A double-groove silicon carbide neutron detector

Abstract

The present invention discloses a double-groove silicon carbide neutron detector structure, comprising: a 4H-SiC substrate, a 4H-SiC epitaxial layer arranged on the 4H-SiC substrate, a first groove and a second groove opened on the front of the 4H-SiC epitaxial layer, wherein the first groove and the second groove are arranged alternately; a neutron conversion material is arranged in the first groove; 10 B powder, neutron conversion material is provided in the second groove 6 LiF powder; a P-type ohmic contact electrode is provided on the front surface of the 4H-SiC epitaxial layer, and an N-type ohmic contact electrode is provided on the back surface. Compared with the traditional single-groove structure silicon carbide neutron detector, the double-groove structure proposed in the present invention makes full use of 10 B and 6 The characteristic of LiF's nuclear reaction with thermal neutrons greatly improves the intrinsic detection efficiency.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor neutron detection, and in particular to a double-groove silicon carbide neutron detector. Background Art

[0002] Semiconductor neutron detectors are generally composed of neutron conversion materials and semiconductor diodes. Since neutrons are uncharged, they do not undergo ionization reactions when passing through the semiconductor material. However, they undergo nuclear reactions with the conversion material, producing secondary charged particles. These secondary charged particles can ionize a large number of electron-hole pairs when passing through the semiconductor diode device. These electron-hole pairs are collected by external electrodes, indirectly detecting the neutrons. Neutron detectors are widely used in spacecraft for cosmic ray and radiation detection, as well as for measuring the nuclear power of reactor nuclear materials and the distribution of neutron fluence in the core.

[0003] Neutron detectors based on conventional semiconductor materials such as silicon (Si) and germanium (Ge) can only operate at low or room temperatures, and radiation damage can also degrade their performance. Therefore, they cannot be used for neutron detection in extreme environments such as high temperatures and intense radiation. Neutron detectors based on the third-generation wide-bandgap semiconductor material 4H-SiC offer numerous advantages, including excellent energy linearity, a wide bandgap energy, high-temperature resistance, and radiation resistance. Compared to 3He proportional counters, plastic scintillator detectors, and conventional semiconductor neutron detectors, 4H-SiC neutron detectors offer unparalleled advantages.

[0004] Due to the self-absorption of the neutron conversion material, the neutron detection efficiency of planar silicon carbide neutron detectors is no more than 5%. However, trench-type silicon carbide neutron detectors can significantly improve neutron detection efficiency by increasing the amount of conversion material filled and the probability of secondary particles entering the SiC detector. Single-trench silicon carbide neutron detectors can etch multiple grooves of the same width in a single cell, and then fill the grooves with neutron conversion material. In comparison, traditional single-trench structure neutron detectors have lower intrinsic detection efficiency due to the single neutron conversion material filled. Summary of the Invention

[0005] The present invention provides a double-groove silicon carbide neutron detector to overcome the problem of low detection efficiency of traditional single-groove structure neutron detectors.

[0006] In order to achieve the above object, the technical solution of the present invention is:

[0007] A double-trench silicon carbide neutron detector, comprising: a 4H-SiC substrate, a 4H-SiC epitaxial layer, a P-type ion implanted + region, a plurality of first trenches and second trenches of different widths;

[0008] The 4H-SiC epitaxial layer is above the 4H-SiC substrate, and a first trench and a second trench are formed on the front surface of the 4H-SiC epitaxial layer, wherein the first trench and the second trench are arranged in a staggered manner;

[0009] The P formed by ion implantation + The area is on the inner wall, bottom surface and step surface of the first groove and the second groove;

[0010] The neutron conversion material is within the first trench and the second trench.

[0011] Furthermore, it also includes a P-type ohmic contact electrode and an N-type ohmic contact electrode, wherein the P-type ohmic contact electrode is formed by ion implantation on the 4H-SiC epitaxial layer table. + The N-type ohmic contact electrode is located above the 4H-SiC epitaxial layer.

[0012] Furthermore, the neutron conversion material includes 10 B powder and 6 LiF powder, 10 B powder is in the first groove, 6 LiF powder is in the second groove.

[0013] Furthermore, the width of the first groove is in the range of 1-10 μm, and the width of the second groove is in the range of 10-50 μm.

[0014] Furthermore, the depth of the first groove and the second groove are both 25 μm.

[0015] Furthermore, 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.

[0016] Beneficial effect: Compared with the traditional single-groove silicon carbide neutron detector, the double-groove silicon carbide neutron detector proposed in the present invention makes full use of 10 B and 6 The characteristics of LiF's nuclear reaction with thermal neutrons are due to 10 B has a larger thermal neutron capture cross section, but the reaction product has low energy and short range, so it is filled inside the groove with a smaller groove width, which can ensure the absorption of neutrons and ensure that the reaction products can easily enter the SiC detector area; filling inside the groove with a larger groove width 6 LiF material is because 6 The reaction products of LiF and thermal neutrons are highly energetic and easily enter the SiC detector area. Given that silicon carbide can only be etched in shallow trenches, the dual-trench structure significantly improves intrinsic detection efficiency without increasing the trench depth compared to the single-trench structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0018] Figure 1 This is a schematic diagram of the structure of a traditional planar silicon carbide neutron detector in the prior art;

[0019] Figure 2 This is a schematic diagram of the structure of a traditional single-groove silicon carbide neutron detector in the prior art;

[0020] Figure 3 This is a schematic structural diagram of a double-groove silicon carbide neutron detector according to the present invention;

[0021] Figure 4 It is a schematic diagram of the change of detection efficiency of three structures with LLD;

[0022] Figure 5 It is a comparative diagram of the detection efficiency of the three structures;

[0023] Figure 6 are the energy deposition spectra of the three structures.

[0024] Reference numerals: 1, 4H-SiC substrate; 2, 4H-SiC epitaxial layer; 3, P formed by ion implantation + region; 4. P-type ohmic contact electrode; 5. N-type ohmic contact electrode; 6. first trench; 7. second trench. DETAILED DESCRIPTION

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0026] Example 1

[0027] This embodiment provides a double-groove silicon carbide neutron detector, such as Figure 3As shown, it includes: a 4H-SiC substrate 1, a 4H-SiC epitaxial layer 2 arranged on the 4H-SiC substrate 1, a first trench 6 with a width of 2.5 μm and a second trench 7 with a width of 15 μm opened on the front of the 4H-SiC epitaxial layer 2, the first trench 6 and the second trench 7 are arranged alternately, and the first trench 6 is backfilled with neutron conversion material 10 B, the second groove 7 is backfilled with neutron conversion material 6 The sidewalls, bottom surfaces and terraces of the first and second trenches 6 and 7 are all formed by ion implantation of P + Region 3; the 4H-SiC epitaxial layer 2 has a P-type ohmic contact electrode 4 on the front surface and an N-type ohmic contact electrode 5 on the back surface.

[0028] like Figure 1 The figure shows a traditional planar SiC neutron detector, where only a layer of neutron conversion material is deposited on the front of the 4H-SiC diode.

[0029] like Figure 2 The figure shows a single-trench SiC neutron detector, in which evenly spaced trenches are etched only on the front surface of the 4H-SiC epitaxial layer 2, and then the same neutron conversion material is backfilled into the trenches;

[0030] Compared to Figure 1 、 Figure 2 The planar and single-groove silicon carbide neutron detectors shown in the figure, the double-groove silicon carbide neutron detector provided by the present invention can not only increase the filling amount of neutron conversion material, but also backfill two neutron conversion materials in grooves of different widths, further improving the intrinsic detection efficiency.

[0031] Example 2

[0032] In this embodiment, if Figure 4 As shown, the Monte Carlo software Geant4 was used to Figure 1 、 Figure 2 、 Figure 3 The intrinsic neutron detection efficiencies of the three neutron detector structures were simulated and compared to verify the advantages of the double-groove silicon carbide neutron detector structure proposed in the present invention.

[0033] In this embodiment, when the optimal solution is taken: the width of the first groove 6 is 2.5 μm, the width of the second groove 7 is 15 μm, the depth of the first groove 6 and the second groove 7 are both 25 μm, and the width of the mesa region of the 4H-SiC epitaxial layer 2 between the first groove 6 and the second groove 7 is 2 μm, the detection efficiency of the planar neutron detector changes the least with LLD, that is, the stability is the best; while the detection efficiency of the dual-trench neutron detector changes the most with LLD, that is, the stability is the worst. The presence of gamma rays and background noise will interfere with the energy spectrum measurement results of the detector, but in actual applications, these interferences can be completely filtered out by setting the LLD to 300 keV. In addition, when the LLD is 300 keV, the dual-trench neutron detector has the highest detection efficiency, significantly improving the detection performance of the device.

[0034] Example 3

[0035] In this embodiment, if Figure 5 Figure 2 shows a comparison of the detection efficiency of three neutron detector structures when the LLD is set at 300keV. It can be seen that when the optimal solution in Example 2 is used, the neutron detection efficiency of the single-trench detector is improved by 3.5% compared to the planar structure, while the neutron detection efficiency of the double-trench detector is improved by 4.6% compared to the single-trench structure. Clearly, the double-trench silicon carbide neutron detector proposed in this invention can effectively improve detection efficiency. Furthermore, deep trench etching is difficult to achieve in silicon carbide processes, while the double-trench structure proposed in this invention can maximize neutron detection efficiency within a limited trench depth.

[0036] Example 4

[0037] In this embodiment, if Figure 6 The figure shows the energy deposition spectra of three types of neutron detectors. 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 a planar SiC neutron detector, only one secondary particle can enter the SiC region and be detected after each nuclear reaction, while for a grooved SiC neutron detector, two secondary particles can enter the SiC detector together after each nuclear reaction. Figure 6 The energy deposition spectrum reveals that the thin-film-coated detector has a distinct α peak to the left of 2.05 MeV and a distinct 3H peak to the left of 2.73 MeV. The energy cutoff corresponds to the energy of the higher-energy 3H particles. In summary, the single-groove detector has higher counts than the thin-film-coated detector across the entire energy spectrum. Furthermore, counts above 2.73 MeV in the energy spectrum represent high-energy peaks formed by the combined entry of α and 3H particles into the silicon carbide region.

[0038] Compared with the single-groove detector, the double-groove neutron detector counts increased significantly in the low energy region and only slightly decreased in the high energy region, which is mainly due to the thermal neutrons and 10 The reaction products of B have lower energy and thus contribute a large number of low energy range counts. Since the surface area of ​​the detector is fixed at 1x1cm 2 , so insert 10 Groove B will result in 6 LiF filling is reduced, making 6 The number of reaction products between LiF and thermal neutrons decreases slightly, resulting in a slight decrease in the number of high-energy regions. For single-groove and double-groove SiC neutron detectors, due to the small groove gap, secondary particles can only deposit part of their energy in the SiC region, 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 groove detector will drop significantly. In addition, 10 The high thermal neutron absorption cross section of the 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. This is also the essential reason why the intrinsic detection efficiency of the double-groove silicon carbide neutron detector is significantly improved compared with the single-groove structure.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A double-groove silicon carbide neutron detector, characterized in that: include: 4H-SiC substrate (1), 4H-SiC epitaxial layer (2), P formed by ion implantation + region (3), a plurality of first grooves (6) and second grooves (7) having different widths; The 4H-SiC epitaxial layer (2) is above the 4H-SiC substrate (1), and a first trench (6) and a second trench (7) are provided on the front surface of the 4H-SiC epitaxial layer (2), wherein the first trench (6) and the second trench (7) are arranged in a staggered manner; The P formed by ion implantation + The area (3) is on the inner wall, bottom surface and 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 material; the neutron conversion material comprises 10 B powder and 6 LiF powder, the 10 The B powder is in the first groove (6), 6 LiF powder is in the second groove (7); the double-groove silicon carbide neutron detector further comprises 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 on the table of the 4H-SiC epitaxial layer (2). + Above the region (3), the N-type ohmic contact electrode (5) is on the back side of the 4H-SiC epitaxial layer (2).

2. The double-trench silicon carbide neutron detector according to claim 1, characterized in that: The width of the first groove (6) is in the range of 1-10 μm, and the width of the second groove (7) is in the range of 10-50 μm.

3. The double-trench silicon carbide neutron detector according to claim 1, characterized in that: The depth of the first groove (6) and the second groove (7) are both 25 μm.

4. The double-trench silicon carbide neutron detector according to claim 1, characterized in that: The width of the mesa region of the 4H-SiC epitaxial layer (2) between the first trench (6) and the second trench (7) is in the range of 1-10 μm.

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