulting in neutron detection. Single-crystal silicon used in semiconductor radiation detectors is a normal I
It has high specific resistance and high purity, unlike silicon used in C or individual semiconductors. Therefore, the high temperature process L-t4IjIE11! used in the normal semiconductor device manufacturing process! Insect killer dog J th m +, +su/<1') 1111
'+' 137 T/7'1 The detector was fabricated using a low-temperature process without deteriorating the lifetime of single crystal silicon. It is obvious that it can detect α, β, r, and X-rays in addition to neutron beams.
It can also be manufactured using crystals of compound semiconductors such as S, CdTe, and the like.

【Effect of the invention】

The present invention was able to solidify a radiation detector that detects neutron beams by fixing hydrogen in a long-life crystalline semiconductor using a unique method called plasma doping. This is superior to conventional ionization chambers that use gas as a sensor medium, and is superior in terms of small size, light weight, robustness, low voltage operation, and low cost, and the effects obtained are far greater.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the structure of a hydrogen plasma generator used to carry out the present invention, FIG. 2 is a hydrogen concentration distribution diagram in a single crystal silicon plate into which hydrogen has been introduced by the device shown in FIG. 1, and FIGS. FIG. 7 is a sectional view showing different embodiments of the present invention. 1: Silicon single crystal plate, 2: Hydrogen penetration region, 3: Schittky barrier ti, 4, 7: Ohmic electrode, 6: aS
i layer, 11: reaction tank, 12, 13: electrode plate, 15: hydrogen gas cylinder, 17: exhaust system. Sai1zu 暉、'Cplfn) -FZ线'I'3图 Sai4 .

Claims (1)

[Claims] 1) In a device that detects radiation by detecting electron-hole pairs generated by radiation incident on a depletion layer spread within a crystalline semiconductor substrate, the semiconductor substrate is exposed to hydrogen plasma in advance to generate hydrogen inside it. A semiconductor radiation detector characterized by being introduced.