A SiC-GaN composite photoconductive switch

Abstract

A SiC-GaN composite photoconductive switch comprises a silicon carbide substrate, a semi-insulating gallium nitride epitaxial layer, and two electrodes. The semi-insulating gallium nitride epitaxial layer is disposed on one surface of the silicon carbide substrate; the two electrodes are disposed on either side of the upper surface of the gallium nitride epitaxial layer; the silicon carbide substrate is either a high-purity semi-insulating silicon carbide substrate or a vanadium-compensated silicon carbide substrate; and the semi-insulating gallium nitride epitaxial layer is doped with deep-level impurities. The SiC-GaN composite photoconductive switch of the present invention can utilize silicon carbide's relatively high absorption depth to increase device thickness and improve mechanical strength to enable backside light incidence; fully utilize gallium nitride's excellent transport properties to achieve low on-resistance and high photoelectric conversion efficiency; and the thin layer of gallium nitride grown epitaxially again has higher crystal quality, fewer internal defects, and lower cost.

Description

Technical Field

[0001] The present invention relates to a photoconductive switch, and in particular to a SiC-GaN composite photoconductive switch. Background Art

[0002] Photoconductive semiconductor switches are a crucial component of electromagnetic pulse generation technology. They are a new type of ultrafast semiconductor electronic device capable of generating high-power, ultrashort pulses. Their outstanding features include low jitter, fast switching times, high repetition rates, precise synchronization, and optical isolation. Consequently, they have been used in applications such as particle accelerators, ultra-wideband radar, directed energy systems, trigger generators, and solid-state compact pulsed power sources. The advent of microwave photonics has made microwave generation based on photoconductive semiconductor switches feasible. The use of wide-bandgap photoconductive semiconductors to generate tunable radio frequency and electromagnetic microwaves is a new technology with significant application prospects. As the core component of this technology, photoconductive semiconductor switches have garnered widespread attention. Photoconductive switches were originally based on silicon (Si) and gallium arsenide (GaAs). However, due to limitations in dielectric breakdown strength and linear operating range, the power handling of these silicon- and GaAs-based photoconductive switches has been difficult to significantly increase. Gallium nitride (GaN) has the advantages of wide bandgap, high critical breakdown electric field, high carrier mobility, high electron saturation drift velocity, and excellent high-frequency characteristics. It has been widely used in the RF microwave field and is also considered to be one of the most promising semiconductor materials for use in high-power photoconductive switching devices.

[0003] Gallium nitride (GaN) is considered to be one of the most promising semiconductor materials in the field of high-power photoconductive switching devices. g ) The advantage of triggering the gallium nitride photoconductive switch is its high photoelectric conversion efficiency. However, its disadvantage is that the intrinsic light absorption depth is shallow and the thickness of the substrate required for back light incidence is too thin, making it difficult to achieve vertical back incidence of the intrinsic light of the gallium nitride photoconductive switch. At the same time, GaN single crystals face the problems of high price, many macroscopic defects, and limitations in high voltage / high power operation.

[0004] Existing photoconductive switches typically consist of a pair of metal electrodes, an anode and a cathode, and a photoconductive device substrate. When a bias voltage is applied to the device electrodes, the substrate generates a large number of photogenerated carriers under laser irradiation, causing a dynamic change in the device resistance, generating a photocurrent between the cathode and anode. Photoconductive semiconductor devices can be categorized as either coplanar or heteroplanar based on the electrode location. In the heteroplanar structure, the electrodes are located on two planes of the wafer, resulting in a more uniform current distribution and better voltage resistance. However, intrinsic light triggering is not possible, and the device is affected by stray electrical parameters, making it difficult to achieve a high response speed. In the coplanar electrode structure, the electrodes are located on the same side of the wafer, allowing for intrinsic light triggering and the potential for high photoelectric efficiency and fast response speed. However, due to the coplanar location of the electrodes, the photocurrent distribution is uneven, which can easily lead to high surface electric fields, strong currents, and localized high temperatures, causing surface breakdown and hindering the improvement of the device's power capacity.

[0005] To improve the withstand voltage of planar devices and reduce on-resistance, C. Hettler of Texas Tech University proposed an intrinsic light back-incident SiC photoconductive switch structure in 2012. Patent CN 112820784 describes a high-power photoconductive switch with vertical back-incident, coplanar electrodes. Patent CN 113823554 describes a method for fabricating a planar electrode silicon carbide photoconductive semiconductor device with back-incident light. This structure thins the substrate to 50-60 μm to enhance the photocurrent amplitude response. This is because the penetration depth of 355 nm ultraviolet laser in silicon carbide (SiC) is approximately 47 μm. In 2023, Xiao Longfei et al. at Shandong University achieved high withstand voltage and low on-resistance by thinning a silicon carbide device with intrinsic light vertical back-incident, demonstrating that vertical back-incident intrinsic light can effectively improve the withstand voltage of planar photoconductive devices.

[0006] Compared to SiC, GaN is a direct bandgap material with higher carrier mobility, shorter carrier lifetime, and faster response capability, offering the potential for higher power and faster response. However, current GaN-based photoconductive devices cannot utilize the aforementioned structure with vertical back-incidence of intrinsic light. This is because GaN has a shallower absorption depth for intrinsic light, requiring device thinning to the micrometer scale to achieve a high photocurrent amplitude response. Using a structure with vertical back-incidence of intrinsic light presents the problem of a thin substrate, which reduces power capacity. Furthermore, the technology for growing single-crystal semi-insulating GaN substrates with low defect density and high bulk resistivity is still immature. Single crystals are expensive, and the presence of numerous defects within the substrate results in poor device performance. Consequently, GaN photoconductive devices utilizing vertical back-incidence of intrinsic light face the aforementioned challenges. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology and provide a SiC-GaN composite photoconductive semiconductor switch with a silicon carbide substrate and an epitaxial thin layer of gallium nitride, which is used to solve the problem that gallium nitride photoconductive switches are difficult to achieve vertical back incidence of intrinsic light and improve the photoelectric conversion efficiency.

[0008] To solve the above technical problems, the present invention proposes a technical solution: a SiC-GaN composite photoconductive switch, comprising a silicon carbide substrate, a semi-insulating gallium nitride epitaxial layer and two electrodes, wherein the semi-insulating gallium nitride epitaxial layer is arranged on one surface of the silicon carbide substrate; the two electrodes are respectively arranged on both sides of the upper surface of the gallium nitride epitaxial layer; the silicon carbide substrate adopts one of a high-purity semi-insulating silicon carbide substrate or a vanadium-compensated silicon carbide substrate; the semi-insulating gallium nitride epitaxial layer is doped with deep-level impurities such as iron or carbon; and the thickness of the silicon carbide substrate is within 200μm.

[0009] In the above-mentioned SiC-GaN composite photoconductive switch, preferably, a passivation layer is provided on the surface of the semi-insulating gallium nitride epitaxial layer; and the two electrodes are exposed from the passivation layer.

[0010] In the above-mentioned SiC-GaN composite photoconductive switch, preferably, an ultraviolet anti-reflection film is provided on the surface of the silicon carbide substrate opposite to the semi-insulating gallium nitride epitaxial layer.

[0011] The above-mentioned SiC-GaN composite photoconductive switch is preferably formed by implanting silicon ions or magnesium ions into the semi-insulating gallium nitride epitaxial layer below the two electrodes, forming two doping concentrations of 10 18 -10 20 cm -3 Highly conductive area.

[0012] In the above-mentioned SiC-GaN composite photoconductive switch, preferably, the thickness of the semi-insulating gallium nitride epitaxial layer is between 0.2 μm and 5 μm; the vanadium concentration of the vanadium-compensated silicon carbide substrate is between 5×10 16 cm -3 -3×10 17 cm -3 between.

[0013] In the above-mentioned SiC-GaN composite photoconductive switch, preferably, the deep energy level impurity doping of the semi-insulating gallium nitride epitaxial layer includes iron (Fe) or carbon (C), and the doping concentration is 10 17 cm -3 -10 19 cm -3 .

[0014] A method for preparing a SiC-GaN composite photoconductive switch, comprising the following steps;

[0015] 1) High-purity semi-insulating silicon carbide or vanadium-compensated silicon carbide substrate and cleaning;

[0016] 2) Epitaxially growing a 0.2-5 μm thick semi-insulating GaN epitaxial layer doped with deep-level impurities on a semi-insulating SiC substrate;

[0017] 3) Spin-coating a photoresist layer on the surface of the semi-insulating GaN epitaxial layer, then using a photolithography machine to create multiple recessed window areas in the photoresist layer, and then fabricating the electrode pattern for the photoconductive switch in the electrode area of ​​the semi-insulating GaN epitaxial layer;

[0018] 4) Vapor-depositing a metal layer on the semi-insulating gallium nitride epitaxial layer processed in step 3), then cleaning and stripping the evaporated metal layer to form an electrode on the electrode region of the semi-insulating gallium nitride epitaxial layer;

[0019] 5) annealing the semi-insulating silicon carbide substrate and the semi-insulating gallium nitride epitaxial layer electrode region after step 4) at a temperature of 800° C. to 900° C. to form an ohmic contact between the electrode and the semi-insulating gallium nitride epitaxial layer;

[0020] 6) Cutting the semi-insulating silicon carbide substrate from the back side of the electrode so that the thickness of the semi-insulating silicon carbide substrate is within 200 μm;

[0021] 7) The electrodes are welded and potted to obtain a SiC-GaN composite photoconductive switch.

[0022] In the above-mentioned method for preparing a SiC-GaN composite photoconductive switch, preferably, in step 1), the thickness of the high-purity semi-insulating silicon carbide or vanadium-compensated silicon carbide substrate is between 0.35 mm and 1.0 mm.

[0023] In the above-mentioned preparation method of the SiC-GaN composite photoconductive switch, preferably, after cleaning in step 1), the surface of the high-purity semi-insulating silicon carbide or vanadium-compensated silicon carbide substrate is cleaned using a plasma stripper and plasma gas.

[0024] In the above-mentioned preparation method based on SiC-GaN composite photoconductive switch, preferably, silicon (Si) ions or magnesium (Mg) ions are implanted into the multiple groove window regions in step 3) to form a doping concentration of 10 in the semi-insulating gallium nitride epitaxial layer. 18 -10 20 cm -3 highly conductive areas.

[0025] Compared with the existing technology, the advantages of the present invention are: the SiC-GaN composite photoconductive switch of the present invention is a composite device structure with vertical back incidence of intrinsic light. The composite device can firstly utilize the relatively high absorption depth of silicon carbide to increase the device thickness and improve the mechanical strength to achieve back light incidence; secondly, it can give full play to the excellent transport properties of gallium nitride to achieve low on-resistance and high photoelectric conversion efficiency; thirdly, the epitaxially grown thin layer of gallium nitride has higher crystal quality, fewer internal defects in the crystal and lower cost; finally, silicon carbide, which is also a wide bandgap semiconductor, is introduced as a substrate, which provides more current channels for the device, improves the photoelectric conversion efficiency and reduces the on-resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the cross-sectional structure of the SiC-GaN composite photoconductive switch in Example 1.

[0027] Figure 2 This is a schematic diagram of the top view of the SiC-GaN composite photoconductive switch in Example 1.

[0028] Figure 3 Schematic diagram of the cross-sectional structure of the SiC-GaN composite photoconductive switch in Example 2.

[0029] Figure 4 This is a comparison diagram of the responses of the SiC-GaN composite photoconductive switch and the SiC photoconductive switch based on the present invention.

[0030] Figure 5 The present invention is based on the internal current distribution of the SiC-GaN composite photoconductive switch.

[0031] Figure 6 The present invention is based on the internal X-axial electric field of the SiC-GaN composite photoconductive switch.

[0032] Figure 7 The present invention is based on the internal Y-axis electric field of the SiC-GaN composite photoconductive switch.

[0033] Figure 8 The present invention is based on the local Y-axis electric field of the SiC-GaN composite photoconductive switch.

[0034] Legend

[0035] 1. Electrode; 2. GaN epitaxial layer; 3. Silicon carbide substrate; 4. Passivation layer; 5. Ion implantation area; 6. UV anti-reflection film. DETAILED DESCRIPTION

[0036] In order to facilitate understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

[0037] It should be noted that when an element is described as being "fixed, fixed, connected or communicated with" another element, it can be directly fixed, fixed, connected or communicated with the other element, or it can be indirectly fixed, fixed, connected or communicated with the other element through other intermediate connectors.

[0038] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0039] The SiC-GaN composite photoconductive switch of the present invention is as follows: Figure 1 and Figure 2 As shown, the device comprises a silicon carbide substrate 3, a semi-insulating gallium nitride epitaxial layer 2, and two electrodes 1. The semi-insulating gallium nitride epitaxial layer 2 is disposed on one surface of the silicon carbide substrate 3; the two electrodes 1 are disposed on either side of the upper surface of the gallium nitride epitaxial layer 2. The silicon carbide substrate 3 is either a high-purity semi-insulating silicon carbide substrate 3 or a vanadium-compensated silicon carbide substrate 3. The semi-insulating gallium nitride epitaxial layer 2 is doped with deep-level impurities; and the thickness of the silicon carbide substrate 3 is less than 200 μm. Laser light passes through the silicon carbide substrate 3 and is incident on the semi-insulating gallium nitride epitaxial layer 2. The triggering light that passes through the silicon carbide substrate 3 is absorbed by the gallium nitride material in the semi-insulating gallium nitride epitaxial layer 2, generating a large number of photogenerated carriers in both the silicon carbide and gallium nitride. Under the action of the bias voltage, a photocurrent is generated.

[0040] The purpose of selecting silicon carbide substrate 3 in the present invention is: compared with traditional first and second generation semiconductor substrates such as silicon (Si) and gallium arsenide (GaAs), silicon carbide substrate 3 operates in linear mode and has the advantages of wide bandgap (~3 eV) and high breakdown electric field (~4 MV / cm); compared with gallium nitride substrate, silicon carbide substrate 3 has higher crystal quality, lower manufacturing cost, and higher intrinsic absorption depth; compared with ultra-wide bandgap semiconductor substrates such as sapphire, silicon carbide substrate 3 can provide additional current channels, significantly improving the photoelectric conversion efficiency.

[0041] In the present invention, to fully leverage the device's advantages, the silicon carbide substrate 3 requires careful design. Since silicon carbide can be either high-purity semi-insulating or vanadium-compensated semi-insulating, the concentration of impurity elements within the substrate can be controlled to meet different requirements (improving photoelectric conversion efficiency or outputting modulated microwaves). If the actual application is a photoconductive switch with high photoelectric efficiency, a high-purity semi-insulating silicon carbide substrate 3 with few deep-level defects is fabricated to improve carrier lifetime and achieve a photoconductive switch with high photoelectric efficiency. If the actual application is a photoconductive microwave device for outputting high-power tunable microwaves, a semi-insulating silicon carbide substrate 3 with a high deep-level concentration is fabricated, heavily doped with vanadium, and the concentration of other intrinsic deep-level defects is appropriately increased to improve device shutdown speed and enhance the photoconductive microwave modulation index.

[0042] The present invention uses gallium nitride epitaxial material for this purpose: Compared to silicon carbide, a material that has been widely studied, gallium nitride is a direct bandgap semiconductor with superior transport properties, enabling rapid on / off switching. However, high cost and low crystal quality have limited the research and development of gallium nitride photoconductive switches. Using a semi-insulating gallium nitride epitaxial layer 2 reduces costs while improving crystal quality. Furthermore, its shallow intrinsic light absorption depth allows it to absorb nearly all of the intrinsic trigger laser light that passes through the substrate, significantly improving light energy utilization.

[0043] This invention improves the semi-insulating gallium nitride epitaxial layer 2: The transport characteristics of gallium nitride photoconductive switches are affected by the energy levels of their internal impurities. To leverage the advantages of composite devices, the internal doping concentration must be tailored to the specific application scenarios of photoconductive switches to achieve controlled carrier lifetimes. Epitaxial layers with long carrier lifetimes are used in fast-turn-on photoconductive switches with high photoelectric efficiency, while epitaxial layers with short carrier lifetimes are used in photoconductive microwave devices that output higher-frequency modulated microwaves.

[0044] In the present invention, the deep energy level impurity doping of the semi-insulating gallium nitride epitaxial layer 2 includes iron (Fe) or carbon (C), and the doping concentration is 10 17 cm -3 -10 19 cm -3 .

[0045] In the present invention, Figure 3 As shown, a passivation layer 4 is provided on the surface of the semi-insulating gallium nitride epitaxial layer 2. Two electrodes 1 are exposed from the passivation layer 4. The material used for the passivation layer 4 has a high dielectric constant and can suppress the surface electric field of the dielectric. The material of the passivation layer 4 is determined by the dielectric constant and its compatibility with gallium nitride, such as silicon dioxide, silicon nitride, and aluminum oxide. A UV antireflection film 6 is provided on the surface of the silicon carbide substrate 3 opposite the semi-insulating gallium nitride epitaxial layer 2.

[0046] In the present invention, Figure 3As shown, an ion implantation region is formed in the semi-insulating gallium nitride epitaxial layer 2 below the two electrodes 1, and magnesium (Mg) ions or silicon (Si) ions are implanted in the ion implantation region. Two doping concentrations of 10 18 -10 20 cm -3的 Ion implantation in highly conductive areas can improve the quality of ohmic contact, homogenize the electric field at the edge of the device, and enhance device performance under high electric fields.

[0047] In the present invention, the thickness of the semi-insulating gallium nitride epitaxial layer 2 is between 0.2 μm and 5 μm; the vanadium concentration of the vanadium-compensated silicon carbide substrate 3 is between 5×10 16 cm -3 -3×10 17 cm -3 between

[0048] The present invention also provides a method for preparing a SiC-GaN composite photoconductive switch, comprising the following steps;

[0049] 1) Prepare and clean a high-purity semi-insulating silicon carbide or vanadium-compensated silicon carbide substrate 3. After cleaning, use a plasma stripper and plasma gas to clean the surface of the high-purity semi-insulating silicon carbide or vanadium-compensated silicon carbide substrate 3. The thickness of the high-purity semi-insulating silicon carbide or vanadium-compensated silicon carbide substrate 3 is between 0.35 mm and 1.0 mm.

[0050] 2) epitaxially growing a semi-insulating gallium nitride epitaxial layer 2 doped with deep energy level impurities with a thickness of 0.2 μm to 5 μm on a semi-insulating silicon carbide substrate 3;

[0051] 3) Spin-coat a photoresist layer on the surface of the semi-insulating gallium nitride epitaxial layer 2, and then use a photolithography machine to photolithographically form multiple groove window areas in the photoresist layer, and prepare the electrode 1 pattern of the photoconductive switch in the electrode 1 area of ​​the semi-insulating gallium nitride epitaxial layer 2; In the multiple groove window areas in step 3), magnesium (Mg) ions or silicon (Si) ions are implanted to form a doping concentration of 10 in the semi-insulating gallium nitride epitaxial layer 2. 18 -10 20 cm -3 Highly conductive area.

[0052] 4) Vapor-depositing a metal layer on the semi-insulating gallium nitride epitaxial layer 2 processed in step 3), then cleaning and stripping the evaporated metal layer to form an electrode 1 on the electrode 1 region of the semi-insulating gallium nitride epitaxial layer 2;

[0053] 5) Annealing the semi-insulating silicon carbide substrate 3 and the electrode 1 region of the semi-insulating gallium nitride epitaxial layer 2 after step 4) at a temperature of 800° C. to 900° C. to form an ohmic contact between the electrode 1 and the semi-insulating gallium nitride epitaxial layer 2;

[0054] 6) cutting the semi-insulating silicon carbide substrate 3 from the back side of the electrode 1 so that the thickness of the semi-insulating silicon carbide substrate 3 is within 200 μm;

[0055] 7) Electrode 1 is welded and potted to obtain a SiC-GaN composite photoconductive switch.

[0056] The SiC-GaN composite photoconductive switching device of the present invention adopts intrinsic light triggering to obtain high photoelectric conversion efficiency compared with the technical route of non-intrinsic light triggering; compared with the surface light incidence of the electrode 1, the vertical back light incidence is adopted to improve the voltage resistance and saturation photocurrent of the planar photoconductive device; the use of epitaxial thin-layer gallium nitride can improve the quality and give full play to the advantages of high mobility and short carrier lifetime of gallium nitride material; the use of silicon carbide substrate 3 or aluminum oxide substrate to reduce light attenuation and thus increase the thickness of the device, solve the problem that the intrinsic light absorption of gallium nitride is shallow and it is difficult to achieve vertical back incidence, prevent the device from being too thin, improve the mechanical strength of the device, and thin the silicon carbide substrate 3 or aluminum oxide substrate to a reasonable thickness to improve the photoelectric conversion efficiency.

[0057] The following is an explanation of the technical effect by combining the numerical simulation calculation of the device. Figure 4 As shown in the figure, compared with the conventional thinned silicon carbide structure, the SiC-GaN composite photoconductive switch can significantly reduce the on-resistance and improve the photoelectric conversion efficiency. Figure 5 As shown in Figure 2, under laser triggering, a large number of conductive channels are formed inside the GaN and on the back of the SiC. The two-dimensional X-axis electric field distribution characteristics are shown in Figure 2. Figure 6 As shown, the two-dimensional Y-axis electric field distribution diagram is as follows Figure 7 and Figure 8 As shown, compared with traditional devices where the electric field is concentrated at the metal-semiconductor interface, the strong electric field in the Y-axis direction is confined to the SiC-GaN interface. The voltage resistance of the wide-bandgap semiconductor interface is significantly greater than that of the metal-semiconductor interface, thus significantly improving performance. Example 1

[0058] The manufacturing method of the SiC-GaN composite photoconductive switch in this embodiment is as follows:

[0059] 1) Select a high-purity semi-insulating or low-doped vanadium-compensated semi-insulating silicon carbide substrate 3 and clean it:

[0060] Manufacturing a high-purity semi-insulating or low-doped vanadium-compensated semi-insulating silicon carbide substrate 3 wafer with a thickness of 0.35mm-1.0mm for cleaning, and using a plasma stripper to further clean the wafer surface using plasma gas;

[0061] 2) Epitaxial growth of low-doping concentration semi-insulating gallium nitride:

[0062] A thin layer of semi-insulating gallium nitride doped with low concentration of iron or carbon and having a thickness of 0.2 μm to 5 μm is grown on the semi-insulating silicon carbide substrate 3 by epitaxial growth.

[0063] 3) Photolithography:

[0064] A photoresist layer is spin-coated on the gallium nitride surface. After the wafer cools to room temperature, a photolithography machine is used to photolithography the photoresist layer on the wafer surface using a metal layer photomask. Several groove window areas obtained by photolithography on the photoresist layer on the wafer surface are used to prepare the electrode 1 pattern of the photoconductive switch on the semi-insulating silicon carbide substrate 3 electrode 1 area.

[0065] 4) Evaporated metal layer:

[0066] A metal layer is evaporated on the semi-insulating gallium nitride epitaxial layer 2 treated in step 3), and the metal layer in other areas except the metal electrode 1 area is cleaned and peeled off to obtain a whole wafer with the electrode 1 structure;

[0067] 5) Annealing:

[0068] After rapid annealing at a high temperature of 800° C. to 900° C., an ohmic contact is formed in the electrode 1 region.

[0069] 6) Device thinning

[0070] The individual discrete photoconductive semiconductor devices are thinned from the initial thickness of the silicon carbide substrate 3 on the back side of the electrode 1 to within 200 μm, and then polished.

[0071] 7) Device packaging:

[0072] The electrode 1 is welded and potted to complete the preparation of the SiC-GaN composite photoconductive switch. Example 2

[0073] 1) Select a high-purity semi-insulating or low-doped vanadium-compensated semi-insulating silicon carbide substrate 3 and clean it:

[0074] Manufacturing a high-purity semi-insulating or low-doped vanadium-compensated semi-insulating silicon carbide substrate 3 wafer with a thickness of 0.35 mm to 1.0 mm and cleaning it, and using a plasma stripper to further clean the wafer surface using plasma gas;

[0075] 2) Epitaxial growth of low-doping concentration semi-insulating gallium nitride:

[0076] A thin layer of semi-insulating gallium nitride doped with low concentration of iron or carbon and having a thickness of 0.2 μm to 5 μm is grown on the semi-insulating silicon carbide substrate 3 by epitaxial growth.

[0077] 3) Photolithography:

[0078] A photoresist layer is spin-coated on the surface of the gallium nitride. After the wafer cools to room temperature, a photolithography machine is used to perform photolithography on the photoresist layer on the wafer surface using a metal layer photomask. Several groove window areas obtained by photolithography on the photoresist layer on the wafer surface form ion implantation areas 5;

[0079] 4) Ion implantation:

[0080] The doping concentration of 10 is formed in GaN by injecting magnesium (Mg) ions or silicon (Si) ions. 18 -10 20 cm -3 highly conductive areas.

[0081] 5) The electrode 1 pattern of the photoconductive switch is prepared on the semi-insulating silicon carbide substrate 3 using a photolithography process.

[0082] 6) Evaporated metal layer:

[0083] After the treatment in step 5), metal is evaporated on the gallium nitride substrate, and the metal layer in other areas except the metal electrode 1 area is cleaned and peeled off to obtain a whole wafer with the electrode 1 structure;

[0084] 7) Annealing:

[0085] An ohmic contact is formed in the electrode 1 region through high temperature rapid annealing.

[0086] 8) Plating of passivation layer 4 and anti-reflection film:

[0087] A high dielectric constant passivation layer 4 is grown on the front side of the wafer after the electrode 1 is evaporated, and a high transmittance antireflection film is grown on the back side; that is, a passivation layer 4 is set on the surface of the semi-insulating gallium nitride epitaxial layer 2; and an ultraviolet light antireflection film 6 is set on the side of the silicon carbide substrate 3 opposite to the semi-insulating gallium nitride epitaxial layer 2.

[0088] 9) Photolithography:

[0089] A window pattern of the electrode 1 of the photoconductive switch is prepared on the surface of the passivation layer 4 by using a photolithography process;

[0090] 10) Passivation layer 4 etching:

[0091] The obtained window pattern is etched using an ICP plasma etcher, with a thickness equal to that of the passivation layer 4 .

[0092] 11) Device thinning

[0093] The individual discrete photoconductive semiconductor devices are thinned from the initial thickness of the silicon carbide substrate 3 on the back side of the electrode 1 to within 200 μm, and then polished.

[0094] 12) Device packaging:

[0095] The electrode 1 is welded and potted to complete the preparation of the SiC-GaN composite photoconductive switch. Example 3

[0096] (1) Selecting a heavily vanadium-doped compensated semi-insulating silicon carbide substrate 3 and cleaning it:

[0097] Increase the vanadium doping concentration of silicon carbide substrate 3 to 1×10 17 cm -3 -3×10 17 cm -3 , making a heavily doped vanadium compensated semi-insulating silicon carbide substrate 3 wafer with a thickness of 0.35mm-1.0mm for cleaning, and using a plasma stripper to further clean the wafer surface using plasma gas;

[0098] 2) Epitaxial growth of heavily doped semi-insulating GaN:

[0099] On the semi-insulating silicon carbide substrate 3, a layer of heavily doped iron (Fe) or carbon (C) with a thickness of 0.2-5 μm is grown epitaxially, with a concentration range of more than 10 18 cm -3 Thin layers of semi-insulating gallium nitride.

[0100] The remaining steps are the same as in Example 1. Example 4

[0101] (1) Selecting a heavily vanadium-doped compensated semi-insulating silicon carbide substrate 3 and cleaning it:

[0102] Increase the vanadium doping concentration of silicon carbide substrate 3, produce heavily doped vanadium compensated semi-insulating silicon carbide substrate 3 wafers with a thickness of 0.35mm-1.0mm and clean them. The concentration range is 1×10 17 cm -3 -3×10 17 cm -3 In between, a plasma stripper is used to further clean the wafer surface using plasma gas;

[0103] (2) Epitaxial growth of heavily doped semi-insulating GaN:

[0104] A heavily doped thin layer of semi-insulating gallium nitride with a thickness of 0.2 μm to 5 μm is grown epitaxially on a semi-insulating silicon carbide substrate 3; the doping material is iron (Fe) or carbon (C), and the doping concentration is greater than 10 18 cm -3 .

[0105] The remaining steps are the same as in Example 2.

Claims

1. A SiC-GaN composite photoconductive switch, characterized by: The device comprises a silicon carbide substrate, a semi-insulating gallium nitride epitaxial layer, and two electrodes, wherein the semi-insulating gallium nitride epitaxial layer is disposed on one surface of the silicon carbide substrate; the two electrodes are disposed on either side of the upper surface of the gallium nitride epitaxial layer; the silicon carbide substrate is a high-purity semi-insulating silicon carbide substrate or a vanadium-compensated silicon carbide substrate; the semi-insulating gallium nitride epitaxial layer is doped with deep-level impurities such as iron or carbon; and the thickness of the silicon carbide substrate is within 200 μm. The laser passes through the silicon carbide substrate and is incident on the semi-insulating gallium nitride epitaxial layer. The trigger light passing through the silicon carbide substrate is absorbed by the gallium nitride material of the semi-insulating gallium nitride epitaxial layer. Photogenerated carriers are generated simultaneously inside the silicon carbide and gallium nitride, and under the action of the bias voltage, photocurrent is formed.

2. The SiC-GaN composite photoconductive switch according to claim 1, characterized in that: A passivation layer is provided on the surface of the semi-insulating gallium nitride epitaxial layer; the two electrodes are exposed from the passivation layer.

3. The SiC-GaN composite photoconductive switch according to claim 1, characterized in that: An ultraviolet anti-reflection film is provided on the surface of the silicon carbide substrate opposite to the semi-insulating gallium nitride epitaxial layer.

4. The SiC-GaN composite photoconductive switch according to claim 1, characterized in that: Silicon ions or magnesium ions are injected into the semi-insulating GaN epitaxial layer below the two electrodes to form two doping concentrations of 10 18 -10 20 cm -3 Highly conductive area.

5. The SiC-GaN composite photoconductive switch according to claim 1, characterized in that: The thickness of the semi-insulating gallium nitride epitaxial layer is between 0.2 μm and 5 μm; the vanadium concentration of the vanadium-compensated silicon carbide substrate is between 5×10 16 cm -3 -3×10 17 cm -3 Between between.

6. The SiC-GaN composite photoconductive switch according to claim 1, characterized in that: The semi-insulating gallium nitride epitaxial layer is doped with carbon or iron at a deep energy level, with a doping concentration of 10 17 cm -3 -10 19 cm -3 .

7. A method for preparing a SiC-GaN composite photoconductive switch, characterized in that: The following steps are included; 1) High-purity semi-insulating silicon carbide or vanadium-compensated silicon carbide substrate and cleaning; 2) Epitaxially growing a 0.2-5 μm thick semi-insulating GaN epitaxial layer doped with deep-level impurities on a semi-insulating SiC substrate; 3) Spin-coating a photoresist layer on the surface of the semi-insulating GaN epitaxial layer, then using a photolithography machine to create multiple recessed window areas in the photoresist layer, and then fabricating the electrode pattern for the photoconductive switch in the electrode area of ​​the semi-insulating GaN epitaxial layer; 4) Vapor-depositing a metal layer on the semi-insulating gallium nitride epitaxial layer processed in step 3), then cleaning and stripping the evaporated metal layer to form an electrode on the electrode region of the semi-insulating gallium nitride epitaxial layer; 5) annealing the semi-insulating silicon carbide substrate and the semi-insulating gallium nitride epitaxial layer electrode region after step 4) at a temperature of 800° C. to 900° C. to form an ohmic contact between the electrode and the semi-insulating gallium nitride epitaxial layer; 6) Cutting the semi-insulating silicon carbide substrate from the back side of the electrode so that the thickness of the semi-insulating silicon carbide substrate is within 200 μm; 7) The electrodes are welded and potted to obtain a SiC-GaN composite photoconductive switch.

8. The method for preparing a SiC-GaN composite photoconductive switch according to claim 7, wherein: In the step 1), the thickness of the high-purity semi-insulating silicon carbide or vanadium-compensated silicon carbide substrate is between 0.35 mm and 1.0 mm.

9. The method for preparing a SiC-GaN composite photoconductive switch according to claim 7, wherein: After cleaning in step 1), the surface of the high-purity semi-insulating silicon carbide or vanadium-compensated silicon carbide substrate is cleaned using a plasma stripper and plasma gas.

10. The method for preparing a SiC-GaN composite photoconductive switch according to claim 7, wherein: In step 3), silicon ions or magnesium ions are implanted into the multiple groove window regions to form a doping concentration of 10 in the semi-insulating gallium nitride epitaxial layer. 18 -10 20 cm -3 Highly conductive area.

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