Radiation detection element, radiation detector and method for manufacturing radiation detection element

Abstract

The invention provides a radiation detection element, a radiation detector, and a method for manufacturing the radiation detection element capable of performing energy measurement of radiation with good precision. A radiation detection element includes: a compound semiconductor crystal substrate formed of zinc cadmium telluride to which indium is added as an impurity; and a metal electrode that is provided on the surface of the compound semiconductor crystal substrate. The energy resolution of the metal electrode with respect to 122 keV gamma rays emitted from 57 Co is 7% or less.

Description

Technical Field

[0001] This invention relates to radiation detection elements, radiation detectors, and methods for manufacturing radiation detection elements. Background Technology

[0002] In the application of direct-conversion radiation detection elements, the development of high-efficiency, high-resolution, and miniaturized compound semiconductors is underway. Among them, zinc cadmium telluride (CdZnTe), a group II-VI compound semiconductor, has attracted attention in recent years as an advantageous material for radiation detection element applications. Compared with other semiconductors, CdZnTe has a larger atomic number, resulting in higher radiation absorption and detection efficiency, as well as a large band gap energy. Therefore, it has the advantages of low leakage current caused by heat even at room temperature and no need for cooling devices (it can operate at room temperature).

[0003] In radiation detection elements using compound semiconductor crystal substrates formed of CdZnTe, it is useful to form ohmic electrodes on both sides of the substrate to suppress the operating current of the element.

[0004] However, the following problems exist: it is difficult to obtain good ohmic characteristics for compound semiconductor crystal substrates formed from CdZnTe with high resistivity. Due to the influence of the bonding state at the junction interface between the semiconductor and the electrode, the operating current increases when a high voltage is applied. In addition, poor ohmic bonding not only affects electrical properties but also radiometric spectral characteristics.

[0005] In Patent Document 1, a compound semiconductor crystal for radiation detection elements was proposed, which is a zinc cadmium telluride compound semiconductor crystal with good radiometric spectral characteristics. Its characteristic is that it is formed from zinc cadmium telluride containing indium as an impurity of 0.2 wt ppm or more and 2.6 wt ppm, and the product of electron mobility μ and electron lifetime τ, μτ(e), is 7.85E⁻⁴ cm⁻¹. 2 For a voltage of 100V or higher, the resistivity when a voltage of 100V is applied is 1.2E+11Ωcm or higher, and the ratio of the change in leakage current b after 60 seconds from the start of the bias voltage application to the leakage current value a at the start of the bias voltage application is 56% or less.

[0006] Existing technical documents Patent documents Patent Document 1: Japanese Patent No. 5953116 Summary of the Invention

[0007] The problem that the invention aims to solve One method for forming ohmic junctions on a compound semiconductor crystal substrate made of CdZnTe with high resistivity is, for example, forming a Pt electrode by electroless substitution plating. However, conventional Pt electrode formation using plating suffers from the following problems: even when fabricating the device from a substrate with good crystal properties, the current-voltage characteristics (hereinafter also referred to as IV characteristics) are poor, and the operating current increases under high voltage application, thus deteriorating the energy resolution of the radiation spectrum. This results in poor accuracy in measuring the energy of the radiation.

[0008] The embodiments of the present invention were made to solve the technical problems described above, and the object is to provide a radiation detection element, a radiation detector, and a method for manufacturing the radiation detection element that can perform radiation energy measurement with good accuracy.

[0009] Solution for solving the problem The above-mentioned technical problems are solved by the present invention as described in (1) to (11) below.

[0010] (1) A radiation detection element comprising: a compound semiconductor crystal substrate formed of zinc cadmium telluride with indium added as an impurity; and a metal electrode disposed on the surface of the compound semiconductor crystal substrate, for detecting radiation from... 57 The energy resolution of the 122 keV gamma rays emitted by Co is below 7%.

[0011] (2) According to the radiation detection element described in (1), wherein, for the radiation from 57 The energy resolution of the 122 keV gamma rays emitted by Co is less than 5%.

[0012] (3) The radiation detection element according to (1) or (2), wherein, for radiation from... 57 The energy resolution of the 122 keV gamma rays emitted by Co is below 3.4%.

[0013] (4) The radiation detection element according to any one of (1) to (3), wherein the ideal coefficient n of the IV characteristic is 1.0 to 1.5.

[0014] (5) The radiation detection element according to any one of (1) to (4), wherein the resistivity at an operating voltage of 500V is 1×10⁻⁶. 11 Ωcm or more.

[0015] (6) A radiation detector comprising: a radiation detection element as described in any one of (1) to (5); and an amplification unit connected to the radiation detection element to amplify an electrical signal output from the radiation detection element.

[0016] (7) A method for manufacturing a radiation detection element, comprising: a step of cutting a wafer from an ingot containing a compound semiconductor crystal of zinc cadmium telluride with indium added as an impurity and grinding it; a step of forming a metal electrode on the surface of the wafer; a step of cutting a radiation detection element from the wafer on which the metal electrode is formed; and a step of placing the radiation detection element in an annealing furnace and annealing it at 100 to 200°C for 10 minutes to 24 hours.

[0017] (8) A method for manufacturing a radiation detection element, comprising: a step of cutting a wafer from an ingot containing a compound semiconductor crystal of zinc cadmium telluride with indium added as an impurity and grinding it; a step of forming a metal electrode on the surface of the wafer; a step of placing the wafer with the metal electrode formed thereon into an annealing furnace and annealing it at 100 to 200°C for 10 minutes to 24 hours; and a step of cutting a radiation detection element from the annealed wafer.

[0018] (9) A method for manufacturing a radiation detection element according to (7) or (8), wherein the radiation detection element is effective for detecting radiation from... 57 The energy resolution of the 122 keV gamma rays emitted by Co is below 7%.

[0019] (10) The method for manufacturing a radiation detection element according to (7), wherein, in the step of cutting the radiation detection element from the wafer, 30 radiation detection elements are cut from one wafer, and after the annealing step, the radiation detection elements are measured under the same conditions. 57 The standard deviation of the energy resolution of the 30 radiation detection elements at the energy resolution of 122 keV gamma rays emitted by Co is less than 2%.

[0020] (11) The method for manufacturing a radiation detection element according to (8), wherein, in the step of cutting the radiation detection element from the wafer, 30 radiation detection elements are cut from one wafer, and the results are measured under the same conditions for radiation detection elements from the wafer. 57 The standard deviation of the energy resolution of the 30 radiation detection elements at the energy resolution of 122 keV gamma rays emitted by Co is less than 2%.

[0021] Invention Effects According to embodiments of the present invention, a radiation detection element, a radiation detector, and a method for manufacturing the radiation detection element are provided, which can perform radiation energy measurement with good accuracy. Attached Figure Description

[0022] Figure 1This is a circuit diagram of a radiation detector according to an embodiment of the present invention.

[0023] Figure 2 This is a perspective view illustrating a radiation detection element according to an embodiment of the present invention.

[0024] Figure 3 yes Figure 2 Section III-III.

[0025] Figure 4 These are the IV characteristic analysis results of each radiation detection element before and after annealing in Example 1, based on the thermionic emission model.

[0026] Figure 5 These are the IV characteristic analysis results of each radiation detection element before and after annealing in Example 2, based on the thermionic emission model.

[0027] Figure 6 These are the IV characteristic analysis results of each radiation detection element before and after annealing in Example 3, based on the hot electron emission model.

[0028] Figure 7 The results are the IV characteristic analysis results of each radiation detection element before and after annealing in Comparative Example 1, based on the thermionic emission model.

[0029] Figure 8 This is the evaluation result of the energy resolution of Experiment Example 3.

[0030] Figure 9 This is the evaluation result of the annealing temperature dependence of resistivity in Experiment Example 4.

[0031] Figure 10 This is the evaluation result of the annealing time dependence of resistivity in Experiment Example 5.

[0032] Figure 11 This is the evaluation result of the annealing temperature dependence of the μτ value in Experiment Example 6.

[0033] Figure 12 This is the evaluation result of the annealing time dependence of the μτ value in Experiment Example 7. Detailed Implementation

[0034] Next, the scheme for implementing the present invention will be described in detail. The present invention is not limited to the following embodiments, and it should be understood that, without departing from the spirit of the present invention, appropriate design changes, modifications, etc., can be made based on ordinary knowledge of those skilled in the art.

[0035] [Structure of a radiation detector] A general structure of the radiation detector according to an embodiment of the present invention will be described. For example... Figure 1As shown, the radiation detector 1 of this embodiment consists of a radiation detection element 2, a capacitor 3, an amplifier (amplification section) 4, and a multi-channel analyzer (MCA) 5. One electrode (common electrode 7) of the radiation detection element 2 is connected to ground, and the other electrode (pixel electrode 8) is connected to a negative potential, thereby applying a predetermined bias voltage. Furthermore, the other electrode is connected to the MCA 5 via the capacitor 3, the amplifier 4, and the MCA 5.

[0036] The compound semiconductor crystal substrate 6 of the radiation detection element 2 is formed of a crystal of zinc cadmium telluride (CdZnTe, a type of CdTe formed by replacing part of the Cd in CdTe with Zn) which is a group II-VI compound semiconductor. When this CdZnTe is exposed to radiation (hard X-rays, gamma rays), it emits electrons, which become an ionization current through a bias voltage. In the radiation detector 1 of this embodiment, the ionization current of the radiation detection element 2 is converted into a pulse signal via a capacitor 3 and an amplifier 4. Then, an MCA5 analyzes the pulse signal to obtain the spectrum of the radiation.

[0037] [Structure of radiation detection element] The specific structure of the radiation detection element according to an embodiment of the present invention will be described. The radiation detection element 2 according to an embodiment of the present invention may be a planar type in which a common electrode 7 is formed on the entire surface of the compound semiconductor crystal substrate 6. The radiation detection element 2 according to an embodiment of the present invention may also be as follows: Figure 2 The pixel type shown is formed by a compound semiconductor crystal substrate 6, a common electrode 7, and a pixel electrode 8. The compound semiconductor crystal substrate 6 is formed as a thin plate, and the main surfaces formed by the common electrode 7 and the pixel electrode 8 are parallel to a predetermined crystal plane (e.g., the (111) plane). Here, the crystal orientation

[111] is the polar axis of CdZnTe. Therefore, when the predetermined crystal plane is the (111) plane, the surface of the compound semiconductor crystal substrate 6 has a higher proportion of Cd on the surface of one main surface (hereinafter A surface) 6a side and a higher proportion of Te on the surface of the other main surface (hereinafter B surface) 6b side.

[0038] exist Figure 2In the pixel-type radiation detection element 2, the common electrode 7 is formed to cover the entire B-side 6b of the compound semiconductor crystal substrate 6. Multiple pixel electrodes 8 are provided on the A-side 6a of the compound semiconductor crystal substrate 6 and arranged in a matrix (four columns in the figure). Both the common electrode 7 and the pixel electrodes 8 are formed into thin films of platinum (Pt), gold (Au), indium (In), and other metals, or alloys containing these metals. That is, the compound semiconductor crystal substrate 6 and the common electrode 7, and the compound semiconductor crystal substrate 6 and the pixel electrodes 8, are in ohmic contact. Hereinafter, without distinguishing between the common electrode 7 and the pixel electrodes 8, the two electrodes will be collectively referred to as metal electrodes 7 and 8.

[0039] In addition, such as Figure 3 As shown, at the location where metal electrodes 7 and 8 (pixel electrodes 8) are formed on the surface of the compound semiconductor crystal substrate 6 (A-side in this case), that is, between the bulk crystal 61 of the compound semiconductor crystal substrate 6 and the metal electrodes 7 and 8, an intermediate layer 62 mainly composed of tellurium oxide and metals such as Pt constituting the metal electrodes can be formed.

[0040] There are no particular limitations as long as the composition of the compound semiconductor crystal substrate 6 (in the case of having a bulk crystal 61 and an intermediate layer 62) contains zinc cadmium telluride, for example, it can be represented by the following formula 1.

[0041] Formula 1: Cd 1－x Zn x Te (In Equation 1, X is the molar ratio, X = 0 to 0.1.) Furthermore, the compound semiconductor crystal substrate 6 is doped (added as an impurity) with indium (In). The In doping is performed to increase the resistivity of the compound semiconductor crystal substrate 6, and the doping amount can be appropriately prepared according to the desired resistivity. From this perspective, the In concentration of the compound semiconductor crystal substrate 6 can be set, for example, to 0.1–2.6 ppm by mass.

[0042] The radiation detection element of the embodiments of the present invention is for radiation detection from 57The energy resolution of 122 keV gamma rays emitted by Co is less than 7%. Energy resolution is an indicator of the accuracy of radiation energy measurement. In principle, the energy spectrum of radiation of a fixed energy, which loses all its energy in a detector, becomes a line spectrum. However, in practical detectors, it is detected as a spectrum with some degree of expansion. The narrower this distribution, the more accurately the radiation energy distribution can be measured. In this invention, the energy resolution is calculated as ΔE / E, obtained by dividing the half-value width ΔE of the peak of the distribution spectrum by the radiation energy (peak channel value) E. If the energy resolution of the radiation detection element is less than 7%, then the radiation detector using the radiation detection element can accurately measure the radiation energy distribution. The radiation detection element of the embodiments of the present invention is suitable for radiation emitted from... 57 The energy resolution of the 122 keV gamma rays emitted by Co is preferably 5% or less, more preferably 3.4% or less.

[0043] When fabricating ohmic radiation detection elements from high-resistivity CdZnTe substrates, it is difficult to form a good ohmic bond, which sometimes leads to an increase in operating current under high voltage, resulting in a deterioration of the radiation-sensitive operating characteristics. Here, operating current refers to the current flowing to the radiation detection element when an external voltage is applied. To obtain good radiation-sensitive operating characteristics, it is preferable to apply a high external voltage, at which point the operating current is low. The radiation detection element of the embodiments of the present invention is suitable for applications involving radiation... 57 The energy resolution of the 122 keV gamma rays emitted by Co is less than 7%, thus enabling the measurement of radiation energy with good accuracy.

[0044] The energy resolution of the radiation detection element according to embodiments of the present invention can be measured in the following manner. That is, regarding the radiation detection element, the configuration... Figure 1 The radiation detector shown measures the emission from cobalt ( ) when a bias voltage of 500V is applied. 57 The spectrum of 122 keV gamma rays emitted by Co is obtained. Based on the radiation spectrum, the peak half-width ΔE and the radiation energy (peak channel value) E are calculated, and ΔE / E is calculated to obtain the energy resolution (%). In embodiments of the present invention, the energy resolution of the radiation detection element is preferably the average value obtained from multiple measurements performed under the same conditions.

[0045] The ideal coefficient n of the IV characteristics of the radiation detection element according to the embodiments of the present invention is preferably 1.0 to 1.5. With such a structure, the interface state of the radiation detection element is good, the operating current under high voltage application is reduced, and the spectral characteristics are improved. It should be noted that the closer the ideal coefficient n of the IV characteristics is to 1.0, the more ideal the interface state of the radiation detection element is; the closer it is to 2.0, the more poor the interface state of the radiation detection element is. The ideal coefficient n of the IV characteristics of the radiation detection element according to the embodiments of the present invention is more preferably 1.0 to 1.3, and even more preferably 1.0 to 1.2.

[0046] The ideal coefficient n of the IV characteristic of the radiation detection element according to the embodiments of the present invention can be determined by gradually applying a voltage to the radiation detection element, thereby plotting an IV curve (IV characteristic) on a graph based on the applied voltage (V) and the accompanying current (I). Then, the IV characteristic is analyzed by the thermionic emission model (electron conduction model of metal (conductor)-semiconductor interface) shown in the following equations (1) and (2).

[0047] [Formula 1] In equations (1) and (2), q: elementary charge, V: applied voltage, n: ideality coefficient, k: Boltzmann constant, T: absolute temperature, S: element area, A: Richardson constant, φ B Energy barrier height. The ideal coefficient n of the IV characteristic is calculated using the above equations (1) and (2).

[0048] The resistivity of the radiation detection element in the embodiments of the present invention is preferably 1×10⁻⁶ at an operating voltage of 500V. 11 Above Ωcm. Resistivity is determined by the current value relative to the applied voltage, so generally the resistivity decreases as the operating current increases. Therefore, high resistivity implies a constant (non-increasing) operating current. If the resistivity of a radiation detection element at an operating voltage of 500V is 1×10⁻⁶, then... 11 If the resistivity is above Ωcm, the operating current does not increase even under high voltage, resulting in better IV characteristics of the radiation detection element. More preferably, the resistivity of the radiation detection element in the embodiment of the present invention at an operating voltage of 500V is 3×10⁻⁶. 11 Ωcm or more.

[0049] The resistivity (ρ) of the radiation detection element under the operating voltage of 500V in the embodiments of the present invention can be calculated by the formula R = V / I based on the current value (I) and voltage value (V) when the operating voltage of 500V is applied to the radiation detection element, and the resistance value (R) can be calculated by the formula ρ = R × S / L based on the cross-sectional area (S) and thickness (L) of the element.

[0050] [Manufacturing method of radiation detection element] Next, a method for manufacturing the radiation detection element according to an embodiment of the present invention will be described.

[0051] First, a thin, disk-shaped wafer (compound semiconductor crystal substrate) is cut out by cutting a single crystal ingot (ingot of compound semiconductor crystal) formed from zinc cadmium telluride with indium added as an impurity along a specified crystal plane (e.g., crystal plane (111)).

[0052] It should be noted that the fabrication of ingots containing single crystals of zinc cadmium telluride can be carried out using the vertical gradient solidification (VGF) method described in Patent Document 1. Alternatively, a crucible filled with Cd, Zn, and Te can be placed inside a vacuum-sealed quartz ampoule, and a Cd-filled reservoir section can be provided at the bottom of the quartz ampoule to apply Cd vapor pressure to the quartz ampoule during single crystal growth. Then, while controlling the position of the crucible filled with raw materials and the Cd-filled reservoir section at a specified temperature, the raw materials for single crystal growth are melted and Cd is volatilized from the reservoir section. This allows for the control of Cd vapor pressure while growing single crystals of zinc cadmium telluride. After single crystal growth, ingot annealing at 940–960°C for approximately 20 hours can also be performed.

[0053] Next, the cut surfaces of the wafers are physically mirror-polished using abrasives such as alumina powder. This polishing process can be repeated multiple times.

[0054] Next, if the radiation detection element is planar, the process of forming metal electrodes by plating, described later, is performed. On the other hand, if the radiation detection element is pixel-type, after the above-mentioned polishing process, a resist film patterned into a predetermined shape is formed in an area outside the predetermined area formed on the electrode portion of the wafer. Specifically, first, the wafer is immersed in methanol and ultrasonically cleaned at room temperature for a predetermined time to remove foreign matter adhering to the wafer. Next, photoresist is coated on the surface of the wafer, and the photoresist is exposed using a photomask with a pixel electrode pattern. Next, the photosensitive photoresist is removed by development. Next, the wafer is immersed in an etching solution mixed with bromine (bromethanol solution) and the polished surface of the wafer is etched at room temperature for a predetermined time to remove the processing degradation layer from the wafer surface. Next, the etching solution is removed from the wafer using methanol or the like, and the methanol or the like is removed from the wafer using pure water.

[0055] Next, the wafer is immersed in a plating solution containing an aqueous solution of chloroplatinic acid (IV) hexahydrate mixed with hydrochloric acid, thereby forming a metal electrode (Pt electrode) in a predetermined area of ​​the electrode section (metal electrode formation process). If an Au electrode, In electrode, or similar electrode is not formed, a plating solution is prepared accordingly.

[0056] After the metal electrodes are formed, the wafer is cleaned with pure water as is, provided the radiation detection element is planar. If the radiation detection element is pixel-type, unwanted photoresist is removed, and the wafer is then cleaned with pure water. Next, inert gases such as nitrogen are sprayed onto the wafer and metal electrodes to dry them.

[0057] Next, the wafer with metal electrodes formed on the polished surface is cut out and divided into multiple substrates, and each radiation detection element is cut out from the wafer.

[0058] Through the above processes, a radiation detection element is manufactured by forming a metal electrode on the surface of a compound semiconductor crystal substrate formed of zinc cadmium telluride with indium added as an impurity. Furthermore, at this time, the metal electrode is formed on the surface layer of the compound semiconductor crystal substrate, i.e., at the location where the metal electrode is formed, such as... Figure 3 As shown, an intermediate layer mainly composed of tellurium oxide and metals such as Pt constituting the metal electrode is formed between the bulk crystal of the compound semiconductor crystal substrate and the metal electrode.

[0059] Next, the radiation detection element is placed in an annealing furnace and annealed at 100–200°C for 10 minutes to 24 hours. The annealing temperature is preferably 110–190°C, more preferably 115–185°C, even more preferably 120–180°C, even more preferably 125–175°C, even more preferably 130–170°C, even more preferably 135–165°C, even more preferably 140–160°C, and even more preferably 150°C. An inert gas atmosphere such as N2 is preferably used for annealing. By annealing the radiation detection element under such conditions, the interface condition is good, and the operating current of the element is reduced without deteriorating the μτ value (the product of mobility and carrier lifetime), thus improving the operating characteristics (energy resolution) for radiation. In this way, the radiation detection element according to the embodiment of the present invention is obtained. Furthermore, in the above embodiment, a wafer with metal electrodes formed on its polished surface is cut out and divided into multiple substrates, and after each radiation detection element is cut out from the wafer, the radiation detection element is annealed, but this is not limited to this. That is, the radiation detection element may also be cut out from the annealed wafer after the wafer with metal electrodes formed on its polished surface has been annealed.

[0060] The radiation detection element manufactured according to embodiments of the present invention, as described above, is for detecting radiation from... 57 The energy resolution of the 122 keV gamma rays emitted by Co is below 7%. Furthermore, in the process of cutting radiation detection elements from a wafer, after cutting 30 radiation detection elements from a wafer and performing annealing, measurements were taken under the same conditions for the radiation detection elements emitted from the wafer. 57 When the energy resolution of the 122 keV gamma rays emitted by Co is considered, the standard deviation of the energy resolution of the 30 radiation detection elements is preferably 2% or less. With such a structure, multiple radiation detection elements with well-suppressed energy resolution deviations can be obtained from a single wafer, resulting in good manufacturing efficiency. Here, "the standard deviation of the energy resolution of the 30 radiation detection elements" is the positive square root obtained by summing the squares of the differences between the target data value and the average value of the 30 data points, and then dividing by the total number of data points (30). The standard deviation of the energy resolution of the 30 radiation detection elements is more preferably 1.5% or less, and even more preferably 1% or less. The standard deviation of the energy resolution of the radiation detection elements can be affected by conditions such as the growth conditions of the compound semiconductor crystal, the ingot annealing after ingot formation, and the plating conditions in the metal electrode formation process of the element. However, in the embodiments of the present invention, it is particularly important to optimize the annealing conditions after electrode formation, thereby controlling the standard deviation of the energy resolution.

[0061] Example The following are embodiments provided to better understand the present invention and its advantages, but the present invention is not limited to these embodiments.

[0062] (Experimental Example 1: Fabrication of Radiation Detection Element) Single crystals (Cd) formed from zinc cadmium telluride with indium added as an impurity 0.965 Zn 0.035 A thin, disk-shaped wafer (compound semiconductor crystal substrate) is cut from an ingot of zinc cadmium telluride (Te) along a predetermined crystal plane (111). It should be noted that the growth method for single crystals formed from zinc cadmium telluride is performed using the vertical gradient solidification (VGF) method as described in Patent Document 1. Specifically, a crucible filled with Cd, Zn, and Te is placed inside a vacuum-sealed quartz ampoule, and a storage section for Cd filling is provided at the bottom of the quartz ampoule to apply Cd vapor pressure to the quartz ampoule during single crystal growth. Then, while controlling the position of the crucible filled with raw materials and the storage section filled with Cd at a predetermined temperature, the raw materials for single crystal growth are melted and Cd is volatilized from the storage section, allowing for control of the Cd vapor pressure while growing a single crystal formed from zinc cadmium telluride. After single crystal growth, an ingot annealing process is performed at 945°C for 20 hours.

[0063] Next, alumina powder is used as an abrasive to physically mirror polish the cut surfaces of the wafers.

[0064] Next, the wafer is immersed in a plating solution containing hydrochloric acid mixed with an aqueous solution of chloroplatinic acid (IV) hexahydrate, thereby forming a Pt electrode on the entire surface (polished surface) of one side of the wafer. The wafer is then cleaned with pure water.

[0065] Next, nitrogen gas is blown onto the wafer and Pt electrode to dry them. The wafer has dimensions of length × width × thickness of approximately 50 mm × 50 mm × 1.4 mm.

[0066] Next, the wafer with Pt electrodes is cut into multiple substrates with dimensions of length × width × thickness = 4mm × 4mm × 1.4mm, and each radiation detection element is cut out from the wafer.

[0067] Through the above processes, a radiation detection element is manufactured in which a metal electrode is formed on the surface of a compound semiconductor crystal substrate formed of zinc cadmium telluride with indium added as an impurity. Furthermore, an intermediate layer mainly composed of tellurium oxide is formed between the bulk crystal of the compound semiconductor crystal substrate and the metal electrode.

[0068] (Experimental Example 2: Evaluation of IV characteristics) Four radiation detection elements manufactured in Test Example 1 were selected and designated as Examples 1-3 and Comparative Example 1.

[0069] Next, they were placed in an annealing furnace and annealed (electrode annealing) under the conditions shown below. The annealing atmosphere was set as a flow of N2 gas at a flow rate of 10 L / min.

[0070] • Example 1 (150°C, 24 hours), Example 2 (150°C, 30 minutes), Example 3 (150°C, 10 minutes), Comparative Example 1 (300°C, 24 hours) Next, a voltage is applied to each radiation detection element and the current is measured. Furthermore, for each radiation detection element before annealing, a voltage is applied beforehand and the current is measured.

[0071] Here, a voltage is gradually applied to the radiation detection element, and an IV curve (IV characteristic) is plotted in a graph based on the applied voltage (V) and the accompanying current (I). Then, the IV characteristic is analyzed using the thermionic emission model (electron conduction model at the metal (conductor)-semiconductor interface) shown in the following equations (1) and (2).

[0072] [Formula 2] In equations (1) and (2), q: elementary charge, V: applied voltage, n: ideality coefficient, k: Boltzmann constant, T: absolute temperature, S: element area, A: Richardson constant, φ B Energy barrier height. The ideal coefficient n of the IV characteristic is calculated using the above equations (1) and (2).

[0073] The IV characteristic analysis results of each radiation detection element before and after annealing, based on the thermionic emission model, are presented below. Figure 4 (Example 1) Figure 5 (Example 2) Figure 6 (Example 3) and Figure 7 (Comparative Example 1).

[0074] For Examples 1-3, the ideal coefficient n for IV characteristics is 1.4. Therefore, the junction interface of the radiation detection element in Examples 1-3 is in good condition, the operating current under high voltage is reduced, and improved spectral characteristics can be expected.

[0075] On the other hand, for Comparative Example 1, the ideal coefficient n of the IV characteristic could not be determined.

[0076] (Experimental Example 3: Evaluation of Energy Resolution) The charge amplifier (Clear-Pulse, type 581), waveform shaping amplifier (Clear-Pulse, type 4417), and MCA (Clear-Pulse, ADC 1125) were connected to the radiation detection element manufactured in Example 1 to form a... Figure 1 The radiation detector shown is used. Measurements were taken when a bias voltage of 500V was applied to the radiation detector using a CLEAR-PULSE power supply (model 6671PN) from cobalt (…). 57 The spectrum of 122 keV gamma rays emitted by Co was obtained. The half-width at half-maximum (WHM) ΔE and the energy (peak channel value) E of the radiation were calculated from the radiation spectrum, and ΔE / E was calculated to obtain the energy resolution (%). Furthermore, for 30 radiation detection elements manufactured in Example 1, the energy resolution (%) of each element was evaluated in the above order, and their average value and standard deviation were calculated. It should be noted that values ​​from samples whose spectra could not be measured were excluded from the calculations.

[0077] Furthermore, each of the 30 radiation detection elements was placed in an annealing furnace and annealed (electrode annealing) at 150°C for 1 hour. The annealing atmosphere was set as a flowing gas of N2 at a flow rate of 10 L / min. The energy resolution (%) of the 30 annealed radiation detection elements was evaluated under the same conditions as described above. The mean and standard deviation of the energy resolution (%) of the 30 radiation detection elements were calculated. It should be noted that values ​​for samples for which spectra could not be measured were excluded from the calculations. The evaluation results are shown in Table 1 and... Figure 8 .

[0078] As shown in Table 1 and Figure 8 As shown, for a radiation detection element after electrode annealing at 150°C for 1 hour, for the... 57 The average energy resolution of the 122 keV gamma rays emitted by Co is 6.1%. Furthermore, the standard deviation of the energy resolution of the 30 radiation detection elements is 1.26%. Therefore, radiation detection elements with well-suppressed deviations in energy resolution can be obtained from a single wafer, demonstrating good manufacturing efficiency. It should be noted that for samples No. 20 (before annealing) and No. 26 (before annealing), there was a poor state of the interface between the metal electrode and the wafer, and an abnormal increase in the operating current, making normal spectral measurements impossible. It can be assumed that the interface state improved after annealing, thus allowing spectral measurements. For No. 30 (before and after annealing), the crystal characteristics of the wafer region were poor, therefore spectral measurements were impossible. (Experimental Example 4: Evaluation of the annealing temperature dependence of resistivity) Multiple radiation detection elements manufactured in Example 1 were placed in an annealing furnace and subjected to annealing (electrode annealing) at 100°C for 24 hours, 150°C for 24 hours, 200°C for 24 hours, 250°C for 24 hours, and 300°C for 24 hours, respectively. The annealing atmosphere was set as a flowing gas of N2 at a flow rate of 10 L / min.

[0079] Next, the resistivity (ρ) of the radiation detection elements before and after annealing was measured at an operating voltage of 500V. Specifically, the current (I) and voltage (V) values ​​were measured when an operating voltage of 500V was applied to the radiation detection elements, and the resistance (R) was calculated using the formula R = V / I. Based on the element's cross-sectional area (S): 4mm × 4mm and thickness (L): 1.4mm, the resistance was calculated using the formula ρ = R × S / L. The evaluation results are shown in Table 2 and... Figure 9 .

[0080] According to Table 2 and Figure 9 It can be seen that in the samples that underwent annealing at 150℃ for 24 hours and at 200℃ for 24 hours, the resistivity at a working voltage of 500V was 1×10⁻⁶. 11 Ωcm or higher. Furthermore, it is known that annealing at low temperatures below 200°C increases resistivity, while annealing at temperatures above 250°C decreases resistivity compared to before annealing. (Experimental Example 5: Evaluation of the annealing time dependence of resistivity) Multiple radiation detection elements manufactured in Experimental Example 1 were placed in an annealing furnace and subjected to annealing (electrode annealing) at 150°C for 30 minutes, 1 hour, 6 hours, and 24 hours, respectively. The annealing atmosphere was set as a flowing gas of N2 at a flow rate of 10 L / min.

[0081] Next, the resistivity (ρ) of the radiation detection elements before and after annealing was measured at an operating voltage of 500V. Specifically, the current (I) and voltage (V) values ​​were measured when an operating voltage of 500V was applied to the radiation detection elements, and the resistance (R) was calculated using the formula R = V / I. Based on the element's cross-sectional area (S): 4mm × 4mm and thickness (L): 1.4mm, the resistance was calculated using the formula ρ = R × S / L. The evaluation results are shown in Table 3 and... Figure 10 .

[0082] According to Table 3 and Figure 10It can be seen that in the samples that underwent annealing at 150℃ for 30 minutes, 1 hour, 6 hours, and 24 hours, the resistivity at a working voltage of 500V was 1×10⁻⁶. 11 Above Ωcm. Furthermore, it is known that annealing for such a short time as 30 minutes increases resistivity, showing a saturation trend. (Experimental Example 6: Evaluation of the annealing temperature dependence of μτ value) Multiple radiation detection elements manufactured in Example 1 were placed in an annealing furnace and subjected to annealing (electrode annealing) at 100°C for 24 hours, 150°C for 24 hours, 200°C for 24 hours, and 250°C for 24 hours, respectively. The annealing atmosphere was set as a flowing gas of N2 at a flow rate of 10 L / min.

[0083] Next, the radiation detection elements before annealing and the radiation detection elements after annealing are respectively configured... Figure 1 The radiation detector shown measures the emission of cobalt (cobalt) when bias voltages of 250V, 500V, 700V, and 900V are applied. 57 The spectrum of 122 keV gamma rays emitted by Co.

[0084] Next, the peak channels (peak positions) of the spectra at each bias voltage are determined, and the bias dependence of the peak channels is plotted graphically. The correlation of the peak channels is then fitted using the model formula "Hecht formula" shown in equation (3) below (μτ is the feedback parameter). In equation (3), CH is shown. peak Peak channel, V out Signal voltage, V bias : Bias voltage, D: Component thickness.

[0085] [Formula 3] The evaluation results are shown in Table 4 and Figure 11 According to Table 4 and Figure 11 It is known that the μτ value remains almost unchanged before and after annealing (no change up to 250°C). Therefore, it is expected that the operating current of the device can be reduced without deteriorating the μτ value (the product of mobility and carrier lifetime), thereby improving the operating characteristics (energy resolution) against radiation. (Experimental Example 7: Evaluation of the annealing time dependence of μτ value) Multiple radiation detection elements manufactured in Experimental Example 1 were placed in an annealing furnace and subjected to annealing (electrode annealing) at 150°C for 30 minutes, 1 hour, 6 hours, and 24 hours, respectively. The annealing atmosphere was set as a flowing gas of N2 at a flow rate of 10 L / min.

[0086] Next, the radiation detection elements before annealing and the radiation detection elements after annealing are respectively configured... Figure 1 The radiation detector shown measures the emission of cobalt (cobalt) when bias voltages of 250V, 500V, 700V, and 900V are applied. 57 The spectrum of 122 keV gamma rays emitted by Co.

[0087] Next, the peak channels (peak positions) of the spectra of each bias voltage are obtained, the bias voltage dependence of the peak channels is plotted, and the correlation of the peak channels is fitted using the model formula "Hecht formula" shown in the above formula (3) (μτ is the feedback parameter).

[0088] The evaluation results are shown in Table 5 and Figure 12 According to Table 5 and Figure 12 It is known that the μτ value remains almost unchanged until at least 24 hours of annealing. Therefore, it is expected that the operating current of the device can be reduced without deteriorating the μτ value (the product of mobility and carrier lifetime), thereby improving the operating characteristics (energy resolution) against radiation. Explanation of reference numerals in the attached figures 1: Radiation detector; 2: Radiation detection element; 3: Capacitor; 4: Amplifier (amplification section); 5: Multichannel analyzer; 6: Compound semiconductor crystal substrate; 6a: Main surface (A surface); 6b: Main surface (B surface); 7: Common electrode (metal electrode); 8: Pixel electrode (metal electrode); 61: Bulk crystal; 62: Intermediate layer.

Claims

1. A radiation detection element, wherein, include: A compound semiconductor crystal substrate formed from zinc cadmium telluride with indium added as an impurity; as well as Metal electrodes disposed on the surface of the compound semiconductor crystal substrate, The radiation detection element is for... 57 The energy resolution of the 122 keV gamma rays emitted by Co is below 7%.

2. The radiation detection element according to claim 1, wherein, The above refers to the from 57 The energy resolution of the 122 keV gamma rays emitted by Co is less than 5%.

3. The radiation detection element according to claim 1, wherein, The above refers to the from 57 The energy resolution of the 122 keV gamma rays emitted by Co is below 3.4%.

4. The radiation detection element according to claim 1, wherein, The ideal coefficient n for IV characteristics is 1.0 to 1.

5.

5. The radiation detection element according to claim 1, wherein, The resistivity at an operating voltage of 500V is 1×10⁻⁶. 11 Ωcm or more.

6. A radiation detector, wherein, include: Radiation detection element as described in any one of claims 1 to 5; as well as The amplification section is connected to the radiation detection element and amplifies the electrical signal output from the radiation detection element.

7. A method for manufacturing a radiation detection element, wherein, include: The process of cutting wafers from an ingot containing zinc cadmium telluride compound semiconductor crystals with indium added as an impurity, and then grinding them; The process of forming metal electrodes on the surface of the wafer; The process of cutting out a radiation detection element from a wafer on which the metal electrodes are formed; and The radiation detection element is placed in an annealing furnace and annealed at 100-200°C for 10 minutes to 24 hours.

8. A method for manufacturing a radiation detection element, wherein, include: The process of cutting wafers from an ingot containing zinc cadmium telluride compound semiconductor crystals with indium added as an impurity, and then grinding them; The process of forming metal electrodes on the surface of the wafer; The wafer with the metal electrodes formed thereon is placed in an annealing furnace and annealed at 100–200°C for 10 minutes to 24 hours; and The process of cutting radiation detection elements from the annealed wafer.

9. The method for manufacturing a radiation detection element according to claim 7 or 8, wherein, The radiation detection element is for... 57 The energy resolution of the 122 keV gamma rays emitted by Co is below 7%.

10. The method for manufacturing a radiation detection element according to claim 7, wherein, In the process of cutting radiation detection elements from the wafer, 30 radiation detection elements are cut from one wafer. After the annealing process, the results are measured under the same conditions for the radiation detection elements from the wafer. 57 The standard deviation of the energy resolution of the 30 radiation detection elements at the energy resolution of 122 keV gamma rays emitted by Co is less than 2%.

11. The method for manufacturing a radiation detection element according to claim 8, wherein, In the process of cutting radiation detection elements from the wafer, 30 radiation detection elements are cut from one wafer, and the results are measured under the same conditions for radiation detection elements from the wafer. 57 The standard deviation of the energy resolution of the 30 radiation detection elements at the energy resolution of 122 keV gamma rays emitted by Co is less than 2%.

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