Method for realizing high-performance X-ray detection based on two-dimensional semiconductor transistor

Abstract

The invention discloses a method for realizing high-performance X-ray detection based on a two-dimensional semiconductor transistor, which is a method for realizing excellent X-ray detection performance by regulating and controlling a novel two-dimensional material NbOI2 transistor through grid voltage, and belongs to the field of photoelectric information. A transistor device is prepared on the basis of a two-dimensional semiconductor NbOI2 nanosheet, and excellent X-ray detection performance is realized by applying grid voltage to a transistor by utilizing the excellent absorption characteristic of heavy atoms of the transistor device to X-rays. At present, the technology is not reported yet, and the invention realizes the technology for the first time. According to the invention, effective amplification of the number of carriers generated by X-rays is realized mainly based on the high-efficiency regulation and control characteristic of the grid voltage to the carriers of the two-dimensional semiconductor NbOI2 nanosheet, so that the response of the transistor to the X-rays is enhanced, and the sensitivity of the X-ray detector is improved. The invention has important significance on the application of a two-dimensional high-integration X-ray detector, especially a high-sensitivity X-ray detector.

Description

Technical Field

[0001] The present invention relates to a method for realizing efficient improvement of X-ray detection performance of two-dimensional semiconductor materials by utilizing electrical methods, and belongs to the field of optoelectronic information. Background Art

[0002] In recent years, with the widespread application of X-ray imaging technology in medical diagnosis, industrial detection and security, the demand for high-performance X-ray detectors has increased. Although traditional X-ray detection materials, such as silicon and germanium, have made certain progress in performance, they still have certain limitations in detection efficiency, response time, cost and flexibility. To this end, researchers have begun to explore new two-dimensional materials as core materials for X-ray detectors, especially transition metal dichalcogenides (TMDCs), black phosphorus and graphene, which have become a hot topic of research due to their excellent electrical, optical and mechanical properties.

[0003] Two-dimensional materials have shown great potential in X-ray detection due to their atomic-level thickness, excellent electrical conductivity and highly adjustable photoelectric properties. In particular, under the excitation of X-ray radiation, two-dimensional materials show a strong photoelectric effect and can effectively convert X-ray energy into electrical signals. In addition, the large specific surface area and strong heterojunction effect of two-dimensional materials give them high sensitivity and response speed in X-ray absorption and detection. In particular, by designing heterostructures or adjusting the defects and interface characteristics of materials, the performance of detectors can be significantly improved.

[0004] At present, X-ray detectors made of two-dimensional materials have shown relatively higher detection efficiency, flexibility and integration than traditional materials. However, there are still some challenges in terms of detector sensitivity and how to achieve efficient and low-cost integration in practical applications. Therefore, the development of two-dimensional material X-ray detection technology with higher sensitivity, better response characteristics and efficient integration is still an urgent problem to be solved in this field. Summary of the invention

[0005] The technical problem solved by the present invention is: in order to solve the problem of low sensitivity and difficulty in effective regulation of two-dimensional semiconductor X-ray detection, the present invention uses an electrical regulation method to achieve effective regulation and improvement of the sensitivity parameter in the X-ray detection performance of two-dimensional semiconductor transistors. Transistor devices are prepared based on two-dimensional semiconductor NbOI2 nanosheets, and the excellent absorption characteristics of heavy atoms to X-rays are utilized. By applying gate voltage to the transistor, excellent X-ray detection performance is achieved. By regulating the gate voltage of two-dimensional semiconductor transistors, the highest sensitivity that can be achieved is 5×10 9 µC / (Gy·cm 2 ) high-performance X-ray detection, which is of great significance for the application of two-dimensional high-integration X-ray detection.

[0006] In order to solve the technical problem of the present invention, a technical solution is proposed: A method for realizing high-performance X-ray detection based on a two-dimensional semiconductor transistor, comprising the following steps:

[0007] S1: A two-dimensional semiconductor NbOI2 nanosheet with a maximum side greater than 10 microns and a thickness of a single layer or a few layers is obtained on a Si / SiO2 substrate by mechanical exfoliation;

[0008] S2: Using micromachining technology to prepare a transistor on the NbOI2 nanosheet in step S1, including three metal electrodes: source, drain and gate;

[0009] S3: Add bias voltage to the source and drain, add gate voltage to the gate, irradiate the transistor with X-rays at different dose rates, and by adjusting the bias voltage or gate voltage, high-performance two-dimensional semiconductor transistor X-ray detection can be achieved;

[0010] In step S2, the channel width of the transistor is less than 10 micrometers, and the metal electrode is an Au electrode;

[0011] In step S3, the magnitudes of the gate voltage and bias voltage applied are: the bias voltage does not exceed 5 V, and the gate voltage does not exceed ±60 V.

[0012] Preferably, in step S3, the magnitudes of the gate voltage and bias voltage applied are: the bias voltage is 5 V, and the gate voltage is ±60 V.

[0013] Preferably, the method comprises the following steps:

[0014] S1: A two-dimensional semiconductor NbOI2 nanosheet with a maximum side of 10-45 μm and a thickness of 0.78 nm per monolayer was obtained on a Si / SiO2 substrate by mechanical exfoliation.

[0015] S2: Using micromachining technology to prepare a transistor on the NbOI2 nanosheet in step S1, including three metal electrodes: source, drain and gate;

[0016] S3: Apply bias voltage to the source and drain, apply gate voltage to the gate, irradiate X-rays to the transistor, and by adjusting the bias voltage or gate voltage, high-sensitivity X-ray detection of two-dimensional semiconductor transistors can be achieved;

[0017] In step S2, the channel width of the transistor is 1 micrometer to 10 micrometers, and the metal electrode is an Au electrode;

[0018] In step S3, the magnitudes of the gate voltage and bias voltage applied are: the bias voltage is 5 V, and the gate voltage is ±60 V.

[0019] Preferably, the method comprises the following steps:

[0020] S1: A two-dimensional semiconductor NbOI2 nanosheet with a size of 20 microns and a thickness of 0.78 nm was obtained on a Si / SiO2 substrate by mechanical exfoliation;

[0021] S2: Using micromachining technology to prepare a transistor on the NbOI2 nanosheet in step S1, including three metal electrodes: source, drain and gate; the narrowest part of the transistor channel is 1.5 microns, and the metal electrode is an Au electrode;

[0022] S3: Apply bias voltage to the source and drain, and gate voltage to the gate. The magnitudes of the gate voltage and bias voltage applied are 5 V for the bias voltage and +60 V for the gate voltage.

[0023] Preferably, the method comprises the following steps:

[0024] S1: A two-dimensional semiconductor NbOI2 nanosheet with a size of 20 μm, a width of 3 μm, and a thickness of 0.78 nm per monolayer was obtained on a Si / SiO2 substrate by mechanical exfoliation.

[0025] S2: Using micromachining technology, a transistor is prepared on the NbOI2 nanosheet in step S1, including three metal electrodes: source, drain and gate. The narrowest part of the transistor channel is 1.5 microns, and the metal electrode is an Au electrode. Before evaporating the Au electrode, a 10 nm thick Bi electrode is first evaporated.

[0026] S3: Apply bias voltage to the source and drain, and gate voltage to the gate. The magnitude of the gate voltage and bias voltage applied is 5 V for the bias voltage and 60 V for the gate voltage.

[0027] S4: With an X-ray dose rate of 25 Gy / h, the maximum sensitivity can be 5×10 9 µC / (Gy·cm 2 ) Two-dimensional semiconductor transistor X-ray detection.

[0028] The grown NbOI2 crystals were adhered to a special tape for mechanical peeling (purchased from Zhongke Materials Company). After repeated sticking on the tape, the required nanosheets were obtained by multiple peeling using a weakly sticky polydimethylsiloxane (PDMS) film (purchased from Zhongke Materials Company). The nanosheets were transferred to the SiO2 substrate via a transfer platform. Finally, two-dimensional semiconductor NbOI2 nanosheets with a size greater than 20 microns and a thickness of a single layer or a few layers were obtained on the substrate; the substrate was 1 mm thick moderately doped Si with a mirror-polished 200 nm thick SiO2 on it. The substrate was purchased from Suzhou Research Materials Company.

[0029] SiO2 is used as the gate dielectric. The gate voltage is applied to Si. By changing the size and direction of the electric field, the charge density in the device channel is regulated, thereby adjusting the conductivity of the device.

[0030] The transistor is fabricated on the NbOI2 nanosheet in step S3 using micromachining technology. The channel width of the transistor is less than 10 microns and contains three metal electrodes: source, drain and gate. The schematic diagram of the device structure is shown in Figure 2. Figure 6 As shown. The metal electrode is an Au electrode. Before evaporating the Au electrode, a 10 nm thick Bi electrode is first evaporated to increase the adhesion between the Au electrode and the substrate. The Au electrode is selected and matched according to the work function of the NbOI2 material.

[0031] Apply bias voltage to the source and drain, apply gate voltage to the gate, apply X-rays of different dose rates to the transistor, and adjust the bias voltage or gate voltage. The size of the gate voltage and bias voltage applied is not more than 5 V, and the gate voltage is not more than ±60 V. High-performance X-ray detection of two-dimensional semiconductor transistors can be achieved; the specific detection method is to place the prepared NbOI2 transistor at the X-ray source, and then when the X-ray passes through the NbOI2 transistor and enters the X-ray detector, the detector converts the collected signal into current and displays it on the oscilloscope. During measurement, bias voltage is applied to both ends of the device, and X-rays are applied or blocked by switching the shutter to change the X-ray dose, and the change of current over time is continuously detected.

[0032] Beneficial effects:

[0033] The present invention is mainly based on the effective regulation characteristics of gate voltage on the carriers of two-dimensional semiconductor NbOI2 nanosheets, which realizes the effective amplification of carriers generated by X-rays, thereby enhancing the response of transistors to X-rays and improving the sensitivity of X-ray detectors.

[0034] The selection of NbOI2 material as the channel material for high-performance X-ray detection transistors is mainly based on the following: 1) the material must have heavy atoms with a large atomic number, which can absorb X-rays well; 2) it must be easy to obtain ultra-thin nanosheets by mechanical exfoliation, which is easy to realize highly integrated devices; 3) it must have a suitable band gap, which is convenient for using gate voltage to control the Fermi level; 4) the element must be non-toxic and environmentally friendly. Its molecular structure is as follows: Figure 5 As shown, NbOI2 belongs to the monoclinic space group C2, with lattice constants of a = 15.18Å, b = 3.92Å, c = 7.52Å, β = 105.5°, and is composed of NbO2I4 octahedra, which are connected by I−I shared edges along the c axis, angularly share O atoms along the b axis, and Nb atoms show distortion along the c axis, resulting in alternation of two unequal Nb-Nb distances in the Nb-Nb…Nb chain.

[0035] In Example 1, when the thickness of the NbOI2 nanosheet is changed from a single layer to a multilayer, the sensitivity will decrease while other conditions remain unchanged. For example, when the thickness is 20 nm and 50 nm, the sensitivity is 2×106 µC / (Gy·cm 2 ) and 9×10 5 µC / (Gy·cm 2 ).

[0036] It can be seen from Examples 1-5 that the smaller the channel width of the two-dimensional material transistor, the better. However, due to the limitation of micro-machining level, the channel width cannot be infinitely small. The larger the bias voltage, the higher the sensitivity, but the smaller the bias voltage, the more conducive to low power consumption of the device. The gate voltage is the main method to regulate and improve the X-ray detection sensitivity of two-dimensional semiconductor material transistors. When the gate voltage is 60 V, the sensitivity improvement effect is most obvious, and the maximum sensitivity can reach 5×10 9 µC / (Gy·cm 2 ). However, when the gate voltage exceeds 60V, the device will be easily broken down.

[0037] The present invention uses a method to achieve excellent X-ray detection performance by regulating the gate voltage of the new two-dimensional material NbOI2, which effectively improves the sensitivity parameter in the X-ray detection performance of two-dimensional semiconductor transistors. The sensitivity obtained by this method is 5×10 9 µC / (Gy·cm 2 ) parameters are higher than those of all reported two-dimensional semiconductor transistor X-ray detection devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Photo of NbOI2 crystal and optical photo of nanosheets.

[0039] Figure 2 Raman spectrum of NbOI2 nanosheets.

[0040] Figure 3 AFM image of NbOI2 nanosheets.

[0041] Figure 4 XRD pattern of NbOI2.

[0042] Figure 5 This is the atomic structure diagram of the channel material NbOI2.

[0043] Figure 6 Schematic diagram of the device structure in Example 1.

[0044] Figure 7 This is an optical photograph of the device structure in Example 1.

[0045] Figure 8 Graph showing the output and transfer characteristics of the transistor in Example 1.

[0046] Fig. 9This is a data graph of the X-ray sensitivity of the semiconductor transistor under different X-ray dose rates and different bias voltages in Example 4.

[0047] Fig.10 This is a data graph of the signal-to-noise ratio in Example 1.

[0048] Fig.11 This is a data graph of the response time in Example 1.

[0049] Fig.12 This is a data graph of the X-ray sensitivity of the semiconductor transistor under different X-ray dose rates and different gate voltages in Example 5.

[0050] Fig.13 This is a data graph of the X-ray sensitivity of the semiconductor transistor at different X-ray dose rates and different channel widths in Example 3. DETAILED DESCRIPTION

[0051] The present invention will be further described below in conjunction with the embodiments.

[0052] Embodiment 1:

[0053] A method for realizing high-performance X-ray detection based on two-dimensional semiconductor transistors, the specific implementation steps are as follows:

[0054] S1: Bulk NbOI2 material was prepared by chemical vapor transport using a commercial tube furnace (Hefei Kejing). The specific method is that the starting reactants Nb, Nb2O5 and I2 powders with a mass ratio of 3:1:6 are sealed in a vacuum quartz tube. The tube is slowly heated to 700°C, maintained at this temperature for 3 days, and then cooled to room temperature while the furnace is naturally cooled. The product is soaked in alcohol to remove excess I2. The harvested crystals are shiny rectangular plates with dimensions of 6×8×0.5mm.

[0055] S2: The grown NbOI2 crystals are adhered to a special tape for mechanical peeling (purchased from Zhongke Materials Co., Ltd.). After repeatedly sticking to the tape, a weakly sticky polydimethylsiloxane (PDMS) film (purchased from Zhongke Materials Co., Ltd.) is used to peel off the desired nanosheets multiple times. Figure 1 Optical images of NbOI2 crystals and nanosheets, respectively. Figure 2 is the Raman spectrum of the nanosheet, Figure 3 For AFM images, Figure 4The XRD pattern is shown in Figure 1. The nanosheets are transferred to the SiO2 substrate through a transfer platform. Finally, a two-dimensional semiconductor NbOI2 nanosheet with a size of 20 microns, a width of 3 microns, and a thickness of a single layer (0.78 nm) is obtained on the substrate; the substrate is a 1 mm thick moderately doped Si with a mirror-polished 200 nm thick SiO2 on it. The substrate was purchased from Suzhou Research Materials Co., Ltd. SiO2 is used as a gate dielectric. The gate voltage is applied to Si. By changing the size and direction of the electric field, the charge density in the device channel is regulated, thereby adjusting the conductivity of the device.

[0056] S3: A transistor is fabricated on the NbOI2 nanosheet in step S3 using micromachining technology. The narrowest channel width of the transistor is 1.5 microns. It contains three metal electrodes: source, drain and gate. The metal electrodes are Bi / Au electrodes. The optical photo is as follows: Figure 7 shown.

[0057] The schematic diagram of the device structure is as follows Figure 6 As shown. The metal electrode is an Au electrode. Before evaporating the Au electrode, a 10nm thick Bi electrode is first evaporated to increase the adhesion between the Au electrode and the substrate. The Au electrode is selected and matched according to the work function of the NbOI2 material.

[0058] S4: Apply bias voltage to the source and drain, apply gate voltage to the gate, apply X-rays of different dose rates to the transistor, and adjust the bias voltage or gate voltage. The size of the gate voltage and bias voltage applied is not more than 5 V, and the gate voltage is not more than ±60 V. High-performance X-ray detection of two-dimensional semiconductor transistors can be achieved; the specific detection method is to place the prepared NbOI2 transistor at the X-ray source, and then when the X-ray passes through the NbOI2 transistor and enters the X-ray detector, the detector converts the collected signal into current and displays it on the oscilloscope. During measurement, bias voltage is applied to both ends of the device, and X-rays are applied or blocked by switching the shutter to change the X-ray dose, and the change of current over time is continuously detected.

[0059] In step S4, bias voltage is applied to the source and drain, gate voltage is applied to the gate, and the transfer curve and output curve of the transistor are characterized, such as Figure 8 As shown, the output curve on the left shows that the device has a good ohmic contact, and the transfer curve on the right shows that the device is n-type. Figure 8 This indicates that the transistor device is working well. The sensitivity and photocurrent of the device at different dose rates and different bias voltages are shown in Figure 2. Fig. 9 As shown in Figure 2, the photocurrent and sensitivity of the device can be effectively controlled by the X-ray dose rate and bias voltage. The signal-to-noise ratio of the device at different dose rates under 1V and 3V bias is Fig.10 As shown, the signal-to-noise ratio of the device is good. The rising and falling edges of the device's response time are shown in Fig.11 As shown in the figure, the rising edge is 64 ms, the falling edge is 40 ms, and the response speed is sub-hundred milliseconds. By applying gate voltage to the device, we can obtain sensitivity data at different gate voltages and different dose rates, such as Fig.12 As shown, it can be seen that the sensitivity of the device at different X-ray dose rates can be effectively controlled by the gate voltage.

[0060] The applied X-ray dose rate is 25 Gy / h, the applied bias voltage is 5 V, and the gate voltage is 60 V, which can achieve a maximum sensitivity of 5×10 9 µC / (Gy·cm 2 ) Two-dimensional semiconductor transistor X-ray detection, which has the highest sensitivity reported so far for two-dimensional semiconductor transistor X-ray detection.

[0061] Embodiment 2:

[0062] In Example 1, when the thickness of the NbOI2 nanosheet is changed from a single layer to a multilayer, the sensitivity will decrease while other conditions remain unchanged. For example, when the thickness is 20 nm and 50 nm, the sensitivity is 2×10 6 µC / (Gy·cm 2 ) and 9×10 5 µC / (Gy·cm 2 ).

[0063] Embodiment 3:

[0064] In Example 1, devices with different transistor channel widths are tested, and other conditions remain unchanged. The smaller the channel width, the higher the sensitivity. Fig.13 As shown, when the width is 2.5 µm and 7 µm, the sensitivity is 1×10 6 µC / (Gy·cm 2 ) and 2.7×10 5 µC / (Gy·cm 2 ). The smaller the channel width, the better. However, due to the limitations of micro-machining technology, it is impossible to make it infinitely small.

[0065] Embodiment 4:

[0066] In Example 1, the bias voltage is changed, and other conditions remain unchanged. As the bias voltage increases, the sensitivity will increase. Fig. 9 As shown, when the bias voltage is 1V, 3V, 5V, and 10V, the sensitivity is 4.3×10 5 µC / (Gy·cm 2 ), 2.4×10 7 µC / (Gy·cm 2 ), 3.8×10 8 µC / (Gy·cm2 ) and 1.9×10 9 µC / (Gy·cm 2 ). The maximum applied bias voltage is 10V. Under the same conditions, the sensitivity is highest when the bias voltage is 10V. When the bias voltage is higher than 10V, the device power consumption will increase significantly, the dark current will increase, and the current drift phenomenon will occur.

[0067] Embodiment 5:

[0068] In Example 1, different gate voltages are applied, and other conditions remain unchanged. The greater the gate voltage, the higher the sensitivity. Fig.12 As shown, when the gate voltage is 30V, 40V and 60V, the sensitivity is 3.3×10 9 µC / (Gy·cm 2 ), 4.3×10 9 µC / (Gy·cm 2 ) and 5×10 9 µC / (Gy·cm 2 ). The maximum gate voltage applied is 60V. When other conditions remain unchanged, the sensitivity value is the highest at 60V gate voltage. When the gate voltage is higher than 60V, the device is prone to breakdown.

Claims

1. A method for realizing high-performance X-ray detection based on two-dimensional semiconductor transistors, characterized in that: The following steps are involved: S1: A two-dimensional semiconductor NbOI2 nanosheet with a maximum side greater than 10 microns and a thickness of a single layer or a few layers is obtained on a Si / SiO2 substrate by mechanical exfoliation; S2: Using micromachining technology to prepare a transistor on the NbOI2 nanosheet in step S1, including three metal electrodes: source, drain and gate; S3: Add bias voltage to the source and drain, add gate voltage to the gate, irradiate the transistor with X-rays at different dose rates, and by adjusting the bias voltage or gate voltage, high-performance two-dimensional semiconductor transistor X-ray detection can be achieved; In step S2, the channel width of the transistor is less than 10 micrometers, and the metal electrode is an Au electrode; In step S3, the magnitudes of the gate voltage and bias voltage applied are: the bias voltage does not exceed 5 V, and the gate voltage does not exceed ±60 V.

2. The method for realizing high-performance X-ray detection based on two-dimensional semiconductor transistors according to claim 1, characterized in that: The step S1 is a single-layer two-dimensional semiconductor NbOI2 nanosheet. In the step S3, the magnitudes of the gate voltage and bias voltage applied are 5 V for the bias voltage and ±60 V for the gate voltage.

3. The method for realizing high-performance X-ray detection based on two-dimensional semiconductor transistors according to claim 1, characterized in that: The following steps are involved: S1: A two-dimensional semiconductor NbOI2 nanosheet with a maximum side of 10-45 μm and a thickness of 0.78 nm per monolayer was obtained on a Si / SiO2 substrate by mechanical exfoliation. S2: Using micromachining technology to prepare a transistor on the NbOI2 nanosheet in step S1, including three metal electrodes: source, drain and gate; S3: Apply bias voltage to the source and drain, apply gate voltage to the gate, irradiate X-rays to the transistor, and by adjusting the bias voltage or gate voltage, high-sensitivity X-ray detection of two-dimensional semiconductor transistors can be achieved; In the step S2, the channel width of the transistor is 1 micrometer to 2.5 micrometers, and the metal electrode is an Au electrode; In step S3, the magnitudes of the gate voltage and bias voltage applied are: the bias voltage is 5 V, and the gate voltage is ±60 V.

4. The method for realizing high-performance X-ray detection based on two-dimensional semiconductor transistors according to claim 2, characterized in that: The following steps are involved: S1: A two-dimensional semiconductor NbOI2 nanosheet with a size of 20 μm and a thickness of 0.78 nm was obtained on a Si / SiO2 substrate by mechanical exfoliation. S2: Using micromachining technology to prepare a transistor on the NbOI2 nanosheet in step S1, including three metal electrodes: source, drain and gate; the channel of the transistor is 1.5 microns, and the metal electrode is an Au electrode; S3: Apply bias voltage to the source and drain, and gate voltage to the gate. The magnitudes of the gate voltage and bias voltage applied are 5 V for the bias voltage and +60 V for the gate voltage.

5. The method for realizing high-performance X-ray detection based on two-dimensional semiconductor transistors according to claim 2, characterized in that: The following steps are involved: S1: A two-dimensional semiconductor NbOI2 nanosheet with a size of 20 μm, a width of 3 μm, and a thickness of 0.78 nm per monolayer was obtained on a Si / SiO2 substrate by mechanical exfoliation. S2: Using micromachining technology, a transistor is prepared on the NbOI2 nanosheet in step S1, including three metal electrodes: source, drain and gate. The channel of the transistor is 1.5 microns, and the metal electrode is an Au electrode. Before evaporating the Au electrode, a 10 nm thick Bi electrode is first evaporated. S3: Apply bias voltage to the source and drain, and gate voltage to the gate. The magnitude of the gate voltage and bias voltage applied is 5 V for the bias voltage and 60 V for the gate voltage. S4: With an X-ray dose rate of 25 Gy / h, the maximum sensitivity can be 5×10 9 µC / (Gy·cm 2 ) Two-dimensional semiconductor transistor X-ray detection.

Images