CN115332377A - Double-groove type silicon carbide neutron detector - Google Patents

Abstract

The invention discloses a double-groove type silicon carbide neutron detector structure, which comprises: the device comprises a 4H-SiC substrate, a 4H-SiC epitaxial layer arranged above the 4H-SiC substrate, and a first groove and a second groove which are arranged on the front surface of the 4H-SiC epitaxial layer, wherein the first groove and the second groove are arranged in a staggered manner; neutron conversion material is arranged in the first groove ¹⁰ B powder, neutron conversion material in the second groove ⁶ LiF powder; and a P-type ohmic contact electrode is arranged on the table top on the front surface of the 4H-SiC epitaxial layer, and an N-type ohmic contact electrode is arranged on the table top on the back surface. Compared with the traditional silicon carbide neutron detector with a single-groove structure, the double-groove structure provided by the invention makes full use of ¹⁰ B and ⁶ LiF and thermal neutrons generate nuclear reaction, and intrinsic detection efficiency is greatly improved.

Description

A double-groove silicon carbide neutron detector

technical field

The invention relates to the field of semiconductor neutron detection, in particular to a double-groove silicon carbide neutron detector.

Background technique

Semiconductor neutron detectors are generally composed of neutron conversion materials and semiconductor diodes. Since neutrons are not charged, ionization reactions will not occur when passing through semiconductor materials, but neutrons will undergo nuclear reactions with conversion materials to produce secondary charged particles. , these secondary charged particles can ionize a large number of electron-hole pairs when passing through the semiconductor diode device, and the detection of neutrons can be realized indirectly by collecting these electron-hole pairs through external electrodes. Neutron detectors are widely used in cosmic ray detection and radiation detection on spacecraft, as well as nuclear power measurement of reactor nuclear materials and distribution measurement of neutron fluence rate in the core.

Neutron detectors based on conventional semiconductor materials such as silicon (Si) and germanium (Ge) can only operate in low temperature or normal temperature environments, and radiation damage will also reduce their performance, so they cannot be used in extreme environments such as high temperature and strong radiation. Neutron detection. The neutron detector based on the third-generation wide-bandgap semiconductor material 4H-SiC has many advantages such as good energy linearity, wide bandgap energy, high temperature resistance, and radiation resistance. Compared with 3He proportional counter tubes, plastic scintillator detectors and conventional semiconductor neutron detectors, 4H-SiC neutron detectors have incomparable advantages.

The neutron detection efficiency of the planar silicon carbide neutron detector will not be higher than 5% due to the self-absorption of the neutron conversion material. The trench-type silicon carbide neutron detector can greatly improve the neutron detection efficiency by increasing the filling amount of the conversion material and the probability of secondary particles entering the SiC detector. The single-trench silicon carbide neutron detector can etch multiple trenches with the same width in a single cell, and then fill the trenches with neutron conversion material, compared with the traditional single-trench Structural neutron detectors are filled with a single neutron conversion material, resulting in low intrinsic detection efficiency.

Contents of the invention

The invention provides a double-groove silicon carbide neutron detector to overcome the problem of low detection efficiency of the traditional single-groove structure neutron detector.

In order to achieve the above object, technical scheme of the present invention is:

A double-trench silicon carbide neutron detector, comprising: a 4H-SiC substrate, a 4H-SiC epitaxial layer, a P ⁺ region formed by ion implantation, a plurality of first trenches and second trenches with different widths;

The 4H-SiC epitaxial layer is above the 4H-SiC substrate, and the front side of the 4H-SiC epitaxial layer is provided with a first groove and a second groove, and the first groove and the second groove are arranged alternately;

The P ⁺ region formed by the ion implantation is on the inner wall, bottom surface and step surface of the first trench and the second trench;

The neutron conversion material is within the first trench and the second trench.

Further, it also includes a P-type ohmic contact electrode and an N-type ohmic contact electrode, the P-type ohmic contact electrode is above the P ⁺ region formed by ion implantation on the 4H-SiC epitaxial layer mesa, and the N-type ohmic contact electrode The electrodes are on the back of the 4H-SiC epitaxial layer.

Further, the neutron conversion material includes ¹⁰ B powder and ⁶ LiF powder, the ¹⁰ B powder is in the first groove, and the ⁶ LiF powder is in the second groove.

Further, the first groove has a width in the range of 1-10 μm, and the second groove has a width in the range of 10-50 μm.

Further, the depths of the first groove and the second groove are both 25 μm.

Further, the width of the mesa region of the 4H-SiC epitaxial layer between the first trench and the second trench is in the range of 1-10 μm.

Beneficial effects: Compared with the traditional single-groove silicon carbide neutron detector, the dual-groove silicon carbide neutron detector proposed by the present invention makes full use of the characteristics of nuclear reactions between ¹⁰ B and ⁶ LiF and thermal neutrons , because ¹⁰ B has a large thermal neutron capture cross-section, but the reaction product has low energy and short range, so it is filled inside the trench with a small trench width, which can not only ensure the neutron absorption amount but also ensure that the reaction product is very small. It is easy to enter the SiC detector area; the reason why the ⁶ LiF material is filled inside the trench with a larger trench width is that the reaction product of ⁶ LiF and thermal neutrons has higher energy and can easily enter the SiC detector area. In view of the current situation that silicon carbide can only be used for shallow trench etching technology, compared with the single trench structure, the double trench structure can greatly improve the intrinsic detection efficiency without increasing the trench depth.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description These are some embodiments of the present invention. For those skilled in the art, other drawings can also be obtained according to these drawings without any creative effort.

Fig. 1 is a schematic structural diagram of a traditional planar silicon carbide neutron detector in the prior art;

Fig. 2 is a schematic structural diagram of a traditional single-groove silicon carbide neutron detector in the prior art;

Fig. 3 is a schematic structural diagram of a double-groove silicon carbide neutron detector of the present invention;

Figure 4 is a schematic diagram of the variation of detection efficiency of three structures with LLD;

Figure 5 is a schematic diagram of the comparison of detection efficiencies of the three structures;

Figure 6 is the energy deposition spectrum of the three structures.

Reference signs: 1. 4H-SiC substrate; 2. 4H-SiC epitaxial layer; 3. P ⁺ region formed by ion implantation; 4. P-type ohmic contact electrode; 5. N-type ohmic contact electrode; 6. First Groove; 7, the second groove.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments It is a part of embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

Example 1

This embodiment provides a double-trench type silicon carbide neutron detector, as shown in FIG. The first trenches 6 with a width of 2.5 μm and the second trenches 7 with a width of 15 μm are opened on the front surface of the 4H-SiC epitaxial layer 2, the first trenches 6 and the second trenches 7 are alternately arranged, and the first A trench 6 is backfilled with a neutron conversion material ^10B , and the second trench 7 is backfilled with a neutron conversion material ⁶ LiF; the side walls, bottom surfaces and surfaces of the first trench 6 and the second trench 7 The mesa has a P ⁺ region 3 formed by ion implantation; the 4H-SiC epitaxial layer 2 is provided with a P-type ohmic contact electrode 4 on the front mesa, and an N-type ohmic contact electrode 5 on the back mesa.

As shown in Figure 1, it is a traditional planar silicon carbide neutron detector, and only a layer of neutron conversion material is deposited on the front of the 4H-SiC diode;

As shown in Figure 2, it is a single-groove silicon carbide neutron detector, and only grooves are etched at equal intervals on the front side of the 4H-SiC epitaxial layer 2, and then the same neutron conversion material is backfilled into the grooves;

Compared with the planar and single-groove silicon carbide neutron detectors shown in Fig. 1 and Fig. 2, a double-groove silicon carbide neutron detector provided by the present invention can not only increase the neutron conversion material The amount of filling can also be backfilled with two types of neutron conversion materials in trenches of different widths, further improving the intrinsic detection efficiency.

Example 2

In this embodiment, as shown in Figure 4, the Monte Carlo software Geant4 is used to perform simulation verification and comparative discussion on the intrinsic neutron detection efficiency of the neutron detector structures of the three structures shown in Figure 1, Figure 2, and Figure 3 , to verify the advantages of the double-groove silicon carbide neutron detector structure proposed by the present invention.

In this embodiment, when the value is the best solution: the width of the first groove 6 is 2.5 μm, the width of the second groove 7 is 15 μm, and the depths of the first groove 6 and the second groove 7 are both When the mesa region width of the 4H-SiC epitaxial layer 2 between the first trench 6 and the second trench 7 is 25 μm and the width is 2 μm, the detection efficiency of the planar neutron detector has the smallest change with the LLD, that is, the stability is the most Good; while the detection efficiency of the double-groove neutron detector varies the most with the LLD, that is, the stability is the worst. The existence of gamma rays and background noise will interfere with the energy spectrum measurement results of the detector, but in practical applications, these interferences can be completely filtered out by setting the LLD to 300keV. In addition, when the LLD is 300keV, the double-groove neutron detector has the highest detection efficiency, which significantly improves the detection performance of the device.

Example 3

In the present embodiment, as shown in Figure 5, it is the comparison of the detection efficiency when the LLD is set at 300keV for three kinds of neutron detector structures, it can be seen that when the value is the best solution in the embodiment 2, the same as Compared with the planar structure, the neutron detection efficiency of the single-groove detector is increased by 3.5%; and compared with the single-groove structure, the neutron detection efficiency of the double-groove detector is increased by 4.6%. Obviously, the double-groove silicon carbide neutron detector proposed by the present invention can effectively improve the detection efficiency; The structure can improve the neutron detection efficiency as much as possible within the limited groove depth.

Example 4

In this embodiment, as shown in FIG. 6 , it is the energy deposition spectrum of neutron detectors with three structures. In order to satisfy the law of conservation of momentum, the products of the nuclear reaction between thermal neutrons and neutron conversion materials will be ejected in two opposite directions. Therefore, for planar SiC neutron detectors, only one secondary particle can enter the SiC region and be detected after each nuclear reaction, while for trench SiC neutron detectors, after each nuclear reaction, two secondary particles Class particles can enter the silicon carbide detector together. Combined with the energy deposition spectrum in Figure 6, it can be found that the thin-film coating detector can see an obvious α peak on the left side of 2.05MeV, and an obvious 3H peak can be seen on the left side of 2.73MeV, and the energy cutoff value is higher energy The energy value of the 3H particle. In summary, the counts of single-groove detectors are higher than those of thin-film coating detectors in the entire energy spectrum, and there are counts with energy higher than 2.73MeV in the energy spectrum, which is formed by the entry of α and 3H particles into the silicon carbide region. high energy peak.

Compared with the single-trench detector, the count of the double-trench neutron detector increases significantly in the low-energy region and only slightly decreases in the high-energy region, which is mainly due to the lower energy of the reaction products of thermal neutrons and ¹⁰ B. Low, thus contributing a large number of low-energy range counts. Since the surface area of the detector is fixed at 1x1 cm ² , insertion of the ¹⁰ B trench will result in a decrease in the filling of ⁶ LiF and a slight reduction in the number of reaction products between ⁶ LiF and thermal neutrons, resulting in a slight decrease in the number of high energy regions. For single-trench and double-trench neutron detectors, secondary particles can only deposit part of their energy in the SiC region due to the small gap between the trenches, resulting in a large number of counts in the low-energy range below 1 MeV, Therefore, when the LLD increases from 0 to 1 MeV, the detection efficiency of the trench detector will drop significantly. In addition, the high thermal neutron absorption cross-section of the ¹⁰ B groove will increase the absorption probability of thermal neutrons, greatly increase the count in the low-energy region, and only slightly reduce the count in the high-energy region, which is also the advantage of the double-trench silicon carbide neutron detector. The intrinsic reason why the intrinsic detection efficiency is significantly improved compared with the single trench structure.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: It is still possible to modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the various embodiments of the present invention. scope.

Claims (6)

1. A double trench type silicon carbide neutron detector, comprising:

4H-SiC substrate (1), 4H-SiC epitaxial layer (2), P formed by ion implantation ⁺ A region (3), a plurality of first trenches (6) and second trenches (7) of different widths;

the 4H-SiC epitaxial layer (2) is arranged above the 4H-SiC substrate (1), the front surface of the 4H-SiC epitaxial layer (2) is provided with first grooves (6) and second grooves (7), and the first grooves (6) and the second grooves (7) are arranged in a staggered mode;

p formed by the ion implantation ⁺ The region (3) is arranged on the inner wall, the bottom surface and the step surface of the first groove (6) and the second groove (7);

the first groove (6) and the second groove (7) are filled with neutron conversion materials.

2. The double-channel silicon carbide neutron detector of claim 1, wherein the neutron conversion material comprises ¹⁰ B powder and ⁶ LiF powder, said ¹⁰ B powder is in the first groove (6), the ⁶ LiF powder is in the second groove (7).

3. The double-trench type silicon carbide neutron detector of claim 1, further comprising a P-type ohmic contact electrode (4) and an N-type ohmic contact electrode (5), wherein the P-type ohmic contact electrode (4) is formed by ion implantation of P on the mesa of the 4H-SiC epitaxial layer (2) ⁺ And the N-type ohmic contact electrode (5) is arranged on the back surface of the 4H-SiC epitaxial layer (2) above the region (3).

4. The silicon carbide neutron detector of claim 1, wherein the width of the first trench (6) is in the range of 1-10 μm, and the width of the second trench (7) is in the range of 10-50 μm.

5. The double-trench silicon carbide neutron detector of claim 1, wherein the first trench (6) and the second trench (7) are both 25 μm deep.

6. The double-trench silicon carbide neutron detector of claim 1, wherein the width of the mesa region of the 4H-SiC epitaxial layer (2) between the first trench (6) and the second trench (7) ranges from 1 μ ι η to 10 μ ι η.

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