JPS60240161A - Semiconductor radiation detector - Google Patents

Abstract

PURPOSE:To obtain a detector, in which neutron nuclear transformation reaction material need not be mounted on the front surface in order to detect thermal neutron-rays, by forming a film comprising boron on the surface of the semiconductor substrate of a detecting element or on the surface of an electrode. CONSTITUTION:In the case of a detecting element having a surface barrier structure, e.g., aluminum is evaporated in a vacuum for barrier metal 6, and gold is evaporated in a vacuum for an ohmic contact electrode 7 for P type silicon. A boron film 8 is formed on at least one surface of said electrodes 6 and 7. A reverse voltage is applied to the element having the surface barrier structure. When thermal neutron rays 4 are inputted under this state, alpha rays are generated by the reaction of the neutron transformation <10>B+n <7>Li+alpha in the boron film 8. Pairs of electrons and holes are generated in a depletion layer by the alpha rays, and a current flows. Therefore the thermal neutron rays can be detected. When the boron films 8 are formed on both surfaces of the electrodes 6 and 7, the alpha rays, which are generated on the back surface, are detected. Therefore, the detecting efficiency of the thermal neutron is further enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention 1 relates to a semiconductor radiation detector that detects radiation including thermal neutron beams.

[Prior art and its problems]

As a typical example of the semiconductor radiation detector is shown in FIG.
Region 2 is formed, and radiation is detected by a current flowing between both electrodes on both sides (not shown) based on electron-hole pairs generated when radiation enters a depletion layer created by applying a reverse voltage to this Pn junction. It is something.

However, since neutron beams have no electric 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. For this reason,
Transmits a neutron beam through a material with a large neutron absorption cross section,
The neutron transmutation reaction generates alpha rays, which generate electron-hole pairs in the depletion layer. That is, conventionally, the window portion K where radiation enters the silicon plate 1 of the detector
.

For example, a Boral plate 3 containing boron is attached, and a thermal neutron beam 4 is attached.
B(n) of the isotope of boron, which is about five orders of magnitude larger than the neutron absorption cross section in boron upon incidence of B.

α) Generate α-rays 5 using the reaction and detect them.

[Purpose of the invention]

An object of the present invention is thus to provide a semiconductor radiation detector that does not require a front-facing neutron transmutation reaction material for thermal neutron beam detection.

[Key points of the invention]

This invention forms a film made of boron on the surface of a semiconductor substrate or an electrode of a detection element, and B(n) of isotope B present in the boron-free film.

α) It is possible to detect neutron beams by generating α rays using reactions and detecting these α rays.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings. In each figure, parts common to those in FIG. 8 are given the same reference numerals. In FIGS. 1 to 7, 6 and 7 are electrodes formed on both sides of this detection element, and radiation is transmitted to the semiconductor substrate 1.
This is for extracting as a pulse signal electron-hole pairs generated by interacting with crystals in the depletion layer generated when a reverse bias voltage is applied.

1 and 2 show the case of a detection element having a surface barrier type structure, for example, in P-type silicon, aluminum is vacuum-deposited as the barrier metal 6, and gold is vacuum-deposited as the ohmic contact electrode 7. A porosity removal film 8 is formed on at least one surface of the electrodes 6 and 7. When a thermal neutron beam 4 is incident on an element with this surface barrier type structure while a reverse voltage is applied, "B+n→'7 L i+α
α rays 5 are generated by the neutron transmutation reaction, and the α rays generate electron-hole pairs in the depletion layer, causing current to flow, so thermal neutron beams can be detected. When the boron removal film 8 is formed on the surfaces of both electrodes 6 and 70, as shown in FIG. 2, the alpha rays generated on the back surface are also detected, so the thermal neutron detection efficiency is lower than that shown in FIG. Even higher than the example.

3, 4, and 5 show the case of a Pn junction type radiation detection element, in which a boron removal film 8 is selectively formed on an n-type silicon substrate 9. A boron interstitial layer, ie, two layers 10, is formed on the n-type silicon substrate 9 directly under the boron removal film 8. Since this P layer has an extremely high boron concentration of 10 to 10 atoms/CrIL3, it efficiently detects thermal neutron beams. Furthermore, in order to improve the detection efficiency of thermal neutron beams, a boron removal film 8 is also formed on the surfaces of the electrodes 6 and 7, as shown in FIGS. 4 and 5. As a result, the same effect as in Figure 2 can be obtained.

Figures 6 and 7 show surface barrier type and Pnn junction tank structure detection elements using a P-type silicon substrate.
A KP+ layer 10, that is, an ohmic contact layer, is formed directly under the electrode -H, and a boron removal film 8 is also formed on the electrode -H.

The above-mentioned boron removal film is produced by storing the substrate to be deposited in a vacuum container, heating it to a predetermined temperature, for example, 300'O, and introducing diborane gas into the container to generate a glow discharge in the container. It is preferable to form the boron-free film by decomposing the gas and depositing a boron-free film on the substrate. The boron concentration at this time is 1023 cm/cr/L3 or more, and the thickness of the boron removal film is about 500A. The above-mentioned method for forming a porosity-free film and the formation of a highly doped region on the surface of a semiconductor substrate by depositing a boron-free film are described in Patent Application Nos. 58-93218 and 58-58 filed by the present applicant. 9
See specification No. 3220. Of course, this boron removal film contains 11B and 10B at a ratio of 4:1, so the content of 10B is 17. It's nothing more than that. However, the boron concentration of the boron-free film formed in this way was 10
Since it is more than 23 atoms/α3, for example, JP-A-57-8
Compared to the amount of ion implantation that forms a boron layer by mass-separating only B as shown in Publication No. Efficiency is increased.

Since the structure itself of the radiation detector according to the present invention is similar to that of conventional detectors, it is naturally possible to detect radiation other than thermal neutron beams. For example, in the case of r-rays, curve 1 in Figure 5 is used to detect secondary electron beams due to the photoelectric effect and Compton effect.
1, the output shows a continuous spectrum with respect to the pulse height, so it can be clearly distinguished from the pulse height of the thermal neutron beam shown in curve 1. Furthermore, if a polyethylene plate is placed in the entrance window, fast neutron beams can also be detected. That is, when a fast neutron beam is incident on a polyethylene plate, protons knocked out by elastic collisions enter the depletion layer and generate electron-hole pairs, so it can be detected like other radiation.

The semiconductor substrate used here may be a compound semiconductor such as GaAg or CdTe in addition to the above-mentioned silicon or germanium, but the temperature at which the silicone-free film is formed is 300°C.
Because of the following, it does not impair crystallinity and is effective as a radiation detector including neutron beams.

〔Effect of the invention〕

According to the present invention, thermal neutron beams can be detected without attaching a neutron transmutation reactant to the front surface of a radiation detection element as in the prior art. Moreover, since this boron-free film is in close contact with the radiation detection element, B(n
, α) Since the α rays generated by the reaction efficiently penetrate into the semiconductor substrate, the detection efficiency of thermal neutron beams is increased, and at the same time, the thickness of the matrix removal film is approximately 50 OA, and the width of the dead layer is also reduced. Can be made extremely thin. As a result, there is no particular problem in detecting α rays and low energy β rays and γ rays.

[Brief explanation of the drawing]

1 to 7 are cross-sectional views showing different embodiments of the present invention, FIG. 8 is a cross-sectional view showing an example of detecting a thermal neutron beam using a conventional semiconductor radiation detector, and FIG. 9 is a cross-sectional view showing an example of detecting a thermal neutron beam using a conventional semiconductor radiation detector. FIG. 3 is a diagram illustrating the output pulse height of a detector. 1...P-type silicon substrate, 4...thermal neutron beam, 5...
・・・α ray, 6, 7... Electrode, 8... Base removal membrane, 9
. . . N-type silicon substrate, 10 . . . P region. Talent 1, genius 2? 3 Sensai Otsu (3) Sai 5 Sen

Claims (1)

[Scope of Claims] 1) A semiconductor radiation detector characterized in that the surface K of at least one of the surface of a semiconductor substrate and the surface of an electrode formed on the semiconductor substrate has a boron coating layer. . 2. The semiconductor according to claim 1, wherein the boron coating layer is formed on the surface by glow discharge in an atmosphere containing diborane gas. Radiation detector.