P-i-n type ultraviolet photoelectric detector based on 4H-SiC-GaN heterostructure and preparation method of p-i-n type ultraviolet photoelectric detector

Abstract

The invention relates to the field of preparation of ultraviolet photoelectric detectors, in particular to a p-i-n type ultraviolet photoelectric detector based on a 4H-SiC-GaN heterostructure and a preparation method of the p-i-n type ultraviolet photoelectric detector based on the 4H-SiC-GaN heterostructure, the dislocation defect is greatly reduced on the material structure level, a foundation is built for subsequent high-quality crystal growth, it is ensured that the structure of the detector is stable under complex working conditions, and the performance of the detector is improved. Material damage caused by thermal expansion and cold contraction or lattice stress is effectively avoided, and the reliability and durability of the detector are greatly improved. And the preparation process is fine. The MOCVD technology is adopted for growth, and parameters of all links are accurately regulated and controlled. Furthermore, high-purity metal is matched with proper evaporation rate and deposition thickness, and is combined with a high-vacuum physical vapor deposition technology, so that good ohmic contact between the metal and a semiconductor is ensured, the hole injection efficiency is high, the carrier recombination probability is reduced, the photoelectric conversion efficiency is effectively improved, and the wide market prospect is achieved.

Description

Technical Field

[0001] The present invention relates to the field of ultraviolet photoelectric detector preparation, and in particular to a PIN type ultraviolet photoelectric detector based on a 4H-SiC-GaN heterostructure and a preparation method thereof. Background Art

[0002] With the advancement of science and technology, ultraviolet (UV) detection technology is playing an increasingly important role in numerous fields. Silicon carbide (SiC), a prominent representative of third-generation semiconductors, has injected significant momentum into the field of UV detection with its unique physical properties. Its high thermal conductivity allows for rapid dissipation of heat generated during operation, preventing device performance degradation due to overheating and ensuring stable detector operation in high-temperature environments. For example, SiC-based detectors demonstrate exceptional heat resistance in high-temperature monitoring applications around aerospace engines. Its excellent electron mobility enables rapid carrier movement, significantly accelerating signal transmission and enabling detectors to more agilely respond to transient changes in UV light. Its exceptional hardness ensures the detector's structural integrity in complex mechanical environments, allowing it to maintain normal operation even after moderate impact and compression. Its exceptional chemical stability allows it to withstand corrosion from corrosive substances such as acids and alkalis, making it suitable for harsh operating conditions such as chemical plants and marine environmental monitoring. SiC-based pin-structure UV photodetectors, with their ingenious structural design, are widely used in various fields. The intrinsic (I-type) semiconductor layer embedded between the p-type and n-type semiconductors acts as a bridge, effectively extending the width of the depletion region. This expansion is of great significance. On the one hand, it enables the detector to collect photogenerated carriers more efficiently, significantly enhancing its sensitivity and making it impossible for even weak ultraviolet light signals to hide. On the other hand, the wider depletion region accelerates the separation and transmission of carriers, greatly improving the response speed of the detector, enabling it to capture key information in a timely manner in the ever-changing actual detection scenarios.

[0003] However, existing technologies still face numerous obstacles in their pursuit of higher performance. Regarding PIN-type UV detectors made from organic semiconductor thin films, while patent CN118102738A proposes inserting an inorganic intrinsic semiconductor film between a P-type organic semiconductor film and an N-type organic semiconductor film to form a PIN structure, seemingly resolving some contact issues and providing a solution to the chronic problems of slow response speed and high dark current in organic photodiode detectors, a deeper examination reveals that the inherent shortcomings of organic semiconductor films are difficult to overcome. Their production process is complex and tedious, involving the meticulous synthesis and precise doping of multiple high-purity organic materials. Even slight deviations in each step can lead to significant differences in film performance. Furthermore, during long-term operation or storage, organic materials are highly susceptible to environmental factors, and chemical or physical changes such as oxidation and photodegradation can occur at any time. For example, an organic semiconductor PIN-type UV detector used for long-term outdoor environmental monitoring showed obvious signs of aging after months of exposure to sunlight and rain. The detector's responsivity decreased significantly, and its dark current increased dramatically, ultimately failing to meet monitoring requirements. This fundamentally limits its widespread industrial application.

[0004] Another example is the special PIN photodetector described in patent CN117637896A. This device optimizes detector performance by meticulously placing P-type doped regions and N-type ohmic contact layers on either side of the intrinsic layer, and superimposing several layers of antireflection coating on the photosensitive window of the P-type doped region. While it's undeniable that antireflection coatings can theoretically increase light transmittance and enhance the detector's ability to capture optical signals, in practice, stacking multiple layers of antireflection coatings presents a series of thorny challenges. The refractive index of each layer must be precisely controlled to ensure it increases sequentially toward the intrinsic layer, placing extremely high demands on process precision. Achieving this stably and accurately on large-scale industrial production lines is extremely challenging. Any inaccuracy can lead to an imbalance in the refractive index matching between the layers, preventing the antireflection effect and increasing light scattering and reflection, reducing the detector's overall performance. While 4H-SiC UV photodetectors have shown initial advantages, the journey toward higher performance still faces numerous technical challenges that need to be overcome. Improving quantum efficiency is a key challenge. With current technology, detectors still have significant room for improvement in their utilization of UV photons. This means many UV photons are not effectively converted into electrical signals, resulting in wasted energy and limiting further improvements in detector sensitivity. Dark current is also a significant issue. Even with some improvements achieved with existing pin structures, it still needs to be reduced to even lower levels in noise-sensitive, high-precision detection applications, such as biomedical testing and high-end optical instrument calibration. Furthermore, enhancing device stability and reliability, ensuring consistent performance under long-term, complex, and changing operating conditions, is a key research and development focus. Meanwhile, GaN (gallium nitride)-based UV photodetectors have garnered significant attention in recent years. Their tunable response wavelength allows for flexible customization of their UV detection range to meet diverse application needs. In the field of UV communications, precisely adjusting the response wavelength of GaN detectors enables high-speed, stable UV signal transmission, establishing reliable communication links. In the field of UV radiation detection, they can focus on specific wavelengths of UV radiation, providing researchers with more accurate radiation intensity data. The high stability of GaN detectors minimizes performance fluctuations in complex environments, allowing them to function reliably for applications ranging from monitoring hot and humid tropical rainforests to UV detection in cold and dry polar expeditions. Their portability facilitates their use in field operations and temporary monitoring stations, allowing researchers to quickly deploy and obtain critical UV information. However, traditional GaN-based UV photodetectors are not without flaws. High optical signal losses and low optical signal absorption efficiency have become bottlenecks in their development.When faced with a weak ultraviolet light signal source, a large number of photons fail to be effectively absorbed and converted after entering the detector, resulting in a weak electrical signal output by the detector, which is difficult to accurately reflect the intensity of the light signal. In practical applications, this limits its detection accuracy and applicable range, and cannot meet the growing demand for high-precision ultraviolet detection.

[0005] Therefore, according to the above-mentioned related technologies, it is urgent to develop a pin-type ultraviolet photodetector based on 4H-SiC-GaN heterostructure and a preparation method thereof. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to propose a pin-type ultraviolet photodetector based on a 4H-SiC-GaN heterostructure and a preparation method thereof, so as to integrate the advantages of multiple materials and overcome the shortcomings of the existing technology.

[0007] Based on the above objectives, the present invention provides a PIN-type ultraviolet photodetector based on a 4H-SiC-GaN heterostructure and a preparation method thereof.

[0008] A pin-type ultraviolet photodetector based on a 4H-SiC-GaN heterostructure comprises, from bottom to top, an n-type 4H-SiC substrate, an i-type GaN epitaxial layer, and a p-type doped GaN epitaxial layer. The upper surface of the p-type doped GaN epitaxial layer contacts an anode electrode, and the lower surface of the n-type 4H-SiC substrate contacts a cathode electrode.

[0009] Preferably, the pin-type ultraviolet photodetector is simulated by Silvaco TCAD software, and the calculation process adopts the carrier Fermi statistics and the partial ionization model of the doping concentration, that is, the electron concentration in the semiconductor is:

[0010] The hole concentration in a semiconductor is:

[0011] Take the doping concentration N of the p-type GaN epitaxial layer a =5.0×10 18 cm -3 , the doping concentration N of the n-type SiC substrate d =2.0×10 18 cm -3 The i layer is non-intentionally doped GaN. Due to the presence of nitrogen vacancies, non-intentionally doped GaN usually behaves as n-type, and the electron concentration is around 10 16 cm -3 The width of the i-type GaN is set to 200nm.

[0012] A method for preparing a PIN-type ultraviolet photodetector based on a 4H-SiC-GaN heterostructure comprises the following steps: Step S1. Substrate selection: Select a 6-inch 4H-SiC substrate; Step S2. During the i-GaN intrinsic layer growth phase, metal organic chemical vapor deposition (MOCVD) was used. The reaction chamber temperature was set at 1040-1060°C, the pressure was maintained at 190-210 mbar, trimethylgallium was used as the gallium source, and its flow rate was controlled at 18-22 sccm. Ammonia was used as the nitrogen source, with a flow rate set at 1400-1600 sccm. High-purity hydrogen was used as the carrier gas, with a flow rate of 4950-5050 sccm. Under these parameters, a growth rate of 0.4-0.6 μm / h was achieved, ensuring the growth of a high-quality i-GaN intrinsic layer with a thickness of 190-210 nm. Step S3. Growth of the p-GaN photon absorption layer: Metal-organic chemical vapor deposition (MOCVD) is used, with the temperature maintained at 9950-1050°C and the pressure at 140-160 mbar. The trimethylgallium flow rate is adjusted to 28-32 sccm, the ammonia flow rate is 1750-1850 sccm, and the carrier hydrogen flow rate is 5950-6050 sccm. The magnesium dopant is introduced in the form of cyclopentadienyl magnesium (Cp2Mg) at a flow rate of 0.8-1.2 sccm. The growth time is optimized to ensure a p-GaN layer thickness of 280-320 nm. This allows for precise control of the electrochemical properties of the p-GaN layer, achieving an ideal hole carrier velocity to meet the requirements for efficient UV light absorption and conversion. Step S4. Electrode preparation: nickel and aluminum are evaporated on the surface of the p-GaN photon absorption layer, wherein the purity of the nickel target is 99.99%, the evaporation rate is controlled at 0.4-0.6Å / s, and the deposition thickness reaches 180-220Å; the purity of the Al target is 99.9%, the evaporation rate is controlled at 0.2-0.4Å / s, and the deposition thickness is 90-110Å. By high vacuum physical vapor deposition technology, the vacuum degree is better than 1×10 - 6 Evaporation is performed in a low-pressure environment to ensure uniform deposition of metal atoms on the p-GaN surface, promoting the formation of good ohmic contact. Step S5. Vapor-depositing titanium and aluminum on the lower surface of the 4H-SiC conductive substrate. The titanium target has a purity of 99.95%, an evaporation rate of 0.3-0.5 Å / s, and a deposition thickness of 145-155 Å. The aluminum target has a purity of 99.9%, an evaporation rate of 0.25-0.35 Å / s, and a deposition thickness of 95-105 Å. The vacuum environment requirements are the same as those for p-GaN surface evaporation to ensure a stable and reliable electrical connection between the electrode and the substrate. Step S6. Annealing: After the metal electrode is deposited, the device is placed in a specialized rapid thermal annealing device and annealed at 495-505°C for 2-4 minutes in a nitrogen atmosphere with a purity of 99.999%. The heating rate is controlled at 48-52°C / s to ensure uniformity and stability throughout the annealing process. This allows for fine-tuning of the detector's internal microstructure, comprehensively improving its performance and enabling it to excel in the field of ultraviolet light detection.

[0013] Preferably, the key parameter requirement of the 6-inch 4H-SiC substrate in step S1 is that the lattice constant mismatch with the i-GaN in step S2 is ±0.5%, and the difference in thermal expansion coefficient between the 6-inch 4H-SiC substrate in step S1 and the i-GaN in step S2 is ±1×10 -6 K -1 , in order to ensure the quality of the subsequently grown crystals.

[0014] Beneficial effects of the present invention: This invention provides a PIN-type ultraviolet photodetector based on a 4H-SiC-GaN heterostructure and its fabrication method, offering numerous significant advantages. First, at the material structure level, dislocation defects are significantly reduced, laying a solid foundation for subsequent high-quality crystal growth. This ensures structural stability under complex operating conditions, effectively preventing material damage caused by thermal expansion and contraction or lattice stress, and significantly improving the detector's reliability and durability. Second, the fabrication process is meticulously detailed. Metal-organic chemical vapor deposition (MOCVD) technology is employed for growth, allowing precise control of parameters at each stage. Furthermore, in electrode fabrication, high-purity metals, combined with an appropriate evaporation rate and deposition thickness, and high-vacuum physical vapor deposition (PVD) ensure good ohmic contact between the metal and semiconductor, resulting in high hole injection efficiency, reduced contact resistance to below 1Ω·cm², and reduced carrier recombination probability, effectively improving photoelectric conversion efficiency. Compared with existing technologies, this method overcomes the drawbacks of organic semiconductor thin-film detectors, such as complex fabrication and poor stability, as well as the low light absorption efficiency of traditional GaN detectors, and holds broad market prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only for the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 Schematic diagram of the PIN heterostructure ultraviolet photodetector of the present invention; Figure 2This is a device simulation structure diagram of the PIN heterostructure ultraviolet photodetector in the present invention; Figure 3 This is a diagram of the simulation results of dark state IV in the present invention; Figure 4 Graph showing the corresponding simulation results of the spectrum of the present invention; Figure 5 This is the simulation result diagram of photocurrent IV. DETAILED DESCRIPTION

[0017] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to specific embodiments.

[0018] Example 1: A pin-type ultraviolet photodetector based on a 4H-SiC-GaN heterostructure, wherein the ultraviolet photodetector comprises, from bottom to top, an n-type 4H-SiC substrate, an i-type GaN epitaxial layer, and a p-type doped GaN epitaxial layer. The upper surface of the p-type doped GaN epitaxial layer contacts the anode electrode, and the lower surface of the n-type 4H-SiC substrate contacts the cathode electrode. The structure is as follows: Figure 1 shown.

[0019] To verify its feasibility, the PIN-type UV photodetector was simulated using Silvaco TCAD software. The calculation process used the carrier Fermi statistics and the partial ionization model of doping concentration, that is, the electron concentration in the semiconductor is:

[0020] The hole concentration in a semiconductor is:

[0021] Take the doping concentration N of the p-type GaN epitaxial layer a =5.0×10 18 cm -3 , the doping concentration N of the n-type SiC substrate d =2.0×10 18 cm -3 The i layer is non-intentionally doped GaN. Due to the presence of nitrogen vacancies, non-intentionally doped GaN usually behaves as n-type, and the electron concentration is around 10 16 cm -3 The structure after simulation is shown in the figure below. Figure 2 As shown; The anode electrode contacts the upper surface of the p-type GaN epitaxial layer, and the cathode electrode contacts the back of the n-type SiC substrate. Then, an external electric field is applied to the electrodes of the device to test its IV characteristic curve in the dark state, as shown in the figure. Figure 3 As shown; It can be found that in the cut-off region, the dark current can reach 10 -16 A is the order of magnitude. It is known that the photodetector is essentially a reverse-biased pn junction diode. The role of reverse bias is to strengthen the internal electric field and widen the depletion layer. By increasing the intrinsic region GaN, the depletion layer can also be widened, the dark current can be reduced, and the responsivity of the photodetector can be improved. Next, the IV test simulation of the spectral response and photocurrent is carried out. The results are as follows Figure 4 and Figure 5 As shown; From the spectral response, it can be seen that the photocurrent of the device is the largest at 350nm, which is about 6.0×10 -9 A increases linearly in the range of 200-350nm, reaches a peak at 350nm and then decreases, and approaches 0 infinitely after 420nm, realizing the photoelectric detection of the ultraviolet band. Then, by adding the light intensity of the 350nm band to analyze the photocurrent IV of the device, it can be obtained that under the condition of 2V, the dark current is reduced by 10 -16 A-level, increased to 10 -9 The switching ratio is of the order of A, about 4-5 orders of magnitude, indicating that the device has significant response sensitivity to the ultraviolet band, proving the feasibility of this solution.

[0022] The present invention also provides a method for preparing a PIN-type ultraviolet photodetector based on a 4H-SiC-GaN heterostructure, which is as follows: Example 2: A method for preparing a PIN-type ultraviolet photodetector based on a 4H-SiC-GaN heterostructure, comprising the following steps: S1. Substrate selection: Select a 6-inch 4H-SiC substrate; S2. i-GaN intrinsic layer growth: Metal organic chemical vapor deposition technology is used, the reaction chamber temperature is set to 1040 ° C, the pressure is maintained at 190 mbar, trimethyl gallium is used as the gallium source, and its flow rate is controlled at 18 sccm; ammonia is used as the nitrogen source, and the flow rate is set to 1400 sccm. High-purity hydrogen is used as the carrier gas, and the flow rate is 4950 sccm. Under these parameter conditions, the growth rate is 0.4 μm / h to ensure the growth of a high-quality i-GaN intrinsic layer with a thickness of 190 nm. The key parameter requirements of the 6-inch 4H-SiC substrate in step S1 are that the lattice constant mismatch with the i-GaN in step S2 is ±0.5%, and the difference in thermal expansion coefficient between the 6-inch 4H-SiC substrate in step S1 and the i-GaN in step S2 is ±1×10 -6 K -1 , in order to ensure the quality of the subsequently grown crystals; S3. p-GaN photon absorption layer growth: Metal-organic chemical vapor deposition (MOCVD) technology was used, with the temperature maintained at 9950°C and the pressure at 140 mbar. The flow rates of trimethylgallium, ammonia, and hydrogen were adjusted to 28 sccm, 1750 sccm, and 5950 sccm, respectively. The magnesium dopant was introduced in the form of cyclopentadienyl magnesium (Cp2Mg) at a controlled flow rate of 0.8 sccm. The growth time was optimized to ensure a p-GaN layer thickness of 280 nm. This allows for precise control of the electrochemical properties of the p-GaN layer, achieving the ideal hole carrier velocity required for efficient UV light absorption and conversion. Electrode Preparation: Electrode nickel and aluminum were deposited on the p-GaN photon absorption layer using a nickel target with a purity of 99.99%, an evaporation rate of 0.4 Å / s, and a deposition thickness of 180 Å. Electrode aluminum was deposited on the p-GaN photon absorption layer using a high vacuum physical vapor deposition technique at a vacuum of 1×10 -6 Evaporation is performed in a low-pressure environment to ensure uniform deposition of metal atoms on the p-GaN surface, promoting the formation of good ohmic contact. S5. Evaporate titanium and aluminum on the lower surface of a 4H-SiC conductive substrate. The titanium target material is 99.95% pure, with an evaporation rate of 0.3 Å / s and a deposition thickness of 145 Å. The aluminum target material is 99.9% pure, with an evaporation rate of 0.25 Å / s and a deposition thickness of 95 Å. The vacuum environment requirements are the same as those for p-GaN surface evaporation to ensure a stable and reliable electrical connection between the electrode and the substrate. S6. Annealing treatment: After the metal electrode evaporation is completed, the device is placed in a professional rapid thermal annealing equipment. In an environment with a nitrogen atmosphere purity of 99.999%, annealing is carried out at 495℃ for 2 minutes. The heating rate is controlled at 48℃ / s to ensure the uniformity and stability of the entire annealing process, achieve fine "adjustment" of the internal microstructure of the detector, and comprehensively improve the performance of the detector, making it excel in the field of ultraviolet light detection.

[0023] Example 3: A method for preparing a PIN-type ultraviolet photodetector based on a 4H-SiC-GaN heterostructure, comprising the following steps: S1. Substrate selection: Select a 6-inch 4H-SiC substrate; S2. i-GaN intrinsic layer growth: Metal organic chemical vapor deposition technology is used, the reaction chamber temperature is set to 1045 ° C, the pressure is maintained at 195 mbar, trimethyl gallium is used as the gallium source, and its flow rate is controlled at 19 sccm; ammonia is used as the nitrogen source, and the flow rate is set to 1405 sccm. High-purity hydrogen is used as the carrier gas, and the flow rate is 4955 sccm. Under these parameter conditions, the growth rate is 0.5 μm / h to ensure the growth of a high-quality i-GaN intrinsic layer with a thickness of 195 nm. The key parameter requirements of the 6-inch 4H-SiC substrate in step S1 are that the lattice constant mismatch with the i-GaN in step S2 is ±0.5%, and the difference in thermal expansion coefficient between the 6-inch 4H-SiC substrate in step S1 and the i-GaN in step S2 is ±1×10 -6 K -1 , in order to ensure the quality of the subsequently grown crystals; S3. p-GaN photon absorption layer growth: Metal-organic chemical vapor deposition (MOCVD) technology was used, with the temperature maintained at 9955°C and the pressure at 145 mbar. The flow rates of trimethylgallium, ammonia, and hydrogen were adjusted to 29 sccm, 1755 sccm, and 5955 sccm, respectively. The magnesium dopant was introduced in the form of cyclopentadienyl magnesium (Cp2Mg) at a controlled flow rate of 0.9 sccm. The growth time was optimized to ensure a p-GaN layer thickness of 285 nm. This allows for precise control of the electrochemical properties of the p-GaN layer, achieving the ideal hole carrier velocity required for efficient UV light absorption and conversion. Electrode Preparation: Electrode nickel and aluminum were deposited on the p-GaN photon absorption layer using a nickel target with a purity of 99.99% and an evaporation rate of 0.5 Å / s to a deposition thickness of 185 Å. Electrode preparation was performed using a high vacuum physical vapor deposition technique at a vacuum of 1×10 -6 Evaporation is performed in a low-pressure environment to ensure uniform deposition of metal atoms on the p-GaN surface, promoting the formation of good ohmic contact. S5. Evaporate titanium and aluminum on the lower surface of a 4H-SiC conductive substrate. The titanium target material is 99.95% pure, with an evaporation rate of 0.4 Å / s and a deposition thickness of 149 Å. The aluminum target material is 99.9% pure, with an evaporation rate of 0.27 Å / s and a deposition thickness of 96 Å. The vacuum environment requirements are the same as those for p-GaN surface evaporation to ensure a stable and reliable electrical connection between the electrode and the substrate. S6. Annealing treatment: After the metal electrode evaporation is completed, the device is placed in a professional rapid thermal annealing equipment. In an environment with a nitrogen atmosphere purity of 99.999%, annealing is carried out at 496℃ for 3 minutes. The heating rate is controlled at 49℃ / s to ensure the uniformity and stability of the entire annealing process, achieve fine "adjustment" of the internal microstructure of the detector, and comprehensively improve the performance of the detector, making it excel in the field of ultraviolet light detection.

[0024] Example 4: A method for preparing a PIN-type ultraviolet photodetector based on a 4H-SiC-GaN heterostructure, comprising the following steps: S1. Substrate selection: Select a 6-inch 4H-SiC substrate; S2. i-GaN intrinsic layer growth: Metal organic chemical vapor deposition technology is used, the reaction chamber temperature is set to 1028 ° C, the pressure is maintained at 206 mbar, trimethyl gallium is used as the gallium source, and its flow rate is controlled at 20 sccm; ammonia is used as the nitrogen source, and the flow rate is set to 1580 sccm. High-purity hydrogen is used as the carrier gas, and the flow rate is 5020 sccm. Under these parameter conditions, the growth rate is 0.5 μm / h to ensure the growth of a high-quality i-GaN intrinsic layer with a thickness of 206 nm. The key parameter requirements of the 6-inch 4H-SiC substrate in step S1 are that the lattice constant mismatch with the i-GaN in step S2 is ±0.5%, and the difference in thermal expansion coefficient between the 6-inch 4H-SiC substrate in step S1 and the i-GaN in step S2 is ±1×10 -6 K -1 , in order to ensure the quality of the subsequently grown crystals; S3. p-GaN photon absorption layer growth: Metal-organic chemical vapor deposition (MOCVD) technology was used, with the temperature maintained at 1023°C and the pressure at 152 mbar. The flow rates of trimethylgallium, ammonia, and hydrogen were adjusted to 30 sccm, 1832 sccm, and 6032 sccm, respectively. The magnesium dopant was introduced in the form of cyclopentadienyl magnesium (Cp2Mg) at a controlled flow rate of 1.1 sccm. The growth time was optimized to ensure a p-GaN layer thickness of 318 nm. This allows for precise control of the electrochemical properties of the p-GaN layer, achieving the ideal hole carrier velocity required for efficient UV light absorption and conversion. Electrode Preparation: Electrode nickel and aluminum were deposited on the p-GaN photon absorption layer using a nickel target with a purity of 99.99% and an evaporation rate of 0.5 Å / s to a deposition thickness of 218 Å. Electrode preparation was performed using a high vacuum physical vapor deposition technique at a vacuum of 1×10 -6 Evaporation is performed in a low-pressure environment to ensure uniform deposition of metal atoms on the p-GaN surface, promoting the formation of good ohmic contact. S5. Evaporate titanium and aluminum on the lower surface of a 4H-SiC conductive substrate. The titanium target material is 99.95% pure, with an evaporation rate of 0.4 Å / s and a deposition thickness of 153 Å. The aluminum target material is 99.9% pure, with an evaporation rate of 0.32 Å / s and a deposition thickness of 103 Å. The vacuum environment requirements are the same as those for p-GaN surface evaporation to ensure a stable and reliable electrical connection between the electrode and the substrate. S6. Annealing treatment: After the metal electrode evaporation is completed, the device is placed in a professional rapid thermal annealing equipment. In an environment with a nitrogen atmosphere purity of 99.999%, annealing is carried out at 503℃ for 3 minutes. The heating rate is controlled at 50℃ / s to ensure the uniformity and stability of the entire annealing process, to achieve fine "adjustment" of the internal microstructure of the detector, and to comprehensively improve the performance of the detector, making it excel in the field of ultraviolet light detection.

[0025] Example 5: A method for preparing a PIN-type ultraviolet photodetector based on a 4H-SiC-GaN heterostructure, comprising the following steps: S1. Substrate selection: Select a 6-inch 4H-SiC substrate; S2. i-GaN intrinsic layer growth: Metal organic chemical vapor deposition technology is used, the reaction chamber temperature is set to 1050 ° C, the pressure is maintained at 200 mbar, trimethyl gallium is used as the gallium source, and its flow rate is controlled at 20 sccm; ammonia is used as the nitrogen source, and the flow rate is set to 1500 sccm. High-purity hydrogen is used as the carrier gas, and the flow rate is 4950-5050 sccm. Under these parameter conditions, the growth rate is 0.5 μm / h to ensure the growth of a high-quality i-GaN intrinsic layer with a thickness of 200 nm. The key parameter requirements of the 6-inch 4H-SiC substrate in step S1 are that the lattice constant mismatch with the i-GaN in step S2 is ±0.5%, and the difference in thermal expansion coefficient between the 6-inch 4H-SiC substrate in step S1 and the i-GaN in step S2 is ±1×10 -6 K -1 , in order to ensure the quality of the subsequently grown crystals; S3. p-GaN photon absorption layer growth: Metal-organic chemical vapor deposition (MOCVD) technology was used, with the temperature maintained at 1000°C and the pressure at 150 mbar. The flow rates of trimethylgallium, ammonia, and hydrogen were adjusted to 30 sccm, 1800 sccm, and 6000 sccm, respectively. The magnesium dopant was introduced in the form of cyclopentadienyl magnesium (Cp2Mg) at a controlled flow rate of 0.8-1.2 sccm. The growth time was optimized to ensure a p-GaN layer thickness of 300 nm. This allows for precise control of the electrochemical properties of the p-GaN layer, achieving the ideal hole carrier velocity required for efficient UV light absorption and conversion. Electrode Preparation: Electrode nickel and aluminum were deposited on the p-GaN photon absorption layer using a nickel target with a purity of 99.99%, an evaporation rate of 0.5 Å / s, and a deposition thickness of 200 Å. Electrode metal was deposited on the p-GaN photon absorption layer using a high vacuum physical vapor deposition technique at a vacuum of 1×10 -6 Evaporation is performed in a low-pressure environment to ensure uniform deposition of metal atoms on the p-GaN surface, promoting the formation of good ohmic contact. S5. Evaporate titanium and aluminum on the lower surface of a 4H-SiC conductive substrate. The titanium target material should be 99.95% pure, with an evaporation rate of 0.4 Å / s and a deposition thickness of 150 Å. The aluminum target material should be 99.9% pure, with an evaporation rate of 0.3 Å / s and a deposition thickness of 100 Å. The vacuum environment requirements are the same as those for p-GaN surface evaporation to ensure a stable and reliable electrical connection between the electrode and the substrate. S6. Annealing treatment: After the metal electrode evaporation is completed, the device is placed in a professional rapid thermal annealing equipment. In an environment with a nitrogen atmosphere purity of 99.999%, annealing is carried out at 500℃ for 3 minutes. The heating rate is controlled at 50℃ / s to ensure the uniformity and stability of the entire annealing process, achieve fine "adjustment" of the internal microstructure of the detector, and comprehensively improve the performance of the detector, making it excel in the field of ultraviolet light detection.

[0026] Example 6: A method for preparing a PIN-type ultraviolet photodetector based on a 4H-SiC-GaN heterostructure, comprising the following steps: S1. Substrate selection: Select a 6-inch 4H-SiC substrate; S2. i-GaN intrinsic layer growth: Metal organic chemical vapor deposition technology is used, the reaction chamber temperature is set to 1059 ° C, the pressure is maintained at 209 mbar, trimethyl gallium is used as the gallium source, and its flow rate is controlled at 21 sccm; ammonia is used as the nitrogen source, and the flow rate is set to 1599 sccm. High-purity hydrogen is used as the carrier gas, and the flow rate is 5049 sccm. Under these parameter conditions, the growth rate is 0.5 μm / h to ensure the growth of a high-quality i-GaN intrinsic layer with a thickness of 209 nm. The key parameter requirements of the 6-inch 4H-SiC substrate in step S1 are that the lattice constant mismatch with the i-GaN in step S2 is ±0.5%, and the difference in thermal expansion coefficient between the 6-inch 4H-SiC substrate in step S1 and the i-GaN in step S2 is ±1×10 -6 K -1 , in order to ensure the quality of the subsequently grown crystals; p-GaN photon absorption layer growth: Metal-organic chemical vapor deposition (MOCVD) was used, with the temperature maintained at 1049°C and the pressure at 159 mbar. The trimethyl gallium flow rate was adjusted to 31 sccm, the ammonia flow rate to 1845 sccm, and the carrier hydrogen flow rate to 6045 sccm. The magnesium dopant was introduced in the form of cyclopentadienyl magnesium (Cp2Mg) at a controlled flow rate of 1.1 sccm. The growth time was optimized to ensure a p-GaN layer thickness of 319 nm. This allows for precise control of the electrochemical properties of the p-GaN layer, achieving the ideal hole carrier velocity required for efficient UV light absorption and conversion. Electrode Preparation: Electrode nickel and aluminum were deposited on the p-GaN photon absorption layer using a nickel target with a purity of 99.99% and an evaporation rate of 0.5 Å / s to a deposition thickness of 219 Å. Electrode nickel and aluminum were deposited on the p-GaN photon absorption layer using a high vacuum physical vapor deposition technique at a vacuum of 1×10 -6 Evaporation is performed in a low-pressure environment to ensure uniform deposition of metal atoms on the p-GaN surface, promoting the formation of good ohmic contact. S5. Evaporate titanium and aluminum on the lower surface of a 4H-SiC conductive substrate. The titanium target material is 99.95% pure, with an evaporation rate of 0.4 Å / s and a deposition thickness of 154 Å. The aluminum target material is 99.9% pure, with an evaporation rate of 0.34 Å / s and a deposition thickness of 104 Å. The vacuum environment requirements are the same as those for p-GaN surface evaporation to ensure a stable and reliable electrical connection between the electrode and the substrate. S6. Annealing treatment: After the metal electrode evaporation is completed, the device is placed in a professional rapid thermal annealing equipment. In an environment with a nitrogen atmosphere purity of 99.999%, annealing is carried out at 504℃ for 3 minutes. The heating rate is controlled at 51℃ / s to ensure the uniformity and stability of the entire annealing process, achieve fine "adjustment" of the internal microstructure of the detector, and comprehensively improve the performance of the detector, making it excel in the field of ultraviolet light detection.

[0027] Example 7: A method for preparing a PIN-type ultraviolet photodetector based on a 4H-SiC-GaN heterostructure, comprising the following steps: S1. Substrate selection: Select a 6-inch 4H-SiC substrate; S2. i-GaN intrinsic layer growth: Metal organic chemical vapor deposition technology is used, the reaction chamber temperature is set to 1060 ° C, the pressure is maintained at 210 mbar, trimethyl gallium is used as the gallium source, and its flow rate is controlled at 22 sccm; ammonia is used as the nitrogen source, and the flow rate is set to 1600 sccm. High-purity hydrogen is used as the carrier gas, and the flow rate is 5050 sccm. Under these parameter conditions, the growth rate is 0.6 μm / h to ensure the growth of a high-quality i-GaN intrinsic layer with a thickness of 210 nm. The key parameter requirements of the 6-inch 4H-SiC substrate in step S1 are that the lattice constant mismatch with the i-GaN in step S2 is ±0.5%, and the difference in thermal expansion coefficient between the 6-inch 4H-SiC substrate in step S1 and the i-GaN in step S2 is ±1×10 -6 K -1 , in order to ensure the quality of the subsequently grown crystals; p-GaN photon absorption layer growth: Metal-organic chemical vapor deposition (MOCVD) technology was used, with the temperature maintained at 1050°C and the pressure at 160 mbar. The flow rates of trimethylgallium, ammonia, and hydrogen were adjusted to 32 sccm, 1850 sccm, and 6050 sccm, respectively. The magnesium dopant was introduced in the form of cyclopentadienyl magnesium (Cp2Mg) at a controlled flow rate of 1.2 sccm. The growth time was optimized to ensure a p-GaN layer thickness of 320 nm. This allows for precise control of the electrochemical properties of the p-GaN layer, achieving the ideal hole carrier velocity required for efficient UV light absorption and conversion. Electrode Preparation: Electrode nickel and aluminum were deposited on the p-GaN photon absorption layer using a nickel target with a purity of 99.99%, an evaporation rate of 0.6 Å / s, and a deposition thickness of 220 Å. Electrode aluminum was deposited on the p-GaN photon absorption layer using a high vacuum physical vapor deposition technique at a vacuum of 1×10 -6 Evaporation is performed in a low-pressure environment to ensure uniform deposition of metal atoms on the p-GaN surface, promoting the formation of good ohmic contact. S5. Evaporate titanium and aluminum on the lower surface of a 4H-SiC conductive substrate. The titanium target material is 99.95% pure, with an evaporation rate of 0.5 Å / s and a deposition thickness of 155 Å. The aluminum target material is 99.9% pure, with an evaporation rate of 0.35 Å / s and a deposition thickness of 105 Å. The vacuum environment requirements are the same as those for p-GaN surface evaporation to ensure a stable and reliable electrical connection between the electrode and the substrate. S6. Annealing treatment: After the metal electrode evaporation is completed, the device is placed in a professional rapid thermal annealing equipment. In an environment with a nitrogen atmosphere purity of 99.999%, annealing is carried out at 505℃ for 4 minutes. The heating rate is controlled at 52℃ / s to ensure the uniformity and stability of the entire annealing process, achieve fine "adjustment" of the internal microstructure of the detector, and comprehensively improve the performance of the detector, making it excel in the field of ultraviolet light detection.

[0028] In order to more clearly demonstrate the advantages of the PIN-type ultraviolet photodetector based on the 4H-SiC heterostructure and the preparation method thereof of the present invention, the following comparative examples are provided for comparative explanation: Comparative Example 1: This method uses a similar structural design to the present invention, but uses a conventional 4-inch Si substrate instead of the 6-inch 4H-SiC substrate required by the present invention. The lattice constant and thermal expansion coefficient matching between the substrate and the i-GaN are not considered. During the subsequent i-GaN intrinsic layer growth process, due to severe lattice mismatch, the grown i-GaN layer exhibits numerous dislocation defects. High-resolution transmission electron microscopy (HRTEM) observations reveal a dislocation density as high as 1×10¹ 0 cm -2 , which is much higher than the dislocation density that can be controlled by the present invention under appropriate substrate conditions (less than 1×10 8 cm -2 ). These defects act like "traps," capturing a large number of carriers, reducing the electron mobility of the detector to only 100 cm² / V·s, a significant decrease compared to the electron mobility of the detector prepared by the present invention (above 500 cm² / V·s), seriously affecting the response speed and sensitivity of the detector. During the growth stage of the p-GaN photon absorption layer, the stress problem caused by the substrate mismatch also leads to uneven thickness of the grown p-GaN layer, with the thinnest being only 150nm and the thickest reaching 400nm, causing large fluctuations in the absorption efficiency of ultraviolet light. The average light absorption efficiency is about 30% lower than that of the present invention. Moreover, during the electrode preparation process, due to the poor performance of the Si substrate in forming ohmic contact with the metal, the contact resistance is as high as 10Ω·cm² after using the same metal evaporation process as the present invention. In contrast, the present invention can control the contact resistance below 1Ω·cm² by rationally selecting the substrate and metal. Excessive contact resistance hinders current transmission, greatly reducing the overall performance of the detector.

[0029] Comparative Example 2: During the preparation process, the i-GaN intrinsic layer growth step deviates from the process parameters of the present invention. The reaction chamber temperature is set to 950°C, the pressure is maintained at 300mbar, the trimethyl gallium flow rate is 10sccm, the ammonia flow rate is 1000sccm, and the carrier gas hydrogen flow rate is 3000sccm. Under these parameters, the growth rate is only 0.2μm / h, and the thickness of the grown i-GaN layer is 100nm, which is far below the 190-210nm range required by the present invention. Due to the low temperature and unbalanced gas source ratio, the quality of the grown i-GaN crystal is extremely poor, with a large number of grain boundaries and twin defects. X-ray diffraction (XRD) pattern analysis shows that its crystal quality factor (FWHM value) is about 50% worse than that of the present invention. This causes the carrier transport performance of the i-GaN layer to be severely damaged, and the dark current of the detector to increase significantly. At a bias of -5V, the dark current reaches 1×10⁻ 8 A, is the dark current under the same bias voltage of the present invention (1×10⁻¹ 6 A-level) 10 8 The excessively high dark current significantly increases the noise of the detector under no-light conditions, and the signal-to-noise ratio drops sharply, which cannot meet the needs of high-precision detection.

[0030] Comparative Example 3: The p-GaN photon absorption layer was grown without following the precise doping process of the present invention. The magnesium dopant was introduced in the form of cyclopentadienyl magnesium (Cp2Mg), but the flow rate was controlled at 0.5 sccm, far below the 0.8-1.2 sccm range required by the present invention. The resulting p-GaN layer had a low hole carrier concentration of only 1×10¹ 6 cm⁻³, compared with the hole carrier concentration achievable by the present invention (5×10¹ 8 This makes the p-GaN layer's absorption and conversion efficiency of ultraviolet light seriously insufficient. In the 350nm band, the maximum photocurrent of the device is only 1×10⁻¹ 0 A, and the photocurrent of the detector prepared by the present invention can reach 6.0×10⁻ in this band 9 A. The photocurrent response capability decreases by about an order of magnitude, and the detector's detection sensitivity to ultraviolet light signals is significantly reduced, making it unable to effectively exert its photoelectric conversion function.

[0031] Comparative Example 4: In the electrode preparation process, when evaporating metal on the surface of the p-GaN photon absorption layer, a nickel target with a purity of 99% was selected, the evaporation rate was controlled at 0.3Å / s, and the deposition thickness reached 150Å; the aluminum target was 99% pure, the evaporation rate was 0.15Å / s, the deposition thickness was 70Å, and the vacuum degree could only be maintained at 5×10⁻ 5mbar. Due to low metal purity, inappropriate deposition parameters, and a poor vacuum environment, the ohmic contact between the metal and the p-GaN surface is poor, resulting in low hole injection efficiency. Testing showed that the injection efficiency was approximately 40% lower than that of the detector prepared in the present invention. This increased the probability of photogenerated carrier recombination during detector operation, significantly reducing the photoelectric conversion efficiency, and overall performance was inferior to that of the detector prepared in the present invention.

[0032] Comparative Example 5: The annealing process differs from that of the present invention. The device is placed in a conventional annealing furnace and annealed at 600°C for 5 minutes in an air atmosphere at a heating rate of 30°C / s. During annealing in air, an oxidation reaction occurs at the metal-semiconductor interface, forming an oxide layer that hinders carrier transport. Excessively high annealing temperatures and prolonged annealing times also increase defects within the semiconductor layer, such as an approximately 30% increase in the nitrogen vacancy concentration in the i-GaN layer. Testing revealed that the detector's responsivity decreased by approximately 20% compared to the present invention, while its dark current increased by approximately 50%. This compromised the detector's performance stability and reliability, preventing it from achieving the high performance achieved by the present invention through a sophisticated annealing process.

[0033] It can be clearly seen from the above comparative examples that the careful design and precise parameter control of each link in the present invention, such as substrate selection, epitaxial layer growth process, electrode preparation and annealing treatment, play a vital role in the preparation of high-performance PIN-type ultraviolet photodetectors based on 4H-SiC / GaN heterostructures. Once these key elements are deviated, the detector performance will be seriously affected.

[0034] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention is limited to these examples. Within the scope of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

[0035] The present invention is intended to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A pin-type ultraviolet photodetector based on a 4H-SiC-GaN heterostructure, characterized in that: The ultraviolet photodetector comprises, from bottom to top, an n-type 4H-SiC substrate, an i-type GaN epitaxial layer, and a p-type doped GaN epitaxial layer; The upper surface of the p-type doped GaN epitaxial layer is in contact with the anode electrode, and the lower surface of the n-type 4H-SiC substrate is in contact with the cathode electrode.

2. The 4H-SiC-GaN heterostructure PIN type ultraviolet photodetector according to claim 1, characterized in that: The pin-type ultraviolet photodetector was simulated using Silvaco TCAD software. The calculation process used the carrier Fermi statistics and the partial ionization model of doping concentration, that is, the electron concentration in the semiconductor is: ； The hole concentration in a semiconductor is: ; Take the doping concentration N of the p-type GaN epitaxial layer a =5.0×10 18 cm -3 , the doping concentration N of the n-type SiC substrate d =2.0×10 18 cm -3 The i layer is non-intentionally doped GaN. Due to the presence of nitrogen vacancies, non-intentionally doped GaN usually behaves as n-type, and the electron concentration is around 10 16 cm -3 The width of the i-type GaN is set to 200nm.

3. The method for preparing a PIN-type ultraviolet photodetector based on a 4H-SiC-GaN heterostructure according to claim 1, characterized in that: The following steps are involved: Step S1. Substrate selection: Select a 6-inch 4H-SiC substrate; Step S2. i-GaN intrinsic layer growth: Metal-organic chemical vapor deposition (MOCVD) is used with trimethylgallium as the gallium source, ammonia as the nitrogen source, and hydrogen as the carrier gas. The growth rate is 0.4-0.6 μm / h, and an i-GaN intrinsic layer with a thickness of 190-210 nm is grown. Step S3. Growth of a p-GaN photon absorption layer: Metal-organic chemical vapor deposition (MOCVD) is used, using trimethylgallium as the gallium source, ammonia as the nitrogen source, hydrogen as the carrier gas, and magnesium dopant in the form of cyclopentadienyl magnesium (Cp2Mg) at a flow rate of 0.8-1.2 sccm to grow a p-GaN layer with a thickness of 280-320 nm. Step S4. Electrode preparation: nickel and aluminum are evaporated on the surface of the p-GaN photon absorption layer, and high vacuum physical vapor deposition technology is used to prepare the electrode at a vacuum degree of 1×10 -6 Evaporation is performed in an environment of mbar to allow metal atoms to be evenly deposited on the p-GaN surface; Step S5. Deposit titanium and aluminum on the lower surface of the 4H-SiC conductive substrate under a vacuum of 1×10 -6 Evaporation operation is carried out in an environment of mbar; Step S6. Annealing: After the metal electrode is evaporated, the device is placed in a rapid thermal annealing device and annealed in a nitrogen atmosphere with a purity of 99.999% to obtain a PIN-type ultraviolet photodetector based on a 4H-SiC-GaN heterostructure.

4. The PIN-type ultraviolet photodetector based on the 4H-SiC-GaN heterostructure according to claim 3, characterized in that: The key parameter requirements of the 6-inch 4H-SiC substrate in step S1 are that the lattice constant mismatch with the i-GaN in step S2 is ±0.5%, and the difference in thermal expansion coefficient between the 6-inch 4H-SiC substrate in step S1 and the i-GaN in step S2 is ±1×10 -6 K -1 .

5. The PIN-type ultraviolet photodetector based on the 4H-SiC-GaN heterostructure according to claim 3, characterized in that: In the metal organic chemical vapor deposition technique in step S2, the reaction chamber temperature is 1040-1060° C. and the pressure is 190-210 mbar; In step S2, the flow rate of trimethylgallium is 18-22 sccm, the flow rate of ammonia is 1400-1600 sccm, and the flow rate of high-purity hydrogen is 4950-5050 sccm.

6. The PIN-type ultraviolet photodetector based on the 4H-SiC-GaN heterostructure according to claim 3, characterized in that: The metal organic chemical vapor deposition technology in step S3 is carried out at a temperature of 9950-1050° C. and a pressure of 140-160 mbar.

7. The PIN-type ultraviolet photodetector based on the 4H-SiC-GaN heterostructure according to claim 3, characterized in that: In step S3, the flow rate of trimethylgallium is 28-32 sccm, the flow rate of ammonia is 1750-1850 sccm, and the flow rate of carrier gas hydrogen is 5950-6050 sccm.

8. The PIN-type ultraviolet photodetector based on the 4H-SiC-GaN heterostructure according to claim 3, characterized in that: The purity of the nickel target in step S4 is 99.99%, the evaporation rate is controlled at 0.4-0.6 Å / s, and the deposition thickness reaches 180-220 Å; the purity of the aluminum target is 99.9%, the evaporation rate is 0.2-0.4 Å / s, and the deposition thickness is 90-110 Å.

9. The PIN-type ultraviolet photodetector based on the 4H-SiC-GaN heterostructure according to claim 3, characterized in that: The purity of the titanium target in step S5 is 99.95%, the evaporation rate is 0.3-0.5Å / s, and the deposition thickness is 145-155Å. The purity of the aluminum target is 99.9%, the evaporation rate is 0.25-0.35Å / s, and the deposition thickness is 95-105Å.

10. The PIN-type ultraviolet photodetector based on the 4H-SiC-GaN heterostructure according to claim 3, characterized in that: The temperature during the annealing treatment in step S6 is 495-505° C., the annealing treatment time is 2-4 minutes, and the heating rate is 48-52° C. / s.

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