Barium nitrate single crystal X-ray detector and preparation method thereof

Abstract

The invention belongs to the field of X-ray detection, and particularly relates to a barium nitrate single crystal X-ray detector and a preparation method thereof. The barium nitrate single crystal X-ray detector comprises a barium nitrate single crystal as well as a positive electrode and a negative electrode which are oppositely arranged on two sides of the barium nitrate single crystal, wherein the barium nitrate single crystal is a cubic crystal system. The barium nitrate single crystal X-ray detector is low in growth temperature, simple in preparation process, high in economic benefit, safe and environment-friendly, and high sensitivity and low dark current drift are realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of X-ray detection, and particularly relates to a barium nitrate single crystal X-ray detector and a preparation method thereof. BACKGROUND

[0002] The information disclosed in this Background section is only for the purpose of increasing the understanding of the general background of the application and does not necessarily constitute an admission by the patent applicant or the patent owner that this information constitutes prior art.

[0003] At present, X-ray detectors have been widely applied in the fields of medical imaging, customs security inspection, industrial product quality monitoring, nuclear detection and the like. However, the direct detection type X-ray detector has relatively high requirements for semiconductor materials, so the types of semiconductor materials capable of being used for X-ray detection are very limited and the sensitivity is low. However, many commercialized direct X-ray detection semiconductor materials have various problems. For example, the amorphous selenium (α-Se) commonly used in medical CT imaging has weak X-ray absorption, which leads to the need for a relatively high X-ray dose in application, and long-term use can cause harm to the human body. The material and manufacturing cost of cadmium telluride and cadmium zinc telluride (CdTe, CdZnTe) detectors are high, and the manufacturing process is too high to be directly integrated with a readout circuit. Considering that X-rays are difficult to focus, the area of the X-ray detector needs to be large enough, although many single crystal semiconductors have excellent performance, but the controllable large-size preparation is difficult, and cannot meet the detection imaging application. Polycrystalline semiconductors PbI2 and HgI2 can be prepared in a large area in principle, but their grain boundaries will limit the charge transport and cause high dark current. Perovskite is concerned due to its excellent carrier transport performance in the outstanding performance of solar cells and light emitting applications, and the low hardness and elastic modulus lead to poor mechanical stability and serious halogen ion migration, which bring great challenges to its further application. SUMMARY

[0004] In order to solve the problems of the prior art, the present application aims at a barium nitrate single crystal X-ray detector and a preparation method thereof. The barium nitrate single crystal X-ray detector comprises a barium nitrate single crystal and electrodes, has low growth temperature, simple preparation process, high economic benefit, safety and environmental protection, realizes high sensitivity and low dark current drift.

[0005] In order to achieve the above-mentioned purpose, the present application is realized by the following technical scheme:

[0006] In a first aspect, a barium nitrate single crystal X-ray detector comprises a barium nitrate single crystal and positive and negative electrodes oppositely arranged on both sides of the barium nitrate single crystal, and the barium nitrate single crystal is of cubic system.

[0007] Preferably, the positive and negative electrodes comprise gold electrodes.

[0008] Preferably, the barium nitrate single crystal is cubic structure, with a size of (20-30mm)*(20-30mm)*(1-3mm).

[0009] Preferably, the thickness of the positive electrode and the negative electrode is 50-150nm.

[0010] In a second aspect, a method for preparing the barium nitrate single crystal X-ray detector according to the first aspect, comprising the following steps:

[0011] A positive electrode is deposited on one side of the barium nitrate single crystal, and a negative electrode is deposited on the other side, to obtain a barium nitrate single crystal X-ray detector.

[0012] Preferably, before depositing the positive electrode and the negative electrode, the barium nitrate single crystal is oriented, cut and polished.

[0013] Preferably, the method for depositing the positive electrode and the negative electrode comprises ion sputtering.

[0014] Preferably, the method further comprises a method for preparing the barium nitrate single crystal:

[0015] The barium nitrate solution is heated to supersaturation, and after cooling to the saturation temperature, a barium nitrate seed crystal is added. The barium nitrate seed crystal is rotated and cooled to grow the barium nitrate single crystal.

[0016] Further preferably, the barium nitrate seed crystal is in the (100) direction.

[0017] Further preferably, the rotation speed is 40-60rpm, and the rotation is performed in a clockwise rotation-stop counterclockwise rotation reciprocating manner.

[0018] The above one or more technical solutions of the present application have the following beneficial effects:

[0019] The barium nitrate single crystal has high resistivity, good air stability and other advantages, high X-ray absorption coefficient, high mobility lifetime product and low dark current drift, and the positive electrode and the negative electrode effectively improve the carrier migration performance, so that the barium nitrate X-ray detector can achieve high sensitivity, ultra-low dark current drift and good stability.

[0020] The barium nitrate single crystal can be prepared by low-temperature aqueous solution method, which has simple preparation process and low cost, large single crystal size, high quality, no cracks, crystal clear and transparent, and no obvious defects inside. BRIEF DESCRIPTION OF DRAWINGS

[0021] The drawings accompanying the specification of the present application form a part thereof, serve to provide further understanding of the present application, and together with the description, explain the present application. The present application is not limited by the inappropriate limitations of the illustrative embodiments thereof and their description.

[0022] Figure 1 Optical photograph of barium nitrate single crystal (100) wafer in Example 1;

[0023] Figure 2 X-ray absorption coefficient of barium nitrate single crystal (100) wafer, a-Se single crystal and Cd 0.9 Zn 0.1 Te single crystal in Example 1;

[0024] Figure 3 Schematic diagram of detection principle of barium nitrate single crystal X-ray detector in Example 1;

[0025] Figure 4 Photocurrent curve of barium nitrate single crystal X-ray detector in Example 1 under different X-ray doses under an applied electric field of 1000V;

[0026] Figure 5 Sensitivity test diagram of barium nitrate single crystal X-ray detector in Example 1;

[0027] Figure 6 Resistivity test diagram of barium nitrate single crystal X-ray detector in Example 1;

[0028] Figure 7 Dark current drift curve of barium nitrate single crystal X-ray detector in Example 1. DETAILED DESCRIPTION

[0029] In order to enable those skilled in the art to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below in combination with specific examples and comparative examples.

[0030] Example 1

[0031] A barium nitrate single crystal was grown from a barium nitrate solution using the "point seed" growth technique. A growth solution was prepared in a 5000 mL glass crystallizer from Ba(NO3)2 raw material and deionized water according to the Ba(NO3)2 solubility curve, the solution was usually overheated in a water bath above the saturation point temperature, and then filtered to remove impurities using a micron-sized aperture membrane. The filtered solution was continuously overheated in a water bath, and after the solution temperature stabilized, it was slowly cooled below the saturation point temperature and a seed crystal in the (100) direction was introduced, which was placed in the center hole of a growth rack made of polytetrafluoroethylene. The growth rack was rotated at 50 rpm in a "positive-stop-reverse" mode, the crystallization tank was placed in a water bath tank, and the water bath tank was controlled by a temperature controller. The solution was kept supersaturated at a cooling rate of 0.3°C / d + a crystal with a growth section diameter of 20-60 mm, and the growth period was 30-120 days. The bulk single crystal grown was processed to obtain a wafer with a diameter of 50 mm as shown in Figure 1The barium nitrate single crystal (100) wafer with a size of (25mm)*(25mm)*(2mm) is shown. As shown in Figure 2 Compared with the amorphous selenium (a-Se) single crystal and cadmium zinc telluride (Cd 0.9 Zn 0.1 Te) single crystal used by commercial X-ray detectors, the barium nitrate single crystal (100) wafer has a higher X-ray absorption coefficient.

[0032] The upper and lower planes of the barium nitrate single crystal (100) wafer are selected, and Au electrodes are deposited on both sides as positive and negative electrodes by ion sputtering method. The thickness of the Au electrode is 100 nm, and a barium nitrate single crystal X-ray detector with a structure of Au / Ba(NO3)2 single crystal / Au is prepared.

[0033] As shown in Figure 3 X-ray excitation of the barium nitrate single crystal separates the carriers, and a photovoltage and a photocurrent are formed between the positive and negative electrodes. By measuring the photovoltage or the photocurrent, the X-ray can be detected.

[0034] The relationship between the photocurrent generated by 120 keV X-rays and the X-ray dose rate of the detector is shown in Table 1.

[0035] Table 1 Relationship between photocurrent and dose rate under 120 keV X-ray energy

[0036]

[0037] As shown in Figure 4 With the increase of X-ray dose, the photocurrent increases accordingly. As shown in Figure 5 The sensitivity of the barium nitrate single crystal X-ray detector is 512 μC Gy air -1 cm -2 As shown in Figure 6 The resistivity of the barium nitrate single crystal X-ray detector is 1.79×10 12 Ωcm. As shown in Figure 7 The dark current drift of the barium nitrate single crystal X-ray detector is 8.36×10 -10 nA cm -1 s -1 V -1 .

[0038] The heavy element barium in barium nitrate has a high attenuation coefficient to X-ray, which can compensate for the disadvantage of insufficient blocking ability of the crystalline silicon material to rays. Secondly, the bulk resistivity of the material is also high, which can ensure that the dark current and noise are very small during work, and the signal-to-noise ratio is improved. The high-quality, size-controllable single crystal is grown by a low-cost aqueous solution method, and the growth conditions are mild and the growth equipment is simple. The obtained barium nitrate single crystal has high quality and does not have charge density defects, has good air stability, and can also maintain good radiation resistance and working stability under ray irradiation. Most importantly, the low-temperature preparation characteristics (45 DEG C) of barium nitrate make it compatible with the temperature tolerance of TFT or CMOS readout circuit, and the detection sensitivity to X-ray can reach 512 mu CGy air - 1 cm -2 , which is better than the commercial silicon, amorphous selenium and cadmium zinc telluride.

[0039] Example 2

[0040] The growth process of the barium nitrate single crystal is the same as that in Example 1, and the barium nitrate single crystal (010) wafer with a crystal direction of (010) is obtained by directional processing, and the size is (20mm)*(20mm)*(1mm).

[0041] The upper and lower corresponding planes of the barium nitrate single crystal (010) wafer are selected, and Au electrodes are deposited on the two surfaces by ion sputtering method as positive and negative electrodes, and the thickness of the Au electrode is 50nm, and the barium nitrate single crystal X-ray detector with the structure of Au / Ba(NO3)2 single crystal / Au is prepared.

[0042] Example 3

[0043] The growth process of the barium nitrate single crystal is the same as that in Example 1, and the barium nitrate single crystal (001) wafer with a crystal direction of (001) is obtained by directional processing, and the size is (30mm)*(30mm)*(3mm).

[0044] The upper and lower corresponding planes of the barium nitrate single crystal (001) wafer are selected, and Au electrodes are deposited on the two surfaces by ion sputtering method as positive and negative electrodes, and the thickness of the Au electrode is 150nm, and the barium nitrate single crystal X-ray detector with the structure of Au / Ba(NO3)2 single crystal / Au is prepared.

[0045] The above only describes the preferred embodiments of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A barium nitrate single crystal X-ray detector, characterized by, The application relates to a barium nitrate single crystal and a positive electrode and a negative electrode arranged oppositely on two sides of the barium nitrate single crystal, wherein the barium nitrate single crystal is cubic.

2. The barium nitrate single crystal X-ray detector of claim 1, wherein, The positive electrode and the negative electrode comprise gold electrodes.

3. The barium nitrate single crystal X-ray detector of claim 1, wherein, The barium nitrate single crystal is cubic with a size of (20-30mm)*(20-30mm)*(1-3mm).

4. The barium nitrate single crystal X-ray detector of claim 1, wherein, The thickness of the positive electrode and the negative electrode is 50-150nm.

5. A method of producing a barium nitrate single crystal X-ray detector as claimed in any one of claims 1 to 4, characterized in that, The application further relates to a preparation method of the barium nitrate single crystal. A positive electrode is deposited on one side of the barium nitrate single crystal, and a negative electrode is deposited on the other side to obtain a barium nitrate single crystal X-ray detector.

6. The production method according to claim 5, wherein Before the positive electrode and the negative electrode are deposited, the barium nitrate single crystal is oriented, cut and polished.

7. The production method according to claim 5, wherein The method for depositing the positive electrode and the negative electrode comprises an ion sputtering method.

8. The production method according to claim 5, wherein The application further relates to a preparation method of the barium nitrate single crystal. The barium nitrate solution is heated to supersaturation, and then barium nitrate seed crystals are added after the temperature is lowered to a saturation temperature; the barium nitrate seed crystals are rotated and cooled to grow the barium nitrate single crystal.

9. The production method according to claim 8, wherein The barium nitrate seed crystals are in a (100) direction.

10. The production method according to claim 8, wherein The rotating speed is 40-60rpm, and the rotation is performed in a clockwise rotation-stop counterclockwise rotation reciprocating mode.

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