Preparation of irradiation-based V-doped SiC photoconductive switch and carrier lifetime regulation and control method thereof

Abstract

The invention discloses a preparation method of an irradiation-based V-doped SiC photoconductive switch and a carrier lifetime regulation and control method of the photoconductive switch, and mainly solves the problem of inaccurate carrier lifetime regulation and control of a device in the prior art. According to the implementation scheme, the method comprises the following steps: pretreating the surface of a single crystal SiC substrate; growing a homoepitaxial layer with V-doped front and back surfaces on the pretreated SiC substrate, and performing high-temperature annealing on the homoepitaxial layer; the annealed sample is irradiated, that is, different types of irradiation defects are introduced into the V-doped SiC material, and the V-doped SiC material and the V deep energy level center have a synergistic effect, so that a multi-carrier composite channel is formed, and accurate regulation and control of the service life of carriers are realized; and manufacturing a metal electrode and an insulating passivation layer structure on the SiC surface of the irradiated epitaxial wafer through photoetching, etching and metallization processes. According to the method, the service life of the current carrier can be accurately controlled, the method is stable at high temperature and uniform in space, and the method can be used for preparing different types of SiC photoconductive switch devices.

Description

Technical Field

[0001] The present invention belongs to the field of microelectronics technology, and particularly relates to a method for preparing a SiC photoconductive switch device and regulating its carrier lifetime, which can be used for the production of high-temperature, high-frequency or high-power optoelectronic devices. Background Art

[0002] Silicon carbide (SiC), a third-generation wide-bandgap semiconductor material, holds broad application prospects in high-temperature, high-frequency, and high-power electronic devices. SiC photoconductive switches are important high-power pulse switching devices, finding applications in radar, communications, and other fields. The carrier lifetime of SiC is a key parameter affecting the performance of SiC photoconductive switches, directly impacting their switching speed and conduction losses.

[0003] Patent document CN89108602.1 discloses a method for axially regulating carrier lifetimes. Its implementation steps include: first, diffusing impurity atoms into a semiconductor substrate. These impurity atoms are characterized by their tendency to recombine at lattice sites but not at lattice interstitials, and their diffusion occurs interstitially via a vacancy mechanism rather than a substitutional mechanism; second, irradiating the semiconductor substrate with high-energy particles to achieve a desired lattice defect concentration distribution within a certain depth; and finally, heat-treating the diffused impurity atoms. This method, however, is difficult to ensure that impurity atoms recombine and diffuse only in the intended manner during the actual process, and the distribution and state of impurity atoms may change during the heat treatment. Consequently, impurity atoms may migrate from lattice sites to interstitial sites or form other impurity clusters, thereby affecting the accuracy of carrier lifetime regulation.

[0004] Patent document CN201710586010.1 discloses a method for improving the carrier lifetime of a silicon carbide epitaxial layer. It combines a low-speed high carbon-silicon ratio process with a high-speed low carbon-silicon ratio process to periodically grow the required thick silicon carbide epitaxial layer. Compared with a single low-speed high carbon-silicon ratio process, this method can effectively improve the growth rate of the epitaxial layer. At the same time, combined with high-temperature annealing treatment, the migration of carbon elements under the thermodynamic equilibrium conditions of chemical vapor deposition can eliminate carbon vacancies, achieve effective repair of carbon vacancies during in-situ growth, and improve the carrier lifetime of the silicon carbide epitaxial layer. However, since this method adopts two different growth processes, low-speed high carbon-silicon ratio and high-speed low carbon-silicon ratio, and periodically grows the epitaxial layer, the growth process of the entire epitaxial layer becomes complicated, and during the process switching process, interface defects may be generated due to changes in parameters such as reaction gas flow, temperature, and pressure. These interface defects will affect the crystal quality of the epitaxial layer, and then have adverse effects such as scattering on the transmission of carriers, reducing the effect of improving the carrier lifetime.

[0005] Currently, existing technologies have proposed some methods for regulating SiC carrier lifetime through simple V doping, that is, adjusting SiC carrier lifetime by controlling the V doping concentration. The typical process is to introduce a V-containing precursor, such as VCl4, during the SiC epitaxial growth process to allow V atoms to be incorporated into the SiC lattice, thereby changing the SiC material's carrier lifetime through atomic scattering. However, simple V doping technology has the following disadvantages:

[0006] First, the carrier lifetime control accuracy is not high, and the ability to control the carrier lifetime is limited. Moreover, since the V doping concentration and the carrier lifetime are not in a simple linear relationship, it is difficult to control accurately.

[0007] The second is poor high-temperature stability. In a high-temperature working environment, V atoms are prone to diffusion, which will cause the carrier lifetime to drift.

[0008] The third problem is poor uniformity. Since the distribution of V atoms in SiC is uneven, the spatial distribution of carrier lifetime is inconsistent. Summary of the Invention

[0009] The purpose of the present invention is to address the deficiencies of the above-mentioned technologies and propose a method for preparing a V-doped SiC photoconductive switch based on irradiation and a method for regulating the carrier lifetime thereof, so as to achieve precise control of the carrier lifetime in the SiC photoconductive switch.

[0010] The key technology to achieve the purpose of the present invention is: it involves a SiC carrier lifetime regulation method based on the combination of V doping and irradiation, which is used to achieve precise controllable, high-temperature stable and spatially uniform regulation of carrier lifetime, and is suitable for the needs of different types of SiC photoconductive switching devices.

[0011] The technical solution of the present invention is achieved as follows:

[0012] 1. A method for preparing a V-doped SiC photoconductive switching device, wherein the device comprises a SiC substrate, a V-doped epitaxial layer, a metal electrode, and an insulating passivation layer, wherein the preparation process comprises the following steps:

[0013] S1: Select a semi-insulating 4H-SiC or 6H-SiC single crystal substrate and pre-treat its surface by cleaning and polishing;

[0014] S2: Growing V doping concentration of 1×10 on both sides of the pre-treated SiC substrate 16 -1×10 18 cm - 3 orders of magnitude, homoepitaxial layer with a thickness of 20-100 μm;

[0015] S3: performing high temperature annealing on the V-doped SiC homoepitaxial layer;

[0016] S4: irradiating the annealed samples with different doses;

[0017] S5: Fabricate metal electrodes and insulating passivation layer structures on the irradiated epitaxial SiC surface through photolithography, etching, and metallization processes.

[0018] Furthermore, the V-doped homoepitaxial layers on both sides of the pretreated SiC substrate are grown by metal organic chemical vapor deposition (MOCVD) with the following process parameters: growth temperature of 1500-1600°C, growth pressure of 50-100 mbar, and precursors of SiH4, C3H8, and VCl4.

[0019] Furthermore, the high temperature annealing treatment is to anneal the V-doped SiC epitaxial wafer sample in a high-purity argon atmosphere at a temperature of 1600° C.-1800° C. for 30-60 minutes to activate the V-doped atoms and improve the crystal quality.

[0020] Furthermore, the irradiation treatment of the V-doped SiC epitaxial wafer is performed by using any one of electron beam irradiation, proton beam irradiation, gamma ray irradiation and neutron irradiation or a combination thereof.

[0021] 2. A method for regulating the carrier lifetime of a V-doped SiC photoconductive switching device, comprising:

[0022] Irradiating the V-doped SiC epitaxial wafer, i.e., using any one of electron beam irradiation, proton beam irradiation, gamma ray irradiation and neutron irradiation, or a combination thereof;

[0023] Different types of irradiation defects are introduced by irradiation, which work synergistically with the V deep energy level center to form multiple carrier recombination channels, promote the recombination of electrons and holes, and achieve precise control of the carrier lifetime τ. The formula is expressed as follows:

[0024] 1 / τ=1 / τ0+Σ i (σ i v th N i )

[0025] Where τ0 is the carrier lifetime before irradiation, σ i is the capture cross section of the i-th defect, v th is the carrier thermal velocity, N i is the concentration of the i-th defect.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] First, the carrier lifetime can be controlled with higher precision.

[0028] By adjusting the combination of V doping concentration and irradiation dose, the present invention can precisely control the carrier lifetime over a wider range. For example, carrier lifetime can be controlled within a range of 1ns to 100ps to meet different application requirements.

[0029] Second, it has better high temperature stability.

[0030] The defects introduced by irradiation in the present invention have good thermal stability and reduce the drift of carrier lifetime at high temperature. Experiments show that at an operating temperature of 200°C, the change of carrier lifetime can be controlled within ±10% of the initial value.

[0031] Third, the spatial uniformity is better.

[0032] The present invention can uniformly introduce defects into the entire sample body through irradiation treatment, thereby improving the spatial distribution of carrier lifetime. Within the range of a 2-inch wafer, the variation of carrier lifetime can be controlled within ±15%.

[0033] Fourth, the process is highly flexible. By adjusting the V doping and irradiation parameters, carrier lifetime can be controlled at different depths and lateral distributions, which is beneficial for optimizing the switching characteristics and conduction loss of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a structural schematic diagram of an existing photoconductive switching device;

[0035] Figure 2 Process flow chart for preparing a photoconductive switch device according to the present invention;

[0036] Figure 3 This is a diagram showing the locations of the main defect energy levels of V-doped SiC caused by irradiation in the present invention;

[0037] Figure 4 Single pulse laser response curve of the photoconductive switch device prepared by the present invention. DETAILED DESCRIPTION

[0038] The specific examples of the present invention are described in detail below with reference to the accompanying drawings.

[0039] Reference Figure 1 The irradiation-based V-doped SiC photoconductive switching device comprises a SiC substrate 1, a V-doped epitaxial layer 2, a metal electrode 3, and an insulating layer 4, wherein:

[0040] The SiC substrate 1 is made of semi-insulating 4H-SiC or 6H-SiC single crystal material with a thickness of 350-500 μm and a resistivity greater than 10 4 Ω·cm, surface roughness is less than 0.5nm;

[0041] The V-doped epitaxial layer 2 is located on the upper and lower surfaces of the SiC substrate 1 and is grown by metal organic chemical vapor deposition (MOCVD) with a thickness of 20-100 μm and a V doping concentration of 1×10 16 -1×10 18 cm - 3. After high temperature annealing at 1600-1800℃ and electron beam or proton beam irradiation treatment;

[0042] The metal electrode 3 adopts an ohmic contact structure, is located on the surface of the epitaxial layer, and is made of Ni / Ti / Al / Au or Ti / Al / Ni / Au composite metal layer, with an electrode thickness of 50-500 μm;

[0043] The insulating passivation layer 4 is made of SiO2 or Si3N4 material, which is located on the surface of the epitaxial layer and is placed around the OHMC1 metal layer. The thickness is 100-500nm and is used to prevent surface flashover;

[0044] The above device has a dark resistance greater than 101 0 Ω, the switching rise time is less than 1ns, and the switching fall time is less than 1ns.

[0045] Reference Figure 2 The present invention provides the following four embodiments for preparing the irradiation-based V-doped SiC photoconductive switching device.

[0046] Example 1: 5×10 17 cm -3 V doping concentration epitaxial layer, total dose is 5×10 14 cm -2 , photoconductive switching devices with electron beam irradiation energy of 2MeV.

[0047] Step 1: Pretreatment of 4H-SiC SiC substrate.

[0048] First, a 400 μm thick 4H-SiC single crystal substrate was selected and ultrasonically cleaned with acetone, isopropyl alcohol, and deionized water, respectively, for 5 minutes each time.

[0049] Next, RCA cleaning was performed: the substrate after ultrasonic cleaning was immersed in SC-1 solution with a ratio of NH4OH:H2O2:H2O=1:1:5 for 10 minutes, 5% HF solution for 2 minutes, and SC-2 solution with a ratio of HCl:H2O2:H2O=1:1:6 for 10 minutes.

[0050] Finally, the RCA-cleaned substrate is polished using the CMP method to obtain an atomic-level flat surface.

[0051] Step 2: Grow a V-doped SiC homoepitaxial layer.

[0052] The process conditions are set as SiH4 flow rate 20 sccm, C3H8 flow rate 10 sccm, VCl4 flow rate 0.5 sccm, carrier gas H2 flow rate 10 slm, pressure 80 mbar, and growth rate of about 5 μm / h. A 50 μm thick V-doped SiC homoepitaxial layer is grown on the pretreated SiC substrate using the MOCVD method.

[0053] Step 3: High temperature annealing treatment.

[0054] The sample with the grown homoepitaxial layer was placed in a graphite crucible and sealed with a graphite lid to prevent surface decomposition;

[0055] The process conditions were set at 1700°C, high-purity argon atmosphere, and a heating rate of 50°C / min. Annealing was performed in a tube furnace for 45 minutes, followed by natural cooling. After annealing, the V atom activation rate reached more than 95%.

[0056] Step 4: Irradiation treatment.

[0057] Set the beam current density to 1×10 12 cm -2 s -1 The total dose was 5×10 14 cm -2 The annealed samples were irradiated with an electron beam under the process conditions of 2 MeV energy and room temperature, using a closed-loop segmented control strategy: first, the beam was started to irradiate the sample for 100 seconds, and the surface temperature was monitored in real time by an infrared thermal imager; a copper cold stage + liquid nitrogen circulation heat dissipation method was used to control the sample temperature below 50°C to avoid irradiation-induced annealing effects. If the temperature in any area was ≥50°C, the beam cut-off protection was immediately triggered; after a single irradiation, the liquid nitrogen cooling system was forced to start for 30 seconds, and the beam was automatically restarted when the overall sample temperature dropped to ≤30°C; this "irradiation-cooling" operation was repeated 5 times until the total dose reached 5×10 14 cm -2 .

[0058] During the irradiation process, the lattice atoms are ionized by electron beam bombardment to generate carbon vacancies V C 、Silicon vacancy V si , carbon interstitial atom C i different defects, which act as recombination centers to promote the recombination of electron and hole carriers;

[0059] According to the quantitative relationship between defects and lifespan 1 / τ=1 / τ0+Σ i (σ i v th N i) to achieve precise control of the carrier lifetime τ, where τ0 is the carrier lifetime before irradiation, σ i is the capture cross section of the i-th defect, v th is the carrier thermal velocity, N i is the concentration of the i-th defect;

[0060] After irradiation, annealing was performed at 200°C for 10 min in a N2 atmosphere to promote the migration of interstitial atoms to stable lattice sites and fix vacancy defects.

[0061] Step 5: Device processing.

[0062] First, the epitaxial wafer coated with photoresist is photolithographically processed through a mask and developed into a rectangular electrode shape. Then, the first layer of metal is grown by evaporation and the metal outside the metal electrode area is stripped to form the OHMC1 metal layer.

[0063] Next, Si3N4 is deposited on the surface of the epitaxial layer through low-temperature plasma-enhanced chemical vapor deposition (PECVD). The epitaxial wafer coated with anti-resist is then photolithographically etched and developed using a mask. The Si3N4 is etched on the pattern formed by the development to form an insulating passivation layer around the OHMC1 metal layer with a thickness of 100nm.

[0064] Finally, the final Ti / Al / Ni / Au composite metal layers with thicknesses of 20 / 40 / 20 / 200 nm were formed by sputtering, electroplating, and photolithography to complete the device processing.

[0065] In this example, a V-doped SiC photoconductive switch device treated with electron beam irradiation was tested for response triggering using a single laser pulse at 532 nm, 10 ns pulse width, and 0.2 mJ energy. The switch response time was: rise time < 500 ps, ​​fall time < 800 ps, ​​and the on / off ratio was 2.7 × 10 9 , the on-state current reaches 2.2A under 100V bias, and the carrier lifetime of the device is characterized as about 300ps.

[0066] Example 2: Preparation of 5×10 16 cm -3 V doping concentration epitaxial layer, the total dose is 8×10 13 cm -2 , photoconductive switching devices with proton beam irradiation energy of 1.5MeV.

[0067] Step 1: Pretreatment of 4H-SiC substrate.

[0068] The implementation of this step is the same as step 1 in Example 1.

[0069] Step 2: Growth of V-doped SiC epitaxial layer.

[0070] Using MOCVD method, under the process conditions of SiH4 flow rate of 20sccm, C3H8 flow rate of 10sccm, and VCl4 flow rate of 0.5sccm, a doping concentration of 5×101 was grown on the pretreated substrate. 6 cm - 3. V-doped epitaxial layer with a thickness of 60 μm.

[0071] Step 3: High temperature annealing treatment.

[0072] The sample with the grown homoepitaxial layer was placed in a graphite crucible and sealed with a graphite lid to prevent surface decomposition;

[0073] The process conditions were set at a temperature of 1650°C, a high-purity argon atmosphere, and a heating rate of 50°C / min. Annealing was performed in a tube furnace for 45 minutes, followed by natural cooling. After annealing, the V atom activation rate reached more than 95%.

[0074] Step 4: Proton beam irradiation treatment.

[0075] The total dose was set to 8 × 10 13 cm -2 The sample was irradiated with a proton beam under the process conditions of energy of 1.5MeV and temperature at room temperature, that is, through three steps of energy reduction, the defect distribution at different depths was achieved and three defect peaks were constructed.

[0076] During the irradiation process, a copper cooling platform and liquid nitrogen circulation heat dissipation method were used to control the sample temperature below 50°C to avoid irradiation-induced annealing effects. Proton beam bombardment ionized the lattice atoms to produce dislocation loops and defect clusters containing multiple point defects. These defects act as recombination centers to promote the recombination of electron and hole carriers.

[0077] According to the quantitative relationship between defects and lifespan 1 / τ=1 / τ0+Σ i (σ i v th N i ) to achieve precise control of the carrier lifetime τ, where τ0 is the carrier lifetime before irradiation, σ i is the capture cross section of the i-th defect, v th is the carrier thermal velocity, N i is the concentration of the i-th defect;

[0078] After irradiation, annealing was performed at 450°C for 60 min in an Ar atmosphere to eliminate cascading damage clusters.

[0079] Step 5: Device processing.

[0080] 5-1) Photolithography is performed on the epitaxial wafer coated with photoresist through a mask, and a rectangular electrode shape is formed by development. Then, a first layer of metal is grown by evaporation and the metal outside the metal electrode area is stripped to form an OHMC1 metal layer;

[0081] 5-2) depositing Si3N4 on the surface of the epitaxial layer by low-temperature plasma-enhanced chemical vapor deposition (PECVD), then performing photolithography and development on the epitaxial wafer coated with the reverse resist using a mask, and etching the Si3N4 in the pattern formed by the development to form an insulating passivation layer with a thickness of 100 nm surrounding the OHMC1 metal layer;

[0082] 5-3) The final Ti / Al / Ni / Au composite metal layer with a thickness of 50 / 500 / 100 / 200 nm is formed by sputtering, electroplating and photolithography to complete the device processing.

[0083] In this example, a V-doped SiC photoconductive switch device treated with proton beam irradiation was tested with a single-pulse laser trigger at 532 nm, 10 ns pulse width, and 0.2 mJ energy. The switch response time was: rise time < 500 ps, ​​fall time < 800 ps, ​​and the on-off ratio was 2.8 × 10 9 , the on-state current reaches 2.3A under 100V bias, and the carrier lifetime is about 280ps.

[0084] Example 3: Preparation of 3×10 16 cm -3 A photoconductive switching device with a V-doped epitaxial layer and a total γ-ray irradiation dose of 500 kGy.

[0085] Step A: Pre-treating the 6H-SiC single crystal substrate.

[0086] The implementation of this step is the same as step 1 in Example 1.

[0087] Step B: growing a V-doped SiC homoepitaxial layer.

[0088] The MOCVD method was used to grow V doping concentration of 3×101 on the pretreated SiC substrate. 6 cm - 3. A SiC homoepitaxial layer with a thickness of 40 μm was grown with the following process conditions: SiH4 flow rate of 18 sccm, C3H8 flow rate of 9 sccm, VCl4 flow rate of 0.5 sccm, carrier gas H2 flow rate of 8 slm, pressure of 70 mbar, and a growth rate of approximately 4 μm / h.

[0089] Step C: high temperature annealing treatment.

[0090] The sample with the homoepitaxial layer was placed in a graphite crucible, sealed with a graphite cover to prevent surface decomposition, and annealed under the following annealing conditions: temperature of 1680°C, atmosphere of high-purity argon, heating rate of 50°C / min, and annealing time of 45 minutes.

[0091] After natural cooling, the V atom activation rate reaches more than 93% after annealing.

[0092] Step D: Gamma ray irradiation treatment

[0093] The annealed samples were irradiated with γ-rays at an activity of 15 kCi. 60 Coγ-ray source, place the sample in a lead-shielded irradiation chamber and fix it on a rotating table, 1.5m away from the center of the radiation source. Set the dose rate to 5kGy / h. Turn on the rotating table and irradiate continuously for 100 hours, with a total cumulative dose of 500kGy. Maintain the sample temperature at 25±2℃ during irradiation.

[0094] Gamma rays interact with the SiC lattice through Compton scattering, producing uniformly distributed ex-situ damage and forming carbon and silicon vacancies with a concentration ratio of >3:1 at room temperature and low dose rate. At the same time, vacancy clustering is suppressed, ensuring that the defects function as efficient recombination centers.

[0095] According to the quantitative relationship between carrier lifetime τ and dose: τ = 1.8×10 -6 / Φ can achieve precise control of carrier lifetime, where Φ is the total dose in kGy, R 2 =0.98.

[0096] Step E: Device processing.

[0097] E1) performing photolithography on the epitaxial wafer coated with photoresist through a mask, developing to form a rectangular electrode shape, then growing a first layer of metal by evaporation and stripping the metal outside the metal electrode area to form an OHMC1 metal layer;

[0098] E2) depositing Si3N4 on the surface of the epitaxial layer by low-temperature plasma enhanced chemical vapor deposition (PECVD), then performing photolithography and development on the epitaxial wafer coated with the reverse resist using a mask, and performing opening etching on the Si3N4 on the pattern formed by the development to form an insulating passivation layer with a thickness of 250 nm surrounding the OHMC1 metal layer;

[0099] E3) Thickening the OHMC1 metal layer by sputtering, electroplating, and photolithography to form a Ti / Al / Ni / Au composite metal layer with thicknesses of 100 / 50 / 150 / 400 nm, completing the device processing.

[0100] In this example, a V-doped SiC photoconductive switch device irradiated with γ-rays was tested by a single-pulse laser triggering test at 532 nm, 10 ns pulse width, and 0.2 mJ energy. The switch response had a rise time of <650 ps, ​​a fall time of <950 ps, ​​and an on / off ratio of 1.5×10 9 , the on-state current reaches 1.6A under 80V bias, and the carrier lifetime is about 420ps.

[0101] Example 4: Preparation of 8×10 16 cm -3 V doping concentration epitaxial layer, the total fast neutron irradiation dose is 1×10 12 cm -2 , photoconductive switching device with energy of 0.1MeV.

[0102] Step 1: Pretreatment of 6H-SiC single crystal substrate.

[0103] The implementation of this step is the same as step 1 in Example 1.

[0104] Step 2: Growth of V-doped SiC homoepitaxial layer.

[0105] The process conditions are set as SiH4 flow rate 25sccm, C3H8 flow rate 12sccm, VCl4 flow rate 0.9sccm, carrier gas H2 flow rate 12slm, pressure 90mbar, and growth rate of about 6μm / h. MOCVD method is used to grow V doping concentration of 8×101 on the pretreated SiC substrate. 6 cm - 3. SiC homoepitaxial layer with a thickness of 80 μm.

[0106] Step 3: High temperature annealing treatment.

[0107] The sample with the grown homoepitaxial layer was placed in a graphite crucible and sealed with a graphite lid to prevent surface decomposition;

[0108] The process conditions were set at 1720°C, high-purity argon atmosphere, and a heating rate of 50°C / min. Annealing was performed in a tube furnace for 50 minutes, followed by natural cooling. After annealing, the V atom activation rate reached more than 97%.

[0109] Step 4: Fast neutron irradiation treatment.

[0110] Set the energy to 0.1 MeV and the injection volume to 1×10 12 cm -2. Under inert gas atmosphere conditions, the annealed samples were subjected to fast neutron irradiation treatment. This involved placing the photoconductive switch sample in an aluminum cladding filled with high-conductivity tropical beryllium oxide powder. The aluminum cladding was then sealed and filled with 0.5 MPa helium gas. The cladding was then fixed in the center of the irradiation channel to ensure that the neutron beam was perpendicular to the sample surface.

[0111] Start the neutron beam to generate uniformly distributed displacement damage, Frenkel pairs, and antisite defects C in the sample with a penetration depth of >1 mm. si Si c , composite defect clusters and other defects, and use these defects as deep energy level recombination centers of carriers;

[0112] According to the quantitative relationship between carrier lifetime and neutron injection: τ=τ0 / (1+K·Φ n ) to precisely control the carrier lifetime, where K is the damage constant, Φ is the neutron injection, and n = 0.6-0.8.

[0113] Step 5: Device processing.

[0114] 5.1) Using a mask, the epitaxial wafer coated with photoresist is photolithographically etched and developed to form a rectangular electrode shape. The first metal layer is then grown by evaporation and the metal outside the metal electrode area is stripped to form the OHMC1 metal layer.

[0115] 5.2) Depositing Si3N4 on the epitaxial layer surface by low-temperature plasma-enhanced chemical vapor deposition (PECVD). The epitaxial wafer coated with the reverse resist was then photolithographically etched and developed using a mask. The Si3N4 was then etched in the pattern formed by the development to form an insulating passivation layer lapped around the OHMC1 metal layer with a thickness of 250 nm.

[0116] 5.3) Thicken the OHMC1 metal layer by sputtering, electroplating, and photolithography to form a Ti / Al / Ni / Au composite metal layer with thicknesses of 100 / 50 / 150 / 400 nm, completing the device processing.

[0117] In this example, a V-doped SiC photoconductive switch device irradiated by neutrons was triggered by a single pulse laser at 532 nm, 10 ns pulse width, and 0.1 mJ energy. The switching response time was tested, and the results showed that the rise time was <400 ps, ​​the fall time was <700 ps, ​​and the on-off ratio was 3.8×10 9 , the on-state current reaches 2.8A under 100V bias, and the carrier lifetime is about 400ps.

[0118] The effects of the present invention can be further illustrated by the following test results:

[0119] Test 1: The defects of the SiC photoconductive switch devices of Examples 1 to 4 were characterized by deep level transient spectroscopy (DLTS). The results are as follows: Figure 3 shown.

[0120] from Figure 3 It can be seen that the defect energy level positions introduced by the irradiation of the embodiment of the present invention are

[0121] The carbon vacancies V generated by electron beam irradiation in Example 1 C 、Silicon vacancy V si , carbon interstitial atom C i They are located at Ec-0.3eV, Ev+0.5eV and Ev+1.0eV of the 4H-SiC energy band respectively;

[0122] The energy level position of the dislocation ring generated in Example 2 falls as follows Figure 3 The dislocation-related defects shown in the figure are within the scope of the typical carbon-silicon vacancy V in the composite defect cluster. c V Si Located at the deep energy level of Ec-1.3eV;

[0123] The off-site damage produced in Example 3 falls on Figure 3 The range of dislocation-related defects shown, as well as carbon vacancies V C 、Silicon vacancy V si Located at Ec-0.3eV and Ev+0.5eV of the energy band.

[0124] The displacement damage produced in Example 4 falls into the following Figure 3 The dislocation-related defects shown in the figure are within the scope of the typical carbon-silicon vacancy V in the composite defect cluster. c V Si Located at the deep energy level of Ec-1.3eV;

[0125] The doped V energy level is located near the center of the band gap, which is Ev+1.6eV.

[0126] Test 2: A single-pulse laser response trigger test was performed on the irradiated V-doped silicon carbide photoconductive switching device. The laser pulse used was 532nm, the laser energy was 0.2mJ, the laser pulse width was 1ns, and the bias voltage was 10-200V. The falling edge of the response was used to characterize the carrier lifetime of the device.

[0127] Taking the neutron beam irradiation in Example 4 as an example, the single pulse laser response results of the device under different neutron beam irradiation doses are tested, as shown in FIG. Figure 4 shown.

[0128] Depend on Figure 4 It can be seen that the neutron beam irradiation dose ranges from 1×10 13 cm-2 to 1×10 15 cm -2 , the carrier lifetime gradually decreases, but at the same time the output current also decreases, which is not conducive to the high power output of the device. Under the balance, the neutron beam irradiation dose is 1×10 14 cm -2 The optimal carrier lifetime is about 400ps.

[0129] The above descriptions are merely specific examples of the present invention and do not constitute any limitation thereto. It is apparent that, after understanding the content and principles of the present invention, those skilled in the art may, without departing from the principles and structure of the present invention, make various modifications and alterations in form and detail, such as those regarding the energy, dose, and temperature of electron beam irradiation, the energy and dose of proton beam irradiation, the dose rate and total dose of gamma ray irradiation, and the energy and fluence of neutron irradiation. However, such modifications and alterations based on the principles of the present invention remain within the scope of protection of the claims.

Claims

1. A method for preparing a V-doped SiC photoconductive switching device, wherein the device comprises a SiC substrate, a V-doped epitaxial layer, a metal electrode, and an insulating passivation layer, characterized in that: The preparation process steps include: S1: Select a semi-insulating 4H-SiC or 6H-SiC single crystal substrate and pre-treat its surface by cleaning and polishing; S2: Growing V doping concentration of 1×10 on both sides of the pre-treated SiC substrate 16 -1×10 18 cm - 3 orders of magnitude, homoepitaxial layer with a thickness of 20-100 μm; S3: performing high temperature annealing on the V-doped SiC homoepitaxial layer; S4: irradiate the annealed sample; S5: Fabricate metal electrodes and insulating passivation layer structures on the irradiated epitaxial SiC surface through photolithography, etching, and metallization processes.

2. The method according to claim 1, characterized in that The cleaning and polishing of the SiC substrate surface comprises: Select 4H-SiC or 6H-SiC single crystal material with a thickness of 350-1000μm. As a semi-insulating material, the resistivity is greater than 10 9 Ω·cm, surface roughness is less than 0.5nm; First, the substrate was ultrasonically cleaned with acetone, isopropanol, and deionized water for 5-10 minutes each; then, the substrate was ultrasonically cleaned with SC-1 solution of NH4OH:H2O2:H2O=1:1:5, 5% HF solution, Soak in SC-2 solution of HCl:H2O2:H2O=1:1:6 for 1-10 minutes each; Finally, the cleaned substrate surface is polished using CMP to obtain an atomic-level flat surface.

3. The method according to claim 1, characterized in that The V-doped homoepitaxial layers on both sides of the pretreated SiC substrate are grown by metal organic chemical vapor deposition (MOCVD) with the following process parameters: growth temperature of 1500-1600°C, growth pressure of 50-100 mbar, and precursors of SiH4, C3H8, and VCl4.

4. The method according to claim 1, wherein The high-temperature annealing treatment is to anneal the V-doped SiC epitaxial wafer sample in a high-purity argon atmosphere at a temperature of 1600° C.-1800° C. for 30-60 minutes to activate the V-doped atoms and improve the crystal quality.

5. The method according to claim 1, wherein The irradiation treatment of the V-doped SiC epitaxial wafer is performed by adopting any one of electron beam irradiation, proton beam irradiation, gamma ray irradiation and neutron irradiation or a combination thereof.

6. The method according to claim 1, characterized in that The method of fabricating a metal electrode and an insulating passivation layer structure on the surface of the SiC epitaxial layer by photolithography, etching, and metallization processes includes: First, the epitaxial wafer coated with photoresist is photolithographically processed through a mask and developed into a rectangular electrode shape. Then, the first layer of metal is grown by evaporation and the metal outside the metal electrode area is stripped to form the OHMC1 metal layer. Next, SiO2 or Si3N4 is deposited on the surface of the epitaxial layer by low-temperature plasma-enhanced chemical vapor deposition (PECVD). The epitaxial wafer coated with the reverse resist is then photolithographically etched and developed using a mask. The SiO2 or Si3N4 is etched on the pattern formed by the development to form an insulating passivation layer with a thickness of 100-500nm surrounding the OHMC1 metal layer. Finally, the final Ni / Ti / Al / Au or Ti / Al / Ni / Au composite metal layer is formed by sputtering, electroplating and photolithography to complete the device processing.

7. A method for regulating the carrier lifetime of a V-doped SiC photoconductive switching device, characterized by: include: Irradiating the V-doped SiC epitaxial wafer, i.e., using any one of electron beam irradiation, proton beam irradiation, gamma ray irradiation and neutron irradiation, or a combination thereof; Different types of irradiation defects are introduced by irradiation, which work synergistically with the V deep energy level center to form multiple carrier recombination channels, promote the recombination of electrons and holes, and achieve precise control of the carrier lifetime τ. The formula is expressed as follows: 1 / τ=1 / τ0+Σ i (s i v th N i ) Where τ0 is the carrier lifetime before irradiation, σ i is the capture cross section of the i-th defect, v th is the carrier thermal velocity, N i is the concentration of the i-th defect.

8. The method according to claim 7, characterized in that The electron beam irradiation has an energy range of 0.5-2 MeV and a dose range of 1×10 13 -1×10 15 cm -2 The temperature range is 23℃-600℃, and the irradiation defects generated at different temperatures are different in form, among which: At room temperature, carbon vacancies V are mainly generated C 、Silicon vacancy V si , carbon interstitial atom C i These point defects; At 300℃, the main production is to promote the migration of point defects and form VV C 、VV si Composite defects, whose activation energy is 0.8-1.2eV; Complex defect clusters are formed at 600℃, including (V C V si ) n and V-(V C V si ) clusters, and the defect cluster size is 2-10nm.

9. The method according to claim 7, characterized in that The proton beam irradiation has an energy range of 0.5-2 MeV and a dose range of 1×10 13 -1×10 15 cm -2 ; The diameter of the dislocation ring is 5-50nm and the density is 10 14 -10 16 cm -3 The defects formed are defect clusters containing 10-100 point defects, and the damage is most serious in the Bragg peak area, and the carrier lifetime is most significantly reduced.

10. The method according to claim 7, wherein: The gamma ray irradiation has a dose rate of 0.1-10 kGy / h and a total dose of 10-1000 kGy, which mainly produces an ionization effect to form electron-hole pairs. The generation of electron-hole pairs generates ionization energy, wherein part of the ionization energy is converted into displacement defect damage due to the non-ionization energy loss effect; The neutron irradiation, wherein the neutron energy is greater than 0.1MeV and the injection amount is 1×10 12 -1×10 16 cm -2 , producing uniformly distributed displacement damage with a penetration depth of >1 mm, as well as Frenkel's si S i c antisite defects, compound defect clusters and other major defects.

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