Nuclear radiation detector with protection ring structure and preparation method thereof

Abstract

The invention discloses a nuclear radiation detector with a protection ring structure and a preparation method thereof, and relates to the technical field of semiconductor devices, the nuclear radiation detector comprises a detector main body, the top surface of the detector main body is provided with an anode, and the bottom surface of the detector main body is provided with a cathode; wherein the anode comprises a sunny plane electrode and a protection ring electrode arranged around the sunny plane electrode, and an oxide layer is arranged between the sunny plane electrode and the protection ring electrode; the cathode is a negative plane electrode, and the negative plane electrode and the positive plane electrode are symmetrically arranged. According to the protection ring electrode structure developed by the invention, a transverse electric field generated between the protection ring electrode structure and an anode center electrode is utilized to push electrons to the center electrode from an edge position, so that the overall carrier characteristic is improved, and the surface leakage current of a device is reduced and the energy resolution is improved in a macroscopic scale.

Description

Technical Field

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

[0002] Cadmium telluride zinc (CdZnTe) is an excellent nuclear radiation detection material, belonging to the category of the third-generation compound semiconductors. This material has the characteristics of a large average atomic number, a high resistivity, good energy resolution and spatial resolution, and can work stably at room temperature. Based on the above advantages, CdZnTe nuclear radiation detectors have broad application prospects in aerospace, security detection, industrial flaw detection and other aspects.

[0003] CdZnTe nuclear radiation detectors have a variety of electrode structures, and the most common one is the planar electrode. However, due to the low charge collection efficiency, the detection of γ-rays by planar CdZnTe nuclear radiation detectors is limited, and effects such as hole trapping or hole tailing are likely to occur. Therefore, starting from the electrode structure has always been an effective idea to solve the poor hole characteristics of CdZnTe nuclear radiation detectors.

[0004] To solve the problem of poor hole characteristics in CdZnTe detectors starting from the electrode structure, a new type of unipolar electrode is usually selected; the unipolar electrodes include a quasi-hemispherical type, a Frisch grid type, a pixel array type, etc. These electrode structures can all reduce the influence of holes on the performance of CdZnTe nuclear radiation detectors to a certain extent. However, the preparation of the above unipolar electrodes is difficult. As the designed electrode structure becomes complex, high-precision electrode plating processes such as photolithography are often required, and the difficulty in mass production is also greatly increased.

[0005] Therefore, providing an electrode structure with strong applicability, simple preparation and effectiveness for improving the hole characteristics of CdZnTe nuclear radiation detectors is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] 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 uses the lateral 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 a reduction in the surface leakage current of the device and an improvement in energy resolution at the macroscopic scale.

[0007] To achieve the above purpose, the present invention adopts the following technical solutions:

[0008] A nuclear radiation detector with a guard ring structure, comprising a detector main body, an anode is provided on the top surface of the detector main body, and a cathode is provided on the bottom surface of the detector main body;

[0009] Among them, the anode includes a positive-plane planar electrode and a guard-ring electrode disposed around the positive-plane planar electrode, and an oxide layer is provided between the positive-plane planar electrode and the guard-ring electrode;

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

[0011] The cadmium telluride nuclear radiation detector with a guard-ring structure of the present invention can effectively reduce the surface leakage current of the device, and finally improve the energy resolution.

[0012] Preferably, the detector body is a cuboid, and the top surface and the bottom surface are squares;

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

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

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

[0016] The materials of the positive-plane planar electrode, the guard-ring electrode and the negative-plane planar electrode are 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 - 10×10×5 mm 3 ;

[0019] The sizes of the positive-plane planar electrode and the negative-plane planar electrode are 5×5 - 8×8 mm 2 ;

[0020] The ring width of the guard-ring electrode is 0.1 - 1 mm.

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

[0022] Preferably, when the detector is operating normally, the forward voltage applied to the planar electrode on the anode side is 100 - 300V; the planar electrode on the anode side 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 not greater than the voltage applied to the planar electrode on the anode side. The guard ring electrode under the above-mentioned applied voltage conditions can achieve a transverse electric field at the anode, thereby pushing some electrons at the edge position onto the central electrode for collection, improving the carrier collection efficiency to a certain extent, and improving the electrical performance and energy resolution of the detector.

[0023] According to the preparation method of a nuclear radiation detector with a guard ring structure described above, the specific steps are as follows:

[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 guard ring structure is obtained.

[0025] The detector of the present invention uses an ion sputtering instrument in cooperation with a specific mask plate to complete electrode plating after conventional surface treatment, thereby realizing device preparation. The order of the preparation steps of the present invention cannot be reversed. Electrode plating must be carried out after surface chemical etching and completed before surface passivation; the anode electrode of the present invention includes a central electrode and a guard ring electrode. For the cadmium telluride detector prepared according to the above steps, the surface leakage current will be blocked by the high-resistance passivation layer between the central electrode and the guard ring electrode, achieving a reduction in surface leakage current.

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

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

[0028] Preferably, the electrode plating uses the ion sputtering method.

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

[0030] Preferably, 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 - 15min.

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

[0032] The guard ring electrode structure proposed by the detector of the present invention is an electrode structure with strong versatility and stable performance. Different from 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 for any center electrode. In addition, the guard ring electrode can be plated by an ion sputtering instrument combined with a specific-shaped mask, which has a certain production feasibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] 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 required for the description of the embodiments or the prior art. The drawings in this description are only the embodiments of the present invention.

[0034] Figure 1 It is a three-dimensional structure diagram of the detector proposed by the present invention;

[0035] Figure 2 It is a side view of the detector proposed by the present invention;

[0036] Figure 3 It is a top view of the detector proposed by the present invention;

[0037] Figure 4 It is a surface leakage current test result diagram of Embodiment 1 of the present invention;

[0038] Figure 5 It is a surface leakage current test result diagram of Embodiment 2 of the present invention;

[0039] Figure 6 It is an energy resolution test result diagram of Embodiment 1 of the present invention without a guard ring;

[0040] Figure 7 It is an energy resolution test result diagram of Embodiment 1 of the present invention with a guard ring;

[0041] Figure 8 It is a surface leakage current test result diagram of Embodiment 3 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0042] The following describes the embodiments of the present invention. The examples of the embodiments are shown in the drawings. The embodiments described with reference to the drawings are exemplary and are intended to explain the present invention, rather than to be construed as a limitation to the present invention.

[0043] Embodiment 1

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

[0045] It includes a detector main body 1. An anode is provided on the top surface of the detector main body 1, and a cathode is provided on the bottom surface of the detector main body.

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

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

[0048] The detector body 1 is a cuboid, and the material is cadmium zinc telluride crystal (grown with different resistivity according to different indium doping ratios by the vertical gradient solidification method). The resistivity is 10 8 -10 9 Ω·cm. The top and bottom surfaces are squares, and the dimensions of the cuboid are 10×10×2 mm 3 The dimensions of the positive-plane planar electrode 2 and the negative-plane planar electrode 5 are 8×8 mm 2 The guard-ring electrode 3 is a square ring. The distance between the positive-plane planar 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 materials of the positive-plane planar electrode 2, the guard-ring electrode 3 and the negative-plane planar electrode 5 are Au, and the thickness is 80 nm;

[0050] The preparation method includes the following steps:

[0051] 1) Surface etching: Use a 3wt% bromine methanol solution to perform surface etching treatment on the cadmium zinc telluride crystal. After the surface etching treatment, perform ultrasonic cleaning multiple times. The first ultrasonic cleaning is treated with anhydrous methanol for 5 - 10 min, the second step is treated with anhydrous acetone for 5 - 10 min, then treated with anhydrous ethanol for 10 - 15 min, and finally treated with ultrapure water for 10 - 15 min to ensure that there is no residual etching solution on the surface of the cadmium zinc telluride crystal, and then dry it with nitrogen for standby;

[0052] 2) Electrode plating: Use an ion sputtering instrument to perform electrode plating on the cadmium zinc telluride crystal etched in step 1). The plated electrodes include the central electrode of the anode and the guard-ring electrode, and the central electrode of the cathode;

[0053] 3) Surface passivation: Use a 10wt% / 10wt% NH4F / H2O2 mixed solution to perform surface passivation treatment on the cadmium zinc telluride crystal after electrode plating in step 2) for 15 min. After the treatment, perform ultrasonic cleaning and dry it for standby;

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

[0055] Example 2

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

[0057] It includes a detector body 1. An anode is provided on the top surface of the detector body 1, and a cathode is provided on the bottom surface of the detector body;

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

[0059] The cathode is a negative surface planar electrode 5, and the negative surface planar electrode 5 and the positive surface planar electrode 2 are symmetrically arranged (completely the same in size and position);

[0060] The detector body 1 is a cuboid, and the material is a cadmium telluride crystal (grown with different indium doping ratios by the vertical gradient solidification method to obtain different resistivities). The resistivity is 10 10 -10 11 Ω·cm. The top and bottom surfaces are squares, and the dimensions of the cuboid are 10×10×2 mm 3 , and the dimensions of the positive surface planar electrode 2 and the negative surface planar electrode 5 are 8×8 mm 2 , the guard ring electrode 3 is a square ring, the distance between the positive surface planar 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 planar electrode 2, the guard ring electrode 3, and the negative surface planar electrode 5 are all Au, and the thickness is 80 nm;

[0062] The preparation method includes the following steps:

[0063] 1) Surface etching: Use a 3 wt% bromine methanol solution to perform surface etching treatment on the cadmium telluride crystal. After the surface etching treatment, perform ultrasonic cleaning multiple times. The first ultrasonic cleaning is treated with anhydrous methanol for 5 - 10 min, the second step is treated with anhydrous acetone for 5 - 10 min, then treated with anhydrous ethanol for 10 - 15 min, and finally treated with ultrapure water for 10 - 15 min to ensure that there is no residual etching solution on the surface of the cadmium telluride crystal, and then dry it with nitrogen for standby;

[0064] 2) Electrode plating: Use an ion sputtering instrument to plate electrodes on the surface-etched cadmium telluride crystal in step 1). The plated electrodes include the central electrode and the guard ring electrode of the anode, and the central electrode of the cathode;

[0065] 3) Surface passivation: Use a 10wt% / 10wt% NH4F / H2O2 mixed solution to perform surface passivation treatment on the cadmium telluride crystal after electrode plating in step 2) for 15 minutes. After treatment, perform ultrasonic cleaning and dry it for standby;

[0066] 4) Test connection: Use a semiconductor analyzer to perform electrical performance tests on the cadmium telluride crystal after surface passivation in step 3). Before testing, ensure that the central electrode of the anode is connected to a 300V positive bias voltage, the guard ring electrode of the anode is connected to a -60V negative bias voltage, and at the same time, the central electrode of the cathode is grounded.

[0067] Figure 4 and 5 are respectively the surface leakage current test result diagrams of the detectors in Embodiment 1 and 2. It can be seen from the figures that: for the planar cadmium telluride nuclear radiation detector in Embodiment 1, after adding an external guard ring, the surface leakage current decreases significantly. At a voltage of 300V, it decreases from 39.2nA without the guard ring to 17.4nA, with a decrease amplitude of about 55.6%; for the planar cadmium telluride nuclear radiation detector in Embodiment 2, after adding an external guard ring, the surface leakage current decreases significantly. At a voltage of 300V, it decreases from 11.5nA without the guard ring to 4.6nA, with a decrease amplitude of about 60%;

[0068] Figure 6 and 7 are respectively the energy resolution test result diagrams of the detector in Embodiment 1 without and with a guard ring. It can be seen from the figures that: for the planar cadmium telluride nuclear radiation detector, after adding an external guard ring, the energy resolution improves significantly. In the case of using 241Am as the radiation source, it improves from 21.09% without the guard ring to 14.30%, with an improvement amplitude of about 47.48%.

[0069] Embodiment 3

[0070] The rest are the same as the parameters and methods in Embodiment 2, only modify the lengths of the planar electrode 2 on the positive side and the planar electrode 5 on the negative side, and conduct relevant explorations. Figure 8 is the surface leakage current test result diagram of the detector in this embodiment. It can be seen from the figure that for the planar cadmium telluride nuclear radiation detector in this embodiment, after adding an external guard ring, the surface leakage current decreases significantly.

[0071] The present invention provides a guard ring electrode structure suitable for an anode of a cadmium telluride nuclear radiation detector. This structure can be plated around any anode electrode in a simple and easy-to-implement manner, improving the hole performance of the cadmium telluride nuclear radiation detector; it provides an effective method for reducing the surface leakage current and improving the energy resolution of the cadmium telluride nuclear radiation detector.

[0072] 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 foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A nuclear radiation detector with a guard ring structure, characterized in that, It includes a detector body, with an anode provided on the top surface of the detector body and a cathode provided on the bottom surface of the detector body; Among them, the anode includes a planar anode electrode and a guard ring electrode provided around the planar anode electrode, and an oxide layer is provided between the planar anode electrode and the guard ring electrode; The cathode is a planar cathode electrode and an oxide layer provided around the planar cathode electrode, and the planar cathode electrode and the planar anode electrode are symmetrically arranged.

2. The nuclear radiation detector with a guard ring structure according to claim 1, wherein, The detector body is a cuboid, and the top surface and the bottom surface are squares; The planar anode electrode is square, and the side length is not less than 1 / 2 of the side length of the square on the bottom surface; The guard ring electrode is a square ring, and the distance between the planar anode electrode and the guard ring electrode is 0.5 - 0.8 mm.

3. The nuclear radiation detector with a protection ring structure according to claim 1, characterized in that, The material of the detector body is cadmium zinc telluride, and the resistivity is greater than 10 9 Ω·cm; The materials of the planar anode electrode, the guard ring electrode and the planar cathode electrode are any one of Au, Pt and Ag; The resistivity of the oxide layer is greater than 10 12 Ω·cm.

4. The nuclear radiation detector with a protection ring structure according to claim 2, characterized in that, The dimensions of the cuboid are 10×10×2 - 10×10×5 mm 3 ; The sizes of the anode planar electrode and the cathode planar electrode are 5×5 - 8×8 mm 2 ; The ring width of the guard ring electrode is 0.1 - 1 mm.

5. The nuclear radiation detector with a protection ring structure according to claim 1, characterized in that, The thicknesses of the planar anode electrode, the guard ring electrode and the planar cathode electrode are 60 - 100 nm; the thickness of the oxide layer is 30 - 50 nm.

6. The preparation method of a nuclear radiation detector with a protection ring structure according to any one of claims 1-5, characterized in that, Specifically, it includes the following steps: After the detector body undergoes surface rough polishing, surface chemical etching, electrode plating and surface passivation in sequence, a nuclear radiation detector with a guard ring structure is obtained.

7. The preparation method of 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 bromo-methanol solution.

8. The preparation method of a nuclear radiation detector with a guard ring structure according to claim 7, characterized in that, The concentration of the bromo-methanol solution is 2 - 5 wt%, and the etching time is 1 - 3 min.

9. The preparation method of a nuclear radiation detector with a protection ring structure according to claim 6, characterized in that, Ion sputtering method is used for the electrode plating.

10. The preparation method of a nuclear radiation detector with a protection ring structure according to claim 6, characterized in that, The surface passivation uses a mixed solution of ammonium fluoride and hydrogen peroxide. The mass fraction of ammonium fluoride in the mixed solution is 8 - 12%, and the mass fraction of hydrogen peroxide is 10 - 15 wt%; the treatment time is 5 - 15 min.

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