X-ray detector based on carbon-doped sapphire crystal and preparation method thereof

Abstract

The invention relates to an X-ray detector based on a carbon-doped sapphire crystal, and belongs to the technical field of X-ray direct detection and semiconductor radiation detectors. The carbon-doped sapphire crystal grown based on an edge-defined film-fed growth method shows semiconductor characteristics for direct detection, efficient collection of X-ray photon-generated carriers is realized through a planar electrode structure, and the sensitivity far higher than that of a traditional silicon-based detector is obtained. The wide bandgap oxide crystal has remarkable advantages in the aspects of irradiation resistance, high-temperature stability, detection efficiency and cost controllability, and the application boundary of the wide bandgap oxide crystal in a radiation detector is expanded.

Description

Technical Field

[0001] This invention belongs to the field of X-ray direct detection and semiconductor radiation detector technology, and relates to an X-ray detector based on carbon-doped sapphire crystal and its preparation method. Background Technology

[0002] X-rays, due to their short wavelength and high energy, can be used to detect information within matter. Based on this, X-ray detectors are widely used in medical testing, industrial inspection, security checks, scientific research, and space exploration. According to different mechanisms, X-ray detectors can be divided into gas detectors, scintillator detectors, and semiconductor detectors. Among them, semiconductor detectors are direct detectors, possessing high energy and spatial resolution, fast response speed, and compact size for easy portability, making them a promising candidate to become the mainstream X-ray detector. Currently, silicon-based (Si) detectors are widely used in clinical medical imaging and industrial radiation detection. However, silicon materials have the following shortcomings in the mid-to-high energy X-ray region: 1. Low atomic number (Z=14), resulting in lower absorption efficiency for high-energy X-rays; 2. A thicker silicon wafer is required to achieve sufficient absorption, leading to an increase in device size; 3. Surface leakage current and dark current have an adverse effect on detection sensitivity; 4. Irradiation stability is limited, and performance degrades significantly under long-term high doses.

[0003] In recent years, with the widespread application and development of semiconductor detectors, the requirements for X-ray detection materials have been continuously increasing. A good X-ray detection material needs to have a good combination of response time and sensitivity, as well as excellent carrier transport performance. Currently, widely used semiconductor detection materials include CdTe crystals, CdZnTe crystals, and perovskite materials such as CsPbBr3 crystals, MAPbI3 thin films, and MAPbBr3 single crystals. Among them, CsPbBr3 crystals have high resistivity and a large carrier mobility-lifetime product, and their resolution is constantly being improved by research groups both domestically and internationally. X-ray detectors made from MAPbBr3 crystals in perovskite materials have achieved a sensitivity of 80 Hz. μ C·Gy -1 ·cm 2 The lowest detection limit is as low as 36 nGy·s -1 ( Nat. Photonics 2016, 10 (5), 333-339. ).

[0004] sapphire( αWhile sapphire (C:Al₂O₃) possesses high hardness, high thermal stability, and high radiation tolerance as an insulating material, its large bandgap (approximately 9 eV) prevents its use in semiconductor detectors. However, by doping sapphire with appropriate amounts of carbon (C:Al₂O₃), controllable energy levels can be introduced within the bandgap, significantly improving conductivity and enabling the generation, drift, and effective collection of charge carriers in an irradiated electric field. This makes sapphire feasible as a direct semiconductor detection material for the first time.

[0005] Against this technological backdrop, the development of novel detection materials with higher atomic numbers, better radiation stability, and superior charge collection efficiency has become an urgent need for the industry. Carbon-doped sapphire crystals, with their unique material properties, offer a new technological path to overcome existing technological bottlenecks. Summary of the Invention

[0006] To address the above problems, this invention aims to provide an X-ray direct detector based on carbon-doped sapphire crystal, overcoming the shortcomings of silicon-based detectors such as severe irradiation damage and low absorption efficiency, while avoiding the problems of complex structure and slow response of scintillator detectors.

[0007] The present invention employs the following technical solutions to achieve the above objectives: An X-ray detector based on carbon-doped sapphire crystal, wherein the detector uses carbon-doped sapphire as a substrate and Ti-Au is deposited on the surface of the carbon-doped sapphire as the S-terminus and D-terminus of the electrodes.

[0008] This invention provides a method for preparing the above-mentioned X-ray detector: Step 1, Pretreatment: The carbon-doped sapphire crystal is cut into sheet-like structures, polished on both sides with diamond suspension to optimize the surface roughness of the crystal, and then cleaned with oxygen plasma. Step 2: A Ti-Au layer is uniformly deposited on the surface of the pretreated carbon-doped sapphire crystal using electron beam evaporation. Two symmetrical planar electrodes, namely the S-end and the D-end, are formed without obstructing the channel region, thus obtaining a planar electrode type semiconductor X-ray detector based on carbon-doped sapphire crystal.

[0009] As a preferred method, the carbon-doped sapphire crystal in step 1 is prepared by the guided mode method.

[0010] More preferably, the method for preparing the carbon-doped sapphire crystal includes the following steps: Step A, Pre-sintering: Sintering with a mole fraction of 10... -4 -10 -2 The graphite powder and ultra-high purity Al2O3 powder are thoroughly mixed and then sintered at 1500℃ for 6-8 hours. Step B: Add the sintered powder to the EFG growth furnace. After loading, evacuate the furnace and check its airtightness to ensure there are no leaks. Start the vacuum pump and continuously monitor the vacuum level. Once the vacuum level drops below 10 Pa, turn off the vacuum pump and start the pressure holding program. After starting the operation, first click the argon filling button, then manually rotate the filling valve to perform the filling operation. Monitor the argon pressure in real time. When the pressure reaches the standard value of 4000 Pa, immediately close the filling valve to complete the argon filling. Subsequently, turn on the gas flow meter and accurately set the flow parameters of each gas according to the process requirements: argon 2.9 SLPM, carbon dioxide 0.2 SCCM, and carbon monoxide 250 SCCM to ensure that the gas environment meets the process requirements for sapphire crystal growth. After confirming that there are no abnormalities in the atmosphere control, start heating and strictly follow the process curve to raise the temperature to 2135℃, simultaneously starting the crucible raising program. After the raw materials are completely melted, the crucible is precisely positioned and held at a constant temperature for a period of time until the temperature distribution within the melt stabilizes. Then, the seed crystal is lowered at the process-adapted rate, entering the seed crystal and mold bonding stage. Once fully bonded, the surface layer is melted away, and the pulling speed is set according to predetermined parameters to officially begin the crystal pulling and lifting operation. During the crystal growth stage, the lifting rate is strictly maintained to ensure the stability and uniformity of crystal growth. After the growth process reaches a stable state, the crystal width can be precisely controlled by finely adjusting the furnace temperature. The growth rate is maintained at 35 mm / h during this stage, and the entire steady-state growth process takes approximately 36 hours. This stage ends when the crystal length reaches 1200 mm. After the crystal length and width reach the preset targets, the finishing procedure begins: by adjusting the lifting speed, the seed crystal rod moves the crystal smoothly along the growth direction, with real-time monitoring to prevent scratches. Once the crystal is completely detached from the mold, the crucible is lowered to a safe position according to the parameters. The cooling process is executed according to a customized curve, and the temperature control system precisely controls the speed to prevent stress cracking, and monitors the temperature in real time until it reaches room temperature (25℃±5℃).

[0011] As a preferred method, in step 1, the carbon-doped sapphire crystal is cut into 5×5×0.5 mm pieces. 3 The sheet-like structure.

[0012] As a preferred embodiment, the diamond particle size in step 1 is 0.05μm~0.5μm.

[0013] As a preferred approach, the crystal surface roughness in step 1 is optimized to Ra < 5 nm.

[0014] As a preferred embodiment, in step 2, the thickness of the Ti layer is 20 nm and the thickness of the Au layer is 80~120 nm.

[0015] As a preferred embodiment, the distance between the two symmetrical planar electrodes in step 2 is 100~500μm.

[0016] The present invention has the following beneficial effects: To address the problems of traditional silicon-based detectors, such as easy saturation under high-energy radiation, limited thickness, insufficient absorption efficiency, and poor stability under high-dose environments, this invention utilizes sapphire single crystals grown through carbon doping and guided mode methods as both absorbers and active detectors. This achieves direct X-ray detection with high resistivity, low leakage current, strong radiation resistance, and high sensitivity. This technology breaks through the traditional positioning of sapphire as merely an insulator and substrate material, endowing it with semiconductor-type carrier collection capabilities, thus forming a novel wide-bandgap direct detection material system.

[0017] This invention employs a mode-guided method to prepare carbon-doped sapphire crystals. By introducing a carbon source into the Al₂O₃ melt, some carbon atoms modify the deep-level structure of the sapphire through energy level modification, significantly suppressing deep-level trapping centers caused by intrinsic defects and enhancing the excitation and migration capabilities of free carriers. The mode-guided method enables the growth of large-size, controllable-section, and uniformly sized sapphire crystals, which is beneficial for manufacturing detector chips with thicknesses suitable for X-ray absorption. The carbon-doped crystal exhibits lower dark current than traditional wide-bandgap oxide materials and maintains low leakage current at room temperature, facilitating stable semiconductor-type detection without the need for cooling.

[0018] This invention fabricates planar electrodes on both sides of a polished carbon-doped sapphire crystal. The electrodes are made of inert metal gold (Au), and a detector device is formed by electron beam evaporation deposition. The electrode structure is a symmetrical MSM type, which helps to reduce the interface barrier, enhance carrier collection efficiency, and maintain structural stability. Simultaneously, the device thickness can cover the typical X-ray energy range, enabling the detector to achieve good absorption depth and conversion efficiency. Under an 800 V bias, the device achieves a detection sensitivity of 387.7 μC Gy⁻¹ cm⁻², significantly higher than silicon-based detectors of the same thickness, and exhibits a wide dynamic range and low background noise.

[0019] Compared to traditional silicon-based X-ray detectors, the material of this invention has a larger band gap (8.7-9.0 eV), stronger radiation resistance and thermal stability, and can operate for extended periods under high-energy, high-dose, and high-temperature fluctuation environments without significant performance degradation. Carbon-doped sapphire possesses extremely high breakdown field strength, enabling the device to withstand higher bias voltages for enhanced charge collection efficiency. Furthermore, the detector of this invention can operate at room temperature, eliminating the need for cooling structures commonly required for silicon detectors, thereby reducing system complexity and improving the engineering adaptability of medical imaging equipment and industrial testing equipment.

[0020] This invention achieves synergistic innovation at the material, structural, and application levels. By utilizing carbon-doped sapphire crystal prepared using the guided-mode method as the direct detection material and constructing a planar MSM electrode structure, a traditional insulator is endowed with semiconductor-type carrier collection capabilities, successfully overcoming the inherent property limitations of sapphire materials in the field of radiation detection. This detector combines high sensitivity, high stability, low noise, and wide energy range adaptability, making it widely applicable in medical imaging diagnostics, high-energy ray industrial non-destructive testing, security inspection equipment, and other radiation monitoring scenarios. This technical approach possesses significant engineering scale-up potential, providing a new material foundation and industrialization possibilities for next-generation wide-bandgap direct detectors. Attached Figure Description

[0021] Figure 1 The carbon-doped sapphire crystal grown using the guided-mode method in Example 1; Figure 2 Example 1: X-ray detector based on carbon-doped sapphire crystal; Figure 3 Performance Test 2: X-ray detection sensitivity based on carbon-doped sapphire crystal. Detailed Implementation

[0022] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art will fall within the scope of protection of the claims of this application.

[0023] Example 1 First, carbon-doped sapphire is prepared using the guided-mode method: Step A, Pre-sintering: Graphite powder and ultra-high purity Al2O3 powder are thoroughly mixed and sintered at 1500℃ for 6 hours; the mass fraction of graphite powder is 0.0012 wt%. Step B: Add the sintered powder to the EFG growth furnace. After loading, evacuate the furnace and check its airtightness to ensure there are no leaks. Start the vacuum pump and continuously monitor the vacuum level. Once the vacuum level drops below 10 Pa, turn off the vacuum pump and start the pressure holding program. After starting the operation, first click the argon filling button, then manually rotate the filling valve to perform the filling operation. Monitor the argon pressure in real time. When the pressure reaches the standard value of 4000 Pa, immediately close the filling valve to complete the argon filling. Subsequently, turn on the gas flow meter and accurately set the flow parameters of each gas according to the process requirements: argon 2.9 SLPM, carbon dioxide 0.2 SCCM, and carbon monoxide 250 SCCM to ensure that the gas environment meets the process requirements for sapphire crystal growth. After confirming that there are no abnormalities in the atmosphere control, start heating and strictly follow the process curve to raise the temperature to 2135℃, simultaneously starting the crucible raising program. After the raw materials are completely melted, the crucible is precisely positioned and held at a constant temperature for a period of time until the temperature distribution within the melt stabilizes. Then, the seed crystal is lowered at the process-adapted rate, entering the seed crystal and mold bonding stage. Once fully bonded, the surface layer is melted away, and the pulling speed is set according to predetermined parameters to officially begin the crystal pulling and lifting operation. During the crystal growth stage, the lifting rate is strictly maintained to ensure the stability and uniformity of crystal growth. After the growth process reaches a stable state, the crystal width can be precisely controlled by finely adjusting the furnace temperature. The growth rate is maintained at 35 mm / h during this stage, and the entire steady-state growth process takes approximately 36 hours. This stage ends when the crystal length reaches 1200 mm. After the crystal length and width reach the preset targets, the finishing procedure begins: by adjusting the lifting speed, the seed crystal rod moves the crystal smoothly along the growth direction, with real-time monitoring to prevent scratches. Once the crystal is completely detached from the mold, the crucible is lowered to a safe position according to the parameters. The cooling process is executed according to a customized curve, and the temperature control system precisely controls the speed to prevent stress cracking, and monitors the temperature in real time until it reaches room temperature (25℃±5℃).

[0024] Secondly, X-ray detectors are fabricated. Step 1, Preprocessing: The sapphire crystal strip prepared above was cut into pieces approximately 5×5×0.5 mm. 3 The sheet-like structure was subjected to double-sided mechanical polishing with a 0.5μm diamond suspension to optimize the surface roughness to Ra<5 nm; then oxygen plasma cleaning was used to remove residual organic matter and microcrack layer from the surface. Step 2: Ti-Au layers are uniformly deposited sequentially on the surface of the pretreated carbon-doped sapphire crystal using electron beam evaporation. The thicknesses are approximately 20 nm and 120 nm, respectively. Two symmetrical planar electrodes, namely the S-end and D-end, are formed without obstructing the channel region. The electrode spacing is controlled at 500 μm, thus obtaining a planar electrode type semiconductor X-ray detector based on carbon-doped sapphire crystal.

[0025] Example 2 First, carbon-doped sapphire is prepared using the guided-mode method: Step A, Pre-sintering: Graphite powder and ultra-high purity Al2O3 powder are thoroughly mixed and sintered at 1500℃ for 8 hours; the mass fraction of graphite powder is 0.12 wt%. Step B: Add the sintered powder to the EFG growth furnace. After loading, evacuate the furnace and check its airtightness to ensure there are no leaks. Start the vacuum pump and continuously monitor the vacuum level. Once the vacuum level drops below 10 Pa, turn off the vacuum pump and start the pressure holding program. After starting the operation, first click the argon filling button, then manually rotate the filling valve to perform the filling operation. Monitor the argon pressure in real time. When the pressure reaches the standard value of 4000 Pa, immediately close the filling valve to complete the argon filling. Subsequently, turn on the gas flow meter and accurately set the flow parameters of each gas according to the process requirements: argon 2.9 SLPM, carbon dioxide 0.2 SCCM, and carbon monoxide 250 SCCM to ensure that the gas environment meets the process requirements for sapphire crystal growth. After confirming that there are no abnormalities in the atmosphere control, start heating and strictly follow the process curve to raise the temperature to 2135℃, simultaneously starting the crucible raising program. After the raw materials are completely melted, the crucible is precisely positioned and held at a constant temperature for a period of time until the temperature distribution within the melt stabilizes. Then, the seed crystal is lowered at the process-adapted rate, entering the seed crystal and mold bonding stage. Once fully bonded, the surface layer is melted away, and the pulling speed is set according to predetermined parameters to officially begin the crystal pulling and lifting operation. During the crystal growth stage, the lifting rate is strictly maintained to ensure the stability and uniformity of crystal growth. After the growth process reaches a stable state, the crystal width can be precisely controlled by finely adjusting the furnace temperature. The growth rate is maintained at 35 mm / h during this stage, and the entire steady-state growth process takes approximately 36 hours. This stage ends when the crystal length reaches 1200 mm. After the crystal length and width reach the preset targets, the finishing procedure begins: by adjusting the lifting speed, the seed crystal rod moves the crystal smoothly along the growth direction, with real-time monitoring to prevent scratches. Once the crystal is completely detached from the mold, the crucible is lowered to a safe position according to the parameters. The cooling process is executed according to a customized curve, and the temperature control system precisely controls the speed to prevent stress cracking, and monitors the temperature in real time until it reaches room temperature (25℃±5℃).

[0026] Secondly, X-ray detectors are fabricated. Step 1, Preprocessing: The sapphire crystal strip prepared above was cut into pieces approximately 5×5×0.5 mm. 3 The sheet-like structure was subjected to double-sided mechanical polishing with a 0.05μm diamond suspension to optimize the surface roughness to Ra<5 nm; then oxygen plasma cleaning was used to remove residual organic matter and microcrack layer from the surface. Step 2: Ti-Au layers are uniformly deposited sequentially on the surface of the pretreated carbon-doped sapphire crystal using electron beam evaporation. The thicknesses are approximately 20 nm and 80 nm, respectively. Two symmetrical planar electrodes, namely the S-end and D-end, are formed without obstructing the channel region. The electrode spacing is controlled at 100 μm, thus obtaining a planar electrode type semiconductor X-ray detector based on carbon-doped sapphire crystal.

[0027] Example 3 First, carbon-doped sapphire is prepared using the guided-mode method: Step A, Pre-sintering: Graphite powder and ultra-high purity Al2O3 powder are thoroughly mixed and sintered at 1500℃ for 6 hours; the mass fraction of graphite powder is 0.05 wt%. Step B: Add the sintered powder to the EFG growth furnace. After loading, evacuate the furnace and check its airtightness to ensure there are no leaks. Start the vacuum pump and continuously monitor the vacuum level. Once the vacuum level drops below 10 Pa, turn off the vacuum pump and start the pressure holding program. After starting the operation, first click the argon filling button, then manually rotate the filling valve to perform the filling operation. Monitor the argon pressure in real time. When the pressure reaches the standard value of 4000 Pa, immediately close the filling valve to complete the argon filling. Subsequently, turn on the gas flow meter and accurately set the flow parameters of each gas according to the process requirements: argon 2.9 SLPM, carbon dioxide 0.2 SCCM, and carbon monoxide 250 SCCM to ensure that the gas environment meets the process requirements for sapphire crystal growth. After confirming that there are no abnormalities in the atmosphere control, start heating and strictly follow the process curve to raise the temperature to 2135℃, simultaneously starting the crucible raising program. After the raw materials are completely melted, the crucible is precisely positioned and held at a constant temperature for a period of time until the temperature distribution within the melt stabilizes. Then, the seed crystal is lowered at the process-adapted rate, entering the seed crystal and mold bonding stage. Once fully bonded, the surface layer is melted away, and the pulling speed is set according to predetermined parameters to officially begin the crystal pulling and lifting operation. During the crystal growth stage, the lifting rate is strictly maintained to ensure the stability and uniformity of crystal growth. After the growth process reaches a stable state, the crystal width can be precisely controlled by finely adjusting the furnace temperature. The growth rate is maintained at 35 mm / h during this stage, and the entire steady-state growth process takes approximately 36 hours. This stage ends when the crystal length reaches 1200 mm. After the crystal length and width reach the preset targets, the finishing procedure begins: by adjusting the lifting speed, the seed crystal rod moves the crystal smoothly along the growth direction, with real-time monitoring to prevent scratches. Once the crystal is completely detached from the mold, the crucible is lowered to a safe position according to the parameters. The cooling process is executed according to a customized curve, and the temperature control system precisely controls the speed to prevent stress cracking, and monitors the temperature in real time until it reaches room temperature (25℃±5℃).

[0028] Secondly, X-ray detectors are fabricated. Step 1, Preprocessing: The sapphire crystal strip prepared above was cut into pieces approximately 5×5×0.5 mm. 3 The sheet-like structure was subjected to double-sided mechanical polishing with a 0.3μm diamond suspension to optimize the surface roughness to Ra<5 nm; then oxygen plasma cleaning was used to remove residual organic matter and microcrack layers from the surface. Step 2: Ti-Au layers are uniformly deposited sequentially on the surface of the pretreated carbon-doped sapphire crystal using electron beam evaporation. The thicknesses are approximately 20 nm and 100 nm, respectively. Two symmetrical planar electrodes, namely the S-end and D-end, are formed without obstructing the channel region. The electrode spacing is controlled at 300 μm, thus obtaining a planar electrode type semiconductor X-ray detector based on carbon-doped sapphire crystal.

[0029] Performance Test 1 The X-ray detector prepared above was installed in a general test platform for photodetectors and its performance was tested using a bias voltage of 800 V.

[0030] The results show that carbon-doped sapphire in this structure can generate a significant photocurrent signal under X-ray irradiation, with a detection sensitivity of 387.7 μC·Gy-1·cm-2. Meanwhile, the detection sensitivity of Si-based detectors is generally between 150-250 μC·Gy-1·cm-2.

[0031] This result demonstrates that by designing the electrodes appropriately and introducing deep energy levels through carbon doping, sapphire materials can exhibit carrier response, providing an effective technical route for fabricating non-silicon-based, highly radiation-resistant, and highly stable detectors.

[0032] Performance Test 2 The X-ray detector prepared above was subjected to system performance testing and compared with a conventional silicon-based detector. The tests used an X-ray source with a dose rate of 50–100 μGy / s. First, I–V curve testing was performed on the device to confirm a quasi-ohmic contact between the electrode and the crystal, avoiding the influence of the Schottky barrier on carrier transport. In the dark state, the leakage current of the device remained at the nA level, demonstrating the extremely low intrinsic noise level of the sapphire-based material. Subsequently, X-ray irradiation was applied, and the curve of its photocurrent as a function of dose rate was recorded. The obtained response showed a good linear relationship, and the sensitivity stabilized at 387.7 μC·Gy⁻¹·cm⁻².

[0033] Further comparison with typical 300 μm thick silicon-based detectors revealed that silicon devices typically exhibit a sensitivity of approximately 150–250 μC·Gy⁻¹·cm⁻² under the same bias voltage, and are temperature-sensitive and susceptible to damage from high-dose irradiation. In contrast, carbon-doped sapphire detectors offer higher sensitivity, and thanks to the high radiation resistance and thermal stability of Al₂O₃, they can operate stably over a wider temperature range and at higher radiation doses. Particularly in industrial non-destructive testing and high-energy medical imaging applications, their environmental resistance surpasses that of silicon-based devices, demonstrating strong application potential.

Claims

1. An X-ray detector based on carbon-doped sapphire crystal, characterized in that, The detector uses carbon-doped sapphire as a substrate, and Ti-Au is deposited on the surface of the carbon-doped sapphire as the S-terminus and D-terminus of the electrodes.

2. The X-ray detector as described in claim 1, characterized in that, The method for preparing the X-ray detector includes the following steps: Step 1, Pretreatment: The carbon-doped sapphire crystal is cut into sheet-like structures, polished on both sides with diamond suspension to optimize the surface roughness of the crystal, and then cleaned with oxygen plasma. Step 2: A Ti-Au layer is uniformly deposited on the surface of the pretreated carbon-doped sapphire crystal using electron beam evaporation. Two symmetrical planar electrodes, namely the S-end and the D-end, are formed without obstructing the channel region, thus obtaining a planar electrode type semiconductor X-ray detector based on carbon-doped sapphire crystal.

3. The X-ray detector as described in claim 1, characterized in that, In step 1, the carbon-doped sapphire crystal is prepared using the guided mode method.

4. The X-ray detector as described in claim 3, characterized in that, The method for preparing the carbon-doped sapphire crystal includes the following steps: Step A, pre-sintering: After thoroughly mixing graphite powder and ultra-high purity Al2O3 powder, sinter at 1500℃ for 6-8 hours; Step B: Add the sintered powder to the EFG growth furnace. After loading, evacuate the furnace. When the vacuum level drops below 10 Pa, start the pressure holding program. Then fill with argon gas and monitor the argon pressure. When the pressure reaches the standard value of 4000 Pa, the argon filling is completed. Adjust the gas environment to 2.9 SLPM of argon, 0.2 SCCM of carbon dioxide, and 250 SCCM of carbon monoxide, and start heating. According to the process curve, raise the temperature to 2135℃. After the raw material melts, hold it at the temperature until the temperature in all parts of the melt is stable. Lower the seed crystal to make it fit with the mold, melt away the surface layer, and start crystal pulling. During the pulling stage, the crystal growth rate is kept constant at 35 mm / h. The entire steady-state growth process takes about 36 hours. When the crystal growth length reaches 1200 mm, the pulling is stopped, and the finishing program is started to obtain the carbon-doped sapphire crystal.

5. The X-ray detector as described in claim 1, characterized in that, The mass fraction of graphite powder in step A is 0.0012wt%-0.12wt%.

6. The X-ray detector as claimed in claim 1, characterized in that, In step 1, the carbon-doped sapphire crystal is cut into 5×5×0.5 mm pieces. 3 The sheet-like structure.

7. The X-ray detector as claimed in claim 1, characterized in that, The diamond particle size in step 1 is 0.05μm~0.5μm.

8. The X-ray detector as claimed in claim 1, characterized in that, In step 1, the surface roughness of the crystal is optimized to Ra < 5 nm.

9. The X-ray detector as claimed in claim 1, characterized in that, In step 2, the thickness of the Ti layer is 20 nm, and the thickness of the Au layer is 80~120 nm.

10. The X-ray detector as claimed in claim 1, characterized in that, In step 2, the distance between the two symmetrical planar electrodes is 100~500μm.

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