CN112054087B - Graphene semiconductor radiation detection device and preparation method thereof - Google Patents

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

A kind of graphene semiconductor radiation detection device and preparation method thereof

technical field

The invention belongs to the field of radiation detection devices, in particular to a semiconductor radiation detection device and a preparation method thereof

Background technique

The invention relates to the technical field of radiation energy spectrum detection such as X-rays, Gamma rays and neutron rays, in particular to a radiation energy spectrum detection chip structure based on semiconductor radiation medium materials for detecting the amplitude of ray photon pulses and discriminating and counting.

For radiation detectors, different X-rays or radionuclides can be distinguished by the difference in ray radiation energy, so as to realize the measurement of X-ray intensity and different nuclide energies contained in Gamma rays.

Radiation detectors can be classified into gas ionization counters, scintillator detectors, and semiconductor detectors, depending on the materials used in the detectors. The gas ionization counter appeared the earliest, but since the same pulse output is generated for different ray inputs, the sensitivity is poor, and it is difficult to distinguish the type of ray. The scintillator detector must be used together with photomultiplier tubes, which limits the improvement of energy resolution. Semiconductor radiation detectors have high detection efficiency and energy resolution, and are typical representatives of current high-energy-resolution radiation detectors.

Compared with traditional gas and scintillator radiation detectors, the main advantage of semiconductor radiation detectors is that they can detect and discriminate the energy information of incident radiation photons by detecting the amount of induced charges generated by the migration of photogenerated carriers, and at the same time read out with the front-end. SoCs are packaged together to create high-resolution and small-area imaging detectors.

Generally, semiconductor radiation detectors are mainly composed of semiconductor crystal materials, readout electrodes, inductive signal processing circuits and control systems. In terms of semiconductor crystal materials, different radiation-acting dielectric crystal materials can be used according to the radiation energy range to be detected. For low-energy X-ray detection, undoped Si crystal materials can be used; for medium and high-energy X-rays, Gamma rays and neutron radiation High atomic number CdTe/CdZnTe materials can be used.

At present, semiconductor radiation detectors all adopt a more efficient detector structure with unipolar carrier collection characteristics, that is, the response signal of the detector is mainly induced by the migration of electron carriers, which can well improve the semiconductor crystal. Problems such as low energy resolution caused by low hole mobility of materials. At present, the unipolar detector structure in which the anode is a pixel array electrode and the cathode is an overall planar electrode has always been one of the main structural forms of semiconductor imaging and energy spectrum detectors.

The pixel array semiconductor radiation detector has the characteristics of position sensitivity. The size of the pixel anode directly determines the spatial resolution of the imaging detector. At the same time, the "small pixel effect" of the pixel array electrode structure makes the detector have unipolar carrier collection characteristics. , the energy resolution can be significantly improved. Therefore, large-area pixel array detectors with small-sized anode units have become the mainstream semiconductor radiation detector structures for X-ray and Gamma-ray radiation detection at home and abroad.

The semiconductor radiation detector of the surface element pixel array structure is mainly composed of the following core components: the semiconductor material cadmium zinc telluride (CdZnTe) crystal that interacts with the radiation photons, the surface element array readout electrode prepared on the surface of the semiconductor material, and the readout electrode. Tightly connected application specific integrated circuits (ASICs). As can be seen from Figure 1, the surface element pixel array semiconductor radiation detector uses an integral semiconductor crystal to interact with radiation photons, and then the induced charge signals generated inside the crystal are collected by the surface element pixel array electrodes. Imaging capability, the surface element pixel array electrodes are all connected to the readout ASIC through a flip-chip bonding process.

As far as the detector signal generation and processing process is concerned, when the incident ray photons interact in the semiconductor material, charge carriers proportional to the energy of the incident photons are generated inside the crystal. Migrating to the pixel electrode, in the process of electron carrier migration, an induced charge will be generated on the readout electrode at the corresponding position, and the ASIC circuit flip-chip connected to the readout electrode will pass the charge-sensitive preamplifier in each electrode signal channel. The circuit converts the induced charge signal into a voltage signal, and further processes the low signal-to-noise ratio voltage pulse signal output by the preamplifier circuit into a high signal-to-noise ratio Gaussian voltage pulse through the pulse shaping circuit and the voltage pulse height comparator, and then performs Processing of subsequent pulse amplitude spectra. Disadvantages of the prior art: At present, traditional semiconductor radiation detectors use the measurement and processing of the induced charge signal generated by the photo-generated carrier signal during the migration process as the main signal processing process. The circuit technology is used to denoise and amplify the charge signal, and convert the induced charge signal into a voltage signal for later pulse amplitude discrimination processing.

In this signal processing process, the induced charge signal is used as the original signal output by the detector, and its anti-interference performance is poor. The charge-sensitive amplifying circuit usually used has extremely high requirements on signal noise and electromagnetic shielding of the detector, so it is usually necessary to The preamplifier circuit and the readout electrode are tightly connected by flip-chip bonding to reduce the signal transmission path. At the same time, different low-noise charge-sensitive amplifier circuits are designed for the first-stage processing circuit of the induced charge signal. Due to the requirements of high sensitivity and high signal-to-noise ratio, the pre-amplifier circuits are usually more complex, resulting in a larger circuit area of the corresponding ASIC chip. , the cost is higher, and the noise performance is not ideal, and usually requires a further shaping and amplifying circuit for processing.

SUMMARY OF THE INVENTION

The present invention aims to solve the above problems of the prior art. A graphene semiconductor radiation detection device and a preparation method thereof are proposed. The technical scheme of the present invention is as follows:

A graphene semiconductor radiation detection device, which adopts a graphene field effect tube resistance value as a measurement physical quantity, and specifically includes: a semiconductor crystal material layer, an insulating isolation layer, a graphene material layer and an inductive signal electrode layer, wherein the semiconductor crystal material layer An insulating isolation layer is arranged on the surface of the material layer, a graphene material layer is arranged on the insulating isolation layer, an inductive signal electrode layer is arranged on the surface of the graphene material layer, and the semiconductor crystal material layer is prepared with a high atomic number CdZnTe crystal, which is used for and incident radiation. The photons interact and generate electron clouds. The metal electrode cathode layer is prepared on the radiation receiving surface, and an external bias voltage is applied. The insulating isolation layer is used to block the leakage current of the detector semiconductor, and the graphene material layer is used to sense the effect of radiation. The resulting electric field changes inside the semiconductor material, and the sensing signal electrode layer is used to connect the graphene material and the front-end signal collection of the resistance measurement circuit, mainly collecting electrical signals proportional to the resistance state of the graphene material layer. The resistance state of the graphene material layer of the surface element array structure is proportional to the incident radiation intensity, and a graphene field effect tube structure in the form of a surface element array is constructed. In the detector structure, the insulating isolation layer, the graphene material layer and the sensing signal collecting layer form a graphene field effect tube structure.

Further, the thickness of the semiconductor crystal material layer and the thickness of the insulating isolation layer satisfy a proportional relationship of 1000:1 (eg: 5 mm for the semiconductor crystal layer, 5 μm for the insulating isolation layer), and the thickness of the graphene material layer is the usual physical thickness of the graphene material.

Further, the insulating isolation layer adopts SiO2.

Further, before the semiconductor radiation detection device performs radiation detection normally, the external bias voltage needs to be optimally adjusted so that the graphene material layer is at the critical point of the Dirac curve. Under this condition, once the graphene material layer is biased by the electric field When the change occurs, the resistance value of the graphene material layer will change significantly.

A preparation method based on a radiation detection device, comprising the following steps:

Step 1. First, a graphene layer is prepared on the surface of CdTe and CdZnTe crystals by mechanical exfoliation and chemical vapor deposition, and the graphene is deposited on the surface of the CdZnTe crystal to which the bias voltage has been applied;

Step 2. Use standard plasma enhanced chemical vapor deposition (PECVD) to prepare a SiO2 film on the surface of CdZnTe crystal as an insulating isolation layer, and realize 500nm SiO2 film deposition at a lower temperature. The SiO2 insulating layer is used as the base, and chemical vapor deposition is used to prepare graphite graphene, and then transfer graphene from the prepared substrate to the SiO2 insulating layer;

Step 3. After the graphene transfer is completed, a standard semiconductor lithography technique is used to prepare a plane element array graphene layer. The lithography pattern is in the shape of a plane element array, and a plane element array graphene layer is formed on the graphene layer of the device. The key step It is: the part of the graphene panel array that needs to be retained retains the photoresist, the rest is removed by the developer solution, and the excess graphene material of the device is removed by a dry etching machine, and the etching parameter is an oxygen plasma pressure of 20 mTorr (milliseconds). Torr), power 30W (W), oxygen flow 30sccm (standard state ml/min) conditions, etching time 20s (seconds);

Step 4. After the surface element array graphene layer is prepared, the standard semiconductor process is used to prepare electrodes again. The lithography pattern is in the shape of a surface element array. A surface element array electrode is formed on the surface element array graphene layer, and an electron beam evaporation apparatus is used. A metal electrode (Au, gold electrode or In, indium electrode) with a thickness of 100 nm is grown, and the device preparation is completed.

Further, according to the different doping degrees of the CdZnTe crystal used in the step 1, the corresponding relaxation temperature, carrier mobility, purity, and carrier lifetime are also different, which will affect the final resistance signal.

Further, the step of transferring graphene from the prepared substrate to the SiO2 insulating layer in step 2 is as follows:

(1) Prepare PMMA colloid on graphene surface by spin coating process;

(2) stand for 15 minutes in a high temperature environment, improve the uniformity of the PMMA colloid through the volatilization of the organic solvent of the PMMA colloid, and enhance the degree of bonding between the graphene film and the PMMA colloid;

(3) 8% Fe(NO3)3 solution was used to etch and remove graphene to prepare the substrate. The etching time was 9 hours. After the substrate corrosion was completed, the PMMA glue on which the graphene was prepared was cleaned with deionized water, and the SiO2 thin film layer of CdZnTe crystal was used. One side adsorbs the graphene layer on one side;

(4) drying the device in an environment of 50 degrees Celsius until the surface water evaporates, heating to 90 degrees Celsius for 15 minutes, and 130 degrees Celsius for 10 minutes;

(5) Invert the device, use a washing device to rinse the graphene/PMMA layer side of the device with acetone solution from bottom to top, remove the PMMA colloid, and finally obtain a graphene film on the surface of the CdZnTe/SiO2 substrate.

Further, the radiation detection device can be replaced by the interdigitated grid, the hemispherical electrode detector preparation.

The advantages and beneficial effects of the present invention are as follows:

The invention describes a structure of a semiconductor radiation detection system that adopts the resistance value of a graphene field effect tube as a measured physical quantity and a preparation method of a graphene material layer related to the generation of detection signals.

In the invention, a SiO2 insulating isolation layer is prepared on the surface of a high atomic number CdZnTe crystal anode, a graphene signal layer with a surface element array structure and a high work function metal electrode layer are prepared on the insulating isolation layer, and a graphene field effect tube in the form of a surface element array is constructed. Structure, the detector signal output terminal is a high work function material output electrode. Therefore, different from the traditional semiconductor radiation detectors that rely on charge collection for radiation detection, the graphene resistance state change radiation detector proposed by the present invention relies on the obvious change of the graphene material impedance to detect the amount of ionizing radiation in the absorption medium. The induced charge on the graphene electrode side will cause the change of the internal electric field and then the change of its conductivity. Since the impedance value of the graphene material is very sensitive to the slight change of the internal electric field near the preset Dirac state, the detector graphite The graphene signal generation layer has the same function as the charge sensitive preamplifier circuit used in the traditional radiation detector, but the difference is that it does not require the charge migration process and the corresponding induction charge collection time, and the resistance value of the graphene material layer is used to detect the physical quantity. , Under the condition that the working environment remains unchanged, the change of the resistance value of the graphene material layer is only related to the radiation intensity, so that the resistance value measurement circuit with strong anti-interference ability and simpler circuit structure can be used to detect the radiation intensity, which can effectively reduce the The high cost and complexity of the traditional charge-sensitive preamplifier circuit can effectively improve the anti-interference of the signal transmission link. This also makes the signal processing process of the detector simpler and more direct, reduces the possibility of being interfered by noise, and improves the signal-to-noise ratio of the device.

Description of drawings

1 is a schematic structural diagram of a conventional pixel array semiconductor radiation detector;

2 is a schematic structural diagram of a graphene resistance radiation detection system according to a preferred embodiment provided by the present invention;

Fig. 3 is the signal transmission schematic diagram of graphene resistance state radiation detection system;

Fig. 4 is the schematic diagram of the resistance value change of graphene layer under different radiation intensity conditions;

Fig. 5 is graphene resistance state sensitive interdigital electrode;

Figure 6 is a graphene resistance-sensitive hemispherical electrode.

Detailed ways

The technical solutions in the embodiments of the present invention will be described clearly and in detail below with reference to the accompanying drawings in the embodiments of the present invention. The described embodiments are only some of the embodiments of the invention.

The technical scheme that the present invention solves the above-mentioned technical problems is:

The invention describes a semiconductor radiation detection device using the resistance value of a graphene field effect tube as a measurement physical quantity. The key technical points involved in the invention are the structure of the graphene resistance value sensitive detector and the sequential preparation method of the corresponding detector structure, Including the preparation of insulating layer, graphene layer and signal electrode layer.

The detector structure is shown in Figure 2. An insulating isolation layer (SiO ₂ ) is prepared on the surface of the high atomic number CdZnTe crystal anode. On the insulating isolation layer, a graphene blocking state signal layer with a planar element array structure is prepared, and a graphite in the form of a planar element array is constructed. The structure of the olefin field effect transistor, the signal output end of the detector is the signal output electrode layer, and the electrode is usually prepared by using a high work function material, such as (gold, Au). The thickness of the semiconductor crystal material layer and the thickness of the insulating layer satisfy the ratio of 1000:1, and the thickness of the graphene layer is the usual physical thickness of the graphene material.

The basic principle and signal transmission process of the radiation detector described in the present invention are mainly shown in Figure 3. The detector signal is mainly generated by the semiconductor dielectric CdZnTe crystal after receiving radiation, and a graphene field effect tube with a bias voltage is used as the output signal generating element.

Since an insulating _SiO2 layer was prepared between the graphene and CdZnTe crystals, a bias voltage was applied across the graphene layer and the crystal layer and an external electric field was generated inside the detector. The radiation detector involved in the present invention needs to optimize and adjust the external bias voltage before normal radiation detection, so that the graphene layer is at the critical point of the Dirac curve. Under this condition, once the bias electric field of the graphene layer changes, its resistance will change significantly. The high work function metal surface electrodes prepared on the graphene surface serve as the drain and source electrodes of the graphene field effect tube to provide an applied current to the graphene layer and complete the measurement of the surface resistivity. To put it simply, due to the different concentrations of photogenerated carriers generated by different radiation intensities, the distribution of carrier concentration inside the CdZnTe crystal changes accordingly, which directly affects the change of the internal electric field of the graphene material layer, which in turn leads to a decrease in the surface resistance of the graphene layer. Variety.

Therefore, unlike conventional semiconductor radiation detectors that rely on charge collection for radiation detection, graphene resistance-change radiation detectors rely on significant changes in impedance to detect the amount of ionizing radiation in the absorbing medium. The induced charge on the graphene electrode side will cause the change of the internal electric field and then the change of its conductivity. Since the impedance value of the graphene material is very sensitive to the slight change of the internal electric field near the preset Dirac state, the detector graphene The signal generation layer has the same function as the charge-sensitive preamplifier circuit used in the traditional radiation detector, but does not require charge migration and corresponding induction 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:

·First, a graphene layer was prepared on the surface of CdTe and CdZnTe crystals by mechanical exfoliation and chemical vapor deposition. Graphene is deposited on the surface of the CdZnTe crystal to which the bias voltage has been applied. It should be noted that the corresponding relaxation temperature, carrier mobility, purity, and carrier lifetime are different depending on the doping degree of the CdZnTe crystal used. , will affect the final resistance signal.

The standard plasma-enhanced chemical vapor deposition (PECVD) was used to prepare a SiO2 film on the surface of the CdZnTe crystal as an insulating spacer, and 500nm SiO2 film deposition was achieved at a lower temperature

Take the SiO2 insulating layer as the substrate, prepare graphene by chemical vapor deposition, and then transfer the graphene from the prepared substrate to the SiO2 insulating layer. The transfer steps are as follows:

(1) Preparation of PMMA colloid on graphene surface by spin coating process

(2) Stand at a high temperature for 15 minutes, improve the uniformity of the PMMA colloid by volatilizing the organic solvent of the PMMA colloid, and enhance the degree of bonding between the graphene film and the PMMA colloid.

(3) 8% Fe(NO3)3 solution was used to etch and remove graphene to prepare the substrate. The etching time was 9 hours. After the substrate corrosion was completed, the PMMA glue on which the graphene was prepared was cleaned with deionized water, and the SiO2 thin film layer of CdZnTe crystal was used. One side adsorbs the graphene layer side.

(4) The device was dried in an environment of 50 degrees Celsius until the surface water evaporated, heated to 90 degrees Celsius for 15 minutes, and 130 degrees Celsius for 10 minutes.

(5) invert the device, rinse the graphene/PMMA layer side of the device from bottom to top with acetone solution using a washing device, remove the PMMA colloid, and finally obtain a graphene film on the surface of the CdZnTe/SiO2 substrate

After the graphene transfer is completed, the standard semiconductor lithography technology is further used to prepare the surface element array graphene layer. The lithography pattern is in the shape of the surface element array, and the surface element array graphene layer is formed on the graphene layer of the device. The key steps are: : Part of the graphene panel array that needs to be retained retains the photoresist, the rest is removed by the developer solution, and the excess graphene material of the device is removed by a dry etching machine. The etching parameter is the oxygen plasma pressure of 20 mTorr (mTorr (mTorr). ), the power is 30W (W), the oxygen flow rate is 30sccm (standard state ml/min), and the etching time is 20s (seconds).

After the graphene layer of the surface element array is prepared, the electrode is prepared by standard semiconductor technology again. The lithography pattern is in the shape of the surface element array. The surface element array electrode is formed on the graphene layer of the surface element array, and the thickness of 100nm is grown by the electron beam evaporation apparatus. Metal electrode (Au, gold electrode or In, indium electrode), device preparation is completed

The structure and preparation method of the radiation detector described in the present invention are based on the structure of the signal output electrode being a surface element pixel array structure, and the structure of the signal output electrode being an interdigitated grid electrode, a hemispherical electrode and other electrode structures, which can also realize the resistance state based on graphene layers 5 and 6, the device fabrication method described in the present invention is also applicable to the fabrication of detectors with interdigitated grids and hemispherical electrodes.

The systems, devices, modules or units described in the above embodiments may be specifically implemented by computer chips or entities, or by products with certain functions. A typical implementation device is a computer. Specifically, the computer can be, for example, a personal computer, a laptop computer, a cellular phone, a camera phone, a smart phone, 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 "comprising", "comprising" or any other variation thereof are intended to encompass a non-exclusive inclusion such that a process, method, article or device comprising a series of elements includes not only those elements, but also Other elements not expressly listed, or which are inherent to such a process, method, article of manufacture, or apparatus are also included. Without further limitation, an element qualified by the phrase "comprising a..." does not preclude the presence of additional identical elements in the process, method, article of manufacture, or device that includes the element.

The above embodiments should be understood as only for illustrating the present invention and not for limiting the protection scope of the present invention. After reading the contents of the description of the present invention, the skilled person can make various changes or modifications to the present invention, and these equivalent changes and modifications also fall within the scope defined by the claims of the present invention.

Claims (2)

1. a preparation method based on graphene semiconductor radiation detection device, described graphene semiconductor radiation detection device adopts graphene field effect tube resistance value as measuring physical quantity, specifically comprises: semiconductor crystal material layer, insulating isolation layer, graphene material layer and sensing signal electrode layer, wherein, the surface of the semiconductor crystal material layer is provided with an insulating isolation layer, a graphene material layer is provided on the insulating isolation layer, the surface of the graphene material layer is provided with an sensing signal electrode layer, and the semiconductor crystal material layer is provided It is prepared by high atomic number CdZnTe crystal, which is used to interact with incident radiation photons and generate electron clouds. The radiation receiving surface is used to prepare a metal electrode cathode layer, and an external bias voltage is applied. The insulating isolation layer is used to block the detector semiconductor. Leakage current, the graphene material layer is used to sense the internal electric field change of the semiconductor material due to radiation, and the sensing signal electrode layer is used to connect the graphene material and the front-end signal collection of the resistance measurement circuit, and the collection is related to the resistance state of the graphene material layer. A proportional electrical signal, the graphene material layer is a graphene material layer with a surface element array structure, and its resistance state is proportional to the incident radiation intensity, and a graphene field effect tube structure in the form of a surface element array is constructed, and the detector signal output end In order to sense the signal electrode layer, the electrode is prepared by using high work function material. In the detector structure, the insulating isolation layer, the graphene material layer and the sensing signal collection layer form a graphene field effect tube structure; the thickness of the semiconductor crystal material layer and the insulation isolation The layer thickness satisfies the proportional relationship of 1000:1; before the semiconductor radiation detection device performs radiation detection normally, the external bias voltage needs to be optimally adjusted so that the graphene material layer is at the critical point of the Dirac curve. When the bias electric field of the material layer changes, the resistance value of the graphene material layer will change significantly, and the insulating isolation layer is made of SiO ₂ , which is characterized in that it includes the following steps: Step 1. First, a graphene layer is prepared on the surface of CdTe and CdZnTe crystals by mechanical exfoliation and chemical vapor deposition, and the graphene is deposited on the surface of the CdZnTe crystal to which the bias voltage has been applied; Step 2. Use standard plasma enhanced chemical vapor deposition (PECVD) to prepare a SiO2 film on the surface of CdZnTe crystal as an insulating isolation layer to achieve 500 nm SiO2 film deposition. Using the SiO2 insulating layer as the base, chemical vapor deposition is used to prepare graphene, and then from the preparation Transfer graphene on the substrate to the SiO2 insulating layer; Step 3. After the graphene transfer is completed, a standard semiconductor lithography technique is used to prepare a plane element array graphene layer. The lithography pattern is in the shape of a plane element array, and a plane element array graphene layer is formed on the graphene layer of the device. The key step It is: the part of the graphene panel array that needs to be retained retains the photoresist, the rest is removed by the developer solution, and the excess graphene material of the device is removed by a dry etching machine, and the etching parameter is an oxygen plasma pressure of 20 mTorr (milliseconds). Torr), power 30W (W), oxygen flow 30sccm (standard state ml/min) conditions, etching time 20s (seconds); Step 4. After the surface element array graphene layer is prepared, the standard semiconductor process is used to prepare electrodes again. The lithography pattern is in the shape of a surface element array. A surface element array electrode is formed on the surface element array graphene layer, and an electron beam evaporation apparatus is used. A metal electrode with a thickness of 100 nm is grown, and the device preparation is completed. 2. The method for preparing a radiation detection device according to claim 1, wherein, The step of transferring graphene from the prepared substrate to the SiO2 insulating layer in step 2 is as follows: (1) Prepare PMMA colloid on graphene surface by spin coating process; (2) stand for 15 minutes in a high temperature environment, improve the uniformity of the PMMA colloid through the volatilization of the organic solvent of the PMMA colloid, and enhance the degree of bonding between the graphene film and the PMMA colloid; (3) 8% Fe(NO3)3 solution was used to etch and remove graphene to prepare the substrate. The etching time was 9 hours. After the substrate corrosion was completed, the PMMA glue on which the graphene was prepared was cleaned with deionized water, and the SiO2 thin film layer of CdZnTe crystal was used. One side adsorbs the graphene layer on one side; (4) drying the device in an environment of 50 degrees Celsius until the surface water evaporates, heating to 90 degrees Celsius for 15 minutes, and 130 degrees Celsius for 10 minutes; (5) Invert the device, use a washing device to rinse the graphene/PMMA layer side of the device with acetone solution from bottom to top, remove the PMMA colloid, and finally obtain a graphene film on the surface of the CdZnTe/SiO2 substrate.

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