A nuclear radiation detector with a protective ring structure and a preparation method thereof

Abstract

The present invention discloses a nuclear radiation detector with a guard ring structure and a method for manufacturing the same. The invention relates to the field of semiconductor device technology and comprises a detector body, wherein the top surface of the detector body is provided with an anode, and the bottom surface of the detector body is provided with a cathode. The anode comprises a positive-facing planar electrode and a guard ring electrode disposed around the positive-facing planar electrode, with an oxide layer disposed between the positive-facing planar electrode and the guard ring electrode. The cathode is a negative-facing planar electrode, and the negative-facing planar electrode and the positive-facing planar electrode are symmetrically arranged. The guard ring electrode structure developed in the present invention utilizes the transverse electric field generated between the guard ring electrode and the central electrode of the anode to push electrons from the edge to the central electrode, thereby improving the overall carrier characteristics and demonstrating reduced surface leakage current and improved energy resolution on a macroscopic scale.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor devices, and in particular to a nuclear radiation detector with a guard ring structure and a preparation method thereof. Background Art

[0002] Cadmium zinc telluride (CdZnTe) is a third-generation compound semiconductor material with excellent performance for nuclear radiation detection. It boasts a high average atomic number, high resistivity, excellent energy and spatial resolution, and stable operation at room temperature. These advantages have broad application prospects in aerospace, safety testing, industrial flaw detection, and other fields.

[0003] Cadmium zinc telluride (CZN) nuclear radiation detectors have various electrode structures, the most common being planar electrodes. However, due to low charge collection efficiency, planar CZN detectors are limited in their ability to detect gamma rays and are susceptible to effects such as hole capture and hole tailing. Therefore, addressing the poor hole-retention characteristics of CZN detectors has long been an effective approach.

[0004] To address the poor hole characteristics of CdZnTe detectors through electrode structure, novel unipolar electrodes are often designed. These include quasi-hemispherical, Frisch-grid, and pixel array types. These structures can, to a certain extent, reduce the impact of holes on the performance of CdZnTe nuclear radiation detectors. However, these unipolar electrodes are difficult to fabricate. As the designed electrode structure becomes more complex, high-precision electrode plating processes such as photolithography are often required, significantly increasing the difficulty of mass production.

[0005] Therefore, providing an electrode structure that is highly applicable, simple to prepare, and effective for improving the hole characteristics of cadmium zinc telluride nuclear radiation detectors is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] In order to solve the above problems, the present invention provides a nuclear radiation detector with a guard ring structure and a preparation method thereof. The guard ring electrode structure developed by the present invention utilizes the transverse electric field generated between it and the anode center electrode to push electrons from the edge position to the center electrode, thereby improving the overall carrier characteristics and showing reduced surface leakage current and improved energy resolution of the device on a macro scale.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A nuclear radiation detector with a protective ring structure comprises a detector body, wherein the top surface of the detector body is provided with an anode, and the bottom surface of the detector body is provided with a cathode;

[0009] The anode includes a positive-side planar electrode and a guard ring electrode arranged around the positive-side planar electrode, and an oxide layer is provided between the positive-side planar electrode and the guard ring electrode;

[0010] The cathode is a negative plane electrode and an oxide layer arranged around the negative plane electrode, and the negative plane electrode and the positive plane electrode are symmetrically arranged.

[0011] The cadmium zinc telluride nuclear radiation detector with a guard ring structure of the present invention can effectively reduce the surface leakage current of the device, thereby ultimately improving the energy resolution.

[0012] Preferably, the detector body is a rectangular parallelepiped, and the top surface and the bottom surface are square;

[0013] The positive surface planar electrode is a square, and the side length is not less than 1 / 2 of the side length of the bottom surface square;

[0014] The guard ring electrode is a square ring, and the distance between the positive surface plane electrode and the guard ring electrode is 0.5-0.8 mm.

[0015] Preferably, the material of the detector body is cadmium zinc telluride, and the resistivity is greater than 10 9 Ω·cm;

[0016] The material of the positive surface planar electrode, the guard ring electrode and the negative surface planar electrode is any one of Au, Pt and Ag;

[0017] The resistivity of the oxide layer is greater than 10 12 Ω·cm.

[0018] Preferably, the size of the cuboid is 10×10×2-10×10×5mm 3 ;

[0019] The dimensions of the positive surface planar electrode and the negative surface planar electrode are 5×5-8×8 mm. 2 ;

[0020] The guard ring electrode has a ring width of 0.1-1 mm.

[0021] Preferably, the thickness of the positive-side planar electrode, the guard ring electrode and the negative-side planar electrode is 60-100 nm; and the thickness of the oxide layer is 30-50 nm.

[0022] Preferably, when the detector is operating normally, the forward voltage applied to the positive-facing planar electrode is 100-300V; the positive-facing planar electrode remains grounded, and the voltage applied to the guard ring electrode is 0-(-300)V; the absolute value of the voltage applied to the guard ring electrode is no greater than the voltage applied to the positive-facing planar electrode. Under these applied voltage conditions, the guard ring electrode can achieve a transverse electric field at the anode, thereby pushing some electrons at the edge to the central electrode for collection, thereby increasing carrier collection efficiency to a certain extent and improving the detector's electrical performance and energy resolution.

[0023] The method for preparing a nuclear radiation detector with a guard ring structure as described above specifically includes the following steps:

[0024] After the detector body undergoes surface rough polishing, surface chemical etching, electrode plating and surface passivation in sequence, a nuclear radiation detector with a protective ring structure is obtained.

[0025] After conventional surface treatment, the detector of the present invention uses an ion sputtering instrument with a specific mask to complete electrode plating, thereby achieving device fabrication. The order of the preparation steps in the present invention cannot be changed. Electrode plating must be performed after surface chemical etching and before surface passivation. The anode electrode of the present invention includes a central electrode and a guard ring electrode. In the CdZnTe detector prepared according to the above steps, the surface leakage current is blocked by the high-resistance passivation layer between the central electrode and the guard ring electrode, thereby reducing the surface leakage current.

[0026] Preferably, the reagent used for the surface chemical etching is bromine methanol solution.

[0027] Preferably, the concentration of the bromine methanol solution is 2-5 wt %, and the corrosion time is 1-3 min.

[0028] Preferably, the electrode is plated by ion sputtering.

[0029] Preferably, the surface passivation adopts a mixed solution of ammonium fluoride and hydrogen peroxide.

[0030] Preferably, the mass fraction of ammonium fluoride in the mixed solution is 8-12%, the mass fraction of hydrogen peroxide is 10-15 wt %; and the treatment time is 5-15 min.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The guard ring electrode structure proposed in the detector of the present invention is an electrode structure with strong versatility and stable performance. Unlike the previous unipolar electrode structure, the guard ring electrode structure does not need to change the shape of the anode center electrode, and can optimize the hole characteristics of any center electrode; in addition, the guard ring electrode can be plated through an ion sputtering device combined with a mask of a specific shape, which has certain production feasibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. The drawings in this description are merely embodiments of the present invention.

[0034] Figure 1 A structural stereogram of the detector proposed in the present invention;

[0035] Figure 2 A side view of the detector proposed for the present invention;

[0036] Figure 3 A top view of the detector proposed for the present invention;

[0037] Figure 4 This is a graph showing the surface leakage current test results of Example 1 of the present invention;

[0038] Figure 5 This is a graph showing the surface leakage current test results of Example 2 of the present invention;

[0039] Figure 6 This is a diagram showing the energy resolution test results when there is no guard ring in Example 1 of the present invention;

[0040] Figure 7 This is a diagram showing the energy resolution test results when a guard ring is provided in Example 1 of the present invention;

[0041] Figure 8 This is a graph showing the surface leakage current test results of Example 3 of the present invention. DETAILED DESCRIPTION

[0042] The following describes embodiments of the present invention, examples of which are shown in the accompanying drawings. The embodiments described with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but are not to be construed as limiting the present invention.

[0043] Example 1

[0044] like Figure 1-3 , the present invention provides a nuclear radiation detector with a guard ring structure:

[0045] The detector body 1 comprises a detector body 1, wherein the top surface of the detector body 1 is provided with an anode, and the bottom surface of the detector body 1 is provided with a cathode;

[0046] The anode includes a positive plane electrode 2 and a guard ring electrode 3 arranged around the positive plane electrode 2. An oxide layer 4 is provided between the positive plane electrode 2 and the guard ring electrode 3. The resistivity of the oxide layer is about 10 13 Ω·cm, thickness is about 35nm;

[0047] The cathode is a negative plane electrode 5 and an oxide layer 4 arranged around the negative plane electrode 5. The negative plane electrode 5 and the positive plane electrode 2 are symmetrically arranged (completely identical in size and position).

[0048] The detector body 1 is a rectangular parallelepiped, made of cadmium zinc telluride crystal (different resistivities are grown by vertical gradient solidification method according to different indium doping ratios), with a resistivity of 10 8 -10 9 Ω·cm, the top and bottom surfaces are square, and the dimensions of the cuboid are 10×10×2mm 3 The size of the positive surface electrode 2 and the negative surface electrode 5 is 8×8 mm. 2 The guard ring electrode 3 is a square ring, the distance between the positive plane electrode 2 and the guard ring electrode 3 is 0.5 mm, and the ring width of the guard ring electrode 3 is 0.5 mm;

[0049] The material of the positive surface planar electrode 2, the guard ring electrode 3 and the negative surface planar electrode 5 is Au, with a thickness of 80 nm;

[0050] The preparation method comprises the following steps:

[0051] 1) Surface corrosion: The CdZnTe crystals were subjected to surface corrosion treatment using a 3 wt% bromine methanol solution. After the surface corrosion treatment, the crystals were ultrasonically cleaned multiple times. The first ultrasonic cleaning step was performed using anhydrous methanol for 5-10 minutes, the second step was performed using anhydrous acetone for 5-10 minutes, and then using anhydrous ethanol for 10-15 minutes. Finally, the crystals were treated with ultrapure water for 10-15 minutes to ensure that no corrosion solution remained on the surface of the CdZnTe crystals. The crystals were then dried with nitrogen and set aside.

[0052] 2) Electrode plating: Electrode plating is performed on the CdZnTe crystals that have been surface-etched in step 1) using an ion sputtering apparatus. The plated electrodes include a central electrode and a guard ring electrode of the anode, and a central electrode of the cathode;

[0053] 3) Surface passivation: The CdZnTe crystals after electrode plating in step 2) were subjected to surface passivation treatment for 15 minutes using a 10 wt% / 10 wt% NH4F / H2O2 mixed solution. After treatment, the surfaces were ultrasonically cleaned and dried for later use.

[0054] 4) Test connection: Use a semiconductor analyzer to test the electrical properties of the CdZnTe crystal after surface passivation in step 3). Before testing, ensure that the anode center electrode is connected to a 300V positive bias, the anode guard ring electrode is connected to a -60V negative bias, and the cathode center electrode is grounded.

[0055] Example 2

[0056] like Figure 1-3 , the present invention provides a nuclear radiation detector with a guard ring structure:

[0057] The detector body 1 comprises a detector body 1, wherein the top surface of the detector body 1 is provided with an anode, and the bottom surface of the detector body 1 is provided with a cathode;

[0058] The anode includes a positive surface electrode 2 and a guard ring electrode 3 arranged around the positive surface electrode. An oxide layer 4 is provided between the positive surface electrode 2 and the guard ring electrode 3. The resistivity of the oxide layer is about 10 13 Ω·cm, thickness is about 35nm;

[0059] The cathode is a negative plane electrode 5, which is symmetrically arranged with the positive plane electrode 2 (completely identical in size and position);

[0060] The detector body 1 is a rectangular parallelepiped, made of cadmium zinc telluride crystal (different resistivities are grown by vertical gradient solidification method according to different indium doping ratios), with a resistivity of 10 10 -10 11 Ω·cm, the top and bottom surfaces are square, and the dimensions of the cuboid are 10×10×2mm 3 The size of the positive surface electrode 2 and the negative surface electrode 5 is 8×8 mm. 2 The guard ring electrode 3 is a square ring, the distance between the positive plane electrode 2 and the guard ring electrode 3 is 0.5 mm, and the ring width of the guard ring electrode 3 is 0.5 mm;

[0061] The materials of the positive surface electrode 2, the guard ring electrode 3 and the negative surface electrode 5 are all Au, with a thickness of 80nm;

[0062] The preparation method comprises the following steps:

[0063] 1) Surface corrosion: The CdZnTe crystals were subjected to surface corrosion treatment using a 3 wt% bromine methanol solution. After the surface corrosion treatment, the crystals were ultrasonically cleaned multiple times. The first ultrasonic cleaning step was performed using anhydrous methanol for 5-10 minutes, the second step was performed using anhydrous acetone for 5-10 minutes, and then using anhydrous ethanol for 10-15 minutes. Finally, the crystals were treated with ultrapure water for 10-15 minutes to ensure that no corrosion solution remained on the surface of the CdZnTe crystals. The crystals were then dried with nitrogen and set aside.

[0064] 2) Electrode plating: Electrode plating is performed on the CdZnTe crystals that have been surface-etched in step 1) using an ion sputtering apparatus. The plated electrodes include a central electrode and a guard ring electrode of the anode, and a central electrode of the cathode;

[0065] 3) Surface passivation: The CdZnTe crystals after electrode plating in step 2) were subjected to surface passivation treatment for 15 minutes using a 10 wt% / 10 wt% NH4F / H2O2 mixed solution. After treatment, the surfaces were ultrasonically cleaned and dried for later use.

[0066] 4) Test connection: Use a semiconductor analyzer to test the electrical properties of the CdZnTe crystal after surface passivation in step 3). Before testing, ensure that the anode center electrode is connected to a 300V positive bias, the anode guard ring electrode is connected to a -60V negative bias, and the cathode center electrode is grounded.

[0067] Figure 4 and 5 The figures show the surface leakage current test results of the detectors of Examples 1 and 2, respectively. As can be seen from the figures, after the guard ring is added to the planar CdZnTe nuclear radiation detector of Example 1, the surface leakage current is significantly reduced, from 39.2nA without the guard ring to 17.4nA at 300V, a decrease of about 55.6%; after the guard ring is added to the planar CdZnTe nuclear radiation detector of Example 2, the surface leakage current is significantly reduced, from 11.5nA without the guard ring to 4.6nA at 300V, a decrease of about 60%.

[0068] Figure 6 and 7 The energy resolution test results of the detector of Example 1 with and without a guard ring are shown in the figure. As can be seen from the figure, the energy resolution of the planar CdZnTe nuclear radiation detector is significantly improved after the guard ring is added. When 241Am is the radiation source, the energy resolution is increased from 21.09% without a guard ring to 14.30%, an increase of about 47.48%.

[0069] Example 3

[0070] The rest of the parameters and methods are the same as those in Example 2, only the lengths of the positive plane electrode 2 and the negative plane electrode 5 are modified, and relevant exploration is performed. Figure 8 3 is a graph showing the surface leakage current test results of the detector of this embodiment. As can be seen from the graph, the surface leakage current of the planar CdZnTe nuclear radiation detector of this embodiment is significantly reduced after the guard ring is added.

[0071] The present invention proposes a guard ring electrode structure suitable for the anode of a CdZnTe nuclear radiation detector. This structure can be plated on the periphery of any anode electrode in a simple and easy manner, thereby improving the hole performance of the CdZnTe nuclear radiation detector and providing an effective method for reducing surface leakage current and improving energy resolution of the CdZnTe nuclear radiation detector.

[0072] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A nuclear radiation detector with a protective ring structure, characterized in that: It comprises a detector body, wherein the top surface of the detector body is provided with an anode, and the bottom surface of the detector body is provided with a cathode; The anode includes a positive-side planar electrode and a guard ring electrode arranged around the positive-side planar electrode, and an oxide layer is provided between the positive-side planar electrode and the guard ring electrode; The cathode is a negative plane electrode and an oxide layer arranged around the negative plane electrode, and the negative plane electrode and the positive plane electrode are symmetrically arranged; The resistivity of the oxide layer is greater than 10 12 Ω·cm; The detector body is a rectangular parallelepiped, and the top surface and the bottom surface are square; the positive surface planar electrode is a square, and the side length is not less than 1 / 2 of the side length of the bottom surface square.

2. The nuclear radiation detector with a protective ring structure according to claim 1, characterized in that: The guard ring electrode is a square ring, and the distance between the positive surface plane electrode and the guard ring electrode is 0.5-0.8 mm.

3. The nuclear radiation detector with a protective ring structure according to claim 1, characterized in that: The material of the detector body is cadmium zinc telluride, with a resistivity greater than 10 9 Ω·cm; The material of the positive-side planar electrode, the guard ring electrode and the negative-side planar electrode is any one of Au, Pt and Ag.

4. The nuclear radiation detector with a protective ring structure according to claim 2, characterized in that: The size of the cuboid is 10×10×2-10×10×5 mm 3 ; The dimensions of the positive surface planar electrode and the negative surface planar electrode are 5×5-8×8 mm. 2 ; The guard ring electrode has a ring width of 0.1-1 mm.

5. The nuclear radiation detector with a protective ring structure according to claim 1, characterized in that: The thickness of the positive-side planar electrode, the guard ring electrode and the negative-side planar electrode is 60-100 nm; the thickness of the oxide layer is 30-50 nm.

6. A method for preparing a nuclear radiation detector with a guard ring structure according to any one of claims 1 to 5, characterized in that: The specific steps include: After the detector body undergoes surface rough polishing, surface chemical etching, electrode plating and surface passivation in sequence, a nuclear radiation detector with a protective ring structure is obtained.

7. The method for preparing a nuclear radiation detector with a guard ring structure according to claim 6, characterized in that: The reagent used for the surface chemical etching is bromine methanol solution.

8. The method for preparing a nuclear radiation detector with a guard ring structure according to claim 7, characterized in that: The concentration of the bromomethanol solution is 2-5 wt %, and the corrosion time is 1-3 min.

9. The method for preparing a nuclear radiation detector with a guard ring structure according to claim 6, characterized in that: The electrode is plated by ion sputtering.

10. The method for preparing a nuclear radiation detector with a guard ring structure according to claim 6, characterized in that: The surface passivation adopts a mixed solution of ammonium fluoride and hydrogen peroxide, wherein the mass fraction of ammonium fluoride in the mixed solution is 8-12%, and the mass fraction of hydrogen peroxide is 10-15wt%; the treatment time is 5-15 minutes.

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