A method for achieving high-performance X-ray detection based on two-dimensional semiconductor transistors

Abstract

This invention discloses a method for achieving high-performance X-ray detection based on two-dimensional semiconductor transistors. The method utilizes gate voltage modulation of novel two-dimensional NbOI2 material transistors to achieve excellent X-ray detection performance, belonging to the field of optoelectronic information. The method involves fabricating transistor devices based on two-dimensional semiconductor NbOI2 nanosheets, leveraging the excellent X-ray absorption characteristics of its heavy atoms, and achieving superior X-ray detection performance by applying a gate voltage to the transistor. This technology has not been reported before, and this invention is the first to realize it. The invention primarily relies on the highly efficient modulation of charge carriers in two-dimensional semiconductor NbOI2 nanosheets by gate voltage, effectively amplifying the number of charge carriers generated by X-rays, thereby enhancing the transistor's response to X-rays and improving the sensitivity of the X-ray detector. This invention is of great significance for the application of highly integrated two-dimensional X-ray detectors, especially high-sensitivity X-ray detectors.

Description

Technical Field

[0001] This invention relates to a method for efficiently improving the X-ray detection performance of two-dimensional semiconductor materials using electrical methods, belonging 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 inspection, and security, the demand for high-performance X-ray detectors has been increasing. Traditional X-ray detection materials, such as silicon and germanium, while showing some progress in performance, still have limitations in detection efficiency, response time, cost, and flexibility. Therefore, researchers have begun exploring novel two-dimensional materials as core materials for X-ray detectors, especially transition metal dichalcogenides (TMDCs), black phosphorus, and graphene, which have become research hotspots due to their excellent electrical, optical, and mechanical properties.

[0003] Two-dimensional materials (2D materials) exhibit great potential in X-ray detection due to their atomic-level thickness, excellent electrical conductivity, and highly tunable photoelectric properties. In particular, under X-ray radiation excitation, 2D materials demonstrate a strong photoelectric effect, effectively converting X-ray energy into electrical signals. Furthermore, the large specific surface area and strong heterojunction effect of 2D materials result in high sensitivity and response speed in X-ray absorption and detection. Especially by designing heterostructures or adjusting the defects and interface properties of the materials, the performance of the detector can be significantly improved.

[0004] Currently, X-ray detectors made from two-dimensional materials have demonstrated higher detection efficiency, flexibility, and integration compared to those made from traditional materials. However, challenges remain regarding detector sensitivity and how to achieve efficient and low-cost integration in practical applications. Therefore, developing two-dimensional material X-ray detection technology with higher sensitivity, better response characteristics, and efficient integration remains a pressing issue in this field. Summary of the Invention

[0005] The technical problem solved by this invention is to address the low sensitivity and difficulty in effectively controlling the X-ray detection performance of two-dimensional semiconductor transistors. This invention utilizes an electrical control method to effectively control and improve the sensitivity parameter in the X-ray detection performance of two-dimensional semiconductor transistors. Based on two-dimensional semiconductor NbOI2 nanosheets, transistor devices are fabricated, leveraging the excellent X-ray absorption characteristics of heavy atoms. By applying a gate voltage to the transistor, superior X-ray detection performance is achieved. Using gate voltage control of two-dimensional semiconductor transistors, a sensitivity of up to 5 × 10⁻⁶ can be achieved. 9 µC / (Gy·cm 2 This high-performance X-ray detection technology is of great significance for the application of two-dimensional highly integrated X-ray detection.

[0006] To solve the technical problem of this invention, the proposed technical solution is as follows: A method for achieving high-performance X-ray detection based on two-dimensional semiconductor transistors, comprising the following steps:

[0007] S1: Two-dimensional semiconductor NbOI2 nanosheets with a longest side greater than 10 micrometers and a thickness of one or fewer layers are obtained on a Si / SiO2 substrate by mechanical exfoliation.

[0008] S2: Using microfabrication techniques, transistors are fabricated on NbOI2 nanosheets from step S1, including three metal electrodes: source, drain, and gate.

[0009] S3: By applying bias voltage to the source and drain and gate voltage to the gate, X-rays of different dose rates are irradiated onto the transistor. 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 applied gate voltage and bias voltage are such that the bias voltage does not exceed 5 V and the gate voltage does not exceed ±60 V.

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

[0013] Preferably, it includes the following steps:

[0014] S1: Two-dimensional semiconductor NbOI2 nanosheets with a longest side of 10-45 micrometers and a single layer thickness of 0.78 nm were obtained on a Si / SiO2 substrate by mechanical exfoliation.

[0015] S2: Using microfabrication techniques, transistors are fabricated on NbOI2 nanosheets from step S1, including three metal electrodes: source, drain, and gate.

[0016] S3: Apply bias voltage to the source and drain, and gate voltage to the gate, and irradiate the transistor with X-rays. By adjusting the bias voltage or gate voltage, high-sensitivity two-dimensional semiconductor transistor X-ray detection 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 applied gate voltage and bias voltage are as follows: the bias voltage is 5 V and the gate voltage is ±60 V.

[0019] Preferably, it includes the following steps:

[0020] S1: Two-dimensional semiconductor NbOI2 nanosheets with a size of 20 micrometers and a single layer thickness of 0.78 nm were obtained on a Si / SiO2 substrate by mechanical exfoliation.

[0021] S2: Using microfabrication techniques, a transistor is fabricated on the NbOI2 nanosheets from step S1, comprising three metal electrodes: source, drain, and gate; the narrowest point of the transistor channel is 1.5 micrometers, and the metal electrode is an Au electrode;

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

[0023] Preferably, it includes the following steps:

[0024] S1: Two-dimensional semiconductor NbOI2 nanosheets with a size of 20 micrometers, a width of 3 micrometers, and a single layer thickness of 0.78 nm were obtained on a Si / SiO2 substrate by mechanical exfoliation.

[0025] S2: Using microfabrication technology, a transistor is fabricated on the NbOI2 nanosheet from step S1, which includes three metal electrodes: source, drain, and gate. The narrowest part of the transistor channel is 1.5 micrometers, and the metal electrode is an Au electrode. Before evaporating the Au electrode, a 10 nm thick Bi electrode is first deposited.

[0026] S3: Apply bias voltage to the source and drain, and apply gate voltage to the gate. The magnitudes of the applied gate voltage and bias voltage are as follows: bias voltage is 5 V, and gate voltage is 60 V.

[0027] S4: Applying X-rays at a dose rate of 25 Gy / h can achieve a sensitivity of up to 5 × 10⁻⁶. 9 µC / (Gy·cm 2 Two-dimensional semiconductor transistor X-ray detection.

[0028] The grown NbOI2 crystals were adhered to a mechanically exfoliating tape (purchased from Zhongke Materials Co., Ltd.). After repeated adhesion to the tape, the desired nanosheets were obtained through multiple exfoliations using a weakly adhesive polydimethylsiloxane (PDMS) film (also purchased from Zhongke Materials Co., Ltd.). The nanosheets were then transferred to a SiO2 substrate using a transfer platform. Finally, two-dimensional semiconductor NbOI2 nanosheets with dimensions greater than 20 micrometers and a single or few layers thick were obtained on the substrate. The substrate consisted of 1 mm thick moderately doped Si with a 200 nm thick mirror-polished SiO2 layer on top. The substrate was purchased from Suzhou Research Institute of Materials Technology and Engineering Co., Ltd.

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

[0030] Transistors were fabricated on NbOI2 nanosheets in step S3 using microfabrication techniques. The channel width of the transistors was less than 10 micrometers, and they included three metal electrodes: source, drain, and gate. A schematic diagram of the device structure is shown below. Figure 6 As shown. The metal electrode is an Au electrode. Before depositing the Au electrode, a 10 nm thick Bi electrode is first deposited to increase the adhesion between the Au electrode and the substrate. The Au electrode was selected based on the work function of the NbOI2 material.

[0031] By applying bias voltages to the source and drain, and a gate voltage to the gate, and applying X-rays at different dose rates to the transistor, high-performance two-dimensional semiconductor transistor X-ray detection can be achieved by adjusting the magnitude of the bias voltage or gate voltage. The bias voltage should not exceed 5 V, and the gate voltage should not exceed ±60 V. Specifically, the fabricated NbOI2 transistor is placed at the X-ray source. X-rays pass through the NbOI2 transistor and enter the X-ray detector. The detector converts the collected signal into a current, which is displayed on an oscilloscope. During measurement, a bias voltage is applied across the device, and the X-ray dose is changed by switching the shutter on and off, allowing for continuous monitoring of the current change over time.

[0032] Beneficial effects:

[0033] This invention is based on the effective control characteristics of gate voltage on charge carriers in two-dimensional semiconductor NbOI2 nanosheets, which enables effective amplification of charge carriers generated by X-rays, thereby enhancing the transistor's response to X-rays and improving the sensitivity of the X-ray detector.

[0034] NbOI2 was chosen as the channel material for high-performance X-ray detector transistors primarily based on the following criteria: 1) The material should contain heavy atoms with high atomic numbers to effectively absorb X-rays; 2) It should be easily exfoliated into ultrathin nanosheets for efficient high-integration devices; 3) It should have a suitable band gap to facilitate Fermi level modulation using gate voltage; and 4) The material should be non-toxic and environmentally friendly. Its molecular structure is as follows: Figure 5 As shown, NbOI2 belongs to the monoclinic crystal system space group C2, with lattice constants a=15.18Å, b=3.92Å, c=7.52Å, and β=105.5°. It is composed of NbO2I4 octahedra, which are connected along the c-axis by I−I along the common edge, and share O atoms along the b-axis. Nb atoms exhibit distortion along the c-axis, resulting in alternating unequal Nb-Nb distances in the Nb-Nb...Nb chain.

[0035] In Example 1, when the thickness of the NbOI2 nanosheets was changed from a single layer to multiple layers while keeping other conditions constant, the sensitivity decreased. For example, the sensitivities were 2 × 10⁻⁶ for thicknesses of 20 nm and 50 nm, respectively.6 µC / (Gy·cm 2 ) and 9×10 5 µC / (Gy·cm 2 ).

[0036] As demonstrated in Examples 1-5, a smaller channel width is better for two-dimensional material transistors; however, due to limitations in microfabrication technology, the channel width cannot be infinitely small. Higher bias voltage results in higher sensitivity, while lower bias voltage is more beneficial for low power consumption. Gate voltage is the primary method for regulating and improving the X-ray detection sensitivity of two-dimensional semiconductor material transistors. The sensitivity improvement is most significant at a gate voltage of 60 V, with the highest sensitivity reaching 5 × 10⁻⁶. 9 µC / (Gy·cm 2 However, if the gate voltage exceeds 60V, the device may be easily damaged by breakdown.

[0037] This invention presents a method for achieving superior X-ray detection performance using a novel two-dimensional material, NbOI2, through gate voltage modulation. This method effectively improves the sensitivity parameter in the X-ray detection performance of two-dimensional semiconductor transistors. The sensitivity achieved by this method is 5 × 10⁻⁶. 9 µC / (Gy·cm 2 Its parameters are higher than those of all previously reported two-dimensional semiconductor transistor X-ray detectors. Attached Figure Description

[0038] Figure 1 Photographs of NbOI2 crystals and nanosheets.

[0039] Figure 2 Raman spectroscopy 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 This is a 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 This is a data graph showing the transistor output and transfer characteristics in Example 1.

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

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

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

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

[0050] Figure 13 This is a graph showing the X-ray sensitivity of the semiconductor transistor under different X-ray dose rates and different channel widths in Example 3. Detailed Implementation

[0051] The present invention will be further described below with reference to embodiments.

[0052] Example 1:

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

[0054] S1: The bulk NbOI2 material was prepared using a commercial tube furnace (Hefei Kejing) via chemical vapor deposition. Specifically, the starting reactants Nb, Nb2O5, and I2 powders in a mass ratio of 3:1:6 were sealed in a vacuum quartz tube. The tube was slowly heated to 700°C and maintained at this temperature for 3 days, then cooled to room temperature under natural furnace cooling. The product was then immersed in alcohol to remove excess I2. The harvested crystals were shiny rectangular plates measuring 6 × 8 × 0.5 mm.

[0055] S2: The grown NbOI2 crystals are adhered to a mechanically exfoliating tape (purchased from Zhongke Materials Co., Ltd.). After repeated adhesion to the tape, the desired nanosheets are obtained by repeatedly exfoliating with a weakly adhesive polydimethylsiloxane (PDMS) film (purchased from Zhongke Materials Co., Ltd.). Figure 1 Optical images of NbOI2 crystals and nanosheets, respectively. Figure 2 Raman spectra of nanosheets Figure 3 For AFM images, Figure 4XRD patterns were obtained by transferring nanosheets onto a SiO2 substrate using a transfer platform. Finally, two-dimensional NbOI2 semiconductor nanosheets with dimensions of 20 μm, a width of 3 μm, and a single-layer thickness (0.78 nm) were obtained on the substrate. The substrate consisted of a 1 mm thick, moderately doped Si layer topped with a 200 nm thick, mirror-polished SiO2 layer. The substrate was purchased from Suzhou Research Institute of Materials Technology and Engineering Co., Ltd. SiO2 was used as the gate dielectric. A gate voltage was applied to the Si, and by changing the magnitude and direction of the electric field, the charge density in the device channel was controlled, thereby regulating the conductivity of the device.

[0056] S3: Using microfabrication techniques, transistors were fabricated on the NbOI2 nanosheets from step S3. The narrowest channel width of the transistor was 1.5 micrometers, and it contained three metal electrodes: source, drain, and gate. The metal electrodes were Bi / Au electrodes. Optical images are shown below. Figure 7 As shown.

[0057] Device structure diagram as shown Figure 6 As shown. The metal electrode is an Au electrode. Before depositing the Au electrode, a 10nm thick Bi electrode is first deposited to increase the adhesion between the Au electrode and the substrate. The Au electrode was selected based on the work function of the NbOI2 material.

[0058] S4: By applying bias voltages to the source and drain, and a gate voltage to the gate, and applying X-rays at different dose rates to the transistor, high-performance two-dimensional semiconductor transistor X-ray detection can be achieved by adjusting the bias voltage or gate voltage. The bias voltage should not exceed 5 V, and the gate voltage should not exceed ±60 V. Specifically, the fabricated NbOI2 transistor is placed at the X-ray source. X-rays pass through the NbOI2 transistor and enter the X-ray detector. The detector converts the collected signal into a current, which is displayed on an oscilloscope. During measurement, a bias voltage is applied across the device, and the X-ray dose is changed by switching the shutter on and off. The change in current over time is continuously monitored.

[0059] In step S4, bias voltages are applied to the source and drain, and a gate voltage is applied to the gate. The transistor's transfer curve and output curve are then characterized, as shown below. Figure 8 As shown, the output curve in the left figure indicates that the device has a good ohmic contact, while the transfer curve in the right figure indicates that the device is n-type. Figure 8 This indicates that the transistor device is functioning correctly. The device's sensitivity and photocurrent under different dose rates and bias voltages are as follows: Figure 9 As shown, the photocurrent and sensitivity of the device can be effectively controlled by the X-ray dose rate and bias voltage. Specifically, the signal-to-noise ratio (SNR) of the device at different dose rates under 1V and 3V bias voltages is shown in the figure. Figure 10 As shown, this indicates that the device's signal-to-noise ratio is good. The rise and fall times of the device's response time are shown below. Figure 11 As shown, the rise time is 64 ms and the fall time is 40 ms, with a response speed on the sub-millisecond scale. By applying a gate voltage to the device, sensitivity data for different dose rates at different gate voltages can be obtained, such as... Figure 12 As shown, the sensitivity of the device at different X-ray dose rates can be effectively controlled by the gate voltage.

[0060] With an X-ray dose rate of 25 Gy / h, a bias voltage of 5 V, and a grid voltage of 60 V, a maximum sensitivity of 5 × 10⁻⁶ can be achieved. 9 µC / (Gy·cm 2 This is the highest reported X-ray detection sensitivity for a two-dimensional semiconductor transistor to date.

[0061] Example 2:

[0062] In Example 1, when the thickness of the NbOI2 nanosheets was changed from a single layer to multiple layers while keeping other conditions constant, the sensitivity decreased. For example, the sensitivities were 2 × 10⁻⁶ for thicknesses of 20 nm and 50 nm, respectively. 6 µC / (Gy·cm 2 ) and 9×10 5 µC / (Gy·cm 2 ).

[0063] Example 3:

[0064] In Example 1, devices with different transistor channel widths were tested, with all other conditions remaining constant. The smaller the channel width, the higher the sensitivity. For example... Figure 13 As shown, the sensitivities are 1×10⁻⁶ for widths of 2.5 µm and 7 µm, respectively. 6 µC / (Gy·cm 2 ) and 2.7×10 5 µC / (Gy·cm 2 The channel width should be as small as possible, but due to limitations in microfabrication technology, it is impossible to make it infinitely small.

[0065] Example 4:

[0066] In Example 1, by changing the bias voltage while keeping other conditions constant, increasing the bias voltage will increase the sensitivity. Figure 9 As shown, the sensitivities are 4.3 × 10⁻⁶ at bias voltages of 1V, 3V, 5V, and 10V, respectively. 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 at a bias voltage of 10V. A bias voltage higher than 10V will significantly increase the power consumption of the device, increase the dark current, and cause current drift.

[0067] Example 5:

[0068] In Example 1, different gate voltages were applied while other conditions remained constant; the higher the gate voltage, the higher the sensitivity. Figure 12 As shown, the sensitivities are 3.3 × 10⁻⁶ when the gate voltage is 30V, 40V, and 60V, respectively. 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. Under otherwise unchanged conditions, the highest sensitivity value is obtained at a gate voltage of 60V. When the gate voltage is higher than 60V, the device is easily damaged.

Claims

1. A method for achieving high-performance X-ray detection based on two-dimensional semiconductor transistors, characterized in that, The following steps are involved: S1: Two-dimensional semiconductor NbOI2 nanosheets with a longest side greater than 10 micrometers and a thickness of one or fewer layers are obtained on a Si / SiO2 substrate by mechanical exfoliation. S2: Using microfabrication techniques, transistors are fabricated on NbOI2 nanosheets from step S1, including three metal electrodes: source, drain, and gate. S3: By applying bias voltage to the source and drain and gate voltage to the gate, X-rays of different dose rates are irradiated onto the transistor. 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 applied gate voltage and bias voltage are such that the bias voltage does not exceed 5 V and the gate voltage does not exceed ±60 V.

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

3. The method for achieving high-performance X-ray detection based on two-dimensional semiconductor transistors according to claim 1, characterized in that, The following steps are involved: S1: Two-dimensional semiconductor NbOI2 nanosheets with a longest side of 10-45 micrometers and a single layer thickness of 0.78 nm were obtained on a Si / SiO2 substrate by mechanical exfoliation. S2: Using microfabrication techniques, transistors are fabricated on NbOI2 nanosheets from step S1, including three metal electrodes: source, drain, and gate. S3: Apply bias voltage to the source and drain, and gate voltage to the gate, and irradiate the transistor with X-rays. By adjusting the bias voltage or gate voltage, high-sensitivity two-dimensional semiconductor transistor X-ray detection can be achieved. In 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 applied gate voltage and bias voltage are as follows: the bias voltage is 5 V and the gate voltage is ±60 V.

4. The method for achieving high-performance X-ray detection based on two-dimensional semiconductor transistors according to claim 2, characterized in that, The following steps are involved: S1: Two-dimensional semiconductor NbOI2 nanosheets with a size of 20 micrometers and a single layer thickness of 0.78 nm were obtained on a Si / SiO2 substrate by mechanical exfoliation. S2: Using microfabrication techniques, a transistor is fabricated on the NbOI2 nanosheets from step S1, comprising three metal electrodes: source, drain, and gate; the transistor channel is 1.5 micrometers, and the metal electrode is an Au electrode; S3: Apply bias voltage to the source and drain, and apply gate voltage to the gate. The magnitudes of the applied gate voltage and bias voltage are as follows: bias voltage is 5 V, and gate voltage is +60 V.

5. The method for achieving high-performance X-ray detection based on two-dimensional semiconductor transistors according to claim 2, characterized in that, The following steps are involved: S1: Two-dimensional semiconductor NbOI2 nanosheets with a size of 20 micrometers, a width of 3 micrometers, and a single layer thickness of 0.78 nm were obtained on a Si / SiO2 substrate by mechanical exfoliation. S2: Using microfabrication technology, a transistor is fabricated on the NbOI2 nanosheet from step S1, comprising three metal electrodes: source, drain, and gate. The channel of the transistor is 1.5 micrometers, and the metal electrode is an Au electrode. Before evaporating the Au electrode, a 10 nm thick Bi electrode is first deposited. S3: Apply bias voltage to the source and drain, and apply gate voltage to the gate. The magnitudes of the applied gate voltage and bias voltage are as follows: bias voltage is 5 V, and gate voltage is 60 V. S4: Applying X-rays at a dose rate of 25 Gy / h can achieve a sensitivity of up to 5 × 10⁻⁶. 9 µC / (Gy·cm 2 Two-dimensional semiconductor transistor X-ray detection.

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