CN112054087B - Graphene semiconductor radiation detection device and preparation method thereof - Google Patents
Graphene semiconductor radiation detection device and preparation method thereof Download PDFInfo
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Abstract
The invention provides a graphene semiconductor radiation detector and a preparation method thereof, which adopts a resistance value of a graphene field effect transistor as a physical measurement quantity and specifically comprises the following steps: the surface element array graphene field effect transistor structure is constructed by preparing a surface element array graphene structure layer on a crystal surface with high atomic number radiation effect, and the surface element array graphene field effect transistor structure adopts a semiconductor medium CdZnTe crystal material as a ray photon absorption medium and a graphene field effect transistor applied with bias voltage as a signal generation layer. According to the invention, the resistance value of the graphene material layer is used as a detection physical quantity, so that the high cost and complexity of the traditional charge sensitive preamplifier circuit can be effectively reduced, and meanwhile, the anti-interference performance of a signal transmission link can be effectively improved.
Description
Technical Field
The invention belongs to the field of radiation detection devices, and particularly relates to a semiconductor radiation detection device and a preparation method thereof
Background
The invention relates to the technical field of radiation energy spectrum detection of X-rays, Gamma-rays, neutron rays and the like, in particular to a radiation energy spectrum detection chip framework for ray photon pulse amplitude detection and discrimination and counting based on a semiconductor radiation medium material.
For a radiation detector, different X-rays or radioactive nuclides can be distinguished through the difference of radiation energy of the rays, and the measurement of the intensity of the X-rays and the energy of different nuclides contained in Gamma rays is realized.
Radiation detectors can be classified into gas ionization counters, scintillator detectors, semiconductor detectors, and the like, depending on the materials used for the detectors. Gas ionization counters appeared earliest, but since the same pulse output was generated for different radiation inputs, the sensitivity was poor and it was difficult to distinguish the type of radiation. The scintillator detector must be used in combination with a photomultiplier tube or the like, limiting the improvement in energy resolution. Semiconductor radiation detectors have high detection efficiency and energy resolution and are representative of high energy resolution radiation detectors today.
Compared with the traditional gas and scintillator radiation detectors, the semiconductor radiation detector has the main advantages that the detection and discrimination of incident radiation photon energy information can be realized by detecting induced charge generated by photon-generated carrier migration, and meanwhile, the semiconductor radiation detector is packaged with a front-end reading system chip and can be manufactured into an imaging detector with high resolution and small area.
Typically, a semiconductor radiation detector consists essentially of a semiconductor crystal material, readout electrodes, sensing signal processing circuitry and a control system. In the aspect of semiconductor crystal materials, different radiation medium crystal materials can be adopted according to the radiation energy range required to be detected, and undoped Si crystal materials can be adopted for low-energy X-ray detection; high atomic number CdTe/CdZnTe material may be used for high energy X ray, Gamma ray and neutron radiation.
At present, the semiconductor radiation detector adopts a detector structure with a more efficient unipolar carrier collection characteristic, namely, a response signal of the detector mainly takes an induction signal caused by electron carrier migration, and the problems of low energy resolution and the like caused by low hole mobility of a semiconductor crystal material can be well improved. At present, a unipolar detector structure in which an anode is a pixel array electrode and a cathode is an integral planar electrode has been one of the main structural forms of a semiconductor imaging and energy spectrum detector, and specifically, refer to fig. 1, which is a schematic structural view of a conventional pixel array semiconductor radiation detector.
The pixel array semiconductor radiation detector has the position sensitivity characteristic, the size of a pixel anode directly determines the spatial resolution of the imaging detector, and meanwhile the small pixel effect existing in the pixel array electrode structure enables the detector to have the unipolar carrier collection characteristic, so that the energy resolution can be obviously improved. Therefore, a large-area pixel array detector with a small-sized anode unit becomes a mainstream semiconductor radiation detector structure for detecting X-ray and Gamma-ray radiation at home and abroad.
The semiconductor radiation detector with the surface element pixel array structure mainly comprises the following core components: the device comprises a semiconductor material cadmium zinc telluride (CdZnTe) crystal which interacts with radiation photons, a surface element array reading electrode prepared on the surface of the semiconductor material and an Application Specific Integrated Circuit (ASIC) tightly connected with the reading electrode. As can be seen from fig. 1, the surface element pixel array semiconductor radiation detector uses an integral semiconductor crystal to react with radiation photons, and then the surface element pixel array electrodes collect induced charge signals generated inside the crystal, and meanwhile, in order to make the detector have position sensitivity and imaging capability, the surface element pixel array electrodes are connected with the readout ASIC through a flip chip bonding process.
In terms of a detector signal generation and processing process, when incident ray photons generate interaction in a semiconductor material, charge carriers in direct proportion to the energy of the incident photons are generated in a crystal, the carriers migrate to a pixel electrode under the influence of an external electric field, induced charges are generated on a reading electrode at a corresponding position in the electronic carrier migration process, an ASIC circuit connected with the reading electrode in an inverted mode converts the induced charge signals into voltage signals through a charge sensitive preamplification circuit in each electrode signal channel, voltage pulse signals with low signal to noise ratio output by a front discharge circuit are further processed into Gaussian voltage pulses with high signal to noise ratio through a pulse shaping circuit and a voltage pulse height comparator, and then subsequent pulse amplitude spectrum processing is carried out on the Gaussian voltage pulses. The prior art has the following disadvantages: at present, the traditional semiconductor radiation detector adopts the main signal processing flow of measuring and processing the induced charge signal generated in the migration process of the photon-generated carrier signal, carries out noise reduction and amplification processing on the charge signal through various low-noise and high-signal-to-noise ratio electronic circuit technologies, and converts the induced charge signal into a voltage signal so as to facilitate the screening processing of the pulse amplitude in the later period.
In this signal processing flow, the induced charge signal is used as an original signal output by the detector, which has poor anti-interference performance, and the charge sensitive amplifying circuit usually adopted has extremely high requirements on signal noise and electromagnetic shielding of the detector, so that the pre-amplifying circuit and the readout electrode must be tightly connected by flip-chip bonding to reduce the signal transmission path. Meanwhile, different low-noise charge sensitive amplifying circuits are designed to sense a first-stage processing circuit of a charge signal, due to the requirements of high sensitivity and high signal-to-noise ratio, the preamplification circuits are generally complex, so that the corresponding ASIC chip circuit area is large, the cost is high, the noise performance is not ideal, and the first-stage processing circuit generally needs a further shaping amplifying circuit to process.
Disclosure of Invention
The present invention is directed to solving the above problems of the prior art. A graphene semiconductor radiation detection device and a preparation method thereof are provided. The technical scheme of the invention is as follows:
a graphene semiconductor radiation detection device adopts a resistance value of a graphene field effect transistor as a physical measurement quantity, and specifically comprises: the detector comprises a semiconductor crystal material layer, an insulating isolation layer, a graphene material layer and an induction signal electrode layer, wherein the insulating isolation layer is arranged on the surface of the semiconductor crystal material layer, the graphene material layer is arranged on the insulating isolation layer, the induction signal electrode layer is arranged on the surface of the graphene material layer, the semiconductor crystal material layer is prepared from CdZnTe crystals with high atomic number and is used for generating interaction with incident radiation photons and generating electron cloud, the semiconductor crystal material layer receives radiation surface to prepare a metal electrode cathode layer, an external bias voltage is applied to the metal electrode cathode layer, the insulating isolation layer is used for blocking the leakage current of the detector semiconductor, the graphene material layer is used for inducing the change of an electric field inside the semiconductor material caused by radiation, the induction signal electrode layer is used for connecting the graphene material and the front-end signal collection of a resistance measurement circuit, and mainly collects an electric signal in direct proportion to the resistance state of the graphene material layer, the graphene material layer is of a surface element array structure, the resistance state of the graphene material layer is in direct proportion to the incident radiation intensity, the graphene field effect tube structure in the surface element array form is constructed, the signal output end of the detector is an induction signal electrode layer, the electrode is prepared from a high-work-function material, and the graphene field effect tube structure is formed by an insulating isolation layer, the graphene material layer and an induction signal collecting layer in the detector structure.
Further, the thickness of the semiconductor crystal material layer and the thickness of the insulating isolation layer satisfy 1000: 1 (e.g. semi-conducting)5mm of bulk crystal layer and 5 mu m of insulating separation layer), wherein the thickness of the graphene material layer is the common physical thickness of the graphene material
Further, the insulating isolation layer is made of SiO 2.
Further, before the radiation detection of the semiconductor radiation detection device is normally performed, the external bias voltage needs to be optimally adjusted to enable the graphene material layer to be at a critical point of a Dirac curve, and under the condition, once a bias electric field of the graphene material layer changes, the resistance value of the graphene material layer can obviously change.
A preparation method based on a radiation detection device comprises the following steps:
and 4, after the surface element array graphene layer is prepared, preparing electrodes by using a standard semiconductor process again, forming a surface element array electrode on the surface element array graphene layer by using a photoetching pattern In a surface element array shape, growing a metal electrode (Au, gold electrode or In, indium electrode) with the thickness of 100nm by using an electron beam evaporation instrument, and completing the preparation of the device.
Further, in the step 1, according to different doping degrees of the adopted CdZnTe crystal, corresponding relaxation temperatures, carrier mobility, purity and carrier lifetime are also different, and the final resistance signal is affected.
Further, the step 2 of transferring graphene to the SiO2 insulating layer from the preparation substrate comprises the following steps:
(1) preparing PMMA colloid on the surface of the graphene by adopting a spin coating process;
(2) standing for 15 minutes in a high-temperature environment, improving the uniformity of the PMMA colloid through the volatilization of the PMMA colloid organic solvent, and enhancing the combination degree of the graphene film and the PMMA colloid;
(3) removing the graphene preparation substrate through 8% Fe (NO3)3 solution corrosion, wherein the corrosion time is 9 hours, after the substrate is corroded, cleaning PMMA glue with the graphene prepared on the surface by using deionized water, and adsorbing one side of the graphene layer by using one side of a SiO2 thin film layer of a CdZnTe crystal;
(4) placing the device in an environment with the temperature of 50 ℃ for drying until the moisture on the surface is evaporated, and respectively heating the device for 15 minutes at the temperature of 90 ℃ and 10 minutes at the temperature of 130 ℃;
(5) inverting the device, washing one side of the graphene/PMMA layer of the device from bottom to top by using an acetone solution through a washing device, removing PMMA colloid, and finally obtaining the graphene film on the surface of the CdZnTe/SiO2 substrate.
Furthermore, the radiation detection device can be prepared by replacing the detector with an interdigital grid and a hemispherical electrode.
The invention has the following advantages and beneficial effects:
the invention discloses a semiconductor radiation detection system structure adopting a resistance value of a graphene field effect transistor as a physical quantity to be measured and a preparation method of a graphene material layer related to detection signal generation.
According to the invention, a SiO2 insulating isolation layer is prepared on the surface of a CdZnTe transistor anode with a high atomic number, a surface element array structure graphene signal layer and a high work function metal electrode layer are prepared on the insulating isolation layer, a surface element array type graphene field effect transistor structure is constructed, and a signal output end of a detector is a high work function material output electrode. Therefore, unlike the conventional semiconductor radiation detector which relies on charge collection for radiation detection, the graphene resistance state change radiation detector provided by the present invention relies on a significant change in the impedance of the graphene material to detect the amount of ionizing radiation in the absorbing medium. The induced charge at the graphene electrode side causes a change in the internal electric field and thus a change in its conductivity, because the impedance value of the graphene material is very sensitive to the weak change of the internal electric field near the preset Dirac state, therefore, the graphene signal generation layer of the detector has the same function as a charge sensitive preamplifier circuit adopted by the traditional radiation detector, but the difference is that the resistance value of the graphene material layer is taken as the detection physical quantity without the charge transfer process and the corresponding induced charge collection time, under the condition of unchanged working environment, the resistance value change of the graphene material layer is only related to the radiation intensity, therefore, the radiation intensity can be detected by adopting the resistance measuring circuit with strong anti-interference capability and simpler circuit structure, the high cost and the complexity of the traditional charge sensitive preamplification circuit can be effectively reduced, and the anti-interference performance of a signal transmission link can be effectively improved. The signal processing process of the detector is simpler and more direct, the possibility of noise interference is reduced, and the signal-to-noise ratio of the device is improved.
Drawings
FIG. 1 is a schematic diagram of a conventional pixel array semiconductor radiation detector configuration;
FIG. 2 is a schematic diagram of a graphene resistive radiation detection system according to a preferred embodiment of the present invention;
FIG. 3 is a schematic signal transmission diagram of a graphene resistance state radiation detection system;
fig. 4 is a schematic diagram of resistance variation of graphene layers under different radiation intensity conditions;
FIG. 5 is a graphene resistance state sensitive interdigital electrode;
fig. 6 is a graphene resistance state sensitive hemispherical electrode.
Detailed Description
The technical solutions in the embodiments of the present invention will be described in detail and clearly with reference to the accompanying drawings. The described embodiments are only some of the embodiments of the present invention.
The technical scheme for solving the technical problems is as follows:
the invention discloses a semiconductor radiation detection device adopting a resistance value of a graphene field effect transistor as a physical quantity to be measured, and relates to a key technical point of a structure of a graphene resistance value sensitive detector and a sequential preparation method of a corresponding detector structure, wherein the preparation method comprises the preparation of an insulating layer, a graphene layer and a signal electrode layer.
The detector structure is shown in FIG. 2, an insulating isolation layer (SiO) is prepared on the surface of the CdZnTe crystal anode with high atomic number 2 ) The method comprises the steps of preparing a surface element array structure graphene resistance state signal layer on an insulating isolation layer, constructing a surface element array type graphene field effect tube structure, enabling a signal output end of a detector to be a signal output electrode layer, and preparing electrodes such as (gold and Au) by adopting high work function materials. Wherein the thickness of the semiconductor crystal material layer and the thickness of the insulating layer satisfy 1000: 1, the thickness of the graphene layer is the general physical thickness of the graphene material
The basic principle and the signal transmission process of the radiation detector described in the invention are mainly shown in fig. 3, the detector signal is mainly generated by a semiconductor medium CdZnTe crystal after receiving radiation, and a graphene field effect tube applied with bias voltage is adopted as an output signal generating element.
Because insulating SiO is prepared between the graphene and the CdZnTe crystal 2 And applying bias voltage to the graphene layer and the crystal layer and generating an external electric field inside the detector. The radiation detector needs to optimally adjust an external bias before normal radiation detection is carried out, so that the graphene layer is positioned at the critical point of a Dirac curve. Under the condition, once the bias electric field of the graphene layer is changed, the resistance value of the graphene layer can be obviously changed. In thatThe high work function metal surface electrode prepared on the surface of the graphene is used as a drain electrode (drain) and a source electrode (source) of the graphene field effect transistor to provide impressed current for the graphene layer and complete the measurement of the surface resistivity. Briefly, the concentration of photon-generated carriers generated by different radiation intensities is different, so that the concentration distribution of carriers in the CdZnTe crystal is correspondingly changed, the change of an electric field in the graphene material layer is directly influenced, and the change of the surface resistance of the graphene layer is further caused.
Thus, unlike conventional semiconductor radiation detectors that rely on charge collection for radiation detection, graphene resistance state change radiation detectors rely on a significant change in impedance to detect the amount of ionizing radiation in an absorbing medium. The induced charge on the graphene electrode side can cause the change of an internal electric field and further cause the change of the conductivity of the graphene electrode, and because the impedance value of the graphene material is very sensitive to the weak change of the internal electric field near the preset Dirac state, the graphene signal generation layer of the detector has the same function as a charge sensitive preamplification circuit adopted by the traditional radiation detector, but does not need charge migration and corresponding induced charge collection time.
As mentioned above, the key technical points involved in the present invention also include the preparation method of the corresponding detector structure:
firstly, graphene layers are prepared on the surfaces of CdTe and CdZnTe crystals by mechanical stripping and chemical vapor deposition. Graphene is deposited on the surface of the CdZnTe crystal to which bias voltage is applied, and it is noted that corresponding relaxation temperature, carrier mobility, purity and carrier lifetime are different according to different doping degrees of the CdZnTe crystal, and the final resistance signal is affected.
Preparing a SiO2 film on the surface of the CdZnTe crystal as an insulating isolation layer by adopting a standard Plasma Enhanced Chemical Vapor Deposition (PECVD) method, and realizing the deposition of a 500nm SiO2 film at a lower temperature
Preparing graphene by chemical vapor deposition with the SiO2 insulating layer as a substrate, and transferring the graphene to the SiO2 insulating layer from the prepared substrate, wherein the transferring step is as follows:
(1) preparation of PMMA colloid on graphene surface by adopting spin coating process
(2) Standing for 15 minutes in a high-temperature environment, improving the uniformity of the PMMA colloid through volatilization of the PMMA colloid organic solvent, and enhancing the combination degree of the graphene film and the PMMA colloid.
(3) And removing the graphene preparation substrate by 8% Fe (NO3)3 solution corrosion, wherein the corrosion time is 9 hours, after the substrate is corroded, cleaning PMMA glue with the graphene prepared on the surface by using deionized water, and adsorbing one side of the graphene layer by using one side of a SiO2 thin film layer of a CdZnTe crystal.
(4) And (3) placing the device in an environment with the temperature of 50 ℃ for drying until the moisture on the surface is evaporated, and heating to 90 ℃ for 15 minutes and 130 ℃ for 10 minutes respectively.
(5) Inverting the device, washing one side of the graphene/PMMA layer of the device from bottom to top by using an acetone solution by using a washing device, removing PMMA colloid, and finally obtaining the graphene film on the surface of the CdZnTe/SiO2 substrate
After the transfer of graphene is completed, further preparing a surface element array graphene layer by adopting a standard semiconductor photoetching technology, wherein a photoetching pattern is in a surface element array shape, and the surface element array graphene layer is formed on the graphene layer of the device, and the key steps are as follows: and (3) reserving photoresist on the part of the graphene surface element array needing to be reserved, removing the photoresist on the rest part through developing solution, and removing redundant graphene materials of the device through a dry etching machine, wherein the etching parameters are oxygen plasma pressure of 20mTorr (millitorr), power of 30W (watt), oxygen flow of 30sccm (standard state milliliter/minute) and etching time of 20s (second).
Preparing electrodes by using a standard semiconductor process again after the preparation of the surface element array graphene layer is finished, forming surface element array electrodes on the surface element array graphene layer by photoetching a pattern In a surface element array shape, growing metal electrodes (Au, gold electrodes or In, indium electrodes) with the thickness of 100nm by using an electron beam evaporation instrument, and completing the preparation of devices
The radiation detector structure and the preparation method described in the present invention are both surface element pixel array structures based on the signal output electrode structure, and the signal output electrode structure is an electrode structure such as an interdigital grid, a hemispherical electrode, and the like, and can also achieve the effect of detecting the incident radiation intensity based on the resistance state change of the graphene layer, as shown in fig. 5 and 6, the device preparation method described in the present invention is also applicable to the preparation of detectors of interdigital grids and hemispherical electrodes.
The systems, apparatuses, modules or units described in the above embodiments may be specifically implemented by a computer chip or an entity, or implemented by a product with certain functions. One typical implementation device is a computer. In particular, the computer may be, for example, a personal computer, a laptop computer, a cellular telephone, a camera phone, a smartphone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or a combination of any of these devices.
It should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
The above examples are to be construed as merely illustrative and not limitative of the remainder of the disclosure in any way whatsoever. After reading the description of the invention, the skilled person can make various changes or modifications to the invention, and these equivalent changes and modifications also fall into the scope of the invention defined by the claims.
Claims (2)
1. A preparation method based on a graphene semiconductor radiation detection device, wherein the graphene semiconductor radiation detection device adopts a resistance value of a graphene field effect transistor as a physical measurement quantity, and specifically comprises the following steps: the sensor comprises a semiconductor crystal material layer, an insulation isolation layer, a graphene material layer and an induction signal electrode layer, wherein the insulation layer is arranged on the surface of the semiconductor crystal material layerThe detector comprises an insulating layer, a graphene material layer is arranged on the insulating layer, an induction signal electrode layer is arranged on the surface of the graphene material layer, the semiconductor crystal material layer is prepared from high atomic number CdZnTe crystals and used for generating interaction with incident radiation photons and generating an electron cloud, the semiconductor crystal material layer is used for receiving the radiation surface to prepare a metal electrode cathode layer and applying an external bias voltage, the insulating layer is used for blocking the leakage current of a detector semiconductor, the graphene material layer is used for inducing the change of an electric field in the semiconductor material caused by radiation, the induction signal electrode layer is used for connecting the graphene material and the front end signal collection of a resistance value measuring circuit and collecting an electric signal in direct proportion to the resistance state of the graphene material layer, the graphene material layer is a surface element array structure graphene material layer, the resistance state of the graphene material layer is in direct proportion to the intensity of the incident radiation, and a surface element array type graphene field effect transistor structure is constructed, the signal output end of the detector is an induction signal electrode layer, an electrode is prepared from a high-work-function material, and a graphene field effect tube structure is formed by an insulating isolation layer, a graphene material layer and an induction signal collecting layer in the detector structure; the thickness of the semiconductor crystal material layer and the thickness of the insulating isolation layer meet 1000: 1 in a proportional relationship; before the radiation detection of the semiconductor radiation detection device is normally carried out, external bias voltage needs to be optimally adjusted to enable the graphene material layer to be located at the critical point of a Dirac curve, under the condition, once the bias electric field of the graphene material layer changes, the resistance value of the graphene material layer can obviously change, and the insulating isolation layer adopts SiO 2 The method is characterized by comprising the following steps:
step 1, firstly, preparing a graphene layer on the surfaces of CdTe and CdZnTe crystals by adopting a mechanical stripping and chemical vapor deposition method, and depositing graphene on the surface of the CdZnTe crystals to which bias voltage is applied;
step 2, preparing a SiO2 film on the surface of the CdZnTe crystal by adopting a standard Plasma Enhanced Chemical Vapor Deposition (PECVD) method as an insulating isolation layer, depositing a 500nm SiO2 film by taking a SiO2 insulating layer as a substrate, preparing graphene by adopting chemical vapor deposition, and transferring the graphene to the SiO2 insulating layer from the prepared substrate;
step 3, after the graphene transfer is completed, preparing a surface element array graphene layer by adopting a standard semiconductor photoetching technology, forming a photoetching pattern into a surface element array shape, and forming the surface element array graphene layer on the graphene layer of the device, wherein the key steps are as follows: the method comprises the following steps that photoresist is reserved on a part, needing to be reserved, of a graphene surface element array, the photoresist is removed on the other part through developing solution, redundant graphene materials of a device are removed through a dry etching machine, the etching parameters are oxygen plasma pressure of 20mTorr (millitorr), power of 30W (watt), oxygen flow of 30sccm (standard state milliliter/minute) and etching time of 20s (second);
and 4, after the surface element array graphene layer is prepared, preparing electrodes by using a standard semiconductor process again, forming a surface element array electrode on the surface element array graphene layer by using a photoetching pattern in a surface element array shape, growing a metal electrode with the thickness of 100nm by using an electron beam evaporation instrument, and completing the preparation of the device.
2. The method of manufacturing a radiation detecting device according to claim 1,
the step 2 of transferring graphene to the SiO2 insulating layer from the preparation substrate comprises the following steps:
(1) preparing PMMA colloid on the surface of the graphene by adopting a spin coating process;
(2) standing for 15 minutes in a high-temperature environment, improving the uniformity of PMMA colloid through the volatilization of the PMMA colloid organic solvent, and enhancing the combination degree of the graphene film and the PMMA colloid;
(3) removing the graphene preparation substrate by corroding with 8% Fe (NO3)3 solution for 9 hours, cleaning PMMA (polymethyl methacrylate) glue with graphene prepared on the surface by using deionized water after the substrate is corroded, and adsorbing one side of the graphene layer by using one side of a SiO2 thin film layer of a CdZnTe crystal;
(4) placing the device in an environment with the temperature of 50 ℃ for drying until the moisture on the surface is evaporated, and respectively heating the device for 15 minutes at the temperature of 90 ℃ and 10 minutes at the temperature of 130 ℃;
(5) inverting the device, washing one side of the graphene/PMMA layer of the device from bottom to top by using an acetone solution through a washing device, removing PMMA colloid, and finally obtaining the graphene film on the surface of the CdZnTe/SiO2 substrate.
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